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Title: Synchrotron x-ray study of a low roughness and high efficiency K 2 CsSb photocathode during film growth

Abstract

Reduction of roughness to the nm level is critical of achieving the ultimate performance from photocathodes used in high gradient fields. The thrust of this paper is to explore the evolution of roughness during sequential growth, and to show that deposition of multilayer structures consisting of very thin reacted layers results in an nm level smooth photocathode. Synchrotron x-ray methods were applied to study the multi-step growth process of a high efficiency K 2CsSb photocathode. We observed a transition point of the Sb film grown on Si at the film thickness of similar to 40 angstrom with the substrate temperature at 100 degrees C and the growth rate at 0.1 Å s -1. The final K 2CsSb photocathode exhibits a thickness of around five times that of the total deposited Sb film regardless of how the Sb film was grown. The film surface roughening process occurs first at the step when K diffuses into the crystalline Sb. Furthermore, the photocathode we obtained from the multi-step growth exhibits roughness in an order of magnitude lower than the normal sequential process. X-ray diffraction measurements show that the material goes through two structural changes of the crystalline phase during formation, from crystalline Sbmore » to K 3Sb and finally to K 2CsSb.« less

Authors:
 [1];  [1];  [1];  [2];  [3];  [3];  [3];  [3];  [4];  [4];  [4];  [5];  [5];  [5];  [5];  [6]
  1. Argonne National Lab. (ANL), Argonne, IL (United States)
  2. Brookhaven National Lab. (BNL), Upton, NY (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  3. Brookhaven National Lab. (BNL), Upton, NY (United States)
  4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  5. Stony Brook Univ., NY (United States)
  6. Brookhaven National Lab. (BNL), Upton, NY (United States); Stony Brook Univ., NY (United States)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
OSTI Identifier:
1374541
Grant/Contract Number:
AC02-06CH11357; AC02-05CH11231; AC02-98CH10886; KC0407-ALSJNT-I0013; SC0005713; DMR-1332208
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Physics. D, Applied Physics
Additional Journal Information:
Journal Volume: 50; Journal Issue: 20; Journal ID: ISSN 0022-3727
Publisher:
IOP Publishing
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; bialkali antimonide photocathode; grazing incidence small angle x-ray scattering; thickness; roughness; critical angle; structure; x-ray diffraction; x-ray reflectivity; 36 MATERIALS SCIENCE

Citation Formats

Xie, Junqi, Demarteau, Marcel, Wagner, Robert, Schubert, Susanne, Gaowei, Mengjia, Attenkofer, Klaus, Walsh, John, Smedley, John, Wong, Jared, Feng, Jun, Padmore, Howard, Ruiz-Oses, Miguel, Ding, Zihao, Liang, Xue, Muller, Erik, and Ben-Zvi, Ilan. Synchrotron x-ray study of a low roughness and high efficiency K 2 CsSb photocathode during film growth. United States: N. p., 2017. Web. doi:10.1088/1361-6463/aa6882.
Xie, Junqi, Demarteau, Marcel, Wagner, Robert, Schubert, Susanne, Gaowei, Mengjia, Attenkofer, Klaus, Walsh, John, Smedley, John, Wong, Jared, Feng, Jun, Padmore, Howard, Ruiz-Oses, Miguel, Ding, Zihao, Liang, Xue, Muller, Erik, & Ben-Zvi, Ilan. Synchrotron x-ray study of a low roughness and high efficiency K 2 CsSb photocathode during film growth. United States. doi:10.1088/1361-6463/aa6882.
Xie, Junqi, Demarteau, Marcel, Wagner, Robert, Schubert, Susanne, Gaowei, Mengjia, Attenkofer, Klaus, Walsh, John, Smedley, John, Wong, Jared, Feng, Jun, Padmore, Howard, Ruiz-Oses, Miguel, Ding, Zihao, Liang, Xue, Muller, Erik, and Ben-Zvi, Ilan. 2017. "Synchrotron x-ray study of a low roughness and high efficiency K 2 CsSb photocathode during film growth". United States. doi:10.1088/1361-6463/aa6882.
@article{osti_1374541,
title = {Synchrotron x-ray study of a low roughness and high efficiency K 2 CsSb photocathode during film growth},
author = {Xie, Junqi and Demarteau, Marcel and Wagner, Robert and Schubert, Susanne and Gaowei, Mengjia and Attenkofer, Klaus and Walsh, John and Smedley, John and Wong, Jared and Feng, Jun and Padmore, Howard and Ruiz-Oses, Miguel and Ding, Zihao and Liang, Xue and Muller, Erik and Ben-Zvi, Ilan},
abstractNote = {Reduction of roughness to the nm level is critical of achieving the ultimate performance from photocathodes used in high gradient fields. The thrust of this paper is to explore the evolution of roughness during sequential growth, and to show that deposition of multilayer structures consisting of very thin reacted layers results in an nm level smooth photocathode. Synchrotron x-ray methods were applied to study the multi-step growth process of a high efficiency K2CsSb photocathode. We observed a transition point of the Sb film grown on Si at the film thickness of similar to 40 angstrom with the substrate temperature at 100 degrees C and the growth rate at 0.1 Å s-1. The final K2CsSb photocathode exhibits a thickness of around five times that of the total deposited Sb film regardless of how the Sb film was grown. The film surface roughening process occurs first at the step when K diffuses into the crystalline Sb. Furthermore, the photocathode we obtained from the multi-step growth exhibits roughness in an order of magnitude lower than the normal sequential process. X-ray diffraction measurements show that the material goes through two structural changes of the crystalline phase during formation, from crystalline Sb to K3Sb and finally to K2CsSb.},
doi = {10.1088/1361-6463/aa6882},
journal = {Journal of Physics. D, Applied Physics},
number = 20,
volume = 50,
place = {United States},
year = 2017,
month = 4
}

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  • Reduction of roughness to the nm level is critical of achieving the ultimate performance from photocathodes used in high gradient fields. The thrust of this paper is to explore the evolution of roughness during sequential growth, and to show that deposition of multilayer structures consisting of very thin reacted layers results in an nm level smooth photocathode. Synchrotron x-ray methods were applied to study the multi-step growth process of a high efficiency K 2 CsSb photocathode. A transition point of the Sb film grown on Si was observed at the film thickness of ~40 Å with the substrate temperature atmore » 100 °C and the growth rate at 0.1 Å s -1 . The final K 2 CsSb photocathode exhibits a thickness of around five times that of the total deposited Sb film regardless of how the Sb film was grown. The film surface roughening process occurs first at the step when K diffuses into the crystalline Sb. The photocathode obtained from the multi-step growth exhibits roughness in an order of magnitude lower than the normal sequential process. X-ray diffraction measurements show that the material goes through two structural changes of the crystalline phase during formation, from crystalline Sb to K 3 Sb and finally to K 2 CsSb.« less
  • The spatial and temporal evolution of the surface of a tungsten film deposited by magnetron sputtering is investigated in situ and in real time by an x-ray scattering technique. The evolution of roughness is described in terms of its power spectral density and derived from scattering measurements performed using synchrotron x-rays at the energy of 17.5 keV. The data are analyzed in the frame of the first-order perturbation theory, which does not require any model of film growth and correlation function. The approach allows extracting quantitatively both the degree of conformity and the evolution of the in-plane characteristic length ofmore » the replication as a function of the growing film thickness.« less
  • Two K{sub 2}CsSb photocathodes were manufactured at Brookhaven National Lab and delivered to Jefferson Lab within a compact vacuum apparatus at pressure ~ 10{sup -11} Torr. These photocathodes were evaluated using a dc high voltage photogun biased at voltages up to 200 kV, and illuminated with laser light at wavelengths 440 or 532 nm, to generate dc electron beams at currents up to 20 mA. Some conditions produced exceptionally large photocathode charge lifetimes, without measurable quantum efficiency (QE) decay, even from the center of the photocathode where operation using GaAs photocathodes is precluded due to ion bombardment. Under other conditionsmore » the charge lifetime was poor, suggesting a complex QE decay mechanism likely related to chemistry and localized heating via the laser beam. Following beam delivery, the photocathodes were evaluated using a scanning electron microscope with energy dispersive x-ray spectroscopy capability, to determine surface morphology and chemical composition.« less
  • The roughness evolution during plasma deposition of amorphous hydrogenated carbon (a-C:H) films is investigated. Films were deposited from an inductively coupled methane plasma using a wide range of process parameters. Plasma deposition is uniquely described by the dissipated energy per source gas molecule E{sub mean}. Depending on E{sub mean}, a specific set of radicals contributes to film growth causing a characteristic roughness development. The film roughness is measured using atomic force microscopy and spectroscopic ellipsometry and is expressed using the static and dynamic scaling coefficients {alpha} and {beta}, respectively. For low E{sub mean}<20 eV, {alpha}{approx}0.65 and {beta}{approx}0.19 indicating film depositionmore » via a growth precursor with a large surface diffusion length. For E{sub mean}>20 eV, {alpha}{approx}0.9 and {beta}{approx}0.25 indicating film deposition via a growth precursor with a small surface diffusion length.« less