Determining how thermal vacancies are created and destroyed in solids is crucial for understanding many of their physical properties, such as solid-state diffusion. Surfaces are known to be good sources and sinks for bulk vacancies, but directly determining where the exchange between the surface and the bulk occurs is difficult. Here we show that vacancy generation (and annihilation) on the (110) surface of an ordered nickel-aluminium intermetallic alloy does not occur over the entire surface, but only near atomic step edges. This has been determined by oscillating the sample's temperature and observing in real time the response of the surface structure as a function of frequency (a version of Angström's method of measuring thermal conductivity) using low-energy electron microscopy. Although the surface-exchange process is slow compared with bulk diffusion, the vacancy-generation rate nevertheless controls the dynamics of the alloy surface morphology. These observations, demonstrating that surface smoothing can occur through bulk vacancy transport rather than surface diffusion, should have important implications for the stability of fabricated nanoscale structures.

We find that small temperature changes cause steps on the NiAl͑110͒ surface to move. We show that this step motion occurs because mass is transferred between the bulk and the surface as the concentration of bulk thermal defects ͑i.e., vacancies͒ changes with temperature. Since the change in an island's area with a temperature change is found to scale strictly with the island's step length, the thermally generated defects are created ͑annihilated͒ very near the surface steps. To quantify the bulk/surface exchange, we oscillate the sample temperature and measure the amplitude and phase lag of the system response, i.e., the change in an island's area normalized to its perimeter. Using a one-dimensional model of defect diffusion through the bulk in a direction perpendicular to the surface, we determine the migration and formation energies of the bulk thermal defects. During surface smoothing, we show that there is no flow of material between islands on the same terrace and that all islands in a stack shrink at the same rate. We conclude that smoothing occurs by mass transport through the bulk of the crystal rather than via surface diffusion. Based on the measured relative sizes of the activation energies for island decay, defect migration, and defect formation, we show that attachment/ detachment at the steps is the rate-limiting step in smoothing.

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We use the k. p Pidgeon-Brown model with exchange included to fit Shubnikovde Haas (SdH) data for Hg& Mn Se for x=0.025. We find that inversion-asymmetry parameters (IAP's) are needed to explain the beats in the data. Our values for the IAP's are i C~=3.384&&10 ' eVcm, G=0.38, and Nz --0.50, and for the exchange parameters we get a= -0.732 eV and P=1.638 eV.We demonstrate that the IAP's introduce two frequencies into the SdH oscillations and that the temperature dependence of the resulting beats is solely due to the exchange interaction between the electrons and the magnetic ions in the sample. We further calculate the Fermi surface and small-k band structure.