Heteroepitaxial gold (111) rings on mica substrates

Two-dimensionally arranged gold rings were prepared by depositing a polymeric membrane bearing a dense array of uniform pores onto a mica substrate, filling the pores with a solution of a gold precursor, evaporation of the solvent and calcinations. The epitaxy of gold rings is confirmed by x-ray diffraction measurements, and the epitaxial relationship between gold rings and the mica was found to be Au(111)[1-10]parallel to mica(001)[010]. The polar and azimuthal angular spreads are 0.3 degrees and 1 degrees, respectively, which is at least equal to or better than the quality of the corresponding epitaxial gold-film on mica. (c) 2005 American Institute of Physics.

Adsorption behaviors of methanol, ethanol, n-butanol, n-hexanol and n-octanol on mica surface studied by atomic force microscopy

The adsorption behavior of methanol, ethanol, n-butanol, n-hexanol and n-octanol on mica surface was investigated by atomic force microscopy. All these alcohols have formed homogeneous films with different characteristics. Upright standing bilayer structure was formed on methanol adsorbed mica surface. For ethanol, bilayer structure and monolayer one were simultaneously formed, while for n-butanol and n-hexanol, rough films were observed. What was formed for n-octanol? Close-packed flat film was observed on n-octanol adsorbed mica substrate, the film was assumed to be a tilted monolayer. The possible adsorption model for each alcohol molecule was proposed according to its adsorption behavior.

Direct patterning of rhodamine 6G molecules on mica by dip-pen nanolithography

Dip-pen nanolithography (DPN) has been developed to pattern monolayer film of various molecules on suitable substrate through the controlled movement of ink-coated atomic force microscopy (AFM) tip, which makes DPN a potentially powerful tool for making the functional nanoscale devices. In this paper, the direct patterning of rhodamine 6G on mica by dip-pen nanolithography was demonstrated. R6G features patterned on the mica was successfully achieved with different tip movement which can be programmed by Nanoscript(TM) language. From the AFM image of R6G patterns, we know that R6G molecule is flatly binding to the mica surface through electrostatic interaction, thus stable R6G nanostructures could be formed on mica. The influence of translation speed and contact time on DPN was discussed. The method can be extended to direct patterning of many other organic molecules, and should open many opportunities for miniaturized optical device and site-specific biological staining.

A novel strategy to construct a flat-lying DNA monolayer on a mica surface

Flat-lying, densely packed DNA monolayers in which DNA chains are well organized have been successfully constructed on a mica surface by dropping a droplet of a DNA solution on a freshly cleaved mica surface and subsequently transferring the mica to ultrapure water for developing. The formation kinetics of such monolayers was studied by tapping mode atomic force microscopy (TMAFM) technique. A series of TMAFM images of DNA films obtained at various developing times show that before the sample was immersed into water for developing the DNA chains always seriously aggregated by contacting, crossing, or overlapping and formed large-scale networks on the mica surface. During developing, the fibers of DNA networks gradually dispersed into many smaller fibers up to single DNA chains. At the same time, the fibers or DNA chains also experienced rearrangement to decrease electrostatic repulsion and interfacial Gibbs free energy. Finally, a flat-lying, densely packed DNA monolayer was formed. A formation mechanism of the DNA monolayers was proposed that consists of aggregation, dispersion, and rearrangement. The effects of both DNA and Mg2+ concentration in the formation solution on DNA monolayer formation were also investigated in detail.

Self-assembled monolayer growth of octanol on mica: Atomic force microscopy and Fourier-transform infrared spectroscopy studies

The growth kinetics of self-assembled monolayers formed by exposing freshly cleaved mica to octanol solution has been studied by atomic force microscopy (AFM) and Fourier-transform infrared spectroscopy (FTIR). AFM images of samples immersed in octanol for varying exposure times showed that before forming a complete monolayer the octanol molecules aggregated in the form of small islands on the mica surface. With the proceeding of immersion, these islands gradually grew and merged into larger patches. Finally, a close-packed film with uniform appearance and few defects was formed. The thickness of the final film showed 0.8 nm in height, which corresponded to the 40degrees tilt molecular conformation of the octanol monolayer. The growth mechanisms consisted of nucleation, growth, and coalescence of the submonolayer films. The growth process was also confirmed by FTIR. And the surface coverage of the submonolayer islands estimated from AFM images and FTIR spectra as a function of immersion time was quite consistent.

AFM studies of DNA structures on mica in the presence of alkaline earth metal ions

As counterions of DNA on mica, Mg2+, Ca2+, Sr2+ and Ba2+ were used for,clarifying whether DNA molecules equilibrate or are trapped on mica surface. End to end distance and contour lengths were determined from statistical analysis of AFM data. It was revealed that DNA molecules can equilibrate on mica when Mg2+, Ca2+ and Sr2+ are counterions. When Ba2+ is present, significantly crossovered DNA molecules indicate that it is most difficult for DNA to equilibrate on mica and the trapping degree is different under different preparation conditions. In the presence of ethanol, using AFM we have also observed the dependence of B A conformational transition on counterion identities. The four alkaline earth metal ions cause the B-A transition in different degrees, in which Sr2+ induces the greatest structural transition.

Study of methanol adsorption on mica, graphite and ITO glass by using tapping mode atomic force microscopy

Tapping mode atomic force microscopy (AFM) was applied to study the adsorption behavior of methanol on mica, highly oriented pyrolytic graphite (HOPG) and indium-tin oxide (ITO) coated glass substrates. On mica and HOPG substrates surfaces, the thin films of methanol with bilayer and multilayer were observed, respectively. The formation of irregular islands of methanol was also found on HOPG surface. On ITO surface only aggregates and clusters of methanol molecules were formed. The influence of sample preparation on the adsorption was discussed.

A mica-modified quartz resonator for a quartz crystal microbalance study

Mica, as a bridge of the study for combining between quartz crystal microbalance (QCM) and atomic force microscope (AFM), was successfully modified onto the piezoelectric quartz crystal (PQC). This mica-modified piezoelectric quartz crystal (mica-PQC) can be stably oscillated with a shift frequency of +/-1 Hz per half an hour in air. Using this mica-PQC, the processes of DNA adsorbed onto the mica surface were studied in liquid phase. The results show that a bivalent cation, such as Mn2+, can be used as an ionic bridge to immobilize DNA on mica surface. The image of DNA on the mica surface was also obtained by AFM. Mica-PQC gives the possibility of a combination between QCM and AFM in situ.

一种基于新型数据预测方法的MICA仿真研究

在多元统计过程监控中,为解决因未知过程数据统计分布而产生误报漏报的现象,提出一种结合多向独立元分析法(MICA)和广义相关系数(GCC)数据预测的综合方法,进行在线监控过程的仿真。MICA分析方法能有效分解各变量的关联关系,且不需考虑建模数据是否符合正态分布,用此方法计算的独立元变量能更好地描述过程的变化规律。为提高预报未来过程故障的能力,提出用广义相关系数法进行数据预测:确定与运行轨迹相似的监控模型库中的轨迹,并使其相应部分承接于运行轨迹之后。现场采集聚氯乙烯聚合过程的数据进行仿真,仿真结果显示:对于在线监控和在线故障诊断方面,这种新型预测方法优于其它传统处理预测问题的方法。

Growth of liquid bridge in AFM

Capillary forces are dominant in adhesive forces measured with an atomic force microscope (AFM) in ambient air, which are thought to be dependent on water film thickness, relative humidity and the free energy of the water film. In this paper, besides these factors, we study the nature of the 'pull-off' force on a variety of atmospheres as a function of the contact time. It is found that capillary forces strongly depend on the contact time. In lower relative humidity atmosphere, the adhesion force is almost independent of the contact time. However, in higher relative humidity, the adhesion force increases with the contact time. Based on the experiment and a model that we present in this paper, the growth of the liquid bridge can be seen as undergoing two processes: one is water vapour condensation; the other is the motion of the thin liquid film that is absorbed on the substrate. The experiment and the growth model presented in this paper have direct relevance to the working mechanism of AFM in ambient air.

掺铒碲酸盐玻璃中的浓度猝灭机理研究

测试了掺铒碲酸盐玻璃在不同掺杂浓度下的荧光特性．根据Dexter能量转移理论计算了Er^3+在碲酸盐玻璃中发生浓度猝灭的临界距离R0及Er^3+间相互作用参数CEr-Er，并与其他基质玻璃中CEr-Er数值进行了比较．最后建立了Er^3+基于OH^-作为猝灭中心下碲酸盐玻璃中的浓度猝灭模型．

A comparison between contactless electroreflectance and photoreflectance spectra from n-doped GaAs on a semi-insulating GaAs substrate

Contactless electroreflectance (CER) and photoreflectance (PR) measurements have been performed on samples with the structure of an n-doped GaAs epitaxial layer on a semi- insulating GaAs substrate. Modulated reflectance signals from the n-GaAs surface and those from the n-GaAs/SI-GaAs interface are superposed in PR spectra. For the case of CER measurement, however, Franz-Keldysh oscillations (FKOs) from the interface, which are observed in PR spectra, cannot be detected. This discrepancy is attributed to different modulation mechanisms of CER and PR. In CER experiments, the electric field modulation cannot be added to the interfacial electric field because of the effective screening by the fast response of carriers across the interface. FKOs from the interface without any perturbation by the surface signals are extracted by subtracting CER spectra from PR spectra.