Ultra-Smooth Silver Single Crystal Films

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Silver is a highly desirable metal for photonics applications due to its low loss at optical and near infrared (near-IR) frequencies. However, it is hard to produce high-quality, ultra-smooth single crystal silver films.

In this study published in Scientific Reports, an international team led by Ilya Rodionov from Nara Institute of Science and Technology used a new two-step deposition process to deposit atomically smooth, high-quality single crystalline silver films. They deposited these silver films on lattice-matched and non-lattice-matched silicon substrates and demonstrated high quality of the films by their root mean square surface roughness, X-ray diffraction (XRD), atomic-resolution wide angle scattering characterization and field emission scanning electron microscopy with energy dispersive spectroscopy (FESEM) analysis.

The structure of the studied silver(I) complex is solved in the centrosymmetric, triclinic space group P-1 with a formula based on two silver(I), one 2,4,6-trimorpholino-1,3,5-triazine (L) and four coordinated water ions ligands. The structure is stabilized by strong hydrogen bonds and a weak van der Waals interaction.

XRD rocking curves show that the deposited films are biaxially textured on Si substrates with epitaxial relationships (111)Ag/Si, (110)Ag/Si and (111)Si/Si. The FWHM of the XRD rocking curve profiles shows that mosaic spread does not exceed 0.1 deg for all the deposited samples.

FESEM analysis of the S1 and S5 films reveals that both films are composed of a single crystalline phase with an atomic level RMS surface roughness of only 90 pm, the lowest value for a reported single-crystalline silver film. Moreover, the typical peaks observed in the e2 spectrum due to surface reaction with adsorbed sulphur are almost eliminated in the S5 sample, suggesting that the S1 silver film has better chemical stability32 and reduced sorptivity to the ambient chemicals33.