Pushing Colloidal Limits: ~200 nm InAs Colloidal Quantum Nanorods for Extended Shortwave Infrared Photodetection

By Kseniia Kosolapova

Abstract

InAs colloidal quantum dots (CQDs) are promising for shortwave infrared (SWIR) optoelectronics, due to their size-tunable optical properties, compatibility with CMOS technology, and compliance with the RoHS directive. However, increasing CQD size to achieve extended SWIR (eSWIR) bandgaps and improving charge transport often compromises colloidal stability. Here, we report a growth strategy for ultra-long InAs colloidal quantum nanorods (CQNRs) that maintain quantum confinement while enhancing colloidal stability and charge transport. A key innovation is the precise chemical control through lithium bis(trimethylsilyl)amide (LiN(Si(CH₃)₃)₂) that directly controls their anisotropic growth, enabling the synthesis of nanorods up to ~200 nm in length, orders of magnitude longer than previously reported for colloidal InAs. Transitioning from spherical QDs to nanorods allows size extension without inducing aggregation or precipitation. The resulting CQNRs exhibit excellent colloidal stability and absorption up to 2000 nm in the eSWIR region. Photodiodes fabricated from these CQNRs exhibit very low dark current (6 μA cm^-2) and high external quantum efficiency (10.6%), attributed to reduced interparticle grain boundaries confirmed by four-dimensional scanning transmission electron microscopy. This work demonstrates the controlled growth of ultra-long, colloidally stable InAs CQNRs and provides a route to environmentally compliant large CQDs for next-generation high-performance eSWIR optoelectronic devices.

On-Surface Reactions of Electronically Active Self-Assembled Monolayers for Electrode Work Function Tuning

By Ricardo Ruvalcaba

Abstract

Self-assembled monolayers (SAMs) help improve the performance of organic electronic devices through interface passivation and enhanced carrier transport. Yet, there is limited information regarding the chemical structure of the SAMs upon functionalization and subsequent thermal treatment. Here, we studied the on-surface reaction of carbazole-derived SAMs on model gold electrodes, focusing on the chemical structure changes induced by thermal treatments. Furthermore, we correlate the microscopic changes with their impact on the electrode’s work function. The carbazole-based SAMs first transform into organometallic complexes. At higher annealing temperatures, SAMs convert to oligomeric complexes. The observed chemical reactions significantly reduce the electrode work function and facilitate electron injection in n-type organic thin-film transistors. Our results highlight the on-surface synthesis of electronically active SAMs as an alternative approach for modifying the work function of electrodes for organic electronics.

Biography

Ricardo is a PhD candidate at the King Abdullah University of Science and Technology (KAUST), where he is conducting research under the mentorship of Prof. Shadi Fatayer in the Manipulation Of NAnosystems group. His work centers on the investigation of nanostructure properties at the atomic scale, combining scanning tunneling and atomic force microscopies with first-principles simulations.