• 한국반도체및디스플레이장비학회:학술대회논문집
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• 한국반도체및디스플레이장비학회 2003년도 추계학술대회 발표 논문집
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• pp.109-116
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• 2003

Amorphous GaN Quantum dots(a-GaN QDs) with particle diameters less than bohr radius(~11nm) were successfully fabricated at room temperature by a laser ablation of high densified GaN target. Transmission electron microscopy, SAED diffraction pattern and X-ray photoelectron spectroscopy confirmed the presence of a-GaN QDs with particle size of 7.9, 6.9, 4.4nm under the Ar gas pressures of 50, 100 and 200 Pa, respectively. The room temperature PL and absorbance spectra showed a strong band emission centered at 3.9 eV in a-GaN QDs made under the gas pressures of 100 and 200 Pa, which is nearly 0.5eV blueshifted with respect to the bulk crystal band gap.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제55권1호
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• pp.26-29
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• 2006

Transparent ZnO thin films were prepared by KrF pulsed laser deposition (PLD) technique and applied to a bottom-gate type thin film transistor device as an active channel layer. A high conductive crystalline Si substrate was used as an metal-like bottom gate and SiN insulating layer was then deposited by LPCVD(low pressure chemical vapour deposition). An aluminum layer was then vacuum evaporated and patterned to form a source/drain metal contact. Oxygen partial pressure and substrate temperature were varied during the ZnO PLD deposition process and their influence on the thin film properties were investigated by X-ray diffraction(XRD) and Hall-van der Pauw method. Optical transparency of the ZnO thin film was analyzed by UV-visible phometer. The resulting ZnO-TFT devices showed an on-off ration of $10^6$ and field effect mobility of 2.4-6.1 $cm^2/V{\cdot}s$.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 C
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• pp.1430-1431
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• 2006

We investigated the formation of 2-dimension hologram grating by means of selective etching characteristic and photo-expansion effect according to photo irradiation on amorphous As-Ge-Se-S thin film. By method of phase holography, we made the 2-dimensional hologram grating by each (S:P) and ($+45^{\circ}:-45^{\circ}$) polarized beam with DPSS laser(532nm) and He-Ne laser(632nm). A recording property was observed at each polarized beam through 2-dimensional hologram surface relief grating. Chalcogenide thin film was etched selectively by NaOH solution after the formation of 1-dimensional diffraction grating. And then etched sample was rotated 90 degree to fabricate 2 dimensional hologram grating. We found that it was observed the formation of 2-dimensional hologram grating by AFM(Atomic Force Microscopy).

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.340-341
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• 2007

Thin film of ZnO was deposited on various substrate by Nd:YAG Pulsed Laser Deposition(PLD) with a wavelength of 355nm. Further more, Thin filme of ZnO conducted by various temperature conditions. The surface morphology of the ZnO thin film was investigated by X-Ray Diffraction(XRD) and Atomic Force Microscopy(AFM). Effects of various substrates and Temperature conditions were analyzed. The best properties were obtained on $600^{\circ}C$ with post-deposition annealing at $600^{\circ}C$ in flowing $O_2$ atmosphere for several hours.

• Bulletin of the Korean Chemical Society
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• 제18권6호
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• pp.640-643
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• 1997

Pure titanium dioxide $(TiO_2)$ films were prepared by pulsed laser deposition on a single crystal Si(100) substrate. We have investigated the growth of crystalline titanium dioxide films with respect to substrate temperature and ambient oxygen pressure. The structural properties of the films were analyzed by X-ray diffraction. We found that the anatase as well as the rutile phases could be formed from the original rutile phase of the target $TiO_2$. At 0.75 torr of ambient oxygen pressure, the structure of $TiO_2$ film was amorphous at room temperature, anatase between 300 and 600 ℃, a mixture of anatase and rutile between 700 and 800 ℃, and only rutile at 900 ℃ and above. However, at a low ambient oxygen pressure, the rutile phase became dominant; the only rutile phase was obtained at the ambient oxygen pressure of 0.01 torr and the substrate temperature of 800 ℃. Therefore, the film structures were largely influenced by substrate temperature and ambient oxygen pressure.

• 한국광학회지
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• 제2권4호
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• pp.186-192
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• 1991

엑시머 레이저빔($\lambda$ 0.248$\mu\textrm{m}$)을 사용하여 micro-lithography를 위해 축소배율 $5\times$를 갖는 4개의 구면으로 구성된 반사경계를 설계하였다. 먼저 초기광학계로서 Seidel 3차 수차 내에서 구면수차, 코마, 상면만곡, 왜곡수차가 제거된 4구면경계를 해석적으로 구하였다. 이 초기광학계의 성능 향상을 위해 컴퓨터를 이용한 최적화 기법을 사용하였고 그 결과 KrF 엑시머 레이저 광에 대해 N.A. 0.15와 image field diameter 3.3 mm 이내에서 회절 한계까지 제거된 수차 성능을 얻었다.

• 한국광학회지
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• 제32권4호
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• pp.147-152
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• 2021

본 논문에서는 최고 출력 3.0 kW 발진 단일 모드 이터븀(ytterbium, Yb) 첨가 광섬유 레이저에 대해 보고한다. 고출력 광섬유 레이저의 출력을 제한하는 주된 요소인 유도 라만 산란 문턱 값과 광섬유 내 온도 분포를 계산하고 이를 바탕으로 양방향 펌핑 구조의 단일 공진기 Yb 광섬유 레이저 시스템을 제작하였다. 그 결과 4.1 kW의 펌프 출력에서 최고 출력 3.0 kW의 레이저 빔을 얻을 수 있었고, 그때의 기울기 효율은 81.5%로 계산되었다. 최고 출력에서 측정된 출력 빔의 빔질(M²)은 1.26으로 단일 공간 모드 빔 출력 특성을 가지고 있음을 확인하였고, 유도 라만 산란 및 횡모드 불안정 현상은 관측되지 않았다. 본 연구에서 얻은 광섬유 레이저 출력 결과는 지금까지 국내에서 보고된 다이오드 레이저로 펌핑한 광섬유 레이저 출력 중 가장 높은 출력이며, 향후 더 높은 출력을 얻기 위한 방법에 대해 논의하고자 한다.

• Nuclear Engineering and Technology
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• 제52권9호
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• pp.2054-2063
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• 2020

The high-temperature oxidation behavior of ZrSi₂ used as a coating material for nuclear fuel cladding was investigated for developing accident-tolerant fuel cladding of light water reactors. Bulk ZrSi₂ samples were prepared by spark plasma sintering. In situ X-ray diffraction was conducted in air at 900, 1000, and 1100 ℃ for 20 h. The microstructures of the samples before and after oxidation were examined by scanning electron microscopy and transmission electron microscopy. The results showed that the oxide layer of zirconium silicide exhibited a layer-by-layer structure of crystalline ZrO₂ and amorphous SiO₂, and the high-temperature oxidation resistance was superior to that of Zircaloy-4 owing to the SiO₂ layer formed. ZrSi₂ was coated on the Zircaloy-4 tube surface using laser 3D printing, and the coated tube was oxidized for 2000 s at 1200 ℃ under a vapor/argon mixture atmosphere. The outer surface of the coated tube was hardly oxidized (10-30 ㎛), while the inner surface of the uncoated tube was significantly oxidized to approximately 300 ㎛.

• International Journal of Precision Engineering and Manufacturing
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• 제8권4호
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• pp.63-69
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• 2007

The two-photon stereolithography (TPS) process is a promising technique for the fabrication of real three-dimensional (3D) nano/micro-structures via application of a femto-second laser, In TPS, when a near-infrared ultrashort-pulsed laser is closely focused onto a confined volume of photocurable resin, only the local area at the center of the focus is cured. Therefore, real 3D microstructures with resolution under the diffraction limit can be fabricated through a layer-by-layer accumulative technique, This process provides opportunities to develop neo-conceptive nano/micro devices in IT/BT industries, However, a number of issues, including development of effective fabrication methods, highly sensitive and functional materials, and neo-conceptive devices using TPS, must be addressed for the realization of industrial application of TPS. In this review article, we discuss our efforts related to TPS: effective fabrication methods, diverse two-photon curable materials for high functional devices, and applications.

• 한국광학회지
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• 제12권1호
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• pp.48-54
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• 2001

광굴절 광기전력 특성을 갖는 Fe를 도핑한 LiNbO$_3$결정에서의 어두운 공간 솔리톤의 발생과 이의 광도파로 역할에 대해 연구하였다. 파장이 488nm인 cw $Ar^{+}$ 레이저를 이용하여 입사빔의 세기가 10mW/$cm^2$ 이하에서도 어두운 공간솔리톤이 발생됨을 관측하였다. 빔의 세기 변화 방향이 광축에 수직인 경우에는 자기확산 효과를 관측할 수 없었으나 광축에 평행한 경우에는 이 효과를 관측할 수 있었다. 이를 통해 매질에서의 굴절률 변화가 빔의 세기 변화 방향과 광축방향이 평행할 때만 일어남을 확인하였다 파장이 633nm인 He-Ne 레이저를 어두운 공간솔리톤에 통과시킴으로써 빔의 집속효과를 관측하였다. 이를 통해 어두운 공간솔리톤의 광도파로 역할을 확인하였다.