Recovery Improvement for Large-Area Tungsten Diselenide Gas

Subscriber access provided by - Access paid by the | UCSB Libraries

Energy, Environmental, and Catalysis Applications

Recovery Improvement for Large-Area Tungsten Diselenide Gas Sensor Kyung Yong Ko, Kyunam Park, Sangyoon Lee, Youngjun Kim, Whang Je Woo, Donghyun Kim, Jeong-Gyu Song, Jusang Park, and Hyungjun Kim ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b07034 • Publication Date (Web): 22 Jun 2018 Downloaded from http://pubs.acs.org on June 24, 2018

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 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 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.

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 24 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 Applied Materials & Interfaces

Recovery Improvement for Large-Area Tungsten Diselenide Gas Sensor Kyung Yong Ko1, Kyunam Park1, Sangyoon Lee1, Youngjun Kim1, Whang Je Woo1, Donghyun Kim1, Jeong-Gyu Song1, Jusang Park1, and Hyungjun Kim1*

1

School of Electrical and Electronic Engineering, Yonsei University, 50 Yonsei-Ro, Seodaemun-Gu, Seoul, 03722, Rep. of Korea

*

Corresponding author. E-mail: [email protected]

KEYWORDS: transition metal dichalcogenide, gas sensor, room temperature operating, recovery improvement, tungsten diselenide, atomic layer deposition, selective catalytic reduction

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 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

Page 2 of 24

1

ABSTRACT: Semiconducting two-dimensional (2D) transition metal dichalcogenides (TMDCs) are considered promising gas-sensing materials because of their large surface-tovolume ratio, excellent electrical conductivity, and susceptible surfaces. However, enhancement of the recovery performance has not yet been intensively explored. In this study, a large-area uniform WSe2 is synthesized for use in a high-performance semiconductor gas sensor. At room temperature, the WSe2 gas sensor shows a significantly high response (4140 %) to NO2 compared to use of NH3, CO2, and acetone. This paper demonstrates improved recovery of the WSe2 gas sensor’s NO2-sensing performance by utilizing external thermal energy. In addition, a novel strategy for improving the recovery of the WSe2 gas sensor is realized by reacting NH3 and adsorbed NO2 on the surface of WSe2: the NO2 molecules are spontaneously desorbed, and the recovery time is dramatically decreased (85 min 43 s). It is expected that the fast recovery of the WSe2 gas sensor achieved here will be used to develop an environmental monitoring system platform.


Page 3 of 24 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


2

Various electronic sensors based on human sensory nervous system responses are being used to prevent injury and death. For example, gas sensors are used to detect the presence of industrial chemical and are also employed in indoor/outdoor air pollution monitoring, in emission management of automotive vehicles, and at power plants. Among the various air pollutants, toxic gaseous species such as NO and NO2 are the most commonly emitted from diesel trucks, marine diesel engines, waste incinerators, and thermal power plants. NO easily converts to NO2 in the air, and reducing the NO2 concentration is essential for controlling NOx emissions, as continuous NO2 exposure can cause respiratory diseases such as respiratory irritation, chronic bronchitis, and emphysema. For this reason, a 5 min emergency exposure limit for NO2 (35 parts per million (ppm)) was set by the American Industrial Hygiene Association.1 It is thus important to develop high-performance gas sensors to predict and monitor air conditions, with the aim of preventing human exposure to high levels of pollutants. Two-dimensional (2D) transition metal dichalcogenides (TMDCs; MX2: M = Mo, W; X = S, Se) are layered materials based on the existence of weak van der Waals bonding toward the out-of-plane and strong covalent bonding toward the in-plane. TMDCs have been actively studied to explore their positive attributes, such as electrical transport,2,3 optical luminescence,4–7 photocurrent,8–10 and strain effects,11,12 and they are considered to be promising semiconducting materials. Due to their remarkable electronic and chemical stability, large surface-to-volume ratio,13–18 and semiconducting property,2,3,15 they show a high response to various gaseous species, such NO2,13,16–18 NH3,13,16,17 triethylamine,14 tetrahydrofuran,14 acetone.14,18 In particular, TMDCs have the unique advantage of being suitable for use in low power-operating monitoring systems, as they provide a high response even at room temperature, while conventional metal oxide gas sensors only exhibit responses



Page 4 of 24

3 at operating temperatures of over 300–500 °C.13,14,17 It is expected that an increasing number of studies will focus on using TMDCs as a gas sensing material. TMDCs also have unique features relating to layer numbers, such as magnitude of band gap,19 indirect-to-direct band gap transition,20 electronic transport19, and photo absorption.21 Also, layer number-dependent gas sensing properties of MoS2 and WS2 have been reported.15,18 However, multi-layers show a higher and stable response than monolayers, although the reason for this has not yet been defined. It is thus important to control layer number synthesis of TMDCs to enable realization of a practical TMDCs gas sensor that is highly responsive and offers repeatable use and reliability. We previously reported the selflimiting layer synthesis (SLS) of TMDCs based on the atomic layer deposition (ALD) process, thereby introducing the ability to conduct layer-controlled, large-area uniform TMDCs synthesis.22,23 As controllability of the layer number is now excellent, it is possible to achieve wafer-scale uniformity of MoS2 and WSe2, and thus synthesis for use in various 2D TMDCs-based electronic device and high-performance gas sensor is now possible and affordable. Although TMDCs gas sensors exhibit an immediate response to various gases, they show a slow and incomplete recovery at room temperature.17,18 Nevertheless, the recovery of a TMDCs gas sensor can be improved by increasing the desorption rate of gas molecules with the application of thermal energy.24 The recovery of the sensor is significantly improved even with the mild increase of temperature (100–200 °C). However, the inclusion of a heating layer in the gas sensor causes an increase in process complexity and requires continuous thermal power consumption to detect the gas molecules. It is thus necessary to discover other methods that can enhance the recovery property of the TMDCs gas sensor. This paper reports the development of a high-performance gas sensor that uses a large-area uniform 3L WSe2 synthesized by the ALD process with WCl6 and diethyl selenide. The 3L


Page 5 of 24 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


4

WSe2 gas sensor shows a significantly high response (4140 %) to 500 ppm NO2 exposure at room temperature. We also investigate the desorption characteristics of gases from the surface of the WSe2 gas sensor by focusing on the temperature dependency. This study also suggests use of a novel enhancement method for improving the WSe2 gas sensor recovery time (~ 43 s, ~120 times faster than using N2 only purging). This is achieved at room temperature using a mixture of N2 and NH3 as a purging gas; success is attributed to the SCR reaction.

Results and Discussion

Figure 1. Schematic images of (a) ALD equipment and (b) synthesized 3L WSe2; (c) Raman spectra of 3L WSe2; (d) AFM image and height profile of 3L WSe2; XPS spectra of (e) W 4f and (f) Se 3d core levels of 3L WSe2. All XPS spectra were normalized by W 4f7/2 peak intensity.



Page 6 of 24

5

As previously reported, ALD WSe2 exhibits a self-limiting layer growth depending on the growth temperature.22 Figure S1 shows temperature-dependent self-limiting layer synthesis (SLS) of WSe2 (See Supporting information, Figure S1): as the growth of WSe2 is based on the physically adsorbed precursor during the ALD process, the thickness of WSe2 decreases with an increase in the growth temperature. A 1L WSe2 was achieved at 800 °C, as confirmed by PL measurements shown in Figure S1b. It is thus evident that this unique synthesis process is feasible for use in gas sensor applications as it provides a large-area of uniform 2D WSe2. As shown in Figure 1a-b, we synthesized 3L WSe2 on SiO2/Si substrate using ALD equipment at 700 °C. The Raman spectra (λexc = 532 nm) of Figure 1c shows that the 3-layer thick WSe2 exhibits E12g and A1g modes relating to in-plane and out-of-plane vibrations at around 251 and 258 cm-1. The characteristic A21g (out-of-plane mode) peak observed at ~308 cm-1 has only been previously observed in WSe2 at a bilayer or thicker.22 The thickness of WSe2 was measured using AFM measurements, and Figure 1d presents the AFM image and height profile of WSe2. Transference of this WSe2 to new SiO2 substrates provided a thickness of 2.5 nm, which corresponded to 3L WSe2. The atomic composition of WSe2 was then confirmed using XPS measurement relating to the W 4f and Se 3d binding energies: Figure 1e shows the W 5p3/2, W 4f5/2, and W 4f7/2 binding energies of W4+ at 38.4 eV, 34.9 eV, and 32.9 eV respectively. XPS peaks related to the Se binding energy are shown in Figure 1f, and the peaks corresponding to Se 3d5/2 and Se 3d7/2 are observed at 55.9 eV and 55.1 eV respectively. In addition, a stoichiometric ratio of 2 was calculated for Se/W.


Page 7 of 24 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


6

Figure 2. (a) Schematic image of WSe2 gas sensor; (b) photographic image of WSe2 gas sensor; (c) I-V characteristics of WSe2 gas sensor; (d) energy band alignment of WSe2 and Pd; (e) energy band diagram of WSe2 gas sensor junction with Pd electrodes.

We then fabricated gas sensors using the large-area synthesized 3L WSe2. According to recent TMDCs gas sensor studies, a multilayer TMDCs shows better stable and high response than 1L TMDCs.15,17 Thus, 3L WSe2 was selected and studied gas sensing property. As schematically shown in Figure 2a, the WSe2 gas sensor was fabricated with thermally evaporated metal interdigitated electrodes (Pd 40 nm) using a shadow mask, and Figure 2b shows a photograph of the WSe2 gas sensor fabricated using large-area 3L WSe2. To confirm that Pd metal electrodes were synthesized to WSe2, the I-V Characteristic of the WSe2 gas sensor were observed prior to conducting the gas sensing test. As shown in Figure 2c, the developed WSe2 gas sensor shows a linear I-V curve for the voltage bias sweep; it can be assumed from this Ohmic behavior that very low contact resistance was formed at the interface between WSe2 and Pd, as shown in Figure 2d-e. To determine the energy band



Page 8 of 24

7

alignment, we considered the electron affinity, band gap, and work functions of WSe2 and Pd. Reported values of the electron affinity for WSe2 range from 4.03 eV to 4.1 eV, the reported band gap of 3L WSe2 is 1.2 eV,25–27 and literature values for the Pd work function range from 5.12 eV to 5.55 eV28,29. As Pd is a high work function metal, it transports the hole carriers into the valence band of WSe2 with a low Schottky barrier height.

Figure 3. (a) Gas-sensing results for WSe2 gas sensors relating to 3L WSe2 gas sensor upon NO2 exposure at 10, 20, 50, 100, 200, and 500 ppm. (b) Energy band diagram of WSe2 gas sensor under bias (+1 V) and effect of NO2 gas exposure. Upward energy band bending for NO2 based on charge transfer mechanism. (c) Response to NO2 exposure of 3L WSe2 gas sensor. (d) Selectivity of 2D WSe2 gas sensor upon exposure to 500 ppm of various gases (NO2, NH3, and CO2) and 10 ppm of acetone.


Page 9 of 24 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


8

The gas-sensing performance of the WSe2 gas sensors consisting of 3L WSe2 was evaluated with a constant voltage bias (+1 V) between each pair of metal electrodes at room temperature. Figure 3a shows the current change of the pristine WSe2 gas sensors upon exposure to NO2 (concentration: 10, 20, 50, 100, 200, and 500 ppm). Exposure to the target gas was maintained for 20 min, while exposure to N2 was maintained for 50 min to allow the gas sensors to recover. As shown in Figure 3a, the WSe2 gas sensor shows an immediate and greater increase in the current upon NO2 exposure which indicates a p-type semiconductor behavior because the NO2 is a well-known electron acceptor for WSe2.30 The gas sensing characteristic of 2D TMDCs depends on physisorption of the gas molecule and charge transfer, as schematically shown in the inset within Figure 3a.16 The energy band diagram in Figure 3b summarizes the gas-sensing mechanism of the WSe2 gas sensor. When the WSe2 gas sensor is exposed to NO2 gas, NO2 molecules are spontaneously adsorbed and electrons are extracted from WSe2.30 These extracted electrons cause an increase in the hole concentration and the subsequent upward bend of the conduction/valence band of WSe2. This energy band banding leads to a decrease in resistance, and hole carrier transport is increased from the Pd electrode to the valence band of WSe2. The response to NO2 was calculated using a quantitative analysis, and the sensor response is defined as follows,

(%) =

− ∆ × 100 % = × 100 % (1)

where I0 and Ig are currents of the gas sensor before and after exposure to the target gas, respectively. Figure 3c shows the linear response increase depending on NO2 concentration. There was a 162% response to 10 ppm NO2, and this response increased to 4140 % with 500 ppm NO2, which is 4.5-fold higher than the best response recorded using a MoS2 gas



Page 10 of 24

9 sensor.17 To the authors’ knowledge, this response value is the best response ever recorded for NO2-sensing using 2D TMDCs. Furthermore, selectivity of the WSe2 gas sensor was investigated upon exposure to various gases, including NO2, NH3, CO2, and acetone at room temperature. The WSe2 gas sensor showed an excellent gas-sensing performance to NH3, CO2, and acetone, as shown in Figure S2 (see Supporting information). However, the values for the current variation were lower than those for the NO2 sensing result. Contrary to NO2-sensing result, when the WSe2 gas sensor is exposed to NH3, CO2, and acetone gas, the decrease of current is observed which is related to the decrease in the hole concentration. Although the specific roles of adsorbed CO2 and acetone molecules have not studied, the adsorbed NH3 molecule is known electron donor.30 Thus, the hole concentration of WSe2 can be decreased by transferred electrons from gas molecules to WSe2. As shown in Figure S2b, Figure S2d, and Figure S2f, the responses to NH3, CO2, and acetone gas were calculated by equation (1). Figure 3d shows the comparative response to various gases. A positive response was shown upon NO2 exposure, while a negative response occurred with NH3, CO2 and acetone exposure. It is also very evident that the NO2 response was much higher than other gases. This is related to the different adsorption energy and degree of charge transfer to various gases, which is recently reported study based on density functional theory calculation.30 In previous calculation study, it is reported that NO2 molecule has much higher adsorption energy and degree of charge transfer than other molecules such as O2, CO, NH3, H2O, NO.


Page 11 of 24 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


10

Figure 4. (a) Schematic images of gas sensing chamber for temperature-dependent gas sensing measurements. Gas sensing measurements were conducted at room temperature and at 100 °C using a furnace system. Gas delivery comprised NO2 at 500 ppm exposure (500 sccm) and N2 purging (500 sccm). Temperature-dependent gas sensing property of 2D WSe2 gas sensor upon NO2 exposure (500 ppm) at (b) RT and (c) at 100 °C of measuring temperature.

To verify the temperature effect with respect to the recovery property of the WSe2 gas sensor, gas sensing experiments were conducted at room temperature (27 °C) and at 100 °C using a furnace system, as shown in Figure 4a. All conditions (target gas concentration, gas flow rate, exposure time, and bias voltage) except measurement temperature were maintained in both experiments. The comparison presented in Figure 4b-c shows there was a slight decrease in the response to NO2 at 100 °C. This means decreased physisorption in higher



Page 12 of 24

11

temperature because the kinetic energy of adsorbed molecules is increased and they overcome the electrostatic force of attraction by the adsorbent surface.16 Also, the recovery property was improved for the same reason. To quantitatively analyze the effect of temperature, the response time and recovery time were calculated at 500 ppm NO2. The response time, tresponse, is defined as the interval between the time immediately prior to target gas exposure and the time when the response reached 90% of the maximum value. Conversely, recovery time (trecovery) is defined as the time interval between the time when the response reached a maximum value to the time at which it reached 10% of the minimum value. With an increase in the measurement temperature from room temperature to 100 °C, there was a decrease in the recovery time from 85 min to 21.5 min because of the increased desorption rate of NO2 molecules. However, in relation to improving recovery properties, although the increased measurement temperature (100 °C) was much lower than the operating temperature of the conventional metal oxide gas sensor (300–500 °C), the need for continuous thermal power consumption is an associated limitation.13,14,17


Page 13 of 24 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


12

Figure 5. (a) Schematic image of gas sensing chamber for enhanced recovery. Gas delivery comprised NO2 at 500 ppm exposure (500 sccm) and mixed gas (NH3 and N2) purging (500 sccm). (b) Gas sensing property of 2D WSe2 gas sensor. (c) Response time and recovery time of WSe2 gas sensor. (d) Recovery time comparison at different conditions. (e) Schematic image of recovery using mixed purging gas.

We then designed an experimental setup to improve recovery of the WSe2 gas sensor without the requirement of thermal power consumption. We modified the purging gas as a mixed gas (NH3 and N2) from N2 purging gas, as shown in Figure 5a: the mixed gas consisted of 10 sccm of 500 ppm NH3 and 490 sccm of N2 (= 500 sccm of 10 ppm NH3). The total gas flow rate was maintained as 500 sccm. Figure 5b shows a cyclic test conducted using the WSe2 gas sensor. It is worth noting that the baseline current is selected when the state is



Page 14 of 24

13

saturated by using mixed gas (NH3 and N2) purging to calculate a normalized response of Figure 5b-c. There was an immediate and repeated gas sensing response to 500 ppm NO2. In addition, the WSe2 gas sensor rapidly recovered and was saturated to baseline: the calculated recovery time dramatically decreased to 43 s, as shown in Figure 5c. Figure 5d shows the comparison of recovery time with the different condition. When the mixed purging gas is used, the recovery of the WSe2 gas sensor is approximately 120-times faster than before NH3 gas was added. Furthermore, we experimented regarding recovery time and concentration of NH3, as shown in Figure S3 (see Supporting information). We can observe the recovery speed enhancement by increasing the NH3 concentration. Figure S3e shows that recovery time exhibit under 20 sec over 20 ppm of NH3. We assume that this enhanced recovery is related to the reaction of NO2 and NH3 on the surface of WSe2, as shown in Figure 5e, which is a similar mechanism to that of the “selective catalytic reduction (SCR)” reaction.31,32 The detailed mechanism of fast recovery is described in Supporting Information (Figure S4). With respect to environmental regulations, use of the SCR reaction as a post-combustion technology treatment for diesel engines has been studied. The SCR reaction has been actively applied in the automotive industry to reduce NOx emissions: exhaust NO2 gas can be efficiently reacted with NH3 by representative catalysts such as MoO3, WO3, V2O5, and zeolite, and converted into harmless N2 and H2O gas.

31,32

This SCR reaction relates to the

surface reaction of the catalyst. Therefore, the fast recovery of the WSe2 gas sensor is related to this reaction type occurring with NH3 and adsorbed NO2 on the surface of WSe2. To date, 2D TMDCs gas sensors have shown improved recovery by the addition of thermal energy via heating16 and with optical energy via illumination.17 However, the improved recovery characteristics based on the SCR reaction has not yet been reported, and it is considered that the results achieved here are superior to those reported in previous studies.


Page 15 of 24 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


14

Conclusion In summary, we demonstrate the development of a high-performance 2D WSe2 gas sensor synthesized using the ALD process. The outstanding NO2-sensing performance of this 2D WSe2 gas sensor was evaluated at room temperature and then compared to performances using NH3, CO2, and acetone. The gas sensing response to NO2 (4140%) was the best recorded for all various TMDCs gas sensors to date. The dependence of temperature in the recovery of the WSe2 gas sensor was also quantitatively investigated, and a novel study was conducted on use of the SCR reaction in the associated recovery property. By reacting the NH3 and adsorbed NO2 on the surface of WSe2, NO2 molecules spontaneously desorbed, and the recovery time was dramatically decreased (85 min 43 s). It is thus expected that the fast recovery time of this WSe2 gas sensor will subsequently lead to the development of an environmental monitoring system using semiconducting 2D TMDCs.

Methods and Materials Synthesis of WSe2: 2D WSe2 was synthesized using the previously reported ALD process.22 Synthesis of WSe2 directly onto SiO2 (285 nm)/Si substrates was conducted in a tube-type furnace reactor using WCl6 and diethyl selenide (DESe) as the precursor and reactant, respectively. A bubbler containing the precursor was heated to 85 ºC to ensure that adequate vapor pressure was acquired to carry the precursor molecules into the tube by the pure Ar (99.999%) carrier gas. The ALD cycle consisted of four steps using the same ALD procedure: precursor exposure for 4 s, 5 s Ar purge, 3 s DESe reactant exposure, and a final 5 s Ar purge. As previously reported, ALD WSe2 exhibits self-limiting layer growth depending on the growth temperature.22 In this work, 100 cycles of ALD WSe2 were conducted at a growth temperature of 700 °C to obtain uniform 3L WSe2.



Page 16 of 24

15

Characterization of WSe2: An optical microscopy (OM) image was obtained using an Olympus DX51, and Raman spectroscopy and photoluminescence (PL) were conducted using a LabRam ARAMIS (HORIBA, 532 nm wavelength laser). Characterisation using X-ray photoelectron spectroscopy (XPS) was performed using a K-Alpha model (Thermo Scientiﬁc Co.). An atomic force microscopy (AFM) image of WSe2 using a Multimode scanning microscope (Veeco) was taken to conduct measurements, and I-V curves of WSe2 gas sensor were measured using a source meter (Keithley 2400).

Gas Sensor Fabrication: Pd electrodes (40 nm) were deposited on the WSe2 using a thermal evaporator. A stainless-steel shadow mask (designed as an interdigitated electrode) was used to form electrode patterns. Substrate dimensions were 15 mm × 25 mm, and the electrodes had 300 of channel width/length ratio with a 100-µm channel length.

Gas Sensing Experiment: The gas sensing performance of the WSe2 sensor was monitored within a sealed gas-sensing chamber. An electrical feed-through and gas inlet and outlet were installed in the chamber, and N2 was used as the purging gas (the target gas was diluted with N2 and the experiment was conducted at room temperature (27 °C)). The concentration of each gas was adjusted by controlling the flow rates of the target gas and balance gas (N2), which was achieved using mass-flow controllers. The target gas and purging gas were exposed for 20 min and 50 min, respectively, for each cycle of the gas-sensing test. Prior to target-gas injection, the gas sensors were stabilized under N2 exposure for ~1 h. The input voltage (+1 V) was biased to the source/drain electrodes of sensors, and the real-time output signal (current) was acquired using the source meter (Keithley 2400).


Page 17 of 24 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


16

ASSOCIATED CONTENT

Supporting Information. Raman spectra and Photoluminescence of 1L, 3L, and 5L WSe2, Gas-sensing results and response of 3L WSe2 gas sensor upon NH3, CO2, and Acetone

AUTHOR INFORMATION

Corresponding Author Hyungjun Kim* School of Electrical and Electronic Engineering, Yonsei University, 50 Yonsei-Ro, Seodaemun-Gu, Seoul, 03722, Rep. of Korea *E-mail: [email protected], Tel: 82-2-2123-5773, Fax: 82-2-313-2879

Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by the following: the Materials and Components Technology Development Program of MOTIE/KEIT. [10080527, Development of commercialization technology of high sensitive gas sensor based on chalcogenide 2D nano material]; and a grant from the National Research Foundation of Korea (NRF) funded by the Korea government (MSIP) (No. NRF-2014R1A2A1A11052588); Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education, Science and Technology(No.2015R1D1A1A01060064).

ABBREVIATIONS 2D, two-dimensional; TMDCs, transition metal dichalcogenides; SCR, selective catalytic



Page 18 of 24

17

reduction; ALD, atomic layer deposition; DESe, diethyl selenide; OM, optical microscopy; PL, photoluminescence; XPS, X-ray photoelectron spectroscopy; AFM, atomic force microscopy; SLS, self-limiting layer synthesis.


Page 19 of 24 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


18

REFERENCES (1)

John P. Frawley Ph.D. Emergency Exposure Limits American Industrial Hygiene Association, Toxicology Committee. Am. Ind. Hyg. Assoc. J. 1964, 25 (6), 578–586.

(2)

Fang, H.; Chuang, S.; Chang, T. C.; Takei, K.; Takahashi, T.; Javey, A. HighPerformance Single Layered WSe 2 p-FETs with Chemically Doped Contacts. Nano

Lett. 2012, 12 (7), 3788–3792. (3)

Zhao, P.; Kiriya, D.; Azcatl, A.; Zhang, C.; Tosun, M.; Liu, Y. S.; Hettick, M.; Kang, J. S.; McDonnell, S.; K C, S.; Guo, J.; Cho, K.; Wallace, R. M.; Javey, A. Air Stable PDoping of WSe2 by Covalent Functionalization. ACS Nano 2014, 8 (10), 10808– 10814.

(4)

Sundaram, R. S.; Engel, M.; Lombardo, A.; Krupke, R.; Ferrari, A. C.; Avouris, P.; Steiner, M. Electroluminescence in Single Layer MoS2. Nano Lett. 2013, 13 (4), 1416–1421.

(5)

Mak, K. F.; Lee, C.; Hone, J.; Shan, J.; Heinz, T. F. Atomically Thin MoS2: A New Direct-Gap Semiconductor. Phys. Rev. Lett. 2010, 105 (13), 2–5.

(6)

Gutiérrez, H. R.; Perea-López, N.; Elías, A. L.; Berkdemir, A.; Wang, B.; Lv, R.; López-Urías, F.; Crespi, V. H.; Terrones, H.; Terrones, M. Extraordinary RoomTemperature Photoluminescence in Triangular WS 2 Monolayers. Nano Lett. 2013, 13 (8), 3447–3454.

(7)

Eda, G.; Yamaguchi, H.; Voiry, D.; Fujita, T.; Chen, M.; Chhowalla, M. Photoluminescence from Chemically Exfoliated MoS 2. Nano Lett. 2011, 11 (12), 5111–5116.

(8)

Perea-Lõpez, N.; Elías, A. L.; Berkdemir, A.; Castro-Beltran, A.; Gutiérrez, H. R.; Feng, S.; Lv, R.; Hayashi, T.; Lõpez-Urías, F.; Ghosh, S.; Muchharla, B.; Talapatra, S.; Terrones, H.; Terrones, M. Photosensor Device Based on Few-Layered WS2 Films.

Adv. Funct. Mater. 2013, 23 (44), 5511–5517. (9)

Zhang, C.; Wang, S.; Yang, L.; Liu, Y.; Xu, T.; Ning, Z.; Zak, A.; Zhang, Z.; Tenne, R.; Chen, Q. High-Performance Photodetectors for Visible and near-Infrared Lights Based on Individual WS 2 Nanotubes. Appl. Phys. Lett. 2012, 100 (24).

(10)

Lee, H. S.; Min, S. W.; Chang, Y. G.; Park, M. K.; Nam, T.; Kim, H.; Kim, J. H.; Ryu,



Page 20 of 24

19

S.; Im, S. MoS 2 Nanosheet Phototransistors with Thickness-Modulated Optical Energy Gap. Nano Lett. 2012, 12 (7), 3695–3700. (11)

Lu, P.; Wu, X.; Guo, W.; Zeng, X. C. Strain-Dependent Electronic and Magnetic Properties of MoS2 Monolayer, Bilayer, Nanoribbons and Nanotubes. Phys. Chem.

Chem. Phys. 2012, 14 (37), 13035. (12)

Peelaers, H.; Van De Walle, C. G. Effects of Strain on Band Structure and Effective Masses in MoS2. Phys. Rev. B - Condens. Matter Mater. Phys. 2012, 86 (24), 1–5.

(13)

Liu, B.; Chen, L.; Liu, G.; Abbas, A. N.; Fathi, M.; Zhou, C. High-Performance Chemical Sensing Using Schottky-Contacted Chemical Vapor Deposition Grown Monolayer MoS2 Transistors. ACS Nano 2014, 8 (5), 5304–5314.

(14)

Perkins, F. K.; Friedman, A. L.; Cobas, E.; Campbell, P. M.; Jernigan, G. G.; Jonker, B. T. Chemical Vapor Sensing with Monolayer MoS2. Nano Lett. 2013, 13 (2), 668– 673.

(15)

Li, H. H.; Yin, Z.; He, Q.; Li, H. H.; Huang, X.; Lu, G.; Fam, D. W. H.; Tok, A. I. Y.; Zhang, Q.; Zhang, H. Fabrication of Single- and Multilayer MoS 2 Film-Based FieldEffect Transistors for Sensing NO at Room Temperature. Small 2012, 8 (1), 63–67.

(16)

Cho, B.; Hahm, M. G.; Choi, M.; Yoon, J.; Kim, A. R.; Lee, Y.-J.; Park, S.-G.; Kwon, J.-D.; Kim, C. S.; Song, M.; Jeong, Y.; Nam, K.-S.; Lee, S.; Yoo, T. J.; Kang, C. G.; Lee, B. H.; Ko, H. C.; Ajayan, P. M.; Kim, D.-H. Charge-Transfer-Based Gas Sensing Using Atomic-Layer MoS2. Sci. Rep. 2015, 5 (1), 8052.

(17)

Late, D. J.; Huang, Y. K.; Liu, B.; Acharya, J.; Shirodkar, S. N.; Luo, J.; Yan, A.; Charles, D.; Waghmare, U. V.; Dravid, V. P.; Rao, C. N. R. Sensing Behavior of Atomically Thin-Layered MoS2 Transistors. ACS Nano 2013, 7 (6), 4879–4891.

(18)

Ko, K. Y.; Song, J. -G.; Kim, Y.; Choi, T.; Shin, S.; Lee, C. W.; Lee, K.; Koo, J.; Lee, H.; Kim, J.; et al. Improvement of Gas-Sensing Performance of Large-Area Tungsten Disulfide Nanosheets by Surface Functionalization. ACS Nano 2016, 10 (10), 9287– 9296.

(19)

Wang, Q. H.; Kalantar-Zadeh, K.; Kis, A.; Coleman, J. N.; Strano, M. S. Electronics and Optoelectronics of Two-Dimensional Transition Metal Dichalcogenides. Nat.

Nanotechnol. 2012, 7 (11), 699–712. (20)

Yeh, P. C.; Jin, W.; Zaki, N.; Zhang, D.; Liou, J. T.; Sadowski, J. T.; Al-Mahboob, A.; ACS Paragon Plus Environment

Page 21 of 24 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


20

Dadap, J. I.; Herman, I. P.; Sutter, P.; Osgood, Jr, R. M. Layer-Dependent Electronic Structure of an Atomically Heavy Two-Dimensional Dichalcogenide. Phys. Rev. B -

Condens. Matter Mater. Phys. 2015, 91 (4), 1–6. (21)

Son, Y.; Wang, Q. H.; Paulson, J. A.; Shih, C. J.; Rajan, A. G.; Tvrdy, K.; Kim, S.; Alfeeli, B.; Braatz, R. D.; Strano, M. S. Layer Number Dependence of MoS2 Photoconductivity Using Photocurrent Spectral Atomic Force Microscopic Imaging.

ACS Nano 2015, 9 (3), 2843–2855. (22)

Park, K.; Kim, Y.; Song, J.-G.; Jin Kim, S.; Wan Lee, C.; Hee Ryu, G.; Lee, Z.; Park, J.; Kim, H. Uniform, Large-Area Self-Limiting Layer Synthesis of Tungsten Diselenide. 2D Mater. 2016, 3 (1), 014004.

(23)

Kim, Y.; Song, J.-G.; Park, Y. J.; Ryu, G. H.; Lee, S. J.; Kim, J. S.; Jeon, P. J.; Lee, C. W.; Woo, W. J.; Choi, T.; Jung, H.; Lee, H.-B.-R.; Myoung, J.-M.; Im, S.; Lee, Z.; Ahn, J.-H.; Park, J. Kim, H. Self-Limiting Layer Synthesis of Transition Metal Dichalcogenides. Sci. Rep. 2016, 6 (1), 18754.

(24)

Cho, B.; Kim, A. R.; Park, Y.; Yoon, J.; Lee, Y. J.; Lee, S.; Yoo, T. J.; Kang, C. G.; Lee, B. H.; Ko, H. C.; Kim, D.-H.; Hahm, M. G. Bifunctional Sensing Characteristics of Chemical Vapor Deposition Synthesized Atomic-Layered MoS2. ACS Appl. Mater.

Interfaces 2015, 7 (4), 2952–2959. (25)

Smyth, C. M.; Addou, R.; McDonnell, S.; Hinkle, C. L.; Wallace, R. M. WSe2Contact Metal Interface Chemistry and Band Alignment under High Vacuum and Ultra High Vacuum Deposition Conditions. 2D Mater. 2017, 4, 025084.

(26)

Yi, Y.; Wu, C.; Liu, H.; Zeng, J.; He, H.; Wang, J. A Study of Lateral Schottky Contacts in WSe2 and MoS2 Field Effect Transistors Using Scanning Photocurrent Microscopy. Nanoscale 2015, 7 (38), 15711–15718.

(27)

Das, S.; Appenzeller, J. WSe2 Field Effect Transistors with Enhanced Ambipolar Characteristics WSe 2 Field Effect Transistors with Enhanced Ambipolar Characteristics. Appl. Phys. Lett. 2013, 103 (2013), 103501.

(28)

Nieuwenhuys, B. E.; Bouwman, R.; Sachtler, W. M. H. The Changes in Work Function of Group Ib and VIII Metals on Xenon Adsorption, Determined by Field Electron and Photoelectron Emission. Thin Solid Films 1974, 21 (1), 51–58.

(29)

Eastman, D. E. Photoelectric Work Functions of Transition, Rare-Earth, and Noble



Page 22 of 24

21

Metals. Phys. Rev. B 1970, 2 (1), 1–2. (30)

Wang, T.; Zhao, R.; Zhao, X.; An, Y.; Dai, X.; Xia, C. Tunable Donor and Acceptor Impurity States in a WSe 2 Monolayer by Adsorption of Common Gas Molecules. RSC

Adv. 2016, 6 (86), 82793–82800. (31) Marani, D.; Silva, R. H.; Dankeaw, A.; Norrman, K.; Werchmeister, R. M. L.; Ippolito, D.; Gudik-Sørensen, M.; Hansen, K. K.; Esposito, V. NOx Selective Catalytic Reduction (SCR) on Self-Supported V–W-Doped TiO

2

Nanofibers. New J. Chem.

2017, 41 (9), 3466–3472. (32)

Song, Z.; Ning, P.; Zhang, Q.; Li, H.; Zhang, J.; Wang, Y.; Liu, X.; Huang, Z. Activity and Hydrothermal Stability of CeO2-ZrO2-WO3 for the Selective Catalytic Reduction of NOx with NH3. J. Environ. Sci. (China) 2016, 42, 168–177.


Page 23 of 24 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


22

Graphical TOC Entry



Page 24 of 24

23


Recovery Improvement for Large-Area Tungsten Diselenide Gas

Recommend Documents