Modification on Single-Layer Graphene Induced by Low-Energy Electron-Beam Irradiation

In this work, we present studies of the effects of electron-beam irradiation on the modification of single-layer graphene. Micro-Raman spectra show that the D, D′, and D + G Raman bands, which are invisible for pristine graphene, appear after the graphenes are irradiated by low-energy electron-beam irradiation (10 keV), and the intensities of these peaks increase with increasing irradiation time, indicating disorder in graphene. The characteristics of G and 2D bands of graphene are also studied before and after irradiation. In the meantime, the height of graphene is studied by atomic force microscopy and found to increase for increasing irradiation time due to the contaminant deposition on graphene. The effects introduced by irradiation can be recovered partly by vacuum annealing. These results provide important information about the modification of graphene under electron-beam irradiation

Architecture of CuS/PbS Heterojunction Semiconductor Nanowire Arrays for Electrical Switches and Diodes

CuS/PbS p–n heterojunction nanowires arrays have been successfully synthesized. Association of template and DC power sources by controllable electrochemistry processes offers a technique platform to efficiently grow a combined heterojunction nanowire arrays driven by a minimization of interfacial energy. The resulting p–n junction materials of CuS/PbS show highly uniform 1D wire architecture. The single CuS/PbS p–n heterojunction nanowire based devices were fabricated, and their electrical behaviors were investigated. The independent nanowires exhibited a very high ON/OFF ratio of 1195, due to the association effect of electrical switches and diodes

Low-Temperature, Directly Depositing Individual Single-Walled Carbon Nanotubes for Fabrication of Suspended Nanotube Devices

Single-walled carbon nanotubes (SWNTs) grown by chemical vapor deposition (CVD) are widely used for fabrication of high-performance nanotube devices. However, the high-temperature growth is incompatible with the current complementary metal-oxide semiconductor (CMOS) technology. We demonstrate a low-temperature and direct deposition of the CVD-grown SWNTs. The nanotubes are synthesized by floating catalytic CVD technique and further carried by the flowing gas directly to the low-temperature area. Individual SWNTs have been successfully deposited on Si/SiO₂ substrates covered with a polymethylmethacrylate layer, which results in a suspended geometry of the nanotube in the fabricated devices. We subsequently investigate the electrical-transport properties of a representative small band gap nanotube, which exhibits an ambipolar feature with <i>p</i>-channel mobility up to 1410 cm² V^–1 S^–1 at room temperature. Furthermore, low-temperature measurements down to 4 K reveal different transport characteristics with the gate voltage biased near zero or at a large negative value, respectively

Large-Scale Fabrication of Suspended, Aligned, and Strained Single-Walled Carbon Nanotube Networks

Large-scale fabrication of suspended single-walled carbon nanotubes remains a challenge, especially at specific locations and in specific directions. In this work, we demonstrate an effective, fast and large-scale technique to fabricate suspended, strained, and aligned SWNT networks, which is based on a dynamic motion of silver liquid to suspend and align the SWNTs between each two prefabricated palladium patterns in high temperature. The SWNTs are aligned in eight directions: up, down, left, right, upper right, lower right, upper left, and lower left. The simulated calculations show that the driving force leading the silver liquid motion on the substrate is around 0.66 μN. The Raman spectra of the SWNTs network were measured, and the downshift of the G+ band indicates that, for the suspended SWNTs, the uniaxial strain is around 0.13%. This technique could be extended to two-dimensional material systems and open the pathway toward better optoelectronic and nanoelectromechanical systems

Energy Harvesting from the Mixture of Water and Ethanol Flowing through Three-Dimensional Graphene Foam

In this work, the electrical conductance and induced current of three-dimensional graphene foam (GF) are investigated when the mixture of water and ethanol flows through it. When different mixing ratios of ethanol:water (ethanol:water = 25:75, 50:50, 75:25, and 100:0 by volume) flow through the GFs, their electrical conductance is almost the same as that of the original GF. Meanwhile, the induced current can be obtained when the mixture flows through the GF. The direction of induced current depends on that of the flow of the mixture, the value of induced current has no dependence on the flow direction of the mixture but is closely related to the flow velocity and polarity of the mixture. The mechanism of the induced electricity is discussed, which is attributed to the coupling of flowing solution molecules with the charge carriers of graphene at the solid/liquid interface. These results indicate that GFs have a bright potential application in realizing the self-powered function of nano/micro electromechanical systems (N/MEMS) in many special environments

Drastically Enhanced High-Rate Performance of Carbon-Coated LiFePO₄ Nanorods Using a Green Chemical Vapor Deposition (CVD) Method for Lithium Ion Battery: A Selective Carbon Coating Process

Application of LiFePO₄ (LFP) to large current power supplies is greatly hindered by its poor electrical conductivity (10^–9 S cm^–1) and sluggish Li⁺ transport. Carbon coating is considered to be necessary for improving its interparticle electronic conductivity and thus electrochemical performance. Here, we proposed a novel, green, low cost and controllable CVD approach using solid glucose as carbon source which can be extended to most cathode and anode materials in need of carbon coating. Hydrothermally synthesized LFP nanorods with optimized thickness of carbon coated by this recipe are shown to have superb high-rate performance, high energy, and power densities, as well as long high-rate cycle lifetime. For 200 C (18s) charge and discharge, the discharge capacity and voltage are 89.69 mAh g^–1 and 3.030 V, respectively, and the energy and power densities are 271.80 Wh kg^–1 and 54.36 kW kg^–1, respectively. The capacity retention of 93.0%, and the energy and power density retention of 93.6% after 500 cycles at 100 C were achieved. Compared to the conventional carbon coating through direct mixing with glucose (or other organic substances) followed by annealing (DMGA), the carbon phase coated using this CVD recipe is of higher quality and better uniformity. Undoubtedly, this approach enhances significantly the electrochemical performance of high power LFP and thus broadens greatly the prospect of its applications to large current power supplies such as electric and hybrid electric vehicles