Published: October 10, 2011 r2011 American Chemical Society 5507 dx.doi.org/10.1021/cg201163v | Cryst. Growth Des. 2011, 11, 5507–5514 ARTICLE pubs.acs.org/crystal Formation of Inert Bi 2 Se 3 (0001) Cleaved Surface V. V. Atuchin,* ,† V. A. Golyashov, ‡ K. A. Kokh, § I. V. Korolkov, # A. S. Kozhukhov, ^ V. N. Kruchinin, || S. V. Makarenko, ‡ L. D. Pokrovsky, † I. P. Prosvirin, O K. N. Romanyuk, ‡ and O. E. Tereshchenko ‡,b † Laboratory of Optical Materials and Structures, Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090, Russia ‡ Department of Physics, Novosibirsk State University, Novosibirsk 630090, Russia § Laboratory of Crystal Growth, Institute of Geology and Mineralogy, SB RAS, Novosibirsk 630090, Russia # Laboratory of Crystal Chemistry, Institute of Inorganic Chemistry, SB RAS, Novosibirsk 630090, Russia ^ Laboratory of Nanodiagnostics and Nanolithography, Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090, Russia ) Laboratory for Ellipsometry of Semiconductor Materials and Structures, Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090, Russia O Boreskov Institute of Catalysis, SB RAS, Novosibirsk 630090, Russia b Laboratory of Molecular Beam Epitaxy of III-V Semiconductors, Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090, Russia b S Supporting Information ’ INTRODUCTION Bismuth selenide, Bi 2 Se 3 , is a compound well-known for its pronounced layered crystal structure and good thermoelectric properties. 1À3 In recent years, the crystal has attracted great attention as a three-dimensional topological insulator (TI). 4À9 This new electronic system is characterized by a combination of an insulating bulk and conducting surface states of massless Dirac fermions. Several methods have been proposed for the experi- mental realization of such electronic states at the crystalline surface of Bi 2 Se 3 . Epitaxial thin films and nanocrystals can be used for an observation of the TI surface electronic effects. 6,10À14 Because of good cleavage properties of Bi 2 Se 3 crystal, the (0001) surface can be prepared by mechanical cleaving of the bulk crystal, and this method was also used in several experiments on the TI effect observation but without a clear description of crystal growth conditions and surface preparation. 7,9,15À18 The forma- tion and stability of TI state at the crystalÀvacuum (or crystal Àair) boundary, however, may be strongly dependent on the structural and chemical quality of Bi 2 Se 3 crystal, and the top surface properties seem to be among the governing factors. Generally, it is known that halcogenide compounds tend to oxidize in air due to their drastic affinity with oxygen. 19À24 For many complex halcogenide compounds, the chemical interaction with air agents results in complete decomposition and amorphization with time that limits the crystal living period. From this common point of view, the Bi 2 Se 3 crystal appears to be not an exception, and, respectively, oxide presence could be expected at the crystal surface. Indeed, oxygen signal was detected by X-ray photoelec- tron spectroscopy in several studies devoted to a complex evaluation of the Bi 2 Se 3 nanocrystals prepared by hydrothermal reactions. 25À27 The behavior of cleaved Bi 2 Se 3 (0001) surface is less clear. On the one hand, there are reports on swift oxidation of Bi 2 Se 3 (0001) surface in air at ambient and increased tempera- tures. 28,29 On the other hand, layered halcogenide crystals generally display a pronounced chemical inertness of the cleaved surface. For example, the cleaved Se-terminated optical-quality surface of GaSe crystal is long-living in air and widely applied in nonlinear optical devices. 30 The crystal structure of trigonal Bi 2 Se 3 , space group R 3m, is shown in Figure 1. 31,32 The crystal lattice of this modification is formed by bilayers of face-sharing BiSe 6 octahedrons (quintuple). The bilayers are stacked along the c axis by weak van der Waals bonds with a SeÀSe distance as long as 351 pm. On cleavage these long SeÀSe bonds are disrupted, and after relaxation the Received: August 18, 2011 Revised: October 5, 2011 ABSTRACT: A high quality inclusion-free Bi 2 Se 3 crystal has been grown by the Bridgman method with the use of a rotating heat field. A large-area atomically flat Bi 2 Se 3 (0001) surface of excellent crystallographic quality has been formed by cleavage. Chemical and microstructural properties of the surface have been evaluated with reflection high-energy electron diffraction, atomic force microscopy (AFM), scanning tunneling microscopy (STM), spectroscopic ellipsometry, and X-ray photoelectron spectroscopy. There was no Bi 2 Se 3 (0001) surface oxidation detected after over a month in air under ambient conditions as shown by comparative core level spectroscopy, AFM, and STM.