To analyze the solitary internal wave(SIW) influence on acoustic field interference pattern and thereby monitor SIW, for broadband pulse signal propagating through SIWs, we adopt a parabolic equation model, and simulate the variation of received single normal mode(SNM) pulse sequence with SIW position, and analyze the spatiotemporal interference characteristics and mechanism of the sequence. Based on the coupled mode theory, we derive the relationship between SIW position and interference striation slope(ISS). The relationship can monitor the SIW position precisely, with greatly improved precision and robustness compared with previous work. Furthermore, based on the SNM interference pattern periodicity in frequency, we also develop another method to estimate SIW range, with better real-time property than the first method. The SIW-normal mode interference relationship can be used for improving acoustic field localization in the presence of SIWs, which has great value for oceanology,marine engineering, marine military and so on. Besides, the relationship can be expanded to other detection for local variation, e.g., detecting metal flaw and locating dramatic variation in seabed topography.
Recently, ZrTe5 has received a lot of attention as it exhibits various topological phases, such as weak and strong topological insulators, a Dirac semimetal, a three-dimensional quantum Hall state, and a quantum spin Hall insulator in the monolayer limit. While most of studies have been focused on the three-dimensional bulk material, it is highly desired to obtain nanostructured materials due to their advantages in device applications. We report the synthesis and characterizations of ZrTe5 nanoribbons. Via a silicon-assisted chemical vapor transport method, long nanoribbons with thickness as thin as 20 nm can be grown. The growth rate is over an order of magnitude faster than the previous method for the bulk crystals.Moreover, transport studies show that the nanoribbons are of low unintentional doping and high carrier mobility, over30000 cm2/V·s, which enable reliable determination of the Berry phase of π in the ac plane from quantum oscillations. Our method holds great potential in growth of high quality ultra-thin nanostructures of ZrTe5.
Various novel physical properties have emerged in Dirac electronic systems, especially the topological characters pro- tected by symmetry. Current studies on these systems have been greatly promoted by the intuitive concepts of Berry phase and Berry curvature, which provide precise definitions of the topological phases. In this topical review, transport properties of topological insulator （Bi2Se3）, topological Dirac semimetal （Cd3As2）, and topological insulator-graphene heterojunc- tion are presented and discussed. Perspectives about transport properties of two-dimensional topological nontrivial systems, including topological edge transport, topological valley transport, and topological Weyl semimetals, are provided.
Artificial modulation of electronic structures and control of the transport dynamics of carriers and excitons in Cd Se nanowire are important for its application in optoelectronic nanodevices. Here, we demonstrate the aggregative flow of excitons by bending Cd Se nanowires. The bending strain induces spatial variance of bandgap, and the energy bandgap gradient will result in the flow of excitons towards the bending outer edge of Cd Se nanowire. The exciton emission energy shows a uniform redshift in the bending region due to the aggregative flow of excitons, and the energy redshift increases linearly with increasing the strain at the outer edge of the Cd Se nanowire. Our results show an effective method to drive, concentrate, and utilize the excitons in Cd Se nanowires, which provides a guide for the design of high performance and flexible optoelectronic nanodevices.
A foundation of the modern technology that uses single-crystal silicon has been the growth of highquality single-crystal Si ingots with diameters up to 12 inches or larger. For many applications of graphene, large-area high-quality(ideally of single-crystal) material will be enabling. Since the first growth on copper foil a decade ago, inch-sized single-crystal graphene has been achieved. We present here the growth, in 20 min, of a graphene film of(5 ×50) cm^2 dimension with >99% ultra-highly oriented grains.This growth was achieved by:(1) synthesis of metre-sized single-crystal Cu(1 1 1) foil as substrate;(2)epitaxial growth of graphene islands on the Cu(1 1 1) surface;(3) seamless merging of such graphene islands into a graphene film with high single crystallinity and(4) the ultrafast growth of graphene film.These achievements were realized by a temperature-gradient-driven annealing technique to produce single-crystal Cu(1 1 1) from industrial polycrystalline Cu foil and the marvellous effects of a continuous oxygen supply from an adjacent oxide. The as-synthesized graphene film, with very few misoriented grains(if any), has a mobility up to ~23,000 cm^2 V^(-1)s^(-1)at 4 K and room temperature sheet resistance of ~230 Ω/□. It is very likely that this approach can be scaled up to achieve exceptionally large and high-quality graphene films with single crystallinity, and thus realize various industrial-level applications at a low cost.
Solid-state nanopore is found to be a promising tool to detect proteins and their complexes. Nanopore-protein interaction is a fundamental and ubiquitous process in biology and medical biotechnology. By translocating phi29 connector protein through silicon nitride nanopores, we demonstrate preliminarily probing the surface hydrophobicity of individual protein at single-molecule resolution. The unique 'double-level event' observed in the translocation and the ratio of two current drop levels suggest that the position where the interaction occurs is the hydrophobic surface of the protein. We provide a potential method to locate the hydrophobic region of a specific protein surface. This study is of fundamental significance in revealing the important role that hydrophobic interaction plays in nanopore-protein interaction and holds great potential for detecting local surface chemical property of individual protein using solid-state nanopores.
