͑Zn,Al͒O thin films have been prepared by a dc reactive magnetron sputtering system with the Al contents in a wide range of 0 -50 at. %. The structural, optical, and electrical properties of ͑Zn,Al͒O films were detailedly and systematically studied. The amount of Al in the film was nearly the same as, but often lower than, that in the sputtering target. The growth rate of films monotonically decreased as the Al content increased. In a low Al content region ͑Ͻ10 at. % ͒, Al-doped ZnO ͑AZO͒ thin films could be obtained at 400°C in an Ar-O 2 ambient with good properties. The optimal results of n-type AZO films were obtained at an Al content of 4 at. %, with low resistivity ϳ10 −4 ⍀ cm, high transmittance ϳ90% in the visible region, and acceptable crystal quality with a high c-axis orientation. The band gap could be widened to 3.52 eV at 4 at. % Al due to the Burstein-Moss shift ͓E. Burstein, Phys. Rev. 93, 632 ͑1954͔͒ modulated by many-body effects. An appropriate Al-doping concentration served effectively to release the residual, compressive stress in film, which may be the reason for the improvement in film stability and the increment in grain size as well. In a medium Al content region ͑10-30 at. % ͒, however, the film quality was degraded, which was presumably due to the formation of clusters or precipitates in the grains and boundaries. Besides the ͑002͒ plane, other diffraction peaks such as ͑100͒ and ͑101͒ planes of ZnO were observed, but the ͑Zn,Al͒O films still exhibited a single-phase wurtzite ZnO structure. An intragrain cluster scattering mechanism was proposed to interpret the reduction of carrier mobility in films with the Al contents in the 7 -20 at. % region. The solubility limit of Al in ZnO film was identified to be in the 20-30 at. % range, much higher than the thermodynamic solubility limit of 2 -3 at. % in ZnO. In a high Al content region ͑ജ30 at. % ͒, there were distinct observations for ͑Zn,Al͒O films. As the Al content was 30 at. %, the film appeared in a two-phase nature with ZnO hexagonal and Al 2 O 3 rhombohedral structures. At the 50 at. % Al content, the matrix of the ͑Zn,Al͒O film was Al 2 O 3 , and no evident trace of wurtzite ZnO was observed. The electrical and optical properties for both cases were also very different from those at the Al contents below 30 at. %.

A Li–N dual-acceptor doping method has been developed to prepare p-type ZnO thin films by pulsed laser deposition. The lowest room-temperature resistivity is found to be ∼0.93Ωcm, much lower than that of Li or N monodoped ZnO films. The p-type conductivity of ZnO:(Li,N) films is very reproducible and stable, with acceptable crystal quality. The acceptor activation energy in ZnO:(Li,N) is about 95meV. ZnO-based homostructural p-n junctions were fabricated by depositing an n-type ZnO:Al layer on a p-type ZnO:(Li,N) layer, confirmed by secondary ion mass spectroscopy. The current-voltage characteristics exhibit their inherent rectifying behaviors.

Self-assembled ZnO quantum dots ͑QDs͒ were achieved by a vapor phase transport process. ZnO nanodots were naturally formed on solid substrates in the Volmer-Weber growth mode. Size control of nanodots could be readily realized by varying the growth time. The as-prepared ZnO QDs are of high quality and very stable after formation. The blueshift of band gap energies derived from quantum confinement effects was confirmed by optical absorption spectra. Photoluminescence spectra revealed the tunable behavior of ultraviolet luminescence due to exciton localization. The realization of size-tuned color from ZnO QDs makes them more promising for practical applications.

N-doped, p-type ZnO (ZnO : N) thin films were prepared by magnetron sputtering using NO as the N-doping source. The introduction of Ar in the growth ambient could evidently improve the p-type conductivity and crystal quality of the ZnO : N films, with the lowest room-temperature resistivity of 3.51 Ω cm obtained at an optimal Ar partial pressure of 30%. The p-type ZnO : N films have high optical quality, as suggested by temperature-dependent photoluminescence spectra. The NO substitution acceptor state with an energy level of 180 meV was identified from the free-to-neutral-acceptor (e, A 0) transition. The NO-acceptor bound-exciton binding energy was derived to be 17 meV from the neutral-acceptor-bound-exciton and free exciton emissions. The Haynes factor was about 0.094 for the NO acceptor in ZnO. Besides the NO acceptor, a zinc vacancy (VZn) acceptor state with an energy level of 255 meV was also identified in ZnO : N from the (e, A 0) transition, which might also contribute to the observed p-type conductivity.

In recent years, with the widespread application of information network technology, information security has become increasingly important. More information leaks occur during the exchange of information flows, and opacity is a very important concept in the exchange of system information flows. It refers to the inability of external intruders to observe and infer the nature of key system behaviors through system non secret behaviors. "Opacity" is an inherent attribute of a system. The related research on opacity is widely used in various industrial control fields to meet system security and privacy requirements. This article summarizes and compares various definitions and implementation methods related to the research on opacity in discrete event systems, and analyzes their respective use scenarios and differences based on the characteristics of various types of opacity; The mathematical conditions and complexity of various opacity implementations are summarized, and the complexity of different implementations is compared. The reasons for the different complexity of different implementations are analyzed; Finally, according to the current development direction of opacity research, the future research direction of opacity is prospected.