Spinodal decomposition of reactively sputtered (V0.64Al0.36)(0.49)N-0.51 thin films

• We investigate the decomposition mechanisms of metastable cubic (c-)(V0.64Al0.36)(0.49)N-0.51 thin films, grown by reactive high power pulsed magnetron sputtering, by combination of structural and compositional characterization at the nanometer scale with density functional theory (DFT) calculations. Based on thermodynamic considerations of partial derivative(2)Delta G/partial derivative x(2) < 0, spinodal decomposition is expected for c-V1-xAlxN with x >= 0.35. While no indications for spinodal decomposition are observable from laboratory and synchroton diffraction data after annealing in Ar atmosphere at 1300 degrees C, the formation of wurtzite (w-)AlN is evident after annealing at 900 degrees C by utilizing high energy synchrotron X-ray diffraction. However, the complementary nature of elemental V and Al maps, obtained by energy dispersive X-ray spectroscopy in scanning transmission electron microscopy mode, imply spinodal decomposition of c-(V0.64Al0.36)(0.49)N-0.51 into V- and Al-rich cubic nitride phases after annealing at 900 degrees C. These chemical modulations are quantified by atom probe tomography and maximum variations of x in V1-xAlxN are in the range of 0.36 to 0.50. The magnitude of the compositional modulations is enhanced after annealing at 1100 degrees C as x varies on average between 0.30 and 0.61, while the modulation wavelength remains unchanged at approximately 8 nm. Based on DFT data, the local x variation from 0.30 to 0.61 would cause lattice parameter variations from 4.111 to 4.099 angstrom. This difference corresponds to a shift of the (200) peak from 44.0 to 44.1 degrees. As the maximum decomposition-induced peak separation magnitude of 0.1 degrees is significantly smaller than the measured full width at half maximum of 0.4 degrees, spinodal decomposition cannot be unravelled by diffraction data. However, consistent with DFT predictions, spinodal decomposition in c-(V0.64Al0.36)(0.49)N-0.51 is revealed by chemical composition characterization at the nanometer scale.

Ämnesord

NATURVETENSKAP  -- Kemi -- Materialkemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Materials Chemistry (hsv//eng)

Nyckelord

Spinodal decomposition

VAlN

Chemical composition modulation

Density functional theory

Atom probe tomography

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)