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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 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.

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.

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.

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.

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.

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.

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.

We have examined the common methods for determination of the crystallinity of mixed phase silicon thin films from the TO–LO phonon band in Raman spectra. Spectra are decomposed into contributions of amorphous and crystalline phase and empirical formulas are used to obtain crystallinity either from the integral intensities (peak areas) or from magnitudes (peak maxima). Crystallinity values obtained from Raman spectra excited by Ar+ laser green line (514.5 nm) for a special sample with a profile of structure from amorphous to fully microcrystalline were compared with surface crystallinity obtained independently from atomic force microscopy (AFM). Analysis of the Raman collection depth in material composed of grains with absorption depth 1000 nm in an amorphous matrix (absorption depth 100 nm), was used to explain reasons for systematic difference between surface and Raman crystallinities. Recommendations are given for obtaining consistent results.

Amorphous/microcrystalline transition was studied in the high growth-rate depositions of hydrogenated silicon films at a high pressure (700 Pa) in a depletion regime using a series of samples with the ratio of hydrogen to silane flows from 10 to 32. Results show the characteristic features of the amorphous/microcrystalline transition: abrupt change of dark conductivity and crystallinity accompanied by peaks of roughness and diffusion length, observed previously at standard growth rates.

Polycrystalline silicon films for solar cells grown by atmospheric pressure chemical vapour deposition require hydrogenation to passivate defects at grain boundaries. Passivation by remote plasma hydrogenation of 12-μm-thick poly-Si films increased Hall effect carrier mobility from 3 to 20 cm2/Vs, photoluminescence intensity at 0.98 eV band more than 2 times and decreased contrast of local electronic conductivity between grains, observed by combined AFM. However, excessive hydrogenation led to surface damage and defect creation evidenced by widths of Raman LO–TO peak at 520 cm− 1 and X-ray rocking curve of (220) diffraction line. Depth profile by repeated etching of the surface and following the signature of Si–H2 and H2 bonding in Raman spectra showed that the damage extended up to 100 nm from the surface.

Changes in the growth of thin silicon films at very low substrate temperatures (35 °C

The nanostructure of carbon nanowalls (CNWs) was investigated by Torsion Resonance (TR) Atomic Force Microscopy (AFM). In this dynamic non-contact imaging mode a cantilever oscillates torsionally and the amplitude of oscillations is used for the AFM feedback. The technique includes benefits of the semicontact (tapping) mode and at the same time allows one to measure the local conductivity. Moreover, the phase signal is much stronger and fine structures of the CNWs were observed. We also present a comparison of the results obtained by TR, tapping, and contact modes.

We have used plasma enhanced chemical vapor deposition (PECVD) to deposit silicon thin films (∼0.2–1 μm) with different crystallinity fractions on Nanosensors PtIr5 coated atomic force microscopy (AFM) cantilevers (450 × 50 × 2 μm 3 ). Microscopic measurements of Raman scattering were used to map both internal stress and extrinsic stress induced in the films by bending the cantilevers using a nanomanipulator (Kleindiek Nanotechnik MM3A). Thanks to the excellent elasticity of the cantilevers, the films could be bent to curvature radii down to 300 μm. We observed the stress induced shift of the TO–LO phonon Raman band of more than 3 cm −1 for fully microcrystalline film corresponding to the stress ∼0.8 GPa. The shift of the similar film with amorphous structure was ∼2.5 cm −1 .

Advanced characterization methods avoiding transient effects in combination with solar cell performance monitoring reveal details of reversible light-induced perovskite degradation under vacuum. A clear signature of related deep defects in at least the 1 ppm range is observed by low absorptance photocurrent spectroscopy. An efficiency drop, together with deep defects, appears after minutes-long blue illumination and disappears after 1 h or more in the dark. Systematic comparison of perovskite materials prepared by different methods indicates that this behavior is caused by the lead halide residual phase inherently present in material prepared by the two-step method. X-ray photoelectron spectroscopy confirms that lead halide when illuminated decomposes into metallic lead and mobile iodine, which diffuses into the perovskite phase, likely producing interstitial defects. Single-step preparation, as well as preventing lead halide illumination, eliminates this effect.