Tip-induced dynamic characterization of multilayers and variable morphologies of cytochrome c molecules on highly oriented pyrolytic graphite revealed by in-situ scanning tunnelling microscopy

The dynamic states of cytochrome c multilayers on electrochemically pretreated highly oriented pyrolytic graphite (HOPG) have been studied by in-situ scanning tunnelling microscopy (STM) under potential control of both the tip and the substrate in cytochrome c and phosphate buffer solution. The dynamic characterization of cytochrome c multilayers and relatively stable adsorbed single cytochrome c molecules scattered on HOPG imply that physically adsorbed multilayers were more easily influenced by the STM tip than those of chemically adsorbed single molecules. In-situ STM images of chemically adsorbed cytochrome c molecules with discernible internal structures on HOPG revealed that morphologies of cytochrome c molecules also suffered tip influence; possible tip-sample-substrate interactions have been discussed.

Reduced deep-tissue image degradation in three-dimensional multiphoton microscopy with concentric two-color two-photon fluorescence excitation

We theoretically demonstrate that enhanced penetration depth in three-dimensional multiphoton microscopy can be achieved using concentric two-color two-photon (C2C2P) fluorescence excitation in which the two excitation beams are separated in space before reaching their common focal spot. Monte Carlo simulation shows that, in comparison with the one-color two-photon excitation scheme, the C2C2P fluorescence microscopy provides a significantly greater penetration depth for imaging into a highly scattering medium. (C) 2008 Optical Society of America.

Femtosecond laser pulse irradiation of Sb-rich AgInSbTe films: Scanning electron microscopy and atomic force microscopy investigations

The single-layer and multilayer Sb-rich AgInSbTe films were irradiated by a single femtosecond laser pulse with the duration of 120 fs. The morphological feature resulting from the laser irradiation have been investigated by scanning electron microscopy and atom force microscopy. For the single-layer film, the center of the irradiated spot is a dark depression and the border is a bright protrusion; however, for the multilayer film, the center morphology changes from a depression to a protrusion as the energy increases. The crystallization threshold fluence of the single-layer and the multilayer films is 46.36 mJ/cm(2), 63.74 mJ/cm(2), respectively.

Super-resolution scanning laser microscopy with a third-order optical nonlinear thin film

In a configuration of optical far-field scanning microscopy, super-resolution achieved by inserting a third-order optical nonlinear thin film is demonstrated and analyzed in terms of the frequency response function. Without the thin film the microscopy is diffraction limited; thus, subwavelength features cannot be resolved. With the nonlinear thin film inserted, the resolution is dramatically improved and thus the microscopy resolves features significantly smaller than the smallest spacing allowed by the diffraction limit. A theoretical model is established and the device is analyzed for the frequency response function. The results show that the frequency response function exceeds the cutoff spatial frequency of the microscopy defined by the laser wavelength and the numerical aperture of the convergent lens. The main contribution to the improvement of the cutoff spatial frequency is from the phase change induced by the complex transmission of the nonlinear thin film. Experimental results are presented and are shown to be consistent with the results of theoretical simulations.

Scanning electron microscopy of Aspidogaster ijimai Kawamura, 1913 and A-conchicola Baer, 1827 (Aspidogastrea, Aspidogastridae) with reference to their fish definitive-host specificity

Two species of aspidogastreans, namely Aspidogaster ijimai and A. conchicola, were studied by scanning electron microscopy. In nine lakes and an old river course, the Tian'ezhou oxbow, investigated in the flood plain of the Yangtze River, A. ijimai was obtained from the common carp (Cyprinus carpio) in three lakes, and A. conchicola from the black carp Mylopharyngodon piceus in three lakes and the oxbow. In none of the localities, however, were the two species found together. It is suggested that A. ijimai may be considered as a specialist parasite for the common carp, at least in the flood-plain lakes of the Yangtze River. The two parasites were similar in many aspects of their morphology. Their bodies can both be separated into a dorsal part and a ventral disc, with the body surface of the dorsal part elevated by transverse folds, and the disc subdivided into alveoli by transverse and longitudinal septa, although the number of alveoli was different in the two species. The depression on the ventral surface of the neck region was prominent for both species, and their ventral disc was covered densely with non-ciliated bulbous papillae. The position of mouth, osmo-regulatory pore and marginal organ was also similar for A. ijimai and A. conchicola. However, microridges in the trough of the folds in the neck region and numerous small pits on the upper part of the septa were found exclusively in A. ijimai, but uniciliated sensory papillae in A. conchicola.

Scanning electron microscopy observation of in-device InAs/AlAs quantum dots by selective etching of capping layers

Self-assembled InAs/AlAs quantum dots embedded in a resonant tunneling diode device structure are grown by molecular beam epitaxy. Through the selective etching in a C6H8O7 center dot H2O-K3C6H5O7 center dot H2O-H2O2 buffer solution, 310 nm GaAs capping layers are removed and the InAs/AlAs quantum dots are observed by field-emission scanning electron microscopy. It is shown that as-fabricated quantum dots have a diameter of several tens of nanometers and a density of 10(10) cm(-2) order. The images taken by this means are comparable or slightly better than those of transmission electron microscopy. The undercut of the InAs/AlAs layer near the edges of mesas is detected and that verifies the reliability of the quantum dot images. The inhomogeneous oxidation of the upper AlAs barrier in H2O2 is also observed. By comparing the morphologies of the mesa edge adjacent regions and the rest areas of the sample, it is concluded that the physicochemical reaction introduced in this letter is diffusion limited.

A novel contactless method for characterization of semiconductors: Surface electron beam induced voltage in scanning electron microscopy

We present a novel contactless and nondestructive method called the surface electron beam induced voltage (SEBIV) method for characterizing semiconductor materials and devices. The SEBIV method is based on the detection of the surface potential induced by electron beams of scanning electron microscopy (SEM). The core part of the SEBIV detection set-up is a circular metal detector placed above the sample surface. The capacitance between the circular detector and whole surface of the sample is estimated to be about 0.64 pf It is large enough for the detection of the induced surface potential. The irradiation mode of electron beam (e-beam) influences the signal generation. When the e-beam irradiates on the surface of semiconductors continuously, a differential signal is obtained. The real distribution of surface potentials can be obtained when a pulsed e-beam with a fixed frequency is used for irradiation and a lock-in amplifier is employed for detection. The polarity of induced potential depends on the structure of potential barriers and surface states of samples. The contrast of SEBIV images in SEM changes with irradiation time and e-beam intensity.

INVESTIGATION OF POROUS SILICON BY SCANNING-TUNNELING-MICROSCOPY AND ATOMIC-FORCE MICROSCOPY

The size and distribution of surface features of porous silicon layers have been investigated by scanning tunneling and atomic force microscopy. Pores and hillocks down to 1-2 nm size were observed, with their shape and distribution on the sample surface being influenced by crystallographic effects. The local density of electronic states show a strong increase above 2 eV, in agreement with recent theoretical predictions.

Effects of Thickness on Properties of ZnO Films Grown on Si by MOCVD

High quality ZnO films are successfully grown on Si（100） substrates by metal-organic chemical vapor deposition at 300℃. The effects of the thickness of the ZnO films on crystal structure, surface morphology,and optical properties are investigated using X-ray diffraction, scanning probe microscopy,and photoluminescence spectra, respectively. It is shown that the ZnO films grown on Si substrates have a highly-preferential C-axis orientation,but it is difficult to obtain the better structural and optical properties of the ZnO films with the increasing of thickness. It is maybe due to that the grain size and the growth model are changed in the growth process.

Broadband short-range surface plasmon structures for absorption enhancement in organic photovoltaics

We theoretically demonstrate a polarization-independent nanopatterned ultra-thin metallic structure supporting short-range surface plasmon polariton (SRSPP) modes to improve the performance of organic solar cells. The physical mechanism and the mode distribution of the SRSPP excited in the cell device were analyzed, and reveal that the SRSPP-assisted broadband absorption enhancement peak could be tuned by tailoring the parameters of the nanopatterned metallic structure. Three-dimensional finite-difference time domain calculations show that this plasmonic structure can enhance the optical absorption of polymer-based photovoltaics by 39% to 112%, depending on the nature of the active layer (corresponding to an enhancement in short-circuit current density by 47% to 130%). These results are promising for the design of organic photovoltaics with enhanced performance.

In Situ Scanning Tunneling Microscopy on the Dynamic Process of the Replacement of Coronene on Au (111) by 6-Mercapto-1-Hexanol

The replacement of coronene monolayer on Au (111) by 6-mercapto-1-hexanol (MHO) was studied by in situ scanning tunneling microscopy (STM) in solutions. It was found that the rate of replacement depends strongly on the concentration of MHO. The replacement finished within a second at a higher concentration of MHO. At a lower concentration, the slow replacement could be followed by in situ STM. The replacement occurred initially near the elbow position of reconstructed Au (111) with the formation of pits in a single or several missing molecules. With the proceeding of replacement, these small pits expanded, and the surrounding coronene molecules were gradually substituted by MHO, which developed into ordered domains within a spatial confined environment. Meanwhile, the reconstruction of Au (111) was lifted. The replacement expanded fast along the reconstruction lines in the domain. For the fast replacement, a (root 3 x root 3) R30 degrees adlattice was observed, while a c(4 x 2) superlattice was observed for the slow replacement.

Immobilization of the nanoparticle monolayer onto self-assembled monolayers by combined sterically enhanced hydrophobic and electrophoretic forces

The immobilization of surface-derivatized gold nanoparticles onto methyl-terminated self-assembled monolayers (SAMs) on gold surface was achieved by the cooperation of hydrophobic and electrophoretic forces. Electrochemical and scanning probe microscopy techniques were utilized to explore the influence of the SAM's structure and properties of the nanoparticle/SAM/gold system. SAMs prepared from 1-decanethiol (DT) and 2-mercapto-3-n-octylthiophene (MOT) were used as hydrophobic substrates. The DT SAM is a closely packed and organized monolayer, which can effectively block the underlying gold and inhibit a variety of solution species including organic and inorganic molecules from penetrating, whereas the MOT monolayer is poorly packed or disorganized (because of a large difference in dimension between the thiophene head and the alkylchain tail) and permeable to many organic probes in aqueous solution but not to inorganic probes. Thus, the MOT monolayer provides a more energetically favorable hydrophobic surface for the penetration and adsorption of organic species than the DT monolayer.