D. N. Goryachev

Bio: D. N. Goryachev is an academic researcher from Russian Academy of Sciences. The author has contributed to research in topics: Silicon & Porous silicon. The author has an hindex of 7, co-authored 30 publications receiving 125 citations.

On the Mechanism of Porous Silicon Formation

Abstract: A new qualitative mechanism of pore nucleation and initial stages of porous silicon (por-Si) growth was proposed. The emphasis was on the charge exchange between Si2+ ions generated by electrolytic or chemical oxidation of initial silicon (disproportionation reaction). The mechanism eliminates, to a large extent, the contradictions typical of earlier proposed schemes of por-Si growth; in particular, it explains the morphological features of por-Si produced under various experimental conditions. The impact of light in these processes was also considered.

Electrolytic Fabrication of Porous Silicon with the Use of Internal Current Source

Abstract: A new method of porous silicon fabrication is suggested which uses as a current source the potential difference arising between the silicon wafer and the platinum counter electrode immersed in an electrolyte solution. Addition of hydrogen peroxide to HF/ethanol electrolyte enables control over the current density in the process and fabrication of photoluminescent layers without an external current source.

Photoresponse and electroluminescence of silicon-〈porous silicon〉-〈chemically deposited metal〉 structures

Abstract: Photoelectric and electroluminescent properties of silicon-〈porous silicon〉 structures with chemically deposited metal contacts were investigated. The large specific surface area of the contact and selective metal deposition only on the macrocrystalline elements of the structure provide better photoelectric performance of the photodiodes compared to the structures with evaporated contacts, especially in the short-wavelength spectral range. The obtained electroluminescence spectra are explained by metal-silicon barrier properties under forward bias and by double carrier injection into nanocrystallites under reverse bias.

Preparation and study of carbidized porous silicon

Abstract: Porous silicon layers with introduced carbon-containing substances (fullerenes, ultradisperse diamond, carbohydrates) have been studied. It was found that high-temperature annealing of such layers in a hydrogen atmosphere leads to substantial transformation of the photoluminescence spectra. It is assumed that this results from the formation of cubic silicon carbide crystallites and the occurrence of the quantum-confinement effect in these crystallites.

Role of singlet oxygen in formation of nanoporous silicon

Abstract: The effect of singlet oxygen on the formation of nanoporous silicon in the case of photoelectrochemical etching of p-Si is studied. Pulsed electrolysis was used to discriminate between chemical and electrochemical processes. The pulsed etching of silicon was accompanied by pulsed illumination coinciding either with current pulses or with zero-current periods. An analysis of the results obtained demonstrated that, as the number of silicon nanocrystals increases under illumination, singlet oxygen starts to be generated from molecular oxygen dissolved in the electrolyte. This process leads to oxidation of the surface of silicon nanocrystallites and to a change in its passivation.

The structural and luminescence properties of porous silicon

Abstract: A large amount of work world-wide has been directed towards obtaining an understanding of the fundamental characteristics of porous Si. Much progress has been made following the demonstration in 1990 that highly porous material could emit very efficient visible photoluminescence at room temperature. Since that time, all features of the structural, optical and electronic properties of the material have been subjected to in-depth scrutiny. It is the purpose of the present review to survey the work which has been carried out and to detail the level of understanding which has been attained. The key importance of crystalline Si nanostructures in determining the behaviour of porous Si is highlighted. The fabrication of solid-state electroluminescent devices is a prominent goal of many studies and the impressive progress in this area is described.

Electrochemical engineering of hollow nanoarchitectures: pulse/step anodization (Si, Al, Ti) and their applications

Abstract: Hollow nanoarchitectured materials with straight channels play a crucial role in the fields of renewable energy, environment and biotechnology due to their one-dimensional morphology and extraordinary properties. The current challenge is the difficulty on tailoring hollow nanoarchitectures with well-controlled morphology at a relatively low cost. As a conventional technique, electrochemistry exhibits its unique advantage on machining nanostructures. In this review, we present the progress of electrochemistry as a valuable tool in construction of novel hollow nanoarchitectures through pulse/step anodization, such as surface pre-texturing, modulated, branched and multilayered pore architectures, and free-standing membranes. Basic principles for electrochemical engineering of mono- or multi-ordered nanostructures as well as free-standing membranes are extracted from specific examples (i.e. porous silicon, aluminum and titanium oxide). The potential of such nanoarchitectures are further demonstrated for the applications of photovoltaics, water splitting, organic degradation, nanostructure templates, biosensors and drug release. The electrochemical techniques provide a powerful approach to produce nanostructures with morphological complexity, which could have far-reaching implications in the design of future nanoscale systems.

Band alignment and carrier injection at the porous‐silicon–crystalline‐silicon interface

Abstract: The current‐voltage characteristics and the photoresponse of metal‐porous Si–p‐type Si heterostructures have been studied. It is shown that the common interpretation of the current‐voltage characteristics, which assumes that the current is limited by the Schottky barrier at the metal‐porous Si interface, is wrong. An alternative explanation based on the electric‐field dependence of the porous Si conductivity is suggested. It is shown that the rectifying behavior originates from a depletion inside the c‐Si substrate at its interface to the porous Si.

Metal Deposition onto a Porous Silicon Layer by Immersion Plating from Aqueous and Nonaqueous Solutions

Abstract: Immersion plating of metals (Ag, Cu. Ni) onto a porous silicon (PS) layer from aqueous and nonaqueous solutions has been studied. The modified PS layers after the immersion plating were analyzed by X-ray diffraction and X-ray photoelectron spectroscopy. Fourier transform infrared spectroscopy and scanning electron microscopy were also performed to investigate the structural changes and microstructure of PS samples after the plating process. In booth solutions, the deposition of metal oxidizes PS simultaneously to SiO 2 . The different deposition behaviors are discussed in terms of different rest potentials of PS in these solutions and electrode potential of each metal. Immersion plating in nonaqueous organic solutions shows that a trace of residual water affects the metal deposition. Based on the results obtained, the mechanism of metal deposition is proposed. The metal deposition proceeds by nucleation and growth via the local cell mechanism. It is also found that metal deposition proceeds very differently on Si wafer and PS surfaces. The different deposition behaviors on both surfaces are discussed.

Mixed electron and proton conductivity of polyaniline films in aqueous solutions of acids: beyond the 1000 S cm−1 limit

Abstract: BACKGROUND: The application potential of conducting polymers depends on their conductivity. It is generally assumed that the conductivity determined in the dry state is a parameter that unambiguously characterizes them. RESULTS: The conductivity of polyaniline (PANI) films immersed in aqueous solutions of sulfuric acid may be more than 1000 times higher compared with that obtained by measurement of dry films in air, and is estimated to reach a value exceeding 3300 S cm−1 in 1 mol L−1 sulfuric acid. This is explained by the reduction of conductivity barriers between conducting PANI islands. CONCLUSION: The organized polymer chains in the conducting islands of a PANI film are separated by disordered regions of low conductivity in the dry state. The penetration of sulfuric acid solution into the disordered areas increases the overall conductivity of the PANI film by improving the electrical contact between the islands through ionic charge transport. The electronic conductivity of the PANI film in the dry state thus converts to mixed electron–proton conduction in acidic aqueous solutions, electron conductivity being dominant in ordered regions and ionic conductivity in disordered regions separating them. Weakly bound protons are the most important ionic charge carriers hopping along the PANI chains. Copyright © 2009 Society of Chemical Industry