Top-gated graphene field-effect transistors on SiC substrates

We report on a demonstration of top-gated graphene field-effect transistors(FETs) fabricated on epitaxial SiC substrate.Composite stacks,benzocyclobutene and atomic layer deposition Al2O3,are used as the gate dielectrics to maintain intrinsic carrier mobility of graphene.All graphene FETs exhibit n-type transistor characteristics and the drain current is nearly linear dependence on gate and drain voltages.Despite a low field-effect mobility of 40 cm2/(V s),a maximum cutoff frequency of 4.6 GHz and a maximum oscillation frequency of 1.5 GHz were obtained for the graphene devices with a gate length of 1 μm.     

电化学法制备石墨烯及其性能表征

在0.2 mol·L氯化胆碱体系下以电化学法剥离石墨箔得到石墨烯,采用高分辨透射电子显微镜、扫描隧道电子显微镜、红外光谱、拉曼光谱等方法研究了所得到的石墨烯的形貌与结构.结果表明:所得的产物最薄仅为2～4层,多数为6～8层,并且具有较好的完整性,无明显团聚与褶皱.与氧化还原法相比结构缺陷及氧化官能团含量明显降低.将石墨烯制成无支撑石墨烯薄膜,测量其导电性可知在其面密度为0.5 mg·cm时其方块电阻仅为19.3 Ω/□,显示出良好的导电性能.     

用电火花技术制作P型高阻硅的欧姆接触

检测高阳硅单晶材料的杂质补偿度和迁移率时,必须要有良好的欧姆接触。本文提出用银头烙铁将多元合金(InBAlNi)涂敷在P型硅片上,经电火花放电技术可对电阻率高达1000Ωcm的样品制成欧姆接触。通过电流电压特性、接触电阻率和离子探针的测量,讨论了欧姆接触的机理和载流子输运的特征。电火花技术使多元合金与高阻P型硅样品在电容器放电的瞬间所产生的高能量作用下,交界面处的硅与合金相互熔融,冷却时,电活性受主元素又以高浓度析出,使原来的高阻硅变为P~ ,形成了欧姆接触。不同温度的接触电阻率测量,结合与掺杂浓度关系的计算表明,穿过金属与半导体硅接触的电流输运是热离子场发射机理,载流子隧穿势垒是主要的输运过程。     

共价键结合的石墨烯和碳纳米管三维复合材料的载流子迁移率研究

应用密度泛函理论对共价键结合的多孔石墨烯和单壁碳纳米管三维复合材料进行结构优化和能带计算，确定石墨烯和碳纳米管以共价键的形式结合.基于第一性原理计算出石墨烯二维平面上的弹性常数和形变势常数，得到石墨烯电子和空穴迁移率约为104 cm2/(Vs), 比完整的单层石墨烯低1个数量级.该模型可以扩展到共价键结合的碳元素三维空间结构，在未来的有机电子学领域具有广阔的发展前景.     

镍基纳米SiC复合镀层的摩擦学性能

为研究镍基纳米 Si C复合镀层的摩擦学性能 ,在A3钢板上制备了该镀层 ,利用扫描电镜对镀层显微组织进行观察 ,通过纳米显微力学探针测量镀层微区硬度 ,在 MM-2 0 0摩擦磨损试验机上对镀层进行磨损试验 ,研究阴极电流密度、温度和镀液中 Si C浓度等主要工艺参数对镀层耐磨性能的影响。结果表明 :Si C颗粒在镀层中分布均匀 ;Si C颗粒附近镀层的硬度是纯镍镀层的 3倍 ,但随着远离 Si C,复合镀层硬度明显下降 ;复合镀层的耐磨性能与普通镍镀层相比有较大幅度的提高 ,在油润滑条件下磨损体积为普通镍镀层的 1/ 8。     

Preparation and characterization of cobalt-doped iron pyrite(FeS_2) thin films

Iron pyrite (FeS_2) incorporated with cobalt dopant varying from 2%to 6%atomic ratio,was synthesized by using an aqueous hydrothermal process.The thin films of Co-doped FeS_2were fabricated by a vacuum thermal evaporation of synthesized FeS_2powder.The structural,electrical and optical properties of as-deposited and sulfurized films were investigated.The X-ray diffraction results indicated that the synthesized powder and thin films showed a cubic pyrite structure.The crystallinity of FeS_2was slightly degraded by the doping of cobalt.The dependence of thin-film resistance on the temperature indicated an increase of activation energy until 3 at%cobalt doping and then decreased the resistance with the increase of cobalt concentration.Hall effect measurements showed that the Co-doped samples have n-type conduction except for the 2 at%.The carrier concentration was in the order of 10~(18)cm~(-3),whereas,the carrier mobility decreased from 6.52 cm~2/V.s to 4.3 cm~2/V.s with the increase of cobalt dopant.The photosensitivity of undoped and cobalt-doped FeS_2films was measured under AM 1.5G and NIR light.The sulfurized films showed a higher photoresponse than the asdeposited films for both visible and IR lights.     

SiC/Ti(C,N)/Al2O3陶瓷复合材料的抗热震性能设计及其切削应用

抗热震性能是结构陶瓷材料的重要性能之一．以抗热震断裂参数表征材料的抗热震性能，采用理论与实验相结合的方法，建立了基于抗热震性能的陶瓷复合材料的组分设计模型，并采用计算机辅助优化设计技术求得材料的最优组分．结果表明：当Ti（C，N）和SiC的体积含量分别为10．4％和27．1％时，该材料具有最高的抗热震性能，比纯氧化铝陶瓷提高约55％．在此基础上，利用热压技术制得一种SiC／Ti（C，N）／Al2O3复合陶瓷材料．将该材料制成切削刀具，并在切削实验中通过设计切削条件使得刀具主要承受热载荷和热应力的作用，从而发生热）中击破损．实验发现，SiC／Ti（C，N）／Al2O3复合陶瓷刀具切削淬火钢时的抗热）中击破损性能较纯Al2O3陶瓷提高约62-68％，与抗热震性能设计的理论预测基本吻合．这表明，该设计方法是可行的．     

石墨烯复合材料电热除冰实验研究

石墨烯复合材料因其优良的导电性和高导热性,在各个领域均得到了广泛的关注。为研究石墨烯加热膜在电热除冰上的应用,通过实验比较石墨烯和电阻丝作为加热元件时的温升速率;将加热元件制备成可用于电热除冰的加热膜,在相同加热功率下验证两者的发热均匀性;根据自行搭建的电热除冰实验台,研究不同热流密度和结冰温度对石墨烯加热膜除冰效果的影响。实验结果表明：单纯的石墨烯加热元件比电阻丝升温速率快,由石墨烯作为加热元件制备而成的加热膜发热更加均匀;随着热流密度的不断增加,石墨烯加热膜除冰时间越短,效果越好;结冰温度越低,除冰时间越长。验证了石墨烯可以作为一种理想的加热膜材料应用于电热除冰领域。     

石墨烯/聚合物纳米复合材料研究进展

 石墨烯是由单层碳原子通过共价键结合形成的二维片层状结构,是一种新型碳类纳米材料,具有优异的力学、电学和热学等性能,被认为是一种非常有前景的材料,近年来广泛用于改性各种聚合物。本文回顾了石墨烯/聚合物纳米复合材料的制备方法、性能和应用现状;综述了石墨烯/聚合物纳米复合材料的强度、刚度、韧性、电学和热学等性能的研究进展。主要内容包括石墨烯改性聚合物常见的3种制备方法(溶液共混、熔融共混和原位聚合)及其对石墨烯在聚合物基体中分散性的影响,石墨烯/聚合物纳米复合材料力学性能变化规律与作用机理,石墨烯微观结构等因素对材料热学性能以及导电阈值的影响等;讨论了石墨烯/聚合物纳米复合材料的潜在应用和面临的挑战和机遇,并展望了其低成本产业化的发展前景。     

化学法制备石墨烯对环氧树脂导电性能的影响

通过化学氧化热解膨胀还原法制备了石墨烯,并对石墨烯的化学结构及微观形貌进行表征.将自制的石墨烯以及商业级的碳纳米管、富勒烯、石墨分别作为纳米导电填料加入到环氧树脂中,考察不同碳纳米材料对环氧树脂导电性能的影响.结果表明:所制备的石墨烯是不同于氧化石墨烯和热解膨胀石墨薄层的单层或少数层的二维材料;当石墨烯体积分数为0.25%时,复合材料的电导率发生渗流突变,而当体积分数增大到0.50%时,其电导率为2.02×10-7 S·m-1,导电性能得到显著增强.     

石墨烯/二氧化锰复合材料的制备及其电化学性能

通过水热法在160℃条件下成功制备了手风琴状石墨烯/MnO2复合材料.通过场发射扫描电镜、透射电镜、X射线衍射、X射线能量色散谱、BET法以及拉曼光谱对材料进行表征.结果表明,手风琴状二氧化锰与层状石墨烯之间具有十分高效的贴合,这种创新性设计有效地利用了石墨烯的高电导率、大比表面积以及二氧化锰的优秀赝电容行为.电化学测试结果给出在0.2 A·g-1时,样品的比电容高达138 F·g-1,数倍增强于单独的二氧化锰或石墨烯样品.     

Ultrahigh-quality silicon carbide single crystals

Silicon carbide (SiC) has a range of useful physical, mechanical and electronic properties that make it a promising material for next-generation electronic devices. Careful consideration of the thermal conditions in which SiC [0001] is grown has resulted in improvements in crystal diameter and quality: the quantity of macroscopic defects such as hollow core dislocations (micropipes), inclusions, small-angle boundaries and long-range lattice warp has been reduced. But some macroscopic defects (about 1-10 cm(-2)) and a large density of elementary dislocations (approximately 10(4) cm(-2)), such as edge, basal plane and screw dislocations, remain within the crystal, and have so far prevented the realization of high-efficiency, reliable electronic devices in SiC (refs 12-16). Here we report a method, inspired by the dislocation structure of SiC grown perpendicular to the c-axis (a-face growth), to reduce the number of dislocations in SiC single crystals by two to three orders of magnitude, rendering them virtually dislocation-free. These substrates will promote the development of high-power SiC devices and reduce energy losses of the resulting electrical systems.     

Designing fast oxide-ion conductors based on La2Mo2O9

The ability of solid oxides to conduct oxide ions has been known for more than a century, and fast oxide-ion conductors (or oxide electrolytes) are now being used for applications ranging from oxide fuel cells to oxygen pumping devices. To be technologically viable, these oxide electrolytes must exhibit high oxide-ion mobility at low operating temperatures. Because of the size and interaction of oxygen ions with the cationic network, high mobility can only be achieved with classes of materials with suitable structural features. So far, high mobility has been observed in only a small number of structural families, such as fluorite, perovskites, intergrowth perovskite/Bi2O2 layers and pyrochlores. Here we report a family of solid oxides based on the parent compound La2Mo2O9 (with a different crystal structure from all known oxide electrolytes) which exhibits fast oxide-ion conducting properties. Like other ionic conductors, this material undergoes a structural transition around 580 degrees C resulting in an increase of conduction by almost two orders of magnitude. Its conductivity is about 6 x 10(-2) S cm(-1) at 800 degrees C, which is comparable to that of stabilized zirconia, the most widely used oxide electrolyte. The structural similarity of La2Mo2O9 with beta-SnWO4 (ref. 14) suggests a structural model for the origin of the oxide-ion conduction. More generally, substitution of a cation that has a lone pair of electrons by a different cation that does not have a lone pair--and which has a higher oxidation state--could be used as an original way to design other oxide-ion conductors.     

Al-N 共掺杂p 型ZnO 薄膜制备及电学性能的研究

利用射频磁控溅射技术在石英玻璃上制备了ZnO:Al薄膜,继而N离子注入实现薄膜的Al-N共掺杂,随后进行了不同温度和时间的热处理。并借助X射线衍射(XRD)、霍耳测试(Hall)、X射线光电能谱仪(XPS)等手段对ZnO薄膜的性能进行了表征。实验结果表明,Al-N共掺杂ZnO薄膜在578℃退火8 min表现出较稳定的p型导电,其载流子数高达1×1018～6×1018个·cm-3,对应的电阻率为1～9Ω·cm,迁移率为1～2 cm2·V-1·s-1。与单掺N相比,实现p型导电所需的退火温度有明显降低,这很可能与Al的掺入有关。此外,XPS测试结果证实大量的Ni取代O空位是薄膜p型导电的根本原因。     

Preparation of graphene and TiO2 layer by layer composite with highly photocatalytic efficiency

A process for fabricating graphene and TiO₂ layer by layer composite was introduced to improve the photocatalytic activity by controlling the layers, thickness and the mass ratio between graphene and TiO₂. The graphene oxide (GO) was synthesized from natural graphite powder by the modified Hummers method. Large-area uniform GO and TiO₂ thin films were made by a spin-coating process in turn. After exposure of the TiO₂/GO multilayer film to UV light irradiation which allows the reduction of GO to graphene, a novel photocatalytic structure as graphene and TiO₂ layer by layer composite was synthesized. The cross-sectional SEM image showed that a clear layer by layer microstructure with a single layer thickness of graphene or TiO₂ was in the range of about 50 nm. The total thickness of the film was around 5 μm which was varied according to the layer number of spin coating process. Raman spectra revealed that significant structural changes occurred through UV light irradiation. Photodegradation for methylene blue (MB) exhibited that the layer by layer composite is of higher photocatalytic activity than the pure TiO₂ layer.     

石墨烯增强铝基SiC复合材料的动态失效机理与抗侵彻性能

研究石墨烯增强铝基复合材料的动态力学性能、失效机理以及抗侵彻性能.通过静、动态压缩测试掌握了材料在0.001~5 200.000 s-1应变率范围内的力学性能,揭示了该材料的应变率效应,结合光学显微镜（OM）和扫描电镜（SEM）分析了该材料在静、动态压缩下的断裂机理;通过弹道枪试验掌握了该材料与Q235钢面板层叠构成复合结构及12~18 mm厚Q235A钢板的弹道极限速度及极限比吸收能.试验结果表明,Q235A钢/石墨烯增强铝基复合结构的极限比吸收能是12~14 mm厚度范围Q235A钢板的1.79倍,34.10 mm厚石墨烯增强铝基SiC复合材料的极限比吸收能与16.70 mm厚Q235A钢相当.      

MnO2/C复合纳米纤维纱线的制备及其导电性能

采用共轭静电纺丝法制备聚丙烯腈(PAN)纳米纤维纱线,并在不同温度下将PAN纳米纤维碳化得到碳纳米纤维纱线。以KMnO 4为锰源,通过水热合成法在碳纳米纤维纱线上原位生长纳米二氧化锰(MnO 2),形成MnO 2/C复合纳米纤维纱线,分别采用傅里叶变换红外光谱(FTIR)、扫描电子显微镜(SEM)、场发射扫描电子显微镜(FE-SEM)、数字万用表对碳纳米纤维纱线和MnO 2/C复合纳米纤维纱线的化学组成、表观形貌、电学性能等进行表征,并分析碳化温度对碳纳米纤维纱线的形貌和电学性能的影响,以及水热反应中盐酸浓度对纳米MnO 2形貌和MnO 2/C复合纳米纤维纱线的影响。结果表明:碳化温度越高,得到的纱线表面越光洁,石墨化程度越高,电学性能也越好,1000℃碳化工艺得到的碳纳米纤维纱线电导率最高,为31.5 S/cm;与MnO 2复合后的碳纳米纤维纱线电导率大幅下降,当盐酸与高锰酸钾摩尔浓度比为4∶1时得到的复合纳米纤维纱线的电导率最高,为0.1200 S/cm。     

石墨烯在光电器件中的应用

 讨论了近年来石墨烯在太阳能电池、有机发光二极管以及场致发射器件方面的应用研究。石墨烯是碳的同素异形体的一种,是二维的薄膜材料,具有独特的导电特性及机械弯曲性能,可以作为太阳能电池、有机发光器件的柔性电极;石墨烯与有机聚合物材料复合可以形成大的给体受体界面,有利于太阳能电池中激子的扩散速率、载流子迁移率的提高,可以作为有机太阳能电池的电子受体材料;石墨烯具有一维尖锐的刀口状边缘,具有大的电场增强系数,同时由于石墨烯自身的良好导电能力,可以作为场致发射器件中的电子传导与电场发射材料。石墨烯在光电器件中应用的深入研究有望突破目前光电技术的发展瓶颈,是一个极具前景的新研究领域。     

磁控溅射在PI/石墨烯基体上制备氧化锌薄膜

聚酰亚胺(PI)/石墨烯复合薄膜兼备了可挠曲性及透明、导电性,可作为柔性透明导电电极用于柔性电子器件中。但附着于PI上的石墨烯易划伤,使其导电性变差。本文采用脉冲直流磁控溅射法,以PI/石墨烯为基体,镀制保护石墨烯的氧化锌薄膜。分别采用原子力显微镜、X射线衍射仪、台阶仪、霍尔效应仪及紫外-可见分光光度计检测PI/石墨烯/ZnO复合薄膜的表面形貌、晶体结构、薄膜厚度及导电、透光性能。结果表明,PI/石墨烯/ZnO复合薄膜结构致密,氧化锌以(002)为择优取向,最低方阻为1.9×104Ω/sq,略低于石墨烯的方阻,可见光区平均透光率达80%。     

化学沉积法制备Ni-P-SiC(C)复合镀层的研究

选择廉价的SiC和石C颗粒作为复合镀层添加物，用化学沉积法在碳钢表面制度Ni-P-SiC(C)复合镀层，研究了复合镀层的制备工艺，镀液配方以及复合镀层的性能等，结果显示：风表面开成的复合镀层厚薄均一，SiC和石墨C颗粒在镀层中分布均匀，镀层开成速度理想，表明本文采用的工艺技术合理可行，与单一的Ni-P镀层相比，Ni-P-SiC和Ni-P-C复镀层耐磨性能均有不同程度的提高，而将2种不同性能的SiC和C颗粒同时加入槽液，形成的Ni-P-SiC－C复合镀层具有最优异的耐磨性能。