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1.
Amorphous Lu2O3 high-k gate dielectrics were grown directly on n-type (100) Si substrates by the pulsed laser deposition (PLD) technique. High-resolution transmission electron microscope (HRTEM) observation illustrated that the Lu2O3 film has amorphous structure and the interface with Si substrate is free from amorphous SiO2. An equivalent oxide thickness (EOT) of 1.1 nm with a leakage current density of 2.6×10−5 A/cm2 at 1 V accumulation bias was obtained for 4.5 nm thick Lu2O3 thin film deposited at room temperature followed by post-deposition anneal (PDA) at 600 °C in oxygen ambient. The effects of PDA process and light illumination were studied by capacitance-voltage (C-V) and current density-voltage (J-V) measurements. It was proposed that the net fixed charge density and leakage current density could be altered significantly depending on the post-annealing conditions and the capability of traps to trap and release charges.  相似文献   

2.
Neodymium doped strontium gallogermanate crystals were grown successfully by the Bridgman technique. The linear thermal expansion coefficients for the c- and a-axes were measured as 5.8 × 10−6 °C−1 and 6.5 × 10−6 °C−1. Absorption spectra, and fluorescence spectra, as well as fluorescence decay curves of Nd3+-doped Sr3Ga2Ge4O14 crystal, have been recorded at room temperature and used to calculate the absorption and stimulated emission cross-sections. Based on the Judd-Ofelt theory, three intensity parameters were obtained. The luminescent quantum efficiency of the 4F3/2 level was determined to be approximately 73.8% for this material. Compared with other Nd3+-doped laser crystals, Nd3+-doped Sr3Ga2Ge4O14 crystal displays special laser properties due to its disorder structure.  相似文献   

3.
Nanocomposite made of 10 wt% of Co2.4Al0.6O4 particles dispersed in an amorphous SiO2 matrix has been synthesized by a sol-gel method. X-ray diffraction, transmission electron microscopy and magnetic measurements have been used to characterize the properties of nanocomposite. Most of the particles are well crystallized and have an average diameter below 100 nm. Smaller particles with size below 10 nm have also been observed. A large value of the effective magnetic moment per Co2+ ion of 5.08 μB and negative and the low Curie-Weiss paramagnetic temperature Θ∼−6 K, obtained from the high-temperature susceptibility data, indicate a possible mixing of Co2+ and Co3+ ions between tetrahedral and octahedral sites of the spinel crystal lattice. The measurements of static and dynamic magnetic susceptibilities have shown that Co2.4Al0.6O4 particles in SiO2 matrix display a spin glass behavior at low temperatures.  相似文献   

4.
The effects of temperature and pressure on the formation and decomposition of C6H5C2H2O2 in the C6H5C2H2 + O2 reaction have been investigated at temperatures from 298 to 378 K by directly monitoring the C6H5C2H2O2 radical in the visible region by cavity ringdown spectrometry (CRDS). The rate constant for the C6H5C2H2 + O2 association and that for fragmentation of C6H5C2H2O2 were found to be k1 (C6H5C2H2 + O2 → C6H5C2H2O2) = (3.20 ± 1.19) × 1011 exp(+760/T) cm3 mol−1 s−1 and k2 (C6H5C2H2 O2 → C6H5CHO + HCO) = (1.68 ± 0.13) × 104 s−1, respectively. Additional kinetic measurements by pulsed laser photolysis/mass spectrometry show that C6H5CHO was produced in the C6H5C2H2 + O2 reaction as predicted and the formation of C6H5CHO from the decomposition of C6H5C2H2O2 is temperature-independent, consistent with the CRDS experimental data.  相似文献   

5.
Magnetic measurements have been performed on 40-nm sphere-like Fe3 − δO4 (δ=0.043) nanoparticles using a Quantum Design vibrating sample magnetometer. Coating Fe3 − δO4 nanoparticles with SiO2 effectively eliminates magnetic interparticle interactions so that the coercive field HC in the high-temperature range between 300 K and the Curie temperature (855 K) can be well fitted by an expression for noninteracting randomly oriented single-domain particles. From the fitting parameters, the effective anisotropy constant K is found to be (1.38±0.11)×105 erg/cm3, which is very close to the bulk magnetocrystalline anisotropy constant of 1.35×105 erg/cm3. Moreover, the inferred mean particle diameter from the fitting parameters is in quantitative agreement with that determined from transmission electron microscope. Such a quantitative agreement between data and theory suggests that the ensemble of our SiO2-coated sphere-like Fe3 − δO4 nanoparticles represents a good system of noninteracting randomly-oriented single-domain particles.  相似文献   

6.
D.R. Mullins 《Surface science》2006,600(13):2718-2725
A dysprosium oxide thin film was deposited on Ru(0 0 0 1) by vapor depositing Dy in 2 × 10−7 torr O2 while the Ru was at 700 K. The film was ca. 5 nm thick and produced a p(1.4 × 1.4) LEED pattern relative to the Ru(0 0 0 1) substrate. The adsorption and reaction of CO and C2H4 adsorbed on Rh supported on the Dy2O3 film were studied by TPD and SXPS. The CO initially reacted with loosely bound oxygen in the substrate to produce CO2. After the loosely bound oxygen was removed, the CO adsorbed non-dissociatively in a manner similar to what is seen on Rh(1 1 1). C2H4 adsorbed on the Rh particles and underwent progressive dehydrogenation to produce H2 during TPD. The C from the C2H4 reacted with the O in Dy2O3 to produce CO. CO dissociation on the Rh particles could be promoted by treating the Dy2O3 with C2H4 before CO exposure.  相似文献   

7.
Ytterbium-doped scandium oxide nanocrystals measuring less than 25 nm with compositions of Sc2−xYbxO3 (x=0.001-1) were prepared using the modified Pechini method. The Yb:Sc2O3 nanocrystals were obtained by calcination at low temperature such as 1073 K for 2 h. X-ray powder diffraction (XRD) and transmission electronic microscopy (TEM) were used to perform the structural characterization of nanocrystals; these studies indicated that the nanocrystals have high crystalline quality with cubic structure and Ia3¯ space group. The morphology and particle size were studied using electron microscopy. A detailed study of the effect of the nanodimension and the ytterbium concentration on the spectroscopic characteristics of Yb3+ as an active ion was carried out in terms of optical absorption, optical emission and fluorescence decay time at room and low temperature.  相似文献   

8.
CdFe2O4 particles were synthesized by the microwave assisted combustion method using two different fuels—glycine and urea. Microwave heating provides higher chemical yield within a minute. The synthesized particles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), ac impedance spectroscopy, vibrating sample magnetometry (VSM) and electron spin resonance (ESR) methods. XRD analysis shows the cubic structure of CdFe2O4. The high and low frequency absorption bands of CdFe2O4 were found using FTIR analysis. Spherical morphology was revealed from the SEM images. ESR and VSM measurements reveal the antiferromagnetic behavior of CdFe2O4. The electrical conductivities of CdFe2O4 synthesized using glycine and urea are 6.5×10−7 S cm−1 and 4.7×10−8 S cm−1 respectively at 240 oC. At elevated temperatures an occurrence of increase in conductivity was observed, which indicates the semiconducting behavior of CdFe2O4. The dielectric spectral analysis reveals that dielectric constant of CdFe2O4 decreases with frequency and increases with temperature.  相似文献   

9.
Emission and absorption spectra of Tm3+ in single crystal K2YF5 with different concentrations are reported and analyzed. The non-exponential feature of the fluorescence decay of 1D2 level for the high concentration sample indicates the existence of a cross-relaxation process. Energy level simulation has been carried out by using a phenomenological model with 16 parameters accounting simultaneously for the free ion and crystal field (CF) effects. A good fit was achieved with a root mean square deviation σ=18 cm−1. The free ion and CF effects were then discussed by comparing the available data of K2YF5:Nd3+, LiYF4:Tm3+ and LiYF4:Nd3+.  相似文献   

10.
Y2O3 transparent ceramics with different Nd concentration (0.1-7.0at%) were fabricated using ZrO2 as additive. All the samples exhibit high transparency over a broad spectral region. The elements (Y, O and Nd) are uniformly distributed in the ceramic body, and the average grain size increases with Nd content. Based on the absorption spectrum, the Judd-Ofelt intensity parameters are calculated (Ω2=4.364×10−20 cm2, Ω4=3.609×10−20 cm2 and Ω6=2.919×10−20 cm2). The absorption coefficients increase linearly with Nd3+ doping concentration. The absorption cross-section at 804 nm and stimulated emission cross-section at 1078 nm are calculated to be 1.54×10−20 and 7.24×10−20 cm2, respectively. All the emission bands exhibit the highest emission intensities with 1.0at% Nd3+ ion content, while the lifetime decreases dramatically from 321.5 μs (0.1at% Nd) to 17.9 μs (7.0at% Nd). According to the emission spectra and measured lifetime, the optimum doping concentration of Nd3+ ion in Y2O3 transparent ceramic might be around 1.0at%.  相似文献   

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