Spin Spiral State at a Ferromagnetic Gd Vacuum Interface.

Centrosymmetric bulk magnets made of layered Gd intermetallics had been discovered recently to exhibit helical spin spirals with a wavelength of ≈2  nm that transform into skyrmion lattices at certain magnetic fields. Here we report on the observation of a spin spiral state at the Gd(0001) surface. Spin-polarized scanning tunneling microscopy images show striped regions with a periodicity of about 2 nm.

Probing Spin-Dependent Ballistic Charge Transport at Single-Nanometer Length Scales.

The coherent transport of charge and spin is a key requirement of future devices for quantum computing and communication. Scattering at defects or impurities may significantly reduce the coherence of quantum-mechanical states, thereby affecting the device functionality. While numerous methods exist to experimentally assess charge transport, the real-space detection of a material's ballistic spin transport properties with nanometer resolution remains a challenge.

Anisotropic coupling of individual vibrational modes to a Cu(110) substrate.

We present a study on the excitation of individual vibrational modes with ballistic charge carriers propagating along the Cu(110) surface. By means of the molecular nanoprobe technique, where the reversible switching of a molecule-in this case tautomerization of porphycene-is utilized to detect excitation events, we reveal anisotropic coupling of two distinct vibrational modes to the substrate. The N-H bending mode, excited below || ≈ 376 meV, exhibits maxima perpendicular to the rows of the Cu(110) substrate and minima along the rows.

Real-space resolved surface reactions: deprotonation and metalation of phthalocyanine.

Upon deposition on a surface, molecules can undergo a plethora of changes, such as reactions with adsorbates and surface atoms and catalytic decomposition. Since different reaction pathways may coexist, spatially averaging techniques can be insufficient for the characterization and distinction of all on-surface products. Here, we present a study of single phthalocyanine molecules on a Cu(111) surface which was performed using high-resolution low-temperature STM.

Controlled Formation of Porous 2D Lattices from C -symmetric Ph -Me-Tribenzotriquinacene-OAc.

The on-surface self-assembly of molecules to form holey nanographenes is a promising approach to control the properties of the resulting 2D lattice. Usually, planar molecules are utilized to prepare flat, structurally confined molecular layers, with only a few recent examples of warped precursors. However, control of the superstructures is limited thus far.

Anisotropic Ballistic Transport Revealed by Molecular Nanoprobe Experiments.

Atomic-scale charge transport properties are not only of significant fundamental interest but also highly relevant for numerous technical applications. However, experimental methods that are capable of detecting charge transport at the relevant single-digit nanometer length scale are scarce. Here we report on molecular nanoprobe experiments on Pd(110), where we use the charge carrier-driven switching of a single cis-2-butene molecule to detect ballistic transport properties over length scales of a few nanometers.

Imprinting Directionality into Proton Transfer Reactions of an Achiral Molecule.

Directionality is key for the functionality of molecular machines, which is often achieved by built-in structural chiralities. Here, we present a scanning tunneling microscopy study of achiral HPc and HPc molecules that acquire chirality by adsorption onto a Ag(100) surface. The adsorption-geometry-induced chirality is caused by a -29° (+29°) rotation of the molecules with respect to the [011] substrate direction, resulting in tautomerization processes that preferentially occur in a clockwise (counterclockwise) direction.

Analyzing the Wave Nature of Hot Electrons with a Molecular Nanoprobe.

We report on a novel method, the molecular nanoprobe (MONA) technique, which allows us to measure the nanoscale quasiparticle transport between two arbitrary surface points. In these experiments, hot electrons are injected into the sample surface from the probe tip of a scanning tunneling microscope (STM) and detected by tautomerization switching events of a single deprotonated phthalocyanine (HPc) molecule. By making use of atom-by-atom-engineered interferometers on a Ag(111) surface, we demonstrate that the quantum-mechanical wave nature of hot electrons leads to characteristic oscillations of the molecule tautomerization probability.

Remote Single-Molecule Switching: Identification and Nanoengineering of Hot Electron-Induced Tautomerization.

Molecular electronics where single molecules perform basic functionalities of digital circuits is a fascinating concept that one day may augment or even replace nowadays semiconductor technologies. The tautomerization of molecules, that is, the bistable functional position of hydrogen protons within an organic frame, has recently been intensively discussed as a potential avenue toward nanoscale switches. It has been shown that tautomerization can be triggered locally or nonlocally, that is, by a scanning tunneling microscope (STM) tip positioned directly above or in close vicinity to the molecule.