| Surface roughness is an important surface property of thin-film materials,which determines many properties such as friction coefficient,hydrophobicity and diffuse reflection.With the development of catalysis,self-cleaning,biomedicine,solid lubrication and precision contact technologies,there has been an increasing need for smooth and rough functional thin films.At present,although the required roughness can be obtained by post-processing of substrates and pre-processing of films,the complexity and high cost are always an intractable problem.To reduce the cost and time of the processing technology,researchers have studied the in-situ growth of smooth and rough films.However,there still exists some problems:?1?The surface roughening mechanism of thin films remains vague.After a lot of research on the surface evolution during the film growth process,researchers have observed two phenomena:I.surface roughening,that is,surface roughness?R?increases with increasing film thickness?d?or deposition time;II.mound growth,that is,surface mounds gradually grow during thin-film growth.If one can quantitatively describe the correlation between surface roughening and mound growth,the surface roughening mechanism of the film can be improved,and the surface roughening can be further controlled.However,because the relationship between surface roughening and mound growth has not been explored experimentally,the mechanism of surface roughening has not yet been well revealed.?2?An effective idea/method for in-situ growth of smooth and rough hafnium nitride films has not been proposed.With the development of some emerging areas such as dry processing and hull drag reduction,hafnium nitride films with tailorable surface roughness have been demanded.However,because the growth conditions of smooth and rough films have not been provided,the effective ideas and methods for in-situ growth of smooth and rough hafnium nitride films have not yet been proposed.To solve the issues above,we have conducted the following three studies through a combination of experiments and simulations:?1?The mechanisms of thin-film surface roughening.Through a series of experiments and simulations on hafnium nitride films,we have successfully given the definition and characterization of the surface roughening rate??R?and the effective mound growth coefficient???,giving a linear proportional relationship between?R and???R=k???.We have also verified the universality of this linear relationship using the typical materials with covalent bonding,ionic bonding,and metal bonding?hafnium nitride,hafnium oxide and silver?.Furthermore,using this proportional relationship,we have revealed that the in-situ growth conditions of the smooth and rough surfaces are?<<1?horizontal mound growth is much larger than vertical mound growth?and?>>1?horizontal mound growth is much smaller than vertical mound growth?,respectively.?2?The experimental idea/method for in-situ growth of smooth films.According to the in-situ growth conditions of smooth films??<<1?,we have proposed that the idea for in-situ growth of smooth films is to suppress the vertical mound growth during thin film growth.Subsequently,we have successfully prepared smooth hafnium nitride films(R=0.24 nm with d=1386 nm;?R=5×10-5,?=0.09<<1)by periodically introducing thin amorphous carbon-nitrogen layer.Moreover,the smooth hafnium nitride films not only have good durability,but also obtain ultra-low friction coefficient,which is expected to be the next generation of low-friction protective coatings.?3?The experimental idea/method for in-situ growth of rough films.According to the in-situ growth conditions of rough films??>>1?,we have proposed that the idea for in-situ growth of rough films is to suppress the horizontal mound growth.Subsequently,we have successfully prepared rough hafnium nitride films(R=13.6 nm with d=1408 nm;?R=9×10-3,?=14.09>>1)by doping inert metal silver.Moreover,the rough hafnium nitride films not only have good durability,but also obtain a large static water contact angle?>150°?,which is expected to be the next generation of durable hydrophobic coatings using in hull drag reduction. |
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