197 resultados para test preparation
Resumo:
Al-doped and B, Al co-doped SiO2 xerogels with Eu2+ ions were prepared only by sol-gel reaction in air without reducing heat-treatment or post-doping. The luminescence characteristics and mechanism of europium doping SiO2 xerogels were studied as a function of the concentration of Al, B, the europium concentration and the host composition. The emission spectra of the Al-doped and B, Al codoped samples all show an efficient emission broad band in the blue violet range. The blue emission of the Al-doped sample was centered at 437 nm, whereas the B, Al co-doped xerogel emission maximum shifted to 423 nm and the intensity became weaker. Concentration quenching effect occurred in both the Al-doped and B, Al co-doped samples, which probably is the result of the transfer of the excitation energy from Eu2+ ions to defects. The highest Eu2+ emission intensity was observed for samples with the Si(OC2H5)(4):C2H5OH:H2O molar ratio of 1:2:4. (c) 2006 Elsevier B.V. All rights reserved.
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A novel inorganic-organic hybrid hydrophobic anti-reflection silica film used for laser crystal was obtained by sol-gel process. The film consisted of silica sols mixed with a small amount of polymethyl methacrylate (PMMA) or polystyrene (PS). The optical transparency, hydrophobic property and surface morphology of the film were characterized by UV-VIS-NIR spectrophotometer; contact angle instrument and Scanning Electron Microscopy (SEM), respectively. The results showed that the anti-reflection coating had good hydrophobility and optical transparency from 400 nm to 1200 nm. The contact angle reached to 130-140 degrees. SEM images indicated the hydrophobic films modified with PMMA or PS had compact structure compared to the pure silica sol film. (C) 2008 Elsevier B.V. All rights reserved.
Resumo:
Langmuir-Blodgett(LB)膜技术由于在电子学、非线性光学以及化学传感器等领域具有潜在的应用前景而引起了人们的研究兴趣,其中它的热稳定性对LB膜的应用领域和范围具有一定的影响。本论文在此领域的主要研究内容如下: 利用LB膜技术分别制备了十八胺及硬脂酸、氘代硬脂酸的多层LB膜,采用变温傅立叶变换红外光谱研究了三种LB膜的相变行为。实验发现:十八胺LB膜在55-75 oC温度区间内发生相变,其CH2对称和反对称伸缩振动频率向高能量区发生明显移动;硬脂酸LB膜在70-80 oC的温度区间内发生了明显的相转变,CH2对称和反对称伸缩振动的强度比在升温过程中也有显著改变;氘代硬脂酸LB膜的相行为发生在65-70 oC的温度区间内。 利用LB膜技术制备了十八铵硬脂酸盐(C18H37NH3+C17H35COO-, ODASA)与十八铵氘代硬脂酸盐(C18H37NH3+C17D35COO-, ODASA-d35) Langmuir-Blodgett (LB)膜,使用变温傅立叶变换红外透射光谱研究了它们的热行为。发现LB膜中十八铵硬脂酸盐分子的两个碳氢链高度有序,然而在十八铵氘代硬脂酸盐LB分子中的来自于十八胺的碳氢链部分无序,即在常温下有一些扭曲构象存在于碳氢链中。而十八铵硬脂酸盐的热稳定性也与十八铵氘代硬脂酸盐的热稳定性有些不同。在十八铵硬脂酸盐LB膜中,碳氢链在85 oC到90 oC的温度区间内发生非常明显的有序-无序变化。而在十八铵氘代硬脂酸盐LB膜中,碳氢链和来自于硬脂酸的氘代的烃链各自呈现出不同的热行为,即:碳氢链在80-90 oC的温度区间发生有序-无序变化,尤其是在80-85 oC的温度范围内这个变化非常显著;而氘代的烃链则在70 oC到85 oC这个较长的温度区间发生缓慢的相变。 分别制备了十八铵十二酸盐 (C18H37NH3+C11H23COO-,ODALA)和十八铵二十四酸盐(C18H37NH3+C23H45COO-,ODATA)LB膜,并用变温傅立叶变换红外透射光谱法研究了十八铵十二酸盐和十八铵二十四酸盐LB膜的热行为,比较了十八铵十二酸盐、十八铵硬脂酸盐和十八铵二十四酸盐这三种双链化合物LB膜的热行为。温度相关的红外光谱显示,这三种物质LB膜的热稳定性取决于碳链的长度。其中,十八铵十二酸盐LB膜在50-65 oC的温度区间内发生相变。对应的,十八铵二十四酸盐LB膜在80-90 oC的温度范围内发生有序-无序变化。令人感兴趣的是,十八铵二十四酸盐LB膜的相变温度与十八铵硬脂酸盐LB膜的相变温度基本一样,都是80-90 oC,也即在十八铵二十四酸盐和十八铵硬脂酸盐两种LB膜中,即使二十四酸取代了硬脂酸对前者的热稳定性的影响非常小。以上结果说明,在双长链化合物中,有效链长度取决于双链中的较短的那个烃链,从而来决定膜的热稳定性。在十八铵二十四酸盐LB膜中,十八胺的全部碳链对膜的热稳定性有贡献,而二十四酸的碳链则只有部分(有效部分)烃链有贡献。 制备了十八胺单层和多层LB膜和粒径为几个纳米的金纳米粒子。由于十八胺在pH值小于10.3的溶液中氨基带正电荷,使其置于金纳米溶胶中,利用带正电荷的十八胺和附着负电荷的金纳米粒子之间的静电作用,使得金纳米颗粒成功地吸附组装到十八胺的有序分子膜中,形成有规律的纳米颗粒层。通过紫外-可见光谱、红外光谱以及扫描电镜观察到,金纳米颗粒通过这种方法能够很好的组装在有机分子膜上,而且由于十八胺LB膜的高度有序性使得金纳米颗粒的组装层有序。而且,不同层数的十八胺LB膜对金纳米粒子呈现出不同的吸附行为。 测量了含微量甲醇(体积分数为0.04%~0.24%)的系列乙醇水溶液的近红外光谱,利用近红外光谱分析建立了预测甲醇含量的定量分析模型。比较了用外部检验法(Test Set-Validation)和交叉检验法(Cross-Validaton)建立的数学模型以及研究了使用外部检验法时校正集和检验集样品数的改变对模型预测结果的影响。结果发现,当校正集样品数为15检验集样品数为6(总样品数为21)时,使用外部检验法建立的数学模型预测结果较好,外部检验与交叉检验的预测均方根误差(分别为RMSEE和RMSEP)都较小(分别为0.0105和0.0115)而且很接近。结果表明,近红外光谱方法简单,准确而且实用。
Resumo:
我国江西龙南稀土矿是目前世界上储量最大的富钇稀土矿、研制具有多种用途的钇(Y)-铝(Al)或富钇混合稀土(Ymm)-铝中间合金,对于开拓我国龙南稀土矿的应用领域扩大稀土合金出口具有重要意义。基于这一背景并针对目前氟化物体系制取Ymm-Al合金时存在着电解温度高,腐蚀现象严重,电效偏低等缺点,本文系统开展了在氯化物熔盐体系中电解制取Ymm-Al合金的研究工作。本工作由三部分组成:在第一部分工作中,开展了熔盐电解所需要基本原料-无水稀土氯化物制取的工艺研究。利用化学分析和结构分析手段,弄清了干法氯化过程中YmmCl_3水解的机理,提出了减弱水解的措施,即YmmCl_3先在850-900 ℃灼烧1.5 + 0.2hr,脱掉吸附水并将碱式碳酸盐转化为氧化物,增加稀土氧化物的比表面。通过条件试验得到最佳工艺条件为:采用NH_4 Cl:Ymm_2 O_3 = 14:1(摩尔比)的配料比,每次投入氯化装置的原料量为0.26 - 0.36 kg, 在400-450 ℃氯化反应激烈开始后迅速降温至400 ℃以下,待物料粘结现象消失后,再行升温氯化。出料及后期控制温在475 ± 25 ℃。经过3.8 ± 0.2hr氯化,可制得水不溶物小于1%并符合熔盐电解要求的YmmCl_3原料。此新工艺与原有干法工艺相比,流程短,装置简单,不需密闭抽真空,成本低,适于制取任何量的优质熔盐电解所需氯化稀土原料。在第二部分工作中,利用上述YmmCl_3原料,以液态铝为阴极,在氯化物体系中进行熔盐电解,通过试验得出在小型试验规模制取Ymm-Al合金的最隹工艺条件为:电解质组成(重量比)40%YmmCl_3-1%NaF-59%等摩尔的NaCl-KCl;电解温度为790 ± 5 ℃;阴极电流密为0.7 - 0.02A/cm~2;电解电量为333 ± 5库仑/克铝,制得钇铝合金中Ymm含量为10 ± 2%。添加1%的NaF可消除阴极表面生成枝状物,减少合金中夹渣和熔盐中沉渣。在电解工作中,将方差分析应用于试验数据处理,方差分析结果表明,各种试验因素对电效有明显影响,试验数据可靠,试验误差在允许范围以内。在第三部分工作中,利用线性扫描伏安法测定了在最隹电解工艺条件下Y~(3+)和Ymm在液态铝及钼电极上的析出电位。测定结果表明:Y~(3+)和Ymm~(3+)在液态铝阴极上的析出电位比在钼阴极上偏正0.2 ~ 0.8伏,氟离子的加入要比不加氟时析出电位不有同程度的负移,但考虑到氟离了具有消渣作用,加入少量氟比物添加剂对提高电效有利。
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The Mass Analyzed Low Energy Dual Ion Beam Epitaxy (MALE-DIBE) system has been designed and constructed in our laboratory. We believe that the system, which was installed and came into full operation in 1988, is the first facility of this kind. With our system we have carried out studies, for the first time, on compound synthesis of GaN and CoSi2 epitaxial thin films. RHEED and AES results show that GaN films, which were deposited on Si and sapphire substrates, are monocrystalline and of good stoichiometry. To our knowledge, GaN film heteroepitaxially grown on Si. which is more lattice-mismatched than GaN on sapphire, has not been reported before by other authors. RBS and TEM investigations indicated a rather good crystallinity of CoSi2 with a distinct interface between CoSi2 and the Si substrate. The channelling minimum yield chi(min) from the Co profile is approximately 4%. The results showed that the DIBE system with simultaneous arrival of two beams at the target is particularly useful in the formation of novel compounds at a relatively low substrate temperature.
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A thermal model for concentrator solar cells based on energy conservation principles was designed. Under 400X concentration with no cooling aid, the cell temperature would get up to about 1200℃.Metal plates were used as heat sinks for cooling the system, which remarkably reduce the cell temperature. For a fixed concentration ratio, the cell temperature reduced as the heat sink area increased. In order to keep the cell at a constant temperature, the heat sink area needs to increase linearly as a function of the concentration ratio. GaInP/GaAs/Ge triple-junction solar cells were fabricated to verify the model. A cell temperature of 37℃ was measured when using a heat sink at 400X concentratration.
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With the principles of microwave circuits and semiconductor device physics, two microwave power device test circuits combined with a test fixture are designed and simulated, whose properties are evaluated by a parameter network analyzer within the frequency range from 3 to 8GHz. The simulation and experimental results verify that the test circuit with a radial stub is better than that without. As an example, a C-band AlGaN/GaN HEMT microwave power device is tested with the designed circuit and fixture. With a 5.4GHz microwave input signal, the maximum gain is 8.75dB, and the maximum output power is 33.2dBm.
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ZnO films were deposited on Si(100) substrates at 300℃ by metal - organic chemical vapor deposition(MOCVD). The effect of different ratios of DEZn to N2O on crystal quality was analyzed. It is found that the optimum ratio of DEZn to N2O is 2.1. And in this optimum growth condition, X - ray diffraction (XRD) and scanning probe morphology (SPM) images indicate that the films grow along the c - axis orientation. ZnO film exhibits a strong UV optical absorption near 388 nm. And the optical absorbance is close to zero,that indicates nearly 100% optical transparence. Photoluminescence (PL) spectrum shows only strong near - band - edge emissions with little or no deep - level emission related to defects. The full - width at half - maximum (FWHM) of the ultraviolet emission peak is 80meV. The results indicate that better crystal quality can be obtained.
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50mm SiC films with high electrical uniformity are grown on Si(111) by a newly developed vertical low-pressure chemical vapor deposition (LPCVD) reactor.Both in-situ n- and p-type doping of 3C-SiC are achieved by intentional introduction of ammonia and boron into the precursor gases.The dependence of growth rate and surface morphology on the C/Si ratio and optimized growth conditions is obtained.The best electrical uniformity of 50mm 3C-SiC films obtained by non-contact sheet resistance measurement is ±2.58%.GaN films are grown atop the as-grown 3C-SiC/Si(111) layers using molecular beam epitaxy (MBE).The data of both X-ray diffraction and low temperature photoluminescence of GaN/3C-SiC/Si(111) show that 3C-SiC is an appropriate substrate or buffer layer for the growth of Ⅲ-nitrides on Si substrates with no cracks.
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Semi-insulating (SI) InP wafers of 50 and 75mm in diameter can be obtained by annealing of undoped liquid encapsulated Czochralski (LEC) InP at 930 ℃ for 80h. The annealing ambient can be pure phosphorus (PP) or iron phosphide (IP). The IP-SI InP wafers have good electrical parameters and uniformity of whole wafer. However, PP-SI InP wafers exhibit poor uniformity and electrical parameters, Photoluminescence which is subtle to deep defect appears in IP-annealed semi-insulating InP. Traps in annealed SI InP are detected by the spectroscopy of photo-induced current transient. The results indicate that there are fewer traps in IP-annealed undoped SI InP than those in as-grown Fe-doped and PP-undoped SI-undoped SI InP. The formation mechanism of deep defects in annealed undoped InP is discussed.
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The open-short-load (OSL) method is very simple and widely used, for one-port test fixture calibration. In this paper, this method. is extended to the two-port calibration of test fixtures for the first time. The problem of phase uncertainty arising in this application has been solved. The comparison between our results and those obtained with the short-open-load-thru (SOLT) method shows that the method established is accurate enough for practical applications.
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The problem of frequency limitation arising in calibration of the test fixtures is investigated in this paper. It is found that at some frequencies periodically, the accuracy of the methods becomes very low, and. the denominators of the expressions of the required S-parameters approach zero. This conclusion can be drawn whether-the test fixtures, are symmetric or not. A good agreement between theory and experiment is obtained.