Controlling the Spin Polarization of the Electron Current in a Semimagnetic Resonant-Tunneling Diode

The spin filtering effect of the electron current in a double-barrier resonant-tunneling diode (RTD) consisting of ZnMnSe semimagnetic layers has been studied theoretically. The influence of the distribution of the magnesium ions on the coefficient of the spin polarization of the electron current has been investigated. The dependence of the spin filtering degree of the electron current on the external magnetic field and the bias voltage has been obtained. The effect of the total spin polarization of the electron current has been predicted. This effect is characterized by total suppression of the spin-up component of electron current, that takes place when the Fermi level coincides with the lowest Landau level for spin-up electrons in the RTD semimagnetic emitter

Metabolic Syndrome Prediction Using Machine Learning Models with Genetic and Clinical Information from a Nonobese Healthy Population

The prevalence of metabolic syndrome (MS) in the nonobese population is not low. However, the identification and risk mitigation of MS are not easy in this population. We aimed to develop an MS prediction model using genetic and clinical factors of nonobese Koreans through machine learning methods. A prediction model for MS was designed for a nonobese population using clinical and genetic polymorphism information with five machine learning algorithms, including naïve Bayes classification (NB). The analysis was performed in two stages (training and test sets). Model A was designed with only clinical information (age, sex, body mass index, smoking status, alcohol consumption status, and exercise status), and for model B, genetic information (for 10 polymorphisms) was added to model A. Of the 7,502 nonobese participants, 647 (8.6%) had MS. In the test set analysis, for the maximum sensitivity criterion, NB showed the highest sensitivity: 0.38 for model A and 0.42 for model B. The specificity of NB was 0.79 for model A and 0.80 for model B. In a comparison of the performances of models A and B by NB, model B (area under the receiver operating characteristic curve [AUC] = 0.69, clinical and genetic information input) showed better performance than model A (AUC = 0.65, clinical information only input). We designed a prediction model for MS in a nonobese population using clinical and genetic information. With this model, we might convince nonobese MS individuals to undergo health checks and adopt behaviors associated with a preventive lifestyle

Optical properties of diluted magnetic semiconductors: I. Magnetooptics. II. Inelastic light scattering

Faraday effect in the wurtzite (uniaxial) diluted magnetic semiconductor (DMS), Cd\sb{\rm 1-x}Mn\sb{\rm x}Se, is studied with the magnetic field (H) either parallel or perpendicular its optic axis (c). For H$\Vert$c, the Faraday effect is qualitatively similar to that in the cubic DMS\u27s. The Faraday rotation, positive for CdSe, becomes negative and very large when Mn\sp{2+} replaces Cd\sp{2+}. The sign of the rotation and its dependence on x, H, and temperature T are dominated by the spin-spin exchange interaction between band electrons and Mn\sp{2+} electrons (sp-d exchange interaction). The dispersion of the Faraday effect is well described by an excitonic model. The antiferromagnetic coupling between Mn\sp{2+} ions is manifested in the Faraday effect through the phenomenological effective temperature (T+T\sb{\rm AF}), as well as with hysteresis effects associated with the formation of spin-glass phase for high x and low T. For H$\bot$c, the natural birefringence of Cd\sb{\rm 1-x}Mn\sb{\rm x}Se as well as the Faraday rotation affects the polarization of the light. Decomposing the combined effect into the separate contributions due to the birefringence and the Faraday effect, it is found that the dispersion of the Faraday constant is very similar for H$\bot$c and H$\Vert$c, although the Faraday effect for the former is smaller. In the Voigt geometry (H$\bot$k), the refractive index parallel to H differs from that perpendicular to H, resulting in a linear double refraction, called the Voigt effect. This effect is found to be very large in the DMS\u27s due to the large sp-d exchange interaction. An excitonic model describes the dispersion and H\sp2-dependence of the Voigt effect in Cd\sb{\rm 1-x}Mn\sb{\rm x}Te. The Voigt effect in Cd\sb{\rm 1-x}Mn\sb{\rm x}Se shows an anisotropy due to the crystal field splitting presented in the wurtzite DMS\u27s. The Raman scattering in a II-VI quaternary (Cd\sb{\rm 1-x-y}Zn\sb{\rm x}Mn\sb{\rm y}Te) exhibits vibrational excitation, the composition dependence of the frequencies of the zone-center optical phonons being amenable to an extension of the modified random-element isodisplacement model. As a member of DMS alloys Cd\sb{\rm 1-x-y}Zn\sb{\rm x}Mn\sb{\rm y}Te exhibits the pronounced magnetic-field dependence of the excitonic photoluminescence, Raman-electron paramagnetic resonance of Mn\sp{2+}, and evidence of Raman-antiferromagnetic resonance

Multi-Mode behavior of optical phonons in II-VI ternary and quaternary alloys

Zone-center optical phonons of tetrahedrally coordinatedII-VI semiconductor ternary (AB1-xCx) and quaternary (AB1-x-yCxDy) alloys display a variety of distinct multi-mode behavior patterns. A brief review of the modified random element isodisplacement model, which can satisfactorily account for the composition dependence of the frequencies of the zone-center optical phonons, is presented; in this model, one uses the macroscopic parameters of the binary end members and their LO-TO phonon frequencies. When a constituent is present in extreme dilution in a binary (or in a ternary), e.g., C in AB (or in AB1-yDy), one sees either a local or a gap mode associated with it. For higher concentrations, one can see two (three) LO-TO phonon pairs for the ternary (quaternary) in the first order Raman spectrum or in the infra-red deduced from an analysis of the reststrahlen bands, when the masses of B and C differ significantly but are lighter than that of A. We illustrate these features in the Raman spectra of Cd1-xMgxTe and Cd1-x-y MgxMnyTe. Also shown are the infra-red spectra of the local mode of Mg2+ and Mn2+ in Cd Te, where their isotopic nature is clearly manifested

Influence of Air Flow on Luminescence Quenching in Polymer Films towards Explosives Detection Using Drones

Explosive detection has become an increased priority in recent years for homeland security and counter-terrorism applications. Although drones may not be able to pinpoint the exact location of the landmines and explosives, the identification of the explosive vapor present in the surrounding air provides significant information and comfort to the personnel and explosives removal equipment operators. Several optical methods, such as the luminescence quenching of fluorescent polymers, have been used for explosive detection. In order to utilize sensing technique via unmanned vehicles or drones, it is very important to study how the air flow affects the luminescence quenching. We investigated the effects of air flow on the quenching efficiency of Poly(2,5-di(2′-ethylhexyl)-1,4-ethynylene) (PEE) by TNT molecules. We treated the TNT molecules incorporated into the polymer film as non-radiative recombination centers, and found that the time derivative of the non-radiative recombination rates was greater with faster air flows. Our investigations show that relatively high air flow into an optical sensing part is crucial to achieving fast PL quenching. We also found that a “continuous light excitation” condition during the exposure of TNT vapor greatly influences the PL quenching

Lateral PbS Photovoltaic Devices for High Performance Infrared and Terahertz Photodetectors

We fabricated a lateral photovoltaic device for use as infrared to terahertz (THz) detectors by chemically depositing PbS films on titanium substrates. We discussed the material properties of PbS films grown on glass with varying deposition conditions. PbS was deposited on Ti substrates and by taking advantage of the Ti/PbS Schottky junction, we discussed the photocurrent transients as well as the room temperature spectrum response measured by Fourier transform infrared (FTIR) spectrometer. Our photovoltaic PbS device operates at room temperature for wavelength ranges up to 50 µm, which is in the terahertz region, making the device highly applicable in many fields

Magneto-optic phenomena in II-VI diluted magnetic semiconductors: the Faraday and the Voigt effect

Pronounced magneto-optic effects - Faraday rotation and Voigt birefringence - characterize the II-VI diluted magnetic semiconductors. The large sp-d exchange interaction and the antiferromagnetic coupling between the magnetic ions manifest themselves in the studies of these effects as a function of magnetic field, temperature and the concentration of the magnetic ions. Illustrative examples are presented

Magneto-modulation of reflectivity of diluted magnetic semiconductors

The large sp-d exchange-enhanced g-factors, characteristic of the excitonic transitions of the II-VI diluted magnetic semiconductors, can be exploited in modulating the reflectivity spectra with applied alternating magnetic field. The magneto-modulated reflectivity spectrum thus obtained shows strong signatures in the vicinity of the excitonic transition, whose line-shape is the first derivative of the reflectivity spectrum. This technique has been demonstrated by applying it to bulk Cd<SUB>1-x</SUB>Mn<SUB>x</SUB>Te and Cd<SUB>1-x</SUB>Mn<SUB>x</SUB>Se and to a Zn<SUB>1-x</SUB>Cd<SUB>x</SUB>Se/Zn<SUB>1-y</SUB>Mn<SUB>y</SUB>Se superlattice

Detection of Explosives by SERS Platform Using Metal Nanogap Substrates

Detecting trace amounts of explosives to ensure personal safety is important, and this is possible by using laser-based spectroscopy techniques. We performed surface-enhanced Raman scattering (SERS) using plasmonic nanogap substrates for the solution phase detection of some nitro-based compounds, taking advantage of the hot spot at the nanogap. An excitation wavelength of 785 nm with an incident power of as low as ≈0.1 mW was used to excite the nanogap substrates. Since both RDX and PETN cannot be dissolved in water, acetone was used as a solvent. TNT was dissolved in water as well as in hexane. The main SERS peaks of TNT, RDX, and PETN were clearly observed down to the order of picomolar concentration. The variations in SERS spectra observed from different explosives can be useful in distinguishing and identifying different nitro-based compounds. This result indicates that our nanogap substrates offer an effective approach for explosives identification

Effect of point defect and Mn concentration in time-resolved differential reflection in GaMnAs

We measured the transmission spectra and the time-resolved differential reflectivity Delta R in Ga1-xMnxAs for x &lt;= 0.05 for several excitation wavelengths. The sign of Delta R in Ga1-xMnxAs (x=0.015 and x=0.03) was negative for photon energy larger than band gap at room temperature. The negative component of Delta R was explained by defect induced absorption and/or the reduction of exciton bleaching, rather than by the change in density of near band edge states associated with Mn incorporation. For Ga0.95Mn0.05As, absorption edge broadening was observed in the transmission spectra and the induced absorption effect was reduced by the screening of Mn local potential by photocarriers