CHARGE AND SPIN TRANSPORT STUDIES IN GRAPHENE AND BLACK PHOSPHORUS

Ph.DDOCTOR OF PHILOSOPH

Large Frequency Change with Thickness in Interlayer Breathing Mode - Significant Interlayer Interactions in Few Layer Black Phosphorus

Bulk black phosphorus (BP) consists of puckered layers of phosphorus atoms. Few-layer BP, obtained from bulk BP by exfoliation, is an emerging candidate as a channel material in post-silicon electronics. A deep understanding of its physical properties and its full range of applications are still being uncovered. In this paper, we present a theoretical and experimental investigation of phonon properties in few-layer BP, focusing on the low-frequency regime corresponding to interlayer vibrational modes. We show that the interlayer breathing mode A3g shows a large redshift with increasing thickness; the experimental and theoretical results agreeing well. This thickness dependence is two times larger than that in the chalcogenide materials such as few-layer MoS2 and WSe2, because of the significantly larger interlayer force constant and smaller atomic mass in BP. The derived interlayer out-of-plane force constant is about 50% larger than that in graphene and MoS2. We show that this large interlayer force constant arises from the sizable covalent interaction between phosphorus atoms in adjacent layers, and that interlayer interactions are not merely of the weak van der Waals type. These significant interlayer interactions are consistent with the known surface reactivity of BP, and have been shown to be important for electric-field induced formation of Dirac cones in thin film BP.Comment: Nano Letters, 201

Large Frequency Change with Thickness in Interlayer Breathing Mode-Significant Interlayer Interactions in Few Layer Black Phosphorus

10.1021/acs.nanolett.5b00775NANO LETTERS1563931-393

Dataset for the synthesis and characterization of disordered metallic carbon materials from graphene edge chemistry

This dataset provides a comprehensive account of the intricate processes involved in the rational design, synthesis, and characterization of anisotropic metallic carbon materials. The materials were derived through the hydrolytic oxidation of graphene sheets, followed by meticulous self-assembly and mild annealing. The resulting products are highly percolated carbon networks, preserving the essential basal area of the source graphene. Structured into various sections, this dataset aims to furnish detailed insights crucial for supporting extensive investigations into these carbon materials. Section S1 delves into simulations that elucidate the reactivity of hydroxyl radicals in the hydrolytic oxidation process, pinpointing optimal conditions for their selective use in edge-hydrolysis of graphene. Additionally, it explores the molecular dynamics of edge-hydrolyzed graphene sheets, unraveling their self-assembly behavior and the formation of highly ordered films. Section S2 meticulously describes the source materials and optimal protocols, aligning with insights gained from simulations. In Section S3, the dataset explores the impact of synthesis protocols on the processability of hydrolyzed graphene and anticipates potential applications. Sections S4 to S7 present detailed characterization protocols, meticulously divided into morphology, composition, mechanical properties, and thermal/electronic transport, ensuring the inclusion of all essential details for reproducibility in core characterizations. Finally, Section S8 presents a table summarizing the general properties of the final annealed metallic carbon film (G0). This dataset thus serves as a valuable resource, providing a robust foundation for in-depth studies and fostering a comprehensive understanding of the multifaceted aspects of anisotropic metallic carbon materials

Colossal Ultraviolet Photoresponsivity of Few-Layer Black Phosphorus

Black phosphorus has an orthorhombic layered structure with a layer-dependent direct band gap from monolayer to bulk, making this material an emerging material for photodetection. Inspired by this and the recent excitement over this material, we studied the optoelectronics characteristics of high-quality, few-layer black phosphorus-based photodetectors over a wide spectrum ranging from near-ultraviolet (UV) to near-infrared (NIR). It is demonstrated for the first time that black phosphorus can be configured as an excellent UV photodetector with a specific detectivity ∼3 × 10¹³ Jones. More critically, we found that the UV photoresponsivity can be significantly enhanced to ∼9 × 10⁴ A W^–1 by applying a source-drain bias (<i>V</i>_SD) of 3 V, which is the highest ever measured in any 2D material and 10⁷ times higher than the previously reported value for black phosphorus. We attribute such a colossal UV photoresponsivity to the resonant-interband transition between two specially nested valence and conduction bands. These nested bands provide an unusually high density of states for highly efficient UV absorption due to the singularity of their nature

Colossal enhancement of spin-orbit coupling in weakly hydrogenated graphene

10.1038/nphys2576Nature Physics95284-28

Assembly of suspended graphene on carbon nanotube scaffolds with improved functionalities

10.1007/s12274-012-0262-xNano Research511783-79