Field‐Dependent Electrical and Thermal Transport in Polycrystalline WSe₂

Abstract

bandgap and exhibit fascinating electrical and optical properties. [1][2][3][4] TMDs have a layered structure in which the transition metal forms a hexagonal layer which is sandwiched between two hexagonal layers of the chalcogen. The TMD monolayers are bonded to each other by weak van der Waals forces, and thus can be considered a 2D material. A number of studies have shown the various applications of TMDs as sensors and in electronic, photonic, and optoelectronic devices. [2,5,6] Another field of critical importance is energy harvesting with thermoelectric power (TEP) which has gained rapid momentum due to the discovery of various nanomaterials. [7][8][9][10][11][12][13][14][15][16][17][18][19] Recently, large thermopower values and efficiencies have been demonstrated in TMDs. [20][21][22][23] Thus, TMDs have great potential as thermoelectric materials; however, most studies have been carried out on mechanically exfoliated TMD mono layers, where it is not possible to control the size and geometry of the device. In order to utilize the high efficiencies and the small device volume of 2D materials for thermoelectric applications, it is an absolute prerequisite to develop a system for homogeneous, large-scale synthesis of TMDs. Thus, the large-scale synthesis of TMDs and device fabrication using such large-scale grown TMD films has become a prominent research area for future semiconductor applications. Recently, TMD films have been synthesized on a large scale by film growth techniques such as chemical vapor deposition (CVD) and thermally assisted conversion (TAC) of the predeposited metal films. [23][24][25][26][27][28][29][30][31] While CVD produces well-defined monolayers, it struggles to produce continuous films. TAC on the other hand produces continuous films of controlled thickness with a polycrystalline morphology. [29,32] Tungsten diselenide (WSe 2 ) is one of the most studied TMDs after molybdenum disulfide (MoS 2 ). Several studies of WSe 2 have discussed its excellent electrical and thermoelectric properties. [4,22,[33][34][35][36] The power factor (S 2 σ) of WSe 2 (≈40 µW K −2 cm −1 ) [22] is comparable with the value of TiS 2 (37 µW K −2 cm −1 ), [37] which is one of the best performing thermoelectric 2D materials. In addition, recently ultralow thermal conductivity in WSe 2 was demonstrated. [38] Thus, a more competitive figure of merit (ZT = S 2 ·σ·T/κ) can be expected for WSe 2 .In this study, WSe 2 films were synthesized on a large scale by TAC on an SiO 2 /Si substrate. The growth of the films takes place Owing to their desirable electrical and thermoelectric properties, transition metal dichalcogenides (TMDs) have attracted significant attention. It is important to develop an easy synthetic method and a simple device fabrication process for TMDs. In this study, WSe 2 films were synthesized on a large scale by thermally assisted conversion (TAC) of W films on SiO 2 /Si substrates at 600 °C. The TAC process yields homogeneous polycrystalline films of controlled thickness over large areas which hav...

Calibration of Nonstationary Gas Sensors Based on Two-Dimensional Materials

“…Raman and X-ray photoelectron spectroscopy (XPS) results reported in our previous publications show the stochiometric transformation of Pt, Mo, and W into PtSe 2 , MoS 2 , and WSe 2 , respectively, by thermally assisted conversion (TAC). − ,,− Here, we present the application of TDSO to the devices based on TMDCs reported in those papers, in which a detailed characterization of TMDCs is presented.…”

Nanoelectromechanical Sensors Based on Suspended 2D Materials

“…For instance, Mo or more commonly MoO 3 can be converted to MoS 2 at high temperature [ 107 – 112 ]. This facile growth method is applicable to a wide range of TMDs, such as MoSe 2 [ 113 , 114 ], WS 2 [ 115 – 117 ], WSe 2 [ 118 ], PtSe 2 [ 119 ], or PtTe 2 [ 120 ]. The method yields continuous polycrystalline films, and therefore, prepatterned transition metals can be directly converted to structured TMDs.…”

Role of metal contacts on the electric and thermoelectric response of hBN/WSe2 based transistors

“…MoS 2 has been extensively studied and thermoelectric powers as large as 2 mV/K at low temperature (∼ 50 K) have been experimentally demonstrated [14][15][16] . Although less studied, WSe 2 has shown maximum S of about ∼ 300 µV/K and power factors PF (PF = S 2 σ ) of ∼ 37 µW/cm K 2 in electrolyte gated transistors [17][18][19] . Moreover, very low in-plane thermal conductivity (1 -2 W/mK) has been experimentally reported and theoretically confirmed in this 2D material [20][21][22][23] , making it particularly appealing for TE applications.…”