Seong Hyeon Kim

Improvement in n-ZnO/p-Si diode properties using ZnO/AZO homogeneous metal contact

In this study, an n-ZnO/p-Si diode with a ZnO/AZO homogeneous metal contact was fabricated and compared with a ZnO/Al metal contact. AZO films were deposited using atomic layer deposition (ALD). Prior to the device fabrication, the AZO films were optimized in terms of their characteristic as TCO on a soda lime glass. Their resistivity is 1.08 × 10−3 Ωcm and their transmittance is over 80% in the visible light region for a 5% Al doping concentration. The leakage current of ZnO/AZO homogeneous contact diodes is lower than that of ZnO/Al devices. In addition, under thermal stress induced by changing substrate temperature from 300 to 450 K, the contact resistance of the ZnO/AZO structure is more stable than that of the ZnO/Al structure.

Seawater Temperature and Wind Speed Dependences and Diurnal Variation of Ambient Noise at the Snapping Shrimp Colony in Shallow Water of Southern Sea of Korea

The seawater temperature and wind dependences and diurnal variation of the ambient noise at the snapping shrimp colony in shallow water of the southern sea of Korea were investigated. The ambient noise levels are significantly affected by the snapping shrimp sound, when the bottom seawater temperature increases and the wind speed decreases. However, they are not exceptively almost affected by the snapping shrimp sound when the wind speed decreases at low seawater temperatures (<10 °C). In diurnal variation, the ambient noise levels are also significantly affected by the snapping shrimp sound in the morning and night time zones. This study shows that the activity of the snapping shrimp affecting the variation in ambient noise level in shallow water can be related to the wind speed as well as the seawater temperature. This study also shows that the snapping shrimp in diurnal activity can be more active in the morning and night time zones.

Effects of coating material on the fabrication accuracy of focused ion beam machining of insulators

Focused ion beam (FIB) machining of insulators is a crucial process in the rapid prototyping of nanodevices for optical applications. A conductive material is generally coated on the insulator prior to FIB machining to achieve high fabrication accuracy. In this paper, we report on the effects on machining accuracy of four coating materials: Pt, Ni, Ag, and Co. The dimensional accuracy at channel sidewalls was improved by selecting a coating material that induces charge-carrier generation in a small range. The geometric and electrical characteristics of the FIB-machined surfaces were evaluated to elucidate the association between the fabrication accuracy and the range of charge-carrier distribution.

Study of underwater sound propagation in the East China sea at spring 2015

In this study, we investigated the effect of water temperature inversion layer on the propagation of acoustic wave in the western coastal sea of Jeju island in April 2015. When the acoustic source and receiver are simultaneously located within the water temperature inversion layer depth, the long range propagation of acoustic wave is confirmed by numerical modeling. This is caused by the duct effect due to the water temperature inversion phenomenon. For the experimental area without the water temperature inversion layer, when the acoustic source and receiver are simultaneously located below thermocline depth, the long range propagation of acoustic wave is also confirmed. This is generally caused by the seasonal water temperature profile.

Radius and thickness estimation of submerged cylindrical objects using broadband signal

Classification of submerged objects can be performed using broadband sonar and underwater sound scattering analysis. The backscattered signals, composed of specular echo and elastic echo, have information on the submerged target, including its dimensions and material characteristics. In this study, we performed shockwave-scattering simulations of backscattered signals when a broadband shockwave (1–60 kHz) was used as the incident wave. The radius and thickness of a cylindrical target was estimated by analyzing the echo signal in the time domain and the echo spectrum in the frequency domain. The validity of the estimated parameters was confirmed by the modeling results.

Effects of water temperature inversion layer on underwater sound propagation in the East China Sea

In the northern side of East China Sea it exists Tsushima Current into the East Sea through the Korea Strait that a branch of Kuroshio Current moving from the Western Kyushu in Japan are coming up to the north. The others pass through the western coastal sea of Jeju island, performing Yellow Sea Warm Current into the Yellow Sea. A part of Yellow Sea Warm Current turns lockwise round in the western coastal sea of Jeju island. This becomes to Jeju Warm Current passing to the Korea Strait[1]. The complicated ocean processes are existed in East China Sea on account of large fresh water inflow from landside[1]. The area to meet a different water mass is called coastal upwelling[2], and near these area the boundaries show complicated ocean physical characteristic such as temperature front. This study was analyzed the temperature inversion phenomenon by tidal current and Jeju Warm Current of the western coastal sea of Jeju island into the complicated northern coastal sea of East China Sea, and researched the underwater sound propagation by the temperature inversion.

Effect of underwater sound channel on variation of ambient noise level in eastern sea of Korea

In this study, we investigated the effect of the underwater sound channel (USC) on variations in the ambient noise level in the eastern sea of Korea. Hydrophone observations near the USC axis indicated that the ambient noise levels for frequencies 200 Hz, only slight variations in the ambient noise level were detected, regardless of hydrophone depth or distance relative to the USC. The results from this study shows a typical example of the low-frequency ambient noise (<200 Hz) in shallow water being effectively propagated a long distance near the USC axis in the deep ocean along continental slope.