Electronic Structure and I-V Characteristics of InSe Nanoribbons

Electric-field-controlled electronic structures and quantum transport in monolayer InSe nanoribbons

Electronic structures and quantum transport properties of the monolayer InSe nanoribbons are studied by adopting the tight-binding model in combination with the lattice Green function method. Besides the normal bulk and edge electronic states, a unique electronic state dubbed as edge-surface is found in the InSe nanoribbon with zigzag edge type. In contrast to the zigzag InSe nanoribbon, a singular electronic state termed as bulk-surface is observed along with the normal bulk and edge electronic states in the armchair InSe nanoribbons. Moreover, the band gap, the transversal electron probability distributions in the two sublayers, and the electronic state of the topmost valence subband can be manipulated by adding a perpendicular electric field to the InSe nanoribbon. Further study shows that the charge conductance of the two-terminal monolayer InSe nanoribbons can be switched on or off by varying the electric field strength. In addition, the transport of the bulk electronic state is delicate to even a weak disorder strength, however, that of the edge and edge-surface electronic states shows a strong robustness against to the disorders. These findings may be helpful to understand the electronic characteristics of the InSe nanostructures and broaden their potential applications in two-dimensional nanoelectronic devices as well.

Nearly Ideal Two-Dimensional Electron Gas Hosted by Multiple Quantized Kronig-Penney States Observed in Few-Layer InSe

A theoretical ideal two-dimensional electron gas (2DEG) was characterized by a flat density of states independent of energy. Compared with conventional two-dimensional free-electron systems in semiconductor heterojunctions and noble metal surfaces, we report here the achievement of ideal 2DEG with multiple quantized states in few-layer InSe films. The multiple quantum well states (QWSs) in few-layer InSe films are found, and the number of QWSs is strictly equal to the number of atomic layers. The multiple stair-like DOS as well as multiple bands with parabolic dispersion both characterize ideal 2DEG features in these QWSs. Density functional theory calculations and numerical simulations based on quasi-bounded square potential wells described as the Kronig-Penney model provide a consistent explanation of 2DEG in the QWSs. Our work demonstrates that 2D van der Waals materials are ideal systems for realizing 2DEG hosted by multiple quantized Kronig-Penney states, and the semiconducting nature of the material provides a better chance for construction of high-performance electronic devices utilizing these states, for example, superlattice devices with negative differential resistance.

Two-dimensional biomaterials: material science, biological effect and biomedical engineering applications

To date, nanotechnology has increasingly been identified as a promising and efficient means to address a number of challenges associated with public health. In the past decade, two-dimensional (2D) biomaterials, as a unique nanoplatform with planar topology, have attracted explosive interest in various fields such as biomedicine due to their unique morphology, physicochemical properties and biological effect. Motivated by the progress of graphene in biomedicine, dozens of types of ultrathin 2D biomaterials have found versatile bio-applications, including biosensing, biomedical imaging, delivery of therapeutic agents, cancer theranostics, tissue engineering, as well as others. The effective utilization of 2D biomaterials stems from the in-depth knowledge of structure-property-bioactivity-biosafety-application-performance relationships. A comprehensive summary of 2D biomaterials for biomedicine is still lacking. In this comprehensive review, we aim to concentrate on the state-of-the-art 2D biomaterials with a particular focus on their versatile biomedical applications. In particular, we discuss the design, fabrication and functionalization of 2D biomaterials used for diverse biomedical applications based on the up-to-date progress. Furthermore, the interactions between 2D biomaterials and biological systems on the spatial-temporal scale are highlighted, which will deepen the understanding of the underlying action mechanism of 2D biomaterials aiding their design with improved functionalities. Finally, taking the bench-to-bedside as a focus, we conclude this review by proposing the current crucial issues/challenges and presenting the future development directions to advance the clinical translation of these emerging 2D biomaterials.

Magneto-electronic properties, carrier mobility and strain effects of InSe nanoribbon

The monolayer InSe has been successfully fabricated recently and studied intensely. Here, we investigate the geometrical stability and various physical properties such as electronic and magnetic feature, carrier mobility and strain effects for InSe nanoribbons. Our calculations show that armchair nanoribbons, regardless of the bare-edged or H-saturated ones, are semiconductors with an indirect bandgaps, but the bandgap size is increased greatly by H-saturation. Their electron mobility is predicted to be moderately large (from ~10² to ~10³ cm² V^-1 s^-1) with the holes being less mobile for wider ribbons, and the carrier polarity phenomenon becomes more prominently for H-saturation. The zigzag InSe nanoribbons are found to be magnetic metals with a bigger magnetic moment and the ferromagnetic ground state at the single edge. The magnetism stems from unpaired electrons at the In-rich edge. More interestingly, it is found that the externally applied mechanical strain can effectively tune the spin polarization efficiency at the Fermi level to two stepwise stages, suggesting that the strain can act as a tool for developing a mechanical switch to control spin-polarized transport under lower bias. The detailed analysis suggests that this strain-tuning mechanism can be attributed to the ionic and covalent bond-configuration competition due to the strain-induced bond-length alterations, which leads to the unpaired electron redistribution in magnetic atoms or vanishing.

Electric Field Controlled Indirect-Direct-Indirect Band Gap Transition in Monolayer InSe

Electronic structures of monolayer InSe with a perpendicular electric field are investigated. Indirect-direct-indirect band gap transition is found in monolayer InSe as the electric field strength is increased continuously. Meanwhile, the global band gap is suppressed gradually to zero, indicating that semiconductor-metal transformation happens. The underlying mechanisms are revealed by analyzing both the orbital contributions to energy band and evolution of band edges. These findings may not only facilitate our further understanding of electronic characteristics of layered group III-VI semiconductors, but also provide useful guidance for designing optoelectronic devices.

Electronic Properties of Armchair Black Phosphorene Nanoribbons Edge-Modified by Transition Elements V, Cr, and Mn

The structural, electrical, and magnetic properties of armchair black phosphorene nanoribbons (APNRs) edge-functionalized by transitional metal (TM) elements V, Cr, and Mn were studied by the density functional theory combined with the non-equilibrium Green's function. Spin-polarized edge states introduce great varieties to the electronic structures of TM-APNRs. For APNRs with Mn-stitched edge, their band structures exhibit half-semiconductor electrical properties in the ferromagnetic state. A transverse electric field can then make the Mn-APNRs metallic by shifting the conduction bands of edge states via the Stark effect. The Mn/Cr-APNR heterojunction may be used to fabricate spin p-n diode where strong rectification acts only on one spin.