Milan C. Buncick

Gold island fiber optic sensor for refractive index sensing........

Abstract A fiber optic chemical sensor based on gold island surface plasmon excitation is presented. The sensing part of the fiber is the end of the fiber onto which a thin layer of gold has been deposited to form a particulate surface. Annealing the gold reshapes the particles and produces an optical absorbance near 535 nm with the fiber in air. The optical absorption resonance of the gold particles is shifted if the fiber is immersed in a medium other than air. These resonance shifts are examined by transmission spectroscopy through the fiber. Experimental results for the sensitivity and dynamic range in the measurement of liquid solutions are in agreement with a basic theoretical model that characterizes the surface plasmon using nonretarded electrodynamics.

Fiber optic sensor based on gold island plasmon resonance

Abstract A fiber optic chemical sensor based on gold-island surface plasmon excitation is presented. The sensing part of the fiber is a one inch portion on which cladding has been removed and onto which a thin layer of gold has been deposited to form a particulate surface. Annealing the gold reshapes the particles and produces an absorbance near 535 nm when the only medium residing outside the surface is air. A range of wavelengths provided by a white light source and monochromator is launched through the optical fiber. The transmitted spectra display shifts in the resonance absorption due to any changes in the medium surrounding, or adsorbed onto the fiber. Experimental results for the sensitivity and dynamic range in the measurement of liquid solutions are in agreement with a basic theoretical model which characterizes the surface plasmon using nonretarded electrodynamics. Furthermore, the model assumes the particles are isolated oblate spheroids with a distribution of eccentricities.

Demonstration of surface plasmons in metal island films and the effect of the surrounding medium—An undergraduate experiment

We present a demonstration of the surface plasmon phenomenon as it occurs in thin metal island films. The metal films are deposited on glass microscope slides. The effect of the surface plasmon resonance may be observed visually on the slide without further apparatus. Heating the film changes the shape of the islands and therefore the resonant frequency of the surface plasmon and changes the color of the film. Placing the film in a dielectric medium changes the resonance condition for the surface plasmon again and changes the color again. We show this by coating the slides with commercially available liquids with different indices of refraction. We present a theoretical model that assumes the islands are oblate spheroids. There are enough details given so that the equations can be programed and the theoretical optical absorbance can be reproduced. We also present a modification to the theory so that the shift in resonant frequency can be calculated when the spheroids are immersed in the index fluids. We d...

Effects of process history and aging on the properties of polyimide films

Polyimide is used extensively in a variety of integrated circuit packaging applications. It is a good dielectric material with excellent planarizing capabilities, but like most polymers, it absorbs moisture. This hygroscopic behavior can lead to reliability problems in integrated circuit packages. The effects of variations in process history on moisture uptake are examined using gravimetric measurement techniques. In particular, the effects of cure schedule and exposure to high temperature/high humidity environments (85 °C/85% RH) on steady state moisture uptake are reported. Steady state moisture uptake is shown to be a decreasing function of cure temperature. Samples cured at 250 °C absorb 25% more moisture by weight than do samples cured at 400 °C. Moreover, the steady state moisture uptake in polyimide is greater after the samples have been “aged” in a high temperature and humidity ambient. The bulk and surface chemical composition are also monitored as a function of aging using Fourier transform infrared spectroscopy (FTIR) and electron spectroscopy for chemical analysis (ESCA), respectively. The PI surface chemistry degrades after 700 h in an 85 °C/85% RH environment. The bulk chemical composition appears to be unaffected.

High-performance microfabricated angular rate sensor

The development of a miniature angular rate sensor based on silicon-on-insulator (SOI) microfabrication technology is presented. The design, fabrication, integration, and inertial testing of a MEMS-based angular rate sensor with large dynamic range were the driving forces behind this research. The design goals of 10-deg/h bias stability while operating through 2000-deg/s roll environments are presented. The sensor design is based on a straightforward single-mask fabrication approach that utilizes deep reactive ion etching of a 100-µm-thick device layer, with a buried 2- to 3-µm oxide layer used as the sacrificial layer, in an SOI substrate. To date, the data show demonstrated bias drift performance of 60 deg/h over this fast-roll environment.

The curing kinetics of polyamic acid in the presence of water vapor

Polyimides (PIs) are used extensively in integrated circuit fabrication due to their attractive physical properties. Variations in physical properties due to variations in processing and sensitivity to moisture can lead to reliability problems for microelectronic applications. We present the details of exposure of polyamic acid (PAA) to 85 °C/85%RH and to 85 °C/dryN2 as part of a long term study of PI degradation. The PAA under study is formed from the polycondensation of pyromellitic dianhydride (PMDA) and oxydianaline (ODA) in N‐methyl pyrrolidone. The acid was spun onto two inch silicon wafers coated with chromium. The PAA cure was followed with electron spectroscopy for chemical analysis (ESCA) and Fourier transform infrared (FTIR) spectroscopy. Results show that the presence of water vapor during heating dramatically raises the initial rate of imidization. Measurements indicate the PAA is 6% cured after 72 h in the 85 °C/dry environment while the PAA is 68% cured after 72 h in the 85 °C/85%RH environ...

Electrostatic force density for a scanned probe above a charged surface

The Coulomb interaction of a dielectric probe tip with a uniform field existing above a semi-infinite, homogeneous dielectric substrate is studied. The induced polarization surface charge density and the field distribution at the bounding surface of the dielectric medium with the geometry of half of a two sheeted hyperboloid of revolution located above the dielectric half space interfaced with a uniform surface charge density is calculated. The force density on the hyperboloidal probe medium is calculated as a function of the probe tip shape. The calculation is based on solving Laplace’s equation and employing a newly derived integral expansion for the vanishing dielectric limit of the potential. The involved numerical simulations comprise the evaluation of infinite double integrals involving conical functions.

Gold island fiber optic sensor

A fiber optic chemical sensor based on gold-island surface plasmon excitation is presented. The sensing part of the fiber is the end of the fiber onto which a thin layer of gold has been deposited to form a particulate surface. Annealing the gold reshapes the particles and produces an optical absorbance near 535 nm with the fiber in air. The optical absorption resonance of the gold particles is shifted if the fiber is immersed in a medium other than air. These resonance shifts are examined by transmission spectroscopy through the fiber. Experimental results for the sensitivity and dynamic range in the measurement of liquid solutions are in agreement with a basic theoretical model which characterizes the surface plasmon using nonretarded electrodynamics.

Microfabrication technologies for missile components

This invited communication presents the microfabrication technologies, and associated issues, being developed by the U.S. Army’s AMRDEC for missile components. Primary components are inertial sensors and radio frequency switches. Two inertial sensor types are discussed -- fiber optic and micro-electromechanical system (MEMS) gyroscopes. The RF switches are also based on MEMS technology and are a natural extension of the microfabrication processes developed for the MEMS gyroscope.

Phase-locked Second Harmonic Generation In Gaas Nanocavities

We theoretically study light propagation through sub-wavelength apertures on a silver substrate filled with GaAs, in the enhanced transmission regime. We predict enhanced conversion efficiencies even under high absorption conditions.