Trace analysis of polycyclic aromatic hydrocarbons using calixarene layered gold colloid film as substrates for surface‐enhanced Raman scattering

A surface‐enhanced Raman scattering (SERS) active substrate for the detection of polycyclic aromatic hydrocarbons (PAHs) was developed, which used 25, 27‐dimercaptoacetic acid‐26, 28‐dihydroxy‐4‐terbutyl calix[4]arene (DMCX) to functionalize a gold colloid film. This SERS‐active substrate prepared by self‐assembly method exhibits a high sensitivity, especially for the detection of PAHs. With the use of this SERS‐active substrate and with the application of the shifted excitation Raman difference spectroscopy (SERDS) technique, Raman signals of pyrene and anthracene in aqueous solutions at low concentration level (500 pM) can be obtained. Moreover, because PAHs are blocked from being directly adsorbed on gold colloid by DMCX and the photochemical reactions of adsorbates are avoided, the Raman bands of PAHs adsorbed on DMCX‐fuctionalized gold colloid film can be one‐to‐one correspondence with those of solid PAHs, and additionally, this SERS‐active substrate can be easily cleaned and reused. The obtained results demonstrate that the DMCX‐functionalized gold colloid films prepared by self‐assembly method have great potential to be developed to an in situ PAHs detection substrate. Copyright © 2012 John Wiley & Sons, Ltd.     

Characterizing unusual metal substrates for gap‐mode tip‐enhanced Raman spectroscopy

In this article, the electromagnetic (EM) field in gap‐mode tip‐enhanced Raman spectroscopy (TERS) is investigated theoretically and experimentally for a range of commonly used and unusual metal and nonmetal substrates. By approaching a metal tip to a substrate, both form a coupled system that confines the EM field created at the tip apex. The influence of the substrate onto the EM field enhancement is observed in a top‐illumination gap‐mode TERS setup for different metal substrates. These include Au, the most commonly used substrate, and also a wide range of rarely or previously unused TERS substrates (Cu, Ag, Al, Pd, Pt, Ni, Ti, Mo, W, stainless steel, Al₂O₃, SiO₂). Self‐assembled monolayers of thiols and brilliant cresyl blue thin film samples are investigated experimentally on nine metal substrates, all showing considerable TERS enhancement. With finite difference time domain and finite element simulations used, the article provides a good estimate of the EM field enhancement for a wide range of substrates for users to estimate how well a substrate of choice will perform in a gap‐mode TERS experiment. The reduction in EM field strength |E²| compared with Au is less than an order of magnitude for many metals (Calculations: Cu 92%, Ag 81%, Ni 53%). This article experimentally shows that a wide variety of conductive substrates can be used, when one is willing to trade a fraction of the EM field enhancement. TERS was seen on all metal substrates including stainless steel, yet quantification was not always possible. These qualitative results were complemented with intensities from calculations. The wider variety of substrates will increase the applicability of TERS and evolve it one step further towards use in standard analytics. Copyright © 2012 John Wiley & Sons, Ltd.     

Explorations and Expectations of Equidistribution Adaptations for Nonlinear Quenching Problems

Finite difference computations that involve spatial adaptation commonly employ an equidistribution principle. In these cases, a new mesh is constructed such that a given monitor function is equidistributed in some sense. Typical choices of the monitor function involve the solution or one of its many derivatives. This straightforward concept has proven to be extremely effective and practical. However, selections of core monitoring functions are often challenging and crucial to the computational success. This paper concerns six different designs of the monitoring function that targets a highly nonlinear partial differential equation that exhibits both quenching-type and degeneracy singularities. While the first four monitoring strategies are within the so-called primitive regime, the rest belong to a later category of the modified type, which requires the priori knowledge of certain important quenching solution characteristics. Simulated examples are given to illustrate our study and conclusions.     

用于温差发生器的高精度温度测量与控制系统设计

讨论了用于温差发生器的高精度温度测量与控制的设计与实现。采用PT100铂电阻作为温度传感器,详细推导了非平衡电桥测量非线性的校正公式,采用24位的Σ-Δ型的模数转换器AD7714保证了0.005℃的温度测量分辨率。控温电路采用线性化电流方式,算法上对积分分离PID算法做出改良,并与不完全微分PID算法结合形成一种优化PID算法,能快速、精确的把温差稳定到目标值,控温精度达到0.01℃。     

从头计算研究1-甲基-次黄嘌呤的电离能

采用从头计算B3LYP/Aug-cc-pVDZ方法研究了1-甲基-次黄嘌呤最稳定的六种可变异构体. 两种异构体N7H 和N9H有着相当的能量,远比其它异构体稳定. 理论计算了各种可变异构体的转动常数和偶极矩. 运用电子传播子理论P3近似方法计算稳定异构体外价壳层轨道的电离能,计算结果与光电子能谱实验结果符合较好. 根据异构体的相对能量以及理论模拟电离能谱和实验光电子能谱之间的比较,说明在气相光电子能谱实验中至少存在两种可变异构体.     

酮缺陷对中性和带电六卟啉芳香性影响的直接可视化研究

利用含时密度泛函理论研究了酮缺陷对中性和带电六卟啉芳香性的影响,并使用多维可视化技术给出了该体系基态电荷分布和电子跃迁的直观图像. 研究结果表明,芳香性是决定这类体系基态密立根电荷分布的主要因素;酮缺陷效应使得体系基态的密立根电荷分布更多地局域在六卟啉基团上,在这类体系的五氟苯基取代基上密立根电荷布居较少,同时使得体系的芳香性发生改变. 进一步,通过计算体系的跃迁密度和电荷差分密度,可视化了酮缺陷对中性和带电六卟啉芳香性的影响. 结果表明,酮缺陷加强了体系电荷转移的能力.     

圆柱振荡绕流中涡旋运动模式(pattern)的数值模拟

提出并发展的一种基于区域分解思想,综合了解N-S方程的有限差分法及涡法各自优点的新数值方法,计算了各种 Keulegan-Carpenter数下(Kc=2~24)振荡流绕圆柱的流动。系统地研究了振荡流中涡旋运动模式随Kc数变化的规律,模拟了不对称区、单对涡区(或模向区)、双对涡区(或对角区)和三对涡区四种不同的涡旋运动模式。将计算所得的阻力系数C_D、惯性系数C_M与国外近期发表的计算结果进行了比较。     

三元结构双反射平行分束偏光镜设计

为了节省冰洲石晶体材料,并实现两束偏振光的平行输出,采用冰洲石与光学玻璃组合的方法,给出一种双反射形式平行分束偏光镜的新设计。该棱镜为ZBaF3玻璃中间加冰洲石晶体薄片的三元结构,采用溴代萘胶合;选择合适的结构角,令电矢量振动方向相互垂直的两束偏振光分别在前胶合面、后端面发生全反射,并垂直上端面平行出射。实验测试表明,棱镜的透射比高于80%,消光比优于10-3。该设计在节省冰洲石晶体前提下,保持了良好的性能。     

Finite Difference/Element Method for a Two-Dimensional Modified Fractional Diffusion Equation

We present the finite difference/element method for a two-dimensional modified fractional diffusion equation. The analysis is carried out first for the time semi-discrete scheme, and then for the full discrete scheme. The time discretization is based on the $L1$-approximation for the fractional derivative terms and the second-order backward differentiation formula for the classical first order derivative term. We use finite element method for the spatial approximation in full discrete scheme. We show that both the semi-discrete and full discrete schemes are unconditionally stable and convergent. Moreover, the optimal convergence rate is obtained. Finally, some numerical examples are tested in the case of one and two space dimensions and the numerical results confirm our theoretical analysis.     

A functional probe with bowtie aperture and bull's eye structure for nanolithograph

The bowtie aperture surrounded by concentric gratings(the bull’s eye structure) integrated on the near-field scanning optical microscopy(NSOM) probe(aluminum coated fiber tip) for nanolithography has been investigated using the finite-difference time domain(FDTD) method.By modifying the parameters of the bowtie aperture and the concentric gratings,a maximal field enhancement factor of 391.69 has been achieved,which is 18 times larger than that obtained from the single bowtie aperture.Additionally,the light spot depends on the gap size of the bowtie aperture and can be confined to sub-wavelength.The superiority of the combination of the bowtie aperture and the bull’s eye structure is confirmed,and the mechanism for the electric field enhancement in this derived structure is analyzed.