This plot shows the temperature dependence of the hydrogen chemical potential for various values of the pressure. The pressure is given in atmospheres on the right.
The relative formation energies for possible -covered surfaces are plotted as a function of . The maximum value of is equal to , which is taken as the zero of the energy scale. is the total energy of an molecule and is the zero point vibrational energy for the molecule. The , , , and structures have between 1 and atoms in each unit cell. The other structures are obtained by bonding one, two, or three atoms to a adatom in each cell. The results shown correspond to a chemical potential of . This is midway between -rich and -rich conditions. .
Relative energies of the clean surface reconstructions and the structure in conditions appropriate for MBE and MOCVD growth. The upper (lower) dashed line is the energy of the surface in MBE (MOCVD) conditions. The chemical potential varies over its thermodynamically allowed range. . In MBE conditions the adlayer and the adatom-on-adlayer reconstructions are stable except in very -rich conditions, where the surface is stable. In MOCVD conditions the surface is stable for almost all : In the -rich limit the adlayer structure and the surface are very close in energy, but for most conditions the surface is most stable.
This diagram illustrates the regions in chemical potential space where the adatom, the adlayer, the adlayer, and the structures are stable. The arrows indicate the chemical potentials typical for MBE and MOCVD growth. For hydrogen chemical potentials less than about a transition from -covered to -covered surfaces occurs as the chemical potential is increased.
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