Photolithography for making electrochemical measurements
Inventors
Policastro, Steven A. • Auyeung, Raymond C Y • Piqué, Alberto • Martin, Farrell
Assignees
Publication Number
US-10018916-B2
Publication Date
2018-07-10
Expiration Date
2032-09-14
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Abstract
An apparatus for electrochemical experimentation with an isolated microstructural region on a surface comprising a metal sample coated with a photoresist, a region of interest, an exposed region of photoresist and unexposed region of photoresist wherein the exposed region is created by light and creating a developed region of unexposed photoresist, and an adhesive strip with a first perforated window over the region of interest and a sealed waterproof container with a second larger perforated window over the first perforated window. A method for isolating microstructural regions for electrochemical experimentation comprising providing a metal sample, identifying regions of interest, coating the metal sample, selecting regions of interest, exposing with light and creating exposed photoresist and unexposed photoresist by laser lithography without a mask, and immersing the metal sample in a developer solution and creating developed regions of unexposed photoresist.
Core Innovation
This invention provides a technique and apparatus for conducting electrochemical experiments on precise microstructural features of a material surface by isolating particular regions of interest. It uses a metal sample coated with a photoresist, where selective exposure of regions by light—specifically using a 355 nm laser—creates exposed and unexposed regions of photoresist. The exposed regions are developed by immersion in a developer solution to reveal bare metal only at these microstructural sites, allowing localized electrochemical measurements. This isolation minimizes loss of signal due to high solution resistance.
The problem addressed by this invention concerns the drawbacks of earlier methods such as microcapillaries and lacquers used for localized electrochemical measurements. Microcapillaries have issues with high solution resistance, leakage, imprecise placement, and limitations on slow potentiodynamic tests due to leakage or blockage. Lacquers involve coating surfaces and creating pinholes but also suffer from similar imprecision and difficulty. Additionally, when samples have multiple grains or phases, it is challenging to determine individual contributions to measured currents, making it difficult to study corrosion resistance or catalytic activity on specific microstructural regions. This invention offers a versatile and reliable technique to isolate and measure individual phase regions or distinct microstructural features with reduced solution resistance and improved signal quality.
Claims Coverage
The patent includes three independent claims presenting inventive features related to an apparatus for electrochemical experimentation with isolated microstructural regions.
Use of a specific laser light source for photoresist exposure
The apparatus employs a 355 nm solid state laser with maximum pulse energies around 300 μJ, pulsewidths of about 30 ns, and laser energy of about 2.6 microJoules corresponding to a fluence of about 200 mJ/cm2 to selectively expose regions of the photoresist on the metal sample surface. It may also use optoelectronic devices such as spatial light modulators or digital micromirror devices for direct modulation of the light distribution to control exposure.
Microstructural region isolation using photoresist and developer solution
The metal sample is coated with a photoresist film, and the light source exposes specific areas of the photoresist. The sample is then immersed in a developer solution which removes the exposed photoresist, thus creating developed regions for electrochemical measurement while protecting the rest of the surface with unexposed photoresist.
Water-resistant and sealed containment for electrochemical measurement
The apparatus includes a water-resistant adhesive strip with a first perforated window aligned over the region of interest on the sample and a sealed waterproof container with a second larger perforated window over the first, providing electrical isolation and containment of the electrolyte during experimentation.
The claims cover an apparatus and method combining selective laser exposure of photoresist-coated metal surfaces, development of exposed regions to reveal isolated microstructural areas, and containment means to enable accurate localized electrochemical measurements with minimized solution resistance and improved measurement quality.
Stated Advantages
Allows selection of exact microstructural features to be measured ahead of time with high precision.
Enables slow potentiodynamic electrochemical measurements without compromising sample integrity or signal quality.
Minimizes loss of signal due to high solution resistance, improving measurement accuracy.
Provides robust masking that resists corrosion and multiple experimental cycles on the same sample.
Documented Applications
Electrochemical testing and measurements on individual phase regions or microstructural features in metals and alloys, e.g., ferrite and austenite phases in duplex stainless steel.
Investigation of corrosion resistance, including critical pitting temperature measurements of isolated regions under different temperatures.
Local DC and AC electrochemical impedance spectroscopy studies of oxide films on isolated microstructural regions.
General application to any electrochemical study that explores the behavior of individual phase or isolated regions of interest on material surfaces.
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