Matching Items (24)
Description
The work described in the thesis involves the synthesis of a molecular triad which is designed to undergo proton coupled electron transfer (PCET) upon irradiation with light. Photoinduced PCET is an important process that many organisms use and the elucidation of its mechanism will allow further understanding of this process and its potential applications. The target compound designed for PCET studies consists of a porphyrin chromophore (also a primary electron donor), covalently linked to a phenol-imidazole (secondary electron donor), and a C60 (primary electron acceptor). The phenol-imidazole moiety of this system is modeled after the TyrZ His-190 residues in the reaction center of Photosystem II (PS II). These residues participate in an intermolecular H-bond between the phenol side chain of TyrZ and the imidazole side chain of His-190. The phenol side chain of TyrZ is the electron transfer mediator between the oxygen evolving complex (OEC) and P680 (primary electron donor) in PSII. During electron transfer from TyrZ to P680*+, the phenolic proton of TyrZ becomes highly acidic (pKa~-2) and the hydrogen is preferentially transferred to the relatively basic imidazole of His-190 through a pre-existing hydrogen bond. This PCET process avoids a charged intermediate, on TyrZ, and results in a neutral phenolic radical (TyrZ*). The current research consists of building a molecular triad, which can mimic the photoinduced PCET process of PSII. The following, documents the synthetic progress in the synthesis of a molecular triad designed to investigate the mechanism of PCET as well as gain further insight on how this process can be applied in artificial photosynthetic devices.
ContributorsPatterson, Dustin (Author) / Moore, Ana L (Thesis advisor) / Gust, Devens (Committee member) / Skibo, Edward B (Committee member) / Arizona State University (Publisher)
Created2011
Description
Natural photosynthesis dedicates specific proteins to achieve the modular division of the essential roles of solar energy harvesting, charge separation and carrier transport within natural photosynthesis. The modern understanding of the fundamental photochemistry by which natural photosynthesis operates is well advanced and solution state mimics of the key photochemical processes have been reported previously. All of the early events in natural photosynthesis responsible for the conversion of solar energy to electric potential energy occur within proteins and phospholipid membranes that act as scaffolds for arranging the active chromophores. Accordingly, for creating artificial photovoltaic (PV) systems, scaffolds are required to imbue structure to the systems. An approach to incorporating modular design into solid-state organic mimics of the natural system is presented together with how conductive scaffolds can be utilized in organic PV systems. To support the chromophore arrays present within this design and to extract separated charges from within the structure, linear pyrazine-containing molecular ribbons were chosen as candidates for forming conductive linear scaffolds that could be functionalized orthogonally to the linear axis. A series of donor-wire-acceptor (D-W-A) compounds employing porphyrins as the donors and a C60 fullerene adduct as the acceptors have been synthesized for studying the ability of the pyrazine-containing hetero-aromatic wires to mediate photoinduced electron transfer between the porphyrin donor and fullerene acceptor. Appropriate substitutions were made and the necessary model compounds useful for dissecting the complex photochemistry that the series is expected to display were also synthesized. A dye was synthesized using a pyrazine-containing heteroaromatic spacer that features two porphyrin chromophores. The dye dramatically outperforms the control dye featuring the same porphyrin and a simple benzoic acid linker. A novel, highly soluble 6+kDa extended phthalocyanine was also synthesized and exhibits absorption out to 900nm. The extensive functionalization of the extended phthalocyanine core with dodecyl groups enabled purification and characterization of an otherwise insoluble entity. Finally, in the interest of incorporating modular design into plastic solar cells, a series of porphyrin-containing monomers have been synthesized that are intended to form dyadic and triadic molecular-heterojunction polymers with dedicated hole and electron transport pathways during electrochemical polymerization.
ContributorsWatson, Brian Lyndon (Author) / Gust, Devens (Thesis advisor) / Gould, Ian (Committee member) / Moore, Ana L (Committee member) / Arizona State University (Publisher)
Created2013
Description
Asymptotic and Numerical methods are popular in applied electromagnetism. In this work, the two methods are applied for collimated antennas and calibration targets, respectively. As an asymptotic method, the diffracted Gaussian beam approach (DGBA) is developed for design and simulation of collimated multi-reflector antenna systems, based upon Huygens principle and independent Gaussian beam expansion, referred to as the frames. To simulate a reflector antenna in hundreds to thousands of wavelength, it requires 1E7 - 1E9 independent Gaussian beams. To this end, high performance parallel computing is implemented, based on Message Passing Interface (MPI). The second part of the dissertation includes the plane wave scattering from a target consisting of doubly periodic array of sharp conducting circular cones by the magnetic field integral equation (MFIE) via Coiflet based Galerkin's procedure in conjunction with the Floquet theorem. Owing to the orthogonally, compact support, continuity and smoothness of the Coiflets, well-conditioned impedance matrices are obtained. Majority of the matrix entries are obtained in the spectral domain by one-point quadrature with high precision. For the oscillatory entries, spatial domain computation is applied, bypassing the slow convergence of the spectral summation of the non-damping propagating modes. The simulation results are compared with the solutions from an RWG-MLFMA based commercial software, FEKO, and excellent agreement is observed.
ContributorsWang, Le, 1975- (Author) / Pan, George (Thesis advisor) / Yu, Hongyu (Committee member) / Aberle, James T., 1961- (Committee member) / Diaz, Rodolfo (Committee member) / Kitchen, Jennifer (Committee member) / Arizona State University (Publisher)
Created2012
Description
The sun provides Earth with a virtually limitless source of energy capable of sustaining all of humanity's needs. Photosynthetic organisms have exploited this energy for eons. However, efficiently converting solar radiation into a readily available and easily transportable form is complex. New materials with optimized physical, electrochemical, and photophysical properties are at the forefront of organic solar energy conversion research. In the work presented herein, porphyrin and organometallic dyes with widely-varied properties were studied for solar energy applications. In one project, porphyrins and porphyrin-fullerene dyads with aniline-like features were polymerized via electrochemical methods into semiconductive thin films. These were shown to have high visible light absorption and stable physical and electrochemical properties. However, experimentation using porphyrin polymer films as both the light absorber and semiconductor in a photoelectrochemical cell showed relatively low efficiency of converting absorbed solar energy into electricity. In separate work, tetra-aryl porphyrin derivatives were examined in conjunction with wide-bandgap semiconductive oxides TiO2 and SnO2. Carboxylic acid-, phosphonic acid-, and silatrane-functionalized porphyrins were obtained or synthesized for attachment to the metal oxide species. Electrochemical, photophysical, photoelectrochemical, and surface stability studies of the porphyrins were performed for comparative purposes. The order of surface linkage stability on TiO2 in alkaline conditions, from most stable to least, was determined to be siloxane > phosphonate > carboxylate. Finally, porphyrin dimers fused via their meso and beta positions were synthesized using a chemical oxidative synthesis with a copper(II) oxidant. The molecules exhibit strong absorption in the visible and near-infrared spectral regions as well as interesting electrochemical properties suggesting possible applications in light harvesting and redox catalysis.
ContributorsBrennan, Bradley J (Author) / Gust, Devens (Thesis advisor) / Moore, Thomas A. (Committee member) / Allen, James P. (Committee member) / Arizona State University (Publisher)
Created2012
Description
Most of the sunlight powering natural photosynthesis is absorbed by antenna arrays that transfer, and regulate the delivery of excitation energy to reaction centers in the chloroplast where photosynthesis takes place. Under intense sunlight the plants and certain organisms cannot fully utilize all of the sunlight received by antennas and excess redox species are formed which could potentially harm them. To prevent this, excess energy is dissipated by antennas before it reaches to the reaction centers to initiate electron transfer needed in the next steps of photosynthesis. This phenomenon is called non-photochemical quenching (NPQ). The mechanism of NPQ is not fully understood, but the process is believed to be initiated by a drop in the pH in thylakoid lumen in cells. This causes changes in otherwise nonresponsive energy acceptors which accept the excess energy, preventing oversensitization of the reaction center. To mimic this phenomenon and get insight into the mechanism of NPQ, a novel pH sensitive dye 3'6'-indolinorhodamine was designed and synthesized which in a neutral solution stays in a closed (colorless) form and does not absorb light while at low pH it opens (colored) and absorbs light. The absorption of the dye overlaps porphyrin emission, thus making energy transfer from the porphyrin to the dye thermodynamically possible. Several self-regulating molecular model systems were designed and synthesized consisting of this dye and zinc porphyrins organized on a hexaphenylbenzene framework to functionally mimic the role of the antenna in NPQ. When a dye-zinc porphyrin dyad is dissolved in an organic solvent, the zinc porphyrin antenna absorbs and emits light by normal photophysical processes. Time resolved fluorescence experiments using the single-photon-timing method with excitation at 425 nm and emission at 600 nm yielded a lifetime of 2.09 ns for the porphyrin first excited singlet state. When acetic acid is added to the solution of the dyad, the pH sensitive dye opens and quenches the zinc porphyrin emission decreasing the lifetime of the porphyrin first excited singlet state to 23 ps, and converting the excitation energy to heat. Under similar experimental conditions in a neutral solution, a model hexad containing the dye and five zinc porphyrins organized on a hexaphenylbenzene core decays exponentially with a time constant of 2.1 ns, which is essentially the same lifetime as observed for related monomeric zinc porphyrins. When a solution of the hexad is acidified, the dye opens and quenches all porphyrin first excited singlet states to <40 ps. This converts the excitation energy to heat and renders the porphyrins kinetically incompetent to readily donate electrons by photoinduced electron transfer, thereby mimicking the role of the antenna in photosynthetic photoprotection.
ContributorsBhushan, Kul (Author) / Gust, Devens (Thesis advisor) / Moore, Ana (Committee member) / Hayes, Mark (Committee member) / Arizona State University (Publisher)
Created2012
Description
In many systems, it is difficult or impossible to measure the phase of a signal. Direct recovery from magnitude is an ill-posed problem. Nevertheless, with a sufficiently large set of magnitude measurements, it is often possible to reconstruct the original signal using algorithms that implicitly impose regularization conditions on this ill-posed problem. Two such algorithms were examined: alternating projections, utilizing iterative Fourier transforms with manipulations performed in each domain on every iteration, and phase lifting, converting the problem to that of trace minimization, allowing for the use of convex optimization algorithms to perform the signal recovery. These recovery algorithms were compared on a basis of robustness as a function of signal-to-noise ratio. A second problem examined was that of unimodular polyphase radar waveform design. Under a finite signal energy constraint, the maximal energy return of a scene operator is obtained by transmitting the eigenvector of the scene Gramian associated with the largest eigenvalue. It is shown that if instead the problem is considered under a power constraint, a unimodular signal can be constructed starting from such an eigenvector that will have a greater return.
ContributorsJones, Scott Robert (Author) / Cochran, Douglas (Thesis director) / Diaz, Rodolfo (Committee member) / Barrett, The Honors College (Contributor) / Electrical Engineering Program (Contributor) / School of Mathematical and Statistical Sciences (Contributor)
Created2014-05
Description
Programmable Metallization Cell (PMC) is a resistance-switching device based on migration of nanoscale quantities of cations in a solid electrolyte and formation of a conducting electrodeposit by the reductions of these cations. This dissertation presents electrical characterization results on Cu-SiO2 based PMC devices, which due to the na- ture of materials can be easily integrated into the current Complimentary metal oxide semiconductor (CMOS) process line. Device structures representing individual mem- ory cells based on W bottom electrode and n-type Si bottom electrode were fabricated for characterization. For the W bottom electrode based devices, switching was ob- served for voltages in the range of 500mV and current value as low as 100 nA showing the electrochemical nature and low power potential. The ON state showed a direct de- pendence on the programming current, showing the possibility of multi-bit storage in a single cell. Room temperature retention was demonstrated in excess of 105 seconds and endurance to approximately 107 cycles. Switching was observed for microsecond duration 3 V amplitude pulses. Material characterization results from Raman, X-ray diffraction, Rutherford backscattering and Secondary-ion mass spectroscopy analysis shows the influence of processing conditions on the Cu concentration within the film and also the presence of Cu as free atoms. The results seemed to indicate stress-induced void formation in the SiO2 matrix as the driving mechanism for Cu diffusion into the SiO2 film. Cu/SiO2
Si based PMC devices were characterized and were shown to have inherent isolation characteristics, proving the feasibility of such a structure for a passive array. The inherent isolation property simplifies fabrication by avoiding the need for a separate diode element in an array. The isolation characteristics were studied mainly in terms of the leakage current. The nature of the diode interface was further studied by extracting a barrier potential which shows it can be approximated to a Cu-nSi metal semiconductor Schottky diode.
Si based PMC devices were characterized and were shown to have inherent isolation characteristics, proving the feasibility of such a structure for a passive array. The inherent isolation property simplifies fabrication by avoiding the need for a separate diode element in an array. The isolation characteristics were studied mainly in terms of the leakage current. The nature of the diode interface was further studied by extracting a barrier potential which shows it can be approximated to a Cu-nSi metal semiconductor Schottky diode.
ContributorsPuthenthermadam, Sarath (Author) / Kozicki, Michael N (Thesis advisor) / Diaz, Rodolfo (Committee member) / Schroder, Dieter K. (Committee member) / Alford, Terry (Committee member) / Arizona State University (Publisher)
Created2011
Description
Titanium dioxide (TiO2) is widely used for photocatalysis and solar cell applications, and the electronic structure of bulk TiO2 is well understood. However, the surface structure of nanoparticulate TiO2, which has a key role in properties such as solubility and catalytic activity, still remains controversial. Detailed understanding of surface defect structures may help explain reactivity and overall materials performance in a wide range of applications. In this work we address the solubility problem and surface defects control on TiO2 nanoparticles. We report the synthesis and characterization of ∼4 nm TiO2 anatase spherical nanoparticles that are soluble and stable in a wide range of organic solvents and water. By controlling the temperature during the synthesis, we are able to tailor the density of defect states on the surface of the TiO2 nanoparticles without affecting parameters such as size, shape, core crystallinity, and solubility. The morphology of both kinds of nanoparticles was determined by TEM. EPR experiments were used to characterize the surface defects, and transient absorption measurements demonstrate the influence of the TiO2 defect states on photoinduced electron transfer dynamics.
ContributorsLlansola Portoles, Manuel (Author) / Bergkamp, Jesse (Author) / Finkelstein Shapiro, Daniel (Author) / Sherman, Benjamin (Author) / Kodis, Gerdenis (Author) / Dimitrijevic, Nada M. (Author) / Gust, Devens (Author) / Moore, Thomas (Author) / Moore, Ana (Author) / Department of Chemistry and Biochemistry (Contributor) / College of Liberal Arts and Sciences (Contributor) / School of Molecular Sciences (Contributor) / Center for Bioenergy and Photosynthesis (Contributor)
Created2014-11-13
Description
The ability to accurately predict the oxidation and reduction potentials of molecules is very useful in various fields and applications. Quantum mechanical calculations can be used to access this information, yet sometimes the usefulness of these calculations can be limited because of the computational requirements for large systems. Methodologies that yield strong linear correlations between calculations and experimental data have been reported, however the balance between accuracy and computational cost is always a major issue. In this work, linear correlations (with an R-2 value of up to 0.9990) between DFT-calculated HOMO/LUMO energies and 70 redox potentials from a series of 51 polycyclic aromatic hydrocarbons (obtained from the literature) are presented. The results are compared to previously reported linear correlations that were obtained with a more expensive computational methodology based on a Born-Haber thermodynamic cycle. It is shown in this article that similar or better correlations can be obtained with a simple and cheaper calculation.
ContributorsMendez-Hernandez, Dalvin (Author) / Pilarisetty, Tarakeshwar (Author) / Gust, Devens (Author) / Moore, Thomas (Author) / Moore, Ana (Author) / Mujica, Vladimiro (Author) / Department of Chemistry and Biochemistry (Contributor) / College of Liberal Arts and Sciences (Contributor) / School of Molecular Sciences (Contributor)
Created2013-10-28
Description
As integrated technologies are scaling down, there is an increasing trend in the
process,voltage and temperature (PVT) variations of highly integrated RF systems.
Accounting for these variations during the design phase requires tremendous amount
of time for prediction of RF performance and optimizing it accordingly. Thus, there
is an increasing gap between the need to relax the RF performance requirements at
the design phase for rapid development and the need to provide high performance
and low cost RF circuits that function with PVT variations. No matter how care-
fully designed, RF integrated circuits (ICs) manufactured with advanced technology
nodes necessitate lengthy post-production calibration and test cycles with expensive
RF test instruments. Hence design-for-test (DFT) is proposed for low-cost and fast
measurement of performance parameters during both post-production and in-eld op-
eration. For example, built-in self-test (BIST) is a DFT solution for low-cost on-chip
measurement of RF performance parameters. In this dissertation, three aspects of
automated test and calibration, including DFT mathematical model, BIST hardware
and built-in calibration are covered for RF front-end blocks.
First, the theoretical foundation of a post-production test of RF integrated phased
array antennas is proposed by developing the mathematical model to measure gain
and phase mismatches between antenna elements without any electrical contact. The
proposed technique is fast, cost-efficient and uses near-field measurement of radiated
power from antennas hence, it requires single test setup, it has easy implementation
and it is short in time which makes it viable for industrialized high volume integrated
IC production test.
Second, a BIST model intended for the characterization of I/Q offset, gain and
phase mismatch of IQ transmitters without relying on external equipment is intro-
duced. The proposed BIST method is based on on-chip amplitude measurement as
in prior works however,here the variations in the BIST circuit do not affect the target
parameter estimation accuracy since measurements are designed to be relative. The
BIST circuit is implemented in 130nm technology and can be used for post-production
and in-field calibration.
Third, a programmable low noise amplifier (LNA) is proposed which is adaptable
to different application scenarios depending on the specification requirements. Its
performance is optimized with regards to required specifications e.g. distance, power
consumption, BER, data rate, etc.The statistical modeling is used to capture the
correlations among measured performance parameters and calibration modes for fast
adaptation. Machine learning technique is used to capture these non-linear correlations and build the probability distribution of a target parameter based on measurement results of the correlated parameters. The proposed concept is demonstrated by
embedding built-in tuning knobs in LNA design in 130nm technology. The tuning
knobs are carefully designed to provide independent combinations of important per-
formance parameters such as gain and linearity. Minimum number of switches are
used to provide the desired tuning range without a need for an external analog input.
process,voltage and temperature (PVT) variations of highly integrated RF systems.
Accounting for these variations during the design phase requires tremendous amount
of time for prediction of RF performance and optimizing it accordingly. Thus, there
is an increasing gap between the need to relax the RF performance requirements at
the design phase for rapid development and the need to provide high performance
and low cost RF circuits that function with PVT variations. No matter how care-
fully designed, RF integrated circuits (ICs) manufactured with advanced technology
nodes necessitate lengthy post-production calibration and test cycles with expensive
RF test instruments. Hence design-for-test (DFT) is proposed for low-cost and fast
measurement of performance parameters during both post-production and in-eld op-
eration. For example, built-in self-test (BIST) is a DFT solution for low-cost on-chip
measurement of RF performance parameters. In this dissertation, three aspects of
automated test and calibration, including DFT mathematical model, BIST hardware
and built-in calibration are covered for RF front-end blocks.
First, the theoretical foundation of a post-production test of RF integrated phased
array antennas is proposed by developing the mathematical model to measure gain
and phase mismatches between antenna elements without any electrical contact. The
proposed technique is fast, cost-efficient and uses near-field measurement of radiated
power from antennas hence, it requires single test setup, it has easy implementation
and it is short in time which makes it viable for industrialized high volume integrated
IC production test.
Second, a BIST model intended for the characterization of I/Q offset, gain and
phase mismatch of IQ transmitters without relying on external equipment is intro-
duced. The proposed BIST method is based on on-chip amplitude measurement as
in prior works however,here the variations in the BIST circuit do not affect the target
parameter estimation accuracy since measurements are designed to be relative. The
BIST circuit is implemented in 130nm technology and can be used for post-production
and in-field calibration.
Third, a programmable low noise amplifier (LNA) is proposed which is adaptable
to different application scenarios depending on the specification requirements. Its
performance is optimized with regards to required specifications e.g. distance, power
consumption, BER, data rate, etc.The statistical modeling is used to capture the
correlations among measured performance parameters and calibration modes for fast
adaptation. Machine learning technique is used to capture these non-linear correlations and build the probability distribution of a target parameter based on measurement results of the correlated parameters. The proposed concept is demonstrated by
embedding built-in tuning knobs in LNA design in 130nm technology. The tuning
knobs are carefully designed to provide independent combinations of important per-
formance parameters such as gain and linearity. Minimum number of switches are
used to provide the desired tuning range without a need for an external analog input.
ContributorsShafiee, Maryam (Author) / Ozev, Sule (Thesis advisor) / Diaz, Rodolfo (Committee member) / Ogras, Umit Y. (Committee member) / Bakkaloglu, Bertan (Committee member) / Arizona State University (Publisher)
Created2018