Order Of Magnitude Enhancement Research Articles

Tailorable Upconversion White Light Emission from Pr3+ Single‐Doped Glass Ceramics via Simultaneous Dual‐Lasers Excitation

AbstractWhite lasers are promising illuminants for emerging visible light communication, which can overcome bottlenecks of lower energy conversion efficiencies and output powers in traditional white light‐emitting (WLE) diodes. However, optical gain materials for white lasers are suffering from great challenges of material growth and growth‐compatible cavity structure where lasing of all three elementary colors can be supported simultaneously. Here, an exquisite physical strategy is demonstrated to realize simultaneous red, green, and blue (RGB) upconversion (UC) photoluminescence for white light modulation for the first time, namely using dual lasers at 850 and 980 nm to stimulate easy‐fabricated glass ceramics (GCs) fiber laser materials (Pr3+ single‐doped germanium oxyfluoride GCs). It is shown that tailorable white light is much more sensitive to lower dopant concentration for GCs than that for glass. Furthermore, compared to glass, UC fluorescence intensities in GCs have approximately two orders of magnitude enhancement. The feasibility of the judicious dual‐lasers excitation tactic is validated for high efficacious RGB fluorescence emission for white light from Pr3+ single‐doped GCs via electronics transition dynamics and theoretical calculations. The white light emission from Pr3+ single‐doped GCs, adjusted by simultaneous dual‐lasers excitation, may open a novel door to develop white light GCs fiber lasers for application in future wireless communication.

Multilayer Graphene-WSe2 Heterostructures for WSe2 Transistors.

Two-dimensional (2D) materials are drawing growing attention for next-generation electronics and optoelectronics owing to its atomic thickness and unique physical properties. One of the challenges posed by 2D materials is the large source/drain (S/D) series resistance due to their thinness, which may be resolved by thickening the source and drain regions. Recently explored lateral graphene-MoS21-3 and graphene-WS21,4 heterostructures shed light on resolving the mentioned issues owing to their superior ohmic contact behaviors. However, recently reported field-effect transistors (FETs) based on graphene-TMD heterostructures have only shown n-type characteristics. The lack of p-type transistor limits their applications in complementary metal-oxide semiconductor electronics. In this work, we demonstrate p-type FETs based on graphene-WSe2 lateral heterojunctions grown with the scalable CVD technique. Few-layer WSe2 is overlapped with the multilayer graphene (MLG) at MLG-WSe2 junctions such that the contact resistance is reduced. Importantly, the few-layer WSe2 only forms at the junction region while the channel is still maintained as a WSe2 monolayer for transistor operation. Furthermore, by imposing doping to graphene S/D, 2 orders of magnitude enhancement in Ion/Ioff ratio to ∼108 and the unipolar p-type characteristics are obtained regardless of the work function of the metal in ambient air condition. The MLG is proposed to serve as a 2D version of emerging raised source/drain approach in electronics.

Multiphoton Effects Enhanced due to Ultrafast Photon-Number Fluctuations.

The rate of an n-photon effect generally scales as the nth order autocorrelation function of the incident light, which is high for light with strong photon-number fluctuations. Therefore, "noisy" light sources are much more efficient for multiphoton effects than coherent sources with the same mean power, pulse duration, and repetition rate. Here we generate optical harmonics of the order of 2-4 from a bright squeezed vacuum, a state of light consisting of only quantum noise with no coherent component. We observe up to 2 orders of magnitude enhancement in the generation of optical harmonics due to ultrafast photon-number fluctuations. This feature is especially important for the nonlinear optics of fragile structures, where the use of a noisy pump can considerably increase the effect without overcoming the damage threshold.

A Compatible Sensitivity Enhancement Strategy for Electrochemiluminescence Immunosensors Based on the Biomimetic Melanin-Like Deposition.

In this work, a compatible strategy was demonstrated for the enhancement of detection sensitivity of sandwich-type electrochemiluminescence (ECL) immunosensors. The enhanced signal response was based on the combination of biomimetic melanin-like deposition with the effective ECL quenching ability of quinone-rich biopolymers. Gold nanoparticle-loaded horseradish peroxidase (HRP) was used as a catalytic label for the secondary antibodies. The intrinsic catalytic property of HRP toward hydrogen peroxide (H2O2) generates reactive oxygen species, which highly promote the autopolymerization of catecholamines. The resulting fast deposition of quinone-rich biopolymers approaching the luminophor-incorporated sensing platform achieves an obvious ECL quenching. A broad-spectrum tumor marker alpha fetoprotein (AFP) was selected as a model analyte to demonstrate the feasibility of the proposed strategy. Under optimal conditions, a very low detection limit of 0.056 pg mL-1 was obtained. Two orders of magnitude enhancement was achieved in contrast to the signal response without the step of catalytic biopolymer deposition. The combination of compatible HRP labeling with unique melanin-like deposition has potential as a universal strategy in other ECL bioassays.

Multifurcate Assembly of Slanted Micropillars Fabricated by Superposition of Optical Vortices and Application in High‐Efficiency Trapping Microparticles

AbstractSelf‐assembly induced by capillary force is abundant in nature and has been widely used in fabrication as a bottom‐up method. Here a rapid and flexible method for achieving an even number of furcate slanted micropillars by single‐exposure under a spatial phase modulated laser beam is reported, which is produced by designing a superimposed hologram with opposite topological charges to split the incident beam into several equal‐weighting sectors. These furcate micropillars with intentional spatial arrangement can be directed to capillary‐assisted self‐assembly process for generating designable hierarchical functional arrays. Due to the slanted characteristic of micropillars (8°–13°), the assembled arrays are very stable and can be used as an effective tool for trapping SiO2 particles to form honeycomb patterns with an ultrahigh trapping ratio (>90%), which can image as a microlens array. The investigation reveals that micropillars with a height of 6 µm exhibit the high trapping ratio of particles, which maintain a fine imaging performance. The fast fabrication (more than 2 orders of magnitude enhancement) of furcate slanted pillars paves an avenue for developing innovative microoptics, microfluidics and biological scaffold engineering.

Enhanced spin Hall effect of reflected light with guided-wave surface plasmon resonance

The photonic spin Hall effect (SHE) has been intensively studied and widely applied, especially in spin photonics. However, the SHE is weak and is difficult to detect directly. In this paper, we propose a method to enhance SHE with the guided-wave surface-plasmon resonance (SPR). By covering a dielectric with high refractive index on the surface of silver film, the photonic SHE can be greatly enhanced, and a giant transverse shift of horizontal polarization state is observed due to the evanescent field enhancement near the interface at the top dielectric layer and air. The maximum transverse shift of the horizontal polarization state with 11.5 μm is obtained when the thickness of Si film is optimum. There is at least an order of magnitude enhancement in contrast with the transverse shift in the conventional SPR configuration. Our research is important for providing an effective way to improve the photonic SHE and may offer the opportunity to characterize the parameters of the dielectric layer with the help of weak measurements and development of sensors based on the photonic SHE.

Effect of Carrier Localization on Electrical Transport and Noise at Individual Grain Boundaries in Monolayer MoS2.

Despite its importance in the large-scale synthesis of transition metal dichalcogenides (TMDC) molecular layers, the generic quantum effects on electrical transport across individual grain boundaries (GBs) in TMDC monolayers remain unclear. Here we demonstrate that strong carrier localization due to the increased density of defects determines both temperature dependence of electrical transport and low-frequency noise at the GBs of chemical vapor deposition (CVD)-grown MoS2 layers. Using field effect devices designed to explore transport across individual GBs, we show that the localization length of electrons in the GB region is ∼30-70% lower than that within the grain, even though the room temperature conductance across the GB, oriented perpendicular to the overall flow of current, may be lower or higher than the intragrain region. Remarkably, we find that the stronger localization is accompanied by nearly 5 orders of magnitude enhancement in the low-frequency noise at the GB region, which increases exponentially when the temperature is reduced. The microscopic framework of electrical transport and noise developed in this paper may be readily extended to other strongly localized two-dimensional systems, including other members of the TMDC family.

Ultra-low intensity UV detection using partitioned mesoporous TiO2

We report five orders of magnitude enhancement in the detection of ultra-low intensity UV light using a partitioned mesoporous TiO2. The device shows a responsivity of ∼ 0.1 A/W at the incident intensity of 100 μW cm−2. The responsivity is slightly dropped to ∼0.01 A/W at the ultra-low intensity of 14 μW cm−2. High responsivity of the partitioned structure is attributed to the increment of electron diffusion length due to anisotropic and directional diffusive transport. Results show that the partitioned mesoporous TiO2 behaves as a quasi-one dimensional transport media.

Toward achieving flexible and high sensitivity hexagonal boron nitride neutron detectors

Hexagonal boron nitride (h-BN) detectors have demonstrated the highest thermal neutron detection efficiency to date among solid-state neutron detectors at about 51%. We report here the realization of h-BN neutron detectors possessing one order of magnitude enhancement in the detection area but maintaining an equal level of detection efficiency of previous achievement. These 3 mm × 3 mm detectors were fabricated from 50 μm thick freestanding and flexible 10B enriched h-BN (h-10BN) films, grown by metal organic chemical vapor deposition followed by mechanical separation from sapphire substrates. Mobility-lifetime results suggested that holes are the majority carriers in unintentionally doped h-BN. The detectors were tested under thermal neutron irradiation from californium-252 (252Cf) moderated by a high density polyethylene moderator. A thermal neutron detection efficiency of ∼53% was achieved at a bias voltage of 200 V. Conforming to traditional solid-state detectors, the realization of h-BN epilayers with enhanced electrical transport properties is the key to enable scaling up the device sizes. More specifically, the present results revealed that achieving an electrical resistivity of greater than 1014 Ω⋅cm and a leakage current density of below 3 × 10−10 A/cm2 is needed to fabricate large area h-BN detectors and provided guidance for achieving high sensitivity solid state neutron detectors based on h-BN.

Crystalline Organic Pigment-Based Field-Effect Transistors.

Three conjugated pigment molecules with fused hydrogen bonds, 3,7-diphenylpyrrolo[2,3-f]indole-2,6(1H,5H)-dione (BDP), (E)-6,6'-dibromo-[3,3'-biindolinylidene]-2,2'-dione (IIDG), and 3,6-di(thiophen-2-yl)-2,5-dihydropyrrolo-[3,4-c]pyrrole-1,4-dione (TDPP), were studied in this work. The insoluble pigment molecules were functionalized with tert-butoxylcarbonyl (t-Boc) groups to form soluble pigment precursors (BDP-Boc, IIDG-Boc, and TDPP-Boc) with latent hydrogen bonding. The single crystals of soluble pigment precursors were obtained. Upon simple thermal annealing, the t-Boc groups were removed and the soluble pigment precursor molecules with latent hydrogen bonding were converted into the original pigment molecules with fused hydrogen bonding. Structural analysis indicated that the highly crystalline soluble precursors were directly converted into highly crystalline insoluble pigments, which are usually only achievable by gas-phase routes like physical vapor transport. The distinct crystal structure after the thermal annealing treatment suggests that fused hydrogen bonding is pivotal for the rearrangement of molecules to form a new crystal in solid state, which leads to over 2 orders of magnitude enhancement in charge mobility in organic field-effect transistor (OFET) devices. This work demonstrated that crystalline OFET devices with insoluble pigment molecules can be fabricated by their soluble precursors. The results indicated that a variety of commercially available conjugated pigments could be potential active materials for high-performance OFETs.

Degradation and recovery of graphene/polymer interfaces under cyclic mechanical loading

Interface failure is a common phenomenon for conventional composite materials when subjected to repeated mechanical loads, and it tends to be critical for nanocomposites due to several orders of magnitude enhancement in interfacial area. Herein, the graphene/poly(methyl methacrylate) (PMMA) interface when subjected to cyclic loading conditions exhibits obvious mechanical degradation through interfacial sliding, which has received little attention yet. Through a joint study of experimental tests and molecular dynamics simulations, the interface weakening is attributed to the formation of graphene buckles that not only reduces the interfacial contact area but also impairs the overall interfacial load transfer. However, reminiscent of the shape memory effect that is commonly triggered by temperature, conformational transition at the interfaces exhibits remarkable mechanical recovery under a moderate thermal stimulus, manifested by the interface reconstruction activated by van der Waals (vdW) forces. These findings elucidate the complex interactions between matrix and nanostructures in composite materials under cyclic loading conditions, and control over this mechanism could provide guidelines upon chemical design through tailoring the interfacial adhesion for specific applications.

Corrugated-enhanced second harmonic generation in metal–insulator–metal plasmonic waveguides

Nonlinear effects such as second-harmonic generation (SHG) are important for applications such as switching and wavelength conversion. In this study, the generation of second harmonic in metal–insulator–metal (MIM) plasmonic waveguides was investigated for both symmetric and asymmetric structures. Symmetric means that the metals at the top and bottom of the dielectric layer are the same and asymmetric means that the metals at the top and bottom of the dielectric layer are different. Two different structures are considered here as plasmonic waveguide for generation of second harmonic and analyzed using finite-difference time domain method. Besides the structure has grating on both sides for more coupling between photons and plasmons. The wavelength duration of grating per length unit (number of grooves) will be optimized to reach the highest second harmonic generation. To perform this optimization, the wavelength of operation λ = 458 nm is considered. It was shown that field enhancement in symmetric MIM waveguides can result in enhancement of SHG magnitude compared to the literature values and asymmetric device results in more than two orders of magnitude enhancement in SHG compared to symmetric structure. It is also shown that the electric field of second harmonic depends on the thickness of crystal (insulator). So, its thickness is optimized to achieve the highest electric field.

Influence of Terephthalic Acid Substituents on the Catalytic Activity of MIL‐101(Cr) in Three Lewis Acid Catalyzed Reactions

AbstractSix isostructural MIL‐101(Cr)‐X (X: H, NO2, SO3H, Cl, CH3, and NH2) materials have been prepared directly by the reaction of CrIII salts and the corresponding terephthalic acid or by postsynthetic treatments of preformed MIL‐101(Cr) following reported procedures. The materials were characterized by using XRD (crystallinity and coincident diffraction pattern), isothermal N2 adsorption (specific surface areas range from 2740 m2 g−1 for MIL‐101(Cr)‐H to 1250 m2 g−1 for MIL‐101(Cr)‐Cl), thermogravimetry (thermal stability up to 400 °C), and IR spectroscopy (detection of the corresponding substituents), and the results were all in agreement with the reported data for these materials. The MIL‐101(Cr) materials were tested as heterogeneous catalysts for epoxide ring opening by methanol, benzaldehyde acetalization by methanol, and Prins coupling, observing a clear influence of the substituent that in general follows a linear relationship with the Hammett σmeta constant of the substituent: the catalytic activity increases as the electron‐withdrawing ability of the substituents increases. An up to three orders of magnitude enhancement in the presence of the NO2 substituent was found for some of these reactions. The present study illustrates the versatility that metal–organic frameworks offer as heterogeneous catalysts that allow the design of actives sites with adequate properties tuned for each reaction.

Enhanced mechanical, dielectric, electrical and thermal conductive properties of HXNBR/HNBR blends filled with ionic liquid-modified multiwalled carbon nanotubes

1-Butyl 3-methylimidazolium bis(trifluoromethylsulfonyl) imide (BMI)-modified multiwalled carbon nanotubes (MWCNTs) were used as nanofillers for the hydrogenated carboxylated nitrile–butadiene rubber/hydrogenated nitrile–butadiene rubber (HXNBR/HNBR) blends. The multifunctional properties of rubber nanocomposites with various filler loadings were investigated. It was found that in the presence of BMI-MWCNTs, the mechanical strength, dielectric properties, electrical and thermal conductivities of HXNBR/HNBR were significantly improved due to the better dispersibility as well as the intrinsic reinforcement effect of MWCNTs. Particularly, in comparison with unfilled rubber blend, the electrical conductivity of BMI-MWCNTs-filled HXNBR/HNBR composites exhibited three orders of magnitude enhancement with a lower electrical percolation threshold. The tensile strength and thermal conductivity of composites filled with 5 phr (parts per hundred rubber) BMI-MWCNTs increased by 52 and 23%, respectively. In addition, the polarizability of composites was also intensified under the applied electric field, which resulted in remarkable dielectric relaxation compared to neat rubber. Our experimental data have indicated that BMI-MWCNTs can be used as a promising candidate for fabricating multifunctional HXNBR/HNBR nanocomposites.

In situ electrochemical high-energy X-ray diffraction using a capillary working electrode cell geometry.

The ability to generate new electrochemically active materials for energy generation and storage with improved properties will likely be derived from an understanding of atomic-scale structure/function relationships during electrochemical events. Here, the design and implementation of a new capillary electrochemical cell designed specifically for in situ high-energy X-ray diffraction measurements is described. By increasing the amount of electrochemically active material in the X-ray path while implementing low-Z cell materials with anisotropic scattering profiles, an order of magnitude enhancement in diffracted X-ray signal over traditional cell geometries for multiple electrochemically active materials is demonstrated. This signal improvement is crucial for high-energy X-ray diffraction measurements and subsequent Fourier transformation into atomic pair distribution functions for atomic-scale structural analysis. As an example, clear structural changes in LiCoO2 under reductive and oxidative conditions using the capillary cell are demonstrated, which agree with prior studies. Accurate modeling of the LiCoO2 diffraction data using reverse Monte Carlo simulations further verifies accurate background subtraction and strong signal from the electrochemically active material, enabled by the capillary working electrode geometry.

Optoelectronic properties of novel alkyl-substituted Triphenylamine derivatives

Hole transport characteristics in three new organic compounds based on triphenylamine (TPA) moiety are presented. The effect on electrical and optical properties of TPA, attached with methyl or tert-butyl side groups, has been investigated through measurement of current density versus voltage (J-V), capacitance versus voltage (C-V), frequency dependent capacitance, ac conductivity, Impedance spectroscopy, UV-Vis spectroscopy, Photoluminescence (PL) spectroscopy and X-Ray Diffraction (XRD) studies. These measurements reveal that, the attachment of methyl or tert-butyl group in the para-position of the TPA moiety leads to improved optoelectronic properties and greater molecular stability. XRD analysis of the samples indicates that the inter-molecular distance is the lowest for TPA with tert-butyl side group (3.43 Å) as compared to pure TPA (3.57 Å). This leads to stronger inter-molecular interaction as evidenced by the UV-Vis spectra. PL studies indicate significant Quantum Efficiency (∼30%) for alkyl attached TPA. In order to get a better understanding of the charge transport phenomena, the effect of molecular structure dynamics on charge transfer kinetics is analyzed by evaluating the charge carrier hopping rate coefficient and dynamic state factor. The dynamic state factor b has higher value for lower bias voltage, corresponding to dc conductivity, whereas, at higher bias, the value of b is smaller, indicating the dominance of ac conductivity. Hopping conductivity is seen to be highest for the device with tert-butyl substitution in TPA moiety. Our experiments indicate an order of magnitude enhancement in charge carrier mobility for alkyl-substituted TPA.

Increased Electric Conductivity upon I2 Uptake and Gas Sorption in a Pillar-Layered Metal-Organic Framework.

The use of molecular iodine to tune the electrical conductivity in metal-organic frameworks is an effective but seldom investigated strategy. Herein, the single-crystal-to-single-crystal transformation of [Co1.5 (bdc)1.5 (H2 bpz)]⋅DMF⋅4 H2 O (1) to [Co1.5 (bdc)1.5 (H2 bpz)]⋅0.5 I2 ⋅DMF (I2 @1) (H2 bdc=1,4-benzenedicarboxylic acid, H2 bpz=3,3',5,5'-tetramethyl-4,4'-bipyrazole) upon I2 loading caused a three orders of magnitude enhancement in electrical conductivity of the framework. Single-crystal X-ray diffraction revealed that I2 exists as a single molecule embedded in the channels of framework, and the C-H⋅⋅⋅I hydrogen bonds between I2 molecules and phenyl units on the porous surface of the framework were suggested to participate in n→σ* host-guest charge transfer, leading to increased electrical conductivity in I2 @1. Furthermore, 1 displayed moderate adsorption selectivity for CO2 over CH4 and N2 .

Chirp control on molecular harmonic generation and distribution in H2+

ABSTRACTChirp control on the molecular harmonic emission and distribution in H2+ has been theoretically investigated. The results show that (i) with the introduction of the up-chirped pulse, the intensities of the higher harmonics are decreased; while with the introduction of the down-chirped pulse, the intensities of the higher harmonics can be enhanced. When E(t) < 0.0, the harmonic emission events (HEEs) from the positive-H are higher than those from the negative-H; while when E(t) > 0.0, the HEEs from the negative-H are higher than those from the positive-H. As a result, when the higher harmonics are produced from E(t) < 0.0 or E(t) > 0.0, the positive-H or the negative-H plays the main role in the harmonic spectra. (ii) The distribution of the higher harmonics from the two-H nuclei can be controlled with the introduction of the chirps and the carrier-envelope-phases of the laser field. (iii) Some minima on the harmonic spectra can be obtained, which is attributed to the coupling of the two-center interference and the electron-nuclear dynamics. (iv) By properly superposing the harmonics from the down-chirped pulse, an isolated attosecond pulse (IAP) with the duration of 45 as can be obtained, which is nearly 1 order of magnitude enhancement in pulse intensity compared with the chirp- free case.

Quantum-coherence-enhanced transient surface plasmon lasing

Quantum coherence and interference offer novel pathways to control light–matter interaction at the atomic scale, with enticing prospects in both fundamental and applied science. Here, we demonstrate coherent control over transient excitation of localized surface plasmon modes of a silver nanosphere adjacent to a quantum coherence medium composed of three-level quantum emitters, using a theoretical approach. We show that quantum interference enables more than two orders of magnitude enhancement in the surface plasmon field generated when the quantum emitters are driven coherently, in comparison to incoherent pumping. Furthermore, under optimal conditions, intense surface plasmon lasing can be induced without population inversion on the spasing transition. Our results open up the possibility of overcoming dissipative losses in plasmonic modes in the transient regime when steady-state population inversion is difficult to achieve due to fast relaxation rates and impractical pumping requirements.

Niobium pentoxide: a promising surface-enhanced Raman scattering active semiconductor substrate

Surface-enhanced Raman scattering technique, as a powerful tool to identify the molecular species, has been severely restricted to the noble metals. The surface-enhanced Raman scattering substrates based on semiconductors would overcome the shortcomings of metal substrates and promote development of surface-enhanced Raman scattering technique in surface science, spectroscopy, and biomedicine studies. However, the detection sensitivity and enhancement effects of semiconductor substrates are suffering from their weak activities. In this work, a semiconductor based on Nb2O5 is reported as a new candidate for highly sensitive surface-enhanced Raman scattering detection of dye molecules. The largest enhancement factor value greater than 107 was observed with the laser excitation at 633 and 780 nm for methylene blue detection. As far as literature review shows, this is in the rank of the highest sensitivity among semiconductor materials; even comparable to the metal nanostructure substrates with “hot spots”. The impressive surface-enhanced Raman scattering activities can be attributed to the chemical enhancement dominated by the photo-induced charge transfer, as well as the electromagnetic enhancement, which have been supported by the density-functional-theory and finite element method calculation results. The chemisorption of dye on Nb2O5 creates a new highest occupied molecular orbital and lowest unoccupied molecular orbital contributed by both fragments in the molecule-Nb2O5 system, which makes the charge transfer more feasible with longer excitation wavelength. In addition, the electromagnetic enhancement mechanism also accounts for two orders of magnitude enhancement in the overall enhancement factor value. This work has revealed Nb2O5 nanoparticles as a new semiconductor surface-enhanced Raman scattering substrate that is able to replace noble metals and shows great potentials applied in the fields of biology related.