REU Talk 1: Nils Bernhardt, Technische Universität Berlin

Characterization of UV Color Centers in Hexagonal Boron Nitride

Friday, May 23, 2023, 10-11am, R1

Abstract: Hexagonal boron nitride (hBN) is an ultra-wide bandgap (~ 6 eV; ~ 206 nm) material with a graphene-like structure. The large bandgap makes it interesting not only for power electronics but also for optical devices. Its van der Waals inter-layer bonds allow direct exfoliation into atomically thin films, rendering it particularly valuable for quantum emitter applications where dimensional confinement and material purity are crucial. Defect quantum emitters in hBN are particularly interesting because they exhibit bright, stable single-photon sources at room temperature, a key requirement for quantum technologies such as secure communications, quantum computing, and advanced sensing. While such quantum emitters have been extensively studied for the near-infrared (IR) and visible regime in hBN, their structural origin is often still elusive. In contrast, ultraviolet (UV) luminescence from hBN defects presents unique opportunities and challenges. For instance, while many novel emitters continue to emerge, the well-established 4.1 eV (303 nm) defect shows a high binding energy far exceeding the thermal energy at room temperature. Consequently, such emitters are stable and have a low probability of thermal dissociation or decay, increasing the reliability of radiated photons. However, site-specific engineering of these defects remains an unsolved challenge. Our investigation provides a comprehensive study of the emission intensity, excitation channels, and carrier dynamics as a function of temperature for several UV emitters. We employ photoluminescence excitation (PLE) spectroscopy alongside temperature-dependent and time-resolved photoluminescence spectroscopy measurements to explore the origin and properties of established as well as newly identified defect luminescences. As such, we aim to promote the understanding of how material composition tuning affects defect formation and luminescence properties in hBN for the UV spectral region by establishing a correlation between growth conditions and luminescence characteristics.

Dr. Duy Le, University of Central Florida

Computational Design of Advanced Materials for Energy Applications

Friday, May 23, 2025, 1:30 pm, PSB 160/161

Abstract: Fossil fuels have long served as the world’s primary energy source. Synthetic fuels offer a promising alternative; help reduce our dependence on fossil fuels. Developing optimized catalyst materials is crucial for improving production of synthetic fuels. Alongside experimental work, computational modeling plays a key role in advancing the design of enhanced catalysts for sustainable, fossil fuel-free fuel production. In the first part of my talk, I will discuss our computational modeling efforts to leverage the electronic structures of two-dimensional materials for catalytic applications. Specifically, I will demonstrate that the defect-laden basal plane of hexagonal boron nitride (h-BN) can catalyze CO₂ hydrogenation to value-added products at nitrogen-vacancy (VN) sites. This catalytic activity arises from the isolated electronic states created by these defects. In the second part, I will discuss the role of non-metal cations, such as ammonium (NH₄⁺) and methylammonium (CH₃NH₃⁺) cations, in electrocatalysis. I will show how these cations can alter reaction pathways, enhancing both CO₂ electroreduction and the hydrogen evolution reaction.

REU Talk 2

Keith Blackman, University of Central Florida

Title: Monitoring the formation of Cn (n=2,3,4) products after photodissociation of CH₃I on fully oxidized and partially reduced

Abstract:Carbon-carbon (C-C) bond formation is paramount for a wide range of industrial and manufacturing processes, including commodities, synthetics, pharmaceuticals, and cosmetics. Understanding the C-C bond formation in heterogeneous catalytic reactions at gas-solid interfaces, and the corresponding surface properties, could be integral to improving the efficiency of various catalysts and catalytic processes.
This study focuses on understanding how single carbon (C₁) species are transformed into multi-carbon species (C_n, n=2,3,4) species through the coupling of CH₃ radicals, and how these species evolve on fully oxidized and reduced TiO₂(110) surfaces. Methyl iodide, employed as a precursor for CH₃ radicals, is continuously dosed on a TiO₂(110) surface held at 150 K and irradiated by femtosecond laser pulses with a central wavelength of 266 nm, power of 300 mW/cm², and repetition rate of 1 KHz. The central wavelength and the intensity of the laser beam are carefully tuned to excite CH₃I into the dissociated A-band, which leads to the formation of neutral CH₃ and I radicals as well as to ionize the reaction intermediates and final products. The ions produced at the surface are detected and analyzed with a time-of-flight mass spectrometer.
The mass spectra reveal the formation of C_n (n=2,3,4) products, such as C₂H₆, C₂H₅, C₂H₄, C₃H₇, C₃H₅, and C₄H₁₀, as well as H₂O. The detection of alkanes and alkenes species along with H₂O indicates an oxidative dehydrogenation process at the surface. Monitoring the yields of these products as a function of laser irradiation and surface degree of oxidation, which will also be presented in this contribution, is critical to fully understand the catalytic reaction mechanism at the oxide surface. This type of investigation could provide important insight into the C-C bond formation on other metal oxide surfaces using a variety of precursor molecules.

REU Talk 3

Ms. S. Faiza Sherazi, University of Central Florida

Tuesday, 6/17/2025, R1 Bldg, Room 103

Revealing Local Coordination of Ag Single Atom Catalyst Supported on CeO₂(110), ZrO₂(1̅11), and Al₂O₃(111)

Abstract: Single atom catalyst (SAC) supported on metal oxide surfaces is a promising candidate for various reactions as it possesses high temperature stability and potentially high selectivity. Determining the SAC’s local atomic coordination and geometric structure is important for understanding its catalytic performance. In this work, we apply the ab initio thermodynamics approach to investigate the coordination environment of Ag SAC supported on CeO₂(110), ZrO2₂(1̅11), and Al₂O₃(111), chosen as accompanying experimental observations find the former to be a more viable support than the latter. We find that the Ag SAC structure in which Ag is embedded in the CeO₂ lattice with one surface oxygen vacancy nearby is the most favorable on the CeO2(110) surface while the structure in which Ag embeds in the ZrO₂ and Al₂O₃ lattice without any oxygen vacancy nearby is the most favorable on the ZrO₂(1̅11) and Al2O3(111) surfaces, respectively. Our results also show that it is easier to create oxygen vacancy near the Ag atom when the support is CeO₂(110) than ZrO₂(1̅11) and Al₂O₃(111). We compare the trends in the energetics of NH3 adsorption and dissociation on Ag SAC supported on CeO2(110) with those on ZrO2(1̅11) and Al2O3(111) to compare with accompanying experimental observations that find the ceria-supported Ag SAC to exhibit a pronounced selectivity in ammonia oxidation. We will report experimental data to compare with our findings and comment on their implications for the catalytic performance of the Ag SAC. Work is supported by the National Science Foundation grant CHE-1955343.

Making sense of distributed quantum computing  

Abstract: The emergence of various quantum technologies has profound implications in advancing scientific discoveries in the many forefronts. One of the prominent applications is quantum chemistry which uses quantum computers to simulate the quantum processes in material synthesis and predict material properties that are beyond the capabilities of classical computers. In this talk, we will review the state-of-the-art quantum hardware platforms from the perspective of quantum information processing. We will discuss the challenges towards the “quantum supremacy” and the necessity for a unified and interconnected quantum network for a scalable distributed quantum computing architecture. I will outline the key technical ingredients for building a network of quantum processors and showcase our efforts in interconnecting distant superconducting quantum systems with optical fibers. We will end by sharing a prospect on how the infrastructure of global internet can be exploited to make quantum computation practical and universal.

Grain boundary movement in single-layer hexagonal boron nitride: insights from molecular dynamics simulation using machine-learned potentials

Abstract: Grain boundaries are commonly found in materials regardless of the growth method and their presence is not always desirable. While there could be some unique properties that come with grain boundaries, many material applications rely on pristine, single crystalline materials.  Being able to stimulate and predict the motion of grain boundaries would be beneficial in developing methodology for improving the quality of materials for which single crystalline structures are desirable.  In this work, we present first the details of a machine-learned potential that we have developed using the Allegro architecture and attest to its robustness. We next present results of molecular dynamics simulations of hexagonal boron nitride (h-BN) that investigate the movement of 4|8 grain boundaries.  These simulations are carried out with ~10,000 atoms to allow for mimicking realistic size of the system.  Our calculations of the activation energy barriers show that the initial movement requires a large amount of energy (~2.2eV). However, subsequent movements of the grain boundary unit need a much lower the barrier (<0.5eV).  Our results suggest that if the first movement could be stimulated, then the rest of the grain boundary has a high chance of following that motion to directionally diffuse to the edge of the h-BN sheet. These results provide some guidelines for removing grain boundaries in the h-BN which, when defect-laden, is a promising material for both catalysis and single photon emission.