arXiv subjects

Simão Meneses João

Publications and source records attributed to Simão Meneses João.

2 recordsLinked to original sources

arXiv2026

Platinum is a Photocatalyst: Large Visible-Light Quantum Efficiency Revealed

Metal-semiconductor junctions in optoelectronic devices are commonly engineered to promote charge separation. In Pt/TiO2 Schottky junctions, Pt is typically regarded as a catalytic electron sink rather than a visible-light-active component. Here, we demonstrate that Pt nanoislands on TiO2 can generate photochemically active carriers under visible light excitation. Using quantitative scanning photoelectrochemical microscopy, we measure the wavelength-resolved external quantum efficiency (EQE) of Au and Pt nanoisland arrays on TiO2, and correlate their reactivity with their morphology and extinction spectra. Discrete 10 nm Pt nanoislands exhibit robust broadband visible light photoactivity - exceeding the photoactivity of similar-sized Au nanoislands under blue-green excitation - whereas Pt's photoactivity is strongly suppressed when the nanoislands are connected. Surprisingly, Pt exhibits an EQE-per-atom approx. 20 times higher than Au at 455 nm and approx. 2 times higher at 595 nm (at Au's optimum). We show an approximately wavelength-independent Pt internal quantum efficiency of approx. 1 percent across the visible spectral region. These findings reposition catalytic metals with strongly damped optical response in the visible as light-responsive components in metal-semiconductor hybrids, challenging the prevailing perception that they function solely as passive co-catalysts in photocatalytic systems.

cond-mat.mes-hall↗

arXiv2023

Magnetotransport properties of a twisted bilayer graphene in the presence of external electric and magnetic field

We extensively investigate the electronic and transport properties of a twisted bilayer graphene when subjected to both an external perpendicular electric field and a magnetic field. Using a basic tight-binding model, we show the flat electronic band properties as well as the density of states (DOS), both without and with the applied electric field. In the presence of an electric field, the degeneracy at the Dirac points is lifted where the non-monotonic behavior of the energy gap exists, especially for twist angles below 3$^\circ$. We also study the behavior of the Landau levels (LL) spectra for different twist angles within a very low energy range. These LL spectra get modified under the influence of the external electric field. Moreover, we calculate the dc Hall conductivity ($σ_{xy}$) for a very large system using the Kernel Polynomial Method (KPM). Interestingly, $σ_{xy}$ makes a transition from a half-integer to an integer quantum Hall effect, \textit{i.e.} the value of $σ_{xy}$ shifts from $\pm 4(n+1/2) (2e^2/h)$ ($n$ is an integer) to $\pm 2n (2e^2/h)$ around a small twist angle of $θ=2.005^\circ$. At this angle, $σ_{xy}$ acquires a Hall plateau at zero Fermi energy. However, the behavior of $σ_{xy}$ remains unaltered when the system is exposed to the electric field, particularly at the magic angle where the bands in both layers can hybridize and strong interlayer coupling plays a crucial role.

cond-mat.mes-hall↗