High photoresponse of individual WS2 nanowire-nanoflake hybrid materials

Abstract

van der Waals solids have been recognized as highly photosensitive materials that compete conventional Si and compound semiconductor based devices. While 2-dimensional nanosheets of single and multiple layers and 1-dimensional nanowires of molybdenum and tungsten chalcogenides have been studied, their nanostructured derivatives with complex morphologies are not explored yet. Here, we report on the electrical and photosensitive properties of WS 2 nanowirenanoflake hybrid materials we developed lately. We probe individual hybrid nanostructured particles along the structure using focused ion beam deposited Pt contacts. Further, we use conductive atomic force microscopy to analyze electrical behavior across the nanostructure in the transverse direction. The electrical measurements are complemented by in situ laser beam illumination to explore the photoresponse of the nanohybrids in the visible optical spectrum. Photodetectors with responsivity up to $0.4 AW À1 are demonstrated outperforming graphene as well as most of the other transition metal dichalcogenide based devices.

WS2 and MoS2 thin film gas sensors with high response to NH3 in air at low temperature

“…Although the primary direct contact with the chalcogenide films was meant to be Ti, some Pt also deposited on the films around the perimeter of the Ti under-metallization due to the imperfect contact between the shadow mask and the substrate. Considering the typical bandgap, electron affinity and the work function values of bulk MoS 2 (E g ∼1.3 eV, χ∼4.0 eV and j∼5.25 eV) [32,33] and WS 2 (1.4, 4.0 and 5.1 eV) [34] as well as the work function values of Ti (j Ti ∼4.3 eV) and Pt (j Pt ∼5.3 eV), we find that the contact between Ti and the chalcogenide films is Schottky-type (figures 2(b) and (e)), whereas it is quasi-ohmic with Pt (figures 2(c) and (f)). Furthermore, because of the better alignment of the Fermi level of Pt with the valence band of MoS 2 in reference to WS 2 , the ohmic character is also expected to be better, which explains the good linearity of the I-V slopes and higher conductivity for the MoS 2 based devices and slight nonlinearity measured for the WS 2 based ones.…”

2D Tungsten Chalcogenides: Synthesis, Properties and Applications

“…Heterostructures of WS 2 nanowires and nanoflakes obtained by the sulfurization of WO 3 nanowires showed p-type properties. [86][87][88] In addition, doping WS 2 lattice with Ta atoms changes the electrical properties of the material from semiconducting to metallic. [70] Room temperature ferromagnetic behavior of WS 2 monolayers was detected for both NAPH [43] and DMF [89] exfoliated samples.…”

Ultrafast photoresponse of vertically oriented TMD films probed in a vertical electrode configuration on Si chips

“…The photoconductivity measurement setup is derived from the one used in our previous studies; 21,31 a constant bias of 3 V is applied to the sample by using a sourcemeter (Keithley 2636A SYSTEM SourceMeter®) connected in series with a 1 MU load resistor. Three different lasers (Coherent® OBIS™ Laser System, TEM00 mode, with wavelengths of 661 nm, 552 nm, and 401 nm and 1/e 2 beam diameters of 9 mm, 7 mm, and 8 mm, respectively) are modulated by using a signal generator (33220A, Agilent Technologies, Inc.) applying square waves with a duty cycle from 5% to 50% and frequency from 10 kHz up to 1 MHz depending on the laser wavelength.…”