It is well known that it becomes energetically favourable for misfit dislocations to be introduced into strained epitaxial layers above a certain ‘critical’ layer thickness, hc. To date, theoretical calculations of hc have only been made for cases of isotropie misfit - i.e. cases where the misfit is the same for every direction in the interface. Using a new formulation of the Frank-Bilby equation and the concept of coherency dislocations, it is now possible to treat cases of anisotropie misfit, such as silicon on sapphire (SOS). The method used to obtain the critical thickness is described, and values of hc and equilibrium dislocation density are given for various materials systems.

The reactions between misfit dislocations arriving by glide at the interface between an In0.12Ga0.88As/GaAs multilayer and a GaAs substrate are analysed and reported. The glide forces for the (a/2)<110> dislocations are calculated as a function of vicinal tilt from (001) to (100). It is observed that the 4% changes in the magnitude of the force for a 2° vicinal angle are not sufficient to significantly alter the relative linear densities of the different types of dislocation.

A novel approach to quantitative interpretation of high-resolution electron microscopy images of defects in materials has been developed. The emphasis of this paper is on the methodology, which has been named Computational Fourier Transform Moiré Analysis. The essential principle of this technique is to extract an accurate displacement field about a defect from its near-atomic-resolution picture using digital Fourier transformation procedures. From this data, the displacement gradient can be calculated which yields much information on the experimental deformation mechanics of the material under investigation. As a by-product, we produce the computational Moiré pattern without the need of an external perfect reference lattice image normally associated with the interference phenomena. This method is illustrated using a bounding Frank partial dislocation for a Frank loop of the vacancy type. Results are presented on its strain field, Burgers vector and dislocation core shape and dimensions. Further mention will be made on the types of J-integral calculations that can result from this experimental study.

Finite element modelling of strain-layer mesa structures shows that edge effects can contribute to the relaxation of in-plane misfit stress. Calculations were performed for a 200 nm thick layer of Si90Ge10 grown epitaxially on an <001> Si substrate which was patterned into 400-nm-high mesas ranging in diameter from 0.6 to 7 μm. These calculations were experimentally investigated using plan-view TEM to study relaxation in patterned and unpatterned material. This composition and film thickness exceeds the critical thickness predicted using simple strain energy considerations. In one experiment, an initially defect-free 200-nm-thick Si90Ge10 layer was annealed at 960°C for 1 hr to create a nearly fully relaxed layer which was then lithographically patterned into an array of sub-micron mesas. The wafer was then annealed for a second time and changes in the character of die pre-existing dislocations were studied.

Nanoindentation experiments are now widely used to study the elastic and plastic properties of thin films. Simulation of these experiments has been performed using finite element analysis. Results show the large influence that pile-up or sink-in behavior have on hardness calculations. Results also show that a compliant substrate significantly affects the measured hardness of a stiffer coating. The measured hardness of a compliant coating is less effected by a stiffer substrate.

SiGe is of interest for use in heterojunction-bipolar transistors, infrared detectors and field-effect transistors. In this study, graded SiGe heterolayers grown on Si, and heterolayers grown on SIMOX by CVD, were characterized using TEM. The graded-heterolayers consisted of ten layers of Si1-xGex on substrate silicon. Misfit dislocations were present at interfaces in the bottom 4–5 layers of the heterostructure. This conforms with predictions from qualitative strain-energy considerations. The greatest density of misfit dislocations was present at the Si1-xGex interface between the bottom two layers of the heterostructure. Dislocations were observed to extend out of the interface and up into the heterolayer structure. The defects were found to interact with interfaces in the structure and finally cease extending upwards towards the surface of the wafer. In addition to graded heterolayers, SiGe heterolayers grown on SIMOX were also investigated. The structures consisted of epi-silicon grown on a Si/Si1-xGex superlattice which was in turn grown on a Si/SiO2 (SIMOX) structure. The behavior of defects in the layers was of interest. TEM characterization showed a large density of extended-defects present in the layers. Dislocations were observed to originate at the SIMOX oxide/Si interface, propagate up through the SiGe superlattice and into the epi-Si layer. Some dislocations were found to interact with the SiGe superlattice and cease propagating up towards the top of the wafer. SiGe superlattices with a higher concentration of Ge are more effective in reducing defect propagation towards the surface of the wafer.

The changes in defect structure caused by an anneal are studied by TEM for thin GaAs layers on Si. A low growth temperature of 450°C is always used for the first 300Å. When it is first deposited this layer contains considerable disorder which consists of planar defects, {112} epitaxy and an irregular distribution of dislocations. Annealing of the layer gives rise to a solid phase regrowth that consumes the misoriented and much of the twinned crystal and produces regular misfit dislocation arrays. Continued growth at high temperature can reduce the twin densities to below the detection limit of TEM. It is this solid phase transformation of this layer that allows good epitaxy to continue.

Strain shift coefficient measurements for longitudinal optical phonons in molecular beam epitaxy grown metastable pseudomorphic Si1−xGex layers on (100) Si (0 < x < 0.35) and Ge (0.80 < x < 1) are reported. Strain in partially relaxed annealed specimens was obtained by double-crystal x-ray diffractometry and the corresponding strain phonon shift was measured by Raman scattering spectroscopy. For epilayers grown on Si it was found that the epilayer Si-Si phonon frequency varies linearly with strain. The magnitude of the strain shift coefficient b however showed a small composition dependence varying from b ≈ -700 cm-1 at x = 0 to b ≈ -950 cm-1 at x = 0.35, corresponding to a stress factor τ = 0.40 + 0.57x: + 0.13x2 cm-1/kbar. For the Ge-Ge vibration mode in epilayers grown on Ge, b decreased from ∼-425 cm-1 at x = 1 to ∼-500 cm-1 at x = 0.8, corresponding to a stress factor τ ≈ 0.52 – 0.14x - 0.08x2 cm-1/kbar.

We demonstrate the use of x-ray diffraction to provide accurate compositional information, together with grazing incidence reflectivity to provide information on layer thicknesses and surface and interface roughnesses, on Si/Si1-xGex superlattice structures of less than 200nm total thickness.

The quality of SiGe interfaces has been investigated in superlattices where x varies from 0.1 to 0.5. At low Ge compositions the interfaces are shown to be smooth to a few angstroms. However, as the Ge composition in the SiGe layer approaches 50%, severe roughness is observed at the SiGe to Si interfaces, although the Si to SiGe interfaces remain relatively smooth.

Upon annealing for one hour at 850°C the Ge diffuses outwards from the SiGe layers and can be closely modelled by inclusion of a (2.4±0.3)nm linearly graded layer either side of the SiGe layer into a simulation program. The long range roughness at the SiGe to Si interface is lost upon annealing leaving only a short range roughness of similar size to the Si to SiGe interface roughness.

Reflectivity measurements have been shown to distinguish between interface roughness and interdiffusion for the annealed system.

By using the techniques of normal Bragg scattering and glancing incidence scattering, we have measured both the out-of-plane and in-plane structures of GaixInxAs epilay-ers grown on GaAs (001) face by MOVPE. The data presented in this paper were collected from two samples: a thick epilayer of 40, 000A Ga0.84In0.16As, and a thin epilayer of 500Å Ga0.84In0.19As, which are lattice-mismatched with the substrate by about 1.14% and 1.36% respectively according to the Vegard's law. The measured average lattice constants of the thick epilayer agree with the expectation both out-of-plane and in-plane and show nearly complete structural relaxation. An uniaxial in-plane modulation in the thick epilayer has been observed. The out-of-plane and in-plane data of the thin epilayer demonstrate a tetragonal distortion of the lattice, and the Poisson's ratio is calculated to be 0.36. The averaged in-plane lattice constant is still 0.18% larger than that of the substrate, which results in a complex structure at the epitaxial interface. An in-plane misalignment along one (110) axis in the thin epilayer has been observed.

A novel method to solve the thermal mismatch problems in a heteroepi-taxial structure is presented, in which an amorphous film deposited on a single crystalline substrate is crystallized in solid phase by annealing under ultra high pressure and both temperature and pressure are decreased proportionally. Under a specific relation between the temperature and pressure, it is expected that the effective thermal expansion coefficients, the expansion coefficients modified by elastic strain, of the film and substrate are equal and that neither defects nor strain is generated in the film during the cooling process. Theoretical consideration and experimental results for Ge films on Si(100) substrates are presented.

Structural deviations from ideal layering of bulk constituents can have dramatic effects on the properties of multilayered materials. We discuss three examples of the use of x-ray diffraction in non-standard geometries to examine these effects. In Mo/Ni multilayers, we use asymmetric diffraction and grazing incidence x-ray scattering (GIXS) to deduce the strain and intermixing. We find that coherency stresses between the BCC Mo and FCC Ni planes play a major role. In the Fe/Cr system, we use rocking curves and asymmetric scans about the small angle superlattice lines to investigate the nature and extent of layer roughness. We find that conformai roughness dominates our best samples, while non-conformal roughness increases with sputter deposition pressure. In the Gd/Co system, we use in-situ GIXS to investigate amorphization reaction during deposition. We find a strong diffusional asymmetry and rapid reaction during growth.

In situ deformation measurements of Fe/Al and Fe/Si multi-layered films on thin substrates were made by detecting the curvature of substrates during deposition. The deformation inside of Fe layers corresponding to the compressive and tensile stresses was detected for the Fe/Al and Fe/Si multi-layered films, respectively. For the Fe/Si multi-layered films, the internal stress in Fe layers became from tensile to compressive during deposition under bombardment of Ar Jons. These stresses in Fe layer were closely related to the soft magnetic properties of these multi-layered films. In situ deformation studies may be useful to make sure the effect of internal stress on the magnetic properties of these multi-layered films.

Iron zirconium multilayer films have been prepared by sputter deposition and studied using x-ray diffraction, high-resolution transmission electron microscopy and Nanoindenter techniques. The composition-modulation wavelength was varied between 0.8 and 92 nm. For modulation wavelengths greater than 4 nm the multilayers are crystalline with amorphous interfaces; for smaller wavelengths the samples are entirely amorphous. It was not possible to obtain layered structures with wavelengths smaller than 0.8 nm.

Both the hardness and the elastic modulus were measured as a function of composition-modulation wavelength by means of continuous indentation testing. The elastic modulus shows some variation with wavelength; the average value being 131 GPa. The hardness increases sharply when the modulation wavelength decreases below 4 nm. We attribute this increase to die crystalline to amorphous transition that occurs in these films at this wavelength.

The mechanical properties of metallic superlattices have been shown to exhibit anomalous properties. Several of the elastic constants are found to exhibit anomalies which are correlated with structural anomalies in lattice mismatched systems which do not form solid solutions. Lattice matched systems which form solid solutions in their thermodynamics phase diagram, show much smaller elastic anomalies and no structural anomalies. Anomalous plastic behavior, on the other hand, seems to be present in both types of superlattices, indicating that the plastic behavior is possibly defect induced. Detailed quantitative structural measurements combined with comprehensive mechanical properties hold the promise of determining the physical origins of the anomalous properties of metallic superlattices.

The modulus hardening mechanism for yield strength enhancement in multilayer materials is theoretically investigated. The multilayer composition profile used in the analysis has a general trapezoidal shape with allowance for two different layer thicknesses and two interface widths. The image force method is used to determine effective stresses on dislocations in the multilayer structure. Analytical expressions are derived for the effective stresses in terms of the shear elastic moduli. Calculations are carried out for representative composition profile shapes. It is found that the dislocation experiences the maximum effective stress when it is in the interface between layers, and that the effective stress increases dramatically with decreasing interface width. However, the effective stress is not strongly affected by either the multilayer wavelength or the relative thickness of the layers.

The free energy γAgNi associated with an interface between layers of silver and nickel has been experimentally determined. Creep tests were conducted on multilayer thin films to determine the load at which the length of the film neither shrank nor stretched. The interfacial free energy was obtained from this zero creep load and microstructural data using a specific model for the grain boundary diffusional creep in multilayers.

The strain tensor components of the PbTe and PbMnTe constituent layers of three superlattices grown on (111) oriented BaF2 substrates are determined from an X-ray analysis. Symmetric (222) and asymmetric (426), (224), (244) Bragg reflections were analysed and a generalization of the Hornstra-Bartels model is used, assuming that the SL (superlattice) can be simulated accordingly. Since in the multilayers also the satellites of the symmetric and asymmetric reflections have been considered the strain tensor components were determined with an accuracy of 1.5×10-4. Consequently the Mn-content of the PbMnTe layers could be determined with an accuracy of ± 0.03%.

Distributions of infinitesimal dislocations have been used to determine stress components near lateral surfaces of strained multilayers. The nucleation of misfit dislocations at these surfaces are discussed.

The sharp tip of a scanning force microscope can be used to make controlled modifications of polymer surfaces. In this paper, we describe the properties of micrometer size pits up to 900 Å deep formed on Kapton-H surfaces. The structure at the bottom of the pits appears to be closely related to the degree of crystallinity near the surface. We also use elasticity theory to estimate that the resolution of scanning force microscopy for polymer surfaces is about 160 Å for tips with 400 Å radius. This estimate agrees well with the resolution obtained in images of polyimide surfaces.