Electron distribution on a tilted sample in the high pressure SEM R. Belkorissat a , A. Kadoun a , B. Khelifa b , C. Mathieu b, * a Laboratoire d’Elaboration et de Caracte ´risation des Mate ´riaux, Universite ´ Djilali Liabe `s de Sidi Bel-Abbe `s, BP 89, 22000 Sidi Bel Abbe `s, Algeria b Centre de Calcul et de Mode ´lisation de Lens, Universite ´ d’Artois, 62307 Lens Cedex, France Received 11 October 2004; revised 22 December 2004; accepted 22 December 2004 Abstract The effect of the specimen inclination on the electron distribution at the specimen surface in an HPSEM was investigated by Monte Carlo simulation. A broadening of the electron profile versus the tilt angle was obtained and a relationship between the r 0.9 radius and this tilt angle is proposed. The plot of the electron distribution at the sample surface shows that the classical scattering profile in the standard conditions is modified so that an inclined truncated shape is obtained. This result confirms the difficulty to carry out X-ray microanalysis in low vacuum conditions. q 2005 Elsevier Ltd. All rights reserved. Keywords: HPSEM; Monte Carlo simulation; Electron scattering; Skirting 1. Introduction The High Pressure Scanning Electron Microscope (HPSEM) is a SEM that allows the examination of non- conductive specimen such as biological or insulator samples. Whereas conventional scanning electron microscopy requires a relatively high vacuum in the specimen chamber, an HPSEM may operate with poor vacuum (up to 10 Torr). In the ‘low vacuum mode’, the specimen chamber is isolated from the column with a pressure-limiting aperture (PLA). When the primary beam reaches the sample surface, secondary and backscattered electrons are ejected and collide with the gas inside the specimen chamber. These collisions are used in the amplifying process involved in the signal detection (Danilatos, 1990; Durkin and Shah, 1993; Moncrieff et al., 1979; Robinson, 1975). The main limitation concerning the use of the HPSEM is the scattering of the electrons of the primary beam with the atoms of the gas. Several authors (Mathieu, 1999; Adamiak and Mathieu, 2000) have studied this beam–gas interaction with the influence of the beam energy, working distance, pressure, and gas nature. In this paper, we examine a new parameter linked to the sample orientation, which is the tilt specimen angle, and we discuss this influence on the electrons distribution at the sample level by Monte Carlo simulation. A good agree- ment has been previously obtained in the comparison between the simulated and measured values of the skirt on such inclined sample. In that work, the skirt has been measured on an inclined phosphorus screen sample that produces a luminescent area after it interacts with the electron beam. A CCD camera maintained in parallel position with the sample visualized the luminescent zone (Belkorissat et al., 2004). 2. Calculation details It is of fundamental importance to know the details of the new electron distribution resulting from the collisions with the gas. A Monte Carlo simulation has been developed in order to answer the question of beam distribution under low vacuum conditions and titled sample position. 0968-4328/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.micron.2004.12.008 Micron 36 (2005) 345–350 www.elsevier.com/locate/micron * Corresponding author. Address: Centre de Calcul et de Mode ´lisation de Lens, Faculte ´ Jean Perrin, Rue Jean Souvraz, SP 18-62307 Lens Cedex, France. Tel./fax: C33 321 791 782. E-mail addresses: belkhorissat_r@yahoo.fr (R. Belkorissat), mathieu@univ-artois.fr (C. Mathieu).