原子力与扫描隧道组合显微镜

由大连理工大学物理系研制的原子力与扫描隧道组合显微镜 ( AF/ PSTM) ,9月 2 3日通过了国家教育部组织的鉴定。鉴定委员会对该成果给予了高度评价。该仪器是同时具有纳米分辨原子力显微镜和纳米分辨光学显微镜双重功能图像分解的纳米成像仪器。仪器技术原理是在 AF/ PSTM中设置一个双功能共振光纤尖 ,当光纤尖在样品表面近场扫描时 ,反馈控制等振幅扫描成像 ,一次扫描中 ,同时采集样品的原子力显微镜 AFM图像和光子扫描隧道显微镜PSTM图像。该仪器在分子生物学、医药学、新材料学、集成光学、纳米科技等领域均很有用 ,高校将来甚至…     

大范围扫描的高精度三维数显镜体的设计

介绍了一种新型扫描探针显微镜镜体的设计,该镜体的扫描工作平台可以在3个方向以每步10nm的精度移动,它突破了扫描探针显微镜中压电陶瓷对扫描范围的限制,采用非压电陶瓷机械传动装置实现了大范围扫描.该设计采用逐级定位扫描放大技术将纳米测量与纳米加工范围延伸到25mm×25mm,甚至更大,镜体设计已经获得国家实用新型专利(ZL02221502.6).将该镜体应用在STM和AFM上,实现了对样品的大范围扫描检测,并保证了测量的高精度.     

自激振荡脉冲射流雾化的机理分析

建立了自激振荡雾化喷嘴的物理模型以及数学模型,通过Fluent软件对自激振荡腔室内部流场进行模拟,分析了自激振荡射流扰动波频率与喷嘴固有频率之间的关系、振荡腔室脉冲发生原因,以及射流脉冲特性其对雾化的影响,解释了自激振荡脉冲射流的雾化机理,说明了自激振荡喷嘴能明显提高射流的雾化效果。数值模拟了不同腔长配比和不同出流扩张锥角.结果表明,在其它条件一定的情况下最佳腔长配比值为腔长与上喷嘴直径之比为2.4,最佳出流扩张锥角为(60~65)°。     

高Q值微机电陀螺的快速起振控制

针对高Q值微机电陀螺的快速起振问题,研究其驱动轴控制方法。分析了高Q值谐振器的振动相位随频率的变化率,阐明了锁相环方案启动时间长且对初始频率偏差敏感的原因。用平均法推导了自激振荡方案下起振初始阶段振幅随时间的变化规律。提出了"自激-锁相"驱动轴控制方案,先采用自激振荡方式使陀螺快速起振,再转为锁相环方式使振动频率精确稳定。经实验测试,采用锁相环方案,当初始频率偏差在±10 Hz以内,陀螺的启动时间为2s;采用自激-锁相方案,只要初始频率偏差在±1 000Hz以内,陀螺均可在0.3s内达到频率误差小于0.01%,在0.4s内达到振幅误差小于0.1%。"自激-锁相"方案大幅度缩短了陀螺的启动时间,而且对陀螺初始频率的设置偏差不敏感,对环境温度变化的适应性好,适用于微机电陀螺的批量生产。     

基于聚偏氟乙烯的扫描探针显微镜系统

采用聚偏氟乙烯(PVDF)压电薄膜和压电陶瓷(PZT),并结合由电化学研磨得到的钨探针,研制了一种具有对称结构的新型轻敲模式扫描测头。在该测头中,PVDF压电薄膜作为振动梁,其下方中间位置固定有钨探针,在PZT的驱动下,PVDF和探针处于谐振振动状态,同时,PVDF作为微力传感器检测探针顶端原子与试样表面原子间的作用力。所构建测头结合三维纳米定位台、控制程序等构成了新型扫描探针显微镜系统。介绍了测头的构成、工作原理、特性以及SPM系统的整体结构、测量原理、三维工作台的定位控制、信号处理过程和整系统特性测试,并以一维标准光栅为试样进行三维图像扫描,证明了该新型扫描探针显微镜系统的可行性和有效性。     

低频力作用下压电发电模型及实验研究

以PZT/PVDF复合压电材料采用热压工艺制备了压电厚膜,并制做了不锈钢/压电厚膜/金电极结构的压电振子。为了表征压电振子的阻抗特性,在室温下对样品介电特性进行了测量和分析。利用制备的压电振子采用简支支撑方式设计和制作了压电发电装置,运用压电方程对该装置建立了压电发电数学模型,并根据模型影响参数进行压电发电实验研究。实验结果表明,单片压电厚膜在外加作用力频率从0~2 Hz发生变化时,在负载电阻值为105 kΩ左右时单个压电振子可以获得约130μW的最大输出电功率。研究中还发现增加并联的厚膜片数目可以成比例的增加输出功率。     

高速大扫描范围原子力显微镜系统的设计

针对目前高速扫描型原子力显微镜(AFM)主要是限于物检测且扫描速度和扫描范围均有待提高,提出了一种高速原子力显微镜结构设计方案。在压电陶瓷致动器驱动的柔性铰链结构式位移台的基础上,构建了AFM大范围扫描器,使原子力显微镜在x-y扫描方向的运动范围达到了100μm×100μm。通过傅里叶频谱分析,计算获得了AFM扫描器常用的三角波驱动信号和正弦波驱动信号的高次谐波特性及其对AFM高速扫描成像的影响程度。为了消除在扫描运动过程中的机械自激振荡,提出了将正弦波信号作为高速扫描的驱动信号,行扫速度达到50line/s。在正弦波驱动的基础上提出了一种基于位置采样的图像获取方法,有效地减小了AFM扫描器的非线性误差造成的图像畸变现象。     

基于纳米操作机的多晶ZnO晶界电学特性研究

文中基于安装在扫描电子显微镜（Scanning Electron Microscopy, SEM）中的纳米操作机,对具有微米级细晶粒的氧化锌（ZnO）压电陶瓷进行了单晶粒边界的直接电学测量。由纳米操作机操纵的双探针作为微电极夹在机械手上,测量了ZnO压电陶瓷晶界的伏安特性曲线、非线性系数以及20个晶粒的平均尺寸。在20 Hz~1 MHz的频率范围内,通过等效电路拟合,以阻抗复平面表示实验数据。实验表明低频直流高阻阻抗的本质可归因于晶界,同时20 Hz下的电阻分布可用于预测ZnO压电陶瓷在某些较低频率下的阻抗特性。     

尺蠖式压电线性作动器设计及实验研究

针对空间环境下小型抓取操作机构对新型作动器的使用需求,考虑压电作动器具有耐温范围宽、无电磁干扰及断电自锁等特点,仿照昆虫尺蠖的行走方式设计一种新型压电线性作动器。首先,利用柔性铰链式位移放大机构放大压电陶瓷（Pb-Zr-Ti,简称PZT）叠堆的输出位移,以增大线性作动器的移动步长及对导轨的夹紧变形量,将多个压电陶瓷叠堆器件分为3组,分别作为尺蠖式压电线性作动器的2个夹持单元和1个推进单元的激励源,以获得较大的驱动力并进一步增大作动器的移动步长;其次,借助有限元仿真分析软件,研究压电陶瓷叠堆力电耦合行为的预测方法,并实验验证该方法的可行性;然后,简化柔性铰链式位移放大机构,提出放大倍数的数值分析方法,对位移放大机构在压电陶瓷叠堆作动方向上的刚度进行仿真分析,并验证放大倍数的数值分析方法的准确性;最后,基于设计的线性作动器开展实验研究。结果表明：位移放大机构对压电陶瓷叠堆输出位移的放大倍数为7.3,处于理论值与仿真值之间;在激励电压频率为5 Hz时,作动器的最大空载移动速度为413 μm/s;作动器的最大推动力为16 N,对应的驱动速度为19 μm/s。以上研究结果能为小型抓取操作机构的智能驱动提供技术支持。     

基于AQWA的锥底振荡浮子水动力特性研究

通过水动力计算软件对圆锥底振荡浮子进行仿真分析,主要针对浮子圆锥角度进行建模仿真,并对各自附加阻尼、附加质量、激振力和RAOs进行频域分析,对位移、速度、加速度和激振力进行时域分析。结果表明,当频率小于0.6 Hz,浮子所受激振力和附加质量下降较快;RAOs值较稳定;辐射阻尼上升较快。当频率大于0.6 Hz时,浮子所受激振力较小且变化缓慢;RAOs值迅速下降;附加质量较小,下降趋势趋缓;辐射阻尼不断下降,100°～120°锥角的振荡浮子下降缓慢,130°～170°振荡浮子下降较快。通过时域分析可以看出,当锥角小于120°时,浮子运动很不稳定,当锥角较大时,浮子所受激振力较大,运动也比较稳定。     

Highly controllable fabrication of fiber probe for photon scanning tunneling microscope

A selective chemical etching was used to fabricate fiber probes for the photon scanning tunneling microscope (PSTM). The cladding diameter of the fiber probe was controlled by varying the first-step etching time. The cone angle of the fiber probe tip was controlled by varying the doping ratio of the fiber and the composition of the etching solution. A cladding diameter of 8 μm and a tip diameter of about 3 nm were fabricated. The smallest cone angle was 14°.     

Highly controllable fabrication of fiber probe for photon scanning tunneling microscope

A selective chemical etching was used to fabricate fiber probes for the photon scanning tunneling microscope (PSTM). The cladding diameter of the fiber probe was controlled by varying the first-step etching time. The cone angle of the fiber probe tip was controlled by varying the doping ratio of the fiber and the composition of the etching solution. A cladding diameter of 8 μm and a tip diameter of about 3 nm were fabricated. The smallest cone angle was 14°.     

Optical Fiber Catheter with Distal End Bending Mechanism Control for Raman Biospectroscopy

Abstract

This work proposes the development of an optical catheter with bending control of the distal end. The probe consists of seven optical fibers wrapped in a resin and a biocompatible flexible teflon tube with a novel mechanical device that allows bending of the distal extremity to access a desired location of a human organ. A central fiber is used for tissue Raman excitation, five fibers are used for Raman signal collection, and the seventh for “optoclinical” treatment applications. Infrared, dispersive Raman spectra at 785 nm excitation were employed to optically characterize the proposed catheter. An excitation transmission loss of 16% was found compared to the traditional six collecting fibers catheter, both with their distal tip straight. By bending of the distal tip at different angles, with turning the intermediated section of the catheter around cylinders of different diameters (one finds a correlation between curvature angle of the tip and cylinder diameter), the transmission loss coefficient and transmission were determined for each distal tip angle. A transmission reduction of 5% was found for a 180° curvature. This optical catheter could be very useful in clinics, providing a way to control the fiber tip position and angle onto the tissue or organ.     

A separation of the refractive index and topography in photon-scanning tunneling microscopy: simulations and experiments

In order to separate the purely optical and topographic information from images in constant-gap mode simultaneously, we proposed the atomic force/photon-scanning tunneling microscopy (AF/PSTM). In this paper, we focus on the principle of separation of the refractive index image from the images of photon-scanning tunneling microscopy. We prove the formula of refractive index imaging by using a three-dimensional finite-difference time-domain method. The formula indicates that the refractive index of a sample is approximately proportional to photon tunneling information (DeltaI/I )2. From the viewpoint of practical use, we simulated the refractive index images for the realistic experiments. We present line scans along two orthogonal directions and the transmitted intensity as a function of the tip position under the constant-gap mode. The experimental results are presented and are in good agreement with the numerical results.     

Common-path optical coherence tomography with side-viewing bare fiber probe for endoscopic optical coherence tomography

All-fiber-optic common-path optical coherence tomography (OCT) using a side-viewing bare fiber probe has been demonstrated and analyzed. A bare single mode fiber tip is angle cleaved at approximately 49 degrees to enable side illumination due to total internal reflection. The bare fiber probe was inserted in an arterial tissue and a circumferential OCT scan was obtained. The research is aimed at realizing highly miniaturized monolithic probes for possible applications in miniature endoscopic OCT or intravascular OCT. The effects of the angle of the cleaved fiber on reference reflection and the sensitivity of the common-path OCT system have been studied theoretically. The angle cleaved fiber probe is also used in series with a microlens to analyze and optimize its performance in a common-path OCT system. Our research aims to explore the combined advantages of common-path OCT and extremely simplified miniature probe design and to discuss how it may greatly simplify the endoscopic OCT instrumentation eventually.     

Shear force distance control in a scanning near-field optical microscope: in resonance excitation of the fiber probe versus out of resonance excitation

The experimental results of the direct measurement of the absolute value of interaction force between the fiber probe of a scanning near-field optical microscope (SNOM) operated in shear force mode and a sample, which were performed using combined SNOM-atomic force microscope setup, are discussed for the out-of-resonance fiber probe excitation mode. We demonstrate that the value of the tapping component of the total force for this mode at typical dither amplitudes is of the order of 10 nN and thus is quite comparable with the value of this force for in resonance fiber probe excitation mode. It is also shown that for all modes this force component is essentially smaller than the usually neglected static attraction force, which is of the order of 200 nN. The true contact nature of the tip-sample interaction during the out of resonance mode is proven. From this, we conclude that such a detection mode is very promising for operation in liquids, where other modes encounter great difficulties.     

Shear force distance control in near-field optical microscopy: experimental evidence of the frictional probe-sample interaction

The properties of the probe-surface contact for a near-field optical microscope driven in the shear force mode have been studied applying lateral amplitudes of the probing fiber tip larger than 15 nm. Electric current measurements between a conductive tip and a conductive sample reveal a pulsed current behavior at the very beginning of the approach curve. In the upper part of the approach curve it turns to the quasiconstant current. From this observation a conclusion is drawn about the presence of permanent mechanical contact between the probe and the surface in the shear force mode. A shift of the approach curve along the z-axis as a function of dither amplitude was discovered. These results are in contradiction to the established conception of possible physical mechanisms of shear force interaction. To settle this issue the friction model is proposed according to which the damping of the probe vibrations is caused by the friction between the tip and the surface.     

An evanescent-field optical microscope

The classic diffraction limit of resolution in optical microscopy (～γ/2) can be overcome by detecting the diffracted field of a submicrometre-size probe in its near field. The present stage of this so-called scanning near-field optical microscopy (SNOM) is reviewed. An evanescent-field optical microscope (EFOM) is presented in which the near-field regime is provided by the exponentially decaying evanescent field caused by total internal reflection at a refractive-index transition. A sample placed in this field causes a spatial variation of the evanescent field which is characteristic for the dielectric and topographic properties of the sample. The evanescent field is frustrated by a dielectric probe and thus converted into a radiative field. In our case the probe consists either of an etched optical fibre or of a highly sharpened diamond tip. The probe is scanned over the sample surface with nanometre precision using a piezo-electric positioner. The distance between probe and sample is controlled by a feedback on the detected optical signal. The resolution of the microscope is determined by both the gradient of the evanescent field and the sharpness of the tip. Details of the experimental set-up are discussed. The coupling of the evanescent field to the submicrometre probe as a function of probe-sample distance, angle of incidence and polarization has been characterized quantitatively. The observed coupling is generally in agreement with presented theoretical calculations. Microscopy has been performed on a regular latex sphere structure, which clearly demonstrates the capacity of the evanescent-field optical microscope for nanometre-scale optical imaging. Resolution is typically 100 nm laterally and 10 nm vertically. The technique is promising for biological applications, especially if combined with optical spectroscopy.     

Improving tapping mode atomic force microscopy with piezoelectric cantilevers

This article summarizes improvements to the speed, simplicity and versatility of tapping mode atomic force microscopy (AFM). Improvements are enabled by a piezoelectric microcantilever with a sharp silicon tip and a thin, low-stress zinc oxide (ZnO) film to both actuate and sense deflection. First, we demonstrate self-sensing tapping mode without laser detection. Similar previous work has been limited by unoptimized probe tips, cantilever thicknesses, and stress in the piezoelectric films. Tests indicate self-sensing amplitude resolution is as good or better than optical detection, with double the sensitivity, using the same type of cantilever. Second, we demonstrate self-oscillating tapping mode AFM. The cantilever's integrated piezoelectric film serves as the frequency-determining component of an oscillator circuit. The circuit oscillates the cantilever near its resonant frequency by applying positive feedback to the film. We present images and force-distance curves using both self-sensing and self-oscillating techniques. Finally, high-speed tapping mode imaging in liquid, where electric components of the cantilever require insulation, is demonstrated. Three cantilever coating schemes are tested. The insulated microactuator is used to simultaneously vibrate and actuate the cantilever over topographical features. Preliminary images in water and saline are presented, including one taken at 75.5 μm/s—a threefold improvement in bandwidth versus conventional piezotube actuators.     

Computational analysis of responses of a wedge-shaped-tip optical fiber probe in bubble measurement

Optical-fiber probing is widely employed in bubble∕droplet measurement in gas-liquid two-phase flows. Several types of optical fiber probes with a very high S∕N ratio and high performance have been developed, but further improvement in the probes' measurement accuracy and reliability for industrial applications is desired. We tried to eliminate optical noise in the probe measurements, and we found that the signals include some peak signs that have potential for advanced measurement with optical-fiber probing. We developed a ray-tracing numerical simulator and identified the mechanisms underlying the generation of the signals. In order to numerically simulate the optical probing signals, the simulator must use 3D frameworks composed of incident beams, the reflection and refraction on the surfaces of the optical elements (i.e., an optical fiber, a sensing tip, an air phase, and a water phase), and beams returning from the sensing tip to the other tip through the fiber. We used all of these in a simple rendering framework based on a ray-tracing algorithm with Fresnel's law, and we observed the mechanism of some promising signals that may be useful for extracting the hidden potential of optical-fiber probing. To verify the simulator's performance, we carried out three comparative experiments with fundamental setups using a wedge-shaped single-tip optical fiber probe, examining: (1) the beam trajectories and energy leaking out from the sensing tip into the surrounding air phase or water phase, (2) the probing signals throughout penetration of the sensing tip at the air-water free interface in light of the three-dimensional deformation, and (3) the probing signals throughout penetration of the sensing tip into a bubble in light of the three-dimensional bubble shape. As a result, (a) we found that an optical fiber probe with a wedge-shaped tip has particular characteristics of beam emissions from the tip, and the emitting angles switched depending on the phases covering the tip. This phenomenon is very effective for further advanced measurement. (b) We observed numerically that the cutting angle of the sensing tip maximizing the air signal level was approximately 30°, and therefore this angle is the best for obtaining the highest S∕N ratio. (c) We found that the meniscus shape clearly affected the probing signal optically. (d) We observed the mechanism of a pre-signal caused by the reflection at the frontal and rear interfaces of a bubble. The pre-signal is very useful for practical measurement because it appears only when the probe penetrates the center region of a bubble. We compared the above numerical results with the results of the three experiments, and there was satisfactory correspondence between the numerical and experimental results.