Looking Outside the Square: The Growth, Structure, and Resilient Two-Dimensional Surface Electron Gas of Square SnO2 Nanotubes

• Main Authors: Adams, R.L (Author), Allen, M.W (Author), Carroll, L.R (Author), Downard, A.J (Author), Martinez-Gazoni, R.F (Author), Reeves, R.J (Author), Scott, J.I (Author), Veal, T.D (Author)
• Format: Article
• Language: English
• Published: John Wiley and Sons Inc 2023
• Subjects: 2D electron gas; 2D electron gas (2DEG); Acetone; Chemical vapor deposition; Electrons; Field effect transistors; Gold nanoparticles; Growth structures; High resolution transmission electron microscopy; Oxide minerals; oxygen vacancies; Oxygen vacancies; Sapphire; Sb-doped; Scalable methods; Schottky barrier diodes; Square nanostructure; square nanostructures; Surface electron; surface hydroxyl; Surface hydroxyl; tin dioxide; Tin dioxide; Titanium dioxide; Two-dimensional surface; Vertically aligned; X ray photoelectron spectroscopy
• Online Access: View Fulltext in Publisher

 Nanotechnology has delivered an amazing range of new materials such as nanowires, tubes, ribbons, belts, cages, flowers, and sheets. However, these are usually circular, cylindrical, or hexagonal in nature, while nanostructures with square geometries are comparatively rare. Here, a highly scalable method is reported for producing vertically aligned Sb-doped SnO2 nanotubes with perfectly-square geometries on Au nanoparticle covered m-plane sapphire using mist chemical vapor deposition. Their inclination can be varied using r- and a-plane sapphire, while unaligned square nanotubes of the same high structural quality can be grown on silicon and quartz. X-ray diffraction measurements and transmission electron microscopy show that they adopt the rutile structure growing in the [001] direction with (110) sidewalls, while synchrotron X-ray photoelectron spectroscopy reveals the presence of an unusually strong and thermally resilient 2D surface electron gas. This is created by donor-like states produced by the hydroxylation of the surface and is sustained at temperatures above 400 °C by the formation of in-plane oxygen vacancies. This persistent high surface electron density is expected to prove useful in gas sensing and catalytic applications of these remarkable structures. To illustrate their device potential, square SnO2 nanotube Schottky diodes and field effect transistors with excellent performance characteristics are fabricated. © 2023 The Authors. Small published by Wiley-VCH GmbH.