Journal of Crystal Growth 111 (1991) 1033—1037 1033 North-Holland Growth of MoSe 2 thin films with Van der Waals epitaxy F.S. Ohuchi, T. Shimada ~, B.A. Parkinson Central Research and Development Department, Experimental Station, E.I. du Pont de Nemours and Company, Wilmington, Delaware 19880, USA K. Ueno and A. Koma Chemistry Department, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan The concept of Van der Waals epitaxy that has been recently introduced removes severe lattice matching requirement by using materials which only have strong bonding in two dimensions. We demonstrate that an epilayer of MoSe2 deposited on various substrates can produce films of high crystalline quality despite of large mismatch. RHEED oscillation, observed in-situ for growing MoSe2 epilayers, shows a layer-by-layer growth with evidence for bilayer type growth, from which the 2Hb polytype is determined. STM provides real space images of the morphology of the epilayer, and shows novel structures resulting from the large lattice mismatch where the epilayer atoms are commensurated. 1. Introduction metal (metal)—chalcogen layers held together by Van der Waals forces, thus a pronounced struct- Heteroepitaxy with a large lattice mismatch ural anisotropy resulting from strong chemical offers the possibility of combining materials with bonds in 2D results in these materials having a wide variety of properties. Today, much effort unique properties. Changing either the metal or has been paid to molecular beam epitaxy (MBE) chalcogen can alter the electronic structure from with strained or graded layers to acconunodate the superconductoring to insulating. Therefore the lattice mismatching, yet the concept of Van der flexibility for fabrication of multilayer structures Waals epitaxy (VDWE), recently introduced by us containing different materials selected for their [1,2], removes this constraint by using materials specific physical and chemical properties, rather which have strong bonding only in two dimen- than their lattice match, makes this an exciting sions (2D). The materials which crystallize in 2D new area for investigation. structures include many transition metal dichal- We present VDWE growth of MoSe 2 thin films cogenides, monochalcogemdes, and tin sulfides on SnS2(0001), MoS2(0001) and GaAs(111) and selenides. VDWE is the growth of such 2D surfaces. While the identity of the substrate materials, one upon the other, where the layers are strongly influences the growth process in conven- bound together by the relatively weak Van der tional epitaxy, the substrates that have been Waals forces. Many metal chalcogenide materials selected in the present investigation differ frOm have 2D structures characterized by chalcogen— each other both electronically and structurally, yet a high quality epitaxial thin film can be grown by VDWE. In this paper we focus on the growing * Also at Chemistry Department, University of Tokyo, Hongo, process of VDWE and resultant unique properties Bunkyo-ku, Tokyo 113, Japan. of the heterointerfaces. 0022-0248/91/$03.50 C 1991 — Elsevier Science Publishers B.V. (North-Holland)