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Title: The interaction of 193 nm excimer laser radiation with single-crystal zinc oxide: Generation of long lived highly excited particles with evidence of Zn Rydberg formation

Abstract

In past studies, we have observed copious emissions of ionic and atomic Zn from single-crystal ZnO accompanying irradiation of single-crystal ZnO with 193-nm excimer laser irradiation at fluences below the onset of optical breakdown. The Zn{sup +} and ground state Zn° are studied using time-of-flight techniques and are mass selected using a quadrupole mass spectrometer. Simultaneously, we have observed emitted particles that are detectable with a Channeltron electron multiplier but cannot be mass selected. It is a reasonable hypothesis that these particles correspond to a neutral atom or molecule in highly excited long lived states. We provide strong evidence that they correspond to high lying Rydberg states of atomic Zn. We propose a production mechanism involving laser excitation via a two photon resonance excitation of Zn°.

Authors:
; ;  [1];  [2]
  1. Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164-2814 (United States)
  2. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)
Publication Date:
OSTI Identifier:
22314680
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 116; Journal Issue: 8; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ATOMS; ELECTRON MULTIPLIERS; EMISSION; EXCIMER LASERS; EXCITATION; GROUND STATES; INTERACTIONS; IRRADIATION; LASER RADIATION; MASS; MASS SPECTROMETERS; MOLECULES; MONOCRYSTALS; PHOTONS; RYDBERG STATES; TIME-OF-FLIGHT METHOD; ZINC IONS; ZINC OXIDES

Citation Formats

Khan, Enamul H., Langford, S. C., Dickinson, J. T., E-mail: jtd@wsu.edu, and Boatner, L. A. The interaction of 193 nm excimer laser radiation with single-crystal zinc oxide: Generation of long lived highly excited particles with evidence of Zn Rydberg formation. United States: N. p., 2014. Web. doi:10.1063/1.4892847.
Khan, Enamul H., Langford, S. C., Dickinson, J. T., E-mail: jtd@wsu.edu, & Boatner, L. A. The interaction of 193 nm excimer laser radiation with single-crystal zinc oxide: Generation of long lived highly excited particles with evidence of Zn Rydberg formation. United States. doi:10.1063/1.4892847.
Khan, Enamul H., Langford, S. C., Dickinson, J. T., E-mail: jtd@wsu.edu, and Boatner, L. A. Thu . "The interaction of 193 nm excimer laser radiation with single-crystal zinc oxide: Generation of long lived highly excited particles with evidence of Zn Rydberg formation". United States. doi:10.1063/1.4892847.
@article{osti_22314680,
title = {The interaction of 193 nm excimer laser radiation with single-crystal zinc oxide: Generation of long lived highly excited particles with evidence of Zn Rydberg formation},
author = {Khan, Enamul H. and Langford, S. C. and Dickinson, J. T., E-mail: jtd@wsu.edu and Boatner, L. A.},
abstractNote = {In past studies, we have observed copious emissions of ionic and atomic Zn from single-crystal ZnO accompanying irradiation of single-crystal ZnO with 193-nm excimer laser irradiation at fluences below the onset of optical breakdown. The Zn{sup +} and ground state Zn° are studied using time-of-flight techniques and are mass selected using a quadrupole mass spectrometer. Simultaneously, we have observed emitted particles that are detectable with a Channeltron electron multiplier but cannot be mass selected. It is a reasonable hypothesis that these particles correspond to a neutral atom or molecule in highly excited long lived states. We provide strong evidence that they correspond to high lying Rydberg states of atomic Zn. We propose a production mechanism involving laser excitation via a two photon resonance excitation of Zn°.},
doi = {10.1063/1.4892847},
journal = {Journal of Applied Physics},
number = 8,
volume = 116,
place = {United States},
year = {Thu Aug 28 00:00:00 EDT 2014},
month = {Thu Aug 28 00:00:00 EDT 2014}
}
  • We observe intense Zn ion and atom emissions when single-crystal ZnO is exposed to 193-nm excimer laser radiation at fluences below the threshold for optical breakdown. Zn+ and ground state Zn are readily identified by mass-selected, time-of-flight techniques using a quadrupole mass spectrometer. Particles are also detected with Channeltron electron multipliers that cannot be mass selected. We provide evidence that these particles correspond to high lying Rydberg states of atomic Zn produced by a resonance excitation involving two laser photons.
  • The production of gas phase atomic and ionic line spectra accompanying the high laser fluence irradiation of solid surfaces is well known and is most often due to the production and interaction of high densities of atoms, ions, and electrons generated from laser-induced breakdown. The resulting plasma expands and moves rapidly away from the irradiated spot and is accompanied by intense emission of light. This type of “plume” is well studied and is frequently exploited in the technique of chemical analysis known as laser induced breakdown spectroscopy. Here, we describe a similar but weaker emission of light generated in vacuummore » by the laser irradiation of single crystal ZnO at fluences well below breakdown; this emission consists entirely of optical line emission from excited atomic Zn. We compare the properties of the resulting laser-generated gas-phase light emission (above and below breakdown) and describe a mechanism for the production of the low-fluence optical emission resulting from a fortuitous choice of material and laser wavelength.« less
  • The production of gas phase atomic and ionic line spectra accompanying the high laser fluence irradiation of solid surfaces is well known and is most often due to the production and interaction of high densities of atoms, ions, and electrons generated from laser-induced breakdown. The resulting plasma expands and moves rapidly away from the irradiated spot and is accompanied by intense emission of light. This type of plume is well studied and is frequently exploited in the technique of chemical analysis known as laser induced breakdown spectroscopy. Here, we describe a similar but weaker emission of light generated in vacuummore » by the laser irradiation of single crystal ZnO at fluences well below breakdown; this emission consists entirely of optical line emission from excited atomic Zn. Furthermore, we compare the properties of the resulting laser-generated gas-phase light emission (above and below breakdown) and describe a mechanism for the production of the low-fluence optical emission resulting from a fortuitous choice of material and laser wavelength.« less
  • We report mass-resolved time-of-flight measurements of neutral particles from the surface of single-crystal ZnO during pulsed 193-nm irradiation at laser fluences below the threshold for avalanche breakdown. The major species emitted are atomic Zn and O. We examine the emissions of atomic Zn as a function of laser fluence and laser exposure. Defects at the ZnO surface appear necessary for the detection of these emissions. Our results suggest that the production of defects is necessary to explain intense sustained emissions at higher fluence. In conclusion, rapid, clean surface etching and high atomic zinc kinetic energies seen at higher laser fluencesmore » are also discussed.« less
  • We examine UV laser-induced ion emission from a wide bandgap semiconductor, single-crystal ZnO, at fluences well below both the damage threshold and plasma formation. At fluences below 200 mJ/cm2, we observe only Zn+, and the Zn+ intensity decreases monotonically during exposure. At higher fluences, after an initial decrease, the emission is sustained; in addition O+ and O2+ are observed. We explain: how Zn ions of several eV in energy can be produced on the surface of a semiconductor, how sustained emission can be maintained, and the origin of an anomalous emission of slow Zn+ ions the latter is shown tomore » arise from photoionization of atomic Zn, also emitted by this radiation.« less