arXiv subjects

Matheus J. S. Matos

Publications and source records attributed to Matheus J. S. Matos.

7 recordsLinked to original sources

arXiv2026

Anisotropic Dopant and Strain Architectures in WS$_2$ Nanocrystals Driven by Growth Kinetics

Dopant distribution in two-dimensional semiconductors is typically assumed to be stochastic, limiting deterministic defect engineering. Here, we show that non-equilibrium growth kinetics can be harnessed to define dopant-driven strain architectures in vanadium-doped WS$_2$ monolayers. Using synchrotron X-ray fluorescence, we identify preferential vanadium incorporation, anti-correlated with tungsten content, along crystallographic bisectors. An adsorption-growth-diffusion model with a single kinetic parameter quantitatively captures the dopant segregation arising from preferential corner adsorption and limited diffusion during chemical vapor deposition growth. Hyperspectral Raman imaging demonstrates mechanically induced vibrational responses, revealing localized tensile strain ($\varepsilon \approx0.70\%$) channels associated with the anisotropic dopant distribution. This regime is marked by the depletion of W-site-sensitive in-plane modes and the emergence of a localized $J2$ mode (210~cm$^{-1}$), which our ab-initio calculations attribute to antiphase V$-$V oscillations. These findings establish kinetic segregation as a route to deterministic chemical and strain architectures in 2D semiconductors, enabling programmable defect landscapes and strain engineering during synthesis.

cond-mat.mtrl-sci↗

arXiv2026

Resonance-Enhanced Four-Wave Mixing Imaging for Mapping Defect Regions in Vanadium-Doped WS2 Monolayers

Defect engineering is crucial for tuning 2D transition metal dichalcogenide properties for quantum and optoelectronic applications. While conventional photoluminescence (PL) and Raman spectroscopies are important characterization tools, their mapping in large area samples can be time-consuming and lacks direct sensitivity for comprehensive defect characterization. Here, we introduce resonance-enhanced four-wave mixing (FWM) imaging for precise imaging and characterization of vanadium-induced defect states in WS2 monolayers. Our multi-modal investigation, integrating hyperspectral PL, Raman, and supported by density functional calculations, reveals nanoscale doping inhomogeneities, their influence on excitonic and vibrational properties. We observe resonance-enhanced FWM signals correlating with vanadium-induced defect regions, evidencing their unique nonlinear optical response. This work establishes FWM as an essential platform for high-resolution, defect-sensitive imaging, advancing defect-engineered excitonic devices and enabling novel nonlinear quantum photonics.

cond-mat.mes-hall↗

arXiv2025

Revealing the Electronic Structure of van der Waals Antiferromagnetic NiPS$_3$ through Synchrotron-Based $μ$-ARPES and Alkali Metal Dosing

This study presents a comprehensive analysis of the band structure in NiPS$_3$, a van der Waals layered antiferromagnet, utilizing high-resolution synchrotron-based angle-resolved photoemission spectroscopy (ARPES) and corroborative density functional theory (DFT) calculations. By tuning the parameters of the light source, we obtained a very clear and wide energy range band structure of NiPS$_3$. Comparison with DFT calculations allows for the identification of the orbital character of the observed bands. Our DFT calculations perfectly match the experimental results, and no adaptations were made to the calculations based on the experimental outcomes. The appearance of novel electronic structure upon alkali metal dosing (AMD) were also obtained in this ARPES study. Above valence band maximum, structure of conduction bands and bands from defect states were firstly observed in NiPS$_3$. We provide the direct determination of the band gap of NiPS$_3$ as 1.3 eV from the band structure by AMD. In addition, detailed temperature dependent ARPES spectra were obtained across a range that spans both below and above the Néel transition temperature of NiPS$_3$. We found that the paramagnetic and antiferromagnetic states have almost identical spectra, indicating the highly localized nature of Ni $d$ states.

cond-mat.mtrl-sci↗

arXiv2025

Strong magneto-optical responses of an ensemble of defect-bound excitons in ambient exposed WS$_{2}$ and WSe$_{2}$ monolayers

Transition metal dichalcogenide (TMD) monolayers present a singular coupling in their spin and valley degrees of freedom. Moreover, by applying an external magnetic field it is possible to break the energy degeneracy between their K and $-$K valleys. This valley Zeeman effect opens the possibility of controlling and distinguishing the spin and valley characters of charge carriers in TMDs by their optical transition energies, making these materials promising for the next generation of spintronic and photonic devices. However, the free excitons of pristine TMD monolayers present a moderate valley Zeeman splitting of $\approx 0.23$ meV/T. Therefore, alternative excitonic states with higher magnetic responses are mandatory for application purposes. Here, we investigate the magneto-optical properties of ambient exposed WS$_2$ and WSe$_2$ monolayers by circularly polarized magneto-photoluminescence experiments at cryogenic temperatures. A broad lower energy photoluminescence emission related to an ensemble of defects is observed, presenting remarkable valley-related splittings of $\approx 1.45$ meV/T and $\approx 1.11$ meV/T for WS$_2$ and WSe$_2$ monolayers, respectively. In addition, we report a significant valley polarization of charge carriers in the defect mid-gap states induced by the external magnetic field. We explain this valley-polarized population and enhanced valley-related splitting in terms of imbalanced intervalley relaxations, leading to a magnetic field-dependent distribution of charge carriers in multiple defect levels. This effect, together with the individual Zeeman shiftings of the mid-gap states, explains the strong magneto-optical responses observed. Our work uncovers the singular potential of manipulating the light emission of ambient exposed TMD monolayers by an external magnetic field.

cond-mat.mes-hall↗

arXiv2023

Phyllosilicates as earth-abundant layered materials for electronics and optoelectronics: Prospects and challenges in their ultrathin limit

Phyllosilicate minerals are an emerging class of naturally occurring layered insulators with large bandgap energy that have gained attention from the scientific community. This class of lamellar materials has been recently explored at the ultrathin two-dimensional level due to their specific mechanical, electrical, magnetic, and optoelectronic properties, which are crucial for engineering novel devices (including heterostructures). Due to these properties, phyllosilicates minerals can be considered promising low-cost nanomaterials for future applications. In this Perspective article, we will present relevant features of these materials for their use in potential 2D-based electronic and optoelectronic applications, also discussing some of the major challenges in working with them.

physics.app-ph↗

arXiv2022

High throughput investigation of an emergent and naturally abundant 2D material: Clinochlore

Phyllosilicate minerals, which form a class of naturally occurring layered materials (LMs), have been recently considered as a low-cost source of two-dimensional (2D) materials. Clinochlore [Mg5Al(AlSi3)O10(OH)8] is one of the most abundant phyllosilicate minerals in nature, exhibiting the capability to be mechanically exfoliated down to a few layers. An important characteristic clinochlore is the natural occurrence of defects and impurities which can strongly affect their optoelectronic properties, possibly in technologically interesting ways. In the present work, we carry out a thorough investigation of the clinochlore structure on both bulk and 2D exfoliated forms, discussing its optical features and the influence of the insertion of impurities on its macroscopic properties. Several experimental techniques are employed, followed by theoretical first-principles calculations considering several types of naturally-ocurring transition metal impurities in the mineral lattice and their effect on electronic and optical properties. We demonstrate the existence of requirements concerning surface quality and insulating properties of clinochlore that are mandatory for its suitable application in nanoelectronic devices. The results presented in this work provide important informations for clinochlore potential applications and establish a basis for further works that intend to optimize its properties to relevant 2D technological applications through defect engineering.

cond-mat.mtrl-sci↗

arXiv2019

Evidence for a pressure-induced phase transition of few-layer graphene to 2D diamond

We unveil the diamondization mechanism of few-layer graphene compressed in the presence of water, providing robust evidence for the pressure-induced formation of 2D diamond. High-pressure Raman spectroscopy provides evidence of a phase transition occurring in the range of 4-7 GPa for 5-layer graphene and graphite. The pressure-induced phase is partially transparent and indents the silicon substrate. Our combined theoretical and experimental results indicate a gradual top-bottom diamondization mechanism, consistent with the formation of diamondene, a 2D ferromagnetic semiconductor. High-pressure x-ray diffraction on graphene indicates the formation of hexagonal diamond, consistent with the bulk limit of eclipsed-conformed diamondene.

cond-mat.mtrl-sci↗