硅纳米线尖端阵列的制备及其场发射性能研究

将银镜反应与金属催化化学刻蚀相结合,在室温附近成功地制备出了硅纳米线尖端阵列,其长度为4~7μm,中间部分的直径在100~300nm之间。该方法操作简单、高效、无毒、可控以及低成本,且不需要高温、复杂的设备,对环境也没有特殊要求。性能测试结果显示:该硅纳米材料能够有效实现电子发射,开启电场约为2.7V/μm(电流密度10μA/cm2处);硅纳米尖端阵列的场增强因子约为692,可应用在场发射器件之上。     

Controlling SERS intensity by tuning the size and height of a silver nanoparticle array

It is demonstrated that the surface-enhanced Raman scattering (SERS) intensity of R6G molecules adsorbed on a Ag nanoparticle array can be controlled by tuning the size and height of the nanoparticles. A firm Ag nanoparticle array was fabricated on glass substrate by using nanosphere lithography (NSL) combined with reactive ion etching (RIE). Different sizes of Ag nanoparticles were fabricated with seed polystyrene nanospheres ranging from 430 nm to 820 nm in diameter. By depositing different thicknesses of Ag film and lifting off nanospheres from the surface of the substrate, the height of the Ag nanoparticles can be tuned. It is observed that the SERS enhancement factor will increase when the size of the Ag nanoparticles decreases and the deposition thickness of the Ag film increases. An enhancement factor as high as 2×10⁶ can be achieved when the size of the polystyrene nanospheres is 430 nm in diameter and the height of the Ag nanoparticles is 96 nm. By using a confocal Raman mapping technique, we also demonstrate that the intensity of Raman scattering is enhanced due to the local surface plasmon resonance (LSPR) occurring in the Ag nanoparticle array.     

Microlens arrays etched into glass and silicon

Microlens arrays fabricated by melting photoresist were transferred by reactive ion etching (RIE) into glass (SiO₂) and silicon (Si). By controlling the etching rates of the mask and the substrate material, radii of curvature and focal lengths within a wide range can be achieved. For example, glass lenses with diameter 120 μm and focal lengths between 500 μm and 1500 μm were made. The scaling possibilities of microlens arrays, given the use of RIE, are discussed.     

刻蚀AlN缓冲层对硅衬底N极性n-GaN表面粗化的影响

研究了等离子体刻蚀AlN缓冲层对硅衬底N极性n-GaN表面粗化行为的影响. 实验结果表明, 表面AlN缓冲层的状态对N极性n-GaN的粗化行为影响很大, 采用等离子体刻蚀去除一部分表面AlN缓冲层即可以有效提高N极性n-GaN在KOH溶液中的粗化效果, AlN缓冲层未经任何刻蚀处理的样品粗化速度过慢, 被刻蚀完全去除AlN缓冲层的样品容易出现粗化过头的现象. 经X射线光电子能谱分析可知, 等离子体刻蚀能够提高样品表面AlN缓冲层Al 2p的电子结合能, 使得样品表面费米能级向导带底靠近, 原子含量测试表明样品表面产生了大量的N空位, N空位提供电子, 使得材料表面费米能级升高, 这降低了KOH溶液和样品表面之间的肖特基势垒, 从而有利于表面粗化的进行. 通过等离子体刻蚀掉表面部分AlN缓冲层, 改善了N极性n-GaN在KOH溶液中的粗化效果, 明显提升了对应发光二级管器件的出光功率.     

Microstructure array on Si and SiOx generated by micro-contact printing, wet chemical etching and reactive ion etching

A method, combining micro-contact printing (μCP), wet chemical etching and reactive ion etching (RIE), is reported to fabricate microstructures on Si and SiOx. Positive and negative structures were generated based on different stamps used for μCP. The reproducibility of the obtained microstructures shows the methodology reported herein could be useful in Micro-Electro-Mechanical Systems (MEMS), optical and biological sensing applications.     

基于直接胶体晶体刻蚀技术的高度有序纳米硅阵列的尺寸及形貌控制

以自组装单层胶体小球阵列为掩模，采用直接胶体晶体刻蚀技术在硅表面制备二维有序尺寸可控的纳米结构.在样品制备过程中，首先通过自组装法在硅表面制备了直径200nm的单层聚苯乙烯(PS)胶体小球的二维有序阵列；然后对样品直接进行反应离子刻蚀(RIE)，以氧气为气源，利用氧等离子体对聚苯乙烯小球和对硅的选择性刻蚀作用，通过改变刻蚀时间，制备出不同尺寸的PS胶体小球的有序单层阵列；接着以此二维PS胶体单层膜为掩模，以四氟化碳为气源对样品进行刻蚀；最后去除胶体球后得到二维有序的硅柱阵列.SEM和AFM的测量结果表明：改变氧等离子体对胶体球的刻蚀时间和四氟化碳对硅的刻蚀时间，可以控制硅柱的尺寸以及形貌，而硅柱阵列的周期取决于原始胶体球的直径. 关键词： 胶体晶体刻蚀 纳米硅柱阵列     

Au诱导形成有序Si纳米孔阵列及其应用

以自组装聚苯乙烯小球(PS)单层膜为掩膜,利用Au对Si表面的催化氧化作用以及KOH溶液对单晶Si的各向异性腐蚀特性,在Si(100)面上制备了一系列尺寸小于100 nm有序可控的Si纳米孔阵列.扫描电镜(SEM)和原子力显微镜(AFM)等的测试结果显示:当PS小球溶液与甲醇溶液的体积比为9:11时,可形成大面积无缺陷的单层膜;但当体积比过大时,会导致类似双层膜结构的形成;而当体积比过小时,会诱导形成点缺陷和线缺陷.对PS小球及溅射Au处理过的Si晶片进行KOH溶液腐蚀,随着腐蚀时间变长,纳米孔的横向尺寸和深度增大,其形貌由圆形逐渐变为倒金字塔型,当腐蚀时间超过10 min,纳米孔阵列的有序性遭到破坏.采用离子束溅射技术在倒金字塔型纳米孔衬底上获得了有序Ge/Si纳米岛,而在圆形纳米孔衬底上获得了有序Ge/Si纳米环.进一步对有序Ge/Si纳米岛及纳米环的形成机理进行了解释.     

Fabrication of high-aspect-ratio silicon nanopillar arrays with the conventional reactive ion etching technique

We fabricate silicon nanopillar arrays with pillar diameters smaller than 200 nm by using the conventional reactive ion etching (RIE) technique and nickel masks. We use the ratio between the lateral and vertical etching rates as an estimate of the etching anisotropy. The dependence of this ratio on the rf power, the chamber pressure, and the gas mixture is investigated systematically to achieve the largest etching anisotropy. Using the optimized etching parameters in the RIE process, we demonstrate silicon pillars with smooth surface, vertical sidewalls, and aspect ratios higher than 20. In addition, we employ dilute aqua regia to treat the pillars and shrink the diameters to 70 nm. The pillar height remains ∼2500 nm after the treatment. PACS 52.77.Bn; 81.65.Cf; 85.40.Hp     

Aluminum-enhanced sharpening of silicon nanocones

Here we report on the fabrication of high-density aligned Si nanotip arrays by chemical vapor deposition followed by dry oxidation and an etching treatment. The dry oxidation investigations indicated that Al-catalyst particles located at the tip of Si nanocones enhance their sharpening. This oxidation behavior is quite different from that of Au-catalyzed Si nanowires and is more favorable to form very sharp Si nanotips. Field emission from an individual Si nanotip showed good field-emission characteristic with a high emission current density of 1×10⁴ A/cm² because of its sharp tip geography, suggesting their potential application for field emitters. Our work provides an effective approach to fabricate high-density Si nanotip arrays, which overcomes some problems in the conventional fabrication approaches, such as high cost, poor controllability, and complicated process.     

氧等离子体处理对GaAs表面单层自组装SiO2纳米球薄膜的影响

二维纳米阵列结构因其重要的光学性能被广泛应用于各类光电子器件。本文对自组装单层SiO2纳米球掩模刻蚀法制备GaAs纳米柱二维阵列结构的关键工艺技术进行了研究。采用旋涂法在GaAs表面制备自组装单层SiO2纳米球,重点研究了GaAs表面氧等离子体亲水处理工艺对纳米球排列特性的影响,获得最佳工艺条件为功率配比100 W+80 W、腔室压力4 Pa、氧气流量20 mL/min、处理时间1200 s,并最终得到排列紧密的大面积单层纳米球薄膜。以单层纳米球为掩模,采用感应耦合等离子体刻蚀技术在GaAs表面制备了纳米柱阵列并测试了其表面光反射谱。测试结果表明,GaAs纳米柱阵列在特定波段的反射率降低至5%,远低于表面无纳米结构的薄膜材料表面高达40%的光反射。分析表明纳米柱可以激发米氏散射共振效应,从而有效降低反射率并提升光吸收。     

Site selective growth of Ge quantum dots on AFM-patterned Si substrates

By combining the atomic force microscope (AFM) local anodic oxidation and etching, a periodic array of nanodimples of 40 nm in diameter and 3.5 nm in depth has been made on a Si surface. Ge atoms deposited onto this patterned substrate by the MBE method nucleate preferentially in the dimples and form an array of nano Ge dots of about 50 nm in diameter and 10 nm in height.     

Spontaneous evolution of nanotips on silicon surface below the laser ablation threshold

A low power density single-pulse laser irradiation of the Si surface has been used for the study of formation and self-organization of silicon nanotips. A two dimensional regular array of hillock-like nanotips has been created in the central region, a disturbed array comprising crossed lines of hillocks in the near-central region, and the “V”-shaped array in the peripheral region. Therefore, the long-range organization of hillocks changes from the center toward the periphery, following the Gaussian-like laser power profile. The evolution of hillocks due to the flow instability of molten silicon is equivalent to the instability of a liquid layer falling down a vertical plate. The novel result is that the hillock-like soliton structures can be identified with the lump solitons resulting from the nonlinear hydrodynamic instability evolution.     

Design,optimization and fabrication of 2D photonic crystals for solar cells

This paper presents the optimization of 2D photonic crystals (PCs) onto Si wafers to improve the performance of c-Si PV cells. The objective is to find a structure capable of minimizing the reflectance of the Si wafer in the spectral range between 400 nm and 1000 nm. The study has been limited to PCs that can be fabricated and characterized with the tools and technology available and to dimensions in the same order as the visible light wavelength. PCs with different shapes and dimensions have been simulated and finally the optimum structure has been fabricated by a process based on laser interference lithography (LIL) and reactive ion etching (RIE). This optimized PC presents an average reflectance of 3.6% in the selected wavelength range, without any other material used as antireflective coating. This result means a drastic reduction in comparison with reflectance obtained out of the standard wet etch texturization used in current solar cell manufacturing lines.     

Reactive ion etching of FePt using inductively coupled plasma

We propose a reactive ion etching (RIE) process of an L1₀-FePt film which is expected as one of the promising materials for the perpendicular magnetic recording media. The etching was carried out using an inductively coupled plasma (ICP) RIE system and an etching gas combination of CH₄/O₂/NH₃ was employed. The L1₀-FePt films were deposited on (1 0 0)-oriented MgO substrates using a magnetron sputtering system. The etching masks of Ti were patterned on the FePt films lithographically. The etch rates of ∼16 and ∼0 nm/min were obtained for the FePt film and the Ti mask, respectively. The atomic force microscopy (AFM) analyses provided the average roughness (R_a) value of 0.95 nm for the etched FePt surface, that is, a very flat etched surface was obtained. Those results show that the highly selective RIE process of L1₀-FePt was successfully realized in the present study.     

场发射冷阴极微栅孔阵列制备技术

实现了一种采用聚苯乙烯纳米球自组装技术和微机械制造技术加工的场发射阴极用亚微米栅极微孔阵列。设计了一套完整的工艺实验方案,首先采用微球自组装技术获得了亚微米级金属网孔掩膜,然后通过反应离子刻蚀技术获得了亚微米栅极孔阵列,从而实现了集成度高、分布均匀的周期性亚微米孔洞阵列的制备,微孔集成度达到108cm-2。实验研究了氧气刻蚀聚苯乙烯微球的规律。采用金属掩膜,四氟化碳干法刻蚀二氧化硅,获得了深度为500 nm的微孔。实验结果证明该工艺方案是一种获得大面积、均匀分布、集成度高的场发射冷阴极栅孔阵列的有效方法。     

大高宽比纳米硅立柱的感应耦合等离子体刻蚀工艺优化

针对氢基硅倍半氧烷(hydrogen silsesquioxane,HSQ)作为深反应离子刻蚀(DRIE)掩膜形成大高宽比纳米硅立柱的工艺进行了系统研究。优化了刻蚀工艺中线圈功率、极板功率和气体流量参数,减小了横向刻蚀,使形貌垂直性得到了更好的控制,并实现了13.3 m高度和低侧壁粗糙度的垂直硅纳米柱阵列,其高宽比（高度/半高宽）达到了36。利用不同的刻蚀工艺条件得到了不同侧壁形貌以及不同尺寸、高度的硅纳米柱结构。     

Frequency selective IR-filter produced by using EB-lithography

This paper reports on the fabrication of Jerusalem cross diplexer by direct write electron beam (EB) lithography followed by reactive ion etching (RIE) on a phosphorus doped polished silicon wafer substrate. Such structures can be used as frequency selective components in visible, microwave and near infra-red wavelength region. Replication of the patterns is accomplished by micron or sub-micron order mould fabricated from the silicon (Si) master. Fourier transform infra-red reflectance (FT-IR) measurements were performed to characterize the structured patterns. The spectral reflectance from these patterns clearly show a reflection dip due to surface plasmon excitation in the near infra-red wavelength at about 1.42 and 2.5 μm, respectively. Potential applications such as antireflection surface (ARS) can be realized.     

Transport properties of nanoperforated Nb thin films

Porous silicon, obtained by electrochemical etching, has been used as a substrate for the growth of nanoperforated Nb thin films. The films, deposited by UHV magnetron sputtering, inherited from the Si substrates their structure, made of holes of 10 nm diameter and of 20 and 40 nm spacing, which provide an artificial pinning lattice. Commensurability effects between the Abrikosov vortex lattice and the artificial array of holes were investigated by transport measurements.     

Highly efficient field emission from nanodiamond films treated by fast reactive ion etching process

A fast reactive ion etching (RIE) treatment method is presented for dramatic enhancement of the field emission performances of nanocrystalline diamond (NCD) films. In this method a moment RIE treatment is able to modify the surface morphologies of NCD films and form a large area of nanoneedle-like arrays on the NCD films, in which the diamond nanoparticles were seeded on the film to serve as an etching mask. These elaborated diamond nanoneedle-like structures showed good uniformity and dense morphology with a controllable aspect ratio and distribution density and thereby significantly increased the electron field emission properties of the NCD films due to the formation of more emitting tips and enhanced field enhancement factor.     

Large-area micro/nanostructures fabrication in quartz by laser interference lithography and dry etching

Laser interference lithography (LIL) has the capability to fabricate large-area microstructures on the photoresist with only a couple of minutes’ exposure and development. In this study, LIL was adopted to fabricate micro/nanostructures in quartz by combining the following dry-etching process either reactive ion etching (RIE) or inductively coupled plasma (ICP). A layer of gold film was coated on the quartz to act as a hard mask during the dry-etching process. A microhole array in quartz with a thin gold film covered on the surface was fabricated when choosing RIE. Each hole in the microhole array was surrounded with gold nanoparticle capped silica (Au/SiO₂) cones when using ICP instead of RIE. This is due to the thin gold film that serves as the mask for creating the surface roughness required for creating the silica cone structure.