Ion-Selective, Atom-Resolved Imaging of a 2D Cu2N Insulator: Field and Current Driven Tip-Enhanced Raman Spectromicroscopy Using a Molecule-Terminated Tip.
Kevin T CramptonJoonhee LeeVartkess Ara ApkarianPublished in: ACS nano (2019)
Tip-enhanced Raman scattering (TERS) with a cobalt tetraphenylporphyrin (CoTPP)- terminated silver tip is used to obtain ion-selective, atomically resolved images of an insulating Cu2N monolayer grown on Cu(100). Ion selective images are obtained through vibrational frequency shift maps using CoTPP vibrations with oppositely signed Stark tuning rates (STR). The images allow a quantitative analysis of the electrostatic field of the ionic lattice using in situ calibrated STRs. Both intensity and Stark shift maps yield atomically resolved images in the tunneling regime of plasmons. We show that the CoTPP is bonded to the Ag tip through its central Co atom, whereby TERS taps into intramolecular currents and polarizations. The bias dependence of vibrational line intensities shows diode-like response with opposite polarity for current carrying modes of opposite polarization phase. The phase sensitive detection of vibrational lines and their voltage gating is explained in terms of distinct field- and phototunneling current-driven Raman, offering an alternate paradigm for the long-sought optoelectronic rectifier in molecular electronics.
Keyphrases
- deep learning
- convolutional neural network
- sensitive detection
- molecular dynamics simulations
- optical coherence tomography
- energy transfer
- density functional theory
- quantum dots
- raman spectroscopy
- high resolution
- molecular dynamics
- metal organic framework
- gold nanoparticles
- machine learning
- mass spectrometry
- high intensity
- single molecule
- electron transfer
- silver nanoparticles
- fluorescence imaging