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Secondary Electron Cascade Dynamics in KI and CsI
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology.
2007 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 46, p. 17442-17447Article in journal (Refereed) Published
Abstract [en]

We present a study of the characteristics of secondary electron cascades in two photocathode materials, KI and CsI. To do so, we have employed a model that enables us to explicitly follow the electron trajectories once the dielectric properties have been derived semiempirically from the energy loss function. Furthermore, we introduce a modification to the model by which the energy loss function is calculated in a first-principle manner using the GW approximation for the self-energy of the electrons. We find good agreement between the two approaches. Our results show comparable saturation times and secondary electron yields for the cascades in the two materials, and a narrower electron energy distribution (51%) for KI compared to that for CsI.

Place, publisher, year, edition, pages
2007. Vol. 111, no 46, p. 17442-17447
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-102110DOI: 10.1021/jp0736692ISI: 000251024500041OAI: oai:DiVA.org:uu-102110DiVA, id: diva2:214349
Available from: 2009-05-06 Created: 2009-05-05 Last updated: 2017-12-13Bibliographically approved
In thesis
1. First Principles Calculations of Electron Transport and Structural Damage by Intense Irradiation
Open this publication in new window or tab >>First Principles Calculations of Electron Transport and Structural Damage by Intense Irradiation
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

First principle electronic structure theory is used to describe the effect of crystal binding on radiation detectors, electron transport properties, and structural damage induced by intense irradiation. A large database containing general electronic structure results to which data mining algorithms can be applied in the search for new functional materials, a case study is presented for scintillator detector materials. Inelastic cross sections for the generation of secondary electron cascades through impact ionization are derived from the dielectric response of an electron gas and evolved in time with Molecular Dynamics (MD). Qualitative and quantitive estimates are presented for the excitation and relaxation of a sample irradiated with Free Electron Laser pulses. A study is presented in where the structural damage on covalent bonded crystals following intense irradiation is derived from a Tight Binding approach and evolved in time with MD in where the evolution of the sample is derived from GW theory for the quasiparticle spectra and a dedicated Boltzmann transport equation for the impact ionization.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. p. 61
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 652
Keywords
Condense matter theory, electronic structure, quasiparticles, GW theory, molecular dynamics, Boltzmann transport, electron transport, impact ionization, structural damage, dielectric response, structural biology, radiation detectors, scintillators, positron emission tommography
National Category
Other Materials Engineering Condensed Matter Physics
Research subject
Physics of Matter
Identifiers
urn:nbn:se:uu:diva-102376 (URN)978-91-554-7547-5 (ISBN)
Public defence
2009-06-12, Polhemsalen, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2009-05-20 Created: 2009-05-06 Last updated: 2013-02-26Bibliographically approved
2. Towards Single Molecule Imaging - Understanding Structural Transitions Using Ultrafast X-ray Sources and Computer Simulations
Open this publication in new window or tab >>Towards Single Molecule Imaging - Understanding Structural Transitions Using Ultrafast X-ray Sources and Computer Simulations
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

X-ray lasers bring us into a new world in photon science by delivering extraordinarily intense beams of x-rays in very short bursts that can be more than ten billion times brighter than pulses from other x-ray sources. These lasers find applications in sciences ranging from astrophysics to structural biology, and could allow us to obtain images of single macromolecules when these are injected into the x-ray beam.

A macromolecule injected into vacuum in a microdroplet will be affected by evaporation and by the dynamics of the carrier liquid before being hit by the x-ray pulse. Simulations of neutral and charged water droplets were performed to predict structural changes and changes of temperature due to evaporation. The results are discussed in the aspect of single molecule imaging.

Further studies show ionization caused by the intense x-ray radiation. These simulations reveal the development of secondary electron cascades in water. Other studies show the development of these cascades in KI and CsI where experimental data exist. The results are in agreement with observation, and show the temporal, spatial and energetic evolution of secondary electron cascades in the sample.

X-ray diffraction is sensitive to structural changes on the length scale of chemical bonds. Using a short infrared pump pulse to trigger structural changes, and a short x-ray pulse for probing it, these changes can be studied with a temporal resolution similar to the pulse lengths. Time resolved diffraction experiments were performed on a phase transition during resolidification of a non-thermally molten InSb crystal. The experiment reveals the dynamics of crystal regrowth.

Computer simulations were performed on the infrared laser-induced melting of bulk ice, giving a comprehension of the dynamics and the wavelength dependence of melting. These studies form a basis for planning experiments with x-ray lasers.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. p. 77
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 315
Keywords
Molecular biophysics, XFEL, Ultrafast Melting, InSb, Molecular Dynamics, Water Cluster, Evaporation, Secondary Electron, Photo-cathode, Electron Scattering, Energy Loss Function, Single Particle Imaging, X-ray Diffraction, Water, Ice, KI, CsI, Molekylär biofysik
Identifiers
urn:nbn:se:uu:diva-7915 (URN)978-91-554-6911-5 (ISBN)
Public defence
2007-06-07, B41, Biomedical Centre, Husargatan 3, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2007-05-16 Created: 2007-05-16 Last updated: 2010-03-16Bibliographically approved

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Ortiz, Carlos

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