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In this article, novel sandwich-structured surface plasmon ultraviolet (UV) photodetectors based on ZnO thin films with engineered rear metal electrode were fabricated by radio-frequency magnetron sputtering. An exhaustive study about the impact of a dissimilar metallic layer (Au and Pt) on the structural, optical, and electrical properties of the device was carried out. The carrier collection property of the sandwich structure devices has the advantages of horizontal and vertical joint collection. In theory, adding a new metal semiconductor layer introduces a contact area and increases the resistance. An ultra-low dark noise current of less than 2.0 × 10–7 A and a responsivity exceeding 1.6 A/W were achieved with the prepared ZnO-based UV-PDs in the rear metallic electrode mode. The devices based on the ZnO/Pt/ZnO and MgZnO/Pt/MgZnO sandwich structures show high responsivity and fast response. This study provides a depletion layer width method for the fabrication of high-response UV photodetectors for surface plasmon-based materials by integrating metal semiconductor nanostructures. A homogeneous two-layer UV photodetector is constructed, which changes the traditional single-layer device structure and overcomes drawbacks of the single device structure.

The responsivity of surface plasmon (SP) modified metal–semiconductor-metal ultraviolet photodetectors (PDs) was increased from 1.15 × 10−3 to 2.5 × 10−3 A/W by varying the number of interdigitated electrode pairs. MgZnO films with Pt nanoparticles (NPs) having a grain size of 6.26 nm in a 25-pair interdigitated electrode arrangement showed improved responsivity and signal to noise ratio in comparison with the bare MgZnO PD. This improvement was attributed to both the enhanced conductivity and increased absorption resulting from the near-field enhancement of the SP. Parallel effect physical simulation results were in reasonable agreement with our experimental results.

Silicene-based materials have attracted great attention due to their easier incorporation into silicon-based devices and components. In addition to the reported hydrogenated 2D tetragonal silicene (γ-SiH), we propose two stable atomic configurations of hydrogenated 2D tetragonal silicene (α-SiH and β-SiH) based on first-principles calculation. The calculated results indicate hydrogenation can effectively open the band gap of 2D tetragonal silicene, α-SiH is a semiconductor with a direct band gap of 2.436 eV whereas β-SiH is indirect band gap of 2.286 eV. We also find that the electronic band structure of α-SiH, β-SiH and γ-SiH can be modulated via biaxial strain. By applying biaxial strain in the range of −10% to 12%, the band gap of α-SiH, β-SiH and γ-SiH can be tuned in a range of 1.732–2.585 eV. Furthermore, direct–indirect or indirect–direct transition can be induced under biaxial strain, showing a high degree of flexibility in electronic band structure. The research not only broadens the diversity of hydrogenated 2D tetragonal silicenes, but also provides more possibilities of their applications in spintronic devices.

In this work, dual-wavelength UV photodetectors were successfully constructed by growing ZnO and MgZnO layers on SiO2 substrates with ZnO/Au/MgZnO structure. The photodetectors exhibited high performance and the influence of different thickness of MgZnO layers was investigated. Moreover, simply by adjusting the applied voltage on the devices, the ratio of the two response peaks (caused by MgZnO and ZnO layers) changed therewith. The detecting properties may originate from the two layers having different increasing rates where the existence of Schottky junctions plays an important role. The photodetectors are meaningful for fabricating dual-wavelength optoelectronic devices for practical applications.

In this work, the responsivity-controlled high performance UV photodetectors fabricated from MgZnO films was investigated with an emphasis on the effect of varying the number of interdigitated electrode pairs. The responsivity of MgZnO photodetectors was optimized by increasing the number of interdigital electrode pairs at a given bias. The result is due to the parallel structure of the interdigital electrodes and the depletion width of the Schottky junctions. This demonstrates a straightforward way of tailoring the responsivity of UV photodetectors for practical applications.

Two-dimensional (2D) materials with intrinsic ferromagnetism, a sizable magnetic anisotropy energy (MAE) and large spin polarization are desirable for realizing the practical spintronic applications. Base on first-principles calculations, the stability, electronic and magnetic properties of monolayer CrOBr are systematically investigated. Monolayer CrOBr is ferromagnetic semiconductor with a band gap of 1.547 eV, it possesses in-plane magnetic anisotropy with a value of −0.017 meV/formula unit (f.u.). The band gap of monolayer CrOBr can be regulated in the range of 1.547-1.145 eV by applying biaxial tensile strain. Monolayer CrOBr changes from FM state to AFM state when tensile strain increases to 8%. The MAE of monolayer CrOBr reaches a large value of −0.057 meV/f.u. at tensile strain of 8%, which is enhanced by 235% compared to that of unstrained system. The tunable MAE and electronic structure indicate that monolayer CrOBr may be a promising candidate in spintronic devices.

Two-dimensional (2D) ferromagnetic material with a sizable magnetic anisotropy energy (MAE) is crucial for exploring and developing the characteristics of spintronic devices. Using first-principles calculations, we study the electronic and magnetic properties of CoB6 monolayer. The CoB6 monolayer shows metallic ferromagnetism and exhibits in-plane magnetic anisotropy. The MAE of CoB6 monolayer is induced by Co atom, its maximum MAE is −0.181 meV/Co at θ = 90 ° ([010] direction), but minimum of −0.157 meV/Co at θ = 0 ° ([100] direction). It is worth noting that MAE of CoB6 monolayer gradually increases when tensile strain gets higher. When tensile strain increases to 8%, the maximum MAE of CoB6 monolayer is estimated to be −0.236 meV/Co at θ = 90 ° , which is enhanced by 50% compared with that of unstrained system. These results may stimulate the development of spintronic nanodevices based on 2D ferromagnetic materials.

Ferromagnetic (FM) materials with high Curie temperature, large spin polarization ratio and large perpendicular magnetic anisotropic (PMA) are the basis of constructing practical spintronic devices. Using first-principles calculations, electronic property, magnetism and magnetic anisotropic energy (MAE) of penta-MnN2 monolayer are investigated. The calculated results indicate that penta-MnN2 monolayer is FM half-metal and exhibits PMA. The PMA is induced by Mn atom of 0.207 meV/Mn, which is one or two orders of magnitude larger than those of bulk Co (−65 μeV/atom), Fe (−1.4 μeV/atom) and Ni (2.7 μeV/atom). It is worth noting that the structure, magnetism and MAE of penta-MnN2 monolayer can be manipulated by applying biaxial strain. By applying tensile strain of 3%, penta-MnN2 monolayer has a second energy minimum and remains the original crystalline symmetry, but the N–N bond length has a sudden change. The MAE of Mn atom in penta-MnN2 monolayer can be enhanced by 21% with compressive strain compared to the unstrained systems. Meanwhile, the MAE decreases with the increase of tensile strain, and it exhibits a more significant decrease due to the sudden drop of N–N bond with tensile strain. These results may broaden the development of two-dimensional (2D) FM materials, which have potential applications in 2D spintronic nanodevices.

As the study about the human body goes forward, some breakthrough in human biological signals is made, especially in EEG signal. At the same time, people are getting to know more about the benefits of EEG. Therefore, EEG research is enjoying a stronger demand around the world. Nowadays, EEG research is carried in several fields and different stages, such as the acquisition of EEG, the processing of EEG, energy recovery of EEG, etc. Scholars are mainly searching for behavioral and electrophysiology, neural network, multi-lead electroencephalogram, non-invasive brain imaging technology, etc. And the current research frontier and the main trend is the comprehensive study of brain function and disease at the molecular, cellular, and global levels and the understanding of the brain structure principle from the brain development process. In this review, three aspects are chosen to study: the processing of EEG, the acquisition of EEG and EEG application. Four EEG acquisition methods, five ways of EEG processing system and three patterns of application are introduced. EEG acquisition system comprises scalp electrodes, a signal isolation amplifier, an analog-to-digital converter, and a wireless transmission module. Low power consumption, small size and portability are the main directions. The research status and difficulties of suitable electrodes, high integration acquisition chip, and analysis algorithm are analyzed and predicted. Due to the rapid development of EEG signal processing, the application of EEG has developed from medical rehabilitation to driving safety, education assistance, and entertainment consumption.

Based on first-principles calculations, we systematically investigate the stability, structural and electronic properties of two-dimensional (2D) hydrogenated tetragonal stanene (tetra-SnH). The calculated binding and formation energies, AIMD simulations and phonon dispersion show 2D tetra-SnH is stable. The hydrogenation also affects the electronic structure of tetragonal stanene monolayer, which is transformed from semimetal to semiconductor with a direct band gap. The optical response of 2D tetra-SnH is isotropic along the in-plane directions. Our results demonstrate that hydrogenation is an efficient way to modulate the electronic properties of tetragonal stanene, and provides a new prospect for the potential application in nanoelectronics.

We report on metal-semiconductor-metal ultraviolet photodetectors based on a ZnO film/Pt nanoparticles/ZnO film composite structure. The responsivity of the sandwich photodetector is 45 times greater for the back-illuminated than the front-illuminated. Surprisingly, the responsivity of a ZnO photodetector without the Pt nanoparticles has rather feeble enhancement under the same conditions (illumination from back and front). The responsivity of the sandwich photodetector can be enhanced from 14 to 45 times by adjusting the embedded depth of the Pt nanoparticles. Combining this result with the optical absorption spectra of ZnO films with and without Pt nanoparticles, we can reasonable to deduce the underlying mechanism and attribute it to the coupling of the localized surface plasmon from Pt nanoparticles with ZnO films. These results demonstrate a method to control the responsivity enhancement by adjusting the embedded depth of the Pt nanoparticles in the sandwich photodetector.

Based on the ZnO/Pt nanoparticles/ZnO multilayer films by magnetron sputtering method, we elaborate the ultraviolet (UV) photodetectors and deduce that they provide an ideal platform for highly using efficient surface plasmon (SP) modes. By only adjusting the thickness of the top layer and remaining other conditions unchanged, we draw a conclusion that the responsivity of the sandwich photodetector can be drastically increased from 0.08 to 0.40 A/W. It firmly provides for our findings that the responsivity enhancement factors without Pt nanoparticles (NPs) are apparently smaller than those by means of introducing Pt NPs. This can be ascribed to the SP of Pt NPs. The near-field effect of SP results in the dependence of the responsivity enhancement of ZnO films on the top layer film thickness. Which are in good agreement with theoretical calculations.

A series of ultraviolet photodetectors have been fabricated on MgZnO films, the molar ratio of Mg/Zn is about 18%, which grown by a radio frequency magnetron sputtering technique. Metal (Pt) nanoparticles are sputtered on the surface of the MgZnO film, embedded into the film and deposited on the substrate to improve the performances of the photodetectors, respectively. I–V characteristics under dark are improved by sputtering Pt nanoparticles on the surface of MgZnO film. Meanwhile, the photoresponse of the photodetectors with Pt nanoparticles are enhanced, especially when nanoparticles embedded into the MgZnO film, the peak responsivity is enhanced from 0.134 to 0.349 A/W at 30 V bias. It is demonstrated that the key role of Pt nanoparticles in the performance enhancement of MgZnO-based photodetectors, revealing the applicability of metal nanoparticles in ultraviolet photodetectors.

The metal-semiconductor-metal (MSM) structured ZnO photodetectors with same electrode spacings are made by radio frequency magnetron sputtering. A study of the thermal annealing effects on photodetectors with sequential annealing temperature (300, 400, 500 and 600 ℃).The responsivity of the photodetector was enlarged greatly after annealing the MSM device. Meanwhile, the enhancement in the dark current that resulted from the experiment was accompanied by the increasing annealing temperature. These results demonstrate that a simple route to improve the responsivities of photodetectors can be realized easily by annealing the devices.

Two sets of ZnO ultraviolet photodetectors were fabricated on the quartz and sapphire, respectively. Because of the different lattice matching of the substrate for the ZnO, the ZnO thin film based on the high matching substrate has a better crystalline quality and it is more sensitive to ultraviolet light. The ultraviolet photodetector based on the sapphire not only has a stronger absorption for the light, but also has a higher photo response than the ultraviolet photodetector based on the quartz. Which will have a profound influence for fabricating the excellent photodetectors.

By integrating ZnO and MgZnO films onto a quartz substrate (both films with the same growth time), the ultraviolet photodetectors (Au/ZnO/MgZnO/SiO2 and Au/MgZnO/ZnO/SiO2 structured photodetectors) have been fabricated. The responsivity peaks blue-shift from 380 to 370 nm (380 to 375 nm) by increasing the bias voltage in 1.0 h (1.5 h) photodetectors, which is denoted by the growth time of one layer of the films. More interestingly, the Au/MgZnO/ZnO/SiO2 photodetectors shift the same response wavelength range at smaller bias voltages than the Au/ZnO/MgZnO/SiO2 photodetectors. The results are well-rationalized in term of the role played by the double-layer structure.