Novel material systems via low-energy off-axis combinatorial sputtering
The vast array of interesting crystal structures and the wealth of elemental choices guarantee that we are never lacking for new opportunities in designing and making "custom-built" materials. In order to facilitate the rapid and controlled synthesis of interesting materials systems, we are building a custom off-axis magnetron sputtering system for thin film deposition. Currently, each thin film vapor deposition technique (sputtering, MBE, CVD, PLD) has unique advantages as well as drawbacks. In the case of magnetron sputtering, spectacular flexibility in deposition environment and elemental selection is offset by high energetics for "on-axis" (substrate directly in front of target) deposition. An improved method is off-axis magnetron sputtering, where the substrate is placed to the side of target and at 70 to 90 degree angle to the target surface. This geometry yields far less energetic deposition, significantly improved crystallinity, and lower defect density.
We have determined that low pressure (~10 mTorr) off-axis sputtering technique that can produce stoichiometric films of complex materials while maintaining crystal quality. However, if the system requires a higher pressure for growth (e.g., a high oxygen partial pressure), scattering of ejected atoms off gas molecules becomes significant and element-selective, leading to off-stoichiometry at the substrate. Careful co-sputtering of ultra-pure elemental or binary oxide targets would allow one to overcome scattering effects with careful calibration. Target cross-contamination will be avoided with automated shutter control, and quartz crystal monitors will calibrate and control film stoichiometry. These innovations will create a UHV (base pressure ~10E-10 Torr) system with low energetics, high purity, wide growth environment ranges, significant freedom in elemental choices, and capabilities to introduce dopants and build heterostructures.
- Unlocking the potential of half-metallic Sr2FeMoO6 films through controlled stoichiometry and double-perovskite ordering
- Fully ordered Sr2CrReO6 epitaxial films: A high-temperature ferrimagnetic semiconductor
- Characterization of electronic structure and defect states of thin epitaxial BiFeO films by UV-visible absorption and cathodoluminescence spectroscopies
- Temperature-dependence of the Hall coefficient of NdNiO3 thin films