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Lee, Wookbin,Leem, Jae-Young 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol. No.
<P>We report the structural, morphological, optical, and ultraviolet (UV) photoresponse properties of Al-doped ZnO (AZO) thin films prepared on silicon substrates with different Al doping concentrations by using the sol-gel spin-coating method. An analysis of the X-ray diffraction patterns of the AZO thin films revealed that the average grain size decreased and the c-axis lattice constant increased with Al content. The field-emission scanning electron microscopy images showed that with Al doping, the grain size decreased, but the film density increased with increasing Al doping concentration from 0% to 3%. These results indicate that the surface area of the film increased with increasing Al doping. The absorbance spectra revealed that the UV absorbance of the AZO thin films increased with increasing Al doping concentration and that the absorption onset shifted towards lower energies. The photoluminescence spectra revealed that with increasing Al doping, the intensity of the visible emission greatly decreased and the visible emission peak shifted forward lower energy (a red shift). The UV sensor based on the AZO thin films exhibited a higher responsivity than that based on the undoped ZnO thin film. Therefore, this study provides a facile method for improving the photoresponsivity of UV sensors.</P>
Size Control of ZnO Nanorods Using the Hydrothermal Method in Conjunction with Substrate Rotation
Lee, Wookbin,Leem, Jae-Young American Scientific Publishers 2017 Journal of Nanoscience and Nanotechnology Vol.17 No.11
<P>In this paper, the effect of substrate rotation at various rpm on the growth of ZnO nanorods using a hydrothermal method at different concentrations of precursor solution (0.025, 0.05 M) was investigated to easily control the size of ZnO nanorods. Scanning electron microscopy images showed that the length and size of the ZnO nanorods increased with increasing substrate rotation speed up to 100 rpm in the 0.025 M aqueous solution. In contrast, the ZnO nanorods were converted to a film form with substrate rotation in the 0.05 M aqueous solution. Photoluminescence spectra showed that the intensity of the near-band-edge and deep-level emission increased with substrate rotation in the 0.025 M aqueous solution, whereas they decreased in the 0.05 M aqueous solution. X-ray diffraction analysis showed an improvement in the c-axis orientation of the ZnO nanorods grown with substrate rotation. The absorbance increased with substrate rotation in the 0.025 M aqueous solution, while they decreased with substrate rotation in the 0.05 M aqueous solution. We expect that this method may offer efficient in situ way of mechanically tuning the size of ZnO nanorods, which enables optical and other properties of ZnO nanorod-based devices to be easily controlled.</P>
Lee, Wookbin,Leem, Jae-Young American Scientific Publishers 2017 Journal of Nanoscience and Nanotechnology Vol.17 No.8
<P>In this study, we investigated the influence of Li doping on the optical, structural, and ultraviolet photoresponse properties of ZnO thin films prepared using the sol-gel spin-coating method on Si substrates. Photoluminescence analysis showed that a visible emission peak related to O vacancy increased with increasing Li doping concentration, resulting in an increase in the formation of substitutional Li at the Zn site. In X-ray diffraction, the intensity of the ZnO (002) peak increased with increasing Li doping concentration, which indicates an improved c-axis orientation. The full width at half maximum (FWHM) of the ZnO (002) diffraction peaks was the lowest at 2.5 at.% Li content, which indicates the highest crystal quality. For measuring UV photoresponse, metal-semiconductor-metal UV sensors were fabricated through the deposition of indium onto Li-doped ZnO (LZO) thin films using a thermal evaporator. The UV sensors based on LZO thin films exhibited enhanced UV sensitivity as well as faster rise and decay times compared with those based on ZnO thin films. The responsivity of the UV sensor based on LZO thin film with 2.5 at.% Li content exponentially increased as the bias voltage increased from 1 to 5 V.</P>
김익현,김영규,남기웅,김동완,Minju Park,Haeun Kim,Wookbin Lee,임재영,김종수,김진수 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.4
Nanocrystalline ZnO thin films grown on fluorine-doped tinoxide (FTO) substrates were fabricatedusing the spin-coating method. The structural and the optical properties of the ZnO thin filmsprepared using different sol concentrations were investigated by using field-emission scanning electronmicroscopy (FE-SEM), X-ray diffractometry (XRD), photoluminescence (PL) measurements,and ultraviolet-visible (UV-vis) spectrometry. The surface morphology of the ZnO thin films, asobserved in the SEM images, exhibited a mountain-chain structure. XRD results indicated thatthe thin films were preferentially orientated along the direction of the c-axis and that the grain sizeof the ZnO thin films increased with increasing sol concentration. The PL spectra showed a strongultraviolet emission peak at 3.22 eV and a broad orange emission peak at 2.0 eV. The intensities ofdeep-level emission (DLE) gradually increased with increasing sol concentration from 0.4 to 1.0 M. The transmittance spectra of the ZnO thin films showed that the ZnO thin films were transparent(85%) in the visible region and exhibited sharp absorption edges at 375 nm. Thus, The Urbachenergy of ZnO thin films decreased with increasing sol concentration.
전착법으로 성장된 산화아연 나노막대의 특성에 전구체 농도 및 전착 전류가 미치는 효과
박영빈(Youngbin Park),남기웅(Giwoong Nam),박선희(Seonhee Park),문지윤(Jiyun Moon),김동완(Dongwan Kim),강해리(Hae Ri Kang),김하은(Haeun Kim),이욱빈(Wookbin Lee),임재영(Jae-Young Leem) 한국표면공학회 2014 한국표면공학회지 Vol.47 No.4
ZnO nanorods have been deposited on ITO glass by electrodeposition method. The optimization of two process parameters (precursor concentration and current) has been studied in order to control the orientation, morphology, and optical property of the ZnO nanorods. The structural and optical properties of ZnO nanorods were systematically investigated by using field-emission scanning electron microscopy, X-ray diffractometer, and photoluminescence. Commonly, the results show that ZnO nanorods with a hexagonal form and wurtzite crystal structure have a c-axis orientation and higher intensity for the ZnO (002) diffraction peaks. Both high precursor concentration and high electrodeposition current cause the increase in nanorods diameter and coverage ratio. ZnO nanorods show a strong UV (3.28 eV) and a weak visible (1.9 ~ 2.4 eV) bands.
Electrodeposition에 의해 성장온도와 시간을 달리하여 성장한 ZnO 나노구조의 특성
박영빈(Youngbin Park),남기웅(Giwoong Nam),박선희(Seonhee Park),문지윤(Jiyun Moon),김동완(Dongwan Kim),강해리(Hae Ri Kang),김하은(Haeun Kim),이욱빈(Wookbin Lee),임재영(Jae-Young Leem) 한국표면공학회 2014 한국표면공학회지 Vol.47 No.4
The electrodeposition of ZnO nanorods was performed on ITO glass. The optimization of two process parameters (solution temperature and growth time) has been studied in order to control the orientation, morphology, density, and growth rate of ZnO nanorods. The structural and optical properties of ZnO nanorods were systematically investigated by using field-emission scanning electron microscopy, X-ray diffractometer, and photoluminescence. Commonly, the results of the structural property show that hexagonal ZnO nanorods with wurtzite crystal structures have a c-axis orientation, and higher intensity for the ZnO (002) diffraction peaks. Furthermore, the nanorods length increased with increasing both the solution temperature and the growth time. The results of the optical property show a strong UV (3.28 eV) peaks and a weak visible (1.9~2.4 eV) bands, the intensity of UV peaks was increased with increasing both the solution temperature and the growth time. Especially, the UV peak for growth of nanorods at 75oC blue-shift than different temperatures.