arXiv subjects

Antonio Cammarata

Publications and source records attributed to Antonio Cammarata.

11 recordsLinked to original sources

arXiv2026

Towards Quantum-Dot Detectors as Barcodes for Dark Matter Interactions

Quantum dots are tunable semiconductor nanocrystals that can be produced at industrial scales. We present the first ab initio calculation of the scattering of dark matter on electrons bound in quantum dots. The momentum-dependence of a quantum dot's electronic response depends on its morphology and on the dark matter mass, interaction operator, mediator coupling, and mediator mass. Therefore, the relative rates across an array of distinct quantum dot targets form a ``barcode'' that carries information about the nature of the dark matter interaction. We project the sensitivity of a detector concept in which a collection of independent target subunits, each loaded with silicon quantum dots of a particular morphology, are read out by Skipper CCDs. Given a future signal, this barcode could discriminate between interaction operators and mediator types. We quantify the discrimination power for a benchmark pair of models as a function of readout noise and exposure.

hep-ph↗

arXiv2026

First principles study of chalcogen vacancy effect on the optoelectronic and photocatalytic properties of transition metal dichalcogenides monolayers

In working conditions, chalcogen vacancies spontaneously occur in two-dimensional transition metal dichalcogenides (TMDCs) monolayers, affecting their optoelectronic and photocatalytic properties. To study how chalcogen vacancies affect such properties, we use quantum mechanical calculations considering prototypical MX$_2$ (M = Mo, W, X = S and Se) TMDCs monolayers. Structural optimisations show that M-X bond lengths about a vacancy are different compared to the bond lengths in the pristine structure. Band structure calculations reveal that the introduction of vacancies produce electronic states about the Fermi level, hence resulting in the reduction of the band gap. Work function and electrostatic potential calculations show that the introduction of vacancies induce an asymmetry in the electrostatic potential facilitating the charge separation; such feature is absent in a pristine monolayer. All the considered defective structures are capable of performing hydrogen evolution reaction, while co-catalyst is required to perform oxygen evolution reaction when used for water splitting. WS$_2$ and WSe$_2$ defective monolayers can serve as an efficient photocatalytic material for reducing CO$_2$ into useful chemical products. The presented results show that vacancy-containing TMDCs monolayers own photocatalytic capabilities compared to the pristine counterparts, thus showing that defective TMD monolayers have prospective applications and should not be regarded as flawed products to be discarded. Finally, the results might constitute guidelines for the experimental synthesis of vacancy-engineered MX$_2$ monolayers for optoelectronic devices and photocatalytic applications.

cond-mat.mtrl-sci↗

arXiv2026

From Defects to Devices: Design Guidelines for High-Performance Diamond-Based Solar Cells and Single-Dopant Diodes

This work establishes key technological guidelines for designing diamond-based optoelectronic devices, derived from a first-principles investigation of two architectures: a PIN junction with a boron-vacancy-boron (BVB) intermediate-band absorber, and a PN junction based on phosphorus-vacancy (PV) defects. For the PIN solar cell, practical design principles include: i) aligning incident light in the xz-plane to exploit anisotropic absorption; ii) using graded junctions to mitigate tunnelling losses at abrupt interfaces; iii) targeting an absorber thickness of ~500 nm to balance absorption and carrier extraction; and iv) leveraging the high transparency of both contact layers for bifacial device configurations. For the PN diode, the PV-doped diamond operates via impurity-band conduction, making it suitable for degenerate p-type applications such as tunnel diodes or asymmetric junctions, while its temperature-dependent Seebeck anisotropy and sign-reversal offer opportunities for thermal management applications. When paired with phosphorus-doped n-type regions, these defects enable single-dopant junctions that significantly simplify device manufacturing. Using density functional theory with GW corrections, Bethe-Salpeter equation calculations and carrier transport modelling coupled to device electrostatics via a Poisson solver, we show that the BVB defect introduces intermediate bands without degrading diamond's high carrier mobility or thermal conductivity, while PV-doping provides high conductivity at room temperature through impurity-band transport. Overall, both defect-engineered systems preserve diamond's superior transport and thermal properties even after doping, offering viable pathways for high-performance diamond optoelectronics. These guidelines provide a practical foundation for fabricating efficient diamond-based photovoltaic and diode devices.

cond-mat.mtrl-sci↗

arXiv2026

Tuning magnitude and direction of lattice thermal conductivity in transition metal dichalcogenide heterobilayers

We investigate the nanoscale mechanisms determining lattice thermal conductivity (LTC) of pristine and W-doped MX$_2$-M$^\prime$X$^\prime_2$ transition metal dichalcogenide heterobilayers from first principles, using the exact solution of the linearised Boltzmann transport equation in both phonon and relaxon bases. Pristine heterobilayers exhibit isotropic in-plane LTC with preserved ordering across temperature. Relaxon analysis identifies descriptors linking LTC to phonon properties such as the phonon group velocity and layer localisation. While systems with lighter atoms generally favour higher LTC, a sufficiently large mass contrast is required to induce layer localisation of the transport-relevant vibrational modes. Further, we show through the thermal viscosity that the relative distribution of vibrational states between metal/non-metal sublattices influences the balance between Normal and Umklapp scattering processes. On the other hand, doped systems exhibit reduced and anisotropic in-plane LTC, retain a well-defined layer character, but are strongly affected by enhanced phonon-phonon scattering due to mass disorder. Notably, we find that both configuration and temperature dictate the direction of maximum thermal transport, which opens the possibility to tune the direction of maximum (and minimum) conductivity via doping in novel 2D functional materials. Thanks to its general formulation, the analysis protocol can be readily extended to other van der Waals heterostructures, and the descriptors may be implemented in high-throughput engines to identify promising layered materials with tailored thermal transport characteristics.

cond-mat.mtrl-sci↗

arXiv2026

Microscopic contributions to the deviation from Amontons friction law

We investigate the nanoscale friction behaviour of MX2 monolayers (M = Mo, W; X = S, Se) on Au(111) and Ag(111) substrates with a silicon tip using classical molecular dynamics simulations with machine-learning-based force fields. This approach enables an accurate description of tip-surface interactions and friction mechanisms at the atomic scale. We observe a pronounced non-monotonic dependence of the friction force on the applied normal load, indicating a breakdown of Amontons's law at the nanoscale. Analysis of lateral force' signals and their spatial Fourier transforms reveals the coexistence of multiple sliding modes, including longitudinal sliding, lateral slip, and zig-zag motions. We show that the overall friction response is governed by the relative contributions of these motions. While the qualitative features of friction are largely substrate-independent, both the magnitude of friction and the balance between sliding modes depend sensitively on the substrate-monolayer combination. In particular, Au/MoSe2/Si exhibits significantly reduced friction due to suppression of lateral slip motion. Our results indicate that the method is broadly applicable for probing nanoscale friction in related heterostructures.

cond-mat.mtrl-sci↗

arXiv2025

Ab initio study on photocatalytic properties of PtSSe-WXY Janus heterostructures

Semiconductor photocatalysis offers a sustainable route for converting solar energy into chemical energy, enabling the production of clean fuels and valuable chemical products. To this aim, we explore van der Waals heterostructures made up of Janus PtSSe and WXY (X, Y $=$ S, Se, Te and X $\neq$Y), in the context of photocatalytic applications. The redox capabilities of various heterostructure configurations (atom facing types and stacking orders) are evaluated by aligning the absolute band edge positions with respect to redox potentials of hydrogen and oxygen evolution reaction (HER and OER) and CO$_2$ reduction reactions. The stability of photocatalyst candidates are checked by layer binding energy calculations and ab initio molecular dynamics simulations. The optical absorption spectra suggest good light absorption in the visible range. Further, strain engineering is applied as a way to tune band edges and evaluate the possible use of the heterostructures as photocatalysts. This study shows that van der Waals heterostructure bilayers composed of Janus PtSSe and WSeTe in specific geometric configurations can be potential materials as photocatalysts for HER, OER and CO$_2$ reduction reactions. Finally, we suggest that, although systems made up of PtSSe and WSTe cannot be used for photocatalytic applications, they can be explored for applications in thermoelectric energy conversion or infrared photovoltaics.

cond-mat.mtrl-sci↗

arXiv2025

Superlubricity of Borophene: Tribological Properties in Comparison to hBN

The tribological performance of 2D materials makes them good candidates toward a reduction of friction at the macroscale. Superlubricity has been observed for graphene, MoS\textsubscript{2} and MXenes and hexagonal boron nitride (hBN) is used to reduce or tune friction, but other materials are investigated as potential candidates for low-lubricity applications. Specifically, borophene is predicted to have ultra-low friction. Here, we experimentally investigate frictional properties of borophene and use a borophene-hBN lateral heterostructure to directly compare the tribological properties of the two complementary 2D materials. In particular, we investigate the friction between a sliding tip and (i) the weakly corrugated $\mathcal{X}_6$-borophene layer on Ir(111) or (ii) the hBN/Ir(111) superlattice structures with a strongly corrugated moiré reconstruction. Our experimental study performed in ultra-high vacuum at room temperature combined with a Prandtl-Tomlinson (PT) model calculation confirms the superlubricity predicted for borophene, while hBN, which exhibits a higher friction, is nevertheless confirmed as a low friction material. Ab initio calculations show that the lower friction of $\mathcal{X}_6$-borophene with respect to hBN can be rationalized by weaker tip/surface interactions. In addition, we assess structural and electrical properties of borophene and hBN by using scanning probe techniques and compare their dissipation under the oscillating tip to investigate the possible path of energy dissipation occurring during friction. Our study demonstrates the low frictional properties of borophene and the potential of lateral heterostructure investigations to directly compare the properties of these 2D materials.

cond-mat.mtrl-sci↗

arXiv2025

Optimal boron-doped graphene substrate for glucose Raman signal enhancement

Surface Enhanced Raman Spectroscopy (SERS) is a highly sensitive and selective technique that greatly enhances the signal of an analyte, compared with its signal from classical Raman Spectroscopy, due to its interaction with a substrates surface. It has been shown that low concentration boron-doped graphene (B-graphene) enhances the Raman signal of simple organic molecules like pyridine. Recent studies also suggest that B-graphene can remain thermodynamically stable when doped with significantly higher concentrations of boron than previously observed. In this framework, we use quantum mechanical simulations to investigate the influence of dopant concentration and geometric distribution on the effectiveness of B-doped graphene as a SERS substrate, with glucose as analyte. By combining analysis of interatomic force constants and of phonon eigenvectors composition, we conclude that higher doping concentrations provide a larger enhancement to glucose's Raman signal, while the molecule orientation relative to the surface plays a fundamental role in the Raman response. We suggest that high concentration B-graphene presents itself as a potential substrate for SERS based detection of glucose, while the used phonon-based analysis can be promptly applied for the search of promising candidates as substrate materials for enhanced Raman response.

cond-mat.mtrl-sci↗

arXiv2020

Experimental realisation of Dual Periodicity Moiré Superlattice in a MoSe$_2$/WSe$_2$ Heterobilayer

Moiré structures in van der Waals heterostructures lead to emergent phenomena including superconductivity in twisted bilayer graphene and optically accessible strongly-correlated electron states in transition metal dichalcogenide heterobilayers. Dual periodicity moiré structures (DPMS) formed in layered structures with more than two layers have been shown to lead to ferromagnetism and multiple secondary Dirac points in TBG. Whilst in principle it is possible to obtain DPMS in bilayers there has not been clear experimental evidence of this yet. In this paper we present signatures of DPMS in a twisted MoSe$_2$/WSe$_2$ bilayer revealed by resonance Raman spectroscopy. We observed zone-folded acoustic and optical phonon modes with a wavevector twice of the moiré wavevector, evidence of a dual periodicity moiré heterostructure. These results simultaneously open up opportunities for new emergent phenomena and an optical method for characterising DPMS in a wide range of van der Waals heterostructures.

cond-mat.mes-hall↗

arXiv2018

Electronic structure of negative charge transfer CaFeO3 across the metal-insulator transition

We investigated the metal-insulator transition for epitaxial thin films of the perovskite CaFeO3, a material with a significant oxygen ligand hole contribution to its electronic structure. We find that biaxial tensile and compressive strain suppress the metal-insulator transition temperature. By combining hard X-ray photoelectron spectroscopy, soft X-ray absorption spectroscopy, and density functional calculations, we resolve the element-specific changes to the electronic structure across the metal-insulator transition. We demonstrate that the Fe electron valence undergoes no observable change between the metallic and insulating states, whereas the O electronic configuration undergoes significant changes. This strongly supports the bond-disproportionation model of the metal-insulator transition for CaFeO3 and highlights the importance of ligand holes in its electronic structure. By sensitively measuring the ligand hole density, however, we find that it increases by ~5-10% in the insulating state, which we ascribe to a further localization of electron charge on the Fe sites. These results provide detailed insight into the metal-insulator transition of negative charge transfer compounds and should prove instructive for understanding metal-insulator transitions in other late transition metal compounds such as the nickelates.

cond-mat.mtrl-sci↗

arXiv2013

Octahedral Engineering of Orbital Polarizations in Charge Transfer Oxides

Negative charge transfer $AB$O$_3$ oxides may undergo electronic metal--insulator transitions (MIT) concomitant with a dilation and contraction of nearly rigid octahedra. On both sides of the MIT are in-phase or out-of-phase (or both) rotations of adjacent octahedra that buckle the $B$--O--$B$ bond angle away from 180$^\circ$. Using density functional theory with the PBEsol$+U$ approach, we describe a novel octahedral engineering avenue to control the $B$ 3d and O $2p$ orbital polarization through enhancement of the $B$O$_6$ rotation "sense" rather than solely through conventional changes to the $B$--O bond lengths, \emph{i.e.} crystal field distortions. Using CaFeO$_3$ as a prototypical material, we show the flavor of the octahedral rotation pattern when combined with strain--rotation coupling and thin film engineering strategies offers a promising avenue to fine tune orbital polarizations near electronic phase boundaries.

cond-mat.mtrl-sci↗