The oxidation of the GaAs (110) surface

It is demonstrated that, contrary to previous proposals, Ga surface atoms are already involved in the oxidation process for the lowest observable oxygen coverages (0.01 monolayer). A similar involvement of As atoms could not be readily ascertained experimentally, although it is to be expected from energetic considerations. An oxidation model consisting of multiple bridge bonds to both Ga and As surface atoms is proposed, which is consistent with diverse experimental data for the GaAs(110) surface.     

The surface geometry of GaAs(110)

Results of a fully dynamical low-energy electron diffraction calculation show that the GaAs(110) surface reconstructs with a top-layer tilt-angle of 27° ≤ ω ≤ 31°. The smaller tilt angle 7° ≤ ω ≤ 10° reported earlier is outside the error limits of the analysis and can be clearly ruled out. The results are independent of which R-factor or which set of existing experimental data is used. Lateral shifts larger than 0.1 Å for the surface atoms are necessary to obtain acceptable agreement with the measured intensity spectra.     

Surface states of GaAs (110): Pseudopotential calculations

In this letter we present calculations for surface states in high symmetry points Γ, M, X and X' of Jones' zone of GaAs (110), using a step barrier potential. It is found that only four surface states appear in the thermal gap; two in Γ point at 0.38 and 1.2 eV from the top of the valence band considered as origin of energies, one at 0.8 eV in M point and another in X′ point at 0.3 eV. Also, we obtain a low band of surface states between ?3 and ?5.5 eV.     

Optical detection of surface states in GaAs(110) and GaP(110)

We present results on the optical detection of surface states in GaAs(110)and GaP(110)by the method of the fractional change of external reflectivity. Optical transitions are observed at ～3.1 eV m GaAs(110) and ～3.4 eV in GaP. A comparison with existing theories suggests a rotational relaxation model for the surface, with partial relaxation for GaAs(110) and full relaxation for GaP(110).     

Electronic states near the band gap for the GaAs(110) surface

The recent theoretical controversy regarding empty surface states at the GaAs cleavage plane is examined by the exact solution of several tight binding models applied to a semi-infinite crystal. We correlate the existence of an empty surface gap state with the anion p/cation p character of this state. This work isolates the specific properties of a Hamiltonian for GaAs which yield band gap states on a relaxed surface and clarifies the essential differences among current theoretical treatments.     

Oxygen adsorption and the surface electronic structure of GaAs (110)

The surface electronic structure of cleaved GaAs (110) is found to be very sensitive to small amounts of adsorbed oxygen. For example, adsorbing oxygen on only a few percent of the surface Ga or As atomic sites can produce changes of a factor of two in the surface electronic structure. Thus, long range effects must be involved, and these are associated with rearrangement of the surface atoms.     

The surface geometry of GaAs(110): A response

A brief survey of the various surface structure analyses for GaAs(110) is presented. The interplay between studies based on low-energy-electron diffraction (LEED), ion channeling, ion scattering, photoemission and isochromat spectroscopy leads to a structure in which a relaxation within the top layer (characterized by a perpendicular displacement of the As and Ga species by $\text{Δ}{}_{\mathrm{1,\; \perp }}\text{= 0.69±0.05}\text{A}\text{?}$ with the As species relaxing outward by $\text{0.21±0.05}\text{A}\text{?}$ and the Ga species inward by $\text{0.48±0.05}\text{A}\text{?}$) is accompanied by a uniform relaxation of the top layer by $\text{0.05±0.1}\text{A}\text{?}$ toward the substrate and a perpendicular displacement in the second layer in the opposite sense by $\text{0.06±0.1}\text{A}\text{?}$. The displacements of the top-layer Ga and As species parallel to the surface remain controversial. LEED and medium-energy ion-scattering analysis favor bond-length-conserving rotated top-layer structures (i.e., large $\text{(Δd}{}_{\mathrm{|}}\text{～ 0.3}\text{A}\text{?}\text{)}$ displacements parallel to the surface) whereas high-energy ion-channeling and isochromat spectroscopy experiments favor small displacements $\text{(Δd}{}_{\mathrm{|}}\text{? 0.1}\text{A}\text{?}\text{)}$ parallel to the surface.     

First-principles calculations of ammonia decomposition on Ni(110) surface

First-principles calculations based on density functional theory (DFT) have been performed to study the adsorption and decomposition of NH₃ on Ni(110). The adsorption sites, the adsorption energies, the transition states and the activation energies of the stepwise dehydrogenation of NH₃ and the associative desorption of N are determined, and the zero point energy correction is included, which makes it possible to compute the rate constants of the elementary steps in NH₃ decomposition. Combined DFT calculations and kinetic analysis at 350 K indicate that the associative desorption of N has a reaction rate lower than NH_x dehydrogenation and is therefore the rate determining step. The distinctly different rate constants over Ni(110), Ni(111) and Ni(211) imply that ammonia decomposition over Ni-based catalyst is a structure-sensitive reaction.     

Surface states and metal overlayers on the (110) surface of GaAs

We have found new surface states related to Al overlayers on the (110) surface of GaAs. These states play a prominent role in the determination of the electronic structure for metal-semiconductor interfaces. The results are consistent with conjectures of Rowe, Christman and Margaritondo based upon recent experimental results for metal overlayers on semiconductor surfaces.     

True atomic resolution imaging of surface structure and surface charge on the GaAs(110)

We demonstrated a novel method to detect the van der Waals and the electrostatic force interactions simultaneously on an atomic scale, which is based on frequency modulation detection method. For the first time, the surface structure and the surface charge at atomic-scale point defects on the GaAs(110) surface have been simultaneously resolved with true atomic resolution under ultra-high vacuum condition. From the bias voltage dependence of the image contrast, we can verify that the sign of the atomically resolved surface charge at the point defect was positive.     

Dependence of the GaAs (110) surface electronic state dispersion curves on the surface relaxation angle

The surface state dispersion curves E($\text{k}$) of the dangling bond states near the fundamental band gap, C₃ and A₅, are computed for both the established θ?27° model and the recently proposed θ?7° model of the (110) surface relaxation of GaAs, where θ is the surface bond rotation angle. The two models produce surface state dispersion curves that are similar to one another and to the data.