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1.
The results of the spectroscopic analysis of transition strengths for Er3+ ions in a series of Hf:Er:LiNbO3 crystals with variable Hf content and fixed Er content are reported. Unpolarized UV-VIS-NIR absorption spectra, upconversion fluorescence spectra excited at 800 nm, and microsecond time-resolved spectra excited at 400 nm and 800 nm by 800 nm femtosecond laser were measured at room temperature. The HfO2 incorporation has influence on Er3+ radiative lifetimes, and fluorescence branching ratios. For Hf(4 mol %):Er(1 mol %):LiNbO3, Ω2=2.63×10-20 cm2, Ω4=2.86×10-20 cm2, and Ω6=0.72×10-20 cm2. Ω24 is contrary to the Er3+ general trend of Ω246 when the Hf content is below its threshold concentration. In addition, the sum of Ω increases with the Hf content when the HfO2 content below 6 mol % is unfamiliar. The upconversion mechanism is discussed in this work. PACS 71.20.Eh; 77.84.Dy; 42.62.Fi; 42.65.Ky  相似文献   

2.
利用红外光源浮区法生长出大尺寸、高质量的磁失措自旋冰化合物Dy2Ti2O7单晶体.X射线衍射实验证实晶体具有面心立方结构,空间群为Fd3m,晶胞参数a=1.0112(2) nm,[111]和[400]方向X射线衍射摇摆曲线半高宽分别仅为0.07°和0.05°.直流磁化率与温度关系测量给出晶体的Van Vleck顺磁因子为2.46×10-5 m3/mol,有效磁矩μeff=10.24(4)μB,Cure-Weiss温度ΘCW=1.1 K,揭示Dy2Ti2O7具有弱的铁磁性.对磁性起源的综合分析表明,该自旋冰晶体磁性质主要来源于磁偶极相互作用,且相关最近邻长程偶极相互作用能量标度Dnn=3.00 K. 关键词: 2Ti2O7')" href="#">Dy2Ti2O7 浮区法晶体生长 关联电子系统 自旋冰  相似文献   

3.
Thermal stability of highly ordered hafnium oxide (HfO2) nanotube arrays prepared through an electrochemical anodization method in the presence of ammonium fluoride is investigated in a temperature range of room temperature to 900 °C in flowing argon atmosphere. The formation of the HfO2 nanotube arrays was monitored by current density transient characteristics during anodization of hafnium metal foil. Morphologies of the as-grown and post-annealed HfO2 nanotube arrays were analyzed by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Although monoclinic HfO2 is thermally stable up to 2000 K in bulk, the morphology of HfO2 nanotube arrays degraded at 900 °C. A detailed X-ray photoelectron spectroscopy (XPS) study revealed that the thermal treatment significantly impacted the composition and the chemical environment of the core elements (Hf and O), as well as F content coming from the electrolyte. Possible reasons for the degradation of the nanotube at high temperature were discussed based on XPS study and possible future improvements have also been suggested. Moreover, dielectric measurements were carried out on both the as-grown amorphous film and 500 °C post-annealed crystalline film. This study will help us to understand the temperature impact on the morphology of nanotube arrays, which is important to its further applications at elevated temperatures.  相似文献   

4.
The hyperfine field at 181Ta lattice sites in a nanostructured HfO2 thin film was studied by the perturbed angular correlation (PAC) technique. The thin oxide film was deposited by pulsed laser ablation on a silicon substrate kept at 673 K. The thickness was about 25 nm. The radioactive 181Hf ions were produced by neutron activation of the very thin film in the Portuguese research reactor by the reaction 180Hf(n,γ)181Hf. PAC measurements were carried out at room temperature after annealing at different temperatures up to 1,473 K in air. The PAC technique allows determining the electric field gradient at the 181Ta probe sites. The 181Ta isotopes appear in the sample as disintegration product of 181Hf.  相似文献   

5.
Er 3+-doped TiO 2-SiO 2 powders are prepared by the sol-gel method,and they are characterized by high resolution transmission electron microscopy (HR-TEM),X-ray diffraction (XRD) spectra,and Raman spectra of the samples.It is shown that the TiO 2 nanocrystals are surrounded by an SiO 2 glass matrix.The photoluminescence (PL) spectra are recorded at room temperature.A strong green luminescence and less intense red emission are observed in the samples when they are excited at 325 nm.The intensity of the emission,which is related to the defect states,is strongest at the annealing temperature of 800 C.The PL intensity of Er 3+ ions increases with increasing Ti/Si ratio due to energy transfer between nano-TiO 2 particles and Er 3+ ions.  相似文献   

6.
This paper reports that the high-K HfO2 gate dielectrics are fabricated on n-germanium substrates by sputtering Hf on Ge and following by a furnace annealing. The impacts of sputtering ambient, annealing ambient and annealing temperature on the electrical properties of high-K HfO2 gate dielectrics on germanium substrates are investigated. Experimental results indicate that high-K HfO2 gate dielectrics on germanium substrates with good electrical characteristics are obtained, the electrical properties of high-K HfO2 gate dielectrics is strongly correlated with sputtering ambient, annealing ambient and annealing temperature.  相似文献   

7.
The perturbed angular correlation (PAC) technique has been used to characterize the degree of atomic order in the neighbourhood of radioactive 181Hf isotopes in HfW2O8. PAC measurements were carried out at temperatures between 14 and 723 K. The compound was synthesized starting with the oxides HfO2 and WO3, using a method involving ball milling, high temperature annealing and quenching in liquid nitrogen. Fast cooling allows to have the compound at temperatures below 1050 K. The compound has a high degree of stability below such temperature and around 430 K atomic ordering occurs. This transition order–disorder is reversible. aAlso at Comisión de Investigasiones Científicas de la Provincia de Buenos Aires, Argentina.  相似文献   

8.
Perturbed angular correlation (PAC) studies have been performed in liquid mercury, HCl media of different acid strengths, H2O and H3PO4 using a 181Hf probe. It is found that, in case of H2O, interaction between the nucleus and its excited atom following the β decay of 181Hf is a possible mechanism for the nuclear spin relaxation in this environment. In the liquid mercury and different acid media, however, the perturbations are found to arise due to molecular fluctuations.  相似文献   

9.
The Raman spectra of the single crystal of K2Zn(SO4)2·6H2O belonging toC 2h 5 space group in the 40–1200 cm−1 region in different scattering geometries and their spectra ofthe microcrystalline salt in the 1500-50 cm−1 region have been reported. The dynamics of the crystal has been described in terms of 186 phonon modes under the unit cell approximation. The weak bands in the region 400–900 cm−1 have been assigned to the libratory modes of H2O molecules in contradiction to the assignments reported by Ananthanarayanan. The ambiguities existing in the literature about the assignments ofν 2 c andν 5 c modes of [Zn(H2O)6]2+ have also been removed. The translatory and libratory modes of different units of the crystal have been identified and assignments are made using farir and Raman data on various isomorphous tutton salts. It has been inferred that both SO 4 2− tetrahedron and [Zn(H2O)6]2+ octahedron undergo linear as well as angular distortions from their free state symmetries in the crystal.  相似文献   

10.
Perturbed Angular Correlations (PAC) technique was applied to measure the electric field gradients (EFG) at 181Ta sites in Hf2Fe. The compound has the cubic structure of the Ti2Ni prototype with two non‐equivalent crystallographic sites for Hf atoms. EFGs for the two sites were measured as a function of the temperature. In addition, one more EFG was observed, which was assigned to the presence of defects in the lattice. The ratio of the measured EFG at the regular lattice sites has been used to assign charges to the ions through a simple calculation using the point charge model and it is shown that the lattice symmetry can explain the very different EFG at both sites. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

11.
Time differential perturbed angular correlation measurements of the 133–482 keVγ-γ cascade of181Ta in Hf-doped YBa2Cu3O7−x are presented. The181Hf precurser nuclei are incorporated into the sample by thermal neutron irradiation. Two quadrupole interaction frequencies are observed in the as-irradiated sample:v Q1=161±10 MHz with intensityf 1=75%, asymmetry parameterη 1=0.32 and damping parameter Λ1=0.42, andv Q2=1108±40 MHz withf 2=25%,η 2=0.62, and Λ2=0.60. On annealing the sample in air at various temperaturesT a and quenching to room temperature,f 1 remained nearly constant forT a<600°C andv Q1 for all annealing temperatures indicating that these are insensitive to oxygen stoichiometry. This frequency is interpreted to be due to181Hf substitutingY sites. BeyondT a=600°C,f 1 increased and reached a constant value of 90% forT a=800°C. The value ofv Q2 showed a slight variation between 1086 and 1160 MHz, whilef 2 remained nearly constant at 25% forT a<600°C. This component is identified to be due to181Hf substituting Cu 1 sites in the Cu-O chains of YBCO. Above 600°Cv Q2 decreased and reached a value of 808 MHz beyond 750°C.  相似文献   

12.
Bartels  J.  Freitag  K.  Marques  J.G.  Soares  J.C.  Vianden  R. 《Hyperfine Interactions》1999,120(1-8):397-402
The perturbed angular correlation (PAC) technique was applied to study the incorporation of the transition metal Hf into GaN after implantation. To this end the PAC probe 181Hf(181Ta) was implanted into epitaxial Wurtzite GaN layers (1.3 μm on sapphire) with an energy of 160 keV and doses of 7× 1012 at/cm2. PAC spectra were recorded during an isochronal annealing programme, using rapid thermal annealing (RTA) and furnace annealing, in the 300–1000oC temperature range. After implantation the spectra show a damped oscillation corresponding to a quadrupole interaction frequency (QIF) of νQ= 340 MHz for 30% of the probe nuclei. Annealing up to 600oC reduces the damping of this frequency without an increase of the probe atom fraction fs in these sites. Above 600oC fs grows rapidly until after the 900oC RTA step more than 80% of the Hf probes experience a well defined QIF due to the incorporation of Hf on undisturbed sites of the hexagonal GaN wurtzite lattice. An interaction frequency of νQ= 340 MHz is derived. RTA and furnace annealing yield similar results for annealing up to 800oC, where the undisturbed fraction reaches about 60%. Then RTA at higher temperatures increases this fraction, while furnace annealing leads to a decrease down to 22% after annealing at 1000oC. To our knowledge this is the first time that a transition metal probe like Hf is incorporated to such a large extent into a semiconductor lattice. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

13.
A series of Hf:Fe:LiNbO3 crystals were grown by the Czochralski technique with various doping concentrations of HfO2. Their defect structures were analyzed by the UV-visible absorption spectra and infrared absorption spectra. The optical damage resistance of Hf:Fe:LiNbO3 crystals was measured by the photo-induced birefringence change and the transmitted light spot distortion method. The results show that the optical damage resistance ability of Hf:Fe:LiNbO3 crystals enhances remarkably with the HfO2 concentration increasing when the HfO2 concentration is lower than its threshold concentration (4 mol%). However, when the HfO2 concentration exceeds its threshold concentration, the optical damage resistance ability of the crystals returns to decrease. This unusual behavior is explained by using the photovoltaic field produced in the crystals.  相似文献   

14.
Large dimensional expansion has been observed at room temperature in erbium metal films implanted at room temperature with high fluences of helium. The interferometrically measured film thickness increases linearly with fluence up to a critical dose of 3 × 1017 He+/cm2 (E = 160 keV) and is superlinear at higher fluences. Annealing at 400°C causes a reduction of the induced expansion for fluences below the critical dose without apparent release of helium. Annealing of samples implanted to fluences greater than 3.5 × 1017 He+/cm2 causes accentuated expansion which is accompanied by formation and rupture of bubbles at the film surface.  相似文献   

15.
The formation of HfO2 and ZrO2 oxides in Hf and Zr hydrides has been detected by181Ta PAC spectroscopy. The oxides were identified by their181Ta quadrupole frequency and asymmetry parameter. The growth of the oxide contamination in a H2 atmosphere has been investigated as a function of temperature and time.  相似文献   

16.
Serge Zhuiykov 《Ionics》2009,15(4):507-512
In situ Fourier transform spectroscopy (FTIR) was used to study interactions of nanostructured ruthenium oxide (RuO2) thin-film sensing electrode with O2 at room temperature. RuO2 nanostructures were pretreated at 1,000 °C for 1 h in order to obtain good crystallinity of amorphous RuO2 nanoparticles. Morphology and properties of nanostructured RuO2 were characterized by X-ray diffraction, thermo-gravimetric/differential thermal analysis, scanning electron microscopy, and FTIR. It was shown that pretreated RuO2 is quite active for O2 , O2 2−, and O2− adsorption with clear 722 cm−1 band for superoxide ions (O2 ) adsorption for the different oxygen concentrations. The results of in situ FTIR measurements revealed that the active sites for oxygen adsorption are not limited to the triple boundaries, but extended to surfaces of RuO2 electrodes. Fundamental vibration frequencies of ruthenium–oxygen bond at a temperature of 23 °C as well as region above fundamental frequencies for the nanostructured RuO2 were identified.  相似文献   

17.
La-doped HfO2 gate dielectric thin films have been deposited on Si substrates using La(acac)3 and Hf(acac)4 (acac = 2,4-pentanedionate) mixing sources by low-pressure metal-organic chemical vapor deposition (MOCVD). The structure, thermal stability, and electrical properties of La-doped HfO2 films have been investigated. Inductive coupled plasma analyses confirm that the La content ranging from 1 to 5 mol% is involved in the films. The films show smaller roughness of ∼0.5 nm and improved thermal stability up to 750 °C. The La-doped HfO2 films on Pt-coated Si and fused quartz substrates have an intrinsic dielectric constant of ∼28 at 1 MHz and a band gap of 5.6 eV, respectively. X-ray photoelectron spectroscopy analyses reveal that the interfacial layer is Hf-based silicate. The reliable value of equivalent oxide thickness (EOT) around 1.2 nm has been obtained, but with a large leakage current density of 3 A/cm2 at Vg = 1V + Vfb. MOCVD-derived La-doped HfO2 is demonstrated to be a potential high-k gate dielectric film for next generation metal oxide semiconductor field effect transistor applications.  相似文献   

18.
Luminescence spectra and excitation spectra in 150-420 nm spectral region have been recorded at room temperature for polycrystalline sample of (0.5%)Eu3+:CsGd2F7. The relatively intense emission has been observed from 5D3, 5D2 and 5D1 levels. Emission and excitation spectra prove that the excitation energy is efficiently transferred from the 6GJ and 6IJ levels of Gd3+ ions to Eu3+ ions. The visible quantum cutting via downconversion has been detected, with efficiency of the cross-relaxation step of ∼50%.  相似文献   

19.
Zirconium oxide nanoparticle (ZrO2) is synthesized by the hydrothermal method at different calcination temperatures. The structural analysis is carried out by X-ray diffraction and Raman spectra. The sample prepared at 400 °C and 1100 °C showed the cubic and monoclinic phase, respectively, and the sample calcined at 600 °C and 800 °C showed the mixed phase with co-existence of cubic and monoclinic phases. Furthermore, the morphology and particle size of these samples were investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis. The band gap estimated from UV–Vis spectra of ZrO2 (zirconia) nanocrystalline materials calcined at different temperatures from 400 °C to 1100 °C was in the range of 2.6–4.2 eV. The frequency dependence of dielectric constant and dielectric loss was investigated at room temperature. The low frequency region of dielectric constant is attributed to space charge effects.  相似文献   

20.
TiO2 thin films were deposited on a glass substrate by the radio frequency magnetron sputtering method, and annealed for 2 h at temperatures of 550°C. Then, 60Co γ rays with different doses were used to irradiate the resulting TiO2 thin films. The surface features of films before and after irradiation were observed by scanning electron microscope (SEM). Simultaneously, the crystal structure and optical properties of films before and after irradiation were studied by X-ray diffraction (XRD), UV–VIS transmission spectrum and Photoluminescence (PL) spectrum, respectively. The SEM analysis shows that the film is smooth with tiny particles on the film surface, and non-crystallization trend was clear after irradiated with γ rays. The XRD results indicated that the structure of the film at the room temperature mainly exists in the form of amorphous and mixed crystal at a sputtering power of 200 W, and non-crystallinity was more obvious after irradiation. Obvious difference can be found for the transmissibility of the irradiated and pre irradiation TiO2 films by the UV-VIS spectra. The color becomes light yellow, and the new absorption edge also appeared at about 430 nm. PL spectra and photocatalysis experiments indicate that the photocatalysis degradation rate of the TiO2 films on methylthionine chloride solution irradiated with the maximum dose can be increased to 90%.  相似文献   

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