Matching Items (17)
Description
Carbon lacks an extended polyanionic chemistry which appears restricted to carbides with C4-, C22-, and C34- moieties. The most common dimeric anion of carbon atoms is C22- with a triple bond between the two carbon atoms. Compounds containing the dicarbide anion can be regarded as salts of acetylene C2H2 (ethyne) and hence are also called acetylides or ethynides. Inspired by the fact that molecular acetylene undergoes pressure induced polymerization to polyacetylene above 3.5 GPa, it is of particular interest to study the effect of pressure on the crystal structures of acetylides as well. In this work, pressure induced polymerization was attempted with two simple metal acetylides, Li2C2 and CaC2. Li2C2 and CaC2 have been synthesized by a direct reaction of the elements at 800ºC and 1200ºC, respectively. Initial high pressure investigations were performed inside Diamond anvil cell (DAC) at room temperature and in situ Raman spectroscopic measurement were carried out up to 30 GPa. Near 15 GPa, Li2C2 undergoes a transition into a high pressure acetylide phase and around 25 GPa this phase turns amorphous. CaC2 is polymorphic at ambient pressure. Monoclinic CaC2-II does not show stability at pressures above 1 GPa. Tetragonal CaC2-I is stable up to at least 12 GPa above which possibly a pressure-induced distortion occurs. At around 18 GPa, CaC2 turns amorphous. In a subsequent series of experiments both Li2C2 and CaC2 were compressed to 10 GPa in a multi anvil (MA) device and heated to temperatures between 300 and 1100oC for Li2C2, and 300°C to 900°C for CaC2. The recovered products were analyzed by PXRD and Raman spectroscopy. It has been observed that reactions at temperature higher than 900°C were very difficult to control and hitherto only short reaction times could be applied. For Li2C2, a new phase, free of starting material was found at 1100°C. Both the PXRD patterns and Raman spectra of products at 1100oC could not be matched to known forms of carbon or carbides. For CaC2 new reflections in PXRD were visible at 900ºC with the starting material phase.
ContributorsKonar, Sumit (Author) / Häussermann, Ulrich (Thesis advisor) / Seo, Dong (Thesis advisor) / Steimle, Timothy (Committee member) / Wolf, George (Committee member) / Arizona State University (Publisher)
Created2012
Description
Broadband dielectric spectroscopy is a powerful technique for understanding the dynamics in supercooled liquids. It generates information about the timescale of the orientational motions of molecular dipoles within the liquid. However, dynamics of liquids measured in the non-linear response regime has recently become an area of significant interest, because additional information can be obtained compared with linear response measurements.
The first part of this thesis describes nonlinear dielectric relaxation experiments performed on various molecular glass forming-liquids, with an emphasis on the response at high frequencies (excess wing). A significant nonlinear dielectric effect (NDE) was found to persist in these modes, and the magnitude of this NDE traces the temperature dependence of the activation energy. A time resolved measurement technique monitoring the dielectric loss revealed that for the steady state NDE to develop it would take a very large number of high amplitude alternating current (ac) field cycles. High frequency modes were found to be ‘slaved’ to the average structural relaxation time, contrary to the standard picture of heterogeneity. Nonlinear measurements were also performed on the Johari-Goldstein β-relaxation process. High ac fields were found to modify the amplitudes of these secondary modes. The nonlinear features of this secondary process are reminiscent of those found for the excess wing regime, suggesting that these two contributions to dynamics have common origins.
The second part of this thesis describes the nonlinear effects observed from the application of high direct current (dc) bias fields superposed with a small amplitude sinusoidal ac field. For several molecular glass formers, the application of a dc field was found to slow down the system via reduction in configurational entropy (Adam-Gibbs relation). Time resolved measurements indicated that the rise of the non-linear effect is slower than its decay, as observed in the electro-optical Kerr effect. A model was discussed which quantitatively captures the observed magnitudes and time dependencies of the NDE. Asymmetry in these rise and decay times was demonstrated as a consequence of the quadratic field dependence of the entropy change. It was demonstrated that the high bias field modifies the polarization response to the field, even including the zero field limit.
The first part of this thesis describes nonlinear dielectric relaxation experiments performed on various molecular glass forming-liquids, with an emphasis on the response at high frequencies (excess wing). A significant nonlinear dielectric effect (NDE) was found to persist in these modes, and the magnitude of this NDE traces the temperature dependence of the activation energy. A time resolved measurement technique monitoring the dielectric loss revealed that for the steady state NDE to develop it would take a very large number of high amplitude alternating current (ac) field cycles. High frequency modes were found to be ‘slaved’ to the average structural relaxation time, contrary to the standard picture of heterogeneity. Nonlinear measurements were also performed on the Johari-Goldstein β-relaxation process. High ac fields were found to modify the amplitudes of these secondary modes. The nonlinear features of this secondary process are reminiscent of those found for the excess wing regime, suggesting that these two contributions to dynamics have common origins.
The second part of this thesis describes the nonlinear effects observed from the application of high direct current (dc) bias fields superposed with a small amplitude sinusoidal ac field. For several molecular glass formers, the application of a dc field was found to slow down the system via reduction in configurational entropy (Adam-Gibbs relation). Time resolved measurements indicated that the rise of the non-linear effect is slower than its decay, as observed in the electro-optical Kerr effect. A model was discussed which quantitatively captures the observed magnitudes and time dependencies of the NDE. Asymmetry in these rise and decay times was demonstrated as a consequence of the quadratic field dependence of the entropy change. It was demonstrated that the high bias field modifies the polarization response to the field, even including the zero field limit.
ContributorsSamanta, Subarna (Author) / Richert, Ranko (Thesis advisor) / Steimle, Timothy (Committee member) / Wolf, George H. (Committee member) / Arizona State University (Publisher)
Created2016
Description
This paper outlines the design and testing of a z-scan spectrometer capable of measuring the third order refraction index of liquids. The spectrometer underwent multiple redesigns, with each explored in this paper with their benefits and drawbacks discussed. The first design was capable of measuring the third order refraction index for glass, and found a value of 8.43 +- 0.392 x 10^(-16) cm^2/W for the glass sample, with the literature stating glass has a refraction index between 1-100 x 10^(-16) cm^2/W. The second design was capable of measuring the third order refraction index of liquids, and found values of 1.23 $\pm$ 0.121 $\e{-16}$ and 9.43 +- 1.00 x 10^(-17) cm^2/W for water and ethanol respectively, with literature values of 2.7 x 10^(-16) and 5.0 x 10^(-17) cm^2/W respectively. The third design gave inconclusive results due to extreme variability in testing, and and the fourth design outlined has not been tested yet due to time constraints.
ContributorsClark, Brian Vincent (Author) / Sayres, Scott (Thesis director) / Steimle, Timothy (Committee member) / Keeler, Cynthia (Committee member) / School of Molecular Sciences (Contributor) / Department of Physics (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
Description
Transition metal oxides are used for numerous applications, includingsemiconductors, batteries, solar cells, catalysis, magnetic devices, and are commonly
observed in interstellar media. However, the atomic-scale properties which dictate the
overall bulk material activity is still lacking fundamental details. Most importantly, how
the electron shells of metals and O atoms mix is inherently significant to reactivity. This
thesis compares the binding and excited state properties of highly correlated first-row
transition metal oxides using four separate transition metal systems of Ti, Cr, Fe and Ni.
Laser ablation coupled with femtosecond pump-probe spectroscopy is utilized to resolve
the time-dependent excited state relaxation dynamics of atomically precise neutral
clusters following 400 nm (3.1 eV) photoexcitation. All transition metal oxides form
unique stable stoichiometries with excited state dynamics that evolve due to oxidation,
size, or geometry. Theoretical calculations assist in experimental analysis, showing
correlations between charge transfer characteristics, electron and hole localization, and
magnetic properties to the experimentally determined excited state lifetimes.
This thesis finds that neutral Ti and Cr form stable stoichiometries of MO2 (M =
Ti, Cr) which easily lose up to two O atoms, while neutral Fe and Ni primarily form MO
(M = Fe, Ni) geometries with suboxides also produced. TiO2 clusters possess excited
state lifetimes that increase with additional cluster units to ~600 fs, owing to a larger
delocalization of excited charge carriers with cluster size. CrO2 clusters show a unique
inversed metallic behavior with O content, where the fast (~30 fs) metallic relaxation
component associated with electron scattering increases with higher O content, connected
to the percent of ligand-to-metal charge transfer (LMCT) character and higher density of
states. FeO clusters show a decreased lifetime with size, reaching a plateau of ~150 fs at
the size of (FeO)5 related to the density of states as clusters form 3D geometries. Finally,
neutral (NiO)n clusters all have similar fast lifetimes (~110 fs), with suboxides possessing
unexpected electronic transitions involving s-orbitals, increasing excited state lifetimes
up to 80% and causing long-lived states lasting over 2.5 ps. Similarities are drawn
between each cluster system, providing valuable information about each metal oxide
species and the evolution of excited state dynamics as a result of the occupied d-shell.
The work presented within this thesis will lead to novel materials of increased reactivity
while facilitating a deeper fundamental understanding on the effect of electron
interactions on chemical properties.
ContributorsGarcia, Jacob M. (Author) / Sayres, Scott G (Thesis advisor) / Yarger, Jeffery (Committee member) / Steimle, Timothy (Committee member) / Arizona State University (Publisher)
Created2021
Description
This document is a guide that can be used by undergraduate physics students alongside Richard J. Jacob and Professor Emeritus’s Tutorials in the Mathematical Methods of Physics to aid in their understanding of the key mathematical concepts from PHY201 and PHY302. This guide can stand on its own and be used in other upper division physics courses as a handbook for common special functions. Additionally, we have created several Mathematica notebooks that showcase and visualize some of the topics discussed (available from the GitHub link in the introduction of the guide).
ContributorsUnterkofler, Eric (Author) / Skinner, Tristin (Co-author) / Covatto, Carl (Thesis director) / Keeler, Cynthia (Committee member) / Barrett, The Honors College (Contributor) / Department of Physics (Contributor) / School of Mathematical and Statistical Sciences (Contributor)
Created2022-12
Description
This document is a guide that can be used by undergraduate physics students alongside Richard J. Jacob and Professor Emeritus’s Tutorials in the Mathematical Methods of Physics to aid in their understanding of the key mathematical concepts from PHY201 and PHY302. This guide can stand on its own and be used in other upper division physics courses as a handbook for common special functions. Additionally, we have created several Mathematica notebooks that showcase and visualize some of the topics discussed (available from the GitHub link in the introduction of the guide).
ContributorsSkinner, Tristin (Author) / Unterkofler, Eric (Co-author) / Covatto, Carl (Thesis director) / Keeler, Cynthia (Committee member) / Barrett, The Honors College (Contributor) / Department of Physics (Contributor) / School of Mathematical and Statistical Sciences (Contributor)
Created2022-12
Description
Much attention has been given to the behavior of quantum fields in expanding Freidmann-Lema\^itre-Robertson-Walker (FLRW) spacetimes, and de Sitter spacetime in particular. In such spacetimes, the S-matrix is ill-defined, so new observables must be constructed that are accessible to both computation and measurement. The most common observable in theories of inflation is an equal-time correlation function, typically computed in the in-in formalism. Weinberg improved upon in-in perturbation theory by reducing the perturbative expansion to a series of nested commutators. Several authors noted a technical difference between Weinberg's formula and standard in-in perturbation theory. In this work, a proof of the order-by-order equivalence of Weinberg's commutators to traditional in-in perturbation theory is presented for all masses and commonly studied spins in a broad class of FLRW spacetimes. Then, a study of the effects of a sector of conformal matter coupled solely to gravity is given. The results can constrain N-naturalness as a complete solution of the hierarchy problem, given a measurement of the tensor fluctuations from inflation. The next part of this work focuses on the thermodynamics of de Sitter. It has been known for decades that there is a temperature associated with a cosmological horizon, which matches the thermal response of a comoving particle detector in de Sitter. A model of a perfectly reflecting cavity is constructed with fixed physical size in two-dimensional de Sitter spacetime. The natural ground state inside the box yields no response from a comoving particle detector, implying that the box screens out the thermal effects of the de Sitter horizon. The total energy inside the box is also shown to be smaller than an equivalent volume of the Bunch-Davies vacuum state. The temperature difference across the wall of the box might drive a heat engine, so an analytical model of the Szil\'ard engine is constructed and studied. It is found that all relevant thermodynamical quantities can be computed exactly at all stages of the engine cycle.
ContributorsThomas, Logan (Author) / Baumgart, Matthew (Thesis advisor) / Davies, Paul (Committee member) / Easson, Damien (Committee member) / Keeler, Cynthia (Committee member) / Arizona State University (Publisher)
Created2023
Description
Here I develop the connection between thermodynamics, entanglement, and gravity. I begin by showing that the classical null energy condition (NEC) can arise as a consequence of the second law of thermodynamics applied to local holographic screens. This is accomplished by essentially reversing the steps of Hawking's area theorem, leading to the Ricci convergence condition as an input, from which an application of Einstein's equations yields the NEC. Using the same argument, I show logarithmic quantum corrections to the Bekenstein-Hawking entropy formula do not alter the form of the Ricci convergence condition, but obscure its connection to the NEC. Then, by attributing thermodynamics to the stretched horizon of future lightcones -- a timelike hypersurface generated by a collection of radially accelerating observers with constant and uniform proper acceleration -- I derive Einstein's equations from the Clausius relation. Based on this derivation I uncover a local first law of gravity, connecting gravitational entropy to matter energy and work. I then provide an entanglement interpretation of stretched lightcone thermodynamics by extending the entanglement equilibrium proposal. Specifically I show that the condition of fixed volume can be understood as subtracting the irreversible contribution to the thermodynamic entropy. Using the AdS/CFT correspondence, I then provide a microscopic explanation of the 'thermodynamic volume' -- the conjugate variable to the pressure in extended black hole thermodynamics -- and reveal the super-entropicity of three-dimensional AdS black holes is due to the gravitational entropy overcounting the number of available dual CFT states. Finally, I conclude by providing a recent generlization of the extended first law of entanglement, and study its non-trivial 2+1- and 1+1-dimensional limits. This thesis is self-contained and pedagogical by including useful background content relevant to emergent gravity.
ContributorsSvesko, Andrew (Author) / Parikh, Maulik (Thesis advisor) / Vachaspati, Tanmay (Thesis advisor) / Keeler, Cynthia (Committee member) / Easson, Damien (Committee member) / Arizona State University (Publisher)
Created2020
Description
In this dissertation, I present the results from my recent
investigations into the interactions involving topological defects, such as
magnetic monopoles and strings, that may have been produced in the early
universe. I performed numerical studies on the interactions of twisted
monopole-antimonopole pairs in the 't Hooft-Polyakov model for a range of
values of the scalar to vector mass ratio. Sphaleron solution predicted by
Taubes was recovered, and I mapped out its energy and size as functions of
parameters. I also looked into the production, and decay modes of $U(1)$ gauge
and global strings. I demonstrated that strings can be produced upon evolution
of gauge wavepackets defined within a certain region of parameter space. The
numerical exploration of the decay modes of cosmic string loops led to the
conclusions that string loops emit particle radiation primarily due to kink
collisions, and that their decay time due to these losses is proportional to
$L^p$, where $L$ is the loop length and $p \approx 2$. In contrast, the decay
time due to gravitational radiation scales in proportion to $L$, and I
concluded that particle emission is the primary energy loss mechanism for loops
smaller than a critical length scale, while gravitational losses dominate for
larger loops. In addition, I analyzed the decay of cosmic global string loops
due to radiation of Goldstone bosons and massive scalar ($\chi$) particles.
The length of loops I studied ranges from 200-1000 times the width of the
string core. I found that the lifetime of a loop is approximately $1.4L$. The
energy spectrum of Goldstone boson radiation has a $k^{-1}$ fall off, where $k$
is the wavenumber, and a sharp peak at $k\approx m_\chi/2$, where $m_\chi$ is
the mass of $\chi$. The latter is a new feature and implies a peak at high
energies (MeV-GeV) in the cosmological distribution of QCD axions.
investigations into the interactions involving topological defects, such as
magnetic monopoles and strings, that may have been produced in the early
universe. I performed numerical studies on the interactions of twisted
monopole-antimonopole pairs in the 't Hooft-Polyakov model for a range of
values of the scalar to vector mass ratio. Sphaleron solution predicted by
Taubes was recovered, and I mapped out its energy and size as functions of
parameters. I also looked into the production, and decay modes of $U(1)$ gauge
and global strings. I demonstrated that strings can be produced upon evolution
of gauge wavepackets defined within a certain region of parameter space. The
numerical exploration of the decay modes of cosmic string loops led to the
conclusions that string loops emit particle radiation primarily due to kink
collisions, and that their decay time due to these losses is proportional to
$L^p$, where $L$ is the loop length and $p \approx 2$. In contrast, the decay
time due to gravitational radiation scales in proportion to $L$, and I
concluded that particle emission is the primary energy loss mechanism for loops
smaller than a critical length scale, while gravitational losses dominate for
larger loops. In addition, I analyzed the decay of cosmic global string loops
due to radiation of Goldstone bosons and massive scalar ($\chi$) particles.
The length of loops I studied ranges from 200-1000 times the width of the
string core. I found that the lifetime of a loop is approximately $1.4L$. The
energy spectrum of Goldstone boson radiation has a $k^{-1}$ fall off, where $k$
is the wavenumber, and a sharp peak at $k\approx m_\chi/2$, where $m_\chi$ is
the mass of $\chi$. The latter is a new feature and implies a peak at high
energies (MeV-GeV) in the cosmological distribution of QCD axions.
ContributorsSaurabh, Ayush (Author) / Vachaspati, Tanmay (Thesis advisor) / Lebed, Richard (Committee member) / Baumgart, Matthew (Committee member) / Keeler, Cynthia (Committee member) / Arizona State University (Publisher)
Created2020
Description
Carbon allotropes are the basis for many exciting advancements in technology. While sp² and sp³ hybridizations are well understood, the sp¹ hybridized carbon has been elusive. However, with recent advances made using a pulsed laser ablation in liquid technique, sp¹ hybridized carbon allotropes have been created. The fabricated carbon chain is composed of sp¹ and sp³ hybridized bonds, but it also incorporates nanoparticles such as gold or possibly silver to stabilize the chain. The polyyne generated in this process is called pseudocarbyne due to its striking resemblance to the theoretical carbyne. The formation of these carbon chains is yet to be fully understood, but significant progress has been made in determining the temperature of the plasma in which the pseudocarbyne is formed. When a 532 nm pulsed laser with a pulsed energy of 250 mJ and pulse length of 10ns is used to ablate a gold target, a peak temperature of 13400 K is measured. When measured using Laser-Induced Breakdown spectroscopy (LIBS) the average temperature of the neutral carbon plasma over one second was 4590±172 K. This temperature strongly suggests that the current theoretical model used to describe the temperature at which pseudocarbyne generates is accurate.
ContributorsWala, Ryland Gerald (Co-author) / Wala, Ryland (Co-author) / Sayres, Scott (Thesis director) / Steimle, Timothy (Committee member) / Drucker, Jeffery (Committee member) / Historical, Philosophical & Religious Studies (Contributor) / Dean, W.P. Carey School of Business (Contributor) / Department of Physics (Contributor, Contributor) / Barrett, The Honors College (Contributor)
Created2019-05