We report a method for electrochemical roughening of thin-film platinum (Pt) electrodes that increases active surface area, decreases electrode impedance, increases charge injection capacity, increases sensitivity of biosensors and improves adhesion of electrochemically deposited films. First, a well-established technique for electrochemical roughening of thick Pt electrodes (wires and foils) by oxidation-reduction pulses was modified for use on thin-film Pt. Optimal roughening of thin-film Pt electrodes with this established protocol in a sulfuric acid solution was found to occur at about four times lower frequency than that typically used for thick Pt. This modification in established procedure created a 21x surface area increase but showed nanoscale cracks from inter-grain Pt dissolution that compromised film integrity. A crack free surface with Pt nanocrystal re-deposition (20-30 nm in size) and higher enhancement in surface area (44x) was obtained when the electrolyte was switched to a non-adsorbing perchloric acid solution. These electrochemically roughened electrodes have charge injection limits comparable to titanium nitride and just below carbon nanotube-based materials. Roughened microelectrodes showed a 2.8x increase in sensitivity to hydrogen peroxide detection, indicative of improved enzymatic biosensor performance. Platinum iridium and iridium oxide coatings on these roughened surfaces showed an improvement in adhesion. Microfabrication techniques have enabled the bulk fabrication of robust, reproducible neural interfaces. 1,2 These neural interfaces typically contain conductive metal electrodes that serve as the 'interface' between the device and the tissue. 3 When microfabricated, these electrodes are typically thin films of metal, a few hundred nanometers thick and recent advances show these interfaces to be constructed on thin flexible substrates, further improving the ability of electrodes to interface with tissue. 4-7 While these thin film electrodes generally act very similar to bulk metal found in non-microfabricated neural interfaces, they can be more delicate than bulk metal, 8 especially when fabricated on a flexible substrate. Both bulk and thin film metal interfaces demand highest performance to ensure that they can properly interface with tissue without causing damage to the tissue. Often, electrode surface modifications are needed to enhance performance.Enhanced electrode performance can be accomplished by 1) roughening the electrode surface to increase the effective surface area; 9-11 or, 2) depositing a thin-film coating of a material with enhanced electrochemical activity. [12][13][14][15] When depositing a different thin film electroactive material over the electrode to improve performance, there is often poor adhesion of the deposited film to the electrode surface. 9,16 Poor film adhesion compromises the mechanical robustness of an implantable device which may result in immediate delamination or decreased lifetime of the electrode upon implantation, ultimately deteriorating sens...

Amorphous titanium dioxide ͑TiO 2 ͒ thin films doped with rhodamine 6G ͑R6G͒ were deposited on glass substrates by the sol-gel process. The optical properties of the films were characterized by photoacoustic, excitation, and fluorescence spectroscopies. The absorption spectra of the R6G-doped TiO 2 films exhibited two well-defined absorption regions: an absorption band over 2.0 eV attributed to rhodamine 6G and a band above 3.0 eV corresponding to TiO 2 absorption. While the onset of the R6G absorption band was shifted by 0.06 eV towards lower energies as the R6G doping concentration increased within the interval of 0.01-0.10 mol %, the onset to high absorption ͑TiO 2 band͒ for the doped films decreased only by 0.01 eV within the same interval. In addition, the optical absorption of undoped rutile-phase bulk TiO 2 was calculated and compared to the experimental results. The estimated theoretical value of rutile TiO 2 sample was 3.0 eV. This theoretical result shows good agreement when compared with the experimental data of undoped TiO 2 sol-gel films, as well as the undoped TiO 2 film prepared by sputtering.

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The optical and electrical properties of methylene blue-doped CdS films, grown by chemical bath deposition, have been studied. Doping was achieved by adding specific volumes of methylene blue (MB) diluted in distilled water to the chemical bath. X-ray diffraction patterns display the zincblende crystalline structure for all the CdS samples, with a remarked preferred orientation along the (111) direction. The interplanar distance among the (111) planes indicates a minimum value when the relative volume (VR) of MB in the growing solution is about 7%. Photoacoustic absorption spectra show an evolution of the CdS band-gap energy (Eg) when VR increases, indicating adsorption of MB on the CdS microcrystals. Starting from an Eg of 2.42 eV for the undoped sample, an Eg value of nearly 2.49 eV is reached for the sample doped with VR=7% of MB. For higher concentrations, no increase is observed, showing rather a saturation effect. Dark conductivity (σ) measurements at room temperature (RT) display an increase of the conductivity from 1×10−4 Ω−1 cm−1, for the undoped film, up to 3.0×10−2 Ω−1 cm−1 for the highest doping value reached, that is when VR=7%. Thermoelectrical power measurements carried out at RT indicate that the layers are n-type doped, with a density of carriers (n) whose data basically oscillate in the range (5.3±1.3)×1016 cm−3. An exception is found for the sample with VR=7%, for which a value of n=1.02×1017 cm−3 is measured.