Self-organization of (001) cubic crystal surfaces

Self-organization on crystal surface is studied as a two dimensional spinodal decomposition in presence of a surface stress. The elastic Green function is calculated for a $(001)$ cubic crystal surface taking into account the crystal anisotropy. Numerical calculations show that the phase separation is driven by the interplay between domain boundary energy and long range elastic interactions. At late stage of the phase separation process, a steady state appears with different nanometric patterns according to the surface coverage and the crystal elastic constants

Coherent Stranski-Krastanov growth in 1+1 dimensions with anharmonic interactions: An equilibrium study

The formation of coherently strained three-dimensional islands on top of the wetting layer in Stranski-Krastanov mode of growth is considered in a model in 1+1 dimensions accounting for the anharmonicity and non-convexity of the real interatomic forces. It is shown that coherent 3D islands can be expected to form in compressed rather than in expanded overlayers beyond a critical lattice misfit. In the latter case the classical Stranski-Krastanov growth is expected to occur because the misfit dislocations can become energetically favored at smaller island sizes. The thermodynamic reason for coherent 3D islanding is the incomplete wetting owing to the weaker adhesion of the edge atoms. Monolayer height islands with a critical size appear as necessary precursors of the 3D islands. The latter explains the experimentally observed narrow size distribution of the 3D islands. The 2D-3D transformation takes place by consecutive rearrangements of mono- to bilayer, bi- to trilayer islands, etc., after exceeding the corresponding critical sizes. The rearrangements are initiated by nucleation events each next one requiring to overcome a lower energetic barrier. The model is in good qualitative agreement with available experimental observations.Comment: 12 pages text, 15 figures, Accepted in Phys.Rev.B, Vol.61, No2

Strain Induced Vertical and Lateral Correlations in Quantum Dot Superlattices

Vertical and lateral ordering of quantum dots in superlattices is shown to be determined by the elastic anisotropy of the matrix material and by the growth orientation. For large anisotropies, complicated dot stacking sequences with correlations inclined to the growth axis may be formed, and the lateral ordering tendency is much stronger than for isotropic materials

Propagation of cortical spreading depolarization in the human cortex after malignant stroke

(c) LIPPINCOTT WILLIAMS & WILKIN

Standard-sampling microdialysis and spreading depolarizations in patients with malignant hemispheric stroke

Spreading depolarizations (SD) occur in high frequency in patients with malignant hemispheric stroke (MHS). Experimentally, SDs cause marked increases in glutamate and lactate, whereas glucose decreases. Here, we studied extracellular brain glutamate, glucose, lactate, pyruvate and the lactate/pyruvate ratio in relationship to SDs after MHS. We inserted two microdialysis probes in peri-infarct tissue at 5 and 15 mm to the infarct in close proximity to a subdural electrode strip. During 2356.6 monitoring hours, electrocorticography (ECoG) revealed 697 SDs in 16 of 18 patients. Ninety-nine SDs in electrically active tissue (spreading depressions, SDd) were single (SDds) and 485 clustered (SDdc), whereas 10 SDs with at least one electrode in electrically inactive tissue (isoelectric SDs, SDi) were single (SDis) and 103 clustered (SDic). More SDs and a significant number of clustered SDs occurred during the first 36 h post-surgery when glutamate was significantly elevated (> 100 mu M). In a grouped analysis, we observed minor glutamate elevations with more than two SDs per hour. Glucose slightly decreased during SDic at 5 mm from the infarct. Directions of SD-related metabolic changes correspond to the experimental setting but the long sampling time of standard microdialysis precludes a more adequate account of the dynamics revealed by ECoG