Subscriber access provided by UNIV OF CALIFORNIA SAN DIEGO LIBRARIES
Article
Tunable Volatile-Organic-Compound Sensor by using Au Nanoparticle Incorporation on MoS2 Soo-Yeon Cho, Hyeong-Jun Koh, Hae-Wook Yoo, Jong-Seon Kim, and Hee-Tae Jung ACS Sens., Just Accepted Manuscript • DOI: 10.1021/acssensors.6b00801 • Publication Date (Web): 05 Jan 2017 Downloaded from http://pubs.acs.org on January 6, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Sensors is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 26
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sensors
Tunable Volatile-Organic-Compound Sensor by using Au Nanoparticle Incorporation on MoS2 Soo-Yeon Cho,†,‡,⊥ Hyeong-Jun Koh,†,‡,⊥ Hae-Wook Yoo,† Jong-Seon Kim,†,‡ and Hee-Tae Jung*,†, ‡
†
Department of Chemical and Biomolecular Engineering (BK-21 Plus), Korea Advanced
Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea ‡
KAIST Institute for Nanocentury, Korea Advanced Institute of Science and Technology
(KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Korea ⊥
These authors contributed equally to this work.
ACS Paragon Plus Environment
ACS Sensors
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ABSTRACT Controlling the charge concentrations of two-dimensional (2D) materials is a critical requirement for realizing versatility and potential application of these materials in highperformance electronics and sensors. In order to exploit the novel chemical-sensing characteristics of 2D materials for sensitive and selective sensors, various functionalization methods are needed to ensure efficient doping of channels based on 2D materials. In the present study, the gas-sensing performance of MoS2 has been significantly enhanced by controlled Au nanoparticle functionalization. By using the difference in reduction potential between the Au precursor and MoS2 work functions, MoS2 prepared by chemical exfoliation process was decorated with nanoparticles with sizes of tens of nanometers. The n-doping effect of Au nanoparticles was observed, that is, these particles were found to have facilitated in electron charge transfer from Au to MoS2. The controlled n-doping effect enables the tuning of the sensing of hydrocarbon-based volatile organic compounds (VOCs) and oxygenfunctionalized compounds by MoS2. A significant step has therefore been made with this study towards solving the limitations imposed by previous MoS2-based sensors, which mostly produce a single response to various VOC analytes. This controllable chemical doping process for tuning the VOC-sensing performance of MoS2 can eventually be used in early detection using multichannel sensing systems that have different responses and recognize patterns for target analytes.
Keywords: Two-dimensional materials, transition-metal dichalcogenides, volatile organic compounds, doping, gas sensor, nanoparticles
ACS Paragon Plus Environment
Page 2 of 26
Page 3 of 26
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sensors
The precise control and modulation of the intrinsic electronic properties of twodimensional (2D) materials can improve their versatility and their potential use in highperformance optoelectronics.1–3 Various applications such as field-effect transistors and photovoltaics require modification of the electronic properties of 2D materials from p-type to n-type, or vice versa, through modulation of the mobile charge concentrations and through functionalization with chemical moieties to make the interface of such materials compatible with other nanosystems.4–6 Methods established for conventional semiconductors, such as ion implantation, are not readily applicable to 2D materials because of their atomically thin structure.7 A wide variety of alternative doping methods such as substitutional doping,8 defect engineering,9 molecule physisorption,10 chemical doping methods,11 and plasma-assisted doping12 have thus been developed to control the charge concentrations in 2D materials, a powerful tool for doping 2D materials. In particular, incorporation of surface adatoms such as noble-metal nanoparticles can be a powerful tool for doping 2D materials because it induces electron exchange between 2D materials and the metal nanoparticles incorporated onto the surfaces, which does not lead to significant defects in the 2D materials. Furthermore, its fabrication process is easy to control. Incorporation of noble metals such as Au, Pt, or Pd can be an effective way of doping 2D materials because they have a high resistance to environmental corrosion and oxidation, resulting in the stability of the doped semiconducting 2D materials under ambient conditions.13,14 Additionally, functionalization processes such as chemical and electrical sensitization of the semiconducting channel can be realized by exploiting the highly catalytic properties of these metals.15–17 Volatile organic compounds (VOCs), which are widely used reagents in industrial processes, are important environmental pollutants that can be highly neurotoxic. Various methods for the detection of VOCs exist, including ion flow-tube mass spectrometry,18 surface acoustic wave sensing,19 gas chromatography–mass spectrometry,20 and quartz crystal
ACS Paragon Plus Environment
ACS Sensors
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
microbalance techniques.21 Among these, the chemiresistor approach is of particular interest because of the portability of its equipment, cost-effectiveness, power efficiency, speed, and high sensitivity.22 Materials such as metal oxides, metal nanoparticles, conducting polymers, and carbon-based nanomaterials have been used as sensing materials for chemiresistor channels in VOC sensors to achieve high performance. In particular, layered transition-metal dichalcogenides (TMDCs) such as molybdenum disulfide (MoS2) have recently emerged as a class of VOC-sensing materials because of their various active sites for functionalization (i.e., sulfur defects, vacancies, and edge sites), high surface-to-bulk atom ratio, sensitivity, layerdependent band gap properties, and their high-yield preparation process.23–26 Although they offer many advantages for use as sensing materials, TMDCs nonspecifically adsorb diverse VOCs such as hydrocarbons, ketones, and alcohols, showing a single response behavior upon adsorption of the target gases. This property implies that MoS2 has poor selectivity, low reliability, and no ability to distinguish between target VOCs. Therefore, functionalization of 2D gas-sensing materials is required in order to optimize their performance. Herein, we provide the first report on the modulation of MoS2 charge concentration through a controllable Au-doping process, as well as observations on its effect on the VOCsensing performance. Au nanoparticles were incorporated into chemically exfoliated MoS2 layers through a simple solution-mixing method and by using the reduction potential difference between the Au precursor and MoS2 work functions. The amount of surface charge transfer caused by the doping effect could be controlled by changing the ratio of Au precursor to MoS2. By changing the carrier type in MoS2 using the Au dopant, we fabricated an Audoped MoS2 sensor that positively responds (i.e. by showing increased resistance) to hydrocarbon molecules lacking oxygen groups, namely, hexane and toluene. We observed a negative response with the oxygen-functionalized reducing gases ethanol, acetaldehyde, and acetone, as well as a consistent positive response of the pristine MoS2 sensor toward such
ACS Paragon Plus Environment
Page 4 of 26
Page 5 of 26
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sensors
gases. The change in gas response in VOC chemisorption behavior is due to the n doping of MoS2 with Au nanoparticles, which facilitates the electron charge transfer. The change in the main carrier of the MoS2 channel from hole to electron is explained by Fermi-level differences between MoS2 and Au nanoparticles. The controlled n-doping effects of Au leads to tunable sensing of MoS2, enabling it to distinguish between hydrocarbon-based and oxygen-functionalized VOCs. This study has thus made a significant step toward solving the limitations imposed by present MoS2-based sensors, which mostly show a single response to various VOC analytes.
EXPERIMENTAL SECTION Preparation of MoS2 suspension and decoration with Au nanoparticles. Layered MoS2 powder (
