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Based on the 3D Dirac semimetals (DSM) supported tilted double elliptical resonators, the tunable propagation properties of quasi-bound in continuum (BIC) resonance have been investigated in the THz regime, including the effects of rotation angles, DSM Fermi level, and the configuration of resonators. The results manifest that by altering the rotation angle of elliptical resonator, an obvious sharp BIC transmission dip is observed with the Q-factor of more than 60. The DSM Fermi level affects the BIC resonance significantly, a sharp resonant dip is observed if Fermi level is larger than 0.05 eV, resulting from the contributions of reflection and absorption. If Fermi level changes in the range of 0.01–0.15 eV, the amplitude and frequency modulation depths are 92.75 and 44.99%, respectively. Additionally, with the modified configurations of elliptical resonators, e.g. inserting a dielectric hole into the elliptical resonator, another transmission dip resonance is excited and indicates a red shift with the increase of the permittivity of the dielectric filling material. The results are very helpful to understand the mechanisms of DSM plasmonic structures and develop novel tunable THz devices, such as modulators, filters, and sensors in the future.

By depositing the trapezoidal dielectric stripe on top of the 3D Dirac semimetal (DSM) hybrid plasmonic waveguide, the thermal tunable propagation properties have been systematically investigated in the terahertz regime, taking into account the influences of the structure of the dielectric stripe, temperature and frequency. The results manifest that as the upper side width of the trapezoidal stripe increases, the propagation length and figure of merit (FOM) both decrease. The propagation properties of hybrid modes are closely associated with temperature, in that when the temperature changes in the scope of 3-600 K, the modulation depth of propagation length is more than 96%. Additionally, at the balance point of plasmonic and dielectric modes, the propagation length and FOM manifest strong peaks and indicate an obvious blue shift with the increase of temperature. Furthermore, the propagation properties can be improved significantly with a Si-SiO2 hybrid dielectric stripe structure, e.g., on the condition that the Si layer width is 5 µm, the maximum value of the propagation length reaches more than 6.46 × 105 µm, which is tens of times larger than those pure SiO2 (4.67 × 104 µm) and Si (1.15 × 104 µm) stripe. The results are very helpful for the design of novel plasmonic devices, such as cutting-edge modulator, lasers and filters.

Based on asymmetric graphene ellipses, the tunable propagation characteristics of metamaterial absorber (MMA) have been investigated in the THz region. Two distinct absorption peaks of 84% and 90% are observed at 1.06 THz and 1.67 THz, respectively. Besides a high Q factor exceeding 20, the Fano resonance can also be modulated in a wide range (e.g., the frequency modulation depth reaches more than 43.8% if the Fermi energy level changes in the range of 0.2–1.0 eV). Additionally, a bidirectional THz MMA is achieved by replacing the metal substrate with a uniform graphene layer. If the terahertz wave is incident in the forward direction, the proposed graphene double stripe microstructure shows a typical MMA with its absorption reaching 88%. On the other hand, if the terahertz wave is incident in the reverse direction, the graphene double stripe microstructure behaves as a reflective modulator, and its amplitude and frequency MD will reach 60% and 85%. These results contribute to the design of tunable THz devices, such as filters, absorbers, and modulators.

BiFeO3 (BFO) and Bi1−x La x Fe0.9Cr0.1O3 (x = 0.1–0.2, BLFC x=0.1–0.2) ceramics were prepared by modified solid-state reaction. The influence of La/Cr codoping on the microstructure, leakage, dielectric and magnetic properties of BFO was studied. It is found that the La/Cr codoping can induce a structural transformation from a rhombohedral (R3c) phase to a triclinic (P1) phase, suppress the formation of oxygen vacancies and modulate the spiral spin structure. With the increasing La concentration, the leakage current density can be diminished by over two orders of magnitude compared with undoped BFO, in a reasonable range for device applications. The dielectric loss follows almost the same trend as the leakage current, while the dielectric constant is raised to 400.8 at 100 kHz for x = 0.2, over eight times larger than that of undoped BFO. The substantially enhanced magnetization can be mainly attributed to the suppression of the spiral spin structure and a new ferromagnetic Fe3+–O2−–Cr3+ super-exchange interaction. More interestingly, abrupt changes are observed around x = 0.15, not only in microstructure but also in electrical and magnetic properties, which may indirectly reflect the coupling effect among them. The BLFC x=0.2 ceramic shows the highest magnetization and dielectric constant together with the lowest leakage current and dielectric loss. The results indicate that the La/Cr codoping can effectively improve the magnetic and electrical properties of BFO ceramic for potential applications in magnetoelectric devices.

The influences of different kinds of phonon scatterings (i.e., acoustic (AC) phonon, impurity, and longitudinal optical (LO) phonon scatterings) on the tunable propagation properties of graphene metamaterials structures have been investigated, also including the effects of graphene pattern structures, Fermi levels, and operation frequencies. The results manifested that, at room temperature, AC phonon scattering dominated, while with the increase in temperature, the LO phonon scattering increased significantly and played a dominate role if temperature goes beyond 600 K. Due to the phonon scatterings, the resonant properties of the graphene metamaterial structure indicated an optimum value (about 0.5&ndash, 0.8 eV) with the increase in Fermi level, which were different from the existing results. The results are very helpful to understand the tunable mechanisms of graphene functional devices, sensors, modulators, and antennas.

Recently, deep learning-based models have exhibited remarkable performance for image manipulation detection. However, most of them suffer from poor universality of handcrafted or predetermined features. Meanwhile, they only focus on manipulation localization and overlook manipulation classification. To address these issues, we propose a coarse-to-fine architecture named Constrained R-CNN for complete and accurate image forensics. First, the learnable manipulation feature extractor learns a unified feature representation directly from data. Second, the attention region proposal network effectively discriminates manipulated regions for the next manipulation classification and coarse localization. Then, the skip structure fuses low-level and high-level information to refine the global manipulation features. Finally, the coarse localization information guides the model to further learn the finer local features and segment out the tampered region. Experimental results show that our model achieves state-of-the-art performance. Especially, the F1 score is increased by 28.4%, 73.2%, 13.3% on the NIST16, COVERAGE, and Columbia dataset., Accepted to IEEE International Conference on Multimedia and Expo (ICME2020)

Cu(Cr0.96−xMg0.04Mnx)O2−δ ceramics (0 ≤ x ≤ 15 at.%) were prepared by solid-state reaction. The influence of Mg acceptor codoping on microstructure, magnetic, and optical properties was studied. The codoping with Mg acceptors and the resulting lattice expansion are both favorable for the enhancement of hole density. Furthermore, the lower valence of Mg2+ compared with Cr3+ enables the mixed valence state of Mn ions: Mn3+ and Mn4+, and hence induces the hole-mediated double-exchange mechanism not only between Mn3+ and Cr3+ but also between Mn3+ and Mn4+. The coexistence of two ferromagnetic interactions and the high hole density are responsible for the improved saturation magnetization and Curie temperature. For photoluminescence, an unusual near-infrared emission at 1.5 eV is observed in the Mn-contained samples and can be attributed to the internal transition between the e and t2 states of the Mn3+ impurity band. The emission intensity is primarily affected by two factors: the Mn3+ concentration and the position of the Fermi level. The results show that codoping with Mg acceptors is an effective way to strengthen the hole-mediated ferromagnetic interactions in CuCrO2 delafossite.

The tunable plasmonic induced transparency has been theoretically investigated based on graphene patterns/SiO2/Si/polymer multilayer structure in the terahertz regime, including the effects of graphene Fermi level, structural parameters and operation frequency. The results manifest that obvious Fano peak can be observed and efficiently modulated because of the strong coupling between incident light and graphene pattern structures. As Fermi level increases, the peak amplitude of Fano resonance increases, and the resonant peak position shifts to high frequency. The amplitude modulation depth of Fano curves is about 40% on condition that the Fermi level changes in the scope of 0.2-1.0 eV. With the distance between cut wire and double semi-circular patterns increases, the peak amplitude and figure of merit increases. The results are very helpful to develop novel graphene plasmonic devices (e.g. sensors, modulators, and antenna) and find potential applications in the fields of biomedical sensing and wireless communications.

Cu(Cr1−xMnx)O2 delafossite thin films (0 ⩽ x ⩽ 15 at.%), with a c-axis quasi-epitaxial orientation, were prepared by pulsed laser deposition. The effects of Mn content on microstructure and physical properties were investigated. Both the variation of lattice constant c and X-ray photoelectron spectroscopy reveal that the Mn ions substitute for Cr3+ as Mn3+ and Mn4+. The proportion of Mn4+ is gradually increased with the Mn doping, leading to the changes of hole density and mobility. As a result, the p-type conductivity is decreased at first and then increased. The conduction mechanism is thermal activation between 130 and 300 K. It is indicated that the PLD method and the Mn3+–O–Mn4+ and Mn3+–O–Cr3+ double-exchange interactions are favorable to the high hole density and mobility, respectively. Meanwhile, the double-exchange interactions produce the near-room-temperature ferromagnetism. The saturation magnetization and Curie temperature are gradually increased with the Mn content. For optical properties, all thin films have a comparatively high transmittance for visible light, with the highest value 70% for x = 15 at.% at the wavelength of 750 nm. As increasing the Mn content, the transparency and direct optical bandgap exhibit the similar trend as the hole density. With the relatively balanced electrical, magnetic and optical properties, these pulsed-laser-deposition-grown Cu(Cr1−xMnx)O2 thin films are expected to become a promising p-type transparent diluted magnetic semiconductor material.

In this work, the solid solutions of 0.8Pb(Zr 0.52 Ti 0.48 )O 3 −(0.2− x )Pb(Zn 1/3 Nb 2/3 )O 3 − x Pb(Al 1/2 Nb 1/2 )O 3 (PZT–PZN– x PAN) were designed and fabricated via the traditional solid state reaction method. The dielectric, ferroelectric, piezoelectric properties of PZT–PZN– x PAN solid solutions were investigated in detail. The optimum electric properties of P m = 46.3 μC/cm 2 , P r = 42 μC/cm 2 , P r / P m = 90.5%, S total = 0.48%, d 33 = 410 pC/N, and T c = 283 °C were achieved in PZT–PZN– x PAN ceramics with x = 0.02. A large strain response of ∼0.24% with normalized strain S max / E max as high as 767 pm/V was obtained for the PZT–PZN–0.1PAN under a low electric field of ∼3 kV/mm at room-temperature.

Fe-doped CuCrO 2 delafossite thin films, with a c -axis quasi-epitaxial orientation, were prepared by pulsed laser deposition, exhibiting reasonably good p-type conductivity, ferromagnetism with T C well above room temperature, and comparatively high transparency in the visible range. The influence of Fe concentration (0–15 at%) on microstructure and physical properties was investigated. The substitution of Fe 3+ for Cr 3+ induces the lattice expansion, which is favorable for the oxygen insertion and thus produces the higher hole concentration. Accordingly the p-type conductivity is remarkably improved to 28 S cm −1 . Moreover, the introduction of Fe 3+ leads to the hole-mediated Fe 3+ –Cr 3+ super-exchange coupling responsible for the room-temperature ferromagnetism. The saturation magnetization is enhanced as the Fe concentration increases, with Curie temperature ⩾550 K. Nevertheless, the transparency in the visible range does not profit from the Fe doping. The transmittance is diminished from 75% for x = 0 to 65% for x = 15 at% at the wavelength of 750 nm, which can be interpreted as the strengthened scattering of photons by charge carriers. The direct optical bandgap is modulated by 3.8% via the Fe addition. The results show that the substitution of iron for chromium is an effective way to achieve high-performance CuCrO 2 thin films which are supposed to become a promising p-type transparent diluted magnetic semiconductor material.

The preferred c-oriented Cu(Cr1−xFex)O2 ceramics (0 ⩽ x ⩽ 15 at.%) were prepared by solid-state reaction. The effects of Fe concentration on microstructure, morphology and magnetism were investigated. All the samples have a pure 3R-CuCrO2 delafossite structure, with a stress-induced preferential orientation. The lattice expansion supports the Fe entrance into the Cr sublattice in the form of Fe3+, which is further certified by the X-ray photoelectron spectra and the Mossbauer spectra. The Mossbauer study also reveals a preferential growth orientation and an increase of Fe–O bond lengths with the Fe addition, matching well with the X-ray diffraction analysis. Ferromagnetism is achieved in the Fe-doped samples with Curie temperatures higher than 246 K, which is expected to originate from the hole-mediated Fe3+–Cr3+ super-exchange interaction. The saturation magnetization of this CuMO2 delafossite (M = Cr, Fe) is decreased almost linearly with the increasing Fe concentration, due to the combined influence of the number of the M–M pairs, the M–M distances and the hole concentration. The present work indicates that Fe-doped CuCrO2 is a dilute magnetic semiconductor and Curie temperature can be remarkably enhanced to close to room temperature by Fe doping.

Using p-type transparent conducting CuCrO 2 as a host material, (Cu 1− x Fe x )CrO 2 (0 ≤ x ≤ 6 at.%) and Cu(Cr 1− y Fe y )O 2 (0 ≤ y ≤ 6 at.%) nanocrystals were prepared by combining solid-state reaction and ball milling. The microstructure, morphology, optical and magnetic properties were characterized by X-ray diffraction, atomic force microscopy, diffuse reflectance spectroscopy and vibrating sample magnetometer. It is found that all the samples have a single CuCrO 2 delafossite structure. The variations in lattice constants support the Fe entrance into the Cu and Cr sublattices, respectively, in (Cu 1− x Fe x )CrO 2 and Cu(Cr 1− y Fe y )O 2 . The gradual increase of optical bandgap with the Fe content and the low-temperature ferromagnetism are observed in two series of samples. The present work indicates that Fe-doped CuCrO 2 is a dilute magnetic semiconductor and the Curie temperature can be expected to enhance by the optical bandgap modulation.

Tunable propagation properties of graphene asymmetrical bowtie metamaterials (MMs) structures have been investigated in the terahertz regime, including the effects of graphene Fermi levels, structural parameters and operation frequencies. Because of its thin film thickness, the strong resonant curves of the proposed graphene MMs structures are dominated by the plasmonic mode instead of the Fabry-Perot mode for the metal structures. Compared with existing tunable graphene devices, the sharp Fano resonant curve manifests a large Q-factor of more than 40. In addition, as the width of graphene bowtie aperture increases, the resonant frequency dip shifts low frequency, and the resonant amplitude and figure of merit increase. The results are very helpful in order to understand the tunable mechanisms of graphene components and design high sensitivity functional devices, sensors, modulators, and antenna.

The (Ba 0.8 K 0.2 )(Ti 0.3 Fe 0.7 )O 3 ceramic was prepared by solid-state reaction, and post-annealed in oxygen ambient. By comparison with Ba(Ti 0.3 Fe 0.7 )O 3 made under identical conditions, the effect of non-isovalent A-site substitution of K + on microstructure and magnetism of as-prepared and annealed Ba(Ti 0.3 Fe 0.7 )O 3 samples was investigated using X-ray diffraction, Mossbauer spectroscopy, vibrating sample magnetometer and iodometric titration. It is found that all samples have a single 6H-BaTiO 3 -type hexagonal perovskite structure without any impurities detected, regardless of A-site K + substitution or annealing. In the as-prepared state, non-isovalent A-site substitution of K + induces the variation in Fe occupational site, resulting in the disappearance of room-temperature ferromagnetism. The super-exchange interactions of Fe 3+ at tetrahedral and octahedral Ti sites determine the paramagnetism of (Ba 0.8 K 0.2 )(Ti 0.3 Fe 0.7 )O 3 . During the O 2 annealing process, the presence of Fe 4+ , an unusual valence for iron, besides Fe 3+ is observed, both distributed over octahedral Ti site. By A-site substitution of K + with a lower valence than Ba 2+ , the charge compensation mechanism is further enhanced, and thus more Fe 3+ ions are oxidized to Fe 4+ in annealed (Ba 0.8 K 0.2 )(Ti 0.3 Fe 0.7 )O 3 . Consequently, the ferromagnetic Fe 4+ –O 2− –Fe 4+ super-exchange interactions are strengthened, which leads not only to a paramagnetism–ferromagnetism transition but also to a higher saturation magnetization compared with annealed Ba(Ti 0.3 Fe 0.7 )O 3 .

Ba(Ti 0.65 M 0.05 Fe 0.3 )O 3 ( M = Cr, Mn and Ni) ceramics were prepared by solid-state reaction, and post-annealed in vacuum and oxygen, respectively. Mossbauer spectroscopy was used to investigate the local environments of Fe atoms. Combined with the configuration of the other transition metal M , the mechanisms responsible for magnetism were discussed for different samples. The results show that all samples are single-phase with a 6H–BaTiO 3 -type hexagonal perovskite structure. The as-prepared ceramics are all paramagnetic, while the annealed ones are all ferromagnetic at room temperature. The origin of ferromagnetism changes with doping element and annealing atmosphere, including the double-exchange mechanism of transition metal M with mixed valences, the super-exchange mechanism of Fe 3+ in different occupational sites, and the super-exchange mechanism of Fe 4+ –O 2− –Fe 4+ .

By using the graphene-SiO2-Si-dielectrics-metallic ground plane (GSiO2SiDM) structures, we investigate the tunable properties of graphene metamaterials (MMs) absorbers in the terahertz region, including the effects of operation frequency, Fermi level, and graphene structure patterns. The results manifest that the graphene tunable GSiO2SiDM structure can achieve net absorption by changing structure parameters and the Fermi level of graphene layer. The resonant absorption and reflection curves of the GSiO2SiDM structures can be shifted in a wide range via controlling the applied electric fields. The modulation depth of resonant amplitude and frequency can reach more than 60% and 30%, respectively. The resonant peak (dip) of the absorption (reflection) curves shift to high frequency with the increase of Fermi level of the graphene layer. Due to broad absorption curve, the graphene MMs absorbers structures are suitable for the fabrication of broad absorber. The results are very useful to design novel devices, such as thermal detectors, imager, and biosensors.