Topography and near-field image measurement of soft biological samples in liquid by using a tuning fork based bent optical-fiber sensor

The fabrication of a tuning fork based bent optical-fiber sensor and its application for topography and near-field image measurement of soft biological samples in physiological solution are reported. By adopting the bent optical fiber and tuning fork feedback scheme, the possibility of signal interference with stray light is minimized, which is especially important for near-field applications. From the measured tuning fork amplitude and its calibration with the preamplifier output voltage, it was determined that the interaction force between the fiber tip and a soft sample in liquid needs to be controlled within approximately 10 nN level and that the image quality depends sensitively to the interaction force. The results of topography measurements of fixed COS-7 and MCF-7 cells in phosphate buffered saline and of the near-field imaging of red blood cell also in phosphate buffered saline with a resolution of about 100 nm are presented.     

Mechanical Property Investigation of Soft Materials by Cantilever‐Based Optical Interfacial Force Microscopy

Cantilever‐based optical interfacial force microscopy (COIFM) was applied to the investigation of the mechanical properties of soft materials to avoid the double‐spring effect and snap‐to‐contact problem associated with atomic force microscopy (AFM). When a force was measured as a function of distance between an oxidized silicon probe and the surface of a soft hydrocarbon film, it increases nonlinearly in the lower force region below ∼10 nN, following the Herzian model with the elastic modulus of ∼50 MPa. Above ∼10 nN, it increases linearly with a small oscillatory sawtooth pattern with amplitude 1–2 nN. The pattern suggests the possible existence of the layered structure within the film. When its internal part of the film was exposed to the probe, the force depends on the distance linearly with an adhesive force of −20 nN. This linear dependence suggests that the adhesive internal material behaved like a linear spring with a spring constant of ∼1 N/m. Constant‐force images taken in the repulsive and attractive contact regimes revealed additional features that were not observed in the images taken in the noncontact regime. At some locations, however, contrast inversions were observed between the two contact regimes while the average roughness remained constant. The result suggests that some embedded materials had spring constants different from those of the surrounding material. This study demonstrated that the COIFM is capable of imaging mechanical properties of local structures such as small impurities and domains at the nanometer scale, which is a formidable challenge with conventional AFM methods. SCANNING 35:59‐67, 2013. © 2012 Wiley Periodicals, Inc.     

Probing material properties of polymeric surface layers with tapping mode AFM: Which cantilever spring constant,tapping amplitude and amplitude set point gives good image contrast and minimal surface damage?

A phase shift between the oscillatory motion and drive motion of an AFM-cantilever used for tapping mode AFM imaging can be related to adhesive and elastic properties of surface layers. In this study it was studied how optimal contrast between hard and soft surface layers can be achieved while minimizing the surface damage. This was investigated by performing classical force-distance measurements while driving the cantilever as in tapping mode imaging. The amplitude and phase response as a function of the average tip-surface separation was recorded. Five different cantilevers with a wide range of spring constants and four different tapping amplitudes were investigated and compared. Based on these experiments it is concluded that too stiff cantilever, high free tapping amplitude and low amplitude set point value often lead to surface damage, while too low spring constant and low free tapping amplitude result in poor phase image contrast. Intermediate values where little surface damage and significant image contrast are obtained were identified. In all cases it was observed that the best image contrast was obtained when the amplitude set point was chosen such that the amplitude during imaging was reduced to approximately 50% of the free amplitude.     

Effects of tip-sample forces and humidity on the imaging of DNA with a scanning force microscope

We have investigated the effects of tip-sample forces and relative humidity when using a scanning force microscope (SFM) to image DNA molecules adsorbed on fresh mica. As the force between the tip and the sample increases, the apparent height of the DNA molecules decreases. After being imaged with high forces, the DNA molecules recover partially in their apparent height, indicating that a plastic deformation of the DNA has been induced by the scanning tip. At low humidities, DNA molecules can be imaged with a force up to 150 nN during the scanning without obvious damages. At higher humidities, however, the DNA molecules can be dissected or swept away by the tip even at a tip-sample force of 30 nN. The net force between the tip and the molecules is the vector sum of several forces, the dominant components of which are the elastic force due to the cantilever bending and the capillary force resulting from the water meniscus formed between the tip and the sample surface. When the relative humidity of the imaging environment is increased, the capillary force becomes stronger.     

生物组织的太赫兹数字全息成像

太赫兹辐射具有低光子能量和较高的透射性,并对水分子等极性物质反应敏感,因此太赫兹数字全息成像法可以快速准确地获取生物组织信息。本文利用太赫兹数字全息成像系统对猪肉和羊肉组织切片进行测量,采用菲涅耳反衍射方法对实验结果进行优化,选取0.9THz分量的振幅图像进行分析。通过计算组织的吸光度获取0.9THz吸光度图像。实验结果显示,肌肉组织的吸光度均在8cm~(-1)以上,脂肪组织的吸光度不超过4cm~(-1)。采用主成分分析方法获得吸光度得分图并进行重建,从重建结果中可以清晰区分生物组织的不同区域。由此表明,太赫兹数字全息成像技术能够直接获取生物组织的二维信息,探测时间短、效率高,在生物检测领域具有广阔的应用前景。     

Electron phase and amplitude images of stained biological thin sections

Very-high-resolution electron microscopy demonstrates similar phase image ‘particles’ in uncontaminated, unsupported thin sections of epoxy-embedded biological material and in simple thin carbon films, both of which show better than 5 Å resolution. Under such conditions it is possible to examine biological specimens for amplitude images well below the 20 Å limit commonly accepted for such preparations. With this very high resolution discrete amplitude images are found in sections after treatment with heavy-metal stain. These amplitude images are as small as 10 Å, a size equal to that of lead aggregates, which they may represent.     

超声变幅杆的设计及有限元分析

超声变幅杆在超声加工中的应用日益广泛。结合超声变幅杆理论,采用ANSYS10．0对变幅杆进行了模态分析和参数修正,在此基础土,设计并加工了一个应用于超声显微切割系统中的、谐振频率为60kHz的半波长圆锥形变幅杆,并进行了相关实验。实验结果表明,利用ANSYS软件辅助设计方法得到的超声变幅杆,其谐振频率与模态分析值非常接近,为超声变幅杆的设计、校核和优化提供了一种新途径。     

基于振幅调制的菲涅耳域的光学图像加密技术

针对基于菲涅耳域的双随机相位加密系统不能抵抗选择明文攻击的弱点,提出了一种基于振幅调制的菲涅耳域的图像加密方法。该方法通过在系统第二块随机相位板后面添加一个振幅调制密钥来实现加密,同时分析了该密钥的安全性,密钥参数对加密效果的影响。实验表明振幅调制密钥的密钥空间非常大,且正常解密时密钥吻合度要求非常高,攻击者很难获取原始图像的信息;另一方面引入振幅调制密钥后扰乱了系统固有的线性性质,添加非线性环节,从而提高了系统的抗选择明文攻击能力。研究可知:引入振幅调制技术后系统的安全性和抗攻击能力大大提高,加密效果良好。     

Unstable amplitude and noisy image induced by tip contamination in dynamic force mode atomic force microscopy

Liquid 1-decanethiol was confined on an atomic force microscope (AFM) tip apex and the effect was investigated by measuring amplitude-distance curves in dynamic force mode. Within the working distance in the dynamic force mode AFM, the thiol showed strong interactions bridging between a gold-coated probe tip and a gold-coated Si substrate, resulting in unstable amplitude and noisy AFM images. We show that under such a situation, the amplitude change is dominated by the extra forces induced by the active material loaded on the tip apex, overwhelming the amplitude change caused by the geometry of the sample surface, thus resulting in noise in the image the tip collects. We also show that such a contaminant may be removed from the apex by pushing the tip into a material soft enough to avoid damage to the tip.     

Rapid in‐focus corrections on quantitative amplitude and phase imaging using transport of intensity equation method

Transport of intensity equation (TIE) method can acquire sample phase distributions with high speed and accuracy, offering another perspective for cellular observations and measurements. However, caused by incorrect focal plane determination, blurs and halos are induced, decreasing resolution and accuracy in both retrieved amplitude and phase information. In order to obtain high‐accurate sample details, we propose TIE based in‐focus correction technique for quantitative amplitude and phase imaging, which can locate focal plane and then retrieve both in‐focus intensity and phase distributions combining with numerical wavefront extraction and propagation as well as physical image recorder translation. Certified by both numerical simulations and practical measurements, it is believed the proposed method not only captures high‐accurate in‐focus sample information, but also provides a potential way for fast autofocusing in microscopic system.     

采用虚设振幅逆解法估算弹性阻尼支承最佳参数

施加于转子－轴承系统的弹性阻尼支承，在设计参数选择合理的情况下可以明显改善系统的固有或强迫振动响应特性。本文采用虚设振幅逆解法计算弹性阻尼支承最佳参数。该方法既具有理论上的合理性，又便于工程设计采用，特别适用于结构复杂的系统设计。文中就单质量转子系统采用该方法估算最佳支承参数以控制系统不平衡响应进行了计算和分析。结果表明，按照虚设振幅逆解法所设计的弹性阻尼支承，在参数匹配得当时，对于改善系统的制振性和减小传递力是极为有效的。     

Adsorption of ZDDP on iron surfaces and its relation with surface tension

This paper reports work on the relationship of surface tension of ZDDP solutions to adsorption isotherms. The surface tension of the solutions varies with their composition, and information about adsorption, decomposition or other chemical changes of ZDDP in solution can be obtained from the correlation of solution concentration and surface tension. From this work, the authors conclude that adsorption of ZDDP on iron can occur at even low concentrations, increasing with temperature, and that decomposition, association and interaction between components may occur in solution at high temperatures.     

Friction property study of the surface of ZDDP and MoDTC antiwear additive films using AFM/LFM and force curve methods

The friction properties and material differences of the surface of ZDDP and MoDTC antiwear additive films, which give clear evidence of different friction coefficients in a pin-on-disc test, have been studied using atomic force microscopy (AFM)/lateral force microscopy (LFM) and force curve methods. The AFM/LFM observations show that the friction force on the surface of MoDTC additive films over the sliding area of a steel disc is lower and the friction force of ZDDP additive films is higher than that of afilmless area. Lateral force scope-trace evaluations reveal that the ratio of the friction forces on the surface of the ZDDP film, the filmless area, and the MoDTC film under the same normal force is approximately 1.5:1.0:0.7. Force curve measurements indicate that the surface materials of the ZDDP film, thefilmless area, and the MoDTC film differ according to their attractive forces, that is 29 nN for the ZDDP film, 22 nN for the filmless area, and 12 nN for the MoDTC film. These results correspond to the friction behaviour in the pin-on-disc test and also agree with the idea of the formation of solid MoS₂ lubricant from MoDTC additives on the surface of the antiwear film.     

大振幅电磁振动机械的电磁分析

大振幅电磁振动机械是运行在机电共振状态并能实现大振动位移的振动系统,分析大振幅电磁振动机械的电磁关系是对电磁振动机械进行结构参数优化设计的基础。为了获得大振幅电磁振动机械的电磁物理关系,依据大振幅电磁振动机械的磁路模型,利用等效磁路分析方法,详细推导了气隙磁通与电流的关系、电磁力和电流有效值,最后验证了等效磁路分析方法的正确性。     

Design of X-ray digital imaging and data acquisition system

X-ray digital imaging technology is a new method of nondestructive testing. Non-film real time digital radiograph, which has high efficiency and low cost, especially the characteristics of digital image exchangeability and storage convenience, has become the development direction. Because the existing system has the disadvantage of low imaging quality and only being used at low X-ray energy, a high quality imaging system based on scientific CCD camera has been developed, which has high spatial solution and high contrast sensitivity and can be used both at high energy and low energy. This paper introduces the constitution of the system, and designs the relative circuits. The experimental results show that the system has the better imaging quality and wider adapting range for X-ray energy, can needs the requirements of measurement.     

The substructure of immunoglobulin G resolved to 25 kDa using amplitude modulation AFM in air

Amplitude modulation (or tapping-mode) atomic force microscopy (AM AFM or TM AFM) in air can reveal sub-molecular details of isolated multi-subunit proteins, such as immunoglobulin G (IgG) antibodies, on atomically flat support surfaces such as mica [A. San Paulo, R. Garcia, Biophys. J. 78(3) (2000) 1599]. This is achieved by controlling the microscope imaging parameters (e.g. cantilever drive frequency and set-point amplitude) to keep the AFM tip predominantly in the attractive force regime. Under these conditions, the 50 kDa F(c) and F(ab) subunits can be resolved when the molecule has the appropriate orientation on the surface. The presence of a water layer on hydrophilic mica is an important factor affecting imaging contrast, a consequence of capillary neck formation between tip and surface [L. Zitzler, S. Herminghaus, F. Mugele, Phys. Rev. B 66(15) (2002) 155436]. Desiccation of samples to remove surface bound water layers can yield reproducible imaging of the IgG substructure [N.H. Thomson, J. Microsc. (Oxford) 217(3) (2004) 193]. This approach has also given higher resolution than previously achieved, down to about 25 kDa, and these data are detailed here. These subdomains are formed as two immunoglobulin folds from the light and heavy peptide chains of the IgG crossover. This result has been validated by comparing the AFM images with X-ray crystallography data from the protein data bank. These data show that the AFM can obtain 25 kDa resolution on isolated protein molecules with commercially available silicon tips, but, as expected for a local probe technique, resolution is highly dependent on the macromolecular orientation on the support surface.     

Digital in-line holography on amplitude and phase objects prepared with electron beam lithography

We report on the fabrication and characterization of amplitude and phase samples consisting of well defined Au or Al features formed on ultrathin silicon nitride membranes. The samples were manufactured using electron beam lithography, metallization and a lift-off technique, which allow precise lateral control and thickness of the metal features. The fabricated specimens were evaluated by conventional microscopy, atomic force microscopy and with the digital in-line holography set-up at the Lund Laser Centre. The latter uses high-order harmonic generation as a light source, and is capable of recovering both the shape and phase shifting properties of the samples. We report on the details of the sample production and on the imaging tests with the holography set-up.     

On the complex three-dimensional amplitude point spread function of lenses and microscope objectives: theoretical aspects, simulations and measurements by digital holography

The point spread function is widely used to characterize the three‐dimensional imaging capabilities of an optical system. Usually, attention is paid only to the intensity point spread function, whereas the phase point spread function is most often neglected because the phase information is not retrieved in noninterferometric imaging systems. However, phase point spread functions are needed to evaluate phase‐sensitive imaging systems and we believe that phase data can play an essential role in the full aberrations' characterization. In this paper, standard diffraction models have been used for the computation of the complex amplitude point spread function. In particular, the Debye vectorial model has been used to compute the amplitude point spread function of ×63/0.85 and ×100/1.3 microscope objectives, exemplifying the phase point spread function specific for each polarization component of the electromagnetic field. The effect of aberrations on the phase point spread function is then analyzed for a microscope objective used under nondesigned conditions, by developing the Gibson model ( Gibson & Lanni, 1991 ), modified to compute the three‐dimensional amplitude point spread function in amplitude and phase. The results have revealed a novel anomalous phase behaviour in the presence of spherical aberration, providing access to the quantification of the aberrations. This work mainly proposes a method to measure the complex three‐dimensional amplitude point spread function of an optical imaging system. The approach consists in measuring and interpreting the amplitude point spread function by evaluating in amplitude and phase the image of a single emitting point, a 60‐nm‐diameter tip of a Near Field Scanning Optical Microscopy fibre, with an original digital holographic experimental setup. A single hologram gives access to the transverse amplitude point spread function. The three‐dimensional amplitude point spread function is obtained by performing an axial scan of the Near Field Scanning Optical Microscopy fibre. The phase measurements accuracy is equivalent to λ/60 when the measurement is performed in air. The method capability is demonstrated on an Achroplan ×20 microscope objective with 0.4 numerical aperture. A more complete study on a ×100 microscope objective with 1.3 numerical aperture is also presented, in which measurements performed with our setup are compared with the prediction of an analytical aberrations model.     

Collision difference between Kerr spatial solitons and nonlinear Kerr spatial solitons

In order to study the collision of the Kerr solitons and the collision of the the nonlinear Kerr solitons,numerical simulation is employed and it is found that the collision of solutions is different.T...