Ion-assisted deposition of MoSx films from laser-generated plume under pulsed electric field

The thickness profiles and compositional distributions of MoSx films deposi ted from a plume generated by pulsed laser irradiation of the MoS2 target w ere investigated at a varying fluence and constant laser pulse energy. It w as shown that films with stoichiometric composition were formed at sufficie ntly low fluence (near the ionization threshold), and increasing fluence ca used intricate nonmonotonic variations of the compositional distribution. A substantial deviation of the film composition from stoichiometric and a si gnificant radial gradient of the sulfur concentration over the substrate su rface (1 < x < 3, where x is the ratio of concentrations of S and Mo atoms, x = S/Mo) were found. These phenomena were caused by: (1) the incongruent target evaporation; (2) the mass dependence of the angular distribution of the ablated particles; and (3) the selective sulfur sputtering and desorpti on induced by energetic particles (ions, excited atoms) of the laser-genera ted plume. When the laser fluence was low, films of stoichiometric composit ion were bombarded by energetic particles with a low intensity, and the num ber of displacements was inadequate for formation of the basal-oriented str ucture (much less than1 displacement per atom). Raising the laser fluence, it is possible to increase the bombardment dose; however, the effect of the factors (1)-(3) has turned the selection of optimal conditions for stoichi ometric film deposition into a rather complicated problem. A new technique is proposed for pulsed laser deposition of high-purity MoSx films with vary ing sulfur concentration and the required ion-irradiation dose. The techniq ue consists in accelerating the ion component of the plume by a pulsed elec tric field up to an energy of a few tens of kilo-electron-volts, thus makin g it possible to significantly increase the number of displaced atoms in th e MoSx film without noticeable change in its composition and to induce ion mixing at the MoSx-substrate interface. The positive voltage pulse of up to 100 kV amplitude was applied to the target during the plume expansion from the target towards the substrate which was grounded. The modification of t he MoSx films by accelerated ions resulted in noticeable improvement of the ir lubrication performance. (C) 2001 American Institute of Physics.