Synchrotron x-ray photoelectron spectroscopy was used to explore the relationship between the hydroxyl termination and band bending at the $\left(\overline{2}01\right)$ surface of $\beta \text{−}\mathrm{G}{\mathrm{a}}_2{\mathrm{O}}_3$ bulk single crystals. All as-received $\left(\overline{2}01\right)$ surfaces were terminated with OH groups, with H/OH binding to surface ${\mathrm{O}}_{\mathrm{s}}/\mathrm{G}{\mathrm{a}}_{\mathrm{s}}$ atoms. Removal of this native OH termination produced a large upward shift in band bending of up to 1.0 eV, consistent with strong electron depletion and a semiconductor to insulator-like transition in the near-surface region. Simple surface treatments were used to control the size and stability of the band bending of as-received $\left(\overline{2}01\right)$ surfaces by modifying the nature of the OH termination. NaOH (${\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4$) treatment consistently produced upward (downward) shifts in band bending and a significant increase (decrease) in the thermal stability of the OH termination that was associated with an increase in the relative density of $\mathrm{G}{\mathrm{a}}_{\mathrm{s}}\text{−}\mathrm{OH}$ (${\mathrm{O}}_{\mathrm{s}}\text{−}\mathrm{H}$) species. Annealing in wet ${\mathrm{O}}_2$ (at 600 °C) produced an extremely stable OH termination and the strongest downward shift in band bending. These effects, combined with the relatively slow dissociation of ${\mathrm{H}}_2\mathrm{O}$ on bare $\left(\overline{2}01\right)$ surfaces, allowed the preparation of surfaces with significant variations in band bending that may prove useful in optimizing the properties of $\beta \text{−}\mathrm{G}{\mathrm{a}}_2{\mathrm{O}}_3$ metal-semiconductor contacts and heterojunctions. A comparison of two methods used to determine the absolute band bending at semiconductor surfaces confirmed that bare $\beta \text{−}\mathrm{G}{\mathrm{a}}_2{\mathrm{O}}_3\left(\overline{2}01\right)$ surfaces are characterized by strong upward band bending (∼0.5 to 1.0 eV) and an electron depletion layer that can be completely removed by the hydroxylation of the surface.

Perfluorododecyl iodide (I-PFC12) is of interest for area-selective deposition (ASD) applications as it exhibits intriguing properties such as ultralow surface energy, the ability to modify silicon’s band gap, low surface friction, and suitability for micro-contact patterning. Traditional photolithography is struggling to reach the required critical dimensions. This study investigates the potential of using I-PFC12 as a way to produce contrast between the growth area and non-growth areas of a surface subsequent to extreme ultraviolet (EUV) exposure. Once exposed to EUV, the I-PFC12 molecule should degrade with the help of the photocatalytic substrate, allowing for the subsequent selective deposition of the hard mask. The stability of a vapor-deposited I-PFC12 self-assembled monolayer (SAM) was examined when exposed to ambient light for extended periods of time by using X-ray photoelectron spectroscopy (XPS). Two substrates, SiO₂ and TiO₂, are investigated to ascertain the suitability of using TiO₂ as a photocatalytic active substrate. Following one month of exposure to light, the atomic concentrations showed a more substantial fluorine loss of 10.2% on the TiO₂ in comparison to a 6.2% loss on the SiO₂ substrate. This more pronounced defluorination seen on the TiO₂ is attributed to its photocatalytic nature. Interestingly, different routes to degradation were observed for each substrate. Reference samples preserved in dark conditions with no light exposure for up to three months show little degradation on the SiO₂ substrate, while no change is observed on the TiO₂ substrate. The results reveal that the I-PFC12 SAM is an ideal candidate for resistless EUV lithography.