Direct View of Cr Atoms Doped in Anatase TiO2(001) Thin Film

Imaging the doping elements is critical for understanding the photocatalytic activity of doped TiO₂ thin film. But it is still a challenge to characterize the interactions between the dopants and the TiO₂ lattice at the atomic level. Here, we use high angle annular dark-field/annular bright-field scanning transmission electron microscope (HAADF/ABF-STEM) combined with electron energy loss spectroscopy (EELS) to directly image the individual Cr atoms doped in anatase TiO₂(001) thin film from [100] direction. The Cr dopants, which are clearly imaged through the atomic-resolution EELS mappings while can not be seen by HADDF/ABF-STEM, occupy both the substitutional sites of Ti atoms and the interstitial sites of TiO₂ matrix. Most of them preferentially locate at the substitutional sites of Ti atoms. These results provide the direct evidence for the doping structure of Cr-doped A-TiO₂ thin film at the atomic level and also prove the EELS mapping is an excellent technique for characterizing the doped materials.     

Action spectroscopy of single molecules reactions with STM – My personal view back from 2001-

Having obtained an invitation to submit this personal view back to 2001 when I started to work with Prof. Maki Kawai for developing a theory of lateral hopping of a single CO molecule on Pd (1 1 0) with Bo Persson, I briefly describe how I got an idea for elementary processes of vibrationally mediated reactions of single molecules on metal surfaces. During the work with Prof. S.G. Thihodeev on a theory of inelastic electron tunneling spectroscopy (IETS) with scanning tunneling spectrum (STM-IETS), I found that IET current is expressed in terms of a vibrational density of states of a single molecule. This enabled me to propose a formula for a reaction rate $R(V)$ or yield per electron $Y(V)=R(V)/I$, here I is a tunneling current, i.e., action spectrum (STM-AS) of a single molecule reaction. I applied this formula to reproduce the experimental result of a CO molecule hopping on Pd (1 1 0) surface and more insights into the elementary process were revealed. Thomas Frederiksen and Magus Paulsson jointed me to develop a general formula of $Y(V)$ and successfully applied it to analyse the experimental results of H-atom relay reaction of a linear chain, H(D)₂O-OH(D)-O(D) H?→?H(D)-H(D)₂-OH(D) ?→?H(D)-H(D)-OH(D)₂ that was observed by Takashi Kumagai and Hiroshi Okuyama. Actually a hydrogen atom excited at one end of a linear chain composed of H₂O and several OH generates another one at the other end. We employed our formula of to reproduce the experimental result of $Y(V)$. It was found that excitation of the three characteristic vibrational modes (free OH/OD stretch, OH¹?=?OD¹ stretch, and H₂O scissors, where H¹?=?D¹ denotes the shared H/D¹ atom in the H bond) were involved in the relay reaction. It was remarked that the OH(D¹)?=?OD(D¹ stretch modes are significantly redshifted from free OH/OD stretch and also characterized by very large broadening. The significant mode softening with respect to the free stretch modes and spectacular enhancement of the width are known to originate in the strong anharmonic character of a single H bond. Thomas investigated the reaction pathway from total energy calculations for the H-atom transfer reaction by the nudged elastic band method. The initial step is translation of the shared H-atom to the center hydroxyl, which is almost barrierless. The subsequent H-bond cleavage between OH and the center water molecule constitutes the highest barrier in which the displacement of the center water molecule along the [0 0 1] direction is mainly involved. The OH, OH¹ stretch and H₂O scissors modes are therefore postulated to couple to the reaction coordinate for the H-bond cleavage. We have demonstrated a vibrationally induced H-atom-bond relay reaction within H-bonded chains assembled on Cu(1 1 0). In this reaction H-atom transfer results in the ‘structural’ transfer of a water molecule from one end of the chain to the other end without changing the platform of the chain, or actually transferring the molecule.I have been thinking the unresolved issue of C₂H(D)₂ rotation on Cu (1 0 0) since it was published in 1998 by the W. Ho group. This experimental methods and the results obtained as the first demonstration of a single molecule switch are widely recognized as a milestone report of a single molecule manipulation by tunneling current and applied bias voltage which excites the vibrational modes of a molecule. They observed the STM images rotated at 90 degrees before and after applying appropriate bias voltage. They further compared the IETS spectrum and the $Y(V)$ for the rotation. The observed peak beautifully agreed with the threshold bias voltage, which clearly evidenced that a rotation is induced by excitation of a particular vibrational mode of C₂H(D)₂. In particular a crossover from a single electron process to a two electron process with increase in a tunneling current are of great interest. Sergei and his PhD student Yulia E. Shchadilova at that time and Magnus helped me much to reproduce all the experimental results by employing the Keldysh Green’s function theory combined with ab initio density functional theory (DFT) calculation of the optimized adsorption geometry and sophisticated vibrational analysis done by Magus. The experimental result of $Y(V)$ was reproduced by assuming a single electron process to excite the C-H stretch mode, and two electron process (ladder climbing of the C-H vibrational levels) and a excitation of the combination band. I also describe a brief theory of STM-AS I developed with Bo, Sergei, Magnus and Thomas.     

Asymmetric N-heterocyclic carbene benzimidazolium salts and their silver(I) complexes: potential as ionic liquid crystals

The synthesis and characterisation of a homologous series of monodentate benzimidazolium salts, 1–4 and their mononuclear silver(I)–NHC (where NHC = N-heterocyclic carbene) complexes, 5–8, are reported. The benzimidazolium salts were prepared from the N-alkylation of 1-methyl-benzimidazole with alkyl halides of varying carbon chain lengths. The mono silver(I)-NHC complexes, 5–8, were prepared by the reaction of the benzimidazolium salts with Ag₂O. All the synthesised compounds were fully characterised by ¹H-nuclear magnetic resonance (¹H-NMR), ¹³C-NMR and fourier-transform infrared (FTIR) spectroscopy. The molecular structures of compounds 3·PF₆, 4·PF₆, 7 and 8 were elucidated through single-crystal X-ray diffraction analyses. We postulate that the attachment of long alkyl chains to the heterocyclic core of 1-methyl benzimidazole could induce mesophase formation. The liquid crystalline behaviour of the benzimidazolium salts was investigated by polarised optical microscope and differential scanning calorimetry. Salts 3 and 4 were found to be thermotropic liquid crystals which exhibited a smectic A phase. However, upon complexation with silver(I) ions, all the Ag(I)–NHC complexes are found to be non-mesogenic.     

Influence of consecutive picosecond pulses at 532 nm wavelength on laser ablation of human teeth

The interaction of 40 ps pulse duration laser emitting at 532 nm wavelength with human dental tissue (enamel, dentin, and dentin–enamel junction) has been investigated. The crater profile and the surface morphology have been studied by using a confocal auto-fluorescence microscope (working in reflection mode) and a scanning electron microscope. Crater profile and crater morphology were studied after applying consecutive laser pulses and it was found that the ablation depth increases with the number of consecutive pulses, leaving the crater diameter unchanged. We found that the thermal damage is reduced by using short duration laser pulses, which implies an increased retention of restorative material. We observe carbonization of the irradiated samples, which does not imply changes in the chemical composition. Finally, the use of 40 ps pulse duration laser may become a state of art in conservative dentistry.     

Polarizing Microscopic and 31P NMR Studies of Decylammonium Chloride/Potassium Chloride/Water System. Containing Phosphoric Acid Monodecyl Ester and H3PO4

The decylammonium chloride (DACl), KCl and D₂O system forms two phases(N_c+N_d) in the nematic range. The N_d phase was ca. 15% by volume and exhibited extinct appearance. From conoscopic measurements it was inferred that the optical axis of the N_d phase was tilted. The lamellar phase of the DACl-KCl-D₂O system as well as the lamellar phase obtained by adding phosphoric acid decylester/phosphoric acid (PDE/H₃PO₄) showed the following phase sequence: L_α + N_d 35°C H_α + N_d 40°C N_c + N_d 45°C N_c 50°C isotropic The line shapes of ³¹P NMR of PDE/H₃PO₄ were found to be sensitive to micelle size and dynamics occuring in the lyotropic system, but they do not differentiate between different micelle shapes.     

聚氨脂的阻尼性能和形态结构的研究——Ⅰ.硬段分布对PPG-TDI-MOCA体系的影响

研究了硬段的含量和交联度对PPG（聚氧化丙烯二醇）-TDI（二苯基甲烷二异氰酸酯）-MOCA（3,3′-二氯-4,4′-二氨基二苯甲烷）聚氨酯体系的动态力学性能的影响。结果表明：随着体系硬段含量的增加，材料的阻尼峰降低，而玻璃化转变温度变化较小；随着体系交联度的增加，聚氨酯在高温部分的阻尼因子提高，玻璃化转变温度向高温方向拓展，软段被“硬化”；但当交联度过大时，软段间的链缠结较多，低温部分的阻尼子下降。用原子力显微镜技术研究了硬段含量对PPG-TDI-MOCA体系的形态结构的影响，发现在硬段质量分数从28.43%增加到42.08%时，软段相区为连续相，但硬段微区的密度和尺寸明显增大，而且软硬段的界面变得清晰，相分离程度变大。     

大鲵精子入卵过程的扫描电镜观察

采用扫描电镜观察了大鲵精子的形状，受精过程中卵壳膜的变化，及精子入卵的过程．人工催产的精子头部具有棒状和辣椒状两种形状．卵壳膜随着受精时间的变化而出现皱褶、沟与嵴，受精完毕，皱褶消失．大鲵属于多精入卵，精、卵相遇６０ｓ，精子接触卵膜，授精７５ｓ精子头部一半进入卵内．授精９０ｓ精子头部和颈部完全进入卵内，但精子尾部留在卵膜外面；授精２ｍｉｎ，受精完毕．     

基于TFCALC软件的薄膜偏光分束镜的设计

根据Macnielle薄膜偏光分束镜的设计原理,利用膜系设计软件对偏光分束镜进行优化设计.总结了偏光镜设计时参考波长、入射角以及膜层数随波长的变化规律,给出了LaK₂基底,ZrO₂和SiO₂为高低膜料的薄膜偏光分束镜优化设计方案,为薄膜偏光分束镜的设计和镀膜工艺提供了参考依据.     

Fatigue crack propagation mechanisms in poly(methyl methacrylate) by in situ observation with a scanning laser microscope

Crack propagation tests were performed on an amorphous polymer, poly(methyl methacrylate), to investigate fatigue crack propagation mechanisms. A scanning laser microscope with a newly developed tensile testing machine was used to observe in situ crack propagation in compact‐type specimens. A crack usually propagated within the craze located at the crack tip under both static and cyclic loading conditions. When a crack stably propagated into the craze under static loading conditions, bright bands composed of the broken craze were observed at the edges along the crack wakes. However, there were successive ridges and valleys in place of bright bands along the crack wakes under cyclic loading conditions. When stable fatigue cracks were propagated at the loading half‐cycle in each cycle, new craze fragments appeared that were similar to the bright bands under static loading. However, the thickness of these fragments decreased in the following loading cycle, and a new valley was formed. This suggested that the valleys were formed by the contact between the fracture surfaces near the crack tip during unloading. Fatigue crack propagation is thought to be due to fibrils weakened by crack closure between fracture surfaces. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 3103–3113, 2001