82 research outputs found

    Computational Methodologies for the Simulation and Analysis of Low-frequency Vibrations in Molecular Crystals

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    Quantum mechanical models are used to calculate a host of physical phenomena in molecular solids ranging from mechanical elasticity to the energetic stability ordering of polymorphs. However, with the many software packages and methodologies available, it can be difficult to select the most suitable model for the problem at hand without prior knowledge. A promising approach for evaluating the performance of solid-state models is the comparison of the simulations to experimentally measured low-frequency (sub-200 cm-1) vibrational spectra. As this region is dominated by weak intermolecular forces and shallow potential energy surfaces, even slight miscalculations in the solid-state packing arrangements can become readily apparent. In this work, terahertz time-domain spectroscopy and low-frequency Raman spectroscopy are used as benchmark experimental targets to develop computational methodologies for simulating and analyzing the lattice vibrations of molecular crystals such as torsions and translations. The developed computational approaches utilize solid-state density functional theory to account for the periodic nature of a molecular crystal and include careful consideration of the effects that functional choice, basis set composition, and energetic tolerances have on the frequencies and spectral intensities of the sub-200 cm-1 vibrations. These computational methodologies serve as standards for accurately modeling low-frequency vibrations across a range of molecular solids from a small molecule that exhibits unusual thermal behavior to the intricacies of an extensively hydrogen bonded oligopeptide

    Advancing nanophotonic devices for biomolecular analysis

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    Propagation of terahertz radiation in non-homogeneous materials and structures

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    The work undertaken is concerned with looking at how terahertz frequency radiation (here defined as 300 GHz -10 THz) propagates through media which have a random structure ("non-homogeneous materials"). Materials of this type are important in a wide range of applications, but are of particular interest in security and surveillance. Propagation of terahertz radiation through non-homogeneous materials is not well understood: both interference and scattering effects become important in this spectral range, where the wavelength and size and separation of the scattering centres are often commensurable. A simple model, which uses the phase change of a wave to describe its transmission through media having relatively small changes in refractive index is developed and compared with both exact theories and experimentally obtained measurements. Overall, a satisfactory agreement between the experimental data for transmission through arrays of cylinders, textiles and powders is seen. It is well known that pulses of terahertz radiation from optoelectronic sources have a complex shape. Post detection signal processing routines can be used to clean up the experimentally determined signals. The development of such algorithms is described, before they are applied to experimental results to determine: the minimum size of gaps between slabs to mimic voids in media; and the response of various compounds to a sharply terminated input pulse. The investigation of scattering from random structures requires the construction of a spectrometer having the capability to measure THz pulses scattered at different angles. Such a system ideally requires fibre-fed detection schemes to be used. The construction of a scattering spectrometer is described and its performance outlined. Pulses of terahertz which have been scattered by a sample of interest can be reconstructed, using methods from conventional tomography, to produce images of the phantom under test. Such measurements are outlined here. To our knowledge, this is the first time that tomography has been undertaken using a fixed sample and rotating detector arrangement

    Optical Fiber, Nanomaterial, and THz-Metasurface-Mediated Nano-Biosensors: A Review

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    The increasing use of nanomaterials and scalable, high-yield nanofabrication process are revolutionizing the development of novel biosensors. Over the past decades, researches on nanotechnology-mediated biosensing have been on the forefront due to their potential application in healthcare, pharmaceutical, cell diagnosis, drug delivery, and water and air quality monitoring. The advancement of nanoscale science relies on a better understanding of theory, manufacturing and fabrication practices, and the application specific methods. The topology and tunable properties of nanoparticles, a part of nanoscale science, can be changed by different manufacturing processes, which separate them from their bulk counterparts. In the recent past, different nanostructures, such as nanosphere, nanorods, nanofiber, core–shell nanoparticles, nanotubes, and thin films, have been exploited to enhance the detectability of labelled or label-free biological molecules with a high accuracy. Furthermore, these engineered-materials-associated transducing devices, e.g., optical waveguides and metasurface-based scattering media, widened the horizon of biosensors over a broad wavelength range from deep-ultraviolet to far-infrared. This review provides a comprehensive overview of the major scientific achievements in nano-biosensors based on optical fiber, nanomaterials and terahertz-domain metasurface-based refractometric, labelled and label-free nano-biosensors

    Neutron Scattering

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    This book brings suitable data concerning theory and experiments of neutron interactions with different materials. Since the neutron discovery by Chadwick in 1932, researchers of the entire world begin to make studies about it. It is well known that neutron have no charge, and their electric dipole moment is either zero or too small to measure, but theories and experiments show that neutron has spin (presence of magnetic moment), and polarization neutron scattering is plausible. The reader can obtain remarks about inelastic scattering cross sections for neutron; polarized neutron reflectivity; scattering methods; neutron reflectometry tool to probe the chemical structures; neutron scattering for amino acid crystals; and small-angle neutron scattering nanoemulsion heat transfer fluids in this book

    Nanofabrication

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    We face many challenges in the 21st century, such as sustainably meeting the world's growing demand for energy and consumer goods. I believe that new developments in science and technology will help solve many of these problems. Nanofabrication is one of the keys to the development of novel materials, devices and systems. Precise control of nanomaterials, nanostructures, nanodevices and their performances is essential for future innovations in technology. The book "Nanofabrication" provides the latest research developments in nanofabrication of organic and inorganic materials, biomaterials and hybrid materials. I hope that "Nanofabrication" will contribute to creating a brighter future for the next generation
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