Understanding the Mechanical and Conductive Properties of Carbon Nanotube Fibers for Smart Electronics

The development of fiber-based smart electronics has provoked increasing demand for high-performance and multifunctional fiber materials. Carbon nanotube (CNT) fibers, the 1D macroassembly of CNTs, have extensively been utilized to construct wearable electronics due to their unique integration of high porosity/surface area, desirable mechanical/physical properties, and extraordinary structural flexibility, as well as their novel corrosion/oxidation resistivity. To take full advantage of CNT fibers, it is essential to understand their mechanical and conductive properties. Herein, the recent progress regarding the intrinsic structure–property relationship of CNT fibers, as well as the strategies of enhancing their mechanical and conductive properties are briefly summarized, providing helpful guidance for scouting ideally structured CNT fibers for specific flexible electronic applications.     

Crossing the blood–brain barrier with graphene nanostructures

Therapeutic approaches for the delivery of drugs to the central nervous system are hampered by the presence of the blood–brain barrier (BBB); overcoming this barrier is the clinical goal for the treatment of neurological disorders, including Alzheimer’s disease and Parkinson’s disease. The BBB is a cellular barrier of a highly impermeable nature that is predominantly formed by a tightly bound continuous layer of endothelial cells; it acts as a gatekeeper to restrict the free diffusion of bloodborne pathogens into the central nervous system. Targeted drug delivery systems have been explored over the past decade for crossing the BBB. Very recently, graphene nanostructures have shown great potential for crossing the BBB due to their exceptional features such as high electron mobility, ease of synthesis and functionalization, as well as control over size, shape, and the drug release profile. Graphene is evolving as a system not only to detect diseased lesions but also, in parallel, to treat neurological disorders while demonstrating minimal side effects. Given the rapid developments of innovative graphene-based delivery platforms, the present review sheds light on the status and prospects of graphene for crossing the BBB by improving, preserving, or rescuing brain energetics, with a specific focus on how graphene alters neuronal cell function.     

High contrast ratio, high uniformity multiple quantum well spatial light modulators

Our latest research results on GaAs-AlGaAs multiple quantum well spatial light modulators are presented.The thickness uniformity of the epitaxial layers across the 3-inch wafer grown by our molecular beam epitaxy is better than 0.1% and the variation of cavity resonance wavelength within the wafer is only 0.9 nm. A contrast ratio (CR) of 102 by varying bias voltage from 0 to 6.7 V is achieved after fine tuning the cavity by etching an adjust layer. Both theoretical and experimental results demonstrate that incorporating an adjust layer is an effective tuning method for obtaining high CR.     

Mesoporous nanocrystalline ceria–zirconia solid solutions supported nickel based catalysts for CO2 reforming of CH4

A series of mesoporous nanocrystalline ceria–zirconia solid solutions with different Ce/Zr ratios were facilely synthesized via improved evaporation induced self-assembly strategy. The obtained materials with advantageous structural properties and excellent thermal stabilities were characterized by various techniques and investigated as the supports of the Ni based catalysts for CO₂ reforming of CH₄. The effects of Ce/Zr ratio and mesopore structure on promoting catalytic performances had been investigated. It was found that the catalyst supported on carrier with 50/50 Ce/Zr ratio behaved the highest catalytic activity. The reason for this might be that the mesoporous ceria–zirconia solid solution carrier contributed to the activation of CO₂ by its own redox property. Compared with the catalyst without obvious mesostructure, the current mesoporous catalyst performed higher catalytic activity and better catalytic stability, demonstrating the advantages of the mesostructure. On the one hand, the predominant textural properties such as large surface area, big pore volume, and uniform channel helped to the high dispersion of the Ni particles among the mesoporous framework, finally leading to higher catalytic activity. On the other hand, the mesoporous matrix could stabilize the Ni nanoparticles under severe reduction and reaction conditions by the “confinement effect”, committed to better catalytic stability. Besides, the properties of the coke over the mesoporous catalyst were also carefully studied. Generally, these mesoporous nanocrystalline ceria–zirconia solid solutions were a series of promising catalytic carriers for CO₂ reforming of CH₄.     

Enhancement of carbon nanotube fibres using different solvents and polymers

Liquid infiltration is an efficient way to densify carbon nanotubes (CNTs) and was used to strengthen CNT fibres in the method of array spinning. Rather than the volatility, the dipole moment of solvent plays a more important role in determining the densification level. The fibres densified by highly polar but non-volatile solvents such as N,N-dimethylformamide, dimethyl sulphoxide, and N-methyl-2-pyrrolidone were 100–200 MPa stronger than those by ethanol and acetone. Ethylene glycol is the most efficient solvent due to its two polar OH groups and improved the fibre strength to 1.45 GPa. Long chain or cross-linked polymers like polyvinyl alcohol, polyimide, and bismaleimide (BMI) were introduced into CNT fibres by infiltration with aid of polar solvents. These polymers reinforced the fibres significantly, as they can connect non-neighboring CNTs and benefit the load transfer. The strongest CNT/BMI fibre was 2.38 GPa in strength and 110 GPa in modulus.     

低温漂高电源抑制的CMOS片上电流源

设计了一种用于驱动电路和模数转换器的片上电流源,该结构利用带隙基准的方法产生了一个与温度无关的参考电平,同时为了满足高电源抑制的要求,电流源中采用了运算放大器的负反馈环路来抑制电源到输出的增益,从而使输出电平与电源电压无关,然后通过电阻把电压转化为电流.该电路在0.35,μm、3.3 V的工艺下实现,芯片面积为0.03 mm2.仿真和测试结果表明,该电流源的温度系数为8.7×10-6/℃,在2.6～4 V的电源电压下均能正常工作,达到了系统要求.     

基于软件预处理的空间光调制器驱动电路研制

研制了一套基于软件预处理的多量子阱空间光调制器驱动电路.针对不同的多量子阱空间光调制器,软件预处理单元根据其反射特性,拟合出它的反射谱线.根据反射谱线产生相应的光电转换控制信号,增强了该驱动电路的通用性,降低了驱动电路的复杂性.改进一次扫描的方式,采用先粗扫再细扫的二次扫描方式,在保证扫描速度及分辨率的同时,有效降低了单元像素驱动电路的面积.SPICE仿真结果和芯片测试结果均证明,驱动电路芯片工作良好,驱动电压输出摆幅为0～VDD.驱动电压分辨率可达256级.总之,所设计的驱动电路满足空间光调制器的需求.     

The development of a conductive carbon nanotube (CNT) network in CNT/polypropylene composite films during biaxial stretching

Two developing stages of conducting network in carbon nanotube (CNT)/polypropylene composite films were found during simultaneous biaxial (SIB) stretching and sequential biaxial (SEB) stretching. The electrical resistivity was first increased up to 10¹¹ Ω cm with the extension of the films, regardless of the stretching modes. Once further stretched to 3.5 × 3.5, the SIB- and SEB-stretched films showed reduction of their resistivity of six and eight orders of magnitude, respectively. Microscopic observations revealed that specimens stretching in SEB mode promoted the elongation of CNTs and their clusters, which was apparently more effective for reconnecting adjacent particles and fabricating a new conducting network.