Photolithography for making electrochemical measurements
Inventors
Policastro, Steven A. • Auyeung, Raymond C Y • Piqué, Alberto • Martin, Farrel
Assignees
Publication Number
US-10824075-B2
Publication Date
2020-11-03
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, a light source, comprising optoelectronic devices such as spatial light modulators or digital micromirror devices for direct modulation of the light distribution itself and avoiding the use of a mask, wherein the exposed region is created by light from the light source and wherein the metal sample is immersed. A method for isolating microstructural regions or features on a surface for electrochemical experimentation comprising the steps of providing a metal sample, coating the metal sample, selecting a region of interest, creating exposed photoresist with direct modulation of the light distribution itself by optoelectronic devices such as spatial light modulators or digital micromirror devices and without a mask.
Core Innovation
This procedure provides a technique for conducting electrochemical experiments on precise microstructural features on a material surface. The method utilizes a photoresist coating on a metal sample and selective exposure to light using optoelectronic devices, such as spatial light modulators or digital micromirror devices, to isolate regions of interest without using a mask. This selective masking enables the creation of exposed areas ranging from tens of microns to millimeters, facilitating localized electrochemical measurements on specific microstructural features.
The problem addressed is the difficulty in distinguishing individual contributions to measured currents in samples with heterogeneous microstructures, such as those including multiple grains, grain boundaries, and precipitates. Earlier methods like microcapillaries and lacquers suffer from drawbacks including high solution resistance, leakage, imprecise placement, and limitations in slow potentiodynamic scanning rates. The disclosed procedure minimizes signal loss due to high solution resistance and enables slow scan rates and precise targeting of electrochemical measurements on isolated microstructural regions.
The innovation is exemplified by the application of this technique to a duplex stainless steel where ultraviolet-sensitive photoresist masks the excluded areas and a 355 nm laser selectively exposes individual phases or dendrite cross-sections. This Selective Masking by Photolithography (SMP) technique allows electrochemical impedance, polarization, and critical pitting temperature measurements on isolated ferrite and austenite regions, demonstrating improved measurement reliability and reduced artifacts from solution resistance compared to previous methods.
Claims Coverage
The patent contains two independent claims directed to methods for isolating microstructural regions or features on a surface for electrochemical experimentation. There are two main inventive features derived from these claims.
Direct modulation of light distribution to expose photoresist without using a mask
The method involves exposing selected regions of a photoresist-coated metal sample by direct modulation of the light distribution itself using optoelectronic devices such as spatial light modulators or digital micromirror devices. This approach avoids the use of traditional masks and enables precise patterning of microstructural regions.
Isolation of microstructural regions using photoresist and laser lithography
The method includes coating the metal sample with a photoresist, selectively exposing regions of interest with UV laser light of around 355 nm using specific energy parameters (e.g., about 2.6 μJ laser energy corresponding to about 200 mJ/cm2 fluence), development to remove exposed or unexposed photoresist according to resist type, hard baking to improve coating reliability, and electrically isolating developed regions for electrochemical experimentation. Additional steps such as placing reference grid marks by laser machining, applying waterproof adhesive strips with perforated windows, and sealing the electrolyte container to isolate measurement areas are also incorporated.
The claims collectively cover methods that enable precise isolation of microstructural features on metal surfaces for electrochemical testing by using photoresist coating patterns created through maskless, direct-modulated UV laser exposure with optoelectronic devices, combined with processes to protect and isolate these regions for reliable localized electrochemical measurements.
Stated Advantages
Provides a technique for conducting electrochemical experiments on precise microstructural features on a metal surface.
Minimizes loss of signal due to high solution resistance, allowing slow potentiodynamic scan rates without compromising data quality.
Enables selection of exact microstructural features to be tested ahead of time, avoiding imprecise placement issues of previous methods.
Supports localized electrochemical DC and AC measurements and critical pitting temperature determinations on isolated regions of alloys.
Improves coating reliability and adhesion during corrosion testing through hard baking steps.
Allows multiple corrosion experiments to be performed on the same sample with robust and repeatable exposed regions.
Documented Applications
Conducting electrochemical measurements on isolated microstructural features such as individual phase regions of duplex stainless steel (ferrite and austenite).
Measuring corrosion resistance, catalytic activity, polarization scans, electrochemical impedance spectroscopy, and critical pitting temperature of specific isolated regions.
Performing slow potentiodynamic tests without signal loss or interference from corrosion product buildup.
Electrochemical studies on regions of metals and alloys with known crystalline orientation, including irregular shapes such as dendrite cross-sections.
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