Hong Tak Kim

Effects of nitrogen flow rate on titanium nitride films deposition by DC facing target sputtering method

TiN films were deposited onto a glass substrate by DC facing target sputtering, and the effects of N2 flow rate on the film properties were investigated. Prepared TiN films had a rock salt (NaCl-type) structure with a very low resistivity (∼30 μΩ·cm) and gold-like color. Increase in the N2 flow rate played an important role in controlling the properties of TiN films, such as Ti/N ratio and growth orientation. The growth orientation changed from a (111) phase to (200), with the ratio of N/Ti becoming near stoichiometric. The change in the growth orientation was caused by the increase in the N2 flow rate, which weakens the kinetic energy of the bombarding particles. The observed phenomenon is explained by an energy loss in the reactive plasma due to the difference in the inner degree of freedom of the molecular gas causing the reduction in the effective energy for radicals.

Difference in chemical reactions in bulk plasma and sheath regions during surface modification of graphene oxide film using capacitively coupled NH3 plasma

Reduced graphene oxide (r-GO) films were obtained from capacitively coupled NH3 plasma treatment of spin-coated graphene oxide (GO) films at room temperature. Variations were evaluated according to the two plasma treatment regions: the bulk plasma region (Rbulk) and the sheath region (Rsheath). Reduction and nitridation of the GO films began as soon as the NH3 plasma was exposed to both regions. However, with the increase in treatment time, the reduction and nitridation reactions differed in each region. In the Rbulk, NH3 plasma ions reacted chemically with oxygen functional groups on the GO films, which was highly effective for reduction and nitridation. While in the Rsheath, physical reactions by ion bombardment were dominant because plasma ions were accelerated by the strong electrical field. The accelerated plasma ions reacted not only with the oxygen functional groups but also with the broken carbon chains, which caused the removal of the GO films by the formation of hydrocarbon gas species. These re...

Effects of Growth Temperature on the Properties of CdSe Nano-Crystals Synthesized Eco-Friendly Using Colloidal Route

In this study, CdSe nanocrystals (NCs) were synthesized by inexpensive, non-toxic, and eco-friendly method, and the effect of growth temperature on the formation of CdSe NCs was investigated. The NCs were formed using oleic acid, and paraffin liquid instead of environmentally harmful materials typically involved in the NC synthesis. As the growth temperature increased from 140°C to 220°C, the diameter of CdSe NCs was changed from 3 nm to 4.5 nm, and the activation energy for the growth of CdSe NCs was 8.1 J/mol. As-synthesized CdSe NCs had a hexagonal crystal structure with wurtzite phase, and the growth of (101) plane was preferred with increasing growth temperature. The energy band-gap of the NCs was shifted from 2.29 eV to 2.18 eV, and the band-gap shift had a linear relationship with the size increase of the NCs. The growth temperature for the formation of CdSe NCs was an important factor to control the properties of the NCs. The developed method is considered to be an efficient CdSe synthesis method using eco-friendly colloidal route.

Characterization of Na-doped CuInS 2 thin film absorber layer formed by a non-vacuum ink process

Na-doped CuInS2 (Na-CIS2) thin films were fabricated by a non-vacuum ink process. The copper (Cu), indium (In) and sulfur (S) precursors were first synthesized by a sonochemical colloidal route, which is simpler and cheaper than the other preparation methods. The CuInS2 (CIS2) thin film absorber layers were then formed via spray-coating method using ink precursors consisting of Cu, In and S components. Finally, sodium (Na) was doped onto the CIS2 thin film by wet solution methods. The Na doping condition and the Cu to In ratio were found to play important roles in controlling the structural and optoelectronic properties of the absorber layer.

Electrical and optical characteristics of Ar plasma generated by low-frequency (60Hz) power source

The optical and electrical properties of Ar plasma, ignited using low-frequency (LF, 60 Hz) power source, were investigated. The plasma resistance, electron temperature, and density were found to be ∼102 Ω, ∼3 eV and ∼108 cm−3, respectively. The plasma parameters are strongly dependent on Ar pressure and discharge current, and the results of optical emission analysis showed similar tendency to the probe measurements. The properties of Ar plasma are similar to DC-pulsed discharge, and the polarity of AC power can be possible of depositions and modifications on both conductive and insulating materials, unlike DC discharge. The a-C films, which are deposited using Ar-diluted CH4 plasma, showed a smooth surface, high transmittance (>80%), high sp3 concentration (∼40%) and wide optical band-gap (3.55 eV). Consequently, the LF power source was found to be a very simple, convenient and inexpensive tool to generate plasmas for various applications.

Epitaxial gallium nitride thin films grown on silicon substrates utilizing gallium nitride seed-layer formed by liquid source precursor

Gallium nitride (GaN) epitaxial thin films were deposited on Si substrates by a modified hydride vapor phase epitaxy (MHVPE) technique utilizing the GaN seed-layer formed from liquid source precursor. Tris N,N-dimethyldithiocarbamato gallium(III) (Ga(mDTC)3) powder was dissolved in chloroform (CHCl3) to prepare the liquid source precursor for seed-layer formation. The developed method was found to be suitable for the epitaxial growth of GaN on Si in spite of the large mismatch in lattice constants and thermal expansion coefficients, resulting in device-quality epitaxial films with fairly smooth surface morphology. The epitaxial GaN films obtained in this study had a hexagonal structure with (0002) preferred orientation with the FWHM value of 428.6 arcsec of the (0002) GaN XRD peak. Photoluminescence spectra of GaN films exhibited a strong and sharp peak at 3.41 eV with the FWHM value of 107meV.

Quantum Dots Transparent Display (QDs-TPD) Using N2 BarrierDischarge with Liquid QDs Layer

Extended Abstract Transparent display (TPD) is an electronic information device that has gained rapidly growing attention recently. Its ability to represent images and texts on the transparent screen enables various applications such as handheld devices, sign boards, decorative windows, head up displays for vehicle and airplane, and information displays for medical and military purpose [1,2]. Various types of TPDs have been developed for suitable applications and each of them exhibits distinctive properties. In general, the TPD can be classified into two types: a see-through type and a projection type. The see-through type is again divided into an emissive and a passive type. The emissive type is a self-luminescence display including an organic electroluminescence display and an inorganic electroluminescence display; the passive type is a non-emissive display such as liquid crystal display, electro-wetting display, and electrochromic display. The emissive type displays represent perfect information under the dark environment, whereas the passive type displays do so under the bright environment. Thus, the emissive type displays in the bright environment must need visibility improvement, and the passive type display in the dark environment must require an edge type back light unit. In addition, the production of the TPD needs much improvement such as a scaling to large display sizes and a low-cost production. It is even necessary to develop new types of TPDs to acquire a high transparency and a high efficiency. The plasma discharge is a transparent medium with a specific color according to discharge gases, and the discharge mainly radiates strong UV and visible lights. In addition, the quantum dots (QDs) exhibit peculiar properties, such as a high luminescence, a color tenability, a strong chemical resistance, and a high dispersion property in liquids [3]. In this study, Quantum dots transparent display (QDs-TPD) was realized using a liquid QDs layer and N2 barrier discharge panel. In the N2 discharge, the 2nd lines of N2 in the range of 300 400 nm (CΠu BΠg), and the 1st lines of N2 at 391.4 and 427.8 nm (BΣu X Σg) were mainly observed, while the visible emission lines were rarely observed. This implies the N2 discharge is suitable for the excitation source of the QDs, due to the strong ultra-violet radiations and the weak visible emissions. The emission centers for red, green, and blue color in QDs-TPD were positioned at 452, 540, and 638 nm, respectively, and the N2 emission peaks were seldom observed in the visible region. The transmittance of QDs-TPD was approximately 40% in the visible region and the luminescence was about 70 cd/m. The CIE (x, y) coordinates of red, green, and blue colors were (0.670, 0.309), (0.378, 0.640), and (0.183, 0.118), respectively, and the color gamut was 71% of a NTSC standard. Thus, the QDs-TPD is expected as a way for realizing the TPD, due to its good transparency, excellent visibility, wide viewing-angle, aesthetical design, low cost production, and good scalability to large sizes.

Effects of a Plasma Generated from a Gas Mixture of Nitrogen, Methane, and Hydrogen on the Reduction of Graphene-Oxide Thin Films

In this study, reduced-graphene-oxide (r-GO) thin films were fabricated using the plasma reduction method, and their physical properties were evaluated. The plasma was generated from a gas mixture of N2, CH4, and H2 by using a radio-frequency (rf) power source (13.56 MHz). The GO films were treated in both the bulk plasma region (Rb) and the sheath region (Rs). When exposed to the plasma, the GO films were rapidly reduced, and their surfaces changed from hydrophilic to hydrophobic. Untill 5 min, the optical transmittances in both regions were over 85% for visible light and over 95% for infrared light. After 5 min, the optical transmittance of the r-GO film kept decreasing in the Rb while its optical transmittance remained constant in the Rs. The sheet resistance of the r-GO film in the Rb continuously decreased while the sheet resistance increased in the Rs. These results originate from the differences between the Rb and the Rs: chemical reactions were dominant in the Rb whereas physical reactions were dominant in the Rs.

Effects of growth temperature on titanium carbide (TiC) film formation using low-frequency (60 Hz) plasma-enhanced chemical vapor deposition

TiC films were formed by low-frequency (60 Hz) plasma-enhanced chemical vapor deposition (LFPECVD) using TiCl4, CH4, and H2 gas mixtures. The effects of the growth temperature and feasibility for the on-glass deposition of TiC films were investigated. The growth kinematics of TiC films was controlled mainly by surface-reactions below 450 ºC, and dominated by a mass-transfer process above 450 ºC. The films exhibited a face-centered cubic structure, and the preferred orientation of film growth was mainly the (200) plane. The [C]/[Ti] ratio was over-stoichiometric below 400 ºC, and became almost stoichiometric above 450 ºC. The optical properties of the films were characterized by high reflectance in near infrared (NIR) region and a steep edge in the visible region, and the reflectance in the NIR region increased gradually with increasing temperature. As a result, LF-PECVD is a useful technique to acquire Cl-free TiC films at relatively low temperatures.

The effects of capacitively coupled CH4 plasma on the reduction of the graphene oxide film

ABSTRACT In this study, the reduced graphene oxide (rGO) films were fabricated at room temperature using capacitively coupled CH4 plasma treatment of the spin-coated graphene oxide (GO) films. The variations of the rGO films were evaluated according to the treatment positions (bulk plasma region (Rb) and sheath region (Rs)) and the treatment time. The reduction of the GO films began immediately after the CH4 plasma was exposed to both regions. However, as the treatment time increased, the physical properties of rGO films became different. The reduction in the Rb was effective to modify the rGO films for transparent conducting films.