贴膜条件下飞秒激光诱导硅基表面锥状微结构

利用波长为800 nm的飞秒脉冲激光,对表面贴有聚对苯二甲酸乙二醇酯透明膜的单晶硅片进行扫描,研究了不同激光制备参数对微结构形成的影响.结果表明,锥状微结构是否形成取决于激光能量密度,能量密度太小时不能形成锥状结构,能量密度太大时易破坏锥状突起;而激光扫描速度可直接影响锥状微结构的质量,扫描速度太小时也易破坏锥状结构突起,扫描速度太大时,由于作用深度太浅使得锥状结构轮廓不分明.在此基础上对实验参数进行优化,得到了较理想的锥状微结构.最后通过分析指出,贴膜条件下锥状微结构的形成是由激光烧蚀作用和氧化作用共同引起的,且激光烧蚀作用占主导.     

Modified thermal evaporation process using GeO2 for growing ZnO structures

In the current work, zinc oxide (ZnO) nano/microstructures are synthesized using a modified thermal-evaporation process by introducing germanium oxide (GeO₂) powder mixed with metallic Zn powder as the raw material. Without the use of any catalyst and oxygen flow in the furnace system, GeO₂ is utilized to provide an oxygen source for the growth of ZnO structure. The samples are treated by different temperatures ranging from 500 to 900 °C. Morphology, phase structure, and photoluminescence properties are investigated by scanning electron microscopy (SEM), X-ray diffractometer (XRD) and photoluminescence (PL) spectrometer. The structures and morphologies of the samples were found to vary with growth temperature. The XRD diffraction peaks show that the films grown at temperature from 600 to 800 °C consist of hexagonal wurtzite ZnO structures. Room-temperature PL measurement revealed ZnO spectra representing two bands: near-band-edge emission in the ultraviolet (UV) region and broad deep-level emission centered at about 500 nm. The strong UV emission in the PL spectra indicates that the GeO₂ supplies sufficient oxygen for formation of ZnO structures with few oxygen vacancies. The growth mechanism and the roles of GeO₂ for formation of ZnO structures are discussed in detail.     

A topographically optimized substrate with well-ordered lattice micropatterns for enhancing the osteogenic differentiation of murine mesenchymal stem cells

Although recently a growing number of reports demonstrate that topography or geometry of the substrate also plays an important role in the fate of the stem cells, most of these studies are usually completed by a few distinct patterns such as simple lines, posts, etc. As a result, there is a lack of quantitative analysis of the relationship between topographical variation and the differentiation of stem cells. Here, the effectiveness of topography variation is studied systematically in several microengineered substrates on osteogenic differentiation. It is found that the effectiveness of the osteogenic differentiation has a peak around 3 μm in the interval length of micropatterns.     

Extracellular matrix functionalized microcavities to control hematopoietic stem and progenitor cell fate

Polymeric microcavities functionalized with extracellular matrix components were used as an experimental in vitro model to investigate principles of hematopoietic stem and progenitor cell (HSPC) fate control. Using human CD133+ HSPC we could demonstrate distinct differences in HSPC cycling and differentiation dependence on the adhesion ligand specificity (i.e., heparin, collagen I) and cytokine levels. The presented microcavity platform provides a powerful in vitro approach to explore the role of exogenous cues in HSPC fate decisions and can therefore be instrumental to progress in stem cell biology and translational research toward new therapies.     

Effect of microstructures restoration on high temperature fatigue behavior of DZ125 superalloy

Combination of hot isostatic pressing (HIP) and rejuvenation heat treatment (RHT) technology was used to restore creep-damaged DZ125 directional solidified superalloy, and the influence of microstructure restoration on high temperature fatigue behavior of the samples was explored. The results show that the HIP+RHT process could effectively heal internal cavities and recover the degraded γ′ phase in creep-damaged DZ125 superalloy to cubic particles similar as in as-received sample. After restoration treatment, the stress concentration areas inside the sample eradicated with the healing of the internal cavities, and the fatigue source areas were limited only to near surface than initiating from inside as in the as-received and creep-damaged samples. As a result, the restored sample had higher crack initiation life and lower crack propagation rate compared to as-received and creep damaged samples. The TEM microstructure characterization near fatigue fracture showed that the restoration of the degraded γ′ phase eliminated tangled dislocation in creep damaged sample and produced evenly distributed dislocations in the γ channel with short curved line-like morphology, like the as-received sample, which effectively hindered the dislocations movement during subsequent deformation, and strengthen the fatigue resistant of alloy. Therefore, it can be concluded that the HIP-RHT process, through the combined effect of internal cavities healing and the restoration of the degraded microstructures, renders higher high temperature fatigue life than creep-damaged and even higher than as-received DZ125 superalloy.     

Synthesis of three-dimensional hierarchical cobalt hydroxide microstructures

β-Co(OH)2 with three-dimensional (3-D) structures was prepared by a simple hydrothermal method. It was found that the amount of cetyltrimethylammonium bromide (CTAB), the pH value, and the reaction time all had an important influence on the formation of this morphology. The products were characterized by X-ray diffraction, energy-dispersive X-ray analysis, and scanning electron microscopy. A possible mechanism of the formation of the 3-D microstructures of β-Co(OH)2 was proposed.     

Tweed microstructures: Experimental observations and some theoretical models

Experimental observations, mainly by transmission electron microscopy, of tweed microstructures in minerals (K-feldspar and cordierite), high-T _c superconductors (Co-doped YBCO) and metals are reviewed. Structural models of the local structure within the tweed are compared and evaluated with respect to spectroscopic measurements in a number of systems. It is concluded that in tweed microstructures which result from symmetry changes driven by cation-ordering, the local degree of order is not itself modulated. A model based on twin-related domains of the low symmetry form is consistent with experimental observations. Mechanisms of coarsening of the tweed microstructure to form the lamellar twinning observed in the fully ordered structure are briefly reviewed.     

ZnO微结构调控及其光学性能的研究

氧化锌不同形貌的合成与控制可以通过一个简单的溶剂热反应来实现,其中乙醇作溶剂,酒石酸做添加剂。通过控制酒石酸的加入量,可以有效地控制ZnO的形貌、尺寸以及到更复杂结构的转变。同时提出了不同形貌ZnO可能的生长机制,并利用FTIR谱进一步证实了酒石酸对ZnO生长的影响。另外,由光致发光光谱可以看出,不同的ZnO形貌,发光性能会有所不同,总体上说,所得ZnO的发光区域主要集中在紫光波段和橙光波段。     

A study of multi-trapping of tapered-tip single fiber optical tweezers

We develop a pair of tapered-tip single fiber optical tweezers, and study its multi-trapping characteristic. The finite difference time domain method is employed to simulate the trapping force characteristic of this pair of single fiber optical tweezers, and the results show that the number of trapped particles depends on the refractive index and the size of the particles. The trapping force of this pair of tapered-tip single fiber optical tweezers is calibrated by the experimental method, and the experimental results are consistent with the theoretical calculation results. The multi-trapping capability realized by the tapered-tip single fiber optical tweezers will be practical and useful for applications in biomedical research fields.