V. K. Vasiliev

Bio: V. K. Vasiliev is an academic researcher from N. I. Lobachevsky State University of Nizhny Novgorod. The author has contributed to research in topics: Silicon & Photoluminescence. The author has an hindex of 4, co-authored 11 publications receiving 70 citations.

Effect of carbon implantation on visible luminescence and composition of Si-implanted SiO2 layers

Abstract: Ion implantation is a convenient tool for synthesis of silicon nanocrystals in SiO 2 matrix which exhibit strong red/near-IR luminescence at room temperature. Ion beams can be successfully used also for controllable modification of the nanostructures by introducing defects or changing their phase composition. In the present work, both possibilities are tested by implantation of carbon into thermal SiO 2 films either containing pre-fabricated Si nanocrystals or as-implanted with Si. In the carbon-free SiO 2 films, Si nanocrystals were synthesized at typical Si excess of about 10 at.% and annealing temperatures of 1000 and 1100 °C. It is shown that carbon ion irradiation of the Si-implanted and then annealed SiO 2 films completely quenches a luminescence band at 650-850 nm related to Si nanocrystals and gives rise to emission in the range of 350-650 nm that originated from oxygen-deficient defects. The subsequent final thermal treatment reduces concentration of the matrix defects, but only partially recovers photoluminescence from Si nanocrystals depending on the C dose. The latter is explained by the hindering effect of implanted carbon on growth and crystallization of Si phase inclusions. Strong "white" emission in the spectral range of 350-800 nm is observed only for the equal Si and C concentrations, irrespective of the sequence of carbon introduction and Si nanocrystal formation. This broad spectral band consists of the three sub-bands at around 400, 500 and 620 nm attributed to inclusions of SiC, C and Si phases, respectively. Electron spectroscopy analysis of the annealed layers confirms the presence of silicon carbide phase and carbon precipitates showing the diamond-like sp 3 , not the graphitic sp 2 hybridization. The Si- and C-rich nanoclusters with a size of 3-5 nm were identified in the co-implanted films by electron microscopy as amorphous nanoparticles.

Effect of ion doping with donor and acceptor impurities on intensity and lifetime of photoluminescence from SiO2 films with silicon quantum dots.

Abstract: Doping with donor and acceptor impurities is an effective way to control light emission originated from quantum-size effect in Si nanocrystals. Combined measurements of photoluminescence intensity and kinetics give valuable information on mechanisms of the doping influence. Phosphorus, boron, and nitrogen were introduced by ion implantation into Si+ -implanted thermal SiO2 films either before or after synthesis of Si nanocrystals performed at Si excess of about 10 at.% and annealing temperatures of 1000 and 1100 degrees C. After the implantation of the impurity ions the samples were finally annealed at 1000 degrees C. It is found that, independently of ion kind, the ion irradiation (the first stage of the doping process) completely quenches the photoluminescence related to Si nanocrystals (peak at around 750 nm) and modifies visible luminescence of oxygen-deficient centers in the oxide matrix. The doping with phosphorus increases significantly intensity of the 750 nm photoluminescence excited by a pulse 337 nm laser for the annealing temperature of 1000 degrees C, while introduction of boron and nitrogen atoms reduces this emission for all the regimes used. In general, the effective lifetimes (ranging from 4 to 40 micros) of the 750 nm photoluminescence correlate with the photoluminescence intensity. Several factors such as radiation damage, influence of impurities on the nanocrystals formation, carrier-impurity interaction are discussed. The photoluminescence decay is dominated by the non-radiative processes due to formation or passivation of dangling bonds, whereas the intensity of photoluminescence (for excitation pulses much shorter than the photoluminescence decay) is mainly determined by the radiative lifetime. The influence of phosphorus doping on radiative recombination in Si quantum dots is analyzed theoretically.

Ion-beam simulation of radiation damage produced by fast neutrons in heterophase structures

Abstract: 3D Monte-Carlo algorithm and computer code have been developed that allows choosing and optimizing the conditions of ion irradiation needed for the adequate ion-beam simulation of radiation damage under fast neutron irradiation. It is established that, by the proper selection of energy and dose of Si+ ions, it is possible to reproduce well the effect of irradiation with fission neutrons of subsurface and buried layers of silicon or Si-based 2D and 3D-heterostructures. The results can be used for testing the radiation hardness of silicon-based electronic and optoelectronic device structures.

Critical-field slope reduction and upward curvature of the phase-transition lines of thin disordered superconducting YBa2Cu3O7−x films in strong magnetic fields

Abstract: We report the effect of disorder on superconducting phase transition of YBa 2 Cu 3 O 7 − x epitaxial thin films in external magnetic fields. The disorder was produced by several successive acts of oxygen ion implantation. Controlling a total accumulated dose of implanted ions nD, we carried out transport measurements in ab-plane for temperatures T below 91 K and external magnetic fields H up to 11 T. Temperature-field dependencies of in-plane resistivity allow us to analyze H − T phase diagrams for primary compound as well as for disordered structure. Considering the upper critical field Hc2 as the magnetic field which corresponds to a local resistivity drop at the onset of superconducting transition, we found out the following results. By gradual increasing of nD, the phase-transition line Hc2(T) suffers an unconventional critical-field slope reduction, while larger defect concentrations usually enhance the upper critical field in the vicinity of Tc0. Besides, for rather large nD, the curvature of Hc2(T) becomes upward for temperatures close to Tc0. Theoretical interpretation of the experimental data is developed in the framework of linearized Ginzburg-Landau theory with an inhomogeneous superconducting coherence length. A simple expression for the critical temperature Tc is obtained: T c = T c 0 ( 1 − h + α h 3 / 2 ) , where h is the dimensionless magnetic field and α is a constant which describes the defects in a specimen. The formula nicely fits our experimental results.

Effect of ion doping on the dislocation-related photoluminescence in Si + -implanted silicon

Abstract: The study is concerned with the effect of the additional implantation of Si samples with C+, O+, B+, P+, and Ge+ impurity ions followed by annealing at 800°C on the behavior of the dislocation photoluminescence line D1, induced in the samples by implantation with Si+ ions at a stabilized temperature followed by annealing in an oxidizing Cl-containing atmosphere. It is established that the intensity of the D1 line strongly depends on the type of incorporated atoms and the dose of additional implantation. An increase in the D1 line intensity is observed upon implantation with oxygen and boron; at the same time, in other cases, the D1 luminescence line is found to be quenched. The mechanisms of such behavior, specifically, the role of oxygen and its interaction with implanted impurities are discussed.

Silicon Nanocrystals: Fundamental Theory and Implications for Stimulated Emission

Abstract: Silicon nanocrystals (NCs) represent one of the most promising material systems for light emission applications in microphotonics. In recent years, several groups have reported on the observation of optical gain or stimulated emission in silicon NCs or in porous silicon (PSi). These results suggest that silicon-NC-based waveguide amplifiers or silicon lasers are achievable. However, in order to obtain clear and reproducible evidence of stimulated emission, it is necessary to understand the physical mechanisms at work in the light emission process. In this paper, we report on the detailed theoretical aspects of the energy levels and recombination rates in doped and undoped Si NCs, and we discuss the effects of energy transfer mechanisms. The theoretical calculations are extended toward computational simulations of ensembles of interacting nanocrystals. We will show that inhomogeneous broadening and energy transfer remain significant problems that must be overcome in order to improve the gain profile and to minimize nonradiative effects. Finally, we suggest means by which these objectives may be achieved.

Self-assembly of folate onto polyethyleneimine-coated CdS/ZnS quantum dots for targeted turn-on fluorescence imaging of folate receptor overexpressed cancer cells.

Abstract: Folate receptor (FR) can be overexpressed by a number of epithelial-derived tumors, but minimally expressed in normal tissues. As folic acid (FA) is a high-affinity ligand to FR, and not produced endogenously, development of FA-conjugated probes for targeted imaging FR overexpressed cancer cells is of significance for assessing cancer therapeutics and for better understanding the expression profile of FR in cancer. Here we report a novel turn-on fluorescence probe for imaging FR overexpressed cancer cells. The probe was easily fabricated via electrostatic self-assembly of FA and polyethyleneimine-coated CdS/ZnS quantum dots (PEI-CdS/ZnS QDs). The primary fluorescence of PEI-CdS/ZnS QDs turned off first upon the electrostatic adsorption of FA onto PEI-CdS/ZnS QDs based on electron transfer to produce negligible fluorescence background. The presence of FR expressed on the surface of cancer cells then made FA desorb from PEI-CdS/ZnS QDs due to specific and high affinity of FA to FR. As a result, the primary ...

Thermodynamic stability of high phosphorus concentration in silicon nanostructures

Abstract: In this work we focus on P doping of Si nanocrystals (NCs) embedded in a SiO 2 matrix. We prove that, at equilibrium, high P concentrations within the Si NCs are thermodynamically favoured. We experimentally estimate the energy barriers for P diffusion in SiO 2 and trapping/de-trapping at the SiO 2 /Si NCs interface, obtaining a complete picture of the system at equilibrium.