+publisher:"University of Colorado" +contributor:("Daniel S. Dessau")

University of Colorado

1. Plumb, Nicholas Clark. New Insights into High-Tc Superconductivity from Angle-Resolved Photoemission at Low Photon Energies.

Degree: PhD, Physics, 2011, University of Colorado

URL: https://scholar.colorado.edu/phys_gradetds/32

► Angle-resolved photoemission spectroscopy (ARPES) is one of the most direct and powerful probes for studying the physics of solids. ARPES takes a "snapshot" of… (more)

▼ Angle-resolved photoemission spectroscopy (ARPES) is one of the most direct and powerful probes for studying the physics of solids. ARPES takes a "snapshot" of electrons in momentum space (k-space) to reveal details of the dispersion relation E(k), as well as information about the lifetimes of interacting quasiparticles. From this we learn not only where the electrons live, but also, if we are crafty, what they are doing. Beginning with work by our group in 2006 using a 6-eV laser, ARPES experiments have begun to make use of a new, low photon energy regime (roughly hν = 6-9 eV). These low photon energies give drastic improvements in momentum resolution, photoelectron escape depths, and overall spectral sharpness. This has led to several important new findings in the intensively-studied problem of high-temperature superconductivity. This thesis will focus on two of the latest results from our group using low-energy ARPES (LE-ARPES) to study the cuprate high-Tc superconductor Bi2Sr2CaCu2O8+δ (Bi2212). The first of these is an investigation into the nature of many-body interactions at a well-known energy scale (~60-70 meV) where the dispersion shows a large bend, or "kink". Using LE-ARPES measurements, the k-dependence of this kink is investigated in unprecedented detail. An attempt is then made to map the feature's k evolution into the scattering q-space of boson dispersions. In our analysis, the q-dispersion of the kink bears more resemblance to dispersive spin excitations than phonons – a surprising finding in light of previous evidence that the the kink originates from interactions with phonons. However, phonons cannot be ruled out, and the results may hint that both types of interactions contribute to the main nodal kink. A second result is the discovery of a new ultralow (< 10 meV) energy scale for electron interactions, corresponding to a distinct, smaller kink in the electron dispersion. The temperature and doping dependence of this feature show not only that it turns on near Tc – signalling a possible relation to the mechanism of high-Tc superconductivity – but also that it leads to a subtle breakdown of the so-called "universal" Fermi velocity vF along nodes of the anisotropic superconducting gap. Moreover, vF is found to depend quite strongly on temperature, which may be an important factor in the physics of cuprates. Advisors/Committee Members: Daniel S. Dessau, Kyle McElroy, Dmitry Reznik.

Subjects/Keywords: angle-resolved photoemission; cuprates; electronic structure; high-temperature superconductivity; Condensed Matter Physics; Physics

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APA (6^th Edition):

Plumb, N. C. (2011). New Insights into High-Tc Superconductivity from Angle-Resolved Photoemission at Low Photon Energies. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/phys_gradetds/32

Chicago Manual of Style (16^th Edition):

Plumb, Nicholas Clark. “New Insights into High-Tc Superconductivity from Angle-Resolved Photoemission at Low Photon Energies.” 2011. Doctoral Dissertation, University of Colorado. Accessed March 08, 2021. https://scholar.colorado.edu/phys_gradetds/32.

MLA Handbook (7^th Edition):

Plumb, Nicholas Clark. “New Insights into High-Tc Superconductivity from Angle-Resolved Photoemission at Low Photon Energies.” 2011. Web. 08 Mar 2021.

Vancouver:

Plumb NC. New Insights into High-Tc Superconductivity from Angle-Resolved Photoemission at Low Photon Energies. [Internet] [Doctoral dissertation]. University of Colorado; 2011. [cited 2021 Mar 08]. Available from: https://scholar.colorado.edu/phys_gradetds/32.

Council of Science Editors:

Plumb NC. New Insights into High-Tc Superconductivity from Angle-Resolved Photoemission at Low Photon Energies. [Doctoral Dissertation]. University of Colorado; 2011. Available from: https://scholar.colorado.edu/phys_gradetds/32

University of Colorado

2. Cavanagh, Andrew S. Advanced Lithium Ion Battery Materials Prepared with Atomic Layer Deposition.

Degree: PhD, Physics, 2011, University of Colorado

URL: https://scholar.colorado.edu/phys_gradetds/39

► As the world consumes the dwindling supply of fossil fuels, an alternative to gasoline powered vehicles will become necessary. Lithium ion batteries (LIBs) are… (more)

▼ As the world consumes the dwindling supply of fossil fuels, an alternative to gasoline powered vehicles will become necessary. Lithium ion batteries (LIBs) are emerging as the dominant power source for portable electronics, and are seen as a promising energy source in the development of electric vehicles. Current LIB technology is not well suited for vehicles, increases in the energy density, power density and durability are needed before LIB are ready for widespread use in electric vehicles. LiCoO₂ and graphite are the dominant cathode and anode active materials, respectively in LIBs. On the cathode side, instabilities in LiCoO₂ can lead to the deterioration of the LIB. Decomposition of electrolyte on the graphite anode surface to form a solid-electrolyte interphase (SEI) consumes lithium from the cathode resulting in a lower battery capacity. Instabilities in the in the SEI can result in catastrophic battery failure. Previous studies have employed metal oxides films, typically grown with wet chemical techniques, to stabilize LiCoO₂ and mitigate the formation of the SEI on graphite. The thicknesses of films grown with wet chemical techniques was typically ∼50-1000 Å. In order to achieve higher power densities, the particle size of LIB active materials is being scaled down. As active materials get smaller the mass contribution of a protective film can become a significant fraction of the total mass. Atomic layer deposition (ALD) has been used to grow ultra thin films of Al₂O₃ on LiCoO₂ and graphite. By altering the interaction between the active material and the battery electrolyte it was possible to improve the stability of both LiCoO₂ and graphite electrodes in LIBs. In the case of graphite, the Al₂O₃ film may be thought of as an artificial SEI. During the initial charge-discharge cycle of a LIB, the electrolyte decomposes on the anode to form the SEI. The formation of the SEI is believed to prevent further decomposition of the electrolyte on the anode surface. The SEI contains electrolyte decomposition products including Li₂CO₃, Li₂O, LiOH, LiF and R-OLi. In order to grow a truly artificial SEI on the graphite anode, i.e. grow a film that mimics the SEI that forms during charge-discharge cycling, new ALD chemistries for the growth of Li₂CO₃ and LiOH have been developed. The ALD of an artificial SEI layer may limit lithium loss and improve the capacity stability during charge-discharge cycles. Advisors/Committee Members: Steven M. George, Daniel S. Dessau, Charles T. Rogers.

Subjects/Keywords: Materials Science and Engineering; Physical Chemistry

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APA (6^th Edition):

Cavanagh, A. S. (2011). Advanced Lithium Ion Battery Materials Prepared with Atomic Layer Deposition. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/phys_gradetds/39

Chicago Manual of Style (16^th Edition):

Cavanagh, Andrew S. “Advanced Lithium Ion Battery Materials Prepared with Atomic Layer Deposition.” 2011. Doctoral Dissertation, University of Colorado. Accessed March 08, 2021. https://scholar.colorado.edu/phys_gradetds/39.

MLA Handbook (7^th Edition):

Cavanagh, Andrew S. “Advanced Lithium Ion Battery Materials Prepared with Atomic Layer Deposition.” 2011. Web. 08 Mar 2021.

Vancouver:

Cavanagh AS. Advanced Lithium Ion Battery Materials Prepared with Atomic Layer Deposition. [Internet] [Doctoral dissertation]. University of Colorado; 2011. [cited 2021 Mar 08]. Available from: https://scholar.colorado.edu/phys_gradetds/39.

Council of Science Editors:

Cavanagh AS. Advanced Lithium Ion Battery Materials Prepared with Atomic Layer Deposition. [Doctoral Dissertation]. University of Colorado; 2011. Available from: https://scholar.colorado.edu/phys_gradetds/39

University of Colorado

3. Wang, Qiang. Angle-Resolved Photoemission Spectroscopy Studies on Cuprate and Iron-Pnictide High-Tc Superconductors.

Degree: PhD, Physics, 2011, University of Colorado

URL: https://scholar.colorado.edu/phys_gradetds/49

► The exotic physics in condensed matter systems, such as High-Tc superconductivity in cuprates and the newly discovered iron-pnictide superconductors, is due to the properties… (more)

▼ The exotic physics in condensed matter systems, such as High-Tc superconductivity in cuprates and the newly discovered iron-pnictide superconductors, is due to the properties of the elementary excitations and their interactions. The "one-electron removal spectral function" measured by angle-resolved photoemission spectroscopy (ARPES) provides a chance to understand these excitations and reveal the mechanism of the high-Tc superconductivity. In most cases, ARPES studies focus on the excitations very close to the Fermi level (usually within tens to hundreds of meVs). In this region, by presuming that the correlation effect is not too strong, we usually can describe the correlated electron system in terms of well-defined "quasiparticles" , i.e. electrons dressed with a manifold of excited states. Then the spectral function measured by ARPES can be separated into two parts: a coherent pole part that contains the information about the dispersion relation E(k) and the lifetime "tau" of the quasiparticles, which is usually the main subject of ARPES studies; and an incoherent smooth part without poles which also contains important information about the many-body interactions in the system but is usually overlooked by physicists due to the lack of analysis techniques and theoretical understanding. In this thesis, we present ARPES measurement on the cuprate High-Tc superconductors PbxBi2-xSr2CaCu2O8 (Pb-Bi2212) and Bi2Sr2CaCu2O8+d (Bi2212) and the iron-pnictide High-Tc superconductor's parent compound CaFe2As2 (Ca122) and BaFe2As2 (Ba122). For Pb-Bi2212 and Bi2212 materials, whose quasiparticle dispersions have already been extensively studied, our work focuses on the incoherent part of the spectral function. By introducing a new ARPES lineshape analysis technique, we separate out the sharp coherent peaks from the higher energy incoherent "background" portions and uncover a new type of scaling behavior of the incoherent portions. In particular, the fraction of weight that is incoherent is found to be intimately linked to the energy of the dispersive coherent feature through a simple quadratic relationship with no special energy scales. This behavior in concert with strong momentum-dependent matrix element effects gives rise to the heavily studied "waterfall" behavior in cuprate superconductors. For the newly discovered Ca122and Ba122 materials, whose intrinsic electronic structure is still missing, our studies aim at understanding its quasiparticle dispersion relation E(k) and the Fermi surface geometry. We observed unequal dispersions and FS geometries along the orthogonal Fe-Fe bond directions. Comparing with the optimized LDA calculations, an orbital-dependent band shifting is introduced to get better agreement, which is consistent with the development of orbital ordering. More interestingly, unidirectional straight and at FS segments are observed near the zone center, which indicates the existence of a unidirectional charge density wave order. Therefore, our studies indicate that beyond the well-known spin density wave… Advisors/Committee Members: Daniel S. Dessau, Dmitry Reznik, Scott Bunch.

Subjects/Keywords: ARPES; Cuprate Superconductors; Electronic Structure; High Energy Anomaly; High Temperature Superconductors; Iron-pnictide Superconductors; Condensed Matter Physics; Physics

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APA (6^th Edition):

Wang, Q. (2011). Angle-Resolved Photoemission Spectroscopy Studies on Cuprate and Iron-Pnictide High-Tc Superconductors. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/phys_gradetds/49

Chicago Manual of Style (16^th Edition):

Wang, Qiang. “Angle-Resolved Photoemission Spectroscopy Studies on Cuprate and Iron-Pnictide High-Tc Superconductors.” 2011. Doctoral Dissertation, University of Colorado. Accessed March 08, 2021. https://scholar.colorado.edu/phys_gradetds/49.

MLA Handbook (7^th Edition):

Wang, Qiang. “Angle-Resolved Photoemission Spectroscopy Studies on Cuprate and Iron-Pnictide High-Tc Superconductors.” 2011. Web. 08 Mar 2021.

Vancouver:

Wang Q. Angle-Resolved Photoemission Spectroscopy Studies on Cuprate and Iron-Pnictide High-Tc Superconductors. [Internet] [Doctoral dissertation]. University of Colorado; 2011. [cited 2021 Mar 08]. Available from: https://scholar.colorado.edu/phys_gradetds/49.

Council of Science Editors:

Wang Q. Angle-Resolved Photoemission Spectroscopy Studies on Cuprate and Iron-Pnictide High-Tc Superconductors. [Doctoral Dissertation]. University of Colorado; 2011. Available from: https://scholar.colorado.edu/phys_gradetds/49

University of Colorado

4. Gray, Jason Michael. Gallium Nitride Nanowire Electromechanical Resonators.

Degree: PhD, Physics, 2011, University of Colorado

URL: https://scholar.colorado.edu/phys_gradetds/53

► Nanoscale mechanical resonators are of great interest for high-resolution sensing applications, where the small resonator mass and high quality factor (Q, defined as resonance… (more)

▼ Nanoscale mechanical resonators are of great interest for high-resolution sensing applications, where the small resonator mass and high quality factor (Q, defined as resonance frequency f₀ over full width at half maximum power) lead to unprecedented sensitivity. Here, we investigate gallium nitride (GaN) nanowire (NW) resonators. The single-crystal, c-axis NWs are 5 μm - 20 μm long, with diameters from 50 nm - 500 nm, and grow essentially free of defects. Our initial experiments involve measuring the resonances of as-grown NWs in a scanning electron microscope, where we observe exceptionally high Q values of 104 - 105, one to two orders of magnitude higher than most NWs of comparable size. Using a single NW as a mass sensor, we then demonstrate a sub-attogram mass sensitivity. To provide a more flexible measurement technique that avoids electron-microscope detection, we fabricate doubly clamped NWs with an entirely electronic drive and readout scheme using a combination of lithographic patterning and dielectrophoresis. An electrostatic gate induces vibration, while readout utilizes the piezoresistivity of GaN. Observed resonances range from 9-36 MHz with Q values typically around 103 at room temperature and 10-4 Pa. We use the behavior of f₀ and Q to sense the NW's local environment, such as the additional sources of energy dissipation not present in the as-grown NWs. By cooling the device to 8 K, Q increases by an order of magnitude to above 104, with a highest value to date of 26,000 under vacuum. We explore additional NW properties through the thermal noise in the NW's mechanical motion and the exponential decay of mechanical motion in the presence of burst drive. Finally, we investigate the low-frequency 1/f parameter noise displayed by f₀. We show that the noise in f₀ is consistent with noise in the NW's resistance leading to temperature noise from local Joule heating, which in turn generates resonance frequency noise. For sensor applications, there will be optimal drive conditions that balance the f₀ noise with the signal-to-noise ratio of the system. With these insights, along with the simple drive and readout technique, these GaN-NW doubly clamped resonators have significant potential for high-resolution sensing applications. Advisors/Committee Members: Charles T. Rogers, Daniel S. Dessau, Kyle P. McElroy.

Subjects/Keywords: 1/f noise; gallium nitride; nanowire; piezoresistance; resonator; sensor; Condensed Matter Physics; Physics

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APA (6^th Edition):

Gray, J. M. (2011). Gallium Nitride Nanowire Electromechanical Resonators. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/phys_gradetds/53

Chicago Manual of Style (16^th Edition):

Gray, Jason Michael. “Gallium Nitride Nanowire Electromechanical Resonators.” 2011. Doctoral Dissertation, University of Colorado. Accessed March 08, 2021. https://scholar.colorado.edu/phys_gradetds/53.

MLA Handbook (7^th Edition):

Gray, Jason Michael. “Gallium Nitride Nanowire Electromechanical Resonators.” 2011. Web. 08 Mar 2021.

Vancouver:

Gray JM. Gallium Nitride Nanowire Electromechanical Resonators. [Internet] [Doctoral dissertation]. University of Colorado; 2011. [cited 2021 Mar 08]. Available from: https://scholar.colorado.edu/phys_gradetds/53.

Council of Science Editors:

Gray JM. Gallium Nitride Nanowire Electromechanical Resonators. [Doctoral Dissertation]. University of Colorado; 2011. Available from: https://scholar.colorado.edu/phys_gradetds/53

University of Colorado

5. Li, Haoxiang. Angle-resolved Photoemission Spectroscopy Study of High Temperature Superconductor Cuprate, and Potential High Temperature Superconductors K-Doped p-Terphenyl and Trilayer Nickelate.

Degree: PhD, 2017, University of Colorado

URL: https://scholar.colorado.edu/phys_gradetds/226

► The macroscopic quantum phenomenology of superconductivity has attracted broad interest from both scientific research and applications. Many exotic physics found in the first high… (more)

▼ The macroscopic quantum phenomenology of superconductivity has attracted broad interest from both scientific research and applications. Many exotic physics found in the first high T_C superconductor family cuprate remain unsolved even after 30 years of intense study. Angle-Resolved Photoemission Spectroscopy (ARPES) provides the direct probe to the major information of the electronic interactions, which plays the key role in these exotic physics including high T_C superconductivity. ARPES is also the best tool to study the electronic structure in materials that potentially hold high T_C superconductivity, providing insight for materials research and design. In this thesis, we present the ARPES study of the cuprate high T_C superconductor Pb doped Bi₂Sr₂CaCu₂O_8+δ, and potential high T_C superconductors K doped p-terphenyl, and trilayer nickelate La₄Ni₃O₁₀. For Pb doped Bi2212, our study focuses on the key part of the electronic interactions – the self-energies. With the development of a novel 2-dimensional analysis technique, we present the first quantitative extraction of the fully causal complex self-energies. The extracted information reveals a conversion of the diffusive strange-metal correlations into a coherent highly renormalized state at low temperature followed by the enhancement of the number of states for pairing. We then further show how this can lead to a strong positive feedback effect that can stabilize and strengthen superconducting pairing. In K doped p-terphenyl, we discover low energy spectral gaps that persist up to 120 K, consistent with potential Meissner effect signal from previous studies. Among a few potential origins for these gaps, we argue that the electron pairing scenario is most likely. For La₄Ni₃O₁₀, we present the Fermiology and electron dynamics of this material, and they show certain similarities to the cuprate electronic structure, as well as a few unique features. Advisors/Committee Members: Daniel S. Dessau, Dmitry Reznik, Gang Cao, Rahul Nandkishore, Josef Michl.

Subjects/Keywords: superconductivity; angle-resolved photoemission spectroscopy; superconductivity; Condensed Matter Physics; Materials Science and Engineering

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APA (6^th Edition):

Li, H. (2017). Angle-resolved Photoemission Spectroscopy Study of High Temperature Superconductor Cuprate, and Potential High Temperature Superconductors K-Doped p-Terphenyl and Trilayer Nickelate. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/phys_gradetds/226

Chicago Manual of Style (16^th Edition):

Li, Haoxiang. “Angle-resolved Photoemission Spectroscopy Study of High Temperature Superconductor Cuprate, and Potential High Temperature Superconductors K-Doped p-Terphenyl and Trilayer Nickelate.” 2017. Doctoral Dissertation, University of Colorado. Accessed March 08, 2021. https://scholar.colorado.edu/phys_gradetds/226.

MLA Handbook (7^th Edition):

Li, Haoxiang. “Angle-resolved Photoemission Spectroscopy Study of High Temperature Superconductor Cuprate, and Potential High Temperature Superconductors K-Doped p-Terphenyl and Trilayer Nickelate.” 2017. Web. 08 Mar 2021.

Vancouver:

Li H. Angle-resolved Photoemission Spectroscopy Study of High Temperature Superconductor Cuprate, and Potential High Temperature Superconductors K-Doped p-Terphenyl and Trilayer Nickelate. [Internet] [Doctoral dissertation]. University of Colorado; 2017. [cited 2021 Mar 08]. Available from: https://scholar.colorado.edu/phys_gradetds/226.

Council of Science Editors:

Li H. Angle-resolved Photoemission Spectroscopy Study of High Temperature Superconductor Cuprate, and Potential High Temperature Superconductors K-Doped p-Terphenyl and Trilayer Nickelate. [Doctoral Dissertation]. University of Colorado; 2017. Available from: https://scholar.colorado.edu/phys_gradetds/226

University of Colorado

6. Parham, Stephen Patrick. Electron Dynamics in High Temperature Superconductors Studied Using Angle and Time-Resolved Photoemission Spectroscopy.

Degree: PhD, Physics, 2015, University of Colorado

URL: https://scholar.colorado.edu/phys_gradetds/147

► High-Temperature Superconductivity (HTSC) has inspired decades of research since its discovery in 1986 but remains an enigmatic subject to this day. At the heart… (more)

Subjects/Keywords: Correlated Electrons; Photoemission Spectroscopy; Superconductivity; Condensed Matter Physics

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APA (6^th Edition):

Parham, S. P. (2015). Electron Dynamics in High Temperature Superconductors Studied Using Angle and Time-Resolved Photoemission Spectroscopy. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/phys_gradetds/147

Chicago Manual of Style (16^th Edition):

Parham, Stephen Patrick. “Electron Dynamics in High Temperature Superconductors Studied Using Angle and Time-Resolved Photoemission Spectroscopy.” 2015. Doctoral Dissertation, University of Colorado. Accessed March 08, 2021. https://scholar.colorado.edu/phys_gradetds/147.

MLA Handbook (7^th Edition):

Parham, Stephen Patrick. “Electron Dynamics in High Temperature Superconductors Studied Using Angle and Time-Resolved Photoemission Spectroscopy.” 2015. Web. 08 Mar 2021.

Vancouver:

Parham SP. Electron Dynamics in High Temperature Superconductors Studied Using Angle and Time-Resolved Photoemission Spectroscopy. [Internet] [Doctoral dissertation]. University of Colorado; 2015. [cited 2021 Mar 08]. Available from: https://scholar.colorado.edu/phys_gradetds/147.

Council of Science Editors:

Parham SP. Electron Dynamics in High Temperature Superconductors Studied Using Angle and Time-Resolved Photoemission Spectroscopy. [Doctoral Dissertation]. University of Colorado; 2015. Available from: https://scholar.colorado.edu/phys_gradetds/147

University of Colorado

7. Millican, Samantha Lynn. Alloy and Defect Properties of Oxides and Nitrides for Energy Applications.

Degree: PhD, 2019, University of Colorado

URL: https://scholar.colorado.edu/chbe_gradetds/138

► Throughout history societal advancement has been dictated largely by the development of new materials – from iron for weaponry and tools to silicon circuits… (more)

▼ Throughout history societal advancement has been dictated largely by the development of new materials – from iron for weaponry and tools to silicon circuits for computing. Today, the physical properties of many predominant and emerging technologies rely on the departure from the ideal structure through the incorporation of defects and alloying. This thesis reports on the investigation of several systems whose properties are driven by defect formation and alloying. Spinel aluminate active materials, FeAl2O4 and CoxFe1-xAl2O4, were evaluated for solar thermochemical hydrogen (STCH) production using computational and experimental techniques Hercynite (FeAl2O4) was shown to be viable for STCH for the first time with a significantly higher H2 production than the cobalt alloy. DFT calculations demonstrated the importance of charged antisite-vacancy defect pairs in the redox behavior in these materials. A solid-state kinetic analysis was performed on hercynite and four cobalt-hercynite alloys and showed that the oxidation reaction in each of the materials was best represented by a first-order reaction model. The computed rate constants, activation energies, and pre-exponential factors were found to all increase with increasing cobalt content, indicating that cobalt may increase the reaction rate by increasing the number of active sites (vacancies) at the surface of the catalyst. Hercynite was further studied for its viability in an isothermal on-sun STCH process at the NREL High Flux Solar Furnace. The total H2 production and mass-weighted H2 production both surpassed the production of the benchmark ceria material in similar on-sun experiments, and the particles were demonstrated to be structurally and compositionally stable over multiple days of on-sun testing. Ceramic fuel cells offer an attractive method for the efficient utilization of H2 with no greenhouse gas emissions. Four complex perovskites used as cathode materials (Ba1-xSrxFe1-yZnyO3, Ba1-xSrxCo1-yFeyO3, and BaCo1-x-y-zFexZryYzO3) were studied computationally to predict their defect properties at elevated temperatures and various gas partial pressures. To do this, a new method for predicting equilibrium defect concentrations and defect formation energies beyond the dilute limit was developed and applied. Computationally-predicted and experimentally-measured oxygen nonstoichiometry were found to match within a factor of two. The Al1−xScxN system is an interesting case study in heterostructural alloying as a tool for property improvement. In this system, wurtzite-structured AlN is alloyed with rocksalt-structured ScN to produce a dramatic increase in the piezoelectric response. DFT calculations were utilized in conjunction with combinatorial thin-film synthesis to provide a unique perspective on this system. Calculations demonstrated that the combination of structural frustration and a flattened free-energy landscape lead to a substantial increase in the electromechanical response of the alloy near the heterostructural phase transition… Advisors/Committee Members: Charles B. Musgrave, Alan W. Weimer, Aaron M. Holder, James W. Medlin, Daniel S. Dessau.

Subjects/Keywords: material development; alloying; composition; stability; Chemical Engineering; Materials Science and Engineering

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APA (6^th Edition):

Millican, S. L. (2019). Alloy and Defect Properties of Oxides and Nitrides for Energy Applications. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/chbe_gradetds/138

Chicago Manual of Style (16^th Edition):

Millican, Samantha Lynn. “Alloy and Defect Properties of Oxides and Nitrides for Energy Applications.” 2019. Doctoral Dissertation, University of Colorado. Accessed March 08, 2021. https://scholar.colorado.edu/chbe_gradetds/138.

MLA Handbook (7^th Edition):

Millican, Samantha Lynn. “Alloy and Defect Properties of Oxides and Nitrides for Energy Applications.” 2019. Web. 08 Mar 2021.

Vancouver:

Millican SL. Alloy and Defect Properties of Oxides and Nitrides for Energy Applications. [Internet] [Doctoral dissertation]. University of Colorado; 2019. [cited 2021 Mar 08]. Available from: https://scholar.colorado.edu/chbe_gradetds/138.

Council of Science Editors:

Millican SL. Alloy and Defect Properties of Oxides and Nitrides for Energy Applications. [Doctoral Dissertation]. University of Colorado; 2019. Available from: https://scholar.colorado.edu/chbe_gradetds/138

University of Colorado

8. Semonin, Octavi Escala. Multiple Exciton Generation in Quantum Dot Solar Cells.

Degree: PhD, Physics, 2012, University of Colorado

URL: https://scholar.colorado.edu/phys_gradetds/66

► Photovoltaics are limited in their power conversion efficiency (PCE) by very rapid relaxation of energetic carriers to the band edge. Therefore, photons from the… (more)

Subjects/Keywords: carrier multiplication; excitonic emigration; nanocrystals; optical modeling; photovoltaics; surface chemistry; Chemistry; Materials Science and Engineering; Physics

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APA (6^th Edition):

Semonin, O. E. (2012). Multiple Exciton Generation in Quantum Dot Solar Cells. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/phys_gradetds/66

Chicago Manual of Style (16^th Edition):

Semonin, Octavi Escala. “Multiple Exciton Generation in Quantum Dot Solar Cells.” 2012. Doctoral Dissertation, University of Colorado. Accessed March 08, 2021. https://scholar.colorado.edu/phys_gradetds/66.

MLA Handbook (7^th Edition):

Semonin, Octavi Escala. “Multiple Exciton Generation in Quantum Dot Solar Cells.” 2012. Web. 08 Mar 2021.

Vancouver:

Semonin OE. Multiple Exciton Generation in Quantum Dot Solar Cells. [Internet] [Doctoral dissertation]. University of Colorado; 2012. [cited 2021 Mar 08]. Available from: https://scholar.colorado.edu/phys_gradetds/66.

Council of Science Editors:

Semonin OE. Multiple Exciton Generation in Quantum Dot Solar Cells. [Doctoral Dissertation]. University of Colorado; 2012. Available from: https://scholar.colorado.edu/phys_gradetds/66

University of Colorado

9. Dai, Jixia. Scanning Tunneling Microscopy Studies of Layered Correlated Electron Systems: Transition Metal Dichalcogenides and Iridates.

Degree: PhD, Physics, 2013, University of Colorado

URL: https://scholar.colorado.edu/phys_gradetds/84

► Strongly correlated electron problems, including high temperature superconductivity, colossal magneto-resistivity, charge-density wave, heavy fermion phenomena, etc., have been major research focuses in condensed-matter physics… (more)

Subjects/Keywords: Iridate; Mott insulator; Scanning Tunneling Microscope; Transition metal dichalcogenide; Condensed Matter Physics

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APA (6^th Edition):

Dai, J. (2013). Scanning Tunneling Microscopy Studies of Layered Correlated Electron Systems: Transition Metal Dichalcogenides and Iridates. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/phys_gradetds/84

Chicago Manual of Style (16^th Edition):

Dai, Jixia. “Scanning Tunneling Microscopy Studies of Layered Correlated Electron Systems: Transition Metal Dichalcogenides and Iridates.” 2013. Doctoral Dissertation, University of Colorado. Accessed March 08, 2021. https://scholar.colorado.edu/phys_gradetds/84.

MLA Handbook (7^th Edition):

Dai, Jixia. “Scanning Tunneling Microscopy Studies of Layered Correlated Electron Systems: Transition Metal Dichalcogenides and Iridates.” 2013. Web. 08 Mar 2021.

Vancouver:

Dai J. Scanning Tunneling Microscopy Studies of Layered Correlated Electron Systems: Transition Metal Dichalcogenides and Iridates. [Internet] [Doctoral dissertation]. University of Colorado; 2013. [cited 2021 Mar 08]. Available from: https://scholar.colorado.edu/phys_gradetds/84.

Council of Science Editors:

Dai J. Scanning Tunneling Microscopy Studies of Layered Correlated Electron Systems: Transition Metal Dichalcogenides and Iridates. [Doctoral Dissertation]. University of Colorado; 2013. Available from: https://scholar.colorado.edu/phys_gradetds/84

University of Colorado

10. Moody, Galan. Confinement Effects on the Electronic and Optical Properties of Semiconductor Quantum Dots Revealed with Two-Dimensional Coherent Spectroscopy.

Degree: PhD, Physics, 2013, University of Colorado

URL: https://scholar.colorado.edu/phys_gradetds/87

► Confinement of electron-hole pairs (excitons) in semiconductor quantum dots (QDs) leads to novel quantum phenomena, tunable optical properties and enhanced Coulomb interactions, all of… (more)

▼ Confinement of electron-hole pairs (excitons) in semiconductor quantum dots (QDs) leads to novel quantum phenomena, tunable optical properties and enhanced Coulomb interactions, all of which are sensitive to the size, shape and material composition of the QDs. This thesis discusses our pursuit in unraveling the complex interrelation between morphology of a QD and its electronic and optical properties. A series of epitaxially-grown semiconductor nanostructures with different QD sizes and composition is studied using optical two-dimensional coherent spectroscopy (2DCS). With the unique capabilities of unambiguously identifying coupling between resonances, isolating quantum pathways and revealing homogeneous dephasing information in heterogeneous systems, 2DCS is a powerful tool for studying QD ensembles. Of paramount importance is the exciton homogeneous line width, which is inversely proportional to the dephasing time. As the dephasing time sets the duration for which coherence is maintained, knowledge of the principal dephasing mechanisms in QDs is essential. 2D spectra of excitons in weakly-confining GaAs QDs reveal that elastic exciton-phonon coupling and intra-dot exciton-exciton interactions are responsible for line width broadening beyond the radiative limit, and the interaction strength of both mechanisms increases for decreasing QD size. These results are compared to those obtained from InAs QDs, which exhibit an order-of-magnitude larger confinement, to illustrate the role quantum confinement plays in exciton dephasing. The lowest energy optical transitions in semiconductor QDs are modified by confinement-enhanced Coulomb interactions, such as exchange-mediated coupling between excitons and correlation effects that can lead to bound and anti-bound states of two excitons. 2D spectra particularly sensitive to these interactions reveal that the electron and hole wave functions – and therefore the strength of Coulomb interactions – are sensitive to variations in QD size for the GaAs ensemble. In the InAs QDs, however, the wave functions are remarkably independent of the details of confinement, leading to similar electronic and optical properties for all QDs. To provide additional insight, the spectra are modeled using perturbative density matrix calculations, and the results are compared to many-body calculations to reveal the significance of the strength and nature of Coulomb interactions on the optical properties of QDs. Advisors/Committee Members: Steven T. Cundiff, David M. Jonas, Daniel S. Dessau, Andreas Becker, Markus B. Raschke.

Subjects/Keywords: Four-Wave Mixing; Multi-Dimensional Coherent Spectroscopy; Quantum Dots; Semiconductor Nanostructures; Ultrafast Coherent Spectroscopy; Physics

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APA (6^th Edition):

Moody, G. (2013). Confinement Effects on the Electronic and Optical Properties of Semiconductor Quantum Dots Revealed with Two-Dimensional Coherent Spectroscopy. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/phys_gradetds/87

Chicago Manual of Style (16^th Edition):

Moody, Galan. “Confinement Effects on the Electronic and Optical Properties of Semiconductor Quantum Dots Revealed with Two-Dimensional Coherent Spectroscopy.” 2013. Doctoral Dissertation, University of Colorado. Accessed March 08, 2021. https://scholar.colorado.edu/phys_gradetds/87.

MLA Handbook (7^th Edition):

Moody, Galan. “Confinement Effects on the Electronic and Optical Properties of Semiconductor Quantum Dots Revealed with Two-Dimensional Coherent Spectroscopy.” 2013. Web. 08 Mar 2021.

Vancouver:

Moody G. Confinement Effects on the Electronic and Optical Properties of Semiconductor Quantum Dots Revealed with Two-Dimensional Coherent Spectroscopy. [Internet] [Doctoral dissertation]. University of Colorado; 2013. [cited 2021 Mar 08]. Available from: https://scholar.colorado.edu/phys_gradetds/87.

Council of Science Editors:

Moody G. Confinement Effects on the Electronic and Optical Properties of Semiconductor Quantum Dots Revealed with Two-Dimensional Coherent Spectroscopy. [Doctoral Dissertation]. University of Colorado; 2013. Available from: https://scholar.colorado.edu/phys_gradetds/87

University of Colorado

11. Calleja, Eduardo Manuel. Uncovering the Nature of Various Scattering Sites, Extended and Magnetic, in Bi2Sr2CaCu2O8+5 Using Atomic Resolved Spectroscopy.

Degree: PhD, Physics, 2013, University of Colorado

URL: https://scholar.colorado.edu/phys_gradetds/93

► The superconducting cuprates represent one of the most intriguing condensed matter systems due to their potential to impact future technologies. As such they have… (more)

▼ The superconducting cuprates represent one of the most intriguing condensed matter systems due to their potential to impact future technologies. As such they have garnered a substantial amount of theoretical and experimental interest over the last 27 years. In spite of this fact, many questions remain unanswered such as the nature of the superconducting pairing mechanism and the origin of the structure of their phase diagram. Spectroscopic Imagining Scanning Tunneling Microscopy (SI-STM) has proven to be an extremely useful probe for studying these materials due to the fact that SI-STM allows for the simultaneous measurement of the real space electronic states with atomic precision and the nature of the momentum K-space states. In this thesis the design and construction of a 5K SI-STM designed for looking at cleavable surfaces, such as the superconducting cuprates, is presented. The k-space nature of the electronic states on Bi2212, as measured by SI-STM, seems to indicate that there is a portion of the Fermi surface which does not super conduct. However, evidence from other probes is mixed. In this thesis, a framework which explains how these “Fermi Arcs” can arise from experimental effects is presented. Followed by an experiment on Bi2212 that shows how one could mistakenly see this “Fermi Arc” signal by adjusting simple experimental dials. In addition, in this thesis we present a comprehensive study of Bi2212 samples where Fe has been substituted for Cu in the CuO plane. This study reveals a highly localized bound state, with the density of states showing a large asymmetry favoring the hole side. The density of states can be interpreted within a co-tunneling picture which is only valid if the impurity is coupled to the conduction electrons resulting in a local Kondo-like effect. This is the first time a Kondo-like impurity is observed in a d-wave superconductor. Comparisons to experiments where Kondo impurities are observed in s-wave superconductors are presented as well. Advisors/Committee Members: Kyle P. McElroy, Minhyea Lee, Charles Roger, Scott Bunch, Daniel S. Dessau.

Subjects/Keywords: Bi2212; Cuprates; Magnetic; STM; superconductors; Condensed Matter Physics; Physics

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Calleja, E. M. (2013). Uncovering the Nature of Various Scattering Sites, Extended and Magnetic, in Bi2Sr2CaCu2O8+5 Using Atomic Resolved Spectroscopy. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/phys_gradetds/93

Chicago Manual of Style (16^th Edition):

Calleja, Eduardo Manuel. “Uncovering the Nature of Various Scattering Sites, Extended and Magnetic, in Bi2Sr2CaCu2O8+5 Using Atomic Resolved Spectroscopy.” 2013. Doctoral Dissertation, University of Colorado. Accessed March 08, 2021. https://scholar.colorado.edu/phys_gradetds/93.

MLA Handbook (7^th Edition):

Calleja, Eduardo Manuel. “Uncovering the Nature of Various Scattering Sites, Extended and Magnetic, in Bi2Sr2CaCu2O8+5 Using Atomic Resolved Spectroscopy.” 2013. Web. 08 Mar 2021.

Vancouver:

Calleja EM. Uncovering the Nature of Various Scattering Sites, Extended and Magnetic, in Bi2Sr2CaCu2O8+5 Using Atomic Resolved Spectroscopy. [Internet] [Doctoral dissertation]. University of Colorado; 2013. [cited 2021 Mar 08]. Available from: https://scholar.colorado.edu/phys_gradetds/93.

Council of Science Editors:

Calleja EM. Uncovering the Nature of Various Scattering Sites, Extended and Magnetic, in Bi2Sr2CaCu2O8+5 Using Atomic Resolved Spectroscopy. [Doctoral Dissertation]. University of Colorado; 2013. Available from: https://scholar.colorado.edu/phys_gradetds/93

University of Colorado

12. Singh, Rohan. Excitons in Semiconductor Quantum Wells Studied Using Two-Dimensional Coherent Spectroscopy.

Degree: PhD, Physics, 2015, University of Colorado

URL: https://scholar.colorado.edu/phys_gradetds/158

► Correlated electron-hole pairs, or excitons, in semiconductor nanostructures have been studied extensively over the past few decades. The optical response of excitons is complicated… (more)

▼ Correlated electron-hole pairs, or excitons, in semiconductor nanostructures have been studied extensively over the past few decades. The optical response of excitons is complicated due to inhomogeneous broadening, presence of multiple states, and exciton-exciton interactions. In this work we bring new perspectives to exciton physics in semiconductor quantum wells (QWs) through two-dimensional coherent spectroscopy (2DCS). The effect of QW growth direction on the optical properties of excitons is explored by studying (110)-oriented GaAs QWs. The homogeneous and inhomogeneous linewidths of the heavy-hole exciton resonance are measured. By probing the optical nonlinear response for polarization along the in-plane crystal axes [1-10] and [001], we measure different homogeneous linewidths for the two orthogonal directions. This difference is found to be due to anisotropic excitation-induced dephasing, caused by a crystal-axis-dependent absorption coefficient. The extrapolated zero-excitation density homogeneous linewidth exhibits an activation-like temperature dependence. Spectral diffusion of excitons in (001)-oriented QWs has been studied. We show that the spectral diffusion characteristics depend strongly on the sample temperature. Spectral diffusion is generally assumed to follow the strong-redistribution approximation, partly because of lack of any evidence to the contrary. We find that this assumption is violated at low sample temperatures for excitons in QWs; high-energy excitons preferentially relax due to a negligible phonon population at low temperatures. The frequency-frequency correlation function is measured through a numerical fitting procedure to quantify spectral diffusion for sample temperatures >20 K. Exciton-exciton interactions affect the light-matter interactions in QWs significantly. We present an intuitive and simple model for these interactions by treating excitons as interacting bosons. We show that the polarization-dependent exciton dephasing rate in GaAs quantum wells is due to the bosonic character of excitons. We fit slices from simulated spectra to those from the experimentally measured spectra and show that interference between two different quantum mechanical pathways results in a slower dephasing rate for co-circular and co-linear polarization of optical excitation pulses. This interference does not exist for cross-linearly polarized excitation pulses resulting in a faster dephasing rate. Additionally, we were able to separately quantify inter- and intra-mode interactions between excitons through exciton-density-dependent measurements. Advisors/Committee Members: Steven T. Cundiff, Markus B. Raschke, Daniel S. Dessau, Richard P. Mirin, Ralph Jimenez.

Subjects/Keywords: excitons; semiconductor nanostructures; decay processes; quantum well; interactions; excitation; Atomic, Molecular and Optical Physics; Quantum Physics

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Singh, R. (2015). Excitons in Semiconductor Quantum Wells Studied Using Two-Dimensional Coherent Spectroscopy. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/phys_gradetds/158

Chicago Manual of Style (16^th Edition):

Singh, Rohan. “Excitons in Semiconductor Quantum Wells Studied Using Two-Dimensional Coherent Spectroscopy.” 2015. Doctoral Dissertation, University of Colorado. Accessed March 08, 2021. https://scholar.colorado.edu/phys_gradetds/158.

MLA Handbook (7^th Edition):

Singh, Rohan. “Excitons in Semiconductor Quantum Wells Studied Using Two-Dimensional Coherent Spectroscopy.” 2015. Web. 08 Mar 2021.

Vancouver:

Singh R. Excitons in Semiconductor Quantum Wells Studied Using Two-Dimensional Coherent Spectroscopy. [Internet] [Doctoral dissertation]. University of Colorado; 2015. [cited 2021 Mar 08]. Available from: https://scholar.colorado.edu/phys_gradetds/158.

Council of Science Editors:

Singh R. Excitons in Semiconductor Quantum Wells Studied Using Two-Dimensional Coherent Spectroscopy. [Doctoral Dissertation]. University of Colorado; 2015. Available from: https://scholar.colorado.edu/phys_gradetds/158

University of Colorado

13. Weingarten, Daniel Harrison. Experimental Verification of Photon Upconversion Via Cooperative Energy Pooling.

Degree: PhD, Physics, 2017, University of Colorado

URL: https://scholar.colorado.edu/phys_gradetds/228

► Photon upconversion, the process of combining multiple low-energy photons into one higher-energy photon, is a fundamental interaction of light and matter that has applications… (more)

Subjects/Keywords: cooperative energy pooling; energy transfer; organic; photon upconversion; two-photon absorption; Optics; Physics; Power and Energy

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Weingarten, D. H. (2017). Experimental Verification of Photon Upconversion Via Cooperative Energy Pooling. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/phys_gradetds/228

Chicago Manual of Style (16^th Edition):

Weingarten, Daniel Harrison. “Experimental Verification of Photon Upconversion Via Cooperative Energy Pooling.” 2017. Doctoral Dissertation, University of Colorado. Accessed March 08, 2021. https://scholar.colorado.edu/phys_gradetds/228.

MLA Handbook (7^th Edition):

Weingarten, Daniel Harrison. “Experimental Verification of Photon Upconversion Via Cooperative Energy Pooling.” 2017. Web. 08 Mar 2021.

Vancouver:

Weingarten DH. Experimental Verification of Photon Upconversion Via Cooperative Energy Pooling. [Internet] [Doctoral dissertation]. University of Colorado; 2017. [cited 2021 Mar 08]. Available from: https://scholar.colorado.edu/phys_gradetds/228.

Council of Science Editors:

Weingarten DH. Experimental Verification of Photon Upconversion Via Cooperative Energy Pooling. [Doctoral Dissertation]. University of Colorado; 2017. Available from: https://scholar.colorado.edu/phys_gradetds/228

University of Colorado

14. Turgut, Emrah. Studying Laser-Induced Spin Currents Using Ultrafast Extreme Ultraviolet Light.

Degree: PhD, Physics, 2014, University of Colorado

URL: https://scholar.colorado.edu/phys_gradetds/108

► Next-generation magnetic-memory devices and heat-assisted magnetic-recording applications will require a better understanding of magnetic multilayers and their interactions with optical-laser pulses. In this thesis,… (more)

Subjects/Keywords: Femtomagnetism; Magnetic Multilayers; Magnetization; Spintronics; Ultrafast; X-ray; Condensed Matter Physics; Optics

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Turgut, E. (2014). Studying Laser-Induced Spin Currents Using Ultrafast Extreme Ultraviolet Light. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/phys_gradetds/108

Chicago Manual of Style (16^th Edition):

Turgut, Emrah. “Studying Laser-Induced Spin Currents Using Ultrafast Extreme Ultraviolet Light.” 2014. Doctoral Dissertation, University of Colorado. Accessed March 08, 2021. https://scholar.colorado.edu/phys_gradetds/108.

MLA Handbook (7^th Edition):

Turgut, Emrah. “Studying Laser-Induced Spin Currents Using Ultrafast Extreme Ultraviolet Light.” 2014. Web. 08 Mar 2021.

Vancouver:

Turgut E. Studying Laser-Induced Spin Currents Using Ultrafast Extreme Ultraviolet Light. [Internet] [Doctoral dissertation]. University of Colorado; 2014. [cited 2021 Mar 08]. Available from: https://scholar.colorado.edu/phys_gradetds/108.

Council of Science Editors:

Turgut E. Studying Laser-Induced Spin Currents Using Ultrafast Extreme Ultraviolet Light. [Doctoral Dissertation]. University of Colorado; 2014. Available from: https://scholar.colorado.edu/phys_gradetds/108

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