Cs halide photocathode for multi-electron-beam pattern generator

Journal of Vacuum Science &Amp; Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena

Liu

Sun

et al. 2006

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CsBr/Cr photocathodes were found [1,2] to meet the requirements of a multi-electron beam lithography system operating with a light energy of 4.8 eV (257nm). The fact that photoemission was observed with a light energy below the reported 7.3 eV band gap for CsBr was not understood. This paper presents experimental results on the presence of intra-band gap absorption sites (IBAS) in CsBr thin film photo electron emitters, and presents a model based on IBAS to explain the observed photoelectron emission behavior at energies below band gap. A fluorescence band centered at 330 nm with a FWHM of about 0.34 eV was observed in CsBr/Cr samples under 257 nm laser illumination which can be attributed to IBAS and agrees well with previously obtained synchrotron photoelectron spectra[1] from the valence band of CsBr films.

Section: Discussionsupporting

confidence: 92%

Section: Model For Photoemissionmentioning

confidence: 91%

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Photoelectron emission studies in CsBr at 257nm

Journal of Vacuum Science &Amp; Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena

Liu

Sun

et al. 2006

Self Cite

“…Building on previous experience [7][8][9], studies were commissioned to measure the quantum efficiency, lifetime, dark current, and intrinsic transverse emittance of CsBr photocathodes in a high gradient rf gun.…”

Section: Introductionmentioning

confidence: 99%

High gradient rf gun studies of CsBr photocathodes

Vecchione

Phys. Rev. ST Accel. Beams

Gierman

et al. 2015

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CsBr photocathodes have 10 times higher quantum efficiency with only 3 times larger intrinsic transverse emittance than copper. They are robust and can withstand 80 MV=m fields without breaking down or emitting dark current. They can operate in 2 × 10 −9 torr vacuum and survive exposure to air. They are well suited for generating high pulse charge in rf guns without a photocathode transfer system.

“…CsBr coatings on photocathodes have been extensively studied [13][14][15][16][17][18] and have desirable properties. They greatly enhance the quantum yield of the emitter by reducing the effective work function and are robust and capable of operation under the demanding conditions of ultra bright FEL sources.…”

mentioning

confidence: 99%

Photocathode device using diamondoid and cesium bromide films

Clay

Applied Physics Letters

Pianetta

et al. 2012

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A photocathode structure is presented that shows promise for use in high brightness electron sources. The structure consists of a metal substrate, a monolayer of a diamondoid derivative, and a thin film of cesium bromide. Diamondoid monolayers reduce the energy spread of electron emitters, while cesium bromide increases the yield and stability of cathodes. We demonstrate that the combined structure retains these properties, producing an emitter with lower energy spread than the corresponding cesium bromide emitter (1.06 eV versus 1.45 eV) and higher yield and stability than un-coated diamondoid emitters. 3 An ideal emitter for these devices would have high intensity, small physical size, good stability under operating conditions, and low energy spread. One method for achieving high yield and small physical size is to use a focused laser beam to create photoelectrons. However, performance of such devices is limited by the quantum yield and the energy spread. In this work, we present a photocathode structure that improves on the quantum yield and reduces the energy spread of laser photoemission devices without sacrificing the other desirable properties. This device consists of a monolayer of diamondoid combined with a thin film of cesium bromide.Diamondoids are hydrocarbon molecules with the same carbon-lattice structure as bulk diamond. They inherit many of the superior properties of diamond 4,5 and possess emergent properties relating to their small size and high surface area ratio. [6][7][8][9][10][11][12] One unique property of these diamondoids is their behavior in photoemission devices. A monolayer of diamondoids on a metal substrate can largely monochromatize the photoemission, with the majority of the electrons emitting in a single peak with a full-width half-max (FWHM) of around 0.3 eV.6,7 This low energy spread is ideal for many cathode applications, but the diamondoid monolayers that have been studied are not stable enough for use in most devices. In order to correct this problem, we have added cesium bromide as a protective over-layer to provide mechanical stability and protection.Cesium bromide provides more than just protection, however. CsBr coatings on photocathodes have been extensively studied [13][14][15][16][17][18] and have desirable properties. They greatly enhance the quantum yield of the emitter by reducing the effective work function and are robust and capable of operation under the demanding conditions of ultra bright FEL sources. 19 Our objective is to combine these attractive properties with the reduced energy spread of diamondoids by creating a device that contains both films using a thiolated diamondoid to create a self-assembled monolayer (SAM).We tested these devices using ultra-violet (UV) laser photoemission, as shown in Figure 1. We measured the quantum yield, the energy spread, and lifetime of devices with and without the diamondoid present with varying thicknesses of CsBr. Through these investigations, we demonstrate that the high quantum yield of the CsBr emitter is preserved ...