共查询到20条相似文献,搜索用时 109 毫秒
1.
J. Pollmann R. Kalla P. Krüger A. Mazur G. Wolfgarten 《Applied Physics A: Materials Science & Processing》1986,41(1):21-38
A brief review on recent progress in the theory of electronic, structural, and vibronic properties of semiconductor surfaces is presented with particular emphasis on the empirical and selfconsistent scattering theoretical method for semiinfinite systems. The current knowledge of the Si(001) (2×1) surface is discussed in detail. The Ge(001) (2×1) surface, as well as, the clean and the Ge-covered GaAs(110) surfaces are addressed, in addition. In the discussion of the results it is shown, that the scattering theoretical method is an extremely versatile tool for calculating electronic surface properties unambiguously with high spectral resolution concerning energy, wavevector, layer-index and orbital type. Currently used approaches for calculating the total energy, Hellmann-Feynman forces and optimal structure models are summarized. Using the total energy as a starting point, the calculation of atomic force constants and surface phonon spectra is exemplified. 相似文献
2.
We review our recent results concerning surface-enhanced Raman scattering (SERS) by confined optical and surface optical phonons in semiconductor nanostructures including CdS, CuS, GaN, and ZnO nanocrystals, GaN and ZnO nanorods, and AlN nanowires. Enhancement of Raman scattering by confined optical phonons as well as appearance of new Raman modes with the frequencies different from those in ZnO bulk attributed to surface optical modes is observed in a series of nanostructures having different morphology located in the vicinity of metal nanoclusters (Ag, Au, and Pt). Assignment of surface optical modes is based on calculations performed in the frame of the dielectric continuum model. It is established that SERS by phonons has a resonant character. A maximal enhancement by optical phonons as high as 730 is achieved for CdS nanocrystals in double resonant conditions at the coincidence of laser energy with that of electronic transitions in semiconductor nanocrystals and localized surface plasmon resonance in metal nanoclusters. Even a higher enhancement is observed for SERS by surface optical modes in ZnO nanocrystals (above 104). Surface enhanced Raman scattering is used for studying phonon spectrum in nanocrystal ensembles with an ultra-low areal density on metal plasmonic nanostructures. 相似文献
3.
L. Mendonça-Ferreira F. T. Dias P. Pureur H. A. Borges P. RodriguesJr. X. Obradors 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,79(4):423-428
Strongly confined nano-systems, such as one-dimensional nanowires, feature deviations in their
structural, electronic and optical properties from the corresponding bulk. In this work, we investigate the
behavior of long-wavelength, optical phonons in vertical arrays of InAs nanowires by Raman spectroscopy. We
attribute the main changes in the spectral features to thermal anharmonicity, due to temperature effects, and
rule out the contribution of quantum confinement and Fano resonances. We also observe the appearance of
surface optical modes, whose details allow for a quantitative, independent estimation of the nanowire
diameter. The results shed light onto the mechanisms of lineshape change in low-dimensional InAs
nanostructures, and are useful to help tailoring their electronic and vibrational properties for novel
functionalities. 相似文献
4.
W.G. Schmidt 《Applied Physics A: Materials Science & Processing》2002,75(1):89-99
There has been renewed interest in the structure of III-V compound semiconductor (001) surfaces caused by recent experimental
and theoretical findings, which indicate that geometries different from the seemingly well-established dimer models describe
the surface ground state for specific preparation conditions. I review briefly the structure information available on the
(001) surfaces of GaP, InP, GaAs and InAs. These data are complemented with first-principles total-energy calculations. The
calculated surface phase diagrams are used to explain the experimental data and reveal that the stability of specific surface
structures depends largely on the relative size of the surface constituents. Several structural models for the Ga-rich GaAs (001)(4×6)
surface are discussed, but dismissed on energetic grounds. I discuss in some detail the electronic properties of the recently
proposed cation-rich GaAs (001)ζ(4×2) geometry.
Received: 18 May 2001 / Revised version: 23 July 2001 / Published online: 3 April 2002 相似文献
5.
A. Milekhin M. Friedrich D.R.T. Zahn L. Sveshnikova S. Repinsky 《Applied Physics A: Materials Science & Processing》1999,69(1):97-100
Structures with CdS quantum dots produced by the Langmuir–Blodgett (LB) technique were investigated by Raman, IR, and UV spectroscopies.
The confinement effect of longitudinal optical (LO) phonons in CdS quantum dots was investigated by Raman spectroscopy. Surface
vibrational modes of CdS quantum dots were observed in IR spectra. It was shown experimentally that the frequency of the surface
vibrational modes depends on the properties of the surrounding media. An average size of CdS quantum dots of about 3–6.4 nm
was obtained from the analysis of UV measurements.
Received: 1 February 1999 / Accepted: 1 April 1999 / Published online: 19 May 1999 相似文献
6.
Gyaneshwar P. Srivastava Huseyin M. T??t??nc?? 《Central European Journal of Physics》2009,7(2):209-219
We present a mini review of progress made towards theoretical modelling of surface phonons. We outline the essential ingredients
of two theoretical methods, viz. an adiabatic bond charge method for semiconductor surfaces and the ab-initio density-functional perturbation method for solid surfaces in general. From the results of theoretical calculations we establish
trends and criteria for the existence of localized phonon modes on group-IV(001) and III-V(110) semiconductor surfaces. We
further obtain signatures of characteristic vibrational modes which develop during dissociative molecular adsorption on Si(001)
surfaces. The results are compared with available experimental measurements. Some remarks are forwarded regarding manipulation
of surface phonon modes for scientific advances and technological applications.
相似文献
7.
A scanning tunneling microscopy study reveals the removal of P and In atoms at intrinsic surface sites of InP (110)-(1x1) through an electronic mechanism under ns-laser excitation. Femtosecond nonresonant ionization spectroscopy detects desorption of P and In atoms associated directly with the bond rupture, and shows their translational energies characteristic of electronic bong breaking. The rate of P-atom removal is 4 times higher than that of In-atom removal, revealing a prominent species-dependent effect of structural instability under electronic excitation on semiconductor surfaces. 相似文献
8.
H. Niehus 《Applied Physics A: Materials Science & Processing》1991,53(5):388-402
Low-energy ion backscattering and scanning tunneling microscopy (STM) have been used in combination to get better insight into the field of surface crystallography. The synergic effectiveness resulting from the complementing character of the two methods has been exemplified at clean NiAl(111) and for oxygen and nitrogen adsorption on Cu(110). The position of the atom cores is accessible by the low-energy noble gas impact collision ion scattering spectroscopy with neutral detection (NICISS). As a technique averaging over a macroscopic area of the sample, NICISS is better suited to supply information on features of completely developed phases, either on clean or adsorbate saturated surfaces. Additional information, on the other hand, can be gained by scanning tunneling microscopy (STM), which as a powerful local probe may be used to image surfaces with atomic resolution and to monitor defects, steps and the growth kinetics of e.g. adsorption-induced phase changes. 相似文献
9.
R. Koch M. Borbonus O. Haase K. H. Rieder 《Applied Physics A: Materials Science & Processing》1992,55(5):417-429
The fcc(110) surfaces are well known for their strong tendency to missing-row (MR) type reconstructions either in the clean state (Au, Pt) or driven by adsorbates (Ni, Cu, Pd, Ag). The present knowledge on the different reconstruction behaviour of flat (110) surfaces is reviewed. The survey focuses on recent scanning tunneling microscopy (STM) studies, which for the first time also elucidate the dynamics of the reconstruction process for the various systems. An overview of our recent STM and low energy electron diffraction studies on vicinal Au(110) and Ni(110) surfaces is given, aiming for a deeper understanding of the influence of steps on reconstruction behaviour of fcc(110) surfaces on the one hand, and on the stability of reconstructing vicinal surfaces on the other. Finally, we report on the reconstruction behaviour of Ir(110), which stabilizes in the clean state by formation of mesoscopic (331) facets and dereconstructs to the (1×1) phase upon oxygen adsorption at 700–900 K. 相似文献
10.
We present a comprehensive vibrational study of the clean and hydrogen- or deuterium-terminated silicon (0 0 1) surface. The modes related to the clean as well as to the H:Si, D:Si, and 2H:Si, 2D:Si surfaces are studied by means of high resolution electron energy loss spectroscopy (HREELS). We pay special attention to the modification of the phonon modes by the surface treatments and compare the data with reported experimental and theoretical results. The analysis of the relative phonon intensities of the clean, mono- and dihydride surfaces yields the assignment of the modes related to the dimer bonds. The isotopic shifts of vibrons related to the Si-H and Si-D bonds and to the surface phonon are discussed and applied to the characterisation of the surface excitations. 相似文献
11.
Anissa Gömann Karsten Gömann Volker Kempter Wolfgang Maus-Friedrichs 《Applied Surface Science》2005,252(1):196-199
Perovskites of ABO3 type like strontium titanate (SrTiO3) are of great practical concern as materials for oxygen sensors operating at high temperatures. It is well known that the surface layer shows different properties compared to the bulk. Numerous studies exist for the SrTiO3(1 0 0) and (1 1 0) surfaces which have investigated the changes in the electronic structure and topography as a function of the preparation conditions. They have indicated a rather complex behaviour of the surface and the near surface region of SrTiO3 at elevated temperatures. Up to now, the behaviour of the SrTiO3(1 1 1) surfaces under thermal treatment is not sufficiently known. This contribution is intended to work out the relation between alteration of the surface topography with respect to the preparation conditions and the simultaneous changes of the electronic structure. We applied scanning tunneling microscopy (STM) to investigate the surface topography and, additionally, metastable impact electron spectroscopy (MIES) to study the surface electronic structure of reconstructed SrTiO3(1 1 1) surfaces. The crystals were heated up to 1000 °C under reducing and oxidizing conditions. Both preparation conditions cause strong changes of the surface topography and electronic structure. A microfaceting of the topmost layers is found. 相似文献
12.
We report on the investigation of reconstructed semiconductor surfaces by Raman spectroscopy from dimer vibrations. Localized modes of Te dimers on the (100) surface of the zinc blende II-VI semiconductor BeTe allow the analysis of Te- and Be-rich surface structures, as well as oxidation effects. The Te-rich surface exhibits one dimer-vibration mode at 165 cm(-1), while two modes appear at the Be-rich surface (157 and 188 cm(-1)). The mode assignment as dimer vibrations is underscored by their symmetry properties and by frozen phonon calculations, yielding mode frequencies and eigenvectors. This approach opens up a new field of surface chemistry analysis by dimer-vibration spectroscopy. 相似文献
13.
T. Hannappel S. Visbeck K. Knorr J. Mahrt M. Zorn F. Willig 《Applied Physics A: Materials Science & Processing》1999,69(4):427-431
For the first time direct contamination-free transfer to UHV was achieved for the P-rich InP(100) surface that is the easiest
to prepare and control in the MOCVD environment. To avoid contamination during transfer a commercial MOCVD apparatus was modified
to allow for transfer of samples to the 10-9 mbar UHV range within a very short time (less than 20 s) [1]. Epitaxial InP(100) films were prepared with TBP (tertiarybutylphosphine)
and TMIn (trimethylindium) as precursors. In situ reflectance anisotropy spectroscopy (RAS) was carried out in the MOCVD environment.
After transfer of the sample to UHV the same RAS spectrum was recovered. Auger-electron spectra (AES) confirmed the P-termination
of the surface reconstructions suggested by RAS.
Received: 19 October 1998 / Accepted: 21 April 1999 / Published online: 14 July 1999 相似文献
14.
F. J. Himpsel 《Applied Physics A: Materials Science & Processing》1985,38(3):205-212
Our present understanding of the electronic structure of semiconductor surfaces is reviewed. It is shown that photoemission and inverse photoemission are ideal techniques for probing occupied and unoccupied electronic states, respectively. All quantum numbers of an electron can be determined, i.e., energy, momentum, spin and angular symmetries. For simple systems, such as clean ordered surfaces with a small unit cell it is possible to understand the electronic structure from first-principles calculations. For complex systems, such as encountered during oxidation and dry etching one is restricted to measuring the properties determined by short-range order. Core level spectroscopy with synchrotron radiation is able to determine the oxidation state and the local bonding of surface and interface atoms. 相似文献
15.
J.B. Gustafsson 《Surface science》2004,572(1):32-42
We have studied the thin film formation and the electronic structure of the organic molecular semiconductor 3,4,9,10 perylene tetracarboxylic dianhydride (PTCDA), on clean and on hydrogen-passivated Si(0 0 1) surfaces. The studies were made by means of high resolution X-ray photoelectron spectroscopy (HRXPS), angle-resolved photoelectron spectroscopy (ARPES), near edge X-ray absorption fine structure (NEXAFS) and low energy electron diffraction (LEED). On the H passivated surface the changes in the electronic structure of the substrate and the molecules with increasing film thickness are very small. The molecular orbitals show a dispersive behavior, indicating that the PTCDA layers are ordered. On the reactive clean surface the anhydride groups of the molecule interact with the substrate as indicated by changes in the core level binding energies. This results in a much lower ordering in the film compared to PTCDA on a passivated silicon surface. There is no sign of decomposition of the molecule because of the more reactive substrate. 相似文献
16.
J. A. Schaefer 《Physica B: Condensed Matter》1991,170(1-4):45-68
In this paper we will review the scientific literature which addresses the atomic geometry and electronic structure of clean and hydrogenated semiconductor surfaces. In particular, results related to vibrational studies will be presented. First, surfaces of elemental semiconductors (Ge, Si), Ge/Si-alloys, and III–V compound semiconductors chemisorb in a first stage atomic hydrogen by saturating surface atom dangling bonds. In a second step surface bonds are broken and a change of the geometrical structure results. Finally, higher hydrogen exposures are able to etch semiconductor surfaces. Best understood to date are surfaces of Si(1 0 0), Si(1 1 1), GexSi1−x(1 0 0), and III–V's after cleavage which have been modeled by dimerized and undimerized structures. (1 0 0) surfaces of III–V semiconductors, like GaAs and InP, tend to be dimerized, too. 相似文献
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19.
Energy-distribution measurements are reported for secondary electrons back-scattered into a narrow angle about the normal direction to three low-index tungsten single-crystal surfaces, viz. (100), (110) and (111). Improved spectral resolution provides unambiguous evidence for scattering out of excited “final” states located above the vacuum level; the results for all three faces correlate closely with high-energy states of a calculated energy band structure, the intensity of emission being directly related to features in the one-dimensional density of unfilled states along the corresponding low-index symmetry directions. In the presence of ordered adsorbate monolayers, additional SEE spectral fine-structure is observed at energies which lie within finalstate band gaps of the crystal. Results are presented for the specific case of CO adsorption on W(110), which shows a distinct disorder-order structural transition after exposure of the clean surface to 10 L of gas at 300 K and subsequent annealing to temperatures ?1000 K. We interpret these adsorbate surface resonances to be due to two-dimensional Bloch-like surface states produced by the periodicity of the adsorbate layer, which manifest themselves as a direct consequence of the special circumstances associated with “band-gap emission”. 相似文献