STM measurements on the InAs(110) surface directly compared with surface electronic structure calculations (original) (raw)
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Surface Science, 2002
The structure of InAs(0 0 1)-ð2 Â 4Þ surfaces equilibrated under typical MBE conditions is studied by scanning tunneling microscopy (STM). Depending on the magnitude of the As flux, typical surfaces are found to contain a mixture of a2ð2 Â 4Þ and b2ð2 Â 4Þ reconstructions. The relative populations of the a2 and b2 reconstructions are found to depend on substrate temperature and the magnitude of the As flux. The atomic-scale details of the reconstructed units on these mixed-phase surfaces are definitively determined by comparing atomic-resolution dual-bias STM images to first-principles calculations. The imaging mechanism for revealing atomic-scale details, particularly the trench dimer, is found to be qualitatively similar to that for GaAs, although the effect is less pronounced. Additionally, a significant population of ad-atom related structures are observed on quenched surfaces, apparently unrelated to any equilibrium ad-atom population. Ó 2001 Published by Elsevier Science B.V.
Structure of the In-rich InAs (001) surface
Surface Science, 2012
Using scanning tunneling microscopy, frequency-modulated scanning atomic-force microscopy, electron diffraction, and density functional theory calculations we investigate a structure of the InAs (001) surface displaying c(8 × 2)/(4 × 2) reconstruction at room temperature. It is found that the room temperature data are satisfactorily interpreted based on the model proposed by Kumpf et al. [Phys. Rev. Lett. 86, 3586 (2001)], however, at cryogenic temperatures the model fails since a different structure, characterized by fourfold period along [110] crystallographic direction, partial disorder and instability, is observed. By the present study we find that the structure is described by corrected Kumpf et al. model where most of atomic rows are left as in the original model and only the dominant indium atom rows running along [110] are changed. At room temperature the dominant rows are disordered and rapidly fluctuate thermally while at cryogenic temperatures they convert to chains of indium aggregates and acquire fourfold period. Moreover, frequently observed incomplete occupancy of the dominant indium rows leads to many different local surface structures, reflected by characteristic "features" in scanning tunneling microscopy patterns. We have classified and explained most of these structures.
Origin of surface and subband states at the InAs(111)A surface
Physical Review Materials
The atomic structure of surfaces and interfaces plays a vital role in the electronic quality and properties of quantum devices. The interplay between the surface and confined bulk subband states in terms of their susceptibility has been investigated in relation to crystal defects on an InAs(111)A-(2 × 2) reconstructed surface, using low-temperature scanning tunneling microscopy and spectroscopy. We measure the two-dimensional quantized subband states arising from the confined potential imposed by downward bending of the conduction band edge. Furthermore, we show evidence of the existence of surface Bloch states within the confined bulk band gap projected on the surface spectrum which have originated from the surface reconstruction. As expected, larger confined bulk band gaps at the surface and conduction band offset are measured to be 0.58 and 0.31 eV, respectively. We further show the scattering of these quantum states at different surface defects and demonstrate that surface states are more susceptible to the defect potential when compared with the corresponding subband states. This apparent contrast follows from the length scale at which these defect potentials actively interact on or near the surface. Our observed experimental results are supported by empirical tight-binding simulations for the subband states and first-principles density functional theory simulations for the surface states present on the surface.
Bi-covered InAs(110) surfaces: An ab initio study
Surface Science, 2004
In this work we have performed an ab initio investigation of the Bi-covered InAs(1 1 0) surface. We have considered two different structural models viz. ECLS and (1 • 2) missing row model. Our total energy results indicate that the (1 • 2) model is energetically more favourable than the ECLS model, thus, supporting the recent experimental results by Betti et al. [Phys. Rev. B 59 (1999) 15760]. However, the calculated equilibrium atomic geometry indicates some disagreement with respect to the experimental measurements. The ''surface electronic topology'' of the Bi/InAs(1 1 0) surface was investigated through simulations of scanning tunneling microscopy (STM) images, where we inferred a semimetallic character along the Bi-chains of the (1 • 2) model.
Applied Surface Science, 1999
We present results of an atomic-scale study on in situ cleaved InAs͑110͒ in the dynamic mode of scanning force microscopy ͑SFM͒ at low temperatures. On a defect-free surface, the dynamic mode SFM images always exhibit strong maxima above the positions of the As atoms, where the total valence charge density has its maximum. Occasionally, with certain tips, the In atoms also become visible. However, their appearance strongly depends on the specific tip-sample interaction: We observed protrusions as well as depressions at the position of the In atoms. In this context, the role of the charge rearrangements induced by the specific electronic structure of the tip on the contrast in atomic-scale images is discussed in detail. Additionally, we investigated the appearance and nature of two different types of atomically resolved point defects. The most frequently observed point defect manifests itself as a missing protrusion, indicating the existence of an As vacancy. A second type of point defect is probably an In vacancy, which could be detected indirectly by its influence on the two neighboring As atoms at the surface. At large tip-sample distances, these As atoms show a reduced corrugation compared to the surrounding lattice, while at smaller tip-sample distances the corrugation is increased. This distance-dependent contrast inversion is explained by a relaxation of the As atoms above the defect which is induced by an attractive tip-sample interaction.
In-rich (4×2) and (2×4) reconstructions of the InAs(001) surface
Surface Science, 2003
Based on a first-principles pseudopotential calculation, within the local density approximation, we have studied a series of different structural models for the In-rich InAs(0 0 1) surface, including a very recent model proposed by Kumpf et al. based in X-ray diffraction experiments. Our data suggests that the f(4 · 2) model corresponds to the most probable structure, from the energetic point of view. The stability of the f(4 · 2) structure is mainly attributed to electrostatic and structural characteristics of the surface. The atomic and electronic structure of this system is analysed in detail. Experimental scanning tunnelling microscopy images are reinterpreted in the lights of our theoretical simulated images for the proposed structure, with a view to explain contradicting experimental and theoretical results.
Atomic structure and energetic stability of the Bi-covered InAs(110) surface
Brazilian Journal of Physics, 2004
We have performed ab initio calculations of the atomic structure and energetic stability of the Bi-covered InAs(110) surface. The calculations were performed within the density-functional theory, using normconserving fully separable ab initio pseudopotentials. Two experimentally proposed structural models have been considered: (1×1)-ECLS and (1×2). Our total energy calculations indicate that the formation of the (1×2) model is energetically more favourable than the (1×1) model by 41 meV/(1×2). The calculated equilibrium geometries, for the InAs(110)-Bi(1×1) and-Bi(1×2) surfaces, show in general a good agreement with the experimental x-ray measurements carried out by Betti et al.
Physical Review B, 2009
Structural properties of monatomic indium chains on Si͑111͒5 ϫ 2-Au surface are investigated by scanning tunneling microscopy ͑STM͒ and first-principles density functional calculations ͑DFT͒. The STM topography data show that submonolayer coverage of indium leads to a well-ordered chain structure with the same periodicity as the Si adatoms form on Si͑111͒5 ϫ 2-Au surface. Bias-dependent STM topography and spectroscopy reveal two different mechanisms of In-atoms adsorption on the surface: bonding to Si adatoms and substitution for Si atoms in the adatom positions. Those mechanisms are further corroborated by DFT calculations. The obtained structural model of In-modified Si͑111͒5 ϫ 2-Au surface remains in good agreement with the experimental data.