An optical fragile watermarking method is proposed based on visual cryptography and QR code for image authentication and tamper detection. On the one hand, the original image is transformed into a QR watermark image to improve the watermark hiding capacity. On the other hand, the visual cryptography and optical phase coding are fused to encrypt the watermark image to enhance system security. The feasibility, vulnerability and imperceptibility of the proposed scheme are tested through a series of attacks and tampering. The simulation results show that the proposed method can not only have good imperceptibility, but also achieve high detection performance under different attacks and tampering.

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Thermoelectric (TE) materials can directly realize the mutual conversion between heat and electricity, and it is an environmentally friendly functional material. At present, the thermoelectric conversion efficiencies of thermoelectric materials are low, which seriously restricts the large-scale application of thermoelectric devices. Therefore, finding new materials with better thermoelectric properties or improving the thermoelectric properties of traditional thermoelectric materials has become the subject of thermoelectric research. Thin film materials, compared with bulk materials, possess both the two-dimensional macroscopic properties and one-dimensional nanostructure characteristics, which makes it much easier to study the relationships between physical mechanisms and properties. Besides, thin film are also suitable for the preparation of wearable electronic devices. This article summarizes five different preparation methods of Cu₂Se thin films, i.e. electrochemical deposition, thermal evaporation, spin coating, sputtering, and pulsed laser deposition. In addition, combing with typical examples, the characterization methods of the film are summarized, and the influence mechanism of each parameter on the thermoelectric performance from electrical conductivity, Seebeck coefficient and thermal conductivity is discussed. Finally, the hot application direction of Cu₂Se thin film thermoelectrics is also introduced.

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