Zone-center Raman active modes in cubic and hexagonal diamond

The recent interest in the growth of thin diamond films has led us to consider the differences between the hexagonal (lonsdaleite) and cubic structures. Both phases have very similar properties, and empirical and theoretical considerations indicate that their structural energies are nearly identical. When thin films are grown the hexagonal phase may compete with the cubic phase, making characterization of the film difficult. Cubic diamond has one Raman active mode, while hexagonal diamond has three. The opportunity thus exists for Raman spectroscopy to differentiate between the two tetrahedrally bonded phases (as well as “amorphous” or graphitic phases). Electronic structure calculations can be used to obtain theoretical Q=0 frequencies of the Raman active modes in both structures. We have used the first principles Linearized Augmented Plane Wave method within the local density approximation to calculate the zone center phonon frequencies. The calculated frequency of the cubic diamond Raman mode is 1336 cm-1, very close to the experimental value of 1333 cm-1. Our calculations indicate that the hexagonal structure A t has a zone-center frequency of 1269 cm-1, the E2g mode is at 1215 cm-1, and the E1gmode is at 430 cm-1. Anharmonic corrections are rather large (2-3%) in the cubic diamond Raman mode and in the hexagonal Al mode, but are not important in the E2g and E1g modes. We will compare our results with the available experimental information. © 1989 SPIE.

Duke Scholars

Author Michael J Mehl Thomas Lord Department of Mechanical Engineering and Materia ...