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Electromagnetic interference (EMI) shielding materials have received considerable attention in recent years. The EMI shielding effectiveness (SE) of materials depends on not only their composition but also their microstructures. Among various microstructure prototypes, porous structures provide the advantages of low density and high terahertz wave absorption. In this study, by using carbonised wood (CW) as a template, 1-mm-thick MAX@CW composites (Ti2AlC@CW, V2AlC@CW, and Cr2AlC@CW) with a porous structure were fabricated through the molten salt method. The MAX@CW composites led to the formation of a conductive network and multilayer interface, which resulted in improved EMI SE. The average EMI SE values of the three MAX@CW composites were > 45 dB in the frequency of 0.6–1.6 THz. Among the composites, V2AlC@CW exhibited the highest average EMI SE of 55 dB.

With the development of terahertz (THz) technology, there is a booming demand of THz shielding/absorption materials to avoid electromagnetic interference (EMI) or pollution. Paints that can be fast solidified to form a film and stably adherent on arbitrary substrates are especially desired for the shielding/absorption applications. Recently, MXenes with high electron conductivity and hydrophilicity have attracted a great interest for EMI shielding. Here, we demonstrate a copolymer-polyacrylic latex (PAL) based MXene waterborne paint (MWP), which not only has strong THz EMI shielding/absorption efficiency but also can easily adhere onto various substrates that are commonly used in the THz band. The viscosity of MWP can be tuned by adjusting the colloidal and viscous forces, and the cyano group in PAL provides a strong intermolecular polar interaction between MWP and the substrate. As a result, a 38.3-μm-thick MWP on quartz exhibits EMI shielding value of 64.9 dB, and an excellent reflection-loss of 32.8 dB is obtained on MWP coated sponge foam. This substrate-independent MWP provides a simple and efficient way to achieving high-performance THz shielding/absorption.

Terahertz (THz) communications have been widely envisioned as a promising enabler to provide adequate bandwidth and achieve ultra-high data rates for sixth generation (6G) wireless networks. In order to mitigate blockage vulnerability caused by serious propagation attenuation and poor diffraction of THz waves, an intelligent reflecting surface (IRS), which manipulates the propagation of incident electromagnetic waves in a programmable manner by adjusting the phase shifts of passive reflecting elements, is proposed to create smart radio environments, improve spectrum efficiency and enhance coverage capability. Firstly, some prospective application scenarios driven by the IRS empowered THz communications are introduced, including wireless mobile communications, secure communications, unmanned aerial vehicle (UAV) scenario, mobile edge computing (MEC) scenario and THz localization scenario. Then, we discuss the enabling technologies employed by the IRS empowered THz system, involving hardware design, channel estimation, capacity optimization, beam control, resource allocation and robustness design. Moreover, the arising challenges and open problems encountered in the future IRS empowered THz communications are also highlighted. Concretely, these emerging problems possibly originate from channel modeling, new material exploration, experimental IRS testbeds and intensive deployment. Ultimately, the combination of THz communications and IRS is capable of accelerating the development of 6G wireless networks.

The increasing development of terahertz (THz) technology has led to various potential applications in THz imaging, spectroscopy and communications. These devices capable of actively manipulating the amplitude, phase and frequency of THz waves are thus gaining numerous interests. All-optical silicon-based spatial terahertz modulators (STMs), as a simple, cost-effective, and reconfigurable technique, are standing the focus of research. Beginning with a fundamental concept of THz radiation, this paper systematically summarized the modulation mechanism and theoretical model for this kind of STM, reviewed the recent advancements in THz functional devices implemented by this optical method and yet, discussed the performance-improved measures with an emphasis on the reflection reduction. Despite that, there has been considerable progress in realizing high-performance STMs, and novel design is urgent to realize higher modulation rate and more functionality.

Graphene/silicon hybrid diodes have been proven efficient for broad-band terahertz (THz) modulation with electrical and optical stimuli. However, the optimal protocol to apply optical and electrical stimuli has not been well-determined to obtain the best performance. Here, band theory of the hybrid diode has been used to analyze the underlying modulation mechanism and to help determine the optimal modulation protocol. Monolayer gold nanoparticles (AuNPs) were coated on the graphene/silicon hybrid diode to enhance the modulation performance. Both high modulation depth (∼93%) and modulation rate (∼4.6 kHz) were obtained with the AuNP-coated hybrid diode using the proper modulation method. To explore the underlying mechanism for a graphene/silicon hybrid diode THz modulator, this work could throw light on other material systems for THz modulation.

Dynamic beam steering with unlimited angular range and fast speed remains a challenge in the terahertz gap, which is urgently needed for next-generation target tracking, wireless communications, and imaging applications. Different from metasurface phased arrays with element-level phase control, here we steer the beam by globally engineering the diffraction of two cascaded metagratings during in-plane rotation. Benefiting from large-angle diffraction and flexible on/off control of the diffraction channels, a pair of metagratings with optimized supercells and proper orientation successfully directs the incoming beam towards any arbitrary direction over the transmission half space, with the steering speed improved more than twice that of the small-angle diffractive designs. Single-beam and dual-beam steering within the solid angle of 1.56 π and elevation angle of ± 77 ° has been demonstrated with average throughput efficiency of 41.4% at 0.14 THz, which can be generalized to multiple-beam cases. The dual diffraction engineering scheme offers a clear physical picture for beamforming and greatly simplifies the device structure, with additional merits of large aperture and low power consumption.

We report the magneto-optical Faraday response of bismuth-gadolinium-substituted rare-earth iron garnet at terahertz frequencies ranging from 100 GHz to 1.2 THz. The maximum transmittance of ±45° component is about 60% near the frequency point of 0.63 THz. When the external magnetic field change from –100 mT to +100 mT, the Faraday rotation angle is between –6° and +7.5°. The overall change of ellipticity is relatively small. The maximum value of the Verdet constant is about 260 °/mm/T at 0.1 THz and then gradually decreases to 80 °/mm/T at 1.2 THz. Within the considered frequency range, the thick film exhibits magnetically tunable, non-reciprocal characters and a strong magneto-optical effect within a small external magnetic field at room temperature, which will be widely used for the terahertz isolators, circulators, nonreciprocal phase shifters, and magneto-optical modulators.

With the development of terahertz (THz) technology, there is a booming demand of THz shielding/absorption materials to avoid electromagnetic interference (EMI) or pollution. Here, we report on a series of THz absorption or shielding materials fabricated from 2D MXene nanosheets. By using simple dip-coating or spray-coating method, lightweight, flexible, thin, and hydrophobic absorption foam are obtained, which shows ultrahigh THz absorption property over 99.99% under the 100% qualified frequency bandwidth ranging from 0.3 to 1.65 THz. Our results indicate that the combination of 2D materials with porous polymer paves a way to achieving high performance THz absorber, which is of significance in electromagnetic interference shielding, 6G communications and beyond.

The terahertz optical and magneto-optical response of Bi-substituted rare-earth iron garnet film were studied from 0.2 to 1.2 THz. The thickness of film is 406 μm. The maximum transmittance is over 55% near the frequency point of 0.35 THz. When the external magnetic field change from -100 mT to +100 mT, the Faraday rotation angle is between -5° and +7°. Large Verdet constants approaching 270 °/T/mm are found. The overall change of ellipticity is relatively small.

Utilizing the in-situ reducing method, a reduced graphene oxide (rGO) paper for 13~14 um was obtained and exhibits great Terahertz (THz) absorbing capability. The absorption of rGO paper exceeds 43% in the whole frequency band from 0.3~1.2 THz and maximum absorption reaches 59.33% at 1.13 THz. This makes it possible to realize ultra-thin broadband THz absorbing materials.

A novel horn fed terahertz transmitarrays(TAs) antenna, which is based on improved planar phase shifting surfaces, is presented in this paper. Based on the principle of scattering-pattern shift theory on metasurfaces [2], the improved planar phase shifting surfaces (PPSSs) are designed. The improved PPSSs have low insertion loss and the phase shift range from 0° to 360°. The antenna has the advantages of higher frequency band, low profile structure, higher gain, and wider beam scanning angle. The full-wave simulation results demonstrate that the designed antenna enables beam steering in H-plane at the 99GHz-101GHz working frequency, with a peak gain of 23.6dBi at 100GHz. And the beam scanning range of the antenna reaches±35°.

With a surface-passivated GaAs, a performance-enhanced, ultrafast, all-optical spatial terahertz modulator was realized. The lower surface recombination rate and longer carrier lifetime induced by passivation render passivated-GaAs superior to pure-GaAs in modulation depth (MD) at a little sacrifice of response rate, eliminating its dependence on intensive laser. At low photodoping levels, the maximum of 1.6-times enhancement in MD was achieved. When the power increased to 60 mW, comparable MD of 94% to that in Si-based one at equivalent photodoping, and simultaneously ultrafast response of 69 MHz which is much faster than 100-kHz level by Si-based, was obtained. This performance-enhanced, ultrafast modulator is highly desired in actual situations and offers a viable avenue to breaking the compromise between MD and speed.

MXene Ti3C2/TiO2 hybrids were successfully synthesized through a simple calcination of F-terminated Ti3C2. The resultant Ti3C2/TiO2 composite photocatalysts retained a 2D multilayer structure like MXene Ti3C2, and TiO2 exhibited a truncated octahedral bipyramidal structure with exposed (001) facets under the participation of fluorine ions. The residual Ti3C2 could act as a co-catalyst to enhance the photocatalytic H2 production activity by capturing photogenerated electrons from TiO2 because of its electron reservoir feature and suitable Fermi level. The (101)–(001) surface heterojunction of the truncated octahedral bipyramidal TiO2 further accelerated the separation of photogenerated carriers. As a result, the Ti3C2/TiO2 hybrids with calcining F-terminated Ti3C2 exhibited photocatalytic hydrogen production that is twofold higher than that of Ti3C2/TiO2 hybrids with calcining OH-terminated Ti3C2. This work presented a new strategy to prepare MXene Ti3C2/TiO2 hybrids for photoconversion applications.

Electromagnetic interference (EMI) shielding materials have received great interests in recent years. The EMI shielding effectiveness (SE) of materials not only depends on their composition, but also is influenced by their microstructures. Among various microstructure prototypes, porous structure has special advantage of low density and high electromagnetic wave reflections ability. Herein, a MAX@CW composite (Ti2AlC@CW, V2AlC@CW, Cr2AlC@CW) with porous structure is fabricated through a molten salt method by using carbonized wood (CW) as template. The MAX@CW forms conductive network constructions and rich interface that can further improve the EMI shielding effectiveness. The average EMI shielding effectiveness of the three kinds of MAX@CW with the thickness of 1 mm are higher than 45 dB in the frequency range of 0.6 ~ 1.6 THz. Among them, V2AlC@CW show the best EMI shielding effectiveness with the average value of 55 dB.

Spatial light modulators (SLMs) exhibited the powerful capability of controlling the electromagnetic wave. They have found numerous applications at terahertz (THz) frequencies, including wireless communication, digital holography, and compressive imaging. However, the development towards large-scale, multi-level and multi-functional THz SLM encounters technical challenges. Here, we present an electrically programmable THz metamaterial consisting of an array of 8⊆8 pixels, in which the phase change material of vanadium dioxide (VO2) is embedded. After successfully suppressing the crosstalk from adjacent pixels, the THz wave could be modulated in a programmable manner. The switching speed of each pixel was on the order of 1 kHz. In particular, utilising the hysteresis effect of VO2, the memory effect is demonstrated. The THz amplitude of each pixel can be written and erased by individual current pulses. Furthermore, multi-state THz images could be generated and stored, with a retention time of more than 5 hours. This programmable metamaterial with memory effect can be extended to other frequency bands and opens a route for electromagnetic information processing.

Diffusional growth in solution is the most efficient method to grow monodisperse colloidal nanoparticles. Instead of calculating for a single nanoparticle, here the growth of an ensemble of nanoparticles has been numerically simulated by the generalized growth rate of nanoparticles, which has been deduced in our previous work from the very fundamental laws and equations. By doing that, the dynamic interaction among nanoparticles through monomer attachment and detachment can be clearly revealed. The constant and diminishing monomer concentrations have been simulated separately and compared together. The simulations give the growth dynamics of batch nanoparticles across a broad range of conditions, where diffusivity, adsorption, and concentration of monomers play a significant role. The relations between the average radius and time, the variance and time, and the variance and average radius have been obtained for different growth conditions. The average radius–time curve can be well-fitted to E[R] = E[R0] +...

In this paper, a facile method was proposed to load CeO2 nanoparticles (NPs) on anodic TiO2 nanotube (NT) arrays, which leads to a formation of CeO2/TiO2 heterojunctions. Highly ordered anatase phase TiO2 NT arrays were fabricated by using anodic oxidation method, then these individual TiO2 NTs were used as tiny “nano-containers” to load a small amount of Ce(NO3)3 solutions. The loaded anodic TiO2 NTs were baked and heated to a high temperature of 450 °C, under which the Ce(NO3)3 would be thermally decomposed inside those nano-containers. After the thermal decomposition of Ce(NO3)3, cubic crystal CeO2 NPs were obtained and successfully loaded into the anodic TiO2 NT arrays. The prepared CeO2/TiO2 heterojunction structures were characterized by a variety of analytical technologies, including XRD, SEM, and Raman spectra. This study provides a facile approach to prepare CeO2/TiO2 films, which could be very useful for environmental and energy-related areas.

Fe3O4 nanoplates were fabricated by an anodic oxidation process and a subsequent water assisted crystallization process at low temperature, which was found to be very efficient and environmentally friendly. The as-prepared Fe3O4 nanoplates have hexagonal outlines with a thickness of about 20 nm. Tremendous grooves were distributed on the entire surfaces of the nanoplates, making the two-dimension nanoplates have a unique 3D morphology. Transmission electron microscopy results confirmed that the single-crystalline nature of the nanoplates was well maintained. Owing to the unique structures and porous morphologies, the as-prepared 3D nanoplates show excellent ability for absorbing solar energy and absorbing organic pollutants, which can be utilized for cleaning up water. Moreover, the Fe3O4 nanoplates show good magnetic properties that enable them to be easily collected and recycled. We believe this study will inspire the application of Fe3O4 nanoplates with 3D structures in energy and environmental areas.

Surface-modified semiconductors show enormous potential for opto-terahertz (THz) spatial modulation due to their enhanced modulation depth (MD) along with their inherent broad bandwidth. Taking full advantage of the surface modification, a performance-enhanced, all-optical, fast switchable THz modulator was achieved here based on the surface-passivated GaAs wafer. With a decreased surface recombination rate and prolonged carrier lifetime induced by passivation, S-passivated GaAs was demonstrated as a viable candidate to enhance THz modulation performance in MD, especially at low photodoping levels. Despite a degraded modulation rate owing to the longer carrier lifetime, this passivated GaAs modulator simultaneously realizes a fast modulation at a 69-MHz speed and as high an MD as ∼ 94 % in a spectral wideband of 0.2–1.2 THz. The results demonstrated a new strategy to alleviate the tradeoff between high MD and speed in contrast to bare surfaces or heterogeneous films/unusual geometry on semiconductors including Si, Ge, and GaAs.

Tuning the magnetic anisotropy of nanoparticle assemblies is critical for their applications such as on-chip magnetic electronic components and electromagnetic wave absorption. In this work, we developed a facile hierarchical self-assembly method to separately control the magnetic shape and magnetocrystalline anistropy of individual nanoparticle assemblies in arrays. Since magnetic nanoparticle assemblies in the array have the same size, shape and alignment, we are able to study the magnetic properties of individual nanoparticle assembly by measuring the whole arrays. The interplay between the two magnetic anisotropies was systematically studied for disk- and bar-shaped nanoparticle assemblies. Maximum magnetic anisotropy was obtained when the easy axis of magnetic nanoparticles was aligned along the long axes of the bar-shaped nanoparticles assemblies.

In this paper, graphene/Bi:YIG(50 nm)/p-Si hybrid nanostructured graphene field effect transistors (GFETs) were fabricated at the first time. A 50 nm Bi-doped Y 3 Fe 5 O 12 (Bi: YIG) garnet film was deposited using a vacuum RF sputtering technique, forming a nanometer thick high-K gate layer. With reduced Coulomb impurity scattering and cavity effect, a significantly improved modulation depth of 15% and modulation speed of 200 kHz have been successfully achieved with the YIG based GFETs. Moreover, since YIG is a magnetic insulator, we characterized and discussed the possibility of magnetic control of these graphene/Bi:YIG/p-Si hybrid structured THz modulators. A 7% enhancement of THz transmittance with applying an in-plane 22 Oe magnetic field has been revealed in the hybrid nanostructure, which provides a new route to realize electrical/magnetic functional modulators. The results show that graphene/Y 3 Fe 5 O 12 /Si hybrid nanostructures with good THz modulation performances have great potential for THz nondestructive evaluation as well as imaging applications.

Nanometer-thick Y 3 Fe 5 O 12 (YIG) films with very low damping constant have been fabricated on gadolinium gallium garnet substrates using chemical metal-organic decomposition method. Both the microstructure and ferromagnetic properties of the YIG thin films have been studied. High resolution X-ray diffraction result displayed an epitaxial structure of the YIG film. Surface morphology was investigated using an atomic force microscopy. The average surface roughness is about 0.8 ± 0.2 nm for a ∼50 nm thick epitaxial growth YIG film, which is comparable to the result of pulse laser deposition grown films. The coercivity field of the YIG film is around 1.5 Oe. Furthermore, magnetization dynamics properties were studied using a coplanar waveguide vector-network-analyzer ferromagnetic resonance spectrometer. The extracted damping constant is as low as 1.4 × 10 −3 . The results show that high quality nanometer YIG films can be obtained through chemical epitaxial growth method. It would be very useful for the garnet based spintronics applications.

With the continuous development of modern information society, all kinds of high-speed wireless communication application are emerging, while the traditional spectrum resources are becoming scarce.The terahertz (THz) band is an enabler for wireless communication (Beyond 5G) since the excellent characteristics of terahertz communication. It is extremely challenging to design the modulator for THz communications.In this paper, an electrically controlled THz metasurface was designed and fabricated based on the phase transition characteristic of Vanadium Dioxide (VO 2 ). It can switch between two resonant states with a large difference in transmittance. The experimental results show that the transmittance of perpendicular incident THz wave reaches to the highest at 0.31 THz. When the applied voltage is increased from 0 V to 8 V, the transmittance significantly decreases to the lowest value at 0.41 THz. The modulation depth can be up to 59% in the entire band of 0.2-0.6 THz. This work is of great significance for the research and development of THz modulators.

Spatial light modulators (SLM), which allow fast imaging with a single detector, are highly demanded for constructing cost-effective, highly sensitive and exceptionally compact terahertz (THz) imager. Here we designed and realized an optical THz-SLM based on micro-structured Si (MS-Si), where the irregular but compactly arranged Si micro-pyramids significantly decrease the reflectivity to ∼10% in the broad optical wavelength range of 400–1050nm, meanwhile greatly increases the active area for THz wave modulation. The novel silicon based modulator provides significant advantages over current THz SLMs in modulation bandwidth, speed and depth with the highest modulation depth of 94.17% and speed of 146.6 kHz. With this unique SLM, a reconfigurable, cost-effective and power-efficient imaging system with a single-pixel detector has been demonstrated.

This article describes the active control of terahertz waves using hybrid metamaterials containing embedded vanadium dioxide. VO${}_{2}$ undergoes an insulator-metal phase transition at around 68 \ifmmode^\circ\else\textdegree\fi{}C, causing its conductivity to change by about 5 orders of magnitude, which yields mode switching in the metamaterial. This mode switching, which is analogous to the resonant mode switching seen in plasmonics, can be realized experimentally using thermal, electrical, or optical stimuli. Such a diverse range of stimuli should be very useful for manipulating terahertz waves in practical applications, with a particular eye toward next-generation wireless communication.

Dynamic terahertz (THz) beam steering is a promising technique for numerous applications, including communication, high-resolution imaging, and radar. However, advances in this technology are considerably limited by inadequate broadband and active phase shifters at THz frequencies. In this paper, we developed a type of VO2-based device capable of broadband THz beam steering. The effect of the tunable Brewster angle of the VO2 thin film along with the insulator-to-metal transition process was verified. We demonstrated that the VO2 grating could realize a dispersive beam deflector in a broad frequency band. Furthermore, upon heating, the VO2 grating could switch between three states of mirror reflector, “rainbow” deflector, and metallic grating. We believe that the proposed reconfigurable and broadband THz beam deflector offers a powerful avenue for manipulating THz beams.

For a Si-based all-optical spatial terahertz modulator (STM), an enhanced modulation efficiency under low illumination density would be of great significance to exploit the competence of THz technology in real-world applications. We presented here an implementation of such a device by microtexturing and passivating the Si surface, forming a truncated pyramidal array (TPA). This TPA structure with SiO2 passivating coatings not only decreases light reflectance and expands the active area for THz modulation but also remarkably increases the photogenerated carrier lifetime. These 3-fold benefits render Si-TPA superior to bare-Si with respect to the achievable modulation efficiency, especially at low irradiation power. Furthermore such a Si-TPA device is also more applicable than its counterpart that is only passivated by SiO2 nanocoatings, even though the Si-SiO2 has a slightly increased modulation efficiency. These periodically aligned pyramids resembled as a mesa array significantly suppress the lateral diffusion induced by longer diffusion, resulting in an equivalent resolution of bare-Si. This novel Si-TPA based STM is highly desired for realizing a high-performance THz imager and provides a feasible approach to breaking the trade-off between resolution and modulation efficiency.

All optical THz wave modulation based on semiconductor is a convenient modulation method for real application, which is superior with wideband, large modulation depth and low insertion loss. In some scenario, it is required to use infrared light rather than visible light as the excitation signal where germanium is a better candidate than silicon. Here monolayer gold nanorods and graphene was used to modify the surface of germanium to enhance the THz wave modulation depth by the 1550 nm laser irradiation. Higher modulation depth was achieved by surface modification, which achieve the highest modulation depth of ~90% at 3.5 W/cm2. And the modulation rate is higher than 35 kHz.

In this paper, a broadband terahertz wave was optically modulated by laser signal using a graphene field effect transistor. The modulation speed and depth were tuned by varying the gate voltage. The modulating laser and gate voltage together can trigger both inter- and intra-band transitions in graphene. The laser light penetrates through graphene into the p-Si substrate forming a thin loss layer at the graphene/p-Si interface, while the gate voltage tuned the intra-band transitions in graphene by changing the carrier density of states and the Fermi level. The change in carrier concentration, density of states, and mobility in the loss layer directly affected the optical conductivity and refractive index, and thus the modulation depth. Modulation depth of the whole device is between 28.5% and 39.3% at modulation frequencies from 100 kHz to 1.0 MHz.

(NdGdBi)3Fe5O12 mono-crystalline films with high magneto-optical figure of merit (FOM) and high laser-induced damage thresholds (LIDTs) at a wavelength of around 1 μm have been grown in this study. Crystal structure, phase composition, magneto-optical (MO) properties and LIDTs of the grown (NdGdBi)3Fe5O12 films were discussed in detail. Tested results show that (NdGdBi)3Fe5O12 films exhibit a low insertion loss of 0.5 dB, a high FOM of 78.7 deg/dB and a high LIDTs of 9.12 J/cm2 at 1.06 μm wavelength. Lattice constant and dopants are two key factors to determine FOM and LIDTs of Bi-doped iron garnet films grown by liquid-phase epitaxial method. The excellent MO properties and LIDTs indicate that (NdGdBi)3Fe5O12 films grown in this study have a great potential to be used in 1–1.1 μm high-power lasers.

The wafer-scale La:YIG single crystal thick films were fabricated on a three-inch gadolinium gallium garnet (GGG) substrate by liquid phase epitaxy method. The terahertz (THz) optical and magneto-optical properties of La:YIG film were demonstrated by THz time domain spectroscopy (THz-TDS). The results show that a high refractive index of approximately 4.09 and a low absorption coefficient of 10–50 cm−1 from 0.1 to 1.6 THz for this La:YIG film. Moreover, the THz Faraday rotation effect of La:YIG film was measured by the orthogonal polarization detection method in THz-TDS system, which can be actively manipulated by a weak longitudinal magnetic field of up to 0.155 T. With 5 samples stacked together, the Faraday rotation angle varies linearly from −15° to 15°, and the Verdet constant of La:YIG is about 100 °/mm/T within the saturation magnetization. This magneto-optical single crystal thick film with large area shows low loss, high permittivity and strong magneto-optical effect in the THz regime, which will be widely used in magneto-optical polarization conversion, nonreciprocal phase shifter and isolator for THz waves.

Rare-earth iron garnet thin films with perpendicular magnetic anisotropy (PMA) have recently attracted a great deal of attention for spintronic applications. In this study, magnetic anisotropy of epitaxial garnet films was analyzed theoretically, and (YBiLuCa)3(FeGe)5O12 mono-crystalline films with PMA have been successfully grown with liquid phase epitaxial (LPE) method on Gd3Ga5O12 (GGG) substrates. Microstructural properties, chemical composition and magnetic properties of the epitaxial films were discussed in detail. We found that growth temperatures played a significant role in the uniaxial anisotropy of the epitaxial (YBiLuCa)3(FeGe)5O12 mono-crystalline films. Ferromagnetic resonance linewidth of (YBiLuCa)3(FeGe)5O12 films with thickness of 170 nm was 8.06 Oe@12 GHz, which indicated that the epitaxial (YBiLuCa)3(FeGe)5O12 mono-crystalline films had a great potential application in spintronic devices.

The Faraday rotation effect of both the La: yttrium iron garnet (YIG) film and the YIG metasurface were experimentally and numerically investigated in the terahertz (THz) region. A THz magneto-optic polarization measurement system was used to observe the transmission, resonance, and magneto-optical effect of the La:YIG film and YIG metasurface. The THz artificial chirality and resonance localization of the helical metasurface generate the superchiral THz field, which enhances the THz magneto-optical effect of the YIG film. The results show that the Faraday effect of the YIG metasurface is about three times that of the pure YIG film, whose differential rotation angle increases from 8° to over 24°. This work achieves more sensitively active polarization control of THz waves, which is of great significance for THz polarization conversion, sensing, and non-reciprocal transmission.

Metasurfaces are nanopatterned structures of sub-wavelength thickness. Their effective refractive index and spectral characteristic can be tailored by material composition, intrinsic and extrinsic resonances, structure size, and ambient conditions. Consequently, they allow for phase, amplitude, polarisation, and spatial control of an optical field beyond what natural materials can offer. Dielectric metasurfaces with lower loss have opened a wide range of new applications such as enhanced imaging, structural colour, holography, and planar sensors. In particular, beam steering and control measures such as nonlinear optics, ultrafast optics, and quantum optics are of increasing importance for quantum communication, computation, and information processing. In this review, the recent progress on dielectric metasurfaces is summarised, including advanced fabrication technologies and novel applications from advanced wavefront shaping to quantum platforms. In addition, a perspective for the future development of the field is presented.

Recently, the negative absorption in graphene-based metamaterials became a very attractive direction of THz electronic devices. Here we propose a graphene-dielectric hybrid meta-structure to realize photo-induced enhanced negative absorption in the THz regime, which results from strong graphene-light interaction. The negative absorption is derived from the degradation of the conductivity of graphene under optical pump. Meanwhile, the graphene-dielectric hybrid meta-structure introduces dispersion relation and resonance mode, which can couple with the incident wave to construct a strong resonance. In this case, both the dispersion of the propagating waves and resonance are contributed to the graphene-light interaction and enhance the negative absorption, in which the resonance coupling determines the distribution of negative absorption, and the maximum is dominated by dispersion. More importantly, compared with the previous work, the negative absorption is increased by nearly 100 times by adopting this meta-structure.

A terahertz spatial modulator is the critical component for active terahertz imaging using compressive sensing. Here small silicon pieces were put in arrays on flexible polymer substrate to fabricate semiconductor terahertz spatial modulators. By doing this, the inter-diffusion of photo-generated charge carriers is prevented for better resolution, and flexibility is achieved. Since the size of silicon is comparable to the wavelength of the terahertz wave, and the dielectric properties of the gap are very different from silicon, the optical modulation of each element is very different from the large silicon. In this Letter, the terahertz wave interaction and optical modulation of the small silicon are systematically studied by time domain spectroscopy. Notably, a strong resonance-like absorption peak was observed in a transmittance spectrum for the small silicon due to the size and edge effect. The spatial modulation of the terahertz wave was also compared between the silicon array and the large silicon samples.

Ge-based alloys have drawn great interest as promising materials for their superior visible to infrared photoelectric performances. In this study, we report the preparation and optical properties of germanium-bismuth (Ge1-xBix) thin films by using molecular beam epitaxy (MBE). GeBi thin films belong to the n-type conductivity semiconductors, which have been rarely reported. With the increasing Bi-doping content from 2 to 22.2%, a series of Ge1-xBix thin film samples were obtained and characterized by X-ray diffraction, scanning electron microscopy, and atomic force microscopy. With the increase of Bi content, the mismatch of lattice constants increases, and the GeBi film shifts from direct energy band-gaps to indirect band-gaps. The moderate increase of Bi content reduces optical reflectance and promotes the transmittance of extinction coefficient in infrared wavelengths. The absorption and transmittance of GeBi films in THz band increase with the increase of Bi contents.

Inverted pyramid hole arrays were fabricated by photolithography and used as templates to direct the growth of colloidal nanoparticle assemblies. Cobalt ferrite nanoparticles deposit in the holes to yield high quality pyramid magnetic nanoparticle assembly arrays by carefully controlling the evaporation of the carrier fluid. Magnetic measurements indicate that the pyramid magnetic nanoparticle assembly arrays preferentially magnetize perpendicular to the substrate.

MnZn ferrite thin films were deposited on p-Si substrate and used as the dielectric layer in the graphene field effect transistor for infrared and terahertz device applications. The conditions for MnZn ferrite thin film deposition were optimized before device fabrication. The infrared properties and terahertz wave modulation were studied at different gate voltage. The resistive and magnetic MnZn ferrite thin films are highly transparent for THz wave, which make it possible to magnetically modulate the transmitted THz wave via the large magnetoresistance of graphene monolayer. Electronic supplementary material The online version of this article (doi:10.1186/s11671-017-2250-2) contains supplementary material, which is available to authorized users.

VO2 thin films were grown on silicon substrates using Al2O3 thin films as the buffer layers. Compared with direct deposition on silicon, VO2 thin films deposited on Al2O3 buffer layers experience a significant improvement in their microstructures and physical properties. By optimizing the growth conditions, the resistance of VO2 thin films can change by four orders of magnitude with a reduced thermal hysteresis of 4 °C at the phase transition temperature. The electrically driven phase transformation was measured in Pt/Si/Al2O3/VO2/Au heterostructures. The introduction of a buffer layer reduces the leakage current and Joule heating during electrically driven phase transitions. The C–V measurement result indicates that the phase transformation of VO2 thin films can be induced by an electrical field. Electronic supplementary material The online version of this article (doi:10.1007/s40820-017-0132-x) contains supplementary material, which is available to authorized users.

We report the successful growth of vanadium dioxide (VO 2 ) films on SiO 2 buffered metal electrode and the fabrication of metal–oxide-insulator–metal (MOIM) junction. The VO 2 film has an abrupt thermal-induced metal–insulator transition (MIT) with a change of resistance of 2 orders of magnitude. The electrically-driven MIT (E-MIT) switching characteristics have been investigated by applying perpendicular voltage to VO 2 based MOIM device at particular temperatures, sharp jumps in electric current were observed in the I – V characteristics under a low threshold voltage of 1.6 V. The Ohmic behavior, non-Ohmic super-linear one, and metallic regime are sequentially observed in the MOIM device with the increase of voltage. It is expected to be of significance in exploring ultrafast electronic devices incorporating correlated oxides based MOIM structure.

Terahertz spectroscopy is becoming a potential tool for characterizing various materials including biomaterial specimens, liquids, and semiconductors. Accuracy of the sample information is important for analysis. In this article, the influences of type and position of window functions on accuracy of extracting sample information are studied. Experimental results show that an appropriate type and position of window functions significantly improve the accuracy of the extracted sample information.

We present a simple method to obtain the optical and dielectric properties of samples without reference measurement in the reflection-type terahertz time-domain spectroscopy. The dielectric properties of the samples of silicon and gallium arsenide were examined. The optical and dielectric properties of the samples were measured through only simple configuration, without the misplacement error. The obtained dielectric functions of the samples in reflection geometry are in good agreement with that predicated by the theory. The main advantage of this method over other methods is its simplicity and accuracy and ease for application of the reflection systems with different incident angle.