Fabrication And Properties Of TiALN Based Light Absorbing Coatings By DC Magnetron Sputtering

In the first part of this work,we have developed thermally stable bi-layered TiAlN based selective solar absorbers on Cu and Si substrates using DC magnetron reactive sputtering system.The TiAlN layer was graded with an antireflection coating to suppress the surface reflections.A high value of absorptance（0.92）and very low emittance（0.06）at 70°C was achieved because of columnar TiAlN structure and porous surface of the tandem absorber.UV-Visible spectroscopy,scanning electron microscopy,transmission electron microscopy,micro-Raman spectroscopy and X-ray photoelectron spectroscopy techniques were employed to test the thermal stability.The tandem absorber showed high thermal stability in air at 550°C.XPS results confirmed that the TiAlN layer also acts as a diffusion barrier for Cu and therefore the absorption property was not degraded even on heating at high temperature for 4 hours.Further,the selectivity was improved by post-deposition annealing of Cu/TiAlN coatings.The annealing temperature was optimized as 300?C and a high selectivity of 27.06 was achieved from Cu/TiAlN/SiO₂ tandem absorber.In second part of the work,ultra-wideband light absorbers were produced.Growing efficient blackbody character absorbers by a simple method,has proven to be challenging for various applications such as solar energy,thermal regulation and suppression of stray light for the optical devices.Nanostructured refractory materials afford exceptional features to manipulate incident photons at subwavelength scale and withstand against severe conditions.Here,we report a sputtering technique-based route to fabricate TiAlN black absorbing coatings with vertically aligned columnar nanostructure,as a unique approach to produce large area metamaterials.The fabrication process is simple,free of any sophisticated patterning approach,substrate-independent（conducting,insulating,single crystal,amorphous,rigid or flexible）,viable and capable to easily be up scaled,benefitting excellent adhesion and appropriate corrosion resistance of the absorbing coatings.An average absorptivity,=0.89,covering a broad range of wavelengths,200nm to 2500 nm,was achieved from the single nanostructured coating and increased to=0.95 after grading with thin anti-reflecting layers,which is higher than any other PVD deposited ceramic coatings on smooth substrates.Robust stability in adverse environments is an exceptional feature of our broadband super absorbers.The proposed sputtering based fabrication process would open new platform to design,prepare and integrate nanophotonic structures,having applications in energy,electronic and optical sectors.