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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 have synthesized oxygen-doped graphite-like carbon nitride (g-C3N4) by the thermal treatment of the thiourea at 450–550°C. With an increase in the annealing temperature, the oxygen concentration in g-C3N4 increases, and the band-gap of the material decreases from 2.64 to 2.47 eV. The semiconductor properties of g-C3N4 doped with oxygen are confirmed by its high photocatalytic activity, determined by decoloration of a Rhodamine B aqueous solution in the presence of g-C3N4 upon irradiation with visible light.

Various cases of electrochemical deposition of indium into oxidized and unoxidized mesoporous silicon were investigated and subsequently compared. The results would suggest that both thermal and chemical oxidation of porous silicon cause the metal particles being deposited into its pores to shift deeper along the pore channels due to the latter's topmost areas being oxidized the most and therefore becoming significantly less conductive and more easily wettable by both the deposition solution and indium itself upon its subsequent thermal processing. However, oxidation becomes less effective as the thickness of the porous layer is increased due to the gradually escalating effect of reduced conductivity at the pore tips. Potentially, porous silicon layers with indium particles localized in the bottommost parts of the pore channels could be used to form germanium nanostructures inside the pores, allowing subsequent creation of Ge-Si alloys by utilizing the electrochemical liquid-liquid-solid approach.

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.

The modern direction of improving the technology of steel production in high-power arc furnaces is the intensification of magnetohydrodynamic effects for mixing the melt. In this article, a furnace design is proposed that contains three roof arc and three bottom electrodes, which provides the formation of additional eddy currents in the melt when the furnace is supplied with direct current or a low-frequency current. For a numerical study of the features of heat transfer in the melt of this furnace, a three-dimensional mathematical model of magnetohydrodynamic and thermal processes was used. The results were processed using the methods of visualization of vortex structures and the Richardson criterion. In an oven with a capacity of 180 tons at currents in the electrodes of 80 kA, the conditions for the interaction of electric vortex and thermogravitational convection were studied. Results showed that thermogravitational convection due to nonuniform heating of the melt led to a decrease in the size of the main electric vortex flow and the formation of an additional flow near the side walls of the furnace. The features of azimuthal flows formed in the areas of electric arcs and hearth electrodes were analyzed. Results showed that the multivortex structure of the flows that formed in the furnace allowed the volume of stagnant zones to be reduced and provided acceptable melt mixing conditions. The results can be used to improve the energy and structural parameters of three-electrode arc furnaces.

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)

The review reports on the results of our research work on nanostructured metal films onto porous silicon. Principal steps of the techniques allowing fabrication of metal films completely inheriting morphological pattern of different types of porous silicon are presented. It is shown, that giving of the nanostructured pattern to metal films by means of porous silicon template opens their new structural, optical, mechanical and electrical properties, which can be successfully applied in nanoelectronics and biomedicine, particularly including devices based on superconductivity effect, SERS analysis with picomolar sensitivity and transdermal drug delivery by electroporation.

The ZnO doped with transitional metals - Ni or Co - were synthesized by chemical hydrothermal deposition. According to SEM study ZnO films obtained on Si wafers consist of separated nanocrystals with diameter up to 1 μm, 30 nm ALD ZnO sublayer changed the structure of hydrothermally grown ZnO films to array of densely packed pillars. It was shown that doping ZnO with Ni and Co decreased the exciton photoluminescence band compared to undoped ZnO crystals.

Superconducting NbN nanonetworks with a very small number of interconnected nanowires, with diameter of the order of 4 nm, are fabricated combining a bottom-up (use of porous silicon nanotemplates) with a top-down technique (high-resolution electron beam lithography). The method is easy to control and allows the fabrication of devices, on a robust support, with electrical properties close to a one-dimensional superconductor that can be used fruitfully for novel applications.

[EN] A highly sensitive photonic sensor based on a porous silicon ring resonator was developed and experimentally characterized. The photonic sensing structure was fabricated by exploiting a porous silicon double layer, where the top layer of a low porosity was used to form photonic elements by e-beam lithography and the bottom layer of a high porosity was used to confine light in the vertical direction. The sensing performance of the ring resonator sensor based on porous silicon was compared for the different resonances within the analyzed wavelength range both for transverse-electric and transverse-magnetic polarizations. We determined that a sensitivity up to 439 nm/RIU for low refractive index changes can be achieved depending on the optical field distribution given by each resonance/polarization. (C) 2017 Optical Society of America under the terms of the OSA Open Access Publishing Agreement, European Commission through the project H2020-644242 SAPHELY; Spanish government through the projects TEC2013-49987-EXP BIOGATE and TEC2015-63838-C3-1-R-OPTONANOSENS; Generalitat Valenciana through the Doctoral Scholarship GRISOLIAP/2014/109.

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.

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.

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.

Since its discovery surface enhanced Raman scattering (SERS) has been attracting a constantly increasing attention of the scientific community as this method demonstrates an extremely high sensitivity and allows detection of the lowest possible concentration of substances including biological specimens up to single molecule [1]. The enormous increase of the Raman signal is observed for the molecules adsorbed on the surfaces consisted of metallic nanoparticles (NPs), especially of the noble metals. The electromagnetic mechanism plays the most valuable role in such enhancement and is caused by plasmon resonance in the certain places on the metallic surfaces. Recently, use of ordered arrays of metallic nanovoids has been found to significantly improve reproducibility and enhancement of SERS signal due to specificity of the plasmon modes within metallic cavities which geometry is well controlled at the fabrication process [2, 3]. However, engineering of such arrays is often connected with an alternation of a number of liquid and dry operations which is desirable to avoid for technology simplification [4]. An urgent problem as well is still a development of the technology that provides an integration of SERS-active substrate with other elements on the single Si substrate. In the present work we propose fabrication of SERS-active metallic/macro porous silicon (PS) nanovoid arrays consisted of only electrochemical and electroless liquid steps. As an initial template we used PS formed by anodizing of p-Si (100) wafer in solution of HF:DMSO=10:46 at 8 mA/cm for 7 min. The depth and diameter of pores varied in the ranges 700-1200 nm and 500-1500 nm, respectively. It is in good agreement with the dimensions of nanovoids usually applied for SERS [24]. Two types of metallized nanovoids (single and hybrid) were fabricated by liquid deposition of Ag and Ni on PS. To form first type of substrate based on single metal (Ag), PS was immersed into the 3mM AgNO3+0.5M HF water solution for 40-200 min. As reaction of Ag reduction has positive standard potential, Ag ions attract electrons from Si atoms. In that way in water-based solutions Si is oxidized to SiO2 while Ag is reduced. The addition of HF provides removing of SiO2 for continuous supplying of Ag ions with electrons. To form hybrid metallization (Ag/Ni), Ni was electrochemically deposited on PS from the solution of 213 g/l NiSO4—7H2O+5 g/l NiCl2—6H2O+25 g/l H3BO3+3 g/l saccharin at 10 mA/cm 2 for 2.5 min. Such regime resulted in covering PS surface with continuous Ni film of 70 nm thickness. After that Ag was deposited by electroless method from the previously described solution for 5-30 min. The morphology and structure of the samples were studied with SEM Hitachi S-4800. SERS activity of substrates was tested using water-soluble CuTMpyP4 as an analyte compound. Raman spectra were registered with the spectrometer Solar TII DM160MS3504I, equipped with CCDdetector. The source of continuous excitation was the HeCd laser Liconix (λ=441.6 nm). Figure 1 shows typical spectra of CuTMpyP4 on the initial PS (a), Ag/PS (b) and Ag/Ni/PS (c). Both of metallized substrates demonstrated SERS-activity. However, hybrid metallization resulted in six orders of magnitude increase of the signal intensity in comparison to pure PS while Ag/PS provided enhancement of five orders of magnitude.

Structural and magnetic properties of Ni nanowires electrochemically deposited into pores of mesoporous silicon template under the stationary galvanostatic regime have been investigated. Samples have been exhaustively studied by using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and specific magnetization measurements. SEM analysis revealed the formation of porous silicon/nickel nanocomposite at the initial stages of Ni deposition with the characteristic dimension of Ni nanoparticles in the range of 40–60 nm. After 60 min of deposition Ni continuous nanowires of 10 μm length have been formed. XRD analysis confirmed the polycrystalline structure of Ni in the mesoporous silicon template with the preferential orientation along [111] axis. Also some amount of silicide Ni2Si was formed, which diffraction peak at 2Θ ≈ 33° was especially pronounced for low deposition times. The possible mechanism of nickel silicide formation during the electrochemical process has been discussed. It was supposed that, the presence of amorphous silicon on pore walls facilitates the diffusion of Ni inside silicon matrix with subsequent nickel silicide formation without heating. The idea has been confirmed by the fact that on crystalline silicon the formation of nickel silicide was not observed. The magnetic properties have been investigated by studying the temperature dependence (77 K–700 K) of the specific magnetization σ. The measured σ values were lower with respect to that of bulk Ni. The effect has been explained by the influence of uncontrolled formation of nickel silicide, which causes, after heating, larger irreversibility of σ(T) curves for samples with less deposition time. The obtained σ(T) dependencies allowed us to determine the Curie temperature, TC, which for low deposition times of Ni was lower (575 K) with respect to the bulk Ni (630 K). This is caused by the influence of dimensional effects on TC value.

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)

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.

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.

Electrochemical deposition of ZnO from aqueous nitrate solutions on nickel and platinum electrodes was investigated using the voltammetry technique to determine the optimal regimes in both potentiostatic and galvanostatic modes for acquiring polycrystalline ZnO films. Scanning electron microscopy, X-ray diffractometry, and X-ray microanalysis of the formed ZnO films are presented, showing a polycrystalline structure of the ZnO films with a preferable orientation in the (0 0 0 2) direction and an exact stoichiometric composition. The deposited ZnO films demonstrate a strong visible yellow-greenish photoluminescence at room temperature with a maximum at 600 nm that can be referred to crystal lattice oxygen defects. The maximum of the photoluminescence excitation spectrum at 370 nm corresponds to the band gap of ZnO (3.3–3.35 eV) confirming that band-to-band excitation mechanism takes place.

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.

A method for fabricating surface-enhanced Raman scattering (SERS)-active substrates by immersion deposition of silver on a macroporous silicon (macro-PS) template with pore diameters and depth ranging from 500-1000 nm is developed. The procedure for the formation of nanostructured silver films in the layers of macro-PS was optimized. Silver particles of dimensions in the nano- and submicron-scale were formed on the external surface of the macro-PS immersed in the water-ethanol solution of AgNO3, while the inner pore walls were covered by smaller, 10-30 nm diameter, silver nanoparticles. Upon introducing the hydrofluoric acid to the reaction mixture, the size of nanoparticles grown on the pore walls increased up to 100-150 nm. Such nanostructures were found to yield SERS-signal intensities from CuTMpyP4 analyte molecules of the same order to those obtained from silvered mesoporous silicon reported previously. The tested storage stability for the silvered macro-PS-based samples reached up to 8 months. However, degradation of the SERS intensity under illumination by the laser beam during spectral measurements was observed. To improve the stability of the SERS-signal a hybrid structure involving graphene oxide deposited on the top of analyte molecules adsorbed on the Ag/macro-PS was formed. A systematic observation of the time evolution of the characteristic peak at 1365 cm-1 showed that the addition of the oxidized graphene layer over the analyte results in ∼2 times slower decay of the Raman intensity, indicating that the graphene coating can be used to enhance the stability of the SERS-signal from the CuTMpyP4 molecules.

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.

Magnetoresistance oscillations were observed on networks of superconducting ultrathin Nb nanowires presenting evidences of either thermal or quantum activated phase slips. The magnetic transport data, discussed in the framework of different scenarios, reveal that the system behaves coherently in the temperature range where the contribution of the fluctuations is important., accepted for publication on Nanotechnology

Low cost concept based on the porous silicon technology is shown to be well suitable for integrating monolithically the photonic devices on a standard silicon wafers by using localized SOI structures fabricated by electrochemical anodization of silicon wafers followed by thermal oxidation of porous silicon. The new approach consists in realizing buried localized porous oxidized silicon by exploiting two different routes: n - epi/n + /n - structures on p-type wafers and ion-implantation on standard CMOS/BiCMOS wafers. The peculiarities of the developed approach, including anodization and thermal oxidation regimes to form oxidized porous silicon regions with the required properties are presented. The advantages of the proposed approach in realizing the fiber-to-chip and power-over-fiber coupling are discussed.

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.

A brief review of 20-years research of formation, processing and utilizing of oxidized porous silicon (OPS) is presented. Electrolytes to form porous silicon (PS) layers, special features of PS chemical cleaning and thermal oxidation are discussed. OPS application for dielectric isolation of components of bipolar ICs and for the formation of silicon-on-insulator structures has been demonstrated. Although these OPS-based techniques have found limited current commercial use, experience gained is applicable to the fabrication of optoelectronic devices. Specifically, integrated optical waveguides based on OPS have been developed.

Electrochemical treatment of porous silicon (PS) in ethanol solution of Er(NO3)3 was investigated to obtain material suitable for optoelectronic application. The voltammograms of n+-type and p-type PS vs. an Ag/AgCl reference electrode were examined and compared with these of a Pt electrode. The basic cathode reactions were marked out the voltammograms: (i) the formation and the adsorption of atomic hydrogen; (ii) the formation of molecular hydrogen; (iii) the electrolysis of water and ethanol. No zones relating to on electrochemical transitions of Er ions were revealed on the voltammograms. Nevertheless, with the cathode polarization, the formation of an Er-containing deposit was observed at the surface of the cathode. The IR and SIMS analysis were used to study the composition of the deposits. The scheme of the electrochemical and chemical reactions at the cathode is discussed.

The properties of porous silicon (PS) are closely connected to its morphology, much investigation has been done in order to correlate the morphological characteristics of PS with the anodisation parameters. In this paper the results of morphological analysis of PS formed on N+type substrates of 〈1 0 0〉 and 〈1 1 1〉 orientation are presented. The dependences of the porosity, thickness of PS, density of pores and of the effective surface on the current density are obtained. Interpretation of these results in terms of diffusion layer and energy levels is given, with special attention given to the low current density case.

Continuous crystalline films of zinc oxide (ZnO) with thicknesses of 6–10 μm were obtained by electrochemical deposition from aqueous zinc nitrate solutions on silicon substrates with a buffer nickel layer. X-ray diffraction measurements showed that the polycrystalline films possess a hexagonal crystal lattice with predominant (0002) orientation. The obtained ZnO films exhibit strong photoluminescence in the visible spectral range at room temperature.

Epitaxial PbS films were grown by molecular-beam epitaxy (MBE) on the surface of porous silicon (PS) formed on the silicon substrate of (111) orientation. The uniform PS layers 5 μm thick were produced by electrochemical anodic treatment of n + -silicon in HF solution. The structure of both PbS and buffer PS was studied by X-ray diffraction analysis as well as scanning electron microscopy. The PbS layer has been demonstrated to have a columnar structure at the early stages of growth, while a solid structure of the grown layer has been observed with increasing a thickness of the epitaxial layer up to 0.5–1.0 μm. PbS epitaxial films grown on the substrates with the 2–5 μm thick PS layers of 20–40% porosity were comparable with the films grown on the BaF 2 substrates.

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.

A low-dimensional matrix of porous silicon (PS) was found to be an effective host material for erbium (Er) electrodeposition from Er(NO 3 ) 3 ·5H 2 O/ethanol solution. After thermal annealing at 850–1200 °C in an O 2 -containing atmosphere, such material exhibited sharp 1.54 μm luminescence at 77 K and 300 K. In contrast to previous studies, strong Er-related photoluminescence (PL) was found not only in the case of red-emitting PS formed in initial p-Si(111) wafers of 0.3 Ω cm resistivity but also for micro-sized material formed in initial 0.01 Ω cm n + -Si(111). Erbium doping of p-type PS resulted in a 1.54 μm peak appearance in addition to two broad PL bands at about 1.3 μm and 0.8–0.9 μm. In contrast, n + -type PS:Er exhibited only a sharp 1.54 μm peak without other PL bands. The intensity of the Er-related peak depended strongly on the Si anodization regime and increased with the PS thickness growth from 1 to 20 μm. Application aspects of PS:Er for light-emitting devices and integrated optical waveguides are discussed. © 1997 Elsevier Science S.A.

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.

Porous-silicon-based white-light-emitting devices are presented. The fabrication process on different substrates is described. The peculiarities of technological steps for device fabrication (porous-silicon formation and aluminum treatment) are underlined. Doping profile of the porous layer, current-voltage characteristics, time response, lifetime tests and electroluminescence emission spectrum of the device are presented. A model for electrical behaviour of Al/porous silicon Schottky junction is presented. Electroluminescence spectrum of the presented devices showed strong similarities with white emission from crystalline silicon junctions in the breakdown region.

Plasma-assisted CVD diamond growth on bias-pretreated porous silicon has been investigated. It was found by micro-Raman spectroscopy and cathodoluminescence that diamond films on porous silicon exhibit less stress compared to those on monocrystalline silicon. Depending on the parameters of the porous silicon layer, it is possible to influence or even to control the stress in diamond films. A nucleation enhancement of CVD diamond by several orders of magnitude was found on porous silicon. Oriented growth of diamond films on silicon with a porous surface with a high degree of orientation and good crystalline quality is demonstrated.

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.