Exfoliation and Analysis of Large-area, Air-Sensitive Two-Dimensional Materials

Abstract

We describe methods for producing and analyzing large, thin flakes of air-sensitive two-dimensional materials. Thin flakes of layered or van der Waals crystals are produced using mechanical exfoliation, in which layers are peeled off a bulk crystal using adhesive tape. This method produces high-quality flakes, but they are often small and can be hard to find, particularly for materials with relatively high cleavage energies such as black phosphorus. By heating the substrate and the tape, two-dimensional material adhesion to the substrate is promoted, and the flake yield can be increased by up to a factor of ten. After exfoliation, it is necessary to image or otherwise analyze these flakes but some twodimensional materials are sensitive to oxygen or water and will degrade when exposed air. We have designed and tested a hermetic transfer cell to temporarily maintain the inert environment of a glovebox so that air-sensitive flakes can be imaged and analyzed with minimal degradation. The compact design of the transfer cell is such that optical analysis of sensitive materials can be performed outside of a glovebox without specialized equipment or modifications to existing equipment.

Superlubricity and Stress-Shielding of Graphene Enables Ultra Scratch-Resistant Glasses

“…The graphene sheets were transferred onto the silica glass surface via the conventional top-down mechanical exfoliation route. Previous reports suggest the deposition of high-quality sheets over a large area with an added thermal routine during exfoliation. , A similar protocol was followed wherein a highly oriented pyrolytic graphite (HOPG, ZYH grade, MikroMasch OÜ, Tallinn, Estonia) mother crystal was repeatedly exfoliated with 3M Scotch tape to delaminate the graphitic layers progressively and then brought in contact with the as-cleaned glass surface. The exfoliation was performed seconds before the plasma treatment, and the pristine surfaces were used within another few seconds for graphene deposition.…”

Integration of multi-layer black phosphorus into photoconductive antennas for THz emission

“…BP and hBN were mechanically exfoliated from bulk crystals, and flakes with thicknesses chosen to maximize absorption at 780 nm (see below) were identified using a hermetic cell with optical access. 32 Flake thicknesses were confirmed using atomic force microscopy inside a nitrogen glovebox (H 2 O, O 2 < 0.5 ppm). Flakes were transferred onto the antenna using polycarbonate-based dry transfer, also inside the glovebox.…”

“…During measurements, the BP PCAs were maintained in a nitrogen environment using a hermetic cell similar to that described in Ref. 32. Under these conditions, no environmental degradation of the BP devices was observed during measurements over at least eight weeks.…”

Modulation Doping via a 2d Atomic Crystalline Acceptor

“…For D5 we used e-beam lithography to pattern thermally deposited Cr/Au top gate and edge contacts (33). The etched contact areas were treated with a six second oxygen plasma "descum" at 50 W forward access and removed from the glovebox to identify locations of thin CrCl 3 (35). Polycarbonatebased dry transfer is used to pick up CrCl 3 for transfer onto the target substrate (36).…”