Scanning tunneling microscopy/spectroscopy study of atomic and electronic structures of In[sub 2]O on InAs and In[sub 0.53]Ga[sub 0.47]As(001)-(4×2) surfaces (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.
Japanese Journal of Applied Physics, 1997
We have investigated monolayer and multilayer islands of La 2 @C 80 and La@C 82 molecules grown on a hydrogen-terminated Si(100)-2 × 1 surfaces by ultrahigh vacuum scanning tunneling microscopy. The observed La 2 @C 80 molecule has a spherical shape, consistent with a recent result by synchrotron X-ray measurements. The energy gap for the La 2 @C 80 multilayer islands is measured to be 1.3−1.5 eV, whereas that for La@C 82 is 0.5 eV, indicating that the I h cage of the La 2 @C 80 molecule is highly stabilized by an electron transfer from the encaged La atoms.
Atom-resolved surface chemistry studied by scanning tunneling microscopy and spectroscopy
Physical review, 1989
We have used scanning tunneling microscopy and spectroscopy to study the reaction of Si(111)-(7X 7) with NH3. We have found that by use of topographs obtained at different energies, as well as atom-resolved spectra, reacted and unreacted surface sites can be imaged selectively. Thus we have been able to probe the spatial distribution of the surface reaction on an atom-by-atom basis. We find that there are significant differences in reactivity between the various dangling-bond sites on the Si(111)-(7X 7) surface. Specifically, rest-atom sites are more reactive than adatom sites and, moreover, center-adatom sites are more reactive than corner-adatom sites. We ascribe the reduced reactivity at adatom sites to the delocalized nature of their dangling-bond state. We suggest that a bonding interaction between adatoms and the Si atoms directly below them is responsible for this behaviora suggestion supported by electronic-structure calculations. Thus, while reaction at a rest-atom site can be considered a dangling-bond saturation process, reaction at an adatom site involves the formation of a hypervalent (fivefold-coordinated) adatom. We tentatively ascribe the reactivity differences between center and corner adatoms to differences in the strain they induce upon reaction on the dimer bonds. Atom-resolved spectroscopy allows us to probe interactions and charge transfer between surface sites, and for the first time, we can directly observe how chemisorption affects the substrate electronic structure at neighboring unreacted sites.
Atomic structure and electronic properties of the In/Si(111)2×2 surface
The Si(111)2×2-In reconstruction can be considered as a precursor phase for the formation of the metallic √ 7 × √ 3 phases of In overlayers on a Si(111) surface. Using the ab initio random structure searching method, comparison of simulated and experimental scanning tunneling microscopy images, and resemblance of the calculated band structure to the experimental angle-resolved photoelectron spectra, we examined various 2 × 2 structure models with 0.5, 0.75, 1.0, and 1.25 monolayer In coverage. The only model which fits well all the requirements is the one-monolayer model, where three In atoms in the T 4 sites form a trimer centered in the H 3 site and the fourth In atom occupies the on-top (T 1 ) site.
Surface Science, 2011
Tin (Sn) induced (1 × 2) reconstructions on GaAs(100) and InAs(100) substrates have been studied by low energy electron diffraction (LEED), photoelectron spectroscopy, scanning tunneling microscopy/spectroscopy (STM/STS) and ab initio calculations. The comparison of measured and calculated STM images and surface core-level shifts shows that these surfaces can be well described with the energetically stable building blocks that consist of Sn-III dimers. Furthermore, a new Sn-induced (1 × 4) reconstruction was found. In this reconstruction the occupied dangling bonds are closer to each other than in the more symmetric (1 × 2) reconstruction, and it is shown that the (1 × 4) reconstruction is stabilized as the adatom size increases.
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.
Physical Review B, 2003
Ab initio density-functional-theory-local-density-approximation electronic structure calculations are performed for the InAs͑110͒ surface and compared with scanning tunnel microscopy ͑STM͒ measurements using the Tersoff-Hamann model. In both, calculations and measurements, we see the same atomic features. At negative and small positive energies, the local density of states is concentrated around the As atom, while at higher positive energies it is centered above the In atom, because of the appearance of the In dangling bond. Moreover, we describe two types of irregular STM images on the InAs͑110͒ surface. First, we measure dI/dV images exhibiting atomic resolution at voltages within the band gap, which, however, still can be understood within the Tersoff-Hamann model as due to a higher-order term. Second, we measure features on the subatomic scale with certain tips at low tip-sample distance, which are most likely caused by elastic interactions between the tip and the surface.
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.
Scanning tunnelling spectroscopy of quantized electron accumulation at InxGa1−xN surfaces
physica status solidi (a), 2006
Electron tunnelling spectroscopy has been used to investigate quantized levels in electron accumulation layers at InGaN surfaces. The tunnelling spectra exhibit a plateau in the normalized conductance which widens with increasing Ga-content, corresponding to the band gap of InGaN. The measured In x Ga 1-x N band gaps (between ~0.65 eV for x = 1 and 1.8 eV for x = 0.43) are consistent with the band gaps determined by previous optical absorption and cathodoluminescence spectroscopy. Additional structures in the spectra reflect the two-dimensional electronic subbands in the surface quantum well. The subband energies depend on Ga-content, bulk doping level and the resultant shape of the surface potential well. The tunnelling spectra are compared with calculations of the potential well, the charge-profile and the subband energies.