As electronic devices have scaled down to line widths of just a few nanometers, the device architecture requires high precision deposition of perfectly conformal films on topographically complex surfaces. The fundamental challenge to deposit conformal thin films is that the rate determining step should be a surface chemical reaction . This renders a surface-controlled deposition process. The premier technique for depositing highly conformal thin films is atomic layer deposition (ALD). An ALD process is a time-resolved chemical vapor deposition (CVD) process, where the substrate is exposed to two gaseous precursors in alternating pulses separated by an inert gas purge. This makes the deposition chemistry fully dependent on surface reactions. If the ALD precursors are chosen properly, the surface chemistry terminates itself when all growth sites are occupied. This enables a fully surface-controlled deposition chemistry, enabling ALD to produce uniform thin films not only on planar substrates but also in complicated recessed features .