垂直腔面发射半导体激光器腔模位置对器件输出波长的影响研究

为得到高温环境下894.6 nm稳定波长激光输出的垂直腔面发射半导体激光器(VCSEL), 设计并制备了腔模位置不同的VCSEL芯片;通过对VCSEL腔模位置、输出波长和温漂系数的测试分析,研究了腔模位置对器件输出波长的影响,发现腔模位置与输出波长具有线性对应关系。设计了腔模位置在890.5 nm的VCSEL外延片结构,经工艺制备得到了85 ℃高温环境下894.6 nm稳定波长激光输出的VCSEL芯片。实验结果表明,通过调控腔模位置可得到目标波长激光输出的VCSEL芯片,该研究为研制其他波段稳定波长激光输出的垂直腔面发射激光器奠定了基础。     

Functionalisation of graphene surfaces with downstream plasma treatments

We report on an adjustable process for the functionalisation of graphene surfaces with a downstream plasma source. The parameters of oxygen plasma treatments are modified such that oxygenated functionalities can be added to the surface of graphene films prepared by chemical vapour deposition in a controlled manner. The nature of induced defects is investigated thoroughly using Raman and X-ray photoelectron spectroscopy. A massive change in the surface properties is observed through the use of contact angle and electrochemical measurements. We propose the usage of such plasma treatments to facilitate the addition of further functional groups to the surface of graphene. The incorporation of nitrogen into the graphene lattice by substitution of oxygenated functional groups is demonstrated outlining the validity of this approach for further functionalisation.     

Half-metallicity and spin-polarization transport properties in transition-metal atoms single-edge-terminated zigzag α-graphyne nanoribbons

By employing the non-equilibrium Green's function method and the spin-polarized density functional theory, we investigated the spin-resolved electronic transport properties of the zigzag α-graphyne nanoribbons (ZαGyNRs) passivated with 3d transition-metal atoms at one of the ribbon edge. Our results exhibit half-metallic behavior in response to the Fe-, Co- and Ni-doping at the edge of ZαGyNRs. The 3d transition-metal edge introduced in this paper can result in large spin polarization on currents of the ZαGyNRs devices, and some interesting phenomena such as half-metallicity, spin-polarization effect and negative differential resistance behavior can be observed. These theoretical results suggest a route to manipulate the spin-resolved electronic transport properties in ZαGyNRs-based spintronics devices.     

Investigation of the tarnish on the surface of a panda gold coin

In natural environment, tarnish was observed on the surface of historic and contemporary gold coins in several countries. Few years after the emergence of panda gold coins, several red spots were appeared on the surface. To identify the stains and to examine the spots, optical microscope （OM）, scanning electron microscope （SEM）, electron microprobe analysis （EMPA）, X-ray photoelectron spectroscopy （XPS）, and X-ray diffraction （XRD） were used. It was found by microscopic observation that the stain has a dark blue central area surrounded by a large area with a nuance of colors from brown to red. Red spots usually contain holes in the center, which are distributed along the forging stress zones formed in the struck process. From the surface analyses using EMPA, sulfur and silver are detected besides gold, and the contents of Ag and S at the tarnish part are higher than those at the other part. Furthermore, distributions of Ag and S are correlated with the morphology of stains. XPS shows that components of stains are Ag2S and Ag2SO4 and the former is much predominant. These results are confirmed using XRD analysis. Accelerated tarnish test of gold in an atmosphere containing sulfur compound proves that the similar phenomenon appears when a small amount of silver is present on the surface of gold. It can be concluded that the occurrence of tarnish stains is caused by the presence of Ag and S.     

Erbium-doped LAS glass ceramics prepared by spark plasma sintering (SPS)

Dense nanocrystalline glass ceramics of the Li₂O–Al₂O₃–SiO₂ (LAS) system were obtained by spark plasma sintering (SPS) of powders prepared by sol–gel method. The low thermal expansion LAS glass ceramic was chosen as host matrix for erbium ions. ZrO₂ was added both as a nucleating agent and as a possible good environment for the rare earth. The developed crystalline phases were analysed by X-ray diffraction (XRD) and the amorphous phase was quantified. Scanning and transmission electron microscopy (SEM, TEM) was used to investigate the microstructure. A different behaviour during the crystallisation process was observed between the sample prepared through the sintering of powders and the glass produced by the melting technique. A photoluminescence characterisation was also performed.     

Effects of catalyst loading amount on the synthesis of poly(3-hexylthiophene) via externally initiated Kumada catalyst-transfer polycondensation

A series of model polymerization are carried out via the one-pot externally initiated Kumada catalyst-transfer polycondensation (KCTP) of 2-bromo-5-chloromagnesium thiophene monomers, and the excess amount of initiators or catalysts are found no need to be isolated during the polycondensation process. Especially, the impacts of the nickel catalyst loading variation on regioregularity (rr), yield, molecular weight (M_n), polydispersity (PDI) and initiation efficiency of poly(3-hexylthiophene) (P3HT) are systematically investigated. The ¹H NMR, size-exclusion chromatography (SEC), and MALDI-TOF mass spectroscopy results indicated that an excess amount of catalyst does not influence yield, rr, M_n, and PDI of P3HT, nor the initiation efficiency. However, the PDI of the product is broad, and the M_n and rr values decreased in the absence of 1,3-bis(diphenylphosphino)propane (dppp). It can be concluded that the in-situ KCTP polymerization of P3HT is a practical and effective process. These results are especially valuable for the synthesis of all-conjugated block copolymers where macroinitiators are used.     

A large increase in the thermal conductivity of carbon nanotube/polymer composites produced by percolation phenomena

We have studied the thermal conductivity of carbon nanotube/polymer composites as a function of the CNT volume fraction using a steady-state measurement technique. The results show a large increase in the thermal conductivity at a small loading of carbon nanotube volume fraction (ca. 1.4 vol.%). The remarkably high increase in the thermal conductivity is described well by thermal transport through networks of carbon nanotubes in the polymer matrix, following a critical power law indicating percolating behavior, which shows the thermal percolation in the vicinity of the electrical percolation threshold concentration.     

3-Dimensional non-fullerene acceptors based on triptycene and perylene diimide for organic solar cells

Two molecules based on triptycene and perylene diimide (PDI) were designed and synthesized as non-fullerene acceptors for organic solar cells (OSCs). The bay-substituted and the imide-substituted molecules, named as TPBA and TPI, respectively, have rigid three-dimensional backbones, which improved the morphological compatibility with the donor polymers. TPBA and TPI exhibit suitable energy levels as acceptors and efficient absorption in the range of 450–600 nm. Their blended films with PTB7-Th displayed power conversion efficiencies of 2.80% and 3.64%, respectively.     

Comparison of commercial supercapacitors and high-power lithium-ion batteries for power-assist applications in hybrid electric vehicles: I. Initial characterization

Commercial supercapacitors, also known as ultracapacitors or electrochemical capacitors, from Saft, Maxwell, Panasonic, CCR, Ness, EPCOS, and Power Systems were tested under constant current and constant power discharges to assess their applicability for power-assist applications in hybrid electric vehicles (HEVs). Commercial lithium-ion batteries from Saft and Shin-Kobe were also tested under similar conditions. Internal resistances were measured by electrochemical impedance spectroscopy (EIS), as well as by the “iR drop” method. Self discharge measurements were also recorded. Compared with earlier generations of supercapacitors, the cells showed improved current and power capability. However, their energy densities are still too low to meet goals set by Partnership for a New Generation of Vehicles (PNGV) for HEV propulsion. Cells that use acetonitrile as the electrolyte solvent yield better performance, although safety issues need to be addressed. New high-power lithium-ion batteries show high energy densities, with high power capabilities.     

Preparation and characterization of nano-porous silica aerogel from rice husk ash by drying at atmospheric pressure

Silica aerogel, a mesoporous material, was prepared from rice husk ash by sol–gel method and dried under atmospheric pressure. In this method, rice husk ash, which is rich in silica, was extracted with sodium hydroxide solution to produce a sodium silicate solution. This solution was neutralized with acid to form a silica hydrosol, and a small amount of tetraethyl silicate (TEOS) to form a gel. The aged gel was washed carefully by distilled water and ethanol and finally dried under atmospheric air. The prepared silica aerogels were characterized by XRF, FT-IR, TG, DTA, DTG, XRD, BET and SEM measurements. The synthesized TEOS-doped silica aerogel was a light solid with specific surface area of 315 m²/g, pore volume 0.78 cm³/g, average pore size 9.8 nm, bulk density 0.32 g/cm³ and porosity 85%.