arXiv subjects

Waqas Pervez

Publications and source records attributed to Waqas Pervez.

3 recordsLinked to original sources

arXiv2026

Photoemission intermittency via stochastic gating in rubrene nanowires coupled to plasmonic silver nanoparticles

In this work, we report a new nanoscale phenomenon observed as photoemission intermittency (On-Off electron emission), manifested as stochastic bursts in electron yield at quasi-one-dimensional organic wires and silver nanoparticles interface. Energy-resolved measurements reveal that the emitted electrons carry out hybrid information, containing photoelectron yield enhancement associated with the nanoparticles and kinetic energies determined by the organic semiconductor. The intermittency results in a dynamic shift of the electron spectra correlating with the photoelectron yield. We attribute the observed behaviour to the photo-hole accumulation and stochastic gating of charge due to electron-hole separation at the nano interface. These findings introduces the photoemission intermittency as a nanoscale phenomenon indicating a new dynamic regime of charge assisted emission at organic-plasmonic interfaces. Keywords: rubrene, nanoparticle, PEEM, exciton, charge

cond-mat.mtrl-sci↗

arXiv2025

Plasmon-assisted photoelectron emission in a model cluster using time-dependent density functional theory and the time-dependent surface-flux method

We investigate plasmon-assisted photoelectron emission using a one-dimensional time-dependent density-functional theory (TDDFT) model. Photoelectron spectra are computed with the time-dependent surface-flux (t-SURFF) method. In addition to the expected above-threshold ionization (ATI) comb, we observe peaks that arise from long-lived plasmon oscillations and the associated electron emission occurring after the laser pulse. We further analyze the positions of these peaks and their scaling behavior with the laser intensity.

quant-ph↗

arXiv2025

Imaging domain boundaries of rubrene thin crystallites by photoemission electron microscopy

The progress of designing organic semiconductors is extensively dependent on the quality of prepared organic molecular assemblies, since the charge transport mechanism is strongly efficient in highly ordered crystals compared to amorphous domains. Here we present a comprehensive photoemission electron microscopy (PEEM) and time-of-flight (TOF) spectroscopic study of rubrene ($\mathrm{C}_{48}\mathrm{H}_{24}$) thin crystals focusing on recently developed orthorhombic crystalline morphologies applied in organic electronic devices. Using femtosecond pulsed lasers with photon energies between 3-6 eV, we explore the interplay between photoemission processes, crystal morphology, and defect states. In a 2-photon photoemission process (2PPE), the PEEM images reveal dominant emission localized at domain boundaries, indicating strong contributions from trap states. In contrast, in 1PPE nm excitation uniform emission across the crystal surface is observed, highlighting a fundamental difference in photoemission mechanisms. Furthermore, in the intermediate photon energy range, we identify a nonlinear, non-integer photon order, where mostly the triclinic morphology contributes to the emission, distinguishing it from the orthorhombic phase. These findings provide a new framework for assessing the quality and internal structure of organic semiconductor thin films via wavelength-dependent photoemission imaging and spectroscopy.

cond-mat.mtrl-sci↗