Department of Physics, Engineering Physics and Astronomy Faculty Publications

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    Computing Vibrational Spectra Using a New Collocation Method With a Pruned Basis and More Points Than Basis Functions: Avoiding Quadrature
    (AIP Publishing, 2023-04-13) Simmons, Jesse; Carrington, Tucker Jr.
    We present a new collocation method for computing the vibrational spectrum of a polyatomic molecule. Some form of quadrature or collocation is necessary when the potential energy surface does not have a simple form that simplifies the calculation of the potential matrix elements required to do a variational calculation. With quadrature, better accuracy is obtained by using more points than basis functions. To achieve the same advantage with collocation, we introduce a collocation method with more points than basis functions. Critically important, the method can be used with a large basis because it is incorporated into an iterative eigensolver. Previous collocation methods with more points than functions were incompatible with iterative eigensolvers. We test the new ideas by computing energy levels of molecules with as many as six atoms. We use pruned bases but expect the new method to be advantageous whenever one uses a basis for which it is not possible to find an accurate quadrature with about as many points as there are basis functions. For our test molecules, accurate energy levels are obtained even using non-optimal, simple, equally spaced points.
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    Low-Cost Molecular Glass Hole Transport Material for Perovskite Solar Cells
    (IOP Publishing, 2021-02-16) Wang, LiangLe; Shahiduzzaman, Md.; Fukaya, Shoko; Muslih, Ersan Y.; Nakano, Masahiro; Karakawa, Makoto; Takahashi, Kohshin; Tomita, Koji; Lebel, Olivier; Nunzi, Jean-Michel; Taima, Tetsuya
    The availability of low-cost hole transport materials (HTMs) that are easy to process is crucial for the eventual commercialization of perovskite solar cells (PSCs), as the commonly used HTM (Spiro-OmeTAD) is expensive, and its processing is complex. In this study, we synthesized an amorphous molecular material (termed as TPA-glass) from the condensation of 2-mexylamino-4-methylamino-6-(4-aminophenylamino)-1,3,5-triazine and N-(4-formylphenyl)diphenylamine with a low-cost and easy process, and applied as an HTM in PSCs. We investigated the effect of TPA-glass thin-films with varying thickness, as well as their corresponding solar cell’s properties. The preliminary performance data indicate that TPA-glass thin-film can be a potential HTM candidate for planar PSCs.
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    Mechanical Strength Characterization and Modeling of Hydroxyapatite / Tricalcium Phosphate Biocomposite Using the Diametral-Compression Test
    (EDP Sciences, 2021-03-17) Es-saddik, M.; Laasri, S.; Laghzizil, A.; Nunzi, Jean-Michel; Taha, M.; Guidara, A.; Hajjaji, A.
    This study reports the enhanced mechanical resistance of the composite bioceramics of hydroxyapatite (HAP) and tricalcium phosphate (b-TCP) used as bone substitute. HAP/b-TCP mixture was prepared by wet mixing of powders and characterized. Effects of powder manufacturing and sintering temperature on the densification, microstructure and mechanical properties of the composite were studied. The rupture strength (sr) was calculated using the Brazilian test. At 1250 °C, the relative density and mechanical strength of the HAP/b-TCP ceramics reached the maximum value of 89% and 43MPa, respectively. Experimental results were modeled by the finite element method to determine the stress distribution in the compacted disc.
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    Frontiers in Photosensor Materials and Designs for New Image Sensor Applications
    (Institute of Electrical and Electronics Engineers, 2020-12-08) Jansen-van Vuuren, Ross; Nunzi, Jean-Michel; Givigi, Sidney
    Certain applications of image sensors require capabilities that are beyond the technology of current image sensors such as automated quality inspection systems based on color discrimination under varying levels of illumination. This paper serves to provide a brief overview of image sensor technologies involving the use of alternative photosensor materials (organic semiconductors and perovskites) being developed to meet these needs. The discussion around such developments is typically confined to chemistry and physics “silos”; by publishing in this special edition, the authors hope to bridge the knowledge gap between scientists developing new photosensor materials and engineers developing image sensors for new machine vision systems.
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    Influence of Polymer Gate Dielectric on Organic Field-Effect Transistors: Interdependence of Molecular Weight, Solvent Polarity, and Surface Energy—A Case Study with PMMA and Pentacene
    (Wiley, 2021-10-26) V. R., Rajeev; Pillai, Stradha; Nunzi, Jean-Michel; K N, Narayanan Unni
    The semiconductor/dielectric interface controls the performance of organic field-effect transistors (OFETs). Herein, the influence of both the molecular weight and the polarity of the solvent of a poly(methyl methacrylate) (PMMA)-based gate dielectric on the performance of pentacene OFETs is systematically investigated, by studying surface energy, surface roughness, morphology, leakage current, and capacitance of the dielectric. Various existing views on the role of the surface energy are considered while deriving a correlation. Larger pentacene grains are observed when the film is grown on high molecular weight-PMMA films cast from high dipole moment-solvent. The electrical properties of the corresponding OFETs show great improvement compared to those of OFETs fabricated with low molecular weight-PMMA film as the gate dielectric, irrespective of the solvent. The authors attribute this enhanced performance to the increased surface energy of the polymeric dielectric which turns out to be a strong function of its molecular weight and the dipole moment of the solvent. Bias-stress measurements on the OFETs confirm this correlation.