A detailed study of the oxidation of Cu substrates was carried out under controlled conditions by regulating the pressure, atmosphere composition, process time, and temperature. By tuning the synthesis conditions, the formation of cuprous oxide (Cu2O) or cupric oxide (CuO) could be preferentially promoted. The oxidation temperature was varied from 400 to 1050 °C, and a gradual oxidation of metallic Cu to Cu2O was achieved at mild oxidation conditions (400-600 °C), while the formation of CuO was only observed at higher temperatures (≥900 °C). The surface morphology was also affected changing from a highly granular texture (400 °C) with grain sizes between 0.59 ± 0.15 μm to smooth large crystallites (≥900 °C) with a size within 2.76 ± 0.97 μm. We also show that by controlling the oxidation temperature (400-1050 °C), it is possible to tune the work function and the ionization potential of the resulting Cu2O/CuO film, properties that are important for various optoelectronic applications.