Slope selection in unstable multilayer growth in 1+1 dimensions: Step flow models with downward funneling.

We study analytically and numerically aspects of the dynamics of slope selection for one-dimensional models describing the motion of line defects, steps, in homoepitaxial crystal growth. The kinetic processes include diffusion of adsorbed atoms (adatoms) on terraces, attachment and detachment of atoms at steps with large yet finite, positive Ehrlich-Schwoebel step-edge barriers, material deposition on the surface from above, and the mechanism of downward funneling (DF) via a phenomenological parameter. In this context, we account for the influence of boundary conditions at extremal steps on the dynamics of slope selection.

Modeling the elastic energy of alloys: Potential pitfalls of continuum treatments.

Some issues that arise when modeling elastic energy for binary alloys are discussed within the context of a Keating model and density-functional calculations. The Keating model is a simplified atomistic formulation based on modeling elastic interactions of a binary alloy with harmonic springs whose equilibrium length is species dependent. It is demonstrated that the continuum limit for the strain field are the usual equations of linear elasticity for alloys and that they correctly capture the coarse-grained behavior of the displacement field.

Island-dynamics model for mound formation: effect of a step-edge barrier.

We formulate and implement a generalized island-dynamics model of epitaxial growth based on the level-set technique to include the effect of an additional energy barrier for the attachment and detachment of atoms at step edges. For this purpose, we invoke a mixed, Robin-type, boundary condition for the flux of adsorbed atoms (adatoms) at each step edge. In addition, we provide an analytic expression for the requisite equilibrium adatom concentration at the island boundary.

Temperature dependence of stacking faults in catalyst-free GaAs nanopillars.

Impressive opto-electronic devices and transistors have recently been fabricated from GaAs nanopillars grown by catalyst-free selective-area epitaxy, but this growth technique has always resulted in high densities of stacking faults. A stacking fault occurs when atoms on the growing (111) surface occupy the sites of a hexagonal-close-pack (hcp) lattice instead of the normal face-centered-cubic (fcc) lattice sites. When stacking faults occur consecutively, the crystal structure is locally wurtzite instead of zinc-blende, and the resulting band offsets are known to negatively impact device performance.

The far-infrared spectra of neutral and cationic niobium clusters: Nb5 0/+ to Nb9 0+.

Far-infrared absorption spectra of small neutral and cationic niobium clusters containing five to nine Nb atoms have been obtained by multiple photon dissociation spectroscopy of their argon complexes. The experimental far-IR spectra are recorded in the 85-600 cm(-1) region and cover the range of the structure-specific vibrational fundamentals, i.e.

Isomer selective infrared spectroscopy of neutral metal clusters.

We report experimental infrared spectra of neutral metal clusters in the gas phase. Multiple photon dissociation of the argon complexes of niobium clusters is used to obtain vibrational spectra in the 80-400 cm(-1) region. The observed spectra for Nb(9)Ar(n) (n=1-4) are different for different values of n.

Structure determination of isolated metal clusters via far-infrared spectroscopy.

We present a new method for the size selective structure determination of small isolated metal clusters in the gas phase. The technique is applied to cationic vanadium clusters containing 6 to 23 atoms, whose far infrared absorption spectra are measured in the 140-450 cm(-1) spectral range. The spectra are unique for each cluster size and are true fingerprints of the cluster's structure.