Author: Chubenko, O.
Paper Title Page
WEPAB169 Towards Ultra-Smooth Alkali Antimonide Photocathode Epitaxy 3001
 
  • E.J. Montgomery
    Private Address, Bolingbrook, USA
  • O. Chubenko, G.S. Gevorkyan, S.S. Karkare, P. Saha
    Arizona State University, Tempe, USA
  • R.G. Hennig, J.T. Paul
    University of Florida, Gainesville, Florida, USA
  • C. Jing, S. Poddar
    Euclid Beamlabs, Bolingbrook, USA
  • H.A. Padmore
    LBNL, Berkeley, California, USA
  
  Funding: Work supported by Department of Energy, Office of Science, Office of Basic Energy Sciences, under grant number DE-SC0020575.
Pho­to­cath­odes lead in bright­ness among elec­tron emit­ters, but trans­verse mo­menta are un­avoid­ably nonzero. Ul­tra-low trans­verse emit­tance would en­able brighter, higher en­ergy x-ray free-elec­tron lasers (FEL), im­proved col­lid­ers, and more co­her­ent, de­tailed ul­tra­fast elec­tron dif­frac­tion/mi­croscopy (UED/UEM). Al­though high quan­tum ef­fi­ciency (QE) is de­sired to avoid laser-in­duced non­lin­ear­i­ties, the state-of-the-art is 100 pC bunches from cop­per, 0.4 mm-mrad emit­tance. Ad­vances to­wards 0.1 mm-mrad re­quire ul­tra-low emit­tance, high QE, cryo-com­pat­i­ble ma­te­ri­als. We re­port ef­forts to­wards epi­tax­ial growth of ce­sium an­ti­monide on lat­tice matched sub­strates. DFT cal­cu­la­tions were per­formed to downs­e­lect from a list of can­di­date lat­tice matches. Co-evap­o­ra­tions achiev­ing >3% QE at 532 nm fol­lowed by atomic force and Kelvin probe mi­croscopy (AFM and KPFM) show ul­tra-low 313 pm rms (root mean square) phys­i­cal and 2.65 mV rms chem­i­cal rough­ness. We sim­u­late rough­ness-in­duced mean trans­verse en­ergy (MTE) to pre­dict <1 meV from rough­ness ef­fects at 10 MV/m in as-grown op­ti­cally thick cath­odes, promis­ing low emit­tance via epi­tax­ial growth. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB169  
About • paper received ※ 19 May 2021       paper accepted ※ 02 June 2021       issue date ※ 11 August 2021  
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THPAB142 Optical and Surface Characterization of Alkali-Antimonide Photocathodes 4037
 
  • P. Saha, O. Chubenko, G.S. Gevorkyan, A.H. Kachwala, S.S. Karkare, C.J. Knill
    Arizona State University, Tempe, USA
  • E.J. Montgomery, S. Poddar
    Euclid Beamlabs, Bolingbrook, USA
  • H.A. Padmore
    LBNL, Berkeley, California, USA
  
  Al­kali-an­ti­monides, char­ac­ter­ized by high quan­tum ef­fi­ciency and low mean trans­verse en­ergy in vis­i­ble light, are ex­cel­lent elec­tron sources to drive x-ray free elec­tron lasers, elec­tron cool­ing and ul­tra­fast elec­tron dif­frac­tion ap­pli­ca­tions etc. Ex­ist­ing stud­ies of al­kali-an­ti­monides have fo­cused on quan­tum ef­fi­ciency and emit­tance, but in­for­ma­tion is lack­ing on the fun­da­men­tal as­pects of the elec­tronic struc­ture, such as the en­ergy gap of the semi­con­duc­tor and the den­sity of de­fects as well as the over­all nano-struc­ture of the ma­te­ri­als. We are, there­fore, con­duct­ing pho­to­con­duc­tiv­ity mea­sure­ments to mea­sure fun­da­men­tal semi­con­duc­tor prop­er­ties as well as using atomic force mi­cro­scope (AFM) and kelvin probe force mi­cro­scope (KPFM) to mea­sure the nanos­truc­ture vari­a­tions in struc­ture and sur­face po­ten­tial.  
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB142  
About • paper received ※ 16 May 2021       paper accepted ※ 14 July 2021       issue date ※ 13 August 2021  
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