The effect of oblique-angle sputtering on large area deposition: a unidirectional ultrathin Au plasmonic film growth design

Abstract

Growing ultrathin nanogranular (NG) metallic films with continuously varying thickness is of great interest for studying regions of criticality and scaling behaviors in the vicinity of quantum phase transitions. In the present work, an ultrathin gold plasmonic NG film was grown on a sapphire substrate by RF magnetron sputtering with an intentional deposition gradient to create a linearly variable thickness ranging from 5 to 13 nm. The aim is to accurately study the electronic phase transition from the quantum tunneling regime to the metallic conduction one. The film structural characterization was performed by means of high-resolution transmission electron microscopy, atomic force microscopy, as well as x-ray diffraction and reflectivity techniques, which indicate the Volmer–Weber film growth mode. The optical and electrical measurements show a transition from dielectric-isolated gold NPs towards a continuous metallic network when t becomes larger than a critical value of tM = 7.8 nm. Our results show that the onset of the percolation region occurs when a localized surface plasma resonance transforms to display a Drude component, indicative of free charge carriers. We demonstrate that, by using a continuously varying thickness, criteria for metallicity can be unambiguously identified. The onset of metallicity is clearly distinguished by the Drude damping factor and by discontinuities in the plasma frequencies as functions of thickness.

Spectroscopic Ellipsometry Study on Tuning the Electrical and Optical Properties of Zr-Doped ZnO Thin Films Grown by Atomic Layer Deposition

“…Consequently, the number of native oxygen vacancies acting as donors in ZnO decreases, making the film more resistive. At T s , most of the oxygen atoms are absorbed and resistivity remains constant. , Interestingly, all of the studied Zr-doped ZnO films saturate at the same resistivity value of 2 × 10 –2 Ω cm. Furthermore, the electron mobility exhibited a substantial decrease in ZnO/Zr films thermally treated at temperatures higher than 250 °C (Figure b), which we attribute to the fact that the mobility of free carriers decreases to a low limit, not decreasing below it with increasing the annealing temperature, favoring the elimination of ZnO native point defects, as Zn interstitials and oxygen vacancies.…”

Scalable Gas Diffusion Electrode Fabrication for Electrochemical CO2 Reduction Using Physical Vapor Deposition Methods

“…More importantly, they are also scalable to very large electrode areas (∼10 4 cm 2 ) 31,32 and enable precise control over morphology and porosity. 33,34 PVD methods also provide a path forward to efficient integration and compositional tuning of Cu alloy catalysts, including nonthermodynamic equilibrium alloy compositions that are difficult to synthesize and integrate otherwise. 35,36 Beyond providing excellent control over coating uniformity, thickness, and composition, physical vapor deposition methods produce less waste and are less labor-intensive than traditional electrodeposition methods, thus making them cost-competitive, despite higher capital costs.…”

“…Both methods have the potential for large-scale production, allow for direct coating of the electrocatalyst on the GDL, and provide excellent thickness control and coating uniformity combined with a high specific surface area. More importantly, they are also scalable to very large electrode areas (∼10 4 cm 2 ) , and enable precise control over morphology and porosity. , PVD methods also provide a path forward to efficient integration and compositional tuning of Cu alloy catalysts, including nonthermodynamic equilibrium alloy compositions that are difficult to synthesize and integrate otherwise. , Beyond providing excellent control over coating uniformity, thickness, and composition, physical vapor deposition methods produce less waste and are less labor-intensive than traditional electrodeposition methods, thus making them cost-competitive, despite higher capital costs . Using a microfluidic gas diffusion electrolyzer, we observed that EB-Cu coatings generally provide better performance than the MS-Cu catalyst coatings in terms of current density, selectivity, and energy efficiency, with an optimum thickness of 400 nm where the energy efficiency (i.e., sum over the Faradaic efficiency times theoretical cell potential divided by the applied potential for all eCO 2 RR products; for details, see below) reaches 51% (56.5% for eCO 2 RR and HER combined).…”