Light Emission From Single Self Decoupled Molecules In A Scanning Tunnelling Microscope

In this work, a clear pathway is presented to achieve well-defined electronically decoupled chromophores from metallic leads without requiring additional insulating layers. To study such self-decoupled molecules, STM equipped with an efficient light detection setup has been used. Results show that the chromophores mounted on tripodal molecular platforms adsorbed on a gold surface present well-defined and efficient electroluminescence down to the single-molecule level.

In this work, a clear pathway is presented to achieve well-defined electronically decoupled chromophores from metallic leads without requiring additional insulating layers. To study such self-decoupled molecules, STM equipped with an efficient light detection setup has been used. Results show that the chromophores mounted on tripodal molecular platforms adsorbed on a gold surface present well-defined and efficient electroluminescence down to the single-molecule level.

This work presents a single molecular motor driven by the current in an STM. Its chiral functional group is supposed to perform a rotation in a preferred direction, proven by Binomial tests to be statistically significant. The rotation is proposedly driven by the chiral-induced spin selectivity effect (CISS). However, the studies of the rotation on the dependence on the lateral tip position, voltage and current indicate that he CISS is unlikely to cause the preferred rotation direction.

Complementary to scattering techniques, scanning tunnelling microscopy provides atomic-scale real space information about a material's electronic state of matter. State-of-the-art designs of a scanning tunnelling microscope (STM) allow measurements at millikelvin temperatures with unprecedented energy resolution. Therefore, this instrument excels in probing the superconducting state at low temperatures and especially its local quasiparticle excitations as well as bosonic degrees of freedom.

In the last decades, superconducting devices have emerged as a promising platform for quantum technologies, including quantum sensing and quantum computing. Their key elements are Josephson junctions, which allow for coherent supercurrent tunneling between two weakly linked superconductors. If such a junction is extended in one direction to a long junction, the superconducting phase difference can vary in space and time and may allow for quantized phase windings that drive supercurrent vortices.

Scanning tunnelling microscopy (STM) is a powerful technique to observe surfaces at the atomic level. The resolution of this STM technique is good enough to study the electronic properties of single molecules adsorbed onto metallic substrates. An important step towards controllable single molecular technologies is the determination of how the molecule-substrate interaction changes the local molecular electronic structure. Since this electronic structure of molecules is strongly perturbed by the electrons of the underlying metallic substrate, an electronic decoupling of the molecules from the metal surface is required to isolate the electronic properties of an individual molecule. Förster resonance energy transfer (FRET) has found many applications in different fields of science, because it allows the determination of the distance between two chromophores in the 1-10 nm range. In addition to other factors, this energy transfer is also dependent on the relative orientation of donor and acceptor chromophores to each other. This thesis describes the design, synthesis and investigations of model compounds for: 1). STM induced light emission experiments from single molecules and 2). for FRET studies. Chapter 1 provides an introduction to cyclophanes, energy transfer and scanning tunnelling microscopy. Chapter 2 gives a description of the aims of this work, which is split into the synthesis of cyclophanes for STM induced luminescence investigations and FRET studies. The later is complemented by the synthesis of a linear NDI system. Chapter 3 describes the design, synthesis and characterisation of all model compounds. In the first half STM investigations are presented and the electronic structure of two cyclophanes and complexation studies of the crown ether model compound are discussed. In the second half a modular synthetic route to asymmetric N,N’-naphthalenediimides is presented for FRET studies. Chapter 4 gives a summary of this thesis and presents a short outlook. Chapter 5 provides the synthesis and characterisation of all the compounds listed in this thesis and experimental details for STM investigations.

Molecular Electronics is self-contained and unified in its presentation. It can be used as a textbook on nanoelectronics by graduate students and advanced undergraduates studying physics and chemistry. In addition, included in this new edition are previously unpublished material that will help researchers gain a deeper understanding into the basic concepts involved in the field of molecular electronics.

This work presents the design and commissioning of a new low-temperature Scanning Tunnelling Microscope equipped with an innovative light collection setup using an integrated, micro-fabricated mirror tip. Commissioning experiments demonstrate the capabilities of this new instrument and reproduce known effects regarding gap plasmons on noble-metal surfaces. Furthermore, different contrasts in the plasmon-mediated light emission from Cobalt nano-islands on a Copper (111) substrate are reported.