Atomic, Molecular and Optical Physics Commons^™

Neutron Energy Tuning Assemblies For Nuclear Weapon Environment Applications At The National Ignition Facility, Nicholas J. Quartemont

Theses and Dissertations

An energy tuning assembly was developed to spectrally shape the National Ignition Facility deuterium-tritium fusion neutron source to a notional thermonuclear and prompt fission neutron spectrum to fulfill neutron source capability gaps. The experimental neutron environment was characterized with activation dosimetry, neutronics and covariance models, and unfolded to determine the as-fielded neutron spectrum. The first energy tuning assembly was demonstrated to create synthetic spectrally accurate post-detonation fission products, enhancing U.S. technical nuclear forensics capabilities. ATHENA, a second-generation energy tuning assembly, was also optimized to meet similar objectives, but the new platform neutron fluence efficiency was increased by a factor of …

Nonlinear Optical Studies Of Interfacial Ferroelectricity And Strain Distribution In Perovskite Dielectric Films, Tony Le

Dissertations, Theses, and Capstone Projects

Dielectric and ferroelectric perovskite films have been model energy storage structures for their low-dielectric loss, extremely high charge-discharge speed, and good temperature stability, yet there is still much to understand about the material’s limitations. This dissertation presents a detailed understanding of the strain-induced ferroelectricity at the boundary between a strontium titanate (SrTiO₃) ultrathin film epitaxially grown on a germanium (Ge) substrate through optical second harmonic generation (SHG), and the polydomain distribution in the Zr-doped BaTiO₃ (BZT) films by time-resolved pump-probe spectroscopy.

First, SHG measurements were performed to reveal interfacial ferroelectricity in the epitaxial SrTiO₃/Ge (100) …

Molecular Interfaces And Heterogeneous Bubble Nucleation From Heated Surfaces At Nanoscale, Manish Gupta

Dissertations - ALL

Heat transfer from a solid surface to fluid occurs in numerous applications, such as boilers, refrigerators, power electronics, etc., and include various underlying phenomena of thin-film evaporation, boiling, condensation, surface wetting, and droplet evaporation. Several studies show that heat transfer can be enhanced significantly by incorporating micro and nanoscale features onto surfaces. Phase change heat transfer plays an important role in dissipating energy from hot surfaces and distributing it to bulk liquid due to high latent heat of liquids. Boiling, a phase change heat transfer phenomenon, happens when the surface is heated to a temperature above the saturation temperature of …

Dicationic Stilbazolium Salts: Structural, Thermal, Optical, And Ionic Conduction Properties, Pradip K. Bhowmik, Jung J. Koh, David King, Haesook Han, Benoît Heinrich, Bertrand Donnio, Daniel Zaton, Alfonso Martinez-Felipe

Chemistry and Biochemistry Faculty Research

Two series of new dicationic stilbazolium salts containing tosylate and triflimide counterions, respectively, were synthesized and characterized by spectroscopic techniques and elemental analysis. Despite of their promesogenic structures, none of these salts are mesomorphous, and instead they solely exhibit crystalline polymorphism, as deduced from differential scanning calorimetry, polarizing optical microscopy and variable temperature X-ray measurements. These salts were also found to be highly thermally stable with decomposition temperatures occurring well above 300 °C, and up to 367 °C for the triflimide salts, as determined by thermogravimetric analysis. UV–Vis absorption and photoluminescent properties were examined in both solution and in the …

High Sensitivity Multi-Axes Rotation Sensing Using Large Momentum Transfer Point Source Atom Interferometry, Jinyang Li, Gregório R. M. Da Silva, Wayne Cheng-Wei Huang, Mohamed Fouda, Jason Bonacum, Timothy L. Kovachy, Selim M. Shahriar

Department of Physics and Astronomy: Faculty Publications

A point source interferometer (PSI) is a device where atoms are split and recombined by applying a temporal sequence of Raman pulses during the expansion of a cloud of cold atoms behaving approximately as a point source. The PSI can work as a sensitive multi-axes gyroscope that can automatically filter out the signal from accelerations. The phase shift arising from the rotations is proportional to the momentum transferred to each atom from the Raman pulses. Therefore, by increasing the momentum transfer, it should be possible to enhance the sensitivity of the PSI. Here, we investigate the degree of enhancement in …

A Combined Theoretical And Photoelectron Spectroscopy Study Of Al3hn- (N=1-9) Clusters, Jing Xu, Xinxing Zhang, Haopeng Wang, Lijuan Fu, Xiang Li, Andrej Grubisic, Rachel M. Harris, Bryan Eichhorn, Gerd Gantefoer, Yihong Ding, Boggavarapu Kiran, Anil K. Kandalam, Kit H. Bowen

Physics & Engineering Faculty Publications

Combined photoelectron spectroscopic experiments and computational studies have been performed on Al3Hn- (n=1-9) clusters. Three modes of hydrogen bonding to the Al-3 moiety have been observed: terminal, bridging, and capping. Among various hydrides, Al3H5- and Al3H8- clusters have highest HOMO-LUMO gap and largest electron affinity, respectively. Our studies indicate that as the number of hydrogen atoms increase the presence of AlH2 groups, representing the tetrahedral coordination of the Al atom, which in turn led to the stoichiometric ring structure.

Modeling Of Argon Bombardment And Densification Of Low Temperature Organic Precursors Using Reactive Md Simulations And Machine Learning, Kwabena Asante-Boahen

Graduate Theses/Dissertations

In this study, an important aspect of the synthesis process for a-BxC:Hy was systematically modeled by utilizing the Reactive Molecular Dynamics (MD) in modeling the argon bombardment from the orthocarborane molecules as the precursor. The MD simulations are used to assess the dynamics associated with the free radicals that result from the ion bombardment. By applying the Data Mining/Machine Learning analysis into the datasets generated from the large reactive MD simulations, I was able to identify and quality the kinetics of these radicals. Overall, this approach allows for a better understanding of the overall mechanism at the atomistic level of …

Beam Formation And Vernier Steering Off Of A Rough Surface, Eric K. Nagamine, Kenneth W. Burgi, Samuel D. Butler

Faculty Publications

Wavefront shaping can refocus light after it reflects from an optically rough surface. One proposed use case of this effect is in indirect imaging; if any rough surface could be turned into an illumination source, objects out of the direct line of sight could be illuminated. In this paper, we demonstrate the superior performance of a genetic algorithm compared to other iterative feedback-based wavefront shaping algorithms in achieving reflective inverse diffusion for a focal plane system. Next, the ability to control the pointing direction of the refocused beam with high precision over a narrow angular range is demonstrated, though the …

Electronic, Magnetic, And Structural Properties Of Comnvsb, Adam Ramker, Pavel Lukashev Ph.D.

Summer Undergraduate Research Program (SURP) Symposium

Background

• Spin degree of freedom in electronic devices.
• Ideal candidate – room temperature half-metal.
• Heusler compounds attractive because of high Curie temperature
• Various mechanisms altering degree of spin polarization – mechanical strain, structural disorder, temperature, termination surface/interface, etc.
• CoMnVSb: nearly a spin gapless semiconductor.

Chemical Substitution Induced Half-Metallicity In Crmnsb0.5si0.5, Lukas Stuelke, Pavel Lukashev Ph.D.

Summer Undergraduate Research Program (SURP) Symposium

Background

⮚Research on magnetic materials for potential applications in spin-based electronics: one of the most active fields in academia and industry. ⮚High degree of spin polarization – wanted in spintronics. ⮚Spintronics – an emerging technology utilizing a spin degree of freedom. ⮚Various mechanisms alter degree of spin polarization – mechanical strain, structural disorder, temperature, termination surface/interface, etc. ⮚Magnetic materials that conduct electrons of only one spin are called half-metals, and have a great potential in spintronics.

54fe(D,P)55fe Single Neutron Transfer Presentation, Matthew Quirin, Raymond Saunders

Physics and Astronomy Presentations

During our summer research at the John D Fox Laboratory, we used the 9 MV Tandem van de Graaff accelerator and the Super Enge Split-Pole Spectrograph to make measurements of the neutron transfer reaction 54Fe(d,p) 55Fe to observe and explore excited states of 55Fe and shell structure beyond the magic number N=28. We have created momentum spectra and angular distribution plots of the protons from the reaction which will be analyzed to determine the angular momentum values of states and single-neutron energies in 55Fe in an effort to better understand nuclear structure.

54fe(D,P)55fe Single Neutron Transfer, Matthew Quirin, Raymond Saunders

Physics and Astronomy Summer Fellows

During our summer research at the John D Fox Laboratory, we used the 9 MV Tandem van de Graaff accelerator and the Super Enge Split-Pole Spectrograph to make measurements of the neutron transfer reaction 54Fe(d,p) 55Fe to observe and explore excited states of 55Fe and shell structure beyond the magic number N=28. We have created momentum spectra and angular distribution plots of the protons from the reaction which will be analyzed to determine the angular momentum values of states and single-neutron energies in 55Fe in an effort to better understand nuclear structure.

Fabrication And Characterization Of Photodetector Devices Based On Nanostructured Materials: Graphene And Colloidal Nanocrystals, Wafaa Gebril

Graduate Theses and Dissertations

Photodetectors are devices that capture light signals and convert them into electrical signals. High performance photodetectors are in demand in a variety of applications, such as optical communication, security, and environmental monitoring. Among many appealing nanomaterials for novel photodetection devices, graphene and semiconductor colloidal nanocrystals are promising candidates because of their desirable and unique properties compared to conventional materials.

Photodetector devices based on different types of nanostructured materials including graphene and colloidal nanocrystals were investigated. First, graphene layers were mechanically exfoliated and characterized for device fabrication. Self-powered few layers graphene phototransistors were studied. At zero drain voltage bias and room …

Evaluation Of Log P, Pka, And Log D Predictions From The Sampl7 Blind Challenge, Teresa Danielle Bergazin, Nicolas Tielker, Yingying Zhang, Junjun Mao, M. R. Gunner, Karol Francisco, Carlo Ballatore, Stefan M. Kast, David L. Mobley

Publications and Research

The Statistical Assessment of Modeling of Proteins and Ligands (SAMPL) challenges focuses the computational modeling community on areas in need of improvement for rational drug design. The SAMPL7 physical property challenge dealt with prediction of octanol-water partition coefficients and pK_a for 22 compounds. The dataset was composed of a series of N-acylsulfonamides and related bioisosteres. 17 research groups participated in the log P challenge, submitting 33 blind submissions total. For the pK_a challenge, 7 different groups participated, submitting 9 blind submissions in total. Overall, the accuracy of octanol-water log P predictions in the SAMPL7 challenge was …

Kapitza-Dirac Blockade: A Universal Tool For The Deterministic Preparation Of Non-Gaussian Oscillator States, Wayne Cheng-Wei Huang, Herman Batelaan, Markus Arndt

Department of Physics and Astronomy: Faculty Publications

Harmonic oscillators count among the most fundamental quantum systems with important applications in molecular physics, nanoparticle trapping, and quantum information processing. Their equidistant energy level spacing is often a desired feature, but at the same time a challenge if the goal is to deterministically populate specific eigenstates. Here, we show how interference in the transition amplitudes in a bichromatic laser field can suppress the sequential climbing of harmonic oscillator states (Kapitza-Dirac blockade) and achieve selective excitation of energy eigenstates, cat states, and other non-Gaussian states. This technique can transform the harmonic oscillator into a coherent two-level system or be used …

Publications Of Paul D. Burrow, Paul Burrow

Paul Burrow Publications

A chronological list of 111 publications (1967-2014), with links to public access copies of 50 or more in the UNL Digital Commons. Updated as of 6/18/2021.

Self-Contained Photon Coincidence Counting With Ni Myrio Ecosystem, Georges Oates Larsen, Andres H. La Rosa

University Honors Theses

Digital coincidence counting units (CCU) have made experimental verification of fundamental quantum mechanical principles financially accessible to undergraduate level teaching programs. However, recent implementations of these systems are not easily ported to National Instruments (NI) FPGAs, making them unsuitable for physics departments that have heavily invested in the NI ecosystem. Therefore, there is clear need for a detailed implementation based on an NI FPGA. We present a formal description of one such implementation, based on the NI myRIO (NI's lower-cost, student-oriented offering) which achieves 6.9 ns minimum guaranteed-distinguishable delay and 32.2 MHz peak coincidence counting rate with four input channels …

Protein Motifs For Proton Transfers That Build The Transmembrane Proton Gradient, Divya Kaur, Umesh Khaniya, Yingying Zhang, M. R. Gunner

Publications and Research

Biological membranes are barriers to polar molecules, so membrane embedded proteins control the transfers between cellular compartments. Protein controlled transport moves substrates and activates cellular signaling cascades. In addition, the electrochemical gradient across mitochondrial, bacterial and chloroplast membranes, is a key source of stored cellular energy. This is generated by electron, proton and ion transfers through proteins. The gradient is used to fuel ATP synthesis and to drive active transport. Here the mechanisms by which protons move into the buried active sites of Photosystem II (PSII), bacterial RCs (bRCs) and through the proton pumps, Bacteriorhodopsin (bR), Complex I and Cytochrome …

Characterizing The Vibrational Spectra Of Hydrogen Bonded Systems With Molecular Dynamics Simulations And Quantum Chemical Methods, Dalton Boutwell

Master of Science in Chemical Sciences Theses

We apply and assess the utility of DMD for the purpose of investigating complex spectral features in N₂H⁺···OC, N₂D⁺···OC, C₂O₄H^-, C₂O₄D^- and (HCOOH)₂. The proton transfer as a vibrational motion consists of diffuse qualities that can be accounted for with classical and quantum chemical analyses. Classical approaches yield a wealth of information about vibrational spectra at a reduced cost, as in the case of previously investigated N₄H⁺. The isoelectronic N₂H⁺···OC has …

The Design Of The N2edm Experiment, N. J. Ayres, G. Ban, L. Bienstman, G. Bison, K. Bodek, V. Bondar, T. Bouillaud, E. Chanel, J. Chen, P.-J. Chiu, B. Clément, C. B. Crawford, M. Daum, B. Dechenaux, C. B. Doorenbos, S. Emmenegger, L. Ferraris-Bouchez, M. Fertl, A. Fratangelo, P. Flaux

Physics and Astronomy Faculty Publications

We present the design of a next-generation experiment, n2EDM, currently under construction at the ultracold neutron source at the Paul Scherrer Institute (PSI) with the aim of carrying out a high-precision search for an electric dipole moment of the neutron. The project builds on experience gained with the previous apparatus operated at PSI until 2017, and is expected to deliver an order of magnitude better sensitivity with provision for further substantial improvements. An overview is of the experimental method and setup is given, the sensitivity requirements for the apparatus are derived, and its technical design is described.