• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.6
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• pp.236-239
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• 2002

Si nanocrystallites thin films on P-type (100) Si substrate have been fabricated by pulsed laser deposition using a Nd:YAG laser. After deposition, samples were annealed in several environmental gases ;It the temperature range of 400 to $800^{\circ}C$ Hydrogen passivation was then performed in the forming gas (95 % $N_2$ + 5 % $H_2$) for 1 hr. Strong violet-indigo photoluminescence has been observed at room temperature on nitrogen ambient-annealed Si nanocrystallites. We report the variation of photoluminescence (PL) properties of Si thin films by changing annealing temperatures and by using hydrogen passivation. The results could suggest that the origin of violet-indigo PL should be related to the Quantum size effect of Si nanocrystallite.

• Proceedings of the KIEE Conference
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• 2004.11a
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• pp.54-57
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• 2004

ZnO thin films on (001) sapphire substrates have been deposited by pulsed laser deposition(PLD) technique using an Nd:YAG laser with a wavelength of 266 m. During deposition, the experiment of the deposition of ZnO thin films has been performed for substrate temperatures in the range of $400^{\circ}C$ and flow rate of 350 sccm, films have been annealed at various substrate temperatures after deposition. After post-annealing treatment in the oxygen ambient, the structural properties of ZnO thin films were characterized by diffraction (XRD), SEM and the optical of the ZnO were characterized by photoluminescence (PL).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.95-98
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• 1999

ZnO thin films on (001) sapphire substrates have been deposited by pulsed laser deposition technique using a Nd:YAG laser with the wavelength of 355 nm. In order to investigate the effect of the deposition conditions on the properties of ZnO thin films at an oxygen pressure of 350 mTorr, the experiment has been Performed at various substrate temperatures in the range of 20$0^{\circ}C$ to $700^{\circ}C$. According to XRD, (002) textured ZnO films of high crystalline quality have been obtained and the intensity of UV emission was the highest at 40$0^{\circ}C$ substrate temperature.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.9
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• pp.64-71
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• 2009

Recently as ultrasonic medical devices are gradually developed, many of those require smaller and more precision coaxial cables in the probe. So, the use of micro coaxial cable becomes an efficient solution for ultrasonic machine. However, there are many difficulties in stripping micro coaxial cable by traditional mechanical process. In this paper we use the Nd:YAG laser for the efficient striping of conduct wire of cable. Through some experiments, we found that there is a new possibility in the proposed method. Also, we propose a pre-process of the cable before stripping in order to enhance the performance.

• Laser Solutions
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• v.8 no.3
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• pp.11-19
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• 2005

In automotive industry, light weight vehicle is one of issues because of the air pollution and the protection of environment. Therefore, automotive manufacturers have tried to adopt light materials such as aluminum alloy to production line. Aluminum welding using laser has some advantages high energy density and high productivity. It is very important to understand weld characteristic according to welding condition in order to determine the possibility of application to car body. In this study, Nd:YAG laser welding of 5182 aluminum alloy with filler wire AA5356 was carried out through experimental design according to wire feed rate, laser power and welding speed. Weld bead shape in terms of cross section photo, bead with, height of reinforcement and penetration depth and mechanical property in terms of tensile strength and formability was investigated. Analysis of variation (ANOVA) was performed to know the effect of weld parameter for weldability, laser power was statistically most significance factor of three variables.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.8
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• pp.961-969
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• 2007

The laser material processing has replaced a conventional material processing such as a welding, cutting, drilling and surface modification and so on. LTH(Laser Transformation Hardening) is one branch of the laser surface modification process. A lot of energy is needed for the LTH process to elevate workpiece surface to temperature of the austenite transformation($A_3$), which results from utilizing a beam with a larger size and lower power intensity comparatively. The absorptivity of the laser energy with respect to material depends on the wave length of a beam. This study is related to the surface hardening for the rod-shaped carbon steel by the high power diode laser(HPDL) whose beam absorptivity is better than conventional types of lasers such as $CO_2$ or Nd:YAG laser. Because a beam proceeds on the rotating specimen the pretreated hardened-phase can be tempered and softened by the overlapping between hardened tracks. Accordingly, the longitudinal hardness measurement and observation of the micro structure was carried out for an assessment of the hardening characteristics. In addition, a hardening characteristics as a hardenability of materials was compared in the point of view of the hardness distribution and hardening depth and width.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.7 s.184
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• pp.39-50
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• 2006

Laser heat treatment technologies have been used to improve characteristics of wear and to enhance the fatigue resistance for automotive parts. The bjective of this research work is to investigate the influence of the process parameters, such as power of laser and defocused spot position, on the characteristics of laser heat treatment for the case of SM45C medium carbon steel. CW Nd:YAG laser is selected as the heat source. The optical lens with the elliptical profile is designed to obtain a wide heat treatment area with a uniform hardness. From the results of the experiments, it has been shown that the maximum hardness is approximatly 780 Hv when the power and the travel of laser are 1,095 W and 0.6 m/min, respectively. In addition, the hardening width using the elliptical lens was three time larger than that using the defocusing of laser beam.

• Laser Solutions
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• v.11 no.4
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• pp.7-12
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• 2008

Laser Transformation Hardening(LTH) is one branch of the laser surface modification processes. A lot of energy is needed for the LTH process to elevate workpiece surface to temperature of the austenite transformation($A_3$), which results from utilizing a beam with a larger size and lower power density comparatively. This study is related to the surface hardening for the rod-shaped carbon steel by the high power diode laser whose beam absorptivity is better than conventional types of lasers such as $CO_2$ or Nd:YAG laser. Because a beam proceeds on the rotating specimen, the pretreated hardened-phase can be tempered and softened by the overlapping between hardened tracks. Accordingly, the longitudinal hardness measurement and observation of the micro structure was carried out for an assessment of the hardening characteristics. In addition, a hardening characteristics as a hardenability of materials was compared in the point of view of the hardness distribution and hardening depth and width.

• Journal of the Korean Society for Heat Treatment
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• v.23 no.5
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• pp.257-262
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• 2010

Recently, metal molding has become essential not only for automobile parts, but also mass production, and has greatly influenced production costs as well as the quality of products. Its surface has been treated by carburizing, nitriding and induction hardening, but these existing treatments cause considerable deformation and increase the expense of postprocessing after treatment; furthermore, these treatments cannot be easily applied to parts that requiring the hardening of only a certain section. This is because the treatment cannot heat the material homogeneously, nor can it heat all of it. Laser surface treatment was developed to overcome these disadvantages, and, when the laser beam is irradiated on the surface and laser speed is appropriate, the laser focal position is rapidly heated and the thermal energy of surface penetrates the material after irradiation, finally imbuing it with a new mechanical characteristic by the process of self-quenching. This research estimates the material characteristic after efficient and functional surface treatment using HPDL, which is more efficient than the existing CW Nd:YAG laser heat source.

• Journal of Welding and Joining
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• v.29 no.2
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• pp.88-93
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• 2011

This study produced hypereutectic Al-Si clad layer on 1050 Al alloy by a novel laser cladding method. Pure Si powder was mixed with organic binder to make fluid paste which could be screen-printed on the 1050 Al alloy plate. Pulsed Nd:YAG laser was irradiated on the Si paste layer to melt and alloy with Al substrate. Different laser power of 99 W, 179 W and 261 W, was used to see the difference of the microstructure, composition and hardness of the clad layers. When laser power of 179 W was used, the clad layer had overall Si content of 38wt% and composed of fine primary Si particles and fine eutectic phase. At laser power of 261 W, the clad layer had overall Si content of 24wt% and composed of mainly fine eutectic phase. Vickers hardness of HV176.7 and HV150.3 on the clad layer was obtained at laser power of 179 W and 261 W, respectively.