Excellent tribological surfaces for nano/micro-scale applications: Nature-based solutions

R. Arvind Singh,Duc-Cuong Pham,Eui-Sung Yoon 한국트라이볼로지학회 2007 한국트라이볼로지학회 학술대회 Vol.2007 No.11

In this work we show - how successful solutions for the tribological issues arising at nano/micro-scales can be got by learning from nature. Taking the lead from the 'Lotus effect', we have fabricated various bio-mimetic surfaces and have characterized them for their tribological properties at nano/micro-scales. The bio-inspired surfaces namely the nano/micro-patterned surfaces were fabricated by capillary force lithography on thin polymeric films using artificial and natural templates. The fabricated surfaces were subjected to tribological testing at nano-scale using atomic force microscope and a micro-tribe-tester was used to conduct tests at micro-scale. Investigations revealed that the bio-inspired surfaces have excellent tribological properties owing to their hydrophobic nature and to the reduction in the real area of contact projected by them. Looking at the superior performance of these surfaces, we propose them as possible solutions to reduce adhesion and friction forces in applications related to miniaturized devices (micro/nano-electro-mechanical systems (MEMS/NEMS)).

Dual pattern for enhancing light extraction efficiency of white organic light-emitting diodes

Kim, Kwan,Han, Kyoung-Hoon,Kim, Yang-Doo,Huh, Daihong,Han, Yoonjay,Lee, Heon,Kim, Jang-Joo Elsevier 2018 ORGANIC ELECTRONICS Vol.57 No.-

<P><B>Abstract</B></P> <P>Nano and micro-patterns (dual patterns) were introduced on a glass substrate as an extraction layer to enhance the light extraction efficiency of white organic light-emitting diodes (WOLEDs). The dual-patterned glass was fabricated by thermal evaporation, direct printing, and reactive ion etching. The combination of nano- and micro-structures imparted highest current density and luminance to the dual-patterned WOLED without electrical degradation. Additionally, the dual-patterned WOLED exhibited higher current and power efficiencies compared to that of the nano- and micro-patterned WOLEDs, which increased by 21% and 27% at 1 mA/cm<SUP>2</SUP>, respectively, as compared to that of the reference.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The dual pattern was fabricated using nanoimprint lithography and reactive ion etching process on the glass substrates. </LI> <LI> The compromised between the nano and micro structures imparted highest current and power efficiencies to the WOLED. </LI> <LI> Light extraction efficiency of dual pattered WOLED was increased by light scattering effect at the glass/air interfaces. </LI> <LI> The current efficiencies and power efficiency of the dual patterned WOLED was enhanced by 21% and 27% at 1 mA/cm<SUP>2</SUP>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Review on Microstencil Lithography Technologies

최진호(Jin Ho Choi),최혜진(Hye Jin Choi),김규만(Gyu Man Kim) Korean Society for Precision Engineering 2018 한국정밀공학회지 Vol.35 No.11

We introduce technological development of stencil lithography, for new micro and nano fabricated method as a patterning technique. Stencil lithography has advantages of photoresistless, reusable patterning technique, and large area micro and nano patterning. The principle of stencil lithography is as follows: Materials are deposited through perforated holes on the membrane surface, of stencil in micro and nanoscale. In this paper, the fabrication method and application of three types of stencils, are reviewed according to the material. Solid-state stencils based on silicon, are fabricated by micro-fabrication processing of photolithography and etching. Metal stencils are fabricated by metal etching, electroforming, and laser machining. Polymer stencils are fabricated by molding and casting of polymers, such as PDMS, Hydrogel and Photocrosslinkable polymer, etc. Stencils fabricated from a variety of ways may be applied to nanopatterns, nano-wire patterning, and metal electrode fabrication, and used in metal deposition or etching masks and non-planar surface metal patterning techniques. Stencil lithography is applied in various areas of flexible displays, bio-devices, wearable sensors, etc.

Submicron-scale Polymeric Patterns for Tribological Application in MEMS/NEMS

R. Arvind Singh,Eui-Sung Yoon,Hong Joon Kim,Hosung Kong,Hoon Eui Jeong,Kahp Y. Suh 한국트라이볼로지학회 2005 KSTLE International Journal Vol.6 No.2

Submicron-scale patterns made of polymethyl methacrylate (PMMA) were fabricated on silicon-wafer using a capillarity-directed soft lithographic technique. Polyurethane acrylate (PUA) stamps (Master molds) were used to fabricate the patterns. Patterns with three different aspect ratios were fabricated by varying the holding time. The patterns fabricated were the negative replica of the master mold. The patterns so obtained were investigated for their adhesion and friction properties at nano-scale using AFM. Friction tests were conducted in the range of 0-80 nN. Glass (Borosilicate) balls of diameter 1.25 ㎜ mounted on cantilever (Contact Mode type NPS) were used as tips. Further, micro-friction tests were performed using a ball-on-flat type micro-tribo tester, under reciprocating motion, using a soda lime bass (1 ㎜ diameter) under a normal load of 3,000 mN. All experiments were conducted at ambient temperature (24±1℃) and relative humidity (45±5%). Results showed that the patterned samples exhibited superior tribological properties when compared to the silicon wafer and non-patterned sample (PMMA thin film) both at the nano and micro-scales, owing to their increased hydrophobicity and reduced real area of contact. In the case of patterns it was observed that their morphology (shape factor and size factor) was decisive in defining the real area of contact.

Submicron-scale Polymeric Patterns for Tribological Application in MEMS/NEMS

Singh R. Arvind,Yoon Eui-Sung,Kim Hong Joon,Kong Hosung,Jeong Hoon Eui,Suh Kahp Y. Korean Tribology Society 2005 KSTLE International Journal Vol.6 No.2

Submicron-scale patterns made of polymethyl methacrylate (PMMA) were fabricated on silicon-wafer using a capillarity-directed soft lithographic technique. Polyurethane acrylate (PUA) stamps (Master molds) were used to fabricate the patterns. Patterns with three different aspect ratios were fabricated by varying the holding time. The patterns fabricated were the negative replica of the master mold. The patterns so obtained were investigated for their adhesion and friction properties at nano-scale using AFM. Friction tests were conducted in the range of 0-80 nN. Glass (Borosilicate) balls of diameter 1.25 mm mounted on cantilever (Contact Mode type NPS) were used as tips. Further, micro-friction tests were performed using a ball-on-flat type micro-tribe tester, under reciprocating motion, using a soda lime ball (1 mm diameter) under a normal load of 3,000 mN. All experiments were conducted at ambient temperature ($24{\pm}1^{\circ}C$) and relative humidity ($45{\pm}5\%$). Results showed that the patterned samples exhibited superior tribological properties when compared to the silicon wafer and non-patterned sample (PMMA thin film) both at the nano and micro-scales, owing to their increased hydrophobicity and reduced real area of contact. In the case of patterns it was observed that their morphology (shape factor and size factor) was decisive in defining the real area of contact.

나노/마이크로 복합 금형 제작을 위한 소프트 마스크 위상 이동 리소그래피 공정 기술 연구

김지원(J. W. Kim),조상욱(S. W. Cho),이태호(T. H. Lee),김창석(C. S. Kim),정명영(M. Y. Jeong) 한국정밀공학회 2013 한국정밀공학회 학술발표대회 논문집 Vol.2013 No.5월

Direct Fabrication of Micro/Nano-Patterned Surfaces by Vertical-Directional Photofluidization of Azobenzene Materials

Choi, Jaeho,Cho, Wonhee,Jung, Yeon Sik,Kang, Hong Suk,Kim, Hee-Tak American Chemical Society 2017 ACS NANO Vol.11 No.2

<P>Anisotropic movement of azobenzene materials (i.e., azobenzene molecules incorporated in polymer, glass, or supramolecules) has provided significant opportunities for the fabrication of micro/nanoarchitectures. The examples include circular holes, line gaps, ellipsoidal holes, and nanofunnels. However, all of the previous studies have only focused on the lateral directional movement for the structural shaping of azobenzene materials. Herein, we propose structural shaping based on a vertical directional movement of azobenzene materials. To do this, light with oblique incidence, containing normal direction light polarization, was illuminated onto azobenzene materials film contact with patterned elastomeric molds (i.e., PDMS) so that the resulting vertical directional movement of azobenzene materials fills in the cavities of the molds and results in pattern formation. As a result, a range of patterns with sizes of features from micro- to sub-100 nm scale was successfully fabricated in a large area (few cm(2)), and the structural height was deterministically controlled by simply adjusting irradiation time. In addition to the notable capability of fabricating the single-scale structures, the technique provides a facile way to fabricate complex hierarchical multiscale structures, ensuring its versatility and wide applicability to various applications. As a selected exemplary application of the multiscale structures, a superhydrophobic surface has been successfully demonstrated.</P>

Characterization on shrinkage of a shape of polymer based Micro-Lens Array in NIL process

Ho-Young Song,Jong-Ho Cho,Eunsong Oh,Moon Kyu Kwak 한국소성가공학회 2018 플라스틱가공 심포지엄(한일 공동 세미나) Vol.2018 No.8

Polymer shrinkage in nano-imprint lithography (NIL) process is one of critical considerations. Especially, it should be considered very cafully when manufacturing the curved shape of optical elements, because micro-lens array (MLA) should be controlled to fit the desired curvature shape in order to achieve the wanted optical performance. In this paper, we have characterized the shrinkage effects during NIL process on MLA curvature shape and produced optical performance with experiments. The master mold of MLA was generated by 2 photon-polymerization (2PP) additive manufacturing method, and tested samples were replicated from master mold with NIL method. Several types of resin were adjusted to make specimens and we compared the shrinkage effects on each case. The shrinkage effects showed the different trends according to the both of NIL materials and MLA shapes. Those characterizations are able to be applied to compensate the MLA design and master mold generation step to achieve a desired performance of MLA products.

Highly improved light extraction with a reduced spectrum distortion of organic light-emitting diodes composed by the sub-visible wavelength nano-scale periodic (~250nm) structure and micro-lens array

Choi, K.B.,Shin, S.J.,Park, T.H.,Lee, H.J.,Hwang, J.H.,Park, J.H.,Hwang, B.Y.,Park, Y.W.,Ju, B.K. Elsevier Science 2014 ORGANIC ELECTRONICS Vol.15 No.1

Out-coupling enhanced organic light-emitting diodes (OLEDs) with micro-lens arrays and a nano-scale periodic light-extraction structure-a photonic crystal (PC)-utilizing laser interference lithography (LIL) are demonstrated. Generally, PC-based OLEDs suffer from a distorted and shifted spectrum, despite a highly improved intensity. However, in this study, we demonstrate PC-based OLEDs with a distortion-free spectrum and a highly improved out-coupling performance. It was found that spectrum distortion decreased with the pitch size of the PC. The PC-based OLED with a 250nm pitch size showed a dramatically reduced spectral shift: International Commission on Illumination 1931 color coordinate of (Δ0.00, Δ0.00) and Δpeak wavelength of 0nm as compared with the reference. Simultaneously, the external quantum efficiency and the power efficiency were enhanced by up to 178% and 264%, respectively, as compared with the reference. Moreover, through the LIL, simple and maskless processes were achieved for a light-extraction structure over a large area.

초발수 표면을 만들기 위한 마이크로-나노 몰드 제작 공정

임동욱,박규백,박정래,고강호,이정우,김지훈 한국금형공학회 2021 한국금형공학회지 Vol.15 No.4

In recent materials industry, researches on the technology to manufacture super hydrophobic surface byeffectively controlling the wettability of solid surface are expanding. Research on the fabrication of super hydrophobicsurface has been studied not only for basic research but also for self-cleaning, anti-icing, anti-friction, flow resistancereduction in construction, textile, communication, military and aviation fields. A super hydrophobic surface is defined asa surface having a water droplet contact angle of 150 ° or more. The contact angle is determined by the surface energyand is influenced not only by the chemical properties of the surface but also by the rough structure. In this paper, maskless lithography using DMD, electro etching, anodizing and hot embossing are used to make thepolymer resin PMMA surface super hydrophobic. In the fabrication of microstructure, DMDs are limited by the spacingof microstructure due to the structural limitations of the mirrors. In order to overcome this, maskless lithography usinga transfer mechanism was used in this paper. In this paper, a super hydrophobic surface with micro and nano compositestructure was fabricated. And the wettability characteristics of the micro pattern surface were analyzed.