Browsing by Author "Krueger, David, committee member"

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Open Access
Development and advancement of thin CdTe-based solar cells for photovoltaic performance improvements
(Colorado State University. Libraries, 2020) Bothwell, Alexandra, author; Sites, James, advisor; Krueger, David, committee member; Gelfand, Martin, committee member; Sampath, Walajabad, committee member; Topič, Marko, committee member
Photovoltaic technologies, with an essentially infinite energy source, large total capacity, and demonstrated cost competitiveness, are well-positioned to meet growing global demand for clean energy. Cadmium-telluride (CdTe) thin-film photovoltaics is advantageous primarily for its direct optical band gap (approximately 1.48 eV) which is well-matched to the standard AM 1.5G solar spectrum, and its high absorption coefficient. These advantages, in tandem with innovations in fabrication and photovoltaic design in the past decade, have significantly increased CdTe photovoltaic device performance and reduced cost. Major advances in CdTe device performance have been achieved through improved current collection and fill factor, however, the open-circuit voltage (VOC) of CdTe devices remains limited compared to the band gap-determined maximum achievable VOC. The voltage deficit could be minimized through various approaches, and this work addresses it through progressive structural changes to a thin CdTe device. Absorbers of less than 2 µm were pursued for ultimate electron-reflector devices which incorporate a wide band-gap material behind the absorber to induce a back-surface field via a back-side conduction-band offset for improved VOC. An optimized and stable base structure is necessary to quantify characteristics and improvements in progressive devices with additional material layers. Thin, 0.4-1.2 µm CdTe absorber devices were optimized and demonstrated respectable and repeatable performance parameters, and a maximum efficiency of 15.0% was achieved with only 1.2 µm CdTe. Capacitance measurements also showed that thinner devices had fully-depleted absorbers into forward bias. To improve device performance through increased current collection, a 1.4-eV band gap CdSeTe layer was introduced as an additional absorber material preceding CdTe. Prior understanding of the effects of the additional CdSeTe material was incomplete, and this work deepens and expands this understanding. Performance improvement was achieved for thin, 1.5-µm absorber devices with no intentional interdiffusion of the CdSeTe and CdTe. The importance of the CdSeTe thickness was demonstrated, where performance was consistently reduced for CdSeTe thickness greater than CdTe thickness, independent of CdSe composition in the close-space sublimation (CSS) CdSeTe source material. Longer time-resolved photoluminescence (TRPL) tail lifetimes in CdSeTe/CdTe devices compared to CdTe devices suggested better bulk properties, and current loss analysis showed that CdSeTe is the dominant absorber in 0.5-µm CdSeTe/1.0-µm devices. 1.5-µm CdSeTe/CdTe devices demonstrated increased current collection and 30-mV voltage deficit reduction due to the 100-meV narrower band gap of CdSeTe compared to CdTe and passivating effects of selenium, for an ultimate efficiency improvement to 15.6%. Lattice-constant matching to CdTe and wide, ~1.8-eV band-gap requirements directed the selection of CdMgTe as the electron-reflector layer. CdMgTe was incorporated into the CdSeTe/CdTe device structure first through CSS, but sputter deposition was found to be more favorable to address the material complexities of CdMgTe (temperature-induced magnesium diffusion and CdCl2 passivation loss, doping, and MgO formation), and produced higher performing CdMgTe electron-reflector devices. Low substrate temperature achievable in sputtered CdMgTe deposition proved the greatest advantage over CSS-CdMgTe: CdCl2 passivation and magnesium can be appropriately maintained with a corresponding maintenance of device performance, whereas temperature-induced CdCl2 passivation loss or magnesium loss will occur for CSS-deposited CdMgTe with incumbent performance reduction. Through low-temperature depositions, doping optimization, and small structural adjustments, 16.0% efficiency was achieved with CdMgTe sputtered on 0.5-µm CdSeTe/1.0-µm CdTe absorbers, the highest-known CdMgTe electron-reflector device performance. The CdMgTe and non-CdMgTe-containing device VOC's suggested that electron reflection was enacted with partial success for the sputter CdMgTe-incorporated structure, but the significant improvements expected based on simulation have not been realized due to MgO formation and a negative valence-band offset which somewhat impedes hole transport to the back contact. Suggestions to overcome or circumvent these limitations are presented and discussed in the context of progressed understanding of CdMgTe electron-reflector devices.
Open Access
Development of a high energy diode-pumped chirped pulse amplification laser system for driving soft x-ray lasers
(Colorado State University. Libraries, 2012) Reagan, Brendan A., author; Rocca, Jorge, advisor; Menoni, Carmen, committee member; Marconi, Mario, committee member; Krueger, David, committee member
There is significant interest in the development of compact high repetition rate soft x-ray lasers for applications. This dissertation describes the development of a high energy, laser diode pumped, chirped pulse amplification laser system for driving soft x-ray lasers in the 10-20 nm spectral region. The compact laser system combines room temperature and cryogenically-cooled Yb:YAG amplifier to produce 1.5 Joule pulses at up to 50 Hz repetition rate. Pulse compression results in 1 J pulses of 5 ps duration. A room temperature pre-amplifier maintains bandwidth for short pulse operation and a novel cryogenic cooling technique for the power amplifier was developed to enable high average power operation of this laser. This laser was used to drive a soft x-ray laser on the 18.9 nm line of nickel-like molybdenum. This is the first demonstration of a soft x-ray laser driven by an all diode-pumped laser.
Open Access
Dynamics of low-density ultracold plasmas in externally applied electric and magnetic fields
(Colorado State University. Libraries, 2013) Wilson, Truman M., author; Roberts, Jacob, advisor; Krueger, David, committee member; Lundeen, Stephen, committee member; Yalin, Azer, committee member
The experiments described in this thesis were focused on the influence of external electric and magnetic fields and electron evaporation on the evolution of ultracold plasmas (UCPs). The UCPs were created from the photoionization of 85Rb which was first captured in a magneto-optical trap (MOT) and then magnetically trapped and transferred by a set of magnetic coils attached to a motorized translation stage to a region of the vacuum chamber with a set of electrodes. The first experiment studied the response of the UCP to sharp electric field pulses, which included 2 cycles of a sine wave pulse. These experiments showed a resonant response to the 2 cycles of rf that was density dependent, but was not a collision based mechanism. Instead, the response was caused by a rapid energy transfer to individual electrons through the collective motion of the electron cloud in the UCP. This density-dependent response allowed us to develop a technique for measuring the expansion rate of the UCPs in our system. It was also observed in second set of experiments that electron evaporation from the UCP had a significant effect on the amount of energy that was transferred to the ions to drive the UCP expansion. Model calculations show that we should expect electron evaporation to have a more significant influence on the UCP expansion rate at the relatively low densities of the UCPs that we create compared to other experiments. By modeling electron evaporation during expansion, our data are consistent with evaporation reducing the electron temperature significantly, which lowers the overall UCP expansion rate. In addition to these studies, we also performed an experiment in which it was observed that in the presence of a magnetic field there was a significant increase in the initial UCP expansion rate coupled with a deceleration of the ion expansion at later times in the UCP evolution. Our observations to date are consistent with the magnetic field influencing electron screening and UCP formation. By restricting the electrons motion in the direction transverse to the magnetic field lines to circular orbits around the magnetic field lines, the electrons cannot move appropriately to screen the internal radial electric fields produced by the excess of ions. Studies of this effect are currently under way. Future studies include direct measurements of the electron temperature and collision rates between the components of the UCP as we move towards trapping the UCP in a Penning trap.
Open Access
Implicit solvation using the superposition approximation applied to many-atom solvents with static geometry and electrostatic dipole
(Colorado State University. Libraries, 2020) Mattson, Max Atticus, author; Krummel, Amber T., advisor; McCullagh, Martin, advisor; Szamel, Grzegorz, committee member; Prieto, Amy, committee member; Krueger, David, committee member
Large-scale molecular aggregation of organic molecules, such as perylene diimides, is a phenomenon that continues to generate interest in the ﬁeld of solar light-harvesting. Functionalization of the molecules can lead to diﬀerent aggregate structures which in turn alter the spectroscopic properties of the molecules. To improve the next generation of perylene diimide solar cells a detailed understanding of their aggregation is necessary. A critical aid in understanding the spectroscopic properties of large-scale aggregating systems is molecular simulation. Thus development of an eﬃcient and accurate method for simulating large-scale aggregating systems at dilute concentrations is imperative. The Implicit Solvation Using the Superposition Approximation model (IS-SPA) was originally developed to eﬃciently model nonpolar solvent–solute interactions for chargeless solutes in TIP3P water, improving the eﬃciency of dilute molecular simulations by two orders of magnitude. In the work presented here, IS-SPA is developed for charged solutes in chloroform solvent. Chloroform is the ﬁrst solvent model developed for IS-SPA that is composed of more than one Lennard-Jones potential. Solvent distribution and force histograms were measured from all-atom explicit-solvent molecular dynamics simulations, instead of using analytic functions, and tested for Lennard-Jones sphere solutes of various sizes. The level of detail employed in describing the 3-dimensional structure of chloroform is tested by approximating chloroform as an ellipsoid, spheroid, and sphere by using 3-, 2-, and 1-dimensional distribution and force histograms respectively. A perylene diimide derivative, lumogen orange, was studied for its unfamiliar aggregation mechanism in chloroform and tetrahydrofuran solvents via Fourier-transform infrared and 2dimensional infrared spectroscopies as well as all-atom explicit-solvent molecular dynamics simulations and quantum mechanical frequency calculations. Molecular simulations identiﬁed two categories of likely aggregate dimer structures: the expected -stack structure, and a less familiar edge-sharing structure where the most highly charged atoms of the perylene diimide core are strongly interacting. Quantum mechanical vibrational frequency calculations were performed for various likely dimer aggregate structures identiﬁed in molecular simulation and compared to experimental spectroscopic results. The experimental spectra of the aggregating system share qualities with the edge-sharing dimer frequency calculations however larger aggregate structures should be tested. A violanthrone derivative, violanthrone-79 (V-79), was studied for its diﬀering aggregation mechanisms in chloroform and tetrahydrofuran solvents via Fourier-transform infrared and 2dimensional infrared spectroscopies as well as all-atom explicit-solvent molecular dynamics simulations and quantum mechanical frequency calculations. The -stacking aggregate structure of V-79 is supported by all methods used, however, the type of -stacking orientations are diﬀerent between the two solvents. Chloroform supports parallel -stacked aggregates while tetrahydrofuran supports anti-parallel -stacked aggregates which show diﬀering vibrational energy delocalization between the aggregated molecules. The publications in chapters 3 and 4 demonstrate the power of combining experimental spectroscopy and computational methods like molecular dynamics simulations and quantum mechanical frequency calculations, however, they also show how having larger simulations with multiple solute molecules are needed. This is why developing IS-SPA to be used for these simulations is necessary. Further developments to IS-SPA are discussed regarding the importance of various symmetries of chloroform and the subsequent dimensionalities of the histograms used to describe its distribution and Lennard-Jones force. Two methods for describing the Coulombic forces of chloroform solvation are discussed and tested on oppositely charged Lennard-Jones sphere solutes. The radially symmetric treatment fails to capture the Coulombic forces of the spherical solute system from all-atom explicit-solvent molecular dynamics simulations. A dipole polarization treatment is presented and tested for the charged spherical solute system which better captures the Coulombic forces measured from all-atom explicit-solvent molecular dynamics simulations. Additional considerations for the improvement of IS-SPA and the developments in this work are presented. The dipole polarization approximation outlined in chapter 5 assumes that each chloroform is a static dipole, allowing the dipole magnitude to ﬂuctuate as well as polarize is a more physically rigorous approximation that will likely improve the accuracy of Coulombic forces in IS-SPA. A novel method, drawn from the knowledge gained studying chloroform, for the eﬃcient modeling of new solvent types including ﬂexible solvent molecules in IS-SPA is discussed.
Open Access
Performance and metastability of CdTe solar cells with a Te back-contact buffer layer
(Colorado State University. Libraries, 2017) Moore, Andrew, author; Sites, James, advisor; Krueger, David, committee member; de la Venta, Jose, committee member; Sampath, W. S., committee member
Thin-film CdTe photovoltaics are quickly maturing into a viable clean-energy solution through demonstration of competitive costs and performance stability with existing energy sources. Over the last half decade, CdTe solar technology has achieved major gains in performance; however, there are still aspects that can be improved to progress toward their theoretical maximum efficiency. Perhaps equally valuable as high photovoltaic efficiency and a low levelized cost of energy, is device reliability. Understanding the root causes for changes in performance is essential for accomplishing long-term stability. One area for potential performance enhancement is the back contact of the CdTe device. This research incorporated a thin-film Te-buffer layer into the contact structure, between the CdTe and contact metal. The device performance and characteristics of many different back contact configurations were rigorously studied. CdTe solar cells fabricated with the Te-buffer contact showed short-circuit current densities and open-circuit voltages that were on par with the traditional back-contacts used at CSU. However, the Te-buffer contact typically produced ~2% larger fill-factors on average, leading to greater conversation efficiency. Furthermore, using the Te buffer allowed for incorporation of ~50% less Cu, which is used for p-type doping but is also known to decrease lifetime and stability. This resulted in an additional ~3% fill-factor gain with no change in other parameters compared to the standard-Cu treated device. In order to better understand the physical mechanisms of the Te-buffer contact, electrical and material properties of the Te layer were extracted and used to construct a simple energy band diagram. The Te layer was found to be highly p-type (>1018 cm-3) and possess a positive valence-band offset of 0.35-0.40 eV with CdTe. An existing simulation model incorporating the Te-layer properties was implemented and validated by comparing simulated results of CdTe device performance to experimental values. The Te layer improves performance is attributed to a reduction in the downward energy band bending between the CdTe and typical contact metals. The stability, or rather the metastability, of CdTe solar cells was also studied with a focus on the Te back contact. A metastable device has a series of quasi-stable local energy-minimuma which the device may transition among. This work primarily focused on changes, both beneficial and detrimental, caused by diffusion and drift of atoms in the CdTe lattice. As atoms moved and/or became ionized their defect states were shifted, which resulted in changes in the CdTe doping and recombination. Changes in performance for devices in equilibrium and under stress conditions were analyzed by electrical and material characterization. Mobile impurities and mechanisms responsible for the changes were identified---primarily the migration of interstitial Cu and Cl. The stability of CdTe solar cells with different back contacts were compared. It was found that any contact that included the Te layer was almost always more stable than the traditional contact used at CSU, most likely because of less sensitivity to the impurity profiles in the CdTe. Moreover, the Te contact configuration that introduced the least amount of Cu into the CdTe was discovered to be the most stable, both in storage and under stress conditions.
Open Access
Quantifying deep convective influence on the tropical tropopause layer (TTL)
(Colorado State University. Libraries, 2011) Paulik, Laura C., author; Birner, Thomas, advisor; Stephens, Graeme, committee member; Heald, Colette, committee member; Krueger, David, committee member
The transition between the troposphere and the stratosphere is best described as a layer containing both tropospheric and stratospheric characteristics. In the tropics, this region is known as the Tropical Tropopause Layer (TTL). The TTL roughly spans the altitude range of 12-18 km, bounded from above by the cold point tropopause (CPT) and from below by the main convective outflow level. This region is unique in that it is subject to both tropospheric and stratospheric processes (e.g. deep convective transport/the stratospheric circulation). Processes in the TTL set the boundary condition for atmospheric constituents entering the stratosphere. This thesis aims to better quantify deep convective influence on the TTL using two approaches. The first approach investigates TTL ozone using the Southern Hemisphere Additional Ozonesondes (SHADOZ) dataset. Low ozone concentrations in the TTL are indicative of deep convective transport from the boundary layer. A new diagnostic, the "ozone mixing height" is introduced that identifies the maximum altitude in a vertical ozone profile up to which reduced ozone concentrations, typical of transport from the boundary layer are observed. Deep convective temperature and stratification signals in the TTL are quantified using this diagnostic. The second approach collocates deep convective clouds identified by CloudSat 2B-CLDCLASS with COSMIC GPS temperature profiles. Results suggest the convective temperature signal is large-scale and persistent in time; however, it is only the convective events that penetrate into the upper half of the TTL that have a significant impact on TTL temperature. Finally, CloudSat 2B-CLDCLASS data is used in conjunction with the SHADOZ dataset revealing that deep convective cloud top heights appear to be well approximated by the level of neutral buoyancy.
Open Access
Spatially-selective optical pumping cooling and two-isotope collision-assisted Zeeman cooling
(Colorado State University. Libraries, 2014) Wilson, Rebekah Ferrier, author; Roberts, Jacob, advisor; Krueger, David, committee member; Lundeen, Stephen, committee member; Marconi, Mario, committee member
In this thesis I describe two non-evaporative cooling schemes for cooling Rb atoms. The first is a Sisyphus-like ultracold gas cooling scheme called Spatially-selecTive Optical Pumping (STOP) cooling. In principle, STOP cooling has wide applicability to both atoms and molecules. STOP cooling works by exploiting the fact that atoms or molecules in a confining potential can be optically pumped out of an otherwise dark state in a spatially-selective way. Selecting atoms or molecules for optical pumping out of a dark state in a region of high potential energy and then waiting a fixed time after the optical pumping allows for the creation of a group of high kinetic energy atoms or molecules moving in a known direction. These can then be slowed using external fields (such as the scattering force from a resonant laser beam) and optically pumped back into the dark state, cooling the gas and closing the cooling cycle. I present theoretical modeling of the STOP cooling technique, including predictions of achievable cooling rates. I have conducted an experimental study of the cooling technique for a single cooling cycle, observing one dimensional cooling rates in excess of 100 micro-K per second in an ultracold gas of 87Rb atoms. I will also comment on the prospects for improving the cooling performance beyond that presented in this work. The second cooling scheme I investigated is called Two-Isotope Collision Assisted Zeeman (2-CAZ) cooling. Through a combination of spin-exchange collisions in a magnetic field and optical pumping, it is possible to cool a gas of atoms without requiring the loss of atoms from the gas. I investigated 2-CAZ cooling using 85Rb and 87Rb. I was able to experimentally confirm that the measured 2-CAZ cooling rate agreed with a cooling rate predicted though a simple analytic model. As part of the measured cooling rate, I quantitatively characterized the heating rates associated with our actual implementation of this cooling technique and found hyperfine-changing collisions to be a significant limitation for the 85/87Rb gas mixture. Possible improvements to this experiment will be discussed as well as the prospects for improved cooling performance using an atom without hyperfine structure as the optically pumped atom.
Open Access
Studies of magnetization dynamics in magnetic recording media and patterned yttrium iron garnet films
(Colorado State University. Libraries, 2018) Richardson, Daniel, author; Wu, Mingzhong, advisor; de la Venta Granda, Jose, committee member; Kabos, Pavel, committee member; Krueger, David, committee member; Marconi, Mario, committee member
Exchange coupling and damping are studied in magnetic media materials for applications in current perpendicular magnetic recording (PMR) technology as well as future heat assisted magnetic recording (HAMR) media technology. Damping and exchange coupling are directly related to magnetization switching time in writing operation and the signal-to-noise ratio in reading, both critical to the performance of hard disk drives. Intergranular exchange is studied in current PMR media to see how exchange is altered in the presence of SiO2 based segregant. By varying the segregant by as much as 30%, there is strong tunability of the exchange field between the grains. The damping in future FePt-based HAMR media is studied near the curie temperature (725 K) of FePt where the writing stage in the recording media takes place. The trends of ferromagnetic resonance (FMR) linewidth varying with the sample temperature, the volume fraction of carbon in the media, and the angle of the external field indicate that the overall damping includes strong contributions from intrinsic magnon-electron scattering as well as extrinsic two-magnon scattering between the grains. Interlayer exchange coupling and damping were studied in magnetic layered systems consisting of a soft ferromagnetic transition metal or alloy layer and a hard FePt layer at room and elevated temperatures. It was found that exchange coupling and damping are strongly dependent on temperature, the soft layer thickness, and the choice of material of the soft layer. Spin waves are studied in the linear and non-linear regimes using magnonic crystals consisting of yttrium iron garnet (YIG) thin film strips with periodic etched lines or periodic metallic lines deposited on top of the YIG strip, as well as YIG strips with randomly spaced metallic lines deposited on top. The various media provide ways of controlling the dispersion by altering the interference of the spin waves, allowing for a wide range of interesting phenomenon to be observed. Spin-wave fractals are observed for the first time in a YIG strip with periodic etched lines. The etched lines serve as position dependent potentials to increase dispersion in the YIG strip large enough for fractal formation in the nonlinear regime. This is also the first time fractals of any type that have been observed without the formation of time-domain solitons. Spin-wave localization is observed in the linear regime for the first time in YIG strips with randomly spaced metallic lines where the metallic lines serve as potential barriers for causing spin wave interference. Magnonic crystals consisting of YIG strips with periodically spaced metallic lines are used to compare a standing wave state with the localized state. The localized state is much stronger and much more confined to a smaller physical space than the standing wave state.
Open Access
The effects of structural confinement and thermal profiles on propagating spin waves
(Colorado State University. Libraries, 2018) Riley, Grant Alston, author; Buchanan, Kristen S., advisor; Neilson, James, committee member; Krueger, David, committee member; Patton, Carl, committee member
Spintronics is a growing field that relies on the spin degree of freedom in the form of spin currents instead of electronic charge to transmit and process information. There are many advantages to spin-based devices including scalability, a wide range of host materials including insulators, and almost no energy loss due to Joule heating. Spin angular momentum can be transmitted in the form of spin-polarized currents that flow through a metal, pure spin currents, or in the form of spin waves, disturbances in the magnetization state that can propagate and hence can carry energy. If such a spin-based paradigm is to be realized, there are many open questions that must be addressed. Two questions of particular importance are: how can short wavelength spin waves that are needed for information transmission be controllably generated? and once generated, how can these spin waves be modified and controlled? This thesis focusses on answering both of these questions through the investigation of spin waves in two different types of samples, patterned microstructures and thin continuous films, performed using Brillouin light scattering (BLS) spectroscopy. In the first experiment, the possibility of generating short wavelength spin waves by dynamically exciting a non-uniform magnetic state called the antivortex (AV) in a Permalloy microstructure is explored. Frequency scans were performed to identify a spectrum of high-frequency modes of the AV state. These modes were then individually mapped out by pumping at the frequency of the mode and performing spatially-resolved BLS scans. Comparing the experimental results with dispersion curves and micromagnetic simulations reveals that some of most prominent modes involve coupling of the AV dynamics to propagating spin waves in the adjacent nanowires highlighting the fact that the local magnetization state has a significant effect on the spin wave dynamics. Due to the natural way that an antivortex state can be incorporated into a nanowire network, this spin configuration may be useful as a means to generate or control spin waves for applications. In the second study we explore the possibility of modifying the propagation characteristics of both spin waves and spin caustic beams, which could be highly useful in spin-wave-based logic devices, using non-uniform thermal gradients up to 4.5 K/mm. These experiments were performed in a yttrium iron garnet (YIG) thin film - a model system for studying spin waves due to extremely low damping characteristics. An intricate diamond-shaped propagation pattern was observed and explained using the dispersion manifold for the YIG film and considering the range of wavevectors excited by the antenna. Significant modifications to the propagation characteristics such as beam angle, temporal pulse shape, mode profiles, and group velocity were observed as spin waves travelled into heated regions. These results will serve to broaden the understanding of how heat can be used to affect and control spin waves.
Open Access
Tropical cyclone kinetic energy and structure evolution in the HWRFx model
(Colorado State University. Libraries, 2011) Maclay, Katherine S., author; Vonder Haar, Thomas, advisor; DeMaria, Mark, advisor; Schubert, Wayne, committee member; Schumacher, Russ, committee member; Krueger, David, committee member
Tropical cyclones exhibit significant variability in their structure, especially in terms of size and asymmetric structures. The variations can influence subsequent evolution in the storm as well as its environmental impacts and play an important role in forecasting. This study uses the Hurricane Weather Research and Forecasting Experimental System (HWRFx) to investigate the horizontal and vertical structure of tropical cyclones. Five real data HWRFx model simulations from the 2005 Atlantic tropical cyclone season (two of Hurricanes Emily and Wilma, and one of Hurricane Katrina) are used. Horizontal structure is investigated via several methods: the decomposition of the integrated kinetic energy field into wavenumber space, composite analysis of the wind fields, and azimuthal wavenumber decomposition of the tangential wind field. Additionally, a spatial and temporal decomposition of the vorticity field to study the vortex Rossby wave contribution to storm asymmetries with an emphasis on azimuthal wavenumber-2 features is completed. Spectral decomposition shows that the average low level kinetic energy in azimuthal wavenumbers 0, 1 and 2 are 92%, 6%, and 1.5% of the total kinetic energy. The kinetic energy in higher wavenumbers is much smaller. Analysis also shows that the low level kinetic energy wavenumber 1 and 2 components can vary between 0.3-36.3% and 0.1-14.1% of the total kinetic energy, respectively. The asymmetries associated with storm motion, environmental shear, and the relative orientation of these vectors are examined. A composite analysis shows a dominant wavenumber-1 asymmetry associated with the storm motion and shear vectors. For storm motion the asymmetry is located in the right front quadrant relative to the motion vector with a magnitude exceeding 2.5 m/s, and for shear the asymmetry is located 90⁰ left of the shear vector with a magnitude exceeding 5 m/s. The locations of these wavenumber-1 asymmetries are consistent with the findings of previous studies. Further composite analysis of the asymmetries associated with the relative orientation of the storm motion and shear vectors reveals that when the vectors are aligned versus opposed the wavenumber-1 asymmetries have roughly equivalent magnitude but very different azimuthal location (when aligned the maximum is located in the left front quadrant relative to the storm motion, and when opposed is located nearly 90⁰ to the right of the storm motion). The magnitude of the wavenumber-2 asymmetries is much larger when the storm motion and shear vectors are aligned (exceeding 2.5 m/s) than when they are opposed (~0.5 m/s). The results indicate that shear induced asymmetries extend more deeply through the troposphere than storm motion induced asymmetries. Furthermore, the vortex Rossby wave analysis provides compelling evidence to support their existence and their contribution to the wavenumber-2 asymmetries in the simulated storms. The vertical structure is studied in terms of the relationship between the size of the radius of maximum wind and its slope, and whether the radius of maximum wind is well approximated by a constant absolute angular momentum surface. The impacts of environmental shear on these relationships are specifically examined. While there is some evidence to suggest that moderate shear can have a constructive influence on the storm, the relationships between the radius of maximum wind and its slope, and the slopes of the radius of maximum wind and the constant absolute angular momentum surface deteriorate quickly with increasing shear. The vertical warm core structure of the tropical cyclones is investigated in terms of the height and magnitude of the primary and any possible secondary warm core features (as measured in terms of the temperature anomalies). The purpose of this analysis is to determine the general warm core structure and establish if there are any significant trends with respect to storm evolution, environmental shear, or storm intensity change. It is determined that there is often a dual warm core structure with a primary warm anomaly located in the 5-10 km height region with a magnitude generally between 5-10 K and a secondary warm anomaly located either below 5 km or in the 16-19 km region of lesser magnitude. The height and magnitude of the primary warm core is not found to be linked to the environmental shear and is weakly correlated to the 6 h averaged intensity change. Finally, the cold pool structure of the storms is briefly examined. The simulated storms exhibit persistent cold pockets at low levels that are likely related to evaporation of rain. An investigation of whether these cold pockets are enhanced in association with extratropical transition processes reveals a notable decrease in the low level cold anomalies for the simulation experiencing extratropical transition.