• Journal of Industrial and Engineering Chemistry
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• 제67권
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• pp.478-485
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• 2018

The effect of reduced graphene oxide (RGO) addition on the dielectric and piezoelectric behavior of the polyvinylidene fluoride (PVDF) films was studied. Dielectric constant increased by four times and piezoelectric coefficient also increased twice by the addition of RGO in the PVDF films. Based on capacitance-voltage and ellipsometry measurements and the Kramers-Kronig transformation, it is concluded that the enhanced dielectric and piezoelectric properties of the PVDF/RGO films resulted from the increased orientational polarization due to a phase transition from nonpolar crystalline ${\alpha}$ phase to polar crystalline ${\beta}$ phase in the PVDF structure.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2000년도 제18회 학술발표회 논문개요집
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• pp.175-175
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• 2000

Si(100) surfaces were exposed to gas-phase thermal-energy hydrogen atoms, H(g). We find that thermal H(g) atoms etch, amorphize, or penetrate into the crystalline silicon substrate, depending on the employed Ts range during the H(g) exposure. We find that etching is enhanced as Ts is lowered in the 300-700K range, while amorphous silicon hydride (a-Si:H) formation dominates at a Ts below 300K. This result was well explained by the fact that formation of the etching precursor, SiHx(a), and amorphization are both facilitated by a lower Ts, whereas the final step for etching, SiH3(a) + H(g) longrightarrow SiH3(g), is suppressed at a lower Ts. we also find that direct absorption of H(g) by the crystalline bulk of Si(100) substrate occurs within a narrow Ts window of 420-530K. The bulk-absorbed hydrogen evolved out molecularly from Si(100) at a Ts 80-120K higher than that for surface monohydride phase ($\beta$1) in temperature-programmed desorption. This bulk-phase H uptake increased with increasing H(g) exposure without saturation within our experimental limits. Direct absorption of H(g) into the bulk lattice occurs only when the surface is atomically roughened by surface etching. While pre-adsorbed hydrogen atoms on the surface, H(a), were readily abstracted and replaced by D(g), the H atoms previously absorbed in the crystalline bulk were also nearly all depleted, albeit at a much lower rate, by a subsequent D(g) at the peak temperature in TPD from the substrate sequentially treated with H(g) and D(g), together with a gas phase-like H2 Raman frequency of 4160cm-1, will be presented.

• 한국결정성장학회지
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• 제5권4호
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• pp.343-350
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• 1995

$\alpha$ - 및 $\beta$-SiC를 출발원료로 하여 일축성형한 후 $1800^{\circ}C$에서 고온가압법으로 소결한 탄화규소에 나타난 우선방위의 정도를 X-ray pole figure analysis로 조사하였다. $\alpha$-SiC를 출발원료로 사용한 경우에 고온 가압소결 후 약한 집합조직을 보인 반면, $\beta$ - SiC를 출발원료로 사용한 경우 고온가압소결 후 강한 집합조직을 보였으며, 이 경우 ${\beta} {\rightarrow} {\alpha}$ 상변태에 기인한 이중미세구조를 나타내었다. 또한, 집합조직의 강도는 고온가압소결 후 행해진 열처리 조건에 따라서도 변화를 보였다.

• 한국표면공학회지
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• 제27권5호
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• pp.253-260
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• 1994

Ta-N films were reactively sputter deposited by dc magnetron sputtering from a Ta target with a various Ar-N, gas ratio. Electrical resistivity of pure Ta film was 150$\mu$$\Omega$cm and decreased initially with nitrogen addition, and then increased to a value of 220$\mu$$\Omega$-cm~260$\mu$$\Omega$-cm at 9%~23% nitrogen partial flow. Rutherford backscattering spectrometry(RBS) and Auger electron spectroscopy (AES) analysis show that nitrogen content in the film is increased with the nitrogen partial flow. The film contains 58at.% nitrogen at 36% nitrogen partial flow. Both the phase and the microstructure of the as-deposisted films were investigated by x-ray diffractometry(XRD) adn transmission electron microscopy (TEM) at various nitrogen content. The phase of pure Ta film is identified as $\beta$-Ta with a 200$\AA$~300$\AA$ grain size. The phase of Ta film is changed to bcc-Ta as small amount of nitrogen is added. Crystalline Ta2N film was deposited at 24at.% nitrogen content. Amorphous phase is formed over a range of nitrogen content from about 33at.% to 35at.% while crystalline fcc-TaN is observed to form at 39at.%~48at.% nitrogen content.

• 폴리머
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• 제29권4호
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• pp.408-412
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• 2005

생체재료로 이용하기 위하여 키토산을 기질로 하여 Bembyx mori로부터 추출한 견 피브로인을 블렌드한 필름에 대한 구조와 특성을 X선 회절분석, 열분석, 적외선 분광분석, 전자현미경 관찰, 접촉각 측정, 흡수율 측정으로 조사하였다. $-\~30wt\%$ 피브로인을 포함하는 블렌드 필름은 리튬이온을 포함하는 초산수용액으로 제조되었다. 키토산/피브로인 블렌드 필름은 키토산의 아미노기와 피브로인의 아미드 카보닐기 사이의 수소결합과 같은 분자간 상호작용의 형성에 의해 결정성이 감소되었다. 피브로인의 비율이 증가할수록 키토산의 무수혈 견정상은 소실되었고, 수화형 결정상은 감소되었으며, 퍼브로인의 P형 결정이 형성되어 혼재된 결정구조를 이루었다. 표면 친수성과 수분 흡수성은 피브로인의 비율이 클수록 증가되었으며, 20 $wt\%$, 이상에서 수화젤 상의 필름을 형성하였다. 전자현미경에 의한 블렌드 필름의 표면과 단면은 균일한 상을 나타내었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.256-256
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• 2013

Carbon nanotubes (CNT) / polyvinylidene fluoride (PVDF) piezoelectric composite films for nanogenerator devices were fabricated by spray coating method. When the CNT/PVDF mixture solution passes through the spray nozzle with small diameter by the compressed nitrogen gas, electric charges are generated in the liquid by a triboelectric effect. Then randomly distributed ${\beta}$ phase PVDF film could be re-oriented by the electric field resulting from the accumulated electrical charges, and might be resulted in extremely one-directionally aligned ${\beta}$ phase PVDF film without additional electric field for poling. X-ray diffraction patterns were used to investigate crystal structure of the CNT/PVDF composite films. It was confirmed that they revealed extremely large portion of the ${\beta}$ phase PVDF crystalline in the film. Therefore we could obtain the poled CNT/PVDF piezoelectric composite films by the spray coating method without additional poling process. Charge accumulation and resulting electric field generation mechanism by spray coating method were shown in Fig. 1. The capacitance of the CNT/PVDF films increased by adding CNTs into the PVDF matrix, and finally saturated. However, the I-V curves didn't show any saturation effect in the CNT concentration range of 0~4 wt%. Therefore we can control the performance of the devices fabricated from the CNT/PVDF composite film by adjusting the current level resulted from the CNT concentration with the uniform capacitance value.

• 한국잠사곤충학회지
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• 제42권1호
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• pp.42-47
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• 2000

Structural and thermal characteristics of silk fibroin/poly(2-hydroxyethyl methacrylate)(PHEMA) blend films were investigated using FTIR, X-ray diffractometer, differential scanning calorimeter, thermogravimeter and scanning electron microscope. FTIR spectra showed that the conformation of silk fibroin prepared by dissolving in formic acid was $\beta$-sheet, which did not affected by blending with PHEMA. The X-ray diffraction patterns also showed that individual crystalline structure of silk fibroin and PHEMA was not affected for the blend films. The initial thermal decomposition temperature of silk fibroin/PHEMA blend film tends to be higher than either of silk fkbroin or PHEMA. Thermal stability of both polymers, more notably PHEMA, can be improved by blending two components. As a result of SEM observation, the phases separation for silk fibroin/PHEMA blend films occured regardless of blend ratio ; continuous and dispersed phase were silk fibroin and PHEMA component, respectively.

• 한국염색가공학회:학술대회논문집
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• 한국염색가공학회 2009년도 학술발표대회
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• pp.118-119
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• 2009

As the rapid development of the electronics, the demand for portable electronics and wireless sensors is growing faster, also with the increased needs of one material which can power it automatically, and then power the electrical devices. The piezoelectric effect of the PVDF material can be used for this. So in this paper, PVDF multilayer films were made for this aim. Make the PVDF / DMAc solution in the 10% concentration; use the spin coater technique to make films with the optimum process parameters: the spin rate is 1260rpm; the spin time is 70s; the dry temperature is 100$^{\circ}C$; the dry time is 30mins. And also, for obtaining the higher $\beta$-phase crystallinity, put the Ca(NH3)2.4H2O into the PVDF / DMAc solution system.

• 대한치과기공학회지
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• 제21권1호
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• pp.5-14
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• 1999

Glass ceramics for dental crown prosthesis were prepared by crystallization of CaO-MgO-SiO2-$P_2O_5-TiO_2$ glasses. Their crystallization behaviors have been investigated as a function of heattreatment temperature, holding time and chemical composition in relation to mechinical properties. Crystallization peak temperatures were determined by differential thermal analysis(DTA). Crystalline phases and mircostructures of heat-treated sample were determined by the means of powder X-ray diffraction(XRD) and scanning electron microscopy(SEM). The final crystalline phase assemblages and the microstructures of the samples were found to be dependent on glass compositions, heattreatment temperature, and holding time. 1st crystallization peak temperature(TP), affected strongly by apatite, was found to be increased or decreased. From the experiment, the following results were obtained : 1. The crystallization peak temperature($T_P$) formed by apatite increased until adding up to 9wt% $TiO_2$ to base glass composition, then decreased above that. 2. Apatite($Ca_{10}P_6O_{25}$), whitlockite(${\beta}-3CaO-P_2O_5$), $\beta$-wollastonite($CaSiO_3$), magnesium tianate($MaTiO_3$) and diopside(CaO-MgO-$2SiO_2$) crystal phase were precipitated in MgO-CaO-$SiO_2-TiO_2-P_2O_5$ glass system containing 9wt% and 11wt% of $TiO_2$ 3. Vickers hardness of samples increased with increasing heat-treatment temperature and Vickers hardness of S415T9 samples heat-treated at 1075 was approxi-mately 813Kg $mm^{-2}$ as maximum value. 4. Vickers hardness of samples increased due to precipitation of apatite, whitlockite, $\beta$-wollastonite, magnesium titanate, and diopside crystal phases within glass matrix.

• 공업화학
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• 제10권5호
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• pp.644-651
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• 1999

본 연구에서는 진공 증착법을 이용하여 철프탈로시아닌(FePc) 박막을 실리콘 웨이퍼와 알루미나 기판 위에 합성하였으며, 박막의 증착 온도와 두께를 변화시켜 실험한 후 일부의 박막을 열처리하였다. 박막의 두께 변화에 따른 표면 구조 변화, 상전이와 전기 저항 감도 변화를 SEM, XRD, 그리고 전기저항의 측정으로 관찰하였다. 증착 온도가 $370^{\circ}C$에서 $350^{\circ}C$로 감소함에 따라 $\alpha$상의 (200)면, (011)면, (211)면, 그리고 (114)면이 사라지며 $\beta$상의 (100)면의 피크가 나타났다. 전구물질의 양을 달리하며 고속 증착시켜 박막 두께를 조절한 결과, 두께 증가에 따라 결정 크기가 증가하고 또한 $\alpha$상에서 $\beta$상으로의 상 전이가 일어남을 알 수 있었다. 열처리한 박막의 결정성을 측정한 결과 열처리 온도가 증가함에 따라 $150^{\circ}C$으로부터 $\alpha$상에서 $\beta$상으로의 상 전이가 일어나기 시작하여 $350^{\circ}C$에서 완전히 $\beta$상으로 전이되었다. $NO_x$에 대한 철프탈로시아닌 박막의 온도에 따른 전기저항감도를 측정한 결과 박막의 두께가 얇을수록 더 좋고 안정된 전기 저항 감도를 보여주었다. 즉 박막의 표면구조가 조밀하게 성장할수록 전기 저항 감도가 더욱 좋아짐을 확인하였다.