PAC2013 - List of Authors (Smedley, J.)

Paper	Title	Page
MOPBA21	Modeling Localized States and Band Bending Effects on Electron Emission Ion from GaAs	225
	D.A. Dimitrov, Y. Choi, C. Nieter Tech-X, Boulder, Colorado, USA I.V. Bazarov, S.S. Karkare, W.J. Schaff Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA I. Ben-Zvi, T. Rao, J. Smedley BNL, Upton, Long Island, New York, USA
	Funding: The authors wish to acknowledge the U.S. Department of Energy (DOE) and the National Science Foundation for funding under grants DOE DE-SC0006246, NSF DMR-0807731, and DOE DE-SC0003965. High acceptor doping of GaAs and (Cs, O) or (Cs, F) surface coating leads to downward band bending terminating with effective negative electron affinity surface. The periodicity breaking at the surface together with the formed potential leads to one or more localized states in the band bending region together with effective Fermi level pinning. We report results on how to calculate the band bending potential, the Fermi level pinning, and localized states as functions of GaAs p-doping density, surface density of states, and temperature. We also consider how these surface properties affect electron emission.

THPAC12	Preparation and Investigation of Antimony Thin Films for Multi-Alkali Photocathodes	1163
	X. Liang, K. Attenkofer, T. Rao, S.G. Schubert, J. Smedley, E. Wang, Q. Wu BNL, Upton, Long Island, New York, USA I. Ben-Zvi, M. Ruiz-Osés Stony Brook University, Stony Brook, USA J. Jordan-Sweet IBM T. J. Watson Center, Yorktown Heights, New York, USA H.A. Padmore, J.J. Wong LBNL, Berkeley, California, USA
	Funding: Work is supported at BNL by Brookhaven Science Associates, LLC under Contract No. DEAC02-98CH10886 with the U.S. DOE. The work at Stony Brook is supported by the US DOE under grant DE-SC0005713. Multialikali antimonide cathodes provide high visible light quantum efficiency, with low thermal emittance and are excellent candidate materials for high average current next generation ERLs or high repetition rate FELs. Although these materials have some excellent characteristics, control of the growth mode of the thin film and ultimately the surface roughness is difficult and will effect the emittance that can be obtained in high gradient fields. To complement our growth studies of crystalline phases using x-ray diffraction studies, here we use the technique of grazing incidence small angle x-ray scattering (GI-SAXS) and atomic force microscopy (AFM) to measure the roughness as a function of film thickness. In this study, we demonstrate these techniques as applied to the growth of Sb, for a range of thicknesses, temperatures and growth rates, and show the wide range of moprphologies that can be formed with relatively minor changes in deposition conditions.

THPAC17	Alkali Antimonide Photocathodes for Everyone	1178
	J. Smedley, K. Attenkofer, S.G. Schubert BNL, Upton, Long Island, New York, USA I. Ben-Zvi, X. Liang, E.M. Muller, M. Ruiz-Osés Stony Brook University, Stony Brook, USA J. DeFazio PHOTONIS USA PENNSYLVANIA, INC., Lancaster, USA H.A. Padmore, J.J. Wong LBNL, Berkeley, California, USA J. Xie ANL, Argonne, USA
	Funding: The authors wish to acknowledge the support of the US DOE, under Contract No. KC0407-ALSJNT-I0013, DE-AC02-98CH10886 and DE-SC0005713. Use of CHESS is supported by NSF award DMR-0936384. Alkali Antimonide photocathodes have yielded the highest current on record for any photoinjector source (75 mA), with QE of ~10% for green light. However, traditional growth methods for these cathodes yield material that is inherently rough, leading to rise of the intrinsic emittance for high gradient injectors such as those for next-generation light sources. It this presentation we will explore the origin of roughness in these materials, as well as the growth dynamics, using in situ and in operando techniques, including Grazing Incidence X-ray Diffraction, Grazing Incidence Small Angle X-ray Scattering, X-ray reflectivity and in vacuum Atomic Force Microscopy.

THPAC18	Progress on Growth of a Multi-alkali Photocathode for ERL	1181
	E. Wang, S.A. Belomestnykh, I. Ben-Zvi, T. Rao, J. Smedley BNL, Upton, Long Island, New York, USA I. Ben-Zvi, M. Ruiz-Osés Stony Brook University, Stony Brook, USA X. Liang SBU, Stony Brook, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy and DOE grant at Stony Brook DE-SC0005713 K2CsSb is a robust photocathode capable of generating electron beams with high peak, high average current and low thermal emittance. During the last two year, a great improvement in the design and fabrication of a reliable deposition system suitable for K2CsSb cathode growth and its insertion into BNL high current ERL SRF gun has been achieved. A standard procedure for the growth of multi-alkali cathodes combined with another procedure to transport these cathodes into the SRF gun was developed. The first cathode growth on a copper insertion was ready to mount into the 704MHz gun. In this article, we will describe the progress of cathode growth and transportation for ERL project. In particular, laser heating and the cathode growth on Ta will be included.

THPAC34	Diamond Amplifier Design and Preliminary Test Results	1211
	T. Xin, S.A. Belomestnykh, I. Ben-Zvi Stony Brook University, Stony Brook, USA S.A. Belomestnykh, I. Ben-Zvi, T. Rao, J. Skaritka, J. Smedley, E. Wang, Q. Wu BNL, Upton, Long Island, New York, USA M. Gaowei, E.M. Muller SBU, Stony Brook, New York, USA
	Funding: Work is supported at BNL by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. The work at Stony Brook is supported by the US DOE under grant DE-SC0005713. Diamond as a large energy gap material can be easily made into a negative electron affinity (NEA) device. Using a few keV primary electrons as input and a few kV bias, the NEA diamond will emit cold electrons into vacuum with a large gain. We had tested and reported the performance of the diamond amplifier in our DC system somewhere else. The best amplification achieved so far was above 170. Next step of the experiment is to test the diamond amplifier in the 112 MHz superconducting RF electron gun. In this report we describe the design and simulations of the diamond amplifier to be tested in our SRF gun, show the finished amplifier containing the DC primary gun and light optics. We also provide preliminary test results of the laser and electron beam transport.

Paper

Title

Page

Modeling Localized States and Band Bending Effects on Electron Emission Ion from GaAs

225

D.A. Dimitrov, Y. Choi, C. Nieter
Tech-X, Boulder, Colorado, USA
I.V. Bazarov, S.S. Karkare, W.J. Schaff
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
I. Ben-Zvi, T. Rao, J. Smedley
BNL, Upton, Long Island, New York, USA

Funding: The authors wish to acknowledge the U.S. Department of Energy (DOE) and the National Science Foundation for funding under grants DOE DE-SC0006246, NSF DMR-0807731, and DOE DE-SC0003965.
High acceptor doping of GaAs and (Cs, O) or (Cs, F) surface coating leads to downward band bending terminating with effective negative electron affinity surface. The periodicity breaking at the surface together with the formed potential leads to one or more localized states in the band bending region together with effective Fermi level pinning. We report results on how to calculate the band bending potential, the Fermi level pinning, and localized states as functions of GaAs p-doping density, surface density of states, and temperature. We also consider how these surface properties affect electron emission.

THPAC12

Preparation and Investigation of Antimony Thin Films for Multi-Alkali Photocathodes

1163

X. Liang, K. Attenkofer, T. Rao, S.G. Schubert, J. Smedley, E. Wang, Q. Wu
BNL, Upton, Long Island, New York, USA
I. Ben-Zvi, M. Ruiz-Osés
Stony Brook University, Stony Brook, USA
J. Jordan-Sweet
IBM T. J. Watson Center, Yorktown Heights, New York, USA
H.A. Padmore, J.J. Wong
LBNL, Berkeley, California, USA

Funding: Work is supported at BNL by Brookhaven Science Associates, LLC under Contract No. DEAC02-98CH10886 with the U.S. DOE. The work at Stony Brook is supported by the US DOE under grant DE-SC0005713.
Multialikali antimonide cathodes provide high visible light quantum efficiency, with low thermal emittance and are excellent candidate materials for high average current next generation ERLs or high repetition rate FELs. Although these materials have some excellent characteristics, control of the growth mode of the thin film and ultimately the surface roughness is difficult and will effect the emittance that can be obtained in high gradient fields. To complement our growth studies of crystalline phases using x-ray diffraction studies, here we use the technique of grazing incidence small angle x-ray scattering (GI-SAXS) and atomic force microscopy (AFM) to measure the roughness as a function of film thickness. In this study, we demonstrate these techniques as applied to the growth of Sb, for a range of thicknesses, temperatures and growth rates, and show the wide range of moprphologies that can be formed with relatively minor changes in deposition conditions.

THPAC17

Alkali Antimonide Photocathodes for Everyone

1178

J. Smedley, K. Attenkofer, S.G. Schubert
BNL, Upton, Long Island, New York, USA
I. Ben-Zvi, X. Liang, E.M. Muller, M. Ruiz-Osés
Stony Brook University, Stony Brook, USA
J. DeFazio
PHOTONIS USA PENNSYLVANIA, INC., Lancaster, USA
H.A. Padmore, J.J. Wong
LBNL, Berkeley, California, USA
J. Xie
ANL, Argonne, USA

Funding: The authors wish to acknowledge the support of the US DOE, under Contract No. KC0407-ALSJNT-I0013, DE-AC02-98CH10886 and DE-SC0005713. Use of CHESS is supported by NSF award DMR-0936384.
Alkali Antimonide photocathodes have yielded the highest current on record for any photoinjector source (75 mA), with QE of ~10% for green light. However, traditional growth methods for these cathodes yield material that is inherently rough, leading to rise of the intrinsic emittance for high gradient injectors such as those for next-generation light sources. It this presentation we will explore the origin of roughness in these materials, as well as the growth dynamics, using in situ and in operando techniques, including Grazing Incidence X-ray Diffraction, Grazing Incidence Small Angle X-ray Scattering, X-ray reflectivity and in vacuum Atomic Force Microscopy.

THPAC18

Progress on Growth of a Multi-alkali Photocathode for ERL

1181

E. Wang, S.A. Belomestnykh, I. Ben-Zvi, T. Rao, J. Smedley
BNL, Upton, Long Island, New York, USA
I. Ben-Zvi, M. Ruiz-Osés
Stony Brook University, Stony Brook, USA
X. Liang
SBU, Stony Brook, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy and DOE grant at Stony Brook DE-SC0005713
K2CsSb is a robust photocathode capable of generating electron beams with high peak, high average current and low thermal emittance. During the last two year, a great improvement in the design and fabrication of a reliable deposition system suitable for K2CsSb cathode growth and its insertion into BNL high current ERL SRF gun has been achieved. A standard procedure for the growth of multi-alkali cathodes combined with another procedure to transport these cathodes into the SRF gun was developed. The first cathode growth on a copper insertion was ready to mount into the 704MHz gun. In this article, we will describe the progress of cathode growth and transportation for ERL project. In particular, laser heating and the cathode growth on Ta will be included.

THPAC34

Diamond Amplifier Design and Preliminary Test Results

1211

T. Xin, S.A. Belomestnykh, I. Ben-Zvi
Stony Brook University, Stony Brook, USA
S.A. Belomestnykh, I. Ben-Zvi, T. Rao, J. Skaritka, J. Smedley, E. Wang, Q. Wu
BNL, Upton, Long Island, New York, USA
M. Gaowei, E.M. Muller
SBU, Stony Brook, New York, USA

Funding: Work is supported at BNL by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. The work at Stony Brook is supported by the US DOE under grant DE-SC0005713.
Diamond as a large energy gap material can be easily made into a negative electron affinity (NEA) device. Using a few keV primary electrons as input and a few kV bias, the NEA diamond will emit cold electrons into vacuum with a large gain. We had tested and reported the performance of the diamond amplifier in our DC system somewhere else. The best amplification achieved so far was above 170. Next step of the experiment is to test the diamond amplifier in the 112 MHz superconducting RF electron gun. In this report we describe the design and simulations of the diamond amplifier to be tested in our SRF gun, show the finished amplifier containing the DC primary gun and light optics. We also provide preliminary test results of the laser and electron beam transport.