InGaAsP/InP photodetectors targeting on 1.06 μm wavelength detection

InP-based InGaAsP photodetectors targeting on 1.06 μm wavelength detection have been grown by gas source molecular beam epitaxy and demonstrated. For the detector with 200 μm mesa diameter, the dark current at 10 mV reverse bias and R₀A are 8.89 pA (2.2 × 10⁻⁸ A/cm²) and 3.9 × 10⁵ Ω cm² at room temperature. The responsivity and detectivity of the InGaAsP detector are 0.30 A/W and 1.45 × 10¹² cm Hz^1/2 W⁻¹ at 1.06 μm wavelength. Comparing to the reference In_0.53Ga_0.47As detector, the dark current of this InGaAsP detector is about 570 times lower and the detectivity is more than ten times higher, which agrees well with the theoretical estimation.     

Synthesis of tunable core–shell nanostructures based on TiO2-graphene architectures and their application in the photodegradation of rhodamine dyes

We present the synthesis of core–shell nanostructural materials with multi-component architectures based on TiO₂ and graphitic layers. The composites have been synthesized by chemical vapor deposition with methane as the carbon source, for 5, 10, 30 and 45 min. The final products were characterized by a combination of analytical approaches which include: electron microscopy, Raman, FT-IR and UV–vis spectroscopy as well as thermogravimetric analysis. The amount of graphene shells covering the TiO₂ surfaces was found to vary linearly with the reaction time. Furthermore, the compounds were shown to have excellent stability and photocatalytic activity towards the UV degradation of rhodamine (RhB) dye solution at room temperature. These composites could have major applications in the area of environmental cleaning of various pollutants, electrochemistry or nanomedicine.     

Cooperative spectrum sharing MIMO systems with successive decoding

A spectrum sharing system with primary and secondary nodes, each equipped with an arbitrary number of antennas, is investigated. Particularly, the outage performance of an underlay cognitive system is analytically studied, in the case when the end-to-end ($e2e$) communication is established via an intermediate relay node. To better enhance the $e2e$ communication, successive interference cancellation (SIC) is adopted, which compensates for both the transmission power constraint and the presence of interference from primary nodes. Both the relay and secondary receiver perform unordered SIC to successively decode the multiple streams, whereas the decode-and-forward relaying protocol is used for the $e2e$ communication. New closed-form expressions for the $e2e$ outage performance of each transmitted stream are derived in terms of finite sum series of the Tricomi confluent hypergeometric function. In addition, simplified yet tight approximations for the asymptotic outage performance are obtained. Useful engineering insights are manifested, such as the diversity order of the considered system and the impact of interference from the primary nodes in conjunction with the constrained transmission power of the secondary nodes.     

Gauge functions and Galilean invariance of Lagrangians

A novel method to make Lagrangians Galilean invariant is developed. The method, based on null Lagrangians and their gauge functions, is used to demonstrate the Galilean invariance of the Lagrangian for Newton's law of inertia. It is suggested that this new solution of an old physics problem may have implications and potential applications to all gauge-based theories of physics.     

Solitons and conservation laws in magneto–optic waveguides having parabolic–nonlocal law of refractive index

This paper reveals soliton solutions to magneto–optic waveguides that maintain parabolic–nonlocal law of refractive index. The unified Riccati equation expansion together with extended auxiliary equation approach together reveal bright, dark, singular as well as straddled optical solitons. These soliton solutions are obtained through a limiting process when the modulus of ellipticity approaches unity. Finally, the conservation laws are also listed.     

Comparative study of optical analysis methods for thin films

Three popular optical analysis methods (the transfer-matrix method, the Tinkham formula, and Beer's law) have been used for analyzing the optical spectra of thin films. While the transfer-matrix method is an accurate method, the Tinkham formula and Beer's law are approximate methods. Here we investigated the three methods using measured transmittance spectra of insulating transition-metal dichalcogenide (TMD) thin films on a quartz substrate. Three different semiconducting 2H-TMD systems (MoS₂, MoSe₂, and MoTe₂) were measured and analyzed. The optical conductivities obtained from the measured transmittance spectra using the transfer-matrix method and Tinkham formula and the absorption coefficients obtained using the transfer-matrix method and Beer's law were compared. The comparisons show some discrepancies. The reasons for the discrepancies between the results obtained via the two different methods were examined and the application limitations of the Tinkham formula and Beer's law were discussed.     

Sonication enhances the stability of MnO2 nanoparticles on silk film template for enzyme mimic application

We have developed an in-situ method using sonication (3 mm probe sonicator, 30 W, 20 kHz) and auto-reduction (control) to study the mechanism of the formation of manganese dioxide (MnO₂) on a solid template (silk film), and its resulting enzymatic activity on tetramethylbenzidine (TMB) substrate. The fabrication of the silk film was first optimized for stability (no degradation) and optical transparency. A factorial approach was used to assess the effect of sonication time and the initial concentration of potassium permanganate (KMnO₄). The result indicated a significant correlation with a fraction of KMnO₄ consumed and MnO₂ formation. Further, we found that the optimal process conditions to obtain a stable silk film with highly catalytic MnO₂ nanoparticles (NPs) was 30 min of sonication in the presence of 0.5 mM of KMnO₄ at a temperature of 20–24 °C. Under the optimal condition, we monitored in-situ the formation of MnO₂ on the silk film, and after thorough rinsing, the in-situ catalysis of 0.8 mM of TMB substrate. For control, we used the auto-reduction of KMnO₄ onto the silk film after about 16 h. The result from single-wavelength analysis confirmed the different kinetics rates for the formation of MnO₂ via sonication and auto-reduction. The result from the multivariate component analysis indicated a three components route for sonication and auto-reduction to form MnO₂-Silk. Overall, we found that the smaller size, more mono-dispersed, and deeper buried MnO₂ NPs in silk film prepared by sonication, conferred a higher catalytic activity and stability to the hybrid material.     

First-principles investigation on ideal strength of B2 NiAl and NiTi alloys

For B2 NiAl and NiTi intermetallic compounds, the ideal stress–strain image is lack from the perspective of elastic constants. We use first-principles calculation to investigate the ideal strength and elastic behavior under the tensile and shear loads. The relation between the ideal strength and elastic constants is found. The uniaxial tension of NiAl and NiTi along <001> crystal direction leads to the change from tetragonal path to orthogonal path, which is driven by the vanishing of the shear constant C(66). The shear failure under {110}{111} shear deformation occurring in process of tension may result in a small ideal tensile strength(~ 2 GPa) for NiTi. The unlikeness in the ideal strength of Ni Al and Ni Ti alloys is discussed based on the charge density difference.     

Magneto-thermoelasticity with thermoelectric properties and fractional derivative heat transfer

In this work, a new model of the magneto-thermoelasticity theory has been constructed in the context of a new consideration of heat conduction with fractional derivative. A one-dimensional application for a conducting half-space of thermoelectric elastic material, which is thermally shocked in the presence of a magnetic field, has been solved using Laplace transform and state-space techniques (Ezzat, 2008 [1]). According to the numerical results and its graphs, a conclusion about the new theory of magneto-thermoelasticity has been constructed. The theories of coupled magneto-thermoelasticity and of generalized magneto-thermoelasticity with one relaxation time follow as limited cases. The result provides a motivation to investigate conducting thermoelectric materials as a new class of applicable materials.     

The structural and catalytic properties of nanoparticles@MOF composites: A case study of Au@ZIF-8 hybrid crystals

Strain analysis of the MOF and its composites using high-resolution X-ray diffractionmeter (XRD) was carried out and the presence of non-uniform, depth-related strain in the MOF crystals was confirmed. Further analysis showed that the magnitude and distribution of strain in MOF crystals can be tuned with the incorporation of nanoparticles (NPs). Moreover, the spatial controlled structures can also optimize functionalities of the NPs@MOF, which was exemplified by their applications on the catalytic reduction of nitroarenes. It is anticipated that the investigation of MOF structure evolution through controlling the architectures of the MOF/NPs hybrid materials will shed a light on the study of optimizing the mechanical and chemical properties of MOF composites.