On the Evaporation of C60 in Vacuum and Inert Gases at Temperatures Between 830 K and 1050 K

The binary diffusion coefficient D_AB of subliming C₆₀ in He, N₂ and Ar gas has been determined at a gas pressure between 5 and 10 kPa. It resulted D_AB/(cm^2/s)=D_o(P_o/P_t(T/T_o)ⁿ as a function of the total pressure P_t of the vapor phase and temperature T. At T_o=273 K and P_o=1.0133×10⁵ P_a, the values D_o = (0.059±0.004) cm²/s, (0.011±0.003) cm²/s, (0.012±0.007) cm²/s, n = 1.77±0.06, 2.02±0.18, 1.77±0.37 were obtained for He, N₂, Ar and (830-1000) K, (800-1020) K, (875-1095) K, respectively. Only 40 wt% of the initial C₆₀ material yielded reliable D_AB where the vapor pressure of C₆₀ followed log₁₀(P/Pa) = -(8976±60)/T/K+(11.05±0.07) for T between 640 and 1055 K.     

铝酸盐的组成对钡钨阴极性能的影响

采用液相共沉淀法制备了612铝酸盐(n(BaO):n(CaO):n(Al₂O₃)=6:1:2)前驱粉末, 在不同气氛(H₂、CO₂、N₂)、不同温度(1300℃、1400℃、1500℃)焙烧制备铝酸盐, 系统研究了不同工艺制备的铝酸盐对钡钨阴极性能的影响。结果表明: 前驱粉末的最佳焙烧工艺为: H₂气氛、1500℃, 可获得主相为Ba₅CaAl₄O₁₂的铝酸盐, 用其制备的钡钨阴极发射电流密度可达12.2 A/cm², 蒸发速率仅为1.09×10^-8 g/(cm²?s)。     

A comparative study of low dielectric constant barrier layer, etch stop and hardmask films of hydrogenated amorphous Si-(C, O, N)

New barrier layer, etch stop and hardmask films, including hydrogenated amorphous a-SiC_x:H (SiC), a-SiC_xO_y:H (SiCO), and a-SiC_xN_y:H (SiCN) films with a dielectric constant (k) approximately 4.3, are produced using the plasma-enhanced chemical vapor deposition technique. The chemical and structural nature, and mechanical properties of these films are characterized using X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and nano-indentation. The leakage current density and breakdown electric field are investigated by a mercury probe on a metal-insulator-semiconductor structure. The properties of the studied films indicate that they are potential candidates as barrier layer, etch stop and hardmask films for the advanced interconnect technology. The SiC film shows a high leakage current density (1.3×10⁻⁷ A/cm² at 1.0 MV/cm) and low breakdown field (1.2 MV/cm at 1.0×10⁻⁶ A/cm²). Considering the mechanical and electrical properties requirements of the interconnect process, SiCN might be a good choice, but the N content may result in via poison problem. The low leakage current (1.2×10⁻⁹ A/cm² at 1.0 MV/cm), high breakdown field (3.1 MV/cm at 1.0×10⁻⁶ A/cm²), and relative high hardness (5.7 GPa) of the SiCO film indicates a good candidate as a barrier layer, etch stop, or hardmask.     

THE LASER CUTTING OF KEVLAR: A STUDY OF THE CHEMICAL BY-PRODUCTS

Several Kevlar (poly (p-phenylene terephthalamide), a product of E.I. Du Pont, Inc.) composites were cut with a CO₂ laser at a rate of 150 inches per minute and 1.0 kwatt of power (approximately 4.9×10⁵ watts/cm²). Atmospheric samples of the chemical by-products formed during the laser cutting were collected and analyzed by gas chromatography (GC), gas chromatography/massspectroscopy (GC/MS), and high pressure liquid chromatography (HPLC). A number of toxic and cancer-producing compounds were identified in the smoke plume produced; therefore, appropriate ventilation must be provided to insure the health and safety of personnel working in laser facilities processing Kevlar containing products.     

Growth and spectroscopy of Dy doped in ZnWO4 crystal

Single-crystal ZnWO₄:Dy³⁺ was grown by Czochralski technique. The XRD, absorption spectra as well as fluorescence spectrum are investigated and the Judd–Ofelt intensity parameters Ω₂, Ω₄, Ω₆ are obtained to be 7.76 × 10⁻²⁰ cm², 0.57 × 10⁻²⁰ cm², 0.31 × 10⁻²⁰ cm², respectively. Calculated radiative transition rate, branching ratios and radiative lifetime for different transition levels of ZnWO₄:Dy³⁺ crystals are presented. Fluorescence lifetime of ⁴F_9/2 level is 158 μs and quantum efficiency is 66%.The most intense fluorescence line at 575 nm correlative with transition ⁴F_9/2 → ⁶H_13/2 is potentially for application of yellow lasers.     

Up-conversion dynamics in GdAlO3:Er single crystal fibre

Green fluorescence has been obtained under continuous laser excitation in the 780–860 nm range in GdAlO₃:Er³⁺. With the help of the Judd-Ofelt treatment we built a model based on population rate equations to describe its time evolution. We found the intensity parameters to be Ω₂ = 2.045 × 10⁻²⁰ cm², Ω₄ = 1.356 × 10⁻²⁰ cm² Ω₆ = 1. 125 × 10⁻²⁰ cm². Even if a two-photon absorption and a looping mechanism are necessary to well describe the dynamics, the main process responsible for up-conversion is energy transfer between erbium ions.     

碳源组成对化学气相渗透C/C复合材料致密化及热解炭结构的影响

为分析碳源在化学气相渗透过程中的沉积机制,以碳纤维针刺整体毡为预制体,添加丙烯（C₃H₆）的天然气混合气体为碳源,研究了碳源组成对C/C复合材料致密化及热解炭结构的影响。结果表明:相比于以天然气为碳源,以添加了适当比例C₃H₆的天然气为碳源,可有效提高C/C复合材料的致密化速率及密度分布均匀性;同时,有利于生成高织构的热解炭。最优条件（9vol% C₃H₆）下沉积100 h后,C/C复合材料的密度和径向密度偏差分别为1.40 g/cm3和0.04 g/cm3,热解炭为均一的粗糙层结构,石墨化度高;而以天然气作碳源时,密度和径向密度偏差分别为1.17 g/cm3和0.07 g/cm3,热解炭为二元带状结构,石墨化度较低;当C₃H₆比例增加到17vol%时,其密度和径向密度偏差分别为1.28 g/cm3和0.10 g/cm3,密度及密度分布均匀性较最优条件下制备的复合材料明显降低。      

氧化铈空心球可控合成及其对Pt基催化剂电催化性能的影响

采用水热合成法, 以碳球为模板, 改变焙烧升温速率, 控制影响铈物种的扩散、渗透及碳球结构的收缩率, 制备了单、双壳层CeO₂空心球。通过微波辅助乙二醇还原氯铂酸法制备了Pt-CeO₂/RGO催化剂, 研究了CeO₂空心球的添加对Pt基催化剂电催化性能的影响。利用X射线衍射仪(XRD)、比表面积及孔径分析仪(BET)、扫描电镜(SEM)和电子能谱(EDAX)、透射电镜(TEM)、X射线光电子能谱(XPS)对CeO₂及催化剂的微观结构进行了表征, 利用电化学工作站对催化剂进行电化学性能测试。结果表明: 单、双壳层CeO₂空心球的比表面积为124.44 m²/g、140.95 m²/g, 孔容为0.014427 cm³/(g·nm)、0.018605 cm³/(g·nm), 孔径分布在2~4 nm范围内。催化剂中的CeO₂保持原有的球状形貌, Pt纳米粒子主要分布在CeO₂附近; 当RGO∶CeO₂=1∶2时, 添加了双壳层CeO₂空心球的Pt-CeO₂/RGO催化剂的电催化性能最优, 电化学活性表面积为94.27 m²/g, 对乙醇氧化的峰电流密度值为613.54 A/g, 1000 s的稳态电流密度值为135.45 A/g。     

Fabrication of robust Bi3.25La0.75Ti3O12 thin film resistant to hydrogen damage

Ferroelectric bismuth lanthanum titanate (Bi_3.25La_0.75Ti₃O₁₂; BLT) thin films were deposited on Pt/TiO₂/SiO₂/Si substrate by chemical solution deposition method. The films were crystallized in the temperature range of 600–700 °C. The spontaneous polarization (P_s) and the switching polarization (2P_r) of BLT film annealed at 700 °C for 30 min were 22.6 μC/cm² and 29.1 μC/cm², respectively. Moreover, the BLT capacitor did not show any significant reduction of hysteresis for 90 min at 300 °C in the forming gas atmosphere.     

Structural properties of swift heavy ion beam irradiated Fe/Si bilayers

The Fe/Si multilayers were prepared by electron beam evaporation in a cryo-pumped vacuum deposition system. Ag⁺ and Au⁺ ions of 100 MeV at two different fluencies such as 1 × 10¹² ions/cm² and 1 × 10¹³ ions/cm² at a pressure of 10^− 7 torr were used to irradiate the Fe/Si samples. The irradiated samples were analyzed by High-Resolution XRD and it reveals that the irradiated films are having polycrystalline nature and it confirms the formation of the β-FeSi₂. The structural parameters such as crystallite size (D), strain (ε) and dislocation density (δ) have been evaluated from the XRD spectrum. The role of the substrates and the influence of swift heavy ions on the formation of β-FeSi₂ have been discussed in this paper.     

MgCo_(2)O_(4)海胆状电极材料的制备及其电化学性能EI北大核心CSCD

采用水热法制得一种尖晶石型MgCo_(2)O_(4)海胆状电极材料,并通过X射线衍射(XRD)、X射线光电子能谱分析(XPS)、扫描电镜(SEM)、透射电镜(TEM)以及电化学工作站对产物进行了表征和电化学性能测试。通过改变所制备材料的水热反应时间,制备出团簇结构、分布较均匀以及密集度较高的MgCo_(2)O_(4)海胆状形貌。结果表明,当水热反应时间为6 h时所获得的MgCo_(2)O_(4)电极材料结构较为完善、尺寸较为均匀、电化学性能较为优异,而且在电流密度为1 mA/cm^(2)情况下,面积比电容高达6.75 F/cm^(2)。另外,对该MgCo_(2)O_(4)海胆状材料在20 mA/cm^(2)的电流密度下循环1000周次后,面积比电容保持为原来的88.4%,表现出良好的循环性能。     

Excited-state absorption at 1.57 μm in U:CaF2 and Co:ZnSe saturable absorbers

Appreciable excited-state absorption (ESA) in U²⁺:CaF₂ and Co²⁺:ZnSe saturable absorbers was measured at λ=1.573 μm by optical transmission versus light fluence curves of 30–40 ns long pulses. The ground- and excited-state absorption cross-sections obtained were (9.15±0.3)×10⁻²⁰ and (3.6±0.2)×10⁻²⁰ cm², respectively, for U²⁺:CaF₂, and (57±4)×10⁻²⁰ and (12.5±1)×10⁻²⁰ cm² for Co²⁺:ZnSe. Thus, ESA is not negligible in U²⁺:CaF₂ and Co²⁺:ZnSe, as previously estimated.     

Investigation of stress behaviors and mechanism of void formation in sputtered TiSix films

We have investigated the stress behaviors and a mechanism of void formation in TiSi_x films during annealing. TiSi_x thin films were prepared by DC magnetron sputtering using a TiSi_2.1 target in the substrate temperature range of 200–500 °C. The as-deposited TiSi_x films at low substrate temperature (<300 °C) have an amorphous structure with low stress of 1×10⁸ dynes/cm². When the substrate temperature increases to 500 °C, the as-deposited TiSi_x film has a mixture of C49 and C54 TiSi₂ phase with stress of 8×10⁹ dynes/cm². No void was observed in the as-deposited TiSi_x film. Amorphous TiSi_x film transforms to C54 TiSi₂ phase with a random orientation of (311) and (040) after annealing at 750 °C. The C49 and C54 TiSi₂ mixture phase transforms to (040) preferred C54 TiSi₂ phase after annealing over 650 °C. By increasing substrate temperature, the transformation temperature for C54 TiSi₂ can be reduced, resulting in relieved stress of TiSi₂ film. The easy nucleation of the C54 phase was attributed to an avoidance of amorphous TiSi_x phase. We found that amorphous TiSi_x→C54 TiSi₂ transformation caused higher tensile stress of 2×10¹⁰ dynes/cm², resulting in more voids in the films, than C49→C54 transformation. It was observed that void formation was increased with thermal treatment. The high tensile stress caused by volume decreases in the silicide must be relieved to retard voids and cracks during C54 TiSi₂ formation.     

Ba0.5Sr0.5Co0.8Fe0.2O3-δ-Ce0.9Gd0.1O2-δ中低温固体氧化物燃料电池复相阴极的研究

采用溶胶-凝胶法制备Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ(BSCF)粉体后, 使用Ce_0.9Gd_0.1O_2-δ(GDC)溶胶包裹BSCF粉的方法制备疏松多孔的BSCF-xGDC(x=30wt%, 40wt%, 50wt%)复相阴极。通过X射线衍射仪、场发射扫描电镜和透射电镜对复相阴极的物相组成、单电池断面形貌及GDC对BSCF颗粒的包裹形貌进行表征。利用阻抗谱测试研究了复相阴极材料的电化学性能, 讨论了掺入GDC量对阴极性能的影响。结果表明：通过GDC溶胶包裹BSCF粉体的制备方法改善了阴极的电化学性能, 在同一温度下, BSCF-40GDC阴极的极化电阻最小, 在650℃时阴极极化阻抗约为0.397 Ω•cm²; 以BSCF-40GDC为阴极制备的单电池, 以H₂+3%H₂O为燃料气、空气为氧化气体, 650℃下电池的最大功率密度为0.514 W/cm², 欧姆电阻为0.257 Ω•cm², 两极极化电阻为0.0588 Ω•cm²。     

α籽晶促进低温反应溅射沉积α-Al2O3薄膜

分别使用反应溅射Al+α-Al₂O₃(15% α-Al₂O₃,质量分数)复合靶和在金箔基体表面预植α-Al₂O₃籽晶,促进α-Al₂O₃薄膜的低温沉积。使用扫描电子显微镜(SEM)、掠入射X射线衍射(GIXRD)和能谱仪(EDS)等方法表征薄膜样品的表面形貌、相结构和元素组成。结果表明,在射频反应溅射Al+α-Al₂O₃复合靶、沉积温度为560℃条件下能在Si(100)基体上沉积出化学计量比的单相α-Al₂O₃薄膜;使用射频反应溅射Al靶、沉积温度为500℃条件下能在预植α-Al₂O₃籽晶(籽晶密度为10⁶/cm²)的金箔表面沉积出化学计量比的单相α-Al₂O₃薄膜。两种研究方案的结果均表明,α-Al₂O₃籽晶能促进低温沉积单相α-Al₂O₃薄膜。     

Anomalous elastic response of amorphous alloys suggesting collective motions of many atoms

The dynamic Young’s modulus, E, of amorphous (a-) Zr₆₀Cu₃₀Al₁₀ (numbers indicate at.%) alloy was measured as a function of frequency, f, with a strain amplitude, _t, of 10⁻⁶, E(10⁻⁶,f), and also as a function of _t for f near 10² Hz, E(_t,10² Hz), by means of the vibrating reed methods. The elasticity study under the passing of electric current (PEC) was carried out too. E(10⁻⁶,f) is lower than E₀ for f between 10 and 10⁴ Hz showing local minima near 5×10, 5×10² and 5×10³ Hz, which are indicative of the resonant collective motion of many atoms, where E₀ is the static Young’s modulus. E(_t,10² Hz) increases showing saturation with increasing _t. Qualitatively, the outlines of E(10⁻⁶,f) and E(_t,10² Hz) observed for a-Zr₆₀Cu₃₀Al₁₀ are similar to those reported for various a-alloys. Quantitatively, a change in E(_t,10² Hz) for a-Zr₆₀Cu₃₀Al₁₀ is smallest among that reported for various a-alloys, presumably reflecting that the crystallization volume, (ΔV/V)_x, is smallest for a-Zr₆₀Cu₃₀Al₁₀. The effective charge number, Z^*, estimated from the change in E(10⁻⁶,10² Hz) due to PEC is 3.0×10⁵, which is comparable with Z^* reported for various a-alloys. We surmise that the number of atoms in the collective motions excited near 10² Hz is similar among various a-alloys. The E(10⁻⁶,f) data suggest that the spatial sizes of the density fluctuations may show a distribution.     

水热法合成锌空气电池氧还原二氧化锰催化剂

在180℃下通过改变K⁺与H⁺摩尔比使用水热法分别制备了δ-MnO₂, α-MnO₂和β-MnO₂ 纳米颗粒, K⁺与H⁺摩尔比分别为3.4、0.85和0.24。所合成的样品通过扫描电子显微镜(SEM), 粉末X射线衍射(XRD), 傅里叶变换红外光谱(FTIR), BET比表面分析, 热重分析(TG)和电化学方法表征。结果表明: K⁺与H⁺的浓度对产品的晶型、形貌以及比表面积有很大影响; 将这三种材料作为锌空电池的阴极材料时, δ-MnO₂与α-MnO₂的电化学性能明显优于β-MnO₂. 在–0.35 V下, δ-MnO₂、α-MnO₂和β-MnO₂的氧还原电流分别为56.28、56.01和40.88 mA/cm²。     

Switching and filament formation in hot-wire CVD p-type a-Si:H devices

We fabricate metal/a-Si/metal thin film switches which incorporate hot-wire chemical vapor deposition (HWCVD) Si layers. A H-diluted gas mixture is used to grow the B-doped, 1000 Å hydrogenated amorphous silicon (a-Si:H) layers at approximately 10 Å/s. We compare switching behavior in Cr/a-Si:H(p)/Ag and c-Si(p)/a-Si:H(p)/Ag structures containing p-type hydrogenated amorphous silicon. We observed that the switching is polarity-dependent only in the sample on c-Si(p). Switching to a low-resistance state occurs at 0.4 mA/cm² when any of the metal contacts are biased positive. When the c-Si(p) is biased positive holes are injected and no switching occurs even up to 4 A/cm². We suggest that the switching requires a blocking metal/a-Si(p) contact, possibly because local electrical breakdown initiates metal filament formation.     

Improved fatigue properties of lead zirconate titanate films made on oxygen-implanted platinum electrodes

Pb(Zr_0.3Ti_0.7)O₃ (PZT) thin film capacitors fabricated on an oxygen-implanted Pt bottom electrode were studied. Oxygen was implanted at a low acceleration voltage (40 kV) and dose (1×10¹⁵ cm⁻²). Structural examination by grazing-incident X-ray diffraction (GIXD) and chemical analysis by X-ray photoelectron spectroscopy (XPS) revealed that the implantation generated a very thin amorphous top surface layer (approx. 20 nm), which contained approximately 7% of oxygen that stayed in the film in the form of PtO bonding. The amorphous layer, however, resumed the crystalline structure accompanied by the dissociation of PtO under the rapid thermal annealing at 600 °C for 5 min. The remnant polarization of sol–gel derived Pb(Zr_0.3Ti_0.7)O₃ (PZT) films fabricated on the oxygen-implanted Pt was slightly reduced from 11.92 μC/cm² for the PZT capacitors fabricated on a Pt electrode without implanted oxygen to 9.07 μC/cm². Nevertheless, the fatigue endurance was significantly increased. The switching polarization of PtO_x/PZT/Pt (O-implanted) capacitors remained within 95% of the starting value after 4×10¹⁰ switching cycles, which is comparable to that of PZT capacitors made with other conducting oxides.     

磷酸处理对多孔SiO2薄膜质子导电特性和双电层薄膜晶体管性能的影响

采用等离子体增强化学气相沉积法(PECVD)制备了多孔SiO₂薄膜, 系统地研究了不同浓度磷酸处理对多孔SiO₂薄膜的质子导电特性、双电层电容和以此多孔SiO₂薄膜为栅介质的铟锌氧(IZO)双电层薄膜晶体管性能的影响。结果表明: 多孔SiO₂薄膜的质子电导率和双电层电容随磷酸浓度升高而增大, 60%浓度磷酸处理后多孔SiO₂薄膜质子电导率和双电层电容分别达到1.51×10^-4 S/cm和6.33 μF/cm²。随磷酸浓度升高, 双电层薄膜晶体管的工作电压降低, 并且, 电流开关比也变大。其中60%浓度磷酸处理后器件工作电压为1.2 V, 迁移率为20 cm²/(V·s), 电流开关比为4×10⁶。这种双电层薄膜晶体管有望应用在化学和生物传感等领域。