Coatings consisting of Ge particles on nonwettable Si oxide surfaces and their resonance reflection spectra

Abstract

The dewetting phenomenon that occurs during annealing of Ge films after their deposition on oxidized Si surfaces at room temperature is studied. The agglomeration of Ge films into compact particles begins at temperature as low as 350 °C. The particle shapes become closer to spherical as the annealing temperature is increased to 700 °C. The reflectance spectra of samples coated with dense arrays of compact Ge particles are measured in the wavelength range of 350–1200 nm. They contain two broad minima, at which the reflection decreases by a factor of 5–10, compared to the bare substrate reflection. The minimum in the long-wavelength region of the spectrum is associated with the excitation of magnetic and electric dipole resonances in individual Ge particles. The appearance of a deeper minimum in the short-wavelength region can be attributed to the excitation of quadrupole resonant modes in combination with the effect of small interparticle spacings. The coatings from the thus obtained particles exhibit strong and broadband antireflection properties.