Layer-dependent and light-tunable surface potential of two-dimensional indium selenide (InSe) flakes

Abstract

As a fundamental surface property of two-dimensional (2D) materials, surface potential is critical for their emerging electronic applications and essential for van der Waals heterostructure engineering. Here, we report the surface potential of few-layer InSe. The effect of layer count, light intensity and different deposited substrates is considered. Few-layer InSe flakes were exfoliated from bulk InSe crystals on Si/SiO2 with 300-nm-thick thermal oxide and Si/SiO2 with 300-nm-thick thermal oxide and prefabricated micro-wells with 3 μm in diameter. The samples were measured by Kelvin probe force microscopy and tuned by an integrated 405-nm (3.06 eV) laser. Based on the work function of SiO2 (5.00 eV), the work functions of supported and suspended InSe are determined. These results show that the work function of InSe decreases with the increase in the layer count of both supported InSe and suspended InSe. Besides, by introducing a tunable laser light, the influence of light intensity on surface potential of supported InSe was studied. The surface potential (SP) and surface potential shift between light and dark states (∆SP =SPlight − SPdark) of supported InSe were measured and determined. These results present that the surface potential of supported InSe decreases with the increase in the light intensity and also decreases with the increase in the layer count. This is evident that light excites electrons, resulting in decreased surface potential, and the amount of electrons excited is correlated with light intensity. Meanwhile, ∆SP between light and dark states decreases with the increase in the layer count, which suggests that the influence of light illumination decreases with the increase in the layer count of few-layer InSe flakes.