• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.265-265
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• 2013

We have investigated the influences of dangling bonds generated by alpha particle irradiation on friction and adhesion properties of graphene. Single layer of graphene grown with chemical vapor deposition on copper foil was irradiated by the alpha beam with the average energy of 3.04 MeV and the irradiation dosing between $1{\times}10^{14}$ and $1{\times}10^{15}$/$cm^3$. Raman spectroscopic showed that the ${\pi}$ electron states below Fermi level arises and the $I_D$/$I_G$ increases as increasing the dosing of alpha particle irradiation. The core level X-ray photoelectron (XPS) revealed that these defects represent the creation of various carbon-related defects and dangling bond. The nanoscale tribological properties were investigated with atomic force microscopy in ultrahigh vacuum. The friction appeared to increase remarkably as increasing the amount of dosing, indicating that the dangling bonds on graphene layers enhances the energy dissipations in friction. This trend can be explained by the additional channel of energy dissipation by dangling bond or O- and H- terminated clusters created by alpha particle irradiation.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.225-225
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• 2013

Nanostructured noble metals have been attractive for their unusual optical properties and are widely utilized for various purposes. The optical properties mainly originating from collective electron oscillation can assist direct energy conversion via surface plasmon resonances. Here, we investigated the effect of surface plasmons of silver nanowires on the generation of hot electrons. It is reported that the surface plasmons of silver nanowires exhibit longitudinal and transverse modes, depending on the aspect ratio of the nanowires. In order to measure the hot electron flow through the metallic nanowires, chemically modified Au/TiO2 Schottky diodes were employed as the electric contact. The silver nanowires were deposited on a Au metal layer via the spray method to control uniformity and the amount of silver nanowire deposited. We measured the hot electron flow generated by photon absorption on the silver nanowires deposited on the Au/TiO2 Schottky diodes. The incident photon-to-current efficiency was measured a function of the photon energy, revealing two polarization modes of siliver nanowires: transverse and longitudinal modes. UV-Vis spectra exhibited two polarization modes, which are also consistent with the photocurrent measurements. Good correlation between the IPCE and UV-vis measurements suggests that hot electron measurement on nanowires on nanodiodes is a useful way to reveal the intrinsic properties of surface plasmons of nanowires.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.110-110
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• 2011

The nanomechanical properties of fully lithiated and unlithiated silicon nanowire deposited on silicon substrate have been studied with atomic force microscopy. Silicon nanowires were synthesized using the vapor-liquid-solid process on stainless steel substrates using Au catalyst. Fully lithiated silicon nanowires were obtained by using the electrochemical method, followed by drop-casting on the silicon substrate. The roughness, derived from a line profile of the surface measured in contact mode atomic force microscopy, has a smaller value for lithiated silicon nanowire and a higher value for unlithiated silicon nanowire. Force spectroscopy was utilitzed to study the influence of lithiation on the tip-surface adhesion force. Lithiated silicon nanowire revealed a smaller value than that of the Si nanowire substrate by a factor of two, while the adhesion force of the silicon nanowire is similar to that of the silicon substrate. The Young's modulus obtained from the force-distance curve, also shows that the unlithiated silicon nanowire has a relatively higher value than lithiated silicon nanowire due to the elastically soft amorphous structures. The frictional forces acting on the tip sliding on the surface of lithiated and unlithiated silicon nanowire were obtained within the range of 0.5-4.0 Hz and 0.01-200 nN for velocity and load dependency, respectively. We explain the trend of adhesion and modulus in light of the materials properties of silicon and lithiated silicon. The results suggest a useful method for chemical identification of the lithiated region during the charging and discharging process.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.317.2-317.2
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• 2013

Ultrathin oxide encapsulated metal-oxide hybrid nanocatalysts have been fabricated by a soft chemical and facile route. First, SiO2 nanoparticles of 25~30 nm size have been synthesized by modified Stobber's method followed by amine functionalization. Metal nanoparticles (Ru, Rh, Pt) capped with polymer/citrate have been deposited on functionalized SiO2 and finally an ultrathin layer of TiO2 coated on surface which prevents sintering and provides high thermal stability while maximizing the metal-oxide interface for higher catalytic activity. TEM studies confirmed that 2.5 nm sized metal nanoparticles are well dispersed and distributed throughout the surface of 25 nm SiO2 nanoparticles with a 3-4 nm TiO2 ultrathin layer. The metal nanoparticles are still well exposed to outer surface, being enabled for surface characterization and catalytic activity. Even after calcination at $600^{\circ}C$, the structure and morphology of hybrid nanocatalysts remain intact confirm the high thermal stability. XPS spectra of hybrid nanocatalyst suggest the metallic states as well as their corresponding oxide states. The catalytic activity has been evaluated for high temperature CO oxidation reaction as well as photocatalytic H2 generation under solar simulation. The design of hybrid structure, high thermal stability, and better exposure of metal active sites are the key parameters for the high catalytic activity. The maximization of metal-TiO2 interface interaction has the great role in photocatalytic H2 production.

• EDISON SW 활용 경진대회 논문집
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• 제6회(2017년)
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• pp.457-462
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• 2017

A linear carbon chain with pure sp hybridization has been intensively studied for the application of its intrinsic electrical properties to electronic devices. Owing to the high chemical reactivity derived from its unsaturated bond, encapsulation by carbon nanotubes (CNT) is provided as a promising method to stabilize the geometry of the linear carbon chain. Although the influence of CNT on the carbon chain has extensively been studied in terms of both electronic structure and geometries, the electron transport properties has not been discussed yet. In this regard, we provide the systematic atomic-scale analyses of the properties of the linear carbon chain within CNT based on a computational approach combining density-functional theory (DFT) and matrix green function (MGF) method. Based on the DFT calculations, the influence of CNT on electronic structures of the linear carbon chain is provided as well as its electrical origin. Via MGF calculations, we also identify the electron transport properties of the carbon chain - CNT complex.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.264-264
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• 2013

Strong metal-support interaction effect is an important issue in determining the catalytic ac-tivity for heterogeneous catalysis. In this study, we investigated the support effect and the role of organic capping layers of two-dimensional Pt nanocatalysts on reducible metal oxide supports under the CO oxidation. Several reducible metal oxide supports including CeO2, Nb2O5, and TiO2 thin films were prepared via sol-gel techniques. The structure, chemical state and optical property were characterized using XRD, XPS, TEM, SEM, and UV-VIS spectrometer. We found that the reducible metal oxide supports have a homogeneous thin thickness and crystalline structure after annealing at high temperature showing the different optical band gap energy. Langmuir-Blodgett technique and arc plasma deposition process were employed to ob-tain Pt nanoparticle arrays with capping and without capping layers, respectively on the oxide support to assess the role of the supports and capping layers on the catalytic activity of Pt catalysts under the CO oxidation. The catalytic performance of CO oxidation over Pt supported on metal oxide thin films under oxidizing reaction conditions (40 Torr CO and 100 Torr O2) was tested. The results show that the catalytic activity significantly depends on the metal oxide support and organic capping layers of Pt nanoparticles, revealing the strong metal-support interaction on these nanocatalysts systems.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.288-288
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• 2013

We report the catalytic activity of Au/$TiO_2$ and Pt/$TiO_2$ nanocatalysts under CO oxidation fabricated by arc plasma deposition (APD), which is a facile dry process with no organic materials involved. Using APD, the catalyst nanoparticles were well dispersed on $TiO_2$ powder with an average particle size (2~4 nm) well below that of nanoparticles prepared by the sol-gel method (10 nm). We found that the average particle size of the dispersed gold nanoparticles can be controlled by changing the plasma discharge voltage of APD. Accordingly, the amount of loaded gold on the $TiO_2$ powder increased with increasing discharge voltage, but the specific surface area of the Au/$TiO_2$ samples decreased. As for catalytic reactivity, Au/$TiO_2$ showed a higher catalytic activity than Pt/$TiO_2$ in CO oxidation. The catalytic activity of the Au/$TiO_2$ samples showed size dependence where higher catalytic activity occurred on smaller gold nanoparticles. The study suggests that APD is a simple way to fabricate catalytically active nanocatalysts.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.669-669
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• 2013

Hierarchical N doped TiO2 nanostructured catalyst with micro, meso and macro porosity have been synthesized by a facile self-formation route using ammonia and titanium isopropoxide precursor. The samples were calcined in different calcination temperature ranging from $300^{\circ}C$ to $800^{\circ}C$ at slow heating rate ($5^{\circ}C$/min) and designated as NHPT-300 to NHPT-800. $TiO_2$ nanostructured catalyst have been characterized by physico-chemical and spectroscopy methods to explore the structural, electronic and optical properties. UV-Vis diffuse reflectance spectra confirmed the red shift and band gap narrowing due to the doping of N species in TiO2 nanoporous catalyst. Hierarchical macro porosity with fibrous channel patterning was observed (confirmed from FESEM) and well preserved even after calcination at $800^{\circ}C$, indicating the thermal stability. BET results showed that micro and mesoporosity was lost after $500^{\circ}C$ calcination. The photocatalytic activity has been evaluated for methanol oxidation to formaldehyde in visible light. The enhanced photocatalytic activity is attributed to combined synergetic effect of N doping for visible light absorption, micro and mesoporosity for increase of effective surface area and light harvestation, and hierarchical macroporous fibrous structure for multiple reflection and effective charge transfer.

• 한국분말재료학회지
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• 제18권6호
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• pp.532-537
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• 2011

Thermally stable $TiO_2$/Pt/$SiO_2$ core-shell nanocatalyst has been synthesized by chemical processes. Citrated capped Pt nanoparticles were deposited on amine functionalized silica produced by Stober process. Ultrathin layer of titania was coated on Pt/$SiO_2$ for preventing sintering of the metal nanoparticles at high temperatures. Thermal stability of the metal-oxide hybrid catalyst was demonstrated heating the sample up to $600^{\circ}C$ in air and by investigating the morphology and integrity of the structure by transmission electron spectroscopy. The surface analysis of the constituent elements was performed by X-ray photoemission spectroscopy. The catalytic activity of the hybrid catalysts was investigated by CO oxidation reaction with oxygen as a model reaction.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.291-291
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• 2013

The wettability of TiO2 layers is controlled by forming highly ordered arrays of nanocones using nanopatterning, based on self-assembly and dry etching. Nanopatterning of TiO2 layers is achieved via formation of self-assembled monolayers of SiO2 spheres fabricated using the Langmuir-Blodgett technique, followed by dry etching. Compared to a thin film TiO2 layer, the nanopatterned TiO2 samples show a smaller static water contact angle, where the water contact angle decreases as the etching time increases, which is attributed to the Wenzel equation. When TiO2 layers are coated by 1H,1H,2H,2H-perfluorooctyltrichlorosilane, we observed the opposite behavior, exhibiting superhydrophobicity (up to contact angle of $155^{\circ}$) on the nanopatterned TiO2 layers. Self-assembled nanopatterning of the TiO2 layer may provide an advanced method for producing multifunctional transparent layers with self-cleaning properties.