Tapered structure suitable for microthermocouples microelectrode

Radiant energy – Inspection of solids or liquids by charged particles

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Details

136228, 374 6, 374124, 374164, H01J 37256

Patent

active

059862610

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates, in general, to the fabrication of straight and bent microelectrodes, microthermocouples, micromagnetic and field emission tips for the measurement of spatially localized rapid temperature changes, electrochemistry and micromagnetic inhomogeneities and the production of directed electron beams, and to the structure of such tips. The disclosed methodology and structure have a wide variety of uses, and allow for the interface of the device of the invention with all current scanned probe microscopes.


BACKGROUND OF THE INVENTION

The measurements of spatially localized rapid temperature changes are required in studies of many physical and biological processes and objects. These can include such diverse subjects as turbulent flows, changes associated with processes of explosion and combustion, microtemperature measurements in biology at the cellular and subcellular level and microtemperature measurements in evolving chemical reactions. For all these applications a microthermocouple is the most convenient detector.
In recent publications, fast microthermocouples have been described with response times of milliseconds and spatial resolutions of from hundreds [L. J. Forney, E. L. Meeks, J. Ma, and G. C. Fralick, Rev.Sci.Instrum. 64, 1280 (1993)] to tens [P. Beckman, R. P. Roy, K. Whitfield, and A. Hasan, Rev.Sci.Instrum. 64, 2947 (1993)] of micrometers. Such microthermocouples may also be used as point radiation microdetectors in a range of wavelengths from the UW to the IR.
In addition to the above Pendley and Abruna [B. D. Pendley and H. Dl Abruna, Anal. Chem. 62, 782 (1990)] have considered the problem of microelectrodes for microchemical measurements and achieved outer diameters of a few microns under non-reproducible conditions. In addition, micromagnetic measurements are made using magnetic wires that are electropolished in which it is difficult to construct such tips [K. Sueoka, F. Sai, K. Parker and J. Arnolddussen, J. Vac.Sci. and Tech. B12, 1618 (1994)]. Furthermore, there is great interest in making microtip field emission tips [C. A. Spindt, et al. J. Appl.Phys. 47, 5248 (1976)] but there is an active interest in new methodologies for making such tips with better characteristics.


STATE OF PRIOR ART

No devices or methodologies have been reported that can provide thermal or electrochemical measurements in isolated submicrometer size volumes or in macrovolumes with submicrometer spatial resolution. In addition, the response time of such measurements are on the order of milliseconds and no shorter response times are known.
Recent publications, as noted above, have described response times of milliseconds with spatial resolutions from hundreds of micrometers. In addition, some recent publications have described thermal imaging using atomic force microscopy (AFM) without specific measurements of the time response of these devices [A. Majumdar, J. P. Carrejo and J. Lai, Appl. Phys. Lett. 62, 2501 (1993)]. The thermocouples that have been used in AFM employed a 2-wire thermocouple junction of 25.mu. diameter which ended in a sharp tip suitable for AFM. The two wire thermocouples that were fabricated acted as a thermal bridge in the measurements, distorting the real thermal picture of the sample. These thermocouples reflected only the relative thermal character of the samples and did not give an absolute thermal measure of the temperature.
In addition to the above, various attempts have been made to obtain microelectrodes for micro-electrochemical measurements. The most successful of these approaches was by Abruna [B. D. Pendley and H. D. Abruna, Anal. Chem 62, 782-784 (1990)]. However, the technology employed was uncontrolled in the fabrication of these electrochemical probes, and limited the dimensionality of the probes. Furthermore, it did not allow for the interfacing of these electrodes with normal force sensing scanned probe microscopes.
Furthermore, micromagnetic measurements have only been performed with magnetic wires and these are notoriously

REFERENCES:
patent: 3819420 (1974-06-01), Schmidt et al.
patent: 4747698 (1988-05-01), Wickramasinghe et al.
patent: 5166520 (1992-11-01), Prater et al.

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