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The Urbach energy is an expression of the static and dynamic disorder in a semiconductor and is directly accessible via optical characterization techniques. The strength of this metric is that it elegantly captures the optoelectronic performance potential of a semiconductor in a single number. For solar cells, the Urbach energy is found to be predictive of a material's minimal open-circuit-voltage deficit. Performance calculations considering the Urbach energy give more realistic power conversion efficiency limits than from classical Shockley-Queisser considerations. The Urbach energy is often also found to correlate well with the Stokes shift and (inversely) with the carrier mobility of a semiconductor. Here, we discuss key features, underlying physics, measurement techniques, and implications for device fabrication, underlining the utility of this metric.

The efficiency of perovskite-based solar cells has increased dramatically over the past decade to as high as 25%, making them very attractive for commercial use. Vapor deposition is a promising technique that potentially enables fabrication of perovskite solar cells on large areas. However, to implement a large-scale deposition method, understanding and controlling the specific growth mechanisms are essential for the reproducible fabrication of high-quality layers. Here, we study the structural and optoelectronic kinetics of MAPbI

We investigate hole-selective passivating contacts that consist of an interfacial layer of silicon oxide (SiOx) and a layer of boron-doped SiCx(p). The fabrication process of these contacts involves an annealing step at temperatures above 750 degrees C which crystallizes the initially amorphous layer and diffuses dopants across the interfacial oxide into the wafer to facilitate charge transport, but it can also disrupt the SiOx layer necessary for wafer-surface passivation. To investigate the transport mechanism of the charge carriers through the selective contact and its changes during the annealing process, we utilize various characterization methods, such as transmission electron microscopy, micro Raman spectroscopy, and conductive atomic force microscopy. Combining the latter with a sequential removal of material, we assemble a tomographic reconstruction of the crystallized layer that reveals the presence of preferential vertical transport channels.

Metal-halide perovskites feature very low deep-defect densities, thereby enabling high operating voltages at the solar cell level. Here, by precise extraction of their absorption spectra, we find t...

The heterostructures of two-dimensional (2D) and three-dimensional (3D) materials represent one of the focal points of current nanotechnology research and development. From an application perspective, the possibility of a direct integration of active 2D layers with exceptional optoelectronic and mechanical properties into the existing semiconductor manufacturing processes is extremely appealing. However, for this purpose, 2D materials should ideally be grown directly on 3D substrates to avoid the transferring step, which induces damage and contamination of the 2D layer. Alternatively, when such an approach is difficult&mdash, as is the case of graphene on noncatalytic substrates such as Si&mdash, inverted structures can be created, where the 3D material is deposited onto the 2D substrate. In the present work, we investigated the possibility of using plasma-enhanced chemical vapor deposition (PECVD) to deposit amorphous hydrogenated Si (a-Si:H) onto graphene resting on a catalytic copper foil. The resulting stacks created at different Si deposition temperatures were investigated by the combination of Raman spectroscopy (to quantify the damage and to estimate the change in resistivity of graphene), temperature-dependent dark conductivity, and constant photocurrent measurements (to monitor the changes in the electronic properties of a-Si:H). The results indicate that the optimum is 100 C deposition temperature, where the graphene still retains most of its properties and the a-Si:H layer presents high-quality, device-ready characteristics.

Plasmon-enhanced absorption, often considered as a promising solution for efficient light trapping in thin film silicon solar cells, suffers from pronounced optical losses i.e. parasitic absorption, which do not contribute to the obtainable photocurrent. Direct measurements of such losses are therefore essential to optimize the design of plasmonic nanostructures and supporting layers. Importantly, contributions of useful and parasitic absorption cannot be measured separately with commonly used optical spectrophotometry. In this study we apply a novel strategy consisting in a combination of photocurrent and photothermal spectroscopic techniques to experimentally quantify the trade-off between useful and parasitic absorption of light in thin hydrogenated microcrystalline silicon (μc-Si:H) films incorporating self-assembled silver nanoparticle arrays located at their rear side. The highly sensitive photothermal technique accounts for all absorption processes that result in a generation of heat i.e. total absorption while the photocurrent spectroscopy accounts only for the photons absorbed in the μc-Si:H layer which generate photocarriers i.e. useful absorption [1]. We demonstrate that for 0.9 μm thick μc-Si:H film the optical losses resulting from the plasmonic light trapping are insignificant below 730 nm, above which they increase rapidly with increasing illumination wavelength. For the films deposited on nanoparticle arrays coupled with a flat silver mirror (plasmonic back reflector), we achieved a significant broadband enhancement of the useful absorption resulting from both surface texturing and plasmonic scattering, and achieving 91% of the theoretical Lambertian limit of absorption. [1] S. Morawiec et al. Experimental Quantification of Useful and Parasitic Absorption of Light in Plasmon-Enhanced Thin Silicon Films for Solar Cells Application. Scientific Reports 6 (2016)

We present Schottky junction solar cell composed of graphene transferred onto hydrogenated amorphous and microcrystalline silicon, a low-cost alternative to well-explored crystalline silicon. We demonstrated sample with open-circuit voltage of 445 mV, a remarkable value for undoped graphene-based solar cell. Photovoltaic characteristics of this sample remained stable over 11 months and could be further improved by doping. The graphene/silicon junctions were characterized by current-voltage curves obtained locally by conductive atomic force microscopy (C-AFM) and macroscopically by standard solar simulator. Very good correlation between both independent measurements proved C-AFM as highly useful tool for photovoltaic characterization on nano- and micrometer scale.

Optical absorptance spectroscopy of polycrystalline CH3NH3PbI3 films usually indicates the presence of a PbI2 phase, either as a preparation residue or due to film degradation, but gives no insight on how this may affect electrical properties. Here, we apply photocurrent spectroscopy to both perovskite solar cells and coplanar-contacted layers at various stages of degradation. In both cases, we find that the presence of a PbI2 phase restricts charge-carrier transport, suggesting that PbI2 encapsulates CH3NH3PbI3 grains. We also find that PbI2 injects holes into the CH3NH3PbI3 grains, increasing the apparent photosensitivity of PbI2. This phenomenon, known as modulation doping, is absent in the photocurrent spectra of solar cells, where holes and electrons have to be collected in pairs. This interpretation provides insights into the photogeneration and carrier transport in dual-phase perovskites.

KLuS2 single crystal samples undoped and doped with a low (5 %) or high (38 %) concentration of trivalent thulium or ytterbium ions were synthesized in the form of thin hexagonal plates. The low phonon energy ( ∼ 220 cm−1) was confirmed using Raman spectroscopy. Samples were studied also by using optical absorption and emission as well as electron paramagnetic resonance spectroscopy and the observed spectral features are discussed. In particular, the 5 % Yb doped samples demonstrate homogeneous dopant distribution inside the material over the lutetium sites. No other signals either from potassium site or the exchange coupled ions were detected. For infrared transitions the luminescence kinetic was determined. Significantly broad infrared emission bands (at 1.4, 1.8 and 2.3 μm for Tm3+, 1 μm for Yb3+) and long decay times (e.g. 0.4 ms from 3H4 to 19 ms from 3F4 levels of Tm3+, 1.4 ms from 2F5/2 level of Yb3+) make those materials perspective for future laser development.

Friction and wear resistance are important factors in almost all branches of industry, as they affect lifetime, power consumption and other properties of all mechanical tools and machines. Diamond-like carbon (DLC) and derived metal-carbon composite (WC:H) layers are known to substantially improve both of these factors and frequently find their use in tribological applications. One of the desired properties of the tribological layers is a smooth surface. However, microscopic analysis of the WC:H layers shows a frequent occurrence of a certain type of structural defects that have major influence on the layer roughness. The defects are conically shaped objects penetrating the layer all the way down to the substrate, being covered with a spherical cap on the top of the layer. The lateral dimensions of the defects vary from several hundreds of nanometers to a few micrometers. To study these defects we prepared several layers at various conditions and analysed them by different methods, such as SEM, FIB, EDX, AFM and Raman spectroscopy. We will discuss the structure of the defects and influence of the preparation conditions on their growth to find the way to control their occurence in the layer.

Radial junction solar cells with only ~100 nm thin amorphous Si absorber layer deposited on Si nanowires can be prepared by a relatively simple and low-cost thin film technology. Metal assisted Si nanowire growth leads to a disorder in nanowire orientations, lengths and shapes, which is then preserved by the conformal absorber layer. Interestingly, high conversion efficiencies are reached in spite of the disorder. In this contribution we describe microscopic methods aiming at exploring the role of structural disorder on the local electronic properties of radial junction cells. A method for locating the same nanostructure in different microscopes, using the nanoindentation marks for orientation on the sample, is described. Indents can be easily located by optical microscopy, scanning electron microscopes or scanning probe microscopes. Groups of three indents arranged in triangles can serve as coordinate systems for triangulation on samples, enabling correlative microscopy even in instruments which were not designed for it. This approach also enables localization of the same positions on samples after repeated mounting in various microscopes with a precision better than 50 nm. This is possible even on samples without any structural features, as demonstrated for flat silicon thin films prepared by solid phase crystallization, for which we have correlated crystallographic maps from electron backscattering diffraction and conductivity maps by atomic force microscopy. The technique allows observing the same locations before and after technological steps, as shown for the hot wire chemical vapor deposition of carbon nanowalls.

We apply a combination of photocurrent and photothermal spectroscopic techniques to experimentally quantify the trade-off between useful and parasitic absorption of light in thin hydrogenated microcrystalline silicon (?c-Si:H) films incorporating self-assembled silver nanoparticle arrays, located at the rear side, for improved light trapping via resonant plasmonic scattering. The photothermal technique is used to measure the total absorptance while the photocurrent spectroscopy accounts only for the photons absorbed in the ?c-Si:H layer (useful absorptance); therefore, the method allows for independent quantification of the useful and parasitic absorptance of the plasmonic (or any other) light trapping structure [1]. We demonstrate that for 0.9 ?m thick ?c-Si:H film the optical losses resulting from the plasmonic light trapping are insignificant below 730 nm, above which they increase rapidly with increasing illumination wavelength. For the films deposited on nanoparticle arrays coupled with a flat silver mirror (plasmonic back reflector), we achieved a significant broadband enhancement of the useful absorption with an average useful absorption of 43% and an average parasitic absorption of 19% over 400?1100 nm wavelength range, achieving 91% of the theoretical Lambertian limit of absorption.

Graphene layers were prepared on copper substrates by thermal chemical vapor deposition (CVD) and microwave (MW) plasma CVD processes. Atomic force microscopy in topography, phase imaging, and conductivity detection (C-AFM) as well as Raman micro-spectroscopy are employed to analyze the graphene layers on a microscopic scale in an as-deposited state on copper. By correlating these data we identify microscopic inhomogeneities (on a micrometer and nanometer scale) in material and electrical properties of both types of graphene. The inhomogeneities are attributed to (i) large but defects including flakes of plasma CVD graphene and (ii) high quality but small flakes of thermal CVD graphene. Moreover, the plasma CVD graphene contains large density of non-conductive openings (0.1–1 μm in size) where no graphene is detected. The obtained data explain two orders of magnitude lower electrical conductivity of the plasma CVD graphene measured macroscopically after substrate transfer. Implications for optimizing the graphene growth processes are discussed.

The hydrogen plasma passivation of thin film polycrystalline silicon (pc-Si) was investigated in conjunction with plasma texturing process to make efficient heterojunction solar cells. The pc-Si layers were first treated using direct and remote hydrogen plasma technologies. The heterojunction solar cells were then fabricated by subsequent deposition of i/n+ a-Si:H. Hydrogenation at high temperature (610 °C) results in enhanced dissolution and diffusion of hydrogen in pc-Si by a factor of about 3 and 4, respectively, in comparison with those at low temperature (420 °C). The hydrogen atoms in the pc-Si layer mainly bond to the silicon dangling bonds and form complexes with dopant atoms. In addition, platelets defects are generated by the hydrogen plasma in the sub-surface region of pc-Si hydrogenated at 420 °C and cause higher saturation current in the space charge region whilst they form in the region deeper than 1 μm at 610 °C. Removal of the platelets using SF6/N2O plasma post-texturing after low-temperature hydrogenation not only enhances the short circuit current but also improves the open circuit voltage and the fill factor simultaneously. Combining plasma pre-texturing with high-temperature hydrogenation, the best 2 µm-thick pc-Si heterojunction solar cell reaches an efficiency of 8.54%.

In this paper we present a comparison of three different methods that can be used for estimating the stiffness of qPlus sensors. The first method is based on continuum theory of elasticity. The second (Cleveland’s method) uses the change in the eigenfrequency that is induced by the loading of small masses. Finally, the stiffness is obtained by analysis of the thermal noise spectrum. We show that all three methods give very similar results. Surprisingly, neither the gold wire nor the gluing give rise to significant changes of the stiffness in the case of our home-built sensors. Furthermore we describe a fast and cost-effective way to perform Cleveland’s method. This method is based on gluing small pieces of a tungsten wire; the mass is obtained from the volume of the wire, which is measured by optical microscopy. To facilitate detection of oscillation eigenfrequencies under ambient conditions, we designed and built a device for testing qPlus sensors.

A combination of photocurrent and photothermal spectroscopic techniques is applied to experimentally quantify the useful and parasitic absorption of light in thin hydrogenated microcrystalline silicon (μc-Si:H) films incorporating optimized metal nanoparticle arrays, located at the rear surface, for improved light trapping via resonant plasmonic scattering. The photothermal technique accounts for the total absorptance and the photocurrent signal accounts only for the photons absorbed in the μc-Si:H layer (useful absorptance); therefore, the method allows for independent quantification of the useful and parasitic absorptance of the plasmonic (or any other) light trapping structure. We demonstrate that with a 0.9 μm thick absorber layer the optical losses related to the plasmonic light trapping in the whole structure are insignificant below 730 nm, above which they increase rapidly with increasing illumination wavelength. An average useful absorption of 43% and an average parasitic absorption of 19% over 400–1100 nm wavelength range is measured for μc-Si:H films deposited on optimized self-assembled Ag nanoparticles coupled with a flat mirror (plasmonic back reflector). For this sample, we demonstrate a significant broadband enhancement of the useful absorption resulting in the achievement of 91% of the maximum theoretical Lambertian limit of absorption.

The dark conductivity of carbon nanowall (CNW) films deposited by hot-wire CVD was investigated. The conductivity of CNW films increased with increasing the film thickness. The CNW films have wall structure stood on substrate and the wall structure grows after initial layer was formed. The conductivity of the wall structure was estimated from above result. The conductivity of the wall structure increased with increasing temperature. Based on these results, the electrical properties of CNW films were discussed.

Microcrystalline silicon (μc-Si:H) thin films were studied by photo-conductive atomic force microscopy (PC-AFM) under top side illumination by HeCd 442 nm laser and/or by scattered light of AFM detection diode. In order to make the top side illumination possible, so called “nose” type cantilevers, with the tip at the end of cantilever, were used for local photo-current map measurements. Local current intensity under different illumination is discussed mainly from a point of view of the absorption depth of the used light. Diffusion length of charge carriers ~ 300 nm was estimated from comparison of the current levels under different illumination.

We employ nanocrystalline diamond (NCD) thin films with average grain sizes of 250 and 80 nm to resolve influence of grain boundaries and sp 2 phase on protein adsorption and electronic function of solution-gated field-effect transistors (SGFET). Microscopic (20 μm × 60 μm) SGFETs are fabricated without gate oxides based on hydrogen-terminated NCD films on glass substrates. We show that NCD with grain sizes down to 80 nm and film thickness of 100 nm is fully operational as SGFET. We find that inherent hysteresis of SGFET transfer characteristics, their reaction time, their negative shift after protein adsorption and cell culturing process, low gate leakage currents and no influence of UV sterilization or rinsing are all independent of the NCD grain size. Thus we propose a microscopic model where the function of NCD SGFET is determined by the H-terminated surface of diamond nanocrystals and its interaction with proteins, not by grain boundaries or sp 2 phase in general.

Electrostatic charging of oxygen-terminated nanocrystalline diamond (NCD) thin films deposited on silicon in sub-100 nm thickness and with intentionally high relative sp2 phase ratio (60%) is characterized on a microscopic level. By correlating Kelvin Force Microscopy, Current-Sensing Atomic Force Microscopy, micro-Raman spectroscopy and cross-sectional Scanning Electron Microscopy data we show that the charging is determined by both the surface topography (grains and grain boundaries) and complex sub-surface morphology (arrangement of grains and sp2 phase) on scales below 2 × 2 μm2. These microscopic data and macroscopic I(V) characteristics evidence that sp2 phase dominates over diamond grains in local electrostatic charging of NCD thin films. Moreover, the tip-surface junction quality is identified as the main factor behind large variations (0.1 to 1 V) of the overall induced electrostatic charge contrast.

Diamond-based materials possess many unique properties, one of them being a broad-band visible photoluminescence due to a variety of color centers. However, a high material refractive index makes the extraction of photoluminescence (PL) from a diamond layer inefficient. In this paper, we show that by periodical nanopatterning of the film's surface into a form of two-dimensional photonic crystal, the extraction of PL can be strongly enhanced within the whole visible spectrum compared to the extraction of PL in a pristine or randomly nanopatterned film. On the basis of theoretical calculations, enhancement is shown to be due to the photonic crystal effect, including efficient coupling of an excitation laser into the diamond.

Nanocrystalline diamond (NCD) thin films are deposited on p-type Si substrates at different deposition temperatures (600― 820 °C) in thicknesses below 100 nm. The films are then terminated by oxygen using r.f. oxygen plasma. Atomic force microscopy (AFM) is used to induce electrostatically charged micrometer-sized patterns on the diamond films by applying a bias voltage on the AFM tip during a contact mode scan. Trapped charge is detected by Kelvin force microscopy, showing potential shifts different in geometry and amplitude on each film for the same absolute bias voltages. The films have similar structure and grain size, measured by AFM and scanning electron microscope (SEM). Fourier transform infrared spectroscopy (FTIR) in reflection regime shows the solidity of the films. Material differences are resolved via micro-Raman spectroscopy. Different charging properties are thus attributed to the differences in relative amount of diamond and sp 2 phase.

Raman maps, i.e., grids of individual spectra of Raman scattering from excitation laser beam focused by optical microscope, were used to characterize mixed phase silicon thin films. Raman maps measured with 442 nm and 785 nm lasers were compared with topography or local current maps recorded by conductive atomic force microscope (C-AFM) in the same field of view. The Raman measurement may irreversibly influence the thin film surface by thermal oxidation, as proved by the change of local conductivity observed in C-AFM. Resolution limit of individual grains in Raman mapping with 442 nm excitation was 350 nm, however, we were able to detect much smaller individual grains (down to ∼160 nm diameter measured by AFM) if they were isolated in amorphous matrix. Polarized Raman spectroscopy is able to detect the crystallographic orientation of the single microcrystalline grain. Resolution of the Raman mapping may be significantly improved by tip enhanced Raman measurement. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We show that local currents observed by the Conductive Atomic Force Microscopy (C-AFM) of silicon thin films measured in ambient atmosphere are generally limited by surface oxide, either native or created by the measurement itself in a process of Local Anodic Oxidation (LAO), as evidenced by observed topographic changes of Si surface. The tip-induced LAO changes the character of the local current maps in repeated scans or even in the first scan of a pristine surface. In particular, the oxidation of the neighboring scan lines leads to the appearance of grain edges as conductive rings. Finally, we have used brief HF acid etch to strip the oxide in order to restore the contrast in the C-AFM maps of aged samples and we compare the observed local current levels to those observed in ultra-high vacuum C-AFM on in-situ deposited samples (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We investigate the role of fetal bovine serum (FBS) proteins in the assembly of osteoblastic cells (SAOS-2) in McCoy's 5A medium on synthetic monocrystalline and nanocrystalline diamonds having H- and O-terminated array patterns. We characterize i) adhesion of proteins and cells to diamond by shaking experiments (1000 rpm), fluorescence, and atomic force microscopy, ii) distribution of FBS proteins by micro-Raman spectroscopy, and iii) influence of pre-adsorbed specific FBS proteins (albumin, fibronectin, vitronectin) on the cell assembly. There is 40% lower adhesion of cells on H-terminated diamond with adsorbed FBS compared to this surface without FBS as well as to O-terminated surfaces. Spatially resolved Raman spectroscopy of C―H stretching bands around 2900 cm− 1 showed uniform coverage of H/O-diamond by the albumin in more than 50 nm thick FBS layers. The other FBS proteins were not detectable by Raman. Pre-adsorption of the specific proteins prior to cell plating indicated that the cell preference to O-terminated diamond is controlled by the fibronectin rather than by the albumin. We discuss the data with a view to the cell preferential assembly on H/O-diamond micro-arrays.

Here, the authors demonstrate the fabrication of silicon nanowire array based solar cells consisting of crystalline Si cores and amorphous a-Si:H layers using a single pump-down plasma-enhanced chemical vapor deposition (PECVD) process. The authors investigate the influence of geometry, physical dimensions, and doping of the nanowire arrays on the solar cell performance. The authors show that the length and thickness of the nanowire radial NIP junction have a significant influence on the current density–voltage characteristics and external quantum efficiency of the cells. The efficiency of radial solar cells is found to be mainly driven by the photogenerated current which is the largest when the thickness of the absorber film is approximately one half of the NIP nanowire length. Doping of the nanowires done by adding phosphine gas in situ in the PECVD growth has affected both the axial and radial nanowire growth rate, leading to the nanowire growth reduction in both directions at higher doping concentrati...

Scanning probe methods (SPMs) such as conductive atomic force microscopy (C-AFM) can be used to probe the structure and local conductivity of the mixed phase silicon thin films with nanometer resolution. Effective medium approximations (EMAs) were used to relate the nanoscale properties with effective macroscopic properties for the dark conductivity measured with coplanar contacts. Comparison of the percolation threshold predicted by diffferent EMAs show partial correlation of the structure, with resistive amorphous phase coating the conductive grains. In sandwich structures (such as solar cells) the local fields may play important role: concentration of both optical and electrical internal fields to the tips of spherically capped conical microcrystalline grains. Adaptive higher-order polynomial finite-element methods (FEMs) were used to calculate the internal field distributions in the C-AFM. The calculated values agree with the experimental C-AFM, providing the first quantitative description of the relation of the nanoscale and macroscopic properties of the mixed phase Si films.

Thin polymer blend films made of donor and acceptor poly-(p-phenylenevinylene) (PPV)-based polymers were prepared. Diverse scanning probe techniques (atomic force microscopy (AFM), Kelvin force microscopy (KFM), current-sensing AFM (CS-AFM), and micro-Raman mapping) are used to characterize morphologic, electronic as well as optoelectronic properties of the heterostructures. Morphologies of the heterostructures are correlated with microscopic and macroscopic electronic response to a broad-band visible illumination. The data are discussed with respect to photovoltaic applications.

A 15-nm lithium fluoride (LiF) thin film evaporated on glass substrate is shown to enhance the nucleation of microcrystalline Si grown by plasma enhanced chemical vapour deposition at the amorphous/microcrystalline boundary conditions. The effect is more pronounced at low substrate temperatures, nucleation density being 10 times higher at ∼ 80 °C. The effect is ascribed to the ionic chemical nature of LiF, the low work function material used in organic electronic devices, and we propose its use for micro patterning crystalline Si regions in otherwise amorphous Si film.

Thin film of polypyrrole is electrochemically deposited on hydrogen terminated surface of intrinsic diamond exhibiting surface conductivity (5 × 10 − 5 S/□). Based on a high bonding strength (40 nN) estimated by AFM-scratching experiments and local changes of surface work function detected by Kelvin force microscopy we suggest that the polypyrrole is covalently attached to the diamond surface via carbon–carbon bond while replacing the hydrogen termination. Electronic measurements show loss of surface conductivity of diamond after the polypyrrole deposition. These results are discussed in terms of electronic and electrochemical properties of polypyrrole–diamond system also in the perspective of its potential device applications.

The authors report on the correlation of the oxygen content for three high growth-rate series of thin Si films crossing the boundary between amorphous and microcrystalline growth together with the evolution of the prefactor and the activation energy of the dark d.c. conductivity. The different roles of oxygen, such as doping, alloying or defect passivation, are discussed in the framework of the model of transport based on the formation of large grain boundaries with an increased band gap due to hydrogen and/or oxygen alloying.

Charge transfer in polypyrrole–diamond system is studied by conductivity measurements of a channel made of H-terminated diamond in the dark and under illumination. Micrometer-sized channels of conductive hydrogen-terminated diamond are lithographically fabricated on the surface of monocrystalline intrinsic diamond crystal by selective oxygen plasma treatment. The channels are interrupted by electrochemically synthesized micrometer-sized polypyrrole clusters. Similar characterizations are performed on channels interrupted by surface oxidation. Based on the increase and spectral response of the photo-current in the system, doping of diamond by charge carriers from polypyrrole is deduced.

Thin films of polypyrrole (PPy) are electrochemically polymerized in the thickness 25 nm on hydrogen-terminated intrinsic diamond surface exhibiting two-dimensional surface conductivity of 5 × 10 − 5 (S/). Opto-electronic properties of the system are characterized by Kelvin force microscopy detecting surface potentials. Shifts of the surface potentials of diamond and PPy under visible light illumination are attributed to sub- and super-band gap surface photovoltage effects changing energetic band bending in the range of 100–200 meV. We present a model considering influence of diamond surface termination, surface states and highly resistive bulk properties as well as excitonic transport in PPy. The model suggests a charge transfer between PPy and diamond.

The preparation and characterization of micrometer gold and silver single-crystals of well-defined shapes are reported here. The shapes of the crystals can be described as plates, polyhedra, and wires. The orientation of the crystal faces was studied using electron and X-ray powder diffraction techniques, and a (111) orientation of the large faces of gold plates was experimentally shown. The surface morphology of the crystal faces was studied by atomic force microscopy. Modifications of gold microplates with the thiolated carborane clusters 1,2-(HS)2-1,2-C2B10H10 (1), 9,12-(HS)2-1,2-C2B10H10 (2), and 1,12-(HS)2-1,12-C2B10H10 (3) are described. The carboranethiol molecules 1 and 2 show dipole moments of 4.1 and 5.9 D. In comparison, the thiolate derivative of compound 1 has a dipole moment of 4.7 D in the opposite direction to 1, and the thiolate form of compound 2 has a dipole moment of 16.7 D in the same direction. On the basis of X-ray photoelectron spectroscopy (XPS) analyses and values of work functio...

Silicon thin films were grown by plasma enhanced chemical vapor deposition at high-pressure (700 Pa), high-power (4– W/cm2) depletion regime using multi-hole cathode. Series of samples were deposited by varying hydrogen/silane ratio or plasma power to study evolution of film structure and transport properties near a-Si:H/μc-Si:H transition. We suggest a simple “μc-Si:H layer quality factor” based on the ratio of subgap optical absorption α (1.4 eV)/α (1 eV) measured by constant photocurrent method. This ratio correlates well with the values of ambipolar diffusion lengths measured by surface photovoltage method perpendicularly to the substrate, i.e., in the direction of the collection of the photogenerated carriers in solar cells.

Four series of intrinsic thin Si films were prepared by plasma enhanced chemical vapor deposition at standard and high growth rate conditions. We suggest a simple ‘μc-Si:H layer quality factor’ based on the ratio of subgap optical absorption coefficient values: α (1.4 eV)/ α (1 eV). This ratio minimizes the light scattering effects for rough films and can serve as a reliable detection of the amorphous/microcrystalline structure transition and also as a figure of merit for the microcrystalline layer. The quality factor is evaluated for series of our samples with well known structure and also compared with samples from other laboratories with different deposition and measurement techniques.

Field-enhanced metal-induced solid phase crystallization (FE-MISPC) at room temperature is employed to create microscopic crystalline regions at predefined positions in hydrogen-rich amorphous silicon (a-Si:H) films. Electric field is applied locally using a sharp conductive tip in atomic force microscope (AFM) and nickel electrode below the a-Si:H film. The process is driven by a constant current of −50 pA to −500 pA while controlling the amount of transferred energy (1–300 nJ) as a function of time. Passing current leads to a formation of nanoscale pits in the a-Si:H films. Depending on the energy amount and rate the pits exhibit lower or orders of magnitude higher conductivity as detected by current-sensing AFM. High conductivity is attributed to a local crystallization of the films. This is confirmed by micro-Raman spectroscopy.

Preparation of thin film silicon at high growth rate is an important target for its application in solar cells. The properties of hydrogenated microcrystalline silicon, prepared with the help of PECVD multi-hole cathode in a high pressure and depletion regime in a wide range of thicknesses are described in detail. We illustrate the surprising result that we can prepare high growth rate microcrystalline silicon from 0.4 up to 30 μm thickness without great peel-off problems. The room temperature dark DC conductivity, as well as the crystallinity, increased up to 5 μm film thickness and then started to decrease again. These results are explained by the initial temperature profiling and a thickness-induced increase of the lateral inhomogeneity.

Lithographically prepared micrometer-sized permalloy ellipses were used to control the growth of nanocrystalline Si in otherwise amorphous Si film prepared by plasma enhanced chemical vapor deposition. Atomic force microscopy and micro-Raman spectroscopy were employed to study the surface structures before and after the deposition of the Si film. The possible applications of the controlled growth of nanocrystalline Si micro-patterns are discussed as well as the mechanisms leading to the growth of these patterns.

Micro-Raman spectroscopy provides laterally resolved microstructural information for a broad range of materials. In this Letter, we apply this technique to tri-iodide (CH3NH3PbI3), tribromide (CH3NH3PbBr3), and mixed iodide–bromide (CH3NH3PbI3–xBrx) organic–inorganic halide perovskite thin films and discuss necessary conditions to obtain reliable data. We explain how to measure Raman spectra of pristine CH3NH3PbI3 layers and discuss the distinct Raman bands that develop during moisture-induced degradation. We also prove unambiguously that the final degradation products contain pure PbI2. Moreover, we describe CH3NH3PbI3–xBrx Raman spectra and discuss how the perovskite crystallographic symmetries affect the Raman band intensities and spectral shapes. On the basis of the dependence of the Raman shift on the iodide-to-bromide ratio, we show that Raman spectroscopy is a fast and nondestructive method for the evaluation of the relative iodide-to-bromide ratio.

Solar cells with radial junctions based on silicon nanowires were investigated using correlative microscopy in order to determine the nature and origin of previously reported inhomogeneity of their electronic properties. For correlating various microscopy techniques, we have prepared sets of three Vickers type nanoindents arranged in a right triangle with 20 µm sides as marks of local frame of reference. Due to the shape of the indents (squares with 4 µm sides and clear diagonals) the position of the marks can be located with high precision by various microscopes. This makes it possible to correlate the results from scanning electron microscopy, Kelvin probe force microscopy and conductive atomic force microscopy techniques on the same place of the sample, with a precision down to individual nanowires, obtaining new information about the electronic inhomogeneity. Using the conductive AFM we analyzed the growth process of silicon nanowires step by step in order to find possible origins of the local (photo)current variations.

We present a complex characterization of thin silicon films, the growth of which has been influenced by permanent magnet, placed under the substrate. The pattern of microcrystalline regions in otherwise amorphous film varied with the orientation of the magnetic field. Study by atomic force microscopy and by micro-Raman spectroscopy revealed that the microcrystalline regions resulted from increased nucleation density of crystalline grains at the locations where the magnetron effect could be expected. This phenomenon allowed us to study in detail the transition between amorphous and microcrystalline growth. Moreover, it can be used as a kind of ‘magnetic lithography’ for preparation of predefined microcrystalline patterns in otherwise amorphous silicon films.

Hydrogen passivation technique is essential for improving the properties of polycrystalline silicon thin films. Elastic Recoil Detection Analysis (ERDA) indicated depth profiles of hydrogen concentration in poly-Si after hydrogen passivation. We have observed that plasma hydrogenation with duration up to 30 min effectively passivated the defects and improved photoluminescence intensity. Over 60 min of hydrogenation, PL intensity started to decrease. Raman scattering spectroscopy and X-ray rocking curve indicated that hydrogen created new defects and/or disorder with an increase in the hydrogen passivation time. Over 60 min, hydrogen started to form Si–H 2 bonding and hydrogen molecules (H 2 ), which lead to degradation of PL intensity. These peak positions were largely influenced by the grain size. These formations must be formed in quasi-stable sites, which are located at close to grain boundaries. Thus hydrogenation treatment may lead to defect passivation and new defects and/or disorder creation.