| Abstract [eng] |
Plasmonic metal nanocomposite films are widely investigated metamaterial class, which exhibits localized surface plasmon resonance effect. Such films show large extinction cross-section at certain excitation wavelengths. It is known that light extinction in such nanocomposites strongly depends on dielectric functions and morphology of the components. Nanocomposite matrices usually are chosen to change plasmon resonance position in the optical spectra and to protect them from external effects. Diamond-like carbon is promising material as a plasmonic nanocomposite matrix due to its large mechanical resistance, chemical inertness, and biocompatibility. Optimizing diamond-like carbon and plasmonic metal (for instance, silver) nanocomposite film deposition parameters, it is possible to achieve broadband high absorbance and low reflectance for wide range of angles of incidence – absorbing anti-reflective coating is obtained. Such films could be useful in solar cells, optical absorbers, and photolithography. In present work, experimental and theoretical investigation of diamond-like carbon and silver nanocomposite (DLC:Ag) thin film optical and mechanical properties was carried out to determine optimal growth conditions for magnetron sputtered nanocomposite films which exhibit broadband high absorbance and low reflectance. According to modified Maxwell-Garnett Mie effective medium theory it was obtained, that increase of filling factor up to 30% leads to increase of width and height of extinction peak. However, to maintain high sp3 bond content in diamond-like carbon, silver content cannot exceed 7% filling factor due to its catalytic properties. It was shown, that decrease of acetylene gas flux from 22.5 sccm to 7.5 sccm increases average nanoparticle radius from 8.0 nm to 10.6 nm, radius distribution width parameter increases from 0.18 to 0.42 and particle surface concentration decreases from 801 µm-2 to 411 µm-2. Dipole as well as quadrupole plasmon resonance modes were observed in extinction spectra. Dipolar mode position was ranging from 350 nm – 450 nm, whereas quadrupole modes were visible as small peaks at around ~ 365 nm wavelength. Furthermore, σ→σ* electron transitions for diamond-like carbon were also observed in 540 nm – 640 nm range as well as silver interband transitions at around 300 nm wavelengths. Lowest reflectance and highest absorbance were obtained for DLC:Ag films with 1% Ag filling factor, whose thickness were 79 nm and 95 nm, respectively. The first sample exhibited lower than 8% reflectance in the λ = 350 – 800 nm range for Θ = 10o. Reflectance of the second sample did not exceed 8% threshold for wavelengths from 509 nm up to 880 nm for Θ = 10o. The increase of reflectance with increase of angle of incidence up to Θ = 50o was relatively low. |
