Jack C. Rife

Miniature valveless ultrasonic pumps and mixers

Abstract Miniature acousto-fluidic devices are described that operate as pumps without valves in channel widths of millimeters and below. These devices can also be configured to produce mixing in low-Reynolds-number flows. The prototypes are based on radio-frequency, ultrasonic piezoelectric transducers that exert a directed body force on the fluid via acoustic attenuation. The process is a type of acoustic streaming termed quartz wind. In microfluidics applications, this mechanism has the advantages of insensitivity to the chemical state of the fluid or walls and greatly reduced crosstalk in a multichannel system. The observed pump flow velocities are on the order of 1 mm/s in 1.6×1.6 mm 2 channels and with a calculated maximum backpressure that can be pumped against of 0.13 Pa. Due to the low backpressure, quartz wind devices are not competitive pumps for open-loop and high-impedance microfluidics systems but could find application in pumping in low-impedance planar and closed-loop systems and for mixing in reservoirs and channels.

Magnetic labeling, detection, and system integration

Among the plethora of affinity biosensor systems based on biomolecular recognition and labeling assays, magnetic labeling and detection is emerging as a promising new approach. Magnetic labels can be non-invasively detected by a wide range of methods, are physically and chemically stable, relatively inexpensive to produce, and can be easily made biocompatible. Here we provide an overview of the various approaches developed for magnetic labeling and detection as applied to biosensing. We illustrate the challenges to integrating one such approach into a complete sensing system with a more detailed discussion of the compact Bead Array Sensor System developed at the U.S. Naval Research Laboratory, the first system to use magnetic labels and microchip-based detection.

A grating/crystal monochromator for the spectral range 5 eV to 5 keV

Abstract An ultrahigh vacuum scanning monochromator using gratings and crystals for the unusually large spectral range of roughly 5 eV to 5 keV has been designed for installation at the X-ray storage ring at Brookhaven National Laboratory. The electron beam at the tangent point of the storage ring is imaged at unit magnification on an exit slit by means of fixed paraboloidal collimating and focusing mirrors illuminated at a small glancing angle. Two dispersing elements, located in the approximately parallel radiation beam between the mirrors, are simultaneously translated and rotated such that the direction of the beam emerging from the monochromator is fixed. When blazed gratings are used, the scanning motion maintains them always at the blaze condition, thus ensuring maximum efficiency. In the double-grating mode, a resolving power of 2000 over the entire range is indicated by ray tracing. When using a pair of crystals, one has a conventional double crystal monochromator. In the resulting instrument design, all motions are fed into the ultrahigh vacuum system via linear translation through opposing bellows, using computer-driven stepper motors and air bearings for the main supports. The rotational motion is coupled from a translational feedthrough via a metal tape drive. Translations and rotations are independent and encoded interferometrically.

Multilayer-coated blazed grating performance in the soft x-ray region.

Useful grating efficiences for a variety of new spectrometer types have been attained. These results are discussed.

On-blaze operation of a Mo/Si multilayer-coated, concave diffraction grating in the 136–142-Å wavelength region and near normal incidence

The efficiency and resolving power of a concave, 2400-groove/mm, blazed diffraction grating that had a Mo/Si multilayer coating were determined. The multilayer coating had a peak reflectance of 55% at 140-A near normal incidence. The efficiency of the multilayer grating for wavelengths in the 136-139-A range was 2% near normal incidence. This efficiency was a factor of 150 greater than the efficiency of a sister replica Au-coated grating in the same wavelength region. The resolving power of the multilayercoated grating in the third order of a V viii transition with a first-order wavelength of 140.451 A was 9100. Comparisons with the Au-coated grating indicated that the application of the multilayer coating did not affect the resolving power or the blaze angle.

Multilayer-coated laminar grating with 16% normal-incidence efficiency in the 150-Å wavelength region

We characterized a laminar grating with a Mo/Si multilayer coating by using synchrotron radiation and atomic force microscopy. The grating substrate had 2400 grooves/mm, 40-A groove depth, and 2080-A groove width. The microroughness of the grating substrate was 5 A rms. The multilayer coating was optimized to have peak normal-incidence reflectance at a wavelength near 150 A. For an angle of incidence of 10 degrees the peak grating efficiency was 16.3% in the +1 order and 15.0% in the -1 order. The efficiency in the zero order was lower by a factor of 40 owing to the excellent matching of the groove depth and groove width to the wavelength of the incident radiation. By dividing the grating efficiencies by the measured reflectance of the multilayer coating, we obtained inferred groove efficiencies of 34% and 32% in the +1 and -1 orders, respectively.

Measurements of the normal-incidence X-ray reflectance of a molybdenum-silicon multilayer deposited on a 2000 l/mm grating

Normal-incidence grating optics coated with appropriate multilayers show great promise as a means of achieving high spectral resolution at x-ray wavelengths. Multilayer-coated mirrors have been made and tested successfully, but comparatively little work on such multilayer-coated gratings has been reported. We describe the results of reflectance meansurements made on a superpolished flat mirror and a Ferranti-Astron ion-etched 2000 l/mm laminar grating, which were coated simultaneously at the Lawrence Livermore National Laboratory with a 25-period Mo-Si multilayer. The multilayer was designed so that at normal incidence the mirror would have a maximum reflectance of 31% at a wavelength of 176 A. The measurements were performed using a reflectometer and monochromator installed on the Naval Research Laboratory X24C beamline at the Brookhaven National Synchrotron Light Source.

Performance of a tungsten/carbon multilayer-coated, blazed grating from 150 to 1700 eV

The advantages of multilayer coated blazed gratings are discussed, and multilayer/grating matching conditions are considered. Measurements of a W/C multilayer-coated, 2000 g/mm 3.8° blaze angle ion-etched grating and superpolished flat are reported. These include reflectometer measurements as well as operational performance of the pair as multilayer-multilayer grating diffraction elements in a two-crystal type monochromator. The results are promising for a variety of new spectrometer types.

Long-term stability of a Mo/Si multilayer structure

The normal-incidence reflectance of a Mo/Si multilayer mirror, with peak reflectance near 130 A, was measured over a period of 20 months by using synchrotron radiation. The measured reflectances were unchanged over this period of time, and this indicates that the material layers and interfaces were stable.

Normal-incidence reflectance of W/B 4 C multilayer mirrors in the 34–50-Å wavelength region

The measured normal-incidence reflectances of W/B(4)C multilayers mirrors are 2% in the 34-50-A wavelength region and are consistent with interfacial roughness in the range of 3-4 A.