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1. Anisotropic fluid flows in black phosphorus nanochannels

   https://doi.org/10.1039/d3cp04736a  

   Jian, Ruda ; Wu, Shiwen ; Tian, Siyu ; Mashhadian, Amirarsalan ; Xu, Zhihao ; Leonardi, Stefano ; Luo, Tengfei ; Xiong, Guoping ( January 2024 , Physical Chemistry Chemical Physics)

   Rijs, Anouk (Ed.)

   With the development of advanced micro/nanoscale technologies, two-dimensional materials have emerged from laboratories and have been applied in practice. To investigate the mechanisms of solid– liquid interactions in potential applications, molecular dynamics simulations are employed to study the flow behavior of n-dodecane (C12) molecules confined in black phosphorus (BP) nanochannels. Under the same external conditions, a significant difference in the velocity profiles of fluid molecules is observed when flowing along the armchair and zigzag directions of the BP walls. The average velocity of C12 molecules flowing along the zigzag direction is 9-fold higher than that along the armchair direction. The friction factor at the interface between C12 molecules and BP nanochannels and the orientations of C12 molecules near the BP walls are analyzed to explain the differences in velocity profiles under various flow directions, external driving forces, and nanochannel widths. The result shows that most C12 molecules are oriented parallel to the flow direction along the zigzag direction, leading to a relatively smaller friction factor hence a higher average velocity. In contrast, along the armchair direction, most C12 molecules are oriented perpendicular to the flow direction, leading to a relatively larger friction factor and thus a lower average velocity. This work provides important insights into understanding the anisotropic liquid flows in nanochannels. 

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2. Black Arsenic: A Layered Semiconductor with Extreme In‐Plane Anisotropy

   https://doi.org/10.1002/adma.201800754  

   Chen, Yabin ; Chen, Chaoyu ; Kealhofer, Robert ; Liu, Huili ; Yuan, Zhiquan ; Jiang, Lili ; Suh, Joonki ; Park, Joonsuk ; Ko, Changhyun ; Choe, Hwan Sung ; et al ( June 2018 , Advanced Materials)

   2D layered materials have emerged in recent years as a new platform to host novel electronic, optical, or excitonic physics and develop unprecedented nanoelectronic and energy applications. By definition, these materials are strongly anisotropic between the basal plane and cross the plane. The structural and property anisotropies inside their basal plane, however, are much less investigated. Black phosphorus, for example, is a 2D material that has such in‐plane anisotropy. Here, a rare chemical form of arsenic, called black‐arsenic (b‐As), is reported as a cousin of black phosphorus, as an extremely anisotropic layered semiconductor. Systematic characterization of the structural, electronic, thermal, and electrical properties of b‐As single crystals is performed, with particular focus on its anisotropies along two in‐plane principle axes, armchair (AC) and zigzag (ZZ). The analysis shows that b‐As exhibits higher or comparable electronic, thermal, and electric transport anisotropies between the AC and ZZ directions than any other known 2D crystals. Such extreme in‐plane anisotropies can potentially implement novel ideas for scientific research and device applications.

    

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3. Orientation‐Dependent Intercalation Channels for Lithium and Sodium in Black Phosphorus

   https://doi.org/10.1002/adma.201904623  

   Kim, Sungkyu ; Cui, Jiang ; Dravid, Vinayak P. ; He, Kai ( October 2019 , Advanced Materials)

   Black phosphorus (BP) with unique 2D structure enables the intercalation of foreign elements or molecules, which makes BP directly relevant to high‐capacity rechargeable batteries and also opens a promising strategy for tunable electronic transport and superconductivity. However, the underlying intercalation mechanism is not fully understood. Here, a comparative investigation on the electrochemically driven intercalation of lithium and sodium using in situ transmission electron microscopy is presented. Despite the same preferable intercalation channels along [100] (zigzag) direction, distinct anisotropic intercalation behaviors are observed, i.e., Li ions activate lateral intercalation along [010] (armchair) direction to form an overall uniform propagation, whereas Na diffusion is limited in the zigzag channels to cause the columnar intercalation. First‐principles calculations indicate that the diffusion of both Li and Na ions along the zigzag direction is energetically favorable, while Li/Na diffusion long the armchair direction encounters an increased energy barrier, but that of Na is significantly larger and insurmountable, which accounts for the orientation‐dependent intercalation channels. The evolution of chemical states during phase transformations (from Li_xP/Na_xP to Li₃P/Na₃P) is identified by analytical electron diffraction and energy‐loss spectroscopy. The findings elucidate atomistic Li/Na intercalation mechanisms in BP and show potential implications for other similar 2D materials.

    

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4. Gate voltage and doping effects on near-field radiation heat transfer in plasmonic heterogeneous pairs of graphene and black phosphorene

   https://doi.org/10.1039/C9RA04695J  

   Debu, Desalegn T. ; Doha, M. Hasan ; Churchill, Hugh O. ; Herzog, Joseph B. ( September 2019 , RSC Advances)

   Plasmon coupling and hybridization in 2D materials plays a significant role for controlling light–matter interaction at the nanoscale. We present a near-field radiation heat transfer (NFRHT) between vertically separated graphene and black phosphorene sheets at different temperatures in nanoscale separations. Radiation exchange from the theory of fluctuation electrodynamics is modulated by the carrier density of graphene and phosphorene. Direct comparison of NFRHT black phosphorene–graphene to symmetric graphene–graphene radiation exchange can be as much as 4 times higher for the selected doping range in both armchair (AC) and zigzag (ZZ) orientations of BP. The strong NFRHT enhancement of the specific optical properties of the heterogenous 2D material is due to the strong coupling of propagating surface plasmon polaritons as demonstrated by the distribution of the heat transfer coefficient. We also demonstrate that the magnitude of the near-field radiation enhancement is found to acutely depend on the vacuum gap of the graphene and BP pair. Interestingly, for separation distances below 200 nm, the total near-field heat transfer between black phosphorene and graphene exceeds that between graphene and graphene by 5 times. The radiation enhancement can be further tuned based on the orientation, AC, and ZZ of black phosphorene. These results prominently enable dynamic control of the total NFRHT relying on tunable anisotropic characteristics of BP irrespective of graphene's optical conductivity. Furthermore, the heterogeneous pairs of 2D materials potentially provide alternative platforms to achieve beyond super-Planckian radiation. 

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5. Ultra‐Narrow Phosphorene Nanoribbons Produced by Facile Electrochemical Process

   https://doi.org/10.1002/advs.202203148  

   Abu, Usman O. ; Akter, Sharmin ; Nepal, Bimal ; Pitton, Kathryn A. ; Guiton, Beth S. ; Strachan, Douglas R. ; Sumanasekera, Gamini ; Wang, Hui ; Jasinski, Jacek B. ( September 2022 , Advanced Science)

   Phosphorene nanoribbons (PNRs) have inspired strong research interests to explore their exciting properties that are associated with the unique two‐dimensional (2D) structure of phosphorene as well as the additional quantum confinement of the nanoribbon morphology, providing new materials strategy for electronic and optoelectronic applications. Despite several important properties of PNRs, the production of these structures with narrow widths is still a great challenge. Here, a facile and straightforward approach to synthesize PNRs via an electrochemical process that utilize the anisotropic Na⁺diffusion barrier in black phosphorus (BP) along the [001] zigzag direction against the [100] armchair direction, is reported. The produced PNRs display widths of good uniformity (10.3 ± 3.8 nm) observed by high‐resolution transmission electron microscopy, and the suppressedB_2gvibrational mode from Raman spectroscopy results. More interestingly, when used in field‐effect transistors, synthesized bundles exhibit the n‐type behavior, which is dramatically different from bulk BP flakes which are p‐type. This work provides insights into a new synthesis approach of PNRs with confined widths, paving the way toward the development of phosphorene and other highly anisotropic nanoribbon materials for high‐quality electronic applications.

    

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