氮流量对六方氮化硼(hBN)薄膜结构和力学性能的影响OA北大核心CSTPCD

The reports on deposition of hexagonal boron nitride(hBN)thin films by intermediate medium-frequency(MF)magnetron sputtering technique and the impact of these structures on mechanical properties are not comprehensive enough.In this paper,hBN thin films with special structures were synthesized by MF magnetron sputtering and the ways the structures changed mechanical properties of the films were investigated.Thin BN films were deposited under different N2 fluxes(6,12,18,24,30 and 36 mL/min,respectively)on Si.Subsequently,the effects of N2 fluxes on the composition,microstructure,surface morphology and mechanical properties of the as-obtained BN films were investigated with characterization tools.Finally,a transmission electron microscopy(TEM)and selected area electron diffraction(SAED)were used to analyze the nanocrystalline grain size and crystal lattice structure of the films.The samples were sequentially named N6,N12,N18,N24,N30 and N36,according to the different N2 introduced during film deposition.According to the SEM,the B and N atoms in the film were uniformly distributed.The film's B and N ratio was shown by XPS to be larger than 1,showing the presence of B-B bonds.The XRD result showed that the as-obtained films were mainly composed of hexagonal BN(hBN).It was observed that the film with the lowest hardness value had the least amount of surface roughness,which was associated with B oxidation.The content of boron oxide(B2O3)was the highest in N24,corresponding to the lowest hardness and surface roughness.This was related to the surface smoothing effect of B2O3.In addition,the hardness and elastic modulus of the films exhibited a trend of first dropping and then rising,and the maximum hardness and elastic modulus could be respectively up to 7.21 GPa and 116.78 GPa,while the lowest hardness and elastic modulus were only 1.2 GPa and 32.68 GPa,respectively.The elastoplasticity of thin films,the elastic failure strain(H/E*)and the plastic deformation resistance(H3/E*2)were also used to evaluate the mechanical properties of thin films.It could be seen that their change trend was the same as that of hardness and elastic modulus.N6 and N36 exhibited the highest H3/E*2 and H/E*,with N6 having H3/E*2 up to 29.77×10-3 GPa and H/E* up to 6.414×10-2.In contrast,N24 exhibited the lowest H3/E*2 and H/E* values,with H3/E*2 reaching 1.77×10-3 GPa and H/E reaching 3.819×10-2.Then,for TEM analysis,N6,N18 and N36 were selected respectively.The result demonstrated that the structure of these films were mostly curly structure.The heart of these curly structures started to crystallize when N2 introduction was 18 sccm,while the outside layer still had a curly shape.The ultimate formation for N36 had a more clearly curly structure.The films with these curly structures had a high load bearing capacity and hardness.This indicated that thin films deposited with certain N2 content during the deposition process had a strong ability to redistribute load,and therefore could exhibit strong resistance to plastic deformation.Obviously,the mechanical properties of the hBN films can be regulated through adjusting the N2 fluxes during the MF magnetron sputtering process.This result offers a new strategy to regulate the microstructure and mechanical strength of hBN films in future.