Precision Rosenbluth Measurement of the Proton Elastic Electromagnetic Form Factors and Their Ratio at Q^2 = 2.64, 3.20, and 4.10 GeV^2

Due to the inconsistency in the results of the GEp/Gmp ratio of the proton, as extracted from the Rosenbluth and recoil polarization techniques, high precision measurements of the e-p elastic scattering cross sections were made at Q^2 = 2.64, 3.20, and 4.10 GeV^2. Protons were detected, in contrast to previous measurements where the scattered electrons were detected, which dramatically decreased epsilon-dependent systematic uncertainties and corrections. A single spectrometer measured the scattered protons of interest while simultaneous measurements at Q^2 = 0.5 GeV^2 were carried out using another spectrometer which served as a luminosity monitor in order to remove any uncertainties due to beam charge and target density fluctuations. The absolute uncertainty in the measured cross sections is \approx 3% for both spectrometers and with relative uncertainties, random and slope, below 1% for the higher Q^2 protons, and below 1% random and 6% slope for the monitor spectrometer. The extracted electric and magnetic form factors were determined to 4%-7% for GEp and 1.5% for GMp. The ratio GEp/Gmp was determined to 4%-7% and showed mu_p GEp/GMp \approx 1.0. The results of this work are in agreement with the previous Rosenbluth data and inconsistent with high-Q^2 recoil polarization results, implying a systematic difference between the two techniques.Comment: Ph.D. Thesis, Northwestern University, Advisor: Ralph E. Sege

Large Negative Poisson\u27s Ratio and Anisotropic Mechanics in New Penta-PBN Monolayer

The scarce negative Poisson\u27s ratio (NPR) in a two-dimensional (2D) material is an exceptional auxetic property that offers an opportunity to develop nanoscale futuristic multi-functional devices and has been drawing extensive research interest. Inspired by the buckled pentagonal iso-structures that often expose NPR, we employ state-of-the-art first-principles density functional theory calculations and analyses to predict a new 2D metallic ternary auxetic penta-phosphorus boron nitride (p-PBN) with a high value of NPR. The new p-PBN is stable structurally, mechanically, and dynamically and sustainable at room temperature, with experimental feasibility. The short and strong quasi sp3-hybridized B-N bond and unique bond variation and geometrical reconstruction with an applied strain allow p-PBN to inherit a high value of NPR (-0.236) along the (010) direction, the highest among any other ternary penta iso-structures reported to date. Despite having a small elastic strength, the highly asymmetric Young\u27s modulus and Poisson\u27s ratio along the (100) and (010) directions indicate large anisotropic mechanics, which are crucial for potential applications in nanomechanics and nanoauxetics

Mossbauer, resistivity, magnetization, and powder x-ray diffraction studies of colossal magnetoresistive La[sub 0.88] Sr[sub 0.12] Mn[sub 1-y] Fe[sub y] O[sub3] (y = 0, 0.02, and 0.04)

Includes bibliographical references (pages [110]-112).Mossbauer, resistivity, magnetization, and powder x-ray diffraction measurements have been made on La[sub 0.88] Sr[sub 0.12 Mn[sub 1-y] ^57Fe[sub y] O[sub 3] (y = 0.02, and 0.04), while measurements on the y = 0.0 sample have been made with all of the above techniques but Mossbauer. ^57Fe is found to be in the (+3) valance state. The effect of increasing ^57Fe doping level on the structural, magnetic, and transport properties of the colossal magnetoresistive rare-earth transition metal oxides is discussed in detail. I have observed a drop in the static orbital ordered coherent Jahn-Teller distortion temperature T[sub [pi]] and an increase in the ferromagnetic ordering temperature T[sub C] with increasing ^57Fe doping level. A strong suppression of the coherent Jahn-Teller distortion due to magnetization is seen suggesting the existence of magneto-lattice-transport coupling. Anisotropic ferromagnetic spin-wave behavior is the main dynamical character of these samples at low temperatures. Such effect gives rise to gap formation and therefore spin canting in these samples. As y increases, the exchange coupling constant increases and the gap energy decreases. This suggests a strong coupling between the exchange coupling constant and the gap energy at low temperatures. Increasing the exchange coupling constant increases the linkage angle of the ^57Fe^+3 - O^-2 - Mn^+3 network and, therefore, increases T[sub C].M.S. (Master of Science

Penta-SiCN: A Highly Auxetic Monolayer

The negative Poisson’s (NPR) ratio in a two-dimensional (2D) material is a counterintuitive mechanical property that facilitates the development of nanoscale devices with sophisticated functionality. Inspired by the peculiar buckled lower-symmetric, trilayered geometry of pentagonal monolayers, we theoretically predict penta-SiCN, a ternary auxetic metallic monolayer with highly tunable NPR. The penta-SiCN is structurally, thermally, dynamically, and mechanically stable, and sustainable at and beyond room temperature with experimental feasibility. It possesses nontrivial geometrical and mechanical isotropy and relatively moderate thickness. Remarkably, the shorter and quasi sp3-hybridized C–N bond and the rigidity against the strain allow the monolayer to possess a high value of NPR (−0.136), even higher than that of black phosphorene, extendable up to −0.639 by 4% of biaxial stretching. On the other hand, the 2D Young’s modulus of 129.88 N/m decreases to 41.34 N/m at equivalent stretching, indicating relative softening and flexibility. Interestingly, a buckled-to-planar phase transition is identified at 10% biaxial strain before it suffers the fracture at 16%. Additionally, the strong optical anisotropy, absorbance (up to 6.51× 105 cm–1), and presence of plasmon frequency demonstrate its potential application in optomechanical and plasmonics.This is a manuscript of an article published as Sharma, Shambhu Bhandari, Issam A. Qattan, Meghnath Jaishi, and Durga Paudyal. "Penta-SiCN: A highly auxetic monolayer." ACS Applied Electronic Materials 4, no. 5 (2022): 2561-2569. DOI: 10.1021/acsaelm.2c00265. Copyright 2022 American Chemical Society. Posted with permission. DOE Contract Number(s): AC02-07CH11358

Effect of bromine deficiency on large elastic moduli of alpha-phase diisopropyl ammonium bromide (

Elastic stiffness moduli were studied using dispersion-corrected density functional theory. The elastic stiffness moduli of α-DIPAB molecular crystals are found to be strongly anisotropic, with exceptionally high values of ~55 GPa. The magnitude of elastic stiffness modulus is strongly correlated with the relative orientation between the underlying hydrogen-bonding networks of DIPA molecules (“stitched” together by Br ions). These values of elastic stiffness modulus are remarkably high and suggest the design of hydrogen bond networks as a route for rational design of ultra-stiff molecular solids. Furthermore, Young’s modulus of α-DIPAB was found to attain extremely large value of as large as 50 GPa along certain crystallographic directions, while Br-deficient DIPAB has reduced Young’s modulus ( ~18 GPa). Anisotropy of Young’s modulus in α-DIPAB is very large with values below 40% of its maximum along specific spatial directions (and even lower in Br-deficient crystals). α-DIPAB and Br-deficient DIPAB show very different directionality of Young’s modulus due to the change in H-Br bond network upon Br deficiency. Additionally, Poisson’s ratio is strongly anisotropic as well with values ranging between a maximum of 0.4 for certain crystallographic directions and about 0.25 for other directions indicating the directionality of bonding in α-DIPAB. DIPAB systems are brittle based on the ratio between bulk and sheer elastic constants. Thus, DIPAB should be used as an element of composite materials to be used in thin-film flexible electronic application

Optical, Structural, and Crystal Defects Characterizations of Dip Synthesized (Fe-Ni) Co-Doped ZnO Thin Films

Sol-gel technique is used to synthesize as-grown zinc oxide (ZnO) and iron-nickel (Fe-Ni) co-doped ZnO thin films deposited on glass substrates using dip coating technique. The structural properties and crystal imperfections of as-prepared thin films are investigated. We performed the structural analysis of films using X-ray diffraction (XRD). The XRD analysis reveal that the as-prepared films exhibit wurtzite structure. Furthermore, XRD-line profile analysis is performed to study the correlation between structural properties and imperfections of the nanocomposite thin films. The crystallite size and microstrains parameters are predicted using the Williamson–Hall method. We found that the crystallites size increases as the co-doped (Fe-Ni) concentration is increased. However, microstrains of the nanocomposite films decreases as (Fe-Ni) concentration is increased. The optical properties of the (Fe-Ni) co-doped nanocomposite films are investigated by performing UV-Vis (250 nm–700 nm) spectrophotometer measurements. We found that as the (Fe-Ni) concentration level is steadily increased, transmittance of the undoped ZnO thin films is decreased. Remarkably, refractive index of undoped ZnO thin films is found to exhibit values extending from 1.55 to1.88 that would increase as (Fe-Ni) concentration is increased

Physicochemical Properties of Organic Molecular Ferroelectric Diisopropylammonium Chloride Thin Films

We fabricated ferroelectric films of the organic molecular diisopropylammonium chloride (DIPAC) using the dip-coating technique and characterized their properties using various methods. Fourier-transform infrared, scanning electron microscopy, and X-ray diffraction analysis revealed the structural features of the films. We also performed ab-initio calculations to investigate the electronic and polar properties of the DIPAC crystal, which were found to be consistent with the experimental results. In particular, the optical band gap of the DIPAC crystal was estimated to be around 4.5 eV from the band structure total density-of-states obtained by HSE06 hybrid functional methods, in good agreement with the value derived from the Tauc plot analysis (4.05 ± 0.16 eV). The films displayed an island-like morphology on the surface and showed increasing electrical conductivity with temperature, with a calculated thermal activation energy of 2.24 ± 0.03 eV. Our findings suggest that DIPAC films could be a promising alternative to lead-based perovskites for various applications such as piezoelectric devices, optoelectronics, sensors, data storage, and microelectromechanical systems