• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.281-281
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• 2010

Very low refractive index (<1.4) materials have been proved to be the key factor improving the performance of various optical components, such as reflectors, filters, photonic crystals, LEDs, and solar cell. Highly porous SiO2 are logically designed for ultralow refractive index materials because of the direct relation between porosity and index of refraction. Among them, ordered macroporous SiO2 is of potential material since their theoretically low refractive index ~1.10. However, in the conventional synthesis of ordered macroporous SiO2, the time required for the crystallization of organic nanoparticles, such as polystyrene (PS), from colloidal solution into well ordered template is typical long (several days for 1 cm substrate) due to the low interaction between particles and particle - substrate. In this study, polystyrene - polyacrylic acid (PS-AA) nanoparticles synthesized by miniemulsion polymerization method have hydrophilic polyacrylic acid tails on the surface of particles which increase the interaction between particle and with substrate giving rise to the formation of PS-AA film by simply spin - coating method. Less ordered with controlled thickness films of PS-AA on silicon wafer were successfully fabricated by changing the spinning speed or concentration of colloidal solution, as confirmed by FE-SEM. Based on these template films, a series of macroporous SiO2 films whose thicknesses varied from 300nm to ~1000nm were fabricated either by conventional sol - gel infiltration or gas phase deposition followed by thermal removal of organic template. Formations of SiO2 films consist of interconnected air balls with size ~100 nm were confirmed by FE-SEM and TEM. These highly porous SiO2 show very low refractive indices (<1.18) over a wide range of wavelength (from 200 to 1000nm) as shown by SE measurement. Refraction indices of SiO2 films at 633nm reported here are of ~1.10 which, to our best knowledge, are among the lowest values having been announced.

• Korean Journal of Materials Research
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• v.23 no.12
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• pp.667-671
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• 2013

We present an easy method of preparing two-dimensional (2D) periodic hollow tin oxide ($SnO_2$) hemisphere array gas sensors using polystyrene (PS) spheres as a template. The structures were fabricated by the sputter deposition of thin tin (Sn) metal over an array of PS spheres on a planar substrate followed by calcination at an elevated temperature to oxidize Sn to $SnO_2$ while removing the PS template cores. The $SnO_2$ hemisphere array structures were examined by scanning electron microscopy and X-ray diffraction. The structures were calcined at various temperatures and their sensing properties were examined with varying operation temperatures and concentrations of nitric oxide (NO) gas. Their gas-sensing properties were investigated by measuring the electrical resistances in air and the target gases. The measurements were conducted at different NO concentrations and substrate temperatures. A minimum detection limit of 30 ppb, showing a sensitivity of S = 1.6, was observed for NO gas at an operation temperature of $150^{\circ}C$ for a sample having an Sn metal layer thickness corresponding to 30 sec sputtering time and calcined at $600^{\circ}C$ for 2 hr in air. We proved that high porosity in a hollow $SnO_2$ hemisphere structure allows easy diffusion of the target gas molecules. The results confirm that a 2D hollow $SnO_2$ hemisphere array structure of micronmeter sizes can be a good structural morphology for high sensitivity gas sensors.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.100-100
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• 2011

Nanomaterial architecture with highly ordered, vertically oriented $TiO_2$ nanotube arrays shows a good promise for diverse technological applications. As inspired from the literature reports that Nickel modification can improve the photocatalytic activity of $TiO_2$, it was planned to coat Ni into the $TiO_2$ matrix. In this study, first $TiO_2$ nanotubes(TiNTs) were prepared by anodization (60V,3min) in HF-free aqueous electrolyte on ultrasonically cleaned polished titanium sheet substrates ($1{\times}7cm^2$). The typical thickness of the sintered TiNT ($500^{\circ}C$for10min) was ~1 micronas confirmed from the FESEM study. In the next part, as-anodized and sintered TiNT/Ti photoanodes were used to coat Ni by AC electrodeposition from aqueous 0.1M nickel sulphate solution. During AC electrodeposition, conditions such as 1V DC offset voltage, 9V amplitude (peak-to-peak) and 750 Hz frequency were fixed constant and the deposition time was varied as 0.5 min, 1 min, 2 min and 10 min. The photoelectrochemical performance of pristine and Ni modified TiNT/Ti photoanodes was measured in 1N NaOH electrolyte under 1 SUN illumination in the potential range of -1V and 1.2V versus Ag/AgCl reference electrode. The photocurrent performance of TiNT/Ti photoanode decreased upon Ni modification and the results were confirmed after repeated experiments. This suggests us that Ni modification inhibits the photoelectrochemical performance of $TiO_2$ nanotubes.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.254-254
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• 2011

The memories with nano-particles are very attractive because they are promising candidates for low operating voltage, long retention time and fast program/erase speed. In recent, various nano-floating gate memories with metal-oxide nanocrystals embedded in organic and inorganic layers have been reported. Because of the carrier generation in semiconductor, induced photon pulse enhanced the program/erase speed of memory device. We studied photo-induced electrical properties of these metal-oxide nanocrystal memory devices. At first, 2~10-nm-thick Sn and In metals were deposited by using thermal evaporation onto Si wafer including a channel with $n^+$ poly-Si source/drain in which the length and width are 10 ${\mu}m$ each. Then, a poly-amic-acid (PAA) was spin coated on the deposited Sn film. The PAA precursor used in this study was prepared by dissolving biphenyl-tetracarboxylic dianhydride-phenylene diamine (BPDA-PDA) commercial polyamic acid in N-methyl-2-pyrrolidon (NMP). Then the samples were cured at 400$^{\circ}C$ for 1 hour in N atmosphere after drying at 135$^{\circ}C$ for 30 min through rapid thermal annealing. The deposition of aluminum layer with thickness of 200 nm was followed by using a thermal evaporator, and then the gate electrode was defined by photolithography and etching. The electrical properties were measured at room temperature using an HP4156a precision semiconductor parameter analyzer and an Agilent 81101A pulse generator. Also, the optical pulse for the study on photo-induced electrical properties was applied by Xeon lamp light source and a monochromator system.

• Journal of the Korean Vacuum Society
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• v.13 no.4
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• pp.157-163
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• 2004

Dependence of residual compressive stress of diamond-like carbon (DLC) films on relative humidity was investigated. Polymeric, graphitic and diamond-like carbon films were prepared by r.f.-PACVD using methane or benzene with the negative self bias voltage of the substrate ranging from -100 to -800 V. In-situ measurements of the residual stress were carried out in an environment chamber where the relative humidity was varied from 10％ to 90％. In dense DLC film of high residual compressive stress and hardness, we could not observe any change in the residual compressive stress with relative humidity. However, in the cases of graphitic and polymeric DLC films, abrupt change in the residual stress occurred by changing the relative humidity. The quantity of the stress change was inversely proportional to the film thickness, which means that the stress change with humidity is not due to the penetration of the water molecule into the film structure, but due to surface interaction between water molecules and film surface.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.183-183
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• 2012

In the era of 45 nm or beyond technology, conventional etch mask using photoresist showed its limitation of etch mask pattern collapse as well as pattern erosion, thus hard mask in etching became necessary for precise control of etch pattern geometry. Currently available hard mask materials are amorphous carbon and polymetric materials spin-on containing carbon or silicon. Amorphous carbon layer (ACL) deposited by PECVD for etch hard mask has appeared in manufacturing, but spin-on carbon (SOC) was also suggested to alleviate concerns of particle, throughput, and cost of ownership (COO) [1]. SOC provides some benefits of reduced process steps, but it also faced with wiggling on a sidewall profile. Diamond like carbon (DLC) was also evaluated for substituting ACL, but etching selectivity of ACL was better than DLC although DLC has superior optical property [2]. Developing a novel material for pattern hard mask is very important in material research, but it is also worthwhile eliminating a potential issue to continuously develop currently existing technology. In this paper, we investigated in-situ dry-cleaning (ISD) monitoring of ACL coated process chamber. End time detection of chamber cleaning not only provides a confidence that the process chamber is being cleaned, but also contributes to minimize wait time waste (WOW). Employing Challenger 300ST, a 300mm ACL PECVD manufactured by TES, a series of experimental chamber cleaning runs was performed after several deposition processes in the deposited film thickness of $2000{\AA}$ and $5000{\AA}$. Ar Actinometry and principle component analysis (PCA) were applied to derive integrated and intuitive trace signal, and the result showed that previously operated cleaning run time can be reduced by more than 20% by employing real-time monitoring in ISD process.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.562-562
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• 2012

Recently, graphene and graphene-based materials such as graphene oxide (GO) or reduced graphene oxide (R-GO) draws a great attention for electronic devices due to their structures of one atomic layer of carbon hexagon that have excellent mechanical, electrical, thermal, optical properties and very high specific surface area that can be high potential for chemical functionalization. R-GO is a promising candidate because it can be prepared with low-cost from solution process by chemical oxidation and exfoliation using strong acids and oxidants to produce graphene oxide (GO) and its subsequent reduction. R-GO has been used as semiconductor or conductor materials as well as sensing layer for bio-molecules or ions. In this work, reduced graphene oxide field-effect transistor (R-GO FET) has been fabricated with ITO extended gate structure that has sensing area on ITO extended gate part. R-GO FET device was encapsulated by tetratetracontane (TTC) layer using thermal evaporation. A thermal annealing process was carried out at $140^{\circ}C$ for 4 hours in the same thermal vacuum chamber to remove defects in R-GO film before deposition of TTC at $50^{\circ}C$ with thickness of 200 nm. As a result of this process, R-GO FET device has a very high stability and durability for months to serve as a transducer for sensing applications.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.200-200
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• 2012

We investigated a flexible transparent film using the spinning multi-walled carbon nanotubes (MWCNTs). Spin-capable MWCNTs on iron catalyzed on a SiO2 wafer was grown by chemical vapor deposition, which was performed at $780^{\circ}C$ using C2H2 and H2 gas. The average diameter and length of MWCNTs grown on the substrate were ~15 nm and $250{\sim}300{\mu}m$, respectively. The MWCNT sheets were produced by continuously pulling out from well-aligned MWCNTs on a substrate. The MWCNT sheet films were produced simply by direct coating on the flexible film or grass. The thickness of sheet film was remarkably decreased by alcohol spraying on the surface of sheet. The alcohol splay increased transmittance and decreased electrical resistance of MWCNT sheet films. Single and double sheets were produced with sheet resistance of ~699 and ${\sim}349{\Omega}/sq$, respectively, transmittance of 81~85 % and 67~72%, respectively. The MWCNT sheet films were heated through the application of direct current power. The flexible transparent heaters showed a rapid thermal response and uniform distribution of temperature. In addition, MWCNT yarns were prepared by spinning a bundle of MWCNTs from vertically super-aligned MWCNTs on a substrate, and field emission from the tip and side of the yarns was induced in a scanning electron microscope. We found that the field emission behavior from the tip of the yarn was better than the field emission from the side. The field emission turn-on voltages from the tip and side of MWCNT yarns were 1.6 and $1.7V/{\mu}m$, respectively, after the yarn was subjected to an aging process. Both the configuration of the tip end and the body of the yarn were changed remarkably during the field emission. We also performed the field emission of the sheet films. The sheet films showed the turn on voltage of ${\sim}1.45V/{\mu}m$ during the field emission.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.567-567
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• 2012

Since the carbon nanotubes (CNTs) have extraordinary material properties, many researchers are trying to make a practical application in various fields [1]. In particular, the high surface area of CNTs was fascinated for nano-template on the catalytic system. $RuO_2$ coated CNTs are useful functional nano-composites in many applications, including super capacitors, fuel cells, biosensors, and field emitters. However, the research of interaction between CNTs and $RuO_2$ was not satisfied with various fields [2]. In this study, we will introduce the change of chemical and electrical state of $RuO_2$/CNTs at different temperatures by synchrotron radiation photoemission spectroscopy (SRPES). The t-MWCNTs used in this experiment were grown on the Ni/TiN/Si substrates by chemical vapor deposition. $RuO_2$ of 4-20 nm in thickness was deposited on the t-MWNTs by sputter. The SRPES measurements were carried out at the 4B1 beamline of the Pohang Accelerator Laboratory in Korea. The result of XPS measurement indicates that the deposited $RuO_2$ on the CNTs was reduced into pure Ru at above $300^{\circ}C$. And we confirmed that the effective work function of $RuO_2$/CNTs was decreased with increasing temperature.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.320-320
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• 2011

We describe fabrication of superhydrophobic surface on non-woven fabric (NWF) having nano-hairy structures and a hydrophobic surface coating. Oxygen plasma was irradiated on NWF for nano-texuring and a precursor of HMDSO (Hexamethydisiloxane) was introduced as a surface chemical modification for obtaining superhydrophobicity using 13.56 MHz radio frequency-Plasma Enhanced Chemical Vapor Deposition (rf-PECVD). O2 plasma treatment time was varied from 1 min to 60 min at a bias voltage of 400V, which fabricated pillar-like structures with diameter of 30 nm and height of 150 nm on NWF. Subsequently, hydrophobic coating using hexamethyldisiloxane vapor was deposited with 10 nm thickness on NWF substrate at a bias voltage of 400 V. We evaluate superhydrophobicity of the modified NWF with sessile drop using goniometer and high speed camera, in which aspect ratio of nanohairy structures, contact angle and contact angle hysteresis of the surfaces were measured. With the increase of aspect ratio, the wetting angle increased from $103^{\circ}$ to $163^{\circ}$, and the contact angle hysteresis decreased dramatically below $5^{\circ}$. In addition, we had conducted experiment for nucleation and condensation of water via E-SEM. During increasing vapor pressure inside E-SEM from 3.7 Torr to over 6 Torr which is beyond saturation point at $2^{\circ}C$, we observed condensation of water droplet on the superhydropobic NWF. While the condensation of water on oxygen plasma treated NWF (superhydrophilic) occurred easily and rapidly, superhydrophobic NWF which was fabricated by oxygen and HMDSO was hardly wet even under supersaturation condition. From the result of wetting experiment and water condensation via E-SEM, it is confirmed that superhydrophobic NWF shows the grate water repellent abilities.