Superconducting thin film having columnar pinning centers utilizing nano dots and method of making the same

Abstract

A superconducting thin film is disclosed having columnar pinning centers utilizing nano dots, and comprising nano dots ( 3 ) which are formed insularly on a substrate ( 2 ) and three-dimensionally in shape and composed of a material other than a superconducting material and also other than a material of which the substrate is formed, columnar defects ( 4 ) composed of the superconducting material and grown on the nano dots ( 3 ), respectively, a lattice defect ( 6 ) formed on a said columnar defect ( 4 ), and a thin film of the superconducting material ( 5 ) formed in those areas on the substrate which are other than those where said columnar defects are formed. The superconducting thin film ( 5 ) is prepared by depositing the material other than the superconducting material on the substrate ( 2 ) while controlling the substrate ( 2 ) temperature, and the film thickness of the material deposited so to coagulate the deposited material to form the nano dots ( 3 ), and then growing a thin film of the superconducting material ( 5 ) on the substrate ( 2 ). An improved superconducting thin film is thus provided which regardless of its type is at least ten times higher in critical current density than an exiting superconducting thin film, and which can also be manufactured at a low cost. And, being large in critical superconducting current density and critical superconducting magnetic field, it is advantageously applicable to the technical fields of cryogenic electronics and microwaves.

1 . A superconducting thin film structure having columnar pinning centers and comprising:
 a substrate,   nano dots or nano stripes which are formed insularly on the substrate and three-dimensionally in shape and composed of a material other than a superconducting material and also other than a material of which the substrate is formed,   amorphous or non-superconducting columnar defects composed of a superconducting material and grown on said nano dots or nano stripes, respectively, and   a superconducting thin film composed of said superconducting material formed in those areas on said substrate which are other than those where said columnar defects are formed.   
   
   
       2 . A superconducting thin film structure having columnar pinning centers and comprising:
 a substrate,   nano dots or nano stripes which are formed insularly on the substrate and three-dimensionally in shape and composed of a material other than a superconducting material and also other than a material of which the substrate is formed,   amorphous or non-superconducting columnar defects composed of a superconducting material and grown on said nano dots or nano stripes, respectively,   a lattice defect which is formed on said amorphous or non-superconducting columnar defects, and   a superconducting thin film composed of said superconducting material formed in those areas on said substrate which are other than those where said columnar defects are formed.   
   
   
       3 . A superconducting thin film structure having columnar pinning centers as set forth in  claim 1  or  claim 2 , characterized in that said material other than a superconducting material and also other than a material of which the substrate is formed is a metal, an insulator, a semiconductor or a ferromagnetic material. 
   
   
       4 . A superconducting thin film structure having columnar pinning centers as set forth in  claim 1  or  claim 2 , characterized in that said nano dots are 20 nm or less in diameter and approximately 6 nm in height, are spaced apart from one another by an average distance of 50 nm or less, and are irregularly or randomly distributed on said substrate. 
   
   
       5 . A superconducting thin film structure having columnar pinning centers as set forth in  claim 1  or  claim 2 , characterized in that said nano stripes are formed, each in the form of a stripe, along flanks of steps formed on said substrate, and said substrate is formed so that its facial orientation is inclined to its crystallographic axis. 
   
   
       6 . A superconducting thin film structure having columnar pinning centers as set forth in  claim 1  or  claim 2 , characterized in that said amorphous or non-superconducting columnar defects are formed columnarly perpendicular to a surface of said substrate. 
   
   
       7 . A superconducting thin film structure having columnar pinning centers as set forth in  claim 2 , characterized in that said lattice defect comprises a crystal dislocation of a portion of said superconducting thin film. 
   
   
       8 . A method of making a superconducting thin film structure having columnar pinning centers comprising the steps of
 forming insularly on a substrate, nano dots or nano stripes shaped three-dimensionally and composed of a material other than a superconducting material, and also other than a material of which the substrate is formed, and   growing on said substrate and on said nano dots or nano stripes, a superconducting thin film composed of said superconducting material, to form amorphous or non-superconducting columnar defects on said nano dots or nano stripes and to form superconducting thin film on those areas on the substrate other than where said nano dots or nano stripes have been formed;   wherein said superconducting thin film structure comprises said substrate, nano dots or nano stripes which are formed insularly on the substrate and three-dimensionally in shape and composed of a material other than a superconducting material and also other than a material of which the substrate is formed, amorphous or non-superconducting columnar defects composed of said superconducting material and grown on said nano dots or nano stripes, and a superconducting thin film composed of said superconducting material formed in those areas on said substrate which are other than those where said columnar defects are formed.   
   
   
       9 . A method of making a superconducting thin film structure having columnar pinning centers as set forth in  claim 8 , characterized in that said three-dimensionally shaped nano dots composed of a material other than said superconducting material are formed by depositing said material insularly on said substrate by a technique selected from the group which consists of sputtering, vaporization, laser ablation, CVD and MBE while controlling the substrate temperature, the deposition rate of said material and the film thickness of said material deposited, thereby coagulating the deposited material on said substrate to form said three-dimensionally shaped nano dots insularly thereon. 
   
   
       10 . A method of making a superconducting thin film structure having columnar pinning centers as set forth in  claim 8 , characterized in that said three-dimensionally shaped nano stripes composed of a material other than said superconducting material, and also other than a material of which the substrate is formed, are formed by forming a substrate so that its facial orientation is inclined to its crystallographic axis, and depositing said material insularly on said substrate by a technique selected from the group which consists of sputtering, vaporization, laser ablation, CVD and MBE while controlling the substrate temperature, the deposition rate of said material and the film thickness of said material deposited, thereby permitting the deposited material on said substrate to selectively grow in regions of steps formed thereon and thereby to form said three-dimensionally shaped nano stripes insularly on said substrate. 
   
   
       11 . A method of making a superconducting thin film structure having columnar pinning centers as set forth in  claim 8 , characterized in that said thin film of the superconducting material is grown on said substrate by crystal growth of said superconducting material, by way of sputtering, vaporization, laser ablation, CVD or MBE, on said substrate having said nano dots or nano stripes formed thereon. 
   
   
       12 . A method of making a thin film structure having columnar pinning centers as set forth in  claim 8 , characterized in that said thin film of the superconducting material is grown on said substrate by crystal growth of said superconducting material, by way of amorphous phase epitaxial process, on said substrate having said nano dots or nano stripes formed thereon.