IPAC2018 - List of Authors (Schroeder, W.A.)

Paper	Title	Page
TUPMF065	The Role of Electron-Phonon Scattering in Transverse Momentum Conservation in PbTe(111) Photocathodes	1414
SUSPF027	use link to see paper's listing under its alternate paper code
	J. K. Nangoi, T.A. Arias Cornell University, Ithaca, New York, USA S.S. Karkare, H.A. Padmore LBNL, Berkeley, California, USA W.A. Schroeder UIC, Chicago, Illinois, USA
	Funding: The U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams. The state of the art in creating high quality electron beams for particle accelerator applications and next generation ultrafast electron diffraction and microscopy involves laser-generated photoemission. A high quality beam requires that electrons emerge from the surface with low mean transverse energy (MTE). Recent density-functional theory calculations by T. Li and W. A. S. [arXiv:1704.00194v1 [physics.acc-ph] (2017)] suggest that PbTe(111) will produce low-MTE photoelectrons due to the low effective electron mass associated with its electronic band structure. Based on this, we measured the distribution of photoelectrons from PbTe(111) and found the MTE to be about 20x larger than expected. To explain the apparent lack of transverse momentum conservation, we carried out many-body photoemission calculations including electron-phonon scattering. Our results are in far better agreement with the experiment, underscoring the importance of electron-phonon scattering in photoemission from PbTe(111), and suggest that cooling could mitigate the phonon effects on the MTE for this material.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF065
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TUPML027	Barium Tin Oxide Ordered Photocathodes: First Measurements and Future Perspectives	1597
	A. Galdi, E. B. Lochocki, H. Paik, C.T. Parzyck, D. G. Schlom, K.M. Shen Cornell University, Ithaca, New York, USA G. Adhikari, W.A. Schroeder UIC, Chicago, Illinois, USA I.V. Bazarov, L. Cultrera, W. H. Li, J.M. Maxson, C. M. Pierce Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams. Single crystalline photocathodes with small electron effective mass are supposed to enable ultra-low emittance beams, by taking advantage of the conservation of transverse (crystal) momentum. We present a preliminary study on photoemission from epitaxial films of La-doped BaSnO₃ with (100) orientation. We demonstrate here the possibility of generating and characterizing electron beams by exciting photoelectrons solely from the conduction band. We report quantum efficiency and mean transverse energy meaurements as a function of photon energy from the bare and Cs-activated La-doped BaSnO₃ surface.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML027
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TUPML061	Study of Mean Transverse Energy of (N)UNCD with Tunable Laser Source	1677
SUSPF050	use link to see paper's listing under its alternate paper code
	G. Chen IIT, Chicago, Illinois, USA G. Adhikari, W.A. Schroeder UIC, Chicago, Illinois, USA S.P. Antipov, C.-J. Jing, K. Kovi Euclid TechLabs, LLC, Solon, Ohio, USA S.V. Baryshev ANL, Argonne, Illinois, USA L.K. Spentzouris Illinois Institute of Technology, Chicago, Illinois, USA
	Funding: NSF grant No. NSF-1739150, DOE SBIR program grant No. DE-SC0013145, NSF grant No. PHYS-1535279, DOE Contract No. DE-AC02-06CH11357. There is a strong motivation to develop and understand novel materials with the potential to be utilized as photocathodes, as these could have desirable photoemission properties for research and industrial applications. Nitrogen-incorporated ultrananocrystalline diamond ((N)UNCD) photocathodes have potential to become a material of choice for photocathode applications. (N)UNCD has high quantum efficiency when processed in hydrogen plasma, low surface roughness, and high electron conductivity through the bulk*. The mean transverse energy (MTE) was calculated for (N)UNCD thin films using the double-solenoid scan method. (N)UNCD thin film with thickness of 160nm was deposited on highly-doped silicon substrate. Studies of the MTE of a (N)UNCD sample were done using a tunable laser source with photon energies of 3.56 eV to 5.26 eV. These results are presented. K.J. Pérez Quintero et al., Appl. Phys. Lett. 105, 123103 (2014). ** S. Bhattacharyya et al., Appl. Phys. Lett. 79, 1441 (2001)
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML061
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THPMF081	Intrinsic Emittance of Single Crystal Cathodes	4263
	S.S. Karkare, H.A. Padmore LBNL, Berkeley, California, USA G. Adhikari, W.A. Schroeder UIC, Chicago, Illinois, USA
	The transverse momentum of electrons is conserved during photoemission from atomically ordered surfaces of single crystal materials. Photocathodes used in all photoinjectors today have disordered surfaces and do not exploit this phenomenon. Recently, using this conservation of transverse momentum, significant reduction in intrinsic emittance was demonstrated from the (111) surface of silver. Here, we present measurements of transverse momentum distributions of electrons photoemitted from the ordered surfaces of Ag and Cu single crystals at several photon energies. These measurements will help in understanding the photoemission process and show how band-structure and the conservation of transverse momentum can be used to obtain further reduction in intrinsic emittance from photocathodes. Karkare et al., Phys. Rev. Lett. 118, 164802 (2017)
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMF081
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Paper

Title

Page

TUPMF065

The Role of Electron-Phonon Scattering in Transverse Momentum Conservation in PbTe(111) Photocathodes

1414

SUSPF027

use link to see paper's listing under its alternate paper code

J. K. Nangoi, T.A. Arias
Cornell University, Ithaca, New York, USA
S.S. Karkare, H.A. Padmore
LBNL, Berkeley, California, USA
W.A. Schroeder
UIC, Chicago, Illinois, USA

Funding: The U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams.
The state of the art in creating high quality electron beams for particle accelerator applications and next generation ultrafast electron diffraction and microscopy involves laser-generated photoemission. A high quality beam requires that electrons emerge from the surface with low mean transverse energy (MTE). Recent density-functional theory calculations by T. Li and W. A. S. [arXiv:1704.00194v1 [physics.acc-ph] (2017)] suggest that PbTe(111) will produce low-MTE photoelectrons due to the low effective electron mass associated with its electronic band structure. Based on this, we measured the distribution of photoelectrons from PbTe(111) and found the MTE to be about 20x larger than expected. To explain the apparent lack of transverse momentum conservation, we carried out many-body photoemission calculations including electron-phonon scattering. Our results are in far better agreement with the experiment, underscoring the importance of electron-phonon scattering in photoemission from PbTe(111), and suggest that cooling could mitigate the phonon effects on the MTE for this material.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF065

Export •

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

TUPML027

Barium Tin Oxide Ordered Photocathodes: First Measurements and Future Perspectives

1597

A. Galdi, E. B. Lochocki, H. Paik, C.T. Parzyck, D. G. Schlom, K.M. Shen
Cornell University, Ithaca, New York, USA
G. Adhikari, W.A. Schroeder
UIC, Chicago, Illinois, USA
I.V. Bazarov, L. Cultrera, W. H. Li, J.M. Maxson, C. M. Pierce
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: This work was supported by the U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams.
Single crystalline photocathodes with small electron effective mass are supposed to enable ultra-low emittance beams, by taking advantage of the conservation of transverse (crystal) momentum. We present a preliminary study on photoemission from epitaxial films of La-doped BaSnO₃ with (100) orientation. We demonstrate here the possibility of generating and characterizing electron beams by exciting photoelectrons solely from the conduction band. We report quantum efficiency and mean transverse energy meaurements as a function of photon energy from the bare and Cs-activated La-doped BaSnO₃ surface.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML027

Export •

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

TUPML061

Study of Mean Transverse Energy of (N)UNCD with Tunable Laser Source

1677

SUSPF050

use link to see paper's listing under its alternate paper code

G. Chen
IIT, Chicago, Illinois, USA
G. Adhikari, W.A. Schroeder
UIC, Chicago, Illinois, USA
S.P. Antipov, C.-J. Jing, K. Kovi
Euclid TechLabs, LLC, Solon, Ohio, USA
S.V. Baryshev
ANL, Argonne, Illinois, USA
L.K. Spentzouris
Illinois Institute of Technology, Chicago, Illinois, USA

Funding: NSF grant No. NSF-1739150, DOE SBIR program grant No. DE-SC0013145, NSF grant No. PHYS-1535279, DOE Contract No. DE-AC02-06CH11357.
There is a strong motivation to develop and understand novel materials with the potential to be utilized as photocathodes, as these could have desirable photoemission properties for research and industrial applications. Nitrogen-incorporated ultrananocrystalline diamond ((N)UNCD) photocathodes have potential to become a material of choice for photocathode applications*. (N)UNCD has high quantum efficiency when processed in hydrogen plasma*, low surface roughness, and high electron conductivity through the bulk**. The mean transverse energy (MTE) was calculated for (N)UNCD thin films using the double-solenoid scan method. (N)UNCD thin film with thickness of 160nm was deposited on highly-doped silicon substrate. Studies of the MTE of a (N)UNCD sample were done using a tunable laser source with photon energies of 3.56 eV to 5.26 eV. These results are presented.
* K.J. Pérez Quintero et al., Appl. Phys. Lett. 105, 123103 (2014).
** S. Bhattacharyya et al., Appl. Phys. Lett. 79, 1441 (2001)

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML061

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

THPMF081

Intrinsic Emittance of Single Crystal Cathodes

4263

S.S. Karkare, H.A. Padmore
LBNL, Berkeley, California, USA
G. Adhikari, W.A. Schroeder
UIC, Chicago, Illinois, USA

The transverse momentum of electrons is conserved during photoemission from atomically ordered surfaces of single crystal materials. Photocathodes used in all photoinjectors today have disordered surfaces and do not exploit this phenomenon. Recently, using this conservation of transverse momentum, significant reduction in intrinsic emittance was demonstrated from the (111) surface of silver*. Here, we present measurements of transverse momentum distributions of electrons photoemitted from the ordered surfaces of Ag and Cu single crystals at several photon energies. These measurements will help in understanding the photoemission process and show how band-structure and the conservation of transverse momentum can be used to obtain further reduction in intrinsic emittance from photocathodes.
*Karkare et al., Phys. Rev. Lett. 118, 164802 (2017)

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMF081

Export •

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