| AVS 63rd International Symposium & Exhibition | |
| Applied Surface Science | Tuesday Sessions |
| Session AS-TuP |
| Session: | Applied Surface Science Division Poster Session |
| Presenter: | Debalaya Sarker, Indian Institute of Technology Delhi, India |
| Authors: | D. Sarker, Indian Institute of Technology Delhi, India S. Bhattacharya, Indian Institute of Technology Delhi, India S. Ghosh, Indian Institute of Technology Delhi P. Srivastava, Indian Institute of Technology Delhi |
| Correspondent: | Click to Email |
In this talk, I shall give a brief overview of engineering ferromagnetic metal-insulator (FMM/SiO2 FMM=FeCo, Ni) nano-composites having application in device physics. Increasing demand of flat displays necessitates to design planar emitters which not only miniaturize the device but also have several other advantages like mechanical durability, temporal stability etc. FMM nanoparticles (NPs) inside SiO2 matrix, when subjected to Swift Heavy Ion (SHI) irradiations get elongated. Using this, we demonstrate here a planar field emitter with maximum current density of 550 μA/cm2 at an applied field of 15 V/μm. The film, irradiated with 5×1013 ions/cm2 fluence (5e13) of 120 MeV Au9+ ions, shows very high electron emitting quantum efficiency in comparison to its unirradiated counterpart. We find experimental evidence of enhanced valence band (VB) density of states (DOS) for 5e13 film from XPS, which is further verified in the electronic structure of a model FMM cluster from combined density functional theory (DFT) and ab initio molecular dynamics (MD) simulations. The MD temperature is taken from the lattice temperature profile from thermal spike model. Increasing the SHI fluence beyond 5e13, results in reduced VB DOS and melting of surface protrusions, thus causing reduction of FE current density. We finally conclude from DFT that change in fluence alters the co-ordination chemistry followed by the charge distribution and spin alignment, which influence the VB DOS and concurrent FE as evident from our experiment.1,2 More recently, we have explored the effect of shape and structural anisotropies on magnetic properties of SHI irradiated FMM/SiO2 flims. Magnetic anisotropy (MA) and exchange bias effect (EBE) were tuned by monitoring SHI irradiation fluence. The in-plane and out-of-plane M-H loops show that the perpendicular MA reaches a maximum value at 5e13 and then decreases. At highest fluence an EBE is observed. Underlying electronic structure was not only probed with XANES and XPS VB, but also is validated from our non-collinear theoretical calculations. We conclude this EBE is an outcome of formation of anti-ferromagnetic domains due to spin-flipping at high temperature. In summary, elongated FMM NPs inside SiO2 matrix are designed using controlled SHI irradiation. Due to its high current density and mechanical/chemical durability, the irradiated films open new possibilities for the development of electronic displays. They also show sufficient promise in magnetic storage media for their interesting MA and EBE properties.
Reference:
1D. Sarker et al., ACS Appl. Mater. Interfaces, 8, 4994 (2016).
2D. Sarker et al., J. Appl. Phys, 115, 174304 (2014).