Applied Surface Science 288 (2014) 458–465 Contents lists available at ScienceDirect Applied Surface Science jou rn al h omepa g e: www.elsevier.com/locate/apsusc Instrument response of reflection high energy electron diffraction pole figure L. Chen a , J. Dash a , P. Su b , C.F. Lin a , I. Bhat b , T.-M. Lu a , G.-C. Wang a,∗ a Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180, USA b Department of Electrical, Computer and System Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, USA a r t i c l e i n f o Article history: Received 10 April 2013 Received in revised form 5 October 2013 Accepted 10 October 2013 Available online 18 October 2013 Keywords: Reflection high energy electron diffraction RHEED pole figure Instrument response of transmitted electrons Epitaxial CdTe film Textured CdTe film a b s t r a c t Reflection high-energy electron diffraction (RHEED) pole figure technique using the transmission mode has been developed to study the texture evolution of thin films. For quantitative evalua- tion of thin film texture, including the dispersion of texture, one would require the knowledge of the instrument response function. We report the characterization of instrument response in RHEED pole figure from an epitaxial CdTe(1 0 0) film grown on GaAs(1 0 0) substrate. We found the finite mean free path of electrons in a film contributes to the broadening of the poles. In addition, the image processing step size used in the construction of a pole figure also affects the broad- ening of constructed poles. We apply the measured instrument response in RHEED pole figure to quantitatively analyze a biaxially textured CdTe(1 1 1) film deposited on a biaxially textured Ge(1 1 1) substrate. Through the deconvolution of the measured dispersions from the poles in the textured CdTe(1 1 1) film by the instrument response function, we obtain the out-of-plane and in-plane disper- sions of the biaxially textured CdTe(1 1 1) film. This method is generic and the instrument response should be considered in order to obtain quantitative texture information for other epitaxial and textured nanostructured films through RHEED pole figure measurements. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Diffraction techniques such as X-ray diffraction and electron diffraction are essential tools to study the crystallography of mate- rials. They are also useful for detecting crystal imperfections, which manifest themselves as distortions in the diffraction profiles [1]. One of the common distortions is a broadening of the diffrac- tion profiles. For a quantitative study of crystal imperfection, one would require to know the distortion, including the broadening, due to inherent instrumental effects called the instrument response function [2]. The nature of the instrument response function had been studied quantitatively in detail and had been reported in the literature for diffraction techniques [3–6]. Any observed X-ray or electron diffraction profile is a convolution of the instrument response function with the intrinsic diffraction profile that reflects the characteristics of a crystal. In order to quantitatively extract the intrinsic properties of the crystal imperfections, one has to de-convolute the observed diffraction profiles by the instrument response function. This strategy has been applied routinely in X-ray diffraction and electron diffraction techniques. ∗ Corresponding author. Tel.: +1 51 8276 2435; fax: +1 51 8276 6680. E-mail address: wangg@rpi.edu (G.-C. Wang). A more sophisticated way to represent crystal imperfections is the pole figure technique. A pole figure is a 2-D graphical repre- sentation of the crystal orientation distribution. It is in the form of spherical projections of 3-D orientation distribution of the crys- tal lattice planes onto a 2-D figure. If the crystals were not perfect, the pole figure would show a distortion of the pole intensity dis- tribution. A pole figure is constructed, using either a point detector or an area detector, by scanning the diffraction intensity profiles over the diffraction space above the sample. A finite scanning step size is normally chosen for this construction. Because of the large diffraction space that the X-ray pole figure needs to cover, the step size usually is chosen to be larger than that used in an individ- ual X-ray rocking curve or in an individual reflection high-energy electron diffraction (RHEED) streak profile. For example, to scan a rocking curve of a film using X-ray point detector, the step size for the detector used is often very small (<0.005 ◦ ). Since only one diffraction spot is scanned, it takes a reasonable time to complete a rocking curve scan even using a small step size. However, to scan the entire diffraction space using a very small step size to con- struct the pole figure is not very realistic. For example using 0.005 ◦ as the step size and 1 s as the rest time, it would take 360,000 h (360 × 90/0.005/0.005 × 1 s) to obtain a complete X-ray pole figure, which is not realistic. Therefore, to save the data acquisition time, the step size chosen to construct a pole is usually much larger than 0.005 ◦ . 0169-4332/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2013.10.055