Al2O3 ceramics under high-fluence irradiation: plasma plume dynamics through space- and time-resolved optical emission spectroscopy

The expansion in vacuum of the plume generated by the UV ablation of a LiYF₄ crystal was analysed as a function of several parameters: distance from the target along the plume axis, laser fluency and angular dislocation with respect to the plume axis. The study was carried out by the optical time of flight technique. Time-resolved signals of the optical emission of the neutral as well as ionised species in the plume were recorded and analysed for different experimental situations. The most probable velocity for each species was calculated and confirmed by the Maxwell-Boltzmann distribution fits of the relative emission temporal profiles. An angular distribution of the ablated species could also be provided.     

Comparison between blue and green stimulated luminescence of Al2O3:C

This paper presents a systematic comparison of OSL signals from Al₂O₃:C when stimulated with blue and green light. Al₂O₃:C detectors were irradiated with various doses and submitted to various bleaching regimes using yellow, green and blue light. Most of the investigations were carried out using Luxel?-type detectors used in the commercial Luxel? and InLight? dosimetry systems (Landauer Inc.). Al₂O₃:C single crystals and Al₂O₃:C powder were also used to complement the investigations. The results show that, although blue stimulation provides faster readout times (OSL curves that decayed faster) and higher initial OSL intensity than green stimulation, blue stimulation introduced complicating factors. These include incomplete bleaching of the dosimetric trap when the Al₂O₃:C detectors are bleached with yellow or green light and the OSL is recorded with blue light stimulation, and an increased residual level due to stimulation of charge carriers from deep traps. The results warrant caution when using blue stimulation to measure the OSL signal from Al₂O₃:C detectors, particularly if the doses involved are low and the detectors have been previously exposed to high doses.     

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基于Mie散射理论和方法,研究了航天器尾喷焰等离子体中Al2O3粒子的光学散射特性,分析了复折射率对单个Al2O3粒子消光效率因子、散射效率因子、吸收效率因子、散射相函数以及单次反照率的影响。同时,基于多分散系粒子尺度单峰分布,分析了Al2O3粒子按粒径分布后散射场的有关效应因子及散射相函数的变化,并进行了相应的数值模拟。理论和数值模拟研究表明,航天器尾喷焰等离子体Al2O3粒子复折射率的虚部和实部、粒径的大小与分布对其散射相函数、消光和散射效率因子以及单次反照率均有明显的影响。     

Comparison of the laser-induced plasma of different metal targets as X-rays sources in vacuum

ABSTRACT

Laser-induced plasma is a good source of X-rays. It has much importance in different fields such as industry and medical field. In the current work, Nd: YAG laser was irradiated on metal targets (Al, Cu, Ni, Zn, Sb and Pb) under vacuum 10^?3?torr. Plasma plume is captured by the charged couple device. The emitted X-rays from plasma plume are detected by BPX-65 PIN photodiode through a proper biasing circuit and electrical signals are stored by digital storage oscilloscope (UNI-T UT2202C, 200?MHz). Energy was calculated from these electrical signals. The parameters of X-rays are strongly dependent on the atomic number.     

Al2O3:C optically stimulated luminescence droplets: Characterization and applications in medical beams

Optically stimulated luminescence (OSL) detectors, which are widely used in radiation protection, offer a number of potential advantages for radiotherapy dosimetry. In this study we characterized 1-μl of OSL droplets consisting of a mixture of Al₂O₃:C powder and a photo-curable polymer, in addition to results described in a previous work (Nascimento et al., 2013). The concentration test showed that droplets have a higher spatial resolution than other commonly used Al₂O₃:C-based detectors. Our results from the dose response, reproducibility and dependence with accumulative dose were obtained for droplets with a powder/polymer concentration that showed a high Signal to Noise Ratio (SNR) without compromising the droplet malleability. Additional test results show the response of such droplets in percentage depth dose curves and dose profiles of clinical beams.     

Synthesis and Characterization of Monodispersed SiO2@Y3Al5O12:Er3+ Core-Shell Particles

Submicron core-shell structure particles SiO₂@Y₃Al₅O₁₂:Er³⁺, which silica spherical particles was coated with an yttrium aluminum garnet (Y₃Al₅O₁₂) layer doped with Er³⁺, were prepared by the modified Pechini-Type sol-gel method for the first time. The structure and morphology of samples were detected by the X-ray powder diffraction (XRD) measurement, field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), respectively. The results indicate that well-crystallized garnet nanocrystallines were formed on the surface of the silica particles. The luminescent spectra in near infrared and visible region of the core-shell structured SiO₂@Y₃Al₅O₁₂:Er³⁺ powders were also investigated and compared with those of the pure Y₃Al₅O₁₂:Er³⁺ and the Er³⁺ doped silicate glass. The results show that mono-dispersed SiO₂@Y₃Al₅O₁₂:Er³⁺ core-shell spherical particles with the near infrared, red and green luminescent emissions under the excitation of 980 nm laser diode have been successfully synthesized.     

The effect of supports (Al2O3, Al2O3-CeO2 and Al2O3-CeZrO2) on the nature of gold-species in supported gold catalysts

This work is concerned with the study of Au specimens produced by gold deposition on nanosized mixed oxides (alumina, ceria, zirconia) prepared by the sol-gel method using organometallic precursors. According to X-ray absorption near edge structure, extended X-ray absorption fine structure, transmission electron microscopy data, and ultraviolet-visible and X-ray photoelectron spectroscopy measurements, mixed Al-Ce-Zr oxides are quite effective for stabilization of different gold specimens. The samples pre- treated in hydrogen at 150°C are characterized by the presence of gold Au³⁺ cations located on the surface in slightly disordered octahedral oxygen coordination. Metallic gold nanoparticles with a size of about 2 nm and gold clusters were found in the samples treated in hydrogen at 300°C.     

激光诱导Al等离子体在背景气体中的流体现象

调Q-YAG脉冲激光（波长1.06μm,脉宽10ns,能量为250mJ/pu1se）烧蚀Al靶,用短焦距照相系统和光学多道分析仪（OMA）记录了等离子体在氩气背景气体及不同压强下所呈现的流体现象及其等离子体辐射的空间分辨光谱。实验发现,当背景气压为400Pa以下时,在靶面上存在一个明亮的发光球体,球体直径远大于激光烧蚀斑的大小,此球体向四周辐射等离子体光谱,只是在垂直靶面的方向辐射相对较强。在气压约为400Pa,等离子体辐射才以较为明显的羽状体形态向前喷散,且随气压增高,喷散的立体角变小。随着背景气压的继续升高,等离子体羽被压缩,成为一个明亮的发光小羽状体,当气压达20～30kPa,发光羽状体开始出现分解的迹象,在羽状体前端形成一个光球。气压继续升高,等离子体羽完全变成一串发光球。离开靶面越远,发光球的半径越大。用光学多道分析系统分析这些发光球的光谱特征,发现在靶面附近主要是Al等离子体的谱线,而较远的发光球,其主要谱线则来自背景气体。在气压为20kPa左右,等离子休羽呈现烧蚀点为明亮的白色亮点,而羽端为鲜艳绿色（氩的514nm）的彩色羽。     

电解等离子体法制备Al2O3陶瓷层及其特性研究

利用电弧喷铝并重熔后进行电解等离子体处理(EPP)的方法在Q235钢基体上制备出呈冶金结合的Al2O3陶瓷层.利用XRD,SEM和EDS等手段对陶瓷层的成分和显微组织进行了分析,测定了陶瓷层的耐蚀性能和耐磨性能.实验结果表明,陶瓷层主要由α-Al2O3,γ-Al2O3,θ-Al2O3以及一些非晶相组成,组织致密,耐蚀性能和耐磨性能良好.     

Fabrication of low-loss channel waveguides in Al2O3 and Y2O3 layers by inductively coupled plasma reactive ion etching

Etching of amorphous Al₂O₃ and polycrystalline Y₂O₃ films has been investigated using an inductively coupled reactive ion etch system. The etch behaviour has been studied by applying various common process gases and combinations of these gases, including CF₄/O₂, BCl₃, BCl₃/HBr, Cl₂, Cl₂/Ar and Ar. The observed etch rates of Al₂O₃ films were much higher than Y₂O₃ for all process gases except for Ar, indicating a much stronger chemical etching component for the Al₂O₃ layers. Based on analysis of the film etch rates and an investigation of the selectivity and patterning feasibility of possible mask materials, optimized optical channel-waveguide structures were fabricated in both materials. In Al₂O₃, channel waveguides were fabricated with BCl₃/HBr plasma and using a standard resist mask, while in Y₂O₃, channel waveguides were fabricated with Ar and using either a resist or a sputter deposited Al₂O₃ mask layer. The etched structures in both materials exhibit straight sidewalls with minimal roughness and sufficient etch depths (up to 530 nm for Al₂O₃ and 250 nm for Y₂O₃) for defining waveguides with strong optical confinement. Using the developed etch processes, low additional optical propagation losses (on the order of 0.1 dB/cm) were demonstrated in single-mode ridge waveguides in both Al₂O₃ and Y₂O₃ layers at 1550 nm. PACS 42.70.-a; 42.82.-m; 42.82.Cr     

Comparison between N2 and O2 anneals on the integrity of an Al2O3/SiaN4/SiO2/Si memory gate stack

In this paper the endurance characteristics and trap generation are investigated to study the effects of different postdeposition anneals （PDAs） on the integrity of an Al2O3/Si3N4/SiOz/Si memory gate stack. The flat-band voltage （Vfb） turnarounds are observed in both the programmed and erased states of the N2-PDA device. In contrast, this turnaround is observed only in the erased state of the O2-PDA device. The Vfb in the programmed state of the O2-PDA device keeps increasing with increasing program/erase （P/E） cycles. Through the analyses of endurance characteristics and the low voltage round-trip current transients, it is concluded that in both kinds of device there are an unknown type of pre-existing characteristic deep traps and P/E stress-induced positive oxide charges. In the O2-PDA device two extra types of trap are also found： the pre-existing border traps and the P/E stress-induced negative traps. Based on these four types of defects we can explain the endurance characteristics of two kinds of device. The switching property of pre-existing characteristic deep traps is also discussed.     

Pt/CeO2-ZrO2/Al2O3催化剂的光谱表征

利用拉曼光谱表征了不同方法添加ＣｅＯ２－ＺｒＯ２混合氧化物对Ｐｔ／Ａｌ２Ｏ３催化剂的影响,并采用了ＸＲＤ,Ｈ２化学吸附,ＢＥＴ表征了相应的分散度影响。结果表明：Ｃｅ、Ｚｒ、与金属Ｐｔ存在着强的相互作用,而ＣｅＯ２－ＺｒＯ２以盐的形式加入时,高度分散在Ａｌ２Ｏ３载体上,提高贵金属Ｐｔ的分散度,进而提高了反应的活性。     

An anomalous enhancement in the electrical conductivity of Li2O : B2O3 : Al2O3 glasses

The study of electrical conductivity of 27.5 Li₂O : (72.5 − x) B₂O₃ : x Al₂O₃ glass samples has been carried out. It has been observed that the conductivity exhibits Arrhenius behavior for all samples up to glass transition temperature T_g. Beyond T_g, an anomalous enhancement followed by decrease in conductivity has been observed. The results have been explained by dividing the temperature range into two regions. In region-I, it has been observed that the conductivity variation exhibits a maximum at 2.5 mol% Al₂O₃, which has been explained on the basis of Mixed Glass Former Effect (MGFE). An anomalous enhancement in the conductivity observed in region-II has been attributed to the nucleation in the glass. The subsequent decrease in the conductivity has been attributed to the crystallization of the glass samples.     

Structural and Magnetic Properties of the Al2O3/Ge-p/Al2O3/Co System

Technical Physics - The Al2O3/Ge-p/Al2O3/Co system with an Al2O3 buffer layer deposited by ion-plasma sputtering has been experimentally investigated. The dependences of the magnetic properties of...     

Experimental study of laser-induced thermal ignition in O2/O3 mixtures

O₂/O₃ mixtures are ignited by absorption of laser pulses of a TEA CO₂ laser along the axis of a cylindrical cell. The dependence of the radial propagation of the O₃ decomposition, detected by uv absorption of the ozone, on laser fluence and on O₃ concentration is investigated. Oscillations of the signals are identified to be the first radial acoustic mode of the cell. For mixtures of 0.35 bar and 0.70 bar total pressure and O₃ percentages within 20–50%, the ignition limit is in the order of 0.1–0.2 J/cm³ (absorbed energy density). These values are in reasonable agreement with the results of the corresponding numerical simulations.