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1.
C. Dubs J. -P. Ruske E. Werner A. Tünnermann Ch. Schmidt G. Bruchlos 《Optical Materials》2001,17(4):477-481
We report on epitaxial {1 0 0} K1−xRbxTiOPO4 waveguide films for the visible spectral range grown on KTiOPO4 substrates by liquid phase epitaxy. Using the m-line technique a refractive index increase of Δnx≈0.007 and Δnz≈0.004 for TM and TE polarisation has been determined for a K0.78Rb0.22TiOPO4 film. Optical transmission and nearfield distribution are comparable to conventional ion-exchanged waveguides. Typical attenuation of about 1 dB/cm for both TM and TE polarisation was obtained at λ=532 and 1064 nm. Energy-dispersive X-ray spectrometry reveals solid-solution films with graded rubidium composition profiles. X-ray rocking curve analyses confirm the epitaxial growth process and indicate perfect and relaxed K1−xRbxTiOPO4 films. Atomic force microscopy investigations reveal regular step structures with step heights Δh<1.3 nm resulting in rms-roughness values of ≈0.4 nm. 相似文献
2.
The results of a study of forward current–voltage characteristics of 4H-SiC pn structures produced by various methods are presented in this paper. In all pn structure types a forward current was identified which is consistent with the model of recombination in the space charge region via a deep level: J=Jo exp(qU/nkT), where Jo=Jo* exp[−Ea/(kT)] (or J=Jo* exp[(qU−2Ea)/nkT)]) with the ideality factor n=2. The values of the other parameters are as follows: Jo(293 K)(10−24–10−25) A cm−2, Ea≈1.75 eV, Jo*(105–106) A cm−2. In the absence of other leaks, this current represents a natural (intrinsic) shunt for the diffusion current at low biases and determines the value of the injection coefficient of a pn junction. In many of the pn structures the forward current, while showing an exponential dependence on voltage and temperature, was significantly higher than the current described above. The ideality factor, in some instances, was close to unity. A situation with such characteristics can be considered as an ideal extrinsic (due to nonuniformities) barrier type shunt. The potential barrier height of this shunt is ≈1.4 eV. This sort of shunt is characteristic of SiC; earlier a similar object, presumably of the same origin, was identified in 6H-SiC pn structures. 相似文献
3.
Measurements of optical constants (absorption coefficient, refractive index, extinction coefficient, real and imaginary part of the dielectric constant) have been made on a-(Se70Te30)100−x (Se98Bi2)x thin films (where x=0, 5, 10, 15 and 20) of thickness 2000 Å in the wavelength range 450–1000 nm. It is found that the optical bandgap decreases with the increase of Se98Bi2 concentration in the a-(Se70Te30)100−x(Se98Bi2)x system. The value of refractive index (n) decreases, while the extinction coefficient (k) increases with increasing photon energy. The results are interpreted in terms of concentration of localized states varying effective Fermi level. 相似文献
4.
Glasses of various compositions in the system (100 − x)(Li2B4O7) − x(SrO–Bi2O3–0.7Nb2O5–0.3V2O5) (10 x 60, in molar ratio) were prepared by splat quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses (DTA). The amorphous nature of the as-quenched glasses and crystallinity of glass nanocrystal composites were confirmed by X-ray powder diffraction studies. Glass composites comprising strontium bismuth niobate doped with vanadium (SrBi2(Nb0.7V0.3)2O9−δ (SBVN)) nanocrystallites were obtained by controlled heat-treatment of the as-quenched glasses at 783 K for 6 h. High resolution transmission electron microscopy (HRTEM) of the glass nanocrystal composites (heat-treated at 783 K/6 h) confirm the presence of rod shaped crystallites of SBVN embedded in Li2B4O7 glass matrix. The optical transmission spectra of these glasses and glass nanocrystal composites of various compositions were recorded in the wavelength range 190–900 nm. Various optical parameters such as optical band gap (Eopt), Urbach energy (ΔE), refractive index (n), optical dielectric constant and ratio of carrier concentration to the effective mass (N/m*) were determined. The effects of composition of the glasses and glass nanocrystal composites on these parameters were studied. 相似文献
5.
Hui Li Zupei Yang Ximei Zong Yunfei Chang 《Materials Science and Engineering: B》2006,130(1-3):288-294
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
6.
We report on the properties of (1−x)SrBi2Ta2O9–xBi3TaTiO9 solid solution thin films for ferroelectric non-volatile memory applications. The solid solution thin films fabricated by modified metalorganic solution deposition technique showed much improved properties compared to SrBi2Ta2O9. A pyrochlore free crystalline phase was obtained at a low annealing temperature of 600°C and grain size was found to be considerably increased for the solid solution compositions. The film properties were found to be strongly dependent on the composition and annealing temperatures. The measured dielectric constant of the solid solution thin films was in the range 180–225 for films with 10–50% of Bi3TaTiO9 content in the solid solution. Ferroelectric properties of (1−x)SrBi2Ta2O9–xBi3TaTiO9 thin films were significantly improved compared to SrBi2Ta2O9. For example, the observed remanent polarization (2Pr) and coercive field (Ec) values for films with 0.7SrBi2Ta2O9–0.3Bi3TaTiO9 composition, annealed at 650°C, were 12.4 μC/cm2 and 80 kV/cm, respectively. The solid solution thin films showed less than 5% decay of the polarization charge after 1010 switching cycles and good memory retention characteristics after about 106 s of memory retention. The improved microstructural and ferroelectric properties of (1−x)SrBi2Ta2O9–xBi3TaTiO9 thin films compared to SrBi2Ta2O9, especially at lower annealing temperatures, suggest their suitability for high density FRAM applications. 相似文献
7.
The volume fractions of stress-induced martensite formed by certain plastic strains were determined by X-ray diffraction and quantitative metallography in an Fe–Mn–Si–Cr–N alloy at room temperature. The results are fitted by least square method and are well consistent with an exponential function fM=1−exp{−β[1−exp(−η)]n} deduced by Olson and Cohen, who used it to fit with experimental data for AISI304 stainless steel. The similarity of and β, as well as the difference in n for these two alloys are discussed in relation to their nucleation mechanisms. 相似文献
8.
Spin-coated poly(o-methoxyaniline) (POMA) thin films on various substrates were investigated using spectroscopic ellipsometry (SE) in the 1.5–4.5 eV photon energy range. Spin-coating process parameters are reported (spin speed and concentration). Substrates with higher surface energy were found to increase polymer film thickness and decrease roughness. An optical model was developed using SE data along with complementary data from atomic force microscopy and UV–vis spectroscopy to obtain optical properties—refractive index n and extinction coefficient k for POMA. The model includes Lorentz oscillators for the POMA film and a Bruggeman effective medium approximation for roughness. In-plane film optical anisotropy was not observed, but a small out of plane anisotropy was detected for the polymer. 相似文献
9.
Optical properties of N,N′-bis(3-phenoxy-3-phenoxy-phenoxy)-1,4,5,8-naphthalene-tetracarboxylic diimide were investigated using variable angle spectroscopic ellipsometry in the visible light range. An oscillator model with one Tauc–Lorentzian and three Gaussian oscillators was constructed and found physically consistent with the experimental results. No measurable optical anisotropy is found in-plane or out of the film plane, indicating a random arrangement of molecules in spin cast thin films. Refractive index n and absorption index k are reported in the 1.5–4.5 eV (840 nm to 280 nm) optical range. 相似文献
10.
The temperature dependence of the optical band gap of Tl2InGaS4 single crystal in the temperature region of 300–500 K and the room temperature refractive index, n(λ), have been investigated. The absorption coefficient, which was calculated from the transmittance and reflectance spectra in the incident photon energy range of 2.28–2.48 eV, increased with increasing temperature. Consistently, the absorption edge shifts to lower energy values as temperature increases. The fundamental absorption edge corresponds to an indirect allowed transitions energy gap (2.35 eV) that exhibits a temperature coefficient of −4.03 × 10−4 eV/K. The room temperature n(λ), calculated from the reflectance and transmittance data, allowed the identification of the oscillator strength and energy, static and lattice dielectric constants, and static refractive index as 16.78 eV and 3.38 eV, 5.96 and 11.77, and 2.43, respectively. 相似文献
11.
J. Wasylak J. Kucharski E. Golis M. Makowska-Janusik A. Mefleh I. V. Kityk 《Optical Materials》1999,12(4):429-440
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
12.
Thermally and optically induced irreversible changes in the optical gap and refractive index were studied for sulphur rich, nearly stoichiometric and sulphur poor Ge–As–S amorphous films prepared by thermal evaporation. For films studied the optical gap in the virgin state decreases from 2.559 (Ge0.121As0.172S0.707) to 1.632 eV (Ge0.254As0.294S0.452) and simultaneously the refractive index increases from 2.21 to 2.87, respectively. The most sensitive composition to illumination seems to be nearly stoichiometric film (Ge0.153As0.201S0.646), where the blue shift of the gap is observed close to 150 meV. Sulphur poor film (Ge0.254As0.294S0.452) was found insensitive to illumination. Highest thermally induced blue shift of the gap, close to 250 meV, we observed just for Ge0.254As0.294S0.452 film and for this film it was observed also nearly “giant” decrease in refractive index from 2.85 to 2.42. The behaviour of Ge0.254As0.294S0.452 film is qualitatively discussed using the concept of network rigidity (insensitivity to illumination) and assuming thermally induced changes in bonding arrangement (refractive index changes). 相似文献
13.
A fibre optic experimental arrangement was used to determine the thermo-optic coefficient (dn/dT) of electron beam deposited titanium dioxide coatings on the cleaved end faces of multimode optical fibres for a wavelength range between 600 and 1050 nm. The temperature-induced change in the index of refraction (n) and extinction coefficient (k) were successfully determined from reflection spectra. Measurements of n and k at various wavelengths for different temperatures enabled the determination of dn/dT and dk/dT. It was found that dn/dT takes different values at different temperature ranges. For example, at 800 nm, dn/dT was (−1.77±0.7)×10−4 K−1, between 18°C and 120°C, and took a value of (−3.04±0.7)×10−4 K−1 between 220°C and 325°C. 相似文献
14.
Metal-free 1,4,8,11,15,18,22,25-octahexylphthalocyanine was prepared directly by the cyclotetramerization of 3,6-dihexylphthalonitrile using lithium butoxide in butanol. Thin films of the material were deposited on glass substrates by the thermal evaporation technique. The structure of the films was found to be in the form, and showed a strong peak indicating preferential orientation. The surface morphology of the thin films was investigated by atomic force microscopy and showed that the molecules of 1,4,8,11,15,18,22,25-octahexylphthalocyanine grow in stacks of parallel rows. The spectrophotometric measurements of transmittance and reflectance were carried out in the wavelength range 190–3000 nm. The refractive index, n, and absorption index, k, were found to be independent of annealing at 373 K. The B band absorption occurred at 356 nm, and the Q band showed a doublet at 667 and 739 nm. Other optical parameters, such as absorption coefficient and optical dielectric constant ε, were determined. 相似文献
15.
C. A. Durante Rincn E. Hernndez M. I. Alonso M. Garriga S. M. Wasim C. Rincn M. Len 《Materials Chemistry and Physics》2001,70(3):294-304
From the analysis of the variation of optical absorption coefficient with incident photon energy between 0.8 and 2.6 eV, obtained from ellipsometric data, the energy EG of the fundamental absorption edge and EG′ of the forbidden direct transition for CuInxGa1−xSe2 alloys are estimated. The change in EG and the spin-orbit splitting ΔSO=EG′−EG with the composition x can be represented by parabolic expression of the form EG(x)=EG(0)+ax+bx2 and ΔSO(x)=ΔSO(0)+a′x+b′x2, respectively. b and b′ are called “bowing parameters”. Theoretical fit gives a=0.875 eV, b=0.198 eV, a′=0.341 eV and b′=−0.431 eV. The positive sign of b and negative sign of b′ are in agreement with the theoretical prediction of Wei and Zunger [Phys. Rev. B 39 (1989) 6279]. 相似文献
16.
Thin films of copper indium di-selenide (CIS) with a wide range of compositions near stoichiometry have been formed on glass substrates in vacuum by the stacked elemental layer (SEL) deposition technique. The compositional and optical properties of the films have been measured by proton-induced X-ray emission (PIXE) and spectrophotometry (photon wavelength range of 300–2500 nm), respectively. Electrical conductivity (σ), charge-carrier concentration (n), and Hall mobility (μH) were measured at temperatures ranging from 143 to 400 K. It was found that more indium-rich films have higher energy gaps than less indium-rich ones while more Cu-rich films have lower energy gaps than less Cu-rich films. The sub-bandgap absorption of photons is minimum in the samples having Cu/In ≈ 1 and it again decreases, as Cu/In ratio becomes less than 0.60. Indium-rich films show n-type conductivities while near-stoichiometric and copper-rich films have p-type conductivities. At 300 K σ, n and μH of the films vary from 2.15 × 10−3 to 1.60 × 10−1 (Ω cm)−1, 2.28 × 1015 to 5.74 × 1017 cm−3 and 1.74 to 5.88 cm2 (V s)−1, respectively, and are dependent on the composition of the films. All the films were found to be non-degenerate. The ionization energies for acceptors and donors vary between 12 and 24, and 3 and 8 meV, respectively, and they are correlated well with the Cu/In ratios. The crystallites of the films were found to be partially depleted in charge carriers. 相似文献
17.
InSe thin films are obtained by evaporating InSe crystal onto ultrasonically cleaned glass substrates under pressure of 10−5 Torr. The structural and compositional analysis revealed that these films are of amorphous nature and are atomically composed of 51% In and 49% Se. The reflectance and transmittance of the films are measured at various temperatures (300–450 K) in the incident photon energy range of 1.1–2.1 eV. The direct allowed transitions band gap – calculated at various temperatures – show a linear dependence on temperature. The absolute zero value band gap and the rate of change of the band gap with temperature are found to be (1.62 ± 0.01) eV and −(4.27 ± 0.02) × 10−4 eV/K, respectively. The room temperature refractive index is estimated from the transmittance spectrum. The later analysis allowed the identification of the static refractive index, static dielectric constant, oscillator strength and oscillator energy. 相似文献
18.
In the development of ZnO-based varistors the electrical properties of ZnO/Bi2O3 junctions and of the two individual oxides are being investigated. Following our recent work on a.c. conductivity in Al---ZnO---Al sandwich structures we currently report d.c. measurements. The structures were prepared by r.f. magnetron sputtering in an argon/oxygen mixture in the ratio 4:1. Capacitance-voltage data confirm that the Al/ZnO interface does not form a Schottky barrier and measurements of the dependence of capacitance on film thickness indicate that the relative permittivity of the films is approximately 9.7. With increasing voltage the current density changed from an ohmic to a power-law dependence with exponent n≈3. Furthermore measurements of current density as a function of reciprocal temperature showed a linear dependence above about 240 K, with a very low activation energy below this temperature consistent with a hopping process. The higher temperature results may be explained assuming a room-temperature electron concentration n0 and space-charge-limited conductivity, dominated by traps exponentially distributed with energy E below the conduction band edge according to N = N0exp(−E/kTt), where k is Boltzmann's constant. Typical derived values of these parameters are: n0 = 7.2 × 1016 m−3, N0 = 1.31 × 1045 J−1 m−3 and Tt = 623 K. The total trap concentration and the electron mobility were estimated to be 1.13 × 1025 m−3 and (5.7−13.1) ×10−3m2V−1s−1 respectively. 相似文献
19.
A series of glasses in the xPb3O4–(1−x)P2O5 (red lead phosphate) (RLP) system with ‘x' varying from 0.075 to 0.4 were prepared by the single-step melt quenching process from Pb3O4 and NH4H2PO4. The optical absorption spectra of these glasses have been recorded in the ultraviolet region from 200 to 400 nm and the fundamental absorption edges have been identified. The optical band gap Eopt values have been determined for all the glasses using the known theories. The (Eopt) values vary from 4.90 to 3.21 eV the highest being 4.57 eV, corresponding to the most stable glass of x=0.225. The absorption edge is attributed to the indirect transitions and the origin of the Urbach energy ΔE is suggested to be thermal vibrations. These glasses promise as potential candidates for application in optical technology compared to simple xPbO–(1−x)P2O5 (lead phosphate) (LP) glasses. 相似文献
20.
The microstructure, electrical properties, dielectric characteristics, and DC-accelerated aging behavior of the ZnO–V2O5–MnO2 system sintered were investigated for MnO2 content of 0.0–2.0 mol% by sintering at 900 °C. For all samples, the microstructure of the ZnO–V2O5–MnO2 system consisted of mainly ZnO grain and secondary phase Zn3(VO4)2. The incorporation of MnO2 to the ZnO–V2O5 system was found to restrict the abnormal grain growth of ZnO. The nonlinear properties and stability against DC-accelerated aging stress improved with the increase of MnO2 content. The ZnO–V2O5–MnO2 system added with MnO2 content of 2.0 mol% exhibited not only a high nonlinearity, in which the nonlinear coefficient is 27.2 and the leakage current density is 0.17 mA/cm2, but also a good stability, in which %ΔE1 mA = −0.6%, %Δ = −26.1%, and %Δtan δ = +22% for DC-accelerated aging stress of 0.85E1 mA/85 °C/24 h. 相似文献