For self-aligned bipolar technologies the sidewall region under the residual spacer, which is very much influenced by the spacer geometry, is a key feature. We have investigated the effect of the spacer geometry on the transistor performance, especially on the current gain β. The spacer geometry is arranged by varying its width separating the n+ and p+ lateral diffusions and by varying its depth penetrating into the monocrystalline silicon. It has been found that these two variations do not cause the same effect on β. Although the increase of both the spacer isolation depth and width causes an increase in β, β has an enhanced dependence on the spacer depth. This latter finding sets a limitation on the maximum spacer depth for the high performance bipolar transistors. A 2-D simulation is performed to demonstrate these effects.

The structure and composition of a Pt(100) surface have been monitored by Rutherford backscattering (RBS), nuclear microanalysis (NMA), LEED, and work function (Δφ) techniques during temporal oscillations in the rate of CO oxidation. For a Δφ oscillation amplitude of 60 mV, a constant 0.46±0.06×1015 Pt atoms are out of registry with the bulk throughout an oscillation cycle. The maximum fraction of the surface that could be oscillating between the hex and (1×1) phases is thus 8%. The average CO and O coverages during the oscillations are 0.19±0.04 and 0.13±0.03 monolayers, respectively. These results are discussed in terms of a recent model for the temporal oscillations. No oscillations in Δφ have been detected in similar experiments on Pt(111).

Isothermal low-pressure oscillations of the rate of catalytic CO oxidation on a Pt(100) surface could be established under appropriate conditions and were monitored through the accompanying periodic variation of the work function. Parallel observations by the Video-LEED technique demonstrated that these oscillations are associated with periodic transformations of the (long-range) surface structure from the reconstructed hex to the 1 × 1 phase and back, which is caused by varying surface concentrations of the reacting particles.

Oscillations of the steady-state rate of catalytic CO oxidation on clean Pt surfaces were observed under low-pressure conditions and are related to the adsorption properties of the reactants. Evidence is presented for a model in which the reversible (5\ifmmode\times\else\texttimes\fi{}20)\ensuremath{\rightleftarrows}(1\ifmmode\times\else\texttimes\fi{}1) phase transition of the Pt(100) surface (which is associated with a marked variation of the oxygen sticking coefficient) is responsible for the oscillations.

The steady-state rate of NH3 decomposition on a clean Ni surface was studied under UHV conditions. The reaction proceeds with an activation energy of 47 kcal/mole which is equal to the desorption energy for N2, demonstrating that recombination and desorption of nitrogen is rate-limiting. Below 700 K the reaction rate is negligibly small. In particular, no anomaly is observed around the Curie point (631 K), in contrast to earlier reports with less well-defined surfaces.