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排序方式: 共有7719条查询结果,搜索用时 31 毫秒
51.
Growth processes of diamond thin films on the fused silica optical fibres (10 cm in length) were investigated at various temperatures. Fused silica pre-treatment by dip-coating in a dispersion consisting of detonation nanodiamond (DND) in dimethyl sulfoxide (DMSO) with polyvinyl alcohol (PVA) was applied. Nanocrystalline diamond (NCD) films were deposited on the fibres using the microwave plasma assisted chemical vapour deposition (MW PA CVD) method. The longitudinal variation of NCD morphology, structure and optical parameters were specifically investigated. The evolution of the film morphology and film thickness along the fibre length was studied using scanning electron microscopy (SEM). The chemical composition of the NCD film was examined with micro-Raman Spectroscopy. The sp3/sp2 band ratio was calculated using the Raman spectra deconvolution method. An approximately 5 cm-long homogeneous diamond film has been obtained on the surface of the fibre sample. Thickness, roughness and optical properties of NCD films in the VIS–NIR range were investigated on the reference quartz slides using spectroscopic ellipsometry. The samples exhibited relatively low deviations of refractive index (2.3 ± 0.25) and extinction coefficient (0.05 ± 0.02) along the length of 5 cm, as estimated at a wavelength of 550 nm. In order to show the effectiveness of deposition process on optical fibres, diamond films were also grown on the fibre with induced long-period grating (LPG). The results of transmission measurements demonstrated that an LPG with diamond overlay exhibits the appropriate dependency on the optical properties of external medium. Thus, the deposition process has a negligible effect on the fibre transmission properties. 相似文献
52.
《Journal of the European Ceramic Society》2014,34(5):1139-1147
Diamond/SiC/(Si) composites were fabricated by Si vapor vacuum reactive infiltration. The coefficient of thermal expansion (CTE) of composites have been measured from 50 to 400 °C. With the diamond content increasing, CTE of composite decreased, simultaneously, the microstructure of the composites changed from core–shell particles embedded in the Si matrix to an interpenetrating network with the matrix. The CTEs of composites versus temperature matched well with those of Si. The Kerner model was modified according to the structural features of the composites, which exhibited more accurate predictions due to considering the core–shell structure of the composites. The thermal expansion behavior of the matrix was constrained by diamond/SiC network during heating. 相似文献
53.
《Journal of the European Ceramic Society》2014,34(6):1501-1509
Hybrid ceramics, polysiloxane-derived materials, feature adjustable surface characteristics and high specific surface areas, making the material promising for applications such as gas separation. For increased permeability in gas separation processes or accessibility of active sites, additional porosity on multiple length scales is desired. In this study, we demonstrate how water soluble templates can be utilized to obtain a controlled hierarchical porosity. KCl sieving fractions are used for adjusting the macroporosity and a polysiloxane precursor, aminopropyltriethoxysilane, to create mesopores. The generation of micro- and mesopores is characterized by nitrogen adsorption while the macroporosity is examined by scanning electron microscopy and mercury intrusion. Water and n-heptane vapor sorption experiments show the control of the surface characteristics of the material by the pyrolysis temperature. In summary, leaching of water soluble templates for meso- and macropores combined with micro pore generation by pyrolytic decomposition enables pore size control on three different length scales. 相似文献
54.
Anna Wajler Anna Kozłowska Magdalena Nakielska Kamila Leśniewska‐Matys Agata Sidorowicz Dariusz Podniesiński Piotr Putyra 《Journal of the American Ceramic Society》2014,97(6):1692-1695
Transparent cobalt‐doped magnesium aluminate spinel (Co:MgAl2O4) ceramics with a submicrometer grain size were prepared by spark plasma sintering. For the first time, the nonlinear absorption of Co:MgAl2O4 transparent ceramics was experimentally demonstrated. Both ground state absorption (σGSA) and excited state absorption (σESA) were estimated using the solid‐state slow saturable absorber model based on absorption saturation measurements performed at 1.535 μm. σGSA and σESA for 0.03 at.% Co:MgAl2O4 were found to be 4.1 × 10?19 cm2 and 4.0 × 10?20 cm2, respectively. In the case of 0.06 at.% Co:MgAl2O4 ceramics, σGSA = 2.6 × 10?19 cm2 and σESA= 5.3 × 10?20 cm2 were determined. 相似文献
55.
《Carbon》2014
Copper foil is the most commonly used substrate for chemical vapor deposition (CVD) growth of graphene, despite the impact of its surface roughness and polycrystalline structure on the resulting graphene. Here we present a method of preparing thick, ultra-flat copper substrates for growing graphene by CVD. We demonstrate the growth of graphene on these substrates using the common Atmospheric Pressure CVD (APCVD) and Low Pressure CVD (LPCVD) methods. We show that compared to copper foil, graphene grown on these thick ultra-flat copper substrates by APCVD results in 50 times smoother graphene on copper. Furthermore, the thick copper substrates have at least 5 times larger copper domains, compared to conventionally prepared copper foil. The evolution of the surface roughness in each growth method is also presented. 相似文献
56.
Teen Hang Meen Jenn Kai Tsai Yu Shin Tu Tian Chiuan Wu Wen Dung Hsu Shoou-Jinn Chang 《Nanoscale research letters》2014,9(1):523
In this study, the P25 titanium dioxide (TiO2) nanoparticle (NP) thin film was coated on the fluorine-doped tin oxide (FTO) glass substrate by a doctor blade method. The film then compressed mechanically to be the photoanode of dye-sensitized solar cells (DSSCs). Various compression pressures on TiO2 NP film were tested to optimize the performance of DSSCs. The mechanical compression reduces TiO2 inter-particle distance improving the electron transport efficiency. The UV–vis spectrophotometer and electrochemical impedance spectroscopy (EIS) were employed to quantify the light-harvesting efficiency and the charge transport impedance at various interfaces in DSSC, respectively. The incident photon-to-current conversion efficiency was also monitored. The results show that when the DSSC fabricated by the TiO2 NP thin film compressed at pressure of 279 kg/cm2, the minimum resistance of 9.38 Ω at dye/TiO2 NP/electrolyte interfaces, the maximum short-circuit photocurrent density of 15.11 mA/cm2, and the photoelectric conversion efficiency of 5.94% were observed. Compared to the DSSC fabricated by the non-compression of TiO2 NP thin film, the overall conversion efficiency is improved over 19.5%. The study proves that under suitable compression pressure the performance of DSSC can be optimized. 相似文献
57.
Immacolata Ruggiero Monica Terracciano Nicola M Martucci Luca De Stefano Nunzia Migliaccio Rosarita Tatè Ivo Rendina Paolo Arcari Annalisa Lamberti Ilaria Rea 《Nanoscale research letters》2014,9(1):329
Diatomite is a natural fossil material of sedimentary origin, constituted by fragments of diatom siliceous skeletons. In this preliminary work, the properties of diatomite nanoparticles as potential system for the delivery of drugs in cancer cells were exploited. A purification procedure, based on thermal treatments in strong acid solutions, was used to remove inorganic and organic impurities from diatomite and to make them a safe material for medical applications. The micrometric diatomite powder was reduced in nanoparticles by mechanical crushing, sonication, and filtering. Morphological analysis performed by dynamic light scattering and transmission electron microscopy reveals a particles size included between 100 and 300 nm. Diatomite nanoparticles were functionalized by 3-aminopropyltriethoxysilane and labeled by tetramethylrhodamine isothiocyanate. Different concentrations of chemically modified nanoparticles were incubated with cancer cells and confocal microscopy was performed. Imaging analysis showed an efficient cellular uptake and homogeneous distribution of nanoparticles in cytoplasm and nucleus, thus suggesting their potentiality as nanocarriers for drug delivery.
PACS
87.85.J81.05.Rm; 61.46. + w 相似文献58.
《Journal of the European Ceramic Society》2022,42(1):154-161
A series of high-k Ba4Nd28/3Ti18-yGa4y/3O54 (0≤y≤2, BNTG) ceramics with temperature stable and ultra-low dielectric loss were synthesized via the conventional solid-state reaction. The main phase of all BNTG ceramics demonstrated an orthorhombic tungsten-bronze structure, but the impurity phase (gallium-rich phase) was found in BNTG (y = 2) ceramic. Partial substitution of Ga3+ for Ti4+ in B-site was a valid method to improve the temperature stability and dielectric loss of BNTG ceramics. The variation of εr values of BNTG ceramics was dominated by the ionic polarizability. The ultra-low dielectric loss (ultra-high Q × f values) was associated with grain size, suppression of Ti3+ and impurity phase. The decrease of TCF values was highly dependent on the tilting of Ti-O octahedra and impurity phase. Finally, outstanding combination dielectric characteristics were achieved for BNTG microwave ceramics at y = 1.5 (εr = 72.8, Q × f = 14,600 GHz, TCF=+4.1 ppm/°C) and at y = 2 (εr = 70.3, Q × f = 15,500 GHz, TCF=+3.9 ppm/°C). 相似文献
59.
《Journal of the European Ceramic Society》2022,42(2):448-452
This study used a traditional solid-state reaction method to prepare a series of composite ceramics in the 0.7Mg4Nb2O9-(0.3-x)ZnAl2O4-xTiO2 ternary system. Crystalline phases and microstructure of Mg4Nb2O9-ZnAl2O4-TiO2 dielectric ceramic composites were investigated and correlated with the relevant dielectric properties. It was observed that the addition of Ti4+ substituted Nb5+ in the Mg4Nb2O9 structure, which promoted the decomposition of Mg4Nb2O9 to form the second phase, Mg5Nb4O15, during sintering. The synergistic effect of ZnAl2O4-TiO2 co-doping promoted the Mg4Nb2O9 ceramic densification. The sample (0.7Mg4Nb2O9-(0.3-x)ZnAl2O4-xTiO2) with x = 0.15?0.2 exhibited dielectric constants of 13–14, larger than those of ZnAl2O4, Mg4Nb2O9 and Mg5Nb4O15, due to the NbO6 octahedra distortion resulting from the substitution of Al3+/Ti4+ for Nb5+ in Mg4Nb2O9 and Mg5Nb4O15. The long-range order of the NbO6 octahedra was enhanced by co-doping ZnAl2O4 and TiO2, thereby enhancing the Qxf value. A dielectric constant of 13.1, Qxf value of 366,000 GHz and a τf of ?60.8 ppm/°C were obtained from 1300 °C sintered 0.7Mg4Nb2O9-0.15ZnAl2O4-0.15TiO2. These results show that 0.7Mg4Nb2O9-0.15 ZnAl2O4-0.15TiO2 ceramic is a good candidate for microwave electronic device applications. 相似文献
60.
《Journal of the European Ceramic Society》2022,42(13):5691-5697
Herein, the improvement of the microwave dielectric properties and sintering characteristics of Zn1?xBixVxW1?xO4(x = 0–0.15)-based ceramics is reported. The results showed that an appropriate amount of doping could not only reduce the optimum sintering temperature from 1100° to 900°C, but also enhance the densification of the microstructures and increase the Q×f value from 5351 to 42525 GHz. Additionally, various structural parameters including the phase composition, crystal structure, vibrational and chemical bond characteristics that are correlated with the dielectric properties were systematically investigated. By considering the chemical bond characteristics, the first-principles calculations and the acquired Raman spectra, the interaction between W-O is stronger than Zn-O in the ZnWO4 structure, while the interaction between V-O is stronger than Bi-O in BiVO4. Interestingly, when the Zn0.97Bi0.03V0.03W0.97O4-based ceramics were sintered at 900 °C, improved microwave dielectric properties were acquired (εr =18.32, Q×f=42525 GHz, τf=?67.51 ppm/°C), which provides a promising candidate in low-temperature co-fired ceramics technology. 相似文献