基于新型探针的双频原子力显微系统开发

传统原子力显微镜(AFM)在接触模式下工作时具有接触力较大、易损伤样品的缺点.本文通过对新型自感应音叉探针施加双频激励,使得AFM工作在轻敲模式下,减小了接触力和扫描过程中的侧向力影响,实现了样品表面力学特性和亚表面结构的表征.然后利用基于DSP的PI反馈控制模块,完成了线扫描实验,证明该双频原子力显微测量系统具有较好的测量能力.     

压膜阻尼对原子力显微镜振动特性的影响研究

原子力显微镜(Atomic Force Microscope, AFM)在轻敲模式下工作时,随着探针针尖与样品距离的逐渐减小,空气压膜阻尼的作用随之增大。为研究压膜阻尼对原子力显微镜振动系统的影响,分别使用无针尖探针和微球针尖探针进行扫频实验,并基于振动理论将该过程简化,得到了两种不同的振动模型的系统刚度。在考虑压膜阻尼作用影响后,将微球针尖振动系统模型进一步简化为一维振子模型,并对压膜阻尼的影响进行讨论。实验表明空气压膜阻尼模型对于探针样品在微尺度下的作用过程是准确合理的。该结果对原子力显微镜轻敲模式研究具有重要意义。     

原子力声显微镜成像及分析

超声检测技术与原子力显微技术相结合,构成原子力声显微镜(AFAM),能够实现样品内部纳米结构的测量,并分析如局域弹性模量、刚度等力学性能.本文在传统的原子力显微镜(AFM)的基础上初步构建了AFAM,利用AFM轻敲模式下的微悬臂梁振动激励信号来驱动样品背面的压电超声换能器,并利用轻敲模式控制系统中的锁相环检测经过样品后由探针收集的振动信号,形成振幅及相位图像.这种AFAM方法不需外接信号发生器、锁相放大器及相关控制电路,从而避免AFM内、外部的仪器及控制电路的不同步而引起的AFAM振幅/相位与形貌图像间的偏移.此外,还分析了形貌结构对AFAM振幅图像的影响,为进一步研究AFAM亚表面成像奠定了基础.     

缓蚀剂对原子力显微镜探针刮擦铜镍合金加速溶解的作用

金属材料在缓蚀剂中受到刮擦会加速溶解,产生相应的腐蚀.采用原子力显微镜(AFM)探针刮伤技术研究了缓蚀剂对探针诱导铜镍合金加速溶解作用的影响.结果表明:在750 nN负载条件下,AFM探针在接触模式下对铜镍合金表面持续扫描,可以加速样品在1.5 mol/L NaCl溶液中的溶解,探针刮擦区域有蚀坑;作为缓蚀剂添加的有机化合物十二胺和无机盐铬酸钠能抑制探针刮擦引起的铜镍合金的加速溶解.     

AFM扫描过程的模拟及针尖形状反求

纳米栅格和台阶等结构的线宽准确测量,是国内外计量领域的研究热点与难点。采用原子力显微镜(AFM)能获得上述结构的三维形貌信息,但其扫描图像却是探针针尖的形貌和被测样品表面的形貌共同作用的结果,这种作用往往导致线宽边缘测量失真。为了更加精确地获得样品的表面形貌特征,首先需要重建探针针尖形貌,进而从得到的扫描图像中尽可能地消除由探针形貌带来的失真影响。基于数学形态学的盲重建理论,利用Matlab对不同形状参数的探针针尖扫描台阶样品表面进行了仿真,评价了探针形状对扫描结果的影响,初步实现了基于真实粗糙测量表面的探针针尖形状重建。     

基于扭转谐振模式3D-AFM的微结构侧壁形貌检测

针对半导体器件微结构侧壁关键尺寸检测需求,设计了一套三维原子力显微镜(3D-AFM)系统.该系统采用针尖末梢为喇叭口形的悬臂梁探针,以扭转谐振模式实现横向轻敲扫描.介绍了该3D-AFM系统的结构组成和工作原理,对系统的横向检测灵敏度进行了标定,获得了喇叭口针尖与样品侧壁横向接近过程中探针扭转振幅的变化曲线.利用该系统对栅格标样侧壁局部形貌进行了线扫描和面扫描,所得轮廓具有较好的重复性,且测量所得形貌特征与常规轻敲模式扫描结果一致,表明本文所述3D-AFM系统及工作模式能够用于微结构侧壁形貌的检测.     

AFM扫描图像重构算法的改进

针对原子力显微镜（AFM）纳米成像中存在的失真问题,研究了通过探针建模实现AFM扫描图像重构方法.目前探针盲建模算法在重构AFM图像时存在较大误差,因此提出基于探针模型预估计的AFM扫描图像重构方法.该方法采用分区探针针尖建模,并通过基于该探针模型的反卷积运算实现AFM扫描图像重构,获得比较接近真实形貌的AFM扫描图像.文中介绍了算法的具体步骤,通过仿真和实验结果证明,该方法能够有效降低AFM图像重构时引入的误差,得到的图像更能反映样品表面真实的形貌.     

扫描Kelvin探针力显微镜:工作原理及在材料腐蚀研究中的应用

扫描Kelvin探针力显微镜(SKPFM)是在原子力显微镜(AFM)的基础上应用扫描Kelvin探针(SKP)技术开发的检测表征手段,它能够在获取材料表面纳米级分辨率形貌的同时,原位得到样品表面高分辨率的接触电势差分布图,为揭示腐蚀反应机理提供了崭新的思路,近年来发展迅速。本文介绍了SKPFM两种工作模式的基本原理,总结了SKPFM在应用中的问题,并讨论了SKPFM和传统扫描Kelvin探针技术(SKP)的优缺点,重点综述了SKPFM在腐蚀科学研究中的应用,最后展望了SKPFM的发展方向与应用前景。     

基于SPM的花生酸LB膜的拉膜工艺及结构表征的研究

通过扫描探针显微镜（SPM）直接观察沉积在基片表面的花生酸LB（Langmuir-Blodgett）薄膜不同范围尺度下的微观结构.研究在经过表面两亲性（亲水性或疏水性）处理的基片上,在相同的制膜条件下,改变其拉膜沉积方式,对花生酸LB膜样品的表面结构、薄膜均匀性和缺陷等的影响.结果显示,花生酸LB膜在不同拉膜沉积方式下,薄膜表面将形成不同的分子自组装形态;改变基片表面的亲水性强弱也直接影响LB膜的表面形貌的均匀性,可能通过选择恰当表面处理和沉积方式来获得平整度更高,缺陷更少的LB膜.     

间歇模原子力显微镜非线性振动的数值模拟

1　引　言　　原子力显微镜 (简记为 AFM)是利用其微悬臂梁的机械振动响应于力敏探针和实验样品表面之间的相互作用力来成像的 ,由于具有原子和分子级的分辨率 ,已成为表面成像及材料微结构研究的新工具 ,在科学技术的各种领域获得了广泛的应用 [1-2 ] 。有几种不同模式的 AFM相继被开发使用。在 AFM的接触模工作中 ,其力敏探针始终保持同样品表面相接触 ,力敏探针和样品之间的相互作用力被微悬臂梁位移产生的弹性力所平衡 ,这种接触模式有极高的分辨率 ,但力敏探针上存在横向力 ,对实验样品有较大的损伤 ;在 AFM的非接触模工作中 ,力…     

Calibration of silicon atomic force microscope cantilevers

We present a comparison of three different methods to calibrate the spring constant of two different types of silicon beam shaped atomic force microscope (AFM) cantilevers to determine each method's accuracy, ease of use and potential destructiveness. The majority of research in calibrating AFM cantilevers has been concerned with contact mode levers. The two types of levers we have studied are used in force modulation and tapping mode in air. Not only can these types of cantilevers have spring constants an order of magnitude greater than contact mode levers, but also their geometries can be quite different from the standard V-shape contact lever. In this work we experimentally determine the correction factors for two of the calibration methods when applied to the tapping mode cantilevers and also demonstrate that the force modulation levers can be calibrated easily and accurately using these same techniques.     

AFM Tip Hammering Nanolithography

Nanolithography at low cost and high speed is made possible by using a vibrating AFM tip in tapping‐mode as a nanohammer to forge polystyrene‐block‐poly(ethylene/butylenes)‐block‐polystyrene triblock copolymer monolayer thin films after annealing to transform their microstructures from as‐cast poorly ordered cylinders into well‐ordered hexagonal spheres. Annealing is accomplished in cyclohexane vapor, a selective solvent for the majority poly(ethylene/butylenes) block. Experimental results demonstrate that such structure‐tailored thin films enable macroscopic AFM tip writing to be performed in their surface; imprinted and embossed patterns can be generated with a sub‐20‐nm line‐width resolution. In addition, it is found that the lithographic patterns generated can be erased within 5 min by thermal annealing at 70 °C, and if necessary the erasion process can be expedited by increasing the annealing temperature.     

Convenient near-field optical measurement and analysis of polystyrene spheres

The modification of a commercial tapping mode atomic force microscope (AFM) into a transmission mode near-field scanning optical microscope (NSOM) is presented and polystyrene spheres in the diameter of 100 nm are used in this experiment. The detection of near-field signals is based on photodiodes with lock-in technique, and resolutions of topography and near-field signals obtained are about 10 and 20 nm, respectively. Furthermore, it is discovered that the computer-simulated near-field energy distribution profile, obtained by scanning over polystyrene spheres under illumination mode, falls within 5% range as compared with experimental values. The near-field absorption coefficient can be determined by this way. This will be a useful theoretical model to analyze the near-field transmission effect from others.     

Characterization of crystalline alumina films formed in alcohol-water solutions

Crystalline aluminum hydrous oxide [γ-AlO(OH)] thin films were prepared by hydration of a high cubicity tunnel-etched Al foil in alcohol—DI-water solutions at 95 °C for times up to 1 h. Presence of free molecular water was found to be an absolute requirement for film formation. In addition, the type of alcohol used in the hydration environment, n-propyl alcohol, ethylene glycol or glycerol, influenced the hydration kinetics, i.e. the induction time for film growth. Denser and low porosity films were suggested by field emission—scanning electron microscopy analysis. X-Ray diffraction showed the presence of only one crystalline phase identified as pseudoboehmite.     

随机噪声激励下轻敲式原子力显微镜动力学特性研究

针对有界随机噪声激励下轻敲式原子力显微镜 (AFM：Atomic force microscope)系统的非线性动力学问题,建立Lennard-Jones力场作用下针尖-样品的集总参数模型,应用现代微分方程和分岔理论,分析了随机扰动强度和弯月面接触角对AFM针尖-样品耦合系统动力学特性的影响。结果表明,轻敲式AFM耦合动力学系统中存在丰富的周期运动和混沌运动,表现出复杂的非线性行为,混沌特性随着随机扰动强度增大而增强,弯月面接触角越大混沌特性越明显,因此在轻敲式AFM优化设计中,随机噪声对AFM系统的影响不可忽视。     

Transmission infrared spectroscopy as a probe of Nafion film structure: analysis of spectral regions fundamental to understanding hydration effects

Transmission infrared spectroscopy was applied to investigate properties of the perfluorosulfonated polymer Nafion. Measurements were made on thin films formed by casting the polymer from solution onto ZnSe windows. Effects of water vapor permeation were studied. A complex band structure between 1350 and 1100 cm(-1) was analyzed qualitatively by fitting the region to Gaussian functions. Features associated with vibrational modes of -CF(2) and -SO(3)(-) groups were identified and observed to be sensitive to film hydration. The intensities of bands for the -SO(3)(-) modes increased with film hydration, while bands assignable to -CF(2) modes decreased. The results were applied to interpret infrared difference spectra of Nafion and shed light on the complicated features that appear. Vibrational bands for water were also examined. In partially hydrated films, the stretching mode of the free -OH group for interfacial water present in pores and channels of the polymer and bands for hydrated proton clusters were detected.     

Surface modifications of polymethylmetacrylate films using atmospheric pressure air dielectric barrier discharge plasma

In this paper, polymethylmetacrylate (PMMA) films are modified using an atmospheric pressure non-thermal plasma generated by a dielectric barrier discharge (DBD) in air. The DBD is generated in a plane-parallel reactor, which is driven by a μs pulse power supply with amplitude of up to 25 kV and repetition rate of 1 kHz, and the plasma generated shows homogeneous mode discharge characteristics verified by electrical measurements and light emission images with 0.5 ms exposure time. The treatment time ranging from 0 to 60 s and the discharge power density ranging from 11.62 to 30.83 W/m² are used to study the effects of discharge parameters on the surface treatment, and the surface properties of PMMA films are studied using contact angle and surface energy measurement, scanning electron microscopy (SEM), atomic force microscopy (AFM), fourier transformed infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). The study shows that, after the plasma treatment, the surface of PMMA film is etched, and oxygen-containing polar groups are introduced into the surface. These two processes can induce a remarkable decrease in water contact and a remarkable increase in surface energy, and the surface properties of PMMA films is improved accordingly. It is shown that the improvement of hydrophobicity depends on the discharge power density and treatment time, and there is a saturation treatment time at each discharge power density. Increasing discharge power density can induce more effective treatment of PMMA films, and less treatment time is needed to achieve the same level of surface treatment by increasing the discharge power density. Because more oxygen-containing polar groups are created and more obvious etching is occurred on the PMMA surface at higher discharge power density.     

An investigation into the feasibility of formulating ‘self-cure’ concrete

To achieve good cure, excessive evaporation of water from a freshly cast concrete surface should be prevented. Failure to do this will lead to the degree of cement hydration being lowered and the concrete developing unsatisfactory properties. Curing can be performed in a number of ways to ensure that an adequate amount of water is available for cement hydration to occur. However, it is not alway possible to cure concrete satisfactorily. This paper is concerned with achieving optimum cure of concrete without the need for applying external curing methods. The feasibility of curing concrete by adding water-soluble chemicals during mixing that reduce water evaporation in the set concrete, making it ‘self-curing’ is discussed. The chemicals' abilities to reduce evaporation from solution and to improve water retention in ordinary Portand cement was monitored by measuring weight-loss. x-Ray powder diffraction and thermogravimetry measurements were made to assess whether any improvement in water retention was matched by an increase in degree of cement hydration. Initial surface absorption tests and compressive strength measurements were made to determine surface permeability and strength development, respectively. The scanning electron microscope was used to determine the influence of the admixtures on cement paste microstructure. It was found that two of the chemicals studied had a significant ‘self-curing’ effect. One of these chemicals enhanced hydration further than simply by means of water retention. A possible explanation of this behaviour is given.     

10 micrometer-scale SPM local oxidation lithography

10 micrometer-scale scanning probe microscopy (SPM) local oxidation lithography was performed on Si. In order to realize large-scale oxidation, an SPM tip with a contact length of 15 microm was prepared by focused-ion-beam (FIB) etching. The oxidation was carried out in contact mode operation with the contact force ranging from 0.1 to 2.1 microN. The applied bias voltage was 50 V, and scanning speed was varied from 10 to 200 microm/s. The scan length was 15 microm for one cycle. The influence of contact force on the large-scale oxidation was investigated. At high contact force, the Si oxide with good size uniformity was obtained even with high scanning speed. The SPM tip with larger contact length may increase the spatial dimensions of the water meniscus between the SPM tip and sample surface, resulting in the larger dimensions of the fabricated oxide. Furthermore, the throughput of large-scale oxidation reached about 10(3) microm2/s by controlling the scanning speed and contact force of the SPM tip. It is suggested that SPM local oxidation can be upscaled by using a SPM tip with large contact length.     

基于中心粒子水化模型的水泥水化动力学研究

在K.B.Park提出的中心粒子水化模型的基础上,考虑内、外部水化产物的具体特征以及自由水与水化产物接触相界面积的减小导致水泥水化速率减小这2个因素,建立硅酸盐水泥的微观水化模型,并用于预测水化速率随水化程度的变化关系。结果表明,在水泥的整个水化过程中,修正的微观水化模型都能够更真实地反应水泥水化速率与水化程度变化的关系。