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.     

Fabrication of excimer laser annealed poly-Si thin film transistor by using an elevated temperature ion shower doping

We have investigated the effect of an ion shower doping of laser annealed poly-Si films at elevated substrate temperatures. The substrate temperature was varied from room temperature to 300°C when the poly-Si film was doped with phosphorus by a non-mass-separated ion shower. Optical, structural, and electrical characterizations have been performed in order to study the effect of the ion shower doping. The sheet resistance of the doped poly-Si films was decreased from 7 × 10⁶ Ω/sq to 700 Ω/sq when the substrate temperature was increased from room temperature to 300°C. This large change in sheet resistance is due to the fact that the doped films do not become amorphous but remain in the polycrystallinephase. The mildly elevated substrate heating appears to contribute mainly to reduction of ion damages incurred in the poly-Si films in addition to the activation of dopants during the ion shower doping. From the fabricated n-channel poly-Si TFTs, the current crowding effect do not occur because of the low contact source-drain resistance and the field effect mobility of 120 cm²/(V s) has been obtained.     

Porous Titania Thin Films Grown by Anodic Oxidation for Hydrogen Sensors

Porous titanium dioxide (Titania) thin films were grown by anodic oxidation using high purity (99.7%) titanium foil in a dilute sulphuric acid (1 M) medium. The anodization process was carried out for 30 minutes with 20 mA/cm² and 50 mA/cm² current densities. The samples were characterized by XRD, SEM, and AFM techniques. It was found that the grown porous titania films were less sensitive to 500 ppm hydrogen in air ambient below 300°C; however, the sensitivity and response behavior of the film at 300°C are very much dependent on the growth conditions. Particularly, the films grown at current density 50 mA/cm² and 1 M acid concentration exhibited the lowest response time of 151 sec at 300°C.     

Epitaxial Si-based tunnel diodes

Tunneling devices in combination with transistors offer a way to extend the performance of existing technologies by increasing circuit speed and decreasing static power dissipation. We have investigated Si-based tunnel diodes grown using molecular beam epitaxy (MBE). The basic structure is a p⁺ layer formed by B delta doping, an undoped spacer layer, and an n⁺ layer formed by Sb delta doping. In the n-on-p configuration, low temperature epitaxy (300–370°C) was used to minimize the effect of dopant segregation and diffusion. In the p-on-n configuration, a combination of growth temperatures from 320 to 550°C was used to exploit the Sb segregation to obtain a low Sb concentration in the B-doped layer. Post-growth rapid thermal anneals for 1 min in the temperature interval between 600 and 825°C were required to optimize the device characteristics. J_p, the peak current density, and the peak-to-valley current ratio (PVCR), were measured at room temperature. An n-on-p diode having a spacer layer composed of 4 nm Si_0.6Ge_0.4, bounded on either side by 1 nm Si, had a J_p=2.3 kA/cm² and PVCR=2.05. A p-on-n tunnel diode with an 8 nm Si spacer (5 nm grown at 320°C, 3 nm grown at 550°C) had a J_p=2.6 kA/cm² and PVCR=1.7.     

High deposition rate of amorphous silicon thick layers using a gas mixture of 10% silane in hydrogen

The deposition rate of amorphous silicon of the order of 0.9 μm/h, has been obtained using a gas mixture of 10% silane (SiH₄) in hydrogen (H₂), with a RF source of 13.56 MHz. Best films were deposited at a total flow rate of 100–200 sccm, 300°C substrate temperature, 66.7 Pa, and RF power density of 150 mW/cm². The geometrical configuration of the reaction chamber included a gas injector that was specially designed for this purpose. Films were characterized by Fourier transform infrared (FTIR), secondary ion mass spectrometry (SIMS), and profilometer. In addition, thick p-i-n diodes were prepared and characterized, obtaining reverse current densities lower than 5×10⁻⁶ A/cm² at full depletion.     

Direct liquid injection metal-organic chemical vapor deposition of HfO2 thin films using Hf(dimethylaminoethoxide)4

Hf(OCH₂CH₂NMe₂)₄, [Hf(dmae)₄] (dmae=dimethylaminoethoxide) was synthesized and used as a chemical vapor deposition precursor for depositing Hf oxide (HfO₂). Hf(dmae)₄ is a liquid at room temperature and has a moderate vapor pressure (4.5 Torr at 80 °C). It was found that HfO₂ film could be deposited as low as 150 °C with carbon level not detected by X-ray photoelectron spectroscopy. As deposited film was amorphous but when the deposition temperature was raised to 400 °C, X-ray diffraction pattern showed that the film was polycrystalline with weak peak of monoclinic (020). Scanning electron microscope analysis indicated that the grain size was not significantly changed with the increase of the annealing temperature. Capacitance–voltage measurement showed that with the increase of annealing temperature, the effective dielectric constant was increased, but above 900 °C, the effective dielectric constant was decreased due to the formation of interface oxide. For 500 Å thin film, the dielectric constant of HfO₂ film annealed at 800 °C was 20.1 and the current–voltage measurements showed that the leakage current density of the HfO₂ thin film annealed at 800 °C was 2.2×10⁻⁶ A/cm² at 5 V.     

Low-temperature, direct synthesis of β-SiC by metal vapor vacuum arc ion source implantation

Crystalline β-SiC surface layers with strong (111) preferred orientation were synthesized by direct ion implantation into Si(111) substrates at a low temperature of 400°C using a metal vapor vacuum arc ion source. Both X-ray diffraction and Fourier transform infrared spectroscopy reveal an augment in the amount of β-SiC with increasing implantation doses at 400°C. Scanning electron microscopy shows the formation of an almost continuous SiC surface layer after implantation at 400°C with a dose of 7×10¹⁷/cm². The full width at half maximum of the X-ray rocking curve of β-SiC(111) was measured to be 1.4° for the sample implanted at a dose of 2×10¹⁷/cm² at 700°C, revealing a good alignment of β-SiC with the Si matrix.     

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.     

Electrical properties of evaporated polycrystalline Ge thin-films

Electrical properties of Ge thin films evaporated on Si₃N₄ CVD-coated Si substrate were improved by introducing a heat treatment after the deposition of Ge films. Evaporation conditions were optimized by changing the substrate temperature and deposition rate, and then, heat treatment was performed. At substrate temperatures during the evaporation lower than 300 °C and higher than 400 °C, deposited films were amorphous and polycrystalline, respectively. At substrate temperatures lower than 400 °C, Ge films were evaporated without degrading the surface roughness. The Hall mobility of films evaporated at room temperature increased with increasing the substrate and heating temperature and showed about 400 cm² V⁻¹ s⁻¹ for the hole concentration of 4 × 10¹⁷ cm⁻³ at the heating temperature of 900 °C. This value was almost comparable to that of p-type Ge single crystal.     

Electropolishing of Al-7Si-0.3Mg cast alloy by using perchloric and nitric acid electrolytes

The aim of the present study was to find a good method for electropolishing Al-7Si-0.3Mg cast alloy. Consideration of the fundamental current density-voltage relation and limiting current density has made it possible to identify an optimum applied voltage for good electropolishing through variation of different parameters (electrolyte, bath temperature, electrode distance, surface roughness before polishing, cathode material, etc.). The significant findings of the present study are that (1) using 30% perchloric acid + 20% glycerol moderator + 50% methanol electrolyte, (2) maintaining 15 mm electrode distance and a temperature of −33 °C, and (3) electropolishing the Al-7Si-0.3Mg cast alloy at 15 V for 2 minutes reveal the microstructures clearly. The limiting current density is about 7 mA/cm² for the preceding conditions for attaining good electropolishing. Electropolishing can also be achieved under the same conditions even at room temperature (26 °C), but the clarity of the microstructure is not as good as that obtained through electropolishing at −33 °C.     

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.     

304不锈钢表面纳米铝改性有机硅涂层的高温氧化和电化学行为

研究了纳米铝改性有机硅高温涂层的固化、抗650℃高温氧化性能和耐3.5% NaCl水溶液电化学腐蚀性能。当聚氨酯:有机硅的质量分数达到1:3或更高时,有机硅涂料可以在24 h内完成常温固化。制备出的纳米铝改性有机硅高温涂层表面致密,没有微观裂纹等缺陷。纳米铝改性的有机硅涂层显著提高了304不锈钢抗氧化性能,经1028 h氧化实验,基体几乎没有发生氧化,涂层没有出现开裂和剥落。纳米铝改性的有机硅涂层还显著提高了氧化后的304不锈钢耐氯化钠水溶液腐蚀性能,无涂层的304不锈钢氧化后形成的氧化膜低频阻抗仅3.2 Ω·cm²,而涂装涂层的不锈钢的低频阻抗约为1.1×10⁵ Ω·cm²。     

The effect of thermal annealing on aerosol-gel deposited SiO2 films: a FTIR deconvolution study

Aerosol-gel process has been used for the deposition of SiO₂ thin films. Layers were deposited from a solution with pH = 3.5 and water to TEOS molar ratio (rw) 2.2 and then treated at various temperatures ranging from room temperature to 700°C. As-prepared thin films have been characterized by FTIR spectroscopy. Spectra were acquired in transmission at 65° angle of incidence or at perpendicular incidence. Characteristic absorption bands of the SiO₂ sol-gel system have been studied with respect to the posttreatment temperature. Bands located at 1250–1000 cm⁻¹ and around 960 cm⁻¹ have been deconvoluted in several peaks. The origin and temperature dependence of these peaks are discussed.     

The low field electron mobility of tetramethylsilane

The room temperature low field electron mobility of tetramethylsilane was measured to be 111±4 cm² s⁻¹ V⁻¹.     

Semiconducting and structural properties of CrSi2 A-type epitaxial films on Si(111)

Chromium disilicide (CrSi₂) films 1 000 Å thick have been prepared by molecular beam epitaxy on CrSi₂ templates grown on Si(111) substrate. The effect of the substrate temperature on the structural, electrical and optical properties of CrSi₂ films has been studied by transmission and scanning electron microscopies, optical microscopy, electrical resistivity and Hall effect measurements and infrared optical spectrometry. The optimal temperature for the formation of the epitaxial A-type CrSi₂ film have been found to be about 750°C. The electrical measurement have shown that the epitaxial A-type CrSi₂ film is p-type semiconductor having a hole concentration of 1 × 10¹⁷cm⁻³ and Hall mobility of 2 980 cm² V⁻¹ s⁻¹ at room temperature. Optical absorption coefficient data have indicated a minimum, direct energy gap of 0.34 eV. The temperature dependence of the Hall mobility (μ) in the temperature range of T = 180–500 K can be expressed as μ = 7.8 × 10¹⁰T⁻³cm²V⁻¹s⁻¹.     

Characterization of SnS films prepared by constant-current electro-deposition

SnS films have been prepared on the indium tin oxide coated glass substrates by the constant-current electro-deposition. By investigating the influence of the deposition parameters on the composition of the deposited films, we obtained the optimum deposition parameters with pH = 2.7, Sn²⁺ / S₂O₃²⁻ = 1 / 5, J = 3.0 mA/cm² and t = 1.5 h. Many nearly stoichiometric SnS films were prepared. These films were characterized with X-ray diffraction and scanning electron microscopy analysis, and they were polycrystalline with orthorhombic structure. Their direct band gaps were estimated to be 1.211.42 eV from optical measurements. The films have p-type conductivity with a resistivity of 7.520 Ω·cm.     

Investigation of nanostructured lipid carriers for transdermal delivery of flurbiprofen

The aim of this study was to develop nanostructured lipid carriers (NLC) for transdermal delivery of Flurbiprofen (FP). The physical stability of FP-NLC and its in vitro permeation profile were investigated. After three months of storage at 4°C, 20°C, and 40°C, no significant differences between the evaluated parameters, such as pH value, the entrapment efficiency, particle size, and zeta potential were observed. In in vitro permeation studies, the cumulative permeated amounts and the release rate from FP-NLC were 412.53 ± 21.37 μg/cm² and 35.25 μg/cm²/h after 12 h (n = 6), respectively, while from saturated FP-PBS (pH = 7.4) were 90.83 ± 8.67 μg/cm² and 6.99 μg/cm²/h, respectively. These results indicated that the FP-NLC were with good physical stability and were able to improve the permeated amounts and the release rate of FP. It could potentially be exploited as a carrier with improved drug entrapment efficiency and permeated amount in the transdermal delivery of FP.     

Effect of negatively charged species on the growth behavior of silicon films in hot wire chemical vapor deposition

The deposition behavior of silicon in hot wire chemical vapor deposition was investigated, focusing on the generation of negatively charged species in the gas phase using a gas mixture of 20% SiH₄ and 80% H₂ at a 450 °C substrate temperature under a working pressure of 66.7 Pa. A negative current of 6–21 µA/cm² was measured on the substrate at all processing conditions, and its absolute value increased with increasing wire temperature in the range of 1400 °C–1900 °C. The surface roughness of the films deposited on the silicon wafers increased with increasing wire temperature in the range of 1510 °C–1800 °C. The film growth rate on the positively biased substrates (+ 100 V, + 200 V) was higher than that on the neutral (0 V) and negatively biased substrates (− 100 V, − 200 V, − 300 V). These results indicate that the negatively charged species are generated in the gas phase and contribute to deposition. The surface roughness evolved during deposition was attributed to the electrostatic interaction between these negatively charged species and the negatively charged growing surface.     

镍掺杂四氧化三钴纳米线阵列的制备及其超级电容特性

采用直流电化学沉积与高温氧化相结合的合成方法, 在氧化铝模板的辅助下, 成功制备了一种新颖的Ni掺杂的Co₃O₄纳米线阵列, 利用X射线衍射仪、扫描电镜和高分辨透射电镜等对所制备的纳米线阵列的物相和形貌进行了表征, 结果表明：所制备的Ni掺杂Co₃O₄纳米线形貌和尺寸均匀、垂直于基底排列, 纳米线的平均直径约为80 nm, 长度约为1.4 μm, 整个纳米线由纳米颗粒堆积而成, 其中Co : Ni的比例约为20 : 1。利用循环伏安和恒流充放电技术在2 mol/L的KOH电解液中对材料的电化学性能进行了测试, 结果显示所制备的纳米线阵列具有优异的电化学电容特性, 当电流密度为10 mA/cm²时, 纳米线阵列的面积比电容为173 mF/cm², 经过1000次充放电后, 比电容值仍能保持最初值的98%, 表现出良好的循环稳定性。优异的性能可归因于材料的比表面积较大以及镍掺杂后材料导电特性的提高。