• 한국태양에너지학회 논문집
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• 제31권4호
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• pp.48-56
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• 2011

Black cobalt solar selective coatings were prepared by thermal oxidation of electroplated cobalt metal on copper and nickel substrates. The optical properties and structure of the black cobalt selective coating for solar energy utilizations were characterized by glow discharge spectrometry (GDS), ultraviolet-visible-near infrared (UV-VIS-NIR) spectrometer, atom force microscopy(AFM) and X-ray photoelectron spectroscopy(XPS). The optical properties of optimum black cobalt selective coating prepared on copper substrate were a solar absorptance of 0.82 and a thermal emittance of 0.01. From the GDS depth profile analysis of these coatings, the concentration of cobalt particles near the interface was higher than at the surface, but oxygen concentration at the surface was higher than at the interface. These results suggest that the selective absorption was dominated by this chemical composition variation in the coating. The surface of this film exhibited morphology with root-mean-square(rms) roughness of about 144.3nm. XPS measurements data showed that several phases of Co coexist($Co_3O_4$,CoO) in the film.

• 한국재료학회지
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• 제19권4호
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• pp.179-185
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• 2009

We fabricated thermally evaporated 30 nm-Ni/(20 nm or 60 nm)a-Si:H/Si films to investigate the energy-saving property of silicides formed by rapid thermal annealing (RTA) at temperatures of $350^{\circ}C$, $450^{\circ}C$, $550^{\circ}C$, and $600^{\circ}C$ for 40 seconds. A transmission electron microscope (TEM) and a high resolution X-ray diffractometer (HRXRD) were used to determine the cross-sectional microstructure and phase changes. A UVVIS-NIR and FT-IR (Fourier transform infrared spectroscopy) were employed for near-IR and middle-IR absorbance. Through TEM and HRXRD analysis, for the nickel silicide formed at low temperatures below $450^{\circ}C$, we confirmed columnar-shaped structures with thicknesses of $20{\sim}30\;nm$ that had ${\delta}-Ni^2Si$ phases. Regarding the nickel silicide formed at high temperatures above $550^{\circ}C$, we confirmed that the nickel silicide had more than 50 nm-thick columnar-shaped structures with a $Ni_{31}Si_{12}$ phase. Through UV-VIS-NIR analysis, nickel silicide showed almost the same absorbance in the near IR region as well as ITO. However, in the middle IR region, the nickel silicides with low temperature showed similar absorbance to those from high temperature silicidation.

• 대한금속재료학회지
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• 제46권11호
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• pp.755-761
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• 2008

We fabricated thermally evaporated 10 nm-Ni/1 nm-Ir/(poly)Si films to investigate the energy saving property of silicides formed by rapid thermal annealing (RTA) at the temperature range of $300{\sim}1200^{\circ}C$ for 40 seconds. Moreover, we fabricated 100 nm-thick ITO/(poly)Si films with an rf-sputter as references. A transmission electron microscope (TEM) and an X-ray diffractometer were used to determine cross-sectional microstructure and phase changes. A UV-VIS-NIR and FT-IR (Fourier transform infrared spectroscopy) were employed for near-IR and middle-IR absorbance. Through TEM analysis, we confirmed 20~65 nm-thick silicide layers formed on the single and polycrystalline silicon substrates. Ir-inserted nickel silicide on single crystalline substrate showed almost the same absorbance in near IR region as well as ITO, but Ir-inserted nickel silicide on polycrystalline substrate, which had the uniform absorbance in specific region, showed better absorbance in near IR region than ITO. The Ir-inserted nickel silicide on polycrystalline substrate particularly showed better absorbance in middle IR region than ITO. The results imply that nano-thick Ir-inserted nickel silicides may have excellent absorbing capacity in near-IR and middle-IR region.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.56-56
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• 2010

Single-walled carbon nanotubes (SWCNTs) have attracted much attention as a promising material for transparent conducting films (TCFs), due to their superior electrical conductivity, high mechanical strength, and complete flexibility as well as their one-dimensional morphological features of extremely high length-to-diameter ratios. This study investigated three kinds of SWCNTs with different purities: as-produced SWCNTs (AP-SWCNTs), thermally purified SWCNTs (TH-SWCNTs), thermally and acid purified SWCNTs (TA-SWCNTs). The purity of each SWCNT sample was assessed by considering absorption peaks in the semiconducting ($S_{22}$) and metallic ($M_{11}$) tubes with UV-Vis NIR spectroscopy and a metal content with thermogravimetric analysis (TGA). The purity increased as proceeding the purification stages from the AP-SWCNTs through the thermal purification to the acid purification. The samples containing different contents of SWCNTs were dispersed in water using sodium dodecyl benzensulfate (SDBS). Aqueous suspensions of different purities of SWCNTs were prepared to have similar absorbances in UV-Vis absorption measurements so that one can make the TCFs possess similar optical transmittances irrespective of the SWCNT purity. Transparent conductive SWCNT networks were formed by spraying an SWCNT suspension onto a poly(ethyleneterephthalate) (PET) substrate. As expected, the TCFs fabricated with AP-SWCNTs showed very high sheet resistances. Interestingly, the TH-SWCNTs gave lower sheet resistances to the TFCs than the TA-SWCNTs although the latter was of higher purity in the SWCNT content than the former. The TA-SWCNTs would be shortened in length and be more bundled by the acid purification, relative to the TH-SWCNTs. For both purified (TH, TA) samples, the subsequent nitric acid ($HNO_3$) treatment greatly lowered the sheet resistances of the TCFs, but almost eliminated the difference of sheet resistances between them. This seems to be because the electrical conductivity increased not only due to further removal of surfactants but also due to p-type doping upon the acid treatment. The doping effect was likely to overwhelm the effect of surfactant removal. Although the nitric acid treatment resulted in the similar. electrical properties to the two samples, the TCFs of TH-SWCNTs showed much lower sheet resistances than those of the TA-SWCNTs prior to the acid treatment.

• 한국재료학회지
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• 제20권5호
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• pp.278-288
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• 2010

High Pressure High Temperature (HPHT) treatment can significantly change the color of diamonds. We studied the variation of the optical properties according to the nitrogen arrangement in natural brown diamonds of various types (type IaAB, type IaB, type IaA > B, type IaA < B, IaA = B) after HPHT treatment. The diamonds with different arrangements of nitrogen were annealed at temperatures in the range $1700-1800^{\circ}C$ under a stabilizing pressure of 5 GPa. HPHT treated samples were analyzed using UV-Vis-NIR, FT-IR, and PL spectroscopy. The absorption and luminescence spectra were measured to compare the variations of nitrogen arrangement in the natural brown diamonds before and after HPHT treatment. After HPHT treatment, the brown coloration in all types of diamonds was reduced and a decrease in the peaks related to the A-aggregate of nitrogen was more predominant than the B-aggregate. Furthermore, the peaks related to N3 (415.4 nm), H4 (496.4 nm), and platelet decreased and the peaks related to H3 (503.2 nm) and G-band increased after HPHT treatment. In conclusion, spectroscopic analysis of natural brown diamonds after HPHT treatment showed that a yellow color was produced by absorption in the H3 centers and a green color was generated by interaction between absorptions of the H3 and H2 centers.

• 대한금속재료학회지
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• 제49권6호
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• pp.498-504
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• 2011

We examined the microstructure and optical properties of crystallized ~30 nm-ZnO/~10 nm amorphous $TiO_2$ nano bilayered films as nano electrodes were deposited at extremely low substrate temperatures of $150-210^{\circ}C$. The bilayered films were deposited on silicon substrates with 10 cm diameters by ALD (atomic layer deposition) using DEZn (diethyl zinc(Zn(C2H5)2)) and TDMAT (tetrakis dimethyl-amid $titanium(Ti(N(CH_3)_2)_4)$ as the ZnO and $TiO_2$ precursors, respectively, and $H_2O$ as the oxidant. The microstructure, phase, and optical properties of the bilayered films were examined by FE-SEM, TEM, XRD, AES, and UV-VIS-NIR spectroscopy. FE-SEM and TEM showed that all bilayered films were deposited very uniformly and showed crystallized ZnO and amorphous $TiO_2$ layers. AES depth profiling showed that the ZnO and $TiO_2$ films had a stoichiometric composition of 1:1 and 1:2, respectively. These bilayered films have optical absorption properties in a wide range of ultraviolet wavelengths, 250-390 nm, whereas the single ZnO and $TiO_2$ films showed an absorption range of 350-380nm.

• 한국재료학회지
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• 제26권4호
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• pp.194-199
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• 2016

We prepared polymethyl methacrylate (PMMA) beads with a particle size of 80 nm to improve the energy conversion efficiency (ECE) by increasing the effective surface area and the dye absorption ability of the working electrodes (WEs) in a dye sensitized solar cell (DSSC). We prepared the $TiO_2$ layer with PMMA beads of 0.0~1.0 wt%; then, finally, a DSSC with $0.45cm^2$ active area was obtained. Optical microscopy, transmission electron microscopy, field emission scanning electron microscopy, and atomic force microscopy were used to characterize the microstructure of the $TiO_2$ layer with PMMA. UV-VIS-NIR was used to determine the optical absorbance of the WEs with PMMA. A solar simulator and a potentiostat were used to determine the photovoltaic properties of the PMMA-added DSSC. Analysis of the microstructure showed that pores of 200 nm were formed by the decomposition of PMMA. Also, root mean square values linearly increased as more PMMA was added. The absorbance in the visible light regime was found to increase as the degree of PMMA dispersion increased. The ECE increased from 4.91% to 5.35% when the amount of PMMA beads added was increased from 0.0 to 0.4 wt%. However, the ECE decreased when more than 0.6 wt% of PMMA was added. Thus, adding a proper amount of PMMA to the $TiO_2$ layer was determined to be an effective method for improving the ECE of a DSSC.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.1
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• pp.420-423
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• 2003

[ $TiO_2$ ] thin films were fabricated by DC magnetron sputtering system at by controlling deposition times, ratios of $Ar:O_2$ partial presser ratio and substrate conditions. And the surface, cross-section morphology, microstructure, and composition ratio of the films were analyzed by FE-SEM, TEM and XPS. Besides, the optical absorption and transmittance of the $TiO_2$ films were measured by a UV-VIS-NIR Spectrophotometer, and photocatalytic properties were studied by G C Analyzer & Data Analysis system. As the result, when $TiO_2$ thin film was made at deposition time of 120[min] and $Ar:O_2$ ratio of 60:40, the best structural and optical properties among many thin films could be accepted. The best results of properties were as follows: thickness; $360{\sim}370[nm]$, grain size; 40[m], gap between two peak binding energy, $5.8{\pm}0.05[eV]$ ($2p_{3/2}$ peak and $2p_{1/2}$ peak of Ti was show at $458.3{\pm}0.05[eV]$ and $464.1{\pm}0.05[eV]$ respectively), binding energy; $530{\pm}0.05\;[eV]$, opticalenergy band gap; 3.4[eV].

• 한국표면공학회지
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• 제51권2호
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• pp.126-132
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• 2018

SnS thin films with different substrate temperatures ($150 {\sim}300^{\circ}C$) as process parameters were grown on soda-lime glass substrates by RF magnetron sputtering. The effects of substrate temperature on the structural and optical properties of SnS thin films were investigated by X-ray diffraction (XRD), Raman spectroscopy (Raman), field-emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), and Ultraviolet-visible-near infrared spectrophotometer (UV-Vis-NIR). All of the SnS thin films prepared at various substrate temperatures were polycrystalline orthorhombic structures with (111) planes preferentially oriented. The diffraction intensity of the (111) plane and the crystallite size were improved with increasing substrate temperature. The three major peaks (189, 222, $289cm^{-1}$) identified in Raman were exactly the same as the Raman spectra of monocrystalline SnS. From the XRD and Raman results, it was confirmed that all of the SnS thin films were formed into a single SnS phase without impurity phases such as $SnS_2$ and $Sn_2S_3$. In the optical transmittance spectrum, the critical wavelength of the absorption edge shifted to the long wavelength region as the substrate temperature increased. The optical bandgap was 1.67 eV at the substrate temperature of $150^{\circ}C$, 1.57 eV at $200^{\circ}C$, 1.50 eV at $250^{\circ}C$, and 1.44 eV at $300^{\circ}C$.

• 한국재료학회지
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• 제23권5호
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• pp.260-265
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• 2013

Silicon nanoparticle is a promising material for electronic devices, photovoltaics, and biological applications. Here, we synthesize silicon nanoparticles via $CO_2$ laser pyrolysis and study the hydrogen flow effects on the characteristics of silicon nanoparticles using high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and UV-Vis-NIR spectrophotometry. In $CO_2$ laser pyrolysis, used to synthesize the silicon nanoparticles, the wavelength of the $CO_2$ laser matches the absorption cross section of silane. Silane absorbs the $CO_2$ laser energy at a wavelength of $10.6{\mu}m$. Therefore, the laser excites silane, dissociating it to Si radical. Finally, nucleation and growth of the Si radicals generates various silicon nanoparticle. In addition, researchers can introduce hydrogen gas into silane to control the characteristics of silicon nanoparticles. Changing the hydrogen flow rate affects the nanoparticle size and crystallinity of silicon nanoparticles. Specifically, a high hydrogen flow rate produces small silicon nanoparticles and induces low crystallinity. We attribute these characteristics to the low density of the Si precursor, high hydrogen passivation probability on the surface of the silicon nanoparticles, and low reaction temperature during the synthesis.