Evaluating Local Elasticity of the Metal Nano-films Quantitatively Based on Referencing Approach of Atomic Force Acoustic Microscopy

Traditional technique such nanoindenter（NI） can＇t measure the local elastic modulus at nano-scale（lateral）. Atomic force acoustic microscopy （AFAM） is a dynamic method, which can quantitatively determine indentation modulus by measuring the contact resonance spectra for high order modes of the cantilever. But there are few reports on the effect of experimental factors, such length of cantilever, contact stiffness on measured value. For three different samples, including copper（Cu） film with 110 nm thickness, zinc（Zn） film of 90 nm thickness and glass slides, are prepared and tested, using referencing approach in which measurements are performed on the test and reference samples （it＇s elastic modulus is known）, and their contact resonance spectra are measured used the AFAM system experimentally. According to the vibration theory, from the lowest two contact resonance frequencies, the tip-sample contact stiffness is calculated, and then the values for the elastic properties of test sample, such as the indentation modulus, are determined. Using AFAM system, the measured indentation modulus of copper nano-film, zinc nano-film and glass slides are 113.53 GPa, 87.92 GPa and 57.04 GPa, which are agreement with literature values Mcu--105-130 GPa, Mzn = 88.44 GPa and Molass = 50-90 GPa. Furthermore, the sensitivity of contact resonance frequency to contact stiffness is analyzed theoretically. The results show that for the cantilevers with the length 160 pm, 225 μm and 520 μm respectively, when contact stiffness increases from 400 N/m to 600 N/m, the increments of first contact resonance frequency are 126 kHz, 93 kHz and 0.6 kHz, which show that the sensitivity of the contact resonance frequency to the contact stiffness reduces with the length of cantilever increasing. The novel method presented can characterize elastic modulus of near surface for nano-film and bulk material, and local elasticity of near surface can be evaluated by optimizing the experimental parameters using the AFAM system.

An automated AFM for nanoindentation and force related measurements

A fully automated atomic force microscope(AFM)is presented.The mechanical motion of the AFM stage was controlled by three steppers.The fine motion of the AFM was controlled by an MCL one-axis piezo plate.A32.768kHz crystal tuning fork(TF)was used as the transducer with a probe attached.An acoustic sensor was used to measure the interactions between the probe and the sample.An SR850lock-in amplifier was used to monitor the TF signals.An additional lock-in amplifier was used to monitor the acoustic signal.A field programmable gate array(FPGA)board was used to collect the data in automatic mode.The main controller was coded with LabVIEW,which was in charge of Z-axis scan,signal processing and data visualization.A manual mode and an automatic mode were implemented in the controller.Users can switch the two modes at any time during the operation.This AFM system showed several advantages during the test operations.It is simple,flexible and easy to use.

Combining infrared and mode synthesizing atomic force microscopy： Application to the study of lipid vesicles inside Streptomyces bacteria

We propose a new analytical approach combining vibrational spectroscopy and acoustic tomography for the detection and characterization of vesicles inside Streptomyces bacteria. Using atomic force microscopy and infrared spectroscopy （AFM-IR）, we detect the presence of triglyceride vesicles. Their sizes in depth are measured with high accuracy using mode synthesizing atomic force microscopy （MS-AFM）. We conducted a comparative study of AFM-IR and MS-AFM, and highlighted the advantages of the coupling of these techniques in having a full characterization （chemical, topographical, and volumetric） of a biological sample. With these complementary techniques, a complete access to the vesicle size distribution has been achieved with an accuracy of less than 50 nm. A 3D reconstruction of bacteria showing the in-depth distribution of vesicles is given to underline the great potential of the acoustic method.

基于AFAM纳米多孔氧化硅薄膜超声幅值成像的试验研究

为研究原子力声学显微镜(atomic force acoustic microscopy,AFAM)技术检测纳米多孔氧化硅薄膜的超声幅值成像的影响因素,通过基于AFAM技术的谐振频率检测及超声幅值成像系统,试验得到了纳米氧化硅薄膜和纳米多孔氧化硅薄膜的前2阶接触谐振频率及其超声幅值成像,分析试验过程中的参数如激励频率、扫描频率对稳定性的影响及超声激励对纳米摩擦力的影响.试验结果显示,超声频率会影响超声幅值成像的对比度,超声激励降低了扫描过程中的摩擦力.

低频低能量超声联合微泡对前列腺细胞的影响

目的:采用原子力声显微镜及透射电镜观察低频低能量超声联合微泡对前列腺癌细胞DU145及正常前列腺上皮细胞RWPE-1的作用。方法:两种细胞均分为对照组、单纯超声组、超声联合微泡组。对照组加入一定比例的生理盐水,不进行超声辐照;单纯超声组加入相同比例的生理盐水,用发射频率为21 k Hz的低频超声辐照,辐照2 min,占空比30%;超声联合微泡组加入同前相同比例的微泡造影剂悬浊液,用与单纯超声组相同的超声辐照。处理过的细胞立即用原子力声显微镜观察其形貌并计算其杨氏模量。同时,对同一处理方式的对照组及超声联合微泡组细胞继续培养24 h后,用透射电镜观察细胞。结果:单纯超声组的DU145细胞及RWPE-1细胞的细胞形态与对照组无明显变化;超声联合微泡组的DU145细胞及RWPE-1细胞形态呈类圆形,细胞表面可见放射状显微丝状结构,细胞膜表面可见多个大孔状结构;超声联合微泡组的DU145细胞的弹性模量较RWPE-1细胞大,且与对照组相比,两种细胞的弹性模量均变大,DU145细胞尤甚。透射电镜观察结果示对照组的两种细胞未见细胞自噬,而超声联合微泡组两种细胞都出现自噬现象,其中DU145细胞中可见凋亡现象。结论:低频低能量超声联合微泡可引起前列腺癌DU145细胞及正常前列腺上皮RWPE-1细胞的细胞膜出现孔状结构,并诱导其自噬,且对DU145细胞的损伤大于RWPE-1细胞。

扫描探针声显微镜原理及其应用

将声学检测技术与扫描探针显微术相结合,构成的扫描探针声显微镜,不仅可以检测材料表面、亚表面和内部的微小缺陷,还可以分析样品的弹性特性、电特性等物理性能,同时还具有分辨率高的特点,在材料科学和生命科学等领域具有很高的应用价值。目前,得到实际应用的扫描探针声显微镜主要有扫描隧道声显微镜和原子力声显微镜。本文介绍了这两类显微镜的基本工作原理,并对扫描探针声显微镜今后的发展方向进行了探讨。

溶液环境中利用声学、磁力、光热和静电力驱动微悬臂的动力学分析比较

原子力显微镜(Atomic force microscopy,AFM)是用来获得样品表面微观信息的重要工具,在液相下振动模式中(Dynamic mode)悬臂振动参数如品质因子Q、振动频谱响应等对能否稳定成像及精确测量起着关键性作用。目前最普遍的驱动方式是声学振动-用压电陶瓷来间接驱动悬臂振动,然而此方法固定悬臂的液体槽和水溶液的耦合作用会产生杂峰,从而影响悬臂正常工作,降低成像品质。因此研究者们发展了各种不同的方法来直接对悬臂进行驱动。本文综合现有的利用声学、磁力、光热和静电力等不同的微悬臂驱动方法,分析、比较这几种方法所产生的振幅和相位响应及应用于振动模式AFM中的优劣,可为研制更高分辨率的AFM提供参考。

超声造影剂微气泡的包膜黏弹特性的定量表征研究

包膜黏弹特性显著影响微气泡超声造影剂的诊断及治疗应用效果.本文结合原子力显微镜技术及声衰减特性测量提出了一种对微气泡造影剂包膜黏弹特性定量表征的新方法.首先采用原子力显微镜技术进行机械特性分析得到包膜微气泡的有效硬度及体弹性模量;然后测量声衰减特性,基于微气泡动力学理论,计算包膜微气泡的体黏度系数.为验证方法的有效性,实验制备了直径为1—5μm的白蛋白包膜微气泡造影剂,原子力显微镜测量的有效硬度和体弹性模量分别为0.149±0.012 N/m和8.31±0.667 MPa,并与粒径无关.声衰减特性测量和动力学理论拟合的包膜微气泡的体黏度系数为0.374±0.003 Pa·s.该方法可推广至其他种类包膜微气泡的黏弹特性表征,对超声造影剂的制备及其诊断和治疗应用有积极意义.