Thermal Transition from a Disordered, 2D Network to a Regular, 1D, Fe(II)–DCNQI Coordination Network

We report the formation of an Fe–DCNQI (DCNQI = dicyano-<i>p</i>-quinodiimine) coordination network on the Ag(111) surface, where the Fe atoms are 4-fold coordinated in a square-planar geometry with the N atoms of the cyano groups. Depending on the formation temperature, the coordination network can be a two-dimensional arrangement of Fe atoms in a hexagonal lattice joined by DCNQI molecules in an apparent random way, or a set of 1D chains bound together by hydrogen bonds, but with the Fe atoms maintaining the same hexagonal lattice. The electronic structure of this network is studied by a combination of photoemission spectroscopy and theoretical calculations based on the density functional theory. In particular, we show that the oxidation state of the Fe atoms in this 1D arrangement is +2, which has been compared with the atomic charges values obtained from first-principles calculations

Probing the Site-Dependent Kondo Response of Nanostructured Graphene with Organic Molecules

TCNQ molecules are used as a sensitive probe for the Kondo response of the electron gas of a nanostructured graphene grown on Ru(0001) presenting a moiré pattern. All adsorbed molecules acquired an extra electron by charge transfer from the substrate, but only those adsorbed in the FCC-Top areas of the moiré show magnetic moment and Kondo resonance in the STS spectra. DFT calculations trace back this behavior to the existence of a surface resonance in the low areas of the graphene moiré, whose density distribution strongly depends on the stacking sequence of the moiré area and effectively quenches the magnetic moment for HCP-Top sites

Charge-Transfer-Induced Isomerization of DCNQI on Cu(100)

This article reports on the temperature-controlled irreversible transition between the two isomeric forms of the strong electron acceptor dicyano-<i>p</i>-quinonediimine (DCNQI) on the Cu(100) surface. A combination of experiment (time-resolved, variable-temperature scanning tunneling microscopy, STM) and theory (density functional theory, DFT) shows that the isomerization barrier is lower than in the gas phase or solution due to the fact that charge transfer from the substrate modifies the bond configuration of the molecule, aromatizing the quinoid ring of DCNQI and enabling a more free rotation of the cyano groups with respect to the molecular axis

Modulation of Magnetic Heating via Dipolar Magnetic Interactions in Monodisperse and Crystalline Iron Oxide Nanoparticles

In the pursuit of controlling the heat exposure mediated by magnetic nanoparticles, we provide new guidelines for tailoring magnetic relaxation processes via dipolar interactions. For this purpose, highly crystalline and monodisperse magnetic iron oxide nanocrystals whose sizes range from 7 to 22 nm were synthesized by thermal decomposition of iron organic precursors in 1-octadecene. The as-synthesized nanoparticles are soft nanomagnets, showing superparamagnetic-like behavior and SAR values which progressively increase with particle size, field frequency, and amplitude up to 3.6 kW/g_Fe. Our data show the influence of media viscosity, particle size, and concentration on dipolar interactions and consequently on the magnetic relaxation processes related to the heat release. Understanding the role of dipolar interactions is of great importance toward the use of iron oxide nanoparticles as efficient hyperthermia mediators

Elastic Response of Graphene Nanodomes

The mechanical behavior of a periodically buckled graphene membrane has been investigated by noncontact atomic force microscopy in ultrahigh vacuum. When a graphene monolayer is grown on Ru(0001), a regular arrangement of 0.075 nm high nanodomes forming a honeycomb lattice with 3 nm periodicity forms spontaneously. This structure responds in a perfectly reversible way to relative normal displacements up to 0.12 nm. Indeed, the elasticity of the nanodomes is proven by realistic DFT calculations, with an estimated normal stiffness <i>k</i> ∼ 40 N/m. Our observations extend previous results on macroscopic graphene samples and confirm that the elastic behavior of this material is maintained down to nanometer length scales, which is important for the development of new high-frequency (terahertz) electromechanical devices

Long-Range Orientational Self-Assembly, Spatially Controlled Deprotonation, and Off-Centered Metalation of an Expanded Porphyrin

Expanded porphyrins are large-cavity macrocycles with enormous potential in coordination chemistry, anion sensing, photodynamic therapy, and optoelectronics. In the last two decades, the surface science community has assessed the physicochemical properties of tetrapyrrolic-like macrocycles. However, to date, the sublimation, self-assembly and atomistic insights of expanded porphyrins on surfaces have remained elusive. Here, we show the self-assembly on Au(111) of an expanded aza-porphyrin, namely, an “expanded hemiporphyrazine”, through a unique growth mechanism based on long-range orientational self-assembly. Furthermore, a spatially controlled “writing” protocol on such self-assembled architecture is presented based on the STM tip-induced deprotonation of the inner protons of individual macrocycles. Finally, the capability of these surface-confined macrocycles to host lanthanide elements is assessed, introducing a novel off-centered coordination motif. The presented findings represent a milestone in the fields of porphyrinoid chemistry and surface science, revealing a great potential for novel surface patterning, opening new avenues for molecular level information storage, and boosting the emerging field of surface-confined coordination chemistry involving f-block elements

Large-Area Heterostructures from Graphene and Encapsulated Colloidal Quantum Dots via the Langmuir–Blodgett Method

This work explores the assembly of large-area heterostructures comprised of a film of silica-encapsulated, semiconducting colloidal quantum dots, deposited via the Langmuir–Blodgett method, sandwiched between two graphene sheets. The luminescent, electrically insulating film served as a dielectric, with the top graphene sheet patterned into an electrode and successfully used as a top gate for an underlying graphene field-effect transistor. This heterostructure paves the way for developing novel hybrid optoelectronic devices through the integration of 2D and 0D materials

High-Performance Implantable Sensors based on Anisotropic Magnetoresistive La_0.67Sr_0.33MnO₃ for Biomedical Applications

We present the design, fabrication, and characterization of an implantable neural interface based on anisotropic magnetoresistive (AMR) magnetic-field sensors that combine reduced size and high performance at body temperature. The sensors are based on La0.67Sr0.33MnO3 (LSMO) as a ferromagnetic material, whose epitaxial growth has been suitably engineered to get uniaxial anisotropy and large AMR output together with low noise even at low frequencies. The performance of LSMO sensors of different film thickness and at different temperatures close to 37 °C has to be explored to find an optimum sensitivity of ∼400%/T (with typical detectivity values of 2 nT·Hz–1/2 at a frequency of 1 Hz and 0.3 nT·Hz–1/2 at 1 kHz), fitted for the detection of low magnetic signals coming from neural activity. Biocompatibility tests of devices consisting of submillimeter-size LSMO sensors coated by a thin poly(dimethyl siloxane) polymeric layer, both in vitro and in vivo, support their high suitability as implantable detectors of low-frequency biological magnetic signals emerging from heterogeneous electrically active tissues