Growth of carbon nanotube field emitters on single strand carbon fiber: a linear electron source

The multi-stage effect has been revisited through growing carbon nanotube field emitters on single strand carbon fiber with a thickness of 11 μm. A prepared linear electron source exhibits a turn-on field as low as 0.4 V μm(-1) and an extremely high field enhancement factor of 19,300, when compared with those results from reference nanotube emitters grown on flat silicone wafer; 3.0 V μm(-1) and 2500, respectively. In addition, we introduce a novel method to grow nanotubes uniformly around the circumference of carbon fibers by using direct resistive heating on the continuously feeding carbon threads. These results open up not only a new path for synthesizing nanocomposites, but also offer an excellent linear electron source for special applications such as backlight units for liquid crystal displays and multi-array x-ray sources.     

N silicon solar cells emitters realized using phosphoric acid as doping source in a spray process

The spray technique is used to realize the n⁺ emitter from phosphoric acid H₃PO₄ as a doping source. Emulsions have been prepared using several organic solvents. It was found that H₃PO₄:2-butanol mixture provides the most uniform deposited layer. The sheet resistance and the n⁺ profile were measured with a four point probe and the Hall profiling, respectively. The variety of emitters obtained are characterized by a sheet resistance ranging from 10 to 86 Ω/□ and a junction depth of about 0.2 to 0.7 μm which can be adequate for emitters in a polycrystalline silicon solar cell process.     

深低温星上定标黑体源研究

为匹配红外空间载荷低温光学镜头的光学性能,降低背景噪声,实现载荷高精度星上定标,研制了一种基于制冷机主动制冷的深低温星上定标黑体源装置（低温100 K工作）,该星载黑体源装置由面黑体辐射体、低温制冷机主动制冷系统、冷量传输热管及精密测控温系统组成,通过载荷级真空辐射定标实验校验,最终实现红外遥感器对星上定标黑体源宽光谱（2～16μm）、高发射率（0.987）、深低温（100 K）的高精度定标源需求。该深低温星上定标黑体源可用于对极远极冷极弱目标探测的红外载荷星上辐射定标,其高精度、低功耗、通用性的工程化设计方法,为后续相关研究及推广提供技术支撑。     

Achieving high-current carbon nanotube emitters

When a carbon nanotube emitter is operated at high currents (typically above 1 microA per emitter), a small voltage drop ( approximately few volts) along its length or at its contact generates a reverse/canceling electric field that causes a saturation-like deviation from the classical Fowler-Nordheim behavior with respect to the applied electric field. We present a correction to the Fowler-Nordheim equation to account for this effect, which is experimentally verified using field emission and contact electrical measurements on individual carbon nanotube emitters. By using rapid thermal annealing to improve both the crystallinity of the carbon nanotubes and their electrical contact to the substrate, it is possible to reduce this voltage drop, allowing very high currents of up to 100 microA to be achieved per emitter with no significant deviation from the classical Fowler-Nordheim behavior.     

Aqueous blackbody calibration source for millimeter-wave/terahertz metrology

This paper describes a calibrated broadband emitter for the millimeter-wave through terahertz frequency regime, called the aqueous blackbody calibration source. Due to its extremely high absorption, liquid water is chosen as the emitter on the basis of reciprocity. The water is constrained to a specific shape (an optical trap geometry) in an expanded polystyrene (EPS) container and maintained at a selected, uniform temperature. Uncertainty in the selected radiometric temperature due to the undesirable reflectance present at a water interface is minimized by the trap geometry, ensuring that radiation incident on the entrance aperture encounters a pair of s and a pair of p reflections at 45 degrees. For water reflectance R(w) of 40% at 45 degrees in W-band, this implies a theoretical effective aperture emissivity of (1-R(2)(ws)R(2)(wp))>98.8%. From W-band to 450 GHz, the maximum radiometric temperature uncertainty is +/-0.40 K, independent of water temperature. Uncertainty from 450 GHz to 1 THz is increased due to EPS scattering and absorption, resulting in a maximum uncertainty of -3 K at 1 THz.     

Hybrid carbon nanotube/nanodiamond structures as electron emitters for cold cathodes

The field emission properties of hybrid carbon nanotubes/nanodiamond structures produced by one-step chemical vapor deposition (CVD) process have been investigated in order to assess their application as electron emitters for cold cathodes. The electron emission properties of a series of samples have been investigated by current-pressure, current-voltage and current-time measurements with the aim of testing the emission stability under working conditions relevant to technological applications. Stable emission, high values of current density and lack of arcing have been observed during prolonged working cycles, and without degradation of the material structure.     

Activation-free printed carbon nanotube field emitters

When a carbon nanotube paste is formulated based on highly functional hyperbranched polymers such as dipentaerythritol hexaacrylate, the volume shrinkage during thermal curing builds up internal stress that generates microcrack patterns on the printed surface. The nanotubes exposed in the cracks emit electrons successfully at such an extremely low electric field as 0.5?V?μm( - 1), and reach 25.5?mA?cm( - 2) of current density at 2?Vμm( - 1) from an optimized paste concerning mainly the size and spatial uniformity of the crack. In addition to the superior field emission properties with low manufacturing cost, this activation-free technology can provide a minimized nanohazard in the device fabrication process, compared to those conventional activation technologies developing serious nanoflakes by using destructive methods.     

Facile synthesis of fluorescent carbon dots using watermelon peel as a carbon source

The synthesis of water-soluble fluorescent carbon dots (C-dots) has received much attention recently. Here, high quality fluorescent C-dots have been synthesized through low-temperature carbonization and simple filtration using watermelon peel, a waste and reproducible raw resource, as a novel carbon resource. This facile approach allows large-scale production of aqueous C-dots dispersions without any post-treatment process. The as-prepared C-dots possess small particle sizes (~ 2.0 nm), strong blue luminescence, acceptable fluorescence lifetime and good stability in a wide range of pH values (pH 2.0-11.0) and at a high salt concentration. Besides, the obtained C-dots have been successfully applied in live cell imaging, indicating these carbon nanoparticles can serve as high-performance optical imaging probes.     

Strong enhancement of the radiative decay rate of emitters by single plasmonic nanoantennas

We demonstrate a strong, 5-fold enhancement of the radiative decay rate from highly efficient fluorescent dye molecules around resonant optical nanoantennas. The plasmonic modes of individual gold dimer antennas are tuned by the particle length and the antenna gap, providing control over both the spectral resonance position and the near-field mode profile of the nanoantenna. Resonant enhancement of the radiative and nonradiative decay rates of a fluorescent dye is observed, resulting in an increase of the internal quantum efficiency from 40% up to 53% for single antennas, and up to 59% for antenna clusters. This improvement of the already high quantum efficiency of the dye molecules is in agreement with electrodynamic model calculations that predict a maximum attainable efficiency around 80% due to nonradiative losses in the metal.     

大口径热管面源黑体炉的研制及性能评价

针对红外成像光学系统校正,研制了大口径热管面源黑体炉.通过Monte Carlo方法对具有同心圆V形槽表面的辐射特性进行了分析,借助黑体空腔理论完成黑体炉的结构设计,采用热管技术,PIC16F876微处理器和模糊PID开关切换控制算法实现黑体炉的温控.通过试验测试,验证了此辐射源具有均匀一致的有效发射率和辐射出度.     

Clean carbon nanotube field emitters aligned horizontally

Horizontally aligned carbon nanotube (CNT) field emitters, which strongly adhere to the substrate and show good field emission properties, were fabricated by electrophoresis deposition and fissure formation techniques. A thin film of CNTs was deposited on a substrate, by electrophoresis, from an aqueous mixture of CNT and detergent, and then the detergent was deposited also by electropholysis. CNTs with a clean surface were exposed in the fissures produced by firing. The field emission was increased significantly due to the additional deposition of the detergent. When the CNTs were cut by increasing the firing time, the field emission increased significantly, while their stability decreased considerably. Our method does not require any further treatment for field emission.     

Synergy between thermal and nonthermal effects in plasmonic photocatalysis

Nano Research - Plasmonic photocatalysis represents the synergetic union of two active fields of research: plasmonic effects in illuminated metallic nanoparticles and catalytic effects in tailored...     

Carbon dioxide as a carbon source for synthesis of carbon nanotubes by chemical vapor deposition

Carbon dioxide was successfully used as carbon source in the synthesis of carbon nanotubes (CNTs) by chemical vapor deposition (CVD) over Fe/CaO catalyst. The product was evaluated using both transmission electron microscopy (TEM) and Raman spectroscopy. Crooked and branching structures of multi-walled carbon nanotubes (MCNTs) with diameters of around 50 nm were observed on the TEM micrographs. Raman spectrum results show that the nanotubes have small defects, which is in agreement with the results of TEM. The influence of reaction variable such as furnace temperature and types of support media was also studied and the reaction mechanism was then discussed in this paper.     

Elimination of current non-uniformity in carbon nanotube field emitters

Activation of abnormal emitting sites in Carbon Nano Tube (CNT) field emitters and their elimination is reported. CVD grown, patterned CNT was used as cathode for field emission studies. We encountered the problem of current non-uniformity in CNT cathode. This non-uniformity was attributed to abnormally active emitting sites during voltage ramp-up. The sudden increase in current resulted in region of positive slope in F–N curve, which can’t be explained by conventional F–N theory. Also the grown CNTs can be a mixture of metallic and semi conducting nature, which may cause deviation from the conventional F–N theory. We could eliminate abnormally active sites by electric field treatment, thereby increasing current uniformity and stability. The work is underway to understand the deviation in FN curve at high fields.     

Infrared-spectroscopic nanoimaging with a thermal source

Fourier-transform infrared (FTIR) spectroscopy is a widely used analytical tool for chemical identification of inorganic, organic and biomedical materials, as well as for exploring conduction phenomena. Because of the diffraction limit, however, conventional FTIR cannot be applied for nanoscale imaging. Here we demonstrate a novel FTIR system that allows for infrared-spectroscopic nanoimaging of dielectric properties (nano-FTIR). Based on superfocusing of thermal radiation with an infrared antenna, detection of the scattered light, and strong signal enhancement employing an asymmetric FTIR spectrometer, we improve the spatial resolution of conventional infrared spectroscopy by more than two orders of magnitude. By mapping a semiconductor device, we demonstrate spectroscopic identification of silicon oxides and quantification of the free-carrier concentration in doped Si regions with a spatial resolution better than 100 nm. We envisage nano-FTIR becoming a powerful tool for chemical identification of nanomaterials, as well as for quantitative and contact-free measurement of the local free-carrier concentration and mobility in doped nanostructures.     

UNCD electron emitters using Si nanostructure as a template

The electron field emission (EFE) properties of silicon nanostructures (SiNSs) coated with ultra-nanocrystalline diamond (UNCD) were characterized. The SiNS, comprising cauliflower-like grainy structure and nanorods, was generated by reaction of a Si substrate with an Au film at 1000 °C, and used as templates to grow UNCD. The UNCD films were deposited by microwave plasma-enhanced chemical vapour deposition (MPECVD) using methane and argon as reaction gases. The UNCD films can be grown on the SiNS with or without ultrasonication pretreatment with diamond particles. The EFE properties of the SiNS were improved by adding an UNCD film. The turn-on field (E₀) decreased from 17.6 V/μm for the SiNS to 15.2 V/μm for the UNCD/SiNS, and the emission current density increased from 0.095 to 3.8 mA/cm² at an electric field of 40 V/μm. Ultrasonication pretreatments of SiNS with diamond particles varied the structure and EFE properties of the UNCD/SiNS. It is shown that the ultrasonication pretreatment degraded the field emission properties of the UNCD/SiNS in this study.     

Cerium oxide dispersed multi walled carbon nanotubes as cathode material for flexible field emitters

Nanomaterials based electron sources are omnipresent in modern flat panel displays. Multi walled carbon nanotubes (MWNT) are the well studied electron emitter among the carbon materials. Since the surface modification of MWNT with low work function materials would have a positive impact on the field emission property of MWNT, cerium oxide (CeO2) nanoparticles dispersed multi walled carbon nanotubes (CeO2/MWNT) were synthesized by catalytic chemical vapour deposition followed by chemical reduction and its field emission property was investigated. The high-purity MWNT as well as CeO2/MWNT showed crystalline structure conformed by X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Further characterisation was done with Raman spectroscopy, UV-Visible absorption spectra and Fourier transform IR spectroscopy (FT-IR). The morphology and structural details of CeO2/MWNT composite was probed by field-emission scanning electron microscopy (FESEM) and energy dispersive X-ray analysis (EDX). The direct evidence of the formation of CeO2/MWNT composites was given by transmission electron microscopy (TEM). The synthesized sample was coated over a flexible carbon paper using spin coating technique. The experiment was performed under a vacuum of 1 x 10(-6) Torr and Fowler-Nordheim equation was used to analyse the data. The turn-on voltage for the cerium oxide dispersed MWNT was found for a current density of 10 microA/cm2. The emission current density from the CeO2 nanoparticles dispersed MWNT reached 0.2 mA/cm2 at a reasonable bias field of 2.58 V/microm. The results were compared with those of pure MWNT and pure CeO2 nanoparticles with literature values.