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

The influence of morphological and dimensional parameters of the ensemble of ZnO microstructures on emission spectra when excited by a stream of fast electrons is studied. The research objects are arrays of viscers, tetrapods, and submicron ZnO particles. It was found that the red shift of the exciton luminescence band in ZnO microstructures is associated with their destruction and enrichment of charge carriers and maximum for an array of submicron particles. In the ZnO whisker array, when irradiated with the stream of fast electrons, an increase in the luminescence band associated with recombination of electron-hole plasma is observed.

This article is devoted to measurement of proton beam parameters as one of the stages of proton injector for linear accelerator of compact neutron source DARIA development. Experimental results of ion source operating modes investigation are presented in this work. Gasdynamic electron-cyclotron resonance ion source GISMO is used as a proton injector. The plasma of the ion source is characterized as dense (the electron density is about 10¹³ cm^–3) and hot (the electron temperature is about 30 eV). High volumetric energy input in plasma (up to 250 W cm^–3) is achieved by the use of powerful “technological” gyrotron radiation to the plasma heating. The total ion beam current and beam emittance measurements were conducted during experiment at different facility parameters: inlet gas pressure, microwave power, magnetic lens current, and extraction voltage. The beam emittance was measured using pepper-pot method. The optimal ion source operation mode was found. The total beam current was above 100 mA at the proton beam energy of 40 keV, and the root-mean square normalized emittance was 0.21 π mm mrad. The obtained results of measurements are beneficial from the point of view of possibilities to control the ion source operating modes.

Radiation degradation is a serious problem affecting the service life of many structural materials used in harsh environments. Modern research is aimed at developing materials with improved mechanical and physical properties, as well as increased resistance to radiation damage. Nanoscale multilayer coatings are one such material. The effect of annealing on the microstructure, defect structure, and mechanical properties of nanoscale multilayer materials consisting of alternating Zr and Nb layers after irradiation with He⁺ ions was studied. Multilayers Zr/Nb materials were prepared by magnetron sputtering, with the thickness of each layer being 50 nm. Analysis was performed using the following techniques: positron annihilation spectroscopy, X-ray diffraction analysis, and high-resolution transmission electron microscopy. Defects in the structure were investigated layer by layer using a variable energy positron beam and Doppler broadening spectroscopy. Analysis of changes in nanohardness, Young’s modulus, and structural-phase state has shown that the multilayer structure is preserved in Zr/Nb multilayers with a thicknesses of individual layer of 50 nm after irradiation with He⁺ ions and subsequent annealing in the range from 100 to 300°C.

The article presents an approach to determining the modulus and phase of neutron reflection amplitude using a gadolinium reference layer, which allows reducing the number of necessary experiments from three to two. It is shown that it is possible to reconstruct the reflection amplitude based on the results of only two reflectometric experiments. However, when conducting two experiments, calculating the reflection amplitude is complicated by the fact that there will be two solutions instead of one. Therefore, it is necessary to evaluate the obtained results, since one of these solutions will have no physical meaning. The results are evaluated based on a priori information about the sample or with the help of additional modeling of the interaction potential. The theory of the proposed approach is described in detail, and it is tested on model numerical calculations for the Al₂O₃//Ti film. Experimental results for the test samples Al₂O₃//Nb and Si//Cr/Fe/Cr are presented. A comparison of the moduli and phases of the reflectivity obtained by processing three and two experiments is carried out. It was found that under conditions of poor statistics, conducting two experiments is preferable, since the solution, in this case, contains fewer artifacts of mathematical processing.

This study explores a new type of terahertz-radiation source based on a molecular crystal of rubidium acid phthalate (RbAP) and a tunable metamaterial that functions as a filter. The high-quality oscillatory response of the RbAP crystal lattice in the terahertz frequency range enables the generation of narrowband terahertz radiation at multiple frequencies simultaneously, with high spectral brightness and peak power. Single femtosecond laser pulses excite the crystal. Switching between the generated spectral lines is achieved using a planar metamaterial, the absorption lines of which depend on the incident radiation polarization. The developed source allows for dynamic tuning of the emission spectral line, which makes it more versatile and efficient than conventional narrowband sources, such as quantum cascade lasers.

Modern tomographic studies using laboratory X-ray sources often employ the polychromatic mode due to the relatively low intensity of the radiation. This mode enhances the signal-to-noise ratio and improves the quality of the results of reconstruction. Modeling and analyzing the results of tomographic measurements with polychromatic X-ray radiation requires the consideration of additional aspects of the experiment compared to the monochromatic case. These aspects are related both to the spectral characteristics of the source and the interaction of polychromatic X-ray radiation with the sample and the detector. These aspects affect both the quantitative results of the simulation and interpretation of the reconstructed tomographic data. In this work, a simulation of a tomography experiment using silicon carbide samples and an aqueous solution of iohexol is performed. The influence of the X-ray tube radiation spectrum and the spectral sensitivity of the detector’s scintillator (charge-coupled device) made from various materials and thicknesses on the results of tomographic reconstruction is analyzed. Calculations are carried out both with and without consideration of these aspects. The results show that taking into account the spectral characteristics of the source and the peculiarities of the interaction between polychromatic radiation, the sample, and the detector improves the accuracy of simulating the tomography experiment.

Zinc biodegradable alloys are actively researched as promising materials for creating biomedical implants for osteosynthesis and vascular stents. New zinc alloys of the Zn–Ag–Cu system are of particular interest due to their antimicrobial and bactericidal properties conferred by the addition of silver and copper. The feasibility of producing a defect-free zinc alloy spoke and the influence of combined processing, involving severe plastic deformation techniques, such as equal-channel angular pressing (ECAP) and extrusion, on the microstructural changes and mechanical properties of the Zn 1 wt % Ag 1 wt % Cu (Zn–1Ag–1Cu) alloy were studied. To complement the experimental study, computer modeling of the extrusion of the Zn–1Ag–1Cu alloy at a temperature of 150°C was performed. Data on the distribution of accumulated deformation and average stresses were obtained, indicating structural relaxation. Multipass ECAP treatment resulted in a significant grain refinement to 3 ± 0.5 μm compared to the homogenized state with a grain size of 326 ± 31 μm, while subsequent extrusion led to recrystallization. After combined processing, the average grain size increased to 13 ± 2 μm. Samples subjected to ECAP exhibited a substantial increase in ultimate strength to 204 MPa and ductility to 50%, compared to the homogenized state (78 MPa, 12%). However, extruded samples showed a slight decrease in strength to 181 MPa and ductility to 29%. It was concluded that the combined deformation techniques enable the production of a defect-free spoke with a diameter of 5 mm and a length of 200 mm, exhibiting mechanical properties suitable for medical applications.

A self-forming wave-ordered structure arises on the surface of single-crystal or amorphous silicon during its sputtering with an inclined beam of nitrogen ions. The wave-ordered structure is a solid nanomask, a dense array of silicon nitride nanostripes with a period in the range of 30–90 nm. The induced spatial coherence of the nanomask due to the formation of sharp geometric boundaries on silicon surface in the areas of ion bombardment is considered. Based on the nanomask and etching processes (wet and dry), various nanostructures are formed, which are used in different high technologies. Prototypes of solar cells, nanowire grid polarizers, and nanostructured silicon substrates for surface-enhanced Raman spectroscopy have been created. The results of a study of the initial stages of lysozyme protein crystallization on nanostructured silicon substrates are presented.

Migration of chromium, which acts as an adhesive material for planar electrodes of a MEMS switch, over the surface of a thermally oxidized silicon wafer is demonstrated. Voltage pulses lead to the formation of chromium and carbon nanostructures on the driving electrode and their growth towards the signal electrode. Over time, the structures reach micron sizes and cover the interelectrode gap. Migration is activated by an electric field of about 10⁸ V/m. The first structures appear after applying 10²–10⁵ pulses, but the process accelerates as they grow. For platinum electrodes, migration is faster and requires a lower voltage compared to gold electrodes. Material transfer occurs not only in the gap between the electrodes but also on the SiO₂ surface around the positive electrode. The material also moves under the Pt and Au films, peeling them off from the substrate. The described phenomena can damage electrostatically actuated MEMS switches and other devices that use high electric fields.

This article is devoted to a stage of pulsed proton injector development which is conducted at the Gaponov-Grekhov Institute of Applied Physics, Russian Academy of Sciences. The result of electrostatic chopper numerical modeling is presented. It is a part of proton injector for linear accelerator of compact neutron source DARIA. A continuous wave mode gasdynamic electron cyclotron resonance ion source GISMO is used as an injector. The ion source has high volumetric energy input into plasma due to the use of “technological” gyrotron radiation to maintain and heat the plasma. The optimal geometric parameters (deflecting plates size and distance between them) of electrostatic chopper are determined during the calculations of proton beam propagation through the injector. The minimal voltage, which is enough for full beam deflection without losses inside chopper, is achieved at the optimal chopper geometry. Also, the output beam current dependence on chopper plate voltage is studied. The calculations allow for determining temporal characteristics of pulsed proton beam which escapes the injector at known pulse parameters of chopper voltage supply source.