Synergetic Exterior and Interfacial Approaches by Colloidal Carbon Quantum Dots for More Stable Perovskite Solar Cells Against UV.

The achievement of both efficiency and stability in perovskite solar cells (PSCs) remains a challenging and actively researched topic. In particular, among different environmental factors, ultraviolet (UV) photons play a pivotal role in contributing to device degradation. In this work, by harvesting simultaneously both the optical and the structural properties of bottom-up-synthesized colloidal carbon quantum dots (CQDs), a cost-effective means is provided to circumvent the UV-induced degradation in PSCs without scarification on their power conversion efficiencies (PCEs).

Manipulation of the Magnetic State of a Porphyrin-Based Molecule on Gold: From Kondo to Quantum Nanomagnet via the Charge Fluctuation Regime.

By moving individual Fe-porphyrin-based molecules with the tip of a scanning tunneling microscope in the vicinity of the elbow of the herringbone-reconstructed Au(111) containing a Br atom, we reversibly and continuously control their magnetic state. Several regimes are obtained experimentally and explored theoretically: from the integer spin limit, through intermediate magnetic states with renormalized magnetic anisotropy, until the Kondo-screened regime, corresponding to a progressive increase of charge fluctuations and mixed valency due to an increase in the interaction of the molecular Fe states with the substrate Fermi sea. Our study demonstrates the potential of utilizing charge fluctuations to generate and tune quantum magnetic states in molecule-surface hybrids.

Gold Atoms Promote Macroscopic Superconductivity in an Atomic Monolayer of Pb on Si(111).

Atomically thin superconductivity in Pb monolayers grown on Si(111) is affected by adding a tiny amount of Au atoms. In situ macroscopic electron transport measurements reveal that superconductivity develops at higher temperatures and manifests a sharper superconducting transition to zero resistance as compared to pristine Pb/Si(111). Scanning tunneling microscopy and spectroscopy show that Au atoms decorate atomic step edges of Pb/Si(111) and link the electronic reservoirs of neighboring atomic terraces.

Superconducting Long-Range Proximity Effect through the Atomically Flat Interface of a BiTe Topological Insulator.

We report on structural and electronic properties of superconducting nanohybrids made of Pb grown in the ultrahigh vacuum on the atomically clean surface of single crystals of topological BiTe. In situ scanning tunneling microscopy and spectroscopy demonstrated that the resulting network is composed of Pb-nanoislands dispersed on the surface and linked together by an amorphous atomic layer of Pb, which wets BiTe. As a result, the superconducting state of the system is characterized by a thickness-dependent superconducting gap of Pb-islands and by a very unusual position-independent proximity gap between them.

Quantum Well States for Graphene Spin-Texture Engineering.

The modification of graphene band structure, in particular via induced spin-orbit coupling, is currently a great challenge for the scientific community from both a fundamental and applied point of view. Here, we investigate the modification of the electronic structure of graphene (gr) initially adsorbed on Ir(111) via intercalation of one monolayer Pd by means of angle-resolved photoelectron spectroscopy and density functional theory. We reveal that for the gr/Pd/Ir(111) intercalated system, a spin splitting of graphene π states higher than 200 meV is present near the graphene point.

Superconducting parity effect across the Anderson limit.

How small can superconductors be? For isolated nanoparticles subject to quantum size effects, P.W. Anderson in 1959 conjectured that superconductivity could only exist when the electronic level spacing δ is smaller than the superconducting gap energy Δ.

Two distinct phases of bilayer graphene films on Ru(0001).

By combining angle-resolved photoemission spectroscopy and scanning tunneling microscopy we reveal the structural and electronic properties of multilayer graphene on Ru(0001). We prove that large ethylene exposure allows the synthesis of two distinct phases of bilayer graphene with different properties. The first phase has Bernal AB stacking with respect to the first graphene layer and displays weak vertical interaction and electron doping.

Supramolecular control of the magnetic anisotropy in two-dimensional high-spin Fe arrays at a metal interface.

Magnetic atoms at surfaces are a rich model system for solid-state magnetic bits exhibiting either classical or quantum behaviour. Individual atoms, however, are difficult to arrange in regular patterns. Moreover, their magnetic properties are dominated by interaction with the substrate, which, as in the case of Kondo systems, often leads to a decrease or quench of their local magnetic moment.

Tunable spin gaps in a quantum-confined geometry.

We have studied the interplay of a giant spin-orbit splitting and of quantum confinement in artificial Bi-Ag-Si trilayer structures. Angle-resolved photoelectron spectroscopy reveals the formation of a complex spin-dependent gap structure, which can be tuned by varying the thickness of the Ag buffer layer. This provides a means to tailor the electronic structure at the Fermi energy, with potential applications for silicon-compatible spintronic devices.

Does the surface matter? Hydrogen-bonded chain formation of an oxalic amide derivative in a two- and three-dimensional environment.

We report on a multi-technique investigation of the supramolecular organisation of N,N-diphenyl oxalic amide under differently dimensioned environments, namely three-dimensional (3D) in the bulk crystal, and in two dimensions on the Ag(111) surface as well as on the reconstructed Au(111) surface. With the help of X-ray structure analysis and scanning tunneling microscopy (STM) we find that the molecules organize in hydrogen-bonded chains with the bonding motif qualitatively changed by the surface confinement. In two dimensions, the chains exhibit enantiomorphic order even though they consist of a racemic mixture of chiral entities.

Nanopatterning the electronic properties of gold surfaces with self-organized superlattices of metallic nanostructures.

The self-organized growth of nanostructures on surfaces could offer many advantages in the development of new catalysts, electronic devices and magnetic data-storage media. The local density of electronic states on the surface at the relevant energy scale strongly influences chemical reactivity, as does the shape of the nanoparticles. The electronic properties of surfaces also influence the growth and decay of nanostructures such as dimers, chains and superlattices of atoms or noble metal islands.

Monitoring two-dimensional coordination reactions: directed assembly of co-terephthalate nanosystems on Au(111).

We report scanning tunneling microscopy observations on the formation of 2D Co-based coordination compounds on the reconstructed Au(111) surface. Preorganized arrays of Co bilayer islands are shown to be local reaction sites, which are consumed in the formation of Co-terephthalate aggregates and regular nanoporous grids. The latter exhibit a planar geometry stabilized by the smooth substrate.