B. C. Larson

Domain epitaxy: A unified paradigm for thin film growth

We present a unified model for thin film epitaxy where single crystal films with small and large lattice misfits are grown by domain matching epitaxy (DME). The DME involves matching of lattice planes between the film and the substrate having similar crystal symmetry. In this framework, the conventional lattice matching epitaxy becomes a special case where a matching of lattice constants or the same planes is involved with a small misfit of less than 7%–8%. In large lattice mismatch systems, we show that epitaxial growth of thin films is possible by matching of domains where integral multiples of major lattice planes match across the interface. We illustrate this concept with atomic-level details in the TiN/Si(100) with 3/4 matching, the AlN/Si(100)with 4/5 matching, and the ZnO/α−Al2O3(0001) with 6/7 matching of major planes across the film/substrate interface. By varying the domain size, which is equal to intregral multiple of lattice planes, in a periodic fashion, it is possible to accommodate addition...

Nanosecond resolution time-resolved x-ray study of silicon during pulsed-laser irradiation

We have used the pulsed time structure of the Cornell High-Energy Synchrotron Source (CHESS) to carry out a nanosecond resolution time-resolved x-ray study of silicon during pulsed-laser irradiation. Time-resolved temperature distributions and interfacial overheating and undercooling were measured on and silicon during 25 ns UV laser pulses through the analysis of thermal expansion induced strain. The temperature gradients were found to be >10/sup 7/ K/cm at the liquid--solid interface and the temperature distributions have been shown to be in agreement with numerical heat flow calculations for these laser conditions. The combined overheating and undercooling (during approx.10 m/s melting and approx.6 m/s regrowth) was measured to be 110 +- 30 K on oriented silicon and 50 +- 25 K on silicon. These values have been interpreted in terms of velocity coefficients of overheating and undercooling.

White microbeam diffraction from distorted crystals

We present a general description of white-beam (Laue) scattering from grains with dislocations. This approach is applied to examples with equal numbers of positive and negative Burger’s vectors (paired) and with unpaired dislocations of one sign (geometrically necessary). We find that streaking of the Laue reflections is sensitive to both long-range geometrical rotations introduced by unpaired edge dislocations and to local rotation fluctuations introduced by the total number of dislocations (paired and unpaired). We demonstrate the technique by analyzing the dislocation distribution in a nanoindented Cu single crystal.

Unidirectional contraction in boron‐implanted laser‐annealed silicon

The lattice contraction in boron‐implanted laser‐annealed silicon has been studied by x‐ray Bragg reflection profiles and ion channeling. The contraction was shown to be one dimensional, along the surface normal, for strains as large as 1.3%.

X‐ray study of lattice strain in boron implanted laser annealed silicon

The strain distribution in boron implanted, laser annealed silicon has been investigated using x‐ray Bragg reflection profiles. The 400 Bragg reflection profile from implanted, laser annealed silicon was analyzed, using the dynamical theory of scattering for distorted crystals, to obtain the strain distribution in the implanted layer as a function of depth. The depth distribution of the strain for an implantation dose of 1×1016 35 keV B+/cm2, followed by a 1.6 J/cm2 ruby laser pulse, was found to have a magnitude of −5.8×10−3 near the surface and was found to decrease rapidly for depths greater than 0.2 μm. The shape of the depth distribution of the strain was found to be essentially the same as that for the boron distribution after laser annealing.

Polychromatic X-ray Microdiffraction Studies of Mesoscale Structure and Dynamics

Polychromatic X-ray microdiffraction is an emerging tool for studying mesoscale structure and dynamics. Crystalline phase, orientation (texture), elastic and plastic strain can be nondestructively mapped in three dimensions with good spatial and angular resolution. Local crystallographic orientation can be determined to approximately 0.01 degree and elastic strain tensor elements can be measured with a resolution of approximately 10(-4) or better. Complete strain tensor information can be obtained by augmenting polychromatic microdiffraction with a monochromatic measurement of one Laue-reflection energy. With differential-aperture depth profiling, volumes tens to hundreds of micrometers below the surface are accessible so that three-dimensional distributions of crystalline morphology including grain boundaries, triple points, second phases and inclusions can all be mapped. Volume elements below 0.25 microm3 are routinely resolved so that the grain boundary structure of most materials can be characterized. Here the theory, instrumentation and application of polychromatic microdiffraction are described.

Time-resolved x-ray diffraction measurement of the temperature and temperature gradients in silicon during pulsed laser annealing

Nanosecond resolution time‐resolved x‐ray diffraction measurements have been used to study the temperature and temperature gradients in 〈100〉 and 〈111〉 oriented silicon crsytals during pulsed laser annealing. Thermal strain analysis of time‐resolved extended Bragg scattering has shown the lattice temperature to reach the melting point during 15‐ns, 1.5‐J/cm2 ruby laser pulses and to remain at the melting point during the high reflectivity phase (HRP). The temperature gradients at the liquid‐solid interface were found to be in the range of ∼107 K/cm during the HRP.

Spatially resolved Poisson strain and anticlastic curvature measurements in Si under large deflection bending

A scanning-monochromatic form of differential-aperture x-ray microscopy (DAXM) has been developed that provides micron-resolution depth-resolved dilatational strain measurements. This scanning-monochromatic DAXM technique is applied to measurements of Poisson dilatational strain in 25-μm-thick Si bent into an arch with an apex radius of R=3 mm. Poisson strain measurements agree with anisotropic linear elasticity calculations for a Searle parameter as large as β=1009. Local anticlastic bend radii were shown to oscillate across the arch and reach the R/ν limit for distances less than the plate thickness from the edges, where ν is the anisotropic Poisson’s ratio.

Time-resolved study of SrTiO3 homoepitaxial pulsed-laser deposition using surface x-ray diffraction

Homoepitaxy of SrTiO3 by pulsed-laser deposition has been studied using in situ time-resolved surface x-ray diffraction in the temperature range of 310 °C to 780 °C. Using a two-detector configuration, surface x-ray diffraction intensities were monitored simultaneously at the (0 0 12) specular and the (0 1 12) off-specular truncation rod positions. Abrupt intensity changes in both the specular and off-specular rods after laser pulses indicated prompt crystallization into SrTiO3 layers followed by slower intra- and interlayer surface rearrangements on time scales of seconds. Specular rod intensity oscillations indicated layer-by-layer growth, while off-specular rod intensity measurements suggested the presence of transient in-plane lattice distortions for depositions above 600 °C.

Low‐temperature epitaxy of Si and Ge by direct ion beam deposition

Amorphous, polycrystalline, and epitaxial thin films of Si and Ge have been grown by ion beam deposition (IBD) under ultrahigh‐vacuum conditions. IBD involves the direct deposition of ions onto single‐crystal substrates from mass‐ and energy‐analyzed beams with energies of 10 to 200 eV. The IBD films were characterized by Rutherford backscattering, ion channeling, cross‐section transmission electron microscopy, and x‐ray diffraction. The effects of substrate temperature, ion energy, and substrate cleaning were studied. Differences in the formation of epitaxial thin films on p‐ and n‐type Si substrates were observed with n− Si showing better epitaxy at low temperatures. Epitaxial overlayers which showed good minimum yields by ion channeling (3%–4%) have been produced at temperatures as low as 375 °C for Ge on Ge(100) and Si on Si(100).