This thesis provides a study of different aspects of the mechanical and vibrational properties of disordered and amorphous solids. Resorting to the theoretical framework of non-affine lattice dynamics the attention is focused on the analysis of disordered networks and lattices which serve as tractable model systems for real materials. Firstly, we discuss the static elastic response and the vibrational spectra of defective fcc crystals. The connection to different types of microstructural disorder in the form of bond-depletion and vacancies is described within the context of the inversion symmetry breaking of the local particle configurations. We identify the fluctuations of the local inversion symmetry breaking, which is directly linked to the non-affinity of the disordered solid, as the source of different scalings behaviours of the position of the boson peak. Furthermore, we describe the elastic heterogeneities occurring in a bond-depleted two- dimensional lattice with long-range interactions. The dependence of the concomitant correlations of the local elastic moduli are studied in detail in terms of the interaction range and the degree of disorder. An analytical scaling relation is derived for the radial part of the elastic correlations in the affine limit. Subsequently, we provide an argument for the change of the angular symmetry of the elastic correlation function which was observed in simulations and experiments on glasses and colloids, respectively. Moving to the dynamical behaviour of disordered solids, a framework is developed based on the kernel polynomial method for the approximate computation of the non- affine correlator of displacement fields which is the key requirement to describe the linear viscoelastic response of the system within the quasi-static non-affine formalism. This approach is then extended to the case of multicomponent polymer melts and validated against molecular dynamics simulations at low non-zero temperatures. We also consider the dynamical behaviour of metallic glasses in terms of its shear elasticity and viscosity. A theoretical scheme is suggested which links the repulsive strength of the interatomic potential to the viscoelasticity and fragility in metallic glasses in the quasi-affine limit.

No description available.

An alternative approach to energy integrating systems is photon counting which provides higher dose efficiency through efficient noise rejection and optimal energy weighting, and, moreover, is not susceptible to memory artifacts such as image lag and ghosting. The first large-area photon counting imager was Charpak's Nobel Prize winning invention of the gas-filled multiwire proportional chamber (MWPC), which revolutionized the field of radiation detection in 1968. In most applications, however, the use of a solid detection medium is preferable because solid densities are about three orders-of-magnitude greater than gas, and thus, they can yield much smaller detector dimensions with unsurpassed spatial and temporal resolution. Thus far, crystalline Cadmium Zinc Telluride is the only room-temperature solid-state detector that meets the requirements for photon counting imaging. However, the material is grown in small ingots and production costs are high for large-area imaging applications. The problem is that disordered (or non-crystalline) solids, which are easier and less expensive to develop over large-area than single crystalline solids, have been ruled out as viable photon counting detectors because of their poor temporal resolution, or more specifically, extremely low carrier mobilities and transit-time-limited photoresponse. To circumvent the problem of poor charge transport in disordered solids with a conventional planar detector structure, we propose unipolar charge sensing by establishing a strong near-field effect using an electrostatic shield within the material. We introduce the concept of time-differential photoresponse in unipolar solids and show that their temporal resolution can be improved substantially to reach the intrinsic physical limit set by spatial dispersion. Inspired by Charpak's MWPC and its variants, and for the first time, we have implemented an electrostatic shield inside evaporated amorphous selenium (a-Se) using the proposed lithography-based microstrip solid-state detector (MSSD). The fabricated devices are characterized with optical, x-ray, and gamma-ray impulse-like excitations. Using optical time-of-flight (TOF) measurements, we show for the first time a unipolar Gaussian TOF transient from the new MSSD structure, instead of a rectangular response with a Gaussian-integral at the tail which is a typical response of a conventional planar device. The measured optical and x-ray TOF results verify the time-differential property of the electrostatic shield and the practicality of the dispersion-limited photoresponse. Furthermore, we use single gamma-ray photon excitations to probe detector's temporal resolution in pulse mode for photon counting. For the MSSD, we show a depth-independent signal for photon absorption across the bulk and a reduction in signal risetime by a factor of 350, comparing performance limiting factors being hole-dispersion for the MSSD and electron-transit-time for the conventional planar device. The time-differential response obtained from the proposed unipolar detector structure enables disordered photoconductive films to become viable candidates for large-area photon counting applications.

An alternative approach to energy integrating systems is photon counting which provides higher dose efficiency through efficient noise rejection and optimal energy weighting, and, moreover, is not susceptible to memory artifacts such as image lag and ghosting. The first large-area photon counting imager was Charpak's Nobel Prize winning invention of the gas-filled multiwire proportional chamber (MWPC), which revolutionized the field of radiation detection in 1968. In most applications, however, the use of a solid detection medium is preferable because solid densities are about three orders-of-magnitude greater than gas, and thus, they can yield much smaller detector dimensions with unsurpassed spatial and temporal resolution. Thus far, crystalline Cadmium Zinc Telluride is the only room-temperature solid-state detector that meets the requirements for photon counting imaging. However, the material is grown in small ingots and production costs are high for large-area imaging applications. The problem is that disordered (or non-crystalline) solids, which are easier and less expensive to develop over large-area than single crystalline solids, have been ruled out as viable photon counting detectors because of their poor temporal resolution, or more specifically, extremely low carrier mobilities and transit-time-limited photoresponse. To circumvent the problem of poor charge transport in disordered solids with a conventional planar detector structure, we propose unipolar charge sensing by establishing a strong near-field effect using an electrostatic shield within the material. We introduce the concept of time-differential photoresponse in unipolar solids and show that their temporal resolution can be improved substantially to reach the intrinsic physical limit set by spatial dispersion. Inspired by Charpak's MWPC and its variants, and for the first time, we have implemented an electrostatic shield inside evaporated amorphous selenium (a-Se) using the proposed lithography-based microstrip solid-state detector (MSSD). The fabricated devices are characterized with optical, x-ray, and gamma-ray impulse-like excitations. Using optical time-of-flight (TOF) measurements, we show for the first time a unipolar Gaussian TOF transient from the new MSSD structure, instead of a rectangular response with a Gaussian-integral at the tail which is a typical response of a conventional planar device. The measured optical and x-ray TOF results verify the time-differential property of the electrostatic shield and the practicality of the dispersion-limited photoresponse. Furthermore, we use single gamma-ray photon excitations to probe detector's temporal resolution in pulse mode for photon counting. For the MSSD, we show a depth-independent signal for photon absorption across the bulk and a reduction in signal risetime by a factor of 350, comparing performance limiting factors being hole-dispersion for the MSSD and electron-transit-time for the conventional planar device. The time-differential response obtained from the proposed unipolar detector structure enables disordered photoconductive films to become viable candidates for large-area photon counting applications.

No description available.