Phonon Scattering in Disordered Systems

1986 ◽  
pp. 6-14 ◽  
Author(s):  
A. M. de Goër
Keyword(s):  
Disordered Systems ◽  
Phonon Scattering

scholarly journals A universal Urbach rule for disordered organic semiconductors

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Christina Kaiser ◽  
Oskar J. Sandberg ◽  
Nasim Zarrabi ◽  
Wei Li ◽  
Paul Meredith ◽  
...  
Keyword(s):  
Organic Semiconductors ◽  
Organic Solar Cells ◽  
Disordered Systems ◽  
Urbach Energy ◽  
Phonon Scattering ◽  
Exponential Tail ◽  
Temperature Dependent ◽  
Static Disorder ◽  
Line Shapes ◽  
Gaussian Density

AbstractIn crystalline semiconductors, absorption onset sharpness is characterized by temperature-dependent Urbach energies. These energies quantify the static, structural disorder causing localized exponential-tail states, and dynamic disorder from electron-phonon scattering. Applicability of this exponential-tail model to disordered solids has been long debated. Nonetheless, exponential fittings are routinely applied to sub-gap absorption analysis of organic semiconductors. Herein, we elucidate the sub-gap spectral line-shapes of organic semiconductors and their blends by temperature-dependent quantum efficiency measurements. We find that sub-gap absorption due to singlet excitons is universally dominated by thermal broadening at low photon energies and the associated Urbach energy equals the thermal energy, regardless of static disorder. This is consistent with absorptions obtained from a convolution of Gaussian density of excitonic states weighted by Boltzmann-like thermally activated optical transitions. A simple model is presented that explains absorption line-shapes of disordered systems, and we also provide a strategy to determine the excitonic disorder energy. Our findings elaborate the meaning of the Urbach energy in molecular solids and relate the photo-physics to static disorder, crucial for optimizing organic solar cells for which we present a revisited radiative open-circuit voltage limit.

scholarly journals Phonon Lifetimes and Thermal Conductivity of the Molecular Crystal α-RDX

MRS Advances ◽  
2019 ◽  
Vol 4 (40) ◽  
pp. 2191-2199 ◽  
Author(s):  
Gaurav Kumar ◽  
Francis G. VanGessel ◽  
Daniel C. Elton ◽  
Peter W. Chung
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Disordered Systems ◽  
Molecular Crystal ◽  
Amorphous Materials ◽  
Phonon Scattering ◽  
Large Degree ◽  
Crystalline Materials ◽  
Boltzmann Model ◽  
Transfer Properties

ABSTRACTThe heat transfer properties of the organic molecular crystal α-RDX were studied using three phonon scattering based thermal conductivity models. It was found that the widely used Peierls-Boltzmann model for thermal transport in crystalline materials breaks down for α-RDX. We show this breakdown is due to a large degree of anharmonicity that leads to a dominance of diffusive-like carriers. Despite being developed for disordered systems, the Allen-Feldman theory for thermal conductivity actually gives the best description of thermal transport. This is likely because diffusive carriers contribute to over 95% of the thermal conductivity in α-RDX. The dominance of diffusive carriers is larger than previously observed in other fully ordered crystalline systems. These results indicate that van der Waals bonded organic crystalline solids conduct heat in a manner more akin to amorphous materials than simple atomic crystals.

Towards quantitative simulations of inelastic electron diffraction patterns and images

1992 ◽  
Vol 50 (2) ◽  
pp. 1170-1171
Author(s):  
Z. L. Wang
Keyword(s):  
Phonon Scattering ◽  
Incident Beam ◽  
Dynamical Theory ◽  
Inelastic Electron ◽  
Additional Advantage ◽  
Coupled Equations ◽  
Atomic Vibrations ◽  
Diffraction Patterns ◽  
Primary Advantage ◽  
The One

A new dynamical theory has been developed based on Yoshioka's coupled equations for describing inelastic electron scattering in thin crystals. Compared to existing theories, the primary advantage of this theory is that the incoherent summation of the diffracted intensities contributed by electrons after exciting vast numbers of different excited states has been evaluated before any numerical calculation. An additional advantage is that the phase correlations of atomic vibrations are considered, so that full lattice dynamics can be combined in the phonon scattering calculation. The new theory has been proven to be equivalent to the inelastic multislice theory, and has been applied to calculate energy-filtered diffraction patterns and images formed by phonon, single electron and valence scattered electrons.A calculated diffraction pattern of elastic and phonon scattered electrons for a parallel incident beam case is in agreement with the one observed (Fig. 1), showing thermal diffuse scattering (TDS) streaks and Kikuchi pattern.

On the stochastic transport in disordered systems

1988 ◽  
Vol 49 (10) ◽  
pp. 1731-1736 ◽  
Author(s):  
M.V. Feigel'man ◽  
V.M. Vinokur
Keyword(s):  
Disordered Systems ◽  
Stochastic Transport
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