Ignacio Piquero-Zulaica

Tuning the Graphene on Ir(111) adsorption regime by Fe/Ir surface-alloying

A combined scanning tunneling microscopy, x-ray photoelectron spectroscopy, angle-resolved photoemission spectroscopy, and density functional theory study of graphene on a Fe-Ir(111) alloy with variable Ir concentration is presented. Starting from an intercalated Fe layer between the graphene and Ir(111) surface we find that graphene-substrate interaction can be fine-tuned by Fe-Ir alloying at the interface. When a critical Ir-concentration close to 0.25 is reached in the Fe layer, the Dirac cone of graphene is largely restored and can thereafter be tuned across the Fermi level by further increasing the Ir content. Indeed, our study reveals an abrupt transition between a chemisorbed phase at small Ir concentrations and a physisorbed phase above the critical concentration. The latter phase is highly reminiscent of the graphene on the clean Ir(111) surface. Furthermore, the transition is accompanied by an inversion of the graphenes induced magnetization due to the coupling with the Fe atoms from antiferromagnetic when chemisorbed to weakly ferromagnetic in the physisorption regime, with spin polarizations whose magnitude may be tuned with the amount of Fe content.

Precise engineering of quantum dot array coupling through their barrier widths

Quantum dots are known to confine electrons within their structure. Whenever they periodically aggregate into arrays and cooperative interactions arise, novel quantum properties suitable for technological applications show up. Control over the potential barriers existing between neighboring quantum dots is therefore essential to alter their mutual crosstalk. Here we show that precise engineering of the barrier width can be experimentally achieved on surfaces by a single atom substitution in a haloaromatic compound, which in turn tunes the confinement properties through the degree of quantum dot intercoupling. We achieved this by generating self-assembled molecular nanoporous networks that confine the two-dimensional electron gas present at the surface. Indeed, these extended arrays form up on bulk surface and thin silver films alike, maintaining their overall interdot coupling. These findings pave the way to reach full control over two-dimensional electron gases by means of self-assembled molecular networks.Arrays of quantum dots can exhibit a variety of quantum properties, being sensitive to their spacing. Here, the authors fine tune interdot coupling using hexagonal molecular networks in which the dots are separated by single or double haloaromatic compounds, structurally identical but for a single atom.

Configuring Electronic States in an Atomically Precise Array of Quantum Boxes

A 2D array of electronically coupled quantum boxes is fabricated by means of on-surface self-assembly assuring ultimate precision of each box. The quantum states embedded in the boxes are configured by adsorbates, whose occupancy is controlled with atomic precision. The electronic interbox coupling can be maintained or significantly reduced by proper arrangement of empty and filled boxes.

Polymerization of Well-Aligned Organic Nanowires on a Ferromagnetic Rare-Earth Surface Alloy

The high reactivity of magnetic substrates toward molecular overlayers has so far inhibited the realization of more sophisticated on-surface reactions, thereby depriving these interfaces of a significant class of chemically tailored organics such as graphene nanoribbons, oligonuclear spin-chains, and metal-organic networks. Here, we present a multitechnique characterization of the polymerization of 4,4″-dibromo-p-terphenyl precursors into ordered poly(p-phenylene) arrays on top of the bimetallic GdAu2 surface alloy. The activation temperatures for bromine scission and subsequent homocoupling of molecular precursors were followed by temperature-dependent X-ray photoelectron spectroscopy. The structural characterizations of supramolecular and polymeric phases, performed by low-energy electron diffraction and scanning tunneling microscopy, establish an extraordinary degree of order extending into the mesoscale. Taking advantage of the high homogeneity, the electronic structure of the valence band was determined with angle-resolved photoemission spectroscopy. Importantly, the transition of localized molecular orbitals into a highly dispersive π-band, the fingerprint of successful polymerization, was observed while leaving all surface-related bands intact. Moreover, ferromagnetic ordering in the GdAu2 alloy was demonstrated for all phases by X-ray absorption spectroscopy. The transfer of well-established in situ methods for growing covalently bonded macromolecules with atomic precision onto magnetic rare-earth alloys is an important step toward toward studying and controlling intrinsic carbon- and rare-earth-based magnetism.