Kritika Jha | Searcharxiv

arXiv2026

Physical aging of glasses of an organic semiconductor

All glasses, including organic semiconductor glasses, are non-equilibrium materials whose properties will change with time. This physical aging process is poorly understood for organic semiconductors, hindering the rational design of highly durable devices. In this study, we investigated the volume and enthalpy recovery processes in both thin films and bulk glasses of N,N'-Bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD). Our results revealed that volume recovery kinetics exhibit negligible dependence on film thickness for liquid-cooled TPD films between 400 nm and 100 nm. Additionally, the volume recovery process in TPD films was strongly coupled to the enthalpy recovery observed in bulk TPD glasses during annealing near the glass transition temperature. Remarkably, TPD films prepared by physical vapor deposition at room temperature demonstrated exceptional resistance to physical aging, with an aging rate approximately one order of magnitude lower than that of their liquid-cooled counterparts. These results not only enhance our understanding of the non-equilibrium dynamics in amorphous systems but also offer valuable insights for the design of next-generation organic devices with significantly improved stability and durability.

cond-mat.mtrl-sci↗

arXiv2025

Electrically Tunable Excitonic-Hyperbolicity in Chirality-Pure Carbon Nanotubes

Metamaterials exhibiting hyperbolic dispersion enable unprecedented control over light-matter interactions, from sub-diffraction imaging to enhanced spontaneous emission. However, conventional plasmonic hyperbolic metamaterials suffer from limited tunability and lack intrinsic emission capabilities, constraining their utility for active photonic devices. Here, we demonstrate the first room-temperature, electrically tunable, excitonic hyperbolic metamaterial using aligned films of chirality-pure semiconducting carbon nanotubes. Unlike plasmonic systems, these excitonic metamaterials of aligned nanotubes combine strong optical anisotropy with dynamic electrostatic tunability. Spectroscopic ellipsometry reveals that the hyperbolic dispersion window can be electrically shifted by 53 meV, enabling real-time switching between hyperbolic and elliptical regimes. Theory predicts that this tunability translates to the propagation angle being modulated by 34°, driven by a momentum enhancement 3.11 times that of free space, limited primarily by material losses that can be mitigated through improved alignment. In addition, simulations of the system exhibit a high Purcell factor of 1550 and a modulation of 37 % without an optical cavity for a dipole placed 5 nm above the aligned nanotubes. These findings establish excitonic carbon nanotubes as a versatile platform for dynamically reconfigurable photonic metamaterials, opening pathways for adaptive optical devices, electrically-controlled spontaneous emission, and tunable hyper-lenses operating at room temperature.

physics.optics↗