• Tribology and Lubricants
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• v.29 no.3
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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.

• Tribology and Lubricants
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• v.21 no.1
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• pp.1-7
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• 2005

Effect of Surface roughness on nanoscale adhesion was studied experimentally by using colloidal probe technique. Glass micro balls having the radius of $3.3\~17.4{\mu}m$ were glued at the end of AFM cantilevers to prepare colloidal probes. Adhesion force between the colloidal probe and Si-wafer was measured using pull-off force measuring method. Results showed that the measured adhesion forces are not the function of the radius of the glued balls because the ball surfaces are rough. It is also found that roughness parameters such as $R_a,\;R_q\;and\;R_{max}$ do not have important role on nanoscale adhesion. In order to find the effect of surface roughness on nanoscale adhesion, the bearing areas were extracted from the measured topography of glued balls. After normalizing the measured adhesion force with the bearing area, it was found that the normalized adhesion force kept constant as function of the radius of glued ball.

• Tribology and Lubricants
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• v.27 no.6
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• pp.344-350
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• 2011

Friction and wear behavior of tungsten oxide nanorods (TONs) was investigated using friction force microscopy(FFM) employing colloidal probes instead of conventional sharp tips. Vertically well-ordered TONs with 40 nm diameter, 130 nm length and 100 nm pitch width were synthesized on an anodic aluminium oxide substrate using two step electrochemical anodizing processes. The colloidal probe (diameter 20 ${\mu}m$) attached at the free end of tipless cantilever was oscillated(scanned) against a stationary surface of vertically aligned TONs with various scan speeds (1.2 ${\mu}m/s$, 3.0 ${\mu}m/s$ and 6.0 ${\mu}m/s$) and sliding cycles (100, 200 and 400) under normal load of 800 nN. The friction force and wear depth decreased with the increase of the scan speed. Plastically deformed thin layers were formed and sparsely deposited on the worn nonorod surface. The lower wear rate of the TONs with the longer oscillating cycles was attributed to the decreased real contact pressure due to the increase of real contact area between the colloidal probe and the TONs.

• Tribology and Lubricants
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• v.28 no.5
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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.

• Tribology and Lubricants
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• v.33 no.3
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• pp.92-97
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• 2017

The understanding of the friction characteristics of micro-textured surface is of great importance to enhance the tribological properties of nano- and micro-devices. We fabricate rectangular patterns with submicron-scale structures on a Si wafer surface with various pitches and heights by using a focused ion beam (FIB). In addition, we fabricate tilted rectangular patterns to identify the influence of the tilt angle ($45^{\circ}$ and $135^{\circ}$) on friction behaviour. We perform the friction test using lateral force microscopy (LFM) employing a colloidal probe. We fabricate the colloidal probe by attaching a $10{\pm}1-{\mu}m$-diameter borosilicate glass sphere to a tipless silicon cantilever by using a ultraviolet cure adhesive. The applied normal loads range between 200 nN and 1100 nN and the sliding speed was set to $12{\mu}m/s$. The test results show that the friction behavior varied depending on the pitch, height, and tilt angle of the microstructure. The friction forces were relatively lower for narrower and deeper pitches. The comparison of friction force between the sub-micro-structured surfaces and the original Si surface indicate an improvement of the friction property at a low load range. The current study provides a better understanding of the influence of pitch, height, and tilt angle of the microstructure on their tribological properties, enabling the design of sub-micro- and micro-structured Si surfaces to improve their mechanical durability.

• Tribology and Lubricants
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• v.35 no.3
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• pp.169-175
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• 2019

In lithium-ion batteries (LIBs), the stress induced by the volume change of an electrode during charge-discharge processes may often cause the mechanical integrity of the electrode to degrade. Polymer binders with enhanced mechanical properties are preferred for improved mechanical integrity and cycling stability of the electrode. In addition, given that sliding and shearing between the polymer binder and components in the electrode may readily occur, frictional and adhesion characteristics of the polymer binder may play a critical role in the mechanical integrity of the electrode. In this study, frictional and adhesion characteristics of polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) were investigated using a colloidal probe atomic force microscope. Friction loops were obtained under various normal forces ranging from 0 to 159 nN in air and electrolyte and then the interfacial shear strengths of PAN and PVDF in air were calculated to be $1.4{\pm}0.5$ and $1.3{\pm}0.3MPa$, respectively. The results show that in electrolyte, interfacial shear strength of PAN decreased slightly ($1.2{\pm}0.2MPa$), whereas that of PVDF decreased drastically ($0.06{\pm}0.01MPa$). Decreases in mechanical properties and adhesion in electrolyte may be responsible for the decrease in interfacial shear strength in electrolyte. The findings from this study may be helpful in developing polymer binders to improve the mechanical integrity of electrodes in LIBs.

• Tribology and Lubricants
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• v.11 no.5
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• pp.40-46
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• 1995

This study concerns the design and development of the non-vibrating capacitance probe which could be used as a non-contact sensor for tribological wear. This device detects surface charge through temporal variation in the work function of a material. Experiments are performed to demonstrate the operation of the probe on a roating aluminum shaft. The reference electrode of the probe, made of lead, is placed adjacent (< 1.25-mm distance) to the shaft. Both surfaces which are electrically connected, form a capacitor. An artificial spatial variation in the work function is imposed on the shaft surface by coating a segment along the shaft circumference with a colloidal silver paint. As the shaft rotates, the reference electode senses changing contact potential difference with the shaft surface, owing to compositional variation. Temporal variation in the contact potential difference induces a current through the electrical connection. This current is amplified and converted to a voltage signal by an electoronic circuit with an operational amplifier. The magnitude of the signal decreases asymptotically with the electrode-shaft distance and increases linearly with the rotational frequency. These results are consistent with the theoretical model. Potential applications of the probe on wear monitoring are proposed.

• Bulletin of the Korean Chemical Society
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• v.19 no.10
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• pp.1054-1059
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• 1998

Fluorescence and dynamic light scattering measurements were applied to the study of formation and structure of aggregated colloidal particles in modified poly(ethylene-co-methylacrylate) ionomers in aqueous solution. Both 8-anillino-l-naphthalene-sulfonic acid (ANS) and pyrene were used as fluorescence probe to obtain the information on the structure of particle surface and inside, respectively. Three different ionomers used in this study started to aggregate at very dilute concentration, 3-8 x 10-6 g/mL. In this study, we demonstrate that the polyethylene ionomers can form stable nanoparticles. The hydrophobic core made of the polyethylene backbone chains is stabilized by the ionic groups on the particle surface. Such a formed stable nanoparticles have a relatively narrow size distribution with an average radius in the range of 27-48 nm, depending on the kind of ionic groups. Once the stable particles are formed, the particle size distributions were nearly constant. This study shows another way to prepare surfactant-free polyethylene nanoparticles.

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.186-187
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• 2003

최근 들어 단일 양자점이나 단일 분자에 대한 분광 연구가 매우 관심을 끌고 있는데, 이는 미세구조 물질의 근본 물성을 밝히고자 하는 물리적인 관점뿐만 아니라 이를 실제적으로 이용하려는 실용적인 관점에서도 매우 중요한 주제이기 때문이다. 그러나 단일 양자점이나 단일 분자의 분광을 위해서는 공간적인 분해능이 우수할 뿐만 아니라 그 계에서 나오는 매우 미약한 광 신호를 검출하여야 하는 고도의 기술이 필요하다. (중략)

• Korean Journal of Microbiology
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• v.44 no.4
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• pp.346-351
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• 2008

This study develops DNA array which can detect specific sequence of human papilomavirus (HPV) by using lateral flow membrane assay which is usually used for point of care test including pregnant diagnosis. Principle of HPV DNA array is as follow; fixing DNA probe which is peculiar to HPV type 6, 11, 16, 18, 31, 45 on a surface of lateral flow membrane and inducing hybridization response between probe and HPV PCR products which is obtained by using biotin-labeled MY09/l1 primers. And then, we can see the result of DNA hybridization that streptavidin labelled colloidal gold is responded with hybrid biotin. Lateral flow membrane array developed in this study confirms major HPV type economically and conveniently compared with existing HPV DNA chip method.