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We describe a method for the selective desorption of thiol self-assembled monolayers from gold surfaces having micrometer-scale separations on a substrate. In an electrolyte solution, the electrical resistance between the adjacent areas can be much lower than the resistance between a surface and the counter electrode. Also, both reductive and oxidative thiol desorption may occur. Therefore, the potentials of the surfaces must be independently controlled with a multichannel potentiostat and operating windows for a given thiol/electrolyte system must be established. In this study operating windows were established for 1-dodecanethiol-based SAMs in phosphate buffer, phosphate-buffered saline, and sodium hydroxide solution, and selective SAM removal was successfully performed in a four-electrode configuration.

A method for chemically differentiating the surface of a set of small, closely-spaced, lithographically-defined Au features on a die, from another set of similar features intimately inter-dispersed, is described. The key enabler of the method is a standard electronics probe array adapted to carry out electrochemistry on the features. The probe array is used first to verify the electrical integrity of features and the quality of electrical contacts by measuring electrical resistance, then, in the presence of the electrolyte, simultaneously maintain one potential on one set of Au features and another potential on the other set in order to carry out desired electrochemical reactions. The technique was demonstrated on dies bearing 40 electrically isolated Au features (based on 5 μm wide stripes) accessed via 64 contact pads each 100×100 μm² in area. The array had 64 probes, of which 16 were maintained at a desorbing potential (-1.6 V vs. Ag/AgCl) and 48 at a stability potential (-0.3 V). The surface compositions were analyzed with time-of-flight secondary ion mass spectrometry by imaging ion fragments characteristic to the thiols forming SAMs, thereby validating the process. [ABSTRACT FROM AUTHOR]

A method to chemically differentiate small closely spaced lithographically defined Au features with different thiol-based self-assembled monolayers (SAMs) was developed. The key step in the method is the reductive electrochemical desorption of a SAM from a specific Au feature without affecting SAMs on neighboring Au features by simultaneously controlling their potentials with a multichannel potentiostat. The method is demonstrated by chemically differentiating the arms of a Au plasmonic Mach-Zehnder interferometer such that the arms have different affinities toward an analyte, thus rendering the interferometer useful for (bio)chemical sensing. The simultaneous presence of a poly(ethylene glycol)-terminated SAM on one arm, and of a biotin-terminated SAM on the other, was verified by imaging with time-of-flight secondary ion mass spectrometry (TOF-SIMS) and phase-shift atomic force microscopy. The method can be applied generally to chemically differentiate a large number of electrically isolated Au features simultaneously, leading to low cost wafer-scale functionalization of (bio)chemical sensors and other devices. [ABSTRACT FROM AUTHOR]

A thermally activated variable attenuator for long-range (low-loss) surface plasmon-polariton (LRSPP) waves is discussed in this paper. The surface plasmon waveguide consists of a thin Au stripe on a thick layer of SiO2, which is covered by a thick layer of index-matched polymer. The structure is optically symmetric near room temperature, supporting an LRSPP. Increased attenuation of the mode occurs upon heating of the Au stripe via the passage of current therein. Heating substantially changes the refractive index of the polymer near the stripe, rendering the structure highly optically asymmetric and cutting off the mode. Thermal modeling results that link the injected current density to the refractive-index perturbation are presented and discussed. Experimental results validate the thermal modeling and demonstrate the operation of the device at a free-space optical wavelength near 1550 nm. The resistivity of the stripe is also measured as a function of the drive current, and the simultaneous use of the stripe as a thermal monitor is discussed and demonstrated [ABSTRACT FROM PUBLISHER]