35 research outputs found
Ionic liquid gating of SrTiO lamellas fabricated with a focused ion beam
In this work, we combine two previously-incompatible techniques for defining
electronic devices: shaping three-dimensional crystals by focused ion beam
(FIB), and two-dimensional electrostatic accumulation of charge carriers. The
principal challenge for this integration is nanometer-scale surface damage
inherent to any FIB-based fabrication. We address this by using a sacrificial
protective layer to preserve a selected pristine surface. The test case
presented here is accumulation of 2D carriers by ionic liquid gating at the
surface of a micron-scale SrTiO lamella. Preservation of surface quality is
reflected in superconductivity of the accumulated carriers. This technique
opens new avenues for realizing electrostatic charge tuning in materials that
are not available as large or exfoliatable single crystals, and for patterning
the geometry of the accumulated carriers
Radiochemical, Computational, and Spectroscopic Evaluation of High-Denticity Desferrioxamine Derivatives DFO2 and DFO2p toward an Ideal Zirconium-89 Chelate Platform
Desferrioxamine (DFO) has long been considered the gold
standard
chelator for incorporating [89Zr]Zr4+ in radiopharmaceuticals
for positron emission tomography (PET) imaging. To improve the stability
of DFO with zirconium-89 and to expand its coordination sphere to
enable binding of large therapeutic radiometals, we have synthesized
the highest denticity DFO derivatives to date: dodecadentate DFO2
and DFO2p. In this study, we describe the synthesis and characterization
of a novel DFO-based chelator, DFO2p, which is comprised of two DFO
strands connected by an p-NO2-phenyl linker
and therefore contains double the chelating moieties of DFO (potential
coordination number up to 12 vs 6). The chelator DFO2p offers an optimized
synthesis comprised of only a single reaction step and improves water
solubility relative to DFO2, but the shorter linker reduces molecular
flexibility. Both DFO2 and DFO2p, each with 6 potential hydroxamate
ligands, are able to reach a more energetically favorable 8-coordinate
environment for Zr(IV) than DFO. The zirconium(IV) coordination environment
of these complexes were evaluated by a combination of density functional
theory (DFT) calculations and synchrotron spectroscopy (extended X-ray
absorption fine structure), which suggest the inner-coordination sphere
of zirconium(IV) to be comprised of the outermost four hydroxamate
ligands. These results also confirm a single Zr(IV) in each chelator,
and the hydroxide ligands which complete the coordination sphere of
Zr(IV)-DFO are absent from Zr(IV)-DFO2 and Zr(IV)-DFO2p. Radiochemical
stability studies with zirconium-89 revealed the order of real-world
stability to be DFO2 > DFO2p ≫ DFO. The zirconium-89 complexes
of these new high-denticity chelators were found to be far more stable
than DFO, and the decreased molecular flexibility of DFO2p, relative
to DFO2, could explain its decreased stability, relative to DFO2
Quasinormal mode solvers for resonators with dispersive materials
Optical resonators are widely used in modern photonics. Their spectral response and temporal dynamics are fundamentally driven by their natural resonances, the so-called quasinormal modes (QNMs), with complex frequencies. For optical resonators made of dispersive materials, the QNM computation requires solving a nonlinear eigenvalue problem. This raises a difficulty that is only scarcely documented in the literature. We review our recent efforts for implementing efficient and accurate QNM solvers for computing and normalizing the QNMs of micro- and nanoresonators made of highly dispersive materials. We benchmark several methods for three geometries, a two-dimensional plasmonic crystal, a two-dimensional metal grating, and a three-dimensional nanopatch antenna on a metal substrate, with the perspective to elaborate standards for the computation of resonance modes.Théorie et modélisation numérique des résonances optique