  The effect of nanocrystal orientation on the energy loss spectra of
monoclinic hafnia (m-HfO$_2$) is measured by high resolution transmission
electron microscopy (HRTEM) and valence energy loss spectroscopy (VEELS) on
high quality samples. For the same momentum-transfer directions, the dielectric
properties are also calculated ab initio by time-dependent density-functional
theory (TDDFT). Experiments and simulations evidence anisotropy in the
dielectric properties of m-HfO$_2$, most notably with the direction-dependent
oscillator strength of the main bulk plasmon. The anisotropic nature of
m-HfO$_2$ may contribute to the differences among VEELS spectra reported in
literature. The good agreement between the complex dielectric permittivity
extracted from VEELS with nanometer spatial resolution, TDDFT modeling, and
past literature demonstrates that the present HRTEM-VEELS device-oriented
methodology is a possible solution to the difficult nanocharacterization
challenges given in the International Technology Roadmap for Semiconductors.
