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Role of Counter-substrateSurface Energy in MacroscaleFriction of Nanofiber Arrays
Kim, Yongkwan,Limanto, Francesca,Lee, Dae Ho,Fearing, RonaldS.,Maboudian, Roya American ChemicalSociety 2012 Langmuir Vol.28 No.5
<P>The effect of counter-substrate surface energy on macroscalefrictionof nanofiber array is studied. Low-density polyethylene (LDPE) fibrillararray fabricated from silicon nanowire template is tested againstglass substrates modified with various self-assembled monolayers,which exhibit a wide range of surface energy. A large drop in frictionover a narrow range of surface energy is observed and explained interms of drastically reduced number of fibers in actual contact, inaddition to the reduced surface energy. The relationship between surfaceenergy and fiber engagement is discussed with Johnson–Kendall–Roberts(JKR) and elastic beam models.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2012/langd5.2012.28.issue-5/la204078z/production/images/medium/la-2011-04078z_0002.gif'></P>
Strategies for controlling Si nanowire formation during Au-assisted electroless etching
Lee, Dae Ho,Kim, Yongkwan,Doerk, Gregory S.,Laboriante, Ian,Maboudian, Roya Royal Society of Chemistry 2011 Journal of materials chemistry Vol.21 No.28
<P>Dramatic changes in the morphologies of Si nanowires (NWs) ranging from vertical, to hooked, to ground-collapsed shapes are presented depending on the HF/H<SUB>2</SUB>O<SUB>2</SUB> ratio in the etch solution during Au-assisted electroless etching. It is shown that the deviations from vertical NWs are not due to capillary action but correlated with the development of nanoporous structures, which is attributed to excess hole (h<SUP>+</SUP>) diffusion toward the NWs' sidewalls during the etching process. The role of hole diffusion is made more evident by observation of NWs with the neck formation when transitioning to different etching regimes during SiNW formation. Furthermore, the hooked and ground-collapsed SiNW can be suppressed at the cost of enhanced tapering by adding a strong electrolyte in solution, which is correlated to reduced etching rate resulting from electric screening of the charged Au surfaces. We provide an important finding that common salts such as NaCl, KCl, and CaCl<SUB>2</SUB> can be useful retardants for the metal-assisted electroless etching. The new insights into structural transformation presented in this study afford greater control over the structure of SiNWs produced by metal-assisted electroless etching.</P> <P>Graphic Abstract</P><P>Au-assisted electroless etching is regulated by addition of common electrolytes, which also leads to dramatic change in SiNW morphology. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1jm11164g'> </P>
A simple soft lithographic nanopatterning of gold on gallium arsenide via galvanic displacement.
Lim, Hyuneui,Noh, Jung-Hyun,Choi, Dae-Geun,Kim, Wan-Doo,Maboudian, Roya American Scientific Publishers 2010 Journal of nanoscience and nanotechnology Vol.10 No.8
<P>Nanoscale patterning of gold layers on GaAs substrate is demonstrated using a combination of soft lithographic molding and galvanic displacement deposition. First, an electroless deposition method has been developed to plate gold on GaAs with ease and cost-effectiveness. The electroless metallization process is performed by dipping the GaAs substrates into a gold salt solution without any reducing agents or additives. The deposition proceeds via galvanic displacement in which gold ions in the aqueous solution are reduced by electrons arising from the GaAs substrate itself. The deposition rate, surface morphology and adhesion property can be modulated by the plating parameters such as the choice of acids and the immersion time. Second, soft lithographic patterning of nanodots, nanorings, and nanolines are demonstrated on GaAs substrates with hard-polydimethylsiloxane (h-PDMS) mold and plasma etching. This method can be easily applied to the metallization and nanopatterning of gold on GaAs surfaces.</P>
Chi, Won Seok,Lee, Chang Soo,Long, Hu,Oh, Myoung Hwan,Zettl, Alex,Carraro, Carlo,Kim, Jong Hak,Maboudian, Roya American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.42
<P>A simple and flexible strategy for controlled synthesis of mesoporous metal oxide films using an amphiphilic graft copolymer as sacrificial template is presented and the effectiveness of this approach for gas-sensing applications is reported. The amphiphilic graft copolymer poly(vinyl chloride)-g-poly(oxyethylene methacrylate) (PVC-g POEM) is used as a sacrificial template for the direct synthesis of mesoporous SnO2. The graft copolymer self assembly is shown to enable good control over the morphology of the resulting SnO2 layer. Using this approach, mesoporous SnO2 based sensors with varied porosity are fabricated in situ on a microheater platform. This method reduces the interfacial contact resistance between the chemically sensitive materials and the microheater, while a simple fabrication process is provided. The sensors show significantly different gas-sensing performances depending on the SnO2 porosity, with the highly mesoporous SnO2 sensor exhibiting high sensitivity, low detection limit, and fast response and recovery toward hydrogen gas. This printable solution-based method can be used reproducibly to fabricate a variety of mesoporous metal oxide layers with tunable morphologies on various substrates for high-performance applications.</P>