X ray techniques have enabled a fast characterisation of a new VG Semicon V90S MBE system for growth of Si and SiGe material. X-ray rocking curves have allowed characterization of SiGe layers to tolerances as tight as ± 0.1 At%. X-Y uniformity measurements demonstrated that layers are grown to ± 0.5 % over a 150 mm wafer. Information on the flux rate uniformity during growth can be obtained from analysis of superlattice structures. These enable calculation of “worst case” flux variation during a growth run. An empirical relationship has been found that enables the prediction of the degree of residual strain remaining in a buffer structure grown beyond the metastable critical thickness.

The emergence of synchrotron radiation sources has greatly stimulated the use of X-ray scattering in surface science. The absence of multiple-scattering effects allows a straightforward data analysis. In addition to determining geometric structures, it is also possible with X-ray scattering to obtain information on various types of surface disorder. The large penetration depth enables the investigation of interfaces.

We report the results of our x-ray diffraction studies on epitaxial Al(lll)/Si(lll) films prepared by the partially ionized beam deposition technique. Significant changes were observed in intensity profiles for samples before and after annealing. In the in-plane radial scan of Al(220) peak, the shift of Bragg peak is shown due to misfit strain. A weak satellite is also observed which indicates a semicoherent interfacial structure of the annealed film with misfit dislocations. A possible picture of misfit-induced incommensurate structure of Al films is discussed.

A microscopic strain distribution across commensurate interfaces between GaAs layers grown on semi-insulating GaAs substrates was observed by means of convergent beam electron diffraction (CBED) and large angle convergent beam methods (LACBED). Strain relaxation at a specific distance from the interface was observed in these layers without formation of misfit dislocations. It was proposed that specific point defects distributed close to the interface can explain the asymmetric broadening of high-order Laue zone (HOLZ) lines in the CBED patterns.

High resolution plan view images of clean and Au deposited Si(111) surfaces are presented. Corner holes and small holes between dimers of the DAS model of the 7×7 structure were clearly resolved. In the case of the Si(111)5×1-Au structure the 5 times period fringes did not show fine details.

Homoepitaxy on the {111} face of GaAs has been long known to give films with surfaces marred with macroscopic features. We have identified this problem to be tied to the surface phase regime. We have used Reflection High Energy Electron Diffraction (RHEED) to identify a phase regime wherein specular-surfaced GaAs films can be grown. We have found that it is possible to glean information regarding the macroscopic surface morphology by monitoring the variation in the RHEED specular spot intensity during growth. This has allowed in situ monitoring of the macroscopic surface morphology of a growing film in real time which has made it possible to grow specular-surfaced films reproducibly.

The surface structure of epitaxial Nisi2 films grown on Si(111) has been determined using a new method. The backscattering signals from subsequent Ni layers in the Nisi2 (111) surface are resolved.

The topology of the Nisi2(111) surface is concluded to be bulklike, i.e., it is terminated by a Si – Ni – Si triple layer.

Relaxation modeling for strained epitaxial films depends strongly on the acquisition of accurate structural information. Electron channeling provides such information from bulk samples in a scanning electron microscope and hence is not subject to thin specimen artifacts. Electron channeling patterns (ECPs) were obtained from thin (∼100Å), partially relaxed iron aluminide films grown by MBE on thick (∼1mm) AlAs/GaAs (100) substrates. These systems exhibited low critical thicknesses as determined by in-situ reflection high energy electron diffraction (RHEED). Variation of SEM accelerating voltage provided ECPs from depths ranging from film only to film + substrate. High diffraction order lines were analyzed kinematically to determine lattice parameters in the strained film. ECP and RHEED indicated an elastic strain in the film of approximately 1.2%. A linear elastic finite element approach was then used to estimate the degree of strain redistribution into the substrate in a thinned TEM specimen. Results indicated that reducing the substrate thickness to below ten times the film thickness can decrease the elastic strain in the film by 0.5%.

A dynamical x-ray diffraction theory has been used to obtain microscopic strain profiles in thin Au/Ni multilayers. Depth profiles of strains in these multilayers, with repeat periodicities varying from 0.82 nm to 9.0 nm, are obtained by an iterative fitting of the calculated diffraction pattern with the experimental one. Interfacial coherency is found to play an important role in understanding the origin of the supermodulus effect in metallic multilayers.

Strain can play a critical role in determining the band structure and optical properties of semiconducting superlattices. Mailhiot and Smith [1] have predicted that strain, induced by mismatch, in InxGal-xSb/InAs makes the superlattice a candidate for infrared detectors. We present a preliminary analysis of the structure, in particular the strain in the layers, of an InxGal-xSb/InAs superlattice, which shows infrared absorption. Our ultimate objective is to relate the structural properties to the optical absorption and an extended (kinematical) diffraction treatment is presented for accomplishing this.

By simulation of X-ray rocking curves of Si-Ge alloys grown on Si by molecular beam epitaxy and of Ge implanted samples, the Ge composition, the linear lattice expansion coefficient, the strain depth-distribution and the static Debye-Waller factor in the MBE alloys have been determined.

We have recorded two-dimensional X-ray diffraction patterns from fivebilayer Langmuir-Blodgett multilayer films. The films were deposited on alkylated glass substrates from monolayers of arachidic acid which were spread on barium or cadmium cation containing subphases: the pH was systematically varied from 4 to 9. The diffraction patterns were recorded using doubly-focusing X-ray optics and a two-dimensional position sensitive detector.

Generalized Patterson function analysis of the meridional X-ray diffraction I (qxy = 0, qz), which arises from the profile structure of the multilayer, indicated that the bilayer to bilayer correlations improved with increasing pH value (i.e., with incorporation of divalent metal cations into the film). Experimentally determined electron density profiles have previously shown that the average in-plane density of the down-stroke monolayers was greater than that of the the up-stroke monolayers, in agreement with the observed transfer ratios.

We observed Bragg rods at several qxy-values only for multilayers for which the subphase was of intermediate to high pH. The intensity and degree of sampling of the Bragg rods along qz increased with increasing pH value. At the highest pH values, the in-plane intermolecular correlation lengths were ∼600 Å and the bilayer to bilayer intermolecular correlation lengths were ∼165 Å or ∼2 1/2 bilayers. This indicates that for the fatty-acid salts the monolayers of low average in-plane density are “patched” with separated domains which have been deposited epitaxially on the underlying monolayers of high average inplane density.

An experimental study of x-ray interference effects from GaAs/AlxGa1−xAs multilayer structures was conducted. The presence of a GaAs layer, whose thickness ranged from 50 Å to 10 μm, between two Al0.30Ga0.70As layers was found to significantly affect the x-ray rocking curves from these structures. We determined both the thickness and the composition of the AlxGa1−xAs layers and the thickness of the GaAs layers by comparing the rocking curves to simulated ones using a dynamical x-ray diffraction model. A sensitivity analysis showed that the thickness predicted for the GaAs buried layer was precise to within 90 Å for a ≃ 2000 Å GaAs layer and that the barrier layer Al content and thickness could be determined to within 1% and 80 Å, respectively for ≃ 5000Å layers. This analysis also showed that, within experimental resolution limits, the structure determined from comparing simulated and experimental rocking curves was unique. Both the limits of this technique in determining interfacial grading and applications to specific device structures and other materials systems are discussed.

The relaxation of strain in epitaxial overlayers is studied through an analysis of RHEED patterns. From the separation of the RHEED reflections, we determine the in-plane lattice constants for α-Sn/Cd0.8Zn0.2Te(100), CdS/GaAs(100), and CdS/CdTe(100) heterostructures. The discussion focuses on the critical thickness of the overlayers and the relaxation of the inplane lattice constant (a∥) of epitaxial films which exceed the critical thickness. Predictions based on Matthews and Blakeslee's mechanical equilibrium theory show reasonable agreement with our experimental findings, indicating that the metastability of the epitaxial overlayers does not cause a significant reduction in the critical film thickness.

Using a conventional 30 keV reflection high energy electron diffraction gun on a custom built molecular beam epitaxy system together with an energy loss analyser, we have combined in situ measurements of inelastically scattered electrons from Si L2,3 (99 eV) and Ge L2,3 (1217 eV) core losses with reflection electron diffraction data in order to study the initial stages of Ge heteroepitaxy on Si (001). Diffraction data indicate Stranski-Krastanov growth mode and indicate islanding for Ge thicknesses greater than 0.3 nm. The normalized core loss intensities from electron energy loss data are consistent with a simple model based on grazing incidence electron scattering from the growing Ge film.

Additional experiments designed to determine the surface composition sensitivity from Si K (1840 eV) and Ge L2,3 ionization cross-sections reveal that accurate values of composition for a dilute GexSi1−x alloy (x=0.02) can be obtained from raw data when compared with Rutherford Backscattering and Transmission Electron Microscopy/X-ray microanalysis measurements.

Mirror Electron Microscopy – Low Energy Electron Diffraction (MEMLEED) combines a LEED with MEM in a single simple instrument for studies of surface processes such as phase transitions and premelting under ultra-high vacuum (uhv) conditions. In MEMLEED, 5–20 keV primary electrons are decelerated by an electrostatic mirror-objective lens in which the sample is the mirror element. In the MEN mode, electrons are reflected just above the surface, reaccelerated through the objective lens and imaged. Contrast is due to variations in both surface potential and topography. Current uhv instruments have lateral resolution of about 1 μm. In the LEED mode, 0-100 eV electrons strike the sample at near normal incidence. Diffracted electrons are accelerated through the objective lens. Beam spacings in the imaged diffraction pattern are proportional to k11 and beams do not move as the incident energy is varied. MEMLEED has intrinsically higher transfer width and is less sensitive to magnetic fields near the sample than conventional LEED. Design considerations for uhv instruments are discussed. Applications to the study of order-disorder transitions, premelting phenomena, and to measurements of changes in surface potential are described.

We suggest a new application for elastic scattering of a metastable spin-polarized atomic helium beam at thermal energy. We demonstrate how angle-resolved measurements of the Bragg peaks of scattered surviving metastable atoms can give information about the spin-ordering of an antiferromagnetic (AF) transition metal oxide surface. In this paper, we discuss the feasibility of such measurements for NiO(100) and MnO(100), based on available information about their electronic structure and the properties of spin-polarized metastable helium. On impact with a surface, the survival probability of metastables is generally very low (<10-2). There are two possible decay mechanisms for metastables, a resonance ionization followed by auger neutralization, or an auger de-excitation process. For AF surfaces which fulfill certain requirements on their electronic structure, spin-selection rules will inhibit the decay of the metastable atoms from a favourably aligned magnetic sublattice. The survival probability will then be dramatically enhanced from the chosen sublattice, and the coherently scattered surviving metastables will reflect the periodicity of that magnetic sublattice. In contrast to other methods currently applied to magnetic systems, this method does not rely on difference spectra. Consequently, reversal of spinorientation is not necessary for the observation of magnetic ordering.

The preliminary results of an ongoing investigation of Fe/Cu(001) are presented here. Energy dependent photoelectron diffraction, including the spin-dependent variant using the multiplet split Fe 3s state, is being used to investigate the nanoscale structures formed by near-monolayer deposits of Fe onto Cu(001). Core-level photoemission from the Fe3p and Fe3s states has been generated using synchrotron radiation as the tunable excitation source. Tentatively, a comparison of the experimental Fe3p cross section measurements with multiple scattering calculations indicates that the Fe is in a fourfold hollow site with a spacing of 3.6Å between it and the atom directly beneath it, in the third layer. This is consistent with an FCC structure. The possibility of utilizing spin-dleendent photoelectron diffraction to investigate magnetic ultrathin films will be demonstrated, using our preliminary spectra of the multiplet-split Fe3s of near-monolayer Fe/Cu(001).

A high speed x-ray diffraction system has been built around a Curved Position Sensitive Detector. This system has a hot/cold stage in a modified vacuum chamber to allow for control of the ambient gas mix while in-situ x-ray diffraction spectra are acquired. We have used this system to measure the strain in Al/Cr/SiO2 structures after abrupt changes in temperature. The good adhesion afforded by the Cr layer combined with the large difference in the thermal expansion coefficients of the Al (≃25×10−6/°K) and the quartz (≃0.5×10−6/°K) components make this an ideal sample for demonstrating the capabilities of this system. In-situ resistivity measurement provides an independent indication of the changes in the sample.

The initial stage of epitactic growth of GaSb film on GaAs has been studied by X-ray diffraction. On each island the 8% misfit is accommodated by a periodic network composed of two perpendicular sets of Lomer dislocations. This network is already formed at 10Å nominal thickness. The relaxation of the e ilayer towards its bulk lattice parameter is almost complete so that a supercell is observed. The behaviour of the dislocation satellites is accurately explained by the presence of a periodic displacement field at and close to the interface. A quantitative fit with a simple elastic model is, however, insufficient to fit the data, implying that interdiffusion occurs close to the interface.