In-situ reflection high-energy electron diffraction study of epitaxial growth of Cu on NaCl (100) under oblique angle vapor deposition C. Gaire ⁎, F. Tang, G.-C. Wang Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute,110 8th Street, Troy, NY 12180-3590, USA abstract article info Article history: Received 17 October 2007 Received in revised form 30 October 2008 Accepted 9 December 2008 Available online 24 December 2008 Keywords: Oblique angle vapor deposition Epitaxial growth Reflection high energy electron diffraction Atomic force microscopy Epitaxial growth of copper on annealed NaCl(100) surface was carried out using thermal evaporation at an oblique angle of incidence (75±5)° with respect to the substrate normal. The substrate was kept at a temperature of (150±5)°C. The crystalline structure of the Cu film was studied in situ by reflection high energy electron diffraction at various deposition times. We observed that the film grows through nucleation of epitaxial islands followed by coalescence and then flattening of the film. The chevron shaped diffraction patterns formed by the refraction effect of electrons were used to identify the crystal facets. With longer deposition times, instead of columnar structures, a continuous epitaxial film was formed despite the oblique angle incidence of the vapor. The morphology of the final film was characterized ex situ by atomic force microscopy and shows L-shaped pores asymmetric with respect to the vapor incident direction. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Understanding the growth of noble metal such as Cu on an insulator surface is of great interest for various applications such as heterogeneous catalysis, microelectronics, antithermic, anticorrosion optical coating industries, etc., as well as for a fundamental understanding in surface science. It is well known that the substrate temperature, residual vacuum pressure, evaporation rate and contaminants adsorbed on the substrate have an important effect on the structure of the vapor deposited thin film materials [1–3]. A number of studies have been carried out where these parameters are varied during the deposition of various fcc metals on NaCl cleaved on air or vacuum [4–7]. The parallel epitaxy of Cu(001)[100]//NaCl(001)[100] is often observed despite the 36% large lattice mismatch between Cu and NaCl(100). All of these studies were carried out under normal vapor incidence angle. Over the past several years, modification of the morphology and crystalline structure of thin films by changing the vapor deposition angle has drawn considerable attention [8]. It has been well established that the metal film deposited on amorphous substrates under oblique angle vapor deposition is composed of columnar structures. Moreover, the crystalline orientations on the obliquely deposited films were shown to be different than the normally deposited films [9–11]. The formation of the columnar structure has been attributed to the shadowing effect and random fluctuations during the film growth [12]. Compared with the growth of metals on amorphous substrates by oblique angle vapor deposition, very few studies were done on the oblique angle deposition of metals on the single crystalline substrates [13, 14]. This led us to explore the growth mechanism of Cu on NaCl(100) surface as a generic example of the growth of metal on crystalline substrates under oblique angle vapor deposition. Reflection high-energy electron diffraction (RHEED) is a well established technique to follow the growth front morphology of epitaxial as well as polycrystalline films [15,16]. Also, to avoid the oxidation and the absorption of contaminants on the film, in situ characterization of the film is highly desirable. The in situ RHEED technique has the ability of monitoring the temporal evolution [17] of the film without exposing the samples to the ambient. In this article we discuss an in situ RHEED study of an epitaxial Cu film grown by oblique angle physical vapor deposition on air-cleaved NaCl(100) substrate held at ~150 °C temperature. The deposition was interrupted at various times for in situ RHEED measurements. The morphology of the final film was also characterized by an atomic force microscope (AFM). We found that despite the obliquely incident vapor, the shadowing effect is suppressed by the epitaxial nucleation and flattening of the top surfaces of nucleated islands. With a longer deposition, instead of columnar structures, a continuous epitaxial Cu (100) film is formed. However, the analysis of electron refraction effect through the crystal showed the presence of asymmetry in the crystalline orientation thus indicating the effect of the oblique angle vapor incidence. Finally an overall picture of epitaxial growth under oblique angle deposition is discussed. 2. Experimental details 2.1. Preparation of NaCl substrate The NaCl crystal was cleaved along the edge b100N in air. An AFM (Park Scientific Instruments) was used to take the topographic image Thin Solid Films 517 (2009) 4509–4514 ⁎ Corresponding author. Tel.: +1518 276 8387; fax: +1518 276 6680. E-mail address: gairec@rpi.edu (C. Gaire). 0040-6090/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2008.12.035 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf