Strength of electronic decoupling of fullerene on an AuSiX layer formed on Au(111)

On-surface synthesis of Heisenberg spin-1/2 antiferromagnetic molecular chains

Magnetic exchange interactions between localized spins in π-electron magnetism of carbon-based nanostructures have attracted tremendous interest due to their great potential for nano spintronics. Unique many-body quantum characteristics, such as gaped excitations, strong spin entanglement, and fractionalized excitations, have been demonstrated, but the spin-1/2 Heisenberg model with a single antiferromagnetic coupling J value remained unexplored. Here, we realized the entangled antiferromagnetic quantum spin-1/2 Heisenberg model with diazahexabenzocoronene oligomers (up to 7 units) on Au(111). Extensive low-temperature scanning tunneling microscopy/spectroscopy measurements and density functional theory and many-body calculations show that even-numbered spin chains host a collective state with gapped excitations, while odd-numbered chains feature a Kondo excitation. We found that a given antiferromagnetic coupling J value between first neighbors in the entangled quantum states is responsible for the quantum phenomena, strongly relating to their parities of the chain. The tunable molecular building blocks act as an ideal platform for the experimental realization of topological spin lattices.

Resolving molecular frontier orbitals in molecular junctions with kHz resolution

Designing and building single-molecule circuits with tailored functionalities requires a detailed knowledge of the junction electronic structure. The energy of frontier molecular orbitals and their electronic coupling with the electrodes play a key role in determining the conductance of nanoscale molecular circuits. Here, we developed a method for measuring the current-voltage (I-V) characteristics of single-molecule junctions with a time resolution that is two orders of magnitude higher than previously achieved. These I-V measurements with high temporal resolution, together with atomistic simulations, enabled us to characterize in detail the frontier molecular states and their evolution in sub-angstrom stretching of the junction. For a series of molecules, changes in the electronic structure were resolved as well as their fluctuations prior to junction breakdown. This study describes a new methodology to determine the key frontier MO parameters at single-molecule junctions and demonstrates how these can be mechanically tuned at the single-molecule level.

On-Surface Synthesis of Silole and Disila-Cyclooctene Derivatives

The incorporation of Si atoms into organic compounds significantly increases a variety of functionality, facilitating further applications. Recently, on-surface synthesis was introduced into organosilicon chemistry as 1,4-disilabenzene bridged nanostructures were obtained via coupling between silicon atoms and brominated phenyl groups at the ortho position on Au(111). Here, we demonstrate a high generality of this strategy via syntheses of silole derivatives and nanoribbon structures with eight-membered sila-cyclic rings from dibrominated molecules at the bay and peri positions on Au(111), respectively. Their structures and electronic properties were investigated by a combination of scanning tunneling microscopy/spectroscopy and density functional theory calculations. This work demonstrates a great potential to deal with heavy group 14 elements in on-surface silicon chemistry.

Adsorption properties of a paracyclophane molecule on NaCl/Au surfaces: a first-principles study

Ultrathin insulating layers are commonly applied in scanning tunneling microscope (STM) measurements on molecular systems to preserve the intrinsic properties of a sample. We examine in the present work the adsorption properties of a double-decker 3,3-paracyclophane (PCP) molecule supported on Au surfaces with thin NaCl monolayers (MLs) as the decoupling spacer by using first-principles calculations. The interactions between the adsorbed molecule and the substrate were analyzed in terms of the adsorption energy, dispersion interactions, charge transfer, and molecular structure changes. The simulation results show that the presence of NaCl can significantly reduce the adsorption energy as well as the charge transfer between the molecule and the substrate. Detailed analysis of the differential charge density and partial charge density of states indicates that three MLs of NaCl are sufficient to decouple the molecule from the Au substrate with no significant changes in the adsorption properties of the PCP with the further increase of the thickness of the NaCl spacer. These results could be helpful for the application of the interesting double-decker molecules as functional single-molecule devices where the intrinsic molecular properties need to be preserved.

Manipulation of Spin Polarization in Boron-Substituted Graphene Nanoribbons

The design of magnetic topological states due to spin polarization in an extended π carbon system has great potential in spintronics application. Although magnetic zigzag edges in graphene nanoribbons (GNRs) have been investigated earlier, real-space observation and manipulation of spin polarization in a heteroatom substituted system remains challenging. Here, we investigate a zero-bias peak at a boron site embedded at the center of an armchair-type GNR on a AuSi_X/Au(111) surface with a combination of low-temperature scanning tunneling microscopy/spectroscopy and density functional theory calculations. After the tip-induced removal of a Si atom connected to two adjacent boron atoms, a clear Kondo resonance peak appeared and was further split by an applied magnetic field of 12 T. This magnetic state can be relayed along the longitudinal axis of the GNR by sequential removal of Si atoms.