• Journal of Institute of Control, Robotics and Systems
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• v.6 no.1
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• pp.57-65
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• 2000

In this paper, a model reference adaptive control for the atomic force microscope (AFM) of tapping mode is investigated. The dynamics between the AFM system and al sample is mathematically modeled as a second order spring-mass-damper system with oscillatory inputs. The attractive and repulsive forces between the tip of the AFM system and the sample are derived using the Lennard-Jones potential energy. By non-dimensionalizing the displacement of the tip and the input frequency, the chaotic behavior near a resonance frequency is better depicted through the non-dimensionalized equations. Four nonlinear analysis techniques, a phase portrait, sensitive dependence on initial conditions, a power spectral density function, and a Pomcare map are investigated. Because the equations of motion derived in this paper involve unknown parameter values such as the damping effect of the air and the interaction constants between materials, the standard model reference adaptive control is adopted. Two control objectives, the prevention of chaos and the tracking of reference signal, are pursued. Simulation results are included.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.12 s.255
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• pp.1611-1617
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• 2006

A compact and two-dimensional atomic force microscope (AFM) using an orthogonal sample scanner, a calibrated homodyne laser interferometer and a commercial AFM head was developed for use in the nano-metrology field. The x and y position of the sample with respect to the tip are acquired by using the laser interferometer in the open-loop state, when each z data point of the AFM head is taken. The sample scanner which has a motion amplifying mechanism was designed to move a sample up to $100{\times}100{\mu}m^2$ in orthogonal way, which means less crosstalk between axes. Moreover, the rotational errors between axes are measured to ensure the accuracy of the calibrated AFM within the full scanning range. The conventional homodyne laser interferometer was used to measure the x and y displacements of the sample and compensated via an X-ray interferometer to reduce the nonlinearity of the optical interferometer. The repeatability of the calibrated AFM was measured to sub-nm within a few hundred nm scanning range.

• Tribology and Lubricants
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• v.23 no.1
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• pp.9-13
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• 2007

Despite numerous researches on atomic-scale friction have been carried out for understanding the origin of friction, lots of questions about sliding friction still remain. It is known that friction at atomic-scale always shows unique phenomena called 'stick-slips' which reflect atomic lattice of a scanned surface. In this work, experimental study on the effects of system stiffnesses and load on the atomic-scale stick-slip friction of graphite was performed by using an Atomic Force Microscope and various cantilevers/tips. The objective of this research is to figure out the dependency of atomic-scale friction on the nanomechanical properties in sliding contact such as load, stiffness and contact materials systematically. From this work, the experimental observation of transitions in atomic-scale friction from smooth sliding to multiple stick-slips in air was first made, according to the lateral cantilever stiffness and applied normal load. The superlubricity of graphite could be verified from friction vs. load experiments. Based on the results, the relationship between the stickslip behaviors and contact stiffness was carefully discussed in this work. The results or this work indicate that the atomic-scale stick-slip behaviors can be controlled by adjusting the system stiffnesses and contact materials.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.05a
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• pp.717-718
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• 2010

• Polymer(Korea)
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• v.38 no.3
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• pp.358-363
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• 2014

Adhesion forces between acrylate imprinting resin and a surface treated atomic force microscope (AFM) tip were investigated. Compared to the untreated silicon tip, 38% of the adhesion force is reduced for the hydrophobic tip treated with $CH_4$ plasma whereas 1.6 time increases is found for the hydrophilic tip with $O_2$ plasma treatment. Such a measurement of the adhesion force using AFM provides very quantitative results on adhesion comparing to the crosscut adhesion test which gives qualitative results. Since the adhesion area becomes larger as the imprinting pattern size gets smaller, the surface treatment issue becomes more important in the nano-imprinting process.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.4 s.181
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• pp.52-59
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• 2006

Surface qualities of a micro-processed sample with a pulse laser have been investigated by making use of scanning confocal microscope(SCM) and atomic force microscope(AFM). Samples are bump electrodes and ITO glass of LCD module used in a mobile phone and a wafer surface scribed by UV laser. A image of $140{\times}120{\mu}m^2$ is obtained within 1 second by SCM because scan speed of a x-axis and y-axis are 1kHz and 1Hz, respectively. AFM is able to correctly measure the hight and width of ITO, and scribing depth and width of a wafer with a resolution less than 300nm. However, the scan speed is slow and it is difficult to distinguish a surface composed of different kinds of materials. Results show that SCM is preferable to obtain a image of a sample composed of different kinds of material than AFM because the intensity of a reflected light from the surface is different for each material.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.88-89
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• 2014

In dynamic force microscopy, the cantilever oscillates at a resonant frequency, and the tip deflection is measured at this frequency. The cantilever deflection is, however, highly nonlinear, and the surface properties can be embedded in the deflection at the frequencies other than the original resonant frequency of the cantilever. Multifrequency atomic force microscopy includes the excitation and detection of the deflection in two or more frequencies which are higher harmonics or eigenmodes. This can overcome the limitations of conventional atomic force microscope. We reviewed the multifrequency atomic force microscopy and its applications in many fields.

• Journal of Welding and Joining
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• v.31 no.1
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• pp.43-50
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• 2013

The spot welds of Transformation Induced Plasticity (TRIP) steels are prone to interfacial failure and narrow welding current range. Hard microstructures in weld metal and heat affected zone arenormally considered as one of the main reason to accelerate the interfacial failure mode. There fore, detailed observation of weld microstructure for TRIP steels should be made to ensure better weld quality. However, it is difficult to characterize the microstructure, which has similar color, size, and shape using the optical or electron microscopy. The atomic force microscope (AFM) can help to analyze microstructure by using different energy levels for different surface roughness. In this study, the microstructures of resistance spot welds for AHSS are analyzed by using AFM with measuring the differences in average surface roughness. It has been possible to identify the different phases and their topographic characteristics and to study their morphology using atomic force microscopy in resistance spot weld TRIP steels. The systematic topographic study for each region of weldments confirmed the presence of different microstructures with height of 350nm for martensite, 250nm for bainite, and 150nm for ferrite, respectively.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.04a
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• pp.50-55
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• 2003

Atomic force microscope(AFM) techniques are increasingly used for tribological studies of engineering surfaces at scales ranging from atomic and molecular to microscale. AFM with suitable tips is being used for nanofabrication nanomachining purposes. In this paper, machining characteristics of silicon have been investigated by nano indentation and nano scratch. Mechanisms of material removal on the microscale are studied and the Taguchi method is introduced to acquire optimum parameters for nanomachining. This work shows effectiveness of the Taguchi method in nanomachining. Also, Acoustic Emission(AE) is introduced for the monitoring of nanomachining.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.3
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• pp.163-170
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• 2004

Atomic force microscope (AFM) techniques are increasingly used fur tribological studies of engineering surfaces at scales ranging from atomic and molecular to micro-scale. Recently, AFM with suitable tips is being used for nano fabrication/nano machining purposes. In this paper, machining characteristics of silicon were investigated by nano indentation and nano scratch. Nano-scale material removal mechanisms are studied and the Taguchi method was introduced to acquire optimum parameters for nano machining. Also, Acoustic Emission (AR) is used for the monitoring of nano machining.