Strain Effects in Twisted Spiral Antimonene

Abstract

Van der Waals (vdW) layered materials exhibit fruitful novel physical properties. The energy band of such materials depends strongly on their structures, and a tremendous variation in their physical properties can be deduced from a tiny change in inter-layer spacing, twist angle, or in-plane strain. In this work, a kind of vdW layered material of spiral antimonene is constructed, and the strain effects in the material are studied. The spiral antimonene is grown on a germanium (Ge) substrate and is induced by a helical dislocation penetrating through few atomic-layers of antimonene (β-phase). The as-grown spiral is intrinsically strained, and the lattice distortion is found to be pinned around the dislocation. Both spontaneous inter-layer twist and in-plane anisotropic strain are observed in scanning tunneling microscope (STM) measurements. The strain in the spiral antimonene can be significantly modified by STM tip interaction, leading to a variation in the surface electronic density of states (DOS) and a large modification in the work function of up to a few hundreds of millielectron-volts (meV). Those strain effects are expected to have potential applications in building up novel piezoelectric devices.

Keywords: Antimonene; helical dislocation; spiral; strain effect; vdW layered material.

Figure 1

Spiral antimonene on a Ge (111) substrate. a) Schematic of the antimonene (partially covered) on an As/Ge surface. b) RHEED patterns of the Ge (111) c(2 × 8) surface, the As/Ge (1 × 1) surface and the spiral antimonene surface, respectively. Surface reconstruction is vanished once the substrate is fully covered with As. The “ × 1” feature of the RHEED pattern seen in the lowest panel of b) indicates that all antimonene spirals have the same crystal orientation. c) STM topographic image of the As/Ge surface with “step loops” (taken at 1.03 V and 65 pA). The inset shows an atomic resolution image of the top As atomic layer. d) STM topographic image of antimonene spirals (taken at 1.28 V and 95 pA). The inset shows antimonene flakes between spirals. e) STM image of a spiral (taken at −1.86 V and −150 pA), where a helical dislocation is marked by an arrow. Top‐left inset: 3D view. Top‐right inset: atomic resolution STM image of the antimonene buckled honeycomb lattice. f) XPS data of the spirals. Two main peaks (red fitted curves) correspond to Sb 4d orbits in antimonene, with binding energies of 31.4 eV and 32.6 eV, respectively. g) Raman spectrum of the spirals. Three peaks from left to right arise from the E _g and A _1g modes of the spirals and the A _1g mode of the antimonene flakes, respectively. The Raman shift is accordant with β‐phase antimonene.

Figure 2

Strain in an antimonene spiral. a) Moiré lattice on the spiral. The solid line illustrates a kink on moiré pattern, corresponding to a lattice distortion near the helical dislocation. b) Topographic image of the QPI measuring region (taken at +510 mV and +335 pA). c,d) dI/dV spatial maps at sample voltages of +510 mV and +590 mV, respectively (with a 34 mV modulation and tunneling current of +335 pA). Insets: the corresponding FFT images. The oval contour ring in d) indicates the electron scattering is anisotropic. e) QPI dispersion. Dashed lines illustrate the energy level versus the wave number of intra‐band scattering vectors in two Γ–K directions. f) dI/dV spectrum on the QPI measuring region (taken at +470 mV, +335 pA, and a 4 mV modulation). The red triangle marks the energy position of 465 meV at which the DOS turns to a quicker increase.

Figure 3

DOS modification induced by STM tip manipulating. a) Schematic diagram of the tip manipulating and the spectra measuring. b) The twist of the top layer after tip‐pressing. Twist of 1.0^o±0.3^o is illustrated by the dashed line in STM image (taken at −1.3 and −102 pA). The pressing position is marked by circle. c) The DOS variation induced by tip manipulating. dI/dV spectra are measured on the spiral (−1.3 V, −102 pA, 15 mV modulation), during three cycles of tip pressing and HVI. A broad peak at 0 bias is observed after pressing (red) and disappeared after HVI (black).

Figure 4

Work function variation induced by tip manipulating. a) Work function variation characterized by I–Z spectra. The X‐coordinate is the operation order, tip manipulating of HVT, and “tip pressing” are represented by odd and even numbers, respectively. Error bar is the RMS error from 6 times of measurements. b) Work function variation characterized by dZ/dV spectra. The energy shifts of the “Gundlach oscillation” peaks indicate work function variations of −0.26 ± 0.01 eV and +0.1 ± 0.01 eV, respectively.