Analytical solution of generalized Burton--Cabrera--Frank equations for growth and post--growth equilibration on vicinal surfaces

We investigate growth on vicinal surfaces by molecular beam epitaxy making use of a generalized Burton--Cabrera--Frank model. Our primary aim is to propose and implement a novel analytical program based on a perturbative solution of the non--linear equations describing the coupled adatom and dimer kinetics. These equations are considered as originating from a fully microscopic description that allows the step boundary conditions to be directly formulated in terms of the sticking coefficients at each step. As an example, we study the importance of diffusion barriers for adatoms hopping down descending steps (Schwoebel effect) during growth and post-growth equilibration of the surface.Comment: 16 pages, REVTeX 3.0, IC-DDV-94-00

THE ROLE OF STRAIN AND SURFACE STOCHIOMETRY IN THE SYNTHESIS OF InAs/GaAs (100) MULTILAYER COMPOUNDS

Lattice-mismatched or strained-layer epitaxy is a particularly intriguing problem because of the promise of new materials systems and novel electronic properties derived from straininduced modification of local structure. In addition to the interest in strained-layer systems related to the development of new electronic and optoelectronic devices, the study of the dynamics of their growth using MBE promises to strongly enhance our understanding of IIIV MBE growth mechanisms. Using our RHEED controlled growth techniques, we find that in the InAs/GaAs system these materials grow in registration to the substrate, giving rise to a tetragonal distortion of the local coordination. This modification of the bonding and symmetry of the growing film has serious ramifications for the physisorbed and chemisorbed species which establish the growth front and the surface stochiometrym. The surface transport of In or Ga, the chemical incorporation of As2 or As4 and the details of the terrace and step distributions all show a sensitivity to bond strain and lattice mismatch. The interfacial roughness of heterojunction boundaries in these superlattice systems is likewise affected by local strain and potential variations

The Beagle 2 environmental sensors: science goals and instrument description

A suite of instruments on the Beagle 2 Mars lander was designed and built in order to investigate the environmental conditions at the landing site. The sensor suite was capable of measuring air temperature at two heights, surface level pressure, wind speed and direction, saltated particle momentum, UV flux (diffuse and direct at five wavelengths), the total accumulated radiation dose and investigating the nature of the oxidising environment. The scientific goals of the instruments are discussed within the context of current understanding of the environmental conditions on Mars, and the instruments themselves are described in detail. Beagle 2 landed on Mars in late 2003, as part of the ESA Mars Express mission. The expected lifetime of the lander on the surface was 180 sols, with a landing site in Isidis Planitia, but has not responded to attempts to contact it, and has now been declared lost. The Environmental Sensor Suite (ESS) was intended to monitor and characterise the current local meteorological parameters, investigating specific areas of scientific interest raised from previous missions, most notably dust transport and transient phenomena, and additionally to add context to the conditions that any possible martian micro-organisms would have to face. The design of the instrument suite was strongly influenced by mass limitations, with eight sensor subsystems having a total mass of approximately 100 g. Although Beagle 2 has been now declared lost, the scientific goals of an Environmental Sensors Suite still remain a valid target for any future astrobiology orientated missions