Local field distribution and configuration of CO molecules adsorbed on the nanostructure platinum surface

This paper shows that the local electric field distribution near the nanostructure metallic surface is obtained by solving the Laplace equation, and furthermore, the configuration of CO molecules adsorbed on a Pt nanoparticle surface is obtained by using Monte Carlo simulation. It is found that the uneven local electric field distribution induced by the nanostructure surface can influence the configuration of carbon monoxide (CO) molecules by a force, which drags the adsorbates to the poles of the nanoparticles. This result, together with our results obtained before, may explain the experimental results that the nanostructure metallic surface can lead to abnormal phenomena such as anti-absorption infrared effects.     

Preparation and Annealing—Induced Structural Transition of Self—Organized Nanostripes on the Electropolished Aluminium Surface

Self-organized nanostripe patterns with a wavgelength of 100 nm and an amplitude of 4-5 nm were formed on the surface of high-purity aluminium by electropolishing.The thermal stability of the nanostripe patterns was investigated experimentally by using a needle-sensor atomic force microscope in an ultra-high vacuum after annealing the sample in a high vacuum.We found that the originally highly ordered nanostripe structures transformed into many domains separated by various boundaries,and different nanostripe patterns formed,the belt-like boundaries especially formed “cross” patterns on the surface.We also found that the vacuum annealing had the tendency to efface the nanostripe structures.     

Humidity Effects on Imaging and Nanomanipulation of Individual DNA Molecules on HOPG Surface

Single DNA molecules are aligned on highly ordered pyrolytic graphite （HOPG） surface in ambient air. It is shown that environmental humidity has a remarkable influence on the measured height of DNA by atomic force microscopy （AFM）, probably due to the conformation transition of DNA. We also demonstrate that DNA molecules deposited on HOPG surface can be ＇pushed＇ much more easily by AFM tip at high humidity than at 10W one.     

Effect of Laser Field and Mechanical Force on Deoxyribonucleic Acid Melting

We propose a physics method to study the effect of laser field and mechanical force on the melting process of double-stranded deoxyribonucleic acid （DNA）. A two-dimensional lattice model is established for DNA molecules stuck on the surface, and the stretching energy of the hydrogen bond and stacking energy for each DNA molecule are calculated by using a nonlinear potential. A real-time algorithm is employed to deal with the dynamics process of DNA melting. Numerical results explain the experimental observations. The spatial distribution of the laser field determines the sequences of DNA melting. The simulation has shown the dependence of the final number of melted DNA on the laser field and mechanical force.     

Direct observation of λ-DNA molecule reversal movement within microfluidic channels under electric field with single molecule imaging technique

The electrodynamic characteristics of single DNA molecules moving within micro-/nano-fluidic channels are important in the design of biomedical chips and bimolecular sensors. In this study, the dynamic properties of λ-DNA molecules transferring along the microchannels driven by the external electrickinetic force were systemically investigated with the single molecule fluorescence imaging technique. The experimental results indicated that the velocity of DNA molecules was strictly dependent on the value of the applied electric field and the diameter of the channel. The larger the external electric field, the larger the velocity, and the more significant deformation of DNA molecules. More meaningfully, it was found that the moving directions of DNA molecules had two completely different directions:(i) along the direction of the external electric field, when the electric field intensity was smaller than a certain threshold value;(ii) opposite to the direction of the external electric field, when the electric field intensity was greater than the threshold electric field intensity.The reversal movement of DNA molecules was mainly determined by the competition between the electrophoresis force and the influence of electro-osmosis flow. These new findings will theoretically guide the practical application of fluidic channel sensors and lab-on-chips for precisely manipulating single DNA molecules.     

Low-Dimensional Forest-Like and Desert-Like Fractal Patterns Formed in a DDAN Molecular System

Two kinds of forest-like and desert-like patterns are formed by thermal evaporation of 4-dicyanovinyl-N, Ndimethylamino-1-naphthalene （DDAN） onto SiO2 substrates. Based on thermal kinetics of the molecules on the substrate the transformation between the forest and desert patterns is due to two factors. The first one is the diffusion length, which is related to the deposition rate, the diffusion potential energy barrier and the substrate temperature. The second one is the strong interaction between the two polarity chemical groups of the molecules, which is beneficial to the formation of branches. Totally different patterns are also found on mica substrates, and are attributed to the anisotropic diffusion and the stronger interaction between DDAN molecules and the mica surface.     

Self－Assembled Monolayers Exposed by Metastable Helium for Nano－Patterning： Octanethiol and Dodecanethiol

A large-area gold pattern with nanoscale edge on muscovite mica was fabricated by using a metastable helium beam and octanethiol (OT) and dodecanethiol (DDT) self-assembled monolayers (SAM), in which the width of edge was typically ～70nm for the OT SAM and ～90nm for the DDT SAM, respectively. The mask was reproduced with high fidelity. Combined the analysis of roughness with grain size, more fiat surface and sharper edge of patterns were obtained by using the shorter chain molecules such as the OT. All the information indicated that the OT SAMs on atomically ttat surfaces can be used as a resist for exposure to metastable atom beams.     

Surface-enhanced Raman scattering properties of highly ordered self-assemblies of gold nanorods with different aspect ratios

Gold nanorods with aspect ratios of from 1 (particles) to 31.6 were synthesized by the seed-mediated method and packed in a highly ordered structure on a large scale on silicon substrates through capillary force induced self-assembly behaviour during solvent evaporation.The gold nanorod surface exhibits a strong enhancing effect on Raman scattering spectroscopy.The enhancement of Raman scattering for two model molecules (2-naphthalenethiol and rhodamine 6G) is about 5-6 orders of magnitude.By changing the aspect ratio of the Au nanorods,we found that the enhancement factors decreased with the increase of aspect ratios.The observed Raman scattering enhancement is strong and should be ascribed to the surface plasmon coupling between closely packed nanorods,which may result in huge local electromagnetic field enhancements in those confined junctions.     

Local electric field and configuration of CO molecules adsorbed on a nanostructured surface with nanocones

Based on the nanostructured surface model that the (platinum, Pt) nanocones grow out symmetrically from a plane substrate, the local electric field near the conical nanoparticle surface is computed and discussed. On the basis of these results, the adsorbed CO molecules are modelled as dipoles, and three kinds of interactions, i.e. interactions between dipoles and local electric field, between dipoles and dipoles, as well as between dipoles and nanostructured substrate, are taken into account. The spatial configuration of CO molecules adsorbed on the nanocone surface is then given by Monte-Carlo simulation. Our results show that the CO molecules adsorbed on the nanocone surface cause local agglomeration under the action of an external electric field, and this agglomeration becomes more compact with decreasing conical angle, which results in a stronger interaction among molecules. These results serve as a basis for explaining abnormal phenomena such as the abnormal infrared effect (AIRE), which was found when CO molecules were adsorbed on the nanostructured transition-metal surface.     

Ultrasonic field radiated by a normal shear wave probe

The field of horizontally polarized ultrasonic shear wave radiated by a 2/2 piezoelectric composite normal probe was studied. The strictly analytic field solutions for two different surface forces were deduced and the field distribution and directivity patterns were given by numerical calculations. The vertical radiated field of shear wave was obtained theoretically and compared with experiment. The experimental result of directivity pattern conformed the theoretical prediction, which provided the theoretical basis for the engineering application of the transducer.     

A modal analysis for the acoustic radiation problems, I. Theory

For the acoustic radiation problems from a complex vibrating body surface, a modal analysis approach is put forward. All the normal vibration velocities on a vibrating surface form the Hilbert space. In the Hilbert space, an operator is defined, which includes the radiation property of the vibrating surface and is linear, self-adjoint and positive. Using the operator, a set of basis functions in the Hilbert space are obtained, which describe the radiation patterns and are called the radiation modes. Based on the radiation modes, a set of basis functions of the radiation field are obtained by the Helmholtz simple layer potentials, which describe the distribution patterns of the radiation field and are called the field distribution modes. The radiation behavior can be expressed by expansions of the radiation modes and the field distribution modes. The modal analysis approach is introduced into the acoustic radiation problems.     

Numerical simulation of filler metal droplets spreading in laser brazing

A finite element model was constructed using a commercial software Fidap to analyze the Cu-base filler metal droplet spreading process in laser brazing,in which the temperature distribution,droplet geometry, and fluid flow velocity were calculated.Marangoni and buoyancy convection and gravity force were considered,and the effects of laser power and spot size on the spreading process were evaluated.Special attention was focused on the free surface of the droplet,which determines the profile of the brazing spot. The simulated results indicate that surface tension is the dominant flow driving force and laser spot size determines the droplet spreading domain.     

Lipid membrane: inelastic deformation of surface structure by an atomic force microscope

The stability of the 1,2-Dioleoyl-sn-Glycero-3-[phospho-rac-1-Glycerol-Na] liposome in the liquid crystalline state have been investigated using an atomic force microscope (AFM). We have observed the inelastic deformation of the sample surface. The AFM tip causes persistent deformation of the surface of the lipid membrane, in which some of the lipid molecules are eventually pushed or dragged by the AFM tip. The experiment shows how the surface structure of the lipid membrane can be created by the interaction between the AFM tip and lipid membrane. When the operating force exceeds 10^-8 N, it leads to large deformations of the surface. A square region of about 1×1μm² is created by the scanning probe on the surface. When the operating force is between 10^-11N and 10^-8N, it can image the topography of the surface of the lipid membrane. The stability of the sample is related to the concentration of the medium in which the sample is prepared.     

Atomic force microscopy investigation of growth process of organic TCNQ aggregates on SiO2 and mica substrates

<正>Deposition patterns of tetracyanoquinodimethane(TCNQ) molecules on different surfaces are investigated by atomic force microscopy.A homemade physical vapour deposition system allows the better control of molecule deposition. Taking advantage of this system,we investigate TCNQ thin film growth on both SiO_2 and mica surfaces.It is found that dense island patterns form at a high deposition rate,and a unique seahorse-like pattern forms at a low deposition rate.Growth patterns on different substrates suggest that the fractal pattern formation is dominated by molecule-molecule interaction.Finally,a phenomenal "two-branch" model is proposed to simulate the growth process of the seahorse pattern.     

Influence on the propagation velocity of SAW by a force applied on surface

When a force is directly applied to the propagation surface of surface acoustic wave （SAW）, the velocity of SAW is varied. Then the loading force can be introduced by effective material coefficients and the velocity of SAW is calculated via the general Green＇s Function. The experimental results accord with the above numerical calculation very well. It also shows that the propagation loss will increase with the force load, and the velocity variation of SAW is proportional to the force loaded to the surfaces of SAW resonators, which has a high sensitivity about 5.97 m/s·N.     

Effect of Chemicals on Chemical Mechanical Polishing of Glass Substrates

We investigate the effect of chemicals on chemical mechanical polishing （CMP） of glass substrates. Ceria slurry in an ultra-low concentration of 0.25 wt. % is used and characterized by scanning electron microscopy. Three typical molecules, i.e. acetic acid, citric acid and sodium acrylic polymer, are adopted to investigate the effect on CMP performance in terms of material removal rate （MRR） and surface quality. The addition of sodium acrylic polymer shows the highest MRR as well as the best surface by atomic force microscopy after CMP, while the addition of citric acid shows the worst performance. These results reveal a mechanism that a long-chain molecule without any branches rather than small molecules and common molecules with ramose abundant-electron groups is better for the dispersion of the slurry and thus better for the CMP process.     

Near-Field Birefringence Response of Liquid Crystal Molecules in Thickness Direction of Liquid Crystal Thin Film Orientated by Shear Force

Information of molecular orientation in nematic liquid crystal （LC） is attractive and important for applications in the field of display devices. We demonstrate a novel method using a birefringence scanning near-field optical microscope （Bi-SNOM） with a probe which is inserted into the LC thin film to detect the molecular orientation from its birefringence responses in the thickness direction of the LC thin film. The probe is laterally vibrated when going forward into the LC thin film, and the retardation and azimuth angle are recorded as the probe going down. Firstly, the thickness of the LC thin film is measured by the shear force detection. Since the shear force acts as a stimulation to reorientate the LC molecules above the substrate surface, we can detect the molecular orientation caused by a polyimide alignment substrate and the effect to molecular orientation caused by vibration of fibre probe. As a result, the orientation profiling of the LC film in depth direction is obtained in both the cases that the direction of probe vibrating is vertical/parallel to the rubbing direction of the alignment film. Furthermore, the thickness of completely orientated layers just above the substrate surface can also be obtained by either vibrating probe or no-vibrating probe. Ultimately, the LC thin film can be modelled in thickness direction from all the results using this method.     

The ultrasonic transient field radiated by a normal shear wave probe

The ultrasonic transient field of horizontally polarized shear wave radiated by a 2/2 piezoelectric composite normal probe was analyzed. The analytic field solutions for two different surface force sources were deduced and the transient displacement field distribution on the central cross-section was plotted by numerical calculations. Direct wave and edge wave as well as head wave were observed distinctly in the plots. The experimental results of time domain waveform conformed with the theoretical predictions, which supported the theoretical and numerical results about the transient field of the transducer.     

Computer Modelling of Metal Dissolution in the Presence of Aqueous Electrolyte

The semi-empirical Hartree-Fock intermediate neglect of differential overlap (INDO) method was used to explore the potential energy surface of adsorbed water molecules and to speculate,using fairly simple chuster models,on the reaction path followed by metal ions leaving the surface.As an example,INDO calculations were used to calculate the potential energy curve for a metal atom leaving the surface and entering into a solvation cage composed of tetrahedral arranged water molecules.The effect of adding a NaCl ion pair to the system with the halide ion above the dissolving atom was also explored.     

Cation Effect on Copper Chemical Mechanical Polishing

We examine the effect of cations in solutions containing benzotriazole （BTA） and H202 on copper chemical mechanical polishing （CMP）. On the base of atomic force microscopy （AFM） and material removal rate （MRR） results, it is found that ammonia shows the highest MRR as well as good surface after CMP, while KOH demonstrates the worst performance. These results reveal a mechanism that small molecules with lone-pairs rather than molecules with steric effect and common inorganic cations are better for copper CMP process, which is indirectly confirmed by open circuit potential （OCP）.