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Using water as an example, it is shown that monitoring the change in the loss tangent is a high sensitive method that allows determining the activation energy of relaxation processes in nanostructured water with high accuracy. The use of sensors, the electrodes of which are not in direct contact with the liquid under study is shown to be reasonable. The conditions for obtaining reliable information on the properties of water and its solutions are also justified, namely: measurements should be carried out using pulse methods for several seconds, and then measurements should be stopped to avoid contamination of the solutions studied by electrolysis products. The method of monitoring the magnitude of the loss tangent at fixed frequencies allows the acidity of solutions (pH value) to be controlled at the same time without using specialized instruments for acidity studying.

Films of undoped zinc oxide (ZnO) and of ZnO/C nanocomposite were formed by the sol-gel method on glass substrates and on fiberglass using zinc acetate as a precursor and with the addition of zinc chloride respectively. Analysis of the photoluminescence spectra of ZnO/C films at high (N2-laser) and low (HeCd-laser) excitation levels made it possible to establish the defining role of bound excitons in this process at 20–60 K, due to the presence of chlorine residues in the films. With the temperature raised to 300 K the role of recombination through the 1LO- and 2LO-phonon replicas of free exciton levels and impurity-defect levels begins to dominate in the photoluminescence of the ZnO/C films.

The procedure proposed is the express method for the study of anion distribution profiles in the anodic aluminum oxide film. The method consists in measuring the variation of the steady-state electrode potential during the oxide etching. It allows the influence of the initial aluminum composition, the electrolyte composition, anodization regimes, etc. on the characteristics of dense anodic alumina films to be studied. The method developed can be used to study a chemical evolution in anodic alumina formed to correlate with modelling and simulations across materials science disciplines.

We developed a facile one-step sol–gel technique for fabrication of black zinc oxide/carbon (ZnO/C) nanocomposite films demonstrating an enhanced photocatalytic activity. Amorphous carbon covering ZnO grains inside the films was reduced from organic components of the zinc acetate based sol calcinated at 500 °C. The amount of carbon in the films can be controlled by varying the amount of zinc chloride added to the zinc acetate based sols. The surface layer of the films is composed by randomly oriented hexagon-shaped ZnO grains. Photoluminescence quenching indicating the suppression of electron-hole recombination in the prepared ZnO/C composites were observed. The recorded optical transmittance/reflectance spectra and the performed photocatalytic tests demonstrated that the synthesized ZnO/C nanocomposite is promising for photoinduced decomposition of organic compounds. Related peculiarities are discussed.

Zinc oxide/silicon nanowires (ZnO/SiNWs) nanocomposites is a promising material for heterojunction solar cells. They combine the low-reflectivity of SiNWs, where photogenerated charge carriers are produced and harvested, and the high transparency of ZnO, which serves as a functional transparent conductive electrode. In this paper, we present a study of the anti-reflective properties of ZnO/SiNWs core-shell nanostructures. SiNWs were fabricated by a two-step metal-assisted chemical etching and coated with ZnO by electrochemical deposition. Particularly, the change in the specular reflectance of ZnO/SiNWs nanocomposites as a function of thermal annealing temperature under ambient atmosphere is investigated. First, it was shown that the reflectance in the wavelength range of 400-1000 nm of as-synthesized ZnO/SiNWs nanocomposites increases when compared to the bare SiNWs formed from Si wafers with resistivity of 0.3 and 12 Ω∙cm by an 0.51 % and 0.47 %, respectively. Second, it was found that annealed ZnO/SiNWs had a 0.26 % and 0.17 % lower reflectance in the wavelength range of 400-1000 nm than as-synthesized ZnO/SiNWs and yet higher than bare SiNWs. Potential causes such results are discussed in the context of existing literature.

This article presents the results on a fabrication of silicon nanowires by a two-step metal-assisted chemical etching. Morphological and optical properties of the obtained silicon nanostructures depending on the type and resistivity of the initial silicon wafer have been studied. In addition, we have used the silicon nanowires as templates for zinc oxide and silver deposition. The resulting nanocomposites have been shown to demonstrate intensive photoluminescence and activity in the surface enhanced Raman scattering respectively. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper provides the results of studying the formation kinetics and the structure of mesoporous silicon layers obtained by electrochemical anodization in an electrolyte based on 12% aqueous hydrofluoric acid. The electrolyte consisted only of deionized water and hydrofluoric acid and contained no organic additives in order to prevent contamination of porous silicon with carbon during the anodization. All the experiments were carried out on whole silicon wafers 100 mm in diameter, rather than samples of a small size, which are often used to save silicon. As the initial substrates we used monocrystalline silicon wafers of brand KES-0.01, which were cut from the ingots produced by the Czochralski method. Dependences of the thickness of porous silicon layers, its growth rate, and the volume porosity on the anodic current density and the anodization time are determined. Scanning electron microscopy was used to study the structure of porous silicon layers and to define the size and density of the pore channels. The regimes of obtaining homogeneous porous silicon layers for their subsequent use as buffer layers in epitaxy are found.

In this work, we describe the combination of hydrothermal and atomic layer deposition (ALD) for growing low-resistivity ZnO polycrystalline continuous films. The effect of the thickness of ALD seed layers on the morphology of the hydrothermal ZnO films was studied. It was shown that ZnO films hydrothermally deposited on very thin seed layer consist of separate nanorods but in the case of 20 nm seed layer ZnO films transform to uniform continuous layers comprising of closely packed vertically aligned crystallites. Photoluminescence spectra were shown to exhibit broad band behavior in the visible range, corresponding to radiative recombination processes via oxygen defects of ZnO crystalline lattice, and narrow band in the UV region, associated with band-to-band recombination processes. It was shown that the resistivity of the obtained ZnO films is decreased gradually with the increase of ZnO films thickness and determined by the presence of crystal lattice defects in the seed layer.

ZnO nanostructured films doped with Co and Ni deposited by hydrothermal method on silicon substrates covered with undoped ZnO sublayer were studied. SEM images of the films demonstrated them to consist of densely packed vertical nanopillars. Doping ZnO films with Ni or Co at concentrations up to [Formula: see text][Formula: see text]cm[Formula: see text] quenches their UV-excited photoluminescence. The doping also leads to the slight ferromagnetic behavior of ZnO.

Porous silicon (PS) represents the prospective template for the fabrication of metal/PS nanostructures. However n+-type Sb doped Si Czochralski wafers widely used to fabricate PS may contain resistivity striations and as-grown microdefects with specific spiral distribution which influence Si dissolution during the formation of PS by anodizing. This may strongly affect on the PS microstructure and repeatability of metal/PS properties causing an increase of risk of a device failure. In the present research we studied the morphology and SERS-activity of Ag/PS nanostructures formed by Ag immersion deposition on PS. SEM investigation revealed unequal distribution of pore diameters in the surface regions of PS which corresponds to spiral swirl-like distribution of resistivity revealed in Si wafer by anodizing. Morphological changes of Ag deposit on spiral areas were found to cause decreasing of intensity of SERS signal. Additional implantation of Sb ions followed by high temperature annealing has shown to be a technique to improve homogeneity of Ag/PS SERS substrates. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Copper (II) sulfate was used as a source of copper to achieve uniform distribution of Cu particles deposited on porous silicon. Layers of the porous silicon were formed by electrochemical anodization of Si wafers in a mixture of HF, C3H7OH and deionized water. The well-known chemical displacement technique was modified to grow the copper particles of specific sizes. SEM and XRD analysis revealed that the outer surface of the porous silicon was covered with copper particles of the crystal orientation inherited from the planes of porous silicon skeleton. The copper crystals were found to have the cubic face centering elementary cell. In addition, the traces of Cu2O cubic primitive crystalline phases were identified. The dimensions of Cu particles were determined by the Feret's analysis of the SEM images. The sizes of the particles varied widely from a few to hundreds of nanometers. A phenomenological model of copper deposition was proposed.

Oxidation behavior of a-SiC:H layers deposited by radio-frequency magnetron sputtering technique was examined by Kelvin probe force microscopy (KPFM) in combination with scanning electron microscopy, Fourier-transform infra-red spectroscopy and submicron selected area Raman scattering spectroscopy. Partially oxidized a-SiC:H samples (oxidation at 600 °C in oxygen) were examined to clarify mechanism of the oxidation process. Nanoscale and microscale morphological defects (pits) with dimension of about 50 nm and several microns respectively have appeared after thermal treatment. KPFM measurements exhibited the surface potential of the material in micro pits is significantly smaller in comparison with surrounding material. Submicron RS measurements indicates formation of graphite-like nano-inclusions in the pit defects. We conclude that initial stage of oxidation process in a-SiC:H films takes place not homogeneously throughout the layer but it is initiated in local nanoscale regions followed by spreading over all layer.

Plasmonic nanostructures demonstrating an activity in the surface-enhanced Raman scattering (SERS) spectroscopy have been fabricated by an immersion deposition of silver nanoparticles from silver salt solution on mesoporous silicon (meso-PS). The SERS signal intensity has been found to follow the periodical repacking of the silver nanoparticles, which grow according to the Volmer-Weber mechanism. The ratio of silver salt concentration and immersion time substantially manages the SERS intensity. It has been established that optimal conditions of nanostructured silver layers formation for a maximal Raman enhancement can be chosen taking into account a special parameter called effective time: a product of the silver salt concentration on the immersion deposition time. The detection limit for porphyrin molecules CuTMPyP4 adsorbed on the silvered PS has been evaluated as 10(-11) M.

This article presents the study of the electrochemical deposition of zinc oxide from the non-aqueous solution based on dimethyl sulfoxide and zinc chloride into the porous silicon matrix. The features of the deposition process depending on the thickness of the porous silicon layer are presented. It is shown that after deposition process the porous silicon matrix is filled with zinc oxide nanocrystals with a diameter of 10–50 nm. The electrochemically deposited zinc oxide layers on top of porous silicon are shown to have a crystalline structure. It is also shown that zinc oxide crystals formed by hydrothermal method on the surface of electrochemically deposited zinc oxide film demonstrate ultra-violet luminescence. The effect of the porous silicon layer thickness on the morphology of the zinc oxide is shown. The structures obtained demonstrated two luminescence bands peaking at the 375 and 600 nm wavelengths. Possible applications of ZnO nanostructures, porous and continuous polycrystalline ZnO films such as gas sensors, light-emitting diodes, photovoltaic devices, and nanopiezo energy generators are considered. Aspects of integration with conventional silicon technology are also discussed.

We studied the influence of the thickness and porosity of the buffer layer on the guiding properties of oxidized porous silicon waveguides (OPSWG). It is demonstrated how a modified anodization process acts on the porosity of the final oxidized porous silicon. In this way, it is possible to control the refractive index jump between the core of OPSWG made of compact silicon dioxide and the bottom buffer layer made of porous silicon dioxide. The adoption of a double-step anodization process decreases the propagation losses to 0.5 dB / cm against the 8 dB / cm measured for the waveguide realized using a single-step anodization. The main reason seems not to be the increase of the difference of refractive index values but the more homogeneous buffer layer obtained along the core of the waveguide. This homogeneous layer permits a better lateral confinement of the light as demonstrated by spatial refractive index profile measurement.

In the present work, we report on the heteroepitaxial growth of PbS on porous silicon (PS). Epitaxial PbS films were grown by MBE on the surface of PS formed on the n+-type silicon (111) substrate. The films were comparable with films grown on BaF2 substrates. Beneficial influence of a PS buffer layer on the structure and properties of PbS epitaxial films was supported by implementation of sensitive Schottky-barrier photodiodes fabricated in these films.

The greatest limit in high-speed communications between different circuit blocks is due to the delays introduced by metal interconnections. Knock-down wire communication bottleneck is, therefore, one of the best goals that current research could reach in the field of fast electronics. A possible solution is to build fast optical links and even better if the technology is based on silicon. To attain these ends, we have made studies into possibility to fabricate optical waveguide based on oxidized porous silicon. In the last few years, such a device was realized and characterized. Waveguiding in the visible and in the near infrared was demonstrated, with propagation losses of about 3–5 dB/cm for a light with a wavelength of 632.8 nm. Moreover, a design feature of an integrated waveguide based on oxidized porous silicon is that it offers a spontaneous bending of the waveguiding layer at its ends. The edge bending is provided by a convex camber of a leading edge of forming porous silicon. This bending can be exploited to promote a vertical light output with no use of any additional devices. The paper discusses the properties of edge bending, evaluation of the light losses depending on the radius of curvature, and analysis of possibilities to reduce these losses.

The photoluminescence and photoexcitation spectra of porous silicon films with an initial porosity of 50–60%, produced on single crystals of p-type silicon and subjected to anodic oxidation and chemical etching, are studied. The existence of an amorphous phase in the etched porous silicon is found not to affect the photoluminescence spectrum of porous silicon. Features of the photoexcitation spectra before and after etching, as well as the evolution of the photoluminescence and photoexcitation spectra after etching, can be interpreted in terms of a uniform quantization model that includes elastic stresses in the silicon crystals of the porous silicon.

Porous silicon lattice deformation and its evolution with storage time are the main subjects of the present investigation. Transmission electron microscopy, x-ray diffractometry, and electronic paramagnetic resonance studies are reported. Silicon wafers of 0.01 Ω cm resistivity n + -type and (111) orientation were used as starting material. The porous silicon layers of 1.8 g/cm 3 volume density were formed by anodization in 12% HF aqueous solution at current density of 20 mA/cm 2 . The as-grown porous silicon layers were stored in air atmosphere for a long time and were subjected to heat-treatment in vacuum. Annealed porous silicon samples were stored again in air or in controlled atmosphere of hydrogen, nitrogen, or oxygen. The observed behavior of the porous silicon lattice parameter during storage in air and during thermal treatment allowed us to suppose that absorption/desorption processes, taking place at the inner developed porous silicon surface, are responsible for the lattice deformation.

The electrical behaviour of electroluminescent Schottky diodes fabricated on the base of aluminum and n-type porous silicon is reported. Porous silicon was formed by electrochemical etching in HF aqueous solutions of n-type monocrystalline silicon and of degenerate n + -type polysilicon. The polysilicon layer was formed on monocrystalline silicon substrate by low pressure chemical vapour deposition (LPCVD). The electroluminescence (EL) starting voltage was in the range 4–20 Volt, depending on the doping level of Si substrate; polysilicon samples showed a higher starting voltage. Developed devices showed broad EL spectra, covering the whole visible range. Electrical measurements include current-voltage characteristics and capacitance-voltage characteristics. Time response and stability of the light emitting devices was also measured, showing excellent speed and reliability characteristics.

Changes in the photoluminescence (PL), microstructural morphology and the chemical nature of the surface of porous silicon (PS) when it is attacked with a 1:1 mixture of concentrated hydrofluoric acid and water have been studied. As the PS dissolves, the porous structure is essentially destroyed while the appearance and chemical composition of the surface change. At the same time, the intensity and peak wavelength of the PL change dramatically. The simultaneous investigation of PL, FTIR absorption and SEM observation of porous silicon layers (PSL) lend support to the view that chemical passivation, in particular by oxygen, is the major factor which controls the origin of PL. The PL intensity and the PL shift are ascribed to the changes in hydrogen and oxygen termination of pores.

Optical waveguiding has been observed in oxidized porous silicon layers. Main steps of integrated optical waveguide formation and experimental results on lightguiding in the visible range are presented.

Robust porous silicon substrates were employed for generating interconnected networks of superconducting ultrathin Nb nanowires. Scanning electron microscopy analysis was performed to investigate the morphology of the samples, which constitute of polycrystalline single wires with grain size of about 10 nm. The samples exhibit nonzero resistance over a broad temperature range below the critical temperature, fingerprint of phase slippage processes. The transport data are satisfactory reproduced by models describing both thermal and quantum fluctuations of the superconducting order parameter in thin homogeneous superconducting wires., Comment: accepted for publication on Applied Physics Letters

We report on the superconducting properties of a Nb thin film deposited, with an interleaved insulating layer to avoid the proximity effect, on an array of ferromagnetic (Ni) nanowires embedded in a porous template. By investigating the T c (H) phase boundary and by measuring V(I) characteristics and critical currents as a function of the applied magnetic field, we find that the Nb film exhibits properties similar to those of a network of one-dimensional superconducting nanowires. We attribute this behavior to the stray fields of the magnetic dipoles, which create an almost regular lattice of normal regions in the superconductor, ultimately changing its topology. Furthermore, there is evidence that the magnetic pinning of vortices is negligible in this structure.

Porous silicon (PS) prepared from n-type Si crystal is proposed as a new material for the fabrication of sensitive substrates for surface-enhanced Raman scattering (SERS). The formation procedure for nanostructured silver films on the surface of PS was optimized. Maximum of SERS enhancement for rhodamine 6G probing molecule is observed for samples obtained by the immersion plating from the water solution of AgNO 3 with the 10 mM concentration during 5 min. The dependence of morphological parameters of PS and corresponding silvered surfaces on the anodization current density has been studied. It is shown that the most SERS activities possess substrates produced from PS with lower porosity. The optimum of the PS layer thickness for high Raman signal is about 5 μm. The detection limit for rhodamine 6G adsorbed on Ag-coated PS from the 100 pM solution is established to be comparable with that for p-type PS-based substrates. Thus, the n-type porous silicon is suitable material for the preparation of sensitive SERS-active substrates.

We report 77 K Photoluminescence (PL) and Photoluminescence Excitation (PLE) spectroscopies of Er ions incorporated with Fe in oxidized porous silicon (OPS) in the form of 5-50 nm sized clusters containing Fe, O, and Er. Twenty sharp (FWHM of about 0.4 meV) PL peaks related to the transitions between highly split levels of 4 I 13/2 and 4 I 15/2 multiplets were observed. Two different Er centers having cubic and lower than cubic symmetries were identified. The photoluminescence excitation spectrum of the 1533 nm PL peak comprises no resonant features but a broad band spanning from 300 to 570 nm. The mechanism of excitation of Er ions through Fe : O : Er nanoclusters in the OPS host is presented.

Technological aspects related to the fabrication of buried oxidized porous silicon waveguides (OPSWG) as the influence of swirl defects and a suitable epitaxial method to bury OPSWG have been investigated. The influence of swirl defects on OPSWG performances is presented. The formation of a non-homogeneous porous silicon, caused by swirl defects, results in an incomplete oxidation and in an increase of optical loses. The idea of burying waveguides has been tested by a suitable epi process covering using dichlorosilane and silane as reacting gases. The paper presents and discusses the preliminary results. In this paper, are presented the technological studies related to the fabrication of buried OPSWG: (i) swirl defects influence on the structure and on the guiding properties of OPSWG; (ii) epitaxial deposition process suitable for the realization of defects free silicon layer over the OPSWG.

The chemical processes that occur during the electrochemical treatment of a porous silicon cathode in aqueous solutions of erbium salts are studied. The results obtained show that (i) erbium ions do not take place in the electrochemical reactions and (ii) erbium-containing deposits are formed by chemical reactions at the cathode. The chemical composition and structure of the deposits can be varied by controlling the electrolysis conditions. These observations facilitate the future design of process cells suitable for the effective incorporation of erbium and other rare earth elements into oxidized porous silicon waveguides for optical amplifier applications.

We have developed an original technology to fabricate channel waveguides on monocrystalline silicon wafers, consisting of selective anodization followed by thermal processing. The obtained oxidised porous silicon waveguides show waveguiding properties, moreover, due to the fabrication process, the waveguides are placed just under the surface of the silicon wafer. A hydrogenated amorphous silicon film has been grown on top of the waveguide by a low temperature process, then aluminum contacts have been formed by standard lithography. Different device structures (photodiodes and photoresistors) are presented. Current/voltage properties in the dark and under light excitation accompanied with capacitance/voltage measurements have been used to develop a band diagram model.

Initial stages of Cu immersion deposition in the presence of hydrofluoric acid on bulk and porous silicon were studied. Cu was found to deposit both on bulk and porous silicon as a layer of nanoparticles which grew according to the Volmer-Weber mechanism. It was revealed that at the initial stages of immersion deposition, Cu nanoparticles consisted of crystals with a maximum size of 10 nm and inherited the orientation of the original silicon substrate. Deposited Cu nanoparticles were found to be partially oxidized to Cu2O while CuO was not detected for all samples. In contrast to porous silicon, the crystal orientation of the original silicon substrate significantly affected the sizes, density, and oxidation level of Cu nanoparticles deposited on bulk silicon.

Structure and lattice deformation of porous silicon layers and silicon wafer bending as a result of high, temperature treatment in H2 atmosphere at 900 to 1200 °C are investigated by SEM and X-ray analysis. A significant expansion of the Si lattice of (2 to 4) × 10−4 is observed to appear in as-grown porous silicon. It results in arising of elastic stress and bending of the wafer. High tempreature treatment leads to the evolution of a porous silicon structure, compression of porous silicon lattice, and reverse of wafer deformation. Porous silicon after annealing is found to be crystalline with spheroidal voids of 50 to 500 nm. A model based on the capillary mechanism and sintering theory is developed to explain the experimental results. [Russian Text Ignored].

TiN/Si structures were deposited on Si wafers by pulsed laser deposition technique. The highly conductive TiN films were grown on heated (100) Si substrates by laser ablation of a high purity Ti target in nitrogen reactive atmosphere. Subsequently, the Si layer was deposited by laser ablation of a Si target in vacuum (down to 10 −6 mbar) or in low pressure inert gas. The nitrogen gas pressure and the substrate temperature were found to strongly influence the TiN film structure and orientation. The degree of crystallinity of the Si layer grown on the TiN film was found to depend on Si/TiN collector temperature. Values below 550°C (the threshold of TiN oxidation activation) were used in the experiments. Techniques as X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), High Resolution Transmission Electron Microscopy (HRTEM), Scanning Force Microscopy (SFM) have been used to characterize the deposited structures. The TiN/Si structure rectifying properties were tested. The obtained Si/TiN/Si structure could be suitable for the building of Permeable Base Transistor (PBT, vertical MESFET) devices.

Slightly modified CMOS process has been used for the formation of lateral pn junctions in SOI structures based on oxidized porous silicon. Under forward bias these junctions emit infrared light at 1120 nm. Under reverse bias in the breakdown regime the pn junctions demonstrate both infrared and visible light emissions with efficiencies of 10 −4 and 10 −7 , respectively. The beneficial influence of SOI structures on electroluminescence characterictics of light-emitting pn junctions has been established.

The application of porous silicon as a template for the fabrication of nanosized copper objects is reported. Three different types of nanostructures were formed by displacement deposition of copper on porous silicon from hydrofluoric acid-based solutions of copper sulphate: (1) copper nanoparticles, (2) quasi-continuous copper films, and (3) free porous copper membranes. Managing the parameters of porous silicon (pore sizes, porosity), deposition time, and wettability of the copper sulphate solution has allowed to achieve such variety of the copper structures. Elemental and structural analyses of the obtained structures are presented. Young modulus measurements of the porous copper membrane have been carried out and its modest activity in surface enhanced Raman spectroscopy is declared.