Letter pubs.acs.org/NanoLett
Dielectric Mismatch Mediates Carrier Mobility in OrganicIntercalated Layered TiS2 Chunlei Wan,*,†,‡ Yumi Kodama,‡ Mami Kondo,‡ Ryo Sasai,§ Xin Qian,∥ Xiaokun Gu,∥ Kenji Koga,⊥ Kazuhisa Yabuki,⊥ Ronggui Yang,*,∥ and Kunihito Koumoto*,‡
Downloaded by UNIV OF NEBRASKA-LINCOLN on September 2, 2015 | http://pubs.acs.org Publication Date (Web): September 1, 2015 | doi: 10.1021/acs.nanolett.5b01013
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State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China ‡ Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan § Interdisciplinary Graduate School of Science and Engineering, Shimane University, 1060 Nishikawatsu-cho, Matsue 690-8504, Japan ∥ Department of Mechanical Engineering, University of Colorado, Boulder, Colorado 80309, United States ⊥ KOBELCO Research Institute, Kobe, Hyogo 651-2271, Japan S Supporting Information *
ABSTRACT: The dielectric constant is a key parameter that determines both optical and electronic properties of materials. It is desirable to tune electronic properties though dielectric engineering approach. Here, we present a systematic approach to tune carrier mobilities of hybrid inorganic/organic materials where layered two-dimensional transition-metal dichalcogenide TiS2 is electrochemically intercalated with polar organic molecules. By manipulating the dielectric mismatch using polar organic molecules with different dielectric constants, ranging from 10 to 41, the electron mobility of the TiS2 layers was changed three times due to the dielectric screening of the Coulombimpurity scattering processes. Both the overall thermal conductivity and the lattice thermal conductivity were also found to decrease with an increasing dielectric mismatch. The enhanced electrical mobility along with the decreased thermal conductivity together gave rise to a significantly improved thermoelectric figure of merit of the hybrid inorganic/organic materials at room temperature, which might find applications in wearable electronics. KEYWORDS: Titanium disulfide, transition-metal dichalcogenide, thermoelectrics, hybrid materials, dielectric mismatch
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device where the dielectric constant is maximized. However, this method is limited to ferroelectric materials. Modifying the dielectric environment could be another fruitful approach to optimize the carrier mobility of the recently emerging low-dimensional materials such as nanowires10 and monolayers.11 Different from bulk materials, the electric field of the Coulomb impurities in the low-dimensional materials can penetrate into the surrounding environment, which can be effectively screened and modified by the dielectric environment. The effective Coulomb potential “felt” by the electrons in the low-dimensional materials could be weakened, rendering a lower scattering rate.12−14 For example, the carrier mobility in graphene was increased by three orders-of-magnitude when graphene was suspended in a polar liquid15 with the dielectric constants changing from 1 to 40. In single-layer MoS2 transistors, adding a high-k dielectrics HfO2 as the top-gate dielectrics that effectively screened the Coulomb scattering in MoS2 has resulted in a remarkable improvement in the carrier mobility in this dual-gate device.16,17
he dielectric constant is a key parameter that controls capacitance, refractive index, charge screening, and conductivity of materials.1 In particular, the dielectric constant dominates the screening of electrostatic forces between the electrical carriers and the extra charges, such as ionic impurities or oscillating dipoles in a lattice. Therefore, it has a determining effect on the carrier mobility, which is a fundamental property of electronic materials for field-effect transistors (FET),2 photovoltaic cells,3 and thermoelectric devices.4 For example, the ultrahigh mobility of SrTiO35 and KTaO3,6 higher than 10,000 cm2 V−1 S−1 at low temperatures (
