Large Area Atomically Flat Surfaces via Exfoliation of Bulk Bi₂Se₃ Single Crystals

Abstract

In this work, we present an exfoliation method that produces cm2-area atomically flat surfaces from bulk layered single crystals, with broad applications such as for the formation of lateral heterostructures and for use as substrates for van der Waals epitaxy. Single crystals of Bi2Se3 were grown using the Bridgman method and examined with X-ray reciprocal space maps, Auger spectroscopy, low-energy electron diffraction, and X-ray photoelectron spectroscopy. An indium-bonding exfoliation technique was developed that produces multiple ∼100 μm thick atomically flat, macroscopic (>1 cm2) slabs from each Bi2Se3 source crystal. Two-dimensional X-ray diffraction and reciprocal space maps confirm the high crystalline quality of the exfoliated surfaces. Atomic force microscopy reveals that the exfoliated surfaces have an average root-mean-square (RMS) roughness of ∼0.04 nm across 400 μm2 scans and an average terrace width of 70 μm between step edges. First-principles calculations reveal exfoliation energies of Bi2Se3 and a number of other layered compounds, which demonstrate relevance of our method across the field of 2D materials. While many potential applications exist, excellent lattice matching with the III–V alloy space suggests immediate potential for the use of these exfoliated layered materials as epitaxial substrates for photovoltaic development.

Strain-driven tunable topological states in Bi2Se3

“…We estimate the exfoliation energy of the surface QL, which is under the largest strain considered, as the difference between the energy per surface unit area of the full strained slab and that of the two isolated subsystems (one composed by the first 12 QLs and the other composed by only the surface QL). The difference is 13.0meV Å −2 , of the same order as 22.4meV Å −2 , previously reported for the exfoliation energy of unstrained Bi 2 Se 3 [42]. On the other hand, the energy per surface unit area required to expand Bi 2 Se 3 along the (0001) direction up to a 12.7% strain is obtained as the energy difference between the unstrained bulk and that of the bulk with c=32.0Å, divided by the surface area.…”

Ionic vs. van der Waals layered materials: identification and comparison of elastic anisotropy

“…Van der Waals (vdW) layered materials have served as electrodes, thermoelectrics, optoelectronics, substrates, and as precursors for 2D materials. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] The chemistry of known vdW materials is diverse, ranging from simple unaries and binaries (e.g. graphite, SnSe, Bi 2 Te 3 ) to complex multinaries (e.g.…”

High Stability and Inoxidizability of Monolayer Topological Insulator ZrTe5

“…Thus, the cleavage energy of the monolayer ZrTe 5 was calculated to be 0.21 J/m 2 (see Figure 1c), which is in agreement with the previous results. 38 This value is not only significantly lower than that of 2D Tl Bi 2 Se 3 (0.44 J/m 2 ) 39 but also comparable to that of graphene (0.15 J/m 2 ), 40 suggesting that it can be easily exfoliated from its bulk phase due to the low cleavage energy. The calculated phonon spectra indicated that the monolayer ZrTe 5 is dynamically stable because there is no imaginary frequency in the whole Brillouin zone, as shown in Figure 1d.…”