Photoelectron spectro-holography, represented by differential photoelectron holography and multi-energy X-ray photoelectron diffraction, is a new technique to investigate the structures of surface and interface. Using photoelectron holograms effectively, differential photoelectron holography reconstructs more precious atomic images than other photoelectron techniques, while multi-energy X-ray photoelectron reveals the structures of surface and interface in wide depth range from adsorbates to buried interfaces. In this article, the principle, instrument and recent results of photoelectron spectro-holography method are overviewed briefly.
A new tool for surface structure analysis, thermal diffuse scattering (CTDS), is reviewed. The principle of CTDS is based on a very simple diffraction phenomenon, which is induced by a strong vibrational correlation between neighbor atoms, and could be considered as a diffraction of nearest neighbor atoms. Simple intensity oscillations are experimentally corrected by the medium energy electron diffraction with a very-grazing-incidence condition. Accurate bond lengths and bond orientations are obtained from a three-dimensional Patterson function, which is a Fourier transform of the CTDS pattern, i.e. the simple intensity oscillation of thermal diffuse scattering. The potentia of CTDS as a direct surface structural tool has been reviewed with an application to a Si(111)√3×√3-In surface.
The photoelectron angular distribution (PEAD) from single-crystalline graphite is measured by using a two-dimensional display-type spherical mirror analyzer and a linearly polarized synchrotron radiation by varying the photon and photoelectron kinetic energies. From the study of the photon energy (hν) dependence of umklapp processes, it is found that their intensities are reduced considerably at hν = 50–60 eV. The mechanism of the umklapp process is discussed. The atomic orbitals composing the valence band is shown to be specified from the PEAD pattern by considering a transition matrix as well as umklapp processes. Furthermore, the band structure of graphite over the entire Brillouin zone is measured. The three-dimensional [EB-kx-ky] dispersion of the π and σ bands are extracted and presented for the first time.
High resolution photoemission spectroscopy (HPES) has mostly been performed so far at energies below slightly higher than 100 eV. This is due to the necessity for the high enough resolution of photons. Nowadays high resolution better than a few me V is feasible by use of the state of art electron energy analyzers and very bright He I, II light sources. For angle resolved photoemission spectroscopy (ARPES), even angular resolution of better than ± 0.1 degree is feasible. Thus the low photon energy (hν) PES and ARPES are very popular in many laboratories. However, these measurements are relatively surface sensitive. In many cases of strongly correlated electron systems such as 4 f rare earth and 3 d transition metal systems, the surface electronic structures are much different from the bulk. Therefore bulk sensitive HPES is strongly required for bulk studies. The difference of the surface and bulk electronic states is reviewed by showing recent results of bulk sensitive soft X-ray HPES and ARPES measurements.
Atomic force microscopy (AFM) has been used for nanotribological studies of silicon surfaces covered by oxide layers of various kinds: chemical oxides prepared by SC 1 (NH4OH/H2O2/H2O) and SC 2 (HCl/H2O2/H2O) treatments, a thermally treated silicon surface and a H-terminated oxide-free silicon surface. Only in the case of SC 1 chemical oxide, scratching of the oxide and ploughing of the silicon by a Si3N4 AFM tip were observed. On the other hand, no wear of the sample was noted on other surfaces. By annealing the SC 1-treated surface in N2 gas above 200oC for 30 min, the oxide layer could not be scratched. By soaking the thermal oxide in KOH, the oxide layer was then scratched. It is suggested that the presence of OH bases is a requirement for the nano-scratching of the oxide layers.
We have investigated the origin of methane/hydrogen RIE (reactive ion etching)-induced damages. ZnSe and ZnCdSe/ZnSe-based quntum well wires with wire widths ranging from 1000 nm to 20 nm have been fabricated by electron-beam lithography and a methance/hydrogen RIE. Photoluminescence (9.5 K) is used for the study of the causes of RIE-induced damage. The results indicate that the RIE-induced damage lead to the red shift of peak emission. From PL data of ZnSe wires, we concluded that RIE-induced damage causes lattice defects at the surface.
The hydrolysis and crystallization of the surfaces of sol-gel derived lithium niobate precursor films were analyzed by XPS and XRD. The Nb/Li ratio was 1.3 in the surface composition of amorphous films and 1.2 in that of partially crystallized films. These findings showed that the ratio finally approaches to 1 that is the stoichiometric composition ratio, depending on the progress of the crystallization in the films. The preheat-treatment of the precursor films in humidity was effective for decreasing the crystallization temperature. This was due to the releasing of the acetic acid chelating the precursor molecules. In the process of analyzing the composition of the lithium niobate film surface, Li was selectively etched.
Abstraction reaction of hydrogen atoms on a hydrogenated diamond surface was performed with benzoyl peroxide. In this study, we used the various solvents, such as toluene, acetonitrile, tetrahydrofuran (THF), N, N-dimethylformamide (DMF), cyclohexane, and n-hexane, and confirmed that (1) the radical species generated from the benzoyl peroxide extract the hydrogen atoms on the diamond surface, (2) the reaction rate for the abstraction of the hydrogen atoms from the diamond surface depends on the kinds of solvents, (3) the species of the functional groups produced in the radical reaction is independent of the solvents except for acetonitrile. In order to investigate the abstraction reaction of the hydrogen atoms on the diamond surface with benzoyl peroxide, experiments to determine the dependences of the hydrogen abstruction on the amount of added benzoyl peroxide and on the reaction time were conducted in toluene. The intensity ratio of the peak assigned to the C-H bond to that assigned to the two-phonon peak (IC-H/Itwo-phonon) was calculated to discussed the abstraction reaction quantitatively. The reaction rate was estimated from the IC-H/Itwo-phonon values.
We have constructed a photoelectron spectro-holography apparatus, which consists of a high-power X-ray source generation system with rotating anodes and a high-performance angle-resolving electron energy analyzer. These systems have been specially designed for X-ray photoelectron diffraction and photoelectron holography. In this paper, we describe this apparatus from technical points of view.