arXiv subjects

Abdul Ahad Mamun

Publications and source records attributed to Abdul Ahad Mamun.

7 recordsLinked to original sources

arXiv2026

Tailoring the Frequency-Dependent Optical Response of Hematite through Mono- and Co-Doping: A First-Principles Study

Understanding the effects of doping on the crystal structure and optical properties of semiconductor materials is crucial for advancing next-generation semiconductor and photonic technologies. Although various studies have focused on doped hematite ($α$-Fe$_2$O$_3$), the relationship between dynamical stability and optical properties remains insufficiently explored. This study presents a comprehensive first-principles investigation that simultaneously evaluates the phonon dispersion characteristics and frequency-dependent optical response of B-doped, Y-doped, and (B, Y)-co-doped $α$-Fe$_2$O$_3$, providing deeper insights into the underlying mechanisms. We examined the finite-temperature vibrational properties, dielectric function, and optical characteristics to comprehend the lattice dynamics and light-matter interactions under electromagnetic radiation. Vibrational thermodynamics reveal that pristine and Y-doped hematite maintain dynamic stability, while B-doped hematite exhibits imaginary phonon modes indicating lattice instability due to distortions in the Fe--O framework. Notably, Y co-doping with B helps suppress these soft modes, restoring structural stability through lattice relaxation and improved interatomic forces. B doping enhances low-energy absorption by introducing additional states in the valence band, while Y doping alters orbital hybridization, leading to a broader dispersion. In the optical regime, doped hematite displays dominant interband transitions below $2$ eV and strong absorption between 1.80 eV and 4 eV. The (B, Y) co-doping combines the low-energy benefits with an improved optical response profile. In summary, doping significantly enhances lattice vibrations, light-matter interactions, and optical responses, providing an effective strategy for tailoring hematite for diverse applications in photoactive, optoelectronic, and photonic technologies.

cond-mat.mtrl-sci↗

arXiv2026

Comprehensive Dataset and Signal Processing Framework for Phonocardiogram-Based Heart Rate and Blood Pressure Estimation

Cardiovascular diseases (CVDs) represent significant global health challenges today, necessitating regular and reliable monitoring to enable early intervention. Phonocardiogram (PCG) signals present a promising non-invasive method for assessing cardiovascular health. While recent studies have focused on estimating heart rate (HR) from PCG signals and blood pressure (BP) through multimodal combinations with other physiological data, reliable and cost-effective systems that can predict both HR and BP using only PCG signals remain largely unexplored. In this study, we proposed and developed a lab-scale cost-effective Phonocardiogram Tracking (PhonoTrack) system that can measure both HR and BP using only the PCG signal. We also introduced a corresponding dataset collected from 15 participants to evaluate the effectiveness of the proposed system. HR was determined using several peak detection methods, such as Hilbert Transform (HT), Shannon Entropy (SE), and WES, achieving notable Pearson correlation coefficients of 0.965, 0.973, and 0.955, respectively. The corresponding root mean square errors (RMSEs) were 2.467 bpm, 1.688 bpm, and 1.992 bpm for HT, SE, and WES, respectively. Additionally, we developed an advanced semi-empirical model based on multiple regression techniques to estimate systolic blood pressure (SBP) and diastolic blood pressure (DBP). This model demonstrated standard deviations of 2.10 mmHg for SBP and 3.20 mmHg for DBP across all subjects, with Pearson correlation coefficients of 0.89 and 0.70, respectively. These findings pave the way for developing a non-invasive, low-cost, and portable PhonoTrack device, positioning it as a promising solution for continuous cardiovascular monitoring settings.

eess.SP↗

arXiv2026

Mechanistic Insights into Enhanced Alkaline Oxygen Evolution on Zn-Al Alloy Electrodes

Electrochemical water electrolysis, which produces clean energy carriers to mitigate carbon emissions, lacks suitable, low-cost electrodes for efficient oxygen evolution reaction (OER) in alkaline water splitting. To address this challenge, we developed Zn-Al alloy electrodes with varying Al contents up to 20 wt.% via powder metallurgy method and conducted electrochemical measurements of the OER in alkaline solution to investigate their catalytic performance. We also performed first-principles calculations to examine their thermodynamic phase stability and electronic structures. Both theoretical and experimental results indicated that incorporating $\geq 20$ wt.% Al into Zn led to thermodynamic phase instability and secondary-phase segregation in Al-rich regions, limiting reaction kinetics and reducing catalytic efficiency. Although the Al content of 5 wt.% into Zn exhibited favorable thermodynamic and electronic characteristics, but its electrochemical performance was inefficient and poor due to inadequate reaction active sites on the surface. In contrast, the 10 wt.% and 15 wt.% Al into Zn showed approximately three- and two-fold increases in anodic exchange current density relative to pure Zn, respectively. Additionally, the anodic overpotential losses ($η_{0,a}$) measured at a current density of 12 mAcm$^{-2}$ were 0.240 V for Zn$_{0.9}$Al$_{0.1}$ and 0.5603 V for Zn$_{0.85}$Al$_{0.15}$, significantly lower than that of pure Zn ($η_{0,a} = 1.086$ V). While Zn$_{0.9}$Al$_{0.1}$ and Zn$_{0.85}$Al$_{0.15}$ showed similar charge transfer resistance ($R_{\rm CT}$), Zn$_{0.9}$Al$_{0.1}$ demonstrated superior reaction kinetics and lower $η_{0,a}$ across all samples tested. Furthermore, the improved kinetics and reduced overpotential of the Zn-Al alloys favorably compare with those of other transition-metal-based catalysts, including Fe-Co-Ni-Mo alloys and Fe-doped CuO.

cond-mat.mtrl-sci↗

arXiv2025

Re-Engineering Hematite: Synergistic Co-Doping Routes to Efficient Solar Water Splitting

Solar-driven water electrolysis requires high-performance photoelectrodes that exhibit excellent photoabsorption, superior charge transport, and optimized thermal management. In this work, we conducted a first-principles investigation to explore optimized doping conditions for hematite ($α$-Fe$_2$O$_3$) by incorporating boron (B), yttrium (Y), and niobium (Nb) mono-dopants, as well as (B, Y) and (B, Nb) co-dopants. To identify the optimal dopant elements and concentrations, we evaluated electronic charge transport, thermal properties, and magnetic susceptibility over a temperature ($T$) range of 300 to 900 K and doping densities ($N$) from $10^{19}$ to $10^{21}$ cm$^{-3}$. The B-doped, (B, Y)-doped, and (B, Nb)-doped $α$-Fe$_2$O$_3$ photoelectrodes showed significantly reduced band gap energy ($E_g$) relative to $α$-Fe$_2$O$_3$. In comparison, Y and Nb dopants only slightly reduced $E_g$ relative to $α$-Fe$_2$O$_3$. While B doping introduced impurity states near the Fermi level that limited thermoelectric charge transport, $α$-Fe$_2$O$_3$ photoelectrodes doped by other elements exhibited notable improvements, including enhanced visible-light absorption, increased carrier concentration, improved electrical conductivity ($σ$), and efficient thermal management. Additionally, these doped photoelectrodes exhibited a remarkable increase in Pauli magnetic susceptibility ($χ$) by two orders of magnitude compared to pristine $α$-Fe$_2$O$_3$, indicating exciting potential for generating spin-selective polarized currents. Overall, our findings revealed that the co-doping conditions are the most effective for enhancing the performance of $α$-Fe$_2$O$_3$, providing a low-cost and high-efficiency solution for sustainable green hydrogen (H$_2$) generation in photocatalytic water splitting.

physics.chem-ph↗

arXiv2025

Physics-Informed Electrochemical Model of Cathodic Corrosion in Alkaline Media

Electrochemical corrosion significantly reduces the durability of electrodes in water electrolyzers, adversely affecting hydrogen (H$_2$) production and cell efficiency. Current theoretical models inadequately assess corrosion behaviors in alkaline water electrolyzers. To address this, we developed a physics-informed electrochemical corrosion model evaluating the corrosion characteristics of cathodes in alkaline systems, accounting for factors such as exchange current density ($J_0$), redox potential ($E_0$), Gibbs free energy of hydrogen adsorption ($ΔG_{\rm H}$), electrolyte concentration ($C$), system pressure ($P$), and temperature ($T$). The model calculates metrics including corrosion potential ($E_{\rm corr}$), corrosion current density ($J_{\rm corr}$), and corrosion rate ($C_R$). Our findings from potentiodynamic polarization indicate that gold (Au) shows the highest durability, while copper (Cu) and nickel (Ni) are promising cost-effective alternatives. This work enhances the understanding of corrosion dynamics, contributing to the design of more efficient electrolyzer cells for hydrogen production.

physics.chem-ph↗

arXiv2025

Enhancing Electronic and Optical Properties of $α$-Fe$_2$O$_3$ by Introducing B, Y, and Nb Dopants for Improved Photoelectrochemical Water Splitting

Advanced theoretical investigations are crucial for understanding the structural growth mechanisms, optoelectronic properties, and photocatalytic activity of photoelectrodes for efficient photoelectrochemical water splitting. In this work, we conducted first-principles calculations aimed at designing $α$-Fe2O3 photoelectrodes incorporating mono-dopants such as boron (B), yttrium (Y), and niobium (Nb), as well as co-dopants (B, Y) and (B, Nb) to enhance the performance of photoelectrochemical cells. We assessed the thermodynamic phase stability by calculating formation enthalpy ($E_f$) and examining material properties, including microstrain ($μ_ε$) and crystallite size ($D$). The mono-dopants, Y and Nb, and the co-dopants, (B, Y) and (B, Nb), exhibited negative $E_f$ values under the substitutional doping method, confirming their thermodynamic phase stability and suggesting their practical viability for experimental implementation. Notably, the values of $μ_ε$ and $D$ fell within the ranges observed experimentally for $α$-Fe2O3, indicating their effectiveness in growth mechanisms. To gain a comprehensive understanding of the optoelectronic properties of doped $α$-Fe2O3, we calculated the electronic band structure, density of states, atom's ionic charge, and optical absorption coefficient. This analysis allowed us to examine the improvements in the electronic charge characteristics and photon-electron interactions. B-doped $α$-Fe2O3 led to the formation of impurity bands, which were mitigated by utilizing co-dopants (B, Y) and (B, Nb). The metal dopants, Y and Nb, significantly increased the charge carrier density, while the co-dopants, (B, Y) and (B, Nb), substantially enhanced light absorption in the visible spectrum.

cond-mat.mtrl-sci↗

arXiv2025

Enhanced Hydrogen Evolution Using $β$-MnO$_2$ Monolayer on Ni Electrode with Engineered Oxygen Vacancies

Developing cost-effective and high-performance electrodes is critical for advancing hydrogen (H$_2$) production through electrochemical water splitting. In this study, we present a novel electrode design by depositing a $β$-MnO$_2$ monolayer on a conventional Ni(100) substrate (MnO$_2$(110)/Ni(100)) and systematically investigate its electrocatalytic properties. This work uniquely explores the influence of oxygen vacancies (OVs) at distinct sites -- Osub-top and bridge sites -- on both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Our findings reveal that the Osub-top vacancy (OOV-MnO$_2$(110)/Ni(100)) significantly enhances HER activity, achieving a hydrogen Gibbs free energy ($ΔG_{\rm H}$) of $-0.015$ eV, which surpasses the performance of noble metals such as Pt/C ($-0.082$ eV) and Ir ($-0.08$ eV). Additionally, the cathodic exchange current density $(J_{0,c})$ of OOV-MnO$_2$(110)/Ni(100) reaches $10^{-0.774}$ Acm$^{-2}$, outperforming Pt/C ($10^{-0.92}$ Acm$^{-2}$) and Ir ($10^{-1.44}$ Acm$^{-2}$). Electrochemical analysis confirms a cathodic activation overpotential $(η_{a,c})$ of 0.141 V at 10 mAcm$^{-2}$ in a 0.5 M H$_2$SO$_4$ solution, achieving a hydrogen production rate (HPR) of 0.91 mmolh$^{-1}$cm$^{-2}$ at an applied voltage ($V_{\rm app}$) of 1.60 V. This study provides the first comprehensive analysis of site-specific oxygen vacancy effects on bifunctional MnO$_2$-based electrodes, demonstrating superior HER activity while maintaining dual functionality for both cathodic and anodic processes. Our results highlight the potential of engineered oxygen vacancies to develop low-cost, high-efficiency electrodes for sustainable hydrogen production, offering a competitive alternative to precious metal-based catalysts.

physics.chem-ph↗