Surface Wave Resonance Conditions Research Articles

Relation between Auger enhancements and wave field of high energy electrons for planar surface bilayer of InP(111)A-(1 × 1)

The wave field of reflection high energy electron diffraction has been calculated for the compressed surface bilayer of InP(111)A-(1 × 1). At azimuth, the wave field behavior on In and P atoms in the first bilayer is similar because both atomic positions are close to each other. Depending on the glancing angle, wave field intensities have two prominent peaks under the surface wave resonance condition. Similarly, Auger electron intensities of In-MNN and P-LMM increase with wave field behavior. It has been observed for the first time that the correlation between Auger intensity and wave field intensity exists for such a planar surface bilayer.

Auger intensity anomalies from the Si(001)2 × 1 surface excited by the wave field of RHEED

The Auger intensity of Si‐LVV from the Si(001)2 × 1 surface has been measured at room temperature while changing the glancing angle of the incident electron beam of reflection high‐energy electron diffraction (RHEED). Such a beam‐rocking Auger electron spectroscopy (BRAES) profile shows intensity anomalies under surface wave resonance conditions. The surface structure of Si(001)2 × 1 has been analyzed by rocking curves of diffraction spots within the 0th Laue zone. Since RHEED intensities limited to the 0th Laue zone can be determined by the projected potential of Si atomic rows along the incident azimuth, the phase of asymmetric dimers with flip‐flop motion can be neglected. According to the Si(001)2 × 1 surface structure model which was confirmed by the rocking curve analysis, it was found that the calculated wave‐field intensity profile for Si atoms reveals similar intensity anomalies to those of the experimental BRAES profile. The background profile is also discussed in terms of the beam irradiation area and its transmissivity. Copyright © 2014 John Wiley & Sons, Ltd.

ELECTRON STANDING WAVES AT A SURFACE DURING REFLECTION HIGH ENERGY ELECTRON DIFFRACTION AND APPLICATION TO STRUCTURE ANALYSIS

During observation of reflection high energy electron diffraction (RHEED), the interference between the incident and diffracted beams leads to the formation of surface electron standing waves. Characteristic X-ray emission is strongly excited if the atom exists in a strong wave field. Therefore, X-ray yields depends on the position of the atom and incident glancing angle (θg) of the electron beam, since the distribution of these waves changes with θg. Such anomalous intensities of X-ray emission are clearly observed under both Bragg and surface wave resonance conditions. By using these intensities, the height and adsorption site of surface adatoms can be analyzed. In this review, surface electron channeling and its application to surface structure analysis are discussed.

Anomalous X-Ray Yields under Surface Wave Resonance during Reflection High Energy Electron Diffraction and Adatom Site Determination

In L x-ray emissions from a Si(111)-sqrt[3]xsqrt[3]-In surface induced by electron beam irradiation were measured as functions of the incident glancing angle. Under surface wave resonance conditions, anomalous x-ray intensities were clearly observed. Using dynamical calculations, these intensities are well explained as changes in density of the electron wave field at adatom positions. From these intensities, the adatom site was analyzed, and it was found that the T4 model is better than the H3 model.

Wave fields in Si(111) layers under RHEED conditions

Wave fields under the condition of reflection high-energy electron diffraction have been calculated based on a dynamical theory of electron diffraction. In order to study the fundamental behavior of the wave field, calculations have been carried out for simple crystal models which consist of several atomic layers from a single monolayer to three bilayers of the bulk terminated Si(111) surface. Density maps of the wave fields in the model crystals are presented for various glancing angles. Relations between the wave fields and rocking curves are also discussed in detail. It is found under surface wave resonance conditions of internal emergence threshold that the wave field concentrates very intensely in the middle of the first bilayer. The calculated rocking curve of the specularly reflected beam has a very intense peak. It is demonstrated that examination of the wave field is useful in clarifying the origin of each peak in the rocking curve.

Convergent-beam RHEED calculations of a `forbidden reflection' from the Si (111) surface

Results of convergent-beam reflection high-energy electron diffraction (CB-RHEED) calculations are presented for the (111) surface of silicon. These double rocking calculations are performed using a dynamical scattering approach. This is based on evaluation of the surface parallel multislice matrix for reflection with account taken of the boundary conditions. In particular, calculations are shown for intensities close to a reflection that is kinematically forbidden. Particular note is made of the computational simulation of intensity enhancements corresponding to surface wave resonance conditions.

Surface wave excitation auger electron spectroscopy of lnGaAs/GaAs(001) grown by alternate molecular-beam epitaxy

An angle-resolved electron-beam-excitation Auger-electron-spectroscopy, called as “surface wave excitation Auger electron spectroscopy (SWEAES),” was developed to characterize the semiconductor surface on an atomic scale. SWEAES enables us to get information about (1) surface valence electron states, (2) surface inner potentials concerned with high energy electron diffraction at the surface wave resonance (SWR) condition, (3) surface composition of ultra-thin heterostructures, and (4) confinement effects of diffracted surface electron waves at the SWR condition. These effects were demonstrated for In1-xGaxAs/GaAs(001)-c(8 × 2)-In/Ga and (GaAs)2/(InAs)1/GaAs(001) strained single quantum well surfaces.

Angle-resolved electron energy-loss spectra from Si(111)−7 × 7 surface under surface wave resonance condition for low-energy electrons

Low-energy electron energy-loss spectra (LEELS) from Si(111)−7 × 7 surface were measured under surface wave resonance (SWR) conditions, under which (1) the electron beam forms a surface wave of the 1 7 -order superlattice reflections (SWR s), and (2) the beam forms the surface wave and another surface wave of fundamental lattice reflections (SWR b) simultaneously. The peak heights at 5, 7.5 and 15 eV in energy-loss value, Δ E, which are associated with a bulk band state and two surface states due to backbonds respectively, became slightly large under the SWR b condition. On the other hand, in the LEELS under the SWR s condition, the peak height at ΔE = 1–2 and 8–9 eV was enhanced. Since the peak at 1–2 eV is known to be associated with the surface state due to dangling-bonds, it is considered that LEELS measurement under the SWR s condition reflects some information on electronic structure of Si(111)−7 × 7 surface. Then it is also discussed that the peak at ΔE = 8–9 eV under the SWR s condition is due to excitation of a collective motion for electrons in the dangling-bonds out of the first plane of surface atoms.

Angle-resolved electron energy-loss spectra from Si(111)-7×7 surface under surface wave resonance condition for low-energy electrons

Angle-resolved electron energy-loss spectra from Si(111)-7×7 surface under surface wave resonance condition for low-energy electrons

Surface wave resonance effect in low-energy electron energy-loss spectra from MgO(001)

The study the influence of inelastic diffraction on low-energy electron energy-loss spectra (LEELS), the LEELS from an air-cleaved (001) face of MgO were observed for various values of energy and angle of incidence of primary electrons, scattering angle and azimuthai angle. It has been confirmed that the LEELS consist of two kinds of loss peaks: those associated with an energy loss after the elastic diffraction and those associated with an energy loss before the elastic diffraction (Kikuchi line). The latter is observable only when inelastically scattered electrons are diffracted under the surface wave resonance (SWR) conditions. It has also been found that the Kikuchi Une splits into two with an intensity dip at the centre under one of the SWR conditions.

Intensity anomalies of auger electron signals observed by incident beam rocking method for Si(111)7 × 7 and Si(111)√3 ×√3Ag surfaces

Auger electron signal intensities of Si(LVV) fron clean surface and Si(LVV) and Ag(MNN) from√3 ×√3 Ag surface are measured for various incident angles in [112] orientation of 10 kV electron incidence. RHEED pattern is simultaneously observed during the measurement of the Auger electron signal intensities. Enhancements of Si(LVV) from the clean surface are observed in the surface wave resonance(SWR) conditions due to the 7×7 surface structure. The enhancements are reduced by deposition of silver on clean surface and constructing the √3 ×√3 structure. Enhancements of Ag(MNN) from √3 ×√3Ag surface are observed at the SWR condition due to√3 ×√3 structure. At the angles of the SWR condition due to√3 structure, Si(LVV) signal intensity is not enhanced.

Intensity anomalies of auger electron signals observed by incident beam rocking method for magnesium oxide (001) surface

Auger electron yields of Mg(KLL), Mg(LVV) and O(KLL) from the magnesium oxide (001) surface are measured for various glancing angles of 10 kV incident electron beams in the [010] azimuth. The Auger electron yields are sharply enhanced at the surface wave resonance (SWR) conditions for vacuum cleaved clean surface. The rocking curve of the Mg(LVV) signal intensity is very sensitive to the surface conditions. For a surface contaminated by less than one monolayer of carbon atoms, the rocking curve profile of Mg(LVV) has a large dip at the SWR condition, while the KLL rocking curve profiles are enhanced at the SWR condition. It is considered that the change of the Mg(LVV) rocking curve profile by the contamination is caused by a change of electronic state of the valence electrons at the surface.

Surface wave resonance effect in low-energy electron energy-loss spectra from MgO(001)

The study the influence of inelastic diffraction on low-energy electron energy-loss spectra (LEELS), the LEELS from an air-cleaved (001) face of MgO were observed for various values of energy and angle of incidence of primary electrons, scattering angle and azimuthal angle. It has been confirmed that the LEELS consist of two kinds of loss peaks: those associated with an energy loss after the elastic diffraction and those associated with an energy loss before the elastic diffraction (Kikuchi line). The latter is observable only when inelastically scattered electrons are diffracted under the surface wave resonance (SWR) conditions. It has also been found that the Kikuchi line splits into two with an intensity dip at the centre under one of the SWR conditions.

Low-energy electron diffraction from the cleavage face (001) of magnesium oxide

With a triple-axis low-energy electron diffractometer, the intensity curves of the specular reflexion 00 from the cleaved face (001) of a MgO crystal were measured against the glancing angle, for the electrons in the energy range from 180 eV to 500 eV and for three crystal azimuths in a range near [010]. By the use of diagrams drawn on the basis of the Ewald construction to indicate the surface wave resonance conditions for various reciprocal rods, a number of fine structures as well as gross features of the intensity curves were interpreted fairly well in terms of the resonance effect.