Silicon, Germanium, Diamond and Carbon nanostructures and their nanocomposites with other materials

Resume : Surface functionalization of nanoparticles is an essential tool for the control of their chemical, physical and physiological behaviour. Nanodiamond (ND) can easily be modified by using its variety of surface functional moieties.[1] In addition, NDs, having a low to non-existing toxicity, are attractive for biomedical applications.[2] However, when ND are exposed to bio-fluids, such as cell culture serum, proteins adsorb on the surface of the particles and form in situ a “protein corona”. This corona masks the desired functionalities on the surface and changes the interaction with the surrounding fluid. Both, the colloidal stability and the physiological properties are not controllable anymore.[3] Here, we report on different strategies to control the colloidal stability of nanodiamond in physiological media using surface functionalization as well as colloid chemistry techniques such as electrosteric stabilization. Furthermore, examples for the application of those functionalized nanodiamond conjugates and composites will be presented including the use in regenerative medicine, sensing and drug delivery. The funding of this research by the Volkswagen Foundation (Az.: 88 393) is gratefully acknowledged. [1] A. Krueger, D. Lang, Adv. Funct. Mater. 2012, 22, 890. [2] A. Krueger, Chem. Eur. J. 2008, 14, 1382. [3] W. C. W. Chan, C. D. Walkey, J. Am. Chem. Soc. 2012, 134, 2139.

Resume : We present a novel concept of biomolecular sensors based on operation of quantum colour centres in diamond integrated to a microfluidic biosensor. The developed device is based on a combination of NV centre optical readout combined with an electrochemical device. By this way the device can lock on an electrochemical potential specific for particular reactions and to use the NV centre charge state for detection of specific chemical reaction products. The diamond device consists of highly boron doped diamond electrode capped with a thin (10 nm) NV centres containing layer. The device is then covered by polydimethylsiloxane flow cell and transparent indium tin oxide coated glass slide. Switching of the NV-/NV0 centre population is detected by photoluminescence (PL). We set first the charge state occupation of NV centre by applying a bias voltage between source and gate electrode. The charge state of NV centres then react to electrochemical potential of the environment. To demonstrate the label free optical detection the diamond surface is covered with a monolayer of strongly cationic charged polymer polyethylenimine (PEI) that modify charge state of near surface NV centres to NV0 or NV non-PL state. Immobilization of negatively charged DNA molecules on the sensor surface changes NV centres charge states to preferably NV- and the PL is detected by confocal microscopy. The biochemical reactions in the microfluidic channel are controlled by electrochemical impedance spectroscopy.

Resume : Luminescent nanodiamonds (ND) are attractive tools for nanoscale biologic cellular imaging allowing both photoluminescence (PL) and magnetic resonance imaging [1]. Recent technological developments enable to fabricate bright NDs with high content of nitrogen-vacancy (NV) centres [2] that are anticipated to serve as a cell probes. In this work we present novel method of NDs detection in cellular environment. We demonstrate simultaneous visualization of NDs and of the non-labeled nucleus of living cells based on Raman and PL detection as a new tool for the localization of internalized nanoparticles. To this end, NDs of size ranging from ultra-small particles ~ 5 nm to 60 nm were used, prepared from Ib synthetic diamond. Particles were electron irradiated, annealed and plasma oxidized to create NV centers [3]. Cells used for this experiment were breast cancer (MCF7). Successful internalization of NDs and their localization in cells is determined using a TEM. Whilst standard Raman imaging methods of NDs make use of the sp3 diamond Raman signal, which limits their use to 100 nm size particles or bigger [4], here we employ Raman imaging in a novel way to detect small near-IR cellular probe. Specifically, the Raman signal from the cellular environment is spectrally processed using K-mean cluster analysis of 2D map. By mapping the intensity of the lipid contribution to the C-H Raman peak, we are able to visualize the cell nucleus clearly on non-fixed cells. This information is combined with PL detection of small (~ 5 nm) particles to visualize the position of NDs and distinguish between the internalized and non-internalized particles. Merging of these two images obtained simultaneously allows to obtain a spatially precise ND position and to determine its closer environment. [1] L. Moore, M. Nesladek et al., Nanoscale (2014) [2] J. Havlik, M. Gulka, M. Nesladek et al., Nanoscale (2013) [3] J. Stursa, M. Gulka, M. Nesladek et al., Carbon (2016) [4] C.-Y. Cheng et al., Applied Physics Letter (2007) ACKNOWLEDGMENTS: Czech Science Foundation project GA16-16336S

Resume : The excellent bio-compatibility, high photo-stability, and the long spin coherence time at room temperature make Nitrogen-vacancy (NV) in diamond a promising sensor for biological applications. However, its sensitivity to parameters such as temperature is low when considering the possibly very small temperature variation in biological systems, and it does not respond to many important biochemical parameters including pH and non-magnetic biomolecules. Here we propose a scheme of magnetic nanoparticle/nanodiamond based hybrid structure that can potentially enable the measurement of various biochemical parameters using NV based sensing. In this talk, we show the proof-of-the-concept demonstration of temperature sensing using such a hybrid sensor. The same principle can be well applied to detection of changes in other biochemical parameters using sensors of the same principle.

Resume : Diamond nanocrystals with nitrogen-vacancy (NV) crystal defects are near-infrared fluorescent emitters which have been utilized, for example, as single-photon sources or as fluorescent biomarkers of extreme photostability and low toxicity. Importantly, spin states of NV center show unique sensitivity to magnetic and electric fields, enabling for construction of probes based on quantum mechanical interactions. For preparation and selective operation of such probes in biological environment a functional chemical interface is a key component. Combination of synthetic chemistry with rational molecular design leading to novel sensing interfaces readable with NV centers will be discussed. Modification of nanodiamond using polymers, attachment of responsive sensing structures for detection of charge status of polymers, DNA transfection, pH, redox potential, and physico-chemical properties of these constructs will be explained in detail.

Resume : Silicon is a material with remarkable properties as biocompatibility and biodegradability, which make it an interesting platform for biomedical studies. Silicon nanoparticles (quantum dots) co-doped with boron and phosphorus, with diameter around 4 nanometres evincing fluorescence and dispersability in aqueous solutions were studied in respect to their impact on different human cells. Firstly, it was necessary to determine their level of cytotoxicity in different types of human cells and secondly their interaction with these cells. Osteoblastic cell line and cell line of immune cells, which can be studied in two stages – as monocytes (suspension cells circulating freely in blood) and as macrophages (adherent cells localized in specific tissues) were used. Exposing cells to rising concentrations of quantum dots under different conditions and consecutive evaluation of their cytotoxicity brought an overview on cell specific reaction to their identical doses. Further, colocalization studies of nanoparticle signal and cell specific structures (organelles) of endocytic pathway were performed using fluorescence confocal microscopy and other techniques at different time points. Obtained results show significant importance of cultivation conditions (e.g. formation of protein corona on nanoparticles originating from media supplement) as well as significant impact of cell type (increased sensitivity of monocytes to studied quantum dots in comparison to other cell types). These results thus provide an insight on future directions of related research.

Resume : Nanostructure porous silicon (NanoPSi) is a nanostructured biomaterial which has received considerable attention in biomedical applications due to its biocompatibility, biodegradability, high surface area and the ease to modify its surface chemistry. In the present work, nanoPSi composite microparticles were evaluated as potential drug delivery system. NanoPSi layers were formed by electrochemical etching of silicon wafers in hydroflruoridric acid solutions. This fabrication process allows modifying the main properties of nanoPSi layers including the porosity, average pore size and pore shape, by simply controlling the main parameters in the fabrication process such as the applied current density and electrolyte composition. NanoPSi micro-nano particles were prepared from the removal and facture by ultrasound sonication of nanoPSi layers. Composites were obtained from oxidized nanoPSi (OPSi) microparticles cascade processed with chitosan (CHI) and β-cyclodextrin (β-CD) biopolymers. OPSi, CHI and β-CD composites were evaluated as drug delivery system using florfenicol as model drug, due to the economical and sanitary importance in salmon industry. Drug loaded and release kinetic text were performed in different medias: distilled water, simulated seawater and simulated physiological media. Initial data show that β-CD composites allowed a mayor control in the drug time release kinetic compared with OPSi microparticles and CHI composite.

Resume : Over the past ~15 years, silicon nanowire(SiNW)-based sensor devices have gained increasing interest due to their reliable and reproducible electrical properties, the possibility of down-scaling and integration for the simultaneous detection of multiple parameters. Various types of affinity layers have been deposited onto or bound to the surfaces of the silicon nanowires, aiming to introduce selectivity towards a specific target analyte, including ions and bio(molecules). Recent advances in the design and synthesis of molecular architectures have resulted in the availability of a large variety of porous materials that are interesting candidate building blocks for chemical sensing purposes. In this work, we present several surface modification strategies to chemically bind porous materials to SiNW-based sensors. The functionalized devices were subsequently studied in the depletion regime under different environmental conditions, probing selectivity. In the first case (1) we prepared metal−organic polyhedra (MOPs) from organic ligands and an unsaturated metal site. The MOPs were grafted onto pyridyl-coated SiNW-based sensors at room temperature. Based on a unique confinement effect and host-enhanced charge-transfer interactions the MOP cages enabled the electrical detection and discrimination of structurally related explosives, including 2,4,6-trinitrotoluene (TNT). In a second study (2), we prepared porous organic frameworks directly onto amine-terminated SiNW-based sensor using two organic building blocks that were polycondensated at 453 K. The resulting covalently attached porous affinity layers increased the device response to changes in humidity. Moreover, advanced sensing properties of methanol vapors were realized via the post-synthesis functionalization of the POF-SiNW hybrid by the in-situ formation of platinum nanoparticles (Pt NPs). The surface modification strategies, including surface characterization, and the proposed selectivity mechanisms will be discussed in detail. Our work shows the potential of porous architectures as receptors onto electrode structures. Moreover, the presented NP/MOP system may also find utilization in the fields of gas separations and catalysis. References 1. Enhanced Vapor Sensing using Silicon Nanowire Devices Coated with Pt Nanoparticle Functionalized Porous Organic Frameworks, Cao, Shan, Paltrinieri, Evers, Chu, Poltorak, Klootwijk, Gascon, Sudhölter, de Smet – manuscript under review. 2. Metal-Organic Polyhedra-Coated Si Nanowires for Sensitive Detection of Trace Explosives, Cao, Zhu, Shang, Klootwijk, Sudhölter, Huskens, de Smet, Nano Lett. 2017, 17, 1-7.

Resume : Silicon and germanium nanowires (SiNWs and GeNWs) are anticipated for the realization of next-generation metal-oxide-semiconductor field-effect transistors. Impurity doping is one of the key techniques for the NWs devices [1], while the retardation of carrier mobility due to impurity scattering has to be taken into account. Core-shell NWs composed of Si and Ge are key structures for realizing high mobility transistor channels, since core-shell structures separate the carrier transport region from the impurity doped region, resulting in the suppression of impurity scattering [2,3]. Si/Ge and Ge/Si core-shell NWs were rationally grown on a Si substrate by CVD. The TEM and EDX images of i-Ge/p-Si (i: intrinsic, p: p-type) core-shell NWs clearly show the formation of i-Ge/p-Si core-shell NWs and clear lattice fringes in the shell regions. XRD measurements were performed to evaluate the stress induced in the radial hetero core-shell structures. The results clearly revealed stress in the core and shell regions and characterized the compressive and tensile stress present. The average lattice constant of the Ge core is smaller than bulk Ge, showing that the compressive stress is applied by the radial growth of p-Si shell. The average lattice constant of the p-Si shell is greater than that for bulk Si. This is due to the tensile stress from the Ge core. To confirm the selective B-doping in the shell region, we performed Raman measurements. The electrical activity of B atoms can be clarified by the Fano effect [2], which is due to coupling between discrete optical phonons and the continuum of interband electron excitations in degenerately doped p-type Si. The Si optical phonon peaks observed for i-Ge/p-Si NWs shows an asymmetric broadening toward higher wavenumber, whereas no asymmetric broadening was observed for the i-Si shell. This asymmetric broadening is due to the Fano effect, showing that B atoms are electrical activated in the Si shell, resulting in the formation of p-Si shell. Precise analysis using Raman spectroscopy were further performed. We finally got a conclusive evidence of hole gas accumulation in Ge/Si core-shell NWs [3]. References [1] N. Fukata, Adv. Mater 21, 2829-2832 (2009). [2] N. Fukata et al., ACS NANO 6, 8887-8895 (2012). [3] N. Fukata et al., ACS NANO 9, 12182-12188 (2015).

Resume : The optoelectronic properties arising from the combination of group IV compounds like Si and Ge indicate that their heterostructures are very promising materials for several technological applications. In particular in recent years wide attention has been devoted to Si/Ge and Ge/Si core-shell nanocrystals. These nanostructures present unique electronic and optical properties that are directly linked to their size, structure, composition and organization. Here we will present our recent ab-initio results concerning their structural and optoelectronic properties. In particular we will show how the localization of the electrons and holes, the charge separation, the band-offset and consequently the optical properties are related to the size and the core-shell (Si/Ge or Ge/Si) structure of these compounds.

Resume : The operability and durability of erbium and germanium doped fused silica components in harsh environments are limited by thermal diffusion, responsible for structural changes that induce irreversible material degradation and failure. An alternative solution for improving both the thermal and the radiation resistance of these compounds consists of synthesizing Si-, Ge- and Er-based nanoclusters. This technique enables to control atom diffusion, using chemical trapping effects induced by silicon dangling bonds and the pinning of nanoaggregates by silicon nanoparticles during high temperature annealing. Our experimental approach and methodology combine the fabrication of advanced materials by the use of single or multiple ion implantations, with subsequent advanced characterizations by Raman/photoluminescence spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and nuclear analysis. Our work shed light on the nucleation processes of group-IV nanocrystallites, as well as on the formation of nanocavities in Ge-based materials. The nanoclustering of mixed Si/Er and Si/Ge materials is also found to extend the lifetime of near infrared Er light sources exposed to cosmic radiations, and prevent Ge desorption, more than several hundred degrees above heating conditions where drastic outgassing effects occur. High resolution imaging supported by Monte-Carlo simulations and Rutherford Backscattering Spectroscopy measurements shows how the size, the homogeneity, the depth-distribution, as well as the composition and the crystallinity of the formed nanoclusters can be set as a function of the fabrication parameters, in order to design components with specific properties and superior resistance.

Resume : The formation of new Si-based materials with enhanced light absorption is of great importance for the development of high efficient photovoltaic devices. A possible approach for enhanced light absorption is connected to excitation of localized surface plasmons after interaction of photons with nano-cavities, metallic nano-shells and nano-particles. The plasmonic excitations are then transferred to a semiconductor to generate electron-hole pairs. The concept of the study is based on self-assembled formation of voids in strained Si/SiGe heterostructures. We will briefly review the effects of strain-driven nano-void formation in Si/SiGeSn layers, gettering and segregation of impurities and formation of buried nano-shells and nano-dots of Ge, Sn and Au in Si layers located nearby to p-n-junction. Structural transformation in the Si/SiGe layers during self-assembling of nano-voids, optical and electronic properties of the layers, and resulting effects of nanostructures on the spectral dependence of the photocurrent in the Si/SiGe structures will be reported. It will be discussed in the talk that metallic nano-shells possess tuneable optical resonances. By varying the relative core and shell thicknesses, the absorption and scattering properties of metallic nano-shells can be varied in a broad range. Finally, special attention will be devoted to possible plasmonic structures for enhancement of the efficiency of Si-based photovoltaic devices.

Resume : Silicon carbide (SiC) is a stable, chemically inert wide band gap semiconductor, and a promising material for bioimaging, targeted drug delivery, nanosensing, optoelectronics and for heterogeneous photocatalysis as well, especially in nano size. Biocompatibility of bulk SiC and SiC nanoparticles (NPs) has been proven by several research teams and the aqueous solutions of SiC NPs are exceedingly promising candidates to realize bioinert nonperturbative fluorescent nanoparticles for in vivo bioimaging. However, most of the synthesized luminescent NPs have environment sensitive, size independent violet-blue emission where the typical size of efficiently luminescent SiC NPs is around 3 nm. A redshift in the emission would be advisable for in vivo bioimaging applications that might be achieved by tight control of the size of SiC NPs. We show here that size distribution of SiC NPs can be tuned via the concentration variation of hexagonal inclusions in the precursor bulk SiC matrix used for stain etching. By proper engineering of hexagonal inclusions into the cubic SiC powder, 4-6 nm SiC NPs can be prepared from this cubic SiC powder by stain etching. These new SiC NPs exhibit redshift in the emission that can be explained by quantum confinement effect on the electronic states participating in the emission process. The redshifted luminescence and the significantly quantum yield of these new larger SiC NPs make them very promising biomarkers.

Resume : Si nanocrystals codoped with P (donor) and B (acceptor) impurities exhibit very interesting optical properties, including efficient photoluminescence (PL) in a wide energy range (0.85-1.8 eV) that overcomes the bulk Si bandgap limitation [1]. Furthermore, the codoped nanocrystals are very stable, which is promising for applications. In this talk, I review the theoretical investigations on the electronic structure of (co)doped Si nanocrystals. The theory of Si nanocrystals doped with a single P impurity is compared with the results of Electron Paramagnetic Resonance experiments. Next I present recent results on Si nanocrystals doped with the same number of donor and acceptors. The variation of the gap versus nanocrystal size and impurity concentration is studied in a systematic manner. The experimental trends are discussed in comparison with the theory. I analyze the intrinsic effects of disorder on the linewidth of the PL spectra, as well as the influence of the dopants on the zero-phonon radiative lifetime. [1] H. Sugimoto et al, J. Phys. Chem. C 117, 11850 (2013).

Resume : Couple-nanometer sized silicon nanoparticles (Si NPs) are promising for novel optoelectronic and biological applications as these SiC NPs exhibit relatively strong fluorescence. These Si NPs can be co-doped by boron and phosphorus at very high concentration. The resulted highly co-doped Si NPs show a red-shift in the emission upon illumination. Furthermore, co-doping drastically slows down the oxidation of nanoparticles. Despite the favourable properties of co-doped Si NPs, very little is known about their structure because conventional experimental techniques such as photoluminescence spectroscopy or Raman/infrared spectroscopy offers only limited insight on their structure at the atomic scale. We employ ab initio atomistic simulational methods based on density functional theory (DFT) to study the structural, electronic and optical properties of co-doped Si NPs. We study 1.5-2.0 nm sized NPs with different surface terminations and various dopant concentrations. The optical excitation is calculated by time-dependent DFT, and the emission spectra and resonant Raman spectra are calculated within the Franck-Condon approximation. We focus on the distribution of dopant atoms inside the nanocrystal and study the properties of the NP surface extensively where the presence of oxygen atoms makes the comprehension of the structure more challenging. We show that boron can form such complexes with oxygen at the interface of the core Si and its oxidized layer that lead to non-radiative relaxation of the photoexcited electron. We also provide a detailed analysis on the distribution of phosphorus and boron dopants inside Si NPs, and how the relative position of dopants influence the optical properties of Si NPs.

Resume : Si nanocrystals (NCs) have been a subject of intensive research for many years as biocompatible nano-light-emitters. However, for light emitting and detecting applications, there still remains an essential issues which is the small absorption cross-section (ACS) of Si NCs in the visible range due to the indirect band gap nature. An effective way to overcome this issue is utilizing the surface plasmon resonance excitation of noble metal nanostructures. Although the enhanced emission rate and ACS by the plasmon resonance have been reported in the past decade, the enhancement factors are limited (less than 10) mainly due to the losses of metals that cause nonradiative quenching of nearby emitters. In this work, we propose the dielectric scattering media for enhanced light ACS and emission intensity of Si NCs without suffering from the material losses. We prepare the thin films of polymer using water-dispersible Si NCs and by controlling the concentration of precursors, a highly-scattering xerogel film is produced. The films have submicron pores and exhibit cavity resonances in the visible range, which results in the enhancement of effective ACS of Si NCs by 20 times at 500-600 nm due to the multiple scattering effect. We also show that photoluminescence (PL) of Si NCs is enhanced at most 40-folds and discuss the enhancement mechanism from time-resolved and micro-PL analyses. [1] H. Sugimoto, et al., ACS Appl. Mater. Int. (2017) DOI: 10.1021/acsami.7b04292

Resume : Impurity doping of Si with e.g. P or B is the backbone of CMOS electronics since it allows to determine the conductivity type and the resistivity. However, at the bottom end of the nanoscale, as approached by future technology nodes, conventional impurity doping is a non-trivial task. Some problems are related to technological aspects (diffusion, “dopant fingerprint”), others to fundamental physical obstacles (quantum- and dielectric confinement). Using ultra-small Si nanovolumes of ≤5 nm in diameter as a model system, we demonstrate that P-dopants have twice the substitutional formation energy and up to 5-times the ionization energy compared to P in bulk-Si [1]. Hence, there are diminutive free carrier densities from thermal ionization at room temperature. For boron, the situation is further complicated by the lower solubility of B in Si. By means of atom probe tomography (APT) we measure a much smaller amount of B-incorporating nanocrystals compared to phosphorus. Electrical measurements do not reveal any B-doping-related effects, whereas B-induced defects apparently cause a photoluminescence quenching [2]. In search of alternative doping methods, a potential approach originating from density functional theory (DFT) calculations is presented, which employs an acceptor state in Al-doped SiO2 adjacent to Si to induce p-type behavior in analogy to conventional III-V semiconductor modulation doping [3]. [1] D. Hiller et al., Sci. Rep. 7, 863 (2017) [2] D. Hiller et al., under review [3] D. König et al., Sci. Rep. 7, 46703 (2017)

Resume : The integration of diamond with plasmonic nanoparticles provides a pathway to alter the optical properties of diamond in novel ways. One challenge in synthesizing plasmonic diamond films is that at the the growth temperatures typically used, most metals with suitable optical properties are molten, leading to rapid coarsening and formation of large puddles of metal. We have developed approaches to formation of diamond films on silicon and on quartz with embedded nanoparticles <50 nm in diameter that exhibit clear plasmonic resonances in the visible and near-UV regions. Optical characterization of diamond films grown on quartz show plasmonic resonances in both transmission and reflection mode. Tuning the size of the nanoparticles controllably alters the frequencies of the plasmonic resonances in the expected manner and consistent with numerical modeling of the resulting structures.

Resume : Low-cost, stable, and efficient renewable energy is nowadays increasing in importance. Diamond-based inorganic-organic hybrid systems may have an immense, yet still mostly unexplored potential in photovoltaic solar cells. That was suggested for instance by previously measured transfer of photo-generated charge between bulk diamond and polypyrrole (PPy) or other organic molecules. In this work, we characterize opto-electronic interactions of nanodiamonds (NDs) having various surface chemistry including physisorbed or chemisorbed PPy as organic dye. By using Kelvin probe microscopic and macroscopic measurements we show that even pristine NDs can generate photovoltage, in the range of 5-50 mV, depending on their surface chemistry (characterized by FTIR, Raman) and substrate (i.e. bottom electrode). The photovoltage is further enhanced by merging nanodiamonds with PPy. The hybrid system also exhibits enhanced absorption coefficient. The experimental data are corroborated by DFT calculations showing HOMO-LUMO separation in PPy-NDs hybrid structures. Preliminary tests of nanodiamonds in complete organic solar cells show that the cell fabrication technology must still be optimized though.

Resume : The principle of photoelectric conversion in deep p-n junction is applied to control the presence of carbon nanotubes (SWNT) with adsorbed surfactant (SDBS) in aqueous solution. Surface distribution of photocurrent through the silicon wafer with deep p-n junction and different polymer coatings (1-decene, HEMA) is measured. Interaction of the sensor layer with deionized water and aqueous solutions of SDBS and SWNT results in growth of the photocurrent in 3-4 times. The shift of photocurrent dependence on voltage applied between the aqueous solution and the silicon wafer is registered. This shift depends on presence of SDBS molecules and carbon nanotubes in the water. Changes in effective recombination rate corresponding to surface photocurrent distribution can be caused by modification of surface band bending and capture cross-sections of recombination centers at the polymer-silicon interface. The obtained effect can be used as the instrument for detection of carbon nanotubes with adsorbed surfactant in aqueous solution.

Resume : Optically active color centers in diamond are promising candidates for applications in quantum photonics or biology. In our work, we have tailored dimensions of diamond photonic crystal (PhC) slabs in order to manipulate and enhance the extraction of light emitted by one type of the color centers, the silicon vacancy (SiV) centers. SiV centers possess narrow room-temperature photoluminescence (PL) peak at around 738 nm and thus dimensions of the PhC have to be tuned precisely in order to spectrally overlap the PL with photonic modes of the structure. We have developed relatively simple approach to achieve this spectral overlap, which is based on bottom-up growth of diamond layers on pre-patterned silica substrates. We will show that more than 14-fold enhancement of light extraction from SiV centers can be achieved using this approach. Computer simulation confirmed that the extraction enhancement originates from the efficient light-matter interaction between light emitted from the SiV centers and the PhC slab.

Resume : The interaction of single-walled carbon nanotubes (SWNTs) with DNA is crucial for several nanotechnology applications, including SWNT:DNA nanoscale devices or nanosized building blocks for use in nanosize switches and nanoscale wiring. In biotechnological applications, modulating the DNA:SWNT interaction is important for SWNT purification, DNA recognition, and ultrafast DNA sequencing, and drug delivery. I will present a study of the the conformational equilibrium and the dynamics between B-to-A forms of double-stranded DNA adsorbed onto single-walled carbon nanotubes (SWNT) using free energy profile calculations based on all-atom molecular dynamics simulations. The potential of mean force of the B-to-A transition of ds-DNA in the presence of an uncharged (10,0) carbon nanotube for two dodecamers with poly-AT or poly-GC sequences is calculated as a function of a root-mean-square-distance metric quantifying the B-to-A transition. The calculations reveal that in the presence of a SWNT DNA favors B-form DNA significantly in both poly-GC and poly-AT sequences. Furthermore, the poly-AT DNA:SWNT complex shows a higher energy penalty for adopting an A-like conformation than poly-GC DNA:SWNT by several kcal/mol. The presence of a SWNT on either poly-AT or poly-GC DNA affects the free energy of the transition such that the B form is favored by as much as 10 kcal/mol. The results have consequence for understanding thermal and conduction properties of composites of nanotubes and DNA measured in biotechnology applications.

Resume : Thermal transport through solid-liquid interfaces plays an important role in many chemical and biological processes. Therefore, better understanding of heat transfer through such kind of interfaces will render much more efficient their numerous multidisciplinary applications. Our current contribution reports on thermal conductivity study of carbon-based nanofluids by photoacoustic technique. These biocompatible nanomaterials are successfully applied in biomedical imaging, tissue engineering, drug delivery systems and theranostics. In our research work, photoacoustic technique with piezoelectric detection has been used as an efficient tool for the study of thermal transport properties of the carbon-based nanofluids. Amplitude- and phase-frequency characteristics of the photoacoustic responses from the nanofluids have been measured. Concentration dependence of thermal conductivity of the nanofluid has been studied in details. Additionally, the heat transfer across nanoparticle/fluid interface has been simulated by molecular dynamics. Influence of nanostructuration of solid/liquid interface on some thermal parameters of the nanofluids will be also reported. This research work has been carried out in frames of CARTHER project (proposal #690945) of Marie Skłodowska-Curie Research and Innovation Staff Exchange program.

Resume : Continuous miniaturization and increasing of operating frequencies of electronic devices lead to overheating of their active zones. Therefore, all issues related to elaboration of thermal engineering approaches to perform an efficient heat evacuation from the overheated region are really crucial. In particular, the use of anisotropic nanomaterials allows orientation of heat fluxes along preferential directions due to a high ratio between their thermal conductivities in different directions. Raman technique is already known to be a powerful method for the thermal study of low-dimensional nanomaterials. One of the main advantages of this method is a possibility for contactless and non-destructive measurements. Its principle is based on dependence of relative intensities and spectral shifts of the Raman scattering on exciting laser intensity inducing local heating of the studied samples. Thus, both Raman peak position and Stokes/Anti Stokes ratio allow evaluation of the laser induced temperature rise. The experimental measurements coupled with theoretical models allow reliable evaluation of the thermal conductivity of the studied materials. During our talk, an efficient experimental approach based on Raman scattering measurements with variable laser spot sizes and shapes will be reported. Correlation between experimental and simulated thermal resistances of low-dimensional anisotropic nanocrystalline solids allows a simultaneous estimation of their thermal conductivities in different directions. In particular, our measurement approach is illustrated to be applied for anisotropic thermal conductivity evaluation of porous silicon and silicon nanowire arrays.

Resume : Whenever Si nanostructures are intended to be part of electronics, photonics, thermoelectric, ..., devices, a crucial facet to ensure optimal performances is the heat management. Experimental characterization of heat transport at the nano scale is a difficult task, mainly because alternative heat paths confound the thermal response of the nano-component under study. Atomic-scale computer modelling can help understand heat transport in dedicated nanostructure models. In the present talk, we will present our latest achievements on the modelling of heat transport in Si nanostructures, nanowires and membranes. We generate and exploit a thermal transient at atomic scale by molecular dynamics, following the method we recently proposed, the approach-to-equilibrium molecular dynamics (AEMD). This method is faster than standard ones. Therefore we are able to overcome non physical effects due to a lack of convergence, and study real-size nanostructures. We will discuss the thermal regime in nanowires, and the maximum thermal conductivities. We will also present our theoretical results on nanopatterned membranes, and discuss their application to thermoelectric CMOS compatible devices.

Resume : Understanding nanoscale tribology provide fundamental insights for developing novel applications based on nanomaterials. To this end, in recent years, extensive work on friction of surfaces at atomistic scale have been carried out. The transition between atomic scale to macroscopic friction is largely studied using molecular dynamics methods (MD) [1]. However, understanding the atomic properties from ab initio calculations [2] enables us to evaluate detailed processes from stick-slip to energy dissipation occurred during frictional force microscopy experiments. The interpretation of the nano friction experiments needs more expressive models rather than basic Tomlinson model [3]. In this study, the frictional force between two graphene and functionalized graphene/graphene surfaces have been investigated by using first-principles calculations based on density functional theory. We considered three different geometric configurations which are bilayer graphene (perfect), B-doped graphene/graphene, N-doped graphene/graphene. Also, for the B and N doped graphene/graphene cases, we look at two geometries as top and hexagon. For analyzing the interlayer sliding pathways of perfect and doped graphene/graphene, there are two representative sliding directions: a short (S) (zigzag direction) and a long (L) (armchair direction) pathways. In these ways, one graphene layer (perfect and doped) has been moved relative to perfect graphene surface which is fixed. The binding energy, interlayer distance, frictional force and orbital nature of actual interactions are explored. Based on these calculations, we provide an understanding of the mechanism of interlayer sliding and frictional properties of bilayer perfect and doped graphene. This work is supported by TUBITAK Project No: 114F162. [1] Van Wijk, M.M. Dienwiebel, M., Frenken, J. W. M., Fasolino, A. “Superlubric to stick-slip sliding of incommensurate graphene flakes on graphite”, Phys. Rev. B., 88:235423 (2013). [2] Reguzzoni, M., Fasolino, A., Molinari, E., Righi, M. C., “Potential energy surface for graphene on graphene: Ab initio derivation, analytical description, and microscopic interpretation”, Phys. Rev. B., 86:245434 (2012). [3] Tomlinson, G., Philos. Mag. 7:905 (1929).

Resume : Zirconium alloys can be effectively protected against corrosion in nuclear reactor hot stem or hot water environment by polycrystalline diamond films grown in microwave plasma enhanced linear antenna chemical vapor deposition apparatus. Hot steam and hot water oxidized PCD layers grown on Zr surfaces were investigated. It was found that the presence of the PCD coating blocks hydrogen and oxygen intact into the Zr surface and protects Zr material from degradation. PCD anticorrosion protection of Zr alloy can significantly prolong life of Zr material claddings in nuclear reactors and consequently enhance nuclear fuel burnup. Detailed description of the polycrystalline diamond role in corrosion process is presented.