Invited Paper SE-MoM10
Atomistic Processes during Synthesis of Hard Coatings Revealed by STM and LEEM

Monday, October 15, 2007, 11:00 am, Room 617

Transition-metal nitrides, such as TiN, have a wide variety of applications as hard, wear-resistant coatings, as diffusion barriers, and as scratch-resistant and anti-reflective coatings in optics. Understanding the surface morphological and microstructural evolution of these materials is crucial for improving the performance of devices. Studies of surface step dynamics enable determination of the rate-limiting mechanisms, corresponding surface mass transport parameters, and step energies. However, most models describing these phenomena are limited in application to simple elemental metal and semiconductor surfaces. We summarize recent progress toward elucidating the interplay of surface and bulk diffusion processes on morphological evolution of compound surfaces. Specifically, we analyze the coarsening/decay kinetics of two- and three-dimensional TiN(111) islands and the effect of surface-terminated dislocations on TiN(111) steps. Further, in an attempt to gain better understanding of the origin of TiN-SiNx superhardness, we use in-situ STM and LEED to investigate the atomic-scale structure of the SiNx/TiN interface, of which very little is known. SiNx overlayers were grown onto single-crystal TiN(001) or TiN(111) substrates at temperatures between 700 and 900 ºC. We show both topographic (STM) and diffraction (LEED) evidence that (a) SiNx overlayers on TiN are crystalline with reconstructions including 2x2, c-3x3, and 1x5, depending upon SiNx coverage, surface orientation, and annealing temperature; and (b) TiN grows epitaxially on top of the SiNx layers. Specifically, our results show that for SiNx coverages near 1ML, where maximum TiN-SiNx hardness is attained, the SiNx layer is not amorphous as deposited. Finallly, we will describe a design of a tandem instrument combining a low-energy electron microscope (LEEM) and a negative ion accelerator. This instrument provides video rate imaging of the dynamics of surface microtopography evolution during irradiation by energetic ions, at temperatures up to 1500 K. We will present in-situ real-time atomic-scale studies of energetic epitaxial film growth and etching.