Matching Items (16)
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- All Subjects: Physics
- Creators: Rez, Peter
Description
In this work, a new method, "Nanobonding" [1,2] is conceived and researched to bond Si-based surfaces, via nucleation and growth of a 2 D silicon oxide SiOxHx interphase connecting the surfaces at the nanoscale across macroscopic domains. Nanobonding cross-bridges two smooth surfaces put into mechanical contact in an O2/H2O mixed ambient below T <200 °C via arrays of SiOxHx molecules connecting into a continuous macroscopic bonding interphase. Nano-scale surface planarization via wet chemical processing and new spin technology are compared via Tapping Mode Atomic Force Microscopy (TMAFM) , before and after nano-bonding. Nanobonding uses precursor phases, 2D nano-films of beta-cristobalite (beta-c) SiO2, nucleated on Si(100) via the Herbots-Atluri (H-A) method [1]. beta-c SiO2 on Si(100) is ordered and flat with atomic terraces over 20 nm wide, well above 2 nm found in native oxides. When contacted with SiO2 this ultra-smooth nanophase can nucleate and grow domains with cross-bridging molecular strands of hydroxylated SiOx, instead of point contacts. The high density of molecular bonds across extended terraces forms a strong bond between Si-based substrates, nano- bonding [2] the Si and silica. A new model of beta-cristobalite SiO2 with its <110> axis aligned along Si[100] direction is simulated via ab-initio methods in a nano-bonded stack with beta-c SiO2 in contact with amorphous SiO2 (a-SiO2), modelling cross-bridging molecular bonds between beta-c SiO2 on Si(100) and a-SiO2 as during nanobonding. Computed total energies are compared with those found for Si(100) and a-SiO2 and show that the presence of two lattice cells of !-c SiO2 on Si(100) and a-SiO2 lowers energy when compared to Si(100)/ a-SiO2 Shadow cone calculations on three models of beta-c SiO2 on Si(100) are compared with Ion Beam Analysis of H-A processed Si(100). Total surface energy measurements via 3 liquid contact angle analysis of Si(100) after H-A method processing are also compared. By combining nanobonding experiments, TMAFM results, surface energy data, and ab-initio calculations, an atomistic model is derived and nanobonding is optimized. [1] US Patent 6,613,677 (9/2/03), 7,851,365 (12/14/10), [2] Patent Filed: 4/30/09, 10/1/2011
ContributorsWhaley, Shawn D (Author) / Culbertson, Robert J. (Thesis advisor) / Herbots, Nicole (Committee member) / Rez, Peter (Committee member) / Marzke, Robert F (Committee member) / Lindsay, Stuart (Committee member) / Chamberlin, Ralph V (Committee member) / Arizona State University (Publisher)
Created2011
Raman spectroscopy characterization of anharmonicity and alloying effects in semiconductor materials
Description
The chemical sensitivity and spatial resolution of Raman spectroscopy, combined with the sensitivity of modern systems that can easily detect single atomic layers, have made this technique a preferred choice for the strain characterization of complex systems such as nanoscale complementary metal-oxide-semiconductor - CMOS - devices. A disadvantage of Raman spectroscopy, however, is that the shifts associated with strain are not related to the geometrical deformations in any obvious way, so that careful calibrations are needed to determine the anharmonic coefficients (p, q and r) that relate strain to Raman shifts. A new set of measurements of the Raman shift in strained Ge films grown on relaxed SiGe buffer layers deposited on Si substrates is presented, and thereby, a new consistent set of values for the parameters p and q for Ge has been proposed. In this dissertation the study of the vibrational properties of Ge1-xSnx alloys has also been reported. The temperature dependence of the Raman spectrum of Ge-rich Ge1-x Snx and Ge1-x-ySi xSny alloys has been determined in the 10 K - 450 K range. The Raman line shift and width changes as a function of temperature are found to be virtually identical to those observed in bulk Ge. This result shows that the anharmonic decay process responsible for the temperature dependence is extremely robust against the alloy perturbation.
ContributorsBagchi, Sampriti (Author) / Menéndez, Jose (Thesis advisor) / Treacy, Michael (Committee member) / Ponce, Fernando (Committee member) / Tsen, Kong-Thon (Committee member) / Rez, Peter (Committee member) / Arizona State University (Publisher)
Created2011
Description
This thesis addresses certain quantum aspects of the event horizon using the AdS/CFT correspondence. This correspondence is profound since it describes a quantum theory of gravity in d + 1 dimensions from the perspective of a dual quantum field theory living in d dimensions. We begin by considering Rindler space which is the part of Minkowski space seen by an observer with a constant proper acceleration. Because it has an event horizon, Rindler space has been studied in great detail within the context of quantum field theory. However, a quantum gravitational treatment of Rindler space is handicapped by the fact that quantum gravity in flat space is poorly understood. By contrast, quantum gravity in anti-de Sitter space (AdS), is relatively well understood via the AdS/CFT correspondence. Taking this cue, we construct Rindler coordinates for AdS (Rindler-AdS space) in d + 1 spacetime dimensions. In three spacetime dimensions, we find novel one-parameter families of stationary vacua labeled by a rotation parameter β. The interesting thing about these rotating Rindler-AdS spaces is that they possess an observer-dependent ergoregion in addition to having an event horizon. Turning next to the application of AdS/CFT correspondence to Rindler-AdS space, we posit that the two Rindler wedges in AdSd+1 are dual to an entangled conformal field theory (CFT) that lives on two boundaries with geometry R × Hd-1. Specializing to three spacetime dimensions, we derive the thermodynamics of Rindler-AdS space using the boundary CFT. We then probe the causal structure of the spacetime by sending in a time-like source and observe that the CFT “knows” when the source has fallen past the Rindler horizon. We conclude by proposing an alternate foliation of Rindler-AdS which is dual to a CFT living in de Sitter space. Towards the end, we consider the concept of weak measurements in quantum mechanics, wherein the measuring instrument is weakly coupled to the system being measured. We consider such measurements in the context of two examples, viz. the decay of an excited atom, and the tunneling of a particle trapped in a well, and discuss the salient features of such measurements.
ContributorsSamantray, Prasant (Author) / Parikh, Maulik (Thesis advisor) / Davies, Paul (Committee member) / Vachaspati, Tanmay (Committee member) / Easson, Damien (Committee member) / Alarcon, Ricardo (Committee member) / Arizona State University (Publisher)
Created2012
Description
For this project, the diffuse supernova neutrino background (DSNB) has been calculated based on the recent direct supernova rate measurements and neutrino spectrum from SN1987A. The estimated diffuse electron antineutrino flux is ∼ 0.10 – 0.59 /cm2/s at 99% confidence level, which is 5 times lower than the Super-Kamiokande 2012 upper limit of 3.0 /cm2/s, above energy threshold of 17.3 MeV. With a Megaton scale water detector, 40 events could be detected above the threshold per year. In addition, the detectability of neutrino bursts from direct black hole forming collapses (failed supernovae) at Megaton detectors is calculated. These neutrino bursts are energetic and with short time duration, ∼ 1s. They could be identified by the time coincidence of N ≥2 or N ≥3 events within 1s time window from nearby (4 – 5 Mpc) failed supernovae. The detection rate of these neutrino bursts could get up to one per decade. This is a realistic way to detect a failed supernova and gives a promising method for studying the physics of direct black hole formation mechanism. Finally, the absorption of ultra high energy (UHE) neutrinos by the cosmic neutrino background, with full inclusion of the effect of the thermal distribution of the background on the resonant annihilation channel, is discussed. Results are applied to serval models of UHE neutrino sources. Suppression effects are strong for sources that extend beyond z ∼ 10. This provides a fascinating probe of the physics of the relic neutrino background in the unexplored redshift interval z ∼ 10 – 100. Ultimately this research will examine the detectability of DSNB, neutrino bursts from failed supernovae and absorption effects in the neutrino spectrum.
ContributorsYang, Lili, 1970- (Author) / Lunardini, Cecilia (Thesis advisor) / Alarcon, Ricardo (Committee member) / Shovkovy, Igor (Committee member) / Timmes, Francis (Committee member) / Vachaspati, Tanmay (Committee member) / Arizona State University (Publisher)
Created2013
Description
Zeolites are a class of microporous materials that are immensely useful as molecular sieves and catalysts. While there exist millions of hypothetical zeolite topologies, only 206 have been recognized to exist in nature, and the question remains: What distinguishes known zeolite topologies from their hypothetical counterparts? It has been found that all 206 of the known zeolites can be represented as networks of rigid perfect tetrahedra that hinge freely at the connected corners. The range of configurations over which the corresponding geometric constraints can be met has been termed the "flexibility window". Only a small percentage of hypothetical types exhibit a flexibility window, and it is thus proposed that this simple geometric property, the existence of a flexibility window, provides a reliable benchmark for distinguishing potentially realizable hypothetical structures from their infeasible counterparts. As a first approximation of the behavior of real zeolite materials, the flexibility window provides additional useful insights into structure and composition. In this thesis, various methods for locating and exploring the flexibility window are discussed. Also examined is the assumption that the tetrahedral corners are force-free. This is a reasonable approximation in silicates for Si-O-Si angles above ~135°. However, the approximation is poor for germanates, where Ge-O-Ge angles are constrained to the range ~120°-145°. Lastly, a class of interesting low-density hypothetical zeolites is evaluated based on the feasibility criteria introduced.
ContributorsDawson, Colby (Author) / Treacy, Michael M. J. (Thesis advisor) / O'Keeffe, Michael (Committee member) / Thorpe, Michael F. (Committee member) / Rez, Peter (Committee member) / Bennett, Peter (Committee member) / Arizona State University (Publisher)
Created2013
Description
Many species e.g. sea urchin form amorphous calcium carbonate (ACC) precursor phases that subsequently transform into crystalline CaCO3. It is certainly possible that the biogenic ACC might have more than 10 wt% Mg and ∼ 3 wt% of water. The structure of ACC and the mechanisms by which it transforms to crystalline phase are still poorly understood. In this dissertation our goal is to determine an atomic structure model that is consistent with diffraction and IR measurements of ACC. For this purpose a calcite supercell with 24 formula units, containing 120 atoms, was constructed. Various configurations with substitution of Ca by 6 Mg ions (6 wt.%) and insertion of 3-5 H2O molecules (2.25-3.75 wt.%) in the interstitial positions of the supercell, were relaxed using a robust density function code VASP. The most noticeable effects were the tilts of CO3 groups and the distortion of Ca sub-lattice, especially in the hydrated case. The distributions of Ca-Ca nearest neighbor distance and CO3 tilts were extracted from various configurations. The same methods were also applied to aragonite. Sampling from the calculated distortion distributions, we built models for amorphous calcite/aragonite of size ∼ 1700 nm3 based on a multi-scale modeling scheme. We used these models to generate diffraction patterns and profiles with our diffraction code. We found that the induced distortions were not enough to generate a diffraction profile typical of an amorphous material. We then studied the diffraction profiles from several nano-crystallites as recent studies suggest that ACC might be a random array of nanocryatallites. It was found that the generated diffraction profile from a nano-crystallite of size ∼ 2 nm3 is similar to that from the ACC.
ContributorsSinha, Sourabh (Author) / Rez, Peter (Thesis advisor) / Bearat, Hamdallah A. (Committee member) / Bennett, Peter A. (Committee member) / McCartney, Martha R. (Committee member) / Peng, Xihong (Committee member) / Arizona State University (Publisher)
Created2012
Description
Nuclear proliferation concerns have resulted in a desire for radiation detectors with superior energy resolution. In this dissertation a Monte Carlo code is developed for calculating energy resolution in gamma-ray detector materials. The effects of basic material properties such as the bandgap and plasmon resonance energy are studied using a model for inelastic electron scattering based on electron energy-loss spectra. From a simplified "toy model" for a generic material, energy resolution is found to oscillate as the plasmon resonance energy is increased, and energy resolution can also depend on the valence band width. By incorporating the model developed here as an extension of the radiation transport code Penelope, photon processes are also included. The enhanced version of Penelope is used to calculate the Fano factor and average electron-hole pair energy in semiconductors silicon, gallium arsenide, zinc telluride, and scintillators cerium fluoride and lutetium oxyorthosilicate (LSO). If the effects of the valence band density-of-states and phonon scattering are removed, the calculated energy-resolution for these materials is fairly close to that for a toy model with a uniform electron energy-loss probability density function. This implies that the details of the electron cascade may in some cases have only a marginal effect on energy resolution.
ContributorsNarayan, Raman (Author) / Rez, Peter (Thesis advisor) / Spence, John (Committee member) / Ponce, Fernando (Committee member) / Comfort, Joseph (Committee member) / Chizmeshya, Andrew (Committee member) / Arizona State University (Publisher)
Created2011
Description
This research evaluates the capabilities of typical radiological measures and dual-energy systems to differentiate common kidney stones materials: uric acid, oxalates, phosphates, struvite, and cystine. Two different X-ray spectra (80 kV and 120 kV) were applied and the dual-energy ratio of individual kidney stones was used to figure out the discriminability of different materials. A CT cross-section with a prospective kidney stone was analyzed to see the capabilities of such a technique. Typical radiological measures suggested that phosphates and oxalate stones can be distinguished from uric acid stones while dual-energy seemed to prove similar effectiveness.
ContributorsDelafuente, Nicholas William (Author) / Rez, Peter (Thesis director) / Alarcon, Ricardo (Committee member) / Department of Physics (Contributor) / Economics Program in CLAS (Contributor) / Barrett, The Honors College (Contributor)
Created2020-05
Description
Proton radiotherapy has recently become a popular form of cancer treatment. For maximum effectiveness, accurate models are needed to calculate proton angular scattering and energy loss. Scattering events are statistically independent and may be calculated from the effective number of events per reciprocal multiple scattering angle or energy loss. It is shown that multiple scattering distributions from Molière’s scattering law can be convolved by depth for accurate numerical calculation of angular distributions in several example materials. This obviates the need for correction factors to the analytic solution and its approximations. It is also shown that numerically solving Molière’s scattering law in terms of the complete (non-small angle) differential cross section and large angle approximations extends the validity of Molière theory to large angles. To calculate probability energy loss distributions, Landau-Vavilov theory is adapted to Fourier transforms and extended to very thick targets through convolution over the probability energy loss distributions in each depth interval. When the depth is expressed in terms of the continuous slowing down approximation (CSDA) the resulting probability energy loss distributions rely on the mean excitation energy as the sole material dependent parameter. Through numerical calculation of the CSDA over the desired energy loss, this allows the energy loss cross section to vary across the distribution and accurately accounts for broadening and skewness for thick targets in a compact manner. An analytic, Fourier transform solution to Vavilov’s integral is shown. A single scattering nuclear model that calculates large angle dose distributions that have a similar functional form to FLUKA (FLUktuierende KAskade) Monte Carlo, is also introduced. For incorporation into Monte Carlo or a treatment planning system, lookup tables of the number of scattering events or cross sections for different clinical energies may be used to determine angular or energy loss distributions.
ContributorsBrosch, Ryan Michael (Author) / Rez, Peter (Thesis advisor) / Alarcon, Ricardo O (Thesis advisor) / Vachaspati, Tanmay (Committee member) / Treacy, Michael M.J. (Committee member) / Arizona State University (Publisher)
Created2022
Description
As a demonstration study of low-resolution spectrophotometry, the photometric redshift estimation with narrow-band optical photometry of nine galaxy clusters is presented in this thesis. A complete data reduction process of the photometryusing up to 16 10nm wide narrow-band optical filters from 490nm − 660nm are provided. Narrow-band photometry data are combined with broad-band photometry (SDSS/Pan-STARRS) for photometric redshift fitting. With available spectroscopic
redshift data from eight of the fields, I evaluated the fitted photometric redshift results and showed that combining broad-band photometric data with narrow-band data result in improvements of factor 2-3, compared to redshift estimations from
broad-band photometry alone. With 15 or 16 narrow-band data combined with SDSS (Sloan Digital Sky Survey) or Pan-STARRS1 (The Panoramic Survey Telescope and Rapid Response System) data, a Normalized Median Absolute Deviation of σNMAD ∼ 0.01−0.016 can be achieved.
The multiband images of galaxy cluster ABELL 611 have been used to further study intracluster light around its brightest cluster galaxy (BCG). It can be shown here that fitting of BCG+ICL stellar properties using the averaged 1-dimensional
radial profile is possible up to ∼ 100kpc within this cluster. The decreasing in age of the stellar population as a function of radius from the BCG+ICL profile, though not entirely conclusive, demonstrates possible future application of low-resolution
spectrophotometry on the ICL studies.
Finally, Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx) mission planning study are covered, and a methodology of visualization tool for target availability is described.
ContributorsWang, Pao-Yu (Author) / Mauskopf, Philip (Thesis advisor) / Butler, Nathaniel (Committee member) / Jansen, Rolf (Committee member) / Vachaspati, Tanmay (Committee member) / Arizona State University (Publisher)
Created2022