Characteristics of Er-doped Al2O3 thin filmsdeposited by reactive co-sputtering

Er-doped Al₂O₃ thin films have been deposited by reactive co-sputtering onto thermally oxidized Si-wafers. The deposition process has been optimized with respect to the requirements originating from the application of these multilayer structures as integrated optical amplifiers for the third telecom window, i.e., the wavelength range 1.52-1.55 μm. The films obtained at a substrate temperature of only 400°C are amorphous and show a homogenous structure, without columns or grains. For slabguides, background losses smaller than 0.25 dB/cm have been obtained, even without any annealing. A relatively broad luminescence band, having an FWHM of ~55 nm around the 1.533-μm wavelength, has been measured. From gain versus pumping power curves, an upconversion coefficient lower then 20·10^-25 m³/s has been derived, being half of the values reported up to now in the literature. Simulations based on experimentally determined material parameters and assuming a channel attenuation of 0.5 dB/cm indicate, for 0.24 at.% Er channel devices with an optimal channel length of 7.7 cm, an amplification of 8 dB at 1.533 μm for a pump wavelength of 1.48 μm, and a pump power of only 8.7 mW     

二氧化钛掺杂系统的电子结构和光学性质的研究

采用总能量平面波赝势方法研究了Sc掺杂、含氧空位、氧空位与Sc掺杂共存时的锐钛矿TiO2系统的电子结构和光学性质。结果表明,Sc掺杂对系统的主要贡献在价带区,在可见光区有明显的光吸收;氧空位可以使系统发生莫特相变,系统在可见光区也有较强的吸收;氧空位与Sc掺杂共存时系统在可见光区的吸收相干加强。     

Study of LDPE/TiO2 and PS/TiO2 Composites as Potential Substrates for Microstrip Patch Antennas

Low-density polyethylene (LDPE)/titania (TiO₂) and polystyrene (PS)/titania (TiO₂) composite systems have been developed as alternative substrates for microstrip patch antennas (MPA) for handheld devices. Morphological, thermal, and microwave characterizations of these composites have been conducted for different volume fractions of TiO₂ in the polymer matrix. The size of the titania particles was found to be of the order of 0.5 μm, and their distribution in the composite was quite uniform. Composite materials showed an improvement in thermal and microwave properties over the parent polymer. Verification of these composites as potential substrates for MPA was carried out by fabricating simple rectangular patch X-band antennas. Materials with optimized substrate properties were chosen to design the MPA. The patches were designed with 4% volume fraction TiO₂ in the LDPE composite system and 6% volume fraction TiO₂ in the PS composite system. Return loss of ∼18 dB was observed for both systems.     

TiO2/SiO2多层膜系一维光子晶体缺陷态特性研究

建立了一种基于TiO2/SiO2多层膜系并含缺陷层的一维光子晶体模型。基于时域有限差分(FDTD)算法,对其基本层周期数,缺陷层位置、光学厚度以及不同材料等情况下的带隙特性在理论上进行了系统的模拟与分析,发现这种一维光子晶体的缺陷态的透过率和带隙宽度受基本层周期数、缺陷层所在位置和材料的影响较大,而缺陷态中心波长位置仅由缺陷层的光学厚度决定。     

Electrical properties of SiO2/TiO2 high-k gate dielectric stack

The trapping/detrapping behavior of charge carriers in ultrathin SiO₂/TiO₂ stacked gate dielectric during constant current (CCS) and voltage stressing (CVS) has been investigated. Titanium tetrakis iso-propoxides (TTIP) was used as the organometallic source for the deposition of ultra-thin TiO₂ films at low temperature (<200 °C) on strained-Si/relaxed-Si_0.8Ge_0.2 heterolayers by plasma-enhanced chemical vapor deposition (PECVD) in a microwave (700 W, 2.45 GHz) plasma cavity discharge system at a pressure of 66.67 Pa. Stress-induced leakage current (SILC) through SiO₂/TiO₂ stacked gate dielectric is modeled by taking into account the inelastic trap-assisted tunneling (ITAT) mechanism via traps located below the conduction band of TiO₂ layer. The increase in the gate current density observed during CVS from room temperature up to 125 ^oC has been analyzed and modeled considering both the buildup of charges in the layer as well as the SILC contribution. Trap generation rate and trap cross-section are extracted. A capture cross-section in the range of 10⁻¹⁹ cm² as compared to 10⁻¹⁶ cm² in SiO₂ has been observed. A temperature-dependent trap generation rate and defects have also been investigated using time-dependent current density variation during CVS. The time dependence of defect density variation is calculated within the dispersive transport model, assuming that these defects are produced during random hopping transport of positively charge species in the insulating high-k stacked layers. SILC generation kinetics, i.e. defect generation probability under different injected fluences for various high-constant stress voltages in both polarities have been studied. An empirical relation between trap generation probability and applied stress voltage for various injected fluences has been developed.     

Effect of the top electrode material on the resistive switching of TiO2 thin film

Effect of the top electrode (TE) metal on the resistive switching of (TE)/TiO₂/Pt structure was investigated. It was confirmed that the potential barrier height between the metal and TiO₂ is an important factor on the resistive switching characteristics. When high Schottky barrier was formed with the TiO₂ film, using Pt or Au as a top electrode, both stable URS (unipolar) and BRS (bipolar resistive switching) characteristics were observed depending on the current compliance level. In the case of Ag, which forms a relatively low Schottky barrier, only BRS characteristics were observed, regardless of the current compliance level. In the case of Ni and Al, which have similar work function as Ag, unstable URS and BRS at very low current compliance levels were observed due to a chemical reaction at the interface. For the Ti electrode, resistive switching was not observed, because the work function of Ti is lower than that of TiO₂ and TiO phase was formed at the interface (Ti/TiO_x contact is ohmic).     

Mixtures of iron and anatase TiO2 by mechanical alloying

Fe-doped TiO₂ powders were obtained by mechanical alloying. The starting materials were anatase TiO₂ and metallic iron (α-Fe) or hematite (α-Fe₂O₃). The influence of different milling conditions such as: ball to powder weight ratio, milling time, rotation velocity of supporting disc, and dopant concentration on the structural and magnetic properties were investigated. All experiments were performed in atmospheric conditions. The milled powders were characterized by X-ray diffraction (XRD) using Rietveld refinement and room temperature Mössbauer spectrometry. The XRD patterns of all samples show the coexistence of both anatase and rutile phases and also the high-pressure srilankite phase. Mössbauer spectra reveal the presence of Fe²⁺ and Fe³⁺ states in Fe-doped TiO₂ as well as α-Fe or α-Fe₂O₃ in samples obtained from metallic iron or hematite, respectively. The Fe³⁺ contribution could be attributed to Fe incorporated in the TiO₂ structure and the Fe²⁺ can be probably assigned to surface ferrous ions in the TiO₂.     

可用于探测大气CO2垂直廓线的无线传感系统

大气CO2是一种温室气体,在气候变化等领域起着关键作用。基于NDIR技术研制了可用于探测大气CO2垂直廓线的无线传感系统。系统采用电调制型的红外辐射光源、双通道探测器并结合超低功耗单片机实现大气CO2信号的采集与控制。提出采用调制信号周期内扣除信号起伏与背景噪声的方法,使得本系统具有0.29%的相对测量误差。通过分时工作的方式解决了数字式无线电探空仪中高频发射机对CO2检测电路运算放大器的电磁辐射干扰,进而实现了气象探空仪与小型化的CO2探测系统的高度集成。通过与地面LI-COR LI7500对比分析,两者表现出较好的一致性,24 h测量数据的相关性达0.89,表明所研制的探测系统的稳定性与准确性。为实现大气CO2垂直廓线的探测提供一种选择。     

Photoelectrochemical performance of La3+-doped TiO2

La-doped TiO₂ thin films on titanium substrates were prepared by the sol-gel method with titanium tetrachloride as a precursor and La₂O₃ as a source of lanthanum. The heat-treatment temperature dependence of the photoelectrochemical performance of the La-doped TiO₂ film in 0.2 mol/L Na₂SO₄ was investigated by the Mott-Schottky equation, electrochemical impedance spectroscopy, and the open-circuit potential test. The results from the Mott-Schottky curves show that the obtained films all were n-type semiconductors, and the film at 300 ℃ had the highest conduction band position and the widest space charge layer. The electrochemical impendence spectroscopy (EIS) tests of the 300 ℃ film decreased most during the change from illuminated to dark. The potential of the La-TiO₂ thin film electrode was the lowest after the 300 ℃ heat treatment. The open-circuit potential indicated that the photoelectrical performance of the La-TiO₂ films was enhanced with the addition of the La element and the largest decline (837.8 mV) in the electrode potential was achieved with the 300 ℃ heat treatment.     

TiO_2/SiO_2、ZrO_2/SiO_2多层介质膜光学损耗及激光损伤研究

以TiO_2/SiO_2及ZrO_2/SiO_2多层介质膜为例,测试了不同工艺条件及不同膜系结构下薄膜样品的光学损耗及激光损伤阈值,同时对实验结果作了初步的分析讨论.     

Metal-free indoline-dye-sensitized TiO2 nanotube solar cells

Titanium dioxide nanotubes were directly fabricated from commercial P25 TiO₂ via alkali hydrothermal transformation. The prepared titanate nanotubes were successfully used as an electrode material for dye-sensitized solar cells (DSCs). A metal-free organic dye (indoline dye D102) was used as a sensitizer. The used indoline dye D102 is of high purity (?98%) and high absorption coefficient (67,500 L mol⁻¹ cm⁻¹ at 501 nm). The TiO₂ pastes were prepared with PEG (Mw 20,000) and as-made TiO₂ nanotubes or P25 powders. Titania thin films were grown by screen printing method. High conversion efficiencies of light to electricity of around 9.8% and 7.6% under illumination of simulated AM1.5 sunlight (100 mW/cm²) were achieved with P25 and TiO₂ nanotube cells, respectively. The fill factor of DSCs based on TiO₂ nanotubes increased in comparison with that of DSCs based on TiO₂ nanoparticles. The electron transport and dye adsorption properties in both titanate nanotube and P25 electrodes were evaluated in terms of photovoltaic characteristics of the fabricated cells. The related mechanisms were discussed. The study provides a promising method for the development of high-efficiency and low-cost DSCs.     

Effect of RuO2 electrode on laser-MBE prepared HfO2 gate dielectrics

In this paper, we report our recent study of the effect of RuO₂ as an alternative top electrode for pMOS devices to overcome the serious problems of polysilicon (poly-Si) gate depletion, high gate resistance and dopant penetration in the trend of down to 50 nm devices and beyond. The conductive oxide RuO₂, prepared by RF sputtering, was investigated as the gate electrode on the Laser MBE (LMBE) fabricated HfO₂ for pMOS devices. Structural, dielectric and electric properties were investigated. RuO₂/HfO₂/n-Si capacitors showed negligible flatband voltage shift (<10 mV), very strong breakdown strength (>10 MV cm⁻¹). Compared to the SiO₂ dielectric with the same EOT value, RuO₂/HfO₂/n-Si capacitors exhibited at least 4 orders of leakage current density reduction. The work function value of the RuO₂ top electrode was calculated to be about 5.0 eV by two methods, and the effective fixed oxide charge density was determined to be 3.3 × 10¹² cm⁻². All the results above indicate that RuO₂ is a promising alternative gate electrode for LMBE grown HfO₂ gate dielectrics.     

O2分压和退火对TiO2/SiO2纳米多层膜结构和光学性能的影响

利用Mass软件设计了TiO2/SiO2纳米多层光学增透膜膜系,并采用高真空电子束蒸发系统在不同O2分压条件下制备了TiO2/SiO2纳米多层膜,TiO2/SiO2薄膜多层膜体系在沉积条件下获得了很好的宽光谱光学透射性能,在可见光谱范围内透射率接近设计值,平均透射率达到90%以上。通过一系列测试方法对多层膜退火前后的透射率、组分结构和退火以后的残余应力以及表面形貌进行了研究。实验结果表明:在较高O2分压条件下,由于多层膜结构中O空位的减少,使得多层膜透射率逐渐增加。在退火条件下,随着退火温度的增加,导致了表面均方根粗糙度(RMS)的增加以及晶粒的聚集长大,500℃时多层膜组分结晶化明显加强,使得缺陷增多;同时受退火温度的影响,残余应力逐渐增加,组分相互扩散加剧使得多层膜界面受到破坏。这些因素最终导致TiO2/SiO2多层膜的透射率逐渐降低。     

Effect of Ge-GeO2 co-doping on non-ohmic behaviour of TiO2-V2O5-Y2O3 varistor ceramics

An investigation was made into the effect of doping with the elemental crystal Ge or/and GeO₂ on the TiO₂-V₂O₅-Y₂O₃ varistor ceramics. The result shows that as the doping contents of V₂O₅ and Y₂O₃ are 0.5 mol%, respectively, co-doping with 0.3 mol% Ge and 0.9 mol% GeO₂ makes the highest α value (α = 12.8), the lowest breakdown voltage V_1mA (V_1mA = 15.8 V/mm) and the highest grain boundary barrier Φ_B (Φ_B = 1.48 eV), which is remarkably superior to the TiO₂-V₂O₅-Y₂O₃ varistor ceramics undoped with Ge and GeO₂ and mono-doped with Ge or GeO₂. The TiO₂-V₂O₅-Y₂O₃-Ge-GeO₂ ceramic has the prospect of becoming a novel varistor ceramic with excellent electrical properties.     

CaTiO3含量对PTFE/TiO2复合材料性能的影响

采用类似于粉末冶金的工艺,制备了金红石型TiO2填充的聚四氟乙烯(PTFE)复合材料,研究了CaTiO3掺杂量对所制复合材料热学、介电性能的影响.结果表明:随着CaTiO3含量的增加,复合材料的密度减小,吸水率增大,介电常数和损耗增大,线膨胀系数增大到一个最大值后减小;当CaTiO3添加量达到质量分数16％时,复合材料的相对介电常数达到最大值11.60,损耗为0.002 0.     

Regulation of surface properties of photocatalysis material TiO2 by strain engineering

As a promising photocatalysis material, TiO₂ has long been studied by experimental and theoretical methods. The external strain could affect the catalytic reactivity of TiO₂ significantly due to the difference in surface elastic properties of different surface structures with different surface adsorption or defects. This article reviews our recent work by using density function theory calculations on the effect of strain on the TiO₂ surface properties, including surface relative stability, surface defects, surface adsorption and dissociation.     

TiO2高温电导及缺陷化学分析

对TiO2高温电导机制和缺陷化学进行了详细的理论分析和推导,计算了未掺杂样品的电导激活能。电导激活能不仅与温度有关,而且与载流子的特征有关。在低温高氧分压下,电导激活能大,氧缺位浓度较小,缺陷以一价氧缺位为主;而在高温低氧分压下,电导激活能小,氧缺位浓度较大,缺陷以二价氧缺位为主。     

微等离子法制备原位生长TiO2薄膜电极研究

采用微等离子体氧化法制备用于染料敏化太阳能电池的原位生长TiO2薄膜电极。筛选适合制备较高光电性能原位生长TiO2薄膜电极的电解液,利用扫描电镜(SEM)、X射线衍射(XRD)和交流阻抗谱(EIS)考察电解液类型对所得TiO2薄膜电极的表面形貌、晶相组成和内部阻抗的影响,并利用X射线光电子能谱(XPS)和红外吸收(IR)研究染料敏化剂与TiO2薄膜表面的相互作用。结果表明,以(NH4)2SO4为电解液制备TiO2薄膜的光电性能高于硫酸体系所得TiO2薄膜的光电性能,短路电流、开路电压和光电转换效率分别为49μA/cm2,652mV和0.095%。薄膜主要由大量的金红石和少量的锐钛矿和钛组成,并且以(NH4)2SO4为电解液制备的薄膜中,TiO2含量较高。膜层较厚,约为7.5μm。薄膜的内部阻抗相对较小,有利于染料敏化太阳能电池光电性能的提高。所得TiO2薄膜电极的光电性能较高;cis-Ru(dcbpy)2(NCS)2染料可以吸附在微等离子氧化法制备的TiO2薄膜表面。染料cis-Ru(dcbpy)2(NCS)2敏化后的TiO2薄膜XPS谱中出现了O=C-O基团中的C1s吸收峰,说明染料可以吸附在微等离子氧化法制备的TiO2薄膜表面。在红外光谱中,在1 737nm处出现了一个吸收峰,应为酯键羰基振动所引起的,由此可以推断染料与TiO2表面应以类酯键形式结合。     

TiO_2掺杂量对PTFE/SiO_2复合材料性能的影响

采用新型化学工艺,制备了SiO2与TiO2共同填充的PTFE复合材料,系统研究了TiO2掺杂量对所制复合材料显微结构、微波介电性能和热膨胀系数的影响。结果表明,复合材料的密度、介电常数和热膨胀系数都随着掺杂量的增大而增加,吸水率随着掺杂量的增大而减小,介电损耗随着掺杂量的增大先减小后增大。当TiO2掺杂量为质量分数7%时,PTFE很好地包覆在SiO2表面,复合材料结构致密,具有与铜箔较为匹配的线膨胀系数(17.76×10–6/℃),且介电性能优良(εr=2.94,tanδ=0.000 82)。