Jay N. Zemel

Gas flow in micro-channels

An experimental and theoretical investigation of low Reynolds number, high subsonic Mach number, compressible gas flow in channels is presented. Nitrogen, helium, and argon gases were used. The channels were microfabricated on silicon wafers and were typically 100 μm wide, 10 4 μm long, and ranged in depth from 0.5 to 20 μm. The Knudsen number ranged from 10 -3 to 0.4. The measured friction factor was in good agreement with theoretical predictions assuming isothermal, locally fully developed, first-order, slip flow.

Liquid Transport In Micron And Submicron Channels

There has been a growth of interest in fluid transport in very small structures. The basis for this interest derives from the application of micromachining technology to problems in fluidics. Several aspects of this problem are reviewed and discussed including some of our recent research on this topic. The problems discussed may be separated into those dealing with biological systems and those that explore the applicability of the macroscopic Navier-Stokes equations to very small planar channels. In the work conducted at the University of Pennsylvania, an experimental investigation of fluid flow in extremely small channels was conducted. Three devices have been constructed with channels of rectangular cross-section ranging in area from 7200 to 80 square microns. It was found that in the relatively large flow channels that the experimental observations were in rough agreement with the predictions from the Navier-Stokes equations. However, in the smallest of the chan-nels, there was a significant deviation from the Navier-Stokes predictions.

Liquid transport in micron and submicron channels

Abstract An experimental investigation of fluid flow in extremely small channels is presented. Potential applications for such channels include cooling of electronic circuits, and reactors for modification and separation of biological cells. The immediate goal is to determine at what length scales the continuum assumptions break down and if the Navier-Stokes equations adequately predict fluid behavior. In order to accomplish this, experiments are being conducted in progressively thinner flow channels. We have constructed three channels of rectangular cross-section ranging in area from 7200 to 80 square microns, utilizing the recent advances in microfabrication. In this paper, preliminary results are reported pertaining to friction measurements. It is found that in the relatively large flow channels the experimental observations are in rough agreement with the predictions from the Navier-Stokes equations. However, in the smallest of the channels, there is a significant deviation from the Navier-Stokes predictions.

Organ pipe radiant modes of periodic micromachined silicon surfaces

In recent studies on small pyroelectric thermal anemometers with roughened surfaces we showed that one of the most widely used heat transfer models1,2 yielded calculated anemometer responses for flow and geometric behaviour that agreed functionally with observations, but were significantly smaller than the experimental data3–5. As the first stage in investigating the role of small structures in heat transfer, we initiated a study of emittance from deep gratings. Here we report measurements at 400 °C of infrared (3 µmλ14 µm), normal, s- and p-polarized spectral emittances of 45 µm deep, near square-wave gratings of heavily phosphorus doped (110) silicon (P content ∼5 × 1019 cm−3). The grating surface repeat scales, Λ, were 10, 14, 18 and 22µm, yielding a range of Λ/λ from 0.14 to 7.33. The s-polarization vector was parallel to the grating slots. Both s and p spectral emittances had pronounced resonant periodicities with a characteristic length of ∼42 µm. A reasonable explanation for this behaviour is the presence of standing waves in the air slots perpendicular to the silicon surface similar to those in an organ pipe. While the resonant amplitude of the s polarization does not depend significantly on Λ it does for the p polarization. No explanation for the Λ dependence of the p polarization is known.

pH-sensitive sputtered iridium oxide films

Abstract The results of an extensive series of measurements of the pH response of electrodes consisting of d.c. reactively sputtered iridium oxide on a variety of substrates are reported. After an initial instability, the electrodes behave nearly theoretically between 0 and 100 °C. Preliminary testing has shown these electrodes to be stable in aqueous solutions at temperatures up to 200 °C. Interferences appear to be acceptably small.

Theoretical description of gas-film interaction on SnOx☆

Abstract The Hall measurements recently reported by Chang and Hicks (S. C. Chang and D. B. Hicks, in D. Schuetle and R. Hammerle (eds.), Fundamentals and Applications of Chemical Sensors, American Chemical Society, Washington, DC 1986, p. 58) are a useful test of the influence of reducing gases on free carrier and mobility variations. It is demonstrated here that a simple depletion model for the gas-solid interface adequately accounts for the free carrier and mobility response of the SnOx films. Expressions for the relationship between the surface potential, bulk carrier concentration and the reducing gas concentration are derived using the standard semiconductor electrostatic surface model and first-order kinetic equations for gas-solid interactions. The role of film structure and the interaction of surface and bulk Schottky defects is discussed.

An investigation of the temperature dependence of Poiseuille numbers in microchannel flow

Liquid (1-, 2-propanol and 1-, 3-pentanol) flow measurements through 5, 12, and 25 mu m hydraulic diameter microchannels are reported. These experiments indicate that the Poiseuille number depends on the temperature and, possibly, on the molecular isomerism of the liquid. The Poiseuille number increases by as much as 25% and 10% for the 12 and 25 mu m channels, respectively, as the temperature increases from 0 to 85 degrees C. These results are contrary to the predictions derived from the Navier-Stokes equation, which show that the Poiseuille number is independent of these parameters. The precision of these measurements is of the order of +or-2%, so that the observed deviations from theory are not readily explained by experimental errors.

Pd–thin‐SiO2–Si diode. I. Isothermal variation of H2‐induced interfacial trapping states

The current‐voltage characteristic and the small‐signal frequency‐dependent admittance response of Pd–thin‐SiO2–Si diodes are measured. It is found that the characteristics undergo reversible changes by switching the ambient gas between hydrogen diluted in nitrogen and pure oxygen. Dispersive peaks and structures are observed in the C‐V and G‐V plots obtained under hydrogen which are absent under oxygen. It is concluded that hydrogen‐generated interfacial trapping states are responsible for the induced electrical changes in the Pd–thin‐SiO2–Si diodes.

An impedance tomographic tactile sensor

Disclosed is a container holding a partially conductive ionic fluid with a flexible tactile surface covering the fluid and sealing the container. Along the bottom of the container a series of parallel conductors are located with the farthest spaced apart conductors being connected to a voltage source. Measurements of changes in voltages between individual pairs of conductors will provide an indication of any localized deformation of the flexible tactile surface. Such a tactile sensor can be utilized in any device where an electrical output is desired which is indicative of the surface or surface characteristics of the object to be contacted.

Valinomycin-doped photoresist layers for potassium ion sensing

Abstract In this paper we describe a new ion-conducting polymer system that is suitable for deposition onto ion-controlled diodes (ICDs). Photoresist layers doped with organic ion-carrier species were fabricated using standard photolithographic techniques. Results are shown for both metal-coated and ICD-coated electrodes. Potassium-selective devices were fabricated showing excellent sensitivity and adequate stability.