Solid State Phenomena Vol. 312

Abstract: Resistivity, r (T), and Hall coefficient in weak (B < 1 T) magnetic fields, R (T), are investigated in Ca₂Si and CaSi₂ films at temperatures T between ~ 20 - 300 K. In CaSi₂, r (T) is typical of metals increasing with T within the whole temperature range. On the other hand, the resistivity of Ca₂Si is pertinent of semiconductors. Namely, it is activated below T ~ 200 K, exhibiting different slopes of ln r vs. T ^-1 plots at lower and higher T, and a weak increase between T ~ 200 - 300 K. Both materials demonstrate a complex dependence of R (T), including a change of the sign. Transport properties above have been analyzed assuming two groups of charge carriers, electrons and holes, contributing them.

Abstract: The structural-phase state of two-dimensional (d = 1 - 3 ML) coatings before and after annealing and that of Fe nanolayers (d = 4 - 10 ML) were investigated on Si (001)2×1 by electron spectroscopy methods of Auger-electrons and energy losses. The room (30 °С) and lowed (≤ 1250 °С) temperatures of the Si (001) substrate and Fe vapor, respectively, were used during Fe deposition. This study showed the following. An ordered two-dimensional 1×1 phase of Fe stable up to 600 °C and then a Fe₂Si wetting coating stable at 250 °C form near the thickness 1 ML and 3 ML, respectively. Fe deposition on this Fe₂Si coating leads to the one-after-another formation of the Fe₃Si, the Si-in-Fe solution, and then a stable up to 250 °C Fe nanofilm with segregated Si.

Abstract: An approach to describe the structure of amorphous alloys obtained by fast quenching from a melt, based on the fluctuation theory of phase transitions, is proposed in t in such objects.

Abstract: Radiation stability of ZnO hollow particles under 100 keV proton and electron exposure have been investigated. The experimental data were compared with the calculated ones obtained by modeling in the GEANT4 software package. Hollow particles have better radiation stability compared with bulk microparticles cause by low defects accumulation in the hollow particles, which was confirmed by simulation in GEANT4.

Abstract: The optical properties of silicon dioxide hollow particles with different size were investigated in UV/visible/near-IR region, as well as X-ray photoelectron spectra were analyzed. Synthesis of SiO2 hollow particles was carried out using a template method. It was established that hollow particle reflectance lower than bulk microparticles. Absorptance in the red and near infrared spectral ranges increases with decreasing size of hollow particles, but in the UV-region conversely. This is due to different absorption centers.

Abstract: The paper presents data on the temperature dependence of the conductivity of strontium bismuthate Sr₆Bi₂O₁₁. It is shown that the temperature dependence of conductivity cannot be described in the framework of existing models. It was found that at a temperature of about 400 K a change in the radius of localization of the charge carrier is observed.

Abstract: Studies are devoted to determining the effect of long-term storage (up to 200 days) of untreated and immersion-treated layers of mesoporous silicon in an aqueous lithium bromide solution obtained by anodizing with a current density of 10 mA/cm² in electrolyte HF: CH₃OH = 2: 1. It was found that an increase in the PL intensity and its saturation with a storage time of more than 100 days in all samples is observed. A detailed analysis of absorbance on bonds in m/por-Si showed that during storage, hydrogen bonds are destroyed, and the PL peak intensity is proportional to the increasing concentration of non-stoichiometric oxide, in which oxygen atoms forms radiative states. It was shown that in the treated samples, the PL intensity decreases with increasing immersion time, but the mechanism of photoluminescence through the quantum size confinement (QSC) effect in mesoporous silicon without and with immersion in an aqueous LiBr solution is not significant.

Abstract: The studies are devoted to the development of the technology of multilayer incorporation of nanocrystals (NCs) of semiconductor chromium and iron disilicides with a layer density no less than 2x10¹⁰ cm-2, the establishment of the growth mechanism of heterostructures with two types of NCs, the determination of their crystalline quality and optical properties, as well as the creation and study of rectification and photoelectric properties of p-i-n diodes based on them. Morphologically smooth heterostructures with 6 embedded layers of CrSi2 nanocrystals and two types of embedded nanocrystals (with 4 layers of CrSi2 NCs and 2 layers of β-FeSi2 NCs) for optical studies and built-in silicon p-i-n diodes were grown for the first time. The possibility of optical identification of interband transitions in embedded nanocrystals in the photon energy range of 1.2 - 2.5 eV was determined from the reflection spectra and the strongest peaks in reflection from the integrated nanocrystals were determined: 2.0 eV for CrSi2 NCs and 1.75 eV for β-FeSi2 NCs. The created p-i-n diodes have a contact potential difference of 0.95 V, regardless of the type of embedded NCs. At 80 K, an absorption band (0.7 - 1.1 eV) was detected in the diodes, which was associated with carrier photo generation in the embedded CrSi2 and β-FeSi2 NCs. From the spectra of the photoresponse at 80 K, the band gap widths in the NCs were determined: 0.50 eV in CrSi2 and 0.70 eV in the superposition of the CrSi2 and β-FeSi2 NCs.

Abstract: The article provides a comparative analysis of changes in the PL spectra and infrared spectroscopy (IR) with reference and immersion samples of mesoporous silicon during long-term storage in air at room temperature. Immersion was carried out in an aqueous solution of iron nitrate (Fe (NO₃)₃) with a concentration of 0.2 M and 0.5 M with three times: 5, 10 and 20 minutes. An analysis of the FIR data for etalon and immersion samples showed a number of features found during long-term storage of mesoporous silicon: (1) a sharp decrease in the density of hydride bonds; (2) the polynomial nature of the growth of O₃-SiH and Si-OH bonds saturating dangling bonds; and (3) the polynomial growth of silicon dioxide with the formation of oxygen defects. It was found that after immersion in a solution of 0.5 M Fe (NO₃)₃ for 10 minutes, a more intense increase in the PL in mesoporous silicon is observed while maintaining its nanostructure after 200 days of storage compared with the etalon sample, for which a weak quantum size confinement (QSC) is observed. The main mechanism of photoluminescence increase in mesoporous silicon during long-term storage is radiative recombination from oxygen defect levels, not from a QSC effect.