An AES study of the room temperature conditioning of technological metal surfaces by electron irradiation

Scheuerlein, C.; Taborelli, M.; Hilleret, N.; Brown, A.; Baker, Mark

doi:10.1016/s0169-4332(02)00868-1

Cited by 28 publications

(18 citation statements)

References 24 publications

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“…We want here to underline though, that there are two relevant exceptions to this reasoning, namely TiZV NEG coating and a-C. In case of TiZrV NEG coatings, developed at CERN by Benvenuti as diffuse pumps, 142 a mild thermal annealing in UHV (activation) is shown to remove most of the surface contaminants, 22,119,123,142,167 resulting in a stable and close to atomically clean surface with δ max about 1.1. This can be seen in Fig.…”

Section: Coatingsmentioning

confidence: 93%

“…26, most if not all materials used in accelerator technology have a significantly high SEY, much higher than needed to avoid e − cloud related instabilities. Pioneering work done at CERN in this context, 118,120,122,167,187 observes that when a surface is exposed to an electron beam, its SEY decreases. This is shown in Fig.…”

Section: Electron and Photon Scrubbingmentioning

confidence: 99%

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Electron cloud in accelerators

Cimino

Demma

2014

Int. J. Mod. Phys. A

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Low energy electrons in accelerators are known to interact with the circulating beam, giving rise to the formation of a so-called e − cloud. Such e − cloud may induce detrimental effects on the accelerated beam quality and stability. Those effects have been observed in most accelerators of positively charged particles. A longstanding effort has been so far devoted to understand in detail the physical origin of such e − cloud, its build-up and its interaction with the circulating beam. We will first describe the origin and the basic features causing e − cloud formation in accelerators, then we review some of the theoretical work produced to simulate and analyze such phenomenon. In selected cases, theoretical expectations and experimental observations will be compared, to address the importance of benchmarking codes versus observations to reach the required predictive capability. To this scope, codes need realistic input parameters which correctly describe material and surface properties at the basis of such e − cloud formation and build-up. The experimental efforts, performed worldwide in many surface and material science laboratories, to measure such essential parameters will then be presented and critically reviewed. Finally, we will describe some of the e − cloud mitigation strategies adopted so far and draw some conclusions.

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Section: Coatingsmentioning

confidence: 93%

Section: Electron and Photon Scrubbingmentioning

confidence: 99%

Electron cloud in accelerators

Cimino

Demma

2014

Int. J. Mod. Phys. A

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“…Several surface modifications occur during electron irradiation, which might be responsible for the corresponding SEY decrease. Indeed, both surface cleaning by electron stimulated desorption (ESD) [21,22] and graphitization of the adventitious carbon layer [17,18,23,24] were observed. Furthermore, an increase of carbon amount on the surface was sometimes reported [17,[23][24][25] and found to be necessary to decrease the maximum SEYof copper to about 1.1 by some authors [24].…”

Section: Introductionmentioning

confidence: 99%

Role of the different chemical components in the conditioning process of air exposed copper surfaces

Petit

Taborelli

Neupert

et al. 2019

Phys. Rev. Accel. Beams

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As a source of heat load on cryogenic sections, the electron cloud is currently a major limitation to the intensity of some modern particle accelerators such as the LHC and its high luminosity upgrade at CERN. During LHC operation, conditioning of the copper beam pipe surface occurs, leading to a decrease of the cloud intensity. To understand the role of the different chemical surface components of air exposed copper in the electron conditioning process, air exposed copper samples as well as specific model surfaces produced in the laboratory, namely sputter-cleaned copper and carbon-free cuprous oxide (Cu 2 O), were conditioned by low energy electron irradiation. Conditioning of air exposed copper results in a decrease of the maximum secondary electron yield (SEY) below 1.1. Surface cleaning by electron stimulated desorption and carbon graphitization without increase of the carbon surface concentration are observed by x-ray photoelectron spectroscopy. After conditioning, the maximum SEY of both sputter-cleaned copper and Cu 2 O remains higher than 1.1. No significant surface modification is observed by x-ray photoelectron spectroscopy during irradiation for these two surfaces. These results prove that neither an increase of the amount of surface carbon nor oxide modification is responsible for the SEY reduction observed during electron irradiation of air exposed copper. They confirm that graphitic carbon is required to decrease the maximum SEY of copper below 1.1.

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“…Further Auger electron spectroscopy work on Cu in UHV shows a constant O-KLL peak intensity over 70 min of electron bombardment with a flux of ϳ1.2 ϫ 10 12 e − mm −2 s −1 , suggesting that ESD-generated oxygen products are not supply limited in typical OFHC Cu surfaces. 32 Watkins and Williams 33 examined ESD of OFHC copper surfaces as a possible UHV cleaning technique. Their results at ϳ1 ϫ 10 −10 Torr showed that total desorption efficiency and, therefore, the corresponding cross section, did not change significantly as the incident ͑0.1 A mm −2 ͒ electron energy was increased from 300 to 2000 eV.…”

Section: A Electron Stimulated Desorption From Cumentioning

confidence: 99%

Hyperthermal atomic hydrogen and oxygen etching of vertically oriented graphene sheets

Bagge‐Hansen

Outlaw

Zhu

et al. 2009

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

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Carbon nanosheets have previously been shown to be promising high current field emission cathodes for a variety of potential applications. The vertically oriented planar sp2 carbon nanosheets grown by rf plasma-enhanced chemical vapor deposition terminate with one to seven graphene sheets and grow to ∼1 μm in height. High current field emission, Je∼0.15 mA mm−2 (8 V μm−1), conducted within an ultrahigh vacuum system in a diode configuration in line-of-sight to a mass spectrometer, shows that CH4, CO2, and CO are generated as a result of cathode bombardment by hyperthermal oxygen and hydrogen neutrals and ions generated by electron stimulated desorption at the Cu anode. Confirmation of the mechanism was achieved by repeating the experiments using a Au anode. Simultaneous acquisition of I-V data and the partial pressures of reaction products in the mass spectrometer have shown repeatable, sustained CH4, CO2, and CO production. As these hyperthermal atomic hydrogen and oxygen species impinge on the sidewalls and edges of the carbon nanosheets, they bond to various sites throughout the sp2 carbon array. Progressively, as further hydrogen and oxygen arrive, CH4, CO2, and CO are formed and desorbed, thereby etching the film. Raman spectroscopy has confirmed a corresponding increase in defect sites (ID/IG increased from 0.57 to 0.81) over the test interval. Scanning electron microscopy cross sections of carbon nanosheet cathodes before and after high current lifetime testing (>200 h) show the average etching rate to be ∼1.7×10−3 nm/s.

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An AES study of the room temperature conditioning of technological metal surfaces by electron irradiation

Cited by 28 publications

References 24 publications

Electron cloud in accelerators

Electron cloud in accelerators

Role of the different chemical components in the conditioning process of air exposed copper surfaces

Hyperthermal atomic hydrogen and oxygen etching of vertically oriented graphene sheets

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