Establishing and using variable energy ultraviolet photoemission spectroscopy and gas cluster ion beam etching for probing electronic defect states in organic semiconductor

Nontechnical Description Organic semiconductors are carbon-based materials used in electronics. They make it possible to build electronic devices with capabilities beyond those of traditional technologies. Examples include flexible displays, healthcare sensors, windows that change color at the touch of a button, and devices that convert heat into electricity. A key challenge is to improve device performance and lifetime. One way to do this is by reducing trap state concentrations. Trap states are defects that capture electrical charge and decrease performance. There are few tools that can measure trap states and all have limitations. The project addresses this gap by developing and using advanced experimental methods to directly measure these states. These methods are then used to investigate how molecular structure affects trap states and material degradation. This research helps build a stronger foundation for future electronic devices in consumer electronics, healthcare, and energy. The project trains undergraduate and graduate students in advanced spectroscopy and materials characterization. Project participants promote STEM engagement by hosting workshops for high school students. Technical Description A central scientific problem is the lack of direct methods to measure the energy, density, and spatial distribution of trap states. The project develops two key methods to address this problem, including variable energy ultraviolet photoemission spectroscopy and gas cluster ion beam etching. These tools help quantify the energy, density, and depth distribution of defect states. To develop these methods, the research team systematically evaluates the capabilities and limitations of variable energy ultraviolet photoemission spectroscopy using model materials with controlled defect populations. The team also investigates gas cluster ion beam etching by varying ion energy and cluster size to determine how processing conditions influence material damage and measurement accuracy. These approaches combine to enable depth-resolved measurements of trap states. Using these methods, the team establishes structure–property relationships that link molecular structure, defect formation, and degradation in organic semiconductors. Overall, this research advances spectroscopic methods and fundamental understanding of a critical and underexplored topic with high relevance to advancing electronic materials and devices. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.