IPAC2015 - List of Authors (Smedley, J.)

Paper	Title	Page
MOPMA031	Simulations of Diamond Detectors with Schottky Contacts	617
	G.I. Bell, J.R. Cary, D.A. Dimitrov, D. Meiser, D.N. Smithe, C.D. Zhou Tech-X, Boulder, Colorado, USA M. Gaowei, E.M. Muller SBU, Stony Brook, New York, USA J. Smedley BNL, Upton, Long Island, New York, USA
	Funding: This work is supported by the US DOE Office of Science, department of Basic Energy Sciences, grant numbers DE-SC0006246 and DE-SC0007577. We present simulations of semiconductor devices using the code VSim (formerly Vorpal). The 3D simulations involve the movement and scattering of electrons and holes in the semiconductor, voltages which may be applied to external contacts, and self-consistent electrostatic fields inside the device. Particles may experience a Schottky barrier when moving between the semiconductor and a metal contact. Example devices include MOSFETs as well as a diamond X-ray detector. Our code VSim includes scattering models for GaAs and diamond, and runs in parallel on thousands of processors. We compare our simulation results with experimental results from a prototype diamond X-ray detector.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPMA031
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MOPMA033	Modeling Electron Emission and Surface Effects from Diamond Cathodes	620
	D.A. Dimitrov, J.R. Cary, D.N. Smithe, C.D. Zhou Tech-X, Boulder, Colorado, USA I. Ben-Zvi, T. Rao, J. Smedley, E. Wang BNL, Upton, Long Island, New York, USA
	Funding: We are grateful to the U.S. DoE Office of Basic Energy Sciences for supporting this work under grants DE-SC0006246 and DE-SC0007577. We developed modeling capabilities, within the Vorpal particle-in-cell code, for three-dimensional (3D) simulations of surface effects and electron emission from semiconductor photocathodes. They include calculation of emission probabilities using general, piece-wise continuous, space-time dependent surface potentials, effective mass and band bending field effects. We applied these models, in combination with previously implemented capabilities for modeling charge generation and transport in diamond, to investigate the emission dependence on applied electric field in the range from approximately 2 to 17 MV/m along the [100] direction. The simulation results were compared to experimental data when using different emission models, band bending effects, and surface-dependent electron affinity. Simulations using surface patches with different levels of hydrogenation lead to the closest agreement with the experimental data.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPMA033
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MOPWI052	Responsivity Study of Diamond X-ray Monitors with nUNCD Contact	1273
	M. Gaowei, J. Smedley BNL, Upton, Long Island, New York, USA E.M. Muller, T. Zhou SBU, Stony Brook, New York, USA A.V. Sumant Argonne National Laboratory, Center for Nanoscale Materials, Argonne, USA
	Nitrogen doped ultrananocrystalline diamond (nUNCD) grown on the surface of a CVD single crystal diamond is tested at various beamlines covering an x-ray photon energy range of 200eV to 28 keV. The nUNCD has much lower x-ray absorption than metal contacts and is designed to improve the performance of our device. The responsivity of nUNCD diamond x-ray detector is compared with the conventional platinum coated diamond x-ray beam position monitor and the results are presented in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPWI052
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TUPHA003	Sputter Growth of Alkali Antimonide Photocathodes: An in Operando Materials Analysis	1965
	J. Smedley, K. Attenkofer, M. Gaowei, J. Sinsheimer, J. Walsh BNL, Upton, Long Island, New York, USA H. Bhandari Radiation Monitoring Devices, Watertown, USA Z. Ding, E.M. Muller SBU, Stony Brook, New York, USA H.J. Frisch Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA H.A. Padmore, S.G. Schubert, J.J. Wong LBNL, Berkeley, California, USA
	Funding: Work supported by U.S. DoE, under KC0407-ALSJNT-I0013 and SBIR grant # DE-SC0009540. NSLS was supported by DOE DE-AC02-98CH10886, CHESS is supported by NSF & NIH/NIGMS via NSF DMR-1332208 Alkali antimonide photocathodes are a strong contender for the cathode of choice for next-generation photon sources such as LCLS II or the XFEL. These materials have already found extensive use in photodetectors and image intensifiers. However, only recently have modern synchrotron techniques enabled a systematic study of the formation chemistry of these materials. Such analysis has led to the understanding that these materials are inherently rough when grown through traditional sequential deposition; this roughness has a detrimental impact on the intrinsic emittance of the emitted beam. Sputter deposition may provide a path to achieving a far smoother photocathode, while maintaining adequate quantum efficiency. We report on the creation and vacuum transport of a K2CsSb sputter target, and its use to create an ultra-smooth (sub nm roughness) cathode with a 2% quantum efficiency at 532 nm.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPHA003
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WEPWA032	CsK2Sb Growth Studies: Towards High Quantum Efficiency and Smooth Surfaces	2566
	S.G. Schubert, M. Gaowei, J. Sinsheimer, J. Smedley BNL, Upton, Long Island, New York, USA Z. Ding, E.M. Muller SBU, Stony Brook, New York, USA J. Kühn HZB, Berlin, Germany H.A. Padmore, J.J. Wong LBNL, Berkeley, California, USA J. Xie ANL, Argonne, Illinois, USA
	Funding: This work was supported by the US DOE, under Contracts DE-AC02-05CH11231, DE-AC02-98CH10886, KC0407-ALSJNT-I0013, DE-FG02-12ER41837 and the German BMBF, Helmholtz-Association and Land Berlin. The properties of CsK2Sb, make this material an ideal candidate as photocathode for electron injector use. Producing photocathodes with quantum efficiencies with 7% and greater at 532 nm poses no challenge, nevertheless the traditional growth mechanisms, which are based on a sequential deposition of Antimony, Potassium and Cesium at a temperature gradient yield a rough surface with a rms roughness in the range of 25 nm. Surface roughness’s in this region impacts the emittance. At an accelerating field of 3 MV/m an rms surface roughness of 25 nm is the dominant effect on emittance and will limit injector performance. Studies are performed to optimize roughness. Various growth procedures are exploited and the surface roughness compared.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWA032
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Paper

Title

Page

Simulations of Diamond Detectors with Schottky Contacts

617

G.I. Bell, J.R. Cary, D.A. Dimitrov, D. Meiser, D.N. Smithe, C.D. Zhou
Tech-X, Boulder, Colorado, USA
M. Gaowei, E.M. Muller
SBU, Stony Brook, New York, USA
J. Smedley
BNL, Upton, Long Island, New York, USA

Funding: This work is supported by the US DOE Office of Science, department of Basic Energy Sciences, grant numbers DE-SC0006246 and DE-SC0007577.
We present simulations of semiconductor devices using the code VSim (formerly Vorpal). The 3D simulations involve the movement and scattering of electrons and holes in the semiconductor, voltages which may be applied to external contacts, and self-consistent electrostatic fields inside the device. Particles may experience a Schottky barrier when moving between the semiconductor and a metal contact. Example devices include MOSFETs as well as a diamond X-ray detector. Our code VSim includes scattering models for GaAs and diamond, and runs in parallel on thousands of processors. We compare our simulation results with experimental results from a prototype diamond X-ray detector.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPMA031

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPMA033

Modeling Electron Emission and Surface Effects from Diamond Cathodes

620

D.A. Dimitrov, J.R. Cary, D.N. Smithe, C.D. Zhou
Tech-X, Boulder, Colorado, USA
I. Ben-Zvi, T. Rao, J. Smedley, E. Wang
BNL, Upton, Long Island, New York, USA

Funding: We are grateful to the U.S. DoE Office of Basic Energy Sciences for supporting this work under grants DE-SC0006246 and DE-SC0007577.
We developed modeling capabilities, within the Vorpal particle-in-cell code, for three-dimensional (3D) simulations of surface effects and electron emission from semiconductor photocathodes. They include calculation of emission probabilities using general, piece-wise continuous, space-time dependent surface potentials, effective mass and band bending field effects. We applied these models, in combination with previously implemented capabilities for modeling charge generation and transport in diamond, to investigate the emission dependence on applied electric field in the range from approximately 2 to 17 MV/m along the [100] direction. The simulation results were compared to experimental data when using different emission models, band bending effects, and surface-dependent electron affinity. Simulations using surface patches with different levels of hydrogenation lead to the closest agreement with the experimental data.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPMA033

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPWI052

Responsivity Study of Diamond X-ray Monitors with nUNCD Contact

1273

M. Gaowei, J. Smedley
BNL, Upton, Long Island, New York, USA
E.M. Muller, T. Zhou
SBU, Stony Brook, New York, USA
A.V. Sumant
Argonne National Laboratory, Center for Nanoscale Materials, Argonne, USA

Nitrogen doped ultrananocrystalline diamond (nUNCD) grown on the surface of a CVD single crystal diamond is tested at various beamlines covering an x-ray photon energy range of 200eV to 28 keV. The nUNCD has much lower x-ray absorption than metal contacts and is designed to improve the performance of our device. The responsivity of nUNCD diamond x-ray detector is compared with the conventional platinum coated diamond x-ray beam position monitor and the results are presented in this paper.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPWI052

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPHA003

Sputter Growth of Alkali Antimonide Photocathodes: An in Operando Materials Analysis

1965

J. Smedley, K. Attenkofer, M. Gaowei, J. Sinsheimer, J. Walsh
BNL, Upton, Long Island, New York, USA
H. Bhandari
Radiation Monitoring Devices, Watertown, USA
Z. Ding, E.M. Muller
SBU, Stony Brook, New York, USA
H.J. Frisch
Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA
H.A. Padmore, S.G. Schubert, J.J. Wong
LBNL, Berkeley, California, USA

Funding: Work supported by U.S. DoE, under KC0407-ALSJNT-I0013 and SBIR grant # DE-SC0009540. NSLS was supported by DOE DE-AC02-98CH10886, CHESS is supported by NSF & NIH/NIGMS via NSF DMR-1332208
Alkali antimonide photocathodes are a strong contender for the cathode of choice for next-generation photon sources such as LCLS II or the XFEL. These materials have already found extensive use in photodetectors and image intensifiers. However, only recently have modern synchrotron techniques enabled a systematic study of the formation chemistry of these materials. Such analysis has led to the understanding that these materials are inherently rough when grown through traditional sequential deposition; this roughness has a detrimental impact on the intrinsic emittance of the emitted beam. Sputter deposition may provide a path to achieving a far smoother photocathode, while maintaining adequate quantum efficiency. We report on the creation and vacuum transport of a K2CsSb sputter target, and its use to create an ultra-smooth (sub nm roughness) cathode with a 2% quantum efficiency at 532 nm.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPHA003

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPWA032

CsK2Sb Growth Studies: Towards High Quantum Efficiency and Smooth Surfaces

2566

S.G. Schubert, M. Gaowei, J. Sinsheimer, J. Smedley
BNL, Upton, Long Island, New York, USA
Z. Ding, E.M. Muller
SBU, Stony Brook, New York, USA
J. Kühn
HZB, Berlin, Germany
H.A. Padmore, J.J. Wong
LBNL, Berkeley, California, USA
J. Xie
ANL, Argonne, Illinois, USA

Funding: This work was supported by the US DOE, under Contracts DE-AC02-05CH11231, DE-AC02-98CH10886, KC0407-ALSJNT-I0013, DE-FG02-12ER41837 and the German BMBF, Helmholtz-Association and Land Berlin.
The properties of CsK2Sb, make this material an ideal candidate as photocathode for electron injector use. Producing photocathodes with quantum efficiencies with 7% and greater at 532 nm poses no challenge, nevertheless the traditional growth mechanisms, which are based on a sequential deposition of Antimony, Potassium and Cesium at a temperature gradient yield a rough surface with a rms roughness in the range of 25 nm. Surface roughness’s in this region impacts the emittance. At an accelerating field of 3 MV/m an rms surface roughness of 25 nm is the dominant effect on emittance and will limit injector performance. Studies are performed to optimize roughness. Various growth procedures are exploited and the surface roughness compared.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWA032

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)