A Study on HA Titanium Surface with Atomic Force Microscope (AFM)

Three kinds of titanium surface especially the HA surface are analyzed. Titanium was treated by 3 kinds of methods that were acid ＆ alkali, calcic solution and apathe solution. Samples were observed by optic microscope and atomic force microscope （ AFM ） . The typical surface morphology of the acid and alkali group is little holes, and on the two HA surface the tiny protuberances is typical. The surface treated by apatite solution was smoother than the two formers. The rough surface treated with acid and alkali was propitious to Ca^＋ , P^- and proteins＇ adhesion, and the relatively smooth HA surface was of benefit to the cell adhesion.

MICRO/NANO-MACHINING ON SILICON SURFACE WITH A MODIFIED ATOMIC FORCE MICROSCOPE

To understand the deformation and removal mechanism of material on nano-scale at ultralow loads,a systemic study on AFM micro/nano-machining on single crystal ailicon is conducted. The results indicate that AFM nano- machining has a precisely dimensional controllability and a good surface quality on nanometer scale.A SEM is adopted to observe nano-machined region and chips,the results indicate that the material removal mechanisms change with the applied normal load. An XPS is used to analyze the changes of chemical composition inside and outside the nano-machined region respectively.The nano-indentation which is conducted with the same AFM diamond tip on the machined region shows a big discrepancy compared with that on the macro-scale. The calculated results show higher nano-hardness and elastic modulus than normal values .This phenomenon on be regarded as the indentation size effect(ISE).

Nonlinear control techniques for an atomic force microscope system

Two nonlinear control techniques are proposed for an atomic force microscopesystem. Initially, a learning-based control algorithm is developed for the microcantilever-samplesystem that achieves asymptotic cantilever tip tracking for periodic trajectories. Specifically, thecontrol approach utilizes a learning-based feedforward term to compensate for periodic dynamics andhigh-gain terms to account for non-periodic dynamics. An adaptive control algorithm is thendeveloped to achieve asymptotic cantilever tip tracking for bounded tip trajectories despiteuncertainty throughout the system parameters. Simulation results are provided to illustrate theefficacy and performance of the control strategies.

Surface Electromechanical Coupling on DLC Film with Conductive Atomic Force Microscope

Diamond-like carbon (DLC) film composed of microscopically insulation but microscopically a mixture of conducting (sp2) and insulating (sp3) phases was discussed on the local modification with a conductive atomic force microscope (C-APM). Especially, a topographic change was observed when a direct current (DC) bias-voltage was applied to the DLC film. Experimental results show that a nanoscale pit on DLC surface was formed when applying a positive 25 V on DLC film. According to the interacting force between CoCr-coated microelectronic scanning probe (MESP) tip and DLC surface, as well as the Sondheimer oscillation theory, the 'scalewing effect' of the pit was explained. Electromechanical coupling on DLC film suggested that the depth of pits increased with an increase of load applied to surface when the cantilever-deflected signal was less than a certain threshold voltage.

Sorting Gold and Sand(Silica) Using Atomic Force Microscope-Based Dielectrophoresis

Additive manufacturing-also known as 3D printing-has attracted much attention in recent years as a powerful method for the simple and versatile fabrication of complicated three-dimensional structures.However,the current technology still exhibits a limitation in realizing the selective deposition and sorting of various materials contained in the same reservoir,which can contribute significantly to additive printing or manufacturing by enabling simultaneous sorting and deposition of different substances through a single nozzle.Here,we propose a dielectrophoresis(DEP)-based material-selective deposition and sorting technique using a pipette-based quartz tuning fork(QTF)-atomic force microscope(AFM) platform DEPQA and demonstrate multi-material sorting through a single nozzle in ambient conditions.We used Au and silica nanoparticles for sorting and obtained 95% accuracy for spatial separation,which confirmed the surfaceenhanced Raman spectroscopy(SERS).To validate the scheme,we also performed a simulation for the system and found qualitative agreement with the experimental results.The method that combines DEP,pipette-based AFM,and SERS may widely expand the unique capabilities of 3D printing and nano-micro patterning for multi-material patterning,materials sorting,and diverse advanced applications.

Edge Effects and Coupling Effects in Atomic Force Microscope Images

The AFM images were obtained by an atomic force microscope (AFM) and transformed from the deformation of AFM micro cantilever probe. However, due to the surface topography and surface forces applied on the AFM tip of sample, the deformation of AFM probe results in obvious edge effects and coupling effects in the AFM images.The deformation of AFM probe was analyzed,the mechanism of the edge effects and the coupling effects was investigated, and their results in the AFM images were studied. It is demonstrated by the theoretical analysis and AFM experiments that the edge effects make lateral force images more clear than the topography images,also make extraction of frictional force from lateral force images more complex and difficult. While the coupling effects make the comparison between topography images and lateral force images more advantage to acquire precise topography information by AFM.

Preparation of La-Ti Composite Oxide Nanocrystal and Examination of Their Surface Topography with Atomic Force Microscope

With sol-gel method, nanometer La-Ti composite oxide was successfully prepared at a low temperature (750～800C) using polyethylene glycol as dispersant. By means of atomic force microscope, the surface pattern, particle size distribution, and specific surface area were studied. The compound particle surface appears as a smooth sheet, the mean size of the compound is 25.38 nm. On the specific surface, the particle erects at a height of 4.69 nm. The surface area is 58.90 nm2. The La-Ti composite oxide nanocrystal prefers to narrow and even particle size distribution and the homogeneity of surface topography.

Competitive Adsorption between Bovine Serum Albumin and Collagen Observed by Atomic Force Microscope

Atomic force microscopy (AFM) was used to study the competitive adsorption betweenbovine serum albumin (BSA) and type Ⅰ collagen on hydrophilic and hydrophobic silicon wafers.BSA showed a grain shape and the type Ⅰ collagen displayed fibril-like molecules with relativelyhomogeneous height and width, characterized with clear twisting (helical formation). These AFMimages illustrated that quite a lot of type Ⅰ collagen appeared in the adsorption layer on hydrophilicsurface in a competitive adsorption state, but the adsorption of BSA was more preponderant than thatof type Ⅰ collagen on hydrophobic silicon wafer surface. The experiments showed that theinfluence of BSA on type Ⅰ collagen adsorption on hydrophilic surface was less than that onhydrophobic surface.

Studying Aggregate in Lysozyme Solution by Atomic Force Microscope

The aggregates in lysozyme solution with different NaCl concentration were investigated by Atomic Force Microscope (AFM). The AFM images show that there exist lysozyme monomers, n-mers and clusters in lysozyme solution when the conditions are not suitable for crystal growth. In favorable conditions for crystal growth, the lysozyme clusters disappear and almost only monomers exist in solution.

Development of XY scanner with minimized coupling motions for high-speed atomic force microscope

The design and fabrication processes of a novel scanner with minimized coupling motions for a high-speed atomic force microscope （AFM） were addressed. An appropriate design modification was proposed through the analyses of the dynamic characteristics of existing linear motion stages using a dynamic analysis program, Recurdyn. Because the scanning speed of each direction may differ, the linear motion stage for a high-speed scanner was designed to have different resonance frequencies for the modes, with one dominant displacement in the desired directions. This objective was achieved by using one-direction flexure mechanisms for each direction and mounting one stage for fast motion on the other stage for slow motion. This unsymmetrical configuration separated the frequencies of two vibration modes with one dominant displacement in each desired direction, and hence suppressed the coupling between motions in two directions. A pair of actuators was used for each axis to decrease the crosstalk between the two motions and give a sufficient force to actuate the slow motion stage, which carried the fast motion stage, A lossy material, such as grease, was inserted into the flexure hinge to suppress vibration problems that occurred when using an input triangular waveforrn. With these design modifications and the vibration suppression method, a novel scanner with a scanning speed greater than 20 Hz is achieved.

In situ observation of surface structures of cardiovascular endothelial cells with atomic force microscope

Objective To observe the surface structures of cardiovascular endothelial cells in situ with atomic force microscope （AFM）. Methods Fresh aorta and aortic valve were dissected from 10 healthy male New Zealand white rabbits. Before fixed in 1% formaldehyde, the fresh tissues were washed in the buffer phosphate solution. Under general microscope, the fixed aorta or valve was spread on the double side stick tape which had already been stuck on the glass slide. The intima of aorta or the aorta side of valve was towards upside, Then the specimen was dried under 37 degrees centigrade in an attemperator and was washed with pure water. After dried again, the specimen was loaded on the platform ofNanoScope Ⅲa AFM and was scanned in tapping mode with the scanning speed of 0.5 HZ. Results The surface structures of endothelial cell on the fixed and dried tissue could be observed clearly in situ with AFM. aortic endothelial cells were large, branched and arranged sparsely and parallel to the direction of blood flow, whereas endothelial cells on aorta valve surface were small, less branched and arranged intensively and vertical to the direction of blood flow. When the scanning range was dwindled, granular ultra-structures could be observed on the surface of endothelial cells, and, as the scanning range was dwindled further, fissure and convolution could be seen on the surface of granules from aortic endothelial cells. Centre cavity and surrounding swelling volcano-like structure could be seen on the surface of granules from endothelial cells of aortic valve. Conclusions It＇s feasible to observe the surface ultra-structures of cardiovascular endothelial cells in situ with AFM and morphological information provided by AFM might be of clinical value in future histopathological diagnosis（JGeriatr Cardiol2009; 6：178-181）.

Atomic force microscope study of WC-10Co cemented carbide sintered from nanocrystalline composite powders

In order to compare the spark plasma sintedng （SPS） process plus hot isostatic press （HIP） with vacuum sintedng plus HIP, an investigation was carried out on the topography, microstructure and gain size distribution of nanocrystalline WC-10Co composite powder and the sintered specimens prepared by SPS plus HIP and by vacuum sintering plus HIP by means of atomic force microscopy （AFM）. The mechanical properties of the sintered specimens were also investigated. It is very easy to find cobalt lakes in the specimen prepared by vacuum sintering plus HIP process. But the microstructure of the specimen prepared by SPS plus HIP is more homogeneous, and the grain size is smaller than that prepared by vacuum sintering plus HIP. The WC-10Co ultrafine cemented carbide consolidated by SPS plus HIP can reach a relative density of 99.4%, and the transverse rupture strength （TRS） is higher than 3540 MPa, the Rockwell A hardness （HRA） is higher than 92.8, the average grain size is smaller than 300 nm, and the WC-10Co ultrafine cemented carbide with excellent properties is achieved. The specimen prepared by SPS with HIP has better properties and microstructure than that prepared by vacuum sintering with HIP.

Surface topography of La-Ti composite oxide nanocrystallines examined with atomic force microscope

By means of atomic force microscope, the surface pattern, particle size distribution, and specific surface area of La Ti composite oxide were studied. The compound particle surface appears as a smooth sheet, the even size of the compound ranges from 19.85 nm to 25.38 nm. The particle seems smooth, which erects at a height from 4.69 nm to 5.88 nm.The surface area ranges from 58.90 nm 2 to 1 238.04 nm 2. The La Ti composite oxide nanocrystallines enjoy a narrow and even particle size distribution and accumulate closely.

Constant Force Feedback Controller Design Using PID-Like Fuzzy Technique for Tapping Mode Atomic Force Microscopes

A novel constant force feedback mechanism based on fuzzy logic for tapping mode Atomic Force Microscopes (AFM) is proposed in this paper. A mathematical model for characterizing the cantilever-sample interaction subsystem which is nonlinear and contains large uncertainty is first developed. Then, a PID-like fuzzy controller, combing a PD-like fuzzy controller and a PI controller, is designed to regulate the controller efforts and schedule the applied voltage of the Z-axis of the piezoelectric tube scanner to maintain a constant tip-sample interaction force during sample-scanning. Using the PID-like fuzzy controller allows the cantilever tip to track sample surface rapidly and accurately even though the topography of the surface is arbitrary and not given in advance. This rapid tracking response facilitates us to observe samples with high aspect ratio micro structures accurately and quickly. Besides, the overshoot which will result in tip crash in commercial AFMs with a traditional PID controller could be avoided. Additionally, the controller efforts can be intelligently scheduled by using the fuzzy logic. Thus, continuous manual gain-tuning by trial and error such as those in commercial AFMs is alleviated. In final, computer simulations and experimental verifications are provided to demonstrate the effectiveness and confirm the validity of the proposed controller.

Variation of Surface Adhesion Force During the Formation of OTS Self-assembled Monolayer Investigated by AFM

Variation of the surface adhesion force during the formation of octadecyl trichlorosilane (OTS) self-assembled monolayer on a glass substrate surface was investigated by atomic force microscope (AFM). The research shows that the hydrophobicity and the adhesion force of the sample surface increases gradually while the substrate surface is covered by OTS molecules as the reaction proceeds. After 15min reaction, a close-packed and smooth OTS self-assembled monolayer could form on the glass substrate surface with an advancing contact angle of 105° and an interfacial energy of 55.79mJ·m-2.

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.

Damage of DNA ends induced by mechanical force during AFM nano-manipulation

An experimental and statistical study was carried out to explore the effects of mechanical forces on the ends of linear double-stranded DNA (dsDNA) fragments. Mechanical force was applied onto individual DNA molecules during atomic force microscope (AFM)-based picking-up manipulation. By comparing the PCR efficiency of two DNA fragments with primers either at ends or at the inner regions, it was found that the ends of DNA fragments were damaged during picking-up process.

Mechanical force-induced DNA damage during AFM single-molecule manipulation

Many environmental factors can cause DNA damage, such as radiation, heat, oxygen free radical, etc., which can induce mutation during DNA replication. Meanwhile, DNA molecules are subjected to various mechanical forces in numerous biological processes. However, it is unknown whether the mechanical force would induce DNA damage and introduce mutation during DNA replication. With the combination of single-molecule manipulation based on atomic force microscopy (AFM), single molecular polymerase chain reaction (SM-PCR) and Sanger's sequencing, we investigated the effect of mechanical force on DNA. The results show that mechanical force can cause DNA damage and induce DNA mutation during amplification.

Nanoindentation tests on single crystal copper thin film with an AFM

Nanoindentation tests performed in a commercial atomic force microscope have been utilized to directly measure the elastic modulus and the hardness of single crystal copper thin films fabricated by the vacuum vapor deposition technique. Nanoindentation tests were conducted at various indentation depths to study the effect of indentation depths on the mechanical properties of thin films. The results were interpreted by using the Oliver-Pharr method with which direct observation and measurement of the contact area are not required. The elastic modulus of the single crystal copper film at various indentation depths was determined as (67.0±(6.9) GPa) on average which is in reasonable agreement with the results reported in literature. The indentation hardness constantly increases with decreasing indentation depth, indicating a strong size effect.

Measurement of the friction coefficient of a fluctuating contact line using an AFM-based dual-mode mechanical resonator

A dual-mode mechanical resonator using an atomic force microscope （AFM） as a force sensor is developed. The resonator consists of a long vertical glass fiber with one end glued onto a rectangular cantilever beam and the other end immersed through a liquid-air interface. By measuring the resonant spectrum of the modified AFM cantilever, one is able to accurately determine the longitudinal friction coefficient ξv along the fiber axis associated with the vertical oscillation of the hanging fiber and the traversal friction coefficient ξh perpendicular to the fiber axis associated with the horizontal swing of the fiber around its joint with the cantilever. The technique is tested by measurement of the friction coefficient of a fluctuating （and slipping） contact line between the glass fiber and the liquid interface. The experiment verifies the theory and demonstrates its applications. The dual-mode mechanical resonator provides a powerful tool for the study of the contact line dynamics and the rheological property of anisotropic fluids.