•Substantial magnetization ~14 emu/cm3 has been observed in As implanted ZnO.•The sample contains both As ions and damage due to implantation.•Both the magnetization and the damage increase with larger concentration of As.•Magnetism is due to the defects produced during implantation.•Defects produced by implantation are distinct from those occurring during the growth process.Different concentrations of arsenic ions have been introduced into high quality O polar ZnO films prepared by rf-plasma assisted molecular beam epitaxy on sapphire substrates by ion implantation. Rutherford Backscattering/Channeling, x-ray diffraction, Raman spectroscopy and optical absorption measurements have been carried out to characterize the implantation induced disorder in the ZnO films. Room temperature ferromagnetism has been observed for the films implanted with As dose higher than 6×1018 cm−3. The size of the observed moment is too large to be attributed to the As related defect complex (AsZn-2VZn) and is attributed to defects introduced by the ion implantation process. This was confirmed by the observation that the magnetization could be removed by annealing the films.

•Arsenic implantation causes polar ZnO films to become magnetic.•Magnetization of the As doped O polar film is much larger than for the Zn-polar film.•Magnetism is due to defects produced during implantation.O-polar and Zn-polar ZnO films were prepared by rf-plasma assisted molecular beam epitaxy (MBE) on sapphire substrates. Arsenic ions have been implanted into high quality ZnO with a definite polarity. Substantial temperature-independent ferromagnetism has been observed for both films, with the O-polar film having approximately twice the magnetization as the Zn-polar film. The saturation magnetization is shown to be due to the defects introduced during implantation, rather than to local moments associated with the As ion. Rutherford Backscattering/Channeling and optical absorption measurements confirm that the implantation introduces more defect states in the O-polar films, while X-ray absorption near-edge structure measurements show that the environment of the arsenic ions was similar for both polarities.

Density functional theory (DFT) calculations have been carried out to investigate the interactions between the Si(1 1 1) surface and the Al adatoms. Different adsorption sites and coverage effects have been considered. For low Al coverage, the threefold-filled adsorption site is the most energy favored site. With the increase of Al coverage, adatom–adatom interactions become increasingly important and Al atomic chains or clusters are formed. With the clean Si(1 1 1) surface of metallic feature, we found that 1/3 ML Al adsorption leads to a semiconducting surface. The results for the electronic behavior suggest the formation of the polarized covalent bonding between the Al adatom and the Si(1 1 1) surface.Highlights► We performed DFT study of the interaction between Si(1 1 1) surface and Al adatoms. ► The threefold-filled adsorption site is the most energy favored at low Al coverage. ► With the increase of Al coverage, Al atomic chains or clusters are formed. ► 1/3 ML Al adsorption surface is semiconducting while the clean surface metallic.