Spectrally resolved luminescence from an InGaAs quantum well induced by an ambient scanning tunneling microscope (original) (raw)
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Surface Science, 2002
Scanning tunneling microscopy (STM), Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED) were used to study the interaction of sulfur dioxide with the bulk-terminated (1 Â 1) and the reconstructed (1 Â 2) structure of the TiO 2 (1 1 0) surface at 300 K. During exposure new features appear first on the added rows of the reconstructed (1 Â 2) surface structure. In general these new features are randomly distributed, i.e., no ordered adsorbate phase builds up. However, in some areas locally ordered linear structures can be observed along the (1 Â 2) rows with a periodicity two or three times higher than the substrate. Similar to these observations, randomly distributed spots also appear on single added rows of the (1 Â 2) surface structure that are located on top of the (1 Â 1) structure of the TiO 2 (1 1 0) surface. In contrast, additional features on the (1 Â 1) structure itself can be seen only after higher SO 2 exposure. Here, an ordered adsorbate phase with a (2 Â 1) structure is formed. The new features of this (2 Â 1) structure are located on top of the (1 Â 1) rows along the [0 0 1] direction, which previously have been shown to represent the fivefold coordinated Ti surface cations. Subsequent AE spectra display a single peak in the sulfur region at 151.3 eV, confirming the predominant formation of Ti-S bonds during SO 2 exposures. In LEED a diffuse (1 Â 2) structure with faint (1 Â 2) half-order reflections can be seen, demonstrating the overall disorder on the surface. Point defects on the stoichiometric (1 Â 1) surface structure as well as on the reconstructed (1 Â 2) surface structure are unaffected by SO 2 exposure.
Journal of Molecular Catalysis
A theoretical simulation of STM/STS has been performed for various surface systems, based on the first-principles local density functional (LDA) calculation. Cluster models made of lo-20 atoms are utilized for the tip, and slab models with several atomic layers are adopted for the sample surface. The tunnel current is almost concentrated on a single apex atom, if the other atoms on the top of the tip are not located on the same level. In such a case the STM image is normal, with atomic resolution. However, if the apex of the tip is formed by more than one atom, abnormal images tend to be formed. We verify this feature by numerical results for graphite, Si(loo), and Si (111) /Ag surfaces, and discuss the light emission from STM, based on realistic calculations of the electronic states of the tip/sample systems.
Scanning tunneling microscopy of semiconductor surfaces
Surface Science Reports, 1996
This review describes advances in understanding the structural, electronic, and chemical properties of clean low-index semiconductor surfaces during the first decade following the advent of the scanning tunneling microscope (STM). The principles of STM are discussed together with the instrumentation required to perform STM measurements on semiconductor surfaces in ultrahigh vacuum. A comprehensive review of the structures of the clean, low-index surfaces of elemental and compound semiconductors is presented. These structures are discussed using the general physical principles that determine them.
Tunneling spectroscopy on semiconductors with a low surface state density
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1997
A detailed study of tunneling spectroscopy concerning semiconductors with a low surface state density is presented. For this purpose, I -V curves under dark conditions and under illumination were measured on the ͑0001͒ van der Waals surface of a p-type WS 2 single crystal, which is known to be free of intrinsic surface states. The measurements are interpreted by an analytical one-dimensional metal-insulator-semiconductor model, which shows that the presence of the finite tunneling current has to be considered in the calculation of the tip-induced bandbending. Rectification of the dark I -V curves is explained by the absence of an inversion layer at the semiconductor surface. In contrast, the I -V curves measured for different light intensities and tip-sample separations indicate the existence of an optically induced inversion layer. Since no surface recombination needs to be considered to model these spectra, we conclude that bulk recombination, diffusion and direct tunneling of photogenerated minority charge carriers are the dominant processes for semiconductors with a low density of surface states. In contrast to the standard interpretation of tunneling spectroscopy, which can be applied to semiconductors with a high surface state density, our results clearly show that in this case the normalized differential conductivity (dI/dU)/(I/U) cannot be used to determine the energetic distribution of the local surface state density.
Low-temperature scanning tunneling spectroscopy
Journal of Electron Spectroscopy and Related Phenomena, 2000
Low-temperature scanning tunneling spectroscopy measurements on semiconductor surface are described. We consider both surface which do not possess surface states within the bulk bandgap, such as GaAs , and surfaces which do have states within the gap, such as Ge and Ge(111)c(2×8). Band bending in the semiconductor due to the electric field in the vacuum penetrating the semiconductor is found to be a substantial effect in the former case. Transport limitations in the semiconductor give rise to additional voltage drops, which can be observed by making measurements over a wide range of tunnel current magnitudes.
Theory of Scanning Tunneling Microscopy and Spectroscopy
1990
A method for simulating scanning tunneling microscopy (STM) and spectroscopy (STS) is proposed, 0 which is effective at realistic tip-to-surface distances of 5-10 A, and its application is reported for Si(100) reconstructed surfaces. The vacuum tails of wave functions cannot be accurately described either by linear combination of atomic orbitals or by pure plane-wave expansion. An attempt is made to effectively describe the tail parts by combining this method with realistic calculations of the sample surface electronic states. The method is applied to Si(100) reconstructed surfaces and the features of the STM images and STS spectra of 2X1 dimer structures are clarified. This method confirms that the experimental c(4X2) image of STM is actually obtained from the c (4X2) structure and reveals how the buckling of dimers is rejected on the STM image.
Scanning tunneling spectroscopy reveals a silicon dangling bond charge state transition
New Journal of Physics, 2015
We report the study of single dangling bonds (DB) on the hydrogen terminated silicon (100) surface using a low temperature scanning tunneling microscope (LT-STM). By investigating samples prepared with different annealing temperatures, we establish the critical role of subsurface arsenic dopants on the DB electronic properties. We show that when the near surface concentration of
Scanning tunneling microscopy of sulfide surfaces
Geochimica et Cosmochimica Acta, 1990
A fundamental understanding of reactions that occur at mineral surfaces, many of which have bearing on important environmental issues, requires knowledge of atomic surface structures. Scanning tunneling microscopy (STM) is a new technique which can be used to image atomic surface structures in real space. We briefly review STM theory and interpret STM images of galena ( PbS) and pyrite ( FeS2) surfaces by comparing the bias-voltage dependence of the images to the electronic structures of the materials. This approach amounts to a form of tunneling spectroscopy which may ultimately be used to identify individual atoms on mineral surfaces. STM imaging was accomplished on fresh fracture surfaces as well as on surfaces that had been exposed to air for long periods of time. For galena, the Pb and S sites are distinguishable, and the S sites appear to be imaged preferentially. A galena surface which had been oxidized in air for several months was imaged, suggesting either that oxidation products are very thin, occur in local "patches" on the surface, or are both non-conducfive and not coherently bound to the galena surface. Iron appears to be imaged preferentially on fresh fracture surfaces of pyrite. Atomic positions on a pyrite growth surface were not those expected for a termination of the bulk pyrite structure; it is likely that a surface oxidation product was imaged.