Abstract
Single- or few-layer forms of black phosphorus, so called phosphorene, were isolated by exfoliation in 2014 as 2D layered materials holding great promise in electronic and optoelectronic fields. In this perspective, we highlight recent developments in black phosphorus research, in particular, we will focus on the mechanical properties of its 2D form. Its unique puckered structure is responsible for strong anisotropy in mechanical and transport properties, different from graphene and transition-metal dichalcogenide 2D materials. This peculiar mechanical anisotropy can be exploited for applications such as nanomechanical resonators, thermoelectric devices, and motion sensors with tunable functions inaccessible by isotropic materials. Current bottlenecks hindering further progress in devices applications involve first surface degradation in environmental conditions which, in turn, can be exploited in surface friction mechanics to achieve superlubricity. In this framework, the investigation of mechanical properties of phosphorene will be pivotal for facile fabrication, transfer, and resolution of technical hurdles as well the discovery of novel applications. As research directions in next foreseeable future, we will discuss the challenge of crosstalk between mechanical and transport properties, in particular, how the stress–strain stimulations can be used to tune optoelectronic and thermoelectric performance.
Highlights
AND BACKGROUNDBlack phosphorus (BP), one of the most stable allotropes of phosphorus,[1] has recently been reevaluated as an important layered material.[2,3] The finite, direct bandgap and high charge-carrier mobility of 2D-BACKGROUNDBlack phosphorus (BP) present advantages over extensively studied 2D nanomaterials such as graphene and transitionmetal dichalcogenides
In BP, the puckered lattice has only twofold rotational symmetry, which is much reduced when compared with the sixfold in-plane rotational symmetry in the monolayer graphene with a flat hexagonal lattice.[6]
Each phosphorus atom is covalently bonded with three adjacent atoms to form layers with a puckered honeycomb structure [see Fig. 1(a)], and the layers are stacked together by van der Waals interactions, resulting in three orthogonal principle axes of zigzag (ZZ), armchair (AC), and through plane (TP)
Summary
Black phosphorus (BP), one of the most stable allotropes of phosphorus,[1] has recently (since 2014) been reevaluated as an important layered material.[2,3] The finite, direct bandgap and high charge-carrier mobility of 2D-BP present advantages over extensively studied 2D nanomaterials such as graphene and transitionmetal dichalcogenides These characteristics make 2D-BP an ideal candidate for near and midinfrared optoelectronics applications.[4] The most unique feature of phosphorene is its in-plane anisotropy,[5] which is intrinsic for its mechanical, electronic, electric, transport, thermoelectric, and optical properties and has not been widely used in device design. 2D materials cannot be tested with traditional instrumentation for mechanical testing, requiring specific technology with sensitivity at the nanoscale (i.e., atomic force microscopy) In this framework, a comprehensive perspective article focused on the mechanical properties is missing and it will help to reevaluate the importance of 2D-BP nanomechanics. We will discuss more applicative approaches by combining electrical and mechanical properties, and we will highlight the connection between thermal and mechanical properties
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