Surface modification and structure evolution of aluminum under argon ion bombardment

The surface properties is an important factor in the surface activated bonding of aluminum. The effect of argon (Ar) bombardment on the surface properties of aluminum was investigated in this work. The changes in surface chemical composition, wettability and structure were analyzed. The results revealed that the Al-O bonds of surface oxide film were broken by Ar ion bombardment. The positive aluminum ions (Al+) and oxygen radicals (O*) produced by breaking of Al-O bonds could react with the adsorbed water molecules to form hydrophilic hydroxyl (-OH groups) and Al-OH groups, which improved the wettability of aluminum surface. A large number of dislocations and subgrains with lattice distortion accumulated in the bombard-induced modification layer near the surface. The stress distribution on the surface was transformed from tensile stress into compressive stress with the bombardment power enhanced. The simulation results showed that the regular structure was broken and the point defects were produced from the collision. In the later stage of collision, most of the disordered atoms rearranged with the point defects annihilated, and finally a crater with several stable point defects was left near the surface.