Fabrication of nanostructure on a polymer film using atomic force microscope

SPM based lithographic techniques have been developed to pattern various substrates such as metals, semiconductors, and organic/polymer films due to its simplicity and high spatial precision nanostructure. Fabrication of nanostructure using polymeric materials is a key technique for the development of nanodevices. Here, we report the fabrication of nanostructures from polyacrylicacid (PAA) and polymethacrylicacid (PMAA) film on a silicon substrate using atomic force microscope (AFM). The formation of the nanopattern from the polymer film was studied using electrostatic nanolithography and the optimization of the conditions for nanopatterning of the polymer film was investigated with respect to the applied potential and translational speed of the AFM tip. The nanostructure of size 28 nm was created using the biased AFM tip on the PMAA film coated on Si(100) substrate and found that this method is a direct and reliable method to produce uniform nanostructures on a polymer film.     

基于AFM氮化硅探针刻蚀方法制作聚碳酸酯纳米光栅

基于原子力显微镜(AFM)探针的纳米机械刻蚀技术以其成本低、分辨率高的优势被广泛应用于各种纳米元器件的制造中.为了得到最优的光栅结构,首先通过单次刻蚀实验定量分析了刻蚀方向、加载力和刻蚀速率等3个主要加工参数对所得纳米沟槽形貌和尺寸的影响,给出了普通氮化硅探针对聚碳酸酯(PC)的加工特性及加工效率.然后通过改变沟槽间距(100~500 nm)得到了不同周期的纳米光栅结构,并确定了这种探针与样品的组合对间距的要求及最佳加工参数:沿垂直于微悬臂长轴向右刻蚀,加载力2.3μN,刻蚀速率2.6μm/s.最后利用该技术对实验室已有原子光刻技术所得周期为213 nm的一维Cr原子光栅结构进行了复制加工,得到了均匀的213 nm一维光栅,证明这种基于AFM探针的纳米机械刻蚀技术可被广泛应用于纳米加工.     

A novel tip-induced local electrical decomposition method for thin GeO films nanostructuring

Decomposition of germanium monoxide (GeO) films under the impact of an atomic force microscope (AFM) tip was observed for the first time. It is known that GeO is metastable in the solid phase and decomposes into Ge and GeO(2) under thermal annealing or radiation impact. AFM tip treatments allow us to carry out local decomposition. A novel tip-induced local electrical decomposition (TILED) method of metastable GeO films has been developed. Using?TILED of 10?nm thin GeO film, Ge nanowires on silicon substrates were obtained.     

AFM针尖耦合激光加工PMMA薄膜的加工重复性

利用飞秒激光与原子力显微镜的针尖部分耦合进行加工,是有望突破衍射极限,实现多隧道结加工的技术。本文在室温大气环境下,利用微焦级别脉宽为130fs、波长800nm的飞秒激光照射镀有金薄膜的原子力显微镜的探针针尖,使其耦合产生局域场加强效应在PMMA薄膜表面加工出光栅状纳米图形。通过最大残差法计算了条纹高度和宽度的重复性百分比,计算得到高度和宽度的最大残差值分别为6.3%和2.9%。结果表明在文中所提供的加工条件下,原子力显微镜针尖耦合激光是一种有潜力的激光加工方法。     

Two methods to prepare nanorings/nanoholes for the fabrication of vertical nanotransistors

A self-assembled monolayer of polystyrene (PS) beads is formed on a silicon wafer by spin-coating. After drying at 80?°C, a thin film of metal/oxide is deposited. During the deposition, the PS beads are detached due to forces such as the inner stress induced by plasma sputtering deposition, mechanical vibration, and centrifugal shearing induced by substrate rotation, resulting in nanoring/nanohole formation. Further experiments demonstrate that the PS?detachment can be controlled by scanning probe microscopy (SPM) tip manipulation. We believe this is a promising set of processes for fabricating nanodevice structures such as those of vertical nanotransistors, which provides high flexibility for nanocrystal characterizations and application for single-electron devices.     

小型微纳米图形电子束曝光制作系统(英文)

为了满足科学实验过程中对制作半导体器件和微纳米结构的需要,同时避免受到昂贵的工业级电子束曝光(electron beam lithography,EBL)机的条件制约,构建了一种基于普通扫描电子显微镜(scanning electron microsco-py,SEM)的桌面级小型电子束曝光系统.建立了以浮点DSP为控制核心的高速图形发生器硬件系统.利用线性计算方法实现了电子束曝光场的增益、旋转和位移的校正算法.在本曝光系统中应用了新型压电陶瓷电机驱动的精密位移台来实现纳米级定位.利用此位移台所具有的纳米定位能力,采用标记追逐法实现了电子束曝光场尺寸和形状的校准.电子束曝光实验结果表明,场拼接及套刻精度误差小于100 nm.为了测试曝光分辨率,在PMMA抗蚀剂上完成了宽度为30 nm的密集线条曝光实验.利用此系统,在负胶SU8和双层PMMA胶表面进行了曝光实验;并通过电子束拼接和套刻工艺实现了氮化物相变存储器微电极的电子束曝光工艺.     

Combined AFM nano-machining and reactive ion etching to fabricate high aspect ratio structures

In this paper, a new combined method of sub-micron high aspect ratio structure fabrication is developed which can be used for production of nano imprint template. The process includes atomic force microscope (AFM) scratch nano-machining and reactive ion etching (RIE) fabrication. First, 40 nm aluminum film was deposited on the silicon substrate by magnetron sputtering, and then sub-micron grooves were fabricated on the aluminum film by nano scratch using AFM diamond tip. As aluminum film is a good mask for etching silicon, high aspect ratio structures were finally fabricated by RIE process. The fabricated structures were studied by SEM, which shows that the grooves are about 400 nm in width and 5 microm in depth. To obtain sub-micron scale groove structures on the aluminum film, experiments of nanomachining on aluminum films under various machining conditions were conducted. The depths of the grooves fabricated using different scratch loads were also studied by the AFM. The result shows that the material properties of the film/substrate are elastic-plastic following nearly a bilinear law with isotropic strain hardening. Combined AFM nanomachining and RIE process provides a relative lower cost nano fabrication technique than traditional e-beam lithography, and it has a good prospect in nano imprint template fabrication.     

Optimization of zero-reference grating considering tip distortions for scanning probe microscopy drift measurement

A nonperiodic grating composed of unevenly distributed step elements on a flat substrate can serve as the calibration grating for scanning probe microscopy (SPM) drift measurements. The grating named zero-reference grating (ZRG) is characterized by the number of step elements t, the number of total grating elements n and the maximum correlation peak contrast D. To optimize the ZRG structures considering tip distortions in SPM images, mathematical morphology and genetic algorithms are adopted. Results show that the optimal step elements tend to distribute orderly under the influence of large tip radius and the contrast D decreases with the increase of tip radius when t < or = n/2. On the contrary, the optimal ZRG structures and the contrast D are insensitive to tip distortions when t > n/2. These differences can be interpreted by the effective code mechanism due to tip dilation. For quantitative drift measurements, the parameter t is suggested to be larger than n/2 since the performances of such optimal ZRGs are more robust to tip distortions.     

Fabrication of ferromagnetic nanoconstriction using atomic force microscopy nanoscratching

Nanolithography used in conjunction with atomic force microscopy (AFM) has attracted considerable attention as a technique for fabricating nanoscale structures. To obtain nanostructures and devices, AFM nanoscratching was performed on a photoresist and on NiFe at various values of the applied force, scan speed, and number of scan cycles. The scratching process was carried out using a diamond-coated tip on NiFe and a Si tip on the photoresist. By conducting scratching processes on NiFe and on the photoresist, we investigated the dependence of the size of the scratched part on the scratching parameters. These results show that the width and depth of the scratched part increase as the applied force and number of scan cycles increase, but not as the scan speed increases. This means that it is possible to control the size of the scratched parts by adjusting the applied force and number of scan cycles. AFM nanoscratching was then used to directly fabricate a nanoconstricted area with a width of 139 nm and a cross-sectional area of less than 300 nm2 was fabricated.     

相位扫描法制作变栅距光栅

提出了一种制作变栅距(VLS)光栅的相位扫描方法。该方法的主要装置包括一个用于控制刻划机运动的光栅干涉仪和一个相位扫描机构。如果调整光栅干涉仪,保证接收场中只有两条干涉条纹,然后改变用于对条纹进行计数的光电传感器的位置,就可以刻划出具有变栅距的刻槽。对光电式光栅刻划机的控制系统和结构都做了详细论述。按照上述方法成功刻划出了试验性的VLS光栅,它的最小栅距增量为0.33nm,并对在制作过程中产生的误差进行了讨论。采用测量衍射角的方法进行了栅距检测试验,由变栅距光栅和等栅距光栅作出的拟合曲线表明:相位扫描方法是加工具有亚纳米栅距增量的VLS光栅的有效方法,该方法对超精密定位也具有借鉴作用。     

Single-step electropolymerization patterning of a polypyrrole nanowire by ultra-short pulses via an AFM cantilever

Conducting polymers (CPs) have attracted a great deal of attention due to their unique properties; these properties are useful in implementing various functional devices, such as memory, and chemical and biological sensors. In particular, the nanopatterning of CPs is a key technology that will accelerate the adoption of CPs in fabricating nanoscaled multifunctional devices. This paper presents an innovative technique for forming polypyrrole nanowire (PPy-NW) patterns, without any additional pretreatment on the gold surface, using atomic force microscopy (AFM) and ultra-short pulse voltage. Applying the ultra-short pulse voltage to the AFM tip has the following advantage: since the electrochemical current is extremely localized around the tip, the successful formation of CP nanowires results. This is because the pulse width is much shorter than the resistor-capacitor (RC) time constant of the equivalent electrochemical circuit of our experimental set-up. This paper provides systematic results regarding the dimensional variation of the PPy-NW patterns produced by varying the electrical conditions of the ultra-short pulse, such as the pulse amplitude, width, and frequency. The results show that use of an ultra-short pulse is essential in fabricating PPy-NW patterns. Additionally, an ultra-short pulse offers excellent pattern controllability for both width (353 nm ～ 3.37 μm) and height (2.0 ～ 88.3 nm).     

Dip-pen lithography using pens of different thicknesses

A laboratory method to produce AFM tips of different sizes has been developed based on laser irradiation of the commercial silicon nitride tips. A few shots of 60 mJ at 355 nm were found adequate to induce the desired bluntness from 40 nm to 500 nm in a controlled way. Dip-pen nanolithography (DPN) has been performed with the blunt tips using a colloidal ink consisting of Pd nanocrystals coated with polyvinyl pyrrolidone. The line patterns drawn bear a direct relation with the tip morphology, wider the tip, broader are the patterns, in general. The rate of deposition also increases with the tip dimension, but is not as much proportional for larger tips. The study highlights the potential ability of DPN in integrating nano and microelectronics.     

High-voltage SPM oxidation of ZrN: materials for multiscale applications

Scanning probe microscope (SPM) oxidation was used to form zirconium oxide features on 200?nm thick ZrN films. The features exhibit rapid yet controlled growth kinetics, even in contact mode with 70?V dc applied between the probe tip and substrate. The features grown for times longer than 10?s are higher than 200?nm, and reach more than 1000?nm in height after 300?s. Long-time oxidation experiments and selective etching of the oxides and nitrides lead us to propose that as the oxidation reaches the silicon substrate, delamination occurs with the simultaneous formation of a thin layer of new material at the ZrN/Si interface. High-voltage oxide growth on ZrN is fast and sustainable, and the robust oxide features are promising candidates for multiscale (nanometre-to-micrometre) applications.     

Production and evaluation of silicon immersion gratings for infrared astronomy

Immersion gratings, diffraction gratings where the incident radiation strikes the grooves while immersed in a dielectric medium, offer significant compactness and performance advantages over front-surface gratings. These advantages become particularly large for high-resolution spectroscopy in the near-IR. The production and evaluation of immersion gratings produced by fabricating grooves in silicon substrates using photolithographic patterning and anisotropic etching is described. The gratings produced under this program accommodate beams up to 25 mm in diameter (grating areas to 55 mm x 75 mm). Several devices are complete with appropriate reflective and antireflection coatings. All gratings were tested as front-surface devices as well as immersed gratings. The results of the testing show that the echelles behave according to the predictions of the scalar efficiency model and that tests done on front surfaces are in good agreement with tests done in immersion. The relative efficiencies range from 59% to 75% at 632.8 nm. Tests of fully completed devices in immersion show that the gratings have reached the level where they compete with and, in some cases, exceed the performance of commercially available conventional diffraction gratings (relative efficiencies up to 71%). Several diffraction gratings on silicon substrates up to 75 mm in diameter having been produced, the current state of the silicon grating technology is evaluated.     

A nanoscanning platform for bio-engineering: an in-plane probe with switchable stiffness

Scanning probe microscopy (SPM) has been one of the most important tools to image and, hopefully, to manipulate bio-structures at micro/nanoscales. However, the current out-of-plane cantilever design makes it very difficult to extend the spectrum of the current SPM technology to meet many new functionalities arising from bio-engineering applications. An in-plane scanning probe concept is developed to accommodate the new functional requirements. It is designed to have a single-strand multi-walled carbon nanotube (CNT) tip assembled at the end of the probe, a built-in actuator and a tip deflection sensor, all in the same plane. The coplanar design is compatible with most of the standard MEMS processes and would facilitate the assembly of a carbon nanotube tip to the micromachined probe. The in-plane design features a switchable stiffness which adapts the scanning probe's stiffness to the changing surface hardness of the sample. This paper describes how the variable stiffness is accomplished by engaging or disengaging electrostatically actuated clutches, in addition to the discussions on many possible benefits of the in-plane scanning platform.     

Single-step electrochemical nanolithography of metal thin films by localized etching with an AFM tip

This work introduces electrochemical nanolithography (ENL), a single-step method in which a metal thin film is locally etched without application of a mask on a 100?nm length scale with an electrochemical atomic force microscope (AFM). The method requires the application of ultra-short voltage pulses on the tip (nanosecond range duration, 2-4?V amplitude), while both the sample and the metalized tip are under independent potentiostatic control for full control of interface reactions in an AFM electrochemical cell. It is demonstrated that Cu films as well as Co and Cu/Co sandwich magnetic films can be patterned if negative voltage pulses are applied to the tip. This method also applies to films deposited on an insulating substrate. Moreover the lateral dimension of lithographed structures is tunable, from a few micrometers down to 150?nm, by appropriate choice of ENL conditions. Simulation of the dissolution process is discussed.     

纳米测量及纳米样板

介绍了纳米测量系统的组成以及纳米样板的研究现状．提出了两种制备纳米结构样板的方法：Si基底上的原子力显微镜(AFM)探针诱导阳极氧化工艺和Au膜上的AFM探针机械划刻工艺．最后对Si基底上制备的纳米结构样板进行了精度分析．     

Removing material using atomic force microscopy with single- and multiple-tip sources

Atomic force microscopy (AFM) has been an effective material removing tool for fabricating various nanostructures because of its sub-nanometer precision and simplicity in operation. AFM material removing techniques have evolved from a solely mechanical process to one in which the tip can be loaded by additional energy sources, such as thermal, electric, or chemical, to enhance its fabrication abilities. In this paper, these material removing techniques are reviewed with an emphasis on their capabilities and recent progress. The recent hardware and software developments are first presented to provide a general view on the current status of the technology to be assessed. Following an overview of the feasibility and effectiveness of using mechanical scratching for removing various types of soft and hard materials, the processes of a wide range of approaches using multiple tip sources are then assessed with a focus on their principles, versatilities, and potentials for future applications.     

Electrical Force Microscopy measurements on nanoconductors deposited by electropulsed SPM

The reduced dimensions of novel integrated devices and systems stresses the need for new nanopatterning techniques. We showed that metallic pixels of about 30 nm can be deposited by electropulsed SPM. Deposition is obtained by applying −12 to −17 V pulses to a tip coated with a CoCr metallic film while scanning in tapping mode AFM. By assembling arrays of these pixels it is possible to obtain custom-shaped conductors. We deposited rectangular conductors with dimensions from 50×100 nm up to 2000×400 nm and thickness between 2 and 3 nm.A typical conductor line of 2000×400 nm deposited at 40 Hz pulse frequency, 800 nm/s tip velocity and at a line density of 0.64 nm⁻¹ shows a thickness of approximately 3 nm. For electrical measurements this line is deposited perpendicularly and welded from the edge of a conventional Al pad used for microelectronics. The opposite end of the nanoconductor line is located by AFM and the electrical conductivity is then asserted using the conductive AFM tip in Electrical Force Microscopy (EFM) mode.     

拉曼光谱仪成像定位精度检测方法

激光共焦拉曼光谱仪通常采用逐点扫描的方式进行成像,若三维移动平台定位不准确,图像就会产生畸变,导致图像与样品不能匹配。针对这一问题提出了一种简便的拉曼成像定位精度检测方法,并基于费米函数拟合方法寻找边界来提高测量精度。通过在硅基底上镀一层70nm厚金属铬图形的方法制作了检测模体,利用商业化仪器进行了实验验证,仪器的定位重复性为0.2μm。结果表明:该方法可以用于检测拉曼光谱仪的成像定位精度,具有简便和稳定的特点。