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•BST thin films prepared at different oxygen partial pressures using PLD.•Microwave dielectric properties were estimated by fabricating a CPC structure and measured using on-wafer ...probing technique.•High microwave dielectric tunability was observed in the BST films deposited at higher oxygen pressure.
Thin films of Ba0.5Sr0.5TiO3 (BSTO) were pulsed laser deposited on platinized silicon substrates with varying oxygen pressure from 5 × 10−1 mbar to 5 × 10−6 mbar. A strong correlation between the oxygen partial pressure during the PLD process and the structural and microwave dielectric properties of the PLD-grown BSTO thin films is observed. The structural properties of the PLD-grown BSTO films were analyzed by XRD, Raman spectroscopy, FTIR spectroscopy, and XPS studies, and it is observed that oxygen vacancies are formed in low oxygen pressure deposited films. Dielectric studies at microwave frequencies show that high oxygen pressure deposited BSTO films show good microwave dielectric properties and crystallinity. At 1 GHz frequency, the BSTO film grown at 5 × 10−2 mbar oxygen pressure exhibits a dielectric constant ∼470 and dielectric loss ∼0.15. The oxygen vacancies change the nature of metal-oxide bonding (Ti-O bond), affect the polarizabilities, and, as a result, reduce the dielectric constant. A maximum dielectric tunability of 71 % is observed in microwave frequencies for the BSTO films grown at 5 × 10−2 mbar oxygen pressure.
Electrochromic devices with a wide color gamut distribution have long been sought after for non‐emissive display technologies. The current state‐of‐the‐art multicolor electrochromic displays utilize ...a single electrochromic layer, which restricts their color tunability within a linear or curved segment scope in International Commission on Illumination (CIE) color space and thus leads to limited color hues. Herein, it is demonstrated vivid electrochromic displays with broadened color hues via fabricating Zn‐based multicolor electrochromic displays having 2D CIE color space tunability. In addition, it is revealed that a Fabry–Perot nanocavity structure can further tune the color hues via altering the coordinate of the 2D CIE color space. It is known that this is the first demonstration of 2D CIE color space tunability realization from a single transparent or reflective electrochromic device. These findings represent a novel strategy for fabricating multicolor electrochromic displays and are expected to advance the development of electrochromic displays.
Electrochromic displays provide reversible switch of multiple colors and long‐term bistability. The first example of Zn anode‐based electrochromic displays having 2D color space tunability is presented to display multiple colors traversing a 2D International Commission on Illumination regional color space. These findings accelerate future electrochromic display technology that brings the full‐color tunability in a single electrochromic device within reach.
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•Bimetallic MOFs (BMOFs) exhibit better electrochemical performance than monometal MOFs.•BMOFs can have more electroactive sites through compositional and structural ...engineering.•Functionalization of BMOFs can help enhance capacitive performance with extended durability.•Fabrication of BMOFs offers insights into the development of commercial supercapacitor (SC).•BMOF-SCs are beneficial options with high power densities and fast charging/discharging cycles.
Metal-organic frameworks (MOFs) have drawn a great deal of attention due to a diverse range of advantageous properties (e.g., large surface area, favorable pore-size distribution, structural tunability, versatility, and facile functionalization). The bimetallic MOFs (BMOFs) formed through the incorporation of bimetals in MOF structure are useful to enhance the intrinsic properties of frameworks, as they can favorably introduce defects and high porosity through combinational effects between different metals. As such, the utility of BMOFs can be expanded greatly in diverse applications such as supercapacitor (SC) electrode. In this review, we describe different methods of preparing BMOFs and their derivatives for the construction of diverse BMOF-based SCs. The recent advances achieved in the design and production of pristine BMOFs and their derived nanostructures (e.g., bimetal oxides, sulfides, phosphides, and carbonaceous products) in SC applications are also addressed in association with the evaluation of their electrochemical performance. The present review is thus expected to help establish a technology roadmap for the fabrication and commercialization of novel SC products.
Phononic metamaterials rely on the presence of resonances in a structured medium to control the propagation of elastic waves. Their response depends on the geometry of their fundamental building ...blocks. A major challenge in metamaterials design is the realization of basic building blocks that can be tuned dynamically. Here, a metamaterial plate is realized that can be dynamically tuned by harnessing geometric and magnetic nonlinearities in the individual unit cells. The proposed tuning mechanism allows a stiffness variability of the individual unit cells and can control the amplitude of transmitted excitation through the plate over three orders of magnitude. The concepts can be extended to metamaterials at different scales, and they can be applied in a broad range of engineering applications, from seismic shielding at low frequency to ultrasonic cloaking at higher frequency ranges.
“On‐the‐fly” steering of mechanical waves in time and space is realized. By harnessing geometric and magnetic nonlinearities, 3D‐printed phononic metamaterials change their shape from 2D to 3D. This shape change shifts the dynamical characteristics from attenuating waves to permitting their propagation. Such change is dynamic, element‐wise, noninvasive, and reversible; therefore, it is referred to as reprogramming of matter.
•An acoustic metamaterial plate based on a negative Poisson's ratio structure (NP-AMP) is proposed.•The newly designed structure has a lower frequency bandgap and wider bandwidth compared with ...traditional structures.•Applying mechanical loading to the NP-AMP enables direct control of the bandgap for shifting to lower frequencies.•The range of bandgap variation is related to the auxetic behavior.
Two-dimensional phononic metamaterials, consisting of plates with resonant cylinders, can significantly attenuate waves by opening a subwavelength bandgap, though their characteristic unit cell size is small. To realize the real-time adjustment of the bandgap, external excitations including mechanical load, temperature field, electric field and magnetic field could be introduced, of which applying mechanical load is the most practical way. In this work, an acoustic metamaterial plate based on the negative Poisson's ratio structure (NP-AMP) is proposed and feasible to achieve lower frequency, wider bandgap, and tunable bandgap compared with traditional ones (T-AMP). A counterpart based on the positive Poisson's ratio structure (PP-AMP) is also introduced for comparison. Studies have indicated that the newly designed structure has a lower frequency bandgap and wider bandwidth. With the increase of compression strain, the initial bandgap of PP-AMP gradually moves to a higher-frequency range. In contrast to PP-AMP, the NP-AMP exhibits lower frequency, which is beneficial for the further research of low-frequency bandgap. Moreover, the bandgap variation range can be enlarged by the enhancement of the auxetic behavior. Finally, the variation range of the NP-AMP initial bandgap frequency increased by 62%. The findings in this work will broaden the design of low-frequency broadband acoustic devices used in a dynamic environment, while providing new ideas and methodologies for real-time adjustment of bandgaps.
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Relative humidity is simultaneously a sensing target and a contaminant in gas and volatile organic compound (VOC) sensing systems, where strategies to control humidity interference are required. An ...unmet challenge is the creation of gas‐sensitive materials where the response to humidity is controlled by the material itself. Here, humidity effects are controlled through the design of gelatin formulations in ionic liquids without and with liquid crystals as electrical and optical sensors, respectively. In this design, the anions DCA− and Cl− of room temperature ionic liquids from the 1‐butyl‐3‐methylimidazolium family tailor the response to humidity and, subsequently, sensing of VOCs in dry and humid conditions. Due to the combined effect of the materials formulations and sensing mechanisms, changing the anion from DCA− to the much more hygroscopic Cl−, leads to stronger electrical responses and much weaker optical responses to humidity. Thus, either humidity sensors or humidity‐tolerant VOC sensors that do not require sample preconditioning or signal processing to correct humidity impact are obtained. With the wide spread of 3D‐ and 4D‐printing and intelligent devices, the monitoring and tuning of humidity in sustainable biobased materials offers excellent opportunities in e‐nose sensing arrays and wearable devices compatible with operation at room conditions.
Humidity influence in sensing of volatile organic compounds is tuned by materials design. The anions of ionic liquids tailor the gas sensing material's sensitivity to humidity, yielding either humidity‐sensitive or humidity‐tolerant odorant sensors that do not require sample preconditioning or signal processing to correct humidity impact, thereby contributing to the widespread field of artificial olfaction.
Colloidal CsPbX3 (X = Br, Cl, and I) perovskite nanocrystals exhibit tunable bandgaps over the entire visible spectrum and high photoluminescence quantum yields in the green and red regions. However, ...the lack of highly efficient blue‐emitting perovskite nanocrystals limits their development for optoelectronic applications. Herein, neodymium (III) (Nd3+) doped CsPbBr3 nanocrystals are prepared through the ligand‐assisted reprecipitation method at room temperature with tunable photoemission from green to deep blue. A blue‐emitting nanocrystal with a central wavelength at 459 nm, an exceptionally high photoluminescence quantum yield of 90%, and a spectral width of 19 nm is achieved. First principles calculations reveal that the increase in photoluminescence quantum yield upon doping is driven by an enhancement of the exciton binding energy due to increased electron and hole effective masses and an increase in oscillator strength due to shortening of the PbBr bond. Putting these results together, an all‐perovskite white light‐emitting diode is successfully fabricated, demonstrating that B‐site composition engineering is a reliable strategy to further exploit the perovskite family for wider optoelectronic applications.
Narrowband blue‐emitting CsPbBr3 perovskite nanocrystals with a photoluminescence quantum yield of 90% are achieved by B‐site doping of neodymium ions. The doping concentration can tune the emission spectrum in a controlled manner. First principles calculations reveal that dopant‐induced electronic changes dominate the bandgap tunability and the high quantum yield is associated with enhanced exciton binding energy and oscillator strength.
This work reports the green to red color tunable upconversion emission in a newly synthesized Ho3+/Yb3+ codoped YV0.75Ta0.25O4 phosphor, prepared by solid-state reaction (SSR) method. The crystal ...phase formation has been confirmed by X-Ray diffraction analysis. The Fourier transform infrared (FTIR) spectrum show bands at different frequencies due to V-O and Ta-O, and found to play a vital role in relaxation (radiative and non-radiative) processes. The synthesized phosphor sample show intense upconversion (UC) emission in green (∼539 nm), red (∼659 nm) and in near infrared (NIR∼ 754 nm) regions on 980 nm laser excitation. These bands appear as a result of (5F4+5S2→5I8), (5F5→5I8) and (5F4+5S2→5I7) transitions of Ho3+ ion, respectively. The tunability in color from green to orange-red is observed on varying the pump power of NIR laser (980 nm excitation). The intrinsic optical bistability is observed in both, green & red upconversion bands with the increase and decrease in power of NIR source. The Ln I-Ln P plots suggest that green & red UC emissions are due to two photon absorption at low laser power. A decrease in the slope values at higher pump powers confirms the laser induced optical heating (LIOH) in the material. The pump power based color tunable emission and optical bistability can be utilized in security detection, optical memory, optical color coding, color switching and in various advanced applications.
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•The YV0.75Ta0.25O4: Ho3+/Yb3+ phosphor were prepared by high temperature solid-state reaction method.•The YV0.75Ta0.25O4: Ho3+/Yb3+ emit intense green (∼539 nm), red (∼659 nm) along with week near infrared (∼754 nm) UC emission on 980 nm laser excitation.•The Ln I-Ln P plots suggest that green and red UC emissions are due to two photon process.•Color tunability from green to red is observed with varying the pump power of 980 nm laser.•The intrinsic optical bistability is observed in green and red bands with the pump power of 980 nm laser.
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•A novel graphene integrated module for electromagnetic THz filtering, sensing and high-gain radiation patterns is proposed.•The graphene-based metamaterial introduces an excellent ...tunability to the filters and the antennas in THz regime.•The proposed module exhibits excellent performance for different wave polarizations and oblique incident angles.•The maximum sensitivity of 0.145 THz/RIU is achieved for the proposed sensor.
In this paper, a novel tunable graphene-based bandstop filter/antenna-sensor is presented. This structure is an integrated module that can be used to combine filtering and high-gain radiation performance. The initial design of the unit cell consists of four U-shaped stubs loaded, resembling the arms of a ring and a sensing layer in the substrate. The reflection and transmission spectra are obtained for various graphene’s chemical potentials and refractive index of sensing layer (Ns) of structure in the range of 1.3–1.6 THz. The proposed structure exhibits the attributes of both dual-band filter and single-band antenna-sensor. The conductivity of graphene and its structural parameters are studied to optimize the component performance. In filtering mode, the first bandstop is from 1.23 to 1.6 THz equal to 26% of fractional bandwidth (FBW) at 1.415 THz. The second stopband is centered at 3.12 THz with FBW of 14% for Ns = 1.6 and 0.6 eV chemical potential. In the antenna mode, a single band of the antenna-sensor is centered at 1.95 THz for the same Ns and same chemical potential. It is shown that a sensitivity of 0.145 THz/RIU is achieved at Ns = 1.5 and chemical potential of 0.6 eV. Additionally, the performance of the proposed filter/antenna-sensor module is investigated for different wave polarizations and oblique angles.
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