Journal of Electron Spectroscopy and Related Phenomena 144–147 (2005) 483–486 Photoelectron spectroscopic study of Fe films on NEA surface N. Takahashi a,∗ , S. Nakanishi b , H. Itoh b , S. Koshiba b , T.-H. Shen c , T. Zhang d , S. Tanaka e , K. Takahashi f , M. Kamada f a Department of Physics, Kagawa University, Takamatsu 760-8522, Japan b Department of Advanced Materials Science, Kagawa University, Takamatsu 761-0396, Japan c Joule Physics Laboratory, Institute for Materials Research, University of Salford, Greater Manchester M5 4WT, UK d Blackett Laboratory, Imperial College of Science, Technology and Medicine, London SW7 2BZ, UK e Research Center for Materials Science, Nagoya University, Nagoya 464-8602, Japan f Synchrotron Light Application Center, Saga University, Saga 840-8502, Japan Available online 2 March 2005 Abstract We investigated Fe films on a negative electron affinity (NEA) O/Cs/GaAs(100) surface by photoelectron spectroscopy and photocurrent measurements. From the results, it is shown that the Fe covered surface retains NEA character, which is comparable to that of the standard NEA, even in the thicker Fe coverage region of about 100 ˚ A. It is also found that the change of NEA intensity is independent of the change of the work function. From the core level peak results, it is also discussed that further chemical reaction at the interface and overlayer. © 2005 Elsevier B.V. All rights reserved. Keywords: NEA; GaAs(1 0 0); Photoelectron spectroscopy; Fe; Work function 1. Introduction Negative electron affinity (NEA) semiconductors are used as efficient photocathodes, due to their high degrees of polar- ization and efficiency. However, from a fundamental science point of view, the details of NEA formation are not fully understood. Several models for the mechanism of NEA for- mation have been suggested in the past, such as the dipole model [1,2], the cluster model [3] and so on [4,5]. Many stud- ies have indicated that the compound of caesium and oxygen, which bonds to gallium and arsenic atoms [6], may lower the work function of the surface. Recently, Mor´ e et al. [7] sug- gested that the NEA condition was distinguished with differ- ent activation processes which would make different type of oxidation at interface between the substrate and overlayer. On the other hand, the study of magnetic thin films on semiconductor substrates has been widely carried out due to the applicability to magneto-electronics devices, such as the Spin Polarised Field Effect Transistor [8]. As a typical basis ∗ Corresponding author. E-mail address: naoshi@ed.kagawa-u.ac.jp (N. Takahashi). for such devices, the Fe/GaAs system has been extensively studied for decades [9–12] because of its great promise in the possible use of hybrid ferromagnetic metal–semiconductor structures for applications. In this paper we present a study of a Fe covered NEA. 2. Experiment Fig. 1 shows schematic diagrams of the experimental set- ups used. All experiments were carried out at RT in UHV chamber with the base pressure of about 3 × 10 -8 Pa, and less than 6.5 × 10 -8 Pa during Fe deposition. A Zn doped (1 × 10 19 atoms/cm 3 ) p-GaAs(1 0 0) wafer was used as a sub- strate, having been cleaned by Ne sputtering and annealing. This treatment led to the familiar (8 × 2) surface reconstruc- tion. We employed the ‘Nagoya method’ [13] to activate the NEA surface, in which Cs increases the yield (NEA intensity) and O decreases it. The NEA intensity was measured as the absolute value of the photocurrent from the biased (-10 V) sample while the He–Ne laser was on and off. Fe was de- posited on the NEA surface a total of five times, yielding 0368-2048/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.elspec.2005.01.150