| 1. |
- Broitman, Esteban, et al.
(författare)
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Microstructural, nanomechanical, and microtribological properties of Pb thin films prepared by pulsed laser deposition and thermal evaporation techniques
- 2016
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : A V S AMER INST PHYSICS. - 0734-2101 .- 1520-8559. ; 34:2, s. 021505-
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the authors compare the morphological, structural, nanomechanical, and microtribological properties of Pb films deposited by thermal evaporation (TE) and pulsed laser deposition (PLD) techniques onto Si (111) substrates. Films were investigated by scanning electron microscopy, surface probe microscopy, and x-ray diffraction in theta-2 theta geometry to determine their morphology, root-mean-square (RMS) roughness, and microstructure, respectively. TE films showed a percolated morphology with densely packed fibrous grains while PLD films had a granular morphology with a columnar and tightly packed structure in accordance with the zone growth model of Thornton. Moreover, PLD films presented a more polycrystalline structure with respect to TE films, with RMS roughness of 14 and 10 nm, respectively. Hardness and elastic modulus vary from 2.1 to 0.8 GPa and from 14 to 10 GPa for PLD and TE films, respectively. A reciprocal friction test has shown that PLD films have lower friction coefficient and wear rate than TE films. Our study has demonstrated for first time that, at the microscale, Pb films do not show the same simple lubricious properties measured at the macroscale. (C) 2015 American Vacuum Society.
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| 2. |
- Broitman, Esteban, et al.
(författare)
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Nanomechanical and microtribological properties of yttrium thin films for photocathode engineering
- 2019
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : A V S AMER INST PHYSICS. - 0734-2101 .- 1520-8559. ; 37:3
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Tidskriftsartikel (refereegranskat)abstract
- The authors study the nanomechanical and microtribological properties of yttrium (Y) thin films deposited by pulsed laser deposition on Cu polycrystalline substrates. Nanoindentation tests reveal that such films have a high hardness of H = 2.3 GPa and a reduced elastic modulus of 71.7 GPa with respect to the Cu substrates. The friction coefficient between a diamond tip and the Y film reaches a steady state value of mu similar to 0.34, lower than that for the Cu (mu similar to 0.38). Moreover, nano-scratch experiments show that Y films are more scratch-resistant than the Cu substrates, probably due to their greater hardness, higher elastic recovery, and lower friction coefficient. Their results confirm that the mechanical and tribological properties of the Y films are suitable for designing and fabricating scratch-resistant hybrid photocathodes and can reduce instabilities and unwanted discharges in the cavity of the radio-frequency gun. Furthermore, the low surface roughness and the low work function of the material are important characteristics for a photocathode based on the Y thin film for the production of high-brightness electron beams. Published by the AVS.
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| 3. |
- Gontad, Francisco, et al.
(författare)
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Fabrication of Nb/Pb structures through ultrashort pulsed laser deposition
- 2016
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : AMER INST PHYSICS. - 0734-2101 .- 1520-8559. ; 34:4
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Tidskriftsartikel (refereegranskat)abstract
- This work reports the fabrication of Nb/Pb structures with an application as photocathode devices. The use of relatively low energy densities for the ablation of Nb with ultrashort pulses favors the reduction of droplets during the growth of the film. However, the use of laser fluences in this ablation regime results in a consequent reduction in the average deposition rate. On the other hand, despite the low deposition rate, the films present a superior adherence to the substrate and an excellent coverage of the irregular substrate surface, avoiding the appearance of voids or discontinuities on the film surface. Moreover, the low energy densities used for the ablation favor the growth of nanocrystalline films with a similar crystalline structure to the bulk material. Therefore, the use of low ablation energy densities with ultrashort pulses for the deposition of the Nb thin films allows the growth of very adherent and nanocrystalline films with adequate properties for the fabrication of Nb/Pb structures to be included in superconducting radiofrequency cavities. (C) 2016 American Vacuum Society.
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| 4. |
- Gontad, Francisco, et al.
(författare)
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Growth of lead thin films on silicon and niobium substrates by sputtering technique
- 2017
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : A V S AMER INST PHYSICS. - 0734-2101 .- 1520-8559. ; 35:3
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the authors report the growth of Pb thin films on both Si and Nb substrates by radio-frequency sputtering technique. Deposited films were characterized and tested to deduce the structure, the morphology, the nanomechanical properties, and also the quantum efficiency. Granular structures and large presence of voids were observed by scanning electron microscopy; moreover, the roughness and grain size of the film surface, investigated by surface probe microscopy, increased with the film thickness. Crystallographic orientation, studied by x-ray diffraction, showed the growth of polycrystalline Pb thin films and the presence of weak diffraction peaks related to penta-lead oxide (Pb5O8). The nanomechanical analysis reveals a film hardness with a value (similar to 1.5GPa) well beyond the hardness of Pb bulk (0.04GPa). Finally, twin Pb thin films deposited on Nb substrates were tested as photocathodes showing its great potentiality to be used in superconducting radio-frequency guns with a quantum efficiency of 5 x 10(-5). (C) 2017 American Vacuum Society.
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