Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques最新文献

The properties of a metal contact with a p-GaAs layer ~8 nm thick induced by low-energy Ar⁺ ions on an n-GaAs wafer as a result of the conduction type conversion have been studied. The metal was deposited according to the standard technology on the surface of the semiconductor p-GaAs with a natural oxide layer partially restored when the sample was transferred to a deposition setup. To prevent metallization of the nanolayer the contact was not annealed. Therefore, a Schottky barrier emerged at the interface and a residual oxide layer retained. However, current–voltage characteristics showed that the formed contact is predominantly ohmic. It has been found that a high concentration of ion-induced defects radically reduces the width of the Schottky barrier and ensures the tunneling of holes and electrons of the semiconductor valence band through the barrier in the forward and reverse directions, respectively. It has been shown that ion bombardment of the p-GaAs semiconductor surface makes it possible to obtain an ohmic contact with any metal without annealing. It is concluded that the ion-stimulated modification of the semiconductor and the exclusion of annealing make it possible to obtain a tunnel ohmic contact with an extremely thin p-GaAs nanolayer coated with the residual layer of natural oxide.

To determine the size distribution of structurally ordered clusters dispersed within a structurally disordered alloy matrix, we analyze the diffraction patterns of the Fe₇₄Al₂₆ alloy obtained using a high-resolution neutron diffractometer. This analysis employs the generalized Scherrer method, which involves analyzing diffraction-peak profiles, determining peak widths at heights of 1/5 and 4/5 of the maximum, and assuming a gamma distribution for cluster sizes (Pielaszek method). We compare the results obtained using the Scherrer, Williamson–Hall, and Pielaszek methods, finding them to agree. We propose an algorithm to calculate the log-normal distribution function of cluster/particle sizes. Experimental data are obtained using a time-of-flight neutron diffractometer. The analysis is conducted for two scanning variable options: in the crystallographic (direct) (d scale) and reciprocal (H scale) spaces, and possible systematic errors are evaluated. We conclude that the average sizes determined in this manner possess the necessary degree of stability, showing a weak dependence on the applied scanning variable and the total number of experimental points.

The charging potentials of quartz glass coated with a conductive metal film were estimated. Estimations were made based on the measured dependence of the intensity of the cathodoluminescent signal on the energy of the incident electron beam. Calculations showed that when quartz glass coated with a 14 nm thick Au film is irradiated, the charging potential can reach 1.7 kV at an electron energy of 10 keV and 2.7 kV at 15 keV. An estimation of the electric field generating under the surface of the grounded film demonstrated that the field strength does not exceed 4 × 10⁷ V/cm.

The work is devoted to clarifying the ratio of atoms and molecules of tellurium vapor in interaction with various metal substrates (copper, nickel). Atoms (Te) and molecules (Te₂) present in the tellurium vapor phase in mass spectrometric measurements correspond to ion currents of monomers J(Te⁺) and dimers J(({text{Te}}_{2}^{ + })). The work is performed on a molecular beam epitaxy unit with desorption flow control by mass spectrometry and surface condition by reflection high-energy electron diffraction (RHEED). A molecular tellurium beam is obtained using a Knudsen type source. It is shown that the proportion of monomers in the total desorption beam significantly depends on the temperature of the substrate. This dependence corresponds to the dissociation energy of Te₂ molecules on the order of 1.18 eV. At high temperatures (900 K), the proportion of Te monomers can reach 85%; at low temperatures (650 K), 8%. This circumstance should be taken into account when the composition of the vapor phase from the beam source can affect the processes under study. In particular, in mass spectrometric studies of the interaction of the vapor phase with the surface of a solid, for example, in the process of molecular beam epitaxy of CdTe.

Layers on the surface of aluminum, aluminum alloy, titanium, and tantalum are formed using ion-beam-assisted metal deposition. Deposition of the metal and mixing of the deposited layer with the substrate surface with accelerated (U = 20 kV) ions of the same metal are carried out in an experimental setup, respectively, from the neutral fraction of metal vapor and ionized plasma of a pulsed vacuum (p ~ 10^–2 Pa) arc discharge. Multi-component amorphous layers containing atoms of the deposited metal, components of the substrate material including oxygen of the surface oxide film, as well as hydrocarbon molecules as impurities, are obtained. It is established that during the ion-beam-assisted deposition of metals with getter properties (Zr, Cr, Er, Dy, etc.) onto the surface of the materials under study, significant amounts of gases are captured from the residual atmosphere of the vacuum working chamber and included in the composition of the layer being formed. It is noted that the content of atoms of the substrate material in the layer is small. During the ion-beam-assisted deposition of metals which do not exhibit getter properties, the content of impurities in the resulting layers is significantly less; they contain atoms of the deposited metal and the substrate material.

The temperature dependences of the composition of the outer monolayers of the surface of thermoemitters, namely, oxide, scandate, thoriated tungsten, and carbide cathodes, have been studied by the methods of low-energy ion and recoil atom scattering, Auger spectroscopy, and secondary ion mass spectroscopy. It has been established that the surfaces of oxide, scandate, and tungsten-thorium cathodes at operating temperatures contain a monoatomic film of active material (barium, thorium), which forms on the surface of the emitter when heated to operating temperature and dissolves in volume when the temperature drops to room temperature. As a result of activation, free barium accumulates in the volume of oxide crystals. It is shown that there is a slight increase in tantalum on the surface of tantalum carbide and it contains foreign electronegative adatoms (oxygen, chlorine, and sulfur) that cannot be removed at temperatures of 2500 K.

A high-density ultracold-neutron source based on superfluid helium is being developed at the Petersburg Nuclear Physics Institute (PNPI) of the National Research Center “Kurchatov Institute” for fundamental physics research. This ultracold-neutron source is intended for installation in the largest experimental channel of the PIK reactor complex: the horizontal experimental channel (HEC-4). Calculations indicate that the thermal-neutron flux density at the channel output is 3 × 10¹⁰ cm^–2 s^–1. The new ultracold-neutron source aims to achieve an ultracold neutron density of 3.5 × 10³ cm^–3 at the reactor-chamber output and 200 cm^–3 in the spectrometer designated for measuring the neutron electric dipole moment. The neutron-guide system for ultracold neutrons is designed to support five experimental facilities alternately. Initially, the ultracold-neutron source will be equipped with existing experimental setups: a neutron electric-dipole-moment spectrometer and two setups for measuring the neutron lifetime (utilizing gravitational and magnetic traps). For this ultracold-neutron source, a unique technological cryogenic complex has been designed and implemented to work with superfluid helium under reactor-installation conditions. This complex includes equipment capable of achieving temperatures down to 1 K and removing heat from superfluid helium at a rate of up to 60 W.

The influence of nonthermal plasma on the surface properties of spring wheat seeds was studied. For plasma treatment of seeds a source of volumetric nonthermal argon plasma based on glow discharge at atmospheric pressure was used. The discharge was created in an electrode structure with a multipointed sectioned cathode and a flat metal anode. Two batches of seeds were prepared, each batch containing 100 seeds. Seeds from one batch were exposed to plasma, while seeds from the other batch were used as controls. Wettability measurements and surface modification analysis by electron scanning microscopy were performed to evaluate the plasma effects on the seed material. It was shown that as a result of plasma treatment the surface of seeds becomes hydrophilic, which is characterized by a decrease in the contact angle and an increase in the surface energy of seeds. It was established that plasma exposure of wheat seed coatings leads to modification of the seed surface, which consists in the manifestation of a fine mesh morphology on the seed surface with different cell size and rather sharply defined boundaries; the etching effects on the seed surface increase with increasing exposure duration or discharge power.

Gd₂O₃ coatings are deposited at a rate of 1.6 μm/h using the reactive anodic evaporation of Gd from a water-cooled crucible in a discharge with a self-heated hollow cathode. A power density on the crucible surface (more than 0.5 kW/cm²) sufficient to evaporate Gd is achieved by increasing the discharge current to 30 A and compressing the electron flow in the anode region by the field of a short solenoid, the maximum induction of which is 20 mT. The composition of the gas–metal (Ar/O₂–Gd) plasma is studied using optical emission spectroscopy. It is shown that the high frequency of interaction of electrons with Gd vapor near the surface of the crucible provides an increase in the degree of metal ionization to ~90%; the degree of O₂ dissociation is ~13%. The structural and phase state of Gd₂O₃ coatings deposited at temperatures in the range from 150 to 600°C is studied. It is established that reactive anodic evaporation in a low-pressure arc (0.2 Pa) under conditions of an increased degree of ionization of the metal and reactive gas allows implementation of the low-temperature (150°C) formation of single-phase Gd₂O₃ coatings with a cubic structure, the level of internal stresses in which is ~0.1 GPa. A low level of internal stresses and synthesis temperature make it possible to obtain single-phase adhesively strong coatings with a thickness of ~1 μm.

Hybrid perovskite materials based on metal-organic structures attract considerable attention because they achieve a relatively high conversion of solar radiation into photocurrent while being relatively simple to produce. This study presents a model analysis of the possibility for the experimental detection and characterization of a lead-halide layer that forms at the internal interface during the degradation of a hybrid perovskite photovoltaic film, using in situ neutron reflectometry. By comparing calculated specular-reflection curves, we identify the relationships between the parameters of the system’s components that allow us, despite generally minor changes in the curves, to trace to a certain extent the evolution of the mentioned layer.