• Journal of Industrial and Engineering Chemistry
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• v.67
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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.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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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.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.4
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• pp.343-350
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• 1995

A Abstract Systematic studies of the effects of crystalline forms of starting powders and p processing variables on the texture of hot - pressed silicon carbide are described. The results I indicate that hot - pressing of $\beta$ - SiC can produce strong textures and composite type duplex microstructure due to the ${\beta} {\rightarrow} {\alpha}$ phase transformation of SiC. The texture variations d during post - annealing have been observed. In the case of using a - SiC as starting pow¬d ders, the degree of preferred orientation by hot - pressing is relatively weak.

• Journal of Surface Science and Engineering
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• v.27 no.5
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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.

• Polymer(Korea)
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• v.29 no.4
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• pp.408-412
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• 2005

Structure and characteristic of the films blended chitosan matrix with silk fibroin, extracted from Bombyx mori, were studied by X-ray diffraction, differential scanning calorimetry, FT-IR spectra analysis, SEM photographs, contact angle measurement and water absorbency in order to use as biomaterials. The blend films of $0\~30 wt\%$ fibroin content were prepared in acetic solution with $Li^+$ ion. It was found that the crystallinity of chitosan/fibroin blend films was decreased by the presence of intermolecular interactions such as hydrogen bonding between animo groups of chitosan and carbonyl groups of fibroin. As the proportion of fibroin in the blend increased, anhydrous crystalline phase of chitosan disappeared, and hydrated crystalline phase decreased, and $\beta$-structure crystalline phase of fibroin was formed. Therefore the blend films were crystallized into two different crystalline region of chitosan and fibroin. Surface hydrophilicity and water absorbency increased with blending fibroin. Above 20 $wt\%$ fibroin content, hydrogel film was formed. The surface and section of the film showed uniform microstructure on SEM photographs.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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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.

• Journal of Sericultural and Entomological Science
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• v.42 no.1
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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.

• Proceedings of the Korean Society of Dyers and Finishers Conference
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• 2009.03a
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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.

• Journal of Technologic Dentistry
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• v.21 no.1
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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.

• Applied Chemistry for Engineering
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• v.10 no.5
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• pp.644-651
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• 1999

In this experiment the Iron phthalocyanine (FePc) films on Si-wafer and alumina pallet were prepared using vacuum sublimation with conditions of changing reaction time, temperature, and deposition rate. Then, some samples were annealed following annealing. Techniques such as XRD, SEM, and resistance measurement method, were dedicated to characterize the changes of surface structure, phase transformation and electric resistance sensitivity in accordance with change of film thickness. In proportion to the decrease of deposition temperature from $370^{\circ}C$ to $350^{\circ}C$, intensities of (200), (011), (211) and (114) planes of $\alpha$-phase were decreased and (100) plane of $\beta$-phase were appeared. The film thickness were controlled by regulating the volume of precursor material during rapid deposition. As a result, it was observed that crystalline particle size had been increased according to the increase of film thickness and $\alpha$-phase transformed to $\beta$-phase. In consequence of measuring the crystallinity of films annealed between $150^{\circ}C$ and $350^{\circ}C$, $\alpha$- to $\beta$-phase transformation was appeared to begin at $150^{\circ}C$ and completely transformed to $\beta$-phase at $350^{\circ}C$. Electric resistance sensitivity of FePc film to $NO_x$ gas along temperature change of FePc films was observed to be more stable with the decrease of the film thickness.