Epitaxial Growth of Silicon by Vacuum Sublimation
SINGLE crystal layers of silicon up to several μ thick have been deposited on to a heated single crystal silicon substrate from a sublimating source. We believe we can grow good epitaxial crystals at a lower growing temperature than previous experiments1 by reducing the growth rate in a good vacuum free from contamination.
Films by Molecular-Beam Epitaxy
Epitaxial growth proceeds by the attachment of atoms on the correct positions of a given lattice. The orientation and atomic spacings of the lattice are usually those predicted from a single-crystalline substrate with a clean surface. The attachment of atoms from the vapour phase typically follows a three-step scheme of adsorption, diffusion and incorporation into surface steps (Fig. 6.1). The adsorbed atoms, called adatoms, are in a precursor state for later incorporation into the lattice. The adsorption energy W ad is lower than the binding energy W b, usually 1/2 to 2/3 of W b.
Time lapse photography of clouds from high altitude balloons.
Time lapse pictures of clouds taken by cameras flown at altitudes of 30 km on balloons provide valuable insights into the convection and electrification of cloud systems. Simple camera arrangements for taking such pictures are described.