Developing a surface with low Secondary Electron Yield (SEY) is one of the main ways of mitigating electron cloud and beam-induced electron multipacting in high-energy charged particle accelerators. In our previous publications, a low SEY< 0.9 for as-received metal surfaces modified by a nanosecond pulsed laser was reported. In this paper, the SEY of laser-treated blackened copper has been investigated as a function of different laser irradiation parameters. We explore and study the influence of micro-and nano-structures induced by laser surface treatment in air of copper samples as a function of various laser irradiation parameters such as peak power, laser wavelength ( = 355 nm and 1064 nm), number of pulses per point (scan speed and repetition rate) and fluence, on the SEY. The surface chemical composition was determined by x-ray photoelectron spectroscopy (XPS) which revealed that heating resulted in diffusion of oxygen into the bulk and induced the transformation of CuO to sub-stoichiometric oxide. The surface topography was examined with high resolution scanning electron microscopy (HRSEM) which showed that the laser-treated surfaces are dominated by microstructure grooves and nanostructure features.

Bismuth thin films of thickness in the region of 500 nm have been prepared by planar magnetron sputtering onto glass, silicon and GaAs substrates. Electron microscopy of these films reveals that bismuth whiskers grow spontaneously when the substrate is heated to temperatures between 110ºC and 140ºC during deposition and the optimum temperature for such growth is largely independent of substrate. Depositing films under similar conditions using thermal evaporation does not, however, produce the whisker growth. X-ray diffraction has been employed to investigate film texture with temperature and it has been shown that the and has a higher change-over temperature. The whiskers that grow from the film emerge at off-normal angles between 43.3º and 69.2º with a mean of 54±3º. The projected length of whiskers on a 500 nm film on a GaAs substrate shows a wide distribution to a maximum of more than 100 µm. The mean projected length for this sample was 16±1 µm and the diameter is around 0.5 µm. Measurements of the electrical properties of the whiskers at room temperature reveals ohmic behaviour with an estimated resistivity of 2.2±0.2 µΩm. Detailed examination of scanning electron micrographs, eliminates all growth mechanisms except tip growth by a non-catalysed vapour-solid/vapour-liquid-solid method. By depositing thinner films it is shown that this spontaneous growth of whiskers offers a route to fabricate high quality bismuth nanowires of lengths exceeding 10 µm.2

Pulsed laser deposition has been used to prepare thin films of the high entropy alloy AlCrFeCoNiCu. The 35 nm films were deposited in ultra-high vacuum onto glass at room temperature and above and analysed using X-ray diffraction and X-ray photoelectron spectroscopy. Films deposited at room temperature exhibit a mix of FCC and BCC reflections, the FCC crystallites having size similar to the film thickness, but the BCC crystallites are larger. The intensity of the reflections from both crystal structures reduce with increasing deposition temperature, the fall in BCC commencing at lower temperature than the FCC associated with a reduction of the content of Al and Cu. X-ray photoelectron spectroscopy shows that the films deposited at room temperature are closer to stoichiometry than those at higher temperatures. An important feature of the X-ray photoelectron spectroscopy depth profiles is surface segregation, the outer 3 nm of the high entropy alloy films has higher concentration of Al and, to a lesser extent, Cr. Highlights • The films exhibit mixed FCC and BCC structure. • With increasing deposition temperature, FCC and BCC reflections reduce associated with loss of Al and Cu. • Surface segregation enriches the surface of the films in Al and to a lesser extent Cr.

The spin Seebeck effect, a newly discovered phenomena, has been suggested as a potential ‘game changer’ for thermoelectric technology due to the possibility of separating the electric and thermal conductivities. This is due to a completely different device architecture where, instead of an arrangement of p‐ and n‐type pillars between two ceramic blocks, a thermopile could be deposited directly onto a magnetic film of interest. Here we report on the spin Seebeck effect in polycrystalline Fe3O4:Pt bilayers deposited onto amorphous glass substrates with a view for economically viable energy harvesting. Crucially, these films exhibit large coercive fields (197 Oe) and retain 75% of saturation magnetisation, in conjunction with energy conversion comparable to epitaxially grown films. This demonstrates the potential of this technology for widespread application in harvesting waste heat for electricity.

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