• Tribology and Lubricants
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• v.23 no.6
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• pp.288-297
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• 2007

Adhesion and friction tests were carried out in order to investigate the effect of temperature on the tribological characteristics of poly (methylmethacrylate) (PMMA) film using AFM. The pull-off and friction forces on the PMMA film were measured under a high vacuum condition (below $1{\times}10^{-4}$ Pa) as the temperature of the PMMA film was increased from 300 K to 420 K (heating) and decreased to 300K (cooling). Friction tests were also conducted in both high vacuum and air conditions at room temperature. When the temperature was 420 K, which is 25 K higher than the glass transition temperature $(T_g)$ of PMMA, the PMMA film surface became deformable. Subsequently, the pull-off force was proportional to the maximum applied load during the pull-off force measurement. In contrast, when the temperature was under 395 K, the pull-off force showed no correlation to the maximum applied load. The friction force began to increase when the temperature rose above 370 K, which is 25 K lower than the $T_g$ of PMMA, and rapidly increased at 420 K. Decrease of the PMMA film stiffness and plastic deformation of the PMMA film were observed at 420 K in force-displacement curves. After the heating to 420 K, the fiction coefficient was measured under the air condition at room temperature and was found to be lower than that measured before the heating. Additionally, the RMS roughness increased as a result of the heating.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.390-390
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• 2014

Soft-lithography 기술 중의 하나인 Micro-Contact Printing (${\mu}$-CP) 기술은 패턴이 형성된 mold 위에 고분자 물질을 코팅하고 기판과 접촉시켜, 패턴 된 부분만 기판으로 전사시켜 패턴을 형성하는 방법이다. ${\mu}$-CP 기술은 Imprint 방식과 비교하여 잔여물을 제거하기 위한 ashing 공정이 필요 없으며, 상대적으로 패턴이 전사되기 위한 공정 온도와 압력이 낮은 장점이 있다. 한편, 기존의 Photolithography 기술로 유기기판에 패턴을 형성하는 것은 제한이 있으며, 자외선에 의해 유기기판의 특성이 변화될 수 있다. 또한 패턴 형성 후 고분자 패턴을 제거하는 용매가 기판이 손상 받게 된다. 본 실험에서는 poly (1H,1H,2H,2H-perfluorodecyl methacrylate) polymer (PFDMA) films을 패턴 된 poly (dimethylsiloxane) (PDMS) mold 위에 코팅하고 ${\mu}$-CP 기술을 통해 poly (methylmethacrylate) (PMMA), poly (vinyl pyrrolidone) (PVP)등과 같은 유기기판 위에 고분자 패턴 형성을 하였다. 이때 전사 가능한 온도는 상온이며, 압력은 코팅된 PFDMA films이 기판과 접촉될 수 있는 정도만 필요하다. PFDMA가 상온에서 전사 가능한 이유는 유리전이온도가 상온보다 낮기 때문이다. 또한 접촉각을 측정하여 접착력을 계산하면 PFDMA와 기판과의 접착력이 상대적으로 높기 때문이다. PFDMA는 플루오르계 용매에 제거되기 때문에 유기기판의 손상을 최소화 할 수 있다. ${\mu}$-CP 기술을 이용한 PFDMA의 패턴 형성 방법은 물질의 특성으로 flexible 및 organic device 제작에 응용 될 수 있다.

• Tribology and Lubricants
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• v.21 no.4
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• pp.177-184
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• 2005

The molecular dynamics simulation of nanoimprint lithography (NIL) using $SiO_2$ stamp and amorphous poly-(methylmethacrylate) (PNMA) film is performed to study pattern transfer in NIL. Force fields including bond, angle, torsion, van der Waals and electrostatic potential are used to describe the intermolecular and intramolecular force of PMMA molecules and $SiO_2$ stamp. Nose-Hoover thermostat is used to control the system temperature and cell multipole method is adopted to treat long range interactions. The deformation of PMMA film is observed during pattern transfer in the NIL process. For the detail analysis of deformation characteristics, the distributions of density and stress in PMHA film are calculated. The adhesion and friction forces are obtained by dividing the PMMA film into subregions and calculating the interacting force between subregion and stamp. Their effects on the pattern transfer are also discussed as varying the indentation depth and speed.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.343-348
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• 2007

Molecular dynamics study of thermal NIL (Nano Imprint Lithography) process is performed to examine stamp-resist interactions. A layered structure consists of Ni stamp, poly-(methylmethacrylate) thin film resist and Si substrate was constructed for isothermal ensemble simulations. Imposing confined periodicity to the layered unit-cell, sequential movement of stamp followed by NVT simulation was implemented in accordance with the real NIL process. Both vdW and electrostatic potentials were considered in all non-bond interactions and resultant interaction energy between stamp and PMMA resist was monitored during stamping and releasing procedures. As a result, the stamp-resist interaction energy shows repulsive and adhesive characteristics in indentation and release respectively and irregular atomic concentration near the patterned layer were observed. Also, the spring back and rearrangement of PMMA molecules were analyzed in releasing process.

• Journal of the Korean Graphic Arts Communication Society
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• v.13 no.2
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• pp.1-17
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• 1995

Organic thin film electroluminescene devices were fabricated using by molecularly doped method with N,N`-diphenyl-N,N`-bis(3-methylphenyl)-1,1`-biphenyl-4,4`-diamine(TPD) as a hole transport material, tris(8-quinolinolate) aluminium(III)(Alq3) as an emitting and electron transport agent, fluorescent squarylium(SQ) dye as a dopant, and poly(methylmethacrylate) as polymer materials. A cell structure of ITO/TPD-PMMA/Alq3-dopant/Mg was employed. The EL spectrum covers a wide range of the visible region and orange emission os observed. Two peaks at 520 and 660nm correspond to the emissions 620nm Alq3 and SQ dye, respectively.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.310-313
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• 2008

Recently, study on the weak interaction energy between the soft polymer surface and liquid crystals has been a primary topic for new LC device applications. In this paper, to understand the switching property of nematic liquid crystals (LCs) at the interface with a weak anchoring boundary, we investigate experimentally the rotation property of surface nematic director by electric field on non-treated Poly-Methylmethacrylate (PMMA, $T_g=110^{\circ}C$, Sigma Aldrich) film observed under various temperatures including the glass transition temperature ($T_g$) of the polymer layer.

• Tribology and Lubricants
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• v.22 no.5
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• pp.243-251
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• 2006

Molecular dynamics simulations of nanoimprint lithography NIL) are performed in order to investigate effects of process parameters, such as stamp shape, imprinting temperature and adhesive energy, on nanoimprint lithography process and pattern transfer. The simulation model consists of an amorphous $SiO_{2}$ stamp with line pattern, an amorphous poly-(methylmethacrylate) (PMMA) film and an Si substrate under periodic boundary condition in horizontal direction to represent a real NIL process imprinting long line patterns. The pattern transfer behavior and its related phenomena are investigated by analyzing polymer deformation characteristics, stress distribution and imprinting force. In addition, their dependency on the process parameters are also discussed by varying stamp pattern shapes, adhesive energy between stamp and polymer film, and imprinting temperature. Simulation results indicate that triangular pattern has advantages of low imprinting force, small elastic recovery after separation, and low pattern failure. Adhesive energy between surface is found to be critical to successful pattern transfer without pattern failure. Finally, high imprinting temperature above glass transition temperature reduces the imprinting force.

• Applied Science and Convergence Technology
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• v.24 no.3
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• pp.53-59
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• 2015

The field-effect transistors (FETs) with a graphene-based p-n junction channel were fabricated using the patterned self-assembled monolayers (SAMs). The self-assembled 3-aminopropyltriethoxysilane (APTES) monolayer deposited on $SiO_2$/Si substrate was patterned by hydrogen plasma using selective coating poly-methylmethacrylate (PMMA) as mask. The APTES-SAMS on the $SiO_2$ surface were patterned using selective coating of PMMA. The APTES-SAMs of the region uncovered with PMMA was removed by hydrogen plasma. The graphene synthesized by thermal chemical vapor deposition was transferred onto the patterned APTES-SAM/$SiO_2$ substrate. Both p-type and n-type graphene on the patterned SAM/$SiO_2$ substrate were fabricated. The graphene-based p-n junction was studied using Raman spectroscopy and X-ray photoelectron spectroscopy. To implement low voltage operation device, via ionic liquid ($BmimPF_6$) gate dielectric material, graphene-based p-n junction field effect transistors was fabricated, showing two significant separated Dirac points as a signature for formation of a p-n junction in the graphene channel.