In situ synchrotron X-ray diffraction study of coherently embedded silver nanostructure growth in silicon

Abstract

We report on the in situ growth of coherently embedded Ag nanostructures using real time temperature dependent synchrotron X-ray diffraction (XRD) measurements. ≈17 nm thick GeO_x film was grown on native oxide covered silicon substrates (GeO_x/SiO_x/Si) using a physical vapor deposition (PVD) method, which were used as the substrates for Ag nanostructures growth. For growing Ag nanostructures, two different sources of silver were used. In one system, ≈2 nm silver thin film was grown on the GeO_x/SiO_x/Si substrates using a PVD method, while in another system, silver wires were kept on the specimen hot stage (chemical vapor deposition) along with the above substrates. All the in situ growth and real time XRD were done under atmospheric conditions. The lattice constant of the Ag nanostructures obtained from the ex situ growth specimens was used to compare with the real time high temperature XRD measurements. As the temperature is raised from room temperature to 850 °C while performing in situ growth, the evolutions of various diffraction peaks such as (111), (200) and (220), reflecting from the growth facets of Ag nanostructures, were monitored. By measuring the deviation of the Ag lattice parameter due to the shift in the diffraction peak positions as a function of temperature, the thermal expansion coefficients for the Ag nanostructures in a matrix have been determined. In one case, the thermal expansion coefficient was found to decrease from 1.9 × 10⁻⁵/°C to 1.82 × 10⁻⁵/°C with the increase of annealing temperature from 750 °C to 850 °C.