On the basis of results of surface structure analyses by reflection high-energy electron diffraction(RHEED) with dynamical calculations, adsorption processes on Si(111) surface are discussed. On adsorption processes on Si(111)7×7 surface at room temperature, adatom bonds of the dimer-adatom-stacking-fault(DAS) structure are broken by adsorbed atoms and the structure changes into other 7×7 one called δ7×7. At the transition into the δ7×7 structure the dimer-stacking-fault(DSF) frame work is preserved. From rocking curve analyses during adsorption of Li and Si, back bonds of the adatoms of ])AS structure are cut off in the initial stage of the adsorption at about 0.2 monolayer coverage of the adsorbates. Metal adsorbed δ7×7 structures axe unstable and changes into structure by heating at about 300 °C with dissolution of the stacking fault layer into the normal stacking arrangement. During homoepitaxial growth of Si on Si(111)7×7 surface at about 300 °C, a new metastable surface structure is foundby RHEEDdynamical analysis. This structure is concluded as pyramidal cluster structure formed on the DSF frame work. It is discussed that formation of metastable structure promotes transition to from the 7×7, and promotes successive epitaxial growth accompanied with stacking fault dissolution at the DSF frame work.

We present the processes necessary for the development of a lensless electron microscope with a resolution of ≤ 0.6Å and an image position accuracy of ≤ 0.3Å. The technique inverts interference fringes of emitted electrons from localized sources embedded in a material. Unlike conventional methods which use the Helmholtz-Kirchhoff integral theorem, the new process starts with 3-dimensional Fourier transformation with phaseshift correction, SWEEP for forward-scattering electrons and REEP for back-scattering electrons. These processes are applicable to strong multiple scattering systems as well as systems whose source atoms are buried below the surface. Materials with long-range or local order can be studied; coupled to a small spot-sized incident beam, images of disordered materials can be formed.

We have studied the surface structure of Cu(110) from 153 to 973 K. Reflection high energy electron diffraction (RHEED) was employed to analyze the surface modifications taken place at the crystal surface. We performed careful spot profile intensity measurements as a function of temperature.The typical characteristics of forward scattering, the short wavelength at high energy, and the small grazing incidence angle in RHEED provide strong surface sensitivity and are therefore ideal to study surface structures and especially surface roughness. We observe at low temperatures strong diffraction streaks in the patterns as well as Kikuchi lines. The diffraction intensities reduce slowly when the temperature is raised from 153 K to 473 K, then fall off more rapidly after that, and from 573 K, the intensities decrease drastically. High resolution LEED measurements indicate a reduction in the coherence length at high temperatures.

We investigate the evolution of the microstructure of a reconstructed Au (001) single crystal surface using ultra high vacuum transmission electron microscopy (UHV-TEM). Bulk single crystal Au (001) surfaces were prepared via standard metallographic techniques and sputter anneal cycles. After a clean surface was obtained, the (001) surface was found to reconstruct into two nearly orthogonal domains of dimensions (5 × ∼ 20 ) along the <110> directions of the unreconstructed F.C.C. (001) surface. Transmission electron diffraction patterns (TED) and dark field microscopy are the two primary techniques used to determine the symmetry and dimensions of the reconstructed surface.

RHEED intensity oscillations have been observed during the epitaxial growth of layered NbSe2, MoSe2 on GaAs(111) substrates. Monolayer- and bilayer- mode oscillations have been observed at different diffraction points. The existence of bilayer-mode oscillation is interpreted as showing the polytype of the grown films. The present report demonstrate the utility of RHEED oscillation for analyzing the structure of ultrathin films of layered materials. The epitaxial growth of TaSe2 on layered substrates is also reported.

We have examined the behaviour of the clean Si (111) 7x7 reconstructed surface during exposure to oxygen over a range of temperature and pressure in a UHV transmission electron microscope (TEM). We present preliminary results of our study, discussing both the etching of the silicon surface by oxygen at elevated temperatures and lower oxygen pressures, and its roughening and oxidation at higher oxygen pressures. We achieve great sensitivity to the structure of the surface monolayers by analysing the diffraction of high energy electrons by these surface layers and can resolve the movement of individual monatomic surface steps. Our most dramatic result to date is a demonstation that surface steps do not move during the growth of native oxide.

We present elastic He-beam scattering data of the Pd(111)/H system. Diffraction intensities were measured as a function of surface temperature in the range 140°K–320°K. Two remarkable features are observed : the first is the presence of C3v symmetry at (1 × 1) saturation coverage (140°K) and its transformation to C6v symmetry at lower coverages (270°K). The second feature is the anomalous attenuation of the specular He beam accompanying this transformation. Taken together these features provide strong evidence of a fundamental change in the surface charge density corrugation. A classical interpretation of the motion of hydrogen either fails to reproduce the measured attenuation or leads to contradictory and unphysical conclusions regarding the H-metal bond length or surface equilibrium. An alternative quantum mechanical interpretation is developed and is shown to provide consistent and satisfactory explanation of the measurements.

EXtended Electron Energy Loss Fine Structure (EXELFS) spectra have been obtained above the K-edge of nitrogen atoms adsorbed on Cu. The radial distribution functions obtained from the fine structure indicate N-Cu bond lengths of 1.84(±.03) Å and 1.81(±.03) Å for nitrogen on the Cu(100) and Cu(110) surfaces respectively. As in previous EXELFS measurements, the actual measurements made are of N"(E) rather than direct measurement of N(E), the electron energy loss distribution. The EXELFS spectra from these two surfaces are used to illustrate the influence of this collection scheme on the radial distribution function obtained by Fourier transformation of the raw data. To obtain the direct analog of the radial distribution function found from the EXAFS experiment one must either resort to spectral integration or appropriate scaling of the distribution function found in the EXELFS experiment.

Helium atom diffraction yields a wealth of information complementary to that obtainable from other experimental surface sensitive techniques. Atomic He scattering is extremely sensitive to surface defects. Also time of flight measurements enable energy transfer processes to be studied. An analysis of the energy broadening in quasi-elastic scattering can yield information on surface diffusion coefficients and may also be used to investigate diffusion mechanisms. The paper reviews how intensities of both coherent and incoherent scattering can be employed to study the kinetics of ordering at surfaces.

We review two different experiments in order to demonstrate the power of grazing incidence diffraction of x-rays in studying phase transitions near surfaces and to show that it is well suited to get information on structural details even from subsurface layers: We have measured the near surface critical scattering at the continuous order disorder transition of an Fe3Al single crystal which provides information on modifications of critical behavior of a bulk transition near a surface. These modifications are detectable to a considerable depth due to the diverging range of correlations. We determined three different critical surface exponents which allow, for the first time, to confirm scaling laws for near surface critical behavior.- The experiment at a (100) surface of a discontinuous ordering Cu3Au single crystal shows that the surface is wetted by a disordered layer below the transition temperature. By means of the adjustable depth sensitivity of grazing incidence scattering we were able to demonstrate that the thickness of this layer increases logarithmically when approaching the transition temperature.

We have used neutral helium beam scattering to probe structural and thermodynamic properties of in-situ deposited ultra-thin films of metals on well characterized substrates. We show the capabilities of this technique by presenting some recent results of our studies of Hg adsorption of Cu(001) and on monolayer phases of Pb on Cu(001).

Replacement of the pinhole collimator on a double axis X-ray diffractometer with a device incorporating a channel-cut crystal permits the beam to be pre-conditioned in angular divergence. We examine the merits of such devices, known as channel-cut collimators (CCC's), of different materials and reflections. The experimental performance of InP 004 and Si 022 CCC's is presented.

With a reference crystal on the first axis, set in the dispersive peometry with respect to the CCC, conditioning in wavelength spread is achieved. Dispersion broadening is effectively eliminated and no resetting of the reference crystal is required when changing specimen materials or reflections. The devices have extremely low background and reduced Bragg tails. Application of the 4-reflection CCC to rocking curve analysis of thin epitaxial layers, ultra-low angle scattering from biological systems, grazing incidence reflectometry and triple axis diffraction of semi-conductors is discussed.

PC-based software for the rapid simulation of double-axis X-ray rocking curves from epitaxial thin films by solution of the Takagi-Taupin equations is described. The principles of the mathematical model are discussed. Graded layers and interface roughness are treated by piece-wise approximation to linear or quadratic functions and fractional relaxation of each epilayer may be included. The reliability of the data-bases incororated are examined and the requirement for internal consistency demonstrated. Bench-mark tests are reported for various PC-compatible microcomputers. The shift in epilayer peak position, which occurs experimentally on reducing layer thickness at constant composition, is predicted in the simulations and compared with other simulated data in the literature. Detailed studies of generated data have been undertaken and compared with independent simulations and experimental data. Agreement is excellent.

A new desk-side double-axis X-ray diffractometer capable of rapid, automatic measurement of lattice mismatch between epitaxial thin films and substrate in a two dimensional grid 150 mm square has been built. The design principles behind the five independent axis systems, specimen loading, and the fail-to-safety X-ray shutter are elucidated, and examples of typical data from substrate material and thin epitaxial films of III-V compounds are presented.

Some of today's most promising and interesting semiconductor devices use only a few thin epitaxial layers of III-V materials, where each layer may be only 100 to 1,000A thick. There is a need for fast, accurate, non-destructive analysis techniques for these structures. Double-crystal x-ray diffraction has proven to be an excellent method for measuring composition, thickness, interface sharpness, and overall crystalline quality of III-V heterostructures. Data is presented on the use of a Bede QC1 automated table-top double-crystal diffractometer for the analysis of (AI,Ga)As, (ln,Ga)As, and GaAs epitaxial layers grown by Molecular Beam Epitaxy (MBE). It is shown that this technique can directly detect and analyze single layers of (In,Ga)As as thin as 200A, and in some cases, can indirectly detect layers of GaAs or (AI,Ga)As as thin as 100A without unusual measures such as glancing angle diffraction. The rocking curve results are compared with values predicted by RHEED intensity oscillation measurements, and with computer simulations using a commercial software package.

The characteristics of Si+ implanted into SI GaAs and its annealing behavior have been studied by x-ray double-crystal diffraction method. Results show that there is much information on strain contained in the rocking curves. When implanting at low doses, most of the implanted Si+ is in interstitial positions in the GaAs, and this produces tensile strain. After annealing, most of the implanted Si+ can be activated and the strain can be relieved. But when implanting at large doses, the strain can not be completely relieved even after annealing at high temperature

Thin films of zirconium dioxide are deposited by e-beam evaporation on optically polished borosilicate crown glass. Two different oxygen partial pressures in the chamber are used. The optical properties of the films are characterized by ellipsometry. The influence of oxygen stoichiometry on the composition and microstructure of the material is investigated by polycrystalline X-ray diffraction for different film thicknesses. The films are found to be inhomogeneous, and a composition gradient (i.e. amorphous ⇔ tetragonal ⇔ monoclinic) is observed from the substrate to the surface. The oxygen partial pressure influences the growth of the films.

Multilayer structures composed of alternating, ultrathin layers of Ru and B4C have been fabricated using DC magnetron sputtering. These multilayers are potentially important as normal incidence x-ray reflectors at wavelengths above the boron K-absorption edge at 65Å. The detailed structure of the layers has been characterized using x-ray diffraction and high-resolution transmission electron microscopy. It is found that, under optimized deposition conditions, continuous layers can be grown that have smooth and abrupt interfaces. The normal incidence reflectivity at x-ray wavelengths of ∼70Å has been measured, and values as high as 20% have been obtained.

A new boundary condition is used in the kinematical x-ray diffraction model analysis of rocking curves. The boundary condition is the dynamical reflection amplitude instead of the previously used dynamical intensity for the substrate. It is shown that this boundary condition properly accounts for the angular shift effect in the Bragg peak profile of very thin epitaxial layers and in the 0th-order superlattice peak. We present experimental and simulated rocking curves for various samples. The simulation was performed by using the dynamical diffraction theory, the kinematical model with the new amplitude boundary condition, and the kinematical model with the old intensity boundary condition. We also analyzed the strained resonant tunneling device structure and single strained quantum well samples by x-ray interference technique. Our x-ray interference results showed a good agreement with the nominal values for both experimental and simulated rocking curves.

Reflection electron microscopy (REM) was applied to image in-situ the dynamic changes of atomic-height steps on the surfaces of a-alumina bulk crystals heated to high temperatures. Atomic diffusion, desorption and adsorption processes on cleaved a-alumina (012) surfaces were directly observed at temperatures of 1470 to 1670 K. The surface started to show visible structural changes at 1470–1520 K. The main surface process appears to be atomic desorption, which creates large, flat vacancy-type terraces on the surface.