Black titanium oxynitride thin films prepared by nitrogen plasma-assisted pulsed laser deposition for flat-panel displays

Preference for a classy black turn-off appearance and for distinct dark colors on flat-panel displays has led to a high demand for optically black materials. Titanium oxynitrides and tungsten-doped oxynitrides were prepared using nitrogen plasma assisted pulsed laser deposition, and their optical absorption properties were investigated. A selection of Ti-O-N films were prepared with different compositions by controlling the emission current (I_e) and discharge voltage (V_d) of the ion source. It was found that the nitrogen content of the Ti(O,N)_x could be adjusted by controlling the I_e. The large, flat absorption coefficient of approximately 40 μm⁻¹ in the visible range (400–700 nm) attained for the samples deposited at high V_d was attributed to tungsten doping from a W filament in the ion source. The 4.1 mol%W-doped Ti(O,N)_x, which had a rock-salt-type structure, was optically jet-black. The origin of the flat wavelength dispersion in the W-doped Ti(O,N)_x was attributed to the coexistence of semiconducting absorption and metallic absorption mechanisms. DFT calculations suggest that the 5d states achieved when using doped tungsten provide high absorption in the mid-wavelength range, whereas undoped-Ti(O,N)_x was characterized by weak absorption.