External magnetic field guiding in HiPIMS to control sp³ fraction of tetrahedral amorphous carbon films

Amorphous carbon films have many applications that require control over their sp³ fraction to customise the electrical, optical and mechanical properties. Examples of these applications include coatings for machine parts, biomedical and microelectromechanical devices. In this work, we demonstrate the use of a magnetic field with a high-power impulse magnetron sputtering (HiPIMS) source as a simple, new approach to give control over the sp³ fraction. We provide evidence that this strategy enhances the deposition rate by focusing the flux, giving films with high tetrahedral bonding at the centre of the deposition field and lower sp³ fractions further from the centre. Resistive switching appears in films with intermediate sp³ fractions. The production of thin amorphous carbon films with selected properties without the need for electrical bias opens up applications where insulating substrates are required. For example, deposition of sp³ rich films on polymers for wear resistant coatings as well as fabrication of resistive switching devices for neuromorphic technologies that require tuning of the sp³ fraction on insulating substrates are now possible. (paper)