Sung-Youp Lee

Effects of gas exposure on the field-emission properties of ZnO nanorods

The effect of diverse gases on the field emission (FE) properties of ZnO nanorods was investigated. The FE properties of nanorods were fully recovered after evacuating to the initial pressure, even after an abrupt current drop under severe vacuum conditions of Torr induced by the presence of O2, N2, Ar and air. The reversible and sensitive response of the FE of the nanorods with variation in pressure was found for all gases tested except for H2. Exposure of H2 causes a permanent increase in the FE current and a decrease in the turn-on field. The pressure-dependent field emission behaviour of nanorods must be considered when field emission data are compared and characterized.

A genetic variation in microRNA target site of KRT81 gene is associated with survival in early stage non-small cell lung cancer

BACKGROUND MicroRNAs (miRNAs) have a key role in carcinogenesis through negative regulation of their target genes. Therefore, genetic variations in miRNAs or their target sites may affect miRNA-mRNA interactions, thereby result in altered expression of target genes. This study was conducted to investigate the associations between single-nucleotide polymorphisms (SNP) located in the miRNA target sites (poly-miRTSs) and survival of patients with early-stage non-small-cell lung cancer (NSCLC). METHODS Using public SNP database and miRNA target sites prediction program, 354 poly-miRTSs were selected for genotyping. Among these, 154 SNPs applicable to Sequenoms MassARRAY platform were investigated in 357 patients. A replication study was carried out on an independent patient population (n = 479). Renilla luciferase assay and reverse transcription-polymerase chain reaction were conducted to examine functional relevance of potentially functional poly-miRTSs. RESULTS Of the 154 SNPs analyzed in a discovery set, 14 SNPs were significantly associated with survival outcomes. Among these, KRT81 rs3660G>C was found to be associated with survival outcomes in the validation cohort. In the combined analysis, patients with the rs3660 GC + CC genotype had a significantly better overall survival compared with those with GG genotype [adjusted hazard ratio (aHR) for OS, 0.65; 95% confidence interval (CI) 0.50-0.85; P = 0.001]. An increased expression of the reporter gene for the C allele of rs3660 compared with the G allele was observed by luciferase assay. Consistently, the C allele was associated with higher relative expression level of KRT81 in tumor tissues. CONCLUSION The rs3660G>C affects KRT81 expression and thus influences survival in early-stage NSCLC. The analysis of the rs3660G>C polymorphism may be useful to identify patients at high risk of a poor disease outcome.BACKGROUND MicroRNAs (miRNAs) have a key role in carcinogenesis through negative regulation of their target genes. Therefore, genetic variations in miRNAs or their target sites may affect miRNA-mRNA interactions, thereby result in altered expression of target genes. This study was conducted to investigate the associations between single-nucleotide polymorphisms (SNP) located in the miRNA target sites (poly-miRTSs) and survival of patients with early-stage non-small-cell lung cancer (NSCLC). METHODS Using public SNP database and miRNA target sites prediction program, 354 poly-miRTSs were selected for genotyping. Among these, 154 SNPs applicable to Sequenoms MassARRAY platform were investigated in 357 patients. A replication study was carried out on an independent patient population (n = 479). Renilla luciferase assay and reverse transcription-polymerase chain reaction were conducted to examine functional relevance of potentially functional poly-miRTSs. RESULTS Of the 154 SNPs analyzed in a discovery set, 14 SNPs were significantly associated with survival outcomes. Among these, KRT81 rs3660G>C was found to be associated with survival outcomes in the validation cohort. In the combined analysis, patients with the rs3660 GC + CC genotype had a significantly better overall survival compared with those with GG genotype [adjusted hazard ratio (aHR) for OS, 0.65; 95% confidence interval (CI) 0.50-0.85; P = 0.001]. An increased expression of the reporter gene for the C allele of rs3660 compared with the G allele was observed by luciferase assay. Consistently, the C allele was associated with higher relative expression level of KRT81 in tumor tissues. CONCLUSION The rs3660G>C affects KRT81 expression and thus influences survival in early-stage NSCLC. The analysis of the rs3660G>C polymorphism may be useful to identify patients at high risk of a poor disease outcome.

In situ characterization of the field-emission behaviour of individual carbon nanotubes

The current–voltage (I–V) characteristics of carbon nanotubes (CNTs) during field emission were investigated by in situ imaging and field-emission (FE) measurement inside a field-emission scanning electron microscope (FE-SEM). A primary electron of the FE-SEM could induce and enhance a large stimulated electron emission from a CNT which might be due to the strong local field on the tip of the CNT in the presence of an applied voltage. FE of bent nanotubes (BNTs) can initially occur after they are fully straightened or it can start in the bent state (during geometrical straightening) as the applied field increases. The FE from a single CNT follows FN (Fowler–Nordheim) behaviour with a single linear slope in the FN plot. The FE from two nanotubes with a geometrical change during FE showed transition of the FN slope from the low voltage to the high voltage region, which could be due to interactions between two dynamic neighbouring BNTs.

Effects of Surface Roughness on Gas Barrier Property of Thin Film Passivation with Mg-Zn-F

The thin film passivation is the key technology for the application of flexible organic light emitting diodes. We fabricated very effective gas barrier with Mg-Zn-F thin film using the RF magnetron sputter. In this study, we employed inorganic and organic buffer layers between Mg-Zn-F gas barrier and polyethylene naphthalate substrate to evaluate the effects of surface morphology. Organic layer had much lower surface roughness than that of inorganic layer. It is very effective to decrease water vapor transmission rate (WVTR). We showed that WVTR of gas barrier using organic layer and Mg-Zn-F film reached 4.5 × 10−4g/(m2·day) using calcium corrosion test.

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.

Field emission from single crystalline tin oxide nanowires synthesized by thermal chemical vapor deposition

ABSTRACT In this study, tin oxide (SnO2) nanowires were synthesized on cobalt coated silicon wafer at 850°C for 1 hour via carbo thermal reduction vapor method by using thermal chemical vapor deposition. The diameter and the length of SnO2 nanowires were approximately 120 nm and 10 μm, respectively. The SnO2 nanowires had tetragonal structure with lattice constants of a = b = 4.743 Å and c = 3.186 Å. In the results of field emission characteristics, the turn-on field was approximately 15 V/μm, which was defined as the field to produce a 1.1 × 10−7 A/cm2. The field emission from the SnO2 nanowires successfully followed the Fowler–Nordheim behavior. The average γ value of SnO2 nanowires was calculated to be about 467, assuming the work function of the SnO2.

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.

Synthesis of Ga(S2CN(CH3)2)3 nanoparticles using ultrasonic spray method as GaN precursor

ABSTRACT Ga(S2CN(CH3)2)3 (Ga(mDTC)3) nanoparticles (NPs) were prepared using ultrasonic spray method, and well mono-dispersed, with a mean particles size of 82 nm. Ga(mDTC)3 NPs changed into Ga2S3 at 300°C under N2 environment, and the spin-coated films transformed into GaN films above 700°C under NH3 environment. From these results, Ga(mDTC)3 films were transformed into γ-Ga2S3 films by thermal decomposition, and S elements were substituted simultaneously by N elements. In this stage, the pyrolytic GaN film underwent a recrystallization process, and a preferred direction of GaN films was mainly aligned to z-axis direction due to the lower energy surface of hexagonal structure.