Joon-sig Jung

Electrode-dependent electrical properties of metal/Nb-doped SrTiO3 junctions

In this study, we discuss the electrical properties of junctions consisting of metal electrodes and Nb-doped SrTiO3(001) single crystals. The junctions formed with large work function metals (Ni, Au, Pd, and Pt) resulted in rectifying transport. A hysteretic feature was observed in the current (I)-voltage (V) and capacitance (C)-V characteristics of these junctions upon polarity reversal. The ideal Schottky–Mott rule could not explain the barrier height obtained from the I-V data, indicating the existence of interface states. Analyses of the C-V data revealed that a low dielectric constant layer existed at the interface. The interface states and layers affected the transport and the related resistance switching characteristics of the junctions.

Formation mechanism of ZnSiO3 nanoparticles embedded in an amorphous interfacial layer between a ZnO thin film and an n-Si (001) substrate due to thermal treatment

The x-ray diffraction patterns, transmission electron microscopy images, and selected-area electron diffraction patterns for the ZnO∕Si heterostructures annealed at 900°C showed that orthorhombic ZnSiO3 nanoparticles were formed in the amorphous layer between the ZnO film and the Si substrate, resulting from the interdiffusion between the ZnO film and the Si substrate due to thermal treatment. Auger electron spectroscopy depth profiles for the ZnO∕Si heterostructures annealed at 900°C demonstrated the formation of amorphous Zn2xSi1−xO2, an interfacial layer. A formation mechanism for the orthorhombic ZnSiO3 nanoparticles embedded in the amorphous Zn2xSi1−xO2 layer is described on the basis of the experimental results.

Optical properties of self-assembled Cu2O nanocrystals embedded in a polyimide layer

Self-assembled Cu2O nanoparticles embedded in a polyimide (PI) matrix were formed by curing Cu thin films with PI precursor layers. Transmission electron microscopy images and selected area electron diffraction patterns showed that Cu2O nanocrystals were created inside the PI layer. The excitonic peaks corresponding to the transitions from the electronic sublevel to the heavy-hole sublevel in the Cu2O nanocrystals embedded in the PI layer shifted to the lower energy side with increasing curing time, and this behavior is attributed to a decrease in the confinement effects because the size of the nanocrystals increases with the curing time. The activation energy of the electrons confined in the ground state of the Cu2O nanocrystals embedded in the PI layer, as obtained from the temperature-dependent photoluminescence spectra, was larger than that of those confined in the excited state. The present results can help us to improve understanding of the optical properties of Cu2O nanocrystals embedded in a PI layer.

Multilevel charging and discharging mechanisms of vertically stacked Ni1-xFex self-assembled nanoparticle arrays embedded in polyimide layers

Capacitance-voltage curves for the Al/polyimide (PI)/multilayered Ni1−xFex nanoparticle array/PI/p-Si (100) devices at 300K showed that the flatband voltage shift of the metal-insulator-semiconductor capacitor was affected by the value of sweep voltage, indicative of the variations in the charged electron number in the multiple-stacked Ni1−xFex nanoparticle arrays in the floating gate. Current-voltage results showed that the electron charging and discharging in the Ni1−xFex nanoparticles were attributed to thermionic emission and Fowler-Nordheim tunneling, respectively. The multilevel charging and discharging mechanisms of vertically stacked Ni1−xFex self-assembled nanoparticle arrays embedded in PI layers are described on the basis of the experimental results.

Carrier transport mechanisms of the writing and the erasing processes for Al∕ZnO nanoparticles embedded in a polyimide layer/p-Si diodes

Capacitance-voltage measurements on Al∕ZnO nanocrystals embedded in polyimide (PI) layer/p-Si diodes at 300K showed a metal-insulator-semiconductor behavior with a flatband voltage shift. Current-voltage (I-V) measurements on the diodes showed that carrier transport processes were attributed to the Poole-Frenkel effect and to thermionic emission. Possible carrier transport mechanisms of the writing and the erasing processes for the Al∕ZnO nanocrystals embedded in PI layer/p-Si diodes are described on the basis of the I-V results.

Influencing factors on female university students` sexual experience and sexual assertiveness

This study examined the sexual behaviors, such as sexual experience, sexual attitudes, sexual knowledge of female university students, and to identify the factors that affect sexual assertiveness and to encourage female university students to improve the level of sexual assertiveness. The subjects were 398 single, female students (undergraduate and graduate) from a university in Seoul. The research tool was a self-administered questionnaire. The data obtained was analyzed using a t-test and ANOVA, and regression analysis on SAS 9.3. The sexual intercourse experience rates showed a positive relation with higher age, having religion, more allowance. The sex knowledge showed a positive relation with higher age, major related humanities or science & technology, and more allowance, and sex attitudes had a significantly positive relation with higher age, major related humanities, no religion, and more allowances. The factors affecting sexual assertiveness were sexual attitudes and lower age. Overall, education programs should be developed to encourage sexual assertiveness and sexual attitudes from elementary school.

Atomic arrangements of (Ga1-xMnx)N nanorods grown on Al2O3 substrates

X-ray diffraction (XRD) and selected area electron diffraction pattern (SADP) results showed that the (Ga1−xMnx)N nanorods had preferential c-axial growth direction. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) images showed that one-dimensional (Ga1−xMnx)N nanorods without defects had c-axis-oriented crystalline wurzite structures. Atomic arrangements for the (Ga1−xMnx)N nanorods grown on the Al2O3 (0001) substrates are described on the basis of the XRD, the TEM, the SADP, and the HRTEM results.

EFFECT OF SUBSTRATE TEMPERATURE ON THE STRUCTURAL AND THE OPTICAL PROPERTIES OF CdTe (100) EPITAXIAL FILMS GROWN ON GaAs (100) SUBSTRATES

CdTe thin films were grown on GaAs(100) substrates by using molecular beam epitaxy at various temperatures. The results of the X-ray diffraction (XRD) patterns showed that the orientation of the grown CdTe thin films was the (100) orientation. XRD patterns, atomic force microscopy images, high-resolution transmission electron microscopy (HRTEM) images, and photoluminescence spectra showed that the crystallinity of CdTe(100) epilayers grown on GaAs(100) substrates was improved by increasing the substrate temperature. HRTEM images showed that misfit dislocations existed at the CdTe/GaAs heterointerface. These results can help improve understanding of the substrate temperature effect on the structural and the optical properties of CdTe(100)/GaAs(100) heterostructures.

Airborne Bacteria Concentration and Species Identification in Residential Living Spaces

Objectives: Exposure to airborne bacteria is associated with adverse health effects such as respiratory and infectious diseases. This study evaluated airborne bacterial concentrations in the living rooms, kitchens, and toilets of 30 homes. Methods: Bacteria were sampled with an MAS100 impactor in three spaces in the subject homes between April 2014 and February 2015. Bacteria were grown on TSA plates for 48 hours at 35C. The bacterial strains were isolated and amplified by polymerase chain reaction. Results: The most culturable bacteria were found in toilets (624.0 CFU/m, GM: 417.3 CFU/m), followed by in the kitchen (503.8 CFU/m, GM: 324.9 CFU/m). The dominant genera identified were: Staphylococcus sp.(19%), Micrococcus sp.(16%), and Bacillus sp.(11%) in the indoor air and Bacillus sp. (30%) in the outdoor air. Gram-positive bacteria comprised more than half of all colonies. Conclusion: In this study, culturable bacteria concentrations were higher than those reported in other spaces. Therefore, it is important to control relative humidity and remove moisture to prevent bacteria from multiplying. Additionally, the dominant species in indoor air were Staphylococcus sp. and Micrococcus sp. These are found on the human skin, mucous membranes, and hair, so human activity can affect bacterial distribution. Therefore, cleaning and controlling moisture are important for reducing indoor bacterial concentrations.

A Study on the PM 10 and CO 2 Concentrations at Public Places

The objective of this study was to investigate PM10 and CO2 concentrations in the classrooms of 286 elementary schools in Suwon, Ansan, and Hwaseong in the province of Gyeonggi between August 2008 and December 2012. By gaining an understanding of the environmental factors that influence these concentrations, this study also aimed to establish a management plan for indoor air quality in schools, which substantially affects the health of elementary students. When the schools were classified by region, no statistically significant difference in PM10 concentration was observed. However, PM10 concentration was relatively high in industrial areas and low in rural areas. No difference in CO2 concentration was observed among the surveyed cities. Analysis of annual PM10 concentration showed that the highest values for Suwon and Hwaseong occurred in 2008 and 2009, respectively (p<0.01). In the case of Ansan, the highest concentration occurred during 2009, but the difference was not significant compared to the other years. Analysis of the annual CO2 concentration of each city shows no significant difference among the cities (p-value=0.366,0.730,0.210). According to a time series analysis of PM10 and CO2 by season, from autumn 2008 to winter 2012, PM10 concentration was high during 2009, then it gradually decreased until 2012, and started to increase again. While no difference in annual CO2 concentration was observed, the concentration had a tendency to be higher in spring and winter than in summer. By analyzing the relationship between PM10 and CO2 and the environmental factors (years of construction, average students of classroom, temperature, and humidity), it showed a significant negative correlation was found between CO2 and the environmental temperature and humidity, at -0.329 and -0.188, respectively (p<0.01).