Supporting Information for: Nanoscale Chemical Imaging of a Dynamic Molecular Phase. Boundary with Ultrahigh Vacuum Tip-Enhanced Raman.

Transcription

1 Supporting Information for: Nanoscale Chemical Imaging of a Dynamic Molecular Phase Boundary with Ultrahigh Vacuum Tip-Enhanced Raman Spectroscopy Nan Jiang,,,* Naihao Chiang, Lindsey R. Madison, Eric A. Pozzi, Michael R. Wasielewski, Tamar Seideman,, Mark A. Ratner, Mark C. Hersam,,, George C. Schatz,, and Richard P. Van Duyne,,* Department of Chemistry, Applied Physics Graduate Program and Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States Department of Chemistry, University of Illinois at Chicago, Illinois 60607, United States AUTHOR INFORMATION Corresponding Author * njiang@uic.edu, vanduyne@northwestern.edu.

2 S1. Tunneling current statistics Figure S1. (a)tunneling current statistics of left ¼ area in Figure 2b (50nm x 12.5nm), (b)the areas selected in Figure2b, (c)tunneling current statistics of right ¼ area in Figure 2b (50nm x 12.5nm). S2. TERS mapping data analysis TERS spectra were acquired with 1.0 mw excitation from a Spectra-Physics Excelsior 532 nm continuous wave laser and detection using a Princeton Instrument SCT320 spectrograph equipped with a Princeton Instrument PIXIS 400BR charged-coupled device (CCD). A custom made software written in LabView which utilized the "spectroscopy on a grid" function of the Nanonis controller was used to synchronize the CCD with the SPM controller. The TERS image was performed in a 20 nm 16 nm area with a 2.5 nm step size and 10 s acquisition per step. After acquiring the TERS mapping data, the data was fed into a home-made MatLab routine for plotting the TERS image: Matlab function msbackadj is automatically applied to each individual spectrum to remove the background, follow by calling function Peakfit.m 1 to fit all Raman peaks at once. Figure S2 shows the fitted result for pixel (3, 4) and (7, 4) in Figure 2c of the main

3 manuscript. The TERS image was generated by plotting the integrated intensity (area under the peak) of the 1350 cm -1 mode by MatLab function pcolor. Figure S2. Peakfit results for pixel (3, 4) and (7, 4) in Figure 2c. All peaks were fitted by a lorentzian function. The plots were generated by MatLab function Peakfit.m. S3. The diffusing phase isotropic resonance Raman scattering spectrum of PPDI The resonance Raman scattering cross section is calculated from the derivative of the isotropic polarizability tensor, α p as follows: σ Ω = π2 2 ε (ω ω p) 4 0 h 1 (S 8πcω p ) p 45(1 exp( hcω p /k B T)) where ω is the frequency of the incident field, and ωp is the frequency of the p th vibrational mode. The scattering factor, Sp, is a molecular property composed of the isotropic polarizability derivative, α, and the anisotropic γ and is calculated as:

4 S = 45α p 2 + 7γ p 2 α = 1 3 (α ii ) p i γ = 1 2 i,j 3(α ij ) p (α ij ) p (α ii ) p (α ii ) p Figure S3. The diffusing phase isotropic resonance Raman scattering spectrum of PPDI from TDDFT simulation.

5 S4. Electronic excitation of PPDI In this calculation, a geometry that has C(s) symmetry, PBE functional and the TZP basis set are used. we choose the z coordinate to be perpendicular to the perylene ring system, with x along the long axis. The simulation results are summarized in Table.S4. Excitation number and symmetry label Energy (ev) Wavelength (nm) Oscillator strength Transition dipole moment vector Direction 3B [2.68, 1.39, 0.00] x,y 6A [0.00, 0.00, -0.48] z 7B [2.20, -0.64, 0.00] x,y 38A [0.00, 0.00, -0.40] z 49B [0.15, -1.03, 0.00] y Table S4. Electronic transition dipole strength of PPDI. The two strongest excitations that have transition dipoles perpendicular to the perylene plane are highlighted in red. The excitations with the strongest oscillator strengths have transition dipole moments along the long axis of the molecule (x-axis) and the short axis of the perylene plan (y-axis). The excitations that are perpendicular to the plane of the molecule (along z-axis) are an order of magnitude lower in oscillator strength.

6 S5. Complete Raman peak assignments for PPDI between 500 cm -1 to 1600 cm -1 Experiment (cm -1 ) TDDFT Simulation (cm -1 ) Assignment , 535 Out of plane perylene distortions x, y, z 631 Phenoxy ring distortions y, z 731, 734 Out of plane perylene distortions y, z 765 In plane perylene distortions y, z 925 Phenoxy ring distortions y, z 936 Methylethyl asymmetric C-C stretching y, z 955 Immide Phenyls out of plane distortions y, z 997 perylene distortions with significant kekule y, z modes on the phenoxy ring Tert butyl asymmetric stretching y, z 1138 In plane perylene distortions y, z 1153 Kekule mode on phenyl coupled to y, z isopropyl symmetric stretching Perylene ring distortions with dominant x ring breathing Kekule modes coupled to ring breathing x In plane, asymmetric bending of perylene x rings In plane, asymmetric bending of perylene x rings A Ring quinoidal like mode, B ring symmetric C-C stretching ring distortions, C ring RDB bending, x , 1574 A Ring breathing, B ring symmetric C-C stretching ring distortion, C RDB bending mode Table S5. Raman Peak Assignments for PPDI between 500 cm 1 to 1600 cm 1. Principle Molecular axis of Vibrational Motion x

7 S6. The XYZ coordinates of PPDI used in the TDDFT calculations of the Raman scattering and the electronic excitation are provided below. Geometry optimization was performed at the TZP level of theory and C 2 symmetry was enforced. H H C C O C C C C C N H H C C C C C H C H O C C O C

8 C C C C N C C C H C C H C H H H C H C H H H H H H H H H H C

9 H H C H C C H C H H H H H C H C H C C H C H H H C C C C C C

10 H C H H H O C C H C H C H H C C C O C C C C C C C H C H H C

11 O C C C H H H H H H H H H H C H H H C C H C H H H H

12 Reference: 1. T. C. O'Haver. Version 7.6; A pragmatic Introduction to signal Processing. Available at: accessed on March 2016.