首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
Eu3+-activated scintillating glasses with molar compositions of 35SiO2–15B2O3–30Ln2O3–20AlF3 (Ln = Y, La, Gd, Lu) have been prepared. The effects of Ln3+ ions on the density, transmission, photoluminescence and radioluminescence have been studied. The glasses have high density, ranging from 4.0 to 6.1 g/cm3 in the order of Y < La < Gd < Lu. Gd-containing glass exhibits a much higher light yield than the other glasses. The effect of complete substitution of fluorine by oxygen on the scintillation properties is also investigated.  相似文献   

2.
《Optical Materials》2008,30(12):1768-1773
Theoretical and experimental studies of a double layer antireflection coating deposited onto silicon wafers have been carried out. Magnesium oxide and cerium oxide fabricated by physical vapor deposition method have been applied as low- and high-refractive index materials. MgF2–CeO2–Si structures exhibited the reflectivity below 3% in the wavelength window from 0.5 μm to 1.2 μm. Theoretical simulations of spectral characteristics of the reflectivity of these coatings have been performed. A good correlation between experimental data and theoretical curves has been observed with the assumption that a thin SiO2 layer of a thickness of 16 nm is formed onto Si substrates.  相似文献   

3.
In impact ionization studies the target normally consists of a metal surface of compact solid density. In the present experiments, we investigate the use of a layer of a highly porous structure of nanometre-sized grains, sometimes also called “metal black”, as an alternative target. In our comparative experiments, spherical iron particles (0.1<dp<1.5 μm) were shot with velocities 2–30 km/s onto both a compact solid silver plate and a silver metal black layer of about 7 μm thickness (grain size 20–40 nm, mean density ≈1 g/cm3), deposited on a compact solid gold plate. Impact generated ions were analysed by means of time-of-flight mass spectrometry. The results reveal important advantages of the porous black layer, such as better mass resolution and a larger amount of ions from the impacting particle. Therefore metal blacks may be very suitable targets for the purposes of identification and characterisation of the impacting particle's composition. An attempt is made to give a physical explanation of the results in the frame of existing empirical ionization models. The study is part of a programme to improve devices for in-situ analysis of fast moving cosmic dust particles.  相似文献   

4.
Dense TiC–Al2O3–Al composite was prepared with Al, C and TiO2 powders by means of electric field-activated combustion synthesis and infiltration of the molten metal (here Al) into the synthesized TiC–Al2O3 ceramic. An external electric field can effectively improve the adiabatic combustion temperature of the reactive system and overcome the thermodynamic limitation of reaction with x < 10 mol. Thereby, it can induce a self-sustaining combustion synthesis process. During the formation of Al2O3–TiC–Al composite, Al is molten first, and reacted with TiO2 to form Al2O3, followed by the formation of TiC through the reaction between the displaced Ti and C. Highly dense TiC–Al2O3–Al with relative density of up to 92.5% was directly fabricated with the application of a 14 mol excess Al content and a 25 V cm−1 field strength, in which TiC and Al2O3 particles possess fine-structured sizes of 0.2–1.0 μm, with uniform distribution in metal Al. The hardness, bending strength and fracture toughness of the synthesized TiC–Al2O3–Al composite are 56.5 GPa, 531 MPa and 10.96 MPa m1/2, respectively.  相似文献   

5.
We investigated a possibility of electrochemical formation and control of zinc nitride in a molten LiCl–KCl–Li3N system at 673 K. Zinc nitride films were obtained by means of potentiostatic electrolysis of zinc electrodes in the melt. From XRD analysis, it was confirmed that obtained films consisted of Zn3N2 and LiZnN and that the composition of each film was effected by the applied potential value. In the potential range from 0.75 to 1.6 V (versus Li+/Li), the ratio of Zn3N2 increased as the applied potential was more positive. Based on the result, we achieved the formation of Zn3N2 film (3–5 μm) in anti-scandium oxide structure (a = 0.977 nm) by means of potentiostatic electrolysis at 1.6 V for 3 h.  相似文献   

6.
Nanoparticles of ZnS:Mn have been grown by radio frequency magnetron sputtering technique on glass and Si substrates at a substrate temperature 300 K. X-ray diffraction patterns and selected area electron diffraction patterns confirmed the nanocrystalline cubic ZnS phase formation. TEM micrographs of the films revealed the manifestation of ZnS:Mn nanoparticles with an average size 6 nm. UV–Vis–NIR spectrophotometric measurement showed that the films are highly transparent (90%) in the wavelength range 400–2600 nm. From the measurements of transmittance spectra of the films the direct allowed bandgap values have been calculated and they lie in the range 3.89–4.12 eV. The bandgap decreased with the increase of Mn concentration in the films. The Mn concentrations in the films have been varied from 0% to 8.9% and was measured by energy dispersive X-ray analysis. The photoluminescence of the Mn doped ZnS nanoparticles was measured. The intensity of the PL peaks at first increased with the increase of Mn concentration in the films up to 3.8% of Mn doping and at a Mn concentration higher than this, the intensity of PL peak decreased. Nanocrystalline ZnS:Mn showed good field emission property with a turn on field lying in the range 5.26–6.78 V/μm for a variation of anode to sample distance from 60 μm to 100 μm.  相似文献   

7.
Photoinduced structural transformations in amorphous Sb2Se3–BaCl2–PbCl2 glasses were studied using a differential IR spectroscopy Fourier technique in the spectral region between 100 and 300 cm−1. A stage of the reversible photodarkening is realized in the Sb2Se3 fragments after the first cycle of photoexposure and thermoannealing. The whole scheme of the photo- and thermoinduced transformations in the amorphous system may be explained as a coordination of formation and annihilation of defects. The vibrational density of states calculated using quantum chemical solid state methods confirms our experimental results and their interpretation. Photoinduced photodarkening changes using a CO2 pulse laser (λ=10.6 μm) in new synthesized Sb2Se3–BaCl2–PbCl2 glasses were investigated. At the same time we have studied photoinduced second harmonic generation (SHG) and two-photon absorption (TPA). The possibility of using this glass as perspective materials for IR optoelectronics and nonlinear optics was shown.  相似文献   

8.
Sm-doped cerium dioxide (SDC) with fcc structure was formed using a gas–liquid chemical co-precipitation process at room temperature. Morphology and structure of the as-prepared samples were characterized using TG, XRD, TEM, HRTEM and SAED techniques. Under our specific experimental conditions, two kinds of 1D nano-structures SDC have been mainly obtained. SDC nanowires are 0.3–1.2 μm in lengths and 5–20 nm in diameters. SDC nanotubes have outer diameters in 10–40 nm with lengths up to 2 μm. The as-prepared SDC shows very strong UV absorption ability and the maximum absorption peak redshifts compared with that of SDC nanoparticles.  相似文献   

9.
Bi2Ti2O7 thin films have been grown directly on n-type GaAs (1 0 0) by the chemical solution decomposition technique. X-ray diffraction analysis shows that the Bi2Ti2O7 thin films are polycrystalline. The optical properties of the thin films are investigated using infrared spectroscopic ellipsometry (3.0–12.5 μm). By fitting the measured ellipsometric parameter (Ψ and Δ) data with a three-phase model (air/Bi2Ti2O7/GaAs), and Lorentz–Drude dispersion relation, the optical constants and thickness of the thin films have been obtained simultaneously. The refractive index and extinction coefficient increase with increasing wavelength. The fitted plasma frequency ωp is 1.64×1014 Hz, and the electron collision frequency γ is 1.05×1014 Hz, and it states that the electron average scattering time is 0.95×10−14 s. The absorption coefficient variation with respect to increasing wavelength has been obtained.  相似文献   

10.
Gold nanosheets having single crystalline structure were successfully synthesized using the bulk phase mixture of HAuCl4 and poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) block copolymers through the irradiation of a glow lamp for 5 days. When the molar ratio of propylene oxide to ethylene oxide block units in the block copolymer is about 1.75, mostly gold nanosheets were obtained. Gold nanosheets with an average width of 8 and 5 μm were obtained from the when the molar ratio of gold salt to the ethylene oxide units in the block copolymer were 1/80 and 1/160, respectively.  相似文献   

11.
β-Si3N4 whiskers with diameter of 0.5–2 μm and aspect ratio of 10–15 have been successfully prepared by combustion synthesis under 30–50 atm nitrogen pressure. The addition of MgSiN2 powder plays a significant role in the growth of β-Si3N4 whiskers. The as-prepared products were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM).  相似文献   

12.
We use infrared-visible sum-frequency generation (SFG) spectroscopy in order to investigate the adsorption properties on Pt(111) of molecules having CH3–C6H4–(O–CH2–CH2)n–O–(CH2)m–SH as general chemical formula. We synthesized three molecules defined by the values m = 5 n = 4, m = 11 n = 4, m = 11 n = 8 and characterized them by Nuclear Magnetic Resonance spectroscopy. Thanks to spectroscopic measurements, we show that these molecules build self-assembled monolayers on Pt(111). First, the weak SFG signals arising from the ad-layer indicate low order and surface coverage of the substrate by these molecules. Next, the vibrational fingerprints of the aforementioned molecules are determined between 2825 and 3125 cm 1 and the observed SFG spectral features are ascribed on the basis of the analysis of shorter and simpler molecules (1-dodecanethiol, 4-methylbenzenethiol and CH3–C6H4–O–(CH2)11–SH) also adsorbed on Pt(111). The occurrence of methylene vibration modes indicates a significant amount of chain defects whatever the n and m numbers are. Finally, the identification of a particular vibration mode, characteristic of the aromatic ring, enables us to qualitatively discuss the effect of the number of methylene and ethylene glycol entities on its orientation. More precisely, higher these numbers, more tilted (with respect to the substrate normal) the aromatic ring plane is.  相似文献   

13.
The ceramics were prepared successfully by the addition of WO3 to the Mn-modified Pb(Zr0.52Ti0.48)O3–Pb(Mn1/3Sb2/3)O3–Pb(Zn1/3Nb2/3)O3 (PZT–PMS–PZN) for high power piezoelectric transformers application. XRD analysis indicated that the ceramics were mainly composed of a tetragonal phase in the range of 0–1.0 wt.% WO3 addition. The grain size of the ceramics significantly decreased from 10.0 to 2.9 μm by addition of WO3. Moreover, the addition of WO3 promoted densification of the ceramics and increased mechanical quality factor (Qm), planar coupling factor (Kp) and piezoelectric constant (d33) kept high values, whereas, dielectric loss (tan δ) was low. Δf (=fa − fr) slightly changed when WO3 addition was above 0.5 wt.%. The ceramics with 0.6 wt.% WO3 addition, sintered at 1150 °C showed the optimized piezoelectric and dielectric properties with Qm of 1852, Kp of 0.58, d33 of 243 pC/N and tan δ of 0.0050. The ceramics are promising candidates for high power piezoelectric transformers application.  相似文献   

14.
The microstructure and piezoelectric properties of the 0.01Pb(Mg1/2W1/2)O3–0.41Pb(Ni1/3Nb2/3)O3–0.35PbTiO3–0.23PbZrO3 + 0.1 and 0.3 wt.% Y2O3 + x ZnO ceramics were investigated. The crystal structure changed from psudocubic to tetragonal when ZnO added. The average grain size increased from 4 μm to 8 μm with the addition of ZnO by oxygen diffusion, even if the growth rate was low. When ZnO added until 0.5 wt.%, the , kp and d33 values of specimens were slightly increased regardless Y2O3 contents. The curie point of PMW–PNN–PT–PZ ceramics were increased from 162 °C to 232 °C, as increasing the ZnO contents. When ZnO added, the kp of specimens slightly was increased regardless Y2O3 contents. The mechanical quality factors were abruptly decreased regardless Y2O3 contents, when ZnO added until 0.75 wt.%. The optimized piezoelectric properties were obtained; d33 = 730 (pC/N), kp = 60, Qm = 50, and  = 4750, when PMW–PNN–PT–PZ + 0.3 wt.% Y2O3 + 0.5 wt.% ZnO sintered at 1200 °C for 1 h.  相似文献   

15.
The corrosion of magnesia–chrome (MgO–Cr2O3) brick in molten MgO–Al2O3–SiO2–CaO–FetO slag has been characterized using a dynamic rotary slag corrosion testing for various test cycles at 1650 °C. The open porosity decreases from 15.3 to 4.0% for three cycles, then it gradually increases from 4.0 to 4.8% when the test is extended to nine cycles, in which the permeating depth of the slag maintains at about 20 mm. The XRD pattern of the permeated layer shows the presence of the MgO, MgCr2O4 and CaMgSiO4 phases. In the interior of the permeating layer cracks are formed and corrosion starts at the pores and cracks of MgO and decreases gradually. However, at 20–40 mm beneath the permeated layer edge, different shapes of MgO particles are found.  相似文献   

16.
Field-emission characteristics of chemical vapor deposition-diamond films   总被引:1,自引:0,他引:1  
X. L. Peng   《Thin solid films》2000,370(1-2):63-69
Discontinuous and continuous diamond films with different morphologies and qualities were deposited on n2+-type Si(100) substrates, using the hot-filament chemical vapor deposition (CVD) technique from CH4–H2 gas mixtures. The field-emission characteristics of these diamond films were investigated. The turn-on fields at a 0.01mA/cm2 current density were recorded for all the tested CVD-diamond films. It was found that discontinuous diamond films showed a much lower turn-on field (1.2 V/μm) than continuous ones (20 V/μm). The effective working function of continuous diamond films was around 0.1 eV, while that for discontinuous diamond films is about 0.03 eV. O2 plasma post-deposition sharpening of thick diamond films indicated that the geometrical-field enhancement, caused by the surface topographic changes, has no significant influence on the turn-on field.  相似文献   

17.
The work focuses the formation of hydroxyapatite (HA) layers from simulated body fluids (SBF) onto titanium coated with NH2-, SH-, and SO3H-SAMs, respectively, at room temperature and 37 °C as well as pH values of SBF of 7.4, 8, and 8.4. At an upside up arrangement of the samples in the SBF, the formation of sufficient thick HA layers with a pillow like structure onto all SAMs were observed, which is believed to be caused by combined homogeneous and heterogeneous precipitation of HA from the SBF. These layers do not show sufficient adhesive strength. An upside down arrangement of the samples result in the formation of up to 5–10 μm thick flat HA layers with a much higher adhesive strength, which is believed to be due to formation of HA from the SBF only by heterogeneous precipitation. Also HA layers were obtained onto all studied SAMs, SH-SAM appears to favour the formation of HA resulting in a layer with a thickness of about 10 μm and an almost stoichiometric Ca/P-ratio of the layer of 1.72. All other layers exhibit much lower ratios.  相似文献   

18.
This study reports a new, simple and effective pre-calcined method for fabrication BaO–TiO2–B2O3–SiO2 low temperature co-fired ceramics (LTCC) at a sintering temperature below 900 °C, and with dielectric losses (tan δ) lower than 2 × 10−3. The research results have shown that the addition of 2–5 wt% Al2O3 could easily eliminate the porosity of the glass-ceramics because of the excellent wetting behavior between alumina and the BaO–B2O3–SiO2 glass liquid phase in the low temperature co-fired ceramic system.  相似文献   

19.
Ferroelectric SrBi2Ta2O9/SrBi2Nb2O9 (SBT/SBN) multilayer thin films with various stacking periodicity were deposited on Pt/TiO2/SiO2/Si substrate by pulsed laser deposition technique. The X-ray diffraction patterns indicated that the perovskite phase was fully formed with polycrystalline structure in all the films. The Raman spectra showed the frequency of the O–Ta–O stretching mode for multilayer and single layer SrBi2(Ta0.5Nb0.5)2O9 (SBNT) samples was 827–829 cm−1, which was in between the stretching mode frequency in SBT (813 cm−1) and SBN (834 cm−1) thin films. The dielectric constant was increased from 300 (SBT) to 373 at 100 kHz in the double layer SBT/SBN sample with thickness of each layer being 200 nm. The remanent polarization (2Pr) for this film was obtained 41.7 μC/cm2, which is much higher, compared to pure SBT film (19.2 μC/cm2). The coercive field of this double layer film (67 kV/cm) was found to be lower than SBN film (98 kV/cm).  相似文献   

20.
Si–C films with the Si compositions ranging from 40 to 70% have been grown by Cat-CVD using dimethylsilane [DMSi, Si(CH3)2H2] compounds. Tetraethoxysilane [TEOS, Si(OC2H5)4] and dimethyldimethoxysilane [DMDMOS, Si(CH3)2(OCH3)2] gas source gave us Si–C–O (C-doped SiOx) films with wide ternary alloy compositions. The dielectric constant of a Si–C film has been evaluated by CV measurements (at 1 MHz) using Al/Si–C/n-Si(001)/Cu MIS structure. The relative dielectric constant value of a Si–C film was estimated to be 3.0. The resistivity of the Si–C layer with 1 mm diameter and 0.24 μm thickness was estimated to be more than 24.5 Gohm·cm. These results gave us promising characteristics of Si–C and Si–C–O films grown by alkylsilane- and alcoxysilane-based Cat-CVD.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号