arXiv subjects

Carlos Garcia

Publications and source records attributed to Carlos Garcia.

15 recordsLinked to original sources

arXiv2026

$Ab$ $initio$ Study of Substitutional Defects in Li$_{3}$OCl Solid Electrolyte for Li-ion Batteries

Improving ion transport in solid electrolytes and cathode coatings remains a key challenge for all-solid-state Li-ion batteries because their room-temperature ionic conductivity is still substantially lower than that of liquid electrolytes. In our previous combined experimental and theoretical study, we showed that thermal neutron irradiation enables defect engineering in LiBO$_2$ through the transmutation of $^6$Li and $^{10}$B, generating lattice vacancies that enhance ionic conductivity. Here, we examine whether this approach can be extended to Li$_3$OCl, a representative antiperovskite solid electrolyte. Using density functional theory, we investigate substitutional defects at Li sites involving B, He, and H, associated with B doping and the neutron-capture reactions $^{6}\mathrm{Li}+n\rightarrow\,^{3}\mathrm{H}+α$ and $^{10}\mathrm{B}+n\rightarrow\,^{7}\mathrm{Li}+α+γ$. We evaluate defect formation energetics, the resulting structural distortions, and compare these substitutional defects with other mono-, di-, and trication substitutions at Li sites. Our results show that substitutional defects associated with neutron irradiation provide a feasible route to tune the defect chemistry of antiperovskite solid electrolytes and support neutron-driven defect engineering as a strategy for developing advanced materials for high-performance all-solid-state Li-ion batteries.

cond-mat.mtrl-sci↗

arXiv2026

A Computational Framework Integrating Physics-based Model and Equivalent Circuit Network Model to Simulate Li-ion Batteries

Battery models generally fall into two categories: physics-based models and ECM models. Physics-based Doyle-Fuller-Newman (DFN) models can accurately simulate the battery internal electrochemical processes, but to properly account for thermal effects requires a strong coupling between a DFN model and a 3D thermal model, which is computationally unaffordable. Distributed Equivalent Circuit Network (ECN) models can perform simulations with high speed and reasonable accuracy. However, these models rely heavily on the characterisation experiments for ECN parameter identification, which is resource-intensive and can lead to inaccurate parametrisation outcomes due to internal thermal inhomogeneity. To harness the strengths of both models, we propose a computational framework to integrate electrochemical DFN model and 3D distributed ECN model together. Using this framework, we simulate constant current discharge experiments of Kokam 7.5 Ah pouch cell (Model SLPB75106100) and compare the simulations with the commonly-used lumped DFN-thermal model. The computational model outperforms the lumped DFN model at low-temperature and/or high C-rate scenarios significantly. The largest predicting error of the framework at 3 C-rate &Tam = 25oC and at 1 C-rate &Tam = 0 oC is approximately 1/3 of that for DFN model. At 3 C-rate &Tam = 5oC, the difference between these two can rise to 377 mV. By integrating DFN and 3D-distributed ECN together, the computational framework can simulate the complicated interplay between electrochemistry, thermal process, and electricity within a cell fast and accurately. We anticipate this computational framework to be a valuable toolset to assist researchers and engineers in the design and control of Li-ion batteries.

physics.app-ph↗

arXiv2026

Reproducing and Improving CheXNet: Deep Learning for Chest X-ray Disease Classification

Deep learning for radiologic image analysis is a rapidly growing field in biomedical research and is likely to become a standard practice in modern medicine. On the publicly available NIH ChestX-ray14 dataset, containing X-ray images that are classified by the presence or absence of 14 different diseases, we reproduced an algorithm known as CheXNet, as well as explored other algorithms that outperform CheXNet's baseline metrics. Model performance was primarily evaluated using the F1 score and AUC-ROC, both of which are critical metrics for imbalanced, multi-label classification tasks in medical imaging. The best model achieved an average AUC-ROC score of 0.85 and an average F1 score of 0.39 across all 14 disease classifications present in the dataset.

eess.IV↗

arXiv2025

TheBlueScrubs-v1, a comprehensive curated medical dataset derived from the internet

The need for robust and diverse data sets to train clinical large language models (cLLMs) is critical given that currently available public repositories often prove too limited in size or scope for comprehensive medical use. While resources like PubMed provide foundational medical literature, they capture only a narrow range of formal publications and omit the broader medical discourse on the internet. To address these deficits, we introduce TheBlueScrubs-v1, a curated dataset of over 25 billion medical tokens - nearly three times larger than PubMed - drawn from a broad-scale internet corpus. Our two-stage filtering pipeline employs a Logistic Regression model for document screening (achieving an AUC of approximately 0.95 on external validation), followed by verification via a 70B-parameter Llama 3.1 instruct model. Each text is assigned three LLM-based quality scores encompassing medical relevance, precision and factual detail, and safety and ethical standards. Clinician reviews confirm high concordance with these automated evaluations, and a specialized cancer classifier further labels approximately 11 billion oncology tokens. Two demonstration tasks highlight the dataset's practical value: first, we distill the safety evaluations to a smaller BERT-style model that reaches an AUC near 0.96 on unseen data; second, we fine-tune a compact LLM on a filtered subset, showing measurable improvements over standard baselines in medical benchmarks as well as private ones. This Data Descriptor details the dataset's creation and validation, underscoring its potential utility for medical AI research.

cs.CL↗

arXiv2025

Tailoring magnetic properties of CoFeB films via tungsten buffer and capping layers

Controlling the interface between W and CoFeB-based buffer or capping layers at an appropriate temperature is essential for modifying the strength of magnetic anisotropy. In this work, we systematically explore the impact of W buffer and capping layers on the structural, topological, and magnetic anisotropy properties of W (5 nm)/CoFeB(10 nm) and CoFeB(10 nm)/W(3 nm) bilayers sputtered at room temperature (RT) and annealed at an optimal annealing temperature (TA) of 400 C. Our findings demonstrate that the bilayer films uniaxial magnetic anisotropy (UMA) with out-of-plane coercivity (Hcp) is highly influenced by the W buffer, capping layers, and TA. Specifically, the Hcp of the CoFeB layer with the buffer and capping layers annealed at 400 C samples exceed several times the coercivity of those unannealed. CoFeB buffered with W and annealed at 400 C shows larger Hcp, two-fold UMA, and higher in-plane UMA energy density (Keff) than the CoFeB/W bilayers, which can be attributed to the W buffer layer inducing the crystallization of CoFeB during annealing. The W buffer, capping layers, and the TA for W and CoFeB-based bilayer samples significantly alter the surface morphology, grain sizes, and surface roughness. The XRD analysis reveals nano-crystallites embedded in the larger grains of the 400 C annealed samples. Hence, this work offers a promising approach to achieving high thermal stability of UMA in W and CoFeB-based spintronic applications.

cond-mat.mtrl-sci↗

arXiv2024

Effects of Interfacial Oxygen Diffusion on the Magnetic Properties and Thermal Stability of Pd/CoFeB/Pd/Ta Heterostructure

We investigated the effects of annealing temperatures (TA) on a Pd (5 nm)/CoFeB (10 nm)/Pd (3 nm)/Ta (10 nm) multilayer structure. The as-deposited sample showed an amorphous state with in-plane uniaxial magnetic anisotropy (UMA), resulting in low coercivity and moderate damping constant (α) values. Increasing TA led to crystallization, forming bcc-CoFe (110) crystals, which increased in-plane coercivity and introduced isotropic magnetic anisotropy, slightly reducing the α. The two-fold UMA persists up to 600 C, and the thermal stability of the in-plane magnetic anisotropy remains intact even TA = 700 C. The TA significantly influenced the magnetic properties such as in-plane saturation magnetization (Ms//), in-plane and out-of-plane coercivities, and in-plane effective magnetic anisotropy energy density (Keff). Above 600 C, Keff decreased, indicating a transition towards uniaxial perpendicular magnetic anisotropy. Interfacial oxidation and diffusion from the Ta capping layer to the Pd/CoFeB/Pd interfaces were observed, influencing chemical bonding states. Annealing at 700 C, reduced oxygen within TaOx through a redox reaction involving Ta crystallization, forming TaB, PdO, and BOx states. Ferromagnetic resonance spectra analysis indicated variations in resonance field (Hr) due to local chemical environments. The α reduction, reaching a minimum at 300 C annealing, was attributed to reduced structural disorder from inhomogeneities. Tailoring magnetic anisotropy and spin dynamic properties in Pd/CoFeB/Pd/Ta structures through TA-controlled oxygen diffusion/oxidation highlights their potential for SOT, DMI, and magnetic skyrmion-based spintronic devices.

cond-mat.mtrl-sci↗

arXiv2024

Impact of Annealing on Perpendicular Magnetic Anisotropy in W/MgAl2O4/CoFeMnSi/W/CoFeMnSi/MgAl2O4/W. Double Storage Layers for Upcoming MTJs

In this study, we achieved the improvement of uniaxial perpendicular magnetic anisotropy (PMA) in the W/MgAl2O4/CoFeMnSi/W/CoFeMnSi/MgAl2O4/W heterostructure by manipulating the annealing temperature (TA) [350 C, 450 C, and 550 C]. We observed a maximum effective PMA energy density (Keff) of = 1.604 x 106 erg/cc with low saturation magnetization (Ms) at the specified TA. The enhancement of Keff with Ms is significantly influenced by structural variations at the interfaces of CoFeMnSi and MgAl2O4, attributed to sufficient interfacial oxidation dependent on the TA. The TA was identified as a critical factor affecting the surface morphology, grain size, and surface roughness of the multilayer. Fourier-transform infrared (FT-IR) measurements were employed to confirm the presence of Co-O or Fe-O bond in the multilayer structures, elucidating the true origin of PMA. The control of interfacial oxidation at the interface during annealing is crucial for regulating the strength of PMA. Therefore, this double CoFeMnSi/MgAl2O4-based multilayer presents a promising avenue, serving as a favorable candidate for future p-MTJs-based spintronic devices with enhanced thermal stability.

cond-mat.mtrl-sci↗

arXiv2024

Tuning the Spin Interaction in Non-planar Organic Diradicals Through Mechanical Manipulation

Open-shell polycyclic aromatic hydrocarbons (PAHs) represent promising building blocks for carbon-based functional magnetic materials. Their magnetic properties stem from the presence of unpaired electrons localized in radical states of $π$ character. Consequently, these materials are inclined to exhibit spin delocalization, form extended collective states, and respond to the flexibility of the molecular backbones. However, they are also highly reactive, requiring structural strategies to protect the radical states from reacting with the environment. Here, we demonstrate that the open-shell ground state of the diradical 2-OS survives on a Au(111) substrate as a global singlet formed by two unpaired electrons with anti-parallel spins coupled through a conformational dependent interaction. The 2-OS molecule is a protected derivative of the Chichibabin's diradical, featuring a non-planar geometry that destabilizes the closed-shell quinoidal structure. Using scanning tunneling microscopy (STM), we localized the two interacting spins at the molecular edges, and detected an excited triplet state a few millielectronvolts above the singlet ground state. Mean-field Hubbard simulations reveal that the exchange coupling between the two spins strongly depends on the torsional angles between the different molecular moieties, suggesting the possibility of influencing the molecule's magnetic state through structural changes. This was demonstrated here using the STM tip to manipulate the molecular conformation, while simultaneously detecting changes in the spin excitation spectrum. Our work suggests the potential of these PAHs for a new class of all-carbon spin-crossover materials.

cond-mat.mes-hall↗

arXiv2023

Magnetization reversal in FePt thin films: Experiments and simulations

The competition between shape and perpendicular magnetic anisotropies (PMA) in magnetic thin films gives rise to unusual magnetic behaviors. In ferromagnetic films with moderate PMA the magnetic domain configuration transitions from planar to stripe-like domains above a critical thickness, $t_c$. In this article, we present a detailed study of the magnetization switching mechanism in FePt thin films, where this phenomenon is observed. Using micromagnetic simulations and experiments, we found that below $t_c$ the reversal mechanism is well described by the two-phase model while above this thickness the magnetization within each stripe reverses by coherent rotation. We also analyzed the PMA and its temperature dependence, probing that substrate-induced strains are responsible for the abnormal coercive field behavior observed for FePt films with $t>t_c$.

cond-mat.mtrl-sci↗

arXiv2020

Assembly of nanocube super-structures directed by surface and magnetic interactions

We model the stabilization of clusters and lattices of cuboidal particles with long-ranged magnetic dipolar and short-ranged surface interactions. Two realistic systems were considered: one with magnetization orientated in the [001] crystallographic direction, and the other with magnetization along the [111] direction. We have studied magnetic nanocubes clusters first in the limit of $T=0$~K intending to elucidate the structural genesis of low energy configurations and then analyzed finite-temperature behavior of the same systems in simulations. Our results demonstrate that dipolar coupling can stabilize nanoparticle assemblies with cubic, planar, and linear arrangements seen previously in experiments. While attractive surface energy supports the formation of super-cubes, the repulsion results in the elongated structures in the form of rods and chains. We observe the stabilization of the ferromagnetic planar arrangements of the cubes standing on their corners and in contact over edges. We illustrate that minimal energy structures depend only on the size of the assembly and balance of surface repulsion and magnetic dipolar coupling. The presented results are scalable to different particle sizes and material parameters.

cond-mat.soft↗

arXiv2018

Phase Modulators Based on High Mobility Ambipolar ReSe2 Field-Effect Transistors

We fabricated ambipolar field-effect transistors (FETs) from multi-layered triclinic ReSe2, mechanically exfoliated onto a SiO2 layer grown on p-doped Si. In contrast to previous reports on thin layers (~2 to 3 layers), we extract field-effect carrier mobilities in excess of 10^2 cm^2/Vs at room temperature in crystals with nearly ~10 atomic layers. These thicker FETs also show nearly zero threshold gate voltage for conduction and high ON to OFF current ratios when compared to the FETs built from thinner layers. We also demonstrate that it is possible to utilize this ambipolarity to fabricate logical elements or digital synthesizers. For instance, we demonstrate that one can produce simple, gate-voltage tunable phase modulators with the ability to shift the phase of the input signal by either 90^o or nearly 180^o. Given that it is possible to engineer these same elements with improved architectures, for example on h-BN in order to decrease the threshold gate voltage and increase the carrier mobilities, it is possible to improve their characteristics in order to engineer ultra-thin layered logic elements based on ReSe2.

cond-mat.mes-hall↗

arXiv2017

First Experiences Optimizing Smith-Waterman on Intel's Knights Landing Processor

The well-known Smith-Waterman (SW) algorithm is the most commonly used method for local sequence alignments. However, SW is very computationally demanding for large protein databases. There exist several implementations that take advantage of computing parallelization on many-cores, FPGAs or GPUs, in order to increase the alignment throughtput. In this paper, we have explored SW acceleration on Intel KNL processor. The novelty of this architecture requires the revision of previous programming and optimization techniques on many-core architectures. To the best of authors knowledge, this is the first KNL architecture assessment for SW algorithm. Our evaluation, using the renowned Environmental NR database as benchmark, has shown that multi-threading and SIMD exploitation reports competitive performance (351 GCUPS) in comparison with other implementations.

cs.DC↗

arXiv2016

Photoconductivity of few-layered p-WSe2 phototransistors via multi-terminal measurements

Recently, two-dimensional materials and in particular transition metal dichalcogenides (TMDs) were extensively studied because of their strong light-matter interaction and the remarkable optoelectronic response of their field-effect transistors (FETs). Here, we report a photoconductivity study from FETs built from few-layers of p-WSe2 measured in a multi-terminal configuration under illumination by a 532 nm laser source. The photogenerated current was measured as a function of the incident optical power, of the drain-to-source bias and of the gate voltage. We observe a considerably larger photoconductivity when the phototransistors were measured via a four-terminal configuration when compared to a two-terminal one. For an incident laser power of 248 nW, we extract 18 A/W and ~4000% for the two-terminal responsivity (R) and the concomitant external quantum efficiency (EQE) respectively, when a bias voltage Vds = 1 V and a gate voltage Vbg = 10 V are applied to the sample. R and EQE are observed to increase by 370% to ~85 A/W and ~20000% respectively, when using a four-terminal configuration. Thus, we conclude that previous reports have severely underestimated the optoelectronic response of transition metal dichalcogenides, which in fact reveals a remarkable potential for photosensing applications.

cond-mat.mes-hall↗

arXiv2003

Monte Carlo Investigation of Ising Nanotubes and Nanostrips

Monte Carlo simulations of the magnetization temperature dependence in $D\times L$ nanotubes (periodic lateral boundary conditions) and nanostrips (free lateral boundary conditions) with $D$=8, 16, 32, 64$\ll L\longrightarrow 5000$ have been performed. The apparent critical temperature was determinated using the Binder Cumulant method (crossing of data for $D\times L$ with data for $D\times 2L)$ and it was found to be $ T_{C}=0 $ for small $D$ values $(D<D^{\ast})$, as it might have been expected.

cond-mat.stat-mech↗

arXiv2003

Effective Critical Exponents of Ising Strips D*L with D<<L

Monte Carlo data simulating phase transitions in Ising strips $D\times L,$ ($D\llL) $ with periodic boundary conditions show that $T_{c}(D)=0$ for $D\leq D^{\ast}\simeq 6$ and $0 D^{\ast}.$ Regular scaling of $ML^{β/ν}$ vs $|T-T_{c}|L^{1/ν}$ is obtained only for $% D>D^{\ast}$and the Monte Carlo effective susceptibility critical exponent $γ_{eff} (D)$ is shown to be well described by $γ(d)=β(d)[δ(d)-1]$ with $% d_{eff}(D)$ given by $d_{eff}(D)\simeq 1.5+({1/200})(D-6)$ and $β(d)=(\frac{3d%}{16}-{1/4}),$ $δ^{-1}(d)=(\frac{2d}{15}-{1/5})$, which can be understood as valid with $d_{eff}(D)$.

cond-mat.stat-mech↗