Infrared and high-energy electron diffraction analyses of electron-beam-evaporated MgO films

Abstract

Infrared spectroscopy and reflection high-energy electron diffraction have been used to analyze MgO films deposited at various deposition rates on "infrared" silicon wafers and hard glass substrates at various temperatures. Infrared spectra obtained for MgO films deposited at rates of 1350-1500 Å/min on substrates at room temperature and at 200 °C showed that the amount of hydroxyl groups present was significantly less in the 200 °C deposited films. The spectra also showed that the amount of hydroxyl groups present in films deposited at a very fast rate (∼7800 Å/min) was much less than that in films deposited at a very slow rate (∼160 Å/min) on substrates at 200 °C. Some of the hydroxyl groups initially present in films deposited at ∼160 Å/min and most of the hydroxyl groups in films deposited at ∼1350 Å/min were removed by annealing the films in dry nitrogen at 500 °C. The electron diffraction patterns obtained for MgO films (100-3000 Å) deposited at rates of 1350-1500 Å/min on substrates at a temperature in the range from room temperature to 200 °C showed that the films initially nucleated in random orientation and as the film thickness was increased to and above 500 Å, a 〈111〉 preferred orientation developed at the surface independent of substrate temperature. These results suggest that adsorption of residual water on MgO does not influence the mode of film growth. The 〈111〉 preferred orientation developed in films deposited on substrates at 200 °C dissolved, and some degree of the 〈100〉 preferred orientation developed upon annealing in dry nitrogen at 500 °C. The preferred orientation remained, however, unchanged when these films were annealed in dry air. The orientation also remained unchanged when films deposited on substrates at room temperature were annealed in dry nitrogen at 500 °C. These results suggest that the presence of hydroxyl ions and oxygen adsorption inhibit surface diffusion and, hence, the dissolution of the orientation during annealing.