Study On Preparation And Properties Of Ultrathin NiCr/Dielectric Composite Films With High Absorption

It is reported that the energy of visible light,accounts for 49.64%of total energy of solar radiation.Achieving high absorption in visible region can not only solve the problem of energy crisis,and eliminate the stray light in optical path system.Meanwhile,visible light is the only region that can be detected by human eyes.Selective absorber in the visible light has been exploited in a variety of application fields,such as building integrated solar collector,image sensors,solar military and so on.Consequently,manipulating or tailed the visible light purposefully and selectively has become the hotspot in recent years.In this paper,we prepared the metal films of NiCr in different thicknesses.We studied the parameters of optical constants n,k,sheet resistance,absorptivity,and surface roughness of single-layer NiCr metal films.Based on the structure of ultrathin NiCr/dielectric composite films,a novel method to achieve high or selective absorption in visible region has proposed.The results are summarized as follows:?1?As thickness increased,the reflectivity of single-layer NiCr metal films in visible region gradually increased,and the transmittance gradually decreased.Meanwhile,the maximum value of absorbtivity did not exceed 50%.XPS was used to characterize the component and elements valence of NiCr film.The results showed that the composition of the film was consistent with that of the target and the Cr element of prepared NiCr film has been oxidized.The sheet resistance of NiCr decreased with increase the thickness.?2?Based on the NiCr/dielectric composite films,we proposed a new selective absorption structure in visible region-Al/SiO₂/NiCr/Si₃N₄/NiCr.We studied the effect of the thickness of NiCr or Si₃N₄ film on the absorbtivity in visible region.The results show that the absorption peak of this structure in the visible region gradually disappeared with increase of the thickness of the NiCr metal film.When the thickness of NiCr metal film was about 4.7 nm,the absorption peak of this structure in visible region was close to perfect absorption.Moreover,the absorption peak of the structure exhibited the red shift with the increase of Si₃N₄ thickness.The color of the samples gradually changed from dark blue to light blue.The total thickness of this structure is no more than 200nm.?3?Based on the NiCr/dielectric composite films,we proposed a new high absorption structure in visible region-Al//Si₃N₄/NiCr/SiO₂.When choosing the right thickness of each material,the average absorptivity in the visible region of this structure was up to 90%.Compared with the simulation results of Comsol software and detected data by the spectrometer,we can obtain the following main conclusions:when the thickness of NiCr metal film ranged from 15nm to 25nm,this structure can keep high absorption in visible spectrum.The area of high absorption exhibited the red shift with the increase of thickness of Si₃N₄ film.To detect the thermal stability of this structure,it was annealed at the temperature of 500°C for 4 hours.Compared with the sample before annealing,the absorption attenuation in visible region after annealing was only 3%.