Two-dimensional (2D) materials play a significant role in flexible electronics due to their unique features, such as strong tensile strength and favorable optical properties. Here, we present a low-dimensional nanostructure-based flexible photodetector fabricated on a trilayer MoS2/mica substrate. The photodetector showed a broadband photoresponse from the visible to ultraviolet region. The maximum responsivity and detectivity of the photodetector were found to be 1.10 mA/W and 3.86 × 1010 Jones, respectively, which are much higher than those of the previously reported flexible MoS2/mica photodetector. This is the first report on a flexible broadband photodetector fabricated on the mica substrate that we are aware of. The device photocurrent remained stable even after applying maximum tensile strain (0.86%) by bending the device. Before fabricating the flexible photodetector, an etchant- and polymer-free quasi-dry layer transfer process was optimized, which is essential to enhance the applicability of 2D materials at the industrial level. This transfer method works with various 2D materials and growth/target substrates, rapidly producing high-performance 2D electrical devices and van der Waals heterostructures. As a proof of concept, monolayer MoS2/WS2 (inverse) heterostructures were assembled by the proposed transfer process. Furthermore, photodetectors were fabricated on the as-grown trilayer MoS2/SiO2 and transferred trilayer MoS2/SiO2 samples. The current in the transferred MoS2 photodetector is 100 times more than that of the as-grown photodetector, implying the improved electrical properties of the transferred film. The photo-to-dark current ratio (PDCR), responsivity, and detectivity have been enhanced by 12, 100, and 10 times, respectively, in the transferred photodetector. These advantages show the potential applicability of the proposed transfer process in the field of flexible nanoelectronics, wearable electronics, and the internet on things.

Two-dimensional transition metal dichalcogenides offer exciting opportunities to tailor their electrical and optoelectronic properties, which provide them with a multitude of applications, following which their large-area synthesis holds high significance. Herein, we demonstrate NaCl-assisted centimeter-scale (1.5 × 1 cm 2 ) growth of monolayer WS 2 using an atmospheric-pressure chemical vapor deposition technique. We attempt to explicate the growth mechanism with the Volmer− Weber, Stranski−Krastanov, and Frank−van der Merwe modes by incorporating the importance of NaCl as a growth promoter and other parameters like the quantity of sulfur, temperature, gas flow rate, and hold time. The parameters optimized for large-area monolayer growth were found at a NaCl to WO 3 w/w ratio of 1:2 and a sulfur to WO 3 w/w ratio of 3:1, with a 1 min hold time at 820 °C in a 120 sccm argon gas flow. The optical microscope images along with the corresponding Raman and photoluminescence spectra were employed to examine the growth of the WS 2 film at different sets of synthesis parameters. The photodetector fabricated on the as-grown film showed a high responsivity and specific detectivity of 4.27 mA/W and 1.27 × 10 10 Jones, respectively, in the visible region and 261 mA/W and 7.72 × 10 11 Jones, respectively, in the ultraviolet (UV) region. These results support its application in UV−visible photodetection.

Layer transfer offers enormous potential for the industrial implementation of two-dimensional (2D) material technology platforms. However, the transfer method used must retain the as-grown uniformity and cleanliness in the transferred films for the fabrication of 2D material-based devices. Additionally, the method used must be capable of large-area transfer to maintain wafer-scale fabrication standards. Here, a facile route to transfer centimeter-scale synthesized 2D transition metal dichalcogenides (TMDCs) (3L MoS 2 , 1L WS 2 ) onto various substrates such as sapphire, SiO 2 /Si, and flexible substrates (mica, polyimide) has been developed using a water-soluble layer (Na 2 S/Na 2 SO 4 ) underneath the as-grown film. The developed transfer process represents a fast, clean, generic, and scalable technique to transfer 2D atomic layers. The key strategy used in this process includes the dissolution of the Na 2 S/Na 2 SO 4 layer due to the penetration of NaOH solution between the growth substrate and hydrophobic 2D TMDC film. As a proof-of-concept device, a broadband photodetector has been fabricated onto the transferred 3L MoS 2 , which shows photoresponse behavior for a wide range of wavelengths ranging from near-infrared (NIR) to UV. The enhancement in photocurrent was found to be 100 times and 10 times the dark current in the UV and visible regions, respectively. The fabricated photodetector shows a higher responsivity of 8.6 mA/W even at a low applied voltage (1.5 V) and low power density (0.6 μW/mm 2 ). The detector enables a high detectivity of 2.9 × 10 11 Jones. This work opens up the pathway toward flexible electronics and optoelectronics.

This work reports the effect of γ radiation on the surface morphology and surface-charge redistribution in a monolayer WS2 film by comparing the film before and after irradiation (1, 50, 100, 200, and 400 kGy dosage). The surface morphology was monitored through optical microscopy and atomic force microscopy. Raman and photoluminescence spectroscopy were used to study the effect on phonon modes and excitonic properties. The results indicated p-type doping and increased trion-to-exciton transitions. Because of the high energy and lower atomic mass of sulfur atoms, γ irradiation induces sulfur vacancies, which creates dangling bonds at vacant sites. The adsorption of oxygen at these reactive sites results in a charge-transfer mechanism, in which electrons get transferred from the WS2 film to the adsorbed oxygen, which forms oxides and induces p-type doping. An increase in the work function of the film from 4.50 eV for a pristine film to 4.82 eV for an irradiated film (at 200 kGy) was calculated from Kelvin probe force microscopy, which indicates shifting of the Fermi level toward the valence band (VB) maxima. Further, VB spectra deduced from X-ray photoelectron spectroscopy showed a red shift of 0.17 eV after irradiation and confirms p-type doping.