Bilayers of transition metal dichalcogenides: Different stackings and heterostructures
- PDF / 1,079,645 Bytes
- 10 Pages / 584.957 x 782.986 pts Page_size
- 71 Downloads / 225 Views
Mauricio Terronesb) Department of Physics and Center for 2-D and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802; and Department of Chemistry, Department of Materials Science and Engineering and Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802 (Received 10 July 2013; accepted 9 September 2013)
Besides graphene and hexagonal boron nitride, transition metal dichalcogenides (TMDs) also exhibit a layered structure in which the layers weakly interact via van der Waals forces. Semiconducting TMDs in bulk are indirect band gap materials. However, an isolated sheet exhibits a direct gap. This particular behavior makes them very attractive in terms of optical properties. Moreover, NbS2 and NbSe2 in bulk and their monolayers are metallic. Density functional theory calculations were carried out to study different TMD bilayer systems. First, different bilayer geometries with different stackings were considered. It was found that the indirect and direct band gaps compete; however, the indirect band gap always dominates. Surprisingly, bilayer heterostructures of different TMDs have been found to possess direct band gaps. Finally, heterobilayers composed of one metallic monolayer and a semiconducting layer are predicted as novel metallic van der Waals solids that might find applications in new two-dimensional nanodevices.
I. INTRODUCTION
Studies of transition metal dichalcogenides (TMDs) and the search for monolayers or two-dimensional (2D) systems are not new; monolayers of TMDs consist of metal layers sandwiched by sulfur, selenium, or tellurium atomic layers. Wilson and Yoffe1 published a seminal paper in which the physicochemical properties of TMDs are described in detail. Perhaps the first work on MoS2 exfoliation by the adhesive type method resulting in few-layer MoS2 and monolayers of MoS2 is the work of Frindt.2 One year earlier, the same author published a manuscript in which the optical properties of few-layered MoS2 were reported3: In this manuscript, the differences between the absorption spectra of thin (few layers) and bulk MoS2 were established. Later, Joensen et al.4 published an article entitled “single-layer MoS2” obtained by lithium intercalation. Here, it was found that after drying the exfoliated MoS2, the material restacked in a random fashion. As in graphite and hexagonal boron nitride, layered systems of TMDs (including inorganic fullerenes and nanotubes) are held together by weak van der Waals a)
Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this focus issue during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs. org_jmr_policy. DOI: 10.1557/jmr.2013.284 J. Mater. Res., Vol. 29, No. 3, Feb 14, 2014
http://journals.cambridge.org
Downloaded: 28 Oct 2014
forces that make them suitable for lubrication.5–7 It is noteworthy that these inorganic fullerenes and nanotubes of
Data Loading...
