Anisotropic Properties of Black Arsenic in Layered Semiconductors
The paper titled "BlackArsenic: A Layered Semiconductor with Extreme in-plane Anisotropy" delves into the exploration of black arsenic (b-As), a less-studied allotrope of arsenic, with a focus on its anisotropic properties in two-dimensional (2D) layered materials. Contrary to common isotropic cubic semiconductors, b-As exhibits pronounced anisotropic behaviors, particularly along armchair (AC) and zigzag (ZZ) directions within the basal plane, marking it as a unique entrant in the field of layered semiconductors.
Structural Characterization and Insights
The study begins with a thorough characterization of b-As single crystals using XRD, Auger electron spectroscopy, and energy-dispersive x-ray spectroscopy, affirming high purity and crystallinity. The puckered layer structure, akin to black phosphorus (b-P), holds significance due to its mechanical exfoliation capabilities, enabling the formation of atomically thin layers. Notably, density functional theory (DFT) computes lattice parameters which align with experimental data, showcasing lattice spacing in AC and ZZ directions and emphasizing the orthorhombic structure of b-As.
Extremes of Anisotropy in Electronic and Thermal Properties
b-As reveals exceptional in-plane anisotropic properties surpassing those of other 2D layered materials. The anisotropy in carrier mobility reaches a value of ~28, significantly higher than observed in b-P and other crystals. This stark contrast in mobility between AC and ZZ directions stems from the anisotropic electronic band structure, evidenced by DFT calculations and angle-resolved photoemission spectroscopy (NanoARPES). The effective mass discrepancy (0.35 m versus 0.56 m ) corroborates the variation in electronic structure anisotropy.
Thermal transport similarly exhibits anisotropy, with thermal conductivity κ along ZZ direction being approximately 50% higher than in the AC direction, attributed to stiffness and reduced anharmonicity along ZZ direction. These pivotal differences manifest from variations in lattice properties and are supported by phonon dispersion calculations alongside angle-resolved polarized Raman spectroscopy data.
Implications and Prospective Applications
The extreme anisotropies in the physical properties of b-As suggest numerous potential applications. The oppositional anisotropy in electrical and thermal conductivities may inspire novel device designs, such as transverse thermoelectrics, which leverage the diverse directional properties for enhanced performance. The findings open up the prospect of employing b-As in nanoelectronic and energy-efficient technologies, contributing to developments in semiconductors with tunable and direction-dependent characteristics.
Future Research Directions
While the paper advances the understanding of b-As properties, it also outlines potential exploration areas. Future research might focus on the synthesis of b-As with varied compositions to analyze stability and broader applicability. Additionally, probing into other allotropes or analogs within the arsenic family may yield insights into electronic and thermal responses across different lattice configurations, aiding in the development of advanced semiconductor materials.
This study serves as a foundational step in recognizing b-As as a significant player among layered 2D crystals, with implications spanning electronic, photonic, and thermal domains. The emphasis on in-plane anisotropies offers a new dimension to semiconductor research, fueling innovative applications and theoretical explorations.