Reduction of Intrinsic Electron Emittance from Photocathodes Using Ordered Crystalline Surfaces

Karkare, Siddharth; Feng, Jun; Chen, Xumin; Wan, Weishi; Palomares, F. J.; Chiang, T.‐C.; Padmore, H. A.

doi:10.1103/physrevlett.118.164802

Cited by 20 publications

(11 citation statements)

References 38 publications

(39 reference statements)

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“…For example, it is known that surface treatments for metallic substrates play an important role in securing maximum QE of deposited photocathodes. Only limited literature is available on this topic [7][8][9] , but the consensus indicates benefits from electrochemically etching the surfaces to smoothen morphology (i.e. electropolishing) and further chemical passivation by exposing them to gases at elevated temperatures, etc.…”

Section: Introductionmentioning

confidence: 99%

Quantum Efficiency Enhancement of Bialkali Photocathodes by an Atomically Thin Layer on Substrates

Yamaguchi

Liu

DeFazio³

et al. 2019

Physica Status Solidi (a)

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Quantum efficiency (QE) enhancement in accelerator technology relevant to antimonide photocathodes (K2CsSb) is achieved by interfacing them with atomically thin 2D crystal layers. The enhancement occurs in a reflection mode, when a 2D crystal is placed in between the photocathodes and optically reflective substrates. Specifically, the peak QE at 405 nm (3.1 eV) increases by a relative 10%, whereas the long wavelength response at 633 nm (2.0 eV) increases by a relative 36% on average and up to 80% at localized “hot spot” regions when photocathodes are deposited onto graphene‐coated stainless steel. There is a similar effect for photocathodes deposited on hexagonal boron nitride monolayer coatings using nickel substrates. The enhancement does not occur when reflective substrates are replaced with optically transparent sapphire. Optical transmission, X‐ray diffraction (XRD), and X‐ray fluorescence (XRF) revealed that thickness, crystal orientation, quality, and elemental stoichiometry of photocathodes do not appreciably change due to 2D crystal coatings. These results suggest that optical interactions are responsible for the QE enhancements when 2D crystal sublayers are present on reflective substrates, and provide a pathway toward a simple method of QE enhancement in semiconductor photocathodes by an atomically thin 2D crystal on substrates.

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Section: Introductionmentioning

confidence: 99%

Quantum Efficiency Enhancement of Bialkali Photocathodes by an Atomically Thin Layer on Substrates

Yamaguchi

Liu

DeFazio³

et al. 2019

Physica Status Solidi (a)

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“…First and foremost, the photoemission simulations do not include the matrix element describing the optical excitation of the electrons into the emitting 'virtual' states. This of course important for an Ab initio determination of the QE [24], but it is unlikely to affect the MTE evaluations from the simulated electron emission distributions unless the matrix element has a significant variation in momentum space for the excited virtual state. Second, the employed exact triangular barrier solution of Forbes and Deane [30] does not allow for the inclusion of the Schottky effect [15,16,35] in a formal manner.…”

Section: Photoemission Formalismmentioning

confidence: 99%

“…effective mass, m * ) and density of states variation affects, and can limit, the MTE of the emitted electrons through transverse momentum conservation in photoemission [22]. Together with the work function variation with crystal orientation [23], this is now leading to experimental investigations of the spectral emission properties of singlecrystal photocathodes [24][25][26][27] for which a functional theory [28] is required to aid our understanding of photoemission and, consequently, the selection of future high brightness (low MTE and high quantum efficiency (QE)) photocathode materials.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of photocathode emission properties in an electron gun: one-step photoemission from bulk band to vacuum states

Schroeder

Adhikari

2019

New J. Phys.

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A one-step photoemission analysis is developed, using the exact one-dimensional quantum solution for transmission over and through a triangular barrier presented by Forbes and Deane (2011 Proc. R. Soc. A 467 2927), to evaluate the emission properties of a photocathode in an electron gun. The analysis, which employs transverse momentum conservation in electron emission, includes the physical attributes (density of states and energy-momentum dispersion) of both the bulk band emission states and the recipient vacuum states in its evaluation of the mean transverse energy and relative quantum efficiency of the emitted electrons.

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“…In state of the art photoemission electron sources, the cathode sets ultimate limits on achievable beam quality. Therefore lowering the intrinsic emittance is of vital importance in both the FEL and UED communities [7][8][9].…”

Section: Introductionmentioning

confidence: 99%

Photoemission and degradation of semiconductor photocathode

Huang

Qian

et al. 2019

Phys. Rev. Accel. Beams

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In state of the art photoemission electron sources, the transverse emittance of the electron beam is approaching its intrinsic value from the cathode. To reduce the intrinsic emittance, it is straightforward to tune the photon energy of the drive laser toward the photocathode emission threshold. This paper aims at constructing an improved model which takes into account an intermediate energy level to better explain the near threshold photoemission for semiconductors. A dynamic model is also proposed to evaluate the cathode degradation process due to surface oxidation. The models agree well with published results for different materials under various conditions, including electric field, temperature and vacuum condition. The dynamic model predicts that near threshold emission of an oxidized Cs 3 Sb cathode outperforms UV photoemission of typical metal cathodes in terms of both quantum efficiency and intrinsic emittance. With the oxidization layer, the robustness of semiconductor cathodes to gun vacuum condition may be comparable to a metal cathode. This, however, needs further testing.

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Reduction of Intrinsic Electron Emittance from Photocathodes Using Ordered Crystalline Surfaces

Cited by 20 publications

References 38 publications

Quantum Efficiency Enhancement of Bialkali Photocathodes by an Atomically Thin Layer on Substrates

Quantum Efficiency Enhancement of Bialkali Photocathodes by an Atomically Thin Layer on Substrates

Evaluation of photocathode emission properties in an electron gun: one-step photoemission from bulk band to vacuum states

Photoemission and degradation of semiconductor photocathode

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