Luminescence spectra correlated with AFM images!

Inspired by the recent advances in TERS and STM-LE, we have recently implemented an experimental version of the optical detection line into the UHV AFM/STM available in our laboratory. Up to our knowledge, this is the first example of such working combination that gives luminescence spectra with submolecular resolution and can directly correlate them with the AFM signal. We have used a ShamRock grating-type spectrograph equipped with an Andor iStar intensified charge-coupled detector to detect fluorescence of the ZnPc molecules on trilayer NaCl on Au(111) substrates (Fig.1). It shows individual spectra taken at different sites on the ZnPc and on the substrate nearby (Fig.1a), and the correlation of the tunneling current image with the photon gain on the molecule (Fig.1b.c). The AFM image at low voltage taken on the same molecule taken after these measurements reveals a bistability in the adsorption configuration of the molecule, similarly to the case of MgPc on bilayer NaCl on Ag(111) [1]. This clearly demonstrates the capability of the combined AFM/STM-LE technique to reveal essential information about the studied systems. The fluorescence spectra can be now obtained on daily basis, however we understand the highest-quality spectra are crucial for successful detection of minor vibronic features (can be 50x smaller than the main peak in Fig.1a) and therefore we constantly aim to optimize the optical path in order to optimize the photon yield, signal-to-noise ratio and spectral resolution.


[1] Kuniyuki Miwa, Hiroshi Imada, Shota Kawahara, and Yousoo Kim, Phys. Rev. B 93, 16541