A Metastable-atom Deexcitation Spectroscopy (MDS) study on the First Atomic Layer of a Polycrystalline Titanium Surface
- PDF / 373,119 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 31 Downloads / 187 Views
STUDY ON THE FIRST ATOMIC LAYER OF A POLYCRYSTALLINE TITANIUM SURFACE M. KURAHASHI and Y.YAMAUCHI National Research Institute for Metals, 1-2-1 Sengen Tsukuba Ibaraki 305, Japan, kura@)nrim.go.jp ABSTRACT The oxygen adsorption on a polycrystalline titanium surface at room temperature has been studied by MDS in conjunction with UPS and AES. MDS and UPS spectra were measured using a pulsed-dischaxge-type metastable helium atom source which we have newly developed. FRom the analysis of the measured spectra, we found the following about the local density of states (LDOS) of the oxygen-adsorbed titanium surface: (1)With increasing oxygen exposure at 0-2 L, the LDOS on the first atomic layer (SDOS) at 0-1 eV below the Fermi level (EF) decreases more steeply than that of deeper layers. (2) The SDOS at 5-8 eV below EF remains small at 0-2 L, and begins to increase at ca. 2 L while the LDOS of subsurface layer increases first. We discuss the positions of adsorbed oxygen atoms based on these results.
INTRODUCTION MDS is an extremely surface-sensitive technique, which provides information on the electronic states at the first atomic layer of solids [1-3]. Owing to this unique feature, MDS has been widely used to study surface electronic states of various materials. No attempts have been made, however, to our knowledge, to use MDS to analyze the clean or oxygen-adsorbed titanium surface. Titanium is highly reactive to oxygen, and its initial interaction has been extensively studied using various surface analysis techniques [4-15]. The nature of the oxygen adsorption mechanism on the titanium surface, however, remains highly controversial, and still has not been clarified. Certain characteristic behavior has been reported for initial stage of oxygen adsorption: With increasing oxygen exposure, work function initially decreases, increasing again at 1-2 L (1 L•_I x l0- 6 Torr.s) [4-8]. The electron-stimulated desorption (ESD) [9] and photon stimulated ion desorption (PSD) [4] rates also exhibit an onset at 1-2 L. These results are explained by a model in which the adsorbed oxygen atoms initially occupy subsurface sites [4-7]. On the other hand, some researchers have concluded [8, 10], based on the results of direct recoil spectroscopy measurement, that adsorbed oxygen atoms initially occupy sites over the top titanium layer. To clarify the initial oxidation mechanism, information on the first atomic layer of the oxygen-adsorbed titanium is needed. In this study, we measure the MDS spectra of the oxygen-adsorbed titanium surface. To clarify differences in electronic states between the first atomic layer and deeper layers, we also measure the ultraviolet photoelectron spectra (UPS) and compare the two types of spectra. We then discuss the electronic states at the first atomic layer of oxygen-adsorbed polycrystalline titanium, and the positions of adsorbed oxygen atoms.
67 Mat. Res. Soc. Symp. Proc. Vol. 501 © 1998 Materials Research Society
EXPERIMENT In the experimental setup (Fig. 1), the analysis chamber is equipped with a s
Data Loading...
