A simple growth mechanism between TMA and NH3 from our study is illustrated in Fig. . The change in the m/z = 16 signal during the TMA pulse with temperature in Fig. suggest that the chemisorption reactions of TMA on the presumably 12 -NH2 terminated surface have a significantly higher activation energy than the chemisorption reactions of NH3 on the presumably -CH3 terminated surface. The m/z = 16 signal during the NH3 pulse did not exhibit any temperature dependence in the studied temperature range. This also suggests that the TMA halfcycle is the rate-determining step. The higher levels of C impurities from XPS (supplementary information Table ) are most likely due to TMA decomposition 17 at these temperatures. This suggests that other chemical mechanisms are activated at these temperatures, which is also suggested by the temperature dependence on the GPC in Fig. .