Supplementary Figure 1 Dark-field optical images of as prepared PMMA-assisted transferred CVD graphene films on silicon substrates (a) and the one after PBASE monolayer growth (b). 1
Supplementary Figure 2 Average J(V) curves and distribution histogram of SLG/SLG and BLG/BLG devices. The error bars refers to the log-standard deviations of the log-average J values. (a) Average J(V) curve of BLG/BLG devices. (b) Average J(V) curves of SLG/SLG devices (c) current density distribution histogram of SLG/SLG devices. (d) Current density distribution histogram of SLG/SLG devices. (e) Average J(V) curve of BLG/PBASE/BLG devices. (f) Average J(V) curve of SLG/PBASE/SLG devices. 2
Supplementary Figure 3 Average J(V) curves and histograms of G/PBASE/G devices with various PBASE SAM growth time. The error bars refers to the log-standard deviations of the log-average J values. In histograms, the Gaussian fitting curves are represented in black lines. 3
Supplementary Figure 4 Schematic drawings of G/G (a) and G/PBASE/G (b) devices and I-V curves with various PBASE SAM growth time (c). The error bars are indicated in black lines. 4
Supplementary Figure 5 Raman characterization of CVD bilayer graphene before and after PBASE growth. (a) and (b) Raman color mapping of the position and FWHM of 2D peak of pristine CVD bilayer graphene. (c) and (d) Raman color mapping of the position and FWHM of 2D peak of CVD bilayer graphene with PBASE SAM on top. All scale bars are 1 m. (e) Distributions histograms abstracted from (a) and (c). (f) Distributions histograms abstracted from (b) and (d). 5
Supplementary Figure 6 UPS (a) and FTIR (b) characterization of CVD bilayer graphene before and after PBASE growth. For UPS, -5V bias is applied to the substrate to overcome the work function of the analyser (~4.4 ev). The work function of sample is calculated from the equation where is the UV light energy (21.2 ev), W is the energy at secondary electron cut-off and is the voltage bias. 6
Supplementary Figure 7 Device resistance versus back-gated voltage (V BG ) of CVD bilayer graphene field-effect transistor. Blue curve indicates the device performance of pristine CVD bilayer graphene while red curve represents that of PBASE-absorbed CVD bilayer graphene. 7
Supplementary Figure 8 XPS characterization of CVD bilayer graphene before and after PBASE growth. (a) XPS wide spectrum of pristine CVD graphene and PBASE/G samples. (b) C 1s of pristine CVD graphene. (c) C 1s of CVD graphene with PBASE layer. (d) O 1s of pristine CVD graphene. (e) O 1s of CVD graphene with PBASE SAM layer. 8
Supplementary Figure 9 Histograms of G/molecules/G devices with various molecules. The Gaussian fitting curves are represented in black lines. These molecules are separately dissolved in DMF with concentrations of 5 mm for the SAM growth. 360 traces were recorded for eight specified samples. 9
Supplementary Figure 10 Average J(V) curves of G/molecules/G devices and their corresponding AFM images. All SAM were grown for 8 hours. (a) Average J(V) curve of G/1-Pyrenebutanol/G device. (b) Topography of 1-Pyrenebutanol on graphene film. The inserted profile indicates that it forms monolayer but with large pinholes. (c) Average J(V) curve of G/1-Pyrenecarboxylic acid/g device. (d) AFM imaging of 1-Pyrenecarboxylic acid layer on graphene films. Inserted profile of the molecules edge shows that the height of the absorbed molecules is ~2nm. (e) Schematic structure of repeat unit of two 1-Pyrenecarboxylic acid molecules due to strong intermolecular hydrogen bonding by COOH groups. (f) Typical herringbone-packed structure of the bi-molecular unit. 10
Supplementary Figure 11 Projected DOS (PDOS) comparisons of G/PBASE/G and G/1-Pyrenebutanol/G devices. (a) PDOS of G/PBASE/G structure. (b) PDOS of G/1-Pyrenenbutanol/G structure. 11
Supplementary Figure 12 Transparency of various devices. (a) Transparency comparisons of SLG/SLG and SLG/PBASE/SLG devices. (b) Transparency comparisons BLG/BLG and BLG/PBASE/BLG devices. Four types of samples were prepared on quartz substrates 12
Supplementary Figure 13 Sheet resistances of various graphene and PBASE layer. For clarification, the pristine sheet resistance of one CVD BLG in this comparison is 265±15 /sq.. 13
Supplementary Figure 14 Average J(V) curves and histograms of G/PBASE/G devices fresh prepared and after exposed in air for three months. The error bars refers to the log-standard deviations of the log-average J values. In histograms, the Gaussian fitting curves are represented in black lines. 14
Supplementary Figure 15 PBASE monolayer resistibility to commonly used solvents. The PBASE/G samples were soaked in acetone for two hours and then rinsed by IPA, followed by drying in a stream of nitrogen. (a) AFM morphology of PBASE monolayer on graphene films after exposed to acetone and isopropanol. the scale bar is 400nm. (b) Raman spectrums of PBASE/G before and after acetone and isopropanol washing. 15
Supplementary Figure 16 Raman spectrums of CVD bilayer graphene before and after PBASE growth. (a) Typical Raman spectrum comparison of CVD graphene before and after PBASE growth. (b) and (c) 2D peak fitting of CVD bilayer graphene before and after PBASE growth. 16
Supplementary Note 1 Electrical properties of SLG/SLG and BLG/BLG devices To investigate how the rigidity of the graphene films affect the vertical conductivity, the tunneling conductance were measured on both LBL stacked CVD single layer graphene (SLG) as well as bilayer graphene, using the EGaIn system. The thickness of single layer graphene is half of that of bilayer graphene (BLG), hence, its bending rigidity is ~12.5% of that of BLG. This is based on the bending rigidity equation: κ=ed 3 /12(1-v 2 ) (2) where E is Young s modulus, v is Poisson s ration, and d is the film thickness. 1, 2 SLG will have a higher tendency to form ripples during various process steps compared to the thicker BLG. As we expected, SLG/SLG device shows larger error bar and wide distribution (Supplementary Fig. 2 b and d). 17
Supplementary Note 2 EGaIn setup and junctions fabrications After CVD growth, the graphene films were transferred onto Au/Cr (100mn/5nm)-coated silicon substrates by the conventional PMMA method. After removing the PMMA by acetone solution, the samples were immersed in isopropanol solution for 5 minutes and then blown dry in nitrogen. The graphene films were soaked into 5 mm PBASE in dimethylformaldehyde (DMF) solution at 80 ºC to allow the SAM of PBASE by π-π interactions. At the end of the desired SAM growth time, DMF solution was used to wash away unwanted residues and the sample was dried in a gentle stream of N 2. After this, another small piece of graphene films produced in the same CVD batch was stacked onto the center of bottom graphene films to prevent the contact with gold coating layer. The same washing steps were repeated to remove the polymer. To measure the reproducibility of the data, we followed the same method mentioned above to prepare three different batches of devices. The EGaIn junctions of each type of G/PBASE/G were measured on three different batches of samples fabricated by the methods mentioned above. On each sample, we formed six to eight junctions from randomly selected top-contact on top layer of graphene by moving the EGaIn tip controlled by a micromanipulator. After each three junctions, we fabricated a new EGaIn tip from a sacrificial clean Au surface to avoid physisorbed materials accumulated on the surface of old EGaIn tip. In this study, the diameters of contact were ~10 m for all the measurements. All these processes were monitored by a USB camera (Edmund optics, EO-3112C color USB camera). For each junction, we recorded 24 scans (0 V -1.0 V 1.0 V and back to 0 V) with a 50 mv step and 0.1 s delay of each step voltage. Each scan as one J(V) trace contains 43 J(V) data points. We measured 360 traces for each type of G/PBASE/G devices (in total, 2520 traces for 7 types of devices) and we calculated log J using previously reported methods. 13,3 Supplementary Fig. 3 shows the log-average J(V) curves with log-standard deviations error bars and its corresponding histograms. 18
Supplementary Note 3 In-plane conductivity of G/PBASE/G devices These G/PBASE/G devices on silicon substrate were also patterned into micro-size arrays by photolithography and oxygen plasma etching to conduct the in-plane conductivity measurement. We fabricated two electrodes (Au/Cr, 60/5nm) on two parallel sides leaving 250 m 250 m working areas. The current-voltage (I-V) curves were recorded using a four probe station equipped with Keithley 4200 semiconductor characterization system. Fifty arrays on five sample batches were recorded for six types of devices and their I-V curves are listed out in Supplementary Fig. 4c. The conductivity ( ) is expressed as (3) where n is the carrier density and is the carrier mobility. After the insertion of PBASE SAM layer, the current at 0.1V bias increases to 1.41 ma from 0.64 ma, which come from increased carrier density n as a result of the hole doping ability of PBASE verified by Raman (Supplementary Fig. 5) and UPS ( Supplementary Fig. 6a) data. This enhancement is much smaller than that of out-of-plane conductivity, but it is reasonable as the in-plane conductivity of graphene is already quite high to begin. 12 19
Supplementary Note 4 FET of CVD graphene and doping by PBASE To evaluate the electronic quality of CVD bilayer graphene and the doping effect of PBASE, we fabricated back gate field-effect transistors on silicon substrates with 300 nm silicon oxide. Ti/Au (5/80 nm) was employed as the source and drain electrodes. CVD bilayer graphene was etched into 2 m 1 m (length width) using oxygen plasma. All transport studies were conducted at room temperature using four-probe station in a glove box to minimize the effect of oxygen and moisture. The resistance R versus back-gated voltage V BG plot shows typical ambipolar curve in Supplementary Fig 7. Using a device model 4 that includes the device dimension, the extracted carrier mobility of our CVD bilayer graphene is ~3600 cm 2 V -1 s -1, with the residual carrier density n 0 =5.90 10 11 cm -2 at the Dirac point. This mobility value of CVD bilayer graphene is comparable to that of the recently reported exfoliated bilayer graphene on SiO 2 /Si substrates (1000-4000 cm 2 V -1 s -1 ), 5,6 and larger than that of CVD bilayer graphene film at room temperature (350-580 cm 2 V -1 s -1 ). 7,8 After the absorption of PBASE SAM layer, the resistance (R) at V BG =0V decreases from ~6 k to ~4 k and the residual carrier density increase to 1.24 10 12 cm -2 (the mobility reduces to ~900 cm 2 V -1 s -1 ). The Dirac point is very sensitive to charge impurity center (PBASE molecules this case), it is worth noting that the Dirac point was shifted to ~51.5 ev from -2.7 ev, which reveals that PBASE is a good p-type dopant (carrier doping level ~4 10 12 cm -2 at 0 V back-gated bias based on ) for graphene (the intrinsic carrier density of pristine CVD bilayer graphene is in the order of 10 11 cm -2 ). The p-doping result is consistent with above Raman and UPS results. 9,10 20
Supplementary Note 5 Side group effect of small molecules In the conductivity enhancement, what role does the functional side group play? To answer this question, two other pyrene derivatives (with OH group: 1-Pyrenebutanol; with COOH group: 1-Pyrenecarboxylic acid.) are chosen to form SAM on CVD graphene under the same conditions. Both molecules undergo intermolecular H-bonding and their packing order will be determined by competition between π-π stacking and H-bonding. 11 For 1-Pyrenebutanol, it can undergo both H-bonding and π-π stacking, which is illustrated by the aggregation and underlying monolayer-like films in Supplementary Fig. 10b. For 1-Pyrenecarboxylic acid, the H-bonding is much stronger than the π-π stacking, hence H-bonding determines its packing order to form herringbone structure instead of the flat-lying structure, which is in good agreement with AFM profile in Supplementary Fig. 10d. 21
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