中文摘要：

利用混合物理化学气相沉积法在6H-SiC（001）衬底上制备干净的MgB2超导超薄膜.在本底气体压强、载气氢气流量等条件一定的情况下,改变B2H6流量及沉积时间,制备得到不同厚度的系列MgB2超薄膜样品,并研究了超导转变温度Tc、剩余电阻率ρ（42K）、上临界磁场Hc2等与膜厚的关系.该系列超薄膜沿c轴外延生长,随膜厚度的变小,Tc（0）降低,ρ（42K）升高.膜在衬底上的生长遵循Volmer-Weber岛状生长模式.对于厚度为7.5nm的MgB2超薄膜,Tc（0）=32.8K,ρ（42K）=118μΩcm,是迄今为止所观测到的厚度为7.5nm的MgB2超薄膜最高的Tc值;对于厚度为10nm的MgB2膜,Tc（0）=35.5K,ρ（42K）=17.7μΩcm,上临界磁场μ0Hc2估算为12T左右,零磁场、4K时的临界电流密度Jc=1.0×107A/cm2,是迄今为止10nm厚MgB2超薄膜的最高Jc值,且其表面连接性良好,均方根粗糙度为0.731nm.这预示MgB2超薄膜在超导纳米器件上具有广阔的应用前景.

英文摘要：

We fabricate MgB2 ultra-thin films via hybrid physical-chemical vapor deposition technique.Under the same background pressure,the same H2 flow rate,by changing B2H6 flow rate and deposition time,we fabricate a series of ultra-thin films with thickness ranging from 5 nm to 80 nm.These films grow on SiC substrate,and are all c-axis epitaxial.We study the Volmer-Weber mode in the film formation.As the thickness increases,critical transition temperature Tc（0） also increases and the residual resistivity decreases.Especially,a very high Tc（0） ≈ 32.8 K for the 7.5 nm film,and Tc（0） ≈ 36.5 K,low residual resistivity ρ（42 K）≈ 17.7 μΩcm,and extremely high critical current density Jc （0 T,4 K） ≈ 107 A/cm2,upper critical field Hc2（0） for 10 nm film are achieved.Moreover,by optimizing the H2 flow rate,we obtain relatively smooth surface of the 10 nm epitaxial film,with a root-mean-square roughness of 0.731 nm,which makes them well qualified for device applications.