Structure of clean and arsenic-covered GaN(0 0 0 1) surfaces
Abstract The effect of trace arsenic on the growth and surface structure of GaN(0 0 0 1) has been studied. We find that a partial pressure of only 10 −9  Torr of arsenic during molecular beam epitaxial growth significantly modifies the growth kinetics. Such a small background pressure of arsenic leads to an arsenic-terminated surface displaying a 2×2 reconstruction during growth which is absent for the clean surface. First-principles theoretical calculations show that As-terminated surfaces are energetically more favorable than Ga-terminated surfaces for arsenic pressures of 10 −9  Torr, and structural models for the As-adatom 2×2 reconstruction are presented.
Observation of highly dispersive surface states on GaN(0001)1×1
The electronic structure of {ital n}-type, Si-doped, wurtzite GaN(0001)1{times}1 surfaces has been studied using synchrotron radiation excited angle-resolved photoemission. The GaN thin films were grown by metal-organic chemical-vapor deposition on SiC. Two previously unobserved surface bands were measured and fully characterized. One of the states is highly nonlocalized, dispersing throughout much of the valence band along the {bar {Gamma}}-{bar K}-{bar M}and {bar {Gamma}}-{bar M} directions of the 1{times}1 surface Brillouin zone. The identification of these states as surface bands was confirmed both by their lack of dispersion perpendicular to the surface, and by the sensitivity of the states to hydrogen adsorption. The symmetry properties of the states were determined using the linear polarization of the incident synchrotron radiation. These states are quite distant from the localized nondispersive surface state previously observed on GaN. {copyright} {ital 1999} {ital The American Physical Society}
Observations of nearshore infragravity waves: Seaward and shoreward propagating components
[1] The variation of seaward and shoreward infragravity energy fluxes across the shoaling and surf zones of a gently sloping sandy beach is estimated from field observations and related to forcing by groups of sea and swell, dissipation, and shoreline reflection. Data from collocated pressure and velocity sensors deployed between 1 and 6 m water depth are combined, using the assumption of cross-shore propagation, to decompose the infragravity wave field into shoreward and seaward propagating components. Seaward of the surf zone, shoreward propagating infragravity waves are amplified by nonlinear interactions with groups of sea and swell, and the shoreward infragravity energy flux increases in the onshore direction. In the surf zone, nonlinear phase coupling between infragravity waves and groups of sea and swell decreases, as does the shoreward infragravity energy flux, consistent with the cessation of nonlinear forcing and the increased importance of infragravity wave dissipation. Seaward propagating infragravity waves are not phase coupled to incident wave groups, and their energy levels suggest strong infragravity wave reflection near the shoreline. The cross-shore variation of the seaward energy flux is weaker than that of the shoreward flux, resulting in cross-shore variation of the squared infragravity reflection coefficient (ratio of seaward to shoreward energy flux) between about 0.4 and 1.5.