Resolving and Tuning Mechanical Anisotropy in Black Phosphorus via Nanomechanical Multimode Resonance Spectromicroscopy

Abstract

Black phosphorus (P) has emerged asWang Z.H., Jia H., Zheng X.-Q., Yang R., Ye G.J., Chen X.H., Feng P.X.-L., Nano Letters 16, 5394-5400 (2016) [Accepted Version] DOI: 10.1021/acs.nanolett.6b01598, Online Publication: August 9, 2016-2-Efficiently exploiting anisotropic properties in crystals plays important roles in many areas in science and technology, ranging from timing and signal processing using a rich variety of crystalline cut orientations in quartz to the modulation and conversion of light using anisotropic crystals. In state-of-the-art miniature devices and integrated systems, crystalline anisotropy enables a number of important dynamic characteristics in microelectromechanical systems (MEMS) such as gyroscopes, rotation rate sensors, and accelerometers. 1,2,3,4 Single crystal silicon (Si), the hallmark of semiconductors and the most commonly used crystal in MEMS, possesses clear mechanical anisotropy that has been extensively characterized and utilized (e.g., Young's moduli in the <110> and <100> directions are E Y<110> = 169 GPa and E Y<100> = 130 GPa). 5 , 6 As devices continue to be scaled down to nanoscale, anisotropy in mechanical properties may not always be readily preserved at device level due to lattice defects or surface effects, 7 , 8 , 9 and thus remain largely unexplored in emerging nanoelectromechanical systems (NEMS) built upon conventional crystals.The recent advent of atomic-layer crystals offer exciting opportunities for building twodimensional (2D) NEMS using single-crystal layered materials, in which many desired material properties are preserved, or even intensified, as the crystal thickness approaches genuinely atomic scale. One unique crystal is black phosphorus (P), not only a single-element directbandgap semiconductor with bandgap depending on the number of atomic layers (covering a wide range from visible light to IR) and with high carrier mobility, but also hitherto the bestknown atomic-layer crystal with strong in-plane anisotropy. The intrinsically anisotropic lattice structure (Figure 1a) of black P dictates a number of anisotropic material properties. In particular, it is theoretically predicted to exhibit in-plane mechanical anisotropy ( Figure 1a) 10,11,12,13 much stronger than that of Si, which shall lead to previously inaccessible dynamic responses in resonant NEMS 14 and new opportunities for studying carrier-lattice interaction in atomic layers. 15,16,17,18,19 To date, while extensive and rapidly growing efforts have been devoted to studying optical and electrical properties of black P and anisotropic effects in such devices, experiments on black P mechanical devices and mechanical anisotropic effects therein have been lacking. It is therefore of both fundamental and technological importance to systematically investigate the mechanical anisotropy in black P crystal.In bulk materials, such as crystalline Si, mechanical anisotropy is often characterized by measuring the sound velocity in different directions, 20,21,22,23 and fitting data to the Christoff...

Separating the ferromagnetic and glassy behavior within the metal-organic magnetNi(TCNQ)2

“…We note that a T 3 implies a 3D lattice contribution to the low temperature heat capacity of the Ni(TCNQ − D 4 ) 2 sample which consists of nanograins. However, there have been reports of other nanostructured materials exhibiting such a temperature dependence, though the measured Debye temperatures did not correspond to bulk values [52,53]. This suggests that, in Ni(TCNQ − D 4 ) 2 , there is strong enough coupling between the nanograins to allow long wavelength lattice vibrations to contribute to the heat capacity.…”

Hexagonal boron nitride nanomechanical resonators with spatially visualized motion

“…4), semiconducting MoS 2 (Refs. 3,5-7) and black phosphorus 8,9 . These devices are primarily actuated by electrostatic forces.…”

“…4), semiconducting MoS 2 (Refs. 3,5-7), and black phosphorus 8,9 , which opens a wide spectrum of emerging applications, such as sensing 10,11 and signal processing with ultralow power and broad tunability 12,13 . Although atomic layer crystals with bandgaps ranging from 0 to 2 eV have been studied in earlier explorations (such as 0 eV graphene 1,2,12 , 0.3-1.5 eV black phosphorus 8,9 , 1.2-1.9 eV MoS 2 (Refs.…”

Emerging in‐plane anisotropic two‐dimensional materials

“…As shown in Figure 5E, the mode pairs of the multimode resonances in BP are offset in frequency, indicating the mechanical anisotropy of BP, and the simulated anisotropic factor for elastic modulus is 2 along zigzag direction than along armchair direction. 42 Interestingly, the mechanical anisotropy can be tuned via electrostatic gating, and at 1% strain, BP become nearly isotropic. 42 4 | APPLICATIONS…”

“…42 Interestingly, the mechanical anisotropy can be tuned via electrostatic gating, and at 1% strain, BP become nearly isotropic. 42 4 | APPLICATIONS…”