Georgii E. Cirlin

A3B5 nanowires are usually grown via the vapor-liquid-solid mechanism. Species from the vapor are incorporated into the nanowires using a catalyst droplet. Typically, the droplet is a low-melting-point eutectic alloy of catalyst and group III metal. This growth imposes a set of limitations on the heterostructure formation and doping. Axial A3B5 heterostructure nanowires obtained via an interchange of group III metals suffer from blurring and kinking. Amphoteric dopants such as Si could act as donors and acceptors, leading to electron-to-hole ratio oscillations along the nanowire. To overcome these limits, the growth with a catalyst, which could dissolve both components of the nanowire, is studied. Tin has a eutectic with both components, As and Ga. This makes the growth of GaAs nanowires with a tin catalyst different from that with standard catalysts. Nanowire growth occurs with at least two types of catalysts, Ga-rich and Ga-poor (As-rich). This article aims to study the nanowire growth with an Sn catalyst. For the first time, the growth of GaAs nanowires using a tin catalyst by molecular beam epitaxy is shown. Tin can serve as a catalyst not only for the chemical growth of GaAs nanowires but also as a nucleation site for their growth. Both compositions of the catalyst are observed. The annealing of a thin film of tin on a Si and GaAs substrate has also been studied. At temperatures below 450 °C, small metal droplets form, while tin dissolves into the substrate at higher temperatures.

Subject of study . In this study, Si epitaxial layers with embedded indium arsenide (InAs) quantum dots (QDs) were investigated. Aim of study . The aim was to experimentally examine the luminescent characteristics of InAs QDs in a Si matrix. In addition, the dependence of the photoluminescence (PL) intensity of the heterostructure on the temperature and growth method of the Si capping layer was investigated. Method. Si epitaxial layers with embedded InAs QDs were fabricated via molecular beam epitaxy. The optical properties in the range of 10–120 K were studied using low-temperature PL spectroscopy. Main results. The influence of the growth conditions of the Si capping layer on the optical properties of heterostructures with submonolayer InAs QDs embedded in a Si matrix was investigated. A PL signal at 1.65 µm, originating from submonolayer QDs, was obtained at temperatures up to 120 K. The two-stage Si overgrowth method for InAs nanoislands increased the PL intensity by improving the crystalline quality of the heterostructures. Based on an analysis of the temperature dependence, the activation energy of electrons confined in the QD potential well was estimated to be 30 meV, which was comparable with the thermal energy at room temperature (25 meV). Practical significance. The results obtained from the optical property analysis of heterostructures with submonolayer InAs QDs can serve as a basis for developing new optoelectronic devices based on Si technologies.

The influence of growth regimes of the silicon capping layer on the optical properties of heterostructures with submonolayer InAs quantum dots embedded in a silicon matrix has been studied. The photoluminescence signal at 1650 nm from submonolayer quantum dots at low temperatures up to 120 K was obtained. It was established that the use of a two-stage method of silicon overgrowing InAs nanoislands makes it possible to increase the photoluminescence intensity by improving the crystalline quality of heterostructures. Analysis of the temperature dependence allowed us to calculate an activation energy for electrons confined in the quantum dots potential well at the level of the thermal energy at room temperature.

Subject of the study. This study addresses the quantitative and qualitative features of the complex formation of nanoparticles (NPs) of metallic silver and phthalates. The purpose of this work was to determine the conditions for the formation of stable complexes of silver NPs (Ag NPs) with dibutyl phthalate (DBP) in an aqueous solution. To achieve this goal, a full cycle of comparative studies of Ag NPs was carried out from synthesis to establishment of the possibility of binding DBP for further creation of an accessible sensor based on them capable of detecting various phthalates in water. Methods. Chemical methods were used for the synthesis of NPs, modification of their surface with nucleotides, and connection of NPs with phthalates. To study the interaction of Ag NPs with each component of an organic–inorganic complex, namely, sodium citrate (hereinafter referred to as citrate), uridine-5^′-triphosphate (hereinafter referred to as uridine or UTP), copper ions (Cu²⁺), and DBP, optical spectroscopy and transmission electron microscopy were used. Main results. Metallic Ag NPs were synthesized using four agents safe for humans, which acted simultaneously as reducing agents and stabilizers (citrate, polyethylene glycol, polyvinylpyrrolidone, and orange extract). NPs synthesized using sodium citrate were selected for further use as phthalate sensors considering the stability parameters and range of research methods. The change of the Ag NPs’ ligand shell by uridine molecules and the formation of chemical bonds between them and phthalate involving copper ions were shown. Raman spectra and transmission electron microscopy images of Ag/UTP−Cu²⁺−DBP complexes were obtained for the first time to our knowledge, confirming the chemical bonding of Ag NPs and phthalates. The optimal molar ratio of Ag/UTP NPs and copper ions in solution for the subsequent process of complex formation was found. Practical significance. The formation of complexes between DBP and modified Ag NPs in the absence of alcohol and any buffer solutions was shown for the first time to our knowledge. The detection of phthalates using Ag NPs is a promising technology for creating a simple nanosensor with additional plasmonic and antibacterial properties. In addition to its extremely relevant environmental significance today, the study of hybrid systems based on Ag NPs contributes to the development of methods for passivation of the surface of metal NPs. In a broad sense, the research carried out is of interest for the development of technologies for sensory detection of organic–inorganic compounds.

Subject of study. The subject of this study was the integration of indium gallium nitride (InGaN) nanowires with silver nanoparticles and the examination of the photoluminescent properties of the resulting hybrid nanostructures. Aim of study. This study aimed to improve the luminescent characteristics of InGaN nanowires by decorating their surface with colloidal silver nanoparticles. Method. Silver nanoparticles of various sizes and nanoparticles with a silver/silicon oxide core/shell structure were synthesized using colloidal chemistry. Indium gallium nitride nanowires were fabricated using molecular beam epitaxy. The morphology and dimensions of the obtained samples were studied using scanning electron microscopy. The optical properties were characterized using spectral methods. Main results. A red shift in the wavelength of the localized plasmon resonance of the nanoparticles was demonstrated with increasing diameter and passivation of the nanoparticle surface by a silicon oxide shell. Nanowires with a spontaneously formed InGaN/GaN core–shell structure exhibiting photoluminescence at room temperature in the yellow-orange region were synthesized. It was shown for the first time to our knowledge that the deposition of colloidal silver/silicon oxide nanoparticles onto the surface of InGaN nanowires leads to an increase in the photoluminescence intensity of the initial structures by a factor of 2.2. Practical significance. InGaN nanowires are promising solid-state nanostructures for the fabrication of visible-light-emitting devices integrated with a silicon platform. The synthesis of hybrid nanostructures based on InGaN nanowires and silver nanoparticles can increase the luminescence efficiency of the original nanowires. In particular, the hybrid nanostructure proposed herein can be used to develop optically pumped subwavelength lasers based on InGaN nanowires.

At the moment, InGaN ternary compounds are of a great interest for the development of devices for sunlight driven water splitting. However, the synthesis of such materials is hindered by the fact that InxGa1–xN layers are susceptible to phase decomposition at x from 20 to 80%. Nanowires can be a promising solution to this problem. The purpose of our study was to analyze the structural and optical properties of InxGa1–xN nanowires with a gradient x content being inside the miscibility gap. InxGa1–xN nanowires were grown on silicon substrates using plasma-assisted molecular beam epitaxy. The structural properties of nanowires were studied using scanning and transmission electron microscopy. The chemical composition and optical properties of nanowires were analyzed using energy-dispersive microanalysis and photoluminescence spectroscopy. It was shown for the first time that the composition-graded InxGa1–xN nanowires with x from 40 to 60% can be grown using plasma-assisted molecular beam epitaxy. The grown samples exhibit photoluminescence at room temperature with a maximum at about 890 nm, which corresponds to an In content of about 62% according to the modified Vegard’s rule and the transmission electron microscopy data. The obtained results can be of practical interest for the development of devices for water splitting induced by sunlight or sources of near IR radiation

This study is devoted to the confirmation of spontaneous doping of GaN nanowires grown on vicinal SiC/Si hybrid substrates by electron beam induced current mapping. GaN nanowires (NWs) were grown on singular and vicinal SiC/Si substrates by molecular beam epitaxy with nitrogen plasma activation. The morphological properties of the NWs were studied by scanning electron microscopy. The electrophysical properties of the obtained nanostructures were studied by electron beam induced current mapping. By electron beam induced current mapping, we confirmed the spontaneous doping of the GaN NWs grown on vicinal SiC/Si wafers. It was also shown that the GaN NWs grown on singular SiC/Si substrates did not exhibit an induced current signal, indicating that they were not doped

Hybrid nanostructures based on InGaN nanowires with decorated plasmonic silver nanoparticles are investigated in the present study. It is shown that plasmonic nanoparticles induce the redistribution of room temperature photoluminescence between short-wavelength and long-wavelength peaks of InGaN nanowires. It is defined that short-wavelength maxima decreased by 20%, whereas the long-wavelength maxima increased by 19%. We attribute this phenomenon to the energy transfer and enhancement between the coalesced part of the NWs with 10–13% In content and the tips above with an In content of about 20–23%. A proposed Fröhlich resonance model for silver NPs surrounded by a medium with refractive index of 2.45 and spread 0.1 explains the enhancement effect, whereas the decreasing of the short-wavelength peak is associated with the diffusion of charge carriers between the coalesced part of the NWs and the tips above.