OPTICALLY TRANSPARENT GLASS WITH VERTICALLY ALIGNED SURFACE Al2O3 NANOWIRES HAVING SUPERHYDROPHOBIC CHARACTERISTICS

JIN-YEOL KIM,,KUNBAE NOH,CHULMIN CHOI,KARLA S. BRAMMER,MARIANA LOYA,LI-HAN CHEN,SUNGHO JIN,BRAMMER 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2010 NANO Vol.5 No.2

We have shown in this paper that the self-ordered pore structure of anodic aluminum oxide (AAO) can be utilized as a basis to conveniently form large-area Al2O3 nanowire arrays on a glass surface. An aluminum oxide nanowire array has been produced by aluminum film deposition on glass followed by anodization, then simple chemical etching. The glass surface as prepared is highly superhydrophobic, with a contact angle as high as 169°. The thinness (~ 340 nm) and vertical alignment of the aluminum oxide nanowires with empty spaces in-between essentially contribute to maintaining the optical transparency of the glass substrate. Interestingly, substantially suppressed UV transmission in the ~ 300–400 nm spectrum region was observed with the presence of the Al2O3 nanowires on the glass substrate. Such a durable surface ceramic nanowire structure can be useful for producing superhydrophobic, self-cleaning glasses with a variety of potential applications such as UV protecting glass windows for high rise buildings with reduced consumption of water and cleaning chemicals for positive environmental effects.

Influence of sterilization methods on cell behavior and functionality of osteoblasts cultured on TiO₂ nanotubes

Oh, S.,Brammer, K.S.,Moon, K.S.,Bae, J.M.,Jin, S. Elsevier 2011 Materials Science and Engineering C Vol.31 No.5

We investigated the adhesion, proliferation and osteogenic functionality of osteoblasts cultured on titanium dioxide (TiO<SUB>2</SUB>) nanotubes in response to different sterilization methods (dry autoclaving vs. wet autoclaving). We prepared various sizes (30-100nm diameter) of TiO<SUB>2</SUB> nanotubes on titanium substrates by anodization, sterilized nanotubes by different conditions, and seeded osteoblast cells onto the nanotube surfaces with two different cell seeding densities (10,000 vs. 50,000 cells/well in 12-culture well). The result of this study indicates that the adhesion, proliferation and alkaline phosphatase activity of osteoblasts cultured on only the larger 70 and 100nm TiO<SUB>2</SUB> nanotube arrays were dramatically changed by the different sterilization conditions at a low cell seeding density. However, with a higher cell seeding density (50,000 cells/well in 12-cell culture well), the results revealed no significant difference among altered nanotube geometry, 30-100nm diameters, nor sterilization methods. Next, it was revealed that the nanofeatures of proteins adhered on nanotubular TiO<SUB>2</SUB> morphology are altered by the sterilization method. It was determined that this protein adhesion effect, in combination with the cell density of osteoblasts seeded onto such TiO<SUB>2</SUB> nanotube surfaces, has profound effects on cell behavior. This study clearly shows that these are some of the important in vitro culture factors that need to be taken into consideration, as well as TiO<SUB>2</SUB> nanotube diameters which play an important role in the improvement of cell behavior and functionality.

GUIDED NANOSTRUCTURES USING ANODIZED ALUMINUM OXIDE TEMPLATES

KUNBAE NOH,KARLA S. BRAMMER,성태연,진성호 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2011 NANO Vol.6 No.6

Long-range ordered nanoporous aluminum oxide pattern via guided anodization technique in combination with lithographic techniques has been investigated. In addition, modified anodization process can significantly change the resultant pore geometry, which will be of great interest in realizing advanced devices including biomedical and magnetic recording applications.

RANS and LES Simulations at Partial Load in Francis Turbines : Three-Dimensional Topology and Dynamic Behaviour of Inter-Blade Vortices

F Doussot,G Balarac,J Brammer,Y Laurant,O Metais 한국유체기계학회 2020 International journal of fluid machinery and syste Vol.13 No.1

Hydraulic machines are designed to operate in flow conditions close to the best efficiency point. However, to respond to the increasing demand for flexibility mainly due to the integration of renewable energy in the electric grid, the operating range of Francis turbines has to be extended towards smaller discharge levels without restriction. When Francis turbines are operated typically between 30% and 60% of the rated output power, the flow field is characterized by the appearance of inter-blade vortices in the runner. In these off-design operating conditions and due to these phenomena, dynamic stresses level can increase, and potentially lead to fatigue damage of the mechanical structure of the machine. The objective of this paper is to present investigations on the dynamic behaviour of the inter-blade vortices and their impact on the runner by using numerical simulations. Computations were performed with different turbulence modelling approaches to assess their relevance and reliability: Reynolds-Averaged Navier-Stokes (RANS) and Large-Eddy Simulation (LES). Computations aimed to better understand the emergence condition of the inter-blade vortices. The analysis showed that vortices can be generated due to poor inlet adaptation at part load, however other vortices can also be due to a local backflow in the runner. The competition between these both phenomena leads to various topologies of the inter-blade vortices. The numerical results were compared to experimental visualizations performed on scaled model as well as to previous numerical studies results. The impact of these inter-blade vortices on the runner were also investigated by considering the pressure fluctuations induced on the blades. The dynamic loading on the blade has to be known in order to evaluate the lifetime of the runner by mechanical analysis. Different operating conditions have been simulated to understand how the pressure fluctuations depend on the operating conditions. The localization of the pressure fluctuations and their consequences on the frequency signature of the torque fluctuations have been analyzed. This article is presenting a part of the work presented at the 29th IAHR Symposium on Hydraulic Machinery and Systems, Kyoto, 2018 [1], and presents another vortex topology and a comparison of LES results of several operating conditions.

Strongly Superhydrophobic Silicon Nanowires by Supercritical CO₂Drying

최철민,Yeoungchin Yoon,홍대훈,Karla S. Brammer,Kunbae Noh,오영,오승한,Frank E. Talke,Sungho Jin 대한금속·재료학회 2010 ELECTRONIC MATERIALS LETTERS Vol.6 No.2

This paper reports on the extremely superhydrophobic behavior of supercritical CO₂ processed silicon nanowires (SiNWs) with a contact angle in excess of ~177°. Vertically aligned silicon nanowires with 10 nm to 40nm diameter and 1 mm to 3 mm in length were obtained by electroless etching (EE) technique. The asfabricated SiNWs were superhydrophilic with no water droplet formation (zero contact angle), and were then completely transformed to an extreme superhydrophobic state when their nanoscale surface roughness is combined with trichlorosilane hydrophobic coating. The processed SiNW array was so hydrophobic that water droplets always bounced off the surface and did not allow contact angle measurements to be obtained unless the substrate was intentionally given a concave-curvature by vacuum suction. Utilization of a hydrophobically surface-treated micro-pipette syringe enabled the release of a water droplet onto this extremely superhydrophobic surface for contact angle measurement. To prevent severe nanowire agglomeration during the drying process of wet etched SiNWs, supercritical CO₂ drying was utilized, which process significantly improved the nano configuration and enhanced hydrophobicity.

고순도몰리브덴제조기술현황

( Chul Min Choi ),( Yeoung Chin Yoon ),( Dae Hoon Hong ),( Karla S. Brammer ),( Kun Bae Noh ),( Young Oh ),( Seung Han Oh ),( Frank E. Talke ),( Sung Ho Jin ) 대한금속재료학회 ( 구 대한금속학회 ) 2010 재료마당 Vol.23 No.3

This paper reports on the extremely superhydrophobic behavior of supercritical CO2 processed silicon nanowires (SiNWs) with a contact angle in excess of ~177°. Vertically aligned silicon nanowires with 10 nm to 40 nm diameter and 1 mm to 3 mm in length were obtained by electroless etching (EE) technique. The as-fabricated SiNWs were superhydrophilic with no water droplet formation (zero contact angle), and were then completely transformed to an extreme superhydrophobic state when their nanoscale surface roughness is combined with trichlorosilane hydrophobic coating. The processed SiNW array was so hydrophobic that water droplets always bounced off the surface and did not allow contact angle measurements to be obtained unless the substrate was intentionally given a concave-curvature by vacuum suction. Utilization of a hydrophobically surface-treated micro-pipette syringe enabled the release of a water droplet onto this extremely superhydrophobic surface for contact angle measurement. To prevent severe nanowire agglomeration during the drying process of wet etched SiNWs, supercritical CO2 drying was utilized, which process significantly improved the nano configuration and enhanced hydrophobicity.

Long-range ordered aluminum oxide nanotubes by nanoimprint-assisted aluminum film surface engineering

Noh, Kunbae,Choi, Chulmin,Kim, Jin-Yeol,Oh, Young,Brammer, Karla S.,Loya, Mariana C.,Jin, Sungho American Vacuum Society 2010 Journal of Vacuum Science & Technology. B Vol.28 No.6

Geometry transformation and alterations of periodically patterned Si nanotemplates by dry oxidation

Park, Jeongwon,Chen, Li-Han,Hong, Daehoon,Choi, Chulmin,Loya, Mariana,Brammer, Karla,Bandaru, Prab,Jin, Sungho IOP Pub 2009 Nanotechnology Vol.20 No.1

<P>We report on the size-dependent transformation and geometrical modifications of periodically patterned Si templates by a combination of dry oxidation and chemical etching. Deep ultraviolet lithography patterned circular holes with diameters varying between 190 nm and 1 µm on Si wafers were oxidized at 1000 °C using dry oxygen for various durations, with selected samples chemically etched for oxide removal for additional alterations. An interesting phenomenon of a circular-to-square shape transformation of the holes was observed, which was particularly pronounced in the sub-200 nm regime. We tentatively attribute the change to the surface energy and geometry constraints in nanoscale patterns. </P>

MORPHOLOGY CONTROL OF CARBON NANOTUBES THROUGH FOCUSED ION BEAMS

M. LOYA,J. E. PARK,L. H. CHEN,K. S. BRAMMER,P. R. BANDARU,S. JIN 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2008 NANO Vol.3 No.6

This research demonstrates the capability of controlled, focused ion beam (FIB)–assisted tailoring of morphologies in both multiwall carbon nanotubes (CNTs) and Y junction nonlinear CNT systems through defect engineering. We have shown that a 30 keV FIB Ga+ ion beam at low ion milling currents of 1 pA can be used to partially reduce the CNT diameter, to provide electrical conduction bottleneck morphologies for linear CNTs, and to introduce both additive and subractive defects at Y junction locations of Y-CNT samples. Our aim is for this work to provide motivation for additional research to determine the effects of ion-beam-induced changes in modulating the physical and chemical properties of nanotubes.

DISCOVERY OF A STRONG LENSING GALAXY EMBEDDED IN A CLUSTER AT z = 1.62

WONG, KENNETH C.,TRAN, KIM-VY H.,SUYU, SHERRY H.,MOMCHEVA, IVELINA G.,BRAMMER, GABRIEL B.,BRODWIN, MARK,GONZALEZ, ANTHONY H.,HALKOLA, ALEKSI,KACPRZAK, GLENN G.,KOEKEMOER, ANTON M.,PAPOVICH, CASEY J.,R The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2

We identify a strong lensing galaxy in the cluster IRC 0218 that is spectroscopically confirmed to be at z = 1.62, making it the highest-redshift strong lens galaxy known. The lens is one of the two brightest cluster galaxies and lenses a background source galaxy into an arc and a counterimage. With Hubble Space Telescope (HST) grism and Keck/LRIS spectroscopy, we measure the source redshift to be $z_S=2.26$. Using HST imaging, we model the lens mass distribution with an elliptical power-law profile and account for the effects of the cluster halo and nearby galaxies. The Einstein radius is $^{\theta}E=0.38^{+0.02{\prime}{\prime}}_{-0.01}$ ($3.2^{+0.2}_{-0.1}kpc$) and the total enclosed mass is $M_{tot}(<^{\theta}_E)=1.8^{+0.2}_{-0.1}{\times}10^{11}M_{\odot}$. We estimate that the cluster environment contributes ~ 10% of this total mass. Assuming a Chabrier IMF, the dark matter fraction within $^{\theta}E$ is $f^{Chab}_{DM}=0.3^{+0.1}_{-0.3}$, while a Salpeter IMF is marginally inconsistent with the enclosed mass ($f^{Salp}_{DM}=-0.3^{+0.2}_{-0.5}$).