Materials and Breakdown Phenomena: Heterogeneous Molybdenum Metallic Films

Abstract

Technological activities to design, manufacture, and test new accelerating devices using different materials and methods is under way all over the world. The main goal of these studies is to increase the accelerating gradients and reduce the probability of radio-frequency (RF) breakdown. Indeed, it is still not clear why, by increasing the intensity of the applied field, intense surface damage is observed in copper structures, limiting the lifetime and, therefore, the practical applications. A possible solution is represented by a coating of a relatively thick layer of molybdenum in order to improve the breakdown rate. molybdenum can be reliably grown on different substrates with a negligible strain and, for thicknesses up to 600 nm, with a resistivity <100-150·µΩ cm. Moreover, Mo coatings with controlled composition, internal stress, and roughness may allow improving thermo-mechanical properties reaching values not attainable by uncoated copper. Although the Mo conductivity remains lower compared to Cu, a Mo coating represents a very interesting option for high gradient accelerator components manufactured in copper.

Structural Evolution of MoO3 Thin Films Deposited on Copper Substrates upon Annealing: An X-ray Absorption Spectroscopy Study

“…A high WF conductive coating could be used to reduce these detrimental phenomena, extending the lifetime of the device and allowing it to operate at higher electric fields [1,5,11,12]. Hence, MoO 3 coating can significantly enhance the electronic and mechanical properties of copper-based devices via its high WF and relatively higher hardness, compared with copper [5,[13][14][15], without affecting the surface conductivity. Because the thermal evaporation deposition produces disordered and poorly adhesive MoO 3 coatings [5], with the aim to obtain ordered MoO 3 coatings, we tried to optimize the annealing procedure.…”

Effect of Molybdenum Coatings on the Accelerating Cavity Quality Factor

“…As the analysis has been treated in a generalized way, and the respective parametrizations have been explored in a relatively large range, one can safely extrapolate these results to either molybdenum coatings made of different phases (e.g., molybdenum dioxide MoO 2 , or heterogeneous molybdenum metallic films [26]) or other conductive materials.…”

Metallic Interface Induced Ionic Redistribution within Amorphous MoO3 Films

“…The transition metal oxides with high work function and opto‐electronic properties are of utmost interest in several advanced applications, such as photonics and thermochromic as well as protective coatings. [ 1–4 ] Among these materials, molybdenum oxides recently attracted the attention, due to the peculiar features of this class of oxide, originating from the interplay between the large variety of lattice configuration and the multiple valence states of Mo. [ 5–7 ] Even though MoO 3 is a high‐ k dielectric insulator, its electronic structure can be adjusted by modifying the oxygen substoichiometry (MoO 3− x ), introducing electronic gap states that modifies the oxide's electrical conductivity.…”

“…The transition metal oxides with high work function and opto-electronic properties are of utmost interest in several advanced applications, such as photonics and thermochromic as well as protective coatings. [1][2][3][4] Among these materials, the thin film oxides on metallic substrate exhibit an enhanced catalytic activity compared to their bulk counterparts, probably due to the charge-transfer interactions between the metal substrate and the oxide layer on the nanometer length scale. [12] The high work function and hole transport properties of MoO 3−x /Cu system has been also investigated to improve the conversion efficiency of the cell using the doping effect of Cu.…”