高压下锐钛矿TiO2的电阻率及能带结构的研究

应用在位电阻率测量方法研究高压下锐钛矿TiO2的电学性质. 通过研究电阻率随压力变化的异常变化点, 观察到了TiO2从锐钛矿-柯铁矿-斜锆石的相变. 卸压后,电阻率和初始值相差2个数量级, 说明该相变为不可逆相变. 结合第一性原理计算结果表明, 柯铁矿结构更小的带隙是导致TiO2电阻率减小的根本原因.     

TiO_2晶型及其相变的高温拉曼光谱研究

本文测量了锐钛矿型和金红石型TiO2常温至1923K的高温拉曼光谱,观察了锐钛矿型TiO2在1373K～1473K间发生相变,不可逆转化为金红石型TiO2,分析了特征峰随温度变化的规律以及两种结构相的温度依赖性。并为不同晶型TiO2的研究、生产和应用提供重要的实验依据。     

锐钛矿相纳米TiO2晶体生长动力学及生长过程控制

研究了采用溶胶-凝胶法经由前驱物钛酸四异丙酯水解制备纳米TiO2结构相变及锐钛矿晶体生长动力学过程. 研究结果表明,在酸性条件下水解,由于高压热处理温度的变化导致锐钛矿向金红石相的结构相变,锐钛矿相纳米TiO2生长活化能在250℃以下和以上分别为(15.8±4.5) kJ/mol和(80.2±1.0) kJ/mol;而在碱性条件下水解的活化能值为(3.5±0.4 kJ/mol. 在不发生结构相变的条件下,酸性水解条件下锐钛矿相纳米TiO2生长速率相比没有碱性条件下快,即表明在酸性条件下提高锐钛矿生长速率主要依靠提高温度来实现,而在碱性条件下,可以通过延长高压热处理时间使得晶体生长速率加快,该研究成果对实现锐钛矿相纳米TiO2晶体尺寸控制和将来批量化制备提供了理论和实验指导.     

热处理对爆轰合成的纳米TiO_2混晶的结构相变的影响

采用爆轰法制备了纳米TiO2混晶体,初步研究了不同煅烧温度(600℃和720℃)和不同煅烧时间(1 h,2 h,3.5 h和5 h)对其微结构和结构相变行为的影响,并应用热动力学理论讨论了从锐钛矿相到金红石相的结构相变过程和相变机理.研究表明:随着煅烧温度的升高和煅烧时间的增加,纳米TiO2的粒径逐渐增大,混晶中金红石相的含量逐渐提高.与常规方法制备的纳米TiO2不同的是,在相同煅烧温度和煅烧时间下金红石相的平均生长速率明显低于锐钛矿相.锐钛矿相完全相变为金红石的温度也明显低于常规方法报道的相变温度.该研究会对控制纳米TiO2晶体尺寸和批量合成提供一定的理论和实验指导.     

微区Raman光谱在TiO_2高压结构相变研究中的应用

本文以金红石单晶TiO2和锐钛矿多晶TiO2为研究对象,应用金刚石小压机和原位拉曼光谱测量技术,系统研究了室温高压下TiO2的结构相变。原位拉曼测量表明,金红石单晶TiO2在压力达到12.91GPa时开始发生由金红石结构向斜锆石结构(MI)的相变,当压力达到14.16 GPa时,相变完成;继续加压到21.65 GPa,没有发现进一步的相变;卸压时由斜锆石结构转变为PbO2结构,相变发生在大约7.11 GPa处。锐钛矿多晶TiO2在压力达到4.26 GPa时开始向PbO2结构转变,当压力达到8.34 GPa时相变完成;继续加压到12.94 GPa,样品开始发生由PbO2结构向斜锆石结构的相变,当压力达到18.74 GPa时相变完成;继续加压到21.39 GPa,没有发现进一步的相变;卸压时也由斜锆石结构转变为PbO2结构,起始相变压力点应高于8 GPa。     

采用原位变温X射线衍射技术研究不同气氛下TiO2的相变机理

以TiO2凝胶为模型化合物,利用原位变温X射线衍射(XRD)研究了不同气氛下TiO2的相变过程,对比研究原位和非原位情况下的相变情况.研究表明,各种气氛下,原位和非原位时不同气氛下TiO2相变过程均有不同.其中,最常见的空气气氛下非原位与原位测定的TiO2从无定型向锐钛矿转变的温度相差近200℃.在500℃以前,TiO...     

高氧空位简并锐钛矿TiO2半导体电子寿命的第一性原理研究

为了研究锐钛矿TiO2晶体中高氧空位浓度对电子寿命的影响,利用基于局域密度泛函理论框架下的广义梯度近似平面波超软赝势方法,用第一性原理对含高氧空位浓度的锐钛矿TiO2晶体进行了结构优化处理、能带分布和态密度分布计算,表明在温度一定和高氧空位浓度的条件下,锐钛矿TiO2的电子寿命随氧空位浓度的增大而减小;电子浓度的大小对电子寿命无影响.同时,锐钛矿TiO2晶体中高氧空位浓度时,发现有莫特相变的现象.     

纳米二氧化钛材料的相变和声子限制效应(英文)

拉曼光谱用于研究二氧化钛材料的相变和声子限制效应。化学溶液方法制备了TiO2纳米晶材料。其平均粒度为 6 8- 2 7 9nm。最低频率 1 5 2cm- 1 Eg 模随粒度减小出现蓝移和加宽。在声子限制模型下 ,理论上对不同粒度的TiO2 纳米晶 (6 8,1 0 3和 2 7 9nm)的频移和线宽进行计算 ,结果与实验吻合得很好。研究了TiO2 纳米晶锐钛矿 -金红石相变 ,其相变温度为 6 5 0 - 6 90℃ ,比体块TiO2 的相变温度 1 0 0 0℃低 ,表明了相变的尺寸效应     

含氧空位锐钛矿TiO2光学性质的第一性原理研究

为了研究锐钛矿TiO2晶体中氧宅位对光学性质的影响,利用基于局域密度泛函理论框架下的广义梯度近似平面波超软赝势方法.用第一性原理对含氧空位锐钛矿TiO2晶体进行了结构优化处理.计算了完整的和含氧空位锐钛矿TiO2晶体的电子态密度、复数折射率、介电甬数及吸收光谱的偏振特性.二者比较发现,引入氧空位后,锐钛矿TiO2的电子结构发生了变化,电子总态密度的费米面进入了导带,引起了莫特相变;含氧空位的锐钛矿TiO2晶体的Ti 3d态大约在-6.097 eV处出现了新的劈裂峰值.两种模型的介电函数虚部、吸收光谱以及复折射率的实部,它们的峰值位置一一对应.说明它们之间存在着内在的联系,这些都与电子态密度分布直接相关.理论分析和计算发现二者的介电函数虚部和吸收光谱峰值位置移动是弛豫效应影响的结果,同时,峰值大小变化是电子跃迁的几率来决定的.晶体的各向异性是由晶体结构的对称性决定的.     

TiO2混晶光催化性能的第一性原理研究

本文采用第一性原理平面波超软赝势方法,通过搭建混晶界面的方式计算并分析了TiO2混晶的光催化性能.从光的吸收能力、光生电子-空穴对的分离效率以及载流子的转移效率三方面,与锐铁矿相和金红石相TiO2单晶进行对比分析.结果显示TiO2混晶的电子-空穴对分离率高于锐钛矿相TiO2、金红石相TiO2单晶,TiO2混晶中吸收峰明...     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Retrieval of ultraviolet skylight radiances and O3 slant column densities from balloon-borne limb spectrometer

With a novel light-weight and absolutely calibrated ultraviolet （UV） spectrometer, UV skylight radiances and O3 slant column densities are measured by balloon-borne limb measurements in Xinjiang area, China. UV skylight radiances measured at the height of 31 km are compared with the results from Modtran in the wavelength range from 290 to 420 nm. O3 slant column densities are derived from radiance spectra in the Huggins bands （320 - 335 nm） using differential optical absorption spectroscopy method. And the parameter exhibits a good correlation with the same value simulated by radiative transfer model （Tracy）. The O3 profile simultaneously measured by an O3 sonde is used as input in Tracy calculations. The O3 sonde is launched on the same balloon.     

Design optimization of highly sensitive LSPR enhanced surface plasmon resonance biosensors with nanoholes

For breaking through the sensitivity limitation of conventional surface plasmon resonance (SPR) biosensors, novel highly sensitive SPR biosensors with Au nanoparticles and nanogratings enhancement have been proposed recently.But in practice, these structures have obvious disadvantages.In this study, a nanohole based sensitivity enhancement SPR biosensor is proposed and the influence of different structural parameters on the performance is investigated by using rigorous coupled wave analysis (RCWA).Electromagnetic field distributions around the nanohole are also given out to directly explain the performance difference for various structural parameters.The results indicate that significant sensitivity increase is associated with localized surface plasmons (LSPs) excitation mediated by nanoholes.Except to outcome the weakness of other LSP based biosensors, larger resonance angle shift, reflectance amplitude, and sharper SPR curves' width are obtained simultaneously under optimized structural parameters.     

Polymer gratings based on photopolymerization for low-order distributed feedback polymer lasers

Novel polymer distributed feedback(DFB)gratings are fabricated based on photopolymerization to reduce lasing threshold of polymer lasers.A photopolymer formulation sensitive to 355-nm ultraviolet(UV)light is proposed for the fabrication of polymer gratings and it can be used to form polymer films by spin-coating process.A very low surface-relief depth ranging from 12.5 to about 1.0 nm has been demonstrated with a refractive-index modulation of about 0.012.The experimental results indicate that such polymer gratings have promising potentials for the fabrication of low-order DFB organic semiconductor lasers.