Light collection from a low-temperature scanning tunneling microscope using integrated mirror tips fabricated by direct laser writing

Abstract

We report on a cryogenic scanning tunneling microscope (STM) designed for single molecule studies, in which the light emitted from the tunneling junction is collected by an integrated optics on the tip. Using direct laser writing, the tip and the surrounding microscopic parabolic mirror are fabricated as one piece, which is small enough to collimate the collected light directly into an optical multimode fiber fixed inside the STM. This simple and compact setup combines high collection efficiency and ease of handling while not interfering with the cryostat operation, allowing uninterrupted measurements at 1.4 K for up to 5 days with low drift.

Synthesis and Surface Behaviour of NDI Chromophores Mounted on a Tripodal Scaffold: Towards Self‐Decoupled Chromophores for Single‐Molecule Electroluminescence

“…All STM measurements were performed in a homebuilt STM at about 4.4 K in UHV (10 −10 mbar). This STM is equipped with a photon collection system that allows to analyse light that is emitted from the tunnel junction [20] . All photon spectra were corrected for the energy‐dependent detector efficiency (Figure S34a).…”

“…[33] Rarely, light emission above the quantum threshold has been observed, even at low currents, which is an indication for intramolecular up-conversion (Figure S34b). [61] The combination of our highly efficient photon collection setup [20] and an efficient conversion process in the molecular junction results in unusually high count rates observed for Tpd-hNDI. The spectrum recorded at 2.5 V and 5.2 pA shown in Figure 4d corresponds to 1.3 × 10 À 3 photons counted per tunnelling electron, which is, to best of our knowledge, about one order of magnitude higher than the highest external quantum yields reported so far.…”

“…Fathoming the underlying light emission processes from these molecules is thus not only interesting from a scientific point of view, but also key for the development of new materials for optoelectronic devices. Scanning tunnelling microscopy induced luminescence (STML) experiments enable to study electrically induced light emission and the underlying mechanisms of the optoelectronic response with submolecular precision [19–21] . Using STML setups, various pathways for single molecule light emission have been discovered at the single molecule level, including dipole–dipole coupling, hot electroluminescence, plasmon‐exciton coupling, and electro‐fluorochromism [22–25] .…”

Probing Semiconductor Properties with Optical Scanning Tunneling Microscopy

“…Several approaches have been developed since to increase the obtained signal in designated STML systems, including multiple adjustable lenses to focus the light on single photon detectors and an optical spectrometer simultaneously 103 or by using integrated mirror tips to collect the light. 104 One of the first studies enabling the success story of STML was conducted by Gimzewski, Stoll, and Schlittler 105 in 1987 using supported phthalocyanines. Since then, many energy-related materials have been studied using STML: (1) porphyrins e.g., zinc-tetraphenylporphyrin (ZnTPP), [106][107][108] or meso-tetrakis (3,5-ditertiarybutylphenyl)porphyrin (H TBPP), [109][110][111] phthalocyanines (H 2 Pc), 49,112,113 or CuPc and ZnPc; 50,114 (2) rylenes, e.g., 3,4,9,10-perylenetertracarboxylic dianhydride (PTCDA); 51,115 and (3) buckminsterfullerene (C 60 ).…”

3D‐Printed Scanning‐Probe Microscopes with Integrated Optical Actuation and Read‐Out

“…Please note that these experiments represent a first proof‐of‐concept demonstration of compact and highly scalable 3D‐printed SNOM engines and that the performance of the structures has not yet been optimized. As an example, the resolution of the SNOM imaging might be improved by using, e.g., scattering‐mode tips that do not feature an aperture and/or by using 3D‐printed parabolic mirrors for highly efficient high‐NA excitation or read‐out . We believe that further optimization of the design and fabrication techniques will finally enable performance parameters that are on par with highly optimized conventional SNOM systems, for which resolutions down to λ/20 were reported …”