Reflection High-energy Electron Diffraction Observations Research Articles

In situ electron beam irradiation induced in-plane orientation of europium thin film grown by the molecular beam epitaxy technique

Europium thin films were grown on various substrates by the molecular-beam epitaxy technique. X-ray diffraction and in situ reflection high-energy electron diffraction observations revealed that the europium thin films possessed a textured structure with Eu(110) planes which were self oriented parallel to the substrate, independent of the type of substrate. In situ electron-beam irradiation induced transformation of the textured Eu(100) plane to the [111] in-plane orientation. Thus, using this method europium thin films could be locally crystallized to a single phase at growth temperatures above 170 K. It was found necessary to use electron-beam irradiation during the initial growth stage in order to obtain the in-plane orientation.

In situ monitoring of step arrays on vicinal silicon (100) surfaces for heteroepitaxy.

Ordered step arrays on vicinal Si(100) surfaces have been observed with use of reflection high-energy electron diffraction (RHEED). For a 3\ifmmode^\circ\else\textdegree\fi{} misorientation toward a 〈100〉 direction, a stable single-layer step structure is observed. Evidence of a kinked step structure is found for the misorientation toward 〈100〉, with one of the samples showing randomly spaced kinks, and others having regularly spaced kinks along the step edges. For misorientations of up to 3.7\ifmmode^\circ\else\textdegree\fi{} toward a 〈110〉 direction, a step-induced structure which becomes more pronounced for higher misorientation angles is observed in the RHEED patterns. The RHEED observations indicate a transition from single-layer to double-layer steps as the tilt angle toward 〈110〉 is increased.

Growth processes in the initial stage of Ge films on (811)Si surfaces by GeH4 source molecular beam epitaxy

The growth process in the initial stage of growth of Ge films on (811)Si substrate surfaces by GeH4 source molecular-beam epitaxy has been studied by in situ reflection high-energy electron diffraction observation. It has been found that a strained film by the monolayer overgrowth mode is formed initially with an epitaxial relationship of the parallel orientation, and that plate-shaped Ge islands with (811) facets are grown early in the growth, but that the predominant facet changes to {311} and the (100) planes with further growth. These growth processes are similar to those of Ge films on (100)Si surfaces reported previously. It is concluded that Ge islands with {811} facets are energetically stable in the initial stage of the island growth on the (811)Si surfaces as well as on the (100)Si surfaces.

Molecular-beam epitaxial growth of metastable Ge1−xSnx alloys

Substrate-stabilized, metastable, single-crystal Ge1−xSnx films can be grown by molecular-beam epitaxy (MBE). We have grown for the first time single crystal Ge1−xSnx alloys on lattice matched GaSb (with x=0.5) and InP (with x=0.26) substrates up to a thickness of 0.3 μm. Reflection high-energy electron diffraction (RHEED) observations and x-ray measurements show that even at very small lattice mismatch (less than 0.05%), single crystal Ge1−xSnx films cannot be grown thicker than 0.3 μm. Our x-ray results suggest that the critical thickness of α-Sn and Ge1−xSnx single crystal films is mainly determined by a phase transition mechanism, and the dislocation generation equivalent critical thickness is an overestimate. Under practical MBE growth conditions, it is very difficult to grow thick films, due to the sensitivity of the critical thickness to composition fluctuations. We have shown that even under an exact lattice match between substrate and film, the critical film thickness is limited.

Low-temperature growth of ZnSe by molecular beam epitaxy using cracked selenium

The growth of zinc selenide by molecular beam epitaxy using a cracked selenium source is studied. It is found that high quality growth can be achieved at substantially lower substrate temperatures than has been possible using uncracked selenium sources. It is determined from reflection high-energy electron diffraction observations that the use of cracked selenium produces growth dominated by a two-dimensional mechanism at substrate temperatures as low as 225 °C and that exposure of the GaAs substrate to cracked selenium prior to the initiation of growth has a substantial effect on the GaAs substrate and the early stages of ZnSe growth.

Structural and magnetic characteristics of Eu/Mn and Eu/Yb superlattices prepared by the MBE technique

Eu/Mn and Eu/Yb superlattices were grown by the molecular beam epitaxy technique. X-ray diffraction and in situ reflection high-energy electron diffraction observations revealed that the Mn layers were always present in an amorphous state, while the Eu layers changed from amorphous to [110]-oriented crystal with a textured structure as the thickness increased. The high temperature bcc-Yb phase was stabilized by the epitaxial relationship with Eu layers. Amorphous Eu/Mn superlattices with short periodicity cooled under zero-field possesed magnetic-frozen states associated with the Eu interlayer interaction and interfacial interaction between the Eu and Mn layers.

Low temperature growth and properties of YBCO single-crystal films

Single-crystal YBa 2Cu 3O 7− x thin films with T c =90 K have been prepared on SrTiO 3(100) at relatively low temperatures by activated reactive evaporation. X-ray examination revealed that the c-axis of the 1000Å thick film was perfectly perpendicular to the SrTiO 3(100) face and the film consisted of microdomains whose structure was orthorhombic. The in-situ reflection high-energy electron diffraction observation during growth of the film on SrTiO 3(100) and MgO(100) suggests that the initial deposition on both the substrates occurs in the layer-to-layer growth manner. The in-plane lattice spacing of deposit on MgO converted from the bulk value of MgO to that of YBCO while the thickness increased from 12 Å to 24 Å. Some superconducting and surface-structural properties are also reported.

Initial stage of epitaxial growth of YBa 2 Cu 3 O 7-x thin films

Abstract Initial stage of the epitaxial growth of YBa 2 Cu 3 O 7-x thin films on MgO(100) was investigated by means of in situ reflection high energy electron diffraction (RHEED) and X-ray diffraction. In situ RHEED observation showed that the formation of the perovskite structure occured even at initial deposit and the growth manner was layer by layer. The lattice spacing of YBCO converted from the bulk value of MgO to that of YBCO when the layer became thicker than 12 A. X-ray analysis revealed that a 100 A thick YBCO film had the orthorhombic structure.

Heteroepitaxial growth of Y2O3 films on silicon

Yttria (Y2 O3 ) films have been grown on Si (100) and Si (111) substrates heated at 800 °C by vacuum evaporation. X-ray diffraction and reflection high-energy electron diffraction observations reveal the heteroepitaxial growth of Y2 O3 films on Si (100) and Si (111) substrates. The (111) oriented Y2 O3 films are grown directly on Si (111) substrates. The (100) oriented Y2 O3 films are grown on the thin (Y2 O3 )0.09 (ZrO2 )0.91 layer predeposited on Si (100) substrates instead of direct growth on Si (100) substrates.

Evaluation of crystalline quality of heteroepitaxial yttria-stabilized zirconia films on silicon by means of ion beam channeling

Yttria-stabilized zirconia (YSZ) films have been deposited by vacuum evaporation on Si(100) substrates heated at 800 °C. Rutherford backscattering spectra of the YSZ films show that they are epitaxially grown on the Si(100) substrate, which is consistent with x-ray diffraction and reflection high-energy electron diffraction observations. The spread of crystallite orientation in the epitaxial film is estimated to be 0.22°, by analyzing the angular dependence of the total backscattering yield. The dominant defect is suggested to be a stacking fault by dechanneling ion energy dependence measurements and 30% of the oxygen atoms are displaced from the oxygen sublattice site.

I n s i t u scanning microprobe reflection high-energy electron diffraction observation of GaAs surfaces during molecular-beam epitaxial growth

A specially designed molecular-beam epitaxy (MBE) system with scanning microprobe reflection high-energy electron diffraction (RHEED) has been developed. The incident electron beam is designed to focus down to 10 nm in diameter and scan the surface of the substrate under MBE growth conditions. Using the RHEED intensity variation produced by the scanning of the incident beam, we obtain a microscopic image, i.e., which is the scanning reflection electron microscope (SREM) image, highly sensitive to the surface structure. The SREM images of GaAs(001) using the specular beam spot revealed granular features over the entire surfaces of MBE-grown GaAs layers which come from undulations of the surface. The undulation wavelength was typically 0.1–0.5 μm and developed along [1̄10] direction during MBE growth at 570 °C. At higher substrate temperatures, little development of the undulation was observed. As an overall feature of MBE growth, two-dimensional layer-by-layer growth was observed over the whole surface having undulations.

Structural and magnetic studies of an artificial Eu/Mn superlattice

Artificial superlattice materials composed of alternating layers of europium and manganese metals with a periodicity in the range of 19–227 Å were prepared by means of molecular-beam epitaxy. In situ reflection high-energy electron diffraction observations revealed that the Eu metal layer is amorphous up to a thickness of 23 Å, while a [110]-oriented single-crystal Eu layer grows over the amorphous Eu layer as the thickness exceeds 23 Å. On the other hand, the manganese layers were found to always be in an amorphous state independent of the thickness. The synthesized Eu/Mn systems exhibited a unique magnetic property associated with a magnetic interaction between the amorphous Eu layers.

Electron and x-ray diffraction study of ZnTe-ZnS strained-layer superlattices grown by molecular beam epitaxy

Reflection high-energy electron diffraction observation during the growth of ZnTe-ZnS strained-layer superlattices shows that sharp streaks of the substrate were replaced by a spotty pattern which eventually elongated into streaks. X-ray diffraction data of the superlattice with small period show satellite peaks around an intense central peak. These studies indicate a good superlattice structure for the samples with small (<50 Å) periods.

Rheed Observation of Lattice Relaxation During Ge/Si(O01) Heteroepitaxy

ABSTRACTWe report the dynamic RHEED (reflection high energy electron diffraction) observation during Ge/Si(001) heteroepitaxy at various growth temperatures. The RHEED intensityanalysis and the in-plane lattice constant analysis reveal a growth fashion and lattice relaxation. Both of them depend strongly on growth temperature.

Antiphase Defect Reduction Mechanism in Mbe Grown Gaas on Si

ABSTRACTIt is shown that antiphase boundary (APB) is annihilated during the growth, by monitoring the surface with reflection high energy electron diffraction (RHEED). The RHEED observation indicates that double domain GaAs changes to single domain within a thickness of 100 nm, while the transition region is estimated to exist within 200 nm from GaAs-Si interface by scanning electron microscope (SEM) observation of etch pits on vicinally polished surface. The self-annihilation mechanism of APB is discussed from these results.

Chemical dry etching of GaAs and InP by Cl2 using a new ultrahigh-vacuum dry-etching molecular-beam-epitaxy system

Damage and contamination-free chemical dry etching of (100)GaAs and (100)InP by Cl2 was demonstrated using a new ultrahigh-vacuum dry-etching molecular-beam-epitaxy (MBE) system. This system consists of a combined etching chamber, an MBE chamber, and a sample preparation chamber, all at ultrahigh vacuum. A mirrorlike surface was obtained after etching at substrate temperatures ranging from 300 to 400 °C for GaAs, and from 200 to 400 °C for InP. In situ reflection high-energy electron diffraction observations were accomplished for GaAs, with a mirrorlike surface after etching, and (2×4) surface reconstruction was observed. Results show that a smooth surface was formed at an atomic level.

Reflection high-energy electron diffraction observations during growth of ZnS xSe 1− x(0 ⩽ x ⩽ 1) by molecular-beam epitaxy : H J Cornelissen et al, J Vac Sci Technol, B6, 1988, 769–772

Reflection high-energy electron diffraction observations during growth of ZnS xSe 1− x(0 ⩽ x ⩽ 1) by molecular-beam epitaxy : H J Cornelissen et al, J Vac Sci Technol, B6, 1988, 769–772

Ｉｎ‐ｓｉｔｕ ＲＨＥＥＤによるＹＢａ２Ｃｕ３Ｏ７−ｘの結晶成長観察

Epitaxial growth of (001) oriented YBa2Cu3O7-x(YBCO) on SrTiO3(100) and MgO(100) by activated reactive evaporation was investigated by insitu reflection high energy electron diffraction (RHEED). RHEED observation of the YBCO films on both the substrates demonstrated the formation of the perovskite structure even at initial deposit. A sharp streak in every deposition stage revealed the layer-by-layer growth. The initial deposit on the substrate of MgO with the large mismatch of 9% kept the same in-plane lattice spacing as MgO. The lattice spacing converted from the bulk value of Mg0 to that of YBCO when the layer became thicker than 12A.

Tunneling images of gallium on a silicon surface: Reconstructions, superlattices, and incommensuration.

Real-space images of an incommensurate superlattice on a monolayer-gallium-covered silicon (111) surface have been obtained with the tunneling microscope. Large, internally ordered supercells which in turn form a lattice with discrete boundaries are observed. A graphitelike silicon-gallium top layer is suggested that is weakly bonded to the lattice below and stabilized by a periodic array of misfit dislocations. This model unifies reflection high-energy electron diffraction, x-ray standing-wave, and tunneling observations.

The effects of temperature and bias illumination on the spectral sensitivity of CdS-Cu xS heterojunctions

The effects of temperature and bias light illumination on the spectral response of single crystal CdS-Cu x S devices have been studied and correlated with the structural information obtained from reflection high energy electron diffraction (RHEED) patterns. The work demonstrates that the identification of the phase of Cu xS from the spectral sensitivities of devices is in closer agreement with the RHEED observations when the measurement of the response is made at 85 K rather than 295 K. This is because the response due to copper centres is diminished at the lower temperature and that of copper sulphide is enhanced. It is thus essential to be aware of this temperature dependence of spectral response when identifying the phase of Cu x S in devices based on thin films of CdS, where RHEED patterns are complicated by the polycrystallinity of the layers. This is demonstrated by a study of cells based on thin films which were deposited by thermal deposition over a wide range of substrate temperatures.