arXiv subjects

Valentina Zannier

Publications and source records attributed to Valentina Zannier.

At least 19 recordsLinked to original sources

arXiv2026

Oxidation-resilient structural modifications in Nickel-functionalized 3D-graphene for hydrogen storage applications

Porous materials represent a versatile solution for several applications. Indeed, the recent development of a new material, named 3D-Graphene, which combines the exceptional characteristics of graphene with a three-dimensional structure, opens perspectives for applications where a high surface-to-volume ratio is beneficial. In this study, we explore the functionalization of 3D-Graphene with nickel (Ni)-nanoparticles as a strategy to enhance hydrogen storage capabilities, and we assess the influence of the NPs on hydrogen uptake and oxidation resilience. The morphology and structural properties of pristine and Ni-functionalized samples were characterized using Scanning Electron Microscopy. Additionally, X-ray Photoelectron Spectroscopy was employed to analyze the surface chemical composition of the functionalized samples. Samples have been hydrogenated supplying molecular or atomic hydrogen, and hydrogen storage performance was assessed through Thermal Desorption Spectroscopy. Afterwards, oxidation effects were systematically studied by exposing the samples to atmospheric oxygen, followed by further hydrogenation experiments. Our results indicate that Ni functionalization influences both hydrogen adsorption and oxidation behavior, with potential implications for improving the stability of the material, especially for hydrogen storage applications.

cond-mat.mtrl-sci↗

arXiv2026

Emission dynamics in zincblende InAsxP1-x quantum dots in InP nanowires: influence of quantum dot size, composition and nanowire geometry

Hereby, we present an experimental and theoretical investigation of emission dynamics in zincblende InAsxP1-x quantum dots (QDs) embedded in InP nanowires (NWs) grown via vapour-liquid-solid mechanism by chemical beam epitaxy, using Au nanoparticles as a nucleation catalyst. By measuring time-resolved photoluminescence from an ensemble of QD-NWs it was possible to determine the exciton lifetime dependence on QD composition and height. Changes in the InP shell thickness surrounding the InP NW stem with a QD, brought additional insight into the influence of photonic environment on the carrier dynamics. High-resolution transmission electron microscopy, combined with energy-dispersive X-ray spectroscopy, provided actual structural parameters. The experimentally obtained lifetimes were interpreted in the light of results of 8 band kp calculations combined with configuration-interaction model to take into account the Coulomb interactions and finite-difference time domain photonic simulations to include the effect of optical confinement. The full understanding of the experimental results required considering both, the changes in the QD potential and the Purcell effect, the latter leading to spontaneous emission inhibition in the case of NWs with thin InP shell.

cond-mat.mes-hall↗

arXiv2026

Magnetically Induced Switching-Current Jumps in InAs/Al Josephson Junctions

We report Barkhausen-like switching at millitesla fields in an $n$-doped InAs/Al nanowire Josephson junction, which serves as an interferometric probe of intrinsic magnetic reconfigurations, as evidenced by discrete switching-current jumps. At $T=30$~mK the device displays a Fraunhofer-like modulation with $I_{\mathrm{sw}}(0)\approx 0.24~μ\mathrm{A}$ and an abrupt transition at $|B|\approx 3~\mathrm{mT}$ between two branches differing by $ΔI_{\mathrm{sw}}\approx 0.13~μ\mathrm{A}$. By tracking the characteristic field scales from $30$ to $900$~mK, we find that the jump field is essentially temperature-independent, whereas the superconducting critical field decreases with temperature, as expected for thin Al films. The sharp discontinuity, sweep-direction asymmetry, and reproducibility across repeated scans point to avalanche-like switching between metastable magnetic configurations of the local magnetic texture, which are directly coupled to the weak link. Within an effective-field framework, each reconfiguration modifies a local field offset, thereby reshaping the interference response and leading to an abrupt reorganization of the switching-current pattern.

cond-mat.mes-hall↗

arXiv2026

Growth and Transport Properties of InAsSb Nanoflags

The present work reports, for the first time, the growth of high-quality free-standing InAsSb nanoflags and their electronic properties. Different growth conditions have been explored, and zinc-blende InAsSb nanoflags of various composition have been obtained. In particular, InAs0.77Sb0.23 nanoflags are on average (2000+-180) nm long, (640+-50) nm wide, and (130+-30) nm thick. We show that these nanoflags have a Landé g-factor larger than InAs and InSb and a mobility comparable to those of the best performing InAs and InSb nanoflags. Besides, we show evidence for a surface Fermi level pinning in the conductance band of these InAs0.77Sb0.23 nanoflags, similar to the well-known behavior of InAs. This promises to make InAsSb easy to couple to superconductors, while keeping or improving many of the features that make InSb an interesting material for quantum applications.

cond-mat.mtrl-sci↗

arXiv2025

Phonon interference effects in GaAs-GaP superlattice nanowires

Fine-tuning the functional properties of nanomaterials is crucial for technological applications. Superlattices, characterized by periodic repetitions of two or more materials in different dimensions, have emerged as a promising area of investigation. We present a study of the phonon interference effect on thermal transport in GaAs-GaP superlattice nanowires with sharp interfaces between the GaAs and GaP layers, as confirmed by high-resolution transmission electron microscopy. We performed thermal conductivity measurements using the so-called thermal bridge method on superlattice nanowires with a period varying from 4.8 to 23.3 nm. The measurements showed a minimum of the thermal conductivity as a function of superlattice period up to room temperature, that we interpreted as an indication of the crossover from coherent to incoherent thermal transport. Notably, this effect is not destroyed by surface boundary or by phonon-phonon scattering, as the crossover trend is also observed at room temperature. Our results were corroborated by both ab initio lattice dynamics and semiclassical nonequilibrium molecular dynamics calculations. These findings provide insights into the wave-like and particle-like transport of phonons in superlattice nanowires and demonstrate the potential for engineering thermal properties through precise control of the superlattice structure.

cond-mat.mes-hall↗

arXiv2025

Supercurrent modulation in InSb nanoflag-based Josephson junctions by scanning gate microscopy

InSb nanoflags represent an interesting platform for quantum transport and have recently been exploited in the study of hybrid planar Josephson junctions. Due to the uncovered semiconductor surface, they are also good candidates for surface probe techniques. Here, we report the first Scanning Gate Microscopy (SGM) experiments on Nb-contacted InSb nanoflag-based Josephson junctions. In the normal state, sizable conductance modulation via the charged tip of the SGM is recorded. In the superconducting state, we report the first application of Scanning Gate Microscopy to superconducting weak links, demonstrating the possibility of manipulating the supercurrent flow across a semiconductor-superconductor heterostructure at a local level. The experimental findings are consistent with theoretical predictions and establish a new way of investigating the behavior of superconducting weak links, towards the local imaging of supercurrent flow.

cond-mat.supr-con↗

arXiv2025

Superconducting Quantum Interference Devices based on InSb nanoflag Josephson junctions

Planar Josephson junctions (JJs) based on InSb nanoflags have recently emerged as an intriguing platform in superconducting electronics. This letter presents the fabrication and investigation of superconducting quantum interference devices (SQUIDs) employing InSb nanoflag JJs. We provide measurements of interference patterns in both symmetric and asymmetric geometries. The interference patterns in both configurations can be modulated by a back-gate voltage, a feature well reproduced through numerical simulations. The observed behavior aligns with the skewed current-phase relations of the JJs, demonstrating significant contributions from higher harmonics. We explore the magnetic field response of the devices across a wide range of fields ($\pm 30$ mT), up to the single-junction interference regime, where a Fraunhofer-like pattern is detected. Finally, we assess the flux-to-voltage sensitivity of the SQUIDs to evaluate their performance as magnetometers. A magnetic flux noise of $S^{1/2}_Φ= 4.4 \times 10^{-6} Φ_0 / \sqrt{Hz}$ is identified, indicating potential applications in nanoscale magnetometry.

cond-mat.mes-hall↗

arXiv2024

InAs Nanowire-Based Twin Electrical Sensors enabling Simultaneous Gas Detection Measurements: Nanodevice Engineering, Testing and Signal Fluctuation Analysis

Epitaxially grown InAs NWs are relevant for electrical sensing applications due to Fermi level pinning at NW surface, thus very sensitive to surrounding environment. While a single NW growth batch consists of millions virtually identical replicas of the same NW, real samples display subtle differences in NW size, shape, structure which may affect the detection performance. Here, electrical gas detection is investigated the in two NW-based nominally identical or twin devices fabricated starting from the same NW growth batch. Two individual wurtzite InAs NWs are placed onto a fabrication substrate at 2 micrometers distance with 90 degrees relative orientation, each NW is electrically contacted, and the nanodevices are exposed to humidity and NO$_2$ flux diluted in synthetic air. Electrical signal versus time is measured simultaneously in each nanodevice, upon different gases and concentrations. Observed detection limit is 2 ppm for NO$_2$, 20% for relative humidity. Correlation analysis method is exploited by calculating auto- and cross-correlation functions for the experimental signal pairs, indicating lack of cross-correlation in the signal noise of the two nanodevices, suggesting that signal differences could be ascribed mainly to nonidealities of fabrication protocol and nanoscopic differences in the two nanostructures, rather than different environmental conditions.

cond-mat.mes-hall↗

arXiv2024

Side-gate modulation of supercurrent in InSb nanoflag-based Josephson junctions

InSb nanoflags, due to their intrinsic spin-orbit interactions, are an interesting platform in the study of planar Josephson junctions. Ballistic transport, combined with high transparency of the superconductor/semiconductor interfaces, was reported to lead to interesting phenomena such as the Josephson diode effect. The versatility offered by the planar geometry can be exploited to manipulate both carrier concentration and spin-orbit strength by electrical means. Here we present experimental results on InSb nanoflag-based Josephson junctions fabricated with side-gates placed in close proximity to the junction. We show that side-gates can efficiently modulate the current through the junction, both in the dissipative and in the dissipation-less regimes, similarly to what obtained with a conventional back-gate. Furthermore, the side-gates can be used to influence the Fraunhofer interference pattern induced by the presence of an external out-of-plane magnetic field.

cond-mat.supr-con↗

arXiv2024

Engineering nanowire quantum dots with iontronics

Achieving stable, high-quality quantum dots has proven challenging within device architectures rooted in conventional solid-state device fabrication paradigms. In fact, these are grappled with complex protocols in order to balance ease of realization, scalability, and quantum transport properties. Here, we demonstrate a novel paradigm of semiconductor quantum dot engineering by exploiting ion gating. Our approach is found to enable the realization and control of a novel quantum dot system: the iontronic quantum dot. Clear Coulomb blockade peaks and their dependence on an externally applied magnetic field are reported, together with the impact of device architecture and confinement potential on quantum dot quality. Devices incorporating two identical quantum dots in series are realized, addressing the reproducibility of the developed approach. The iontronic quantum dot represents a novel class of zero-dimensional quantum devices engineered to overcome the need for thin dielectric layers, facilitating single-step device fabrication. Overall, the reported approach holds the potential to revolutionize the development of functional quantum materials and devices, driving rapid progress in solid state quantum technologies

cond-mat.mes-hall↗

arXiv2023

Metal Nanoparticle-Functionalized Three-Dimensional Graphene: a versatile platform towards sensors and energy-related applications

We demonstrate the first successful functionalization of epitaxial three-dimensional graphene with metal nanoparticles. The functionalization is obtained by immersing the 3D graphene in a nanoparticle colloidal solution. This method is versatile and here is demonstrated for gold and palladium, but can be extended to other types and shapes of nanoparticles. We have measured the nanoparticle density on the top-surface and in the porous layer volume by Scanning Electron Microscopy and Scanning Transmission Electron Microscopy. Samples exhibit a high coverage of nanoparticles with minimal clustering. High quality graphene has been demonstrated to promote the functionalization leading to higher nanoparticle density, both on the surface and in the pores. X-ray Photoelectron Spectroscopy allowed to verify the absence of contamination after the functionalization process. Moreover, it confirmed the thermal stability of the Au- and Pd-functionalized three-dimensional graphene up to 530°C. Our approach opens up new avenues for utilizing three-dimensional graphene as a versatile platform for catalytic applications, sensors, and energy storage and conversion.

physics.app-ph↗

arXiv2023

GaAs/GaP Superlattice Nanowires for Tailoring Phononic Properties at the Nanoscale: Implications for Thermal Engineering

The possibility to tune the functional properties of nanomaterials is key to their technological applications. Superlattices, i.e., periodic repetitions of two or more materials in different dimensions are being explored for their potential as materials with tailor-made properties. Meanwhile, nanowires offer a myriad of possibilities to engineer systems at the nanoscale, as well as to combine materials which cannot be put together in conventional heterostructures due to the lattice mismatch. In this work, we investigate GaAs/GaP superlattices embedded in GaP nanowires and demonstrate the tunability of their phononic and optoelectronic properties by inelastic light scattering experiments corroborated by ab initio calculations. We observe clear modifications in the dispersion relation for both acoustic and optical phonons in the superlattices nanowires. We find that by controlling the superlattice periodicity we can achieve tunability of the phonon frequencies. We also performed wavelength-dependent Raman microscopy on GaAs/GaP superlattice nanowires and our results indicate a reduction in the electronic bandgap in the superlattice compared to the bulk counterpart. All our experimental results are rationalized with the help of ab initio density functional perturbation theory (DFPT) calculations. This work sheds fresh insights into how material engineering at the nanoscale can tailor phonon dispersion and open pathways for thermal engineering.

cond-mat.mtrl-sci↗

arXiv2023

Half-integer Shapiro steps in highly transmissive InSb nanoflag Josephson junctions

We investigate a ballistic InSb nanoflag-based Josephson junction with Nb superconducting contacts. The high transparency of the superconductor-semiconductor interfaces enables the exploration of quantum transport with parallel short and long conducting channels. Under microwave irradiation, we observe half-integer Shapiro steps that are robust to temperature, suggesting their possible non-equilibrium origin. Our results demonstrate the potential of ballistic InSb nanoflags Josephson junctions as a valuable platform for understanding the physics of hybrid devices and investigating their non-equilibrium dynamics.

cond-mat.supr-con↗

arXiv2022

Josephson Diode Effect in High Mobility InSb Nanoflags

We report evidence of non-reciprocal dissipation-less transport in single ballistic InSb nanoflag Josephson junctions, owing to a strong spin-orbit coupling. Applying an in-plane magnetic field, we observe an inequality in supercurrent for the two opposite current propagation directions. This demonstrates that these devices can work as Josephson diodes, with dissipation-less current flowing in only one direction. For small fields, the supercurrent asymmetry increases linearly with the external field, then it saturates as the Zeeman energy becomes relevant, before it finally decreases to zero at higher fields. We show that the effect is maximum when the in-plane field is perpendicular to the current vector, which identifies Rashba spin-orbit coupling as the main symmetry-breaking mechanism. While a variation in carrier concentration in these high-quality InSb nanoflags does not significantly influence the diode effect, it is instead strongly suppressed by an increase in temperature. Our experimental findings are consistent with a model for ballistic short junctions and show that the diode effect is intrinsic to this material. Our results establish InSb Josephson diodes as a useful element in superconducting electronics.

cond-mat.supr-con↗

arXiv2022

Giant reduction of thermal conductivity in twinning superlattice InAsSb nanowires

Semiconductor nanostructures hold great promise for high-efficiency waste heat recovery exploiting thermoelectric energy conversion, a technological breakthrough that could significantly contribute to providing environmentally friendly energy sources as well as in enabling the realization of self-powered biomedical and wearable devices. A crucial requirement in this field is the reduction of the thermal conductivity of the thermoelectric material without detrimentally affecting its electrical transport properties. In this work we demonstrate a drastic reduction of thermal conductivity in III-V semiconductor nanowires due to the presence of intentionally realized periodic crystal lattice twin planes. The electrical and thermal transport of these nanostructures, known as twinning superlattice nanowires, have been probed and compared with their twin-free counterparts, showing a one order of magnitude decrease of thermal conductivity while maintaining unaltered electrical transport properties, thus yielding a factor ten enhancement of the thermoelectric figure of merit, ZT. Our study reports for the first time the experimental measurement of electrical and thermal properties in twinning superlattice nanowires, which emerge as a novel class of nanomaterials for high efficiency thermoelectric energy harvesting.

cond-mat.mtrl-sci↗

arXiv2022

Spin Cross-Correlation Experiments in an Electron Entangler

Correlations are fundamental in describing many body systems - not only in natural sciences. However, in experiments, correlations are notoriously difficult to assess on the microscopic scale, especially for electron spins. Here, we demonstrate a direct measurement of the spin cross-correlations between the currents of a Cooper pair splitter, an electronic device that emits electrons originating from Cooper pairs in a superconductor. While it is firmly established theoretically that these electron pairs form maximally spin-entangled singlet states with opposite spin projections, no spin correlation experiments have been demonstrated so far. We use ferromagnetic sidegates, compatible with superconducting electronic structures, to individually spin polarize the transmissions of two quantum dots fabricated in the two electronic paths, which act as tunable spin filters. The signals are detected in standard transport and in highly sensitive transconductance experiments. We find that the spin-cross correlation is negative, compatible with spin singlet emission, and deviates from the ideal value mostly due to a finite overlap of the Zeeman split quantum dot states. Our results demonstrate a new route to perform spin auto- and cross correlation experiments in nanometer scaled electronic devices, especially suitable for those relying on magnetic field sensitive superconducting elements, like unconventional, triplet or topologically non-trivial superconductors, or to perform Bell tests with massive particles, like electrons.

cond-mat.mes-hall↗

arXiv2021

High Mobility Free-Standing InSb Nanoflags Grown On InP Nanowire Stems For Quantum Devices

High quality heteroepitaxial two-dimensional (2D) InSb layers are very difficult to realize owing to the large lattice mismatch with other widespread semiconductor substrates. A way around this problem is to grow free-standing 2D InSb nanostructures on nanowire (NW) stems, thanks to the capability of NWs to efficiently relax elastic strain along the sidewalls when lattice-mismatched semiconductor systems are integrated. In this work, we optimize the morphology of free-standing 2D InSb nanoflags (NFs). In particular, robust NW stems, optimized growth parameters, and the use of reflection high-energy electron diffraction (RHEED), to precisely orient the substrate for preferential growth, are implemented to increase the lateral size of the 2D InSb NFs. Transmission electron microscopy (TEM) analysis of these NFs reveals defect-free zinc blend crystal structure, stoichiometric composition, and relaxed lattice parameters. The resulting NFs are large enough to fabricate Hall-bar contacts with suitable length-to-width ratio enabling precise electrical characterization. An electron mobility of ~29,500 cm2/Vs is measured, which is the highest value reported for free-standing 2D InSb nanostrutures in literature. We envision the use of 2D InSb NFs for fabrication of advanced quantum devices.

cond-mat.mes-hall↗

arXiv2021

Gate-controlled Supercurrent in Ballistic InSb Nanoflag Josephson Junctions

High-quality III-V narrow band gap semiconductor materials with strong spin-orbit coupling and large Lande g-factor provide a promising platform for next-generation applications in the field of high-speed electronics, spintronics, and quantum computing. Indium Antimonide (InSb) offers a narrow band gap, high carrier mobility, and a small effective mass, and thus is very appealing in this context. In fact, this material has attracted tremendous attention in recent years for the implementation of topological superconducting states supporting Majorana zero modes. However, high-quality heteroepitaxial two-dimensional (2D) InSb layers are very diffcult to realize owing to the large lattice mismatch with all commonly available semiconductor substrates. An alternative pathway is the growth of free-standing single-crystalline 2D InSb nanostructures, the so-called nanoflags. Here we demonstrate fabrication of ballistic Josephson-junction devices based on InSb nanoflags with Ti/Nb contacts that show gate-tunable proximity-induced supercurrent up to 50 nA at 250 mK and a sizable excess current. The devices show clear signatures of subharmonic gap structures, indicating phase-coherent transport in the junction and a high transparency of the interfaces. This places InSb nanoflags in the spotlight as a versatile and convenient 2D platform for advanced quantum technologies.

cond-mat.mes-hall↗