Diamond for electronic devices II

Resume : Recent work has demonstrated the potential to increase the 2D hole gas density and stability formed by surface transfer doping in hydrogenated diamond using high electron-affinity oxide films such as MoO3 [1] and V2O5 [2]. Despite the promising potential these provide to enhance the performance and stability of diamond-based electronic devices such as transistors, the efficient integration of these materials into devices has so far proven challenging. Understanding the physical and chemical structure of these oxide materials and how these are impacted during processing is therefore vital for their successful implementation in device applications. In this work we will discuss studies into the impact of processing on these films and the progress made and challenges that yet remain for their application in diamond transistor device technology. [1] Stephen A. O. Russell et al, Applied Physics Letters, Volume 103, 202112 (2013) [2] Kevin G. Crawford et al, , Applied Physics Letters. Volume 108, 042103 (2016)

Resume : Diamond has been identified as a potential candidate for high-power and high-frequency devices owing to its superior physical and electric properties. The highest breakdown voltage among wide-band-gap semiconductors with high thermal conductivity and high saturation velocity potentially lead to a higher attainable power density. In addition, exciton-related devices, electron emitters with negative electron affinity, and single photon source with excellent spin characteristics including long coherence time are also considered to be future applications utilizing the unique properties of diamond semiconductors. P- and n-type doping underlay the design of virtually all these applications. Comprehensive achievements of the fundamental processes that control impurity doping are required. For example, heavily doped layer over 1020 cm-3 can reduce the series resistance including n-type Ohmic contact issue, and lightly doped layer can improve the carrier lifetime in the active region of several junction devices, indicating wider doping levels are quite important for electronic applications. Detailed aspects of n-type impurity doping and electrical properties of unique diamond devices will be discussed. Acknowledgements: This work was supported by JSPS KAKENHI Grant Number JP17916364 and JP16776363.

Resume : Diamond is the next generation semiconductor material for high power electronic applications with its unique electrical and thermal properties. In unipolar power devices such as Schottky barrier diode or field effect transistor, the breakdown voltage is linked to the design of the drift layer as well as to the physical properties of the material used. Due to the specificity of diamond, for a given breakdown voltage value, only one drift layer design (doping level and thickness) will offer the lowest ON-state resistance at a specific operating temperature. Based on the ionization integral calculation with impact ionization coefficients adapted to diamond, we performed an accurate analysis of the drift layer design as function of the breakdown voltage in which the doping level, the thickness and the operating temperature are considered as tunable parameter. The optimal designs for few typical classical breakdown voltage values will be given and the importance of the operating temperature will be highlighted in this work. For instance, the optimum operating temperature is 495 K for BV=10 kV while it is 575 K for BV= 3 kV. Then, using these results we will show how some small trade-off on the ON-state resistance and a judiciously chosen operating temperature can allow growing drift layer with achievable design while keeping rather good performances at device and system levels. These results will allow proposing preliminary design rules to fabricate efficient unipolar diamond power devices, which are necessary to convince power electronics community about the interest of diamond.

Resume : Diamond power devices are promising for high-voltage and high-temperature applications [1]. We have so far shown diamond junction field-effect transistors with superior characteristics such as high electric-field operation of ~6 MV/cm [2]. However, achieving high reliability and reproducibility is a major challenge for the realization of power devices based on new materials. In general, fabricated devices often show electric-field concentration, heating, and leakage current, but there has been difficulty in quantitatively monitoring such device parameters with high precision and spatial resolution. Here, we demonstrate sensing of operated diamond power devices using nitrogen-vacancy (NV) centers. The NV center can work as quantitative and nanoscale sensors for physical parameters [3] of electric-field, magnetic-field, and temperature. By utilizing electron spins of the NV center, quantitative information on internal electric-fields has been obtained in diamond devices [4]. We also demonstrate vector sensing using multiple NV centers. Our proposed method will lay the foundation to monitor the physical parameters in operated power devices. This work was supported by TEPCO Memorial Foundation and JST-CREST. [1] M. Willander et al., J. Mater. Sci. 17, 1, 2006. [2] T. Iwasaki et al., IEEE EDL 35, 241, 2014. [3] D. Doherty et al., Phys. Rev. B 85, 205203, 2012. [4] T. Iwasaki et al., ACS Nano, 11, 1238, 2017.

Resume : Diamond has a number of extreme properties that lend themselves readily to applications in quantum information processing and metrology. For example, defects in diamond such as silicon / nitrogen ? vacancy complexes exhibit room temperature single photon emission and the ultra high resonant frequencies achievable in diamond Nano-Electro-Mechanical Systems (NEMS) allow them to be cooled into the ground state at temperatures achievable with a dilution refrigerator. In the case of single photon centres, a key issue is control over position. There are various approaches to this, one of the most promising being to make nanoparticles of diamond containing the required colour centre and position them manually. To this end, diamond films containing SiV or NV centres have been milled to nanoscale particles and stable aqueous colloids produced. This work will detail the production and purification of such particles. For NEMS the main issue is detection of motion for which is exploitation of superconductivity is proposed. Superconductivity QUantum Interference Devices (SQUIDs) are highly sensitive to magnetic flux. This effect can be exploited to detect the motion of a cantilever embedded in a SQUID loop, as its deflection will modulate the area and hence flux through the loop. This work will demonstrate the fabrication of diamond NEMS and SQUIDs towards this device.

Resume : One of the key challenges in environmental and biological sensing is the presence of background fluorescence and scattered light that make it difficult or impossible to identify the fate and transport of nanoparticles in complex systems. The use of optically detected magnetic resonance (ODMR) provide a pathway to selectively image the spatial location of nanodiamond within complex matrices. However, as nanodiamond becomes smaller, factors such as shift in charge state and surface trapping become important. We have investigated the factors that influence ODMR contrast in nanodiamond samples as a function of nanoparticle size and have demonstrated the ability to perform ODMR in a full-frame imaging mode. Some of the factors influencing the ability to use ODMR to improve signal-to-background ratio in environmental imaging applications will be discussed.

Resume : During the last decade the unique properties of the negatively charged nitrogen vacancy center (NV- center) in single crystalline diamond have been exploited for developing new types of scanning probe and wide-field magnetometers with high sensitivity and spatial resolution. This technique has the capability of quantitatively recording magnetic images of nanoscopic systems beyond the limits of standard techniques. In this talk, we will show the development of an all-diamond magnetometric sensor with improved magnetic field sensitivity. To this end, we use 30-50 µm thick membranes of (111)-oriented single crystalline diamond with NV centers. Shallow NV centers were realized by ex-situ Nitrogen implantation or by in-situ growth of Nitrogen delta-doped diamond layers in combination with subsequent ex-situ He_2^+-implantation. Both are followed by a subsequent thermal annealing process. Nitrogen concentration in the diamond lattice can be controlled from the lower ppb level to upper ppm level for delta layers of typically 20 nm thickness. NV centers incorporated in these diamond layers are characterized by measurements of electron paramagnetic resonance (EPR) yielding values for the coherence time T_2 and the magnetic field sensitivity of the NV centers. Vertical waveguide tips are fabricated via a top-down process by use of highly anisotropic plasma dry etching. These tips typically exhibit diameters of 200 nm with lengths ranging from 2 to 4 µm [1]. It is observed that conical shaped nanostructures or nanopillars increase the collected intensity of the NV fluorescence and therefore act as waveguides [2]. Several hundred micro-optical tips are realized on a diamond plate. Tips are singulated and transferred to quartz tuning fork AFM probes by use of micro manipulators (Imina Technolgies SA). For characterization we apply secondary ion mass spectrometry (SIMS) as well as scanning electron microscopy (FIB-SEM) and confocal micro-photoluminescence spectroscopy (µ-PL). We will discuss and summarize our results with respect to tip fabrication technology as well as to demands for scalable production. References [1] C.J. Widmann et al., Fabrication and characterization of single crystalline diamond nanopillars with NV-centers, Diam. Relat. Mater., 54(2015), pp. 2-8. [2] S. A. Momenzadeh et al. Nanoengineered Diamond Waveguide as a Robust Bright Platform for Nanomagnetometry Using Shallow Nitrogen Vacancy Centers, Nano Letters 15 (2015) pp. 165-169

Resume : Diamond is an exceptional semiconductor material due to its wide bandgap, superlative thermal conductivity, and high electron and hole mobilities. By introducing relevant dopant atoms, currently limited to boron and phosphorus, electrically conductive layers can be obtained, useful for the fabrication of device structures. For high power devices, diamond is considered the next generation material with the potential to surpass all other semiconductor materials like silicon, SiC, and GaN. To sustain and block large electric fields in the OFF state, and conduct high current densities in the ON state, the crystalline quality of electronic grade diamond is of paramount importance. Notwithstanding that the first report on the successful n-type doping of diamond with phosphorus by Koizumi and co-workers was already 20 years ago, a full understanding of the parameter window that governs successful n-type doping of high crystalline quality diamond films remains an area of significant current research interest [1]. Here we will present the optimisation of the growth of phosphorus doped singe crystal diamond. A controlled series of doping experiments was carried out to achieve n-type diamond suitable for high power device applications. Characterisation techniques include photocurrent measurements, low temperature Fourier transformed infrared spectroscopy, Hall Effect, Raman spectroscopy, and optical and electron microscopy, to analyse the effect of pretreatment steps, phosphine concentration, and substrate temperature on defect morphology, electrical properties and phosphorus incorporation. Using a contactless probe technique, charge carrier lifetimes of the doped layers are determined, in an attempt to correlate the different structural and electronic properties of the CVD grown layer with the underlying substrate material, sourced from different providers and clearly distinguishable crystalline quality. In the end, strategies for improving the deposition of n-type diamond will be presented. This work was performed within the H2020 Research and Innovation Action Project "GreenDiamond" (www.greendiamond-project.eu) under grant agreement N°640947. [1] S. Koizumi, M. Kamo, Y. Sato, H. Ozaki, T. Inuzuka, Appl. Phys. Lett. 71/8 (1997), 1065-1067.

Resume : Electronic devices are built on the properties of charge carriers in semiconductors, namely independent electrons and holes. When both kinds of charges coexist in the crystal, they tend to attract each other?s by coulombic interaction to form free exciton pseudo-particles. Free excitons present remarkable interactions with the semiconductor dopants: bound excitons are formed by free exciton capture at impurity sites of the crystal lattice. Such properties are at the basis of the luminescence spectroscopy of bound excitons, which appears today as a key experiment for the research on diamond doping. The talk will review the physical properties of bound excitons in diamond and their benefits for analyzing the electrical activity of its shallow dopants: boron [1], phosphorus [2] and arsenic [3]. The formation and recombination mechanisms of bound excitons will be described at the light of recent time-resolved photoluminescence experiments performed on diamond layers doped with phosphorus or boron [4]. The specific capture cross sections of these impurities have been assessed. It will be shown that a specific Auger mechanism governs bound exciton recombinations. This process is non-radiative and its probability dramatically increases for deep dopants, which explains why the luminescence of bound excitons reveals the shallow dopants of diamond. [1] J. Barjon, T. Tillocher, N. Habka, O. Brinza, J. Achard, R. Issaoui, F.Silva, C. Mer, P. Bergonzo, Phys. Rev. B 83 (2011) 073201 [2] J. Barjon, P. Desfonds, M.-A. Pinault, T. Kociniewski, F. Jomard, J. Chevallier, J. Appl. Phys. 101 (2007) 113701 [3] J. Barjon, F. Jomard, S. Morata, Phys. Rev. B 89 (2014) 045201 [4] J. Barjon, P. Valvin, C. Brimont, P. Lefebvre, O. Brinza, A. Tallaire, J. Achard, F. Jomard, M.A. Pinault-Thaury, Phys. Rev. B 93 (2016) 115202

Resume : The incorporation of phosphorus (P) dopants as donor atoms in high pressure and high temperature (HPHT) diamond is investigated. P-doped samples under different HPHT growth conditions are analysed. Convincing confirmation of the phosphorus incorporation in the crystals during HPHT growth process is obtained. The P concentration on diamond (111) growth face ranges up to 2x1017 cm-3 (1 ppm) as measured by secondary ion mass spectroscopy (SIMS). Low temperature cathodoluminescence spectroscopy performed on samples demonstrates the incorporation of phosphorus in donor substitutional sites. A detailed characterization through cathodoluminescence will be presented and correlations between samples morphologies and dopants concentrations will be discussed.

Resume : In this study the growth, mechanical transportation and analysis of large-area conductive diamond sheets for transparent electrodes have been investigated. Diamond films have been fabricated on tantalum and molybdenum thin film substrates. Since used substrates have got low diamond adhesion and low capability for a creation of carbides thin CVD diamond sheets were exfoliated mechanically after growth. Moreover, the substrate surfaces have definitely higher coefficient of thermal expansion than diamond that provides to additional parameter enhancing exfoliation of diamond film. In opposition to the other reported methods of CVD diamond foils fabrication this one does not require any etching or long time stripping to remove diamond sheets from the substrates. The large area (up to 10mm x 10mm) diamond sheets with thickness of ca. 300 nm have been exfoliated from the substrate using mechanical techniques. The diamond sheets have been transported to other substrates like thick SiO2. In summary, the fabrication procedure and parameters of novel freestanding diamond nanosheets has been studied. The phenomena of unique low adhesion and delamination from substrate is under investigation (e.g. lattice mismatch, temperature stress, bonding energies). The very first attempt of diamond nanosheet ? graphene FET transistor. Acknowledgements This work was supported by the Polish National Science Centre (NCN) under the Grants No. 2014/14/M/ST5/00715 and 2016/21/B/ST7/01430. The DS funds of Faculty of Electronics, Telecommunications and Informatics of the Gdansk University of Technology are also acknowledged.

Resume : There is considerable interest in the fabrication and electronic properties of graphene and related 2d materials such as BN for low-dimensional materials engineering. Diamond provides the ideal, lattice-matched substrate for the growth of single-domain graphene growth and, as an alternative to CVD growth and exfoliation, the diamond substrate can also provide the source of carbon for the 2-d overlayers using a method based on metal-catalysed graphitisation. This method enables epitaxial growth at a lower temperature in comparison with metal-free graphitisation and CVD growth (~ 500°C). Using in-situ and real-time optical and photoelectron-based methods, we have shown that epitaxy can be maintained throughout the process by control of the substrate orientation, termination, metallisation and temperature. Since the source of carbon is below the growing layer, it is possible to controllably grow single and multilayer films. In a bilayer structure, the inner layer is bound strongly to the metal catalyst, but the second layer exhibits the electron dispersion characteristic of quasi-free graphene with Dirac points at the Fermi level. Using a similar method, we have demonstrated the hexagonalisation of crystalline cubic BN with the same metal catalyst.

Resume : With the increased interest in the use of thin film diamond in a wide range of applications from micro-electro-mechanical systems [1] to tribological coatings [2], compositional and structural analysis of the initial stages of diamond growth is required in order to optimise the growth conditions used. Unlike conventionally used characterisation techniques including Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron (SEM) and atomic force microscopy (AFM), spectroscopic ellipsometry (SE) has robustly demonstrated the quantitative estimation of the composition of diamond films with varying depth [3, 4]. The aim of this study is to therefore use variable angle spectroscopic ellipsometry to investigate the optical, compositional and structural properties of nanocrystalline diamond films during the early stages of growth. To this end, a series of nanocrystalline samples of varying thickness (25-75 nm) were grown on (100) silicon wafers. Before growth, each wafer was placed into a mono-dispersed diamond colloid known to produce seeding densities > 1011 cm-2 [5]. Characterisation with SE was performed within the spectral range 200-1000 nm using a simple 4-layer model to account for the surface roughness, grain boundary sp2 and void fraction within the bulk, and SiC layer thickness at the interface with the Si substrate. With such a model the seeds and individual islands atop a 5-9 nm SiC layer are observed, before continued growth leads to coalescence at a thickness of ~30 nm as indicated by a reduction in the void content. The subsequent peak in non-diamond content from the addition of grain boundaries is then corroborated with Raman, while the increasing thickness of the surface roughness layer arising from columnar growth is validated with AFM, demonstrating the applicability of SE to the initial stages of diamond film growth. Lastly, the evolution from nano-diamond seeded Si to film was studied with SEM and x-ray diffraction. References [1] A. Gaidarzhy, M. Imboden, P. Mohanty, J. Rankin and B. W. Sheldon, Appl Phys Lett 91 (20) (2007). [2] M. Amaral, C. S. Abreu, F. J. Oliveira, J. R. Gomes and R. F. Silva, Diam Relat Mater 17 (4-5), 848-852 (2008). [3] J. Mistrik, P. Janicek, A. Taylor, F. Fendrych, L. Fekete, A. Jager and M. Nesladek, Thin Solid Films 571, 230-237 (2014). [4] B. Hong, J. Lee, R. W. Collins, Y. Kuang, W. Drawl, R. Messier, T. T. Tsong and Y. E. Strausser, Diam Relat Mater 6 (1), 55-80 (1997). [5] O. A. Williams, Diam Relat Mater 20 (5-6), 621-640 (2011).

Resume : Nanodiamonds (NDs, 5-20nm) are an important class of nanoparticles for a range of applications. The vast majority of investigation to date have studied intrinsic NDs. Here, we present an investigation of purposefully boron-doped, and hence p-type, NDs from a range of production methods. We show, for the first time, that nano-scale Schottky Diodes can be produced on such material. This paper will review the materials used, the device characteristics achieved and the potential applications for these devices.

Resume : The development of diamond power devices are attractive because their expected high voltage and temperature strength, however some specific technological aspects still need to be overcome. One of them is the quality of oxide layer for the performance of metal-oxide-diamond field effect transistor. The authors present a study by transmission electron microscopy techniques of homoepitaxial alumina layers grown on diamond. Specifically, high resolution electron microscopy, electron energy loss spectroscopy and energy dispersive X-Ray spectroscopy were carried out on two samples were the alumina layer was grown at 380 ºC by atomic layer deposition being one of them subjected to a subsequent thermal treatment. This study shows that among the different known transition alumina, ?-alumina is the type of alumina present in both samples, instead of the thermodynamically stable alumina, ?-Al2O3. In the sample without thermal treatment, three zones in the alumina layer were identified: Z1- amorphous alumina, Z2- small grains of alumina and Z3- almost mono crystalline alumina. Fast Fourier transform was used to identify the orientation of the grains in Z2 and Z3. Nevertheless, the sample with thermal treatment showed an almost mono crystalline ?-alumina layer. The crystallographic relationship between the diamond and alumina crystals was determined. Complementary studies by STEM-EDX concluded that, in one hand, the oxygen and aluminium distributions are not uniform, i. e., there is a compositional modulation at the nanometer scale and on the other hand, there is a 1-2 nm width interface between the diamond and alumina where an increasing gradient of oxygen atoms is identified. After the thermal treatment, these aspects were found to be improved

Resume : High quality single crystal diamond with thin ?-shaped boron-doped epilayers have been thought to offer a viable approach towards high speed, high power and high temperature applications. ?- doping diamond has been conjectured to achieve high mobilities and carrier concentrations, proper- ties of real interest for electronic applications. Taking advantage of diamond?s thermal and electronic properties, thin films can be incorporated into realistic nanoscale devices more easily than the parent bulk system. Using angle-resolved-photoemission spectroscopy (ARPES), we uncover the electronic structure of bulk and thin films (? 1.5 nm) of boron-doped diamond. Surprisingly, the ARPES measurements do not reveal any significant differences for these systems, irrespective of their physical dimensionality. This suggests that it is possible to grow nearly atomic-scale structures whilst still preserving the properties of bulk diamond facilitating the use of thin films diamond for devices which necessitate nearly atomic-scale components. Acknowledgements: We acknowledge Johan Adell for the support at the beamline I4. Phil King, Thomas Frederiksen and Ion Errea for the valuable discussions about the data acquisitions and their understanding. The authors gratefully acknowledge Diamond Microwave Ltd (www.diamondmw.com) for access to the 'delta-doped' diamond samples grown under contract by Element Six Ltd (www.e6.com) and for essential help from Dr Richard Lang and Dr Richard Balmer respectively. Likewise the ?bulk? doped samples were grown at the Cardiff Diamond Foundry, under the supervision of Prof Oliver A Williams (www.astro.cardiff.ac.uk) assisted by one of the authors (APT). Diamond Microwave and the UKs Engineering and Physical Sciences Research Council (EPSRC) are also thanked for the award of a PhD ?CASE? award to APK, and EPSRC for an award to one of the applicants (RBJ) for financial support of the work (EP/H020055/1)

Resume : CVD diamond films are an attractive material for electron emission cathode, because of their potentially low or negative electron affinity, which reduces the effective surface potential barrier and enable electrons to be emitted easily from diamond surface into vacuum. It is therefore expected to have good electron emitting characteristics with rather low voltage and high current levels. Phosphorus incorporated NCD films are one of the candidates for emission cathodes. In this study, we prepared phosphorus incorporated NCD films by plasma-enhanced CVD with H2, CH4, and PH3 gas mixture, and characterized the structure and electrical properties by Raman spectroscopy with a green laser of 532 nm at room temperature, scanning electron microscope, transmission electron microscope, and electron energy-less spectroscopy. The grown films show certain conductivity and have a typical structure with a combination of sp3 diamond gains with size around 20-100 nm and sp2 graphitic grain boundaries. Detailed aspects of phosphorus incorporation and electron emission properties will be discussed. Acknowledgements: This work was supported by JSPS KAKENHI Grant Number JP16776363.

Resume : The freestanding diamond microcrystals and highly textured diamond microcrystalline films were synthesized using plasma enhanced chemical vapor deposition method where Ar/CH4/H2 mixture was exploited as working gas. Mo and Si single-crystalline plates were used as substrates for the deposition. The varying of the technological parameters in the mentioned synthesis method such as the temperature and the pressure in CVD reactor as well as methane concentration and substrate material allows preparation of two types of diamond microcrystals – with preferential orientation (100) and (111). For the characterization of freestanding microcrystals the methods of PL and Raman spectroscopies as well as FTIR spectroscopy and SEM were used. In the structure of the (100)-oriented crystals the nitrogen-related defect complexes N-V-N were registered using PL method, which are not typical for the structure of (111)-oriented ones. However, the N-related complexes such as N-V exist in both (100) and (111)-oriented crystals. It is important to note, in the PL spectra of (100)-oriented crystals on Si substrate one can register the luminescence band that is attributed to recombination with participation of defect levels, which include Si atoms. In the Raman spectra of diamond island films on Mo substrate (texture 111) only the sharp and intensive diamond-related (sp3 phase) vibration band is ascertained. The spectra of the island films on Si substrates, except diamond related band, include graphite-related bands D and G attributed to vibrations in the structure of sp2 phase.

Resume : Diamond is a wide band gap semiconductor material known to be one of the serious candidates for electronic power devices due to his exceptional physical properties. These properties are not only electrical because diamond has also a very good thermal conductivity (22 W/cm.K). Recent progress has been done on material allowing diode with excellent performance but improvements are still needed. One of them is the temperature management. The high activation energy of boron impurities in diamond gives a strong relationship between the resistivity and the temperature. Thus, at a given diode current, the diode voltage is linearly decreased for a device temperature increase. The diode voltage drop can then be used as a temperature sensitive electrical parameter to estimate the diamond power device temperature. The original idea is to use as a temperature sensor one diode different of the one used as power device. The second problem is the shared anode observed in our diode structure which implies a common impedance between the sensor and the power diode and that can induce an error in the temperature measurement and that can also play a role when diodes are put in parallel on the resistance measure. To overcome those issues, we will present a new architecture which takes advantages of each diodes present at the surface of our substrate and allowing various power converter designing. Some material and electrical characterizations will also be presented.

Resume : In this study, we have demonstrated the fabrication of novel material called boron-doped carbon nanowalls (B-CNW) which is characterized by remarkable electrochemical properties like high standard rate constant k°, low peak to peak separation value (?E) for oxidation and reduction processes of [Fe(CN)6]3-/4- redox agent and low surface resistivity. The B-CNW samples were deposited by the microwave plasma assisted chemical vapor deposition (CVD) using a gas mixture of H2:CH4:B2H6 and N2 [1]. Growth results in sharp edge, flat and long carbon nanowalls rich in sp2 as well as sp3 hybridized carbon phases. Achieved high value of k° = 1.1×10-2 cm/s and ?E as 85 mV much lower in comparison to undoped carbon nanowalls. The enhanced electrochemical performance of B-CNWs electrode could be applied for the ultrasensitive detection or energy storage devices. The incorporation of boron into B-CNWs films is examined by C 1s X-ray photoemission spectroscopy (XPS), morphology of B-CNWs is revealed using field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The electron diffraction pattern and the Raman spectroscopy display the coexistence of sp3 diamond and sp2 graphitic phases in B DNWs films. In addition, the microstructure investigation, carried out by high-resolution TEM with Fourier transformed pattern, indicates diamond grains and graphitic grain boundaries on surface of B-DNWs. Samples achieved high conductivity of 2.8 × 103 (? cm)-1 with carrier concentration of 6.2 × 1016 cm-2 and mobility of 1.1 × 102 cm2/V s. Interestingly, this specific feature of high conducting grain boundaries of B-DNWs demonstrates a high efficiency in field emission with low turn-on field of 6.8 V/?m and high FEE current density of 0.8 mA/cm2 (at 11.2 V/?m). Acknowledgements This work was supported by the Polish National Science Centre (NCN) under the Grants No. 2014/14/M/ST5/00715 and 2016/21/B/ST7/01430. The DS funds of Faculty of Electronics, Telecommunications and Informatics of the Gdansk University of Technology are also acknowledged. [1]. Siuzdak, K., Ficek, M., Sobaszek, M., Ryl, J., Gnyba, M., Niedzia?kowski, P., ... & Bogdanowicz, R. (2017). Boron-Enhanced Growth of Micron-Scale Carbon-Based Nanowalls: A Route toward High Rates of Electrochemical Biosensing. ACS Applied Materials & Interfaces, 9(15), 12982-12992.

Resume : We report the first nm-scale diamond transistor based on boron-doping showing clear channel modulation and pinch-off, along with exciting quantum transport characteristics. A diamond side-gated nano-transistor (SG-NT) is proposed and demonstrated for the first time. Thin boron doped layers (~5nm) were utilized, then being processed using e-beam lithographic methods with carefully selected resist technology to enable the formation of side-gated transistor structures. An impressive channel depth of 5nm and a channel width of 20nm were achieved. Gate lengths in the 10-500nm range were investigated. These devices are ?normally-on? (depletion-mode) devices, which display clear channel modulation and pinch-off ? key characteristics for any transistor. Further, they show clear quantum-transport phenomena ? an absolute first for diamond devices of this type. This presentation will introduce the fabrication methodology, the results achieved to date and the prospects for this exciting break-through technology.

Resume : Negative electron affinity materials are an important class of materials, particularly when small numbers of free electrons need to be reliably amplified - as is the case with image intensifiers. Here, highlights from several years of study into improving secondary electron emission (SEE) characteristics of nanocrystalline diamond (NCD) layers is presented for the first time. The effect of growth conditions on nanocrystalline diamond growth morphology, composition and SEE has been investigated - using typical diamond growth temperatures down to extremely low growth temperatures in order to successfully integrate NCD into current image intensifier systems. The use of H-terminated diamiond surfaces will be contrasted with monolayer alkali material coatings. The integration of diamond layers within multi-channel plate (MCP) based image intensifiers for night vision applications will be discussed.

Resume : Reactive Ion Etching (RIE) has emerged as a preferred method for diamond substrate surface treatment and device patterning. This process is crucial to achieve the fabrication of devices fully exploiting the exceptional properties of diamond. Following work optimising Inductive Coupled Plasma RIE etching for the removal of sub-surface damage, an investigation into the effects of etch process parameters on diamond patterning is pursued. The aim is the achievement of deep etching with controlled wall angle, minimized micro-masking and etched surface damage. More specifically, the impact of gas ratio and ICP power settings on the physical and chemical properties of the etch is studied with relation to mesa quality. Initial results highlight the importance of high platen/ICP power ratio and increased O2/Ar gas ratio to reduce damage and undesired features on the etched surface, with these improvements and further discussed in this paper.

Resume : Heavy metals such as mercury are highly toxic and tend to form complexes with ligands of biological matter, leading to an accumulation in the food chain. Therefore, even in trace quantities, heavy metals pose a severe threat to both human health and the environment. Boron doped diamond (BDD) electrodes are effective for trace mercury detection due to the low background currents, wide electrochemical window and stability at extreme temperature, pressure and pH associated with the material. Trace mercury detection was investigated by square wave anodic stripping voltammetry (SWASV) measurements, which are considered to be one of the most sensitive electro-analytical techniques appropriate for trace analysis. The lower limit of detection was improved by modification of the BDD electrode surface with gold nanoparticles (20 nm), which act catalytically during the pre-concentration step of the SWASV measurements due to the high affinity of gold and mercury. Investigation into further increasing the sensitivity of these measurements was conducted by analysing the impact of altering the BDD electrode surface roughness.

Resume : Within its supportive action under program H2020, Europe has recently granted support to the GREENDIAMOND project, that gathers 14 partners towards the development of single crystal diamond structures aiming at the fabrication of a MOSFET power converter. Based on the recent demonstration of a MOS structure fabricated on diamond1, the consortium aims at assembling of a complete transistor to be used in high voltage applications: target prototypes aim at devices compatible with 6.5kV and 10kV operating voltages. The project ultimately aims at the fabrication of high voltage converters that overtakes Si, SiC and GaN transistor performances in terms of high voltages and current densities, and compatible with harsh operating environments. The prototypes to be developed aim at high temperature operations (< 250°C) and high switching capabilities (5kHz). The project started on May 2015 for a duration of 4 years. This poster will describe the context, the consortium, and the project objectives.

Resume : Chemical Vapour Deposition (CVD) grown Nanocrystalline Diamond (NCD) thin films have an intrinsic surface roughness, which hinders the development and performance of the films' various applications. Traditional methods of diamond polishing are not effective on NCD thin films. Films either shatter due to the combination of wafer bow and high mechanical pressures or produce uneven surfaces, which has led to the adaptation of the Chemical Mechanical Polishing (CMP) technique for NCD films. This process is poorly understood and in need of optimisation. To compare the effect of slurry composition and pH upon polishing rates, we polished a series of NCD thin films for three hours using a Logitech Tribo CMP System in conjunction with a polyester/polyurethane polishing cloth and six different slurries. The reduction in surface roughness was measured hourly using an atomic force microscope. The final surface chemistry was examined using x-ray photoelectron spectroscopy and a scanning electron microscope. We present the final results comparing and contrasting the effects of the different polishing slurries on the NCD thin films.

Resume : Alternating current (AC) magnetic measurements, in which an AC field is applied to a sample and the resulting AC moment is measured, are an important tool for characterizing many materials. 1 A fundamental property measured by this technique, both AC and direct current (DC), is the susceptibility of the material. The use of an AC field yields greater information about the sample?s magnetization dynamics; this is often described in terms of the susceptibility having an in-phase, or real, component ?' and an out-of-phase, or imaginary, component ?".1 This study uses AC magnetic measurements to examine the ?' and ?" of a series of chemical vapour deposition (CVD) grown boron-doped nanocrystalline diamond (B-NCD) thin films. B-NCD thin films being superconductors2 means ?' and ?" represent measures of flux exclusion due to induced shielding currents and magnetic losses due to the movement of flux lines, respectively.3 The samples were grown under identical conditions with only their grain size varying as a result of changing the film thickness. The AC magnetic response of the samples was measured using a Quantum Design Physical Properties Measurement System.

Resume : Intensive research is being performed into diamond high power devices after the outstanding electrical and thermal properties recently published. The latter demonstrates a high breakdown field (higher than 7.7 MV/cm). However other important aspects as high hole and electron mobility (?p=2000 cm2 V-1 s-1, ?n=1000 cm2 V-1 s-1), and high thermal conductivity (about 22 W cm-1 K-1) should push diamond in new device application in the future. So, in the view of developing high performance metal-oxide-diamond field effect transistor (diamond MOSFET), recent reports presents different approach in the choice of the gate material and, in particular, on the dielectric layer. According to this, Al2O3 can be considered a suitable gate oxide in MOSFETs, and the experimental analysis of the Al2O3/O-terminated diamond interface is of great interest. Thus, the present study shows an analysis of the alumina/O-terminated diamond interfaces in function of the different O termination treatments using several experimental techniques, such as X-Ray Diffraction for analysing the Al2O3 layer, X-Ray Photoelectron Spectroscopy for analysing the chemical state bonding of C and O in the interface, spectroscopic ellipsometry for studying the optical properties and Transmission Electron Microscopy for gaining knowledge about the Al2O3/O-terminated diamond.

Resume : The development of diamond power devices are attractive because their expected high voltage and temperature strength, however some specific technological aspects still need to be overcome. One of them is the quality of oxide layer for the performance of metal-oxide-diamond field effect transistor. The authors present a study by transmission electron microscopy techniques of homoepitaxial alumina layers grown on diamond. Specifically, high resolution electron microscopy, electron energy loss spectroscopy and energy dispersive X-Ray spectroscopy were carried out on two samples were the alumina layer was grown at 380 ºC by atomic layer deposition being one of them subjected to a subsequent thermal treatment. This study shows that among the different known transition alumina, ?-alumina is the type of alumina present in both samples, instead of the thermodynamically stable alumina, ?-Al2O3. In the sample without thermal treatment, three zones in the alumina layer were identified: Z1- amorphous alumina, Z2- small grains of alumina and Z3- almost mono crystalline alumina. Fast Fourier transform was used to identify the orientation of the grains in Z2 and Z3. Nevertheless, the sample with thermal treatment showed an almost mono crystalline ?-alumina layer. The crystallographic relationship between the diamond and alumina crystals was determined. Studies by STEM-EDX concluded that, in one hand, the oxygen and aluminium distributions are not uniform, i. e., there is a compositional modulation at the nanometer scale and on the other hand, there is a 1-2 nm width interface between the diamond and alumina where an increasing gradient of oxygen atoms is identified. After the thermal treatment, these aspects were found to be improved.

Resume : Diamond films has been used in tool applications because of their hardness, excellent wear resistance. Tools are generally made of cemented carbide (WC?Co) with cobalt metal binder. Diamond coating on cemented carbide suffer from some problems. The main issue is the cobalt binder, this promotes the graphite soot formation on substrate surface during CVD diamond deposition, reducing diamond film adhesion. In this work, we studied the influence of carbon black interlayer sintered by laser-cladding on WC-Co substrate. The carbon black powder layer was sprayed by the air gun and subsequently irradiated (sintered) by laser beam. The carbon black interlayer blocked the negative effects of the cobalt binder in the process of coating WC-Co with CVD diamond film. Diamond films were deposited using a Hot Filament Chemical Vapor Deposition (HFCVD) reactor. The residual stress was investigated by micro-Raman Spectroscopy. X-ray Diffraction (XRD) was used for quantitative analysis of phases laser cladding process. Inserts were characterized by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) for qualitative analysis.

Resume : Diamond is the ultimate wide bandgap material for high voltage devices. Its material properties promise to achieve very high voltages and current densities which surpass capabilities of other materials used today for high voltage devices such as Si, SiC and GaN. However, to achieve the voltage and current ratings predicted by theory, significant improvements in material quality as well as in diamond processing must be made. This talk will focus on the optimisation of high voltage devices in diamond material and the challenges that are in front of experts working on material and processing improvements if diamond is to deliver what it promises in theory. Simulation-based analysis of device design requirements for realisation of high voltage MOSFETs and Diodes will be presented. Ideal designs have been identified and more realistic designs which take into account current limitations of epi-growth and other processes needed for realisation of high voltage switches (gate oxides, etching steps, etc.) have been evaluated. Summaries of simulation results for key design and process parameters such as epi thickness and doping, gate oxide thickness, gate shape, latch-up immunity and termination design will be presented. Optimum designs for near-future fabrication of high voltage devices in diamond for energy-efficient power electronics will be shown with the aim of offering direction for future research on diamond material and shortening the time to market for diamond-based high voltage products.

Resume : Diamond has intrinsic properties of interest for being used as power devices. Those properties include wide band gap energy (c.a. 5.5 eV), high hole and electron mobility (up=2000 cm2 V -1 s -1, un=1000 cm2 V -1 s -1), high breakdown field (higher than 10 MV/cm) and high thermal conductivity (22 Wm -1 K -1). Alumina (Al2O3) could be considered as a suitable replacement for silica (SiO2) as gate oxide in metal oxide semiconductor field effect transistors (MOSFET). In this sense the layer deposition of Al2O3 on diamond surfaces would yield an interesting gate oxide in MOSFET. With a larger bandgap, the bands setting respect to that of the diamond allow either depletion or inversion regimes depending on the MOSFET structure. However, in both cases, the knowledge of metal-semiconductor interfaces is necessary to implement such electronic devices based on diamonds. The present study shows a theoretical analysis based on periodic-DFT calculations of the interaction between the Al2O3 and O-terminated diamonds surfaces. Special attention will be taken to the interaction between the metal and the O from the diamond surface to understand the role played by those elements in the interface. To this end analysis of the density of states, Electron Localization Function and Non-Covalent Index interactions will be of interest.

Resume : Through extensive synchrotron-based x-ray experiments, allied to electrical studies, it is shown that boron doped diamond maintains remarkably bulk-like electronic properties even when the doping distribution (10^20 B/cm^3 peak doping level) is reduced to a few nanometres FWHM. From this ??-doped? single crystal diamond, lateral Ohmic nanowires (l-dNWs) are patterned and electrically addressed using Electron Beam Lithography (EBL). Wires can be routinely fabricated with dimensions of 15-20nm wide and (due to the delta doping profile) 1-2 nm in depth. This presentation will briefly introduce high resolution angle resolved photo emission studies on ?-doped diamond compared to semi-infinite bulk doped diamond, while focusing on the fabrication methodology as well as electrical characterisation of the l-dNWs and the prospects for this exciting break-through technology.

Resume : Pressure is an external quantum control parameter that brings out novel type of order in condensed matter with associated new forms of fundamental properties such as magnetism and superconductivity. To explore the associated quantum phase diagrams, many different techniques have been developed in the past years, e.g. by adapting standard magnetic detection schemes to the specific high-pressure environment controlled by a diamond anvil cell (DAC). I will report that the optically detected spin resonance of nitrogen-vacancy (NV) centres created by ion implantation at the culet of a diamond anvil leads to a direct in-situ non-perturbative method for the detection of magnetic properties across a wide pressure range in the DAC environment. As an illustration of the efficiency of this technique, I will describe how it can be used to detect magnetic orders of iron at high pressure.

Resume : The challenges that diamond research community are facing to fabricate diamond power electronic devices motivate the development of new architectures. In this context, selective growth is presented as a powerful method to develop 3D and other unusual architectures. Nevertheless, due to the difficulties in their structural characterization, growth mechanisms at the first steps remain unknown. Here, we overgrew {100}-oriented patterned substrate by MPCVD using very thin boron doped layers to study them by TEM in a stratigraphic approach. Results showed a growth carried out by sectors in which the growth orientation is limited by the corners of the mesa structures. Top corners shaped the structure according the slowest growth rate, as has been usually observed, whereas bottom corners facet the growth along the fastest growth rates. Therefore, depending on the pattern orientation and height, under some particular experimental conditions, it is possible to predict the sequence of growth sectors, and thus to choose the crystallographic orientation of the overgrown surface, by stopping the growth at the right stage. The simple but useful geometric model proposed on this work will allow to fabricate structures adapted to many geometries in according to the requirements of the device.

Resume : With the high breakdown voltage and current handling ability of GaN, AlGaN/GaN on SiC HEMT structures are the current benchmark for high-power, high-frequency applications[1]. However, in such devices the GaN epilayer and particularly the SiC substrate, with thermal conductivity of around 400 W/mK, limit the heat extraction leading to de-rating of the maximum power dissipation[2]. Through replacement of the substrate and capping of the transistor channel with diamond of thermal conductivity of up to 2000 W/mK, large decreases in the thermal resistance should therefore be achievable allowing full utilisation of the properties of GaN based devices[3]. The growth of pinhole free, thin film diamond on non-diamond substrates requires the use of a nucleation enhancement step. One of the most commonly used techniques involves seeding the substrate with nanodiamond particles, resulting in high nucleation densities of the order of 1011 cm-2[4]. As attachment of the particle to the substrate is dependent on both the zeta potential of the surface and the particles, it is essential to measure the zeta potential of the surface and tailor the surface groups of the seeds to reach such nucleation densities. In the present study we have measured the surface zeta potential of the GaN surface. Using such knowledge, diamond films have been successfully grown atop GaN on sapphire wafers, without the addition of a thermally resistant intermediate dielectric layer to aid growth as used within previous studies[1]. Films were grown at 850 °C, under 5% methane admixture (CH4/H2) conditions to a thickness of ~150 nm, as judged by in-situ laser interferometry. Raman and SEM characterization of the resulting samples revealed continuous films over the 15 by 15 mm samples, free of pinholes, and highly crystalline with uniform lateral grain size of 100?150 nm. References 1. J. W. Pomeroy, M. Bernardoni, D. C. Dumka, D. M. Fanning and M. Kuball, Applied Physics Letters 104 (8), 083513 (2014). 2. J. Pomeroy, M. Bernardoni, A. Sarua, A. Manoi, D. C. Dumka, D. M. Fanning and M. Kuball, presented at the 2013 IEEE Compound Semiconductor Integrated Circuit Symposium (CSICS), 2013 (unpublished). 3. O. A. Williams, Diamond and Related Materials 20 (5-6), 621-640 (2011). 4. Oliver A. Williams, Olivier Douhéret, Michael Daenen, Ken Haenen, Eiji ?sawa, Makoto Takahashi, Chemical Physics Letters 445, 255 (2007)

Resume : Nanodiamond has been proposed to be one of the most biocompatible nanomaterials for drug delivery. ND attracted great attention for number of therapeutic applications owing to its low toxicity for many cell lines. Efforts have been devoted on using nanodiamond (ND) for drug loading and for more efficient anticancer drug delivery while ND?s Raman and fluorescence properties are used for bio imaging. Several successful cases have been demonstrated in both cellular and animal models. However, typical cellular models involve culturing cells in a configuration where cells are confined in a two-dimensional growth culturing dish which can be quite different from the cell growth conditions. In this study, we prepare ND complex with clinically anti-cancer drug doxorubicin (Dox) and the efficiency of the ND-drug and pure drug was compared in Human Oral Squamous Carcinoma cell (SAS cell). The 50 nm carboxylated ND (cND) was conjugated with human serum albumin (HSA) to achieve well dispersed suspension in buffer solution. To obtain cND-HSA-Dox, Dox was adsorbed on the particle surface. UV-Vis spectroscopy was used to estimate the conjugation. Besides, Dox release from cND-HSA-Dox at different pH was measured. The cytotoxic effect of Dox and cND-HSA-Dox complex was assessed in 2D- and 3D- cultured SAS cell via MTT assay. A possible mechanism of the drug transportation and delivery are discussed. The results show ND-HSA-Dox is more efficient in 3D-cultured cell compare to 2D-cultured cell.