10 research outputs found
Higher-order triplet interaction in energy-level modeling of excited-state absorption for an expanded porphyrin cadmium complex
Recent measurements of transmission versus fluence for a methanol-solvated asymmetric pentaazadentate porphyrin-like (APPC) cadmium complex, [(C6H4-APPC)Cd]Cl, showed the limitations of current energy-level models in predicting the transmission behavior of organic reverse saturable absorbers at fluences greater than 1 J/cm². A new model has been developed that incorporates higher-order triplet processes and accurately fits both nanosecond and picosecond transmission-versus-fluence data. This model has provided the first known determination of a higher triplet excited-state absorption cross section and lifetime for an APPC complex and also described a previously unreported feature in the transmission-versus-fluence data. The intersystem crossing rate and the previously neglected higher triplet excited-state absorption cross section are shown to govern the excited-state population dynamics of methanol-solvated [(C6H4-APPC)Cd]Cl most strongly at more-practical device energies
Raman spectrometry study of phonon anharmonicity of hafnia at elevated temperatures
Raman spectra of monoclinic hafnium oxide (HfO_2) were measured at temperatures up to 1100 K. Raman peak shifts and broadenings are reported. Phonon dynamics calculations were performed with the shell model to obtain the total and partial phonon density of states, and to identify the individual motions of Hf and O atoms in the Raman modes. Correlating these motions to the thermal peak shifts and broadenings, it was found that modes involving changes in oxygen-oxygen bond length were the most anharmonic. The hafnium-dominated modes were more quasiharmonic and showed less broadening with temperature. Comparatively, the oxygen-dominated modes were more influenced by the cubic term in the interatomic potential than the hafnium-dominated modes. An approximately quadratic correlation was found between phonon-line broadening and softening
AtomSim: web-deployed atomistic dynamics simulator
AtomSim, a collection of interfaces for computational crystallography simulations, has been developed. It uses forcefield-based dynamics through physics engines such as the General Utility Lattice Program, and can be integrated into larger computational frameworks such as the Virtual Neutron Facility for processing its dynamics into scattering functions, dynamical functions etc. It is also available as a Google App Engine-hosted web-deployed interface. Examples of a quartz molecular dynamics run and a hafnium dioxide phonon calculation are presented
Self-Powered Dynamic Systems in the Framework of Optimal Uncertainty Quantification
The energy that is needed for operating a self-powered device is provided by the energy excess in the system in the form of kinetic energy, or a combination of regenerative and renewable energy. This paper addresses the energy exchange issues pertaining to regenerative and renewable energy in the development of a self-powered dynamic system. A rigorous framework that explores the supply and demand of energy for self-powered systems is developed, which considers uncertainties and optimal bounds, in the context of optimal uncertainty quantification. Examples of regenerative and solar-powered systems are given, and the analysis of self-powered feedback control for developing a fully self-powered dynamic system is discussed
A Raman Spectrometry Study of Phonon Anharmonicity of Zirconia at Elevated Temperatures
Raman spectra of monoclinic zirconia (ZrO_2) were measured at temperatures of up to 950 K. Temperature-dependent Raman peak shifts
and broadenings were reported and compared with prior results on hafnia
(HfO_2). Lattice dynamics calculations were performed with both shell
model and density functional theory to obtain Raman frequencies, and
the total and partial phonon density of states. These calculations were
also used to identify the individual motions of metal and oxygen atoms
in the different Raman modes. By correlating these motions to the
thermal peak shifts and broadenings, it was confirmed that modes
involving changes in oxygen-oxygen bond length were the most
anharmonic. The metal-dominated modes were found to be more
quasiharmonic, and thus showed less broadening with temperature. Mass
effects were evident by comparing the mode softening and shifting
between zirconia and hafnia