• Korean Journal of Materials Research
• /
• v.20 no.4
• /
• pp.199-203
• /
• 2010

Hybridization of semiconductor materials with carbon nanotubes (CNTs) is a recent field of interest in which new nanodevice fabrication and applications are expected. In this work, nanowire type GaAs structures are synthesized on porous single-wall carbon nanotubes (SWCNTs) as templates using the molecular beam epitaxy (MBE) technique. The field emission properties of the as-synthesized products were investigated to suggest their potential applications as cold electron sources, as well. The SWCNT template was synthesized by the arc-discharge method. SWCNT samples were heat-treated at $400^{\circ}C$ under an $N_2/O_2$ atmosphere to remove amorphous carbon. After heat treatment, GaAs was grown on the SWCNT template. The growth conditions of the GaAs in the MBE system were set by changing the growth temperatures from $400^{\circ}C$ to $600^{\circ}C$. The morphology of the GaAs synthesized on the SWCNTs strongly depends on the substrate temperature. Namely, nano-crystalline beads of GaAs are formed on the CNTs under $500^{\circ}C$, while nanowire structures begin to form on the beads above $600^{\circ}C$. The crystal qualities of GaAs and SWCNT were examined by X-ray diffraction and Raman spectra. The field emission properties of the synthesized GaAs nanowires were also investigated and a low turn-on field of $2.0\;V/{\mu}m$ was achieved. But, the turn-on field was increased in the second and third measurements. It is thought that arsenic atoms were evaporated during the measurement of the field emission.

• Advances in nano research
• /
• v.5 no.3
• /
• pp.193-201
• /
• 2017

ZnO, ZnO: Cu, Ga, and ZnO: Cu, Ga, Ag thin films were obtained by oxidization of ZnS and ZnS: Cu, Ga films deposited onto glass substrates by electron-beam evaporation from ZnS and ZnS: Cu, Ga targets and from ZnS: Cu, Ga film additionally doped with Ag by the closed space sublimation technique at atmospheric pressure. The film thickness was about $1{\mu}m$. The oxidation was carried out at $600-650^{\circ}C$ in air or in an atmosphere containing water vapor. Structural characteristics were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM). Photoluminescence (PL) spectra of the films were measured at 30-300 K using the excitation wavelengths of 337, 405 and 457.9 nm. As-deposited ZnS and ZnS: Cu, Ga films had cubic structure. The oxidation of the doped films in air or in water vapors led to complete ZnO phase transition. XRD and AFM studies showed that the grain sizes of oxidized films at wet annealing were larger than of the films after dry annealing. As-deposited doped and undoped ZnS thin films did not emit PL. Shape and intensity of the PL emission depended on doping and oxidation conditions. Emission intensity of the films annealed in water vapors was higher than of the films annealed in the air. PL of ZnO: Cu, Ga films excited by 337 nm wavelength exhibits UV (380 nm) and green emission (500 nm). PL spectra at 300 and 30 K excited by 457.9 and 405 nm wavelengths consisted of two bands - the green band at 500 nm and the red band at 650 nm. Location and intensities ratio depended on the preparation conditions.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.36 no.12
• /
• pp.1171-1176
• /
• 2012

The selective patterning of a carbon nanotube (CNT) forest on a Si substrate has been performed using a femtosecond laser. The high shock wave generated by the femtosecond laser effectively removed the CNTs without damage to the Si substrate. This process has many advantages because it is performed without chemicals and can be easily applied to large-area patterning. The CNTs grown by plasma-enhanced chemical vapor deposition (PECVD) have a catalyst cap at the end of the nanotube owing to the tip-growth mode mechanism. For the application of an electron emission and biosensor probe, the catalyst cap is usually removed chemically, which damages the surface of the CNT wall. Precise control of the femtosecond laser power and focal position could solve this problem. Furthermore, selective CNT cutting using a femtosecond laser is also possible without any phase change in the CNTs, which is usually observed in the focused ion beam irradiation of CNTs.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.08a
• /
• pp.259-259
• /
• 2010

Periodically polarity inverted (PPI) ZnO structures on (0001) Al2O3 substrates are demonstrated by plasmas assisted molecular beam epitaxy. The patterning and re-growth methods are used to realize the PPI ZnO by employing the polarity controlling method. For the in-situ polarity controlling of ZnO films, Cr-compound buffer layers are used.[1, 2] The region with the CrN intermediate layer and the region with the Cr2O3 and Al2O3 substrate were used to grow the Zn- and O-polar ZnO films, respectively. The growth behaviors with anisotropic properties of PPI ZnO heterostructures are investigated. The periodical polarity inversion is evaluated by contrast images of piezo-response microscopy. Structural and optical interface properties of PPI ZnO are investigated by the transmission electron microcopy (TEM) and micro photoluminescence ($\mu$-PL). The inversion domain boundaries (IDBs) between the Zn and the O-polar ZnO regions were clearly observed by TEM. Moreover, the investigation of spatially resolved local photoluminescence characteristics of PPI ZnO revealed stronger excitonic emission at the interfacial region with the IDBs compared to the Zn-polar or the O-polar ZnO region. The possible mechanisms will be discussed with the consideration of the atomic configuration, carrier life time, and geometrical effects. The successful realization of PPI structures with nanometer scale period indicates the possibility for the application to the photonic band-gap structures or waveguide fabrication. The details of application and results will be discussed.

• Journal of the Korean Vacuum Society
• /
• v.14 no.3
• /
• pp.119-125
• /
• 2005

The horizontal reflectometer, which uses a neutron beam in the reactor, provides scientists a set of unique tools offering destruction-free investigation of biological membranes in the native-like environments in nano-meter scale. As an intial stage for the development of the first Korean neutron reflectometer with a horizontal sample geometry, we performed the instrumental simulation using MCSTAS, Monte Carlo Simulations of Triple Axis Spectrometers for neutron ray-tracing simulation. The results indicated that modeling of the overall instrument geometry based on the thermal neutron source with a wavelength of 2.55 $2.5{\AA}$ at HANARO was successfully performed, and further the optimization of the individual components of the instrument, including the collimator, monochromators, filter and supermirror has been made.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.35 no.12
• /
• pp.1655-1662
• /
• 2011

We have conducted a study on stainless steel laser-welding materials by using a laser beam for the evaluation. Stainless steel used in a rust and excellent thermal deformation has a variety of application. In this study, to improve the mechanical properties of stainless steel, a 50 W laser thermal source is used and magnetic fields are applied, on the basis of suggestions. The mechanical properties and performance are evaluated by performing a numerical analysis, tensile test, and shape, microstructure, and hardness test. The results show that the mechanical properties of improve increased speed the melting pool, tensile strength of 16 kPa rise, run into the melting zone and hardness 7 Hv.

• JSTS:Journal of Semiconductor Technology and Science
• /
• v.4 no.2
• /
• pp.117-123
• /
• 2004

A 30 nm $In_{0.7}GaAs$ High Electron Mobility Transistor (HEMT) with triple-gate has been successfully fabricated using the $SiO_2/SiN_x$ sidewall process and BCB planarization. The sidewall gate process was used to obtain finer lines, and the width of the initial line could be lessened to half by this process. To fill the Schottky metal effectively to a narrow gate line after applying the developed sidewall process, the sputtered tungsten (W) metal was utilized instead of conventional e-beam evaporated metal. To reduce the parasitic capacitance through dielectric layers and the gate metal resistance ($R_g$), the etchedback BCB with a low dielectric constant was used as the supporting layer of a wide gate head, which also offered extremely low Rg of 1.7 Ohm for a total gate width ($W_g$) of 2x100m. The fabricated 30nm $In_{0.7}GaAs$ HEMTs showed $V_{th}$of -0.4V, $G_{m,max}$ of 1.7S/mm, and $f_T$ of 421GHz. These results indicate that InGaAs nano-HEMT with excellent device performance could be successfully fabricated through a reproducible and damage-free sidewall process without the aid of state-of-the-art lithography equipment. We also believe that the developed process will be directly applicable to the fabrication of deep sub-50nm InGaAs HEMTs if the initial line length can be reduced to below 50nm order.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.1
• /
• pp.37-42
• /
• 2012

LIFT (laser-induced forward transfer) is an advanced laser processing method used for selectively transferring micron-sized objects. In our study, this process was applied in order to deposit solder balls in microsystem packaging processes for electronics. Locally melted solder paste could be transferred to a rigid substrate using laser pulses. A thin glass plate with a solder cream layer was used as a donor film, and an IR laser pulse (wavelength = 1070 nm) was used to transfer a micron-sized solder ball to the receptor. Mass balance and energy balance were applied to analyze the shape and temperature profiles of the solder paste drops. The transferred solder bumps had measured diameters of 30-40 ${\mu}m$ and thicknesses of 50 ${\mu}m$ in our experiment. The limits and applications of this method are also presented.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.31 no.4
• /
• pp.267-271
• /
• 2018

A high directivity TIR (total internal reflection) lens in the UV-A region was designed using a silicone resin, and a UV light source module with a maximum irradiation density of $150mW/cm^2$ was fabricated. The beam angle of the TIR lens was designed to be $8.04^{\circ}$ and the maximum diameter of the TIR lens was Ø13.5. A silicone resin having a UV transmittance of 93% and a refractive index of 1.4 at a wavelength of 365 nm was used, and the lens was manufactured using an aluminum mold, from which silicone could be easily released. The module was fabricated in a metal printed circuit board of COB (chip on board) type using a $0.75{\times}0.75mm^2$ UV chip. A jig was used to adjust the focal length between lens and chip and to fix the position of the lens. The optical characteristics such as illumination distributions of the lens and module were designed using 'LightTools' optical simulation software. The heat dissipation system was designed to use a forced-air cooling method using a heat-sink and fan.

• Journal of Sensor Science and Technology
• /
• v.17 no.5
• /
• pp.369-374
• /
• 2008

A novel fiber optic surface plasmon resonance (SPR) sensor using cyclic olefin copolymer (COC) prism with the spectral modulation is presented. The SPR sensor chip is fabricated using the SU-8 photolithography, Ni-electroplating and COC injection molding process. The sidewall of the COC prism is partially deposited with Au/Cr (45/2.nm thickness) by e-beam evaporator, and the thermal bonding process is conducted for micro fluidic channels and optical fibers alignment. The SPR spectrum for a phosphate buffered saline (0.1.M PBS, pH.7.2) solution shows a distinctive dip at 1300.nm wavelength, which shifts toward longer wavelength with respect to the bovine serum albumin (BSA)concentrations. The sensitivity of the wavelength shift is $1.16\;nm{\cdot}{\mu}g^{-1}{\cdot}{\mu}l^{-1}$. From the wavelength of SPR dips, the refractive indices (RI) of the BSA solutions can be theoretically calculated using Kretchmann configuration, and the change rate of the RI was found to be $2.3{\times}10^{-5}RI{\cdot}{\mu}g^{-1}{\cdot}l^{-1}$. The realized fiber optic SPR sensor with a COC prism has clearly shown the feasibility of a new disposable, low cost and miniaturized SPR biosensor for biochemical molecular analyses.