• Transactions on Electrical and Electronic Materials
• /
• v.11 no.4
• /
• pp.190-193
• /
• 2010

This report covers an effective fabrication method of graphene nanoribbon for top-gated field effect transistors (FETs) utilizing electron beam lithography with a bi-layer resists (XR-1541/poly methtyl methacrylate) process. To improve the variation of the gating properties of FETs, the residues of an e beam resist on the graphene channel are successfully taken off through the combination of reactive ion etching and a lift-off process for the XR-1541 bi-layer. In order to identify the presence of graphene structures, atomic force microscopy measurement and Raman spectrum analysis are performed. We believe that the lift-off process with bi-layer resists could be a good solution to increase gate dielectric properties toward the high quality of graphene FETs.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2009.05a
• /
• pp.294-297
• /
• 2009

The frictional behaviors of Cermets/Cr-Ceramics and Cu-Al coatings of piston ring were investigated. Friction tests were carried out by pin-on-disk test and materials properties of coating layer were analyzed by nano indentation tester. Higher friction coefficient was obtained at harder coating with rougher surface. In case of hard-coating, the scratch depth, width and pile-up height had close relationship with indentation hardness. So the scratch width, depth and pile-up height increases with decreasing friction coefficient. But in case of soft-coating, the friction coefficients are strongly dependent on the morphological characteristics after nano scratching more than indentation hardness.

• Korean Journal of Metals and Materials
• /
• v.49 no.10
• /
• pp.811-817
• /
• 2011

In this study, we have investigated the role of a metal oxide hole injection layer (HIL) between an Indium Tin Oxide (ITO) electrode and an organic hole transporting layer (HTL) in organic light emitting diodes (OLEDs). Nickel Oxide films were deposited at different deposition times of 0 to 60 seconds, thus leading to a thickness from 0 to 15 nm on ITO/glass substrates. To study the influence of NiO film thickness on the properties of OLEDs, the relationships between NiO/ITO morphology and surface properties have been studied by UV-visible spectroscopy measurements and AFM microscopy. The dependences of the I-V-L properties on the thickness of the NiO layers were examined. Comparing these with devices without an NiO buffer layer, turn-on voltage and luminance have been obviously improved by using the NiO buffer layer with a thickness smaller than 10 nm in OLEDs. Moreover, the efficiency of the device ITO/NiO (< 5 nm)/NPB/$Alq_3$/ LiF/Al has increased two times at the same operation voltage (8V). Insertion of a thin NiO layer between the ITO and HTL enhances the hole injection, which can increase the device efficiency and decrease the turn-on voltage, while also decreasing the interface roughness.

• Korean Journal of Metals and Materials
• /
• v.47 no.9
• /
• pp.591-596
• /
• 2009

$TiN_xO_y/TiN_x$ multi-layer thin films with a high resistance(${\sim}k{\Omega}$) were deposited on $SiO_2/Si$ substrates at room temperature by sputtering. The $TiN_x$ thin films show island and smooth surface morphology in samples prepared by ${\alpha}$ and RF magnetron sputtering, respectively. $TiN_xO_y/TiN_x$ multi-layer in has been developed to control temperature coefficient of resistance(TCR) by the incorporation of $TiN_x$ layer(positive TCR) inserted into $TiN_xO_y$ layers(negative TCR). Electrical and structural properties of sputtered $TiN_xO_y/TiN_x$ multi-layer films were investigated as a function of annealing temperature. In order to achieve a stable high resistivity, multi-layer films were annealed at various temperatures in oxygen ambient. Samples annealed at $700^{\circ}C$ for 1 min exhibited good TCR value of approximately $-54 ppm/^{\circ}C$ and a stable high resistivity around $20k{\Omega}/sq$. with good reversibility.

• Journal of the Korean institute of surface engineering
• /
• v.41 no.6
• /
• pp.331-334
• /
• 2008

The replica of highly ordered nano-sphere array patterns were fabricated using hot embossing method. First, silica nano-sphere array on Si substrate was transferred to PVC film at $130^{\circ}C$ and 7 bar using hot embossing process. Then, silica nano-sphere array on PVC template was removed by soaking the PVC film in buffered oxide etcher. In order to form anti-stiction layer, the PVC template was coated with silicon dioxide layer and self-assembled monolayer. Through UV nanoimprint lithography with the fabricated flexible PVC template, highly ordered nano-sphere array pattern was imprinted on curved substrates with high fidelity.

• Journal of the Korean Ceramic Society
• /
• v.49 no.5
• /
• pp.417-422
• /
• 2012

Copper nano particles have been considered as the materials for conductive ink due to its good thermal, electrical conductivity and low cost. However, copper nanoparticles oxidize easily, decreasing dispersion stability and electrical conductivity. Therefore, it is important to develop a method to minimize oxidation of copper nano particles to improve its dispersion stability property in copper nano ink. In this study, copper nano particles were coated with 1-Octanethiol VSAM(Vaporized Self Assembled Multilayers) to prevent oxidation and coated copper powders were dispersed in conductive ink successfully by studying its relationship of different chain length of solvents to 1-Octanethiol coating layer to fabricate nano ink. Various alcohol solvents, such as 1-Hexanol, 1-Octanol, and 1-Decanol were used. The coating layer was observed using FESEM and TEM. Furthermore, dispersion of copper nano particles in nano inks, was characterized using Turbiscan analyzer, viscometer, and contact angle measurement tool.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.273.1-273.1
• /
• 2014

Graphene, a two dimensional plane structure of $sp^2$ bonding, has been promised for a new material in many scientific fields such as physics, chemistry, and so on due to the unique properties. Chemical vapor deposition (CVD) method using transitional metals as a catalyst can synthesize large scale graphene with high quality and transfer on other substrates. However, it is difficult to control the number of graphene layers. Therefore, it is important to manipulate the number of graphene layers. In this work, homogeneous solid solution of Cu and Ni was used to control the number of graphene layers. Each films with different thickness ratio of Cu and Ni were deposited on $SiO_2/Si$ substrate. After annealing, it was confirmed that the thickness ratio accords with the composition ratio by X-ray diffraction (XRD). The synthesized graphene from CVD was analyzed via raman spectroscopy, UV-vis spectroscopy, and 4-point probe to evaluate the properties. Therefore, the number of graphene layers at the same growth condition was controlled, and the correlation between mole fraction of Ni and the number of graphene layers was investigated.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2005.10a
• /
• pp.83-86
• /
• 2005

In this study, SAM (self-assembled monolayer) was applied as an anti-adhesion layer in the nano molding process, to reduce the surface energy between the nano-stamper and the moldeded polymeric nano patterns. Before depositing SAM on the stamper, the nickel stamper was pretreated to remove oxide on the nickel stamper surface. Then, using the solution deposition method, alkanethiol SAM as an anti-adhesion layer was deposited on nickel surface. To examine the effectiveness of the SAM deposition on the metallic nano stamper, the contact angle and the lateral friction force were measured at the actual processing temperature and pressure for the case of nano compression molding and at the actual UV dose for the case of nano UV molding. The surface energy due to SAM deposition on the nickel nano stamper markedly decreased and the high hydrophobic quality of SAM on the nickel stamper maintained under the actual molding environments.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2016.02a
• /
• pp.432.1-432.1
• /
• 2016

We demonstrated that the power conversion efficiency (PCE) of bilayer solar cell was significantly enhanced by inserting interfacial layer between the organic bilayer film and the Al electrode. Moreover, the water contact angle shows that the bilayer solar cells suffer from the undesirable surface component which limits the charge transport to the Al electrode. The AFM measurement has revealed that the pre- and post-thermal annealing treatments results in different morphologies of the interfacial layer which is critical for the higher PCE of the bilayer solar cells. Furthermore we have investigated the electrical properties of the bilayer solar cells and obtained insights into the detailed device mechanisms. The transient photovoltage measurements suggests that the significantly enhanced Voc is caused by reducing the recombination at the interface between the organic films and the Al electrode. By inserting the TiO2 layer between the bilayer film and Al electrode, the open circuit voltage (Voc) was increased from 0.37 to 0.66V. Consequently, the power conversion efficiency (PCE) of bilayer solar cells was significantly enhanced from 1.23% to 3.71%. As the results, the TiO2 interfacial layer can be used to form an ohmic contact layer, serveing as a blocking layer to prevent the penetration of the Al, and to reduce the recombination at the interface.

• Proceedings of the KSME Conference
• /
• 2004.11a
• /
• pp.1086-1091
• /
• 2004

The boundary layer is a very important characteristic of a liquid-vapor interface since it governs the heat and mass transfer phenomena across an interface. However, the thickness of a boundary layer is generally micro- or nano-sized, which requires highly accurate measurement devices and, consequently, costs the related experiments very high and time-consuming. Due to these size dependent limitations, the experiments related with a nano-scaled size have suffered from the errors and the reliability of the obtained data. This study is performed to grasp the characteristics of a liquid-vapor interface, by using a molecular dynamics method. The simulation results were compared with other studies if possible. Although other studies reported that there existed a temperature discontinuity over an interface when the system was reduced to micro- or nano-sized, we confirmed that there was no such a temperature discontinuity.