Ga_2O_3薄膜的常温磁控溅射制备对其结构及光学特性的影响

本文通过常温射频磁控溅射在单抛硅片和石英玻璃基底上溅射制备Ga_2O_3薄膜。采用分光光度计和椭偏仪测试薄膜的紫外光波段的透过率、折射率和光学吸收,利用X射线光电子能谱(XPS)测试了不同氧气氛下Ga_2O_3薄膜中氧元素的化学价态及其含量,X射线衍射(XRD)测试和拉曼散射光谱测试研究退火对薄膜生长及晶相结构的影响,采用微控四探针测试仪测试了薄膜的电阻率。研究了溅射功率、氩氧比、退火等工艺参数对薄膜结构及光电性能的影响。研究发现经过常温溅射后,再经过后退火处理的薄膜,无论在结构还是光学性能都优于之前传统制备工艺。结果显示:在氩氧比为80∶20、溅射功率为175 W、压强1.5 Pa条件下溅射2 h,沉积的薄膜厚度为197.6 nm,在紫外光波段吸收峰在284 nm,峰值透过率达到92.82%。在900℃退火下,薄膜的导电性能最好,电阻率达到137.21 m·cm。XRD测试和拉曼散射光谱结果表明,随着退火温度的升高,薄膜表现出择优生长趋势,发现β-Ga_2O_3的(201)、(401)和(403)的衍射峰随着退火温度的增加进一步增强。利用Tauc公式由透过率数据计算光学带隙结果表明,随着退火温度升高薄膜光学带隙由在4.93～5.28 eV范围内变化。     

sol-gel法制备ZnO·Al薄膜及其特性研究

以Zn(OAC)2·2H2O和AlCl3·6H2O为原料,采用溶胶-凝胶的方法在普通玻璃片基材上获得了掺铝的氧化锌透明导电薄膜.采用XRD、SEM、以及分光光度计等分析手段对薄膜进行研究,实验结果表明,当铝离子掺杂量为2%(wt)、预处理温度400℃、退火温度550℃下保温1h,可使所得薄膜的电阻率最低,为5×10-2Ω·cm,薄膜可见光透过率平均达80%以上.     

气相CdCl2退火对CdTe多晶薄膜性能的影响

利用近空间升华法在Ar O2气氛下沉积了CdTe多晶薄膜,并在气相CdCl2氛围下进行了不同温度的退火,对样品进行了厚度、XRD、SEM、透过谱,σ-T等性能测试,结果表明:退火后CdTe多晶薄膜在(111)面上仍具有择优取向,退火能使晶界钝化,增加再结晶并促进晶粒长大;但对薄膜的透过率没有影响,退火后,暗电导(σdark)增加,电导激活能(Ea)减少.得到了最优化的退火条件.     

磁控溅射技术制备Al_2O_3掺杂ZnO透明导电膜的性能

以纯度为99.9%的98%(质量分数)ZnO、2%(质量分数)Al_2O_3陶瓷靶为溅射靶材,采用射频磁控溅射法在玻璃衬底上制备了Al_2O_3掺杂的ZnO薄膜。采用X射线衍射仪、扫描电子显微镜、紫外可见光谱仪等方法测试和分析了不同衬底温度、溅射偏压以及退火工艺对ZAO薄膜形貌结构、光电学性能的影响。结果表明,在衬底温度200℃、溅射时间30min、负偏压60V、退火温度300℃时制得的薄膜的可见光透过率为81%,最低电阻率为9.2×10~(-1)Ω·cm。     

N掺杂Cu2O薄膜的低温沉积及快速热退火研究

采用氧化亚铜(Cu_2O)陶瓷靶,利用射频磁控溅射沉积法在氮气和氩气的混合气氛下制备了N掺杂Cu_2O(Cu_2O∶N)薄膜,并在N_2气氛下对薄膜进行了快速热退火处理,研究了N_2流量和退火温度对Cu_2O∶N薄膜的生长行为、物相结构、表面形貌及光电性能的影响。结果显示,在衬底温度300℃、N_2流量12sccm条件下生长的薄膜为纯相Cu_2O薄膜;在N_2气氛下对预沉积薄膜进行快速热退火处理不影响薄膜的物相结构,薄膜的结晶质量随退火温度(450℃)的升高而显著改善;快速热退火处理能改善薄膜的结晶质量和缺陷,降低光生载流子的散射,增强载流子的传输,预沉积Cu_2O∶N薄膜经400℃退火处理后展示出较好的电性能,薄膜的霍尔迁移率(μ)为27.8cm~2·V~(-1)·s~(-1)、电阻率(ρ)为2.47×10~3Ω·cm。研究表明低温溅射沉积和快速热退火处理能有效改善Cu_2O∶N薄膜的光电性能。     

退火对ZnO/Cu/ZnO透明导电薄膜性能的影响

室温下利用磁控溅射制备了ZnO/Cu/ZnO透明导电薄膜,采用X射线衍射(XRD)、原子力显微镜(AFM)、扫描电子显微镜(SEM)、霍尔效应测量仪和紫外-可见分光光度计研究了薄膜的结构、形貌、电学及光学等性能与退火温度之间的关系。结果表明:退火前后薄膜均具有ZnO(002)择优取向,随着退火温度的升高,薄膜的晶化程度、晶粒粒径及粗糙度增加,薄膜电阻率先降低后升高,光学透过率和禁带宽度先升高后降低。150℃下真空退火的ZnO/Cu/ZnO薄膜的性能最佳,最高可见光透光率为90.5%,电阻率为1.28×10-4Ω·cm,载流子浓度为4.10×1021cm-3。     

磁控溅射ITO薄膜的退火处理

采用直流磁控溅射方法在室温下玻璃基板上制备ITO(Indium tin oxide)薄膜,并在真空中不同温度(100℃~400℃)下退火处理.研究了退火对薄膜表面形貌、电光特性的影响.XRD测试发现薄膜在200℃退火后结晶,优选晶向为(222).随退火温度升高,方块电阻迅速下降,表面更加平整,薄膜在可见光范围平均透过率提高到85%.     

连续离子层吸附与反应法(SILAR)生长ZnO多晶薄膜的研究

采用连续离子层吸附与反应法(SILAR),以锌氨络离子([Zn(NH₃)₄]²⁺)为前驱体溶液,在玻璃衬底上沉积了ZnO薄膜,以XRD和SEM等手段分析了薄膜的晶体结构和表面、断面形貌,考察了空气气氛下的退火过程对ZnO薄膜晶体结构与微观形貌的影响,并初步探讨了以SILAR方法沉积ZnO薄膜的机理.结果表明,经200次SILAR沉积循环,所得ZnO薄膜为红锌矿结构的多晶薄膜,沿<002>方向择优生长;薄膜表面致密、光滑均匀,厚度约800nm.退火处理使ZnO薄膜氧缺位减少,晶粒沿c轴取向增强;随退火温度升高,锌间隙原子增加;500℃退火时,ZnO薄膜发生再结晶.减小前驱体溶液的[NH₃·H₂O]/[Zn²⁺]比率可提高ZnO薄膜生长速率.     

退火条件对Sn掺杂ZnO薄膜光电性能的影响

采用溶胶-凝胶法在普通载玻片上制备Sn掺杂ZnO薄膜(SZO薄膜)。研究空气退火、低真空退火、高真空退火、氮气退火、三高退火、循环退火6种不同退火条件对SZO薄膜光电性能的影响。结果表明:6种不同的退火条件制备的SZO薄膜均为纤锌矿结构且具有c轴择优取向生长的特性。高真空退火下,SZO薄膜的结晶状况和电学性质最优,最低电阻率可达到5.4×10~(-2)Ω·cm。薄膜的可见光区平均透过率均大于85%。薄膜在390nm和440nm附近(325nm光激发下)都出现光致发光峰,在空气、氮气、低真空中退火后薄膜440nm处发光强度最为显著。     

退火温度对ZnO/Mo/ZnO透明导电薄膜结构及光电性能的影响

采用电子束蒸发法成功制备了透明导电的ZnO/Mo/ZnO(ZMZ)复合薄膜,研究了不同的退火温度对其电学和光学性质的影响规律。利用X射线衍射仪、扫描电子显微镜、X射线能谱仪、紫外可见分光光度计和四探针测试仪等检测手段对样品的性能进行了分析。实验结果表明:随着退火温度的升高,薄膜的结晶程度提高,晶粒尺寸增大;薄膜的电阻率先降低后升高;薄膜的光学透过率先升高后降低。当退火温度为250℃时,ZnO/Mo/ZnO薄膜具有最佳的综合光电性能,在400nm~900nm波长范围内最高透过率为81.4%,平均透过率高于80%,最低电阻率为1.71×10-4Ω·cm,表面电阻为15.5Ω/sq。研究表明所制备的ZMZ复合透明导电薄膜可应用于太阳能电池、液晶显示器等领域。     

Real gas choked flow conditions at low reduced-temperatures

Real gas choked mass flux is calculated for a frictionless stream expanding isentropically until it reaches the speed of sound and without phase changes. The other parameters associated with the choked state are the pressure, density, temperature ratios, and the speed of sound. Departure of the choked mass flux from the ideal gas model is discussed first in absolute terms and then in relative terms, using the Principle of Corresponding States, for gases with boiling points in the low temperature range. Reduced-stagnation pressures are examined up to values of 30 for hydrogen, neon, nitrogen, argon, methane, krypton, xenon, and R-14 and up to 100 for ⁴He. The corresponding reduced-stagnation temperatures go down to 1.4 and in some cases down to 1.2 for nitrogen and argon. Also discussed are the limiting values of stagnation parameters for which no phase change occurs in the choked state. Compared to the ideal gas, the mass flux may almost double and the critical pressure ratio may decrease by an order of magnitude. The relevance of results is discussed qualitatively and quantitatively for Joule-Thomson cryocooling.     

As-cast microstructures and behavior at high temperature of chromium-rich cobalt-based alloys containing hafnium carbides

Hafnium is often used to improve the high temperature oxidation resistance of superalloys but not to form carbides for strengthen them against creep. In this work hafnium was added in cobalt-based alloys for verifying that HfC can be obtained in cobalt-based alloys and for characterizing their behavior at a very temperature. Three Co–25Cr–0.25 and 0.50C alloys containing 3.7 and 7.4 Hf to promote HfC carbides, and four Co–25Cr– 0 to 1C alloys for comparison (all contents in wt.%), were cast and exposed at 1200 °C for 50 h in synthetic air. The HfC carbides formed instead chromium carbides during solidification, in eutectic with matrix and as dispersed compact particles. During the stage at 1200 °C the HfC carbides did not significantly evolve, even near the oxidation front despite oxidation early become very fast and generalized. At the same time the chromium carbides present in the Co–Cr–C alloys totally disappeared in the same conditions. Such HfC-alloys potentially bring efficient and sustainable mechanical strengthening at high temperature, but their hot oxidation resistance must be significantly improved.     

Degradation behaviour of sputtered Co–Al coatings on superalloy

Degradation behaviour of sputtered Co–Al coatings on Superni-718 substrate has been investigated. Cyclic high temperature oxidation tests were conducted on uncoated and coated samples at peak temperatures of 900 °C for up to 100 thermal cycles between the peak and room temperatures. The results showed that a dense scale formed on the coated samples during thermal cycling at the peak temperature of 900 °C. The external scale exhibited good spallation resistance during cyclic oxidation testing at both temperatures. The improvement in oxide scale spallation resistance is believed to be related to the fine-grained structure of the coating. Nanostructured Co–Al coatings on Superni-718 substrate were deposited by DC/RF magnetron sputtering. FE-SEM/EDS, AFM, and XRD were used to characterize the morphology and formation of different phases in the coatings, respectively. The Co–Al coating on superalloy substrate showed better performance of cyclic high temperature oxidation resistance due to its possession of β-CoAl phase as Al reservoir and the formation of Al₂O₃ and spinel phases such as CoCr₂O₄ and CoAl₂O₄ in scale. The oxidation results confirmed an improved oxidation resistance of the Co–Al coating on superalloy as compare to bare substrate in air at 900 °C temperature up to 100 cycles.     

Capacitance based mass metering for cryogenic fluids

This paper describes a method for measuring the mass of cryogenic fluids in on-board rocket propellant tanks or ground storage tanks. Linear approximations to the Clausius-Mossotti relationship serve as the foundation for a capacitance based mass sensor, regardless of fluid density stratification or tank shape. Sensor design considerations are presented along with the experimental results for a capacitance based mass gage tested in liquid nitrogen. This test data is shown to be consistent with theory resulting in a demonstrated mass measurement accuracy of ±0.75% and a deviation from linearity of less than ±0.30% of full scale mass. Theoretical accuracies are also shown to be ±0.73% for hydrogen and ±1.39% for oxygen for a select range of pressures and temperatures.     

Equipment using a “static-analytic” method for solubility measurements in potentially hazardous binary mixtures under cryogenic temperatures

A new apparatus designed to study, at cryogenic temperatures, thermodynamic equilibria of potentially explosive binary systems such as hydrocarbon-oxygen mixtures is described herein. This equipment has an equilibrium cell which was especially designed to minimize hazards while allowing accurate phase equilibrium measurements. Reliability of results, obtained with this equipment has been verified by working on the nitrogen-propane system, for which data are already available in literature, over a large range of compositions and at various temperatures. Four isothermal curves describing liquid phase compositions at 109.98, 113.77, 119.75 and 125.63 K have been determined. Our experimental data are represented within 2% in compositions and in pressures through the Peng-Robinson equation of state implying Mathias-Copeman alpha function and Huron-Vidal mixing rule. Comparisons to literature allow pointing out: good agreement is observed with Kremer and Knapp data (1983) while the three sets of Poon and Lu data (1974) presenting systematic positive deviation are consequently judged as suspicious.     

Thermal Stability of Amorphous Hydride Mg_(50)Ni_(50)H_(54) and Mg_(30)Ni_(70)H_(45)

The thermal stability of amorphous ternary hydrides Mg_(50)Ni_(50)H_(54) and Mg_(30)Ni_(70)H_(45) and their corre-sponding amorphous binary alloys Mg_(50)Ni_(50) and Mg_(30)Ni_(70) were studied with X-ray diffraction(XRD) and differential scanning calorimetry(DSC). Samples of the amorphous alloys were preparedby mechanical alloying and the amorphous hydrides were obtained by charging the alloys with gas-eous hydrogen at 3.0 MPa and 423 K. It was found that the amorphous hydrides released most oftheir hydrogen before the crystallization of the essentially hydrogen depleted amorphous alloy. Thecrystallization temperature of amorphous Mg_(50)Ni_(50)H_(54) elevated and that of amorphousMg_(30)Ni_(70)H_(45) did not change in relation to the original binary amorphous alloy. This is very excep-tional for amorphous hydrides. The reason for the effects of hydrogen absorption/desorption on thecrystallization of amorphous alloys was discussed.     

长余辉材料Sr_4Al_(14)O_(25)∶Eu~(2+),Nd~(3+)的溶胶凝胶法制备及性能研究

首次研究了以Nd~(3+)离子为辅助激活剂,对Eu~(2+)掺杂的发光材料Sr_4Al_(14)O_(25):Eu~(2+)余辉性能的影响.用溶胶凝胶法合成了Eu~(2+), Nd~(3+)共掺杂的Sr_4Al_(14)O_(25):Eu~(2+),Nd~(3+)发光粉末,并用扫描电镜、X射线衍射计、荧光分光光度计、余辉亮度测试仪、热释光剂量计等手段对粉末样品进行了表征.结果表明,在1350℃得到了单一的Sr_4Al_(14)O_(25)相,粉末颗粒平均粒度在1μm左右.Eu~(2+), Nd~(3+)共掺杂的Sr_4Al_(14)O_(25):Eu~(2+),Nd~(3+)发光粉末有402和485nm两个发射峰,与Eu~(2+)单掺杂的Sr_4Al_(14)O_(25):Eu~(2+)相比,发射峰位置没有变化,但适量的掺杂可以大大提高余辉时间和余辉亮度,余辉时间可达18h以上.最后通过对热释光谱的分析解释了双掺杂发光粉余辉性能增强的原因,适宜深度的陷阱可以有效存储光能,增强余辉的时间和强度.     

Development of No-Vent™ liquid hydrogen storage system for space applications

A number of technological advances required to store and maintain normal-boiling-point and densified cryogenic liquids, including liquid hydrogen, under zero boil-off conditions in-space, for long periods of time, have been developed. These technologies include (1) thermally optimized compact cryogen storage systems that reduce environmental heat leak to the lowest-temperature cryogen, which minimizes cryocooler size and input power, and (2) actively-cooled shields that surround the storage systems and intercept heat leak. The processes and tools used to develop these technologies are discussed. A zero boil-off liquid hydrogen storage system technology demonstrator for validating the actively-cooled shield technology is presented.     

链结构对偏氟乙烯铁电共聚物介电性质的影响

用改进的介电松弛谱仪(精度 2‰)测定了 VDF(52)/TrFE(48)和VDF(47.5)/TrFE(47.5)/HeFP(5)在-120—140℃,10~(-2)-10~4Hz 范围的复数介电常数。介电松弛研究结果显示5mol%的 HeFP 导致三元共聚物 T_c 下降(30℃),非晶松弛强度减弱,T_g 降低(3℃),并引起局域松弛活化能升高(10.1kJ/mol),松弛时间增长。     

Percolation and the resistive transition of the critical temperature Tc of Nb3Sn

The relationship between the distribution of the critical temperature, the percolation function, and the resistive transition of the critical temperature is explored for polycrystalline Nb₃Sn. In the neighborhood of the critical temperature, Nb₃Sn is assumed to be a random mixture of superconducting and normal grains. Percolation concepts are applied to a study of the resistivity. A general analysis is made showing that the onset and shape of the resistive transition for composite conductors are determined by the percolation function and the distribution of the critical temperature. An approximate form of the percolation function is determined based on a linear FEM analysis. Example resistive transitions are calculated for an assumed normal distribution of the critical temperature. An argument is presented that relates grain orientation and strain dependence in Nb₃Sn. It is noted that a dependence of the distribution of T_c with strain, in addition to the usual shift in T_c with strain, would be the result of a strain dependence that is a function of grain orientation. The analysis shows the extent to which the slope of the resistive transition is a measure of the distribution of the critical temperature, and therefore a measure of the grain orientation strain sensitivity. Finally, a method is described to determine the percolation function experimentally.