Materials and systems for micro-energy harvesting and storage

Resume : Efficient thermoelectric (TE) energy conversion requires high electrical conductivity σ and Seebeck coefficient S, and low thermal conductivity k. Nanostructured semiconductors are promising for efficient TE energy conversion. The thermal conductivity decreases down to the amorphous material thermal conductivity in nanostructured semiconductors thanks to the enhanced phonon scattering by non-uniformities, interfaces and boundaries. The improvement of the TE transport properties is more challenging. The electrical conductivity typically decreases in nanostructured materials compared to bulk. Seebeck coefficient may though increase significantly in non-uniform nanostructures due to energy filtering of the charge carriers. We discuss the dependence of energy filtering in non-uniformly doped nanofilms and nanowires on the doping profile and concentration. Particular emphasis is attributed to analyzing energy filtering in the distinct transport regimes: (a) degenerate versus non-degenerate carriers transport, and (b) ballistic versus diffusive transport. The various transport regimes may coexist or one of them may dominate, depending on the design of the doping details in the nanostructure. The implications of the transport regime on the TE energy conversion efficiency is discussed and design guidelines are provided using the kinetic Monte Carlo simulation technique, Boltzmann transport equation and derived phenomenology.

Resume : Nanotechnology opens a new way to improve the figure of merit thermoelectric materials. Theoretical calculations and experimental evidences prove that performance of poor thermoelectric materials, like bulk silicon, can be significantly enhanced providing a nanostructured configuration. Nevertheless, up to date the advantages arisen from these phenomena have not been practically exploited due to the lack of cheap high scale techniques capable to produce stable nanostructured materials. In this work, a new material is proposed based on flexible fabrics made of doped silicon nanotubes. Macroscopic easy to handle sheets of several square centimeters were produced by means of scalable fabrication techniques: electrospinning and chemical vapor deposition. The diameter of the constituting nanotubes is around 500 nanometers, presenting wall thicknesses ranging from 10 to 200 nm. Thermal and electrical characterizations were carried out at the produced fibers. An important decrease of the thermal conductivity is evidenced when reducing wall diameter, while the electrical conductivity is preserved. This leads to drastic increase of its figure of merit. In a second perspective, by its nature, the micrometric distribution of fibers presents a very effective barrier for gas convection. For this reason, high thermal gradients are achieved without the need of vacuum encapsulation. The aforementioned features entail a huge potentiality as low cost efficient material for thermal energy harvesting.

Resume : Conjugated polymers have recently gained attention as a valuable choice for electronics applications, due to their low cost, easy processability and environmental stability. Furthermore, safety and flexibility of these materials are interesting features for wearable electronics. Example of this application are thermoelectric body harvesters, i.e. flexible devices able to collect body heat and to convert it into electrical energy. To this aim, still low thermoelectrical power factor (PF) of conjugated polymers has to be improved. A strategy to reach this goal is nanostructuration of the material: such approach aims to generate energy filtering effect, which is known to cause a PF increase in inorganic semiconductors. The path to obtain samples of nanostructured polymer-based material has been to embed inorganic nanoparticles (NPs) with suitable electronic features, i.e. Mn3O4 NPs, into poly(3,4-ethylendioxithiophene):tosylate, or PEDOT:Tos. The NPs have been grafted with succinyl-EDOT and suspended in the polymerization solution, then hybrid films are obtained by in situ polymerization technique. The study on such samples was focused on the influence of the NP density (NP DLS diameter 120±20 nm) on thermoelectrical properties. A conductivity of 240 S/cm and a Seebeck coefficient of 15 μV/K were measured for a NP density of 4E11cm-3, while lower conductivities characterized higher NP densities films. An outlook of the possible improvement strategies will be given.

Resume : Semiconductor or oxide materials are today in the scope in plural technological domains and especially for the energy harvesting applications. Thermoelectric conversion is always driven by the famous Bi2Te3 material with figure of merit ZT above the unity. Nevertheless, according to chemical and electrical properties tuning, semiconductors and oxides became relevant candidates. For a better accuracy on the thermoelectric properties, we developed a micro-ZT-meter with a simultaneous measurement of Seebeck, electrical conductivity and, recently, the thermal conductivity. Besides, an evaluation of the contact resistance between electrodes (made by magnetron sputtering technique) and thin film material is conducted to evaluate the influence of the micro-thermopiles within the structure. We are actually studying thin film materials deposited on silicon and silicon dioxide, in order to correlate the material characteristics with the thermoelectric properties. Electrodes such as platinum, nickel and gold were used. As already shown on other material in the literature, we emphasized on the influence of the substrate on the Seebeck coefficient.

Resume : Thermoelectric energy harvesters convert directly heat into electrical energy. They can use waste heat from different heat sources like industrial or combustion process as well as small amounts like body heat or daily temperature changes. Due to the different heat sources and temperatures different thermoelectric generators are needed. Therefore a survey on state of the art thermoelectric harvesters as well as on actual developments will be given.

Resume : Silicon nanowires are promising candidates for thermoelectric harvesting since they combine the low cost, high availability and easy integration of silicon with a huge enhancement of ZT conferred by nanostructuring. In the work presented herein silicon nanowires were integrated in planar micromachined structures able to exploit their thermoelectric properties. The wires were grown by means of silane fed, gold nanoparticle seeded, chemical-vapour-deposition / vapour-liquid-solid growth (CVD-VLS). This bottom-up approach allows fabricating doped silicon nanowires aligned between the trenches of micro-devices, with controlled properties and epitaxial (and thus low resistance) contacts at each end. Using silicon-based materials and a low temperature fabricating method which allows control, facile integration and low resistance contacts are key enabling points for application in thermoelectric harvesting devices. CVD-VLS conditions and VLS seeding parameters were changed in order to control nanowire areal density, morphology and doping. Nanowire diameter and density strongly correlate to VLS seed size and density. This control could be achieved by tuning gold galvanic displacement conditions. This technique allowed a selective deposition of gold nanoparticles at the active silicon surface while controlling their distribution and size. Following growth, silicon nanowires were structurally and thermoelectrically characterized in order to optimize them for thermoelectric performance.

Resume : Thermoelectric describes the interactions between temperature and voltage, i.e. a temperature difference is converted into usable electrical energy which is called Seebeck-Effect. Key parameters are the electrical conductivity σ and the Seebeck-coefficient S which are combined in the Power-Factor (PF = S²·σ) to express the efficiency of a thermoelectric material. It is desired to manufacture bendable or flexible thermoelectric generators (TEGs) by low-cost and large scale production techniques e.g. printing. Therefore, composites made of intrinsically conducting polymer and nanoparticles, especially carbon nanotubes, which are printable, are the focus of this work. The intrinsically conducting polymer, PEDOT:PSS doped with DMSO, was used in combination with different types of single-walled carbon nanotubes (SWCNT). The SWCNTs were mixed with various dispersants and then added to the PEDOT:PSS disperison. The composite dispersions with different amounts of SWCNTs were deposited by Spin-Coating and characterized. The results showed an increase of the Power-Factor by ~30% compared to pristine PEDOT:PSS. Furthermore the influence of the dispersants and the dispersing methods on PEDOT:PSS and SWCNTs were investigated.

Resume : Nanostructuring of silicon has recently emerged as a promising way to achieve high performance thermoelectric conversion, because of the gain in figure of merit obtained through the enhanced phonon scattering occurring in silicon nanowires (NWs) compared to bulk or thin film silicon. The use of silicon instead of high-performance thermoelectric materials, in addition, is particularly attractive for complex devices based on micro-nano technology, in which the availability of consolidated micro/nanofabrication techniques specifically developed for silicon can be profitably exploited. In this paper, a new fabrication technique suitable for integration of silicon nanowires within silicon micromachined structures is presented, potentially applicable to manufacturing of micro thermoelectric generators (TEGs), suitable for powering other micro devices by harvesting of thermal energy from the environment. The fabrication of top-down silicon nanowire arrays suitable for integration on micromachined thermal harvesters, their structural and electrical characterization will be described. The p (boron) and n-type (phosphorus) doped NW silicon thermoelements obtained show doping level around 1E20 cm-3 an equivalent sheet resistance around 1 kohm and thermoelectric power of about 150 μV/K. By utilizing three-level stacked NWs within SiO2 - Si3N4 nanometric templates, linear nanowire densities up to 1E4 mm-1 have been reached.

Resume : We present different ways of obtaining nanostructured materials in order to enhance their performance for thermoelectric applications. Different strategies have been followed depending on the thermoelectric material under study. For inorganic materials, in most cases the final aim is to achieve a reduction in the thermal conductivity of the lattice while preserving the Seebeck coefficient and electrical conductivity of the original material. In the case of organic materials, the nano-structuration is focused on increasing the electrical conductivity while maintaining their low thermal conductivity. Finally, it has to be kept in mind that the fabrication techniques should be scalable, when possible, in order to obtain technologies which are easily transferred to industry. And if possible, macro-sized pieces of nanostructured materials are also desired in order to make it easier to handle them and measure their properties.

Resume : Thermoelectric materials are capable to scavenge electricity from thermal gradients. The capability of TE material is estimated by a dimensionless TE figure of merit, ZT = (S²)·T/(ρ·κ), where S is the Seebeck coefficient, ρ is the electrical resistivity, T is absolute temperature and κ is the thermal conductivity. The three interdependent physical parameters (S, ρ and κ) are strongly influenced by the doping level and leads to a very complex situation for TE materials. Recent advances in TE materials are associated with the bulk nanocomposites approach [1] where ZT enhances due to combined contribution of constituent elements, grains (/boundaries) and interfaces [2]. Among the very high performance TE materials, Tin Telluride (SnTe) has been explored as an efficient alternative for comparable lead based chalcogenides. The major challenge, for SnTe, is to optimize high hole concentrations, which can be achieved by substituting the transition metal ions at the inherently vacant Sn sites [3-5]. The research presentation will elucidate our results for the enhanced TE performance of transition metal doped SnTe. The positive S, of annealed composite-pellets, enhances about three times for ~10% transition metal doping than in pure SnTe, while the temperature dependent ρ shows a metallic behavior. With doping, the observed transport properties suggest the modification in the electronic band structure. References 1. M. S. Dresselhaus, G. Chen, M. Y. Tang, R. G. Yang, H. Lee, D. Z. Wang, Z. F. Ren, J. P. Fleurial and P. Gogna, Advanced Materials 19 (8), 1043-1053 (2007). 2. A. Soni, Y. Shen, M. Yin, Y. Zhao, L. Yu, X. Hu, Z. Dong, K. A. Khor, M. S. Dresselhaus and Q. Xiong, Nano Letters 12 (8), 4305 (2012). 3. R. F. Brebrick and A. J. Strauss, Physical Review 131 (1), 104-110 (1963). 4. A. Banik, U. S. Shenoy, S. Anand, U. V. Waghmare and K. Biswas, Chemistry of Materials 27 (2), 581-587 (2015). 5. Q. Zhang, B. Liao, Y. Lan, K. Lukas, W. Liu, K. Esfarjani, C. Opeil, D. Broido, G. Chen and Z. Ren, Proceedings of the National Academy of Sciences 110 (33), 13261-13266 (2013).

Resume : Lithium-ion batteries are widely used for applications such as powering laptop, mobile phones, cameras and many portable devices. The fabrication of micro-batteries for its utilization in monolithic hybridization with complementary metal oxide semiconductor random access memory, back-up power for computer memory chips, implantable medical devices, small sensors, hazard cards and other micro-devices has stimulated the research for the development of high performance miniaturized secondary batteries. Among the different cell configurations, all solid thin films batteries have recently attracted great attention owing to the absence of flammable and expensive organic electrolytes. Pulsed Laser Deposition (PLD) present unique characteristics allowing deposit particles with high kinetic energy (~100 eV) and in a wide range of temperature (0-1000 ºC). Films made by PLD can be extremely smooth and amorphous, or crystalline, depending of the synthesis conditions. Such versatility has established PLD as an ideal technique to prepare high quality thin films. Several electroactive materials of high interest in micro-batteries with spinel structure are showed in this communication. The optimized parameters for large area deposition by a multilayering process are reported and the structural and electrochemical properties of the obtained thin films analyzed. These electrode materials supply high capacities with excellent retention and rate capability.

Resume : Lithium-ion microbatteries are important in applications such as smart packaging, sensors, and smartcards as well as energy storage for solar cell devices. Recent research efforts demonstrated the utility of the lithium-ion/block copolymer hybrid materials as membranes in lithium-ion microbattery applications. A key challenge is to achieve a highly ionic conductive membrane that maintains both, high-modulus and chemical stability. The ionic conductivity in relation to the morphology of lithium-doped high-molecular-weight polystyrene-block-polyethylene oxide PS-b-PEO diblock copolymer films was investigated as solid state membranes for lithium ion microbatteries.[1] The tendency of the polyethylene (PEO) block to crystallize is highly suppressed with increasing both the salt doping level and the temperature. The increase of the lamella spacing D of the Li-ion/BC hybrid films with increasing Li salt doping level is attributed to the PEO chain conformation rather than the salt volume contribution or the previously reported increase of the effective interaction parameter. Upon salt upload, the PEO chains change from a compact/highly folded conformation to an amorphous/expanded-like conformation. The ionic conductivity is enhanced by the PEO amorphorization. We will emphasize on the challenges related to the low conductivity of the Li-ion/BC membranes at room temperature which limit their practical implementation. Possible solutions are also suggested. [1] E. Metwalli et al., ChemPhysChem 16, 2882 (2015)

Resume : For the most of applications, the lithium thin film batteries will be used with high current peaks. Moreover, for many applications, very short recharge times are required as well as the need of very high rechargeable currents. The use at high current involves a low internal resistance to maintain good performances. For this, a very high conductive LiPON has been developed (8E-6 S·cm-1). As for lot of high conductive electrolyte, an interfacial resistance appears when the electrolyte is integrated in a battery. The study will present the electrochemical and chemical properties of this LiPON and its interfaces. It has been characterized with impedance spectroscopy, RBS/NRA and ToF-SIMS analysis. The origin of this interfacial resistance measured with impedance spectroscopy measurement has been correlated to structural analysis. A solution to suppress this interfacial resistance has been successfully developed. The integration of this electrolyte in thin film batteries shows an optimization of the performances at very high currents.

Resume : Sulfur, one of the most abundant elements in earth's crust, offers a theoretical capacity of 1672 mA·h·g-1, which is an order of magnitude higher than those of the transition-metal oxide cathodes. However, sulfur and lithium sulfide are both insulators, which necessitates the incorporation of conductive additives into the electrodes. Moreover, the intermediate lithium polysulfides formed during the conversion reaction are soluble in the liquid electrolytes currently used. Recently, macroporous conductive materials are proven to be promising cathodes for lithium-sulfur batteries. We will present a new approach of fabricating large-area macroporous materials from multi-walled carbon nanotubes (MWCTNs), which can be further used as cathodes of lithium-sulfur batteries. We fabricate macroporous networks of MWCNTs of different thicknesses and pore sizes and test the electrochemical performance of lithium-sulfur batteries with macroporous MWCNTs-based cathodes. We find that lithium-sulfur batteries with macroporous MWCNTs-based cathodes have a highly stable cycle performance with a good capacity retention. We further coated the cathodes with different coatings, e.g. metal films, pristine MWCNTs, in order to seal the polysulfides inside the cathodes. The electrochemical results of lithium-sulfur batteries with coated cathodes will be thoroughly discussed.

Resume : Lithium titanate (Li4Ti5O12 or LTO) continues to attract great interest for its use as high power anode materials for lithium ion batteries. Its spinel structure allows the reversible intercalation of three Li+ ions at 1.55 V vs Li+/Li, i.e. well above the decomposition potential of most electrolytes. The relatively high voltage of the LTO anode compared to the more typical graphite anodes, limits the energy density of the Li-ion cell but delivers more safe operation instead. The Li+ intercalation reaction associated with the Ti4+/Ti3+ redox conversion is at too high voltage for the formation of dendritic lithium preventing the risk of short circuiting the battery, which is a potential failure for the low voltage anode cells. Moreover, LTO does not show almost any volume change during battery charging and discharging increasing the cycle life time. In this talk we will report on a novel and low cost fabrication method of lithium titanate thin film electrodes for lithium ion micro-batteries. The process is based on a solid state reaction between TiO2 and Li2CO3 stacked-layers upon thermal annealing. The TiO2 layer was prepared by thermal oxidation of a sputtered Ti film or directly by ALD and the Li2CO3 layer was deposited by from sol-gel solutions by spin-coating. LTO thin films were prepared on both Pt and TiN current collectors. The phase and morphology of the prepared LTO films were investigated using a X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The XRD patterns display intense characteristic diffraction LTO peaks and SEM micrographs show a close and continuous 70 nm thick LTO film. The stoichiometry of the fabricated LTO films was evaluated by X-ray photoelectron spectroscopy (surface spectra and depth profile analyses) and elastic recoil detection (ERD) analyses. The results indicate that the elements ratio of the prepared film is very close to the theoretical values of the spinel Li4Ti5O12 and proves that the thermal treatment causes elements intermixing leading to the formation of a Li4Ti5O12 material with a homogeneous distribution. The electrochemical performance of the different LTO films was studied by performing cyclic voltammetry and charge and discharge measurements. The cyclic voltammogram reveals sharp redox peaks centered around 1.55 V (vs. Li+/Li) corresponding to Li+ ion insertion/extraction in/from the spinel Li4Ti5O12 upon reduction/oxidation of Ti4+/Ti3+. The lithiation and delithiation curves show flat plateaus at 1.55 V (vs. Li+/Li) characteristic of Li4Ti5O12. About 100% of the maximum theoretical capacity was reached at 0.1 C for a 70 nm LTO thin film.

Resume : All solid state microbatteries can only be realised using pinhole free films, particularly for the electrolytes, where also thinner is better in terms of ionic conductivity. The atomic layer deposition (ALD) technique is identified as perhaps the enabling technology for realisation of such structures, also on 3D structures. The current contribution will give an overview of the present status in deposition of materials for microbatteries by ALD, with highlights from both the anodes, electrolytes and cathodes, where recent findings in pseudocapacitive behaviour of LiFePO4 will be given. The ALD technique has traditionally been used for deposition of dielectric materials, also when it comes to ionic conductivities, while battery materials are ideally highly conducting with respect to Li-ions. This has led to challenges in deposition processes containing lithium where the growth perhaps no longer is strictly terminated by the surface reactions. What implications does this have on the ALD-growth?

Resume : Increasing demand for portable charge storage devices is one of the greatest competitions of today's energy market. Thin film lithium ion batteries are in the focus of investigation because they offer improved performance such like having higher average output voltage, lighter weights thus higher energy density and longer cycling life than typical rechargeable batteries. Recently polymerized high internal phase emulsions (polyHIPEs) attracted attention because of their potential application as separators in thin film Li-ion batteries due to their high achievable porosity and rather simple production by high internal phase emulsion (HIPE) templating. Room temperature ionic liquids (RT-IL) are in focus of investigation as possible electrolytes for long time due to their low vapour pressure, flammability and toxicity, high thermal stability and tunable properties such as viscosity, ionic conductivity and stability window. Combining these two concepts gives rise to the possibility of producing highly porous in situ Li+-electrolyte filled separators that are printable as films with thicknesses fare beyond 100 μm. For investigations, new systems on the basis of Lauryl methacrylate and 1,12-Dodecanediol dimethacrylate as external minority phase have been prepared using RT-IL based Li-electrolytes as internal phase. Emulsions, separators and electrolytes have then been characterised in terms of rheology, microstructure, electrical conductivity and mechanical and thermal stability.

Resume : A promising route to improve Li+-ion batteries in terms of capacity and rate-performance, is the development of all solid-state three-dimensional (3D) thin-film Li+-ion batteries. For this, the use of TiO2 as a 3D thin-film electrode was investigated. Using spatial atomic layer deposition (s-ALD), ~ 100 nm thick TiO2 films were deposited on high aspect ratio silicon micro-pillars. Due to the self-limiting nature of atomic layer deposition, high quality, uniform and conformal films can be deposited even on complex three-dimensional (3D) structures. Furthermore, the use of s-ALD opens up possibilities for cost-effective and upscaleable applications. The effects of different deposition parameters were explored in terms of conformality and Li+ insertion/extraction performance. Using optimized deposition parameters, conformal TiO2 films were deposited on the 3D substrates. In terms of storage capacity, the 100 nm TiO2 3D electrodes showed near theoretical Li-ion storage capabilities, highlighting its potential for application in 3D thin-film batteries.

Resume : In the 'Internet of things' scenario with distributed sensing the quantity of energy stored and the rate (power) at which it can be accessed are well recognised issues that ultimately requires a hybrid energy harvesting and storage solution with minimal stored capacity loss during thousands of cycles. In current thin-film microbatteries the active material layer thickness is limited to micron dimensions in a large footprint 2D geometry due to the low conductivity and slow transport of ions in the solid state materials. Decreased footprint 3D or 1D architectures are required where the dimension of the active material and layer separations are minimised to meet high power demands while an increased aspect ratio maintains the energy capacity. High energy density materials that can withstand microelectronics based processing temperature regimes are a further requirement. Ge has many advantages as an anode material for high power applications with a higher theoretical energy density than Li metal, 400 times higher rate of Li+ diffusion at room temperature and 10,000 times the electrical conductivity of Si, the next most promising material. Comsol multiphysics simulations have been used to probe solid state thin-film micro, nanowire and core-shell material geometries. Cu nanotube core/Ge shell anode arrays have shown excellent cycle stability and rate capability. Nano core-shell architectures also alleviate the effect of volume expansion, enhancing mechanical stability at the nanoscale in addition to the improved electronic and ionic characteristics. This work will describe the nano-architectures simulated and fabricated for lithium based on-chip micro-energy storage and the interface characteristics that influence performance.

Resume : Emerging electronic applications for the Internet of Things (IoT) and Body Area Networks (BAN) typically require small-form energy storage devices that possess a high energy and power output per unit area. All-solid-state 3D thin-film Li-ion batteries have the potential of meeting these requirements. In this approach, the functional battery materials (i.e. two Li-ion electrodes and a solid-state electrolyte of a few 100 nm thin) are deposited on a microstructured high-aspect ratio (HAR) current collector. The HAR current collector can take a variety of forms, where we currently focus on densely packed arrays of 60 μm high silicon pillars with diameter and inter-pillar distance of 2 μm. By scaling towards higher aspect ratios of these pillars, the energy and power output per unit area of the battery increases. Indeed, by increasing the height of the pillars, more active material per unit area can be deposited, resulting in a higher capacity. Simultaneously, the power output of the battery improves due to the increased internal surface of the 3D battery. Note that a similar approach is not possible with conventional thin-film batteries with planar geometry. Increasing the active film thickness in these batteries results in more capacity, but this goes at the cost of power output due to the increased resistance of the thicker active layers. Because solid-state 3D batteries do not contain any flammable and corrosive liquid electrolytes, they are considered as intrinsically safe. This is e.g. of prime importance when the battery needs to operate inside or in the close proximity of the human body. Beside presenting the concept of solid-state 3D batteries, the different deposition techniques we utilize to obtain conformal deposition on the HAR current collectors will be presented. Furthermore, the future challenges and opportunities of the solid-state 3D battery is discussed.

Resume : Since the first demonstration of a voltage output from a deflected ZnO nanorod in 2006, a huge range of devices have been demonstrated that use arrays of oriented ZnO nanorods grown on a variety of substrates to convert mechanical deformations into electrical energy, commonly referred to as 'nanogenerators'. Although in principle not an ideal material for piezoelectric energy harvesting for reasons such as low coupling coefficients and high internal losses, the ease of production of ZnO nanostructures on flexible substrates gives an incentive to investigate how to maximise performance of these devices. In order to achieve this, it is essential to minimise screening of the polarisation, both internally by free carriers, and externally at the contacts. We have addressed these issues by integrating p-type materials into the devices - coating the nanorods in CuSCN to minimise the free electrons, and using the conductive polymer PEDOT:PSS as a top contact, which induces a depletion region at the interface with the n-type ZnO. We have shown that despite the relatively low voltage output of these devices, the power transferred to an optimised load is in fact higher than devices that incorporate an insulating layer and generate a higher voltage output, due to the low impedance match of up to ~ 10 kOhm. The key importance of fully characterising these devices in order to understand their operating principles will be discussed, along with the developments we have made to increase their output. In addition, we are investigating these devices for use in wireless sensor nodes for helicopter health monitoring, and the progress and challenges for practical implementation of these devices will be discussed.

Resume : The Internet of Things (IoT) is an increasingly growing topic within both the research community and the industrial sector. From a technological standpoint its full commercial exploitation relies on the development of wireless sensor networks (WSN) that monitor and control specific parameters. Low power radiofrequency (RF) energy harvesters address effectively the increasing demand towards battery-less systems to power these sensors. In the heart of such harvesting systems lies the AC-to-DC rectifier, which, if matched to a suitable antenna, will allow powering of low energy IoT applications. Adhesion Lithography (a-Lith) constitutes an innovative patterning technique for the formation of large aspect ratio (> 100,000) metal nano-diodes on a variety of substrate types and sizes and it is capable of both tackling specific manufacturing challenges as well as delivering high performance rectifiers. Herein we demonstrate high throughput fabrication of asymmetric coplanar electrodes with nanogap distances < 30 nm on glass or plastic flexible substrates. These, when combined with novel solution-processed high mobility n- and p-type organic and inorganic materials, enable the development of RF co-planar Schottky diodes that can drive high currents in a very small active area due to the extreme downscaling of key device dimensions. In particular, it will be shown that high aspect ratio nanodiodes with total widths ranging from 1 cm to 1 m can be fabricated with a-Lith on large areas and lead to high power outputs with cut-off frequencies exceeding by far the 13.56 MHz benchmark. Finally, different device structures, such as full wave bridge rectifiers, will be explored to further boost the output voltage.

Resume : In the landscape of energy harvesting, a new scenario for exploiting contactless mechanical energy was proposed [1]. It uses giant magnetostrictive Terfenol-D material which can produce a high mechanical energy (25 mJ/cm3). This energy can then be converted using high electromechanical coupling factor piezoelectrics (k = 0.35 - 0.75 with PZT) thus generating useful electrical energy from magnetic fields. This scenario would lead to smart compact composite harvesters able to supply a resulting ideal electrical energy density in the mJ/cm3 range. However, the success of the solution will depend on the performance of Terfenol-D. Terfenol-D single crystals are grown since decades (ETREMA Products, Inc.) but most applications use whole rods deformed in length, such as cylindrical actuators and transducers. The knowledge of more detailed and local properties are crucial, yet remain rarely investigated. For this purpose, samples, which are prone to variations associated with inhomogeneities between rods, are used. Our work aims to investigate the detailed relationship between magnetic and structural properties of samples. In particular, their dependence on magnetization, saturation magnetostriction, X-ray and metallography characterizations were carried out. [1] Lafont, Thomas, et al. "Magnetostrictive-piezoelectric composite structure for energy harvesting." PowerMems 2011

Resume : The demand for MEMS based energy harvesting devices continues to increase due to the Internet of Things. Harvesting energy from vibrations is a particularly interesting method since vibrations are observed in most environments. MEMS vibration harvesting devices typically have a high Q-factor and narrow bandwidth, which allow them to generate high power, but only over a small frequency spectrum. This limits their ability to be used in most real-life applications where the vibration source frequency can change by 5% or more. This paper describes a PiezoMEMS device to harvest energy from electromagnetic forces generated by current flowing through a power cable. A piezoelectric-based cantilever is used to harvest the energy whereas a permanent magnet integrated within the cantilever couples with the AC magnetic field from the cable in order to mechanically vibrate the cantilever. Power mains operate at 50/60 Hz with less than 0.1% deviation in frequency which is within the bandwidth of typical MEMS cantilevers. Matching the resonate frequency of the cantilever to 50/60 Hz ensures optimal displacement and power generation. A Si/AlN MEMS cantilever generated a power density of 4 µW/cm3 using a NdFeB magnet with remanence of 0.3 T by placing the device in close proximity to a cable with 2 A of current. A 10 A current is estimated to increase the power density to ~ 100 µW/cm3. Higher power can be achieved through optimization of magnetic material and positioning of the cantilever.

Resume : In comparison to e.g. thermoelectrics piezoelectric energy harvesting provides a much larger set of parameters and requirements given by the diverse nature of the mechanical input energy: While the design of a thermoelectric generator does mostly take heat flux, temperatures and temperature gradients into account, a piezoelectric generator has to be designed with respect to the intended harvesting scheme (resonant vs. non-resonant), frequency characteristics of the mechanical input energy (mono-frequent, multi-frequent, broadband,...), type of vibrations (regular with constant or variable frequency, impulses,...), frequency range ('low frequency' vs. 'high frequency') and, finally, acceleration amplitudes found. This wide parameter space has multiple implications on the choice of a piezoelectric material with its dedicated material properties and on the design of a piezogenerator. The presentation will bridge the span between the choice of piezoelectric material, the modeling of its behavior in a generator design and the design and the application of various types of piezogenerators. Modeling is of essential importance given the wide parameter space described above. This is demonstrated with a theoretical model for mechanically excited PZT cantilevers including the effect of ferroelastic hysteresis and its experimental verification. Design and fabrication will show piezogenerators built with piezo-polymer composite technology for a rapid and easy integration of piezoceramics into the mechanical structure of a vibration harvester. Practical applications will be shown with impact type, array-type and frequency-tunable piezogenerators for applications in sports as well as in building and infrastructure monitoring.

Resume : Future tire pressure monitoring systems (TPMS) will be mounted on the inner-liner of the tire and need an energy harvester for autonomy. We developed a robust MEMS based electrostatic energy harvester consisting of a variable capacitor with integrated electret as polarization source [1]. The proof mass has a footprint of 1 × 1 cm and the electret consists of a 1 µm SiO2 / 150 nm Si3N4 stack charged by corona discharge. The devices are packaged by wafer level bonding for protection of the springs and to prevent decay of the electret charge due to moisture. The main improvements in reliability of the new design includes the integration of flexible Si bumpers in the springs, introduction of dimples in the cavity for prevention of pull-in and stiction of the mass and better hermiticity due to improved wafer level bonding. The dominant vibrations on the inner-liner consist mainly of repetitive high amplitude shocks. With a shock, the mass is displaced, after which it will 'ring-down' at its natural resonance frequency and mechanical energy is harvested. The power output of the devices exceeds 500 µW for sinusoidal excitation and between 10-50 µW for shock excitation, sufficient to power a TPMS. No decay of the generated power over time is observed, indicating the hermiticity of the package. The improved Si springs with flexible Si stopper survive high amplitude shocks up to 2500G. The devices meet TPMS specifications, both on power generation as well as on shock resistance. [1] M. Renaud et al., Smart Mater. Struct. 24 (2015) 085023

Resume : In this work, a novel seed layer is proposed as a key promoter of high aspect ratio ZnO nanosheets under standard hydrothermal growth conditions. This seed layer allows a selective growth of ZnO nanosheets (NS) by patterning of the seed layer showing, in addition, a great uniformity with a surface coverage higher than 90%. Moreover, compared to the growth of ZnO nanowires (NW) in analogous conditions, this method has been demonstrated to be faster and to have higher reproducibility. NSs present a wurtzite crystal structure with hexagonal shape, high aspect ratio and good crystalline quality. Both NS and NW nanostructures were electromechanically characterized using SEM, AFM and PFM, to subsequently fabricate a device comprised of ZnO NSs growth with this novel method, conductive polyimide substrate and protecting PDMS layer. The structure has been tested using an ad-hoc set-up to generate controlled bending and vibration on the sample. Finally, by adjusting the position of the top electrode, the triboelectric and piezoelectric contributions for this type of structure has been determined, showing that the triboelectric working mode exhibits a higher generated voltage compared to the piezoelectric working mode when vertical force is applied. This facile method for NS growth can be a step stone for an application of energy harvesting using ZnO NSs

Resume : Advances in microfabrication and bio-engineering are enabling today a large variety of miniaturized implantable systems for health monitoring and deficiency treatments. Among emerging implants, a new generation of miniaturized pacemakers, called 'leadless pacemakers' is under development by several companies such as LivaNova, Medtronic, St Jude Medical and EBR System. These pacemakers are very small (about 1 cm3) and they are directly implanted on the endocardium within a heart cavity. Considering the current state-of-the art of lithium-based technology used to power pacemakers, a 0.6 cm3 battery could last approximately from 7 to 9 years. Therefore, long lasting regenerative energy sources as alternatives to traditional batteries are particularly interesting to increase the lifetime of leadless pacemakers. We present here a new 3D electrostatic energy harvesting microsystem designed to power leadless pacemakers by using the heart vibration. The harvested power would be about 10 µW, that is to say approximately 5 orders of magnitude lower that the heart mechanical power. Therefore, the energy harvesting process would not disturb the heart operation. We also present a prospective way to increase the power density based on up-frequency conversion. Finally, we propose a new family of interface circuits enabling to efficiently implement electrostatic vibration energy harvesters with ultra low power losses, using very few active components and no magnetic transformer or inductor.

Resume : The zinc antimonide compound ZnxSby is one of the most efficient thermoelectric materials known at high temperatures, due to its exceptional low thermal conductivity. For this reason, it continues to be the focus of active research, especially on its glass-like atomic structure. However, before practical use in actual surroundings such as near a vehicle manifold, it is imperative to analyze the thermal reliability of these materials. Herein we present the thermal cycling behavior of ZnxSby thin films in nitrogen (N2) purged or ambient atmosphere. ZnxSby thin films were prepared by co-sputtering, and reached a power factor of 1.39 mW m-1 K-2 at 321 °C. We found maximum power factor values gradually decreased in N2 atmosphere due to increasing resistivity with repeated cycling, while the specimen in air kept its performance. X-ray diffraction and electron microscopy (TEM, SEM) observations revealed that fluidity of Zn atoms leads to nano precipitates, porous morphologies and even growth of a coating layer or fiber structures on the surface of ZnxSby after repetitive heating and cooling cycles. With this in mind, our results indicate that proper encapsulation of the ZnxSby surface would reduce these unwanted side reactions and the resulting degradation of thermoelectric performance.

Resume : Achieving the high energy density of lithium ion battery is one of the major concerns in consumer as well as research sectors. Setting the anode materials aside, high capacity cathodes are known to be realized by exploring new compounds and crystalline structures in limited chemical elements of atomic table. Adapting high-voltage cathode materials, however, can be an alternative strategy and affordable for achieving the high energy density batteries. Voltage elevation of existing crystal structure is simply accomplished by cation substitution without changing intercalation mechanism, such as partial substitution of Mn in LiMn2O4 spinel with Ni2 /4 . The charged potential elevation of LiMn2O4 from 4.0 V to 4.7 V by Ni substitution, which is LiNi0.5Mn1.5O4 increases the energy density by ~ 20%. However, implementing the high voltage cathodes into the conventional lithium ion batteries is impeded by unsolved issues, such as decomposition of liquid electrolyte and dissolution of transition metals from cathode. It is well known that LiPON solid electrolyte doesn't decompose under anodic current in voltage ranges of 0 ~ 5.5 V, nor worry about cation dissolution from cathode even about flammability. We demonstrate the stable operation of high voltage all-solid-state thin film batteries using a LiNi0.5Mn1.5O4 cathode materials, which delivers excellent cycling performance after 1000 cycles and good rate performance due to the interfacial stability.

Resume : Polyvinylidene fluoride (PVDF) polymer has strong ferroelectric effect when it was subjected to mechanical stretching and external excitation. For this reason PVDF received great attention of researchers. PVDF piezoelectric polymer can be used for generators or actuators, and is valuable material for energy harvesting device, in particular. When a mechanical stress such as sound wave is applied to the piezoelectric polymer PVDF, electrical charges are induced between its two surfaces. Using this property, a piezoelectric material can be applied for an electromechanical energy converter. [1] On the other hand, graphene have been considered as transparent electrode materials due to its outstanding electrical and optical properties including high density, high thermal conductivity, and optical transmittance. [2] In this study, we demonstrate an energy harvesting effect using PVDF and graphene electrode. Graphene was grown using chemical vapor deposition (CVD) method, and transferred on the PVDF film. We transferred graphene on both sides of PVDF film at the same time. We used a conventional wet chemical method for transferring the graphene. We measured and analyzed output voltage induced by sound wave, when a mechanical tension was applied to the device. Also, we fabricated a rectifier circuit to collect the output signal. As a result, when a tension were applied to graphene/PVDF/graphene device, we measured 7.6 V as maximum output voltage.

Resume : The analysis of sulfur distribution in porous carbon/sulfur nanocomposites using small-angle x-ray scattering (SAXS) is presented. Ordered porous CMK-8 carbon was used as host matrix and gradually filled with sulfur (20 - 50% wt.) via melt impregnation. Thanks to the almost complete match between the electron densities of carbon and sulfur, the porous nanocomposites present in essence two-phase systems and the filling of the host material can be precisely followed by this method. The absolute scattering intensities normalized per unit of mass were corrected accounting for the scattering contribution of the turbostratic microstructure of carbon and the amorphous sulfur. The analysis using the Porod parameter and the chord-length distribution (CLD) approach determined the specific surface areas and the filling mechanism of the nanocomposite materials, respectively. Thus, SAXS provides comprehensive characterization of the sulfur distribution in porous carbon and valuable information for deeper understanding of cathode materials of lithium-sulfur batteries.

Resume : Energy harvesting using triboelectric nanogenerators (TENGs) has been investigated due to their high output power and simple fabrication method. Since its first introduction, performance limit has been continuously extended by various approaches. Among them, physically enlarging friction surface area is one of the most distinct ways to enhance the output power generation. Various surface patterning methods using micro sized template, anodized aluminum oxide (AAO) patterns, and block copolymer self-assembly have been adopted for TENGs. However, uniform and scalable nano-sized patterns that can effectively increase friction area has rarely investigated due to difficulties in pattern transfer processes. Here, we report performance enhancement and output power control method of TENGs by surface patterning using nanoimprint lithography. Our TENG demonstrates that distinct performance improvement by enlarging surface area using nanoimprint lithography. Specifically, the TENG with patterned line dimensions of a 200 nm line width, 200 nm pitch and 200 nm depth demonstrates voltage and current up to ~ 400 V and ~ 48 μA·cm-2 at applied force of 0.3 MPa at a contact motion frequency of 2 Hz, which is 2-fold higher values than those from flat surfaces. Besides, to maximize the performance of TENG, nanoimprinted line patterns are also chemically functionalized with poly (diallyldimethylammonium chloride) (PDDA), boosting voltage and current up to ~ 480 V and 60 μA·cm-2, respectively.

Resume : Zinc oxide (ZnO) based piezoelectric nanogenerators (PENGs) have gained great attentions due to its non-toxicity and abundance in nature. However, ZnO PENG's performance has been limited by large excess electron concentration in ZnO, inducing piezoelectric potential screening effect. Various methods have been introduced to address this problem. One of the most effective way is to form p-n junction with p-type materials. Therefore, various p-type materials have been adopted for p-n junction formation to boost PENG's performance. However, ZnO homojunction has not been investigated to date, even if it is more suitable for PENGs, due to difficulties in ZnO p-type doing. Here, we report the performance of phosphorus doped ZnO p-n homojunction PENG with phosphorus doped ZnO (p-ZnO:P) and ZnO on a ITO/Ag/ITO (IAI) coated PET substrate. Our results show that the output voltage and current can be obtained up to ~ 24 V and ~ 6 μA, respectively, at the applied force of 0.5 MPa, which is 6-fold higher than that of PENG only with ZnO layer. Furthermore, optimal thickness ratio between p-ZnO and ZnO has been systemically determined to maximize the performance of ZnO p-n homojunction PENGs.

Resume : Zinc oxide (ZnO)-based piezoelectric nanogenerators (PENGs) have been intensively investigated due to its abundance, biocompatibility, mechanical robustness, and low permittivity. Up to date, consistent efforts to realize high performance ZnO NGs have been made. Various methods, such as surface passivation, p-n junction formation, and triboelectric layer insertion, have been tried to this end. However, high performance ZnO PENGs with mechanical durability have not been much reported due to ZnO's inherently low piezoelectric coefficient and difficulties in forming polymer-piezoelectric ceramic composite structure PENGs. In this work, we present a novel method to realize PENGs with ZnO-polymer composite structure and extend the performance limit of intrinsic ZnO-based PENGs. Specifically, ZnO nanosheets were doped with vanadium during hydrothermal growth process, resulting in ferroelectrically phase transformed ZnO NSs. Thus, electric polarization domain in ZnO NSs can be aligned even in the composite structure by applying external electric field. The fabricated PENGs (4 cm × 4 cm) demonstrated enhanced output power with excelling device reliability, exhibiting output voltage and current of ~ 32 V and ~ 6.2 μA, respectively. The peak output power of the PENG is two orders of magnitude higher than that of PENG fabricated with intrinsic ZnO NWs. In addition, the PENG ensured the superior durability and reproducibility over a month without performance degradation, thanks to NSs encapsulation inside PDMS. The approach introduced here is simple, effective, and suitable for large-scale robust flexible high performance ZnO-based PENGs.

Resume : Recently, triboelectric generators (TEGs), utilizing triboelectric contact electrification, have been widely reported to build self-powered electronic devices, thanks to their high output power density and relatively simple fabrication process. To date, most research efforts in TEGs have been mainly focused on creating various rough nano-/micro-surface features on two materials apart each other in triboelectric series. Thus, it limits material choices and entails processing issue. In the light of this, we developed simple chemical surface functionalization method to greatly improve the output power of TEGs by inducing apart triboelectric charging sequence between two contacting materials. Specifically, polyethylene terephthalates (PETs) were readily coated with poly-L-lysine (PLL) solution and trichloro (1H,1H,2H,2H-perfluorooctyl) silane (FOTS) using solution-coating and vapor deposition, respectively. Owing to the surface functionalization, the PLL coated-PET surface exhibits positive charges while FOTS coated-PET surface is turned into negative charge rich surfce. The output performance of TEGs fabricated with two surfaces was remarkably enhanced compared with that of TEG with non-functionalized surfaces, exceeding ~ 330 V and ~ 270 mA/m2 during cyclic contact motion at an applied force of ~ 0.5 MPa. In addition, the TEGs demonstrated superior mechanical durability and reproducibility, showing stable output signals over ~ 7200 cycles for a month. The approach introduced here is a facile, effective, and cost-competitive route to fabricate high performance TEGs and more importantly broaden the materials choices for TEGs in triboelectric series.

Resume : Due to its high dielectric constant and good chemical stability BaTiO3 (BTO) is the most intensively studied ferroelectric material for about six decades by now. To exhibit ferroelectric and with it pyroelectric properties BTO must reveal the tetragonal crystalline phase, i.e. each titanium ion is shifted from the center of the oxygen octahedra in the z-direction of the unit cell, leading to a distortion of the cubic perovskite type structure. The resulting dipole moment in each unit cell leads to a surface potential on {001} surfaces, named spontaneous polarization. By a change in temperature a changing value of this polarization will be obtained and enables many capabilities such as well-established passive infrared (PIR) sensors up to devices for energy harvesting. However, investigations into the latter are so far quite rare and seldom published [1], [2]. In this paper the results of our investigations on the pyroelectric characteristics of BTO single crystals for hydrogen generation by water electrolysis will be shown. Therefore, irregular pieces of BTO crystals were ground to a particle size dP < 100 µm and poured in small ashlar-formed container (40 x 40 x 4 mm). After subjecting this arrangement to an electric field of E = 2 kV for t = 15 min the container was filled with distillated water and set to a periodic temperature change between T = 40 - 70°C simulating the use of low temperature waste heat sources e.g. the return at a heating system. With the help of a highly sensitive solid-state gas sensor (detection limit of xH2 ≈ 50 Vol.-ppb) hydrogen could be detected after some runs, which provided the desired proof that it is principally possible to use pyroelectric materials to generate hydrogen from waste heat. [1] K.-S. Hong et al., J. Phys. Chem. Lett., 2010, 1 (6), pp 997-1002 [2] S. Nayak et al., Ind. Eng. Chem. Res., 2014, 53 (39), pp 14982-14992

Resume : A dielectric nanocomposite based on cyanoethylated O-(2,3 dihydroxypropyl)-cellulose (CRS) and MMT nanoclay was successfully prepared with different weight percentages (5%, 10% and 15%) of MMT. MMT nanoplatets obtained via sonication of MMT nanoclay in acetone for prolonged period of time were used in the preparation of CRS-MMT nanocomposites. The intermolecular interactions and morphology within the polymer nanocomposites were analysed using ATR-FTIR, XPS, TGA, SEM and AFM. CRS-MMT thin films on SiO2/Si wafers were used to form metal-insulator-metal (MIM) type capacitors (100 nm thick Al metal electrodes were used as current collectors). At 1 kHz CRS-MMT nanocomposites exhibited high dielectric constants of 71, 55 and 42 with low leakage current densities (10-6 - 10-7 A/cm-2) nanocomposites with 5%, 10% and 15% weight of MMT respectively, higher than reported values of pure CRS (30), Na-MMT (10). The Leakage was studied using conductive atomic force microscopy (C-AFM) and leakage is associated with MMT nanoplatelets embedded in the CRS polymer matrix. The energy band diagram for CRS-MMT nanocomposite was constructed using UV-Vis absorption and Ultraviolet photoemission spectroscopy. High permittivity nanohybrid materials with nanoclays dispersed in a high permittivity polymer can be a suitable candidate for energy storage applications.

Resume : Waste recycling is an eco-friendly process to change used materials into potentially useful new products, which reduces not only the consumption of fresh raw materials and the usage of energy, but also protects the environment. Recent studies revealed the South Korean produces 110000 tons of coffee bean waste annually and the waste has been buried in a landfill up to now. However, the landfills eventually leak. Numerous environmental problems (e.g. atmospheric and hydrological effects) now become the talk of the town, waiting for the appearance o f a smart solution. Here, we report a potential way to creatively dispose the coffee bean waste. We transformed the coffee bean waste into nanoporous carbon powder which can be served as an electrode material for an ordinary supercapacitor. We carbonized the coffee bean waste by pyrolysis in a high temperature. Subsequently, by the treatment with KOH and K2CO3, we activated the carbonized waste in order to drive micropores and mesopores. By electrochemical characterizations, we found that the maximum Brunauer-Emmett-Teller surface area and gravimetric specific capacitance of the prepared nanoporous carbon powder are 1834 m2/g and 200 F/g, respectively. The observed supercapacitor performance achieved with the derivatives of the coffee grounds is believed to be attributed to their unique pore structure and distribution, and make them potentially promising for diverse other energy storage devices. We believe that our approach could be adopted as one of creative solutions to effectively recycle and dispose the waste coffee ground for the protection of our environment.

Resume : Recently supercapacitor having graphene electrode has been interested in much fields. For a successful supercapacitor, an adhesion between a metal collector and a graphene electrode is important in manufacturing. In this study, we have tried a bi-continuous carbon structure(BCS) for supercapacitor electrode which has a high surface area as well as a high pore volume. And also we have gotten a supercapacitor having a stable structural status of electrode. We used Polyacrylonitrile(PAN) precursor for BCS active material. It is first pre-heated in the air at 150 - 300 ºC for aromatization with H-elimination. The 2nd heat treatment is performed to convert the aromatized polymer into lamellar phase by carbonization in CO2/Ar mixture at 800 - 1100 ºC. We evaluated BCS active material, conductive material and binder for the electrode of supercapacitors. The electrochemical properties of supercapacitor with BCS electrode such as energy density, power density, charge-discharge (CD), and impedance were evaluated by using a cyclic voltammeter.

Resume : High dielectric constant (high-k) materials have attracted much research attention due to their important applications in modern nanoelectronics including energy harvesters, capacitors, transistors, communication devices, etc.[1] Nanocomposites (with high-k fillers such as barium titanate) have been widely investigated due to their advantages as low-cost, light-weight, flexible and printable high-k materials.[2,3] Strontium doped barium titanate (SBTO) is considered to be one of the most promising ferroelectric materials due to its high tunability and low dielectric loss at room temperature.[4] In order to exploit these properties, SBTO was functionalised to improve wetting between the filler (SBTO nanofibres) and matrix (epoxy or PVDF). Functionalised SBTO was cast into robust films with a range of particle sizes and loadings for dielectric analysis and incorporated as part of the MATFLEXEND energy harvester. References 1. D. Wang, T. Zhou, J.-W. Zha, J. Zhao, C.-Y. Shi and Z.-M. Dang, J. Mater Chem 2013, 1, 6162. 2. H. A. Ávila, L. A. Ramajo, M. S. Góes, M. M. Reboredo, M. S. Castro and R. Parra, ACS App. Mat. Int. 2013, 5, 505. 3. X. Zhang, Y. Ma, C. Zhao and W. Yang ECS J. Solid State Sci. Technol. 2015, 4, N47. 4. L. Zhang, J. Zhai and X. Yao, Materials Research Bulletin, 2009, 44, 1058.

Resume : A facile electrochemical method was used to modify anatase TiO2 with Na+ under a cathodic bias in an ethylene glycol electrolyte. Two different kinds of potential wave (a constant potential of 5 V for 2200 s, and a pulse voltage with 7.5 V 110 s and 2.5 V 110 s for 10 loops) were exerted onto the fabricated electrode samples. TiO2 nanotube arrays (TNTAs) were fabricated by anodization method for the benefit of growing TiO2 directly on the Ti substrate. The obtained perpendicular TNTAs were served as charge collectors in the electrochemical doping process and following application tests. The electrochemical performance of the TiO2 samples was studied by cyclic voltammograms (CV) and galvanostatic charge/discharge (GCD) measurements. The doped TNTAs and pulse doped TNTAs yield a specific capacitance of 9.072 F/g and 12.75 F/g at a discharge current density of 0.5 A/g, which is 18 and 26 times higher than the non-dope TiO2, respectively. Importantly, the doped TNTAs also show remarkable rate capability with over 80% mass capacitance retained when the current densities increase from 0.1 to 2 A/g. The mass capacitance also shows little drop after 10000 cycles at a scan rate of 100 mV s-1.

Resume : Ordered three-dimensional (3-D) tubular arrays are highly attractive candidates for high performance pseudocapacitors electrodes. Here, we report 3-D fluorine doped tin oxide (FTO) tubular arrays fabricated by a cost-effective ultrasonic spray pyrolysis (USP) method in anodic alumina oxide (AAO) channels with high uniformity. The large surface area of such structure leads the remarkable surface area enhancement up to 51.8 times as compared to a planar structure. Combing with electrochemically deposited manganese dioxide (MnO2) nanoflakes on the inner side wall of the FTO nanotubes, the unique hierarchical core-shell structured pseudocapacitor electrode achieved the highest areal capacitance of 196 mF·cm-2 , which is 18.5 times of that of a planar electrode, and volumetric capacitance of 112.6 F·cm-3 . In addition, cyclic stability test also showed that a nanostructured pseudocapacitive electrode has a much larger capacitance retention after 3000 cycles charge-discharge process as compared with a planar electrode, primarily due to the mechanical stability of the nanostructure. With the merit of facile fabrication procedures and largely enhanced electrochemical performance, such a 3-D structure has high potency for energy storage systems for a wide range of practical applications.

Resume : Leadless pacemakers operate by being implanted in the right ventricle of the heart, which offer significant advantages over standard pacemakers. However, the size of the pacemaker needs to be significantly reduced, so long-term battery life is not feasible. Therefore the leadless pacemaker requires a MEMS based vibration energy harvesting device in order to operate. However, the vibrations from the heart operate at low frequency (20 - 30 Hz) which makes silicon based devices challenging. This paper describes a polymer based piezoelectric MEMS cantilever structure that is capable of harvesting energy from the heart. The MEMS devices are made using standard MEMS microfabrication techniques and use a CMOS compatible Aluminium Nitride piezoelectric layer. Traditional energy harvesting applications operate with a continuous sinusoidal acceleration; however, the heart behaves like a series of impulse vibrations. This impulse significantly affects the average power especially in silicon based devices. Based on FEM analysis the average power for a Si-based device is 0.022 µW, whereas a polymer based device would have an average power of 0.37 µW per cantilever due to damping. Pacemaker electronics require 5-10 µW to operate. Therefore, a polymer based device would require 6 - 12 s to harvest enough power to operate a pacemaker. The authors are currently investigating various methods for increasing the power harvested while maintaining high device reliability.

Resume : Energy harvesting from alternate sources with flexible piezoelectric-based nanogenerators is becoming a growing trend to provide power in portable electronic devices. In addition, biomedical implants require such self-sustaining devices which are compatible and biodegradable. In this work, a flexible nanogenerator (NG) is realized with poly(vinylidene fluoride) (PVDF) film, where deoxyribonucleic acid (DNA) is selected as agent for the electroactive β-phase nucleation. The denatured DNA molecule with available H-bonds and surface negative charges co-operates in aligning the CH2/CF2 dipoles of PVDF which are mainly responsible for the piezoelectric behavior of this polymer. It is especially noteworthy that the additional electrical poling step for the β-phase nucleation is not necessary. We have found, that the flexible NG prepared with the DNA-PVDF exhibits energy harvesting from external mechanical motions such as repeated finger impacting, footsteps, and object drops (e.g. football). The electrical energy generated by the NG is capable to charge capacitors and light up several LEDs providing a wide scope for the design of self-powered portable piezoelectric devices in the near future. As DNA is the nucleating agent for the electroactive phase, the lack of toxic heavy metals and compounds render the NG completely biodegradable and compatible making it ideal for biomedical implants and sensors. [1] [1] A. Tamang et al., ACS Appl. Mater. Interfaces 7 (2015) 16143.

Resume : Electrode supports are generated by electrospinning of polyacrylonitrile fibers and subsequent coating of a thin electrically conductive TiO2 layer by atomic layer deposition. The supports are then functionalized with a [NiFe]-hydrogenase-containing membrane fraction from Escherichia coli and are characterized structurally and electrochemically. The morphology of the electrospun nanofibers with and without treating with the hydrogenase fraction is investigated by scanning electron microscopy and the elemental composition is confirmed by energy-dispersive X-ray spectroscopic analysis. The characterization of the titania coating is performed by powder X-ray diffraction as well as by X-ray reflectivity. The electrochemical activity of the fiber mats is studied by cyclic voltammetry and electrochemical impedance spectroscopy. The hydrogenase suspension generates a micron-thick organic film around the fiber mat, which exhibits electrocatalytic activity for hydrogen evolution. Furthermore, the electrode geometric surface area is varied systematically via the electrospinning procedure, which reduces the charge transfer resistance and increases the hydrogen evolution current density to > 500 µA·cm-2 at 0.3 V overpotential.

Resume : The ever growing demand for miniaturized energy storage solutions for electronic devices has attracted much interest in the recent years. However the required large footprint area for traditional on-chip capacitors limits the performance and thus their feasibility for applications. Carbon nanotubes have been previously demonstrated to be suitable for discrete supercapacitor devices by having low electrical resistivity, good structural stability and high surface area-to-volume ratio. These properties can dramatically increase the performance for on-chip capacitors on silicon devices. Here we demonstrate on-chip carbon nanotube based supercapacitor structures by using standard photolithography and silicon etching processes combined with chemical vapor deposition of micropatterned and aligned nanotube forests. The structure of the devices are studied with scanning electron microscopy and the performance device is assessed by cyclic voltammetry and charge/discharge transient current measurements.

Resume : Vanadium Dioxide (VO2) is a strongly correlated material that undergoes a first-order phase transition from a monoclinic insulating phase to a tetragonal metallic phase when heated above its transition temperature (~ 340 K). The change in electrical resistivity due to the metal-insulator transition (MIT) can reach 5 orders of magnitude. This phase transition can also be triggered using electrical excitations, making VO2 an excellent candidate for many ultra-fast, energy efficient applications. We describe the experimental investigation of tunable terahertz scatterers consisting in a planar wideband bowtie metal antennas coated with VO2 layers. The principle exploited in VO2 tuning is the steep reduction of electrical resistivity by MIT. Such a structure scatters a terahertz wave in a broad range of directions, the scattered field being modulated by the switch. A 500 nm VO2 thin film is grown on sapphire by reactive pulsed laser deposition (RPLD) using a KrF laser and a THz antenna is fabricated on the VO2 film. The modulated scatterer is explored by time domain terahertz spectroscopy and demonstrates significant signal strength above 0.5 THz. We discuss how such devices can enable future energy efficient communications, sensing and energy harvesting needed for wireless sensor networks (WSN) in the Terahertz Band.

Resume : The indispensability of electrical energy is such that its storage or transport must be effectively achieved. Although substantial progress has been made in the storage of electrical energy since the discovery of the 'Leyden jar' in the 18th century, the current or future global technological advancements - for improved living - impose new challenges. Truly, the realization of high-performance micro-supercapacitors (miniaturized supercapacitors) is currently a big challenge but the ineluctable applications requiring such miniaturized energy storage devices are continuously emerging. Laboratory scale components are appearing, demonstrating the viability of integrated supercapacitors via micro-fabrication processes. This new field of academic research is still at an early-stage, but it is moving extremely fast with major advances being reported almost monthly. Although major advances have been achieved on the improvement of their areal energy, a wafer-level encapsulation process of these electrolyte-based devices is still an indispensable issue to validate. In this presentation, we will highlight the insights, the progress and the prospects in developing integrated miniaturized supercapacitors. Some clarifications will be made on the unusual properties of these components and on meaningful metrics to use when reporting their characteristics.

Resume : The carbonaceous composites have attracted much attention as anode material for the supercapacitor. Additionally, the transition metal oxides, like Co3O4, essentially have high specific capacitance in the charging/discharging process. Here, we investigated the lithium storage mechanism of Co3O4/graphene/CNTs material via in-situ transmission electron microscopy (TEM). Moreover, we analyzed the structure and composition of the anode material by high resolution TEM image and electron diffraction patterns. We figure out two different mechanisms between the charging and discharging process accompanied with the structural evolution of the transition metal oxide and the volume variation of the electrode material. Furthermore, the porous structures of graphene/CNTs matrix have excellent ability to accommodate the tremendous volume expansion to enhance the life of supercapacitors. Our observations not only provide direct evidence of electrochemical behavior but also improve the structure failed to promote more outstanding performance and application of supercapacitors.

Resume : Transition metal oxides have attracted much interest owing to their high power density in lithium batteries; therefore, to understand the electrochemical behavior and mechanism in lithiation-delithiation processes is significant. In this study, we successfully and directly observed the structural evolution of MnO2/CNTs during the lithiation processes via transmission electron microscopy (TEM). MnO2/CNTs were selected due to their high surface area and capacitance effect. The lithiation mechanism of the CNTs wall expansion was systematically analyzed. Contrastingly, the wall spacing of MnO2/CNTs and CNTs were obviously expanded 10.92% and 2.78%, respectively. The MnO2 layer caused the structural defects on the CNTs surface to allow the penetration of Li+ and Mn4+ through the tube wall, and hence improve the ionic transportation speed. This study provided direct evidence to understand MnO2/CNTs in lithiation process applied in lithium ion battery. This study also has great potential to benefit the applications and envelopment of supercapacitors.

Resume : The present study discusses the impact of metal (M = Fe, Mn, Co and Bi) in large surface area carbon nano fibers (CNFs) as electrode materials on the electrochemical performances of supercapacitors. The M-CNF electrode material was prepared by means of electrospinning techniques in combination with thermal treatments. Each M-CNF was prepared in concentration about 1% w. of metal and was introduced into the polymer blend of Polyacrylonitrile (PAN) of 12% w. in dimethylformamide (DMF) solvent. The electrospinning techniques were optimized by varying the distances between the needle and current collector and voltage applied. The carbonization process consisted in a stabilization process at 270 ºC for 7 h in oxygen atmosphere and carbonization process up to 1000 ºC in argon. The characterization techniques such as P-XRD, FE-SEM, BET surface area analysis and BJH pore size and volume were carried out in order to show the M-doped CNFs material structure and properties. The electrochemical characterization was carried out using cyclic voltammetry techniques, potentiostatic electrochemical impedance spectroscopy and galvanostatic charge-discharge cycling at various current densities several kinds of electrolyte (e.g. organic and aqueous with/without redox-active species) solutions in order to investigate the best performance in terms of capacitance and long term-stability in both 3 electrode test cell and 2 electrode Swagelok cell. The electrochemical performances in 2 electrode Swageok cell among all the M-doped CNFs, 1% Fe-doped CNFs have shown high specific capacitance and specific capacitance retention of 95.4% for 1000 galvanostatic charge-discharge cycles at 1 A/g, would be discussed in the present study. Furthermore, the electrochemical performances of the M-doped CNFs electrodes in our self-design facile volume limiting electrolyte cell would also be discussed in the present study. The implementation of these large surface area M-CNFs were carried out in to laboratory supercapacitor prototype in order to assess their performance. The performance of this supercapacitor is discussed in terms of specific capacitance, power and energy density and coulombic efficiency.

Resume : A brand-new heterostructure material based on metal oxide and metal hydroxide was presented which offered opportunity to optimize the electrochemical performance of supercapacitor electrode material. As a prototype, a new composite material NiCo2O4 @ NiCo(OH)2 nanowires on Ni foam with better electronic conductivity and high areal capacitance was synthesized through electrodeposition and hydrothermal process. The abundant active sites and exposed hydrogen atoms of NiCo(OH)2 endowed the NiCo2O4 @ NiCo(OH)2 nanowires electrode with a large areal capacitance of 4.625 F·cm-2 at the current density of 1 mA·cm-2. Also, the NiCo2O4 @ NiCo(OH)2 nanowires electrode exhibited excellent cycling life, with 87% capacity retention after 1000 charge-discharge cycles, holding great promise for synthesizing supercapacitor electrodes constructing high-energy storage nanodevices.

Resume : Anisotropy of chemical bonds in layered crystals, weak van der Waals bonds between crystalline layers and strong covalent bonds between adjacent atoms inside the layers define anisotropy of electric and dielectric properties of these crystals, which results in instability of synthesis when forming the crystalline lattice of these compounds. The following doping and, first of all, intercalation of the interlayer space in these crystals with foreign atoms or molecules, beside obtaining some expected changes in physical-and-chemical properties of hybrid materials based on them, finds its practical applications in energetics, in particular, as cathode materials in lithium batteries, supercapacitors, solid-state hydrogen storages, solar cells, sensors of gases and physical fields, etc. Performed in this work are: i) intercalation of layered semiconductor crystals InSe and GaSe in melts of ferroelectric saults KNO3 and RbNO3 (the so-called 'intercalates', in what follows) at various melt temperatures and duration of crystal intercalation; ii) investigation of electric and dielectric characteristics inherent to intercalates; iii) optical-microscopic, electron-microscopic (SEM) and energy-dispersive investigations of technological surfaces and fresh cleavages of intercalates; iv) studying the spectra of edge photoluminescence of these intercalates at the temperature range T = 4.5 - 100 K. It has been shown that intercalation in melts of the above saults leads to segmentation of intercalates, in particular, there observed are clearly pronounced interfaces between semiconductor matrix and nano-dispersion ferroelectric phases. Tentative estimations of the specific electrical capacitance (1500 - 2000 F/g) for prototypes of intercalation accumulation capacitors have been made.

Resume : Nowadays printed electronic has attracted more attention due to its significant advantages by increasing the need for higher energy and power density energy storages such as micro-battery and micro-supercapacitors. One the most versatile printing method is 3D dispenser that opens a big window towards printed electronic applications. 3D dispenser is based on FDM (Fused deposition modeling) method, printing layer by layer of ink through micro size needle. One of the greatest challenges for the 3D printing of micro-energy storage is ink formulation with high concentration of active materials. A novel aqueous ink consists of functionalized active carbon, conductive and capacitive additive with aqueous binder was formulated for micro-supercapacitor (ECDL). Printable electrolyte base on ionic liquid with high working temperature > 350 ºC and high windows potential 4.7 V was prepared. The printed 3D micro-supercapacitor demonstrates high specific capacitance of 260 mF·cm-2 and specific energy of 424.8 mJ·cm-2 by cyclic voltammetry method with a scan rate of 2 mV/s.

Resume : Power generation and storage for sensors, miniaturized biomedical devices and integrated on-chip components can significantly benefit from the fabrication of thin film microsupercapacitors. Toward this goal it is pivotal to develop high throughput coating techniques enabling the integration of porous thin films on almost any kind of materials including low cost, lightweight and green substrates like polymers and paper. Supersonic cluster beam deposition (SCBD) of nanostructured materials is a versatile room temperature technique for the fabrication of nanostructured thin films and their integration into microdevices [1]. SCBD consists in the deposition of nanoparticles produced in the gas phase to form films with very low density and high porosity. Supersonic expansions for cluster deposition allow to obtain very high deposition rates and highly collimated beams enabling the deposition of patterned nanostructured films by using shadow masks. Recently, the use of SCBD for the fabrication of carbon binder-free microsupercapacitors on glass and polymeric substrate has been demonstrated [2-4]. Here we report the room temperature fabrication of planar thin film microsupercapacitors where nanostructured current collectors and electrodes are integrated by SCBD on plain paper and ionic liquids are used as electrolyte. As prepared microsupercapacitors are encapsulated within a thin layer of PDMS to avoid electrolyte leakages. Such paper-based microsupercapacitors show promising capacitive performances and could be used to power paper electronics such as transistors or sensors. [1] K. Wegner, P. Piseri, H. Vahedi Tafreshi, P. Milani, J. Phys. D: Appl. Phys. 2006, 39, R439 [2] L.G. Bettini, M. Galluzzi, A. Podestà, P. Milani, P Piseri, Carbon, 2013, 59, 212 [3] L.G. Bettini, G. Divitini, C. Ducati, P. Milani, P. Piseri, Nanotechnology, 2014, 25, 435401 [4] L.G. Bettini, P. Piseri, F. De Giorgio, C. Arbizzani, P. Milani, F. Soavi, Electrochim. Acta, 2015, 170, 57

Resume : Thermoelectric devices are of interest for applications as power generators and heat pumps, which convert heat to electricity via the Seebeck and vice versa via the Peltier effect. The development of thermoelectric thin films has brought a new perspective to the integration of thermoelectric cooling devices into microelectronic systems for thermal management purposes. Bi0.5Sb1.5Te3 (BST) exhibits the highest room-temperature power factor among p-type materials and is considered a state-of-the-art thermoelectric material. The motivation behind the present study is to optimize the transport properties of BST thin films on glass and flexible substrates in the temperature range 200 to 390 K. This study focuses on understanding how the stoichiometry affects the transport properties of deposited and post-annealed thin films. We have grown p-type Bi0.5Sb1.5Te3 and Bi0.5-xSb1.5+xTe3+1%wt thin films onto different types of substrates using pulsed laser deposition and home-made targets. The films were grown at room temperature and then were subjected to a post-annealing process. In this talk, we will discuss how their thermoelectric properties are affected by the substrate type and Bi content. Also, we will address the effect of post-annealing treatment on their structural, electrical and thermoelectric properties.

Resume : Micro energy harvesters can transform kinetics energy in electrical energy and are considered an appealing candidates for application in independent power supply for wireless self-powered microsystems, but unfortunalty, the application is limited in most of the cases by the high production costs. Therefore this work focuses on a polymer based capacitive harvesters which can be fabricated with help of roll-to-roll low cost methods. In contrast to electrostatic MEMS based on parallel plate transducers or dielectric elastomer systems here, the capacitance is varied as function of the mechanical load by changing the top electrode area with help of an electrically conducting composite elastomer. With this approach the power density can be increased over the other concepts if high-k dielectrics were used for the capacitors. These flexible energy harvesters are of particilar interest for wearables devices, including smart textiles, shoes and other applications where mechanical compliance is needed. Numerical simulations were used to identify the influence of material parameters and parasitic circuit elements on the harvester performance as function of actuation frequency. FEM Maxwell simulation of the composite electrodes reveals that not only high electrical conductivity of the electrodes is an important parameter to take into account, but also the homogeneus distribution of the particles within a mean distance lower than 1 µm, and their eventual coverage by the polymer matrix can affect the performances of the devices. On the other hand high mechanical compliance of the eleastomer electrode is required to get a close contact to the dielectric surface. Air entrapment at the inteface between dielectric and elastomerelectrode must be avoided as well. First experiments with several dielectrics and composite elastomer electrodes of various geometrical configurations have been performed. The specific capacities of elastomer electrodes is ca. 5 times smaller than that of metal electrodes. Charges between 25 and 70 nAs per cm2 have been transferred per cycle at 100 V/200 V while the maximum capacity was between 0.4 and 0.8 nF/cm2. Higher charges were observed in case of minus pole connected to the elastomer electrode. This influence of polarity is an indication that the electrical charges were not only transferred to a higher voltage but static electricity contributes to the charge generation as well. Acknowledgements This are results of the FP7 MATFLEXEND project, funded by the European Union under contract: 604093

Resume : Rechargeable micro batteries are considered the power source of choice of wearable and miniaturized electronic devices; in fact the need of thin, in part bendable and adaptable electrochemical storage devices can be satisfied by these technologies, thanks to the various available cell configurations. In our work we develop a special segmented battery packaging concept, employing pre-patterned current collector foils as battery housing, assembled in a laminate cell configuration, following, the electrolyte filling was performed by the means of microfluidic dispenser, finally, the cell was sealed on substrate level. The main advantages of these cell configurations are the tunable size and shape of the battery that can be easily changed by employment of lithography masks with different geometry. The battery thickness is in the range between 0.3 and 1 mm resulting in a specific area capacity between 1 and 5 mAh/cm2. Conventional Li4Ti5O12 (LTO) and LiNi1/3Co1/3Mn1/3O2 (NMC) have been used as anode and cathode material respectively, while the EC:DEC 1:1 1M LiPF6 soaked in a glass fiber separator has been used as electrolyte media. Besides the conventional electrode materials also novel Li4Ti5O12 fibers (LTO-F) have been tested, furthermore self-made ceramic particle polymer binder composites which can be printed were tested as separators. All fabrication steps and materials were optimized towards the foil type segmented micro battery: - The performance of LTO-F anode was tested against commercial powders. - Electrode pastes and separators were optimized for stencil print and dispensing including water based binder. - Electrodes (LTO anode and NMC cathode) and ceramic separator printing processes, required for the segmented electrode shape were developed. - Battery assembly and final sealing was developed, including low water permeation rate lamination between top and bottom package and electrolyte filling with help of a microfluidic adapter. Half and full cell cycling behaviors have been evaluated by galvanostatic cycling test with increasing C-rate, revealing the influence of materials and packaging parameters on the electrochemical performances. A four segment 3 mAh prototype of size 15x40 mm2 is described in detail. Acknowledgements This are results of the FP7 MATFLEXEND project, funded by the European Union under contract: 604093

Resume : High quality lithium phosphate thin films have been deposited by metal-organic chemical vapor deposition, using tert-butyllithium and trimethyl phosphate as precursors [1]. The lithium phosphate films deposited at 300 °C yielded the highest ionic conductivity (3.9×10-8 s·cm-1). Increasing the deposition temperature led to crystallization of the deposited films and, consequently, to lower ionic conductivities. Kinetic studies on planar substrate showed that the lithium phosphate deposition is a diffusion-controlled process in the temperature range of 300 to 500 °C. Thin films have also been deposited on highly structured substrate to investigate the feasibility of 3D deposition of lithium phosphate by MOCVD. Furthermore, very thin films of lithium phosphate have been deposited onto thin film Si anodes as protective layers and it was found that these layers effectively suppress the SEI formation and dramatically improve the cycle performance of Si film anodes. The coulombic efficiency of the Li3PO4-protected Si anode is higher than 99.98%. Up to almost 500 cycles, hardly any capacity loss can be observed. [1] Xie J, Jos F. M. Oudenhoven, Peter-Paul R. M. L. Harks, Dongjiang Li, Peter H. L. Notten; Journal of The Electrochemical Society, 162 (3) A249-A254 (2015)

Resume : Microbattery architectures are required for autonomous operation of miniaturized electronic devices. Higher capacities per footprint area, increased ionic conductivities in solid electrolytes and better electrode/electrolyte interfacing are the currently limiting steps [1]. Here, different routes to solve these will be discussed. First, the realization of on-chip thin-film and interdigit electrode batteries will be detailed. Sol-gel and electrochemical synthesis of the battery electrode materials was coupled to laser microstructuring to enable fast, reproducible and reliable production of solid-state microbattery prototypes. The second part will detail on a simple and reliable route for the synthesis of three-dimensional bicontinuous Nicore-NiOshell core-shell nanowire networks with tunable geometrical parameters. The proposed self-supported Nicore-NiOshell hybrid nanowires efficiently accommodates the volume change - induced stress, resulting in superior lithium storage properties as compared to standard formulations. Noteworthy, the capacity per footprint area is 40 times higher when compared to a conventional two-dimensional thin film system at an equivalent thickness of the active battery material [2]. Such developments are particularly interesting in the context of the 3D micro-battery manufacturing where electrode configurations that provide high power while maintain high specific footprint capacities are critical. Routes for on-chip integration for such systems and the possibility to explore other active electrode materials and solid electrolytes will be also discussed. [1] A. Vlad et al. Adv. Energy Mater. 2015, 5 : 1402115. [2] A. Vlad et al. J. Mater. Chem. A 2016, DOI: 10.1039/c5ta10639g.

Resume : Silicon is considered the fulcrum of the next generation lithium-ion systems due to its exceptional capacity and low working voltage. Many instabilities are associated with the huge volume expansion during lithium alloying, generating material degradation and inducing rapid capacity devolution. Thus, a suitable Si-based anode relies on engineered nanostructures that can avoid the lithiation-induced cracking and architectures that can accommodate the volumes changes, while sustaining scalability and simplicity required for commercial adoption. We detail on the fabrication of an intertwined material based on flexuous Si nanowires (f-SiNWs). The large-scale synthesis of f-SiNWs relies on metal assisted chemical etching. A chemical peeling procedure has been developed to facilitate the separation of f-SiNWs from their substrate by adjusting the concentration of oxidizing agent to favor the formation of a porous segment. By scanning probe microscopy techniques, we study the morphological, electrical and mechanical properties of the f-SiNWs. The three-dimensionally-entangled f-SiNWs-based materials are assembled via a vacuum filtration technique with MWCNTs as percolative conductive pathways. In the absence of binders, the cohesion between layers of active materials and the structural integrity of the assembly are offered by f-SiNWs. These materials exhibit improved electrochemical performance with ionic liquids compared to conventional electrolytes. A thin Ni coating on the f-SiNWs has been found to further enhance the cycling life of these materials. The mechanical and electrochemical robustness of the Si-based electrode are mainly assigned to the flexuous nano-architecture of the SiNWs [G. Sandu et al. submitted].

Resume : Transition metal oxides show great potential for the energy-related applications, like batteries or supercapacitors, due to their excellent catalytic activity or electrochemical properties. Zero-dimensional nanomaterials made of metal oxides, often used as active components in composites for electrode materials, exhibit great promise for integration into devices. Atomic layer deposition (ALD) is a thin film deposition technology, however it also offers a possibility to controllably fabricate metal oxide nanoparticles if the substrate is appropriately chosen. For example, given the chemical inertness of reduced graphene oxide (rGO) or carbon nanotubes (CNTs), metal oxides (like RuO2 or Co3O4) will grow specifically on defect sites (native or intentionally created). The size and the density of the nanoparticles can be controlled with high accuracy by altering the number of applied processing cycles. After the nanoparticle growth, the fabricated rGO/RuO2 system exhibits improved capacitive performance with promise for a use in supercapacitors [1], while the Co3O4/CNT system shows excellent oxygen reduction reaction (ORR) activity with exceptional stability/durability upon further stabilization with a thin carbon shell [2]. This presentation will give insight into the fabrication of the composites as well as the characterization of the electrochemical and catalytic performance of the materials. [1] Yang, F. et al., Functionalization of Defect Sites in Graphene with RuO2 for High Capacitive Performance. ACS Appl. Mater. Interfaces 2015, 7, 20513-20519. [2] Yang, F. et al., Exceptionally Stable Non-Noble Metal Catalyst for Oxygen Reduction Reaction: Uniform CoxOy Nanoparticles Embedded in N-Doped Carbon. In preparation.

Resume : Thanks to the scaling drive of CMOS and the rise of MEMS highly mature techniques for the fabrication of Si-based micro/nano devices exist. These techniques can also be utilized in building advanced energy harvesting/storage devices. In this presentation, we discuss silicon-based micro and nanostructures as potential candidates for harvesting and storage applications. For example, by adopting the so-called work function energy harvesting principle [1] silicon can be utilized in vibrational energy harvesters as the active harvesting material. In thermoelectric harvesting Si is not considered as the best candidate due to its high thermal conductivity. However, in Si nanostructures the phonon heat transport is strongly hindered [2], while maintaining the good electrical properties, and relatively good thermoelectric figure of merit can be reached. What comes to electro-chemical energy storages, chemical reactiveness typically prevents the direct utilization of Si nanostructures, but, for example, by adopting conformal coating of porous Si highly stable supercapacitor elements can be realized.[3] [1] A. Varpula, S. Laakso, T. Havia, J. Kyynäräinen and M. Prunnila, Sci. Rep. 4, 6799 (2014). [2] S. Neogi, J. Reparaz, L. Pereira, B. Graczykowski, M. Wagner, M. Sledzinska, A. Shchepetov, M. Prunnila, J. Ahopelto, C. Sotomayor-Torres, and D. Donadio, ACS Nano 9 3820 (2015). [3] K. Grigoras, J. Keskinen, L. Grönberg, J. Ahopelto and M. Prunnila, J. Phys.: Conf. Ser. 557 012058 (2014).

Resume : The EU NMP MANpower project (www.themanpowerproject.eu) concerns the design and development of an implanted cardiac pacemaker powered by energy harvesters converting the mechanical motion of the heart to electricity. The partners are developing a number of novel electronic components fabricated using a range of materials and structures. These include piezoelectric and electrostatic energy harvesters with novel material combinations, an electrochemical supercapacitor and a new pacemaker capsule design. The aim is that these materials and components should survive at least 400 million heart cycles, approximately 12 years. This paper focuses on the reliability, durability and biocompatibility (RD&B) of the MANpower materials and components. It will particularly focus on the challenges of optimising these three parameters in the context of a project where materials and components are novel, are being developed by multiple partners in multiple countries, test samples become available only in the second half of the project and there is only three years available to demonstrate that a 12-year lifetime is achievable. A further major challenge is that the materials loading conditions within the heart are still unknown as the accelerations and displacements of the inner heart walls are only poorly known. We have therefore had to determine these so we could define the parameters for accelerated testing procedures. The unique design of the pacemaker has driven considerable creativity in modelling and testing of the RD&B of its materials and components. As well as presenting the overall RD&B strategy for MANpower, we will present the specific modelling and testing strategies and results to date for the different materials and components.

Resume : Silicon nanowires (Si NWs) are a promising material for thermoelectric applications. Such nanostructured material together with the use of standard silicon technologies enable envisaging all-silicon thermoelectric microgenerators, which could be mass-produced in a cost-effective way as micro-energy sources for powering sensor nodes in applications where waste heat is available. In any case, Si NWs will need first to be successfully integrated into a silicon structure where a temperature difference can be established. Being silicon-based technologies essentially planar technologies, such silicon housing structure should follow a lateral architecture, mainly consisting in a thin thermally isolated platform surrounded by a bulk silicon rim. The device architecture will be introduced and the two main technological challenges addressed will be shown: (a) micromachining of suspended platforms with a good thermal performance (improved ΔT across Si NWs), and (b) integration of large numbers of Si NWs readily connected with minimum electrical and thermal resistances to the active parts of the device. For the former, an appropriate device design and process sequence have been defined minimizing thermal leaks across the auxiliary and permanent supports of the self-standing platform other than the Si NWs themselves. For the latter, a silane CVD-VLS bottom-up approach has produced ordered arrays of arbitrary long Si NWs with sub-100 nm diameter bridging platform and rim.