Low Energy Electron Reflection Research Articles

E(k) above the Vacuum Level from Low Energy Electron Reflection. ΓK Line of Cu and Ni

Incidence angle dependent electron reflection coefficient curves R(E) measured in the 0 to 30 eV range on Cu(111) and Ni(111) surfaces are analysed. With incidence scanning in ΓK azimuth, some extrema of the dR/dE curves are shown to manifest bands along the ΓK line of the Brillouin zone. Comparing the experimental angular dispersion of these extrema with its calculated counterpart, bands along ΓK are mapped. Experimental technique and details of calculation are briefly discussed. [Russian Text Ignored].

Low energy electron reflection: Possibility for E(k) points mapping above the vacuum level

The elastic electron reflection energy derivative extremums unambiguously correspond to definite critical points of bands. These points may be precisely mapped comparing extremums experimental energies with preliminary roughly calculated ones. Angle dependences allow mapping of whole bands in symmetry planes. Presumable reflection coefficient approximation and experimental conditions are formulated.

Microprobe AES Combined With Scanning RHEED Microscope

Surface micro-structure analysis is very important for surface study in material science. Observations of surface atomic steps and reconstructed structures have been made using several techniques: reflection high energy electron microscopy (RHEEM), low energy electron reflection microscopy (LEERM) and low energy electron diffraction microscopy (LEEDM).In the present experiment, observations of surface micro-structures have been made using a scanning type reflection high energy electron diffraction (RHEED) microscopy. This technique has certain advantages of easy combinations with multiple surface analyzing techniques such as scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and electron energy loss spectroscopy (ELS).A schematic diagram of the scanning RHEED microscope combined with the microprobe AES is shown in Fig. 1. RHEED patterns are observed on the fluorescent screen through a viewing port. To observe the micro-structure (scanning RHEED image or dark field image), a particular diffraction spot is selected by means of the other small fluorescent screen with an aperture.

Spin-dependence of absorbed and reflected current on Fe(110) and a comparison with secondary electron polarization fine structure

Measurements of the normalized difference in the absorption and reflection of low-energy electrons with opposite spin-polarization, and the spin-polarization of low-energy secondary electrons, from Fe(110) are found to be influenced by the spin-split bulk band structure. Maxima and minima in the absorbed and reflected current asymmetries are interpreted in terms of band structure effects and are shown to be directly related to the spin-polarization fine structure in low-energy secondary electron emission from ferromagnets. The feasibility of using spin-dependent low-energy electron reflection from ferromagnets as an electron spin-polarization detector is discussed.

He diffraction study of the structural phase transition on the Ge(111) surface at 550 K

A structural phase transition on the Ge(111) surface is investigated using thermal energy He scattering by observing the temperature dependence of several diffraction peaks. The presence of strong quarter-order peaks confirms that the Ge(111) surface has three orientational domains of a c(2×8) reconstruction at room temperature. As the temperature rises, all the superlattice peaks decrease in intensity without broadening and disappear above 550 K. In addition there is one striking feature which has not been observed in earlier low energy electron diffraction and reflection high energy electron diffraction experiments. The half-order peak shows continuous broadening and a shift of its maximum toward the specular peak as the temperature increases above 550 K. Consideration of several possible explanations for such a peak shift suggests that the transition, which may be driven by a charge density wave, is to an incommensurate phase.

Numerical study of RF discharge caused by secondary electron emission

A numerical method is presented for studying an RF discharge caused by secondary electron emission from the electrode, i.e. the multipactoring discharge. Using this method, the precise thresholds of the electron multiplication are obtained systematically. Also, this method can be extended to a nonuniform configuration of the electrode and the applied field. For example, the simulation results are compared with typical experimental results in the previous work. Good agreement is obtained for parallel electrodes. Furthermore, an intermediate (subharmonics) mode is found between the usual resonant modes. In the case of the coaxial electrodes, the agreement was obtained when the reflection of low-energy electrons on the surface of the electrode was assumed.

On the resolution of the low-energy electron reflection microscope

A wave-electron-optical treatment of the low-energy electron reflection microscope is used to calculate the resolution in the presence of spherical and chromatic aberrations. An estimate based on a simple system shows that the limiting resolution coul be as small as 3 nm.

Transmission Electron Microscopy of Epitaxial silicides grown by ultra high vacuum deposition

The silicides CoSi2 and NiSi2 are both metallic with the fee flourite structure and lattice constants which are close to silicon (1.2% and 0.6% smaller at room temperature respectively) Consequently epitaxial cobalt and nickel disilicide can be grown on silicon. If these layers are formed by ultra high vacuum (UHV) deposition (also known as molecular beam epitaxy or MBE) their thickness can be controlled to within a few monolayers. Such ultrathin metal/silicon systems have many potential applications: for example electronic devices based on ballistic transport. They also provide a model system to study the properties of heterointerfaces. In this work we will discuss results obtained using in situ and ex situ transmission electron microscopy (TEM).In situ TEM is suited to the study of MBE growth for several reasons. It offers high spatial resolution and the ability to penetrate many monolayers of material. This is in contrast to the techniques which are usually employed for in situ measurements in MBE, for example low energy electron diffraction (LEED) and reflection high energy electron diffraction (RHEED), which are both sensitive to only a few monolayers at the surface.

Improvements to the image bandpass filter for electron and positron spectromicroscopy

The design and construction of a low-pass electron energy mirror with controllable image rotation and pass energy to operate in a magnetic field is described. Image rotation is radially uniform and rotations of up to approximately 40 degrees are demonstrated. A low-pass filter is described incorporating a virtual reflecting surface and a novel electron trap also operating in a magnetic field. This reduces the proportion of elastically and inelastically scattered high-energy electrons escaping the filter. Both the above elements are demonstrated working in an image bandpass filter operating in a photoelectron spectromicroscope. Low-energy (0-35 eV) electron absorption and reflection from a number of electrode surfaces is investigated and recommendations made on possible structures. A scheme is proposed whereby azimuthally averaged axial emission angles can be obtained from electrons emitted in a photoelectron spectromicroscope using an image bandpass filter. The devices considered are equally suited to the manipulation of low-energy positrons and will allow simultaneous positron-energy analysis and imaging.

Low-energy electron reflection and transmission on Ar films condensed on polycrystalline platinum

Low-energy electron reflection (LEER) and transmission (LEET) spectra have been recorded in the range 1–16 eV for argon films grown on polycrystalline platinum. The data are compared with low-energy electron diffraction (LEED) calculations of the elastic reflection and transmission of an electron beam incident on the (111) surface of a semi-infinite Ar solid azimuthally disordered. Structures in LEER spectra reflect essentially the band structure characteristics of the Ar(111) surface, whereas in transmission, similar structures are strongly modified by scattering from phonons, defects and imperfections of the film as evidenced by changes in LEET spectral line shapes as a function of incidence angle and film thickness. These findings are discussed in relation with the ability of the LEED formalism to describe elastic or quasi-elastic scattering from partially disordered films at very low energies.

High-resolution low-energy electron reflection from W(100) using the electron energy-loss spectrometer: A step towards quantitative analysis of surface vibrational spectra

High-resolution low-energy electron reflection measurements and electron energy-loss measurements for clean W(100) and for the hydrogen saturated phase (β1) on W(100) are reported. The ability to perform both low-energy reflectance, low-energy electron diffraction, and high-resolution electron energy-loss experiments on the same crystal using the same electron optics permits several novel experiments. For example, it is possible to quantitatively test the dipole scattering mechanism and examine dipole and impact loss cross sections under precisely defined scattering conditions (i.e., under diffracted beam emergence conditions or at energies corresponding to reflectance resonance conditions). Under certain scattering conditions, the ‘‘dipole’’ scattering selection rule is shown to break down. Suitable modifications of the electron optics control electronics also permit direct measurements of the cross-section energy dependence of vibrational losses. These new features represent an important step towards quantitative applications of vibrational spectroscopy based on comparing electron energy-loss spectroscopy signals from chemisorbed species on different crystal surfaces.

Monte carlo simulations of low-energy (

A Monte Carlo method is developed for simulating low-energy (< 10 eV) electron-impact transmission and reflection experiments. This method is applied to test the results obtained with various electron transport models which have recently been proposed for the interpretation of these experiments on thin solid xenon films. Particular attention is given to the critical examination of the adequacy of the assumption of isotropy of the collisions which is generally used in these models to calculate the various electron transport parameters, such as the elastic and inelastic electron scattering mean free paths. The simulation is also used to predict both the variation of the electron current transmitted through the films with the incident angle of the electron beam and the angular distribution of the reflected electrons.

A very low energy electron reflection study of hydrogen adsorption on W(100) and W(110) surfaces

A very low energy electron reflection study of hydrogen adsorption on W(100) and W(110) surfaces

A very low energy electron reflection study of hydrogen adsorption on W(100) and W(110) surfaces

Experimental results of the elastic backscattering of electrons with energies between 0 and 20 eV from the surface systems H/W(100) and H/W(110) are reported and interpreted on the basis of the Darwin model. On W(100) the adatom distance from the reconstructed substrate is found to be different from that on the relaxed surface. Large vertical displacements of the substrate atoms during reconstruction can be excluded. On W(110) the results indicate two different binding states which are occupied sequentially and which differ significantly in their distances from the surface. Work function change data are also reported for both systems.

Kinetics of the (7 × 7) ↔ (1 × 1) Transition on Si(111)

AbstractThe (7 × 7) ↔ (1 × 1) phase transition was investigated in situ by low energy electron reflection microscopy (LEERM). Heterogeneous nucleation of the (7 × 7) domains at monoatomic steps is observed as well as homogeneous nucleation in the atomically flat terraces. The density of nuclei and the domain growth velocity increase with the supercooling ΔT of the surface. The domains start to grow at low ΔT in triangular equilibrium shape; interaction of neighbouring domains leads to a dendritic overall shape. The observations strongly support the view that the transition is of first order.

On the energy dependence of the very low energy reflectance from clean and manganese‐doped MgO(100) surfaces

AbstractExperimental results of the energy dependence of very low incident energy (0 to 20 eV above the vacuum level) electron reflectance from undoped and from Mn‐doped MgO(100) surfaces are obtained. The fine features of the spectrum are discussed in terms of bulk and surface electronic interband transitions, defect center absorption, and impurity level resonance.

Electron reflection measurements on W(001) and W(110) between 0 and 40 eV

High resolution low energy electron reflection measurements from W(001) and W(110) in the range 0–40 eV are reported. Spectra recorded for a variety of angles of incidence in several different azimuths are presented. In particular, some fine structure features associated with beam thresholds are observed for all incidence conditions. However, it is found that other threshold effects are either absent or very weak. It is shown that this phenomenon is probably a consequence of the limited azimuthal resolution of the spectrometer used. Because of the variety of incidence conditions investigated, the measurements comprise a suitable data base for testing LEED calculation schemes in the very low energy range.

Electron reflection measurements on W(001) and W(110) between 0 and 40 eV

Abstract High resolution low energy electron reflection measurements from W(001) and W(110) in the range 0–40 eV are reported. Spectra recorded for a variety of angles of incidence in several different azimuths are presented. In particular, some fine structure features associated with beam thresholds are observed for all incidence conditions. However, it is found that other threshold effects are either absent or very weak. It is shown that this phenomenon is probably a consequence of the limited azimuthal resolution of the spectrometer used. Because of the variety of incidence conditions investigated, the measurements comprise a suitable data base for testing LEED calculation schemes in the very low energy range.

Total yield energy dependence of low-energy electrons from surfaces of ZnO crystals

The energy dependence of the reflection of low-energy incident electrons (of the range 0–18 eV above the vacuum level) from the polar zinc (0001) face, the non-polar (10 1 0) and the (11 2 0) faces of ZnO crystals is explained in terms of the onset of inelastic electron-electron scattering accompanied by interband transitions. Based on the spectra a revision of the band structure diagram for energies near the band gap is proposed.

Total yield energy dependence of low-energy electrons from surfaces of ZnO crystals

The energy dependence of the reflection of low-energy incident electrons (of the range 0–18 eV above the vacuum level) from the polar zinc (0001) face, the non-polar (1010) and the (1120) faces of ZnO crystals is explained in terms of the onset of inelastic electron-electron scattering accompanied by interband transitions. Based on the spectra a revision of the band structure diagram for energies near the band gap is proposed.