Numerical analysis of quantum ring intersubband photodetector for far infrared detection

A quantum ring based intersubband photodetector is designed and its optical performance is studied based on a developed theoretical model. Intersubband absorption of quantum rings is numerically calculated for two transitions, from ground state to first excited state and to continuum energy and the effects of broadening mechanisms are studied. Device show responsivity about 0.2 A/W at T = 80 K and V = 2 V. Dark current of structure with and without the resonant tunneling barriers is calculated. Specific detectivity \((D^*)\) is studied at different temperatures and peak values about \(3\times 10^{12}\,\hbox {cm Hz}^{1/2}/\hbox {W}\) is obtained at T = 50 K. Results show that inclusion of resonant tunneling barriers leads to improvement in \(D^*\) about one order of magnitude.     

Preliminary studies of the Raman spectra of \hbox {Ag}_{2}\hbox {Te}\hbox { and }\hbox {Ag}_{5}\hbox {Te}_{3}

The theoretical calculations indicated that the monoclinic low-temperature phase of silver telluride $(\upbeta \hbox {-Ag}_{2}\hbox {Te})$ is a new binary topological insulator with highly anisotropic single Dirac cone surface. We obtained $\upbeta \hbox {-Ag}_{2}\hbox {Te}$ crystal ingots containing few grains by the Bridgman method. We also deposited thin films of tellurium, $\hbox {Ag}_{5}\hbox {Te}_{3}\hbox { and }(\hbox {Te+Ag}_{5}\hbox {Te}_{3})$ by thermal evaporation method. The Raman spectra of $\upbeta \hbox {-Ag}_{2}\hbox {Te}$ , tellurium and $\hbox {Ag}_{5}\hbox {Te}_{3}$ were measured at three excitation wave lengths: 633, 515 and 488 nm. The Raman active modes of $\upbeta \hbox {-Ag}_{2}\hbox {Te}$ , tellurium and $\hbox {Ag}_{5}\hbox {Te}_{3}$ are situated at frequencies below 300  $\hbox {cm}^{-1}$ while vibrations of other phases appear at higher frequencies.     

Large N approach to Kaon decays and mixing 28 years later: \Delta I=1/2 rule, \hat{B}_K,and \Delta M_K

We review and update our results for $K\rightarrow \pi \pi $ decays and $K^0$ – $\bar{K}^0$ mixing obtained by us in the 1980s within an analytic approximate approach based on the dual representation of QCD as a theory of weakly interacting mesons for large $N$ , where $N$ is the number of colors. In our analytic approach the Standard Model dynamics behind the enhancement of $\hbox {Re}A_0$ and suppression of $\hbox {Re}A_2$ , the so-called $\Delta I=1/2$ rule for $K\rightarrow \pi \pi $ decays, has a simple structure: the usual octet enhancement through the long but slow quark–gluon renormalization group evolution down to the scales $\mathcal{O}(1\, {\hbox { GeV}})$ is continued as a short but fast meson evolution down to zero momentum scales at which the factorization of hadronic matrix elements is at work. The inclusion of lowest-lying vector meson contributions in addition to the pseudoscalar ones and of Wilson coefficients in a momentum scheme improves significantly the matching between quark–gluon and meson evolutions. In particular, the anomalous dimension matrix governing the meson evolution exhibits the structure of the known anomalous dimension matrix in the quark–gluon evolution. While this physical picture did not yet emerge from lattice simulations, the recent results on $\hbox {Re}A_2$ and $\hbox {Re}A_0$ from the RBC-UKQCD collaboration give support for its correctness. In particular, the signs of the two main contractions found numerically by these authors follow uniquely from our analytic approach. Though the current–current operators dominate the $\Delta I=1/2$ rule, working with matching scales $\mathcal{O}(1 \, {\hbox { GeV}})$ we find that the presence of QCD-penguin operator $Q_6$ is required to obtain satisfactory result for $\hbox {Re}A_0$ . At NLO in $1/N$ we obtain $R=\hbox {Re}A_0/\hbox {Re}A_2= 16.0\pm 1.5$ which amounts to an order of magnitude enhancement over the strict large $N$ limit value $\sqrt{2}$ . We also update our results for the parameter $\hat{B}_K$ , finding $\hat{B}_K=0.73\pm 0.02$ . The smallness of $1/N$ corrections to the large $N$ value $\hat{B}_K=3/4$ results within our approach from an approximate cancelation between pseudoscalar and vector meson one-loop contributions. We also summarize the status of $\Delta M_K$ in this approach.     

Influence of temperature on the electric,dielectric and AC conductivity properties of nano-crystalline zinc substituted cobalt ferrite synthesized by solution combustion technique

Cobalt–zinc nanoferrites with formulae Co $_{1-x}$ Zn $_{x}$ Fe $_{2}$ O $_{4}$ , where x = 0.0, 0.1, 0.2 and 0.3, have been synthesized by solution combustion technique. The variation of DC resistivity with temperature shows the semiconducting behavior of all nanoferrites. The dielectric properties such as dielectric constant ( $\varepsilon $ ’) and dielectric loss tangent (tan $\delta )$ are investigated as a function of temperature and frequency. Dielectric constant and loss tangent are found to be increasing with an increase in temperature while with an increase in frequency both, $\varepsilon $ ’ and tan $\delta $ , are found to be decreasing. The dielectric properties have been explained on the basis of space charge polarization according to Maxwell–Wagner’s two-layer model and the hopping of charge between Fe $^{2+}$ and Fe $^{3+}$ . Further, a very high value of dielectric constant and a low value of tan $\delta $ are the prime achievements of the present work. The AC electrical conductivity ( $\sigma _\mathrm{AC})$ is studied as a function of temperature as well as frequency and $\sigma _\mathrm{AC}$ is observed to be increasing with the increase in temperature and frequency.     

Line intensity measurements of methane’s \nu _3-band using a cw-OPO

We report on absolute line strength measurements of P(1), R(0) and R(1) singlet lines in the \(3.3\,\upmu\hbox {m}\,\nu _{3}\) (C–H stretching) band of methane \(^{12}\hbox {CH}_4\) at reference temperature \(T=296\)  K. Line strength measurements are performed at low pressure \((P \le 1\hbox { Torr})\) using direct absorption spectroscopy technique based on a widely tunable continuous-wave singly resonant optical parametric oscillator. The \(1\sigma \) overall accuracy in line strength determinations ranges between 7 and 8 % mostly limited by pressure and frequency measurements. A comparison with previous reported values is made. Our results show good agreement with the HITRAN 2012 database.     

Waveguide laser modelling of Erbium/Ytterbium activated monoclinic double tungstates

Using the overlapping integral method, a rib waveguide laser of monoclinic potassium double tungstate, KRE $(\text{ WO}_{4})_{2}$ , co-doped with Erbium and Ytterbium has been modelled. The laser operation at 1.5 $\upmu $ m is based on an efficient pump scheme via the energy transfer from Yb $^{3+}$ to Er $^{3+}$ ions. The numerical simulation requires spectroscopic parameters of the ions involved and the waveguide geometry and index profiles. This model allows determining the laser power as a function of controllable parameters such as ions doping level, pump power, cavity length or reflectance of the input/output mirrors. It has been found that, for the standard doping level used in this matrix, the optimum cavity length is only few millimeters. Overall, using simulation tools is possible to optimize fabrication parameters, and thus saving effort in the development of experimental prototypes.     

Low-threshold, high SMSR tunable external cavity quantum cascade laser around 4.7\,\upmu \hbox {m}

Room-temperature pulsed and continuous-wave (cw) operation of a tunable external cavity (EC) quantum cascade laser (QCL) at an emitting wavelength of $4.7\,\upmu \hbox {m}$ 4.7 μ m was presented. The effect of different external cavity lengths and grating angles of the EC–QCL system were analyzed numerically. A wide tuning range greater than $131\,\hbox {cm}^{-1}$ 131 cm - 1 was obtained in pulsed mode at room temperature. Without the anti-reflection coating procedure, single-mode cw operation with a side-mode suppression ratio (SMSR) above 20 dB and a wide tuning range greater than $116\, \hbox {cm}^{-1}$ 116 cm - 1 were achieved. Near the center region, SMSR about 30 dB was also realized through designing the external cavity length. Strain-compensation combined with two-phonon resonance in an active region design and the high-reflection coating promised low threshold current density. A record low threshold current density of $0.901\,\hbox {kA/cm}^{2}$ 0.901 kA/cm 2 for an EC–QCL operated in cw mode was realized.     

Pyrid-2-yl and 2-CyanoPhenyl fused heterocyclic compounds as human P2X_{3} inhibitors: a combined approach based on homology modelling,docking and QSAR analysis

P2X receptors are hetero-oligomeric proteins that function as membrane ion channels and are gated by extracellular ATP. The hP2X $_{3}$ subunit is a constituent of the channels on a subset of sensory neurons involved in pain signaling, where ATP released by damaged and inflamed tissue can initiate action potentials. Hence, the inhibition of ATP-activated P2X $_{3}$ receptor is an exciting approach for the treatment of inflammatory and neuropathic pain. Recently, the crystal structures of zebrafish P2X $_{4}$ (zP2X $_{4})$ were obtained in closed, apo state (PDB ID: 3I5D) and ATP-bound, open state (PDB ID: 4DW1). These structures were used to develop a homology model of human P2X $_{3}$ (hP2X $_{3})$ in order to identify through docking studies, the binding modes of known P2X $_{3}$ inhibitors and their key active site interactions, along with a pharmacophore-based 3D-QSAR model for a series of 136 Pyrid-2-yl and 2-CyanoPhenyl fused heterocyclic compounds. These 3D-QSAR models have been developed with different combinations of training and test set divisions obtained by random separation, Jarvis–Patrick clustering, K-means clustering and sphere exclusion methods. The best predictive 3D-QSAR model resulted in training set R $^{2 }$ of 0.75, internal test set Q $^{2}$ of 0.74, Pearson-R value of 0.87 and root mean square error of 0.37. The information generated by the pharmacophore model and docking analyses using the homology model provides valuable clues to design novel potent hP2X $_{3}$ inhibitors.     

Mössbauer spectroscopy in the investigation of new mineral–related materials

New materials based on the composition of the mineral schafarzikite, FeSb $_{2}\textit {O}_{4}$ , have been synthesised. $^{57}$ Fe- and $^{121}$ Sb- Mössbauer spectroscopy shows that iron is present as Fe $^{2+}$ and that antimony is present as Sb $^{3+}$ . The presence of Pb $^{2+}$ on the antimony sites in materials of composition FeSb $_{1.5}$ Pb $_{0.5}\textit {O}_{4}$ induces partial oxidation of Fe $^{2+}_{}$ to Fe $^{3+}$ . The quasi-one-dimensional magnetic structure of schafarzikite is retained in FeSb $_{1.5}$ Pb $_{0.5}\textit {O}_{4}$ and gives rise to weakly coupled non-magnetic Fe $^{2+}$ ions coexisting with Fe $^{3+}$ ions in a magnetically ordered state. A similar model can be applied to account for the spectra recorded from the compound Co $_{0.5}$ Fe $_{0.5}$ Sb $_{1.5}$ Pb $_{0.5}\textit {O}_{4}$ .     

Analysis and design of an electro-optic 2\times 2 switch using Ti: \hbox {KNbO}_3 as a waveguide based on MZI at 1.3\,\upmu \hbox {m}

This work describes an approach to design a $2\times 2$ optoelectronic switch based on the Mach–Zehnder interferometer with a channel profile of Titanium (Ti) diffused in Potassium niobate ( $\hbox {KNbO}_{3}$ ) at a wavelength of $1.3\,\upmu \hbox {m}$ . The evaluation parameters used are the insertion loss and the extinction ratio. The originality of this work is introducing the $\hbox {KNbO}_{3 }$ crystal as a host while optimizing the Ti strip thickness to provide a remarkable switching performance. Optimization leads to a lower switching voltage of 4 V, an insertion loss of 0.0261 dB and extinction ratio of 29.4 dB. The designed switch has a high switching capability and degree of reliability.     

Structural, morphological and optical properties of \hbox {In}_{2}\hbox {S}_{3} thin films obtained by SILAR method

$\hbox {In}_{2}\hbox {S}_{3}$ thin films have been elaborated onto glass substrate by SILAR method at room temperature using different immersion time in the solution of cation and anion and fixing the rinsing time. The film composition, morphology and structure were investigated using energy dispersive X-ray analysis (EDAX), scanning electron microscopy (SEM) and X-ray diffraction techniques. Optical properties, such transmission and band gap have been also analyzed. The effects of annealing on the morphological structure thin films are also described. The x-rays diffraction spectra indicated that the formed compounds are $\upbeta $ - $\hbox {In}_{2}\hbox {S}_{3}$ polycrystalline thin films with $\hbox {In}_{6}\hbox {S}_{7 }$ as second phase in sample S1 and sample S2 and no another phase in sample 3. SEM revealed homogeneous and relatively uniform films and EDAX shows sample 3 with S/In=1.44. For sample 1 and sample 2, we noted an increase of band gap when rinsing time increases.     

Analysis of the {3\over 2}^{+} heavy and doubly heavy baryon states with QCD sum rules

In this article, we study the ${3\over 2}^{+}$ heavy and doubly heavy baryon states $\varXi^{*}_{cc}$ , $\varOmega^{*}_{cc}$ , $\varXi^{*}_{bb}$ , $\varOmega^{*}_{bb}$ , $\varSigma_{c}^{*}$ , $\varXi_{c}^{*}$ , $\varOmega_{c}^{*}$ , $\varSigma_{b}^{*}$ , $\varXi_{b}^{*}$ and $\varOmega_{b}^{*}$ by subtracting the contributions from the corresponding ${3\over 2}^{-}$ heavy and doubly heavy baryon states with the QCD sum rules, and we make reasonable predictions for their masses.     

Laser nanoablation of graphite

Experimental data on laser ablation of highly oriented pyrolitic graphite by nanosecond pulsed UV ( $\lambda =193$  nm) and green ( $\lambda =532$  nm) lasers are presented. It was found that below graphite vaporization threshold $\approx $ 1 J/cm $^{2}$ , the nanoablation regime can be realized with material removal rates as low as 10 $^{-3}$  nm/pulse. The difference between physical (vaporization) and physical–chemical (heating + oxidation) ablation regimes is discussed. Special attention is paid to the influence of laser fluence and pulse number on ablation kinetics. Possibility of laser-induced graphite surface nanostructuring has been demonstrated. Combination of tightly focused laser beam and sharp tip of scanning probe microscope was applied to improve material nanoablation.     

Numerical simulation of solar cells based on III–V nitride compounds

In this paper, we developed a numerical calculation program, using Turbo Pascal, to determine the current–voltage characteristics of a $\hbox {N}^{+}\hbox {P}$ solar cells in order to find the main parameters influencing the conversion efficiency. We adopted a one-dimensional numerical model for the resolution of the three semiconductor equations, which are: the Poisson’s equation and the two continuity equations of electrons and holes. Our system of equations is written in term of $\varphi ,\, \varphi _{n}$ , and $\varphi _{p}$ , and it’s resolved using the finite difference method. This code enables us to draw the current density versus the voltage for different layer thicknesses, the conversion efficiency versus the minority carrier life time and the spectral response versus the wavelength. In order to compare the conversion efficiency of two different solar cells, we simulated a solar cell based on III–V nitride compounds $(\hbox {In}_\mathrm{x}\hbox {Ga}_{1-\mathrm{x}}\hbox {N})$ and a monocrystalline silicon solar cell.     

Magnetotransport properties in \text{ Ni }_{81}\text{ Fe }_{19}\text{/Zr } multi-layers

In this work, we present a study of the magneto transport properties in magnetic multilayered structure $\text{ Ni }_{81}\text{ Fe }_{19}\text{/Zr }$ Ni 81 Fe 19 /Zr . The magnetic $(\text{ Ni }_{81}\text{ Fe }_{19})$ ( Ni 81 Fe 19 ) and non magnetic (Zr) layer thickness $(\mathbf{t}_\mathbf{NiFe}, \mathbf{t}_\mathbf{zr})$ ( t NiFe , t zr ) effects on the magneto resistance (MR) are discussed theoretically in the framework of the Johnson–Camley semi classical approach based on the Boltzmann transport equation. A comparison between calculated and measured MR is obtained. The observed MR ratio oscillates for Zr layer thickness with an average period of 7Å. A generally weak $\text{ MR }(\text{ t }_{\mathrm{NiFe}})$ MR ( t NiFe ) ratio for fixed $\mathbf{t}_\mathbf{zr}$ t zr is obtained and it shows a maxima peak of the MR with a value of 1.8 % located at $\mathbf{t}_\mathbf{NiFe}= 80$ t NiFe = 80 Å.     

Accurate Gouy phase measurement in an astigmatic optical cavity

We present measurements of the Gouy phase accumulation for the fundamental mode of an astigmatic Fabry–Perot cavity over 70?% of its stability range. The method is based on simultaneous measurement of the resonant frequencies of the fundamental mode and the $\text{TEM}_{11}$ Hermite–Gauss mode of the cavity. We achieve an uncertainty of $2.7\times 10^{-6}$ ?rad, which, in the context of displacement metrology, is sufficient to enable measurements over 50?mm with relative uncertainty below $10^{-10}$ .     

Formation and crystallization kinetics of Nd–Fe–B-based bulk amorphous alloy

In order to improve the glass-forming ability (GFA) of Nd–Fe–B ternary alloys to obtain fully amorphous bulk Nd–Fe–B-based alloy, the effects of Mo and Y doping on GFA of the alloys were investigated. It was found that the substitution of Mo for Fe and Y for Nd enhanced the GFA of the Nd–Y–Fe–Mo–B alloys. It was also revealed that the GFA of the samples was optimized by 4 at.% Mo doping and increased with the Y content. The fully amorphous structures were all formed in the Nd $_{6-{x}}$ Y $_{{x}}$ Fe $_{68}$ Mo $_{4}$ B $_{22}$ (x $=$ 1–5) alloy rods with 1.5 mm-diameter. After subsequent crystallization, the devitrified Nd $_{3}$ Y $_{3}$ Fe $_{68}$ Mo $_{4}$ B $_{22}$ alloy rod exhibited a uniform distribution of grains with a coercivity of 364.1 kA/m. The crystallization behavior of Nd $_{3}$ Y $_{3}$ Fe $_{68}$ Mo $_{4}$ B $_{22}$ BMG was investigated in isothermal situation. The Avrami exponent n determined by JAM plot is lower than 2.5, implying that the crystallization is mainly governed by a growth of particles with decreasing nucleation rate.     

On Gravitational Effects in the Schrödinger Equation

The Schrödinger  equation for a particle of rest mass $m$ and electrical charge $ne$ interacting with a four-vector potential $A_i$ can be derived as the non-relativistic limit of the Klein–Gordon  equation $\left( \Box '+m^2\right) \varPsi =0$ for the wave function $\varPsi $ , where $\Box '=\eta ^{jk}\partial '_j\partial '_k$ and $\partial '_j=\partial _j -\mathrm {i}n e A_j$ , or equivalently from the one-dimensional  action $S_1=-\int m ds +\int neA_i dx^i$ for the corresponding point particle in the semi-classical approximation $\varPsi \sim \exp {(\mathrm {i}S_1)}$ , both methods yielding the equation $\mathrm {i}\partial _0\varPsi \approx \left( \frac{1}{2m}\eta ^{\alpha \beta }\partial '_{\alpha }\partial '_{\beta } + m + n e\phi \right) \varPsi $ in Minkowski  space–time  , where $\alpha ,\beta =1,2,3$ and $\phi =-A_0$ . We show that these two methods generally yield equations  that differ in a curved background  space–time   $g_{ij}$ , although they coincide when $g_{0\alpha }=0$ if $m$ is replaced by the effective mass $\mathcal{M}\equiv \sqrt{m^2-\xi R}$ in both the Klein–Gordon  action $S$ and $S_1$ , allowing for non-minimal coupling to the gravitational  field, where $R$ is the Ricci scalar and $\xi $ is a constant. In this case $\mathrm {i}\partial _0\varPsi \approx \left( \frac{1}{2\mathcal{M}'} g^{\alpha \beta }\partial '_{\alpha }\partial '_{\beta } + \mathcal{M}\phi ^{(\mathrm g)} + n e\phi \right) \varPsi $ , where $\phi ^{(\mathrm g)} =\sqrt{g_{00}}$ and $\mathcal{M}'=\mathcal{M}/\phi ^{(\mathrm g)} $ , the correctness of the gravitational  contribution to the potential having been verified to linear order $m\phi ^{(\mathrm g)} $ in the thermal-neutron beam interferometry experiment due to Colella et al. Setting $n=2$ and regarding $\varPsi $ as the quasi-particle wave function, or order parameter, we obtain the generalization of the fundamental macroscopic Ginzburg-Landau equation of superconductivity to curved space–time. Conservation of probability and electrical current requires both electromagnetic gauge and space–time  coordinate conditions to be imposed, which exemplifies the gravito-electromagnetic analogy, particularly in the stationary case, when div ${{\varvec{A}}}=\hbox {div}{{\varvec{A}}}^{(\mathrm g)}=0$ , where ${{\varvec{A}}}^{\alpha }=-A^{\alpha }$ and ${{\varvec{A}}}^{(\mathrm g)\alpha }=-\phi ^{(\mathrm g)}g^{0\alpha }$ . The quantum-cosmological Schrödinger  (Wheeler–DeWitt) equation is also discussed in the $\mathcal{D}$ -dimensional  mini-superspace idealization, with particular regard to the vacuum potential $\mathcal V$ and the characteristics of the ground state, assuming a gravitational  Lagrangian   $L_\mathcal{D}$ which contains higher-derivative  terms up to order $\mathcal{R}^4$ . For the heterotic superstring theory  , $L_\mathcal{D}$ consists of an infinite series in $\alpha '\mathcal{R}$ , where $\alpha '$ is the Regge slope parameter, and in the perturbative approximation $\alpha '|\mathcal{R}| \ll 1$ , $\mathcal V$ is positive semi-definite for $\mathcal{D} \ge 4$ . The maximally symmetric ground state satisfying the field equations is Minkowski  space for $3\le {\mathcal {D}}\le 7$ and anti-de Sitter  space for $8 \le \mathcal {D} \le 10$ .     

Resonance Conversion as the Predominant Decay Mode of ^{229m}Th

Calculations performed within the advanced MCDF method show that the probability of decay of the 3.5-eV level of $^{229m}$ Th through the resonance electronic bridges exceeds the direct radiative nuclear decay width by a factor of around $5\cdot 10^3$ . Experimental consequences for detection of the delayed soft photons or $\alpha$ particles from the decay of the isomer are discussed.     

Design of spectral crosstalk suppressing structure in two-color HgCdTe infrared focal plane arrays detector

Spectral crosstalk suppressing design of two-color HgCdTe medium-wave/long-wave (MW/LW) \(\hbox {n}^{+}\) – \(\hbox {p}_{1}\) – \(\hbox {P}_{2}\) – \(\hbox {P}_{3}\) – \(\hbox {N}^{+}\) infrared focal plane arrays (IRFPAs) detector functioning in simultaneous mode is carried out in this study, using Crosslight Technology Computer Aided Design (TCAD) software. A compositional barrier of \(\hbox {P}_{2}\) -region sandwiched between LW absorption layer of \(\hbox {p}_{1}\) -region and MW absorption layer of \(\hbox {P}_{3}\) -region is designed to suppress spectral crosstalk. MW-to-LW crosstalk can be significantly suppressed to 2.1 % while LW-to-MW crosstalk can be maintained less than 1 % by integrating an optimized compositional barrier.