• Bulletin of the Korean Chemical Society
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• v.33 no.1
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• pp.209-214
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• 2012

In this work, the reduced graphene nanosheets were synthesized from pre-exfoliated graphite flakes. The pristine graphite flakes were firstly pre-exfoliated to graphite nanoplatelets in the presence of acetic acid. The obtained graphite nanoplatelets were treated by Hummer's method to produce graphite oxide sheets and were finally exfoliated to graphene nanosheets by ultrasonication and reduction processes. The prepared graphene nanosheets were studied by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). From the results, it was found that the preexfoliation process showed significant influence on preparation of graphite oxide sheets and graphene nanosheets. The prepared graphene nanosheets were applied to the preparation of conductive materials, which yielded a greatly improved electrical resistance of $200{\Omega}/sq$.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1553-1555
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• 2003

Coatings on glass with highly transparent conducting oxide films(TCOs) are performed mostly by using indium tin oxide(ITO). This Oxide material is very common for applications where both high electrical conductivity. Photovoltaic cells, transparent electrical heater, selective optical filter, and a optical transmittance are essential. In this study, ITO thin films were deposited on $SiO_2$/soda-line glass plates by a dc magnetron sputtering technique. The crystallinity and electrical properties of the films were investigated by X-ray diffraction(XRD), atomic force microscopy(AFM) scanning and 4-point probe. The optical transmittance of ITO films in the range of 300-800nm were measured with a spectrophotometer. As a result, we obtained polycrystalline structured ITO films with (222), (400), and (440) peak. Transmittance of all the films were higher than 90% in the visible range.

• Journal of the Korean Society for Heat Treatment
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• v.25 no.2
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• pp.85-89
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• 2012

Transparent conductive ZnO/Ag/ZnO (ZAZ) multilayer films were deposited by Radio frequency (RF) magnetron sputtering and direct current (DC) magnetron sputtering. The effects of post deposition vacuum annealing temperature on the structural, electrical and optical properties of the ZAZ multilayer films were investigated. The thickness of ZAZ films is kept constant at ZnO 50 nm/Ag 5nm/ZnO 45 nm, while the vacuum annealing temperatures were varied from 200 and $400^{\circ}C$, respectively. As-deposited ZAZ films exhibit a sheet resistance of $6.1{\Omega}/{\Box}$ and optical transmittance of 72.7%. By increasing annealing temperature to $200^{\circ}C$, the resistivity decreased to as low as $5.3{\Omega}/{\Box}$ and optical transmittance also increased to as high as 82.1%. Post-deposition annealing of ZAZ multilayer films lead to considerably lower electrical resistivity and higher optical transparency, simultaneously by increased crystallization of the films.

• Journal of Ceramic Processing Research
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• v.13 no.spc2
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• pp.359-362
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• 2012

We have employed Kelvin force microscopy (KFM) system to measure the potential change of a single SnO2 nanowire which had been synthesized on the Au thin film by a thermal process. By using the KFM probing technique, Rh coated conducting cantilever can approach a single SnO2 nanowire in nano scale and get the potential images with oscillating AC bias between Au electrode and cantilever. Also, during imaging the potential status, we controlled the concentration of oxygen in measuring chamber to change the ionosorption rate. From the results of such experiments, we verified that the surface potential as well as doping type of a single SnO2 nanowire could be changed by oxygen ionosorption.

• 한국태양에너지학회:학술대회논문집
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• 2012.03a
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• pp.149-152
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• 2012

$Cu(In,Ga)Se_2$ (CIGS) is one of the most promising photovoltaic materials because of large conversion efficiency which has been achieved with an optimum Ga/(In+Ga) composition in $CuIn_{1-x}Ga_xSe_2$ (X~0.3). The Ga/(In+Ga) content is important to determine band gap, solar cell performances and carrier behaviors at grain boundary (GB). Effects of Ga/(In+Ga) content on physical properties of the CIGS layers have been extensively studied. In previous research, it is reported that GB is not recombination center of CIGS thin-film solar cells. However, GB recombination and electron-hole pair behavior studies are still lacking, especially influence of with different X on CIGS thin-films. We obtained the GB surface potential, local current and I-V characteristic of different X (00.7 while X~0.3 showed higher potential than 100 mV on GBs. Higher potential on GBs appears positive band bending. It can decrease recombination loss because of carrier separation. Therefore, we suggest recombination and electron-hole behaviors at GBs depending on composition of X.

• Membrane Journal
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• v.20 no.1
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• pp.8-12
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• 2010

Poly(3,4-ethylenedioxythiophene) (PEDOT), which has the highest stability in conducting polymer was employed to electrochromic (EC) film and studied about electrochromic properties according to the film fabrication method. PEDOT films were coated by two different methods, electropolymerization (EP) and vapor phase polymerization (VPP). Both of PEDOT films showed dark blue color at dedoped neutral state. Spectroelectrochemistry, switching ability and stability of the devices were investigated by UV-Vis Spectrophotometer and Cyclic voltammetry. Surface morphologies of the PEDOT VPP film at oxidized and reduced state were obtained by AFM. The average surface roughness of the PEDOT-VPP film was 50 nm and more homogeneous than that of the PEDOT-EP. The EC property from the PEDOT-VPP film was improved compared to that of the PEDOT-EP film, to show a response time of 1.5 sec, transmittancechange of 49%, and coloration efficiency of 402.

• Polymer(Korea)
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• v.35 no.4
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• pp.370-374
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• 2011

A conductive PANI solution was successfully fabricated by doping with camphorsulfonic acid and the polymerization of aniline and the confirmation of doping were characterized by FTIR spectroscopy. In organic thin film transistors, PANI gate electrodes were spin-coated on a PES substrate and their conductivity variations were monitored by a 4-probe method with different annealing temperatures. The surface properties of PANI thin films were investigated by an AFM and an optical microscope, OTFTs with PANI gate electrode had characteristics of carrier mobility as large as 0.15 $cm^2$/Vs and on/off ratio of $2.4{\times}10^6$, Au gate OTFTs with the same configuration were fabricated to investigate the effect of polymer gate electrode for the comparison of device performances. We could obtain the comparable performances of PANI devices to those of Au gate devices, resulting in an excellent alternative as an electrode in flexible OTFTs instead of an expensive Au electrode.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.69.1-69.1
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• 2010

We have fabricated organic photovoltaic cells (OPVs) with highly conductive poly 3,4-ethylenedioxythiophene : poly styrenesulfonate (PEDOT:PSS) layer as an anode without using transparent conducting oxide (TCO), which has been modified by adding some organic solvents like sorbitol (So), dimethyl sulfoxide (DMSO), N-methyl-pyrrolidone (NMP), dimethylformamide (DMF), and ethylene glycol (EG). The conductivity of PEDOT:PSS film modified with each additive was enhanced by three orders of magnitude. According to atomic force microscopy (AFM) study, conductivity enhancement might be related to better connections between the conducting PEDOT chains. TCO-free solar cells with modified PEDOT:PSS layer and the active layer composed of poly(3-hexylthiophene) (P3HT) and phenyl [6,6] C61 butyric acid methyl ester (PCBM) exhibited a comparable device performance to indium tin oxide (ITO) based organic solar cells. The power conversion efficiency (PCE) of the organic solar cells incorporating DMSO, So + DMSO and EG modified PEDOT:PSS layer reached 3.51, 3.64 and 3.77%, respectively, under illumination of AM 1.5 (100mW/$cm^2$).

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.232.2-232.2
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• 2015

Piezoelectric force microscopy (PFM) is a powerful method to characterize inversed piezoelectric effects directly using conductive atomic force microscopy (AFM) tips. Piezoelectric domains respond to an applied AC voltage with a characteristic strain via a contact between the tip and the surface of piezoelectric material. Electroactive piezoelectric polymers are widely investigated due to their advantages such as flexibility, light weight, and microactuation enabling various device features. Although piezoelectric polymers are promising materials for wide applications, they have the primary issue that the piezoelectric coefficient is much lower than that of piezoelectric ceramics. Researchers are studying widely to enhance the piezoelectric coefficient of the materials including nanoscale fabrication and copolymerization with some materials. In this report, nanoscale electroactive polymers are prepared by the electrospinning method that provides advantages of direct poling, scalability, and easy control. The main parameters of the electrospinning process such as distance, bias voltage, viscosity of the solution, and elasticity affects the piezoelectric coefficient and the nanoscale structures which are related to the phase of piezoelectric polymers. The characterization of such electroactive polymers are conducted using piezoelectric force microscopy (PFM). Their morphologies are characterized by field emission-scanning electron microscope (FE-SEM) and the crystallinity of the polymer is determined by X-ray diffractometer.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.10
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• pp.901-906
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• 2006

The transparent conductive oxide(TCO) has been used in necessity as front electrode for increasing efficiency of LED. In our paper, aluminium-doped zinc oxide films(AZO), which has transparent conducting were prepared with RF magnetron sputtering system on glass substrate(corning 1737) and annealed at $400^{\circ}C$ for 2 hr in vacuum ambient and $600^{\circ}C$ for 2hr with $O_2$ ambient respectively. The smooth AZO films were etched in diluted HCL(0.5 %) to examine the surface properties, which in ambient post-annealing process. We confirmed that the electric, structural and optical properties of textured AZO thin films, which implemented using the methods of XRD, FWHM, AFM and Hall measurement. The properties of textured AZO thin films especially depended on the ambient post-annealing process. We presumed that the change of transmittances as R G B LED and the ambient post-annealing process will be increasing the efficiency of LED.