P. Pongratz

Growth diagram and morphologies of AlN thin films grown by molecular beam epitaxy

A growth diagram for molecular beam epitaxy of AlN on sapphire and 6H–SiC was established using reflection high energy electron diffraction, atomic force microscopy, and Rutherford backscattering spectrometry. In varying the Al/N ratio and growth temperature, distinctive surface morphologies emerge, which are assigned to three regimes of growth, one N-rich (Al/N 1) regimes. Under N-rich conditions, AlN films exhibit rough surface morphologies. In contrast, Al-rich conditions produce excellent smooth surface morphologies, but with the constraint of Al droplet formation at very high Al/N ratios and low temperatures. The differentiation between N-rich and Al-rich regimes is given only by the Al/N ratio, while the two Al-rich regimes (intermediate self-regulated and droplet regime) are separated by the boundary line of Al droplet formation. For this boundary an Arrhenius dependence of growth temperature was found, yielding an activation energy of 3.4±0.1 eV. The observed morphology tr...

Pressure-induced orientation control of the growth of epitaxial silicon nanowires.

Single crystal silicon nanowires (SiNWs) were synthesized with silane reactant using Au nanocluster-catalyzed one-dimensional growth. We have shown that under our experimental conditions, SiNWs grown epitaxially on Si(111) via the vapor-liquid-solid growth mechanism change their growth direction as a function of the total pressure. Structural characterization of a large number of samples shows that SiNWs synthesized at a total pressure of 3 mbar grow preferentially in the 111 direction, while the one at 15 mbar favors the 112 direction. Specifically by dynamically changing the system pressure during the growth process morphological changes of the NW growth directions along their length have been demonstrated.

Shock metamorphism of deformed quartz

AbstractDeformed, synthetic quartz containing a dislocation density of 2.9 ± 1.9 × 108/cm2 and abundant bubbles and small inclusions was shocked to peak pressures of 12 and 24 GPa. The resultant material was inhomogeneously deformed and extremely fractured. The 12 GPa sample contained large regions lacking apparent shock deformation, suggesting that the original microstructure of a quartz target may be distinguished in low-stress shocks with minimal annealing. No change in dislocation density was caused by shock loading except in regions containing shock lamellae, where the dislocation density was lowered.Generally the same types of microstructures were induced by shock of deformed quartz as by shock of relatively defect-free as-grown crystals. Glass-filled veins were abundant, especially at lower stresses, and contained angular fragments of quartz welded together. Microfaults formed on

Continuous evolution of Ga adlayer coverages during plasma-assisted molecular-beam epitaxy of (0001) GaN

{{\{ 10\bar 11\} } \mathord{\left/ {\vphantom {{\{ 10\bar 11\} } {\{ 01\bar 11\} }}} \right. \kern-\nulldelimiterspace} {\{ 01\bar 11\} }}

Orientation specific synthesis of kinked silicon nanowires grown by the vapour-liquid-solid mechanism.

and

Growth of branched single-crystalline GaAs whiskers on Si nanowire trunks

{{\{ 11\bar 22\} } \mathord{\left/ {\vphantom {{\{ 11\bar 22\} } {\{ 1\bar 212\} }}} \right. \kern-\nulldelimiterspace} {\{ 1\bar 212\} }}