High-energy Electron Diffraction Research Articles

Two-magnon scattering in a self-assembled nanoscale network of misfit dislocations

The static and dynamic properties of magnetic Pd/Fe(001) ultrathin film crystalline structures prepared on GaAs(001) templates were investigated by ferromagnetic resonance (FMR) from 10 to 73 GHz. It will be shown that the formation of a self-assembled nanoscale network of misfit dislocations in crystalline structures can be detected during the growth by fan-out diffraction features in reflection high electron energy diffraction. This network of defects leads to a strong extrinsic magnetic damping. The out-of-plane measurements of the FMR linewidth have revealed that the extrinsic damping is caused by two-magnon scattering. The contribution to the FMR linewidth from two-magnon scattering is strongly anisotropic and follows the rectangular symmetry of the glide planes of the misfit dislocation network. It will be shown that the observed strong anisotropy in two-magnon scattering can be interpreted by Fourier components of magnetic defects. The angular dependence of the Fourier components results in an effective channelling of scattered spin waves.

Morphologic, magnetic, and Mössbauer spectral properties of Fe 75Co 25 nanoparticles prepared by ultrasound-assisted electrochemistry

Nanopowders of Fe 75Co 25 alloys have been prepared by ultrasound-assisted electrochemistry. Their composition, crystallographic structure, morphology, have been studied by X-ray diffraction, transmission electron microscopy, X-ray fluorescence, and high-energy electron diffraction. The nanopowders are found to present a composition well determined by the electrolyte bath composition, they show a bcc structure. The iron and cobalt atoms exhibit a very homogeneous distribution in the particles. The magnetic properties of the nanopowders have been measured between 5 and 295 K with a vibrating sample magnetometer and their Mössbauer spectra have been obtained at 295 K. The saturation magnetization is characteristic of FeCo alloys. The magnetic behavior and transmission electron microscopy observations of the particles indicate strongly interacting particles with a radius of ca. 2–4 nm, particles which may form agglomerates of larger size. The measured average hyperfine field is situated at the maximum of the Slater–Pauling curve for the FeCo alloys.

Two-Step Growth of MgO Films on Sapphire (0001) Substrates byRadio Frequency Plasma-Assisted Molecular Beam Epitaxy

We report on the growth of rock salt MgO films on sapphire (0001)substrates by rf plasma-assisted molecular beam epitaxy. A two-stepmethod, i.e. high temperature epilayer growth after low-temperaturebuffer layer growth, was adopted to obtain the single crystal MgO film.The epitaxial orientation between the MgO epilayer and the sapphire(0001) substrate was studied by using in situ reflection high energyelectron diffraction and ex situ x-ray diffraction, and it is foundthat the MgO film grows with [111] orientation. The role of the lowtemperature buffer layer in the improvement of crystal quality of theMgO epilayer is discussed based on the cross-sectional scanningelectron microscopy.

電子回折で観察される縮退と臨界現象（２）

Bloch wave degeneracies, which can be observed in high-energy electron diffraction, are summarized. Critical voltages of non-systematic reflections for 4 beam and 5 beam cases, and zone axis critical voltage effect are discussed. Bloch wave degeneracy observed in non-symmorphic space group is explained. Pseudo-critical voltage effect observed in non-centrosymmetric crystal is also discussed. The experimental measurement of the degeneracy is mentioned briefly. Examples of application of the critical voltage effect for estimation of accurate structure factors are discussed.

Deposition and characterization of YBa2Cu3O7−δ/LaMnO3/MgO/TiN heterostructures on Cu metal substrates for development of coated conductors

In this paper a novel buffer layer architecture consisting of LaMnO3/MgO/TiN is proposed as a suitable structural and chemical template for the epitaxial growth of high-transition temperature (Tc) superconductors on Cu metal surfaces. Using techniques such as high-energy electron diffraction and scanning transmission electron microscopy, we present in situ and ex situ analyses of the buffer-layer and superconductor growth with focus on structural properties of the interfaces formed. While MgO is a good barrier to oxygen diffusion, we find that MgO alone is not a suitable buffer layer due to rapid Cu diffusion. Further, growth of MgO with a single epitaxy can be hindered by the presence of impurities such as S, which form strongly bonded superstructures on the metal surface. With the addition of a TiN layer as a barrier to Cu diffusion, oxide formation is suppressed, interfaces are clean, and a single cube-on-cube epitaxy is observed. While the Cu/TiN and TiN/MgO interfaces are rough, the MgO and LaMnO3 layers planarize the material, leading to growth of smooth YBa2Cu3O7−δ (YBCO). Residual strain in the YBCO film is 0.25% or less and does not lead to apparent cracking. The superconducting properties of the samples were investigated by electrical transport and magnetization measurements. For the first time, high critical current density (Jc) values are reported for YBCO films grown on (001) single-crystal and 100‹100›?textured Cu surfaces without intervening metal coatings. Jc on single crystal-like substrates is as high as 3.5 MA/cm2. Reduced Jc of approximately 1 MA/cm2 on rolled Cu tapes is limited by damage to the tape surface during the rolling process.

Quantitative Convergent Beam Electron Diffraction Measurements of Low-Order Structure Factors in Copper

Accurate low-order structure factors for copper metal have been measured by quantitative convergent beam electron diffraction (QCBED). The standard deviation of the measured structure factors is equal to or smaller than the most accurate measurement by any other method, including X-ray single crystal Pendellösung, Bragg gamma-ray diffraction, and high-energy electron diffraction. The electron structure factor for the (440) reflection was used to determine the Debye-Waller (DW) factor. The local heating of the specimen by the electron beam is determined to be 5 K under the current illumination conditions. The low-order structure factors for copper measured by different methods are compared and discussed. The new data set is used to test band theory and to obtain a charge density map. The charge deformation map shows a charge surplus between the atoms and agrees fairly well with the simple model of copper 2+ ions at the atomic sites in a sea of free uniformly distributed electrons.

Nanofaceting of LiNbO 3X-cut surface by high temperature annealing and titanium diffusion

The topmost surface of crystal during Ti-indiffused LiNbO 3 waveguide preparation was studied using atomic force microscopy and high energy electron diffraction. The formation of the flat terraces with high step ∼0.24 nm as a result of high temperature annealing has been detected. The global changing of surface morphology induced by Ti diffusing was observed. No new phase formation on the surface was detected.

Spontaneous and Electrodeposition of Pt on Ru(0001)

Abstract Pt was deposited onto a Ru(0001) electrode from a PtCl6 2−-containing HClO4 solution either electrochemically or spontaneously (i.e. without external current flow). Composition, structure and morphology of the deposit were studied by means of Auger electron spectroscopy (AES), high energy electron diffraction (RHEED), and scanning electron microscopy (SEM). At first pseudomorphic growth of a 2D-Pt adlayer takes place, while with higher coverages 3D-clusters develop for which the most densely packed [011]-rows of the Pt(111) planes are parallel with the most densely packed [1120]-rows of the Ru(0001) substrate. These Pt-clusters exhibit typical diameters between 2 and 10nm, while their average mutual separation varies with the total amount of deposit. If compared with the bare Ru(0001) surface, the samples with Pt deposits exhibit considerably enhanced activity with respect to electrooxidation of formic acid or methanol.

Temperature-induced structure instability and magnetism of Fe/Cu(100)

The structure and magnetism of epitaxially grown Fe films on Cu(100) at 300 K have been investigated in situ using high energy electron diffraction, low energy electron diffraction, scanning tunneling microscopy, and the magneto-optical Kerr effect. Based on a careful thickness calibration, the three well-known regions with distinct magnetic properties are determined accurately for Fe films on Cu(100). We claim that the traditional region II should be further divided into two parts II(1) and II(2), where the former remains region II in the traditional sense but the latter is a transition region between regions II and III. A theoretically predicted temperature driven Martensitic phase transition from face-centered-cubic (fcc) Fe to body-centered-cubic Fe is indeed realized in the transition region II(2).

Growth and structure of L10 ordered FePt films on GaAs(001)

The structural properties of epitaxial L10 ordered FePt(001) films, grown bymolecular beam epitaxy (alternating deposition of Fe and Pt atomic layers) onbuffer-Pt/seed-Fe/GaAs(001) have been studied by in situ reflection high-energyelectron diffraction and by ex situ x-ray scattering as a function of the growthconditions. Reflection high-energy electron diffraction intensity oscillations measuredduring FePt layer growth provide evidence for island growth at Ts = 200°C and quasi layer-by-layer growth at Ts = 350° C.From small-angle and wide-angle x-ray scattering it was found that the degree ofepitaxy depends critically on morphology of the seed layer and the substrateroughness. X-ray diffraction analysis showed that the long-range order parameterincreases from near zero for films grown at 200°C to 0.65 for films grown at 350°C.This confirms the fact that the order parameter is mainly determined by thesurface mobility of the atoms which is controlled experimentally by the substratetemperature.

Modification of the physical and chemical properties of GaAs/Ge surface epitaxy films by ion implantation

The influence of Ar + and Ba + ion implantation on the composition and structure of GaAs films is considered in this work. Information about the density distribution of the electronic states and the parameters of the energy bands of the ion-implanted GaAs films was obtained using Auger electron spectroscopy (AES), ultraviolet photoelectron emission spectroscopy (UPES) and high-energy electron diffraction (HEED).

Epitaxial electrodeposition of lead telluride films on indium phosphide single crystals

Epitaxial PbTe films were electrodeposited on (1 1 1) InP single crystals, from solutions containing Pb 2+ and Cd 2+ ions, the latter being largely in excess. High energy electron diffraction and X-ray diffraction reveal the formation of epitaxial films accompanied by the presence of polycrystalline PbTe. The poor epitaxy is related to a large lattice mismatch with the InP substrate. A low density of planar defects, compared with II–VI chalcogenides, is observed.

Electron diffraction investigation of catalytic particles at the tips of carbon nanotubes

Catalytic nickel particles at the tips of carbon nanotubes grown under different physicochemical conditions are experimentally studied by high-energy electron diffraction. The spacings of the crystal lattice are determined. It is demonstrated that the nanoparticles consist of a supersaturated solid solution of carbon in nickel with an abnormally high carbon content.

Structural studies of Langmuir–Blodgett films containing rare-earth metal cations

Comparative structural study of gadolinium stearate Langmuir–Blodgett (LB) films formed by monolayer deposition from either aqueous gadolinium acetate or gadolinium chloride solutions have been carried out. Structure of the films was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, high-energy electron diffraction, atomic force microscopy and scanning electron microscopy. It was found that when subphase pH had a value at which all monolayer stearic acid molecules were ionized and bound with Gd3+ cations (pH>5), the LB films deposited from gadolinium acetate and gadolinium chloride subphases had substantially different structure. The gadolinium stearate LB films formed with gadolinium acetate subphase were highly ordered and consisted of hexagonal layers with unit cell parameter a≈4.8 Å and interlayer spacing d≈49 Å. LB films formed with GdCl3 subphase under the same conditions (salt concentration, pH) were characterized by a rather disordered structure where along with hexagonal phase, a monoclinic phase with the interlayer parameter d≈40 Å was present. The reason of this phenomenon is discussed. The data obtained indicate that the control of multivalent metal cations complexes formation in the subphase and at the monolayer surface can be an instrument for optimization, the conditions to form metal-containing LB film with regulated structure and properties.

Discrete Mosaic “Spread” at the Surface of ZnSe Layers on GaAs(001)

Thin pseudomorphic ZnSe films can be grown by molecular beam epitaxy on GaAs(001) up to a layer thickness of about 100 nm. Above this critical thickness the topmost layers relax by forming large mosaic-domains which are tilted by 0.2° with respect to the macroscopic surface. This is evidenced by satellites arising in discrete directions close to the fundamental diffraction spots in high resolution low energy electron diffraction (SPA-LEED). Energy dependent SPA-LEED measurements were performed to characterize the satellites and identify their origin. High resolution X-ray diffraction (HRXRD) experiments indicate that this mosaicity is restricted to a near-surface region and does not penetrate deeply into the bulk of the ZnSe film.

Growth of epitaxial CoSi2 on 6H-SiC(0001)Si

Epitaxial growth of (111)-oriented CoSi2 has been achieved on a scratch-free 6H-SiC(0001)Si substrate. The surface was prepared using atmospheric hydrogen etching and ultrahigh vacuum Si cleaning. A high-quality CoSi2 thin film was obtained by a modified template method and co-deposition of Co and Si at 550 °C. The structure and morphology of the film is studied by means of reflection high electron energy diffraction, x-ray absorption fine structure, x-ray diffraction, and atomic force microscopy.

Epitaxial growth and interfacial structure of Sn on Si( [formula omitted])-(7×7)

Room temperature stabilization of up to 3.5 ML epitaxial metastable α-Sn at the Si(1 1 1)-(7×7) surface is reported. The α-Sn layers remain stabilized at the interface even after the deposition of thick Sn layers that undergo the α-Sn→β-Sn transformation. Additionally, a small decrease in the s-electron density at the 119 Sn nucleus is found for submonolayer of Sn at the Sn/Si(1 1 1)-(7×7) interface. The epitaxial relationship between thick β-Sn layers on Si(1 1 1) is also shown. The results were obtained by low and high energy electron diffraction and 119 Sn conversion electron Mössbauer spectroscopy.

Characterization of AlN/SiC Epitaxial Wafers Fabricated by Hydride Vapour Phase Epitaxy

AlN/SiC epitaxial wafers were fabricated using hydride vapor phase epitaxy. The thickness of AlN layer was varied from 0.1 to 0.5 μm. Surface of AlN layers was characterized by high-energy electron diffraction and atomic force microscopy. The crystal structure of AlN layers was studied using X-ray diffraction. The minimum value of the full width at half maximum of ω-scan (0002) reflection rocking curve was about 120 arcsec. The specific resistivity of AlN was measured in the temperature range from 300 to 700 K.

Observation of the fcc-to-bcc Bain transformation in epitaxial Fe ultrathin films on Cu3Au([formula omitted

A continuous fcc-to-bcc crystallographic transition via a homogeneous tetragonal lattice deformation (Bain transformation) with increasing Fe coverage was observed in molecular-beam grown epitaxial Fe ultrathin films on Cu3Au(001), contrary to the usual case of a discontinuous martensitic transformation of Fe. With increasing Fe film thickness, a continuous compression of the interlayer distance perpendicular to the film plane and a simultaneous continuous expansion of the in-plane atomic distance was observed. We did not find evidence for the coexistence of fcc and bcc phases. In the ∼1–12 ML (monolayer) thickness range, the films do exhibit some atomic disorder and do not grow pseudomorphous, but form twisted crystallographic domains that are rotated in the film plane about the film normal direction. The atomic volume of tetragonal states was found to follow closely face-centered tetragonal (fct) or body-centered tetragonal (bct) “epitaxial lines” according to strain-energy calculations [Surf. Rev. Lett. 1 (1994) 15], including a crossover from ferromagnetic high-moment high-volume fct to bct Fe. The results were obtained by in situ X-ray photoelectron diffraction, high-energy electron diffraction, and 57Fe conversion-electron Mössbauer spectroscopy. Correlated with the Bain transformation is a Fe spin reorientation from preferentially perpendicular (for fct) to in-plane (for bct) spin direction at 25 K.

Silicon-on-Insulator Structure Fabricated by Electron Beam Evaporation of Si on Porous Si and Epitaxial Layer Transfer

Epitaxial monocrystalline Si was grown on porous silicon by ultra-highvacuum electron beam evaporation. Results of reflection high-energyelectron diffraction, atomic force microscopy, cross-sectiontransmission electron microscopy and Rutherford backscatteringspectrometry and channelling (RBS/C) show that the epitaxial layeris of a good quality. Furthermore, silicon-on-insulator materials weresuccessfully produced by bond and etch back of porous silicon. Thequality of the silicon-on-insulator samples was investigated by RBS/Cand spreading resistance profiling. Experimental results show that boththe crystalline quality and electrical quality are good. In addition,the interface between the top Si layer and SiO2 buried layer is verysharp.