Exfoliation and Characterization of V₂Se₉ Atomic Crystals

Abstract

Mass production of one-dimensional, V₂Se₉ crystals, was successfully synthesized using the solid-state reaction of vanadium and selenium. Through the mechanical exfoliation method, the bulk V₂Se₉ crystal was easily separated to nanoribbon structure and we have confirmed that as-grown V₂Se₉ crystals consist of innumerable single V₂Se₉ chains linked by van der Waals interaction. The exfoliated V₂Se₉ flakes can be controlled thickness by the repeated-peeling method. In addition, atomic thick nanoribbon structure of V₂Se₉ was also obtained on a 300 nm SiO₂/Si substrate. Scanning Kelvin probe microscopy analysis was used to explore the variation of work function depending on the thickness of V₂Se₉ flakes. We believe that these observations will be of great help in selecting suitable metal contacts for V₂Se₉ and that a V₂Se₉ crystal is expected to have an important role in future nano-electronic devices.

Keywords: V2Se9; atomic crystal; mechanical exfoliation; scanning Kelvin probe microscopy.

Figure 1

(a) Photo-image of mass production of V₂Se₉ crystal. (b) XRD pattern of V₂Se₉ crystal. (c) Low- and (d) high-magnification SEM images of V₂Se₉ crystal. The inset shows an illustration of the crystal structure of V₂Se₉.

Figure 2

(a) Atomic force microscopy (AFM) image of the 1D V₂Se₉ flake on 300 nm SiO₂/Si substrate. (b) Line-profile of a V₂Se₉ flake as marked in Figure 2a.

Figure 3

(a) AFM image of exfoliated V₂Se₉ on 300 nm SiO₂/Si substrate. (b) AFM image of additionally exfoliated V₂Se₉ on 300 nm SiO₂/Si substrate. (c) Line-profile of 1D V₂Se₉ flakes on 300 nm SiO₂/Si substrate before and after 2nd exfoliation.

Figure 4

(a) AFM image of the V₂Se₉ nanoribbon on the 300 nm SiO₂/Si substrate. The inset shows an illustration of the V₂Se₉ nanoribbon. (b) Line-profiles of the V₂Se₉ nanoribbon as marked L1, L2, L3, and L4 in Figure 4a.

Figure 5

(a) Scanning Kelvin probe microscopy (SKPM) image of exfoliated 1D V₂Se₉ flakes on the Si substrate. (b,c) Height and potential energy profiles of the V₂Se₉ flakes and Si substrate as labeled in Figure 5a. (d,e) Variation in potential energy difference and work function depending as a function of thickness of V₂Se₉ flakes.