Electronic Structure

Optical Properties
and
Electronic Structure

Interband Transition Strength of an Intergranular Film in Silicon Nitride

Figure Caption. Interband Transition Strength of an Intergranular Film (Igf) in Polycrystalline Silicon Nitride determined using spatially resolved valence electron energy loss spectroscopy. The 3D spectrum image shows the distance in nanometers across the bottom versus energy along the right side. The band gap of silicon nitride is seen at ~6 eV while into the silicate intergranular film (at approx. 6 nm displacement) the band gap is seen to increase to 8 eV. The thickness of these Igf's is determined by the Igf glass chemistry and the resulting dispersion force as given by the Hamaker Constant.

Overview

Optical property based electronic structure studies emphasize the interatomic bonding and interband transitions of materials, elucidating their physical properties. Optical properties, such as the interband transition strength, Jcv, or the dielectric constant, epsilon, also serve as a quantitative electronic structure basis for comparisons of experimental vacuum ultraviolet (VUV) reflectance results, spatially resolved (< 1 nm) valence electron energy loss (SR-VEEL) results and theoretical LDA band structure results. This is accomplished by Kramers Kronig dispersion analysis of VUV reflectance or single scattering deconvolved SR-VEEL results.

For an abrupt interface, such as the Sigma-11 grain boundary in alpha-Al2O3, critical point analysis yields detailed electronic structure information for the grain boundary core, showing a decreased band gap and reduced electron occupancy of the hybridized Al=O bonds compared to bulk alpha-Al2O3.

For nm-scale intergranular glass films at boundaries analysis of Jcv permits calculation of the Hamaker Constants for these van der Waals forces from the interfacial electronic structure

The scope of these quantitative electronic structure tools presents new opportunities for the field of materials science.

Figure Caption. a) Critical point models of the Interband Transitions from VUV data of alpha-Al2O3, and b) Partial optical sum rules for the critical point sets corresponding to interband transitions from the O 2p bands, Al=O hybridized bands and the O 2s lower valence bands to the Al conduction bands.. An excitonic transition is resolved at the band gap in these Vacuum Ultraviolet measurements.

Optical Properties and Electronic Structure

Overview

Optical Properties
and
Electronic Structure