Solid-State Gamma-Ray Detection Using Quantum Dots

Project Overview

Efficient detection and characterization of gamma-rays, especially those emitted from special nuclear materials, is of utmost importance in matters of national security. Current gamma-ray detectors with state-of-the-art detectivity are composed of large single crystalline materials, which are challenging and expensive to grow, and a need exists for large area gamma-ray detectors that can be produced at lower cost and yet still have high sensitivity, especially for screening applications at borders and other ports of entry. To address these challenges, we proposed to develop a new class of solid-state gamma-ray detectors based on PbSe quantum dots. Colloidal quantum dots are solution processable, meaning that large area detectors could be fabricated by effectively "painting" a solution of quantum dots onto a substrate. In this project we developed a novel method for deposition of thick PbSe quantum dots (QDs) films onto conductive substrates and analyzed their response to both IR light and high energy radiation. The high prevalence of micro cracks in the electrophoretically deposited (EPD) films led us to an alternative approach of compressed PbSe QDs "pellets" which were also analyzed for radiation response.

Based on previous experience with QDs, much of our initial work was focused on making thick compact films with short ligands, to achieve this EPD was our deposition method of choice. We found that EPD is a strong technique to grow thick QD films quickly, however cracking during the film drying process makes it quite difficult to fabricate a vertical device using this method. After determining that thick films grown via EPD was not the proper technique for fabrication of solid-state gamma ray detectors, we moved on to pressing dry QD powders into pellets. We found that longer insulating ligands allowed us to reach the bias levels required for gamma-ray detectors, but we cannot confidently say that the peaks we saw during measurement were related to incident radiation. Electric discharges within the QD pellet during the measurements were quite common, and these could be related to incident radiation, but these discharges also occurred when no gamma-ray source was present.

Mission Impact

Our project was aimed to help the lab's nuclear nonproliferation mission, by aiding in the ability to monitor/locate special nuclear materials. Over the course of the project it has become clear that more mature technologies are still clearly the better option for detection of high energy ionizing radiation. Despite not reaching the final goal set out at the beginning of the project, the work done along the way has provided value to advance the field of nanomaterials and nanomaterial based devices that can be used for future research in various applications.

Publications, Presentations, and Patents

Nakotte, T., S. Singh, and A.M. Hiszpanksi. "Understanding methods to determine energy levels of quantum dot films for device integration." Proc. SPIE 12202. Nanoengineering: Fabrication, Properties, Optics, Thin Films, and Devices XIX, 1220202 (3 October 2022). https://doi.org/10.1117/12.2631667; LLNL-PROC-838313

T. Nakotte,"Understanding methods to determine energy levels of quantum dot films" (Presentation, SPIE Optics + Photonics 2022 Conference, San Diego, CA, August 2022). LLNL-PRES-838943

X. Xu, T. Nakotte, C. Orme,"Single Step Assembly of 3D Nanocrystal Superlattice Films" (Presentation, Gordon Research Conference Crystal Growth and Assembly, Manchester, NH, 2023). LLNL-POST-849976

X. Xu, T. Nakotte, C. Orme, "Single Step Deposition of Thick Compact Quantum Dot Films" (Poster Presentation, ACS Fall 2022, Chicago, IL, August 2022). LLNL-POST-838947