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RISS 인기검색어
- 검색키워드
- 저자 : Ashkan Vaziri (검색결과 5 건)
- 무료
- 기관 내 무료
- 유료
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Nanoscale ripples on polymers created by a focused ion beam
Moon, Myoung-Woon,Han, Jun Hyun,Vaziri, Ashkan,Her, Eun Kyu,Oh, Kyu Hwan,Lee, Kwang-Ryeol,Hutchinson, John W IOP Pub 2009 Nanotechnology Vol.20 No.11
<P>We show that focused ion beam irradiation results in the creation of peculiar one- and two-dimensional nanoscale features on the surface of polyimide—a common polymer in electronics, large scale structures, and the automobile industry, as well as in biomedical applications. The role of ion beam incident angle, acceleration voltage, and fluence on the morphology of the structural features is systematically investigated, and insights into the mechanisms of formation of these nanoscale features are provided. Moreover, by using the maskless patterning method of the focused ion beam system, we have developed a robust technique for controlled modification of the polymeric surface. The technique, which is analogous to using a gray glass with varying darkness to control the radiation from the sun, but at a much smaller scale, enables the ion intensity and angle to be controlled at each surface point of the polymer, giving rise to structural surface features with desired shape and morphology. </P>
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High aspect ratio wrinkles on a soft polymer
Ahmed, Sk. Faruque,Rho, Geon-Ho,Lee, Kwang-Ryeol,Vaziri, Ashkan,Moon, Myoung-Woon Royal Society of Chemistry 2010 SOFT MATTER Vol.6 No.22
<P>Instability of a stiff thin film attached to a compliant substrate often leads to the emergence of exquisite wrinkles with length scales that depend on the system geometry and applied stresses. These patterns have vast potential applications including in tissue engineering, flexible electronics and the semiconductor industry. However, one of the limiting factors in the usage of these patterns is the low amplitude/wavelength ratio that can be achieved using the current surface engineering techniques. Here, we present an effective method that allows the creation of wrinkles with an amplitude/wavelength aspect ratio as large as 2.5 on a soft polymer. In this method, first, the surface of a poly(dimethylsiloxane) (PDMS) is pre-patterned using an Ar ion beam. Then, an amorphous carbon film gets deposited on the pre-patterned polymeric surface using glancing angle deposition (GLAD). We show that the amplitude of the created patterns can be varied between several nm to submicron size by changing the carbon deposition time, allowing us to harness patterned polymeric substrates for a variety of applications. Specifically, we demonstrate a potential application of the high aspect ratio wrinkles for changing the surface optical band gap.</P> <P>Graphic Abstract</P><P>This work presents a method to pattern polymer surfaces with wrinkles with an amplitude/wavelength ratio as large as 2.5. A novel application of high aspect ratio wrinkles in optics is demonstrated. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0sm00386g'> </P>
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문명운(Myoung-Woon Moon),차태곤(Tae-Gon Cha),이광렬(Kwang-Ryeol Lee),Ashkan Vaziri,김호영(Ho-Young Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
Inspired by the gecko's footpad structure, we developed a method to create tilted micropillars on the surface of an elastomeric polymer mimicking the geometry of gecko's setae. The method combines son lithography to create straight micropillars and ion beam irradiation to tilt the straight micropillars in a controlled fashion. We experimentally quantify the asymmetric adhesion and friction characteristics of the fabricated tilted micropillars as a function of the tilting angles. The tilting angle of the pillars was varied by changing the incident angle and duration of the ion beam irradiation. Potential applications of the developed pattern include non-wetting painting and switchable adhesion essential in wall-climbing robots.
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Moon, Myoung-Woon,Cha, Tae-Gon,Lee, Kwang-Ryeol,Vaziri, Ashkan,Kim, Ho-Young Royal Society of Chemistry 2010 Soft matter Vol.6 No.16
<P>Asymmetric adhesion is used by many insects and gecko lizards, allowing them to move on nearly any surface – horizontal, tilted or vertical. The feet of many of these creatures is covered with intricate fibrillar structures that are responsible for their superb manoeuvring ability. Among these creatures, gecko lizards have one of the most efficient and interesting adhesion devices consisting of finely angled arrays of branched fibers (setae). Here, we developed a method to create tilted Janus (two-face) micropillars on the surface of an elastomeric polymer to mimic the geometry of a gecko's footpad. The method combines soft lithography to create straight micropillars and ion beam irradiation to tilt the straight micropillars in a controlled fashion. A set of experiments were performed to measure the adhesion and friction characteristics of the fabricated tilted micropillars. Our experiments showed that the friction force along the tilting direction is approximately three times higher than the friction force associated with the sliding against the tilting direction of tilted micropillars due to the difference in the contact area during sliding of a glass ball.</P> <P>Graphic Abstract</P><P>A simple technique for the fabrication of tilted polymer micropillars that mimics geckos’ footpad structure was demonstrated by exposing straight micropillars to an Ar ion beam. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0sm00126k'> </P>
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Highly Anisotropic Adhesive Film Made from Upside-Down, Flat, and Uniform Vertically Aligned CNTs
Hong, Sanghyun,Lundstrom, Troy,Ghosh, Ranajay,Abdi, Hamed,Hao, Ji,Jeoung, Sun Kyoung,Su, Paul,Suhr, Jonghwan,Vaziri, Ashkan,Jalili, Nader,Jung, Yung Joon American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.49
<P>We have created a multifunctional dry adhesive film with transferred vertically aligned carbon nanotubes (VA-CNTs). This unique VA-CNT film was fabricated by a multistep transfer process, converting the flat and uniform bottom of VA-CNTs grown on atomically flat silicon wafer substrates into the top surface of an adhesive layer. Unlike as grown VA-CNTs, which have a nonuniform surface, randomly entangled CNT arrays, and a weak interface between the CNTs and substrates, this transferred VA-CNT film shows an extremely high coefficient of static friction (COF) of up to 60 and a shear adhesion force 30 times higher (12 N/cm(2)) than that of the as-grown VA-CNTs under a very small preloading of 0.2 N/cm(2). Moreover, a near-zero normal adhesion force was observed with 20 mN/cm(2) preloading and a maximum 100-mu m displacement in a piezo scanner, demonstrating ideal properties for an artificial gecko foot. Using this unique structural feature and anisotropic adhesion properties, we also demonstrate effective removal and assembly of nanoparticles into organized micrometer-scale circular and line patterns by a single brushing of this flat and uniform VA-CNT film.</P>
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