Control of atomic scale structure in ultra-thin films on non-planar substrates is critical to next generation optical, electrical, biological, and magnetic materials and devices. In particular, nanoscale control of materials is essential to enable further decreases in the feature sizes and growth of materials in three dimensional architectures that are being developed for applications such as logic circuitry, memories, and photovoltaics. This research investigates the fundamental rearrangement of single atomic layers on surfaces during thin film growth, and provides important knowledge regarding the factors that influence transformation of disordered layers of atoms into ordered, crystalline arrangements. The primary experimental platform utilizes an electron beam to probe the structure of atomically-thick layers during growth and thermal processing. The research also uses atomically-resolved electron microscopy to probe the structure of these films. The knowledge generated from this research allows for an enhanced control and understanding of the formation of nanoscale crystalline materials that can be created on three dimensional (non-planar) surfaces and impacts a wide variety of fields in nanoelectronics, computing, photovoltaics, and nanoscale mechanical systems. This research activity is integrated with a university thin film course, a hands-on equipment laboratory, and an industrial outreach effort. Graduates typically find employment in national laboratory or industry.
TECHNICAL DETAILS: This research elucidates the fundamental transformations that occur during atomic layer deposition and annealing by utilizing in situ reflection high energy electron diffraction (RHEED). Current atomic layer deposition (ALD) processes are often limited in terms of the structural control that is available due to precursor decomposition at high temperatures, which presents a significant barrier to precisely controlled three dimensional epitaxial architectures that are integral to next generation electronics. Therefore, this work separates the precursor chemisorption steps (ALD component) that result in amorphous layers from thermal processing that provides energy needed to induce crystallization in the model material system gallium oxide. Importantly, electron diffraction is probing in real time the structural transformations that occur to reveal the effect of ambient atmosphere, substrate structure, and orientation with adlayer thicknesses in the range of 0.5-10 nm. Analytical electron microscopy is providing precise structural and compositional details of the films and film-substrate interfaces including defect characteristics. This research captures a slow-motion picture of the structural changes that occur during many traditional thin film epitaxy techniques, and yields new relationships that control crystallization of ultra-thin layers and thus impacts the thin film/epitaxy communities. Undergraduate and graduate students are trained during the research. Industrial engagements are pursued with the Lehigh University Office of Economic Engagement. Mentorship and outreach are conducted with Lehigh University's Clare Booth Scholarship Program, Mountaintop Experience, and a local science center.
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.
