A simple and efficient approach for coating multiwalled carbon nanotubes (MWCNTs) with size-controllable SnO2 nanoparticles by chemical vapor deposition has been developed using tin hydride (SnH4) gas as the source of SnO2 at 550 °C. The size and coverage of SnO2 nanoparticles can be adjusted by simply controlling the deposition time and the flow rate of the SnH4/N2 mixture gas during the CVD procedure. In addition, by using the MWCNTs as a sacrificial template, a kind of one-dimensional chain-like SnO2 nanostructure has been synthesized by increasing the deposition temperature to 730 °C. This technique may provide a good way to produce tunable SnO2-MWCNT composites. 相似文献
In recent years, various chaos-based image encryption algorithms have been proposed to meet the growing demand for real-time secure image transmission. However, chaotic system that is the core component of chaos-based cryptosystem usually degrades under finite computing precision, causing many security issues. In this paper, a novel cryptosystem with analog-digital hybrid chaotic model is proposed. Firstly, the analog Chen chaotic system and the digital Logistic map are adopted to depict the capability of the hybrid model, in which analog system is used to perturb digital system. Dynamic analyses demonstrate that the hybrid method has better complexity, larger chaotic parameter range and good ability to counteract dynamical degradation. The chaos-based key streams generated by the perturbed Logistic map are more suitable for image encryption. Secondly, a parameter selection mechanism is introduced to increase security. The state variables of Chen chaotic system and cipher image are involved in parameter selection process to dynamically change the parameter of the perturbed Logistic map. The involvement of cipher image makes the key streams relevant to plain image and can resist known/chosen-plaintext attacks. Performance, security and comparison analyses indicate that this cryptosystem has high security, low time complexity, and ability to resist common attacks.