  Oblique angle deposition of oxides is being famous for fabricating
inhomogeneous thin films with variation of refractive index along thickness in
a functional form. Inhomogeneous layers play a key role in the development of
rugate interference devices for photo-physical applications. Such obliquely
deposited thin films show high porosity which is a critical issue related to
their mechanical and environmental stability. Hence, it is important to
investigate elastic properties of such film in addition to optical properties.
Using atomic force acoustic microscopy, we report indentation modulus of HfO2
thin films deposited at angles 80, 68, 57, 40 and 0 degree with normal to
substrate plane on Si (100) substrate. Such films were measured to have
indentation modulus of 42 GPa for extreme obliquely deposited film and
indentation modulus increases with decrease in angle to become highest with a
value of 221 GPa for normally deposited films. We also report microstructural
properties and density of films measured by FESEM and grazing angle X-ray
reflectometer respectively. Both indentation modulus and density depict a
parabolic decreasing behavior with angle of deposition. Variation of density is
again confirmed by FESEM cross-sectional morphology of such films.
