using Stencil Masks Oscar Vazquez-Mena, Takumi Sannomiya, Mahmut Tosun, Veronica Savu, Luis G. Villanueva, Janos Voros, Juergen Brugger

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1 High Resolution Resistless Nanopatterning on Polymer and Flexible Substrates for Plasmonic Biosensing using Stencil Masks Oscar Vazquez-Mena, Takumi Sannomiya, Mahmut Tosun, Veronica Savu, Luis G. Villanueva, Janos Voros, Juergen Brugger Supporting Information Page Supporting Information-1: Optical images of nanodot arrays and PDMS flexible substrate... 2 Supporting Information-2: Stencil fabrication and sample preparation... 4 Supporting Information-3: Aluminum nanodots... 7 Supporting Information-4: Gold nanodots 20 nm wide... 9 Supporting Information-5: Stencil-substrate gap and blurring description Supporting Information-6: Comparison of depositions on oxide and polymers Supporting Information-7: spectra for the full set of nanodots Supporting Information-8: Biosensing measurements and PLL-g-PEG-Biotin Supporting Information-9: Electrical contacts and resistivity analysis of nanowires

2 Supporting Information-1: Optical images of nanodot arrays and PDMS flexible substrate Figure SI 1.1. Nanohole arrays. Optical microscope images of low stress silicon nitride (LS SiN) stencil membranes. The membranes are 230 x 300 m 2. Each membrane has six arrays of nanoholes with a different spacing (S=50, 75, 100, 150, 200 and 300 nm) and a fixed nanohole width (W). The bottom right membrane has no nanoholes. Figure SI 1.2. Nanodot arrays. Optical microscope images of Au nanodot arrays deposited on a PI/glass substrate, with geometries corresponding to the stencil nanoholes. 2

3 Figure SI 1.3. Flexible PDMS substrate. Image of a PDMS flexible substrate patterned by stencil lithography. The image shows the area corresponding to the 6x6 mm 2 stencil chip where the nanodots were patterned. 3

4 Supporting Information-2: Stencil fabrication and sample preparation This section contains the following information: - Stencil fabrication - Polymer substrate preparation - Si and glass Supporting wafers details - Summary of substrates prepared Stencil Fabrication 1) 100 nm thick LS SiN on a <100> Si wafer 380 µm thick. 2) Nanohole patterning: EBL+Dry etching 3) Membrane release: Si DRIE partial etching of 340 µm 4) Membrane release: Si KOH final etching of 40 µm Figure SI 2.1. Process flow for stencil fabrication. The stencils consist of chips with low stress silicon nitride (LS SiN) membranes with nanoapertures patterned by electron beam lithography (EBL). The fabrication starts with a conventional 100 mm diameter <100>silicon wafer 380 μm thick. LS SiN 100 nm thick is deposited by low pressure chemical vapor deposition (LPCVD). Then, EBL is used to pattern nanoapertures using a ZEP520 e-beam resist on the silicon nitride. The e-beam resist pattern is transferred to the LS SiN by reactive ion etching using an Alcatel- 601 equipment. Next, the backside of the wafer is patterned with windows to etch the silicon bulk and release the patterned membranes. The bulk silicon is etched in two steps. First, a deep reactive ion etching (DRIE) Bosch process etches 340 m of the silicon bulk, followed by KOH wet etching of the remaining 40 m of silicon. KOH is preferred over dry etching for the final release because LS SiN is practically inert to KOH compared to Si dry etching. After membrane release the wafers are cleaved into chips. The stencils for nanodot deposition were 6x6 mm 2 chips and the stencils for nanowire deposition were 2x2 cm 2. In the case of stencils for nanodots, the nanoholes have widths (W) of nm and interdot edge-to-edge spacing (S) of nm for each width. 4

5 Figure SI 2.2. Stencil for nanodot deposition. The stencils for nanodot deposition are 6x6 mm 2 chips. a) SEM micrograph of a LS SiN stencil membrane with an area of 230x300 m 2 and a thickness of 100 nm. The membranes have 6 arrays of nanoholes with different nanohole spacing ( nm). Each array is 30x30 m 2. b) Magnified SEM micrograph of an array of nanoholes with width of W=100 nm and spacing of S=100 nm. c) Zoom-in on the 100 nm wide nanoholes defining the nanohole width W and inter-dot spacing S. Figure SI 2.3. Stencil for nanowire deposition. The stencils for nanowire deposition are 2x2 cm 2 chips. a) SEM micrograph of a LS SiN stencil membrane 1 mm long and 100 m wide. Each membrane has seven nanoslit apertures. b) Magnified SEM micrograph of a nanoslit 10 m long with two side micrometric apertures. Polymer substrate preparation a) Polyimide (PI-2610) from HD Microsystems was spin coated on Si and glass wafers: 1) Spin coating at 2500 rpm to obtain a 2 m thickness. 2) Soft bake at 150 o C 3) Curing at 300 o C 5

6 b) SU-8 negative tone photo-epoxy from Gersteltec was spin coated on Si and glass wafers: 1) Spin coating at 1000 rpm to obtain a 2 m thickness. 2) Soft bake at 130 o C 3) UV exposure with a dose of 125 mj/cm 2. 4) Post-Exposure bake at 100 o C. c) Parylene-C from Specialty Coating Systems was deposited by chemical vapor deposition on Si and glass wafers. 1) A charge of 7 g. of Parylene-C in solid form was used to obtain a thickness of 2 m. 2) Parylene-C solid in dimer form is heated to 150 o C to form a dimer vapor. 3) The dimer vapor is then heated to pyrolsis at 670 o C dissociating the parylene into a monomer vapor. 4) The monomer vapor is transferred to a deposition chamber at room temperature where parylene is deposited on the substrates where it polymerizes into a film. d) Polydimethylsiloxane (PDMS) (Sylgard 184, Dow Corning, USA) was prepared by mixing 10 parts of the pre-polymer by one part of the curing agent. The mixture was degassed, poured into a Petry dish and cured at 70 o C for 3 hours. The films have a thickness of 2 mm and a diameter of 6 cm. Si and glass Supporting wafers details a) Silicon wafers 525±25 μm thick with a diameter of 100 mm, <100> orientation, boron p-doped ( Ωcm) were used as Supporting substrates for 2 m thick films of polyimide, parylene and SU-8. b) Float glass wafers 550±10 m thick, 100 mm diameter, were also used as Supporting substrates for 2 μm thick films of polyimide, parylene and SU-8. The glass has an amorphous structure and a composition of SiO 2 (7%), Na 2 O (13.9%), K 2 O (%), CaO (8.4%), MgO (4.4%), Al 2 O 3 (1.5%), Fe 2 O 3 (8%) and SO 3 (0.3%). Summary of substrates prepared 1: Polyimide on glass, referred as PI/glass. 2: Polyimide on silicon, referred as PI/Si. 3: SU-8 on glass, referred as SU-8/glass. 4: SU-8 on Si, referred as SU-8/Si. 5: Parylene on glass, referred as Pary/glass. 6: Parylene on silicon, referred as Pary/Si. 7: PDMS films 6

7 Supporting Information-3: Aluminum nanodots SEM images, AFM images and line profiles (AFM) of 30 nm thick Al nanodots deposited on SU-8/Si substrates. The nanodots appear larger in the AFM images due to the convolution with the size and radius of the AFM tip ( 10 nm). Figure SI 3.1. Al nanodots 50 nm wide with 50 nm spacing. (Left: SEM, Right: AFM) Figure SI 3.2. Al nanodots 100 nm wide with 100 nm spacing (Left: SEM, Right: AFM) 7

8 Figure SI 3.3. Al nanodots 200 nm wide with 200 nm spacing (Left: SEM, Right: AFM) Figure SI 3.4. Al nanodots 200 nm wide with 50 nm spacing (Left: SEM, Right: AFM) 8

9 Supporting Information-4: Gold nanodots 20 nm wide Au nanodots were deposited through stencils with 25 nm wide nanoholes on SU-8/Si substrates. In this case, the quality of the nanodots is limited by the blurring and the clogging of the nanoholes. The width and thickness of the nanodots are reduced probably due to rapid clogging of the nanoholes. The nanodots have widths in the nm range. AFM measurements show that the nanodots have a thickness in the 6-10 nm range, which is drastically smaller than the nominal thickness of 50 nm. SEM images also show the presence of scattered particles around the nanodots due to the blurring. The reduced size and scattered particles observed in this deposition illustrate the main factors limiting the resolution in stencil lithography. Figure SI 4.1 Au nanodots 20 nm wide with 30 nm spacing. a) Stencil nanoholes with 25 nm width and 25 nm spacing. b) SEM images of Au nanodots 20 nm wide with 30 nm spacing deposited through the stencil shown in a) on a SU-8/Si substrate. The nanodots have a reduced width due to clogging of the nanoholes. The scattered particles around the nanodots are due to blurring. c) Tapping mode AFM topography images of the Au nanodots. The nanodots look wider than in SEM image due to the convolution with the AFM tip. d) Cross section line profile of the nanodots (AFM) showing a thickness of 6-10 nm, smaller than the nominal thickness of 50 nm. 9

10 Figure SI 4.2. Au nanodots 20 nm wide with 55 nm spacing. a) Stencil nanoholes with 25 nm width and 50 nm spacing. b) SEM images of Au nanodots 20 nm wide with 55 nm spacing deposited through the stencil in a) on a SU-8/Si substrate. c) Tapping mode AFM topography images of the Au nanodots. The nanodots look wider than in SEM due to the convolution with the AFM tip. d) Cross sectione line profile of the nanodots (AFM) showing a thickness of 6-10 nm, which is smaller than the nominal thickness of 50 nm. 10

11 Supporting Information-5: Stencil-substrate gap and blurring description For a detailed study on the gap, blurring and thickness reduction in stencil lithography, the reader is invited to look at Vazquez-Mena et al., Nanotechnology 20 (2009), Stencil-Substrate Gap The blurring in stencil lithography is a consequence of the spatial gap between the stencil membrane and the substrate during material deposition, producing a size enlargement of the deposited structures with respect to the stencil apertures. This gap exists because any conventional silicon or glass wafer, or polymer film, is never perfectly flat. Conventional silicon wafers 100 mm in diameter have curvatures with typical bowings between 10 and 30 μm (Figure SI 5.1.a). Therefore, when two wafers or chips are put in contact, such as a stencil and a silicon substrate, their curvature produces a gap between them (Figure SI 5.1.b). When a stencil chip of 6x6 mm 2 is put on top of a silicon wafer substrate, typically we have observed by optical measurements a gap of less than 2 μm between them. Besides wafer curvature, any bending of the stencil membranes due to stress can also contribute to the stencil-substrate gap. In the case of polymer substrates, this gap can have a different behavior with respect to silicon or glass substrates due to the softness of the polymers and the different adhesion forces at the stencil-substrate interface. a) Curvature of conventional silicon wafers 100 mm diameter wafer Bowing μm b) Stencil and substrate curvature produce a gap <2 μm gap 6 mm stencil chip Substrate Figure SI 5.1 Stencil-Substrate Gap. Gap and Blurring The gap results in blurred structures due to two main factors: i) the divergent flow of material from the source to the substrate and ii) the surface diffusion of material deposited (Figure SI 5.2). The material evaporated from the source has a divergent flow, so the area where the material lands on the substrate is actually larger than the stencil aperture. This is shown in Figure SI 5.2, where W (size of deposited structure) is larger than A (aperture size). This size enlargement, usually named as 11

12 geometrical blurring (B G ), is directly proportional to the gap size (G) and can be estimated from geometrical considerations as: B G G S M W A, D where D is the distance between the material source and the substrate, and S M is the size of the material source. In our evaporator equipment, a LAB600 evaporator, the Au source has a size of S M =5 mm and the distance between source and substrate is D= 1 m. For a stencil-substrate gap of 2 μm, the corresponding geometrical blurring would be B G 10 nm. Besides this geometrical component, surface diffusion also produces blurring. After landing on the substrate, the adsorbed atoms can move laterally and spread. The effect of the surface diffusion on the blurring is still not well understood but recent studies have shown that it is also proportional to the stencil-substrate gap and affected by material properties and deposition conditions. Source (S M ) D Substrate Substrate Surface Diffusion A W B G /2 Surface Diffusion Stencil membrane Gap (G) Figure SI 5.2. Blurring: geometry and surface diffusion. Thickness Reduction The blurring can also produce a reduction in the thickness of very small structures due to both the geometrical effect and surface diffusion. For very small aperture sizes A, such that G>(A)(D)/(S), then the effective source of material is reduced, decreasing the deposition rate and the thickness of the structures. In our geometry, this happens around A 10 nm. Similarly, for small structures, surface diffusion can reduce the thickness of the structures if they are smaller than the diffusion length. A third factor reducing the structure thickness is the clogging of the stencil apertures, which drastically reduces the size and closes the aperture before enough material is deposited to obtain the desired thickness. (Vazquez-Mena et al., Nanotechnology, 2009) 12

13 Supporting Information-6: Comparison of depositions on oxide and polymers The nanodots deposited on polymers show better characteristics in three different aspects: - Blurring - Thickness reduction - Localized Surface Plasmon Resonance a) SiO 2 / Si substrate b) SU-8 / Si substrate 100 nm 100 nm Scattered particles between the nanodots are present on oxide substrate but absent on polymer substrate. Figure SI 6.1. Blurring on Si oxide and polymer substrates. Previous depositions made on silicon oxide show the presence of scattered particles in between the nanodots due to blurring (Vazquez Mena et al, ACS Nano, vol 5, p. 844). However, these scattered particles are absent for depositions on polymer substrates. Figure SI 6.1 shows SEM images of 50 nm wide nanodots with 100 nm spacing deposited on a) a silicon wafer with its native silicon oxide and b) on a SU-8/silicon substrate. The presence of scattered particles in between the main dots on the SiO 2 /Si substrate is clearly seen, whereas such particles are absent in the dots deposited on the SU-8/Si substrate. 13

14 a) Glass (Si Oxide) substrate b) SU-8/glass substrate 70 nm 200nm 200nm 0 nm Z[nm] Z[nm] X[nm] Small nanodots deposited on glass have a reduced thickness X[nm] Figure SI 6.2. Thickness reduction on Si oxide and polymer substrates. The larger blurring observed on silicon oxide substrates also has an effect on the thickness of the structures. This image shows Tapping Mode AFM topography images and line profiles of 50 nm wide nanodots with a nominal thickness of 50 nm deposited on bare glass and on SU-8/glass substrates. The AFM images confirm the presence of scattered particles in between the nanodots as observed also in Figure SI 6.1. The line profiles also show that the thickness of the nanodots on oxide is reduced to 20 nm, whereas the nanodots on SU- 8/glass have the expected thickness of 50 nm. 14

15 Bare glass substrate (Si Oxide) a) Spacing b) W=50 nm S=50nm c) d) W=200 nm W=150 nm 900 W=100 nm W=75 nm W=50 nm 800 Resonance Spacing (nm) 0 Figure SI 6.3 Localized Surface Plasmon Resonance of Au nanodots on Si oxide and polymer substrates. The LSPR of nanodots on polymer substrates have a narrower resonance peak, associated with a reduced blurring. Figures SI 6.3.a and 6.3.b show the optical spectra for 50 nm wide nanodots with different spacing deposited on bare glass and SU-8/glass substrates, respectively. The LSPR peaks on SU-8/glass are sharper and better defined than on bare glass. Figures SI 6.3.c and 6.3.d show the behavior of the resonance wavelength for the nanodots on bare glass and on SU-8/glass, respectively, as function of the spacing for different nanodot widths. An important difference is that the nanodots on glass of 50 and 75 nm width show a strong red-shift when the spacing decreases from 100 to 50 nm. The red-shift with a decreasing spacing is characteristic of static dipole interactions, or near-field coupling, for spacings below 50 nm. This is probably a consequence of larger blurring and scattered particles on glass substrates that enhance the coupling between the nanodots. This red-shift is absent for the nanodots on SU-8 where there are no scattered particles observed. Resonance SU-8/glass substrate W=50 nm W=200 nm W=150 nm W=100 nm W=75 nm W=50 nm Spacing S=50nm Spacing (nm) 15

16 Supporting Information-7: spectra for the full set of nanodots - spectra measurements: The extinction spectra of the nanodots were measured on the transparent substrates: PI/glass, SU-8/glass, PL/glass and PDMS. The spectra were measured in the nm range. The spectra were acquired with a spectrophotometer SpectraPro 2150, Pixis 400, Princeton Instruments (U.S.A.) equipped with an optical microscope Axiovet 200, Carl Zeiss (Germany). A halogen lamp with parallel illumination was used. The characteristic oscillation spectral features due to the interference within the 2 m thick polymer layer (Polyimide, SU-8 and Parylene) were removed by Fourier filtering in 1/ space. A parabolic function was used to detect the resonance wavelength. 16

17 W= 50 nm Polyimide on Glass S=50nm W= 75 nm S=50nm W= 100 nm S=50nm W= 150 nm W=200 nm Resonance W=200 nm W=150 nm W=100 nm W=75 nm W=50 nm Spacing (nm) Figure SI 7.1 LSPR of Au nanodots on polyimide. Spectra of W=50, 75, 100, 150 and 200 nm wide nanodots with different spacings of S=50, 75, 100, 150, 200 and 300 nm deposited on polyimide on glass. The bottom-right plot shows the behavior of the resonance wavelength as function of spacing for different dot size. The 150 and 200 nm dots with spacing of 50 nm dots failed due to breaking of the membrane. 17

18 SU-8 on glass W=50 nm S50nm S75nm S100nm S150nm S200nm S300nm W=75 nm S50nm S75nm S100nm S150nm S200nm S300nm W=100 nm S50nm S75nm S100nm S150nm S200nm S300nm W= 150 nm S75nm S100nm S150nm S200nm S300nm W= 200 nm S75nm S100nm S150nm S200nm S300nm Resonance W=200 nm W=150 nm W=100 nm W=75 nm W=50 nm Spacing (nm) Figure SI 7.2 LSPR of Au nanodots on SU-8. Spectra of W=50, 75, 100, 150 and 200 nm wide nanodots with different spacings of S=50, 75, 100, 150, 200 and 300 nm deposited on SU-8 on glass. The bottom-right plot shows the behavior of the resonance wavelength as function of spacing for different dot size. The 150 and 200 nm dots with spacing of 50 nm dots failed due to breaking of the membrane. 18

19 Parylene on Glass W= 50 nm S=50nm W=75 nm S=50nm W= 100 nm S=50nm W= 150 nm W=200 nm Resonance W=200 nm W=150 nm W=100 nm W=75 nm W=50 nm Spacing (nm) Figure SI 7.3 LSPR of Au nanodots on parylene. Spectra of W=50, 75, 100, 150 and 200 nm wide nanodots with different spacings of S=50, 75, 100, 150, 200 and 300 nm deposited on parylene on glass. The bottom-right plot shows the behavior of the resonance wavelength as function of spacing for different dot size. The 150 and 200 nm dots with spacing of 50 nm dots failed due to breaking of the membrane. 19

20 PDMS W= 50 nm S=50nm W=75 nm S=50nm W= 100 nm S=50nm W= 150 nm S50nm S75nm S100nm S150nm S200nm S300nm S=50nm W= 200 nm Resonance W=200 nm W=150 nm W=100 nm W=75 nm W=50 nm Spacing (nm) Figure SI 7.4 LSPR of Au nanodots on PDMS. Spectra of W=50, 75, 100, 150 and 200 nm wide nanodots with different spacings of S=50, 75, 100, 150, 200 and 300 nm deposited on PDMS. The last plot (bottom right) shows the behavior of the resonance wavelength as function of spacing for different dot size. 20

21 Supporting Information-8: Biosensing measurements and PLL-g-PEG-Biotin -Biosensing measurements: Biosensing measurements were done using 75 nm wide nanodots with 50 nm spacing on a PDMS film. The measurements were carried in 160 mm salt buffer solution adjusted to ph 7.4 containing 10 mm of 4-(2-hydroxyethyl)piperazine-1-ethanesulfonicacid (HEPES) with 150 mm NaCl. The Au nanodots were functionalized with PLL-g-PEG-biotin (biotinylated poly(l- Lysine)-g-poly(ethylene glycol)). The concentration of the PLL-g-PEG-biotin solution was 100 g/ml. The streptavidin (SA) solution had a concentration of 20 g/ml. The measurements were done with a flow cell containing the PDMS film with the nanodot array. The area of the sensing measurements was 30x1.5 m 2. The PLL-g-PEG-biotin molecule is shown in the Supporting Information-8. -PLL-g-PEG-Biotin is a biotin-derivatized Poly(L-Lysine)-g-poly(ethylene glycol). It is a polycationic copolymer that adsorbs onto negatively charged surfaces via electrostatic interactions in aqueous solutions forming densely packed PEG chains. This molecule is shown below in Figure SI 8. The binding of biotin to the protein streptavidin allows using PLL-g-PEG-Biotin as bridge between Au nanodots and streptavidin. Figure SI 8. Structure of PLL-g-PEG-Biotin. Image taken from Huang et al, 2002 (Langmuir, vol 18, p. 220), where more details of this molecule can be found. 21

22 Supporting Information-9: Electrical contacts and resistivity analysis of nanowires This section contains the following information: -Fabrication of stencil and contact deposition -Analysis of nanowire resistivity After the deposition of the nanowires through stencils with a nanoslit (nanostencil), Au/Ti electrical contacts were deposited on the nanowires also by stencil lithography. The electrical contacts allowed measuring the electrical resistance of the nanowires with a probe station. The stencils to deposit the electrical contacts (microstencil) consist of 100 mm silicon wafers 525 m thick with 500 nm thick low stress silicon nitride membranes. The membranes have large micrometric apertures which allow depositing large metal pads of 1 mm x 120 m. These pads serve as electrical contacts to the nanowires using needle probes. These stencils were fabricated using conventional UV lithography followed by KOH etching of the bulk silicon to release the membranes as shown in Figure SI 9.1. a) 500 nm thick LS SiN on a Si wafer b) UV litho and Dry etching c) Final KOH Si bulk etch Figure SI 9.1. Fabrication of microstencils for electrical contact to the nanowires. After the deposition of the nanowires on the PI/Si substrate, electrical contacts were deposited on the nanowires using the micro-stencils. The PI/Si substrate and the micro-stencil were aligned and clamped using a standard bond aligner system (Suss MA6/BA6) that allows an alignment precision of 1 μm. The micro-stencil and the substrate contain markers for alignment that are critical to deposit the contacts precisely on the nanowires. After the alignment and clamping of the microstencil and PI/Si substrate with nanowires, 10 nm of Ti and 80 nm of Au are deposited by e-beam evaporation. The Ti and Au were deposited at 4 Å/s at room temperature and 10-6 mbar. Figure SI 9.2 shows the nanostencil used for nanowire deposition, the microstencil used for the electrical contacts and their corresponding deposited structures. 22

23 Figure SI 9.2. Deposition of nanowires and electrical contacts. a) SEM image of the nanostencil for nanowire deposition. The nanowires are deposited without alignment on a 100 mm wafer PI/Si substrate. b) SEM image of the micro-stencil for electrical contact deposition. After the deposition of the nanowires, Au/Ti contacts are deposited with the micro-stencil aligned with a 1 μm precision c) SEM images of a nanowire between electrical contacts. The resistance of the wires was measured by I-V measurements with a probe station in a two-probe configuration at room temperature and applying a low DC voltage from -5 to 5 mv preventing breakdown of the wires. The resistance was obtained by linear fitting of the I-V curves, showing the expected linear behavior for metallic structures. The obtained resistance, or measured resistance R M, is composed of the resistance of the nanowires R NW and the contact resistance R C which includes the wiring of the measurement setup and the electrical contacts. R M can be expressed as: R M R R (Eq. 1) C NW Since the wiring and electrical pads have the same dimensions for all nanowires with the same length, we will assume that R C is a constant for nanowires of the same length, so that R M can be expressed as: 23

24 R M R C LNW 1 NW RC NW LNW ANW (Eq. 2), A NW where L NW is the nanowire length, A NW is the area cross section of the nanowire and ρ NW is the electrical resistivity of the nanowires. This expression shows that there is a linear relation between R M and the inverse of the area cross section (A -1 ), which can be expressed as: R M 1 ( A ), (Eq. 3) where R and L. C NW NW The experimental data of R M vs A -1 and the linear fittings are shown in Figure SI 9.3. A -1 can be obtained from the SEM and AFM analysis. R M vs A -1 for L NW = 10 μm R M vs A -1 for L NW = 20 μm Linear Fitting (Eq. 3): α= 48.44±2.70 Ω β=6.37±0.16 x Ωm 2 Linear Fitting (Eq. 3): α= 76.19±7.5 Ω β=11.4±5 x Ωm 2 Figure SI 9.3. Linear fittings of electrical resistance versus area cross section. In the case of L NW =10 μm, the linear fitting allows extracting R C = 48.4 Ω and ρ NW,L=10 =6.37x10-8 Ωm=6.37 μωcm. The value of R C = 48.5 Ω can be subtracted from the measured resistance values to obtain the resistances of the nanowires R NW which are plotted in Figure 5.e of the main manuscript. Similarly, for L NW =20 μm, it can be extracted R C = Ω and ρ NW,L=20 =5.73x10-8 Ωm=5.73 μωcm. Taking an average for the resistivites of wires with L NW =10 μm and L NW =20 μm, we can estimate that ρ NW =6.05 μωcm. 24