Thickness-Dependent Thermal Oxidation of Ni into NiO Thin Films

Journal Article · Thu Nov 15 00:00:00 EST 2018 · Journal of Superconductivity and Novel Magnetism

DOI:https://doi.org/10.1007/S10948-018-4651-6· OSTI ID:22773635

Ravikumar, Patta; Taparia, Dolly; Alagarsamy, Perumal ^[1]

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1. Indian institute of Technology Guwahati, Department of Physics (India)

We report thickness-dependent thermal oxidation in Ni (t = 10–300 nm) thin films exposed to air annealing and the resulting vibrational, magnetic and electrical properties of Ni films deposited directly on thermally oxidized Si substrate using magnetron sputtering technique at ambient temperature. As-deposited Ni films exhibit face-centred cubic structure with fine crystals and large lattice constant (a{sub Ni}) at lower t (< 50 nm). With increasing t, a{sub Ni} decreases and approaches to bulk value. With increasing T{sub A}, a{sub Ni} not only decreases to bulk Ni due to improved crystallization but also reduces below bulk Ni for t > 50 due to formation of NiO. The relative fraction of Ni and NiO in annealed films up to 400 {sup ∘}C strongly depends on t. Annealing Ni films at 500 {sup ∘}C results into complete oxidation of Ni into granular-type NiO. X-ray reflectivity studies reveal that oxidation process occurs from surface of the films converting Ni into NiO possibly through layer by layer process, which is subtle to t. Raman spectra show that intensity ratio between one-phonon longitudinal optical (LO) and two-phonon LO bands decreases and intensity of two-magnon band increases with increasing t for films annealed at particular T{sub A}. This confirms the growth of NiO not only with increasing T{sub A}, but also with t. As-deposited films exhibit ferromagnetism at room temperature. The presence of Ni and NiO in annealed films implies coexistence of ferromagnetic and antiferromagnetic interactions, leading to tunable exchange bias (H{sub E}), whose magnitude strongly depends on the ratio between Ni and NiO. Electrical resistance (R) of the as-deposited Ni films decreases with increasing t and follows the Namba’s model. Upon annealing, R increases largely due to oxidation of Ni. The observed results are explained on the basis of thickness dependent thermal oxidation process with increasing T{sub A}.

• OSTI ID: 22773635
• Journal Information: Journal of Superconductivity and Novel Magnetism, Vol. 31, Issue 11; Other Information: Copyright (c) 2018 Springer Science+Business Media, LLC, part of Springer Nature; http://www.springer-ny.com; Country of input: International Atomic Energy Agency (IAEA); ISSN 1557-1939
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
AMBIENT TEMPERATURE
ANNEALING
ANTIFERROMAGNETISM
CRYSTALLIZATION
CRYSTALS
DEPOSITION
ELECTRIC CONDUCTIVITY
FCC LATTICES
FERROMAGNETISM
LATTICE PARAMETERS
MAGNETRONS
MAGNONS
NICKEL
NICKEL OXIDES
OXIDATION
PHONONS
RAMAN SPECTRA
REFLECTIVITY
THICKNESS
THIN FILMS