Giant Enhancement Research Articles

Giant Photoluminescence Enhancement of Ga-Doped ZnO Microwires by X-Ray Irradiation.

Ga-doped zinc oxide (ZnO) microwires hold great promise for developing highly efficient light sources because of the wide bandgap with proper exciton binding energy. However, most microwires grown from one mainstream approach, i.e., chemical vapor deposition (CVD), are morphologically and crystallographically defective, exhibiting limited photoluminescence performances. Herein, a simple and effective X-ray irradiation strategy is demonstrated for enhancing the photoluminescence of Ga-doped ZnO microwire in ambient conditions. Under moderate doses (≤ 150Gy), the photoluminescence monotonically rockets up with X-ray dose increment and achieves nine-fold enhancement at a dose of ≈150Gy, recording high photoluminescence improvement of ZnO microwires to date. The elemental characteristics under different controlled irradiation atmospheres suggest the elimination of surface oxygen vacancy and the cross-section transmission electron microscope reveals prominent lattice relaxations after mild X-ray irradiation. In addition, the X-ray irradiated microwires further exhibit elevated electroluminescence by over three times. The enhanced photoluminescence and electroluminescence as well as long-term stability enable us to imagine the super-rapid applications of ZnO microwires in modern optoelectronic devices.

A giant enhancement of output performance for piezotronic devices via the non-uniform piezoelectric charges induced by strain engineering

A giant enhancement of output performance for piezotronic devices via the non-uniform piezoelectric charges induced by strain engineering

Giant enhancement and quick stabilization of capacitance in antiferroelectrics by phase transition engineering

The antiferroelectric-ferroelectric phase transition is a basic principle that holds promise for antiferroelectric ceramics in high capacitance density nonlinear capacitors. So far, the property optimization based on antiferroelectric-ferroelectric transition is solely undertaken by chemical composition tailoring. Alternately, here we propose a phase transition engineering tactic by applying pulsed electric stimulus near the critical electric field, which finally results in ~54.3% enhancement and quick stabilization of capacitance density in Pb0.97La0.02(Zr0.35Sn0.55Ti0.10)O3 antiferroelectric ceramics. Ex-situ and in-situ structural characterizations show that electric stimuli can induce the charming successive structural evolution, including domain evolution from multidomain to monodomain state, and modulation period change from 7.49 to 7.73. Structure-property correlation indicates that the antiferroelectric-ferroelectric phase transition engineering mainly stems from the unexpected irreversible recovery of the modulated structures. The present findings would deepen the understanding of the structural phase transition and provoke composition-independent post-treatment property innovation in the incommensurate antiferroelectric materials and devices.

A New Organic Laser Material Design Toward Ultra-Low Amplified Spontaneous Red Emission and Ultra-Bright Electroluminescence.

Significant efforts are dedicated to developing new classes of organic semiconductor materials to achieve electrically pumped lasing. However, further advancements are necessary to understand the relationship between the structure and property for the creation of innovative laser materials with high stability, low triplet yield, ultra-low lasing threshold, and low-efficiency roll-off at ultra-bright electroluminescence. Here, a new design principle is validated for organic semiconductor laser materials, demonstrating simultaneous enhancement in the key figures of merit of low amplified spontaneous emission thresholds (Eth), efficient electroluminescence, and low triplet yields. By applying the Einstein stimulated emission rate equation and Strickler-Berg approximation, Two red-emitting laser dimers of Cibalackrot with different linkers are constructed, leading to giant enhancement (≈250%) in oscillator strengths, and stimulated emission cross-sections. When blended in poly(9,9-dioctylfluorene-alt-benzothiadiazole), the new dimers achieve an ultra-low Eth (4.5±0.3µJcm-2) in the deep red region (λASE=655nm), among the lowest reported for deep-red emitters. Organic light-emitting diodes (OLEDs) utilizing the dimer blend exhibit low-efficiency roll-off under DC mode. Under pulse operation, the OLEDs achieve high current densities (90Am-2) and ultrahigh brightness (≈710000cdm-2). These findings highlight the dimerization design as an excellent platform to advance organic semiconductor laser materials.

Giant Enhancement of Negative Friction by Resonant Coupling Between Localized Surface Phonon Polaritons and Graphene Plasmonics

Abstract Negative friction refers to a frictional force that acts in the same direction as the motion of an object, which has been predicted in terahertz (THz) gain systems [Phys. Rev. B 108 (4), 045406(2023)]. In this work, we investigate the enhancement of the negative friction experienced by nanospheres placed near a graphene substrate. We find that the magnitude of negative friction is related to the resonant coupling between the surface plasmon polaritons (SPPs) of the graphene and localized surface phonon-polaritons (LSPhP) of nanospheres. We exam nanospheres consisted of several different materials, including SiO2, SiC, ZnSe, NaCl, lnSb. Our results suggest that the LSPhP of NaCl nanospheres match effectively with the amplified SPPs of graphene sheets. The negative friction for NaCl nanospheres can be enhanced about one-to-two orders of magnitude compared to that of silica (SiO2) nanospheres. At the resonant peak of negative friction, the required quasi-Fermi energy of graphene is lower for NaCl nanospheres. Our finds hold great prospects for the mechanical manipulations of nanoscale particles.

Giant enhancement of nonlinear harmonics of an optical-tweezer phonon laser

Phonon lasers, as mechanical analogues of optical lasers, are unique tools for not only fundamental studies of the emerging field of phononics but also diverse applications such as deep-ocean monitoring, force sensing, and biomedical ultrasonics. Recently, nonlinear phonon-lasing effects were observed in an opto-levitated micro-sphere, i.e., the spontaneous emerging of weak signals of high-order phonon harmonics in the phonon lasing regime. However, both the strengths and the quality factors of the emerging phonon harmonics are very poor, thus severely hindering their potential applications in making and utilizing nonlinear phonon-laser devices. Here we show that, by applying a single-colour electronic injection to this levitated system, giant enhancement can be achieved for all higher-order phonon harmonics, with more than 3 orders enhanced brightness and 5 orders narrowed linewidth. Such an electronically-enhanced phonon laser is also far more stable, with frequency stability extended from a dozen of minutes to over 1 h. More importantly, higher-order phonon correlations, as an essential lasing feature, are confirmed to be enhanced by the electronic injection as well, which as far as we know, has not been reported in previous works using this technique. This work, providing much stronger and better-quality signals of coherent phonon harmonics, is a key step towards controlling and utilizing nonlinear phonon lasers for applications such as phonon frequency combs, broadband phonon sensors, and ultrasonic bio-medical diagnosis.

Mid-infrared photodetector spectrometer concept based on ultrathin all-dielectric metamaterial with azimuth-incidence-angle tuned perfect optical absorption: Design and analysis

Novel concepts for efficient compact spectroscopy are extensively researched due to their fundamental applications in prominent fields such as chemistry, biology, and physics. Here, with an unprecedented spectral-azimuthal resolution, such a concept is introduced and exemplified in the mid-infrared, in which its advantages are paramount and have yet to be established industrially. The concept is based on the design and instrumentation of optical absorption spectral tuning (or sensitivity) to the relative azimuthal component of light impinging on specifically designed metamaterials (MMs). The inversely-designed MMs offer perfect photo-absorption inside λ0/200 ultra-thin layer of lead telluride. Two small-footprint system designs are proposed to instrument the spectral-azimuth-angle tuning for spectrometry. The first is based on a single or few spinning MM layout elements, and the second, to avoid spinning, utilizes a fixed focal-plane-array approach. The latter exploits the inherent variations in the local azimuthal-incidence angle. While low absorption is the Achilles heel of conventional mid-infrared photodetector spectrometers, the optimized MMs, besides their unique spectral-azimuth-angle tuning functionality, provide giant absorption enhancement, facilitating higher resolution and even smaller in-plane form factor. The highlighted concept opens an additional dimension to encode-decode spectral information, yielding profound advantages over conventional designs, such as those based on diffraction gratings.

Giant Enhancement of Hole Mobility for 4H-Silicon Carbide through Suppressing Interband Electron-Phonon Scattering.

4H-silicon carbide (4H-SiC) possesses a high Baliga figure of merit, making it a promising material for power electronics. However, its applications are limited by low hole mobility. Herein, we found that the hole mobility of 4H-SiC is mainly limited by the strong interband electron-phonon scattering using mode-level first-principles calculations. Our research indicates that applying compressive strain can reverse the sign of crystal-field splitting and change the ordering of electron bands close to the valence band maximum. Therefore, the interband electron-phonon scattering is severely suppressed and the electron group velocity is significantly increased. The out-of-plane hole mobility of 4H-SiC can be greatly enhanced by ∼200% with 2% uniaxial compressive strain applied. This work provides new insights into the electron transport mechanisms in semiconductors and suggests a strategy to improve hole mobility that could be applied to other semiconductors with hexagonal crystalline geometries.

Squeezing-enhanced quantum sensing with quadratic optomechanics

Cavity optomechanical (COM) sensors, enhanced by quantum squeezing or entanglement, have become powerful tools for measuring ultra-weak forces with high precision and sensitivity. However, these sensors usually rely on linear COM couplings, a fundamental limitation when measurements of the mechanical energy are desired. Very recently, a giant enhancement of the signal-to-noise ratio was predicted in a quadratic COM system. Here we show that the performance of such a system can be further improved surpassing the standard quantum limit by using quantum squeezed light. Our approach is compatible with available engineering techniques of advanced COM sensors and provides new opportunities for using COM sensors in tests of fundamental laws of physics and quantum metrology applications.

Subwavelength confinement in an all-dielectric slot waveguide with bound states in the continuum for ultrahigh-Q microresonators.

Bound state in the continuum (BIC) has been considered a promising strategy to reduce fabrication complexity and radiative loss. Despite the successful demonstration of many BIC-based configurations, their mode confinement is comparable to conventional dielectric waveguides. Even though plasmonics with strong light localization have been introduced into BICs, the intrinsic ohmic loss is still a facing challenge to be conquered. Herein, we propose a new approach, to our knowledge for the first time, that integrates subwavelength confinement and optical BIC in all dielectric slot waveguides. A nanogap with low refractive index is utilized to separate the top waveguide and high-index substrate, leading to strong mode localization and energy confinement (∼ λ2/30). Surprisingly, leveraging on the concept of optical BICs, the leakage channels of the waveguide bound mode can be readily engineered to cancel each other through destructive interference, which effectively suppresses the optical dissipation. Moreover, the subwavelength confinement is observed in ultrahigh-Q microring resonators, resulting in a giant enhancement of the Purcell factor (> 108). Our findings introduce a new concept into the BIC family and provide novel thoughts to design BIC photonics, which may show superiority in achieving low threshold lasers and highly sensitive sensors.

Giant enhancement of magnon transport by superconductor Meissner screening

Giant enhancement of magnon transport by superconductor Meissner screening

Barrier crossing in a viscoelastic medium under active noise: Predictions of Kramers’ flux-over-population method

The biochemical activity inside a cell has recently been suggested to act as a source of hydrodynamic fluctuations that can speed up or slow down enzyme catalysis [Tripathi et al., Commun. Phys. 5, 101 (2022).] The idea has been tested against and largely corroborated by simulations of activated barrier crossing in a simple fluid in the presence of thermal and athermal noise. The present paper attempts a wholly analytic solution to the same noise-driven barrier crossing problem but generalizes it to include viscoelastic memory effects of the kind likely to be present in cellular interiors. A calculation of the model’s barrier crossing rate, using Kramers’ flux-over-population formalism, reveals that in relation to the case where athermal noise is absent, athermal noise always accelerates barrier crossing, though the extent of enhancement depends on the duration τ0 over which the noise acts. More importantly, there exists a critical τ0—determined by the properties of the medium—at which Kramers’ theory breaks down and, on approach to which, the rate grows significantly. The possibility of such a giant enhancement is potentially open to experimental validation using optically trapped nanoparticles in viscoelastic media that are acted on by externally imposed colored noise.

An effective defect engineering strategy for giant photoluminescence enhancement of MoS2 monolayers

An effective defect engineering strategy for giant photoluminescence enhancement of MoS2 monolayers

Giant enhancement of coercivity in β-Ni(OH)2 decorated Ti3C2T x MXene nanosheets

Ti3C2T x MXenes are of great interest due to their high conductivity, easy synthesis and unique functional properties. Functionalisation and structural engineering are essential for various applications because of their dramatic influences on different chemical and physical properties. Therefore, understanding the mechanism of the etching reaction of Ti3C2T x from its parent MAX phase is crucial. The structural details also need to be understood for application in different practical devices. In this study, 2D Ti3C2T x sheets with an average thickness of 3.48 nm and lateral dimension of 5.5 µm were synthesised by removing Al layers from the Ti3AlC2 MAX phase. The step-by-step etching mechanism was analysed with the help of Rietveld refinement of the powder x-ray diffraction data. The structural details and influence of different functional groups on the surface were also studied using transmission electron microscopy, x-ray photoelectron spectroscopy, and Raman spectroscopy. The magnetic behaviour and magnetic interaction of bare 2D Ti3C2T x decorated with β-Ni(OH)2 nanosheets on its surface was studied. For the bare 2D Ti3C2T x MXene sheets, a weak ferrimagnetic ordering with negligible coercivity was found. However, the β-Ni(OH)2-decorated Ti3C2T x MXene sheets exhibit strong ferrimagnetic ordering with a sufficiently large coercivity of 0.2 T at 2 K and a transition temperature of 246 K. The generation of this interfacial ferrimagnetism is discussed in light of the interfacial charge transfer originating from d-p mixing. These 2D magnets generated at the interface could be useful for application in different spintronic devices.

Origin of giant enhancement of phase contrast in electron holography of modulation-doped [formula omitted]-type GaN

The electron optical phase contrast probed by electron holography at n-n+ GaN doping steps is found to exhibit a giant enhancement, in sharp contrast to the always smaller than expected phase contrast reported for p-n junctions. We unravel the physical origin of the giant enhancement by combining off-axis electron holography data with self-consistent electrostatic potential calculations. The predominant contribution to the phase contrast is shown to arise from the doping dependent screening length of the surface Fermi-level pinning, which is induced by FIB-implanted carbon point defects below the outer amorphous shell. The contribution of the built-in potential is negligible for modulation doping and only relevant for large built-in potentials at e.g. p-n junctions. This work provides a quantitative approach to so-called dead layers at TEM lamellas.

Ultrasensitive terahertz response mediated by split ring antenna induced giant resonant field enhancement

Ultrasensitive terahertz response mediated by split ring antenna induced giant resonant field enhancement

Amplified adsorption and photocatalytic degradation of polycyclic aromatic hydrocarbons using biocompatible nanocrystalline reduced graphene oxide quantum dots

Carcinogenic polycyclic aromatic hydrocarbons (PAHs) have been broadly recognized as significant organic pollutants in the environment, which pose a serious threat to both humans and animals. Therefore, there is an urgent need to develop a solution that effectively removes and reduces PAHs present in the environment. In the present work, we synthesized biocompatible nanocrystalline reduced graphene oxide quantum dots in powdered form (rGOQDTs) of crystallite size 2 nm through hydrothermal method and subsequently used for efficient adsorption and degradation of PAHs for the first time. We noticed that the adsorption of PAHs onto rGOQDTs was faster and more efficient as compared to adsorption on graphene oxide (GO). A 40-fold giant enhancement in the adsorption efficiency of Anthracene and Pyrene on rGOQDTs has been observed as compared to that of graphene oxide. We attribute this enormous enhancement in adsorption efficiency to the stacking of PAHs with rGOQDTs and stronger π-π interactions between rGOQDTs and PAHs. Interestingly, rGOQDTs also exhibit efficient photo-degradation of adsorbed PAHs under visible light irradiation and it degrades almost all PAHs after 80 min of visible light illumination. The degradation efficiency of PAHs is also higher for rGOQDTs as compared to GO. Our work paves the way for efficient removal and degradation of polycyclic aromatic hydrocarbons from the environment.

Strain-induced giant enhancement and transformation of magnetocrystalline anisotropy in 1T-FeSe2 monolayer

The development of magnetic materials with large magnetic anisotropy energy (MAE) is crucial for magnetic storage and spintronics applications. The electronic structure and magnetic properties of 1T-FeSe2 monolayer have been systematically investigated by first-principles computational methods. The monolayer 1T-FeSe2 is confirmed to be a ferromagnetic semimetal with 100% spin polarization and exhibits pronounced magnetic anisotropy. It shows an easy magnetization plane in the two-dimensional plane and its MAE is as high as 8.134 meV. The MAE mainly originates from the contributions of transitions between Fe dyz and dz2, dxy and dx2−y2 orbitals, while the contributions of transitions between p x and p y, p x and p z orbitals of Se are also obvious. The biaxial strain significantly regulates the magnetic properties and electronic structures of the 1T-FeSe2 monolayer. Interestingly, the MAE increases significantly to 77.680 meV when the tensile strain increases to 3.5%, we can expect to achieve a reasonable value of MAE up to 98.951 meV by applying 5% tensile strain. In addition, the easy magnetization plane changes to perpendicular easy magnetization axis direction at −6% compressive strain or 7% tensile strain, which leads to a significant change in the band structure near the Fermi level. The 100% spin-polarized ferromagnetic semi-metallic behavior and the huge strain-induced magnetic anisotropy make the 1T-FeSe2 monolayer material promising for spintronics and magnetic data storage.

Brilliant quantum dots’ photoluminescence from a dual-resonance plasmonic grating

Semiconductor quantum dots (QDs) have recently caused a stir as a promising and powerful lighting material applied in real-time fluorescence detection, display, and imaging. Photonic nanostructures are well suited for enhancing photoluminescence (PL) due to their ability to tailor the electromagnetic field, which raises both radiative and nonradiative decay rate of QDs nearby. However, several proposed structures with a complicated manufacturing process or low PL enhancement hinder their application and commercialization. Here, we present two kinds of dual-resonance gratings to effectively improve PL enhancement and propose a facile fabrication method based on holographic lithography. A maximum of 220-fold PL enhancement from CdSe/CdS/ZnS QDs are realized on 1D Al-coated photoresist (PR) gratings, where dual resonance bands are excited to simultaneously overlap the absorption and emission bands of QDs, much larger than those of some reported structures. Giant PL enhancement realized by cost-effective method further suggests the potential of better developing the nanostructure to QD-based optical and optoelectronic devices.

Giant enhancement of vacuum friction in spinning YIG nanospheres

Experimental observations of vacuum radiation and vacuum frictional torque are challenging due to their vanishingly small effects in practical systems. For example, a nanosphere rotating at 1GHz in free space slows down due to friction from vacuum fluctuations with a stopping time around the age of the Universe. Here, we show that a spinning yttrium iron garnet (YIG) nanosphere near aluminum or YIG slabs generates vacuum radiation with radiation power eight orders of magnitude larger than other metallic or dielectric spinning nanospheres. We achieve this giant enhancement by exploiting the large near-field magnetic local density of states in YIG systems, which occurs in the low-frequency GHz regime comparable to the rotation frequency. Furthermore, we propose a realistic experimental setup for observing the effects of this large vacuum radiation and frictional torque under experimentally accessible conditions.