共查询到20条相似文献,搜索用时 31 毫秒
1.
Magnetization-induced optical surface second harmonic generation (SHG) in the longitudinal geometry was used to study magnetism on the p(1 x 1)O/Fe(001) surface during a layer-by-layer Fe growth with surfactant oxygen. Considerable one-monolayer oscillations were observed. Minima of the magnetization-induced contributions to the second order dielectric susceptibility were detected at half-filled monolayers. These contributions were accessed either by measuring a purely magnetic SHG yield, or indirectly from the magnetization dependence of the overall SHG signal, both providing consistent results. The origin of the oscillatory surface magnetism is consistent with the expected oscillating oxygen induced relaxation due to the surface Fe islands. 相似文献
2.
Native oxidation of the Si(111)(1 x 1)H surface causes the appearance and disappearance of second-harmonic generation (SHG) resonances related to specific bonding configurations of Si atoms at the interface. Resonances at 3.52 eV two-photon energy observed in p-polarized SHG spectra are indicative of a Si suboxide configuration present in a partially oxidized Si surface bilayer. Similar resonances are observed in spectra of thermally oxidized Si(111) and point to Si2+ suboxide states at the buried interface. 相似文献
3.
Deposition of Au nanoparticles from aqueous HF onto H–Si(1 1 1) was studied in situ by surface second harmonic generation (SHG) and ex situ by extinction spectroscopy and non-contact atomic force microscopy (AFM). AFM measurements indicate that the maximum SHG intensities occur at lateral particle diameters of approximately 90–100 nm independent of solution phase composition, but with an intensity that depends on solution phase composition.
Employing the evolution of SHG intensity to monitor lateral cluster growth, simultaneous Au deposition and Si oxidation exhibit apparent kinetic reaction orders of 1/2 and zero with respect to HF and Au(CN)2−, respectively. These results are similar to those obtained purely from ex situ AFM analysis. The variations in SHG intensity with Au(CN)2− concentration can be related to particle nucleation densities. These results demonstrate the utility of SHG as an in situ probe of particle growth. 相似文献
4.
The asymmetric distributions of surface optical second harmonic generation
(SHG) through azimuthally angular scans of (111) silicon wafers on which
thin silver films were deposited, have been detected with different
polarizations of output beams. On account of the inversion symmetry of
silicon crystals, the SHG for the Ag/Si system is mainly contributed by the
silver film and the silicon surface. In this work, we found that the
interface strain implies an asymmetric intensity variation of SHG with
respect to the surface azimuthal angles as an ultra thin Ag film is
deposited on silicon wafers. This asymmetric behavior is prominent as the
deposited silver layer is heated so that the continuous film aggregates to
become granular nanoparticles. Similar changes of the surface asymmetric SHG
are observed for a bare Si wafer imposed upon by an external force. 相似文献
5.
The adsorption process of chlorine on Si(1 1 1) has been studied by means of real time surface differential reflectance (SDR) spectroscopy and second harmonic generation (SHG). The structure observed at 3.6 eV in SDR spectra is attributed to transitions including Si–Cl antibonding states. However, the overall feature is due to the removal of the electronic states of the clean surface. Developments of adsorption on Si adatom dangling bonds and breaking of adatom back bonds are obtained from SDR spectra and second harmonic (SH) intensity. They are well fit by the solutions of the rate equations under the assumption of adsorption of atoms without migration, and the initial sticking probability on the dangling bonds and the initial breaking probability of the back bonds are determined. Dependence of the adsorption kinetics on the carrier concentration is briefly reported. 相似文献
6.
《Surface science》1997,385(1):l917-l921
The structural ordering of surface atoms during Si deposition on singular and vicinal GaAs(001) surfaces has been studied by reflectance difference (RD) spectroscopy using the difference function between the Si-covered and the bare surface. In dependence on the Si coverage the difference spectra correspond to RD spectra of the bare Si(001)-(1×2) or of the As-terminated Si(001):As(2×1) surface. This finding and the behaviour of RD transients recorded at 3.8 eV photon energy allows to define a (3×2)α phase with Si dimers in the top layer and Ga dimers in the third layer, and a (3×2)β phase with As-dimer rows on top of Si in the second layer. 相似文献
7.
The phase and intensity of optical second harmonic generation (SHG) were studied in Ag deposition on the Si(1 1 1) surfaces. The 7×7 reconstruction of the surface changed to the 1×1 structure in room temperature deposition. The SHG intensity reduced and the phase shifted to +180° with this structural change. Meanwhile, the 7×7 reconstruction changed to the
reconstruction in 400 °C deposition. With this structural change, the SHG intensity increased and the phase shifted to −250°. An analysis with anharmonic oscillator model showed that the changes in room temperature deposition were due to the quenching of the surface dangling bond states of the 7×7 reconstruction by the Ag deposition, whereas those in 400 °C deposition were due to the appearance of new surface states of the
reconstruction. 相似文献
8.
Figliozzi P Sun L Jiang Y Matlis N Mattern B Downer MC Withrow SP White CW Mochán WL Mendoza BS 《Physical review letters》2005,94(4):047401
Optical second-harmonic generation (SHG) is used as a noninvasive probe of the interfaces of Si nanocrystals (NCs) embedded uniformly in an SiO2 matrix. Measurements of the generated SH mode verify that the second-harmonic polarization has a nonlocal dipole form proportional to (E x Delta inverted) E that depends on inhomogeneities in the incident field E, as proposed in recent models based on a locally noncentrosymmetric dipolar response averaged over the spherical NC interfaces. A two-beam SHG geometry is found to enhance this polarization greatly compared to single-beam SHG, yielding strong signals useful for scanning, spectroscopy, and real-time monitoring. This configuration provides a general strategy for enhancing the second-order nonlinear response of centrosymmetric samples, as demonstrated here for both Si nanocomposites and their glass substrates. 相似文献
9.
利用缀加平面波加局域轨道(APW+LO)的第一性原理方法计算了β-SiC(001)-(2×1)表面的原子及电子结构. 原子结构的计算结果表明,与Si(001)-(2×1) 表面的非对称性Si二聚体模型不同,β-SiC(001)-(2×1)表面为对称性的Si二聚体模型,其二聚体的Si原子间键长也较大,为0.269nm. 电子结构的计算结果表明,在费米能级处有明显的态密度,因此β-SiC(001)-(2×1)表面呈金属性. 在带隙附近存在四个表面态带,其中的两个占有表面态带已由价带的同步辐射光电子能谱实验得到证实.
关键词:
碳化硅
缀加平面波加局域轨道方法
原子结构
电子结构 相似文献
10.
W. Daum 《Applied Physics A: Materials Science & Processing》2007,87(3):451-460
Optical second-harmonic generation (SHG) studies of Si/SiO2 interfaces by resonant two-photon excitation of Si interband transitions are reviewed. Three different types of interband
resonances at Si interfaces are identified in SHG spectra: (i) E1 and E2 critical-point bulk interband transitions in the space-charge region of charged Si interfaces, (ii) E1- and E2-type transitions associated with Si atoms at the interface in bulk-like tetrahedral coordination, and (iii) transitions related
to Si interface atoms with bonding properties specific of the atomic structure of the interface. The effects of the polarity
of space-charge fields on SHG spectra of Si(100)/SiO2 interfaces are also discussed.
PACS 73.40.Qv; 73.20.-r; 42.65.Ky 相似文献
11.
The growth of thin K films on Si(1 1 1)-7 × 7 has been investigated by selecting the input and output polarizations of second-harmonic generation (SHG) at room temperature (RT) and at an elevated temperature of 350 °C. The SH intensity at 350 °C showed a monotonic increase with K coverages up to a saturated level, where low energy electron diffraction (LEED) showed a 3 × 1 reconstructed structure. The additional deposition onto the K-saturated surface at 350 °C showed only a marginal change in the SH intensity. These variations are different from the multi-component variations up to 1 ML and orders of magnitude increase due to excitation of plasmons in the multilayers at RT. The variations of SHG during desorption of K at 350 °C showed a two-step decay with a marked shoulder which most likely corresponds to the saturation K coverage of the Si(1 1 1)-3 × 1-K surface. The dominant tensor elements contributing to SHG are also identified for each surface. 相似文献
12.
13.
Karl Mandel Wojciech Szczerba Andreas F. Thünemann Heinrich Riesemeier Matthias Girod Gerhard Sextl 《Journal of nanoparticle research》2012,14(8):1-9
Using density functional theory, we systematically investigate the adsorption geometries and electrical properties of (3,3) carbon nanotube (CNT) integrated on hydrogen-terminated Si(001):1?×?1 surface. Prior to adsorption of the CNT, the surface is patterned in two different ways by desorbing selective hydrogen atoms from the surface. The (3,3) CNT which is metallic in nature becomes semiconducting with a band gap around the fermi level when it is supported on patterned hydrogen-terminated Si(001):1?×?1 surface. However, the band gap is reduced when a transverse electric field is applied, allowing the (3,3) CNT on the patterned hydrogen-terminated Si(001):1?×?1 to become metallic at a critical field strength. The tuning of electrical properties of the (3,3) CNT integrated with Si surface may have potential technological applications. 相似文献
14.
The dimer configurations on the Si(001) surface at high temperatures have been investigated using the rocking curve of reflection high-energy electron diffraction. The Si(001) surface shows a displacive phase transition around 900 K, where a well-known asymmetric (tilted) dimer structure on the Si(001) at room temperature transforms to a symmetric dimer structure around 900 K. The metallic feature of the Si(001) surface above 900 K can be explained by the phase transition. 相似文献
15.
The optical, electrical, and chemical properties of semiconductor surfaces are largely determined by their electronic states close to the Fermi level (E{F}). We use scanning tunneling microscopy and density functional theory to clarify the fundamental nature of the ground state Ge(001) electronic structure near E{F}, and resolve previously contradictory photoemission and tunneling spectroscopy data. The highest energy occupied surface states were found to be exclusively back bond states, in contrast to the Si(001) surface, where dangling bond states also lie at the top of the valence band. 相似文献
16.
The chemisorption of one monolayer of Fe atoms on a Au-passivated Si(001) surface is studied by using the self-consistent tight-binding linear muffin-tin orbital method. The Fe adatom chemisorption on an ideal Si(001) surface is also considered for comparison. The chemisorption energy and layer projected density of states for a monolayer of Fe atoms on Au-passivated Si(001) surface are calculated and compared with that of the Fe atoms on an ideal Si(001) surface. The charge transfer is investigated. It is found that the most stable position is at the fourfold hollow site for the adsorbed Fe atoms, which might sit below the Au surface. Therefore there will be a Au-Fe mixed layer at the Fe/Au-Si(100) interface. It is found that the adsorbed Fe atoms cannot sit below the Si surface, indicating that a buffer layer of Au atoms may hinder the intermixing of Fe atoms and Si atoms at the Fe/Au-Si(001) interface effectively, which is in agreement with the experimental results. 相似文献
17.
《Surface science》1987,179(1):L63-L70
A phase transition between c(4 × 2) and (2 × 1) structures on the clean Si(001) surface has been observed at about 200 K by low energy electron diffraction. From the temperature dependence of the width and intensity of the diffraction spots this transition is concluded to be a second order order-disorder transition. The transition proceeds by a single stage, which is in strong contrast with the case of Ge(001) for which a two-stage transition has been reported. 相似文献
18.
用基于Chadi模型和格林函数方法的一种计算表面应力的半经验方法研究了Sb吸附在Si(001) 衬底上的性质.结果显示,Sb原子在Si(001)表面形成对称的dimer,其键长为0.293nm,表 面以下层的弛豫很小.Sb/Si(001)2×1表面沿着dimer方向的张应力为1.0eV/(1×1cell),而 沿垂直于dimer方向的压应力为-1.1eV/(1×1cell).Sb/Si(001)表面应力的主要贡献来自于 最上面三层表面.
关键词:
表面应力
异质生长
格林函数方法 相似文献
19.
?. Kadero?lu Z. Aydu?an B. Alkan M. ?akmak 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,76(3):359-363
The atomic and electronic properties of the adsorption of tert-butanol
[(CH3)3OH] molecule on the Si(001)-(2×1) surface have been
studied by using the ab-initio density functional theory (DFT) based
on pseudopotential approach. We have found that tert-butanol bonded the Si(001) surface by oxygen atom, cleaving
a O–H bond and producing a Si-H bond and tert-butoxy surface species. We
have also investigated the influence of chemisorption of tert-butanol on the
electronic structure of the clean Si(001)-(2×1) surface. Two occupied
surface states situated entirely below the bulk valence band maximum have
been identified, which means that the clean Si(001)-(2×1)surface was passivated by the chemisorption of tert-butanol. In order
to explain
the nature of the surface components we have also plotted the total and partial
charge densities at the [`(K)]\bar{K} point of the surface Brillouin zone (SBZ). 相似文献
20.
N. I. Plyusnin V. M. Il’yashchenko S. A. Kitan’ N. A. Tarima 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2011,5(4):734-745
Auger-electron spectroscopy, electron-energy loss spectroscopy, low-energy electron diffraction, and atomic-force microscopy
are employed to investigate the growth mechanism, composition, structural and phase states, and morphology of Cu films (0.1–1
nm thick) deposited on a Si(001)-2 × 1 surface at a lower temperature of Cu evaporation (900°C) and room temperature of a
substrate. The Cu film phase is shown to start growing on the Si(001)−2 × 1 surface after three Cu monolayers (MLs) are condensed. It has been revealed that atoms of Cu and Si(001) are mixed, a
Cu2Si film phase is formed, and, thereafter, Cu3Si islands arise at a larger coating thickness. Annealing of the first Cu ML leads to reconstruction of the Si(001)-1 × 1-Cu
surface layer, thereby modifying the film growth mechanism. As a consequence, the Cu2Si film phase arises when the thickness reaches two to four MLs, and bulk Cu3Si silicide islands begin growing at five to ten MLs. When islands continue to grow, their height and density reach, respectively,
1.5 nm and 2 × 1011 cm−2 and the island area is 70% of the substrate surface at a thickness of ten MLs. 相似文献