Suppression of the anti-symmetry channel in the conductance of telescoped double-wall nanotubes

The conductance of telescoped double-wall nanotubes (TDWNTs) composed of two armchair nanotubes ($(n_O, n_O)$ and $(n_O-5, n_O-5)$ with $n_O \geq 10$) is calculated using the Landauer formula and a tight binding model. The results are in good agreement with the conductance calculated analytical by replacing each single-wall nanotube with a ladder, as expressed by $(2e^2/h)(T_+ + T_-)$, where $T_+$ and $T_-$ are the transmission rates of the symmetry and anti-symmetry channels, respectively. Perfect transmission in both channels is possible in this TDWNT when $n_O=10$, while $T_-$ is considerably small in the other TDWNTs. $T_-$ is particularly low when either $n_O$ or $n_O-5$ is a multiple of three. In this case, a three body effect of covalent-like interlayer bonds plays a crucial role in determining the finite $T_-$. When $n_O$ is a multiple of five, the five-fold symmetry increases $T_-$, although this effect diminishes with increasing $n_O$.Comment: Owing to errors of the calculation code, the numerical data shown in Figures are incorrect. Nonetheless, the corrected numerical calculations do not change the essential results. See erratum, PHYSICAL REVIEW B 79, 199902 (2009). The responsibility for the errors lies completely with the first author (Ryo Tamura

Edge-sensitive Semiconducting Behaviour in Low-defect Narrow Graphene Nanoribbons

Low-defect graphene nanoribbons (GNRs) derived from the unzipping of carbon nanotubes have exhibited large energy band gaps (transport gaps), despite having widths in the order of ∼100 nm. Here, we report on the unique semiconducting behaviour of very narrow, low-defect GNRs, with widths of less than 20 nm. Narrow GNRs are highly resistive, and additional annealing is required to reduce their resistivity. The GNRs display ambipolar rather than evident semiconducting behaviour (p- and n-types), exhibiting normalized Ion/Ioff as great as ∼106 (close to those in a few nm-order-width GNRs) and which are very sensitive to the atmosphere and the termination of the GNRs’ edges by foreign atoms (hydrogen for n-type and oxygen for p-type). It is also revealed that the activation energy (Ea ∼35 meV) estimated from the temperature dependence of the minimum conductance is smaller than those in ∼100 nm width GNRs. The observed sharp conductance peak on back-gate voltage (Vbg) dependence and its strong correlation with the Ea value suggest the presence of possible resonant tunnelling through shallow impurity levels with the small Ea introduced by the edge terminations by foreign atoms, which provides the observed unique behaviour, including the high Ion/Ioff. An energy band gap as large as ∼215 meV is also confirmed from the Ioff voltage region on Vbg. These narrow GNRs must open the door to large-scale graphene integration circuits based on CMOS-like behaviour

Large edge magnetism in oxidized few-layer black phosphorus nanomeshes

The formation and control of a room-temperature magnetic order in two-dimensional (2D) materials is a challenging quest for the advent of innovative magnetic- and spintronic-based technologies. To date, edge magnetism in 2D materials has been experimentally observed in hydrogen (H)-terminated graphene nanoribbons (GNRs) and graphene nanomeshes (GNMs), but the measured magnetization remains far too small to allow envisioning practical applications. Herein, we report experimental evidences of large room-temperature edge ferromagnetism (FM) obtained from oxygen (O)-terminated zigzag pore edges of few-layer black phosphorus (P) nanomeshes (BPNMs). The magnetization values per unit area are ~100 times larger than those reported for H-terminated GNMs, while the magnetism is absent for H-terminated BPNMs. The magnetization measurements and the first-principles simulations suggest that the origin of such a magnetic order could stem from ferromagnetic spin coupling between edge P with O atoms, resulting in a strong spin localization at the edge valence band, and from uniform oxidation of full pore edges over a large area and interlayer spin interaction. Our findings pave the way for realizing high-efficiency 2D flexible magnetic and spintronic devices without the use of rare magnetic elements

Research and Design of a Routing Protocol in Large-Scale Wireless Sensor Networks

无线传感器网络，作为全球未来十大技术之一，集成了传感器技术、嵌入式计算技术、分布式信息处理和自组织网技术，可实时感知、采集、处理、传输网络分布区域内的各种信息数据，在军事国防、生物医疗、环境监测、抢险救灾、防恐反恐、危险区域远程控制等领域具有十分广阔的应用前景。 本文研究分析了无线传感器网络的已有路由协议，并针对大规模的无线传感器网络设计了一种树状路由协议，它根据节点地址信息来形成路由，从而简化了复杂繁冗的路由表查找和维护，节省了不必要的开销，提高了路由效率，实现了快速有效的数据传输。 为支持此路由协议本文提出了一种自适应动态地址分配算——ADAR（AdaptiveDynamicAddre...As one of the ten high technologies in the future, wireless sensor network, which is the integration of micro-sensors, embedded computing, modern network and Ad Hoc technologies, can apperceive, collect, process and transmit various information data within the region. It can be used in military defense, biomedical, environmental monitoring, disaster relief, counter-terrorism, remote control of haz...学位：工学硕士院系专业：信息科学与技术学院通信工程系_通信与信息系统学号：2332007115216

Graphene and Graphene Nanomesh Spintronics

Spintronics, which manipulate spins but not electron charge, are highly valued as energy and thermal dissipationless systems. A variety of materials are challenging the realization of spintronic devices. Among those, graphene, a carbon mono-atomic layer, is very promising for efficient spin manipulation and the creation of a full spectrum of beyond-CMOS spin-based nano-devices. In the present article, the recent advancements in graphene spintronics are reviewed, introducing the observation of spin coherence and the spin Hall effect. Some research has reported the strong spin coherence of graphene. Avoiding undesirable influences from the substrate are crucial. Magnetism and spintronics arising from graphene edges are reviewed based on my previous results. In spite of carbon-based material with only sp2 bonds, the zigzag-type atomic structure of graphene edges theoretically produces spontaneous spin polarization of electrons due to mutual Coulomb interaction of extremely high electron density of states (edge states) localizing at the flat energy band. We fabricate honeycomb-like arrays of low-defect hexagonal nanopores (graphene nanomeshes; GNMs) on graphenes, which produce a large amount of zigzag pore edges, by using a nonlithographic method (nanoporous alumina templates) and critical temperature annealing under high vacuum and hydrogen atmosphere. We observe large-magnitude ferromagnetism, which arises from polarized spins localizing at the hydrogen-terminated zigzag-nanopore edges of the GNMs, even at room temperature. Moreover, spin pumping effects are found for magnetic fields applied in parallel with the few-layer GNM planes. Strong spin coherence and spontaneously polarized edge spins of graphene can be expected to lead to novel spintronics with invisible, flexible, and ultra-light (wearable) features

Carbon-based superconductors: towards high-Tc superconductivity

Introduction of Condensed Matter Physics; Spin-state Crossover; Li Ion Battery; Huge Thermoelectric Power; Room-temperature Ferromagnetism; Partially Disordered Antiferromagnetic Transition; Superconductivity; Transport Properties Combined with Charge, Spin, and Orbital; Magnetoresistance and Spin Blocade; Intrinsic Inhomogeneity; Move/diffuse and Charge/discharge Effect.</P