Direct Measurements of the Surface Energies of Crystals

TLDR

Quantitative cleavage experiments at −196 °C measured the surface energies of LiF, MgO, CaF₂, BaF₂, CaCO₃, Si, and Zn under irreversible conditions. The measured surface energies (340–1240 erg cm⁻²) agree with ionic lattice theory for LiF and MgO, match binding energies for the others, and show that effective surface energy rises sharply with temperature for metallic Zn and Fe(3 % Si) while remaining only moderately temperature‑dependent for LiF and MgO; a 0.1 at.% Cd addition markedly increases Zn’s cleavage energy.

Abstract

By means of quantitative cleavage experiments, the surface energies of several simple crystals have been measured at −196°C. The crystals and their cleavage planes are: LiF (100), MgO (100), CaF2 (111), BaF2 (111), CaCO3 (1010), Si (111), and Zn (0001). Measured values of their respective surface energies (ergs/cm2) are: 340, 1200, 450, 280, 230, 1240, and 105. The measured values for LiF and MgO are in good agreement with simple ionic lattice theory. Values for the other crystals seem consistent with their binding energies. Under irreversible conditions an effective surface energy is measured. This quantity increases rapidly with increasing temperature for the metallic crystals, Zn and Fe (3% Si). The increase correlates with increasing plastic flow in these crystals. In contrast, the effective surface energy of LiF and MgO is only moderately dependent on temperature. A small amount of cadmium (0.1 at.%) markedly increases the cleavage surface energy of zinc.