Abstract
The nanoscale characteristics of semiconducting transition metal dichalcogenides (TMDCs) are largely determined by their photonic, mechanical, magnetic, thermal, and electronic properties, which can be modulated by adjusting thickness and radiation treatments. In this paper, gamma-rays were applied to irradiate the materials with one to six layers, based on which a comparison was drawn of the frictional and electrical properties before and after irradiation. The changes on a few-layer WSe2 were investigated using Raman spectroscopy, photoluminescence spectroscopy, scanning electron microscopy, transmission electron microscopy, force friction microscopy, and Kelvin probe force microscopy. Under the context of irradiation, there was a phenomenon found different than previously reported. The friction force of WSe2 nano-flakes increased from monolayer to bilayer, decreased at tri-layer, and then increased on a continued basis with thickness. It is suggested that the gamma-ray irradiation treatment could be effective in improving frictional and electronic properties. The range of change to the surface contact potential difference (CPD) was narrowed, and the stability of the device surface potential was enhanced. The continuum mechanics theory was applied to explore the friction force variation between different thickness layers. Based on the puckering effect of tip-flake adhesion, the friction force was determined by bending stiffness. The thermal treatment of WSe2 nanoflakes had a significant impact on the CPD between the sample and the test tip. After thermal treatment, the surface potential increased from one to five layers with thickness. These phenomena were explained in detail. The research contributes to enriching nanotribology and electrical theory in addition to promoting the use of semiconducting TMDCs for nano-components’ design.
Highlights
Due to excellent mechanical, electronic, magnetic, and photoelectric properties, semiconducting transition metal dichalcogenides (TMDCs) have attracted much attention in recent years.1,2 Exhibiting unique physical and chemical properties, the TMDs’ lamellar structure represents a novel type of two-dimensional material.3 The quantum confinement effect4 in the reduced dimension of a monolayer renders it a direct-gap semiconductor,5 in contrast, the strong Coulomb interaction due to reduced dielectric screening endows, among other properties, strong photoluminescence,6–8 and large exciton binding energy,9–13 making it a promising candidate for optoelectronic14 and photovoltaic applications.15 One distinct member of the TMDs’ family is tungsten diselenide (WSe2)
The nanoscale characteristics of semiconducting transition metal dichalcogenides (TMDCs) are largely determined by their photonic, mechanical, magnetic, thermal, and electronic properties, which can be modulated by adjusting thickness and radiation treatments
The thermal treatment of WSe2 nanoflakes had a significant impact on the contact potential difference (CPD) between the sample and the test tip
Summary
Electronic, magnetic, and photoelectric properties, semiconducting transition metal dichalcogenides (TMDCs) have attracted much attention in recent years. Exhibiting unique physical and chemical properties, the TMDs’ lamellar structure represents a novel type of two-dimensional material. The quantum confinement effect in the reduced dimension of a monolayer renders it a direct-gap semiconductor, in contrast, the strong Coulomb interaction due to reduced dielectric screening endows, among other properties, strong photoluminescence, and large exciton binding energy, making it a promising candidate for optoelectronic and photovoltaic applications. One distinct member of the TMDs’ family is tungsten diselenide (WSe2). It has been reported that the gamma-ray can cause a surface cleaning effect for the nanomaterials, reducing the TMD crystals’ defect density due to the filling of vacancies with oxygen atoms.. It has been reported that the gamma-ray can cause a surface cleaning effect for the nanomaterials, reducing the TMD crystals’ defect density due to the filling of vacancies with oxygen atoms.26,27 For these reasons, an investigation was conducted into different environmental factors, such as thickness, radiation, and humidity, so as to reveal the different reaction mechanisms of the device, which is crucial for the engineering design of semiconducting TMDC-based nano-devices. Our work showed a new defect inducing technique to engineer the frictional and electronic properties of atomically thin WSe2. Our results strengthened the understanding of fundamental physical properties of the different thicknesses of WSe2 nanosheets treated under γ-ray irradiation and demonstrated a new technique to engineer the bandgap and control the frictional and electronic properties of atomically thin WSe2 nanosheets
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