Destabilization of Sn²⁺ 5s² Lone-Pair States of SnO through Dimensional Crossover

Materials exhibiting unique electronic properties arisingfroma characteristic crystal structure have physical properties that aresensitive to structural dimensionality. This study involves the destabilizationof Sn 5s(2) lone-pair states of SnO films by decreasing theirstructural dimensionality in the out-of-plane direction. The inherentdispersive band structure of the SnO films remained unchanged between80 and 11 nm. Below 11 nm, their dispersive band structure disappeared,the O/Sn ratio increased, and the carrier type changed from the ptype to the n type, whereas the Sn valency remained constant at +2.These unconventional changes arose from the electronic separationcorresponding to the Debye length, which is proportional to permittivity,and were attributed to weakened interactions between Sn 5s(2) lone-pair electrons. Therefore, designing low-permittivity materialsis beneficial for reducing the crystallite size required for stabilizinglone-pair states. These results are essential for designing emergentp-type oxides and improving their semiconducting properties and performancein transparent or high-power electronics.