Characters of Surface Deformation and Surface Wave in Thermal Capillary Convection

In the field of fluid mechanics, free surface phenomena is one of the most important physical processes. In the present research work, the surface deformation and surface wave caused by temperature difference of sidewalls in a rectangular cavity have been investigated. The horizontal cross-section of the container is 52 mmx42 mm, and there is a silicon oil layer of height 3.5 mm in the experimental cavity. Temperature difference between the two side walls of the cavity is increased gradually, and the flow on the liquid layer will develop from stable convection to un-stable convection. An optical diagnostic system consisting of a modified Michelson interferometer and image processor has been developed for study of the surface deformation and surface wave of thermal capillary convection. The Fourier transformation method is used to interferometer fringe analysis. The quantitative results of surface deformation and surface wave have been calculated from a serial of the interference fringe patterns.The characters of surface deformation and surface wave have been obtained. They are related with temperature gradient and surface tension. Surface deformation is fluctuant with time, which shows the character of surface wave. The cycle period of the wave is 4.8 s, and the amplitudes are from 0 to 0.55 mu m. The phase of the wave near the cool side of the cavity is opposite and correlative to that near the hot side. The present experiment proves that the surface wave of thermal capillary convection exists on liquid free surface, and it is wrapped in surface deformation.

Multi-scale analysis of AFM tip and surface interactions

Thoroughly understanding AFM tip-surface interactions is crucial for many experimental studies and applications. It is important to realize that despite its simple appearance, the system of tip and sample surface involves multiscale interactions. In fact, the system is governed by a combination of molecular force (like the van der Waals force), its macroscopic representations (such as surface force) and gravitational force (a macroscopic force). Hence, in the system, various length scales are operative, from sub-nanoscale (at the molecular level) to the macroscopic scale. By integrating molecular forces into continuum equations, we performed a multiscale analysis and revealed the nonlocality effect between a tip and a rough solid surface and the mechanism governing liquid surface deformation and jumping. The results have several significant implications for practical applications. For instance, nonlocality may affect the measurement accuracy of surface morphology. At the critical state of liquid surface jump, the ratio of the gap between a tip and a liquid dome (delta) over the dome height (y(o)) is approximately (n-4) (for a large tip), which depends on the power law exponent n of the molecular interaction energy. These findings demonstrate that the multiscale analysis is not only useful but also necessary in the understanding of practical phenomena involving molecular forces. (c) 2007 Elsevier Ltd. All rights reserved.

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.

Influence of ion energy and deposition temperature on the surface morphology of carbon films deposited by ion beams

Carbon films were deposited by mass-selected ion beam technique with ion energies 50-200eV at a substrate temperature from room temperature to 80 degreesC,. For the energies used, smooth diamond-like carbon films were deposited at room temperature. When the substrate temperature was 600 degreesC,rough graphitic films were produced. But highly oriented carbon tubes were observed when the energies were larger than 140eV at 800 degreesC. They were perpendicular to the surface and parallel to each other. preferred orientation of graphite basic plane was observed by high-resolution electron microscopy. Shallow ion implantation and stress are responsible for this orientation.

Effect of rapid thermal annealing on Ti-AlN interfaces

The interface diffusion, reaction, and adherence of rapid thermal annealed Ti/ALN were investigated by RES, AES, SIMS, XRD and a scratch test. The experimental results show that diffusion and reaction occurs at the interface of Ti/AlN when the sample is rapidly annealed. During annealing, both the O adsorbed on the surface and doped in the AlN substrate diffuse into the Ti film. At low temperature TiO2 is produced. At higher temperature O reacts with the diffused Al in the Ti film and produces an Al2O3 layer in the middle of the film. N diffuses into the Ti film and produces TiN with an interface reaction. Ti oxide is produced at the interface between the film and the substrate. Scratch test results show that interface adherence is distinctly improved by rapid annealing at low temperature and decreases at higher temperature. (C) 1999 Elsevier Science B.V. All rights reserved.

Influence of band bending and polarization on the valence band offset measured by x-ray photoelectron spectroscopy

The influence of band bending and polarization on the valence band offset measured by x-ray photoelectron spectroscopy (XPS) is discussed, and a modification method based on a modified self-consistent calculation is proposed to eliminate the influence and thus increasing the precision of XPS. Considering the spontaneous polarization at the surfaces and interfaces and the different positions of Fermi levels at the surfaces, we compare the energy band structures of Al/Ga-polar AlN/GaN and N-polar GaN/AlN heterojunctions, and give corrections to the XPS-measured valence band offsets. Other AlN/GaN heterojunctions and the piezoelectric polarization are also introduced and discussed in this paper.

Tunable Ag surface-plasmon-resonance wavelength and its application on the photochromic behavior of TiO2-Ag films

Surface and bulk plasmon resonance of noble metal particles play an essential role in the multicolor photochromism of semiconductor systems containing noble metal particles, Here we examined several key parameters affecting surface plasmon resonance wavelength (SPRW) of Ag particles and investigated the relation between surface plasmon and photochromic reaction wavelength. From the transmission spectra of sandwiched (TiO2/Ag/TiO2) and overcoated (Ag/TiO2) films deposited on quartz substrates at room temperature by rf helicon magnetron sputtering, we demonstrated that the SPRW can be made tunable by changing the surrounding media and thickness of the metal layer. The coloration and bleaching in visible light region due to photochromism were clearly observed for the films inserted with a 0.55 nm Ag layer.

PHOTOLUMINESCENCE AND SURFACE PHOTOVOLTAIC SPECTRA OF STRAINED INP ON GAAS

A high energy shift of the band-band recombination has been observed in the photoluminescence (PL) spectra of the strained InP epilayer on GaAs by metalorganic chemical vapor deposit. The strain determined by PL peak is in good agreement with calculated thermal strain. The surface photovoltalic spectra gives the information about energy gap, lattice mismatching, and composition of heteroepilayers, diffusion length, surface, and interface recombination velocity of minority carriers of heteroepitaxy layers.

The interaction of recombinant Pseudomonas aeruginosa exotoxin A with DNA and mimic biomembrane investigated by surface plasmon resonance and electrochemical methods

Based on the multidomain structure of Pseudomonas aeruginosa exotoxin A, a fusion protein termed rPEA has been constructed, which is expected to serve as a gene carrier in vitro. The expression and purification of rPEA are described. The basal properties of rPEA as a gene carrier are evaluated by investigating its interaction with plasmid DNA and mimic biomembrane by surface plasmon resonance (SPR) and electrochemical methods. rPEA is proved to be able to bind with plasmid DNA with high affinity. It can also interact with lipid membrane and increase permeability of the membrane, so the probe molecules can easily reach the gold surface and exhibit the electrochemical response.

Probing UPD-induced surface atomic rearrangement of polycrystalline gold nanofilms with surface plasmon resonance spectroscopy and cyclic voltammetry

Silver underpotential deposition (UPD)-induced surface atomic rearrangement of polycrystalline gold nanofilms was probed with use of surface plasmon resonance spectroscopy (SPRs) as a novel probe tool in combination with cyclic voltammetry. Interestingly, upon repetitive electrochemical UPD and stripping of Ag, the surface structure of the resulting bare Au film is rearranged due to strong adatom-substrate interactions, which causes a large angle shift of SPR R-theta curves, in a good linear relationship with the number of UPDs, to a lower SPR angle. The n, K values of the surfacial Au monolayers before and after the repetitive Ag UPD and stripping for 27 times are found to be 0.133, 3.60 and 0.565, 9.39, respectively, corresponding to the huge shift of 1.61degrees to the left of the SPR minima. Cyclic voltammetry experiments in 0.10 M H2SO4 are carried out before and after the UPD treatment to examine the quality of the whole electrode surface and confirmed this change. To correlate the angle change in SPRs with the profile change in the cyclic voltammogram, the UPD treatment was also performed on a Au(111) textured thin film. It was therefore confirmed that the resonance position of the SPR spectrum is very sensitive to the surface crystallographic orientation of the bare Au substrates. Some surface atomic rearrangement can cause a pronounced SPR angle shift.

Potential-induced transformation for surfactant aggregates on a metal surface

Surfactant adsorption on metal surfaces has been used to limit the activity of the electrode surface and to stabilize colloidal clusters and nanoparticles in solution, but the adsorption and relative potential-induced structure change of the surfactant were not known. Here, the adsorption of sodium dodecyl sulfate (SDS) on a Au(111) surface under potential control was investigated by in situ scanning tunneling microscopy (STM). The STM images showed that the morphology of SDS on Au(111) was changed from a hemi-cylindrical micellar monolayer to a compact and uniform bilayer through control of the potential. The transition between the hemimicellar monolayer and the compact bilayer is not reversed after a period of time. The model of potential-induced transformation for SDS aggregates on Au(111) was established. (C) 2001 Elsevier Science B.V. All rights reserved.

Potential-dependent adsorption/desorption of organic adsorbate at HOPG electrode and accompanying delamination of graphite surface

In situ electrochemical scanning tunneling microscopy, alternating current voltammetry, and electrochemical quartz crystal microbalance have been employed to follow the potential-dependent adsorption/desorption processes of nucleic acid bases on highly oriented pyrolytic graphite (HOPG) electrode. The results show that (i) potential-dependent adsorption/desorption of nucleic acid bases on HOPG electrode was accompanied by delamination of the HOPG surface, and the delamination initiates from steps or kinks on the electrode surface, which provide highly active sites for adsorption; (ii) the delamination usually occurred when the electrode potential was changed or when the electrode was at potentials where the phase transition of adsorbate occurred. These results suggest that the surface stress resulting from the interaction between the substrate and adsorbate, as well as the interaction due to potential-induced surface charge distribution and the hysteresis of charge equilibrium are the main factors resulting in HOPG delamination. (C) 1999 The Electrochemical Society. S0013-4651(97)12-013-4. All rights reserved.