Reflection high-energy positron diffraction at solid surfaces by improved electrostatic positron beam A. Kawasuso a,* , T. Ishimoto a , S. Okada a , H. Itoh a , A. Ichimiya b a Japan Atomic Energy Research Institute, Takasaki Establishment, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan b Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan Abstract We report observation of reflection high-energy positron diffraction (RHEPD) at the Si(1 1 1) surface using an electrostatic positron beam. The improvement of the beam (i.e., reduction of beam energy spread) was critical to obtaining the higher-order diffraction spots. We could observe the first Laue zone, which was not seen in our previous work. This allows us to study the surface Debye temperature. The obtained rocking curve represents the enhancement of the fourth Bragg peak, as expected from diffraction theory, in addition to previously confirmed total reflection and the first Bragg peak. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Reflection high-energy positron diffraction; Surface; Dipole barrier; Laue zone 1. Introduction In reflection high-energy positron diffraction (RHEPD) experiments, back-reflection of high-energy (>10 keV) positrons at solid surfaces is observed at small glancing angle (<58) [1]. Positrons are diffracted at the surface and the observed pattern represents reciprocal lattice rods related to surface atomic arrangement. The method itself is just the same as reflection high-energy electron diffraction (RHEED). Because of positive crystal potential for positrons, positrons are totally reflected at the topmost surface below a critical angle y C ¼ arcsinðeV 0 =EÞ 1=2 , where eV 0 is the crystal potential and E the incident positron energy [2]. Total reflection is never observed in RHEED experiments due to negative crystal potential for electrons. A positive crystal potential also leads to an appearance of the first Bragg peak even if it is not observed in RHEED [2]. From an analysis of the positron reflectivity in the total reflection region, one can determine the bond length of adsorbed atoms in the topmost surface without disturbance from the bulk layer. Moreover, surface lattice vibration and surface roughness can be determined. These are always problematic in the case of electron diffractions because electrons penetrate deep into the crystal. It is also proposed that the metal surface dipole barrier can be directly measured by RHEPD by taking advantage of the negligible exchange–correlation interaction [3]. The metal surface barrier is an important physical quantity related to the work function. In 1998, we performed a RHEPD experiment in which diffraction patterns from a Si(1 1 1) surface were observed and rocking curves were determined [4]. Applied Surface Science 194 (2002) 287–290 * Corresponding author. Tel.: þ81-27-346-9331; fax: þ81-27-346-9687. E-mail address: ak@taka.jaeri.go.jp (A. Kawasuso). 0169-4332/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0169-4332(02)00136-8