Matrix-assisted dip-pen nanolithography and polymer pen lithography

PEG (MW 2000 g mol^-1) and C₆₀ were purchased from Sigma Aldrich (USA). AuNPs (13-nm)^[29] and 5-nm Fe3O4 MNPs[30] were prepared in our labs following literature protocols. Si/SiO_x (100) wafers with a 500-nm oxide coating layer and GaAs (100) wafers were purchased from Nova Materials Inc. (USA). Au substrates were prepared by thermal evaporation (BOC Edwards Auto306, UK) of an Au thin film (30 nm) on a Si/SiO_x substrate cleaned by sonication in ethanol and pre-coated with a Ti adhesion layer (7 nm). AFM topographical and magnetic force microscopy (MFM) images were recorded on a Veeco Bioscope equipped with a Nanoscope IIIA controller and optical microscopy images were taken using a Zeiss Axiovert 200M (Carl Zeiss, Inc., Germany). DPN and PPL experiments were performed with a NScriptor nanolithography platform (NanoInk, Inc., USA) equipped with an environmental chamber with active humidity control driven by commercially available InkCAD DPN software (NanoInk, Inc., USA). High-resolution magnetic probes for MFM (MESP-HR) were purchased from Veeco Probes (USA) and Pointprobe Plus Si SPM sensors (Nanosensors, Inc., USA) were used for topographical and non-contact imaging. DPN experiments: In a typical experiment, PEG (2000 g mol^-1, 5mgmL^-1) was dissolved in a solvent (10 mL). NM solution (50 μL of 10 mg mL^-1) was added to the PEG solution and sonicated for 1 min. Twelve-pen M-type tip arrays (NanoInk, Inc., USA) were dipped in the solution and dried under a flowing N₂ stream. DPN experiments were performed in an environmental chamber with active humidity control at a relative humidity of 90% at a temperature of 25-29 8°C. The patterns were generated using InkCAD software (NanoInk, Inc., USA) that could control dwell time and position of the tip arrays on the surface. PPL experiments: Polymer-pen tip arrays with 80-mm spacing between tips were prepared as previously reported^[12]. In a typical experiment, PEG (2000 g mol^-1, 5 mg mL^-1) was dissolved in a solvent (10 μL). NM solution (50μL at 10mg mL^-1) was added to the PEG solution and sonicated for 1 min. The ink solution was added to the PDMS tip arrays by spin-coating (1 mL, 2000 rpm, 3min). PPL experiments were carried out on an NScriptor workstation as described previously^[12] using InkCAD software (NanoInk, Inc., USA) with feedback turned off and a relative humidity of <90% and temperature of 25-29 °C. Fabrication of transistor device: A large Au electrode pad was fabricated by conventional photolithography on a Si/SiO_x wafer with a 500-nm thermal oxide layer. The inner nanoelectrodes were patterned by electron-beam lithography followed by thermal evaporation and resist liftoff, resulting in electrodes with a gap of 500 nm (Figure S4). The C₆₀-PEG composite ink was deposited by MA-DPN at a scanning rate of 0.01 μ s-1.