In the present work our experimental results on the energy shifts and energy widths (full width of half-maximum) of the quasi-elastic peaks (1-5 keV) obtained using a high-energy-resolution electron spectrometer and different (C, Si, Ni and Au) surfaces are compared with those calculated by assuming single elastic scattering on free atoms having a Maxwell-Boltzmann thermal velocity distribution. There is a good agreement in the case of the energy shifts as well as for the energy broadenings obtained using higher atomic number polycrystalline samples (Ni, Au). In the case of Si, however, the measured energy broadening is systematically larger by 15-20% than the calculated broadening for the whole primary beam energy range. Compared with the calculated values, considerably larger broadenings (by 30-60%, depending on the primary beam energy) were observed for carbonic samples. The contribution of the multiple elastic scattering to the yield of the electrons backscattered elastically, and the effect of the multiple scattering on the energy shifts and Doppler broadenings, have been determined using Monte Carlo simulations. Our results show that multiple scattering causes only small changes in energy shifts and energy broadenings of elastic peaks in the case of the samples and primary electron energy region studied.

It has been shown by the Auger depth profiling technique that the concentration profile at the initially sharp Si/Ge interface in amorphous Si/Ge multilayers shifted but remained still sharp after a heat treatment at 680 K for 100 h. At the same time the fast diffusion of Si resulted in the formation of an almost homogeneous Ge͑Si͒ amorphous solid solution, while there was practically no diffusion of Ge into the Si layer. This is direct evidence on the strong concentration dependence of the interdiffusion coefficient in amorphous Si/Ge system, and it is in accordance with the previous indirect result obtained from the measurements of the decay of the small angle Bragg peaks, as well as with finite difference simulations. © 2001 American Institute of Physics. ͓DOI: 10.1063/1.1331330͔Changes in atomic structures of amorphous semiconductors and their relationships to physical properties are currently of interest due to their useful optical and electronic features.1,2 Since most structural changes are related to atomic diffusion, any real understanding of the structural transformation, homogenization, etc., must be based on the knowledge of the diffusion processes. The study of diffusion in amorphous materials includes some difficulties. One of the main problems is related to the thermal stability of the amorphous phase; the diffusional measurements should be carried out at low temperatures for very short diffusion times in order to avoid structural changes due, e.g., to structural relaxation. Additionally, in amorphous semiconductors the mechanism of diffusion is also not fully understood.3-5 Thus, for example factors controlling the details of diffusional homogenization in amorphous Si/Ge multilayers are still under discussion. First of all the diffusional asymmetry ͑manifested in the strong concentration dependence of the interdiffusion coefficients͒, 6 the significant pore formation during the diffusional mixing, 7 and the possible role of diffusional stresses 8 are the most important factors indicating the need of a better understanding of the previous process.In this article interdiffusion in amorphous Si-Ge multilayered specimens is studied by Auger depth profiling. The primary objective of the present investigation is to observe the predicted asymmetric change of composition caused by the strong concentration dependence of the diffusion coefficients. Experimental results, obtained from small angle x-ray diffraction ͑SAXRD͒ measurements at different average compositions indicated a strong concentration dependence of the chemical diffusion parameters.9,10 Although such a strong concentration dependence inevitably should lead to a significant curvature on the ln(I/I 0 ) ͑I/I 0 is the normalized height of the first order SAXRD peak͒ versus time plots 11 ͑and to oscillatory behavior of the higher order peaks͒, later on the experimentally observed curvature was rather attributed by the same group to the effects of structural relaxation and coupling back effects of stresses of diffusional origin were also excluded....

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Micropatterning of living single cells and cell clusters over millimeter–centimeter scale areas is of high demand in the development of cell-based biosensors. Micropatterning methodologies require both a suitable biomimetic support and a printing technology. In this work, we present the micropatterning of living mammalian cells on carboxymethyl dextran (CMD) hydrogel layers using the FluidFM BOT technology. In contrast to the ultrathin (few nanometers thick in the dry state) CMD films generally used in label-free biosensor applications, we developed CMD layers with thicknesses of several tens of nanometers in order to provide support for the controlled adhesion of living cells. The fabrication method and detailed characterization of the CMD layers are also described. The antifouling ability of the CMD surfaces is demonstrated by in situ optical waveguide lightmode spectroscopy measurements using serum modeling proteins with different electrostatic properties and molecular weights. Cell micropatterning on the CMD surface was obtained by printing cell adhesion mediating cRGDfK peptide molecules (cyclo­(Arg-Gly-Asp-d-Phe-Lys)) directly from aqueous solution using microchanneled cantilevers with subsequent incubation of the printed surfaces in the living cell culture. Uniquely, we present cell patterns with different geometries (spot, line, and grid arrays) covering both micrometer and millimeter–centimeter scale areas. The adhered patterns were analyzed by phase contrast microscopy and the adhesion process on the patterns was real-time monitored by digital holographic microscopy, enabling to quantify the survival and migration of cells on the printed cRGDfK arrays.

Al2O3 (5 nm)/Si (bulk) sample was subjected to irradiation of 5 keV electrons at room temperature, in a vacuum chamber (pressure 1 × 10−9 mbar) and formation of amorphous SiO2 around the interface was observed. The oxygen for the silicon dioxide growth was provided by the electron bombardment induced bond breaking in Al2O3 and the subsequent production of neutral and/or charged oxygen. The amorphous SiO2 rich layer has grown into the Al2O3 layer showing that oxygen as well as silicon transport occurred during irradiation at room temperature. We propose that both transports are mediated by local electric field and charged and/or uncharged defects created by the electron irradiation. The direct modification of metal oxide/silicon interface by electron-beam irradiation is a promising method of accomplishing direct write electron-beam lithography at buried interfaces.

Ion beam mixing has been used to produce a silicon carbide (SiC)-rich nanolayer for protective coating. Different C/Si/C/Si/C/Si(substrate) multilayer structures (with individual layer thicknesses falling in the range of 10-20 nm) have been irradiated by Ar and Xe ions at room temperature in the energy and fluence ranges of 40-120 keV and 1-6 × 10 ion/cm, respectively. The effects of ion irradiation, including the in-depth distribution of the SiC produced, was determined by Auger electron spectroscopy depth profiling. The thickness of the SiC-rich region was only some nanometers, and it could be tailored by changing the layer structure and the ion irradiation conditions. The corrosion resistance of the layers was investigated by potentiodynamic electrochemical test in 4 M KOH solution. The measured corrosion resistance of the SiC-rich layers was orders of magnitude better than that of pure silicon, and a correlation was found between the corrosion current density and the effective areal density of the SiC.

The inelastic mean free path (IMFP) of electrons was determined experimentally for selected polyaniline and polyacetylene samples with Ag and Ni references using elastic peak electron spectroscopy (EPES). The surface composition was determined by XPS and density by helium pycnometry. The high resolution hemispherical ESA-31 and ADES-400 spectrometers were used for measurements in the energy range E = 0.5–3.0 keV and E =0.4 − 1.6 keV, respectively. The integrated elastic peak intensity ratios for sample and reference were calculated using the Monte Carlo (MC) algorithm based on the electron elastic scattering cross-sections database NIST SRD64 version 3.1 and applying TPP-2M IMFPs for polymers. Surface excitation parameters (SEP) and material parameters (ach) for polymers were determined, using the model of Chen, from comparison of measured and MC calculated elastic peak intensity ratios. These corrections proved to be efficient in decreasing the percentage deviations between the obtained IMFPs and the TPP-2M formula IMFPs. The elastic peak of hydrogen was observed in the EPES spectra of polymers. The experimental contribution of the hydrogen to the total elastic peak was 0.58%, while this value obtained from the MC simulations was 1.98%.

The elastic backscattering probability P, of electrons is proportional to the product of the inelastic mean free path (IMFP), effective backscattering cross section (a,,), and atomic density (N). Thus, experimental evaluation of P,, e.g. from the elastic peak intensity measurements, enables the determination of the IMFP. a,, can be calculated by integrating the differential elastic scattering cross sections using a simplified model based on the first Born approximation and the ThomasFermi-Dirac atomic potential. No significant difference in the values of a,, was found using the ThomasFermi, the Thomas-Fermi-Dirac and the HartreeFock atomic potentials or integrating the scattering cross sections tabulated by Fink ef al. From the experimental values of Pe reported by Schmid et al. and by Gergely the IMFP was determined for a number of elements. A good agreement was found with the data on the IMFP published in the literature. Comparing the elastic peak of two samples and using the data of Ashley and Tung as reference values, the IMFP has been determined for Gap, GaSb, InP, InSb and Si,N, samples. Good agreement with the data of Ashley and Tung was obtained for Si, Ge, Si02 and GaAs.