Prof. Selvamanickam's Research Group
Ion Beam Assisted Deposition to fabricate near single-crystalline/highly biaxially-textured thin films on polycrystalline or amorphous flexible substrates in reel-to-reel mode

Single crystalline films are desired for several applications where grain boundaries, especially those of high-angle type are deleterious to product performance. However, it is very expensive and in several cases, near impossible to fabricate single crystalline films over large areas, long lengths. Ion Beam Assisted Deposition (IBAD) is a very powerful technique to achieve near single crystalline quality on essentially any substrate. The following figure shows a schematic of the IBAD process.

During deposition of a film on a substrate, the growing film is bombarded with Ar+ ions at a particular incident angle. Within certain conditions of ion beam current, voltage, ion to atom ratio, acceleration voltage and film temperature, a biaxial texture rapidly develops in the growing film. The texture development can be monitored in situ during growth using Reflection High Energy Electron Diffraction (RHEED) as display in the figure. A long-range crystallographic alignment of all axes is induced as shown in the figure. So, crystallographic texture is achieved both out-of-the plane as well as in the film plane. The grain-to-grain misorientation about any of the axes is typically less than 5 degrees. Now, the IBAD film can be used as a template to deposit near single-crystalline films by epitaxial growth. This technique is used in our labs to fabricate high quality epitaxial films for applications such as high temperature superconductors and photovoltaics where high angle grain boundaries are deleterious to current transport.

The figure shows XRD polefigure of superconducting YBa2Cu3Ox (YBCO) grown epitaxially atop an IBAD film. A sharp cube texture of 2 degrees is observed. The texture of the IBAD film is sharpened by epitaxial film deposition. We are exploring to use the IBAD technique to synthesize near-single crystalline films on practical substrates for a number of applications.

Ion beam assisted deposition (IBAD) to introduce biaxial texture in thin films on polycrystalline/amorphous substrates