Fluidic applications for atomic force microscopy (AFM) with microcantilever sensors

This review presents the fundamentals of atomic force microscopy (AFM) with microcantilever probes and their use as fluidic sensors for the measurement of micro/nanoscale transport properties. Over the last two decades, AFM has been widely used for, among other purposes, nanoscale topography, nanomechanical characterization, and intermolecular force spectroscopy. Furthermore, a microcantilever, an essential part of AFM, has been modified and exploited as a mechanical transducer for various sensing applications. Among many prospective uses, there appears to be great potential for micro/nanoscale sensing of fluid density and viscosity (Sect. 3.1), temperature (Sect. 3.2), pressure (Sect. 3.3), and flow velocity (Sect. 3.4). These micro/nanomechanical measurement techniques are expected to complement the advanced optical and electrical measurement techniques currently employed for micro/nanoscale fluidic sensors and also to fill the gap between microscale and nanoscale fluidic transport property measurements.     

Applications of laser speckle photography for thermal flow problems

Laser speckle photography measures projected beam deflection of a phase object. The beam deflection measured at the solid surface will directly determine the wall-temperature gradient. Thus, the laser-speckle photography allows the evaluation of the convection-heat-transfer coefficients without the need to correct for conduction and radiation heat losses, which otherwise would be necessary. Selected results and brief discussions are presented for several natural convection-heat-transfer problems. Second, high-temperature applications of laser speckle photography shows potential as a nonintrusive means of measuring flame temperature. A fairly good agreement is shown in comparison of the laser speckle data with intrusive thermocouple data. Suggestive discussions are made to further improve the accuracy and sensitivity of the laser speckle photography technique in high-temperature applications. Finally, tomographic reconstruction of laser speckle photography data is discussed using both actual test fields and computer-synthesized phantom fields. The conventional algebraic reconstruction technique (ART) has been modified to apply for the laser speckle tomography. The efficacy of ART is examined particularly under a limited number of projections.     

Ultrafast dynamics of surface plasmon polaritons in plasmonic metamaterials

Using near-field scanning optical microscopy and ultrafast laser spectroscopy, we study the linear optical properties of subwavelength nanoslit and nanohole arrays in metal films, which are prototype structures for novel plasmonic metamaterials. Near-field microscopy provides direct evidence for surface plasmon polariton (SPP) excitation and allows for spatial imaging of the corresponding SPP modes. By employing spectral interferometry with ultrashort 11-fs light pulses, we directly reconstruct the temporal structure of the electric field of these pulses as they are transmitted through the metallic nanostructures. The analysis of these data allows for a quantitative extraction of the plasmonic band structure and the radiative damping of the corresponding SPP modes. Clear evidence for plasmonic band gap formation is given. Our results reveal that the coherent coupling between different SPP modes can result in a pronounced suppression of radiative SPP damping, increasing the SPP lifetime from 30 fs to more than 200 fs. These findings are relevant for optimizing and manipulating the optical properties of novel nano-plasmonic devices. PACS 42.70.Qs; 07.79.Fc; 42.25.-p     

Dual mode near-field scanning optical microscopy for near-field imaging of surface plasmon polariton

In this paper, we theoretically and experimentally demonstrate that metal coated apertured probes are efficient near-field probes on surfaces with high reflectivity for the scattering as well as for the collection mode near-field scanning optical microscopy (NSOM). We show that a blunt apertured metal coated tip is very effective in suppressing image dipoles which affect strongly the signals scattered from frequently used sharp metal tips or gold nanoparticle attached probes. By using a simultaneous collection and scattering mode (dual mode) NSOM we measure the near-field images of surface plasmon polariton (SPP) launched from a slit. The collection mode measures propagating SPP along lateral distance in a long scan range with high signal-to-noise ratio, and the scattering mode measures the polarization resolved near-field of SPP. Comparisons of the measured data obtained in the dual mode enable to easily characterize SPP and to separate the measured near-field into the propagating SPP and the directly transmitted light.     

Modification of electroosmotic flow for a polydimethylsiloxane electrophoresis microchip via polyelectrolyte coating

Polydimethylsiloxane has been dominantly employed as the substrate material for microchip capillary electrophoresis. The poor surface chemistry, however, generates inconsistent electroosmotic flow under the electrophoretic condition, limiting its broader applications. In this work, different polyelectrolytes, including polydiallyldimethylammonium chloride, polyvinyl sulfate, and dextran sulfate, were successfully deposited onto polydimethylsiloxane microchannel surfaces. The polyelectrolyte coated polydimethylsiloxane microchannel showed improved consistency and reproducibility in electroosmotic flow under an electric field over the uncoated native microchannel.     

Evaluation of transient turbulent flow fields using digital cinematographic particle image velocimetry

This paper describes an experimental development for temporal and spatial reconstruction of continuously varying flow fields by means of digital cinematographic particle image velocimetry (PIV). The system uses a copper-vapor laser illumination synchronized with a high-speed camera, and continuously samples at 250 fps to measure transient and non-periodic turbulent flows with relatively low frequencies, i.e., the surf zone turbulence produced by depth-limited wave break in a long laboratory flume. The use of the developed PIV system comprehensively records the temporal development of both phase-averaged and instantaneous turbulent vortex flows descended from the breaking waves to the bottom. Also, the measured power spectra show harmonic frequencies, ranging from the orbital frequency of 0.5 Hz up to the order of 5 Hz, and the well-known −5/3 dependence upon the turbulence fluctuation frequencies thereafter. Received: 2 December 1999/Accepted: 6 September 2000     

Tomographic-image reconstruction using a hybrid genetic algorithm

An improved tomographic-image reconstruction method is proposed that uses a hybrid genetic algorithm (GA) that hybridizes a conventional GA and a concurrent simplex method. For the purposes of discussion, an axisymmetric phantom density field is used with an interferometric optical projection. Tomographic-image reconstruction using the hybrid GA not only improves the convergence over the pure GA but also significantly reduces the computation time.     

Nonintrusive measurements of mixture concentration fields by analyzing diffraction image patterns (point spread function) of nanoparticles

The diffraction image patterns of small particles are referred to as their point spread function (PSF); these patterns vary distinctively with the refractive index (RI) of a transparent test medium when the particles are imaged through the medium. The RI correlates directly with the mixture concentration, so proper inversion of measured PSFs can provide full-field information on the mixture concentration field. In this study, fluorescent nanoparticles of 500 nm diameter are fixed on a glass surface by means of evaporative self-assembly, and the time-varying test mixture is placed in front of the glass surface. The time-varying and full-field PSF distributions are imaged and digitally analyzed to determine the local RI values as well as the local mixture concentrations. Both immiscible water/oil mixture and miscible water/glycerol mixture are imaged. The present method shows an RI measurement to have an uncertainty of ±5 × 10⁻³ RIU and the mixture concentration measurements to have uncertainty of approximately 4%.