1) The document studies the surface reactions and interface evolution during atomic layer deposition (ALD) of HfO2 on GaAs surfaces using in situ attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR). 2) It is observed that native arsenic oxides on the GaAs surface are gradually removed during the first 20 cycles of HfO2 ALD at 275°C through a self-cleaning process. 3) The removal of arsenic oxides is enhanced at higher deposition temperatures, and methylmethyleneimine (MMI) is found to accumulate in the growing HfO2 film, suggesting it is produced during the H2O half-cycles of A