arXiv subjects

D. Troadec

Publications and source records attributed to D. Troadec.

6 recordsLinked to original sources

arXiv2026

STXM-XANES and TEM analysis of UltraCarbonaceous Antarctic MicroMeteorites (UCAMMs)

The Concordia micrometeorite collection contains UltraCarbonaceous Antarctic MicroMeteorites (UCAMMs) of probable cometary origin. Eight FIB sections of UCAMMs were studied by Scanning Transmission X-ray Microscopy - X-ray Absorption Near Edge Structure and (Scanning)Transmission Electronic Microscopy. Three different phases of organic matter (OM) exist in UCAMMs and small mineral aggregates are distributed in the OM. Two OMs share spectral features with those of insoluble organic matter (IOM) of carbonaceous chondrites and of cometary grains returned by the Stardust mission. The third OM is N-rich (N/C at. ratios up to 0.22) and has only a few equivalents in extraterrestrial OM analyzed so far, such as in cometary particles collected during the Stardust mission, Interplanetary Dust Particles (IDPs) and UCAMMs collected near the Dome Fuji Station. This N-rich OM could have formed by irradiation of N-rich ices in the outer regions of the protoplanetary disk. UCAMMs contain variable amounts of minerals, consisting of crystalline Mg-rich silicates, Fe(Ni) sulfides and Fe oxides, which can be cemented in a Si-rich groundmass. Hypocrystalline mineral assemblages are also observed. Glassy phases showing morphological resemblance to GEMS are also found in some UCAMMs. This mineralogy is mainly consistent with that of previous UCAMM analyses, and is close to what is observed in Chondritic Porous IDPs, which are also considered as cometary dust particles. A mineral exhibiting a phyllosilicate texture has been observed in this work, and raises the question of the possibility of aqueous alteration on comets. Overall, UCAMMs' mineralogical and organic characterization implies a complex formation history of UCAMMs, and the presence of large-scale radial mixing in the early solar system, to transport their mineral components to the outer parts of the protoplanetary disk.

astro-ph.EP↗

arXiv2025

Quantum Coherent Transport of 1D ballistic states in second order topological insulator Bi$_4$Br$_4$

We investigate quantum transport in micrometer-sized single crystals of Bi$_4$Br$_4$, a material predicted to be a second-order topological insulator. 1D topological states with long phase coherence times are revealed via the modulation of quantum interference with magnetic field and gate voltage. In particular, we demonstrate the existence of Aharonov-Bohm interference between 1D ballistic states several micrometers long, that we identify as phase-coherent hinge modes on neighboring step edges at the crystal surface. These Aharonov-Bohm oscillations are made possible by a disordered phase-coherent contact region, the existence of which is confirmed by scanning transmission electron microscopy combined with energy-dispersive X-ray spectroscopy (STEM-EDX) of FIB lamellae. Their coherent nature modulates the transmission of the 1D edge states, leading to weak antilocalization and universal conductance fluctuations with surprisingly large characteristic fields and a strongly anisotropic behavior. These complementary experimental results provide a comprehensive, coherent description of quantum transport in Bi$_4$Br$_4$, and establish the material as a second-order topological insulator with topologically protected 1D ballistic states.

cond-mat.mes-hall↗

arXiv2024

Crystallinity in Niobium oxides: A pathway to mitigate Two-Level System Defects in Niobium 3D Resonator for quantum applications

Materials imperfections in Nniobium based superconducting quantum circuits, in particular, two-level-system (TLS) defects, are a major source of decoherence, ultimately limiting the performance of quantum computation and sensing. Thus, identifying and understanding the microscopic origin of possible TLS defects in these devices and developing strategies to eliminate them is key to superconducting qubit performance improvement. In this paper, we demonstrate the reduction of two-level system losses in three-dimensional superconducting radio frequency (SRF) niobium resonators by a 10-hour high vacuum (HV) heat treatment at 650{\deg}C, even after exposure to air and high pressure rinsing (HPR). By probing the effect of this annealing on niobium samples using X-ray photoelectron spectroscopy (XPS) and high-resolution scanning transmission electron microscopy (STEM), we witness an alteration of the native oxide composition re-grown after air exposure and HPR and the creation of nano-scale crystalline oxide regions, which correlates with the measured tenfold quality factor enhancement at low fields of the 1.3 GHz niobium resonator.

physics.app-ph↗

arXiv2019

Physical mechanisms involved in the formation and operation of memory devices based on a monolayer of gold nanoparticles-polythiophene hybrid materials

Understanding the physical and chemical mechanisms occurring during the forming process and operation of an organic resistive memory device is a major issue for better performances. Various mechanisms were suggested in vertically stacked memory structures, but the analysis remains indirect and needs destructive characterization (e.g. cross-section to access the organic layers sandwiched between electrodes). Here, we report a study on a planar, monolayer thick, hybrid nanoparticle/molecule device (10 nm gold nanoparticles embedded in an electro-generated poly(2-thienyl-3,4-(ethylenedioxy)thiophene) layer), combining, in situ, on the same device, physical (scanning electron microscope, physico-chemical (thermogravimetry and mass spectroscopy, Raman spectroscopy) and electrical (temperature dependent current-voltage) characterizations. We demonstrate that the forming process causes an increase in the gold particle size, almost 4 times larger than the starting nanoparticles, and that the organic layer undergoes a significant chemical rearrangement from a sp3 to sp2 amorphous carbon material. Temperature dependent electrical characterizations of this nonvolatile memory confirm that the charge transport mechanism in the device is consistent with a trap-filled space charge limited current in the off state, the sp2 amorphous carbon material containing many electrically active defects.

physics.app-ph↗

arXiv2011

Large array of sub-10 nm single-grain Au nanodots for use in nanotechnology

A uniform array of single-grain Au nanodots, as small as 5-8 nm, can be formed on silicon using e-beam lithography. The as-fabricated nanodots are amorphous, and thermal annealing converts them to pure Au single crystals covered with a thin SiO2 layer. These findings are based on physical measurements, such as atomic force microscopy (AFM), atomic resolution scanning transmission electron microscopy, and chemical techniques using energy dispersive x-ray spectroscopy. A self-assembled organic monolayer is grafted on the nanodots and characterized chemically with nanometric lateral resolution. We use the extended uniform array of nanodots as a new test-bed for molecular electronics devices.

cond-mat.mes-hall↗

arXiv2011

Characterization of ion/electron beam induced deposition of electrical contacts at the sub-μm scale

We investigate the fabrication of electrical contacts using ion- and electron-beam induced deposition of platinum at the sub-μm scale. Halos associated with the metal surface decoration are characterized electrically in the 0.05-2 μm range using transport measurements, conducting atomic force microscopy and Kelvin probe microscopy. In contrast with IBID, EBID electrodes exhibit weakly conductive halos at the sub-μm scale, and can thus be used to achieve resist-free electrical contacts for transport measurements at the sub-μm scale. Four-point transport measurements using μm-spaced EBID contacts are provided in the case of a multiwalled carbon nanotube.

cond-mat.mes-hall↗