High resolution sputter coater

Nanometer-scale pipet electrodes were fabricated by laser pulling of quartz capillaries (Sutter Instrument Co., Novato CA; O.D. = 1.0 mm, I.D. = 0.7 mm, length = 10 cm) using a P-2000 capillary puller (Sutter Instrument Co., Novato, CA). The pulled pipets were then silanized via vapor deposition as described elsewhere.^{40 (link),45} Pipets were characterized using Scanning Electron Microscopy (SEM) and ion-transfer voltammetry. For SEM imaging, the nanopipets were coated with a thin Au/Pd film by a high-resolution sputter coater (Quorum Technologies LTD, Kent, UK), and the orifices were observed by high resolution field emission SEM (FEI dual-beam 235, FEI Co., Hillsboro OR, USA) under a 20 kV electron beam.

Detailed nanoITIES pipet electrode fabrication and characterization were reported in recent work.^{21 (link),29 (link),30 (link),32 (link)–34 (link)} Briefly, the nanopipets were pulled with a P-2000 Laser Puller (Sutter Instruments Novato, CA) using quartz capillaries (1 mm outer diameter, 0.7 mm inner diameter, 7.5–10 cm length). The pulling parameters are listed in Table S1 under the Supporting Information. A scanning electron microscope (SEM) was used to quantitatively determine the inner radii of the nanopipets. Using a high-resolution sputter coater (Quorum Technologies LTD, Kent, U.K.), the nanopipets were coated with a thin film of Au/Pd, and the nanopipet orifices were imaged through high resolution field emission SEM (FEI dual-beam 235, FEI Co., Hillsboro OR) under a 15 kV electron beam. A transmission electron microscope (TEM; Philips CM200, FEI Co., Hillsboro OR) was also used to quantitatively determine the diameter of the nanopipets under a 120 kV electron beam.