ADSORPTION AND DISSOCIATION OF PH3 ON SiGe(100) (2 × 1) SURFACE

The most stable structures for the adsorption and dissociation of phosphine ( PH 3) on SiGe (100) (2 × 1) surface have been investigated by relative total energy calculations based on density functional theory. According to the optimization calculations, PH 3 is adsorbed on the Si (down) and Ge (down) site of the Ge – Si and Ge – Ge dimers on SiGe surface, respectively. The PH 2 and H products have been found to be thermodynamically favored in the dissociation path of PH 3 on SiGe surface when the system is thermally activated. Although PH 3 is adsorbed on the Ge – Ge and Ge – Si dimers directly, it dissociates on the SiGe surface by passing through a transition state. The asymmetric Ge – Si and Ge – Ge dimers on SiGe surface are found to be approximately symmetric after the dissociation of PH 3 on the surface. The present work has showed that PH 2 prefers to be adsorbed on Ge site of the Ge – Si dimer. Therefore, the adsorption of PH 2 on Ge site of the Ge – Si dimer, while PH 3 being dissociated on the Si site, has indicated the migration of PH 2 on SiGe surface.

DISSOCIATION OF PH3 AND AsH3 ON Ge(100)(2x1) SURFACE

The most stable structures for the dissociation of phosphine and arsine on Ge (100)(2x1) surface have been investigated by relative total energy calculations based on Density Functional Theory. It has been found that the thermodynamically preferred structures in the dissociation path of phosphine and arsine are the same; PH 2 and AsH 2 products prefer to be on a single Ge dimer bond, but PH and AsH prefer to be between the adjacent Ge dimers. According to the optimization calculations, the dissociation path started with the adsorption of PH 3( AsH 3) on the electron deficient side of the Ge dimer bond is ended with the formation of P – P ( As – As ) dimers parallel to the dimers of Ge .

Effect of weight change on the performance of autumn-calving suckler cows

SummaryOver a period of 3 years 18 autumn-calving, single suckled, April-weaned cows were stocked at three rates at pasture to gain 132, 70 or 25 kg (H, M and L respectively) between April and August and fed to lose 100, 54 or – 13 kg (H, M and L respectively) while housed between November and April, the relative total energy intake over winter being 0·64, 0·83 and 1·00 respectively. Milk yield was reduced by 2·68 kg/day on the H and 1·25 kg/day on the M treatment and as a result calves gained 37 and 10 kg less respectively over winter than on the L treatment. However, despite poorer calf performance economic considerations would indicate a preference for high weight gain during the grazing season and a corresponding loss over winter.