Topological insulator thin films of Bi2Te3 with controlled electronic structure can be grown by regulating the molecular beam epitaxy (MBE) growth kinetics without any extrinsic doping. N‐ to p‐type conversion results from the change in the concentrations of TeBi donors and BiTe acceptors. This represents a step toward controlling topological surface states, with potential applications in devices.

The growth and characterization of single-crystalline thin films of topological insulators (TIs) is an important step towards their possible applications. Using in situ scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES), we show that moderately thick Sb 2 Te 3 films grown layer-by-layer by molecular beam epitaxy (MBE) on Si(111) are atomically smooth, single-crystalline, and intrinsically insulating. Furthermore, these films were found to exhibit a robust TI electronic structure with their Fermi energy lying within the energy gap of the bulk that intersects only the Dirac cone of the surface states. Depositing Cs in situ moves the Fermi energy of the Sb 2 Te 3 films without changing the electronic band structure, as predicted by theory. We found that the TI behavior is preserved in Sb 2 Te 3 films down to five quintuple layers (QLs).

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The structural, electrical and magnetic properties of Ni-doped ZnO films with different Ni concentrations (x = 0–0.11, x: Ni concentration) and thicknesses (d = 15–330 nm, d: film thickness) prepared by radio-frequency magnetron sputtering have been systematically investigated. The structural characterizations indicate that Ni ions in the 2+ valence state, uniformly distributed in the film, almost substitute for the Zn ions when x ⩽ 0.07, whereas when x increases up to 0.11, a second phase Ni is formed. Room temperature (RT) ferromagnetism (FM) has been observed for all the Ni-doped ZnO wurtzite films. The saturated magnetization varies drastically with the Ni concentration and the film thickness. A large magnetic moment of 2.80 μB/Ni is obtained in the 15 nm thick Zn0.96Ni0.04O film at RT. The results show that the FM observed is intrinsic for Ni-doped ZnO films and can be explained in terms of the bound magnetic polaron mechanism based on the presence of defects. In addition, the Ni precipitates owing to the excessive doping of Ni in ZnO, as an extrinsic origin, also contribute to the ferromagnetic properties in highly doped samples.