Generation and applications of compressive stress induced by low energy ion beam bombardment

Compressive stress is a widespread phenomenon in films subjected to ion beam bombardment. A thermodynamic treatment of materials under a general stress is used to show that preferred orientation will occur as a result of free energy minimization in a biaxial stress field. The equilibrium between structural phases of materials is also affected by stress. Thermodynamics is used to calculate the equilibrium between graphite and diamond under biaxial stress. Recent molecular dynamics studies of the mechanism of compressive stress generation are reviewed in which the phenomena of focused collision sequences and thermal spikes are studied. Experimental work shows compressive stress is linked to preferred orientation in hexagonal boron nitride films and to stabilization of high pressure phases such as cubic BN and tetrahedral amorphous carbon films, in agreement with the thermodynamic analysis.