Nanostructures DOI: 10.1002/ange.200703175 Two-Dimensional Nanosheet Crystals** Jung-wook Seo, Young-wook Jun, Seung-won Park, Hyunsoo Nah, Taeho Moon, Byungwoo Park, Jin-Gyu Kim, YounJoong Kim, and Jinwoo Cheon* Two-dimensional crystals, which possess a nanoscale dimen- sion only in the c axis and have infinite length in the plane, have been emerging as important new materials owing to their unique properties and potential applications in areas ranging from electronics to catalysis. [1–5] In particular, recent developments of 2D nanosheet crystals such as stable graphene and transition-metal chalcogenides (TMCs) have sparked new discoveries in condensed-matter physics and electronics. [6] Further miniaturization of these 2D structures by lateral confinements can potentially bring not only the modulation of electron-transport phenomena [7] but also the enhancement of their 2D host capabilities which arise from the enlarged surface area and improved diffusion processes upon the intercalation of guest molecules. [8] However, syn- thetic routes for such laterally confined 2D crystals, especially for TMCs, have been challenging since they are unstable and immediately scroll up into closed structures such as quasi-0D onions or 1D tubes owing to increased peripheral dangling bonds. [9–11] Herein, we have developed an entirely new “shape- transformation” concept that proceeds by a rolling out of 1D tungsten oxide nanorods for the fabrication of laterally confined (less than 100 nm) 2D WS 2 nanosheet crystals. Here, a surfactant-assisted low-temperature (lower than 350 8C) solution process is also critical in stabilizing 2D nanosheet structures as opposed to conventional high-tem- perature (higher than 700 8C) gas–solid routes which yield only 0D or 1D structures. [12–14] Our 2D WS 2 nanosheet crystals are synthesized from tungsten oxide (W 18 O 49 ) nanorods [15,16] in the presence of carbon disulfide in hot hexadecylamine solution. Figure 1 a shows an overview of our shape-transformation scheme for the generation of 2D WS 2 nanosheet crystals from the tungsten oxide rods. The reaction between the carbon disulfide and hexadecylamine generates in situ hydrogen disulfide and hexadecylisothiocyanate via N-hexadecyldithio- carbamate as a transient species [Eq. (1); see also Figures S1 and S2 in the Supporting Information], and subsequent Figure 1. 2D WS 2 nanosheet crystal formation through rolling-out shape-transformation processes of 1D W 18 O 49 nanorod precursors. a) Schematic diagram for the synthesis of 2D WS 2 nanosheet crystals. b) TEM image of W 18 O 49 nanorod precursors. c–e) TEM images of 2D WS 2 obtained with the reaction times 10 min (c), 30 min (d), and 1 h (e) after the CS 2 injection. f) XRD analyses of the WS 2 single (top) and stacked (bottom) nanosheet crystals (red lines: JCPDS reference card no. 08-0237). [*] J.-w. Seo, Y.-w. Jun, S.-w. Park, H. Nah, Prof. J. Cheon Department of Chemistry Yonsei University Seoul 120-749 (Korea) Fax: (+ 82)2-364-7050 E-mail: jcheon@yonsei.ac.kr T. Moon, Prof. B. Park Department of Materials Science and Engineering Seoul National University Seoul 151-744 (Korea) J.-G. Kim, Dr. Y. J. Kim Division of Electron Microscopic Research Korea Basic Science Institute Daejeon 305-333 (Korea) [**] This work was supported in part by the National Research Laboratory (NRL-2006-00457), NCRC (R15-2004-024-00000-0), second stage BK 21, KRF (2004-201-C00050), the ERC program of MOST/KOSEF (R11-2002-102-00000-0), and Samsung Electrome- chanics PhD training program. Supporting information for this article is available on the WWW under http://www.angewandte.org or from the author. Zuschriften 8984 # 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. 2007, 119, 8984–8987 &&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&& &&&&&&&&&&&&&&&&&&&&&&&&&&&& Nutzen Sie die blauen Literaturverknüpfungen &&&&&&&&&&&&&&&&&&&&&&&&&&&& &&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&