Investigations On Growth And Properties Of Solution Derived Metal Nitride Superconducting Thin Films

Metal nitrides have many properties,such as high melting point,superhard property,chemical catalysis and many electronic performance characteristics and so on,which lead to researchers a lot of interest.The electronic performances of metal nitrides include isolation state,semiconductor state and metal state.According to the thermal measurement,the metal nitrides exist both positive and negative thermal expansion.The magnetic properties cover paramagnetism and ferromagnetism.Due to the above properties,metal nitrides can be applied in many field.Particularly some metal nitride combined the superhard property,high superconducting transition temperature(TC)and chemical stability at the same time.The combined mechanical properties and superconductivity open a new class of engineering hard superconducting materials,which applied to the radio frequency superconducting accelerator cavities,superconducting hot electron bolometer(HEB)and so on.The previous studies found that preparation of high Tc(more than 1 OK)of 8-MoN ceramic need high temperature and high pressure.On the other hand,the derived Mo-N superconducting thin films prepared by vacuum-based methods such as Pulsed Laser Deposition show TC?4.2 K.For applications of ?-NbN thin films in superconducting thin film devices and for ?-TiN thin film application in superhard coatings and super-isolator transition,which is need to meet conditions such as ultra-thin,large area and so on.Due to the physical process of preparation technology is more complex,making it impossible to obtain large area thin film,and to better study the metal nitride superconducting thin film properties and applications,it is need to explore other film preparation techniques.As an alternative approach,chemical solution deposition(CSD)will offer advantages in terms of low-cost,atomic-scale mixture and coating of large-area onto arbitrary surface.In this dissertation,several kinds of binary metal nitrides superconducting thin films including ?-MoN,?-NbN and ?-Ti1-xCuxN are fabricated by CSD method.Moreover,the processing conditions on microstructures,electrical transport properties and magnetic properties of the above thin films are systematically investigated,and the main results are summarized as follows:(1)The microstructure and superconducting properties of different thickness c-axis orientated 8-MoN/Si thin films are systematically investigated.It is found that the prepared ?-MoN thin films show strong c-axis orientation and high superconducting transition temperature Tc about 12.5 K even on Si(001)substrates with a parasitic SiO2 layer.With thickness increasing,the grain size increased,microstress decreased,the Tc improved slightly,and the upper critical field Bc2(0)decreased slightly.According to the Hall measurement,it found that with thickness increasing the carrier density,which suggests mean free path and degree of order in the thin films improved apparently.(2)The microstructure and superconducting properties of different thickness epitaxial ?-MoN/Al2O3 thin films are investigated.It is found that epitaxy can be controlled through decease the density of the precursors and select the proper substrate with the similar lattice constant.With thickness increasing,the grain size increases,microstress decreases and the normal state resistivity increases,the upper critical field Bc2(0)decreases slightly and the Tc remains at 12.6 K.(3)The influence by thickness and preparation technology in superconducting properties of ?-NbN/Si are investigated.It found that the superconducting transition temperature of polycrystalline ?-NbN thin films is about 10.5 K.With thickness increasing,the grain size and lattice constant are gradually increase.While the upper critical field slightly decreases with thickness increasing.In order to improve the upper critical field,the precursor changed as niobium acid ammonium oxalate and obtained theBc2(0)?12.47 T.(4)The microstructure and superconducting properties of Cu doping in ?-TiN thin films are systematically investigated.It found that the lattice constant increases to 4.26A while the component of Cu arrives 30%.To further dope Cu,the lattice constant decreases.The superconducting transition temperature improves from 2.6 K to 3.6K(Cu component?30%),while then decreases to 2.8 K(Cu component?45%).It means that with the nominal component of Cu increasing,the nitrogen content in the film is increasing intially and decreasing finally.