Interdiffusion behavior in long-period Si1-xGex/Si as a function of growth conditions and external stress is examined using x-ray diffraction and Raman Spectroscopy. Both symmetrically and asymmetrically-strained superlattices have been examined, and an activation energy for interdiffusion of 3.9 eV and 4.6 eV have been obtained, respectively. In addition, an enhanced interdiffusion has also been measured in an externally stressed asymmetric superlattice. In both cases, enhanced interdiffusion has been measured whenever the Si barrier layers experience tensile stress during annealing. The Raman spectroscopy supports this result, showing an enhanced Ge diffusion into the Si barriers when these barriers are put under tensile stress. This result will be discussed in terms of the kinetics of defect formation and motion in the strained Si barriers.

We have studied the pressure-dependence of the interdiffusion rate in amorphous Si/Ge multilayers. Samples were annealed in an externally-heated diamond anvil cell at 693 K at pressures ranging from 0 to 3.1 GPa. Interdiffusion rates were determined by ex situ x-ray diffraction measurements of the decay of the artificial Bragg peaks associated with the multilayer periodicity. Scaling experiments were performed to factor out the effects of concentration and time dependence in the diffusivity. All samples showed a consistent increase in diffusivity with applied pressure, characterized by a negative activation volume ranging from −44±3 to −37±2 percent of the atomic volume of Si for films ranging in average Si composition from 25 to 71 percent, respectively. These results are consistent with a model for diffusion in amorphous Si and Ge based on dangling bond migration.

The decay of X-ray satellite intensities is used to measure interdiffusion in amorphous Ni55Zr45 multilayers as a function of repeat distance, time and temperature. The data are compared to analytical expressions and a numerical simulation based on the analysis of Stephenson for stress effects. It is concluded that stress effects are very strong and that the analysis fits them quantitatively in a system such as a-Ni-Zr with marked diffusional asymmetry.

Thin film structures of crystalline Zr and Co, deposited in UHV, are investigated by bending beam technique and by X-ray diffraction. During isothermal annealing and interdiffusion reaction of the thin film double layer and multilayer packages large compressive stresses are generated while an amorphous ZrCo-phase is formed. This can, at first hand, be understood in terms of the Kirkendall effect where Co atoms, as the main moving species, lead to a volume increase of the film beyond the Co interface. The observed change in Zr lattice spacing in accordance with the evolution of mechanical stress indicates that the compressive stress is built up particularly within the Zr layer due to the solution of Co in Zr grains during the initial amorphization reaction. Film structures, having Co already present in the crystalline Zr layer after film deposition, show a decrease in reaction kinetics combined with a lower stress level, indicating that the interdiffusion reaction is depending on the stress state in the Zr grains. At late stages of annealing in high vacuum a sudden increase of additional compressive stress is observed, which could be attributed to the oxidation of Zr, very likely due to the formation of diffusion paths for oxygen through the Co (cap-) layer (Kirkendall voids). Such oxidation behavior was not observed with samples measured in situ in UHV directly after film deposition.

A two-dimensional numerical simulation is performed to model the morphological evolution of a strained film growing heteroepitaxially on a substrate under simultaneous action of vapor deposition and surface diffusion. To facilitate numerical implementation, a continuum boundary layer model is proposed to account for the influence of film/substrate interface on the film growth pattern. Discussions are focused on the Stranski-Krastanow growth mode, although our model is capable of explaining Frank-van der Merwe and Volmer-Weber growth modes as well. Both first-order perturbation and numerical results are developed to demonstrate that the film surface tends to remain flat during the initial stage of growth and that surface roughening occurs once the film thickness exceeds a critical value, in consistency with experimentally observed patterns of S-K growth. Numerical results further show that, depending on the deposition rate, the surface evolution could lead to a steady state morphology, unstable cusp formation, or growing islands with flattened valleys.

It has been observed that, for some strained epitaxial layer systems, the surface of the layer develops roughness or waviness which correlates spatially with the positions of underlying interface misfit dislocations which partially relax the elastic mismatch strain. A model based on redistribution of mass by surface diffusion is analyzed to estimate the waviness of the three dimensional thermodynamic equilibrium surface due to intersecting arrays of interface misfit dislocations.

The origin of the crosshatched morphology very often observed, for instance in the case of InGaAs on GaAs, is studied theoretically. The calculations are performed on the basis of a microscopic valence force field model.The force on an adatom induced by a periodic array of widely spaced dislocations is first determined. This is found to be attractive, in agreement with a previous classical elasticity description. Total energies of ridges are then calculated showing increased stability due to the misfit dislocations. The importance of the surface tension for the shape of the ridges is discussed. The results are finally compared to experimental evidence.

(001) MgO single crystals were implanted with 150 keV krypton ions (Kr+) at a fluence of 5.1016 ions.cm-2 . The implanted surface, observed with an Atomic Force Microscope (AFM) exhibits striking features that can be described as undulations with a wavelength of 0.5 [μm. We correlate these features to the decrease in density and the stresses induced by the implantation damage. As a matter of fact, a model of surface instabilities provides a relationship between the wavelength of the ondulations and internal stresses. Using this model, implantation stresses are calculated to 2.2 GPa. This is in good agreement with the value of 2 GPa obtained with the help of the microindentation technique and the literature data. Some effects of an ionizing post-irradiation on stress and surface roughness are described.

The morphological instability of an epitaxially-strained, thin film is studied by means of a discrete atom method in a dislocation-free, two-dimensional crystal. The instability of the film-substrate interface is also examined in conjunction with the migration of the free surface. The results show that a mobile film-substrate interface can accelerate merger between the two surfaces, and anisotropic effects facilitate island formation. In addition, the instability of a curved interface is discussed with the results on the morphological evolution of coherent precipitates. A circular, soft precipitate in an isotropic matrix undergoes a series of shape transitions before reaching its equilibrium shape. As in the strained thin film case, transition begins with interfacial waves induced by the coherency strain. The waves then develop small lobes, which coarsen into a lower density of larger lobes. The larger lobes eventually coarsen as the equilibrium shape is approached. Anisotropic effects suppress some of the interfacial waves.

The stress and microstructure of a thin film evolve in time if the deposition is interrupted or terminated. To establish the parameters which control the kinetics of both processes, ultra thin Au layers were sputter deposited on Si membranes and the stress evolution was monitored by a vibrating membrane technique. The evolution of the surface morphology was studied by scanning tunnelling microscopy. Aging after the termination of each deposition causes stress evolution towards higher tension which, around ambient temperature, follows an exponential law with a characteristic relaxation time of the order of tenths of seconds. This time was found to depend strongly on the accumulated film thickness as well as the surface morphology. The intrinsic stress of the depositing layer increases with the coverage of the film on the substrate. Scanning Tunnelling Microscopy shows that the film grows in a Volmer-Weber mode and that the average stress reaches a sharp maximum as the film become continuous.

We have studied the microscopic effects of tensile stress on film thickness and grain growth in gold thin films of 25nm nominal thickness using transmission electron microscopy. Free-standing films were annealed at 150°C resulting in films with columnar grains and 〈111〉 fiber texture. After repeated anneals, tensile stresses caused by grain growth became large enough to cause cracks to form and propagate diffusively. While tensile stress must eventually result in an overall decrease in film thickness, local specimen thickening in front of crack tips is observed. The tensile stress also profoundly affected grain growth in these films. Grains near crack tips are larger than grains 400nm away from the tips, and elongated grains with axial ratios greater than 15 have been observed in cracked regions of the films.

Computer simulations were used to investigate the effect of stresses on the energy of defects in Ge, Ge7% Si93% (referred to as alloy) films on Si and encapsulated aluminum thin films. In Ge films, misfit dislocations were energetically favorable over coherent interfaces. Although the alloy films had lower energy compared to Ge films, they also formed dislocations at film thicknesses greater than 25 – 30 Å. The energy of vacancy insertion at the film surface, which nucleates a misfit dislocation, increased with tensile stress. In encapsulated aluminum, agglomeration of vacancies leads to formation of voids. Simulations indicate that the activation energy of vacancy migration increased with compressive stresses. Thus compressive stresses in aluminum may prevent formation of voids, while tensile stresses in Ge film may prevent formation of misfit dislocations.

The dependence of solid phase epitaxial growth in Si on uniaxial compression applied perpendicular to the amorphous-crystal interface is investigated. Long, thin pure Si bars of square cross section are ion-implanted to produce amorphous layers on the end faces. The bars are placed end-to-end and uniaxially loaded at temperature to partially regrow the amorphous layers. The resulting growth rates are measured ex situ by re-heating the samples on a hot stage and using time-resolved reflectivity to deduce interface depths. Preliminary results are that uniaxial compression is more effective than hydrostatic pressure for enhancing the growth rate, in qualitative but not quantitative agreement with previously made predictions.

An exact expression for the elastic energy associated with a semicircular shear dislocation loop emanating from a free surface, such as that of a stressed thin film, is derived (within continuum dislocation theory) and compared with earlier approximations. The energy required to activate a semicircular dislocation loop into its unstable “saddle-point” configuration is then re-calculated, based on the modified expression for the self-energy. It is found that the shear stress necessary to emit a loop, as a function of temperature, is almost 50% less than earlier estimates. The effects of ledges on the surface, as well as loop geometry, are discussed. The principal drawback to this type of calculation is pointed out, namely, that the critical radius of an incipient dislocation loop can be on the order of one atomic spacing, which is too small for a continuum theory to be valid.

Atomistic simulations were used to study the configurations of defects in copper aluminum alloy (2% copper, 98% aluminum). In the presence of free surface, the copper atoms migrated towards the surface. When the aluminum cell (about 2000 atoms) contained a dislocation, copper atoms segregated near the dislocation core on the compressional side. In presence of a grain boundary, copper atoms moved into the boundary plane. The segregation in these simulations resulted from reduction in localized strain near the structural defects.

Chrysotile asbestos (empirical formula: Mg3Si2O7.2H2O, structural formula: Mg3Si2O5(OH)4) crystallizes in a sheet structure so thin that it is equivalent to a thin film that has no support. The magnesium ions are too large to fit comfortably in their octahedral sites, the size of which is determined by the network of SiO4 tetrahedra. The squeezing of the magnesium ions in sites that are too tight forces the thin layers to bend and coil around themselves. The bending of the unit-cells results in the presence of an enormous amount of highly directional stress, which has been analyzed by X-ray diffraction. The carcinogenic properties of chrysotile asbestos are a direct consequence of this stress.

Complete and dissociated edge dislocations were created near the center of the surface (101) of aluminum small crystals whose surfaces are (111), (111), (101), (101). (121) and (121). Molecular dynamics with N-body embedded atom potentials were used. Higher stress is needed to create a complete edge dislocation than to create a dissociated dislocation.

The strengths and ductility of electrochemically deposited metals generally are different from those of the corresponding ones produced by other means. The difference is due to the growth mechanism of the deposits, that they can contain substances which are unstable at elevated temperature and the presence of various crystal defects. The effects on the mechanical properties of electrodeposits of dislocations, twins, voids, codeposited foreign materials, surface crevices, subgrain and grain boundaries, internal stresses and textures are discussed. The ways polarization, current form, solution temperature and agitation affect the mechanical properties of deposits are reviewed. A discussion of the relationships between hardness, the tensile and the fatigue properties is also included. Annealing effects and those of special structures on the properties are also considered.

Understanding of the stress in thin films is important in controls of the properties of nanometer period x-ray multilayers. Stress evolution at the initial stages of thin film formation was studied by molecular dynamics simulation of Mo atoms impinging on a 5×5×5 unit cell Mo substrate. The simulation shows that the structure initially increases in a compressive state. The stress then decreases when the deposited atoms have covered the substrate surface. Measured stress of Ru films in Ru/C multilayers by laser curvature technique shows similar behavior to the simulated results.

We have measured the stress in Mo/Si multilayer films deposited by magnetron sputtering, using the wafer-curvature technique, and find a strong dependence on background pressure. For multilayers containing 40 bilayers of ˜4.3 nm Si layers and ˜2.6 nm Mo layers, the stress increases from approximately −280 MPa (compressive) to −450 MPa as the background pressure in the deposition chamber (i.e., measured just prior to deposition) decreases from 1.0 } 10−5 to 6.0 } 10−8 torr. For multilayers of the same period but with thicker Mo layers, the dependence on background pressure is even stronger. X-ray (λ = 0.154 nm) diffraction measurements reveal a slight increase in interfacial roughness for films deposited at high background pressure. Atomic concentrations of incorporated oxygen and carbon, measured with Auger electron spectroscopy, were found to be less than ˜0.5 at.% for all samples. However, the average hydrogen concentration, as determined from forward-recoil-scattering measurements, was found to vary from ˜0.3 at.% to ˜1.6 at.%, increasing with both background pressure and Mo layer thickness. We discuss possible mechanisms for the observed dependence of film stress on background pressure, including gas incorporation and the affect of residual gas atoms on adatom mobility.