• Tribology and Lubricants
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• 제28권6호
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• pp.289-296
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• 2012

Atomic force microscopy (AFM) has been used for imaging surfaces and measuring surface forces at the nano-scale. Force calibration is important for the quantitative measurement of forces at the nano-scale using AFM. Normal force calibration is relatively straightforward, whereas the lateral force calibration is more complicated since the lateral stiffness of the cantilever is often comparable to the contact stiffness. In this work, the lateral force calibrations of the rectangular cantilever were performed using torsional Sader's method, thermal noise method, and wedge calibration method. The lateral optical lever sensitivity for the thermal noise method was determined from the friction loop under various normal forces as well. Experimental results showed that the discrepancies among the results of the different methods were as large as 30% due to the effect of the contact stiffness on the lateral force calibration of the cantilever used in this work. After correction for the effect of contact stiffness, all the calibration results agreed with each other, within experimental uncertainties.

• 한국정밀공학회지
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• 제20권12호
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• pp.64-72
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• 2003

This paper presents a small loading and positioning device using VCM (voice coil motor). The developed device consists of a VCM-based linear actuating system, a capacitance displacement sensor and a cantilever deflection sensing system. The trust force of the VCM proportional to applied current moves the column supported on two pairs of parallel leaf springs. The infinitesimal displacement of moved column is detected by capacitance displacement sensor with a resolution of 0.1nm and a repeatability of 1nm. Also, a micro cantilever with known stiffness (200N/m), which is mounted on the end of the column, is used as a force sensor to detect the load applied to a specimen. After the cantilever contacts with the specimen, the deflection of cantilever and the load applied to the specimen are measured by using an optical lever system which consists of a diode laser, a mirror and a PSD (position sensitive detector). In this paper, an experimental system was constructed and its actuator and sensing parts were tested and calibrated. Also, the constructed system was applied to the indentation experiment and the load-displacement curve of aluminum was obtained. Experimental results showed that the developed device can be applied for performing nano indentation.

• Tribology and Lubricants
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• 제29권3호
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• pp.160-166
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• 2013

There is an indispensable need for force calibration for quantitative nanoscale force measurement using atomic force microscopy. Calibrating the normal force is relatively straightforward, whereas doing so for the lateral force is often complicated because of the difficulty in determining the optical lever sensitivity. In particular, the lateral force calibration of a colloidal probe in a liquid environment often has a larger uncertainty as a result of the effects of the epoxy, the location of the colloidal particle on the cantilever, and a decrease in the quality factor. In this work, the lateral force of a colloidal probe using a reference cantilever with a known spring constant was calibrated in a liquid environment. By obtaining the spring constant and the lateral sensitivity at the equator of a spherical colloidal particle, the damage to the bottom surface of the colloidal particle could be eliminated. Further, it was shown that the effect of the contact stiffness on the determination of the lateral spring constant of the cantilever could be minimized. It was concluded that this method can be effectively used for the lateral force calibration of a colloidal probe in a liquid environment.

• 한국주조공학회지
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• 제13권4호
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• pp.359-368
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• 1993

Mg-9wt.%Al and Mg-9wt.%-1.6wt%Zn/SiCp(particle size $40{\mu}m$) metal-matrix-composite specimens were manufactured by rheo-compocasting method, known for its effect of improving the wettability. The ceramic reinforcement particles(SiCp) were dispersed in the semi-solid magnesium alloy matrix slurry being vigorously stirred in a high frequency induction furnace under inert atmosphere. A microstructural study of the dispersed particles in the specimens, prepared under different conditions as regards the time(10min, 20min, 30min) and temperature of the stirring, was made with the aid of optical microscope and SEM. The effect of superheating was also observed. It is revealed that 30 minutes' stirring time of the semi-solid at 40% solid fraction temperature(Mg-9wt.%Al : $590^{\circ}C$, AZ91 : $576^{\circ}C$), as determined by the lever rule, gives a satisfactorily uniform distribution of the particles. The superheating is observed to enhance further the uniformity.

• Tribology and Lubricants
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• 제28권5호
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• pp.212-217
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• 2012

A modified thermal noise method was proposed to measure the normal spring constants of the colloidal probes for an atomic force microscope. We used commercial tipless cantilevers (length 150, width 30, nominal k 7.4 N/m) and borosilicate spheres with a diameter of 20 to fabricate colloidal probes. The inverse optical lever sensitivity of both the tipless cantilever and colloidal probes were used to measure the normal spring constant of the colloidal probes. We confirmed the accuracy and usefulness of our method by comparing the measurement results with those obtained using the nanoforce calibrator (NFC), which reportedly has an uncertainty of 1.00%. The modified thermal method showed a good agreement (~10% difference) with the NFC, allowing us to conclude that the modified thermal method could be employed for the effective measurement of the normal spring constants of colloidal probes.

• 한국광학회지
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• 제22권1호
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• pp.46-52
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• 2011

본 연구에서는 레버 증폭 구조를 이용한 플렉서 기반의 나노 스테이지를 설계, 제작하였다. 제작된 나노 스테이지를 샘플 스테이지로 채용한 공초점현미경을 개발하였다. 2차원 이미징의 구현을 위해서, 기존의 공초점현미경은 레이저를 이미징 평면상에 스캐닝하는 방식으로 구현된다. 본 연구에서는 백 나노미터의 구동정밀도를 가지는 나노 스테이지 위에 놓인 샘플을 2차원으로 스캐닝하면서 2차원 이미지를 구현할 수 있는 공초점현미경을 개발하였다. 플렉서 기반의 나노 스테이지는 이중 판스프링, 변위증폭 레버, PZT 엑추에이터 그리고 변위 센서로 구성 되어 있다. 스테이지의 구동 성능 해석을 위해 상용 유한요소 해석 프로그램을 이용하였다. 현미경에 사용되는 광원은 적색광 레이저이며, 레이저는 여러 광학요소를 거쳐 샘플스테이지의 샘플에 입사되고, 반사된 빛은 광센서인 PMT(Photo Multiplying Tube)로 계측되게 된다. 계측된 빛의 크기를 이용하여서 2차원 이미징을 구현하였다. 개발된 공초점 현미경으로 생쥐 귀의 피부조직을 관찰하여 현미경의 이미징 성능을 검증하였다. 설계된 샘플 스테이지는 기존의 공초점 현미경의 기계적인 Beam 스캐너를 대신함으로써 현미경의 광경로 및 전체시스템을 간소화 하였다.

• International Journal of Precision Engineering and Manufacturing
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• 제8권2호
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• pp.70-74
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• 2007

This paper describes the development of a nano-positioning system for nanoscale science and engineering. Conventional positioning systems, which can be expensive and complicated, require the use of laser interferometers or capacitive transducers to measure nanoscale displacements of the stage. In this study, a new self-displacement sensing (SDS) nano-stage was developed using mechanical magnification of its displacement signal. The SDS nano-stage measured the displacement of its movement using a position-sensitive photodiode (PSPD), a laser source, and a hinge-connected rotating mirror plate. A beam from a laser diode was focused onto the middle of the plate with the rotating mirror. The position variation of the reflected beam from the mirror rotation was then monitored by the PSPD. Finally, the PSPD measured the amplified displacement as opposed to the actual movement of the stage via an optical lever mechanism, providing the ability to more precisely control the nanoscale stage. The displacement amplification process was modeled by structural analysis. The simulation results of the amplification ratio showed that the distance variation between the PSPD and the mirror plate as well as the length L of the mirror plate could be used as the basic design parameters for a SDS nano-stage. The PSPD was originally designed for a total travel range of 30 to 60 mm, and the SDS nano-stage amplified that range by a factor of 15 to 25. Based on these results, a SDS nano-stage was fabricated using principle of displacement amplification.