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Title: Kinetics of alkali-based photocathode degradation

Here, we report on a kinetic model that describes the degradation of the quantum efficiency (QE) of Cs3Sb and negative electron affinity (NEA) GaAs photocathodes under UHV conditions. Additionally, the generally accepted irreversible chemical change of a photocathode’s surface due to reactions with residual gases, such as O2, CO2, and H2O, the model incorporates an intermediate reversible physisorption step, similar to Langmuir adsorption. Moreover, this intermediate step is needed to satisfactorily describe the strongly non-exponential QE degradation curves for two distinctly different classes of photocathodes –surface-activated and “bulk,” indicating that in both systems the QE degradation results from surface damage. The recovery of the QE upon improvement of vacuum conditions is also accurately predicted by this model with three parameters (rates of gas adsorption, desorption, and irreversible chemical reaction with the surface) comprising metrics to better characterize the lifetime of the cathodes, instead of time-pressure exposure expressed in Langmuir units.
Authors:
 [1] ;  [2] ;  [3] ; ORCiD logo [1] ;  [4]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Accelerator Operations and Technology Division
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Materials Physics and Applications Division
  3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Chemistry Division
  4. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Theoretical Division
Publication Date:
Report Number(s):
LA-UR-16-22104
Journal ID: ISSN 2158-3226; TRN: US1701292
Grant/Contract Number:
AC52-06NA25396; 20150394DR
Type:
Published Article
Journal Name:
AIP Advances
Additional Journal Information:
Journal Volume: 6; Journal Issue: 11; Journal ID: ISSN 2158-3226
Publisher:
American Institute of Physics (AIP)
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; photocathodes, alkali cathodes, degradation, Cs3Sb, NEA, quantum efficiency
OSTI Identifier:
1330733
Alternate Identifier(s):
OSTI ID: 1340919