• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.172-172
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• 2008

By thermal evaporation method, well-aligned ZnO nanowires were synthesized on sapphire substrate at $1000^{\circ}C$ with different oxygen flow rate by using pure ZnO powder (99.999 %). The as-synthesized ZnO nanowires were characterized by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The well-aligned nanowires are single crystalline in nature and perpendicularly grown along the c-axis. Also the growth rate of nanowires, such as diameter and length, had a tendency to increase as oxygen flow rate increased. Based on the PL measurement of ZnO nanowires, we found that the near band edge of emission redshifted with the increasing intensity of the defect-related green emission in proportion to the increase of oxygen flow rate. "This research was supported by the Korea Research Foundation Grant funded by the Korean Government(MOEHRD)" (The Regional Research Universities Program/Chungbuk BIT Research-Oriented University Consortium).

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 추계학술대회 논문집 전기물성,응용부문
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• pp.46-47
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• 2006

Ga-doped ZnO nanowires have been synthesized by pulsed laser deposition (PLD) in furnace on gold coated (0001) sapphire substrates. The effect of repetition rate on structural and optical properties of Ga-doped ZnO nanowires are investigated. By controlling repetition rate, the diameter of nanowires is varied between about 60 and 100 nm, and the length of nanowires is varied between about 2 and 4 um. The X-ray diffraction (XRD) reveals the structural defects induced by the Ga doping. The room temperature photoluminescence (PL) spectra of Ga-doped ZnO nanowires show strong UV emission between 382.394 and 385.279 nm with negligible visible emission.

• 한국생산제조학회지
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• 제25권4호
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• pp.301-306
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• 2016

High speed polishing can kinematically increase the polishing removal rate by using the conventional Preston equation, especially for hard substrates such as sapphire or diamond. However, high speed effects should be clarified beforehand considering the lubrication state and process parameter variations. In this paper, we developed a polishing experimental method and apparatus to determine the lubrication state by measuring the real time friction coefficient using two load cells. Through experiments, we obtained a boundary lubrication state above 0.35 of the friction coefficient by using low table speed and high polishing load, indicating a synchronized stable behavior in polishing head rotation. However, larger Stribeck indexes by a high speed above 200 rpm can generate a hydrodynamic lubrication state below 0.25 of the low friction coefficient. This causes the polishing head rotation to stop. A forced and synchronized head rotation is required for high speed polishing.

• 한국입자에어로졸학회지
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• 제6권1호
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• pp.21-27
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• 2010

New process consisting of electrospray and epitaxial crystal growth processes was applied to the preparation of c-plane oriented barium ferrite ($BaFe_{12}O_{19}$) thin film for high density magnetic recording media. Sodium citrate aided process was proper to preparation of amorphous $BaFe_{12}O_{19}$ nanoparticles with geometric mean diameter of 3 nm and geometric standard deviation of 1.1. The electrospray was applicable to the prepare of amorphous $BaFe_{12}O_{19}$ thin film on a substrate, and the film thickness could be controlled by adjusting the electrospray deposition time. The c-plane oriented $BaFe_{12}O_{19}$ thin film was successfully prepared by 3 step annealing process of the $BaFe_{12}O_{19}$ amorphous film on a sapphire($Al_2O_3$) substrate; annealing at $350^{\circ}C$ for 30 min, annealing at $500^{\circ}C$ for 30 min, and annealing at $700^{\circ}C$ for 60 min.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2009년도 춘계학술발표대회
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• pp.35.1-35.1
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• 2009

Vertically aligned zinc oxide (ZnO) nanorods (NRs) with different surface morphology were grown by metal organic chemical vapor deposition (MOCVD) on sapphire substrate. The films thus prepared were characterized by measuring X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) studies. To study the effect of surface morphology on wettability, the contact angle (CA) of water was measured. It was demonstrated that the CA of the deposited ZnO NRs varied between $104^{\circ}$ and $135^{\circ}$ depending upon the surface morphology. Variable temperature photoluminescence (PL) have employed to probe the exciton recombination in high density and vertically aligned ZnO Nanorod arrays. The low-temperature PL characterizes the dominant near-band-edge excitonic emissions from such nanorod arrays.

• 한국광학회지
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• 제12권6호
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• pp.503-506
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• 2001

펨토초 레이저로 여기 되는 transmitter chip에 DC 전압을 최소 573171서 최대 90Vell가지 변화시켜 테라헤르츠 전자기 펄스의 크기와 스펙트럼의 변화를 관찰하였다 전압이 증가괼수록 상대적 스펙트럼의 크기가 고주파 쪽으로 증가되었고 신호 대 잡음비 역시 250:1에서 10,000:1로 개선할 수 있었다 이를 이용한 테라헤르츠 시스템의 재정렬로 테라헤르츠 스펙트럼 을 최대 4 THz 가지 확장 할 수 있었다 또한 dipole 안테나를 이용한 테라헤르츠 전자기 펄스의 검출에서 입사되는 detection 레이저빔이 silicon on sapphire (SOS) receiver chip 뒤 표면에 반사되어 dipole 안테나로 입사될 때 두 개의 테라 헤르츠 펄스가 일정한 시간간격을 두고 동시에 발생됨을 알 수 있었다.

• 한국광학회:학술대회논문집
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• 한국광학회 2006년도 하계학술발표회 논문집
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• pp.379-380
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• 2006

• 한국재료학회지
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• 제12권5호
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• pp.387-390
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• 2002

A new approach of using double buffer layers of AlN and GaN for growth of GaN films on Si has been undertaken via molecular beam epitaxy using ammonia. The first buffers layer of AlN was grown using $N_2$plasma and the second of GaN was grown using ammonia. The surface roughness of the grown films was investigated by atomic force microscope and was compared with the normally grown films on sapphire. Double crystal x-ray rocking curve and low temperature photoluminescence techniques were employed for structural and optical properties examination. Donor bound exciton peak at 3.481 eV with full width half maximum of 41 meV was observed at 13K.

• 한국세라믹학회지
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• 제40권3호
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• pp.262-267
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• 2003

Off-axis 고주파 마그네트론 스퍼터링법으로 사파이어(0001) 기판 위에 이종에피텍셜 ZnO 박막을 제조하였다. ZnO 박막의 결정성은 증착압력, RF power 그리고 기판온도의 공정조건 변화에 많은 영향을 받았으며, 스퍼터링된 입자의 적당한 kinetic energy와 기판표면에서의 표면이동도(surface mobility)가 조화를 이룰 때 결정성이 우수한 이종에피텍셜 박막을 을 얻을 수 있었다. 이종에피텍셜 ZnO 박막의 Photoluminescence(PL) 특성 측정 결과, 저온(17K)에서 약 3.36 eV의 자외선 영역 발광을 관찰할 수 있었으며, 상온에서도 3.28 eV의 자외선 영역 발광을 관찰할 수 있었다. ZnO 박막을 산소 분위기에서 열처리함에 따라 결정성은 향상되는 반면 자외선 영역의 발광은 급격히 감소하는 경향을 보였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 센서 박막재료 반도체 세라믹
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• pp.141-144
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• 2003

This study proposes ZnO thin film as a piezoelectric material for SAW (surface acoustic wave) filter. The ZnO thin film with thickness $2.6{\mu}m$ was deposited (0001)-oriented sapphire by RF magnetron sputtering technique. IDTs (inter-digital transducers) electrodes were patterned upon SAW filter mask with solid finger structure unapodized using lift-off method on ZnO piezoelectric thin film. SAW propagation velocity was measured with the center frequency by HP 8753C network analyzer. A fabricated ZnO SAW filter exhibited a high propagation velocity of 5433 $^m/s$ and relatively insertion loss of -53.391dB at $\lambda=80{\mu}m$. The side-lobe attenuation of the center frequency was about 17dB. When the wavelength was $80{\mu}m$ $(\lambda/4=20{\mu}m)$, the center frequency was 67.907 MHz. $k^2$ (electromechanical coupling coefficient) was 15.84 %.