不同N掺杂构型石墨烯的量子电容研究

超级电容器是一种利用界面双电层储能或在电极材料表面及近表面发生快速可逆氧化还原反应而储能的装置, 其特点是功率密度高、循环寿命长. 制备出兼有高能量密度的电极材料是当前超级电容器研究的重点. 以提高电容储能为目标, 通过掺杂N原子来调制石墨烯的电子结构, 使用基于密度泛函理论的第一原理计算了不同N掺杂构型石墨烯的态密度和能带结构, 拟合出了石墨烯的量子电容, 分析了量子电容储能提升的原因.     

Superior electrochemical performance of carbon cloth electrode-based supercapacitors through surface activation and nitrogen doping

A simple and low-cost strategy is developed to fabricate three-dimensional (3D) nitrogen-doped carbon cloth electrode through surface activation and nitrogen-doping process. The process can exfoliate the smooth surfaces of micro carbon fibers into nanostructures together with the doping of nitrogen-containing species. The as-fabricated carbon cloth electrode shows excellent areal capacitances of 882.36 and 706.68 mF cm^?2 at the current density of 1 and 60 mA cm^?2, respectively, exhibiting good rate performance. It also exhibits outstanding cycling stability with 98.7 % retention of its initial capacitance after 30,000 continuous charging/discharging tests. When the electrodes were assembled and tested as a symmetric supercapacitor, it also demonstrates superior electrochemical performance. It is believed that the 3D carbon structures with enlarged surface area, improved conductivity and electrode/electrolyte wettability, and enhanced pseudocapacitance by doping of nitrogen lead to the vast improvement of electrochemical performance.     

镓铝双质掺杂提高晶闸管性能的机理研究

依据Ga,A1在Si和SiO2中的扩散行为和特性,采用SiO2/Si系统,利用磁控装置精确控制Ga掺杂量,实现镓铝双质掺杂在同一扩散炉中经一次高温连续完成.该项掺杂技术能实现Si中的高均匀掺杂,扩散参数具有良好的重复性和一致性,可获得较理想的杂质浓度分布.Ga,Al与Si的共价半径相接近,高温后又采取缓慢降温等措施,能明显减少晶格缺陷,提高少子寿命,降低压降.研究了受主双质掺杂与晶闸管参数之间的关系,并对镓铝双质掺杂提高晶闸管性能的机理进行了深入的分析与讨论.研究表明,镓铝双质受主掺杂有利于提高晶闸管的耐压水平和浪涌能力,能明显改善电流特性、触发特性和动态特性,优于其他受主掺杂技术.     

Carbon Sphere@Nickel sulfide core-shell nanocomposite for high performance supercapacitor application

The Carbon sphere@Nickel sulfide core-shell nanocomposites for different mole ratios of Carbon sphere (0:1; 0.5:1 and 1:1) have been synthesized by a facile low temperature water-bath method without any further calcination. XRD studies on the core-shell nanocomposites show that characteristic peaks associated with rhombohedral phase structure of nickel sulfide have been retained. TEM morphology presents the interlinked core-shell of Carbon sphere@Nickel sulfide composite with grass-leaf dexterity for better ionic diffusion. BET study confirms the formation of mesoporous structure with high surface area. The existence of elements and its electronic configuration is noted through XPS. The electrochemical studies on pristine nickel sulfide and its Carbon sphere@Nickel sulfide core-shell composites reveal that Carbon sphere@Nickel sulfide (0.5:1) exhibits high specific capacitance of 1022?F?g^?1 at a current density of 1?A?g^?1. It shows good cyclic performance even beyond 4000 consecutive charge/discharge cycles at a relatively high current density of 20?A?g^?1 with the ～83% of retention.     

The influence of doping on the laser performance

We report a comparison, at low inversion population density, between two Yb:YAG ceramics lasers with different doping levels (10 and 20 at %) emitting at 1030 and 1050 nm. At the shorter lasing wavelength, the efficiency and the maximum output power of both samples are almost independent on the concentration of dopants. Conversely, at 1050 nm the two samples show a sizeable difference in the performances for higher values of the pump power. The results are compared with numerical simulations accounting for the pump beam and the laser radiation in order to map the temperature distribution experienced by the samples. We studied the effects of the reinjection of the pump inside the active medium. We obtained an output power of 10 W with a slope efficiency of 59% in respect of the pump power on the 20 at % sample. Finally, we report the tuning range for the heavier-doped sample (20 at %), which, to the best of our knowledge, is the first measurement on an heavily doped sample even reported in literature.     

Effect of nitrogen doping on the properties of AlSiO film for wide bandgap semiconductors

A gate insulator film with a wide bandgap and a high dielectric constant is required to achieve high-power field effect transistors (FET) using wide bandgap semiconductors such as SiC, GaN, and diamond. It is observed that an aluminum silicon oxide (AlSiO) film containing 11% nitrogen has a high resistivity of 5 × 10¹⁵ Ω cm, and the leakage current of a nitrogen-doped aluminum silicon oxide (AlSiON) film is also suppressed at high temperature, as compared to the AlSiO film. For example, the leakage current at 240 °C is four orders of magnitude smaller than that of the AlSiO film, suggesting that the AlSiON film is applicable to high temperature operation of wide bandgap semiconductor devices.     

Effect of nitrogen doping on the thermal conductivity of GeTe thin films

The 3ω method was employed to determine the effect of nitrogen doping (5 at.%) on the thermal conductivity of sputtered thin films of stoichiometric GeTe (a material of interest for phase change memories). It was found that nitrogen doping has a detrimental effect on the thermal conductivity of GeTe in both phases, but less markedly in the amorphous (–25%) than in the crystalline one (–40%). On the opposite, no effect could be detected on the measured thermal boundary resistance between these films and SiO₂, within the experimental error. Our results agree with those obtained by molecular dynamic simulation of amorphous GeTe. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of nitrogen and magnesium doping on the properties of ZnO films

Undoped ZnO and doped ZnO films were deposited on the MgO(111) substrates using oxygen plasma-assisted molecular beam expitaxy. The orientations of the grown ZnO thin film were investigated by in situ reflection high-energy electron diffraction and ex situ x-ray diffraction(XRD). The film roughness was measured by atomic force microscopy, which was correlated with the grain sizes determined by XRD. Synchrotron-based x-ray absorption spectroscopy was performed to study the doping effect on the electronic properties of the ZnO films, compared with density functional theory calculations.It is found that, nitrogen doping would hinder the growth of thin film, and generate the NOdefect, while magnesium doping promotes the quality of nitrogen-doped ZnO films, inhibiting(N_2)Oproduction and increasing nitrogen content.     

Optimize the thermoelectric performance of CdO ceramics by doping Zn

The thermoelectric performance of CdO ceramics was enhanced by simultaneously optimizing the electrical and thermal transport properties via a small amount of Zn doping(≤3%). The introduction of Zn can obviously increase the electrical conductivity of CdO due to the simultaneous increase of carrier concentration and mobility, and eventually results in an improvement in power factor. Zn doping is also effective in suppressing the thermal conductivity of CdO because of stronger phonon scatterings from point defects, Zn-riched second phase, and grain boundaries. A best ZT of about 0.45 has been achieved in the Cd_(1-x)Zn_xO systems at about 1000 K, which is comparable to the highest values reported for other n-type oxide TE materials.     

Tuning poly(p-phenylene) nano-size for enhancing electrical conductivity based on surfactant templates and doping

Nanoparticles play a vital role in the material property improvement. For conductive polymers, nanoparticles have been known to affect various electrical properties. This work reports the size-controlled synthesis of poly(p-phenylene) (PPP) nanoparticles using benzene, AlCl₃, and CuCl₂ as a monomer, catalyst, and oxidant respectively, incorporated with a surfactant template and subsequently doped with various doping agents to increase the electrical conductivity. The effects of surfactant types namely Span65, Tween80, and TritonX100 and surfactant concentrations were investigated. The PPP structure was confirmed by NMR, FT-IR, and XPS techniques. SEM images showed different undoped-PPP (uPPP) morphologies: irregular shape, coral reef shape, spherical shape, and worm-like shape with the particle sizes between ∼30 and ∼120 nm not previously reported. The electrical conductivity of the uPPP with a surfactant was higher than that without a surfactant due to the smaller particle size. From the doping, the electrical conductivity of the doped-PPP (dPPP) increased with the doping agent to monomer mole ratio up to 50:1. The dPPP doped with HClO₄ (dPPP/HClO₄) at the doping agent to monomer mole ratio of 50:1 exhibited the highest electrical conductivity of 74.34 S cm⁻¹ along with the long term stability in air.     

面向单晶SiC原子级表面制造的等离子体辅助抛光技术

目前Si基半导体由于其自身材料特性的限制,已经越来越难以满足高速发展的现代电力电子技术对半导体器件的性能要求.SiC作为新一代半导体材料具有显著的性能优势,但由于其属于典型的难加工材料,实现SiC晶圆的高质量与高效率加工成为了推动其产业化应用进程的关键.本综述在回顾近年来SiC超精密加工技术研究进展的基础上,重点介绍了一种基于等离子体氧化改性的SiC高效超精密抛光技术,分析了该技术的材料去除机理、典型装置、改性过程及抛光效果.分析结果表明,该技术具有较高的去除效率,能够获得原子级平坦表面,并且不会产生亚表面损伤.同时针对表面改性辅助抛光技术加工SiC表面过程中出现的台阶现象,探讨了该台阶结构的产生机理及调控策略.最后对等离子体辅助抛光技术的发展与挑战进行了展望.     

Investigation of electrochemical performance of MgNiO2 prepared by sol-gel synthesis route for aqueous-based supercapacitor application

In this work, we have successfully synthesized MgNiO₂ using a sol-gel wet chemical synthesis technique named MNO - 3. Electrochemical measurements in the presence of aqueous 1 M Li₂SO₄ electrolyte indicate that MNO - 3 samples exhibit a capacitance value of about 30 F/g and an energy density of about 20 Wh/kg. Subsequently, in the experiment involving aqueous 0.5 M Na₂SO₄ electrolyte system, it has been found that the capacitance for MNO - 3 sample is about 34 F/g and the energy density is about 23 Wh/kg for MNO - 3 sample. Finally, in the presence of aqueous-based 1 M Mg(ClO₄)₂ electrolyte, MNO - 3 sample is found to exhibit a capacitance of about 26 F/g and an energy density of about 17 Wh/kg, respectively. In all three electrolyte systems, the MNO -3 sample exhibit a long cycle capacitance retention of greater than 85% for 1000 charge-discharge cycles.     

Reduced graphene oxide/MWCNT hybrid sandwiched film by self-assembly for high performance supercapacitor electrodes

A reduced graphene oxide/multiwalled carbon nanotube (RGO/MWCNT) hybrid sandwiched film with different MWCNTs content was prepared by vacuum-assisted self-assembly from a complex dispersion of graphene oxide (GO) and MWCNTs followed by heat-treating at 200 °C for 1 h in a vacuum oven to reduce the GO into RGO. The free-standing RGO/MWCNT hybrid sandwiched film before heat-treatment showed a layered structure with an entangled network of MWCNTs sandwiched between the GO sheets. This unique structure not merely contribute to remove the oxygen-containing groups in GO during the heat-treatment, but also decrease the defects for electron transfer between RGO layers, which enhances the electrochemical capacitive performances of graphene-based films. A specific capacitance up to 379 F/g was achieved based on RGO/MWCNT with 30 % MWCNTs mass fraction at 0.1 A/g in a 6 M KOH electrolyte. The excellent performance of RGO/MWCNT hybrid sandwiched film signifies the importance of controlling the surface chemistry and sandwiched nanostructure of graphene-based materials.     

Effect of nitrogen doping on nanomechanical and surface properties of silicon film

The effect of nitrogen ion implantation on the nanomechanical properties of single crystal Si was evaluated by means of a conventional Vickers indentation and nanoindentation tests. The images of Si surfaces before and after nitrogen implantation were observed and their average surface roughnesses were measured by an atomic force microscope (AFM), while the changes in the morphology and microstructure of the single crystal Si by N implantation were examined by field emission scanning electron microscope (SEM) and X-ray diffractometer (XRD). In addition, the hydrophilic/hydrophobic surface property of the N-doping Si film was determined from the measurement of water contact angle by the sessile drop technique. Furthermore, the effects of the doping energy on the surface contact angle and the surface roughness and the Vickers hardness of the film are also investigated.     

Effects of nitrogen doping on optical properties of TiO2 thin films

The potential for extending the optical absorption range of TiO₂ by doping with nonmetallic elements was examined in nitrogen-containing TiO₂ thin films. Thin films of TiO_2-xN_x were synthesized on glass and silicon substrates by ion-beam-assisted deposition to obtain a wide range of nitrogen concentrations. The compositions of the films were determined by Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy. The structures of the films were analyzed by X-ray diffraction, transmission electron microscopy, and atomic force microscopy. The optical properties of the films were measured by UV-Vis spectroscopy and ellipsometry. A characteristic decreasing trend in band-gap values of the films was observed within a certain range of increasing dopant concentrations. As the nitrogen concentration increased, the structure of the films evolved from a well-defined anatase to deformed anatase. The reduced band gaps are associated with the N 2p orbital in the TiO_2-xN_x films. PACS 78.66.-w; 78.20.Ci     

Binder-free chemical synthesis of ZnFe2O4 thin films for asymmetric supercapacitor with improved performance

Ionics - In this work, a simple, cost-effective, binder-free, and wet chemical successive ionic layer adsorption and reaction (SILAR) method is developed for the growth of ZnFe2O4 thin films on...     

A study on the performance of metal-oxide-semiconductor-field-effect-transistors with asymmetric junction doping structure

Diode currents of MOSFET were studied and characterized in detail for the ion implanted pn junction of short channel MOSFETs with shallow drain junction doping structure. The diode current in MOSFET junctions was analyzed on the point of view of the gate-induced-drain leakage (GIDL) current. We could found the GIDL current is generated by the band-to-band tunneling (BTBT) of electrons through the reverse biased channel-to-drain junction and had good agreement with BTBT equation. The effect of the lateral electric field on the GIDL current according to the body bias voltage is characterized and discussed. We measured the electrical doping profiling of MOSFETs with a short gate length, ultra thin oxide thickness and asymmetric doped drain structure and checked the profile had good agreement with simulation result. An accurate effective mobility of an asymmetric source–drain junction transistor was successfully extracted by using the split C–V technique.     

氮掺杂手性碳纳米管的电子结构和输运特性的理论研究

运用第一性原理的密度泛函理论,结合非平衡格林函数,研究了氮原子取代掺杂手性单壁(6,3)碳纳米管的电子结构和输运特性.计算结果表明:不同构形和不同数目的氮原子取代掺杂对手性碳管的输运性质有很复杂的影响.研究发现,氮原子掺杂明显改变了碳管的电子结构,使金属型手性碳管的输运性能降低,电流-电压曲线呈非线性变化,而且输运性能随着杂质原子间间距的变化而发生显著改变.在一定条件下,金属型碳管向半导体型转变. 关键词： 手性单壁碳纳米管 氮掺杂 电子结构 输运性能     

Zr掺杂形式对钨电子发射材料组织性能的影响

采用中频感应加热烧结方法制备了W-1.5%La₂O₃-0.1%Y₂O₃-0.1%ZrO₂和W-1.5%La₂O₃-0.1%Y₂O₃-0.08%ZrH₂电子发射材料,烧结样品的致密度约为95.5%。热电子发射测试结果表明,添加氢化锆的热电子发射材料样品的零场发射电流密度大于添加氧化锆的样品,分析认为是添加的氢化锆在烧结时,发生分解,生成活性的Zr可以捕获钨晶界中的杂质氧,净化晶界,从而提高了电子发射;维氏显微硬度表明添加氢化锆样品的硬度高于添加氧化锆的样品,分析表明是氢化锆的添加有效改善了钨晶粒之间的结合性,提升了钨电子发射材料的硬度。利用SEM,EDS,XRD、金相显微镜等表面分析设备对样品进行了表征,样品结构显示添加氢化锆与添加氧化锆相比,不仅钨晶粒尺寸由13.63 μm降至11.63 μm,而且稀土相尺寸由1.87 μm降至1.66 μm,这种组织结构的变化有利于电子发射。