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1.
Nano Lett ; 23(2): 469-475, 2023 Jan 25.
Artigo em Inglês | MEDLINE | ID: mdl-36630601

RESUMO

Sodium (Na) is predicted to be an ideal plasmonic material with ultralow optical loss across visible to near-infrared (NIR). However, there has been limited research on Na plasmonics. Here we develop a scalable fabrication method for Na nanostructures by combining phase-shift photolithography and a thermo-assisted spin-coating process. Using this method, we fabricated Na nanopit arrays with varying periodicities (300-600 nm) and with tunable surface plasmon polariton (SPP) modes spanning visible to NIR. We achieved SPP resonances as narrow as 9.3 nm. In addition, Na nanostructures showed line width narrowing from visible toward NIR, showing their prospect operating in the NIR. To address the challenges associated with the high reactivity of Na, we designed a simple encapsulation strategy and stabilized the Na nanostructures in ambient conditions for more than two months. As a low-cost and low-loss plasmonic material, Na offers a competitive option for nanophotonic devices and plasmon-enhanced applications.

2.
Nano Lett ; 23(15): 7150-7156, 2023 Aug 09.
Artigo em Inglês | MEDLINE | ID: mdl-37477493

RESUMO

Alkali metals have low optical losses in the visible to near-infrared (NIR) compared with noble metals. However, their high reactivity prohibits the exploration of their optical properties. Recently sodium (Na) has been experimentally demonstrated as a low-loss plasmonic material. Here we report on a thermo-assisted nanoscale embossing (TANE) technique for fabricating plasmonic nanostructures from pure potassium (K) and NaK liquid alloys. We show high-quality-factor resonances from K as narrow as 15 nm in the NIR, which we attribute to the high material quality and low optical loss. We further demonstrate liquid Na-K plasmonics by exploiting the Na-K eutectic phase diagram. Our study expands the material library for alkali metal plasmonics and liquid plasmonics, potentially enabling a range of new material platforms for active metamaterials and photonic devices.

3.
Molecules ; 29(8)2024 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-38675709

RESUMO

The pretreatment for torrefaction impacts the performance of biomass fuels and operational costs. Given their diversity, it is crucial to determine the optimal torrefaction conditions for different types of biomass. In this study, three typical solid biofuels, corn stover (CS), agaric fungus bran (AFB), and spent coffee grounds (SCGs), were prepared using fluidized bed torrefaction. The thermal stability of different fuels was extensively discussed and a novel comprehensive fuel index, "displacement level", was analyzed. The functional groups, pore structures, and microstructural differences between the three raw materials and the optimally torrefied biochar were thoroughly characterized. Finally, the biomass fuel consumption for household heating and water supply was calculated. The results showed that the optimal torrefaction temperatures for CS, AFB, and SCGs were 240, 280, and 280 °C, respectively, with comprehensive quality rankings of the optimal torrefied biochar of AFB (260) > SCG (252) > CS (248). Additionally, the economic costs of the optimally torrefied biochar were reduced by 7.03-19.32%. The results indicated that the displacement level is an index universally applicable to the preparation of solid fuels through biomass torrefaction. AFB is the most suitable solid fuel to be upgraded through torrefaction and has the potential to replace coal.


Assuntos
Biocombustíveis , Biomassa , Carvão Vegetal , Zea mays , Carvão Vegetal/química , Zea mays/química , Café/química , Temperatura
4.
Molecules ; 29(9)2024 Apr 27.
Artigo em Inglês | MEDLINE | ID: mdl-38731506

RESUMO

The mechanism of ammonia formation during the pyrolysis of proteins in biomass is currently unclear. To further investigate this issue, this study employed the AMS 2023.104 software to select proteins (actual proteins) as the model compounds and the amino acids contained within them (assembled amino acids) as the comparative models. ReaxFF molecular dynamics simulations were conducted to explore the nitrogen transformation and NH3 generation mechanisms in three-phase products (char, tar, and gas) during protein pyrolysis. The research results revealed several key findings. Regardless of whether the model compounds are actual proteins or assembled amino acids, NH3 is the primary nitrogen-containing product during pyrolysis. However, as the temperature rises to higher levels, such as 2000 K and 2500 K, the amount of NH3 decreases significantly in the later stages of pyrolysis, indicating that it is being converted into other nitrogen-bearing species, such as HCN and N2. Simultaneously, we also observed significant differences between the pyrolysis processes of actual proteins and assembled amino acids. Notably, at 2000 K, the amount of NH3 generated from the pyrolysis of assembled amino acids was twice that of actual proteins. This discrepancy mainly stems from the inherent structural differences between proteins and amino acids. In proteins, nitrogen is predominantly present in a network-like structure (NH-N), which shields it from direct external exposure, thus requiring more energy for nitrogen to participate in pyrolysis reactions, making it more difficult for NH3 to form. Conversely, assembled amino acids can release NH3 through a simpler deamination process, leading to a significant increase in NH3 production during their pyrolysis.


Assuntos
Amônia , Simulação de Dinâmica Molecular , Proteínas , Pirólise , Amônia/química , Proteínas/química , Aminoácidos/química , Nitrogênio/química
5.
Opt Express ; 31(17): 27894-27904, 2023 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-37710855

RESUMO

A doping optimization model towards lower loss and higher efficiency at the target operating current is investigated. This model considers the effect of doping concentration on the series resistance and the internal loss. 780 nm lasers doped with a normal doping profile (Dop_normal) and an optimized doping profile (Dop_optimize) are both designed and fabricated. After doping optimization, the power loss decreased by 17%, the output power of the lasers increased by 26% and the electro-optical conversion efficiency increased by 22%. The model provides significant theoretical guidance for the optimization of the laser doping.

6.
Opt Lett ; 47(13): 3231-3234, 2022 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-35776593

RESUMO

In this study, a low-resistance, low-loss, continuously gradual composition extreme double asymmetric (CGC-EDAS) epitaxial structure is designed to improve efficiency. The structure and facet reflectivity of the broad area (BA) lasers are optimized to maximize the power conversion efficiency (PCE). In the experiment, the peak PCE of 75.36% is measured at 25°C. At 0°C, a peak PCE of 81.10% is measured and the PCE can still reach 77.84% at an output power of 17.10 W, which, to the best of our knowledge, is the highest value to date for any BA lasers.

7.
Opt Lett ; 47(10): 2486-2489, 2022 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-35561382

RESUMO

A high-power tunable dual-wavelength composite external cavity architecture obtained by means of a holographic grating and a volume Bragg grating is proposed and demonstrated. The tunable frequency difference of the dual-wavelength output is from 0.41 THz to 3.89 THz. We obtain an output power of 2.1 W when the frequency difference is 1.86 THz. The side-mode suppression ratio of more than 29 dB is suppressed over the entire tunable dual-wavelength output range. The two corresponding wavelengths of the dual-wavelength output basically maintain the same intensity with the smallest power difference of only 0.10%.

8.
Phys Rev Lett ; 124(18): 187701, 2020 May 08.
Artigo em Inglês | MEDLINE | ID: mdl-32441982

RESUMO

We demonstrate a voltage-controlled exchange bias effect in CoFeB/MgO/CoFeB magnetic tunnel junctions that is related to the interfacial Fe(Co)O_{x} formed between the CoFeB electrodes and the MgO barrier. The unique combination of interfacial antiferromagnetism, giant tunneling magnetoresistance, and sharp switching of the perpendicularly magnetized CoFeB allows sensitive detection of the exchange bias. We find that the exchange bias field can be isothermally controlled by magnetic fields at low temperatures. More importantly, the exchange bias can also be effectively manipulated by the electric field applied to the MgO barrier due to the voltage-controlled antiferromagnetic anisotropy in this system.

9.
Opt Express ; 26(3): 3518-3526, 2018 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-29401879

RESUMO

High-power high-brightness super large optical cavity laser diodes with an optimized epitaxial structure are investigated at the wavelength of 980 nm range. The thicknesses of P- and N-waveguides are prudently chosen based on a systematic consideration about mode characteristics and vertical far-field divergences. Broad area laser diodes show a high internal quantum efficiency of 98% and a low internal optical loss of 0.58 cm-1. The ridge-waveguide laser with 7 µm ridge and 3 mm cavity yields 1.9 W single spatial mode output with far-field divergence angles of 6.8° in lateral and 11.5° in vertical at full width at half maximum under 2 A CW operating current. The corresponding M2 values are 1.77 and 1.47 for lateral and vertical, respectively, and the corresponding brightness is 76.8 MW‧cm-2‧sr-1. The far-field divergence angles with 95% power content are in the range of 24.7° to 26.1° across the whole measured range.

10.
J Magn Magn Mater ; 460: 424-431, 2018 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-33981128

RESUMO

Ferrite-ferroelectric core-shell nanoparticles were prepared by deoxyribonucleic acid (DNA) assisted self-assembly and the strained mediated magneto-electric (ME) interactions between the ferroic phases were studied. The nanoparticle type and size were varied and the DNA linker sequence was also varied. Two kinds of particles, one with 600 nm barium titanate (BTO) core and 200 nm nickel ferrite (NFO) shell and another with 200 nm BTO core and 50 nm nickel cobalt ferrite (NCFO) shell were prepared. The particles were linked by three different oligomeric DNA containing 19, 18 or 30 base pairs. The core-shell structure was evident from electron microscopy and scanning microwave microscopy images. Films and disks of the core-shell particles were assembled in a magnetic field and used for measurements of low frequency ME voltage coefficient (MEVC) and magnet-dielectric effect. The MEVC data on films indicate that particles assembled with DNA with 30 base pairs exhibit the strongest ME coupling suggesting a more fully integrated heterogenous nanocomposite and the weakest interaction for DNA with 18 base pairs. These results indicate that the longer linker region in DNA is the key factor for forming better composites. This result may be due to the irregular shape of the nanoparticles. Longer DNA strands would be able to bridge better generating more linkages. Shorter strands would not able to bridge the irregularly shaped particles as well and therefore result in linkages and less heterogeneity in the composites.

11.
Sensors (Basel) ; 16(2): 262, 2016 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-26907290

RESUMO

Multiferroic composites with ferromagnetic and ferroelectric phases have been studied in recent years for use as sensors of AC and DC magnetic fields. Their operation is based on magneto-electric (ME) coupling between the electric and magnetic subsystems and is mediated by mechanical strain. Such sensors for AC magnetic fields require a bias magnetic field to achieve pT-sensitivity. Novel magnetic sensors with a permanent magnet proof mass, either on a ferroelectric bimorph or a ferromagnetic-ferroelectric composite, are discussed. In both types, the interaction between the applied AC magnetic field and remnant magnetization of the magnet results in a mechanical strain and a voltage response in the ferroelectric. Our studies have been performed on sensors with a Nd-Fe-B permanent magnet proof mass on (i) a bimorph of oppositely-poled lead zirconate titanate (PZT) platelets and (ii) a layered multiferroic composite of PZT-Metglas-Ni. The sensors have been characterized in terms of sensitivity and equivalent magnetic noise N. Noise N in both type of sensors is on the order of 200 pT/√Hz at 1 Hz, a factor of 10 improvement compared to multiferroic sensors without a proof mass. When the AC magnetic field is applied at the bending resonance for the bimorph, the measured N ≈ 700 pT/√Hz. We discuss models based on magneto-electro-mechanical coupling at low frequency and bending resonance in the sensors and theoretical estimates of ME voltage coefficients are in very good agreement with the data.

12.
Opt Lett ; 39(11): 3231-4, 2014 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-24876020

RESUMO

Double-tapered laser diodes with 23rd order laterally coupled surface gratings are fabricated at 913 nm. A narrow ridge waveguide restricts the lateral mode number, and tapered waveguides are utilized to enhance the output power. The gratings defined on the sides of ridge waveguide filter not only the longitudinal modes but also the high-order lateral modes. Experimentally, continuous wave power of over 560 mW/facet is achieved. The lateral far-field pattern exhibits a single-lobe profile and narrow divergence, and the lowest divergence angle is only twice the diffraction-limited one. The measured side-mode suppression ratio is about 27 dB. This device has great potential for high-power single-mode near-diffraction-limited laser emission with easy fabrication.

13.
Opt Express ; 21(1): 877-83, 2013 Jan 14.
Artigo em Inglês | MEDLINE | ID: mdl-23388981

RESUMO

In this paper, a III-V/Silicon hybrid single mode laser operating at a long wavelength for photonic integration circuit is presented. The InGaAlAs gain structure is bonded onto a patterned silicon-on insulator wafer directly. The novel mode selected mechanism based on a slotted silicon waveguide is applied, which only need standard photolithography in the whole technological process. The side mode suppression ratio of larger than 20dB is obtained from experiments.

14.
Opt Express ; 21(7): 8844-55, 2013 Apr 08.
Artigo em Inglês | MEDLINE | ID: mdl-23571974

RESUMO

A lateral cavity photonic crystal surface emitting laser (LC-PCSEL) with airholes of cone-like shape etched near to the active layer is fabricated. It employs only a simple commercial epitaxial wafer without DBR and needs no wafer bonding technique. Surface emitting lasing action at 1575 nm with power of 1.8 mW is observed at room temperature, providing potential values for mass production of electrically driven PCSELs with low cost. Additionally, Fano resonance is utilized to analyze aperture equivalence of PC, and energy distribution in simplified laser structure is simulated to show oscillation and transmission characteristics of laser.


Assuntos
Lasers , Refratometria/instrumentação , Ressonância de Plasmônio de Superfície/instrumentação , Desenho de Equipamento , Análise de Falha de Equipamento , Fótons
15.
Opt Lett ; 38(15): 2770-2, 2013 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-23903137

RESUMO

High-brightness, edge-emitting diode laser arrays integrated with a phase shifter have been designed and fabricated at a wavelength of about 910 nm. Stable out-of-phase mode is generated through coupling evanescently and converted to be nearly in-phase by the phase modulation from the phase shifter. With a very simple manufacture process, stable single-lobe far-field pattern is achieved in the slow axis when the continuous wave output power exceeds 460 mW/facet, and the divergence angle is only 2.7 times the diffraction-limited value. Such device shows a promising future for high-brightness application with low cost and easy fabrication.

16.
Opt Lett ; 38(6): 842-4, 2013 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-23503234

RESUMO

In this Letter, a III-V/silicon hybrid single-mode laser operating at C band for photonic integration circuit is presented. The InGaAlAs gain structure is bonded onto a patterned silicon-on insulator through wafer to wafer directly. The mode selected mechanism based on a hybrid III-V/silicon straight cavity with periodic microstructures is applied, which only need low cost i-line projection photolithography in the whole technological process. At room temperature, we obtain 0.62 mW output power in continuous-wave. The side mode suppression ratio of larger than 20 dB is obtained from experiments. [corrected].

17.
Sensors (Basel) ; 13(5): 5720-36, 2013 May 02.
Artigo em Inglês | MEDLINE | ID: mdl-23645109

RESUMO

This paper presents a fully differential single-axis accelerometer fabricated using the MetalMUMPs process. The unique structural configuration and common-centriod wiring of the metal electrodes enables a fully differential sensing scheme with robust metal sensing structures. CoventorWare is used in structural and electrical design and simulation of the fully differential accelerometer. The MUMPs foundry fabrication process of the sensor allows for high yield, good process consistency and provides 20 µm structural thickness of the sensing element, which makes the capacitive sensing eligible. In device characterization, surface profile of the fabricated device is measured using a Veeco surface profilometer; and mean and gradient residual stress in the nickel structure are calculated as approximately 94.7 MPa and -5.27 MPa/µm, respectively. Dynamic characterization of the sensor is performed using a vibration shaker with a high-end commercial calibrating accelerometer as reference. The sensitivity of the sensor is measured as 0.52 mV/g prior to off-chip amplification. Temperature dependence of the sensing capacitance is also characterized. A -0.021fF/°C is observed. The findings in the presented work will provide useful information for design of sensors and actuators such as accelerometers, gyroscopes and electrothermal actuators that are to be fabricated using MetalMUMPs technology.

18.
Sci Rep ; 13(1): 1179, 2023 Jan 20.
Artigo em Inglês | MEDLINE | ID: mdl-36670190

RESUMO

This work is on the design, fabrication and characterization of a hexagonal ferrite band-pass filter that can be tuned either with a magnetic field or an electric field. The filter operation is based on a straight-edge Y-type hexagonal ferrite resonator symmetrically coupled to the input and output microstrip transmission lines. The Zn2Yfilter demonstrated magnetic field tunability in the 8-12 GHz frequency range by applying an in-plane bias magnetic field H0 provided by a built-in permanent magnet. The insertion loss and 3 dB bandwidth within this band were 8.6 ± 0.4 dB and 350 ± 40 MHz, respectively. The electric field E tunability of the pass-band of the device was facilitated by the nonlinear magnetoelectric effect (NLME) in the ferrite. The E-tuning of the center frequency of the filter by (1150 ± 90) MHz was obtained for an input DC electric power of 200 mW. With efforts directed at a significant reduction in the insertion loss, the compact and power efficient magnetic and electric field tunable Zn2Y band-pass filter has the potential for use in novel reconfigurable RF/microwave devices and communication systems.

19.
Sci Rep ; 13(1): 18346, 2023 Oct 26.
Artigo em Inglês | MEDLINE | ID: mdl-37884633

RESUMO

The nature of nonlinear magnetoelectric (NLME) effect has been investigated at room-temperature in a single-crystal Zn substituted nickel ferrite. Tuning of the frequency of magnetostatic surface wave (MSSW) modes under an applied pulsed DC electric field/current has been utilized to probe the effect. The frequencies of the modes at 8-20 GHz were found to decrease by ~ 400 MHz for an applied DC power P of ~ 100 mW and the frequency shift was the same for all of the MSSW modes and linearly proportional to P. A model is proposed for the effect and the NLME phenomenon was interpreted in terms of a reduction in the saturation magnetization due to the DC current. The decrease of magnetization with applied electric power, estimated from data on mode frequency versus P, was - 2.50 G/mW. The frequency tuning efficiency of the MSSW modes due to NLME effects in the ferrite resonator was found to be 4.1 MHz/mW which is an order of magnitude higher than the shift reported for M-type strontium and barium hexaferrite resonators investigated earlier. The spinel ferrite resonator discussed here has the potential for miniature, electric field tunable, planar microwave devices for the 8-20 GHz frequency range.

20.
Sci Rep ; 12(1): 5374, 2022 Mar 30.
Artigo em Inglês | MEDLINE | ID: mdl-35354882

RESUMO

This report is on the observation and analysis of nonlinear magnetoelectric effects (NLME) for in-plane currents perpendicularly to the hexagonal axis in single crystals and liquid phase epitaxy grown thin films of barium hexaferrite. Measurements involved tuning of ferromagnetic resonance (FMR) at 56-58 GHz in the multidomain and single domain states in the ferrite by applying a current. Data on the shift in the resonance frequency with input electric power was utilized to estimate the variations in the magnetic parameter that showed a linear dependence on the input electric power. The NLME tensor coefficients were determined form the estimated changes in the magnetization and uniaxial anisotropy field. The estimated NLME coefficients for in-plane currents are shown to be much higher than for currents flowing along the hexagonal axis. Although the frequency shift of FMR was higher for the single domain resonance, the multi-domain configuration is preferable for device applications since it eliminates the need for a large bias magnetic field. Thus, multidomain resonance with current in the basal plane is favorable for use in electrically tunable miniature, ferrite microwave signal processing devices requiring low operating power.

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