Molecular dynamics simulations were used to study the interaction of Ar clusters with silicon and germanium single crystals at a fixed cluster size of 923 atoms and a total kinetic energy of 10 keV. A comparative analysis was conducted to examine the effects of argon cluster impacts on the surface morphology of silicon and germanium as the cluster incidence angle varied from 0 degrees to 75 degrees with respect to the surface normal. The depth of amorphization and the height of hillocks induced in silicon and germanium after argon cluster bombardment were estimated. Angular dependences of the crater diameters along and perpendicular to the cluster incidence direction were demonstrated. Comparisons of crater characteristics and the ratios of longitudinal to transverse crater dimensions revealed material-specific features of cluster-surface interactions. At oblique incidence, a peak in the ratio of displaced atoms in the amorphous layer to those above the surface was observed. The potential energy of silicon and germanium target atoms following cluster impact was visualized and estimated. Moreover, the redistribution patterns of the cluster's initial kinetic energy among the target, scattered cluster atoms, and sputtered target atoms were compared for silicon and germanium at incidence angles from 0 degrees to 75 degrees.

The evolution of the self-assembled nanostructures formed on the Ge (100) surface as a result of sputtering by an obliquely incident argon cluster ion beam is studied. The bombardment was carried out with Ar+1000 ions at energy of 10 keV and angle of incidence of 60'from the normal while varying the ion fluence from 8 x 1014 up to 2 x 1016 ions/cm2. It is found that parallel-mode ordered ripples with significant aspect ratios can be produced on the Ge surface at a minimum sputtering depth. Such nanostructures have not previously been formed on the Ge surface with conventional argon ions. Our findings prove that argon cluster ion beam is effective for nanopatterning the surface of single-component semiconductors.

The features of the surface treatment of potassium-gadolinium-tungstate single crystals doped with neodymium ions by low- and high-energy argon cluster ions are considered. Two radically different treatment modes are employed: the low-energy mode for more efficient smoothing of the surface and high-energy for more effective etching of the target. The topography of the target surface is analyzed before and after cluster-ion treatment using atomic force microscopy. It is shown that treatment in the low-energy mode smoothes out irregularities on the target surface formed by chemical and mechanical polishing at an etching depth of less than 100 nm. A comparison is made of the root-mean-square roughness and total roughness of the initial and treated surfaces of potassium-gadolinium tungstate doped with neodymium ions. Survey X-ray photoelectron spectra of the initial surface of a KGd(WO4)2:Nd single crystal and after cluster-ion treatment in various modes are presented. It is demonstrated that the intensities of the potassium and gadolinium peaks decrease after cluster-ion treatment in both modes. A significant decrease in the concentration of potassium atoms in the surface layer of the target is explained by the preferential sputtering of potassium as a lighter chemical element. The mutual decrease in the concentrations of gadolinium and potassium atoms can be explained by the weak bonds of these atoms in the lattice of the KGd(WO4)2:Nd single crystal.

To elucidate the influence of gas cluster-induced impacts on the deep structure of disturbances in tungstate optical materials, experimental studies were carried out. The precision-polished surface of a KGd(WO4)2 (KGW) single crystal was processed by an argon cluster ion beam with the average cluster size of 1000 atom/cluster at the energy of 10 keV, which ensures minimal damage and high processing efficiency. By using high-resolution TEM and EDX techniques of the transversely cut lamellae, the alterations in both the structure and chemical composition at varying depths were explore. In a 15 nm thick subsurface layer of the initial specimen, a nonuniform depth distribution was found for the constituent atoms of KGW. The results showed that, after the cluster bombardment, the initial amorphous layer thickness resulting from precision chemical–mechanical polishing was decreased from 50 to 23 nm. The distribution nonuniformity of constituent KGW atoms decreases in the upper subsurface layer, while it increases at greater depths.

The surface treatment of single-crystal germanium with an argon cluster ion beam has been investigated. The initial surface of germanium wafers was bombarded by argon cluster ions with high (105 eV/atom) and low (10 eV/atom) specific energy. Using an atomic force microscope, images were obtained and the surface topography was compared before and after cluster ion bombardment. Using the power spectral density function of roughness, surface smoothing is demonstrated in the range of spatial frequencies: 1) ν = 1 − 8 µm−1 — for the high-energy mode; 2) ν = 0.7 − 2.5 µm−1 — for low-energy mode.

— Accelerated cluster ions formed during the outflow of inert gases are a unique tool for the precision surface treatment of various materials, including nonlinear optical single crystals. However, the interaction of gas cluster ions with the surface of nonlinear single crystals has been little studied. In this paper, we consider the features of the formation of anomalous craters during treatment of the surface of hygroscopic lithium-triborate single crystals with argon cluster ions at various bombardment doses. The treatment is carried out at a kinetic energy of clusters of 22 keV, an average cluster size of about 210 atoms per cluster at a normal angle of incidence. It is shown that the anomalous craters have a diameter of 150 to 820 nm, which are two orders of magnitude larger than the diameter of ordinary impact craters. The depth of the craters varies from 5 to 9 nm. Such craters are formed at a target etching depth of up to 320 nm. A statistical analysis of the geometrical parameters of anomalous craters is carried out at various treatment doses. It is established that with an increase in the irradiation dose and, accordingly, the etching depth, the density of anomalous craters per unit surface of the target decreases, while their depth and average diameter increase significantly.

The damage in an inorganic single crystal surface caused by gas cluster ion bombardment is still an open issue. In this work, the influence of the kinetic energy per atom in the clusters E/N on the physicochemical structure of KGd(WO4)2:Nd single crystals was evaluated using XPS, Raman spectroscopy and XRD techniques. The high-energy mode with an energy per atom in the cluster E/N of about 100 eV provides a sufficient sputtering efficiency, while the low-energy mode with an energy of a several eV provides the minimal surface damage. The results revealed no substantial damage to the subsurface crystal structure after the cluster bombardment processing. Nevertheless, the unexpected increase in the relative concentration of O atoms by 12% and depletion of K atoms by a factor of 2 in the subsurface layer of KGd(WO4)2:Nd crystals were detected. The features of surface sputtering of inorganic single crystals at different E/N-modes are discussed.

The interactions of the Ne, Ar, and Kr clusters with the fused silica surface were investigated by molecular dynamics simulations. The impacts of noble gas clusters with kinetic energies ranging from 25 to 110 eV per atom were compared. The characteristics of the formed craters were examined at cluster incidence angles of 0 degrees and 60 degrees. It was found that the crater diameter is almost the same for different gas species at normal incidence. However, at oblique incidence, the depths of craters formed by the Ne and Kr clusters differ insignificantly. Additionally, it has been shown that the ratio of crater length to depth is a function of the energy per cluster atom and can be the same for clusters with different energies and sizes. The dependencies of the crater volume on the scaled cluster energy and energy per unit area were studied. The cratering efficiency of different gas species was estimated, and the relationship between crater volume and sputtering yield was revealed. Moreover, it was shown that the ratio of sputtered volume to crater volume is power law related to the ratio of the sputtered atoms energy to the initial kinetic energy of clusters.

The peculiarities of the surface processing of polycrystalline aluminum-nitride films on glass-ceramic and silicon substrates grown under identical conditions are considered. Aluminum-nitride films are obtained using the magnetron sputtering of a pure aluminum target (99.99%) in nitrogen–argon plasma at a magnetron power of 700 W. The consumption of working gases is 10 sccm for nitrogen and 4 sccm for argon. The film thickness is determined using a quartz resonator inside the chamber of the magnetron setup. Atomic force microscopy is used to study the surface relief of the targets before and after treatment by argon cluster ions. Small single crystallites are shown to grow on the initial surfaces, the lateral size of which is in the range of 250–550 nm. The depth of target etching by argon cluster ions is determined. Cluster ions with low energy per atom are shown to have a high efficiency of surface smoothing. A comparison of the surface morphology and surface-roughness parameters of aluminum nitride on different substrates obtained using atomic force microscopy is carried out. It is shown that aluminum nitride on silicon is smoothed more efficiently than on a glass-ceramic substrate.

Рассмотрено формирование самоупорядоченных периодических наноструктур на поверхности титанил-фосфата калия (KTP) при бомбардировки кластерными ионами аргона. Проведено сравнение результатов бомбардировки кластерными ионами аргона с различной энергией, приходящейся на 1 атом кластера E/N mean – 12.5 и 110 эВ/атом. Продемонстрировано изменение рельефа поверхности с помощью атомно-силовой микроскопии (АСМ). Для определения периода наноструктур использовалась функция спектральной плотности мощности (power spectral density, PSD). Выявлены особенности бомбардировки поверхности монокристалла KTP при нормальном и наклонном падениях кластерных ионов.

The interaction of gas cluster projectiles with the surface of the inorganic compounds is still not a fully understood issue. To clarify the features of silica surface sputtering by noble gas cluster projectiles of various species at normal and oblique incidences, molecular dynamics simulations are employed. The impacts of the Ne, Ar, and Kr clusters with the sizes N of 561 and 923 atoms and scaled kinetic energy E/N from 10 to 140 eV/atom are compared. It is found that the projectile energy per impact area unit E/S and per mass unit of cluster E/M are generalizing parameters of the sputtering efficiency of material in the form of scaled yield Y. The preferential sputtering of oxygen atoms is more sensitive to gas cluster species at normal incidence and decreases significantly with increasing projectile energy E/N. The regularities of the redistribution of the initial kinetic energy of projectiles between the scattered cluster atoms, ejected target atoms, and the target are revealed under the various impact conditions.

In this paper, the influence of surface modification on the characteristics and properties of AlN thin films on Si and glass-ceramics substrates is investigated. The surface modification was made at various parameters of argon cluster ions. By using XRD and Raman spectroscopy, it was shown that the obtained AlN films have a hexagonal structure with a characteristic direction of texturing along the c axis and slight deviations from it. A comparison of the AlN surface morphology obtained by atomic force microscopy before and after cluster processing was demonstrated. This demonstrated that the cluster ions with low energy per atom (E/N = 10 eV/atom) have a high efficiency of surface smoothing. A decrease in the intensity of the Raman peaks and an increase in their full-width after bombardment with cluster ions were found, which may be caused by a change in the physicochemical state of the surface. The optical properties, the quality of the boundaries, and the distribution map of the thickness of the functional layer of AlN were investigated by the methods of spectral and spatial resolution ellipsometry. By using the cross-sectional SEM, the direction of crystallite texturing was demonstrated. The influence of argon cluster ion bombardment on the stoichiometry of samples was analyzed by EDX spectroscopy. The results obtained demonstrate the efficiency of the cluster ion smoothing of polycrystalline thin films for microelectronics, particularly when creating surface acoustic wave resonators.

The possibility of surface modification of thin polycrystalline aluminum nitride films by bombardment with argon cluster ion beam is investigated. The processing was carried out with high- (105 eV/atom) and low-energy (10 eV/atom) cluster ions. Using the spectral function of roughness, a highly efficient smoothing of the surface of nanostructured thin films of aluminum nitride was demonstrated in a wide range of spatial frequencies (ν = 0.02–128 μm-1) and at small etching depth (<100 nm).

Surface modification of polycrystalline thin films of aluminum nitride using bombardment with an cluster ion beam has been investigated. The treatment has been performed using high-energy (105 eV/atom) and low-energy (10 eV/atom) argon cluster ions. High-efficiency smoothing of the nanostructured surface in a wide range of spatial frequencies ( $${v}$$ = 0.02–128 μm–1) at ultrasmall etching depth (<100 nm) is demonstrated by atomic force microscopy with the application of the power spectral density function of roughness.

In this work, the formation of periodic nanostructures on the surface of potassium titanyl phosphate (KTP) has been demonstrated. The surface of KTP single crystals after the processing of argon cluster ions with different energy per cluster atom E/Nmean = 12.5 and 110 eV/atom has been studied using atomic force microscopy (AFM). To characterize the nanostructures, the power spectral density (PSD) functions have been used. The features of the formation of periodic nanostructures are revealed depending on the incident angle of clusters and different energy per atom in clusters.

Due to its distinctive features, gas cluster ion beams offer unique capabilities to improve the performance of optical devices based on nonlinear single crystals. In this work, the applicability of the argon cluster ion sputtering at different incident energies for finishing the LiB3O5 surface has been studied. It is demonstrated that a combination of high- and low-energy treatment modes (energy per atom of about 100 eV and several eV, respectively) provides an efficient etching rate comparable to that of a monoatomic ion beam. Besides, the surface roughness is reduced to the angstrom level in a wide range of spatial frequencies (nu = 0.3 100 mu m(-1)). Using XPS measurements, the preferential sputtering of oxygen and, to a lesser extent, boron, and an increase in the concentration of lithium cations in both modes were revealed. Although a chemical alteration of the treated materials could not be fully prevented, chemical and physical damages after a cluster bombardment are much less than that from a monoatomic ion beam.

A measurement method and a calculation algorithm based on the three-layer structure model have been proposed for the refractive index of optical materials. The method has been experimentally tested with refractive index standards. The uniqueness of the reconstruction of the refractive indices of the substrate and subsurface layer, as well as the thickness of the layer, from the measured reflection coefficient of probe radiation near the Brewster angle and the angle of normal incidence has been demonstrated numerically. The measurements of the refractive index of the subsurface layer with an absolute error of 10–4 and the thickness of the subsurface layer with a confidence error of 1 nm have been performed for the first time.

The formation of giant shallow craters was found on the surface of lithium triborate single crystals after the bombardment by argon cluster ions. The diameter of these craters varied from a few dozen nanometers to 500 nm that is more than an order of magnitude greater than the diameter of common gas cluster ion craters. As distinct from the craters produced by an individual cluster ion impact, anomalous ones were revealed only at the high ion fluence (i.e. at multiple overlapped cluster impacts), both in the high and low incident energy-per-atom bombardment modes (E/N = 105 and 10 eV/atom, respectively). Such anomalous sputtering can be a result of a high local energy release in the cluster-solid collision spots coupled with the presence of water molecules in the subsurface layer of hygroscopic borate-base single crystals.