ARTICLE Copyright © 2017 by American Scientific Publishers All rights reserved. Printed in the United States of America Science of Advanced Materials Vol. 9, pp. 1–6, 2017 www.aspbs.com/sam Three Transition Regions Observed in Single Crystalline Bi-Rich Bi 2 Te 3 Nanobelts Sunghun Lee 1, 2 , Juneho In 1 , Sanghyun Ji 2 , Yun Chang Park 3 , Jinhee Kim 4 , Bongsoo Kim 1, * , and Myung-Hwa Jung 2, * 1 Department of Chemistry, KAIST, Daejeon 34141, Korea 2 Department of Physics, Sogang University, Seoul 04107, Korea 3 Measurement and Analysis Team, National Nanofab Center, Daejeon 34141, Korea 4 Center for Electricity and Magnetism, KRISS, Daejeon 34113, Korea ABSTRACT Bi 2 Te 3 has recently received considerable attention because of its various characteristics and applications potential. The effort to incorporate dopants into Bi 2 Te 3 to achieve particular features has continued. We inves- tigated Bi-rich Bi 2 Te 3 nanobelts, which were synthesized by the VLS method. We confirmed that single crys- talline Bi-rich Bi 2 Te 3 nanobelts with 1:1 of Bi:Te atomic ratio had a hexagonal Bi 2 Te 3 crystal structural phase, using X-ray diffraction and scanning transmission electron microscopy. The results from electrical and magneto- transport measurements of a Bi-rich Bi 2 Te 3 nanodevice revealed three different transition regions, in which different magnetoresistance behaviors were observed, and where the maximum magnetoresistance ratio was about 105%. These characteristics could provide a wider perspective for potential of Bi-rich Bi 2 Te 3 nanodevices. KEYWORDS: Bi-Rich Bi 2 Te 3 , Nanobelts, Transition Temperature, Magnetoresistance. 1. INTRODUCTION Bismuth telluride (Bi 2 Te 3 ) continues to attract a great deal of attention because of its wide spectrum of intrigu- ing characteristics and applications potential. For example, Bi 2 Te 3 has proven to be one of the most promising ther- moelectric materials, enabling devices with a very high dimensionless figure of merit at room temperature. 1–5 Furthermore, its application in a phase change memory device operated by a simple electrical pulse has been suggested, where the main operating mechanism is a reversible phase transition between crystalline and amor- phous states. 6 Recently, research interest in Bi 2 Te 3 has dramatically increased due to its topological insulating properties, a new form of quantum matter with conductive massless. Dirac fermions on the surface, which is consid- ered promising in the field of material science for future quantum information technologies. 7–15 Since the discovery of the topological surface states of Bi 2 Te 3 , there have been extensive efforts to tailor enhanced material structures by alloying or doping, to suppress the bulk contributions which originate from intrinsic or extrin- sic defects. 16–20 Adding other materials to the interstitial ∗ Authors to whom correspondence should be addressed. Email: mhjung@sogang.ac.kr Received: 26 September 2016 Accepted: 28 December 2016 structure of Bi 2 Te 3 can result in a change in the den- sity of states, allowing surface carriers to contribute to transport, leading to physically meaningful parameters. Kong et al. reported that tuning the ratio of Bi to anti- mony (Sb) not only reduced the contribution of bulk car- rier density, while retaining the topological surface states, but they also observed an ambipolar gating effect, sim- ilar to that observed in a graphene field effect transis- tor (FET). 16 Wang et al. fabricated sodium (Na) doped Bi 2 Te 3 nanoplate FET, and demonstrated the enhancement of surface states in the Na-doped Bi 2 Te 3 nanoplates and a tunable gating effect from the p-type to n-type. 18 More- over, different electronic phenomena could be observed, resulting from changes in the band structure when Bi and Te atoms were either rich or deficient in the unit cell structure. 21 The effect of nanostructured Bi 2 Te 3 with a rich or deficient ratio of Bi, however, has not been reported yet. In this work, using an additional inserted Bi source, we synthesized single crystalline Bi-rich Bi 2 Te 3 (BiTe) nanobelts (NBs) using the vapor liquid solid (VLS) method. After Fabricating a BiTe NB nanodevice, we observed three transition temperature regions, which were considered to result from competition between the bulk conductions and surface states carriers in the BiTe NB system. Furthermore, the magnetoresistance in each temperature regime revealed peculiar magneto- transport properties. These characteristics could provide Sci. Adv. Mater. 2017, Vol. 9, No. xx 1947-2935/2017/9/001/006 doi:10.1166/sam.2017.3138 1