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Two-dimensional silicon (silicene) and germanium (germanene) have attracted special attention from researchers in recent years. At the same time, highly oriented pyrolytic graphite (HOPG) and graphene are some of the promising substrates for growing silicene and germanene. However, to date, the processes occurring during the epitaxial growth of silicon and germanium on the surface of such substrates have been poorly studied. In this work, the epitaxial growth of silicon and germanium is studied directly during the process of the molecular beam epitaxy deposition of material onto the HOPG surface by reflection high-energy electron diffraction (RHEED). In addition, the obtained samples are studied by Raman spectroscopy and scanning electron microscopy. A wide range of deposition temperatures from 100 to 800 °C is considered and temperature intervals are determined for various growth modes of silicon and germanium on HOPG. Conditions for amorphous and polycrystalline growth are distinguished. Diffraction spots corresponding to the lattice constants of silicene and germanene are identified that may indicate the presence of areas of graphene-like 2D phases during epitaxial deposition of silicon and germanium onto the surface of highly oriented pyrolytic graphite. [ABSTRACT FROM AUTHOR]

It is demonstrated that Kikuchi features become clearly visible if reflection high‐energy electron diffraction (RHEED) patterns are filtered using digital image processing software. The results of such pattern transformations are shown for SrTiO3 with mixed surface termination for data collected at different azimuths of the incident electron beam. A simplified analytical approach for the theoretical description of filtered Kikuchi patterns is proposed and discussed. Some examples of raw and filtered patterns for thin films are shown. RHEED patterns may be treated as a result of coherent and incoherent scattering of electron waves. The effects of coherent scattering may be considered as those occurring due to wave diffraction by an idealized crystal and, usually, only effects of this type are analysed to obtain structural information on samples investigated with the use of RHEED. However, some incoherent scattering effects mostly caused by thermal vibrations of atoms, known as Kikuchi effects, may also be a source of valuable information on the arrangements of atoms near the surface. Typically, for the case of RHEED, Kikuchi features are hidden in the intensity background and researchers cannot easily recognize them. In this paper, it is shown that the visibility of features of this type can be substantially enhanced using computer graphics methods. [ABSTRACT FROM AUTHOR]

The problems of growing short-period InAs/GaSb superlattices on GaSb (100) substrates by molecular-beam epitaxy are studied. For InAs/GaSb epitaxial heterostructures, a method for forming "InSb-like" atomically smooth interfaces with an ultrathin intermediate In(As)Sb layer is developed. This technique allowed growth of a short-period superlattice containing 50 InAs/GaSb periods. In situ growth control using high-energy electron diffraction and post-growth studies of the superlattice using atomic-force microscopy and X-ray diffraction confirm the efficiency of the technique for fabricating detector structures based on type-II superlattices. [ABSTRACT FROM AUTHOR]

We have optimized the growth conditions of the buffer layer for further deposition of Pb1–xSnxTe (x ≥ 0.4), which has the properties of a crystalline topological insulator. To this end, a three-component heterostructure consisting of CaF2, BaF2, and Pb0.7Sn0.3Te:In layers was formed and optimized on the Si(111) surface. The surface morphology of this structure was studied depending on the temperature growth regimes and the optimal combination of growth parameters was selected from the point of view of smoothness and crystalline quality. [ABSTRACT FROM AUTHOR]

This paper presents the results of studying the processes of epitaxial growth of germanium on silicon with crystallographic orientation (111) in a wide temperature range. The temperature dependences of the duration of the transition stage from the 7 × 7 to 5 × 5 superstructure and the values of the critical thickness of the transition from two-dimensional to three-dimensional growth in the range from 250 to 700 °C are determined using the reflection high-energy electron diffraction method. It was shown for the first time that the transition time from the 7 × 7 superstructure to 5 × 5 superstructure depends on the temperature of epitaxial growth. The region of low temperatures of synthesis, which has received insufficient attention so far, is also considered. [ABSTRACT FROM AUTHOR]

Thin film semiconductor sensors based on palladium oxide were produced to analyse the concentration of ozone in the air. The palladium oxide films were obtained by means of thermal oxidation of ~ 20-30 nm metal in air at various temperatures. The oxide films were studied using electron microscopy and reflection high-energy electron diffraction. The optical, electrophysical, and gas sensitivity properties of the films were investigated. The study determined the optimal oxidation annealing temperature that ensures the uniform composition of the films and absence of electrical noise affecting the gas detection process. The article explains that electrical noise in ultrathin films is caused by their fragmentation during oxidation annealing. The study demonstrated the high sensitivity of the obtained films to oxide

This work presents an in-situ technique to quantify the layer-by-layer roughness of thin films and heterostructures by measuring the spectral profile of the reflection high-energy electron diffraction (RHEED). The characteristic features of the diffraction spot, including the vertical to lateral size ratio c/b and the asymmetrical ratio c1/c2 along the vertical direction, are found to be quantitatively dependent on the surface roughness. The quantitative relationships between them are established and discussed for different incident angles of high-energy electrons. As an example, the surface roughnesses of LaCoO3 films grown at different temperatures are obtained using such an in-situ technique, which are confirmed by the ex-situ atomic force microscopy. Moreover, the in-situ measured layer-by-layer roughness oscillations of two LaCoO3 films are demonstrated, revealing drastically different information from the intensity oscillations. The experiments assisted with the in-situ technique demonstrate an outstanding high resolution down to ∼ 0.1 Å. Therefore, the new quantitative RHEED technique with real-time feedbacks significantly escalates the thin film synthesis efficiency, especially for achieving atomically smooth surfaces and interfaces. It opens up new prospects for future generations of thin film growth, such as the artificial intelligence-assisted thin film growth. [ABSTRACT FROM AUTHOR]

Selection and optimization of the technological parameters of growth of Pb0.7Sn0.3Te layers with a thickness up to 300 nm grown on a Si(111) surface at a temperature of 230 to 400°C is carried out. The surface morphology of the resulting films is studied, and the epitaxial relations are determined. It is shown that, depending on the growth temperature, the surface morphology ranges from smooth micrometer-sized islands with monoatomic steps on their surface to narrower terraces. [ABSTRACT FROM AUTHOR]

The paper is concerned with structural, morphological and magnetic properties of magnetite-silica magnetic fluids. The granulometric composition of the magnetic fluids was investigated by scanning and transmission electron microscopy, the phase composition was studied by X-ray diffraction and reflection high-energy electron diffraction, and magnetic properties were studied by vibrating sample magnetometry. In order to reveal the particle size distribution, dynamic light scattering and a proposed modification of depolarized dynamic light scattering were employed. The shape and dimensions of magnetic nanoparticles and also their aggregates are described. While the aspect ratio for the aggregates was 0.5–0.99, individual nanoparticles had an average aspect ratio of 0.9 and were nearly spherical. The sedimentation stability of a diluted magnetic fluid was also investigated. When the fluids were diluted 200 times, the stability was partially lost, and the nanoparticles aggregated, thereby forming clusters, and precipitated. [ABSTRACT FROM AUTHOR]

Atomically smooth (001) surfaces of SrTiO3 cut from the high-quality single crystals at two different miscut angles 0.9 and 7.0 deg between the real flat surfaces and crystallographic planes (001) were analyzed by means of the reflection high energy electron diffraction (RHEED) method from the room down to liquid helium temperatures. The diffraction patterns typical of the RHEED geometry close to ideal for a small miscut angle and those exhibiting distinct features of the specific periodicity associated with regular steps, which form due to the larger miscut angle, are presented. The surface symmetry and energetics were shown to impose differences in lattice parameters in parallel to a surface with respect to the bulk. This effect results in weak incommensurability between lattice parameters in surface layers and the bulk values relaxed due to step edges and misfit dislocations. The special surface nanostructures formed on the etched surfaces treated in chemically active solvents are also analyzed. The intrinsic nanostructures on single crystal surfaces open new prospects for applications when the ordered and controlled nanoscale architecture is required. [ABSTRACT FROM AUTHOR]

The smooth (001) surfaces of SrTiO3 (STO) single crystals were investigated by the reflection high-energy electron diffraction method in the temperature range from 5.5 to 300 K. The Raman scattering confirmed the high quality of STO samples. Five structural anomalies were found depending on temperature. The antiferrodistortive phase transition from the cubic structure to tetragonal, observed in the STO bulk at 105 K, on the surface extends from 70 to 120 K. The anomalies below 7 K and about 35 K are similar to those in the bulk considered as a crossover between the growth of the ferroelectric atomic displacements with decreasing temperature and quantum-mechanical stabilization of this growth due to the zero-point atomic motion. The other two anomalies are related only to a surface. Differentiation of lattice parameters depending on the depth from a surface revealed nonmonotonic changes, which could be used for detecting the structural transformations. The comprehensive understanding of the structural properties of ABO3 perovskite surfaces is important for elucidating the nature of the effects at the boundary of metallic ferromagnetism in similar materials. [ABSTRACT FROM AUTHOR]

The structural and phase changes induced by heat treatment (HT) and brief lamp processing (LP) in 70- and 1500-nm-thick Li–Nb–O films similar in elemental composition to LiNbO3, grown on the surface of unheated substrates (monocrystalline Si wafer and NaCl single crystal) by rf magnetron sputtering and ion-beam sputtering of a LiNbO3 target have been studied by reflection high-energy electron diffraction and X‑ray diffraction. The as-grown films were extremely nanostructured and consisted of crystalline lithium oxides, niobium oxides, and LiNbO3 as the product of reaction between them. We have demonstrated the conceptual feasibility of driving the synthesis of polycrystalline LiNbO3 films to completion using HT or brief LP. In the case of LP, LiNbO3 synthesis is three orders of magnitude faster than in the case of HT. [ABSTRACT FROM AUTHOR]

The structure and properties of the near surface layer of diamond after high-fluence irradiation at elevated temperatures with 30-keV Ar+, Ne+, N+, and C+ ions are studied. Dynamic annealing at temperatures above 500°С results in recrystallization of the diamond phase only in the case of irradiation with carbon ions, and irradiation with impurity ions causes graphitization of the ion-modified layer of diamond. According to Raman spectroscopy and reflection high-energy electron diffraction data, a nanographite structure is formed in the modified layer when irradiated with noble-gas ions. When irradiated with carbon ions, diamond grows and recrystallizes with a thin (~1 nm) graphite-like layer on the surface. In the case of nitrogen ions, a graphite layer is observed up to 720°С. Graphite-like layers on the surface of diamond are thermostable and, according to X-ray photoelectron spectroscopy, are layers of sp2 carbon. The Raman spectroscopy of visible light shows the different optical transparency of ion-induced structures on the surface of diamond, which correlates with the resistivities. The diamond structure disordered during ion irradiation at room temperature and the nanographite structure are more transparent than the graphite structure. [ABSTRACT FROM AUTHOR]

Experimental studies of the formation of a stepped surface structure during molecular-beam epitaxy of silicon on a Si (100) substrate have been carried out in wide ranges of variation of the substrate temperature and silicon growth rate. The conditions of the transition from a two-domain structure of the Si (100) surface to a single-domain structure associated with the formation of diatomic steps are determined using reflection high-energy electron diffraction. It is shown that the effect of an increase in the substrate temperature on the transition to a single-domain structure is non-monotonic: a single-domain surface forms in the region of relatively low temperatures, whereas a two-domain surface forms at high temperatures. The transition to a single-domain structure during the experiment is possible only, if the silicon growth rate is increased above a certain minimum value. [ABSTRACT FROM AUTHOR]

This work investigates the Si/Fe flux ratio (2 and 0.34) influence on the growth of β-FeSi 2 polycrystalline thin films on Si(100) substrate at 630 °C. Lattice deformations for the films obtained are confirmed by X-ray diffraction analysis (XRD). The volume unit cell deviation from that of β-FeSi 2 single crystal are 1.99% and 1.1% for Si/Fe =2 and Si/Fe =0.34, respectively. Absorption measurements show that the indirect transition (~ 0.704 eV) of the Si/Fe =0.34 sample changes to the direct transition with a bandgap value of ~0.816 eV for the sample prepared at Si/Fe =2. The absorption spectrum of the Si/Fe =0.34 sample exhibits an additional peak located below the bandgap energy value with the absorption maximum of ~0.36 eV. Surface magneto-optic Kerr effect (SMOKE) measurements detect the ferromagnetic behavior of the β-FeSi 2 polycrystalline films grown at Si/Fe =0.34 at T=10 K, but no ferromagnetism was observed in the samples grown at Si/Fe =2. Theoretical calculations refute that the cell deformation can cause the emergence of magnetization and argue that the origin of the ferromagnetism, as well as the lower absorption peak, is β-FeSi 2 stoichiometry deviations. Raman spectroscopy measurements evidence that the film obtained at Si/Fe flux ratio equal to 0.34 has the better crystallinity than the Si/Fe =2 sample. [ABSTRACT FROM AUTHOR]

For the growth of InN quantum dots by plasma-assisted molecular beam epitaxy (PA-MBE) via droplet epitaxy technique, the effects of nitridations processes (pre-nitridation on Si (111) substrate and post-nitridation to form InN quantum dots) have been discussed in this report. Pre-nitridation and post-nitridation processes cause lots of impact to the growth mechanism of InN quantum dots. Reflected-high energy electron diffraction (RHEED) analysis can show us the in situ surface condition and assist us to observe the formation of InN quantum dots during the epitaxy. The surface conditions of Si can be modified by the substrate pre-nitridation process, the nitrogen-terminal surface could influence the sticking coefficient and surface diffusion of indium atoms. InN quantum dots with pre-nitridation process grown at temperature 450 °C have relatively high dots density, broad size distribution, and shape in some preferred orientation. Meanwhile, the post-nitridation process of droplet epitaxy can reduce the dots density due to desorption, surface diffusion and aggregation phenomena. Finally, high-resolution transmission electron microscopy (HRTEM) provides the crystallinity of InN quantum dots, which is consistent with the result using RHEED. The InN quantum dots are crystallized as wurtzite structure with the lattice constant of 0.572 nm. The performance of quantum dots has been investigated by photoluminescence spectra with a peak at 1530 nm and a broad-peak around 1130 nm. [ABSTRACT FROM AUTHOR]

The development of growth techniques aimed at the fabrication of nanoscale heterostructures with layers of ferroic 3 d metals on semiconductor substrates is very important for their potential usage in magnetic media recording applications. A structural study is presented of single-crystal nickel island ensembles grown epitaxially on top of CaF2/Si insulator-on-semiconductor heteroepitaxial substrates with (111), (110) and (001) fluorite surface orientations. The CaF2 buffer layer in the studied multilayer system prevents the formation of nickel silicide, guides the nucleation of nickel islands and serves as an insulating layer in a potential tunneling spin injection device. The present study, employing both direct-space and reciprocal-space techniques, is a continuation of earlier research on ferromagnetic 3 d transition metals grown epitaxially on non-magnetic and magnetically ordered fluorides. It is demonstrated that arrays of stand-alone faceted nickel islands with a face-centered cubic lattice can be grown controllably on CaF2 surfaces of (111), (110) and (001) orientations. The proposed two-stage nickel growth technique employs deposition of a thin seeding layer at low temperature followed by formation of the islands at high temperature. The application of an advanced three-dimensional mapping technique exploiting reflection high-energy electron diffraction (RHEED) has proved that the nickel islands tend to inherit the lattice orientation of the underlying fluorite layer, though they exhibit a certain amount of {111} twinning. As shown by scanning electron microscopy, grazing-incidence X-ray diffraction (GIXD) and grazing-incidence small-angle X-ray scattering (GISAXS), the islands are of similar shape, being faceted with {111} and {100} planes. The results obtained are compared with those from earlier studies of Co/CaF2 epitaxial nanoparticles, with special attention paid to the peculiarities related to the differences in lattice structure of the deposited metals: the dual-phase hexagonal close-packed/face-centered cubic lattice structure of cobalt as opposed to the single-phase face-centered cubic lattice structure of nickel. [ABSTRACT FROM AUTHOR]

Abstract Ni nanocrystals (NCs) were embedded in BaTiO3 epitaxial films using the laser molecular beam epitaxy. The processes involving the self-organization of Ni NCs and the epitaxial growth of BaTiO3 were discussed. With the in situ monitoring of reflection high-energy electron diffraction, the nanocomposite films were engineered controllably by the fine alternation of the self-organization of Ni NCs and the epitaxial growth of BaTiO3. The transmission electron microscopy and the X-ray diffraction characterization confirmed that the composite film consists of the Ni NCs layers alternating with the (001)/(100)-oriented epitaxial BaTiO3 separation layers.

Abstract Si and Ge growth on the stripe-patterned Si (001) substrates is studied using in situ reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). During Si buffer growth, the evolution of RHEED patterns reveals a rapid change of the stripe morphology from a multifaceted “U” to a single-faceted “V” geometry with {119} sidewall facets. This allows to control the pattern morphology and to stop Si buffer growth once a well-defined stripe geometry is formed. Subsequent Ge growth on “V”-shaped stripes was performed at two different temperatures of 520 and 600°C. At low temperature of 520°C, pronounced sidewall ripples are formed at a critical coverage of 4.1 monolayers as revealed by the appearance of splitted diffraction streaks in RHEED. At 600°C, the ripple onset is shifted toward higher coverages, and at 5.2 monolayers dome islands are formed at the bottom of the stripes. These observations are in excellent agreement with STM images recorded at different Ge coverages. Therefore, RHEED is an efficient tool for in situ control of the growth process on stripe-patterned substrate templates. The comparison of the results obtained at different temperature reveals the importance of kinetics on the island formation process on patterned substrates.

The dielectric parameters of calcium fluoride films grown on the Si(100) surface by solid-phase epitaxy (group 2) and without it (group 1) are analyzed. It is established experimentally that the deposition mode of CaF films immediately after growth of the Si buffer layer at a substrate temperature of 530°C is not suitable for producing high-quality dielectric layers. The use of solid-phase epitaxy at the initial stage of the nucleation of CaF layers enables the production of single crystal uniformly thick films with high dielectric properties. [ABSTRACT FROM AUTHOR]

An advanced three-dimensional mapping approach utilizing reflection high-energy electron diffraction (RHEED) is introduced. The application of the method is demonstrated in detail by resolving the crystal structure and epitaxial relations of individual components within epitaxially grown magnetically ordered Co/MnF2/CaF2/Si(001) heterostructures. The electron diffraction results are cross-checked using synchrotron X-ray diffraction measurements. A number of advantages of the three-dimensional mapping technique as compared to conventional electron diffraction are demonstrated. Not least amongst these is the possibility to build arbitrary planar cross sections and projections through reciprocal space, including the plan-view projection onto the plane parallel to the sample surface, which is otherwise impossible to obtain. [ABSTRACT FROM AUTHOR]

The results of analysis of the oscillation intensity of RHEED specular reflection during the MBE growth of CaF/Si(111) structures in a wide temperature range from 100 to 600°С are presented. It is shown that the preliminary formation of a 2D Si buffer layer provides the two-dimensional growth of CaF layers. Possible reasons which for the disruption of 2D growth at high substrate temperatures are discussed. [ABSTRACT FROM AUTHOR]

In this report, self-organized indium nitride nanodots have been grown on Si (111) by droplet epitaxy method and their density can reach as high as 2.83 × 10 cm for the growth at low temperature of 250 °C. Based on the in situ reflection high-energy electron diffraction, the surface condition, indium droplets, and the formation of InN nanodots are identified during the epitaxy. The X-ray photoelectron spectroscopy and photoluminescence measurements have shown the formation of InN nanodots as well. The growth mechanism of InN nanodots could be described via the characterizations of indium droplets and InN nanodots using scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. The density of the InN nanodots was less than that of the In droplets due to the surface diffusion and desorption of atoms during the nitridation and annealing process. The average size and density of InN nanodots can be controlled by the substrate temperatures during the growth. For the growth at lower temperature, we obtained the higher density and smaller average size of InN nanodots. To minimize the total surface energy, the coarsening and some preferred orientations of InN nanodots were observed for the growth at high temperature. [ABSTRACT FROM AUTHOR]

The InGaN thin films with indium content of x = 14-18 at.% were successfully grown by using molecular beam epitaxy (MBE) at high growth temperatures from 650°C to 800°C. In situ reflection high-energy electron diffraction (RHEED) of the InGaN films confirmed the Stranski-Krastanov growth mode. X-ray diffraction (XRD) of the films confirmed their highly crystalline nature having c-axis orientation with a small fraction of secondary InN phase admixture. High-resolution cross-sectional scanning electron microscopy images showed two-dimensional epilayers growth with thickness of about ∼260 nm. The high growth temperature of InGaN epilayers is found to be favorable to facilitate more GaN phase than InN phase. All the fundamental electronic states of In, Ga, and N were identified by x-ray photoelectron spectroscopy (XPS) and the indium composition has been calculated from the obtained XPS spectra with CASAXPS software. The composition calculations from XRD, XPS and photoluminescence closely match each other. The biaxial strain has been calculated and found to be increasing with the In content. Growing InGaN at high temperatures resulted in the reduction in stress/strain which affects the radiative electron-hole pair recombination. The InGaN film with lesser strain showed a brighter and stronger green emission than films with the larger built-in strain. A weak S-shaped near band edge emission profile confirms the relatively homogeneous distribution of indium. [ABSTRACT FROM AUTHOR]