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1.
Nano Lett ; 22(2): 652-657, 2022 Jan 26.
Artigo em Inglês | MEDLINE | ID: mdl-34990554

RESUMO

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. The propagation of superconducting correlations across the edges is enhanced, facilitating the coherence between terraces and promoting macroscopic superconductivity at higher temperatures. This finding opens new ways to design and control Josephson junctions at the atomic scale.

2.
J Phys Chem Lett ; 12(37): 9068-9075, 2021 Sep 23.
Artigo em Inglês | MEDLINE | ID: mdl-34516738

RESUMO

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 Bi2Te3. 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 Bi2Te3. 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. Furthermore, the data analysis and DFT calculations demonstrate that the Pb-wetting layer leads to significant modifications of both topological and trivial electronic states of Bi2Te3, which are responsible for the observed long-range proximity effect.

3.
J Phys Chem Lett ; 11(4): 1594-1600, 2020 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-32013453

RESUMO

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 K point. This spin separation arises from the hybridization of the graphene valence band states with spin-polarized quantum well states of a single Pd layer on Ir(111). Our results demonstrate that the proposed approach on the tailoring of the dimensionality of heavy materials interfaced with a graphene layer might lead to a giant spin-orbit splitting of the graphene valence band states.

4.
Nat Commun ; 8: 14549, 2017 02 27.
Artigo em Inglês | MEDLINE | ID: mdl-28240294

RESUMO

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. Here we report a scanning tunnelling spectroscopy study of superconducting lead (Pb) nanocrystals grown on the (110) surface of InAs. We find that for nanocrystals of lateral size smaller than the Fermi wavelength of the 2D electron gas at the surface of InAs, the electronic transmission of the interface is weak; this leads to Coulomb blockade and enables the extraction of electron addition energy of the nanocrystals. For large nanocrystals, the addition energy displays superconducting parity effect, a direct consequence of Cooper pairing. Studying this parity effect as a function of nanocrystal volume, we find the suppression of Cooper pairing when the mean electronic level spacing overcomes the superconducting gap energy, thus demonstrating unambiguously the validity of the Anderson criterion.

5.
ACS Nano ; 6(10): 9299-304, 2012 Oct 23.
Artigo em Inglês | MEDLINE | ID: mdl-23020302

RESUMO

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. The long-range ordered moiré pattern modulates the crystal potential and induces replicas of the Dirac cone and minigaps. The second phase has an AA stacking sequence with respect to the first layer and displays weak structural and electronic modulation and p-doping. The linearly dispersing Dirac state reveals the nearly freestanding character of this novel second-layer phase.


Assuntos
Cristalização/métodos , Grafite/química , Membranas Artificiais , Nanoestruturas/química , Nanoestruturas/ultraestrutura , Rubídio/química , Substâncias Macromoleculares/química , Teste de Materiais , Conformação Molecular , Transição de Fase , Propriedades de Superfície
6.
Nat Mater ; 8(3): 189-93, 2009 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-19182787

RESUMO

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. Here, we show that the supramolecular assembly of Fe and 1,4-benzenedicarboxylic acid molecules on a Cu surface results in ordered arrays of high-spin mononuclear Fe centres on a 1.5 nm square grid. Lateral coordination with the molecular ligands yields unsaturated yet stable coordination bonds, which enable chemical modification of the electronic and magnetic properties of the Fe atoms independently from the substrate. The easy magnetization direction of the Fe centres can be switched by oxygen adsorption, thus opening a way to control the magnetic anisotropy in supramolecular layers akin to that used in metallic thin films.

7.
Phys Rev Lett ; 101(19): 196805, 2008 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-19113296

RESUMO

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.

8.
Chemphyschem ; 9(17): 2522-30, 2008 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-18991309

RESUMO

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. By a combination of the STM data with near-edge X-ray absorption fine-structure spectroscopy, we show that the conformation of the molecule adapts such that the local registry of the functional group with the substrate is optimized while avoiding steric hindrance of the phenyl groups. In the low coverage case, the length of the chains is limited by the Au(111) reconstruction lines restricting the molecules into fcc stacked areas. A kinetic Monte Carlo simulated annealing is used to explain the selective assembly in the fcc stacked regions.

10.
Nat Nanotechnol ; 2(10): 617-21, 2007 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-18654385

RESUMO

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. Controlling these properties on length scales shorter than the diffusion lengths of the electrons and spins (some tens of nanometres for metals) is a major goal in electronics and spintronics. However, to date, there have been few studies of the electronic properties of self-organized nanostructures. Here we report the self-organized growth of macroscopic superlattices of Ag or Cu nanostructures on Au vicinal surfaces, and demonstrate that the electronic properties of these systems depend on the balance between the confinement and the perturbation of the surface states caused by the steps and the nanostructures' superlattice. We also show that the local density of states can be modified in a controlled way by adjusting simple parameters such as the type of metal deposited and the degree of coverage.


Assuntos
Cobre/química , Cristalização/métodos , Nanoestruturas/química , Nanoestruturas/ultraestrutura , Nanotecnologia/métodos , Prata/química , Condutividade Elétrica , Ouro/química , Substâncias Macromoleculares/química , Teste de Materiais , Conformação Molecular , Tamanho da Partícula , Propriedades de Superfície
11.
J Phys Chem B ; 110(11): 5627-32, 2006 Mar 23.
Artigo em Inglês | MEDLINE | ID: mdl-16539506

RESUMO

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. The nanogrids are based on a rectangular motif, which is understood as an intrinsic feature of a 2D cobaltous terephthalate sheet and dominates over the templating influence of the quasihexagonal substrate atomic lattice. The dynamics of the Co island dissolution and metallosupramolecular self-assembly could be monitored in situ. Complementary first-principles calculations were performed to analyze the underlying driving forces and to examine general trends in 2D metal-carboxylate formation. The findings indicate the wide applicability of coordination chemistry concepts at surfaces, which moreover can be spatially confined by using templated substrates, and its potential to synthesize arrangements unavailable in bulk materials.

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