Fig. 2: Fabrication and optical characterization of printed particle-based Au/Si microstructures.
From: Spectral physical unclonable functions: downscaling randomness with multi-resonant hybrid particles
a Schematic illustration of the experimental setup used to fabricate hybrid Au/Si particles, and scanning electron microscopy (SEM) image of an array of created structures (scale bar: 5 μm). The radius of the circles outlined by a femtosecond laser is 1.5 μm. With a laser beam scanning speed of 50 μm/s, this fabrication method allows the creation of up to 200 structures per minute. The size distribution of particles in these structures is presented in Supplementary Fig. 2. b The PL spectrum measured from one of the obtained Au/Si particles (red) vs. the spectrum from the initial bilayer film (gray). For PL excitation, we used a fs-laser system with a central wavelength of 1050 nm (“Methods” section). A sharp peak at 525 nm corresponds to the second harmonic generation (SHG). c Wavelength-dependent PL slopes (i.e., powers of nonlinear dependence of PL intensity on pump intensity at a given wavelength) from four randomly selected particles. Taking into account that 3PA in Au is more efficient than that in Si37, while 2PA is the most probable nonlinear process in Si66, one can assume that the overall white-light signal results from these two separate absorption processes, responsible for their parts of the spectrum. d Bright-Field (BF), Dark-Field (DF), and PL images of a printed pixel illustration of the Yin-Yang symbol. Scale bar: 20 μm.
