Nanoindentation-induced phase transformations in silicon at elevated temperatures.

The nanoindentation-induced phase transformation behavior of silicon at elevated temperatures (25-150 degrees C) has been studied. Nucleation of Si-III/Si-XII on unloading is enhanced with increasing temperature and at the highest temperatures in an amorphous Si matrix, occurs in a continuous fashion without a pop-out event. Interestingly, for slow unloading at the highest temperatures, formation of Si-III/Si-XII in a crystalline Si matrix was not observed. Elevated temperatures enhance the nucleation of Si-III and Si-XII during unloading but the final composition of the phase transformed zone is also dependent on the thermal stability of the phases in their respective matrices.

Dynamics of D2 released from the dissociation of D2O on a zirconium surface.

Hydrogen is efficiently released during water dissociation on zirconium (Zr), while even very rapid temperature programmed heating of a hydrogen covered Zr surface predominantly leads to dissolution (approximately 99% dissolution). To help resolve these apparently contradictory observations, we have studied the dynamics of water (D2O) dissociation on a crystalline Zr surface by probing the rotational and vibrational energy distributions of the D2 produced using resonant enhanced multiphoton ionization spectroscopy. The internal-state energy distribution of the D2 product was found to be rotationally cold and vibrationally hot with respect to the temperature of the surface. The rotational distribution shows slight deviations from Boltzmann's law, with a mean rotational temperature of 426 K while the surface is at 800 K. The population of the nu"=1 vibration is at least four times higher than a 800 K temperature would allow, this corresponding to a vibrational temperature of 1100 K. Information on the translational energy of the D2 product have also been obtained by time-of-flight spectroscopy and it is found to be nearly thermally equilibrated with the surface temperature. Similar results were obtained from studies of D2 scattered from a clean Zr surface, and of D2 released by a slow thermal desorption process which involves dissolved hydrogen as the source. The reconciliation of the present results with those for thermal desorption of preadsorbed hydrogen implies a role for both surface and subsurface adsorption sites on the Zr surface and clearly demonstrates that at high temperatures, the release of D2 arises from the recombinative desorption of adsorbed hydrogen formed by the complete dissociation of D2O.

Biological efficacy of electroless-deposited silver on plasma activated polyurethane.

Silver coating of catheters has been shown to have inhibitory effects on bacterial growth and adhesion to catheter surfaces. In this study, plasma-modification was used to enhance the adhesion of an electroless silver coating on polyurethane. Both the antibacterial and antiadhesive properties of these coatings were investigated. Bacterial growth was inhibited in cultures exposed to silver-treated polyurethane compared to unmodified polyurethane. Higher growth inhibition was observed for polyurethane surfaces with lower silver coverage. Bacterial adhesion was completely inhibited on all silver-coated surfaces.

Some endocrinological aspects of barbiturate dependence.

1. Hypophysectomized rats become dependent on barbitone and show the same withdrawal syndrome as intact animals.2. Barbitone dependent rats have larger thyroid and adrenal glands, a larger liver, smaller gonads and larger secondary sex organs than untreated animals. The levator ani muscle of the males is smaller.3. In contrast, dependent female hypophysectomized rats only showed a decreased gonad weight and increased liver weight.4. Histologically, the thyroid gland of dependent rats appears more active, but the concentration of iodine bound to plasma protein, basal metabolic rate and body temperature are similar in dependent and untreated animals.5. Resting plasma corticosterone concentration appears to be unchanged in barbitone dependent animals, but stress induced increases in the concentration of corticosterone in plasma are less in dependent animals.6. Immature barbitone dependent rats grow at a faster rate than untreated animals, but hypophysectomized rats of similar age receiving barbitone do not.7. The additional body weight gained by barbitone dependent animals is of normal body composition.8. Administration of growth hormone has an identical growth inducing effect in dependent hypophysectomized animals and in untreated hypophysectomized animals.9. Barbitone dependent rats do not exhibit the ;frustration effect' in a double runway. In barbitone dependent rats approach to a potentially ;frustrating' situation is slower than in untreated animals.