Compositional analysis of ferroelectric films coated with carbon layer using laser-induced plasmas spectroscopy

An experimental investigation of the effect of different thickness of carbon layer coated on ferroelectric films on the atomic emission intensity using laser-induced plasmas spectroscopy technique with charge-coupled device (CCD) experimental system has been conducted. The experimental results show that the intensity of the spectra emitted with the carbon layer thickness of 15 μm is much higher than that of pure ferroelectric films. By using this best experimental condition, the atomic concentration ratios of ferroelectric films are evaluated by rationing the integrated intensities of selected spectral emission lines of the plasma produced from the films. And the experimental results show that N_La/N_Co and N_Sr/N_Co atomic concentration ratios are almost in agreement with the corresponding values obtained by traditional compositional analysis techniques of inductively coupled plasma (ICP).     

Photoluminescence of Si from Si nanocrystal-doped SiO2/Si multilayered sample

A multilayered Si nanocrystal-doped SiO₂/Si (or Si-nc:SiO₂/Si) sample structure is studied to acquire strong photoluminescence (PL) emission of Si via modulating excess Si concentration. The Si-nc:SiO₂ results from SiO thin film after thermal annealing. The total thickness of SiO layer remains 150 nm, and is partitioned equally into a number of sublayers (N = 3, 5, 10, or 30) by Si interlayers. For each N-layered sample, a maximal PL intensity of Si can be obtained via optimizing the thickness of Si interlayer (or d_Si). This maximal PL intensity varies with N, but the ratio of Si to O is nearly a constant. The brightest sample is found to be that of N = 10 and d_Si = 1 nm, whose PL intensity is ∼5 times that of N = 1 without additional Si doping, and ∼2.5 times that of Si-nc:SiO₂ prepared by co-evaporating of SiO and Si at the same optimized ratio of Si to O. Discussions are made based on PL, TEM, EDX and reflectance measurements.     

直流磁控溅射YBCO非晶薄膜的卢瑟福背散射研究

利用直流磁控溅射(D.C.Magnetron Sputtering)法,选取总气压为80Pa,沉积时间为60min,溅射靶尺寸为φ80,在磁场强度、靶与基片之间的距离及Ar/O₂比等参数变化的情况下,制备了四组YBCO/Al₂O₃非晶薄膜样品。用MeV Li卢瑟福背散射(RBS)分析技术,测量了各块样品中Ba和Cu相对Y的含量和薄膜厚度随基片的横向分布。分析结果表明:在不同的沉积条件下,薄膜中各点的Ba和Cu相对浓度差别较大,薄膜厚度分布也 关键词：     

飞秒激光低压N2等离子体特性的实验研究

在低于一个标准大气压的条件下对飞秒激光产生的N₂等离子体光谱进行了实验研究.结果表明, 各种样品气压下的激光N₂等离子体光谱均表现为连续谱和线状谱的叠加.随着样品气压的降低, 连续谱和原子谱线的强度经历了由缓慢增强发展为缓慢降低再到迅速降低的过程, 而正一价离子谱线强度呈现逐步增强的特征.在气压低于0.3 atm (1 atm=101325 Pa)时, 出现了正二价态的离子谱线. 给出了低压N₂等离子体对于飞秒激光传输和能量吸收的物理特性, 并初步讨论了低压等离子体通道特性.这些结果有助于加深了解飞秒激光等离子体的特性和机理, 特别是给出了在实验上测量不同价态离子光谱的条件, 为今后的研究提供了有益的实验依据. 关键词： 飞秒激光 气压 等离子体光谱 激光传输     

Quantized Hall effect in gated AlGaAs/GaAs heterostructures: Localization as a function of number density and magnetic field

We report two-terminal magnetoresistance measurements on a short gated GaAsAlGaAs HEMT (High Electrical Mobility Transistor) sample for magnetic fields to 18.5 Telsa and temperatures near 0.5 K. A gated sample was used, permitting variation of the 2D charge density over a wide range. Additional measurements were made on gated Van Der Pauw squares that are consistent with the short gate FET results. Using the localization model, the experimental data shows that in the Quantum Hall Effect (QHE) region, the fraction of localization within a Landau level remains unchanged at different magnetic fields and is also unchanged over a wide range of 2D electron number density (N_s). This is in contrast with the observed large dependence of mobility on N_s at the same temperatures in the same sample.     

Nonlinear change of on-axis pressure and intensity maxima positions and its relation with the linear focal shift effect

A comprehensive experimental, analytical and numerical study of the true focal region drift relative to the geometrical focus (focal shift effect) in acoustic focused beams and its nonlinear evolution is presented. For this aim, the concept of Fresnel number, proportional to the linear gain, is introduced as a convenient parameter for characterizing focused sources. It is shown that the magnitude of the shift is strongly dependent on the Fresnel number of the source, being larger for weakly focused systems where a large initial shift occurs. Analytical expressions for axial pressure distributions in linear regime are presented for the general case of truncated Gaussian beams. The main new contribution of this work is the examination of the connection between the linear and nonlinear stages of the focal shift effect, and its use for the estimation of the more complicated nonlinear stage. Experiments were carried out using a continuous-wave ultrasonic beam in water, radiated by a focused source with nominal frequency f = 1 MHz, aperture radius a = 1.5 cm and geometrical focal distance R = 11.7 cm, corresponding to a Fresnel number N_F = 1.28. The maximum measured shifts for peak pressure and intensity were 4.4 and 1.1 cm, respectively. The evolution of the different maxima with the source amplitude, and the disparity in their axial positions, is interpreted in terms of the dynamics of the nonlinear distortion process. Analytical results for the particular case of a sound beam with initial Gaussian distribution are also presented, demonstrating that the motion of peak pressure and peak intensity may occur in opposite directions.     

Intensity ratios of the KL1L1, KL23L23 oxygen Auger lines in different compounds

A simple model is proposed to interpret the relative intensities of the KLL oxygen Auger lines of several compounds. The basic assumption is that the intensity ratios depend on the atomic charges of the L₁ and L₂₃ orbitals localized at the oxygen site. The appropriate atomic charges can be calculated after Pauling's scale of electronegativity. The theoretical intensity ratios are compared with experimental results of different authors.     

An experimental investigation of the pressure and concentration dependence of muonic Coulomb capture and cascade in gases

Muonic Coulomb capture ratios and x-ray intensity patterns in four binary mixtures of the gases N₂, Ne, Ar, Kr, and Xe have been measured at three atomic ratios. An influence of the concentration has been established. The Lyman series intensity patterns of pure N₂, Ne, Ar, Kr, and Xe were measured at pressures between 0.4 and 51 bar and found to depend on the pressure. Possible explanations are discussed.     

Core level shake up structures of N2 adsorbed on nickel surfaces: Cluster models

Self-consistent Hartee-Fock-LCAO calculations on a linear NiN₂ cluster are used to explain the two-peak structure observed in core level photoemission from N₂ adsorbed on the Ni (100) surface. The two observed peaks are due to different N₂ core hole final states, a screened and an unscreened final state that can be clearly identified in the cluster model. The energy separation and intensity ratio (computed using the sudden approximation) of the two final states in NiN₂ are comparable with the experimental peak separation and intensity ratio for reasonable cluster geometries. A comparison with previous model studies on NiCO is used to explain the different shape of the core level spectra of N₂ and CO adsorbed on nickel surfaces.     

Density, thickness and composition measurements of TiO2SiO2 thin films by coupling X-ray reflectometry, ellipsometry and electron probe microanalysis-X

Mixed TiO₂SiO₂ thin films were deposited by aerosol atmospheric CVD method by using di-acetoxi di-butoxi silane (DADBS) and Ti tetra-butoxide as precursors. By varying the deposition temperatures between 470 and 600 °C and the ratios between the Si and Ti precursors (Si/Ti) from 2 up to 16, films with different compositions and thicknesses were deposited. The coupled analysis of the results of different characterisation methods was used in order to determine the variation of the composition, the thickness and the density of the films. First EPMA measurements were performed at different acceleration voltages with a Cameca SX50 system. By analysing, with specific software, the evolution of the intensity ratio I_x/I_std versus the voltage, the composition and the mass thickness (product of density by the thickness) were determined. In order to measure independently the density, X-ray reflectometry experiments were performed. By analysing the value of the critical angle and the Kiessig fringes, the density and the thickness of the layers were determined. The refractive index and the thickness of the films were also measured by ellipsometry. By assuming a linear interpolation between the index value of the pure SiO₂ and TiO₂ films, the film composition was deduced from the refractive index value. XPS measurements were also performed in order to obtain an independent value of the composition. A good agreement between the ways to measure the density is obtained.     

Experimental studies on the Kβ/Kα intensity ratio of Zn at different thickness and pressure

Kβ/Kα intensity ratios of Zn were measured at a photon excitation energy of using a high-resolution Si(Li) detector for several thickness at different pressure. Present results were compared with theoretical data and other experimental values. The results were in good agreement theoretical values based on Hartree-Fock theory.     

The oscillator strength of the πg shape resonance in the absorption K-spectrum of a nitrogen molecule

Magnitudes of the absorption cross sections of a nitrogen molecule are measured by the transmission method near the ionization K-threshold. Based on these data, the partial absorption NK cross sections are obtained and the oscillator strength of the π_g shape resonance is determined. It is found that the oscillator strength of the π_g-resonance increases as the optical density of nitrogen decreases. This phenomenon is interpreted as a result of the instrumental distortion effect (the thickness effect). By extrapolating to zero pressure, the oscillator strength of the π_g shape resonance is determined to be 0.29.     

用X射线能谱同时测定薄膜成分及厚度

本文提出一个直接利用薄膜和衬底的X射线能谱来同时测定薄膜的成分和厚度的新方法,利用薄膜发出的各元素的标识X射线强度比确定其成分,利用NaCl衬底的Nak_α和Clk_α标识X射线的强度随膜厚增大而衰减的定量关系确定膜厚,本方法不需要纯元素的块状标样,对在NaCl衬底上沉积的Cu-Si合金薄膜的成分和厚度,在各种实验条件下进行了测定,得到了较为满意的结果。 关键词：     

Influence of the diameter and wall thickness of a quartz pipe inserted in the EPR cavity on the signal intensity

Some dependences between the EPR signal intensity of point samples and the diameter and wall thickness of the quartz tubes with which a standard rectangular TE₁₀₂ EPR cavity is loaded are reported. It is found that the EPR signal intensity linearly depends on the wall thickness of the container and can be increased approximately twice when thick sample tubes are used. The microwave power in the location of the sample increases similarly whereas the normalized bell-shape distribution of the signal intensity along thez-axis of the cavity remains unchanged. The effective microwave power necessary to saturate the sample decreases and the cavity filling factor increases.     

The dependence of pulse properties of ferrous borate single crystals on their thickness

It is established that the magnitude of the discontinuity in the slope of a pulse-switching curve defined as the ratio between the switching coefficients S _w1 and S _w2 corresponding to the first and second parts of the switching curve, respectively, decreases with an increase in the thickness of a ferrous borate single crystal. This change is generally caused by a decrease in the coefficient S _w1, whose magnitude is inversely proportional to the sample’s thickness. In order to analyze the results obtained, we used the early proposed expression τ^?1=aH _s ?,bA ², connecting the switching rate τ^?1 with the amplitude of the magnetic field H _s and the intensity A of the magnetoelastic vibrations accompanying the pulse switching. It is found that the coefficient a depends only slightly on the sample’s thickness, while the coefficient b is inversely proportional to the thickness squared. Thus, the main part of the energy losses due to magnetoelastic vibrations is associated with elastic lattice vibrations.     

Non-Voigt line-shape effects on retrievals of atmospheric ozone: Line-mixing effects

A theoretical approach is proposed to model line-mixing (LM) effects on absorption coefficients of O₃ perturbed by N₂ and air. It uses state-to-state rotational cross-sections calculated with a semi-classical approach and two empirical parameters, which enable switching from the state space to the line space. The first, associated with couplings within Q branches is deduced from a room temperature far-infrared spectrum. The second, governing line-couplings between R (or P) lines, is determined from a spectrum measured in the ν₁+ν₂+ν₃ band. The model developed is then successfully compared with measurements performed at room temperature for a relatively large range of pressure (0.7-8 atm) and in four different bands (from 3 to 300 μm). Accurate predictions are, in particular, obtained in the 10 μm (ν₁, ν₃) region, which is widely used for remote sensing purposes. Consequences of LM effects on retrievals of ozone atmospheric volume mixing ratios are then studied using simulated atmospheric spectra. The results show that LM leads to systematic spectra fit residuals and errors on the retrieved ozone amounts, which are small but might be detectable in measured atmospheric spectra.     

Pressure dependence of the Néel temperature of f.c.c. stainless steel

The Néel temperature T_N of f.c.c. stainless steel has been measured as a function of pressure using the Mössbauer effect. A sample with approximately 74 wt.% Fe, doped with ^57Co, and having T_N = 58.4 ± 0.1 K at zero pressure, shows T_N rising with pressure with increasing slope. Our results indicate that T_N is raised to room temperature by a pressure of 175 ± 5 kbar.     

Growth of preferentially-oriented AlN films on amorphous substrate by pulsed laser deposition

Preferentially-oriented aluminum nitride (AlN) films are grown directly on natively-oxidized Si (100) substrate by pulsed laser deposition (PLD) in nitrogen (N₂) environment. The AlN preferential orientation changes from (002) to (100) with increasing N₂ pressure. Such different behaviors are discussed in terms of deposition-rate-dependent preferential orientation, kinetic energy of depositing species and confinement of laser plume. Finally, sample deposited at 0.9 Pa is proved to have the highest (002) peak intensity, the lowest FWHM value, the highest deposition rate and a relatively low RMS roughness (1.138 nm), showing the optimal growth condition for c-axis-oriented AlN growth at this N₂ pressure.     

Analysis of the laser magnetic resonance spectrum of HO2

An analysis of the previously detected laser magnetic resonance spectrum of HO₂ is carried out by (i) assigning M_J quantum numbers to each observed Zeeman line, (ii) determining the quantum numbers (N′_Ka′Kc′-N″_Ka″Kc″) and energies of the zero-field asymmetric rotor transitions involved, and (iii) determining the values of the zero-field spin-rotation doublet splittings in the upper and lower states of each asymmetric rotor transition. The rotational transitions obtained lie in the region 50–150 cm^?1, with quantum numbers 4 ≤ N ≤ 19 and 1 ≤ K_a ≤ 4. They are fit to an asymmetric rotor program to obtain the three rotational constants A, B, C and the three symmetric-top centrifugal distortion constants D_K, D_NK, D_N. The spin splittings are fit to an approximate theoretical expression involving two adjustable linear combinations of components of the spin-rotation interaction tensor ?. Because of the lack of spectra from other isotopic species, a unique molecular geometry cannot be derived.     

Generation of optically active states in a-SiNx by thermal treatment

Amorphous silicon nitride (a-SiN_x) films were deposited using plasma-enhanced chemical-vapor deposition (PECVD) and subsequently, thermal annealing processes were performed at 700-1000 °C in the ultra-high vacuum (UHV) condition. A strong photoluminescence (PL) peak induced by luminescent defect centers was observed at 710 nm for the as-deposited sample. When the sample was annealed at 700-1000 °C, the PL peak intensity became about 3-12 times stronger with no shift of the PL peak. To investigate the origin of the change in PL peak intensity after the thermal annealing, Si 2p and N 1s core-level spectra were systematically analyzed by high-resolution photoemission spectroscopy (HRPES) using synchrotron radiation. In particular, N 1s spectra were decomposed with three characteristic nitrogen-bonding states. It is revealed that the nitrogen bonding state with N-Si and NSi₂ configurations (denoted as N3) contributes mainly to the change in PL peak intensity. We note that luminescent nitrogen related defect centers such as N₄⁺ and N₂° are localized in the state N3. Detailed analysis of the experimental results shows that the state N3 is located in the interface bounded by the region of the nano-sized stoichiometric silicon nitride Si₃N₄ (denoted as N1) and is considerably influenced by the thermal annealing, which is an appropriate process to cause strong photoluminescence of the related samples as mentioned above.