Electrochemical fouling of dopamine and recovery of carbon electrodes

Transcription

1 Supporting Information Electrochemical fouling of dopamine and recovery of carbon electrodes Emilia Peltola 1,2*, Sami Sainio 1, Katherine B. Holt 2, Tommi Palomäki 1, Jari Koskinen 3, Tomi Laurila 1 1 Department of Electrical Engineering and Automation, School of Electrical Engineering, Aalto University, Espoo, Finland 2 Department of Chemistry, University College London, London, UK 3 Department of Chemistry and Materials Science, School of Chemical Engineering, Aalto University, Espoo, Finland * Corresponding author: Tel: , emilia.peltola@aalto.fi Table of Contents Substrate fabrication...s-2 a-c film fabrication... S-2 ta-c film fabrication... S-2 ND deposition... S-2 PyC fabrication... S-2 Microscopy of the surface before and after DA fouling...s-3 Scanning electron microscopy... S-3 Atomic force microscopy... S-3 Unscaled figure of the fouled surfaces...s-5 S-1

2 Substrate fabrication a-c film fabrication The carbon films were deposited on boron-doped Si (100) using closed-field unbalanced magnetron sputtering (CFUBMS) in pulsed DC mode. The target was a 4-inch graphite disk (99.99% purity). The DC power was 2000 W and the frequency 100 khz at a fixed working pressure of 3 mtorr during deposition. Argon gas flow inside the deposition chamber was controlled with a mass flow controller and kept constant at 80 sccm. A reference sample (a-c ref) was made with only Ar gas. For a-c O2, the inflow of oxygen was 2 sccm and for a-c H2 and a-c H12, the inflow of hydrogen was 2 and 12 sccm, respectively. The thickness of the films was < 200nm. The deposition was carried out at room temperature. ta-c film fabrication The ta-c sample were prepared on p-type conductive Si substrates ( Ωcm, Ultrasil, USA), which were cleaned by standard RCA cleaning method followed by ultrasonication for 3 min in HPLC grade acetone (Sigma Aldrich). First, a 20 nm titanium interlayer was deposited by direct current magnetron sputter (DC-MS) to enhance adhesion followed by 7 nm ta-c film deposited by pulsed filtered cathodic vacuum arc (p-fcva). Both deposition systems are installed in one deposition chamber. Wafers were cleaned by standard RCA cleaning procedure before the deposition. The vacuum in the chamber was pumped down by dry scroll vacuum pump (Edwards XDS10) and by a cryo-pump (Cryo-Torr, Helix Technology Corporation). In order to achieve a low vacuum, a high vacuum throttle valve was used. The DC-MS system was equipped with a circular, water cooled magnetron sputtering source with a 2 in. Ti target (Kurt J. Lesker Company) and a DC generator (DCO2 BP). The shutter was utilized for controlling the sputtering time. Pre-sputtering of 2 min was carried out for cleaning the surface of the Ti target. Titanium interlayers were deposited under the following deposition conditions: discharge power fixed at 100 W, total pressure 0.67 Pa, Ar gas flow rate of 29 sccm, and deposition time of 350 s at a distance of 220 mm. For the ta-c film p-fcva deposition system (Lawrence Berkeley National Laboratory, USA) equipped with a 45 bent magnetic filter to reduce macroparticle contamination and two cathodes in a dual cathode configuration was used. Graphite cathodes (Goodfellow) of 99.95% purity were used and a pulse forming network (PFN) was used to strike the triggerless arc with a frequency of 1 Hz. The PFN was controlled with custom-made National Instruments hardware and LabView software. The 2.6 mf capacitor bank was charged to 400 V resulting in an arc current of 0.7 ka and 0.6 ms pulse width. The total pressure during the ta-c deposition process was below 1 x 10-4 Pa. During the depositions the samples were at floating potential and rotation (20 rpm) was used to ensure homogeneous film deposition. The deposition rates for Ti and ta-c films were determined by contact profilometry (Dektac XT). The deposition was carried out at room temperature. ND deposition Two types of functionalized NDs: zeta-positive NDandante with amino and carboxyl functional groups and zeta-positive hydrogen terminated NDH (Carbodeon udiamond, Carbodeon, Vantaa, Finland) were investigated. The NDs were coated on ta-c substrates using a spraying technique. The nanodiamond-water solutions with concentrations of 5 wt-% (NDandante) and 2.5 wt-% (NDH) were diluted in ethanol to prepare a solution with 0.05 wt-%. The spraying was done with pressurized air as carrying gas from a distance of 10 cm and the scanning was repeated ten times, the pressure being 3.5 bars. PyC fabrication First, 4 silicon wafer was dipped for 60 seconds into 10:1 DIW:HF (deionized water : hydrofluoric acid) solution to remove the native silicon dioxide from the wafer surface and to increase S-2

3 hydrophobicity. Next, negative photoactive polymer (Photoresist) SU-8 50 (MicroChem) was spin coated on top of the wafer with BLE spinner (Georgia Tech) with 9000 rpm for 45 seconds in order the achieve 10 μm thick layer. The resist was soft baked on a hotplate with standard protocol, flood exposed at 365 nm wavelength for 8 seconds with MA-6 mask aligner (Süss Microtec) and postexposure baked on a hotplate. The wafer was diced into 10 x 10 mm pieces with Loadpoint Microace 3 dicing saw. The pyrolysis process was carried out in Nabertherm RS 170/1000/13 horizontal tube furnace. The tube was pumped to vacuum and flushed with nitrogen three times in order to remove most of the oxygen inside. After last flush, low nitrogen flow was left on and the inside pressure was kept at room pressure. The furnace was first heated to 300 C and held 40 minutes in order to degas the remaining oxygen from the film. Then the temperature was raised to 900 C and kept for 4 hours for pyrolysis. Subsequently, the furnace was slowly (for 12 hours) cooled down to room temperature. The ramp up rates during heating were 200 C/h. Microscopy of the surface before and after DA fouling Scanning electron microscopy The surfaces were inspected with a scanning electron microscope (JEOL JSM-6335F, field emission SEM). Figure S1 shows examples of surfaces before and after 10 cycles (50 mv/s) in 1 mm DA. Figure S1: Scanning electron microscopy of the surfaces before and after DA fouling. Atomic force microscopy Atomic force microscopy images were taken using Veeco Dimension 5000 in intermittent contact (tapping) mode. Figure S2 shows examples of surfaces before and after 10 cycles (50 mv/s) in 1 mm DA. S-3

4 Figure S2: Atomic force microscopy of the surfaces before and after DA fouling. S-4

5 Unscaled figure of the fouled surfaces Figure S3 is the unscaled version of maniscript Figure 4 and visualizes better the different features of the surfaces. Figure S3: Unscaled version of Figure 4. Pristine surfaces (first column) and surfaces after cycling in 1 mm DA with 50 mv/s (second column) and after subsequent cleaning in H2SO4 10 cycles (third column) or 20 cycles (fourth column). Each graph is 50 µm 50 µm and the scale bar indicates relative current i/iinf. S-5