极化聚合物薄膜电光系数的实时测量

提出了一种极化聚合物薄膜电光系数的实时测量方法。实验结构由耦合棱镜和依次制备在棱镜底面的四层薄膜组成,这四层薄膜分别是金属层（作为上电极）、极化聚合物,缓冲层和下电极。包含导波共振角并具有一定角度的入射光线会聚于棱镜底面,然后用CCD探测拍摄反射光斑,当外加电场作用于上下电极时,就可从光斑暗线位置的变化测量极化聚合物薄膜的电光系数。在测量过程中,使用了计算机图像处理方法和光学空间滤波技术。     

Ge-Ga-S-CdS玻璃的电致二次谐波发生特性

用熔融-急冷法制备了Ge14Ga3S37(CdS)3硫系玻璃样品,使用Maker条纹法观察了电场-温度场极化样品中的二次谐波发生(SHG)现象,研究了极化条件对SHG强度的影响、该效应产生的机理以及SHG现象室温下的稳定性.结果表明,极化样品中存在明显的二次谐波发生现象,入射角在±(40～50)°左右时,SHG的相对强度出现最大值;SHG的强度随着极化电压的增大和极化时间的延长而逐渐增强并渐趋饱和;在5 kV、280℃、30分钟的极化条件下,极化样品的二阶非线性极化系数χ(2)达到最大值4.36 pm/V;根据偶极子取向模型阐释了SHG产生机理以及极化条件对样品二阶光学非线性系数大小的影响机制;发现玻璃的电致极化区域位于阳极表面以下十几微米的区域,SHG效应在室温下是稳定的.     

沉积在Pt电极上的铁电PZT薄膜特性

研究了射频磁控溅射沉积在Pt电极上的Pb（Zr0．53Ti0．47）O3薄膜特性。经过不同温度退火处理后得到了钙钛矿结构的PZT薄膜。在对其结构的形成和变化进行研究的基础上，探讨了薄膜PZT相的形成机理。其电性能的测试表明，这种铁电PZT（53／47）薄膜具有较好的铁电性能和疲劳特性。在600℃下PZT薄膜的剩余极化强度Pr为24．8μC／cm2，矫顽场强度Ec为70kV／cm。210kV／cm的电场下，疲劳循环直到4×108次时，最大极化强度仍有20．6μC／cm2，降低了约34％，其剩余极化强度保持为10μC／cm2左右。     

同步极化聚合及原位二次谐波测试系统的研制

采用同步极化聚合,有效地降低了极化聚合物极化温度。报道了实现这一过程的装置的研制,并结合采用原位二次谐波测试系统实现了对极化过程的实时监测。利用该系统对耐高温聚酰亚胺的极化动力学进行了研究,该聚合物极化膜的ｄ３３值为１５ｐｍ／Ｖ,取向在１９０℃时才开始衰减,具有很好的取向稳定性。     

光漂白对极化聚合物薄膜非线性效应的影响

利用Cerenkov倍频辐射对极化聚合物薄膜在光漂白下二阶非线性效应的变化进行了研究。 实验表明光漂白能破坏有机聚合物中极化分子的取向稳定性,造成其二阶非线性效应衰减。实验测得漂白后交联型材料的二阶倍频信号衰减了28%,而侧链型材料则衰减了75%。     

聚合物通道波导的分析及制备

ＰＤＡ聚合物有较大的三阶非线性极化率和超快的响应特性，是全光器件应用中非常有前景的材料，本文采用有效折射率法分析了下条载聚合物薄膜通道波导的传输特性，讨论了制备单模传输波导的条件及其影响因素，制备了ＰＤＡ薄膜通道波导，并测试了其波导特性。     

Pb(Hf_(0.3)Ti_(0.7))O_3铁电薄膜的制备与性能研究

采用脉冲激光沉积方法在不同温度下生长Pb(Hf0.3Ti0.7)O3(PHT)铁电薄膜,利用各种表征手段测试并分析薄膜的微观结构和电性能。研究表明,生长温度为400℃沉积的PHT薄膜具有良好的(111)择优取向;PHT薄膜矫顽场(2Ec)为390 kV/cm,剩余极化强度(2Pr)为53.1μC/cm2,经1.5×109次翻转后剩余极化强度保持85%;PHT薄膜绝缘性能良好,相对介电常数约为540。PHT薄膜有望应用于铁电随机存储器。     

一种具有电双稳特性的聚合物薄膜

发现了在室温下具有电双稳特性的聚合物材料聚对萘二甲酸乙二酯(PEN)。通过真空蒸发方法制备的PEN薄膜,其表面晶粒尺寸小于100nm,粗糙度也为纳米量级,而且具有较高的热稳定性。在3．5V电压作用下,PEN薄膜可从高阻状态跃变到低阻状态,跃迁时间小于20ns。该材料有可能用于大容量存储器的制作。     

溶胶-凝胶方法制备BiFeO3薄膜及其铁电性质

用溶胶-凝胶方法制备了BiFeO3薄膜,XRD研究表明薄膜呈随机取向,扫描电镜研究表明薄膜表面呈致密的多晶结构,薄膜与底电极之间没有互扩散。铁电性测试表明室温下的剩余极化强度为1．8μC／cm^2,与低温下BiFeO3单晶的剩余极化相当。介电损耗呈弥散型转化,与薄膜中的Bi46Fe2072相有关。     

后处理工艺对POSS-PMMA_8改性凝胶聚合物电解质性能的影响

为解决凝胶聚合物电解质(GPE)的离子电导率低、力学性能差等问题,通过静电纺丝制备星型笼型低聚倍半硅氧烷-聚甲基丙烯酸甲酯(POSS-PMMA_8)改性聚甲基丙烯酸甲酯-聚丙烯腈-聚偏氟乙烯(PMMA-PANPVDF)得到聚合物纺丝薄膜(POSS-PMMA_8/PMMA-PAN-PVDF)M1,将聚合物纺丝薄膜M1在120℃热处理得到聚合物纺丝薄膜M2,或热压并预氧化处理得到聚合物纺丝薄膜M3,将其浸泡于电解液中活化得到POSS-PMMA_8/PMMA-PAN-PVDF的GPE。对不同状态聚合物纺丝薄膜M1、M2、M3的形貌、孔隙率、吸液率、力学性能及其GPE的电导率和电化学稳定窗口进行测试。结果发现,相比于M1,M2的拉伸强度及GPE的电导率分别提高9.2%及181.1%,电化学窗口增至5.3 V;而M3的拉伸强度和GPE电导率分别较M1增加193.7%、20.2%,电化学窗口增至5.5V。     

Near-Unity Polarization of Valley-Dependent Second-Harmonic Generation in Stacked TMDC Layers and Heterostructures at Room Temperature

With unique valley-dependent optical and optoelectronic properties, 2D transition metal dichalcogenides (2D TMDCs) are promising materials for valleytronics. Second-harmonic generation (SHG) in 2D TMDCs monolayers has shown valley-dependent optical selection rules. However, SHG in monolayer TMDCs is generally weak; it is important to obtain materials with both strong SHG signals and a large degree of polarization. In the work, a variety of inversion-symmetry-breaking (3R-like phase) TMDCs (WSe₂, WS₂, MoS₂) atomic layers, spiral structures, and heterostructures are prepared, and their SHG polarization is studied. Through circular-polarization-resolved SHG experiments, it is demonstrated that the SHG intensity is enhanced in thicker samples by breaking inversion symmetry while maintaining the degree of polarization close to unity at room temperature. By studying TMDCs with different twist angles and the spiral structures, it is found that there is no significant effect of multilayer interlayer interaction on valley-dependent SHG. The realization of strong SHG with high degree of polarization may pave the way toward a new platform for nonlinear optical valleytronics devices based on 2D semiconductors.     

Molecular orientation of oxacyanine dye in an LB film determined by second harmonic generation and polarized absorption techniques

The molecular orientation of an oxacyanine dye (DOOC) in an LB film has been determined based on the second harmonic generation (SHG) using a fs-pulsed Ti-sapphire laser and the polarization absorption spectrometry. Both polarization and wavelength dependence of SHG varied with surface concentration of the dye. The dye was either in a monomer, a dimer or a J-aggregate form depending on the surface concentration. The tilt angle to the surface normal was 34° for the monomer, 26–29° for the dimer and 16–23° for the J-aggregate. The J-aggregate stayed more flat on surface and showed larger SHG intensity than the monomer did.     

Relative measurements of second-order susceptibility with reflective second-harmonic generation

There is a strong demand for a simple and reliable technique for second-order susceptibility measurements of thin films. Since the Maker fringe technique is limited to transparent substrates we propose an experimental protocol based on reflective second-harmonic generation (SHG). The proposed protocol is based on relative measurements of Z-cut quartz. An analytical expression of the reflective SHG intensity dependence of the polarizer, analyzer, and sample azimuth is presented. An error analysis is also presented. Thin organic film of the side-chain polymer poly(Disperse Red 1 Methacrylate-Co-Methyl-Methacrylate) is investigated. Results for different wavelengths are reported.     

Stretching and distortion of a photosensitive polymer film by surface plasmon generated near fields in the vicinity of a nanometer sized metal pin hole

Here we demonstrate how a surface plasmon (SP) generated near field pattern in the vicinity of a nano-scale pin hole can be used to generate reversible topography changes in a photosensitive polymer film above the opening. This can be achieved by simply changing the polarization state of the plasmon generating incoming light. In the case of linear polarization, the near field intensity pattern causes the film to laterally expand/contract according to the direction of the polarization. For circular polarization, two pronounced rims corresponding to maxima in the topography are observed. In all cases, the topographical variation is in close agreement with the SP intensity distribution computed from finite difference time domain simulation. Our results demonstrate the versatility of using SP near fields to imprint a variety of structures into photosensitive polymer films using only a single metallic mask.     

Optical second harmonic generation at platinum phthalocyanine-modified platinum electrodes

Optical second harmonic generation (SHG) has been used to observe changes within electronically conducting platinum phthalocyanine (PtPc) films deposited on polycrystalline platinum electrodes as the film undergoes electrochemical modification. PtPc-modified electrodes produced enhanced SHG responses over bare platinum surfaces. This is proposed to be due to an electric quadrupole contribution from the PtPc molecule. Examination of the polarization dependence of the SHG response reveals that electroactive PtPc molecules exist in environments both parallel and perpendicular to the electrode surface. It has been possible to observe redox processes occurring within the films by monitoring the magnitude of the SHG response with variations in potential. The decrease in SHG signal has been shown empirically to be proportional to the charge removed from the film during oxidation of the phthalocyanine (Pc) ring.     

Surface second-harmonic generation from vertical GaP nanopillars

We report on the experimental observation and analysis of second-harmonic generation (SHG) from vertical GaP nanopillars. Periodic arrays of GaP nanopillars with varying diameters ranging from 100 to 250 nm were fabricated on (100) undoped GaP substrate by nanosphere lithography and dry etching. We observed a strong dependence of the SHG intensity on pillar diameter. Analysis of surface and bulk contributions to SHG from the pillars including the calculations of the electric field profiles and coupling efficiencies is in very good agreement with the experimental data. Complementary measurements of surface optical phonons by Raman spectroscopy are also in agreement with the calculated field intensities at the surface. Finally, polarization of the measured light is used to distinguish between the bulk and surface SHG from GaP nanopillars.     

Polarization-Independent Second Harmonic Generation in 2D Van Der Waals Kagome Nb3SeI7 Crystals

Second harmonic generation (SHG) of 2D crystals has been of great interest due to its advantages of phase-matching and easy integration into nanophotonic devices. However, the polarization-dependence character of the SHG signal makes it highly troublesome but necessary to match the laser polarization orientation relative to the crystal, thus achieving the maximum polarized SHG intensity. Here, it is demonstrated a polarization-independent SHG, for the first time, in the van der Waals Nb₃SeI₇ crystals with a breathing Kagome lattice. The Nb₃ triangular clusters and Janus-structure of each Nb₃SeI₇ layer are confirmed by the STEM. Nb₃SeI₇ flake shows a strong SHG response due to its noncentrosymmetric crystal structure. More interestingly, the SHG signals of Nb₃SeI₇ are independent of the polarization of the excitation light owing to the in-plane isotropic arrangement of nonlinear active units. This work provides the first layered nonlinear optical crystal with the polarization-independent SHG effect, providing new possibilities for nonlinear optics.     

Second harmonic generation from electrically polarized CuCl-microcrystallite-doped glass

Second harmonic generation has been observed in electrically polarized CuCl-microcrystallite-doped glass. The glass was prepared by means of melting–quenching method and poled at 200°C for 1 h under applied dc field of 4 kV. The incident angular variation of SHG intensity for the polarized glass was measured. To explain the effect, it is proposed that the second-order nonlinear polarization results from the dipolar orientation in the glass.     

In situ measurements and analysis of imidization extent, thickness, and stress during the curing of polyimide films

The effects of scanning rate and pre-baking time on the imidization extent, thickness, and stress of polyimide films during the curing process were simultaneously analyzed using FTIR and the strip end deflection detector complemented with interferometer systems. Film thickness and stress increased, but imidization extent decreased with increasing scanning rates. Longer pre-baking times significantly reduced the initial film thickness and stress. Imidization extent, thickness, and stress behavior of polyimide films during the curing process were closely related one another.     

Direct determination of effective interfacial optical constants by nonlinear optical null ellipsometry of chiral films

Nonlinear optical null ellipsometry (NONE) measurements of chiral interfaces allowed direct experimental measurement of the linear interfacial optical constants in surface second harmonic generation (SHG) measurements. Since phase information is retained in NONE measurements, the real and imaginary components of the interfacial refractive index (n and k, respectively) were uniquely obtained from the measured chiral chi((2)) tensor elements of a fluorescein-labeled bovine serum albumin film. The sensitivity of the calculated chi((2)) tensor elements on the assumed values of the interfacial optical constants allowed measurements of n and k to four significant figures with no additional adjustable parameters and independent of molecular symmetry. The optical constants measured by SHG agreed within a relative error of 0.8% with values predicted independently using a simple effective medium approximation, also with no adjustable parameters. Additionally, those same optical constants produced relationships between the achiral chi((2)) tensor elements in excellent agreement with predictions for systems exhibiting weak orientational order. This study suggests that the far-field intensity and polarization state of the nonlinear optical beam may be largely independent of the near-field optical constants within the interfacial layer in the limit of a film thickness much less than the wavelength of light.