title: Unraveling The Origin of Enhanced Field Emission from Irradiated FeCo-SiO2 Nanocomposites: A Combined Experimental and First-Principles Based Study.
abstract: This work is driven by the vision of engineering planar field emitters with ferromagnetic metal-insulator nanocomposite thin films, using swift heavy ion (SHI) irradiation method. FeCo nanoparticles inside SiO2 matrix, when subjected to SHI get elongated. Using this, we demonstrate here a planar field emitter with maximum current density of 550 μA/cm(2) at an applied field of 15 V/μm. The film, irradiated with 5 × 10(13) ions/cm(2) fluence (5e13) of 120 MeV Au(9+) ions, shows very high electron emitting quantum efficiency in comparison to its unirradiated counterpart. Surface enhanced Raman spectroscopy analysis of unirradiated and 5e13 films further confirms that the field emission (FE) enhancement is not only due to surface protrusions but also depends on the properties of entire matrix. We find experimental evidence of enhanced valence band density of states (VB DOS) for 5e13 film from XPS, which is verified in the electronic structure of a model FeCo cluster from first-principles based calculations combining density functional theory (DFT) and molecular dynamics (MD) simulations. The MD temperature is selected from the lattice temperature profile inside nanoparticles as deduced from thermal spike model. Increasing the irradiation fluence beyond 5e13, results in reduced VB DOS and melting of surface protrusions, thus causing reduction of FE current density. We finally conclude from theoretical analysis 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.
authors.affiliation: Department of Physics, Indian Institute of Technology Delhi , Hauz Khas, New Delhi 110016, India.
authors.forename: Debalaya
authors.initials: D
authors.lastname: Sarker
authors.affiliation: Department of Physics, Indian Institute of Technology Delhi , Hauz Khas, New Delhi 110016, India.
authors.forename: Saswata
authors.initials: S
authors.lastname: Bhattacharya
authors.affiliation: Institute of Physics, Technische Universität Chemnitz , Chemnitz 09107, Germany.
authors.forename: Raul D
authors.initials: RD
authors.lastname: Rodriguez
authors.affiliation: Institute of Physics, Technische Universität Chemnitz , Chemnitz 09107, Germany.
authors.forename: Evgeniya
authors.initials: E
authors.lastname: Sheremet
authors.affiliation: Material Research Group, IUAC , New Delhi 110067, India.
authors.forename: D
authors.initials: D
authors.lastname: Kabiraj
authors.affiliation: Material Research Group, IUAC , New Delhi 110067, India.
authors.forename: D K
authors.initials: DK
authors.lastname: Avasthi
authors.affiliation: Institute of Physics, Technische Universität Chemnitz , Chemnitz 09107, Germany.
authors.forename: Dietrich R T
authors.initials: DR
authors.lastname: Zahn
authors.affiliation: Department of Electrical Engineering and Information Technology, Technische Universität Chemnitz , Chemnitz 09126, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Schmidt
authors.affiliation: Department of Physics, Indian Institute of Technology Delhi , Hauz Khas, New Delhi 110016, India.
authors.forename: P
authors.initials: P
authors.lastname: Srivastava
authors.affiliation: Department of Physics, Indian Institute of Technology Delhi , Hauz Khas, New Delhi 110016, India.
authors.forename: S
authors.initials: S
authors.lastname: Ghosh
keywords: DFT; DOS; FeCo-SiO2; MD; SERS; elongation; field emission; nano particle; planar field emitter