Bi-alkali antimonide photocathode growth: An X-ray diffraction study

Schubert, S.; Wong, Jonathan; Feng, Jun; Karkare, Siddharth; Padmore, H. A.; Ruiz-Oses, M.; Smedley, J.; Muller, Edward N.; Ding, Zihao; Gaowei, Mengjia; Attenkofer, Klaus; Liang, Xue; Xie, Junqi; Kühn, Julius

doi:10.1063/1.4959218

Cited by 22 publications

(20 citation statements)

References 15 publications

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“…Although it is well known that the CsK 2 Sb cathode performance depends on the substrate material and surface conditions [13,[18][19][20][21], the underlying physics has not been extensively studied to date because of the lack of standardization of the cathode evaporation process. For example, the dependence of the cathode performance on the surface orientation of the CsK 2 Sb or the substrate crystal was studied but not significantly observed [22,23] because the cathode evaporation condition was not fully optimized in these studies. Indeed, the QE in these studies was relatively low (3%).…”

Section: Introductionmentioning

confidence: 99%

pn -type substrate dependence of CsK2Sb photocathode performance

Guo

Katoh

2019

Phys. Rev. Accel. Beams

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The CsK 2 Sb photocathode is capable of generating a high-intensity and low-emittance electron beam with visible laser light. In this study, we examined CsK 2 Sb photocathode evaporation on nand p-type Si(100), GaAs(100), and Si(111) substrates, and compared their cathode performance. We found that the quantum efficiency of the p-type substrate was superior to that of the n-type substrate for the same substrate material and surface orientation. We show that this can be qualitatively analyzed by an energy-band model for the semiconductor(metal)-semiconductor junction between CsK 2 Sb and the substrate. We also evaporated the Cs 3 Sb cathode on nand p-type Si(100) and GaAs(100) substrates, and confirmed that the cathode performance of all substrates was consistent with the model results. This finding indicates the possibility of improving the thin-film cathode performance by revisiting the semiconductor(metal)semiconductor junction between the cathode and the substrate, which improves the understanding of high-performance photocathodes.

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Section: Introductionmentioning

confidence: 99%

pn -type substrate dependence of CsK2Sb photocathode performance

Guo

Katoh

2019

Phys. Rev. Accel. Beams

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“…Models suggest that at the envisaged gradients for SRF photoinjectors (15)(16)(17)(18)(19)(20) the surface roughness of the photocathode must be reduced to values of R q ≤ 10 nm to maintain a roughness induced emittance contribution that is below the intrinsic emittance [9,10]. From recent works of Schubert et al and Ding et al it is apparent that the final roughness of alkali antimonide photocathodes depends strongly on the growth procedure and the crystallization processes involved [11,12]. It has been shown that the sequential growth process delivers very rough photocathodes due to the multiple phase transitions, while smoother photocathodes can be grown using new growth procedures such as triple evaporation of Cs-K-Sb using pure alkali metal sources and magnetron sputtering [13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

“…From recent works of Schubert et al and Ding et al it is apparent that the final roughness of alkali antimonide photocathodes depends strongly on the growth procedure and the crystallization processes involved [11,12]. It has been shown that the sequential growth process delivers very rough photocathodes due to the multiple phase transitions, while smoother photocathodes can be grown using new growth procedures such as triple evaporation of Cs-K-Sb using pure alkali metal sources and magnetron sputtering [13][14][15][16]. In this work an adaptation of a codeposition procedure has been developed, taking into consideration the geometrical condition of our preparation system.…”

Section: Introductionmentioning

confidence: 99%

Towards the operation of Cs-K-Sb photocathodes in superconducting rf photoinjectors

Schmeißer

Mistry

Kirschner

et al. 2018

Phys. Rev. Accel. Beams

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High quantum efficiency photocathodes are mandatory for the operation of photoinjector driven electron accelerators with high average current and high brightness beams. Photocathodes based on bi-alkali antimonides, e.g., CsK 2 Sb, exhibit high quantum efficiencies for visible light and can be operated close to the photoemission threshold, thus they are suitable candidates to provide high current and low emittance electron beams. In this paper, a codeposition procedure of K and Cs on Sb resulting in high quantum efficiency photocathodes is presented and compared to the sequential growth procedure that was established for photomultiplier and accelerator applications. In-situ x-ray photoelectron spectroscopy is applied to gain insights into the reaction pathway of antimony with alkali metals, and to optimize the growth process of CsK 2 Sb on Mo. It has been found that the average stoichiometry of the samples is similar after both procedures. The study also presents the behavior of the photocurrent at cryogenic temperatures, the influence of cooling and warmup cycles on the photocathode lifetime and our experience with storage and transport. This work demonstrates that our codeposition growth procedure reproducibly delivers high quantum efficiency photocathodes, and that their quantum efficiency, when excited with green photons, is not influenced by cryogenic temperatures.

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“…These techniques allow the evaluation of material composition, crystal structure, electrical conductivity, surface morphology (roughness, lateral structure), layer thickness and the extent of interdiffusion, doping concentrations, and other relevant material properties. In some cases, additional insight can be obtained by making these measurements in operando -during the growth process 138,139 allowing for adjusting growth parameters to account for material incorporation into the film during growth. A materials-centric approach to photocathode development now requires the availability of some combination of such techniques.…”

Section: In Situ Surface Science Characterizationmentioning

confidence: 99%

Perspectives on Designer Photocathodes for X-ray Free-Electron Lasers: Influencing Emission Properties with Heterostructures and Nanoengineered Electronic States

et al. 2018

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The development of photoemission electron sources to specifically address the competing and increasingly stringent requirements of advanced light sources such as X-ray Free Electron Lasers (XFELs) motivates a comprehensive material-centric approach that integrates predictive computational physics models, advanced nano-synthesis methods, and sophisticated surface science characterization with in situ correlated study of photoemission performance and properties. Related efforts in material science are adopting various forms of nanostructure (such as compositionally graded stoichiometry in heterostructured architectures, and quantum features) allowing for tailored electronic structure to control and enhance opto-electronic properties. These methods influence the mechanisms of photoemission (absorption, transport, and emission) but have not, as yet, been systematically considered for use in photocathode applications. Recent results and near-term opportunities are described to exploit controlled functionality of nanomaterials for photoemission. An overview of the requirements and status is also provided.

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Bi-alkali antimonide photocathode growth: An X-ray diffraction study

Cited by 22 publications

References 15 publications

pn -type substrate dependence of CsK2Sb photocathode performance

pn -type substrate dependence of CsK2Sb photocathode performance

Towards the operation of Cs-K-Sb photocathodes in superconducting rf photoinjectors

Perspectives on Designer Photocathodes for X-ray Free-Electron Lasers: Influencing Emission Properties with Heterostructures and Nanoengineered Electronic States

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