Fabrication of high aspect ratio AFM probes with different materials inspired by TEM lift-out method

Supplemental material for Fabrication of high aspect ratio AFM probes with different materials inspired by TEM "lift-out" method Swee Ching Tan a) * Department of Materials Science and Engineering, National University of Singapore, Engineering Drive 2, Singapore 117579 Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States Hangbo Zhao * Department of Mechanical Engineering, Massachusetts Institute of Massachusetts Avenue, Cambridge, Massachusetts 02139, United States Technology, 77 Carl V Thompson Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States a)Electronic mail: msetansc@nus.edu.sg * These authors contributed to the work equally Si NW Array Fabrication The Si NW array was fabricated using a combination of interference lithography and metal assisted chemical etching The interference lithography was employed for patterning of hole arrays in Au films deposited on silicon First, a 220 nm-thick antireflection coating (ARC) layer (BARLi, AZ Electronic Materials) was spin-coated on a lightly doped p-type Si wafer A 20 nm-thick SiO interlayer was then deposited using electron beam evaporation to facilitate pattern transfer for subsequent metal film deposition and lift-off This was followed by spin coating of a 200 nm-thick layer of photoresist PFI-88 (Sumitomo Chemical Co.) The trilayer stack on the Si wafer was then exposed with a HeCd laser (λ = 325 nm) using a Lloyd’s mirror setup Two perpendicular exposures were performed to form diperiodic post structures By choosing the half angle of the two incident beams, θ , in the Lloyd’s mirror and the laser exposure time, post arrays of specific period and diameter can be produced For post arrays of 900 nm diameter and 1800 nm period, a half angle θ = 5.18° and exposure time of 18s for a laser power of 0.165 µW was used After exposure, the sample was immersed in CD-26 developer (Shipley Micropost®) for 60 seconds to remove the unexposed PFI-88 photoresist In the subsequent reactive ion etching (RIE) process, a CF plasma (of power 150 W, pressure 10 mTorr) and He + O plasma (of power 300 W, pressure 10 mTorr) were used to transfer the photoresist post array pattern into the underlying SiO and ARC layers A 15 nm-thick gold layer was deposited onto the sample using electron beam evaporation A lift-off process was performed by soaking and sonicating the samples in N-Methyl-2-pyrrolidone (NMP) at 85°C for and min, respectively The samples were then etched in a solution of HF, H 2O2 and H2O (6:1:36) at room temperature For a nanowire height of 2.2 µm shown in Figure 2(b), the etch time was about 15 FIG S1 Photograph of the SEM stub with a sloped (22.1°) sample mounting surface The actual height of the nanopillars was calculated based on the SEM software measurement (2.06 µm, see Fig 2(b)) and the inclination angle of the slope of the SEM sample mounting stub (22.1 °, see Fig S1) Therefore the actual nanopillars height is 2.06 µ m / cos 22.1o = 2.22 µ m ... post arrays of specific period and diameter can be produced For post arrays of 900 nm diameter and 1800 nm period, a half angle θ = 5.18° and exposure time of 18s for a laser power of 0.165 µW... evaporation A lift-off process was performed by soaking and sonicating the samples in N-Methyl-2-pyrrolidone (NMP) at 85°C for and min, respectively The samples were then etched in a solution of. .. HF, H 2O2 and H2O (6:1:36) at room temperature For a nanowire height of 2.2 µm shown in Figure 2(b), the etch time was about 15 FIG S1 Photograph of the SEM stub with a sloped (22.1°) sample mounting