GaAs-Cs: A new type of photoemitter

Scheer, Jens; Laar, J. van de

doi:10.1016/0038-1098(65)90289-9

Cited by 269 publications

(36 citation statements)

References 5 publications

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“…11 These materials owe their high QE under visible illumination to a monolayer of Cs-based dipoles produced during the surface activation process. 13 Besides investigating this previous report, in this Letter we present QE degradation data on a representative sample of another class of photocathodes, the alkali antimonides that we fabricated and measured. These complementary data sets were used to validate the kinetic model presented below and to obtain values for the rate coefficients that characterize QE degradation.…”

confidence: 83%

“…It is well known that as little as a monolayer coverage on a semiconductor photocathode surface can enhance or inhibit QE, at a given wavelength, by many orders of magnitude due to induced changes in the electron affinity. 5,13,14 Lifetimes of photocathodes are typically characterized by indicating how much the QE decreases over a given time interval at a certain base pressure in the UHV system. 7,10,12 Many authors quote 1/e lifetimes without determining whether the degradation curve is exponential.…”

confidence: 99%

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Kinetics of alkali-based photocathode degradation

et al. 2016

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We report on a kinetic model that describes the degradation of the quantum efficiency (QE) of Cs3Sb and negative electron affinity (NEA) GaAs photocathodes under UHV conditions. In addition to the generally accepted irreversible chemical change of a photocathode’s surface due to reactions with residual gases, such as O2, CO2, and H2O, the model incorporates an intermediate reversible physisorption step, similar to Langmuir adsorption. This intermediate step is needed to satisfactorily describe the strongly non-exponential QE degradation curves for two distinctly different classes of photocathodes –surface-activated and “bulk,” indicating that in both systems the QE degradation results from surface damage. The recovery of the QE upon improvement of vacuum conditions is also accurately predicted by this model with three parameters (rates of gas adsorption, desorption, and irreversible chemical reaction with the surface) comprising metrics to better characterize the lifetime of the cathodes, instead of time-pressure exposure expressed in Langmuir units.

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confidence: 83%

confidence: 99%

Kinetics of alkali-based photocathode degradation

et al. 2016

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“…Such surfaces are created by the deposition of Cs and O on III-V surfaces which results in a lowering of the work function below the bulk conduction band minimum thus allowing the direct emission of electrons at the bottom of the conduction band into vacuum [1,2]. The Cs+O / GaAs system has received the most attention during the past several decades and different models describing the origin of the NEA condition have been suggested [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. One of the most important pieces of information for people to understand the NEA surfaces is the chemical composition of the surface Cs/O layer.…”

Section: Introductionmentioning

confidence: 99%

Formation of cesium peroxide and cesium superoxide on InP photocathode activated by cesium and oxygen

Sun

Liu

Pianetta

et al. 2007

Journal of Applied Physics

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Abstract:Activation of p type III-V semiconductors with Cesium and Oxygen has been widely used to prepare Negative Electron Affinity (NEA) photocathodes. However, the nature of the chemical species on the surface after the activation is not well-understood.In this study, InP NEA photocathodes activated with Cesium and Oxygen are studied using Synchrotron Radiation Photoelectron Spectroscopy, also called photoemission.

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“…To release electrons into the vacuum the thermocathode must be heated to 1300-1500 K, which results in electron energy spreads of about 110-120 meV. In the case of GaAs photocathodes the situation is different: GaAs with a thin layer of cesium and oxygen produces a state with effective Negative Electron Affinity (NEA) if the vacuum level lies below the position of the conduction band in the bulk [9] (figure 1). Electrons, photoexcited from the valence band to the conduction band, are rapidly thermalized at the bottom of the conduction band and reach the surface with energy spreads defined by the temperature of the bulk, which is in our case about 80 K. Due to the NEA condition, a large fraction of these electrons can escape into the vacuum.…”

Section: Photoelectron Emission From Gaas(cso)mentioning

confidence: 99%

Photocathodes as electron sources for high resolution merged beam experiments

Orlov

Sprenger

Lestinsky

et al. 2005

J. Phys.: Conf. Ser.

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Abstract. An ultra cold electron source was developed for the storage ring TSR in Heidelberg to study electron-ion interactions with high energy resolution. The heart of the source is a GaAs photocathode which emits electrons with energy spreads below 10 meV. Photoemitted electrons are extracted in the space charge mode and then undergo adiabatic magnetic expansion and adiabatic acceleration to obtain an ultra cold electron beam which is overlapped with the stored ion beam in a straight section of the ring. In the first recombination measurements on HD + unprecedented energy resolution for low-energy resonances was found, demonstrating a transverse and longitudinal temperature of the electron beam of about 0.5 meV and 0.02 meV, respectively. IntroductionMerged beam experiments at storage rings were used successfully to study electron-ion inelastic collisions with high energy resolution (see, e.g., [1]). While the typical energies of the stored ions and electrons are about a few MeV/u and keV, respectively, collision energies below a milli-eV can be realized by small longitudinal velocity detuning between the ion beam and the magnetically guided electron beam. In such experiments the ion velocity is well defined and the collision energy spread is mainly given by the electron energy distribution, being strongly anisotropic in the co-moving reference frame [2]. At zero detuning energy and for typical electron densities n e ∼ 10 5 -10 7 cm −3 , the longitudinal temperature kT || of the electrons is mainly defined by potential energy relaxation: kT || ∼ Cn 1/3 e 2 /4πε 0 . Here the parameter C describes the quality of the acceleration and can be suppressed by slow acceleration [2]. The longitudinal temperature is typically below 0.1 meV and always much smaller than the transverse temperature kT ⊥ which so far has been in the range of 2-30 meV. In recombination experiments, the electron temperatures lead to an asymmetric broadening δ E of the observed cross-section resonances. The low-energy side of the resonance is broadened by kT ⊥ , while kT || broadens the resonance symmetrically by 4(E r kT || ln 2) 1/2 , with E r being the resonance energy [3]. For E r below 0.1 eV, δ E is limited by kT ⊥ . Hence, to improve δ E in this energy range, kT ⊥ has to be decreased. Initially kT ⊥ is given by the cathode temperature kT c and can be reduced by an adiabatic magnetic expansion: kT ⊥ = kT c /α, where α is the expansion coefficient [4]. While for thermocathodes kT c is above 100 meV, semiconductor photocathodes operated at room temperature or below were considered as promising candidates for cold electron sources.We have developed an electron gun with a cryogenic GaAs photocathode which is suitable for obtaining mA currents of emitted electrons with energy spreads of 5-7 meV [5,6]. This electron source has been installed into the TSR electron target section which provides adiabatic magnetic expansion

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GaAs-Cs: A new type of photoemitter

Cited by 269 publications

References 5 publications

Kinetics of alkali-based photocathode degradation

Kinetics of alkali-based photocathode degradation

Formation of cesium peroxide and cesium superoxide on InP photocathode activated by cesium and oxygen

Photocathodes as electron sources for high resolution merged beam experiments

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