Shogo Nakamura

Comparison of the CKLL first-derivative Auger spectra from XPS and AES using diamond, graphite, SiC and diamond-like-carbon films

Abstract The carbon KLL first-derivative Auger spectra obtained by numerically differentiating the XPS N(E) line gives a better fine-structure fingerprint of the carbon state than conventional AES. The first-derivative of the X-ray excited (XAES) CKLL spectrum from a diamond-like-carbon (DLC) film exhibited almost the same spectrum as both the XAES and AES spectra from natural diamond. However, the AES spectrum of the DLC film indicated a graphite-like structure due to electron beam damage. Comparison of the XAES and AES spectra suggested that the electron beam used in conventional AES partially changed the plasmon loss structure of carbon in diamond, graphite and β-SiC as well.

Esca studies of Ga, As, GaAs, Ga2O3, As2O3 and As2O5

Abstract The binding energies of Ga 3 d , As 3 d , Ga L 3 M 4 , 5 M 4 , 5 and O 1 s in Ga, As, GaAs, Ga 2 O 3 , As 2 O 3 and As 2 O 5 are reevaluated by means of ESCA. The calibration lines of the C 1 s and the Au 4 f 7 2 gave different binding energies for the compound materials. In order to determine the absolute binding energies, the chemical shifts in Auger and photoelectron lines from a layered structure composed of thin layer oxide and substrate of a defined material were used. An energy calibration curve, E (Ga 3 d ) vs. Δ E (GA LMM - Ga 3 d ), was found to be useful for determination of binding energies in the material which contains gallium. In the case of the GaAs sample, both the chemical etching and the ion bombardment effects on the chemical structure of the GaAs surface are also discussed.

Surface structures and work functions of the LaB6 (100), (110) and (111) clean surfaces

The structures of the LaB6 (110) and (111) clean surfaces have been studied by angleresolved XPS, ISS and LEED. The LaB6 (110) clean surface has the relaxed and reconstructed c(2 × 2) structure where the surface lanthanum atoms are displaced toward the surface and a c(2 × 2) overlayer structure is caused by a displacement of the surface lanthanum atoms. The LaB6 (111) clean surface has the relaxed (1 × 1) structure where the surface lanthanum atoms are displaced toward the surface. The work functions of the (100), (110) and (111) surfaces have been measured from the width of UPS spectra and are ~2.3, ~2.5 and ~3.3 eV, respectively. The anisotropy of the work functions has been correlated with the surface structures. The origin of the unusually low work functions of the LaB6 (100) and (110) clean surfaces in refractory materials is interpreted by electric dipole moments produced by positive charges of surface lanthanum ions.

X-ray photoemission study of the initial oxidation of the cleaved (110) surfaces of GaAs, GaP and InSb

Abstract The room temperature oxidation of GaAs, GaP and InSb upon exposure to atmospheric dry O 2 has been studied by analyzing XP spectra quantitatively. The rate of oxidation decreases in the order InSb > GaP > GaAs. For GaAs and GaP, evidences of the formation of metastable surface complex are shown: the ratio of A III O bonds to B V O bonds are about 2 and 1, respectively. For InSb, it is shown that both elements are oxidized to comparable extent, giving rise to In 2 O 3 and Sb 2 O 3 probably, by using Auger spectra as well as photoemission spectra.

Surface states on the LaB6(100), (110) and (111) clean surfaces studied by angle-resolved ups

The surface states on the LaB6(100), (110) and (111) clean surfaces have been studied by means of angle-resolved UV photoelectron spectroscopy with unpolarized light. Surface states on LaB6(110) and (111) have been observed for the first time, and the energy-band structures have been determined. The surface states on LaB6(110) are located at ∼1.8 and ∼3.0 eV below EF. They are associated with the occurrence of the c(2 × 2) surface structure on LaB6(110). The surface states on LaB6(111) are located at ∼1.5 and ∼2 eV below EF. The dispersion of the lower band is relatively large (∼0.9 eV) compared with those on LaB6(100) and (110). The surface state at ∼2 eV below EF on LaB6(111) has a maximum energy at Γ point (k∥ = 0), while that on LaB6(100) has a minimum energy at Γpoint. The surface state at ∼2 eV below EFon LaB6(100) possesses Δ1 symmetry at k∥ = 0, and has even parity with respect to the (010) and (011) planes. The surface state at ∼1.8 eV below EF on LaB6(110) has even parity with respect to the (110) plane, and odd parity with respect to the (001) plane. The surface state at ∼3.0 eV below EF has even parity with respect to both the (110) and (001) planes. The low-lying surface state on LaB6(111) has Δ1 symmetry at k∥ = 0. All these surface states on the LaB6 clean surfaces are interpreted in terms of dangling bonds of the surface boron frameworks which are mainly B 2p in character.

Field-ion microscopy of GaAs and GaP

Abstract Clean surfaces of GaAs and GaP were studied by field-ion microscope (FIM). Field-ion images with ordered surfaces were first obtained in pure hydrogen, neon-50% hydrogen and pure neon gases at 78 K, by using channeltron electron multiplier arrays (CEMA). The field-ion images of GaAs were quite similar to those of GaP with respect to the surface structure and the image contrast. They showed the anisotropies of the ion emission and the surface structure between the [111] and [ 1 1 1 ] orientations. Ring steps expected from a spherical surface were observed on the (111) and {100} planes, but not on the [ 1 1 1 ] and {110} planes. The regional brightness of the FIM patterns was discussed in terms of the Knor and Muller model and the atomic and electronic structures of the surface. The image field of these crystals was much lower than that of metals usually used in FIM. For example, the image field strength for the hydrogen and GaAs system was about 1.1 V/A. The reduction of the field necessary to image was also discussed in terms of the field penetration effect.

On field-evaporation end forms of a bcc metal surface observed by a field ion microscope

Abstract Distinct differences in the field-evaporation end forms of W, Ta, and Mo are investigated by comparing the temperature dependence of the contribution of polarization energy and binding energy to the field-evaporation energy. The field-evaporation end form at low temperature is influenced mainly by the polarization energy of atoms under the influence of a strong field; its magnitude decreases in the following sequence: Ta, W and Mo. As the field-evaporation temperature is raised the influence is gradually transferred from polarization energy to binding energy. Binding energies except for the {001} planes, which are estimated from the Morse potential energy, are in fair agreement with the experimental results. The field-evaporation end forms at high temperature are mainly influenced by the magnitude of the activation energy due to the self-migration of the atoms on the surface of each crystal planes. The influence of residual gases and the change of field-evaporation mechanism are discussed.

Oxygen adsorption on the LaB6(100) surface studied by UPS and LEED

Abstract The surface states (∼2 eV below E F ), which are originated mainly from the dangling bonds of boron atoms on the LaB 6 (100) clean surface, disappear at an oxygen exposure of ∼ 1.4 L. At the same exposure, an oxygen sticking-coefficient has a maximum value, ∼1.0. A change in the work function due to oxygen adsorption increases linearly with increasing surface oxygen and varies its slope at the above-mentioned exposure. At a low oxygen-exposure of ∼0.38 L, the first peak appears at ∼6.6 eV below e f in UPS spectra. The second overlapping oxygen peak at ∼6.0 eV below E F in UPS spectra, which grows around l L and overcomes the first peak, shifts to the low binding-energy side above ∼1.4 L. The (1 × 1) LEED pattern does not disappear until an oxygen exposure of several hundreds langmuir. It is suggested that the results support the presence of more than two adsorption states. The results are principally interpreted on the basis of two kinds of chemisorption sites; one is a boron site, and another a lanthanum site.

In-Depth Profiles of Oxide Films on GaAs Studied by XPS

Quantitative depth profiles of chemical composition of the thermal and the anodic oxide of GaAs have been studied by XPS in conjunction with argon ion sputtering. By analyzing the XPS spectra with taking account of the sputtering effects, both the amount and the chemical state of each elemental species in the oxides were obtained. In the thermal oxidation below 530°C in air, Ga2O3 was produced as a primary product and both the amounts of the evaporated-As and the accumulated-As increased with increasing oxide thickness. XPS spectra from the thermal oxides grown at 900°C in air or grown with As at ~530°C suggested that the products contained GaAsO4. The anodic oxidation resulted in films that had an As2O3/Ga2O3 ratio of about 1. The widths of the transition region between the ~500 A thick oxide and GaAs were about 70 A for the anodic oxides and 200 A for the thermal oxides.

Oxygen adsorption on the LaB6(100), (110) and (111) surfaces

Oxygen adsorption on the LaB6(100), (110) and (111) clean surfaces has been studied by means of UPS, XPS and LEED. The results on oxygen adsorption will be discussed on the basis of the structurs and the electronic states on the LaB6(100), (110) and (111) clean surfaces. The surface states on LaB6(110) disappear at the oxygen exposure of 0.4 L where a c(2 × 2) LEED pattern disappears and a (1 × 1) LEED pattern appears. The work function on LaB6(110) is increased to ∼3.8 eV by an oxygen exposure of ∼2 L. The surface states on LaB6(111) disappear at an oxygen exposure of ∼2 L where the work function has a maximum value of ∼4.4 eV. Oxygen is adsorbed on the surface boron atoms of LaB6(111) until an exposure of ∼2 L. Above this exposure, oxygen is adsorbed on another site to lower the work function from ∼4.4 to ∼3.8 eV until an oxygen exposure of ∼100L. The initial sticking coefficient on LaB6(110) has the highest value of ∼1 among the (100), (110) and (111) surfaces. The (100) surface is most stable to oxygen among these surfaces. It is suggested that the dangling bonds of boron atoms play an important role in oxygen adsorption on the LaB6 surfaces.