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。     

GaN-based substrates and optoelectronic materials and devices

In order to solve the problems of GaN heteroepitaxy on sapphire substrate,some techniques were explored.Freestanding GaN substrates have been made by hydride vapor phase epitaxy(HVPE),laser lift-off(LLO),and chemical mechanical polishing techniques.Wafer bending and cracking in the HVPE growth were partly settled by pulsed flow modulation method.High-crystal quality was established for 1.2 mm thick GaN substrate by X-ray diffraction measurement,in which the full width of half maximum values were 72,110 arcsec for(102),(002)peaks.A novel micro-size patterned sapphire substrate(PSS)and a nano PSS were also fabricated.High-power vertical structure light emitting diodes(VSLEDs)have been developed by Au–Sn eutectic wafer bonding,homemade micro-area LLO,and light extraction structure preparation.The high-injection-level active region with low temperature GaN sandwiched layers was used for lowefficiency droop.The light output power of VSLED was achieved as 400 mW driven at 350 mA,and the dominant wavelength is about 460 nm.The structures and properties of strain modulated superlattices(SLs)and quantum wells as well as advanced simulation of carriers transport across the electron blocking layer were investigated in laser diodes.The hole concentration was achieved as high as1.6 9 1018cm-3in AlGaN/GaN SLs:Mg by inserting an AlN layer.High-quality AlGaN epilayers and structures were grown by MOCVD.Some device structures of UV LEDs and detectors were demonstrated.The emission wavelength of 262 nm UV LED has been successfully fabricated.At last,high-quality InN and InGaN materials for solar cell were grown by boundary-temperature-controlled epitaxy and growth-temperature-controlled epitaxy.Hall-effect measurement showed a recorded electron mobility of 3,280 cm2/(V s)and a residual electron concentration of 1.47 9 1017cm-3at 300 K.     

A review of GaN-based optoelectronic devices on silicon substrate

Group Ⅲ-nitride material system possesses some unique properties,such as large spectrum coverage from infrared to deep ultraviolet,wide energy band gap,high electron saturation velocity,high electrical breakdown field,and strong polarization effect,which enables the big family has a very wide application range from optoelectronic to power electronic area.Furthermore,the successful growth of GaN-related III-nitride material on large size silicon substrate enable the above applications easily realize the commercialization,because of the cost-effective device fabrication on the platform of Si-based integrated circuits.In this article,the progress and development of the GaN-based materials and light-emitting diodes grown on Si substrate were summarized,in which some key issues regarding to the material growth and device fabrication were reviewed.     

蛋白基柔性材料的介观重构及其光电子器件

自然界中的蛋白质材料具有天然丰度、多种化学成分、可调控的性能、优异的生物相容及可降解性能等特点,为柔性光电子器件的发展提供了新的机遇.然而,蛋白质化学稳定性差、机械柔性不可控等缺点使得传统加工技术难以应用在其表面,严重制约了其在柔性电子领域的应用.本文首先以丝蛋白和角蛋白为例介绍了天然蛋白材料的介观重构以及加工技术,阐述了天然蛋白质材料的多级网络结构与其物理性能的关系.在此基础上,侧重介绍它们在柔性传感、发光、晶体管及存储等器件中的应用,最后展望了蛋白基柔性材料在光电子器件发展中所面临的挑战以及发展机遇.     

Luminescence of carbon nanotube bulbs

Carbon nanotube (CNT) bulbs made of decimeter-scale double-walled carbon nanotube (DWCNT) strands and films were fabricated and their luminescence properties, including the lighting efficiency, voltage-current relation and thermal stability were investigated. The results show that the DWCNT bulb has a comparable spectrum of visible light with tungsten bulb and its average efficiency is 40% higher than that of a tungsten filament at the same temperature (1400―2300 K). The nanotube filaments show both resistance and thermal stability over a large temperature region. No obvious damage was found for a nanotube bulb illuminating at 2300 K for more than 24 hours in vacuum.     

Ballistic carbon nanotube field-effect transistors

A common feature of the single-walled carbon-nanotube field-effect transistors fabricated to date has been the presence of a Schottky barrier at the nanotube--metal junctions. These energy barriers severely limit transistor conductance in the 'ON' state, and reduce the current delivery capability--a key determinant of device performance. Here we show that contacting semiconducting single-walled nanotubes by palladium, a noble metal with high work function and good wetting interactions with nanotubes, greatly reduces or eliminates the barriers for transport through the valence band of nanotubes. In situ modification of the electrode work function by hydrogen is carried out to shed light on the nature of the contacts. With Pd contacts, the 'ON' states of semiconducting nanotubes can behave like ohmically contacted ballistic metallic tubes, exhibiting room-temperature conductance near the ballistic transport limit of 4e(2)/h (refs 4-6), high current-carrying capability (approximately 25 micro A per tube), and Fabry-Perot interferences at low temperatures. Under high voltage operation, the current saturation appears to be set by backscattering of the charge carriers by optical phonons. High-performance ballistic nanotube field-effect transistors with zero or slightly negative Schottky barriers are thus realized.     

Piezoresistive effect in carbon nanotube films

The piezoresistive effect of the pristine carbon nanotube(CNT)films has been studied.Carbon nanotubes were synthesized by hot filament chemical vapor deposition.The piezoresistive effect in the pristine CNT films was studied by a three-point bending test.The gauge factor for the pristine CNT films under 500 microstrains was found to be at least 65 at room temperature,and increased with temperature,exceeding that of polycrystalline silicon(30at)30℃.The origin of the piezoresistivity in CNT films may be ascribed to a pressure-induced change in the band gap and the defects.     

Spread of double-walled carbon nanotube membrane

A single-layer double-walled carbon nanotube (DWNT) membrane, with 100 cm2 in area, 50 nm in thickness, was spread by adding a few drops of ethanol (or acetone) on the purified DWNTs. Compared with acetone, ethanol is more efficient in spreading DWNT films. The spreading rate of DWNT mem-brane increases with the ethanol concentration, and it also first increases with temperature (below 60℃), then decreases as the temperature rises to above 60℃.     

A tunable carbon nanotube electromechanical oscillator

Nanoelectromechanical systems (NEMS) hold promise for a number of scientific and technological applications. In particular, NEMS oscillators have been proposed for use in ultrasensitive mass detection, radio-frequency signal processing, and as a model system for exploring quantum phenomena in macroscopic systems. Perhaps the ultimate material for these applications is a carbon nanotube. They are the stiffest material known, have low density, ultrasmall cross-sections and can be defect-free. Equally important, a nanotube can act as a transistor and thus may be able to sense its own motion. In spite of this great promise, a room-temperature, self-detecting nanotube oscillator has not been realized, although some progress has been made. Here we report the electrical actuation and detection of the guitar-string-like oscillation modes of doubly clamped nanotube oscillators. We show that the resonance frequency can be widely tuned and that the devices can be used to transduce very small forces.     

Indium phosphide nanowires as building blocks for nanoscale electronic and optoelectronic devices

Nanowires and nanotubes carry charge and excitons efficiently, and are therefore potentially ideal building blocks for nanoscale electronics and optoelectronics. Carbon nanotubes have already been exploited in devices such as field-effect and single-electron transistors, but the practical utility of nanotube components for building electronic circuits is limited, as it is not yet possible to selectively grow semiconducting or metallic nanotubes. Here we report the assembly of functional nanoscale devices from indium phosphide nanowires, the electrical properties of which are controlled by selective doping. Gate-voltage-dependent transport measurements demonstrate that the nanowires can be predictably synthesized as either n- or p-type. These doped nanowires function as nanoscale field-effect transistors, and can be assembled into crossed-wire p-n junctions that exhibit rectifying behaviour. Significantly, the p-n junctions emit light strongly and are perhaps the smallest light-emitting diodes that have yet been made. Finally, we show that electric-field-directed assembly can be used to create highly integrated device arrays from nanowire building blocks.     

Au-Ag合金纳米管填充碳纳米管特性的第一性原理研究

基于密度泛函理论框架下的第一性原理计算,研究了Au-Ag合金纳米管同轴填充不同线径锯齿型(n, 0)碳纳米管所形成复合系统的稳定性、电子特性和力学性能.结果表明,内、外管间距约为4.20?的Au_xAg_(4-x)@(15, 0)复合系统为具有较大填充率的最稳定结构.能带结构分析表明,相对于自由Au-Ag合金纳米管复合系统的量子电导有所增加,电子态密度分析表明复合系统中的传导电子主要来源于内部Au原子和Ag原子的s电子以及外部C原子的p电子.相对于自由金属纳米管而言,碳纳米管的包裹使得金属纳米管的轴向拉伸临界应变和理想强度大大增加,有效地提高了其力学性能.     

High-performance flexural fatigue of carbon nanotube yarns

Carbon nanotube yarns (CNTY) possess good specific strength and specific conductivity. As such, their potential for commercial applications is significant. Fatigue performance is a significant consideration in yarn/wire applications. In this study, the flexural fatigue performance of CNTY spun from super-aligned carbon nanotube arrays was investigated using a reversed bending test. The results showed that CNTY exhibited excellent resistance to pure flexural fatigue, significantly outperforming stainless steel wire; CNTY failed where a combination of flexural fatigue and tension–tension fatigue had special hollow fracture morphology, and CNTY resistance remained fundamentally unchanged in the combination fatigue process.     

High-performance flexural fatigue of carbon nanotube yarns

Carbon nanotube yarns(CNTY)possess good specific strength and specific conductivity.As such,their potential for commercial applications is significant.Fatigue performance is a significant consideration in yarn/wire applications.In this study,the flexural fatigue performance of CNTY spun from super-aligned carbon nanotube arrays was investigated using a reversed bending test.The results showed that CNTY exhibited excellent resistance to pure flexural fatigue,significantly outperforming stainless steel wire;CNTY failed where a combination of flexural fatigue and tension–tension fatigue had special hollow fracture morphology,and CNTY resistance remained fundamentally unchanged in the combination fatigue process.     

碳纳米管复合材料的有效热导率

考虑到碳纳米管的空间取向分布特征，建立了碳纳米管复合材料的有效热导率模型。根据Maxwell理论，推导出了计算碳纳米管复合材料有效热导率的简单公式。应用实例表明，该模型能够很好地解释在碳纳米管纳米流体中观察到的热导率异常增加现象，还可以用来分析纳米管复合材料的渗流性质，而且理论计算结果与实验结果吻合较好。     

碳纳米管复合材料的有效热导率

考虑到碳纳米管的空间取向分布特征,建立了碳纳米管复合材料的有效热导率模型。根据Maxwell理论,推导出了计算碳纳米管复合材料有效热导率的简单公式。应用实例表明,该模型能够很好地解释在碳纳米管纳米流体中观察到的热导率异常增加现象,还可以用来分析纳米管复合材料的渗流性质,而且理论计算结果与实验结果吻合较好。     

High-performance flexural fatigue of carbon nanotube yarns

Carbon nanotube yarns （CNTY） possess good specific strength and specific conductivity. As such, their potential for commercial applications is significant. Fatigue performance is a significant consideration in yarn/wire applications. In this study, the flexural fatigue performance of CNTY spun from super-aligned carbon nanotube arrays was investigated using a reversed bending test. The results showed that CNTY exhibited excellent resistance to pure flexural fatigue, significantly outperforming stainless steel wire; CNTY failed where a combination of flexural fatigue and tension-tension fatigue had special hollow fracture morphology, and CNTY resistance remained fundamentally unchanged in the combination fatigue process.