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1.
Nanomaterials (Basel) ; 12(3)2022 Feb 02.
Artigo em Inglês | MEDLINE | ID: mdl-35159863

RESUMO

The magnetic properties and the atomic scale morphology of bimetallic two-dimensional nanoislands, epitaxially grown on fcc(111) metal surfaces, have been studied by means of Magneto-Optical Kerr Effect and Scanning Tunneling Microscopy. We investigate the effect on blocking temperature of one-dimensional interlines appearing in core-shell structures, of two-dimensional interfaces created by capping, and of random alloying. The islands are grown on Pt(111) and contain a Co-core, surrounded by Ag, Rh, and Pd shells, or capped by Pd. The largest effect is obtained by Pd capping, increasing the blocking temperature by a factor of three compared to pure Co islands. In addition, for Co-core Fe-shell and Co-core FexCo1-x-shell islands, self-assembled into well ordered superlattices on Au(11,12,12) vicinal surfaces, we find a strong enhancement of the blocking temperature compared to pure Co islands of the same size. These ultra-high-density (15 Tdots/in2) superlattices of CoFe nanodots, only 500 atoms in size, have blocking temperature exceeding 100 K. Our findings open new possibilities to tailor the magnetic properties of nanoislands.

2.
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.

3.
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.

4.
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.

5.
J Phys Chem Lett ; 9(10): 2523-2531, 2018 May 17.
Artigo em Inglês | MEDLINE | ID: mdl-29688019

RESUMO

In crystal growth, surfactants are additive molecules used in dilute amount or as dense, permeable layers to control surface morphologies. We investigate the properties of a strikingly different surfactant: a 2D and covalent layer with close atomic packing, graphene. Using in situ, real-time electron microscopy, scanning tunneling microscopy, kinetic Monte Carlo simulations, and continuum mechanics calculations, we reveal why metallic atomic layers can grow in a 2D manner below an impermeable graphene membrane. Upon metal growth, graphene dynamically opens nanochannels called wrinkles, facilitating mass transport while at the same time storing and releasing elastic energy via lattice distortions. Graphene thus behaves as a mechanically active, deformable surfactant. The wrinkle-driven mass transport of the metallic layer intercalated between graphene and the substrate is observed for two graphene-based systems, characterized by different physicochemical interactions, between graphene and the substrate and between the intercalated material and graphene. The deformable surfactant character of graphene that we unveil should then apply to a broad variety of species, opening new avenues for using graphene as a 2D surfactant forcing the growth of flat films, nanostructures, and unconventional crystalline phases.

6.
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.

7.
ACS Nano ; 6(1): 199-204, 2012 Jan 24.
Artigo em Inglês | MEDLINE | ID: mdl-22136502

RESUMO

We investigate the effects of Na adsorption on the electronic structure of bare and Ir cluster superlattice-covered epitaxial graphene on Ir(111) using angle-resolved photoemission spectroscopy and scanning tunneling microscopy. At Na saturation coverage, a massive charge migration from sodium atoms to graphene raises the graphene Fermi level by ~1.4 eV relative to its neutrality point. We find that Na is adsorbed on top of the graphene layer, and when coadsorbed onto an Ir cluster superlattice, it results in the opening of a large band gap of Δ(Na/Ir/G) = 740 meV, comparable to the one of Ge and with preserved high group velocity of the charge carriers.


Assuntos
Grafite/química , Irídio/química , Nanoestruturas/química , Nanoestruturas/ultraestrutura , Sódio/química , Adsorção , Substâncias Macromoleculares/química , Teste de Materiais , Conformação Molecular , Tamanho da Partícula , Semicondutores , Propriedades de Superfície
8.
Rev Sci Instrum ; 80(4): 043904, 2009 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-19405672

RESUMO

Here we report the absolute characterization of a spin polarimeter by measuring the Sherman function with high precision. These results have been obtained from the analysis of the spin and angle-resolved photoemission spectra of Au(111) surface states. The measurements have been performed with a 250 kHz repetition rate Ti:sapphire amplified laser system combined with a high energy-, angle-, and spin-resolving time-of-flight electron spectrometer.

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