Photoluminescence of Si-based nanotips fabricated by anodic aluminum oxide template

Large-area, high-density silicon-based nanotips were fabricated using electrochemical lithography. The morphology and optical properties of the samples were characterized by atomic force microscopy and photoluminescence. The distribution and size of the silicon-based nanotips were uniform. Two photoluminescence peaks were observed at 585 and 620 nm. The peak centered at 585 nm exhibited a narrow full-width at half maximum. No evident peak energy shift was observed when the measurement temperature was increased from 10 K to room temperature, which suggested that the photoluminescence should be attributed to the interface states and/or defects in the silicon-based nanotips.     

Tip-enhanced strong-field photoemission

Nonlinear photoelectron emission from metallic nanotips is explored in the strong-field regime. The passage between the multiphoton and the optical field emission regimes is clearly identified. The experimental observations are in agreement with a quantum mechanical strong-field model.     

a-C:N:H纳米尖端荧光产生的机理

用CH4,H2和NH3为反应气体,利用等离子体增强热丝化学气相沉积在沉积有碳膜的Si衬底上制备了a-C:N:H纳米尖端,并用扫描电子显微镜和微区Raman光谱仪对碳膜和纳米尖端进行了表征。结果表明:Raman谱中含有与碳和氮相关的峰,且纳米尖端的Raman谱比碳膜的Raman谱有很强的荧光背景。Raman谱中的峰说明沉积的碳膜和纳米尖端是a-C:N:H薄膜和a-C:N:H尖端。a-C:N:H纳米尖端的Raman谱中强荧光背景的产生表明其在激发光源照射的过程中发射了强荧光,对a-C:N:H纳米尖端产生强荧光的机理进行了探讨。     

Silicon nanotips formed by self-assembled Au nanoparticle mask

The Au nanoparticle monolayer is formed by self-assembly technology on the Si substrates terminated with different functional groups. Silicon nanotips were fabricated by a self-assembled gold colloidal particle monolayer as an etch mask. The silicon nanotips with high density and uniformity in height and shape were obtained using reactive ion etching (RIE). The Si nanotips on the surface of the 3-aminopropyltrimethoxysilane (APTMS)-treated Si substrate are less-ordered array and uniformity than 3-mercaptopropyltrimethoxysilane (MPTMS)-treated Si substrate at the same etching conditions. The ordered array and uniformity of Si nanotips on the APTMS-modified Si substrate was improved through heat-treatment. This result is implied the different functional groups on the Si surfaces could affect the formation of the Si nanostructures during RIE process. The uniformly nanotip pattern with height of >20 nm is obtained on the etched nanoparticle-coated Si substrate. This method can be applied to patterning a wide variety of thin film materials into tip arrays.     

Reference layer exchange in spin transfer torque experiment using magnetic-coated nanometric point contacts

We investigate the importance of using nanotips on a point contact spin-transfer torque (STT) experiment. A systematic analysis comparing the STT in a magnetic thin film in current-perpendicular-to-plane (CPP) geometry sample for magnetic coated and uncoated tungsten nanotips is shown. The STT effect presents a reverse resistance to current behavior when using a magnetic coating layer on the nanotips. We demonstrate that the magnetic layer on the tip may assume the role of a polarizer layer. This effect opens up the possibility of exploiting simpler architectures in STT-based devices, such as STT-random access memory (STT-RAM).     

非晶碳氮纳米尖端的微结构和发光机理

利用等离子体增强热丝化学气相沉积系统,用CH₄、H₂和N₂为反应气体,在Si衬底上制备了碳氮纳米尖端。用扫描电子显微镜和显微Raman光谱仪对其进行了表征。在室温下测试了它的发光性能,发光谱由中心约为406 nm和506 nm的两条发光带组成。根据Raman散射谱,对其微结构进行了分析。结合非晶碳氮薄膜的结构和发光机理,分析了它的发光性能。     

等离子体增强热丝CVD生长碳纳米尖端的研究

用CH₄，NH₃和H₂为反应气体，利用等离子体增强热丝化学气相沉积系统在不同偏压电流的条件下制备了碳纳米尖端，并用扫描电子显微镜和显微Raman光谱仪对碳纳米尖端进行了研究.结果表明碳纳米尖端是石墨结构，随着偏压电流的增大，碳纳米尖端的顶角减小，生长速率增大.结合有关等离子体和溅射的理论，分析讨论了碳纳米尖端的形成和碳纳米尖端的生长随偏压电流的变化. 关键词： 碳纳米尖端 等离子体 化学气相沉积     

Study on formation and shape of carbon nanotips depending on ion bombardment

Carbon nanotips were grown from carbon film deposited on silicon substrate by plasma-enhanced hot filament chemical vapor deposition. The carbon film and carbon nanotips were investigated by scanning electron microscopy and micro-Raman spectrometry, respectively. The results indicate that the carbon film is composed of amorphous carbon and the carbon nanotips are characteristic of nanographite, and their formation and shapes depend on ion bombardment strongly. Simultaneously, the number of forming the carbon nanotips is increased by the ion bombardment. Because there are ion deposition and sputtering-etching in the process of growing of the carbon nanotips, the theory related to ion deposition and sputtering was used to obtain their formation condition and analyze effects of the ion bombardment on their shapes and the number of forming them.     

Magnetic nanotips: the realisation of an atomic-scale beam-splitter

We present the first realisation of ferromagnetic Fe nanotips. Studies of the field emitted beams of electrons and metallic ions above and under the Curie temperature T_c were made. We have observed a reversible splitting of the electron beams when the temperature crossed through T_c and multiple spot patterns for the emitted metallic ion beams. These phenomena were not observed with Fe microtips or non-magnetic nanotips and thus were correlated to a strong magnetic interaction at the atomic scale apex of the nanotips. The Fe nanotips constitute an atomic scale beam-splitter.     

Nanotips: Growth,Model, and Applications

The tip morphology in the nanoscale is discussed as a member of the one-dimensional nanostructure family. Different growth techniques used for the synthesis of the nanotips have been outlined and compared against each other including, etching, pyrolysis, physical, and chemical vapour deposition. Growth models for hollow and solid nanotips are compared and discussed in detail with a thrust on the ‘cone-helix’ model for the hollow tips and the ‘platelet stacking’ model for the solid tips. Application of the nanotips in field emission, scanning probe microscopy, sensing, anti-reflection, and nanoindentation is discussed.     

Influence of nanotips on the hydrophilicity of metallic nanorod surfaces

The hydrophilicity of vertically aligned metal nanorods with sharp nanotips were investigated experimentally. Ruthenium and platinum nanorod arrays were deposited on flat silicon substrates using oblique angle sputter deposition. We show that the effects of nanotips on nanorods should be considered in the "hemiwicking" model for hydrophilic metallic samples. With the influence of nanotips, we successfully explained the experimental contact angles of water sessile drops on metallic nanorod surfaces. Our experiments confirm that the shape of the nanorods is an important parameter in determining the hydrophilicity of the nanostructured surfaces.     

组合光调制中矢量分析方法

一般文献对光调制的分析方法为矩阵分析法,本文提出用矢量分析的新方法,并用此方法详细分析了电光调制和磁光调制的组合光调制中输出光强信号,得出了与矩阵方法一样的结果。     

Single-atom coherent field electron emitters for practical application to electron microscopy: Buildup controllability, self-repairing function and demountable characteristic

We have fabricated single-atom field emission (FE) tips by annealing Rh-deposited W tips at 900 K, and the FE characteristics were investigated. Due to the formation of the nanotips, the electron beams were confined in a semi-cone angle of 3°, an indication quite different from the conventional FE beams. In repairing-function test where the FE nanotips were intentionally destroyed beforehand, they recovered the peculiar FE characteristics by means of feasible low temperature annealing. Finally, we found that the present nanotips equipped the capability of recovering the unique FE properties even after an exposure to the air. These characteristics are significantly relevant to the practical applications to electron-optics instruments.     

Electron beam nanofabrication of ferromagnetic nanostructures in TEM

Electron beam (e-beam) fabrication of nanostructures by transmission electron microscopy (TEM) is rapidly developing into a top-down nanofabrication method for the sub-5 nm fabrication of structures that cannot usually be realised using resist based lithographic techniques or by the focused ion beam patterning methods. We describe the usage of a variety of e-beam shapes, including point and elliptical line focus, as well as a comparison of LaB₆ and field-emission guns (FEGs), to achieve versatile sculpting of nanodot arrays, nanobridges and nanotips. We operate our patterning on free-standing nickel (Ni) thin film laterally connected to a silicon (Si) substrate as well as to free-standing Ni nanotips, where we achieve a novel three-dimensional (3D) nano-sculpting methodology.     

Measurement of modulation index and half-wave voltage of an electro-optical phase modulator with a dispersion-based phase filter

In this paper, a novel method based on the use of an optical phase filter is proposed to evaluate the modulation index, as well as the half-wave voltage of an optical phase modulator. When a phase modulated signal propagates along the length of a dispersive fiber, the fiber dispersion acts as an optical phase filter and spectrally alters the relative phasing of the phase modulated signal, causing the phase modulation to become intensity modulation, which allows the swept frequency measurement of phase modulators by using a vector network analyzer. The modulation index and half-wave voltage as a function of the modulation frequency are experimentally measured for a commercial phase modulator, which agree well with the results obtained using the widely accepted optical spectrum analysis method. The proposed method requires only a length of dispersive fiber and works without any small-signal approximation, which is applicable for different driving levels and operating wavelengths with the same setup.     

多阶光存储的调制原理分析与编码设计研究

根据编码理论的状态切分算法，提出一种新型的8阶(1,3)游程长度受限码，在最小记录符上能够存储3.0比特的用户数据，并且编码与译码逻辑简明，可用于未来高密度多阶游程长度调制光盘系统.     

频移键控无线光通信系统的Optisystem实验仿真

调制技术是无线激光通信中的关键技术之一.目前国内外无线激光通信所采用的调制方式多为强度调制或相位调制.对研究较少的频率调制系统进行了研究,分析了多普勒效应对系统的影响,借鉴光纤通信领域的最新研究成果提出了高速频移键控(FSK)无线光通信系统的方案设计,并使用Optisystem软件实现系统仿真,对激光器线宽、滤波器带宽...     

Structurally induced FEES from nanotips: implications for scanning tunneling spectroscopy

Recent theoretical studies and experimental data show the existence of energy levels at the apex atom of nanotips. We report here experimental measurements, by field emission electron spectroscopy (FEES), of strong modifications of the local density of states for varying atomic configurations of the nanotips. The local density of states specific to each protrusion must then be considered in interpreting scanning tunneling microscopy and scanning tunneling spectroscopy experiments with atomic resolution instead of the commonly used free-electron model.     

Frequency-dependent optical pumping in atomic ?-systems

We consider the effects of optical pumping on the conversion of laser-frequency modulation into intensity modulation by an atomic absorption line in a vapor of alkali atoms driven in a ?-configuration. It is found that, due to optical pumping in combination with the excited-state hyperfine structure, the absorption line shape is distorted substantially as the Fourier frequency of the FM is changed. The most significant effect of the distortion is a shift of the apparent line center, which depends on how the frequency of the modulation compares with the optical pumping rate. This shift has implications for locking lasers to atomic transitions and also for FM-AM noise conversion in atomic vapors.     

基于综合光学调制技术的光纤无线双向通信系统设计

提出并研究了一种使用单光源的光纤无线双向传输系统.该系统只需在中心站配置一个可调谐激光器,以产生频率恒定的激光光源,通过综合光学调制（频率调制、强度调制）技术将基带信号调制到光载波上,最终形成60 GHz毫米波下行信号|同时,相同的光载波在基站被重用,作为上行链路传输光源.系统结合光载波重用技术和综合调制技术特点,合理利用资源,基站结构更为简化.仿真结果表明,该系统可以将速率达2.5 Gbit/s的数据在单模光纤中双向传输20 km,功率代价小于0.5 dB,相对已有的技术方案,该传输系统在传输功率、传输距离、传输性能方面具有明显优势.