Step annealing effects on the structural and optical properties of InAs quantum dots grown on GaAs

The effects of multi-step rapid thermal annealing (RTA) for the self-assembled InAs quantum dots (QDs), which were grown by a molecular beam epitaxy (MBE), were investigated through photoluminescence (PL) and transmission electron microscopy (TEM). Postgrowth multi-step RTA was used to modify the structural and optical properties of the self-assembled InAs QDs. Postgrowth multi-step RTAs are as follows: one step (20 s at 750 °C); two step (20 s at 650 °C, 20 s at 750 °C); three step (30 s at 450 °C, 20 s at 650 °C, 20 s at 750 °C). It is found that significant narrowing of the luminescence linewidth (from 132 to 31 meV) from the InAs QDs occurs together with about 150 meV blueshift by two-step annealing, compared to as-grown InAs QDs. Observation of transmission electron microscopy (TEM) shows the existence of the dots under one- and two-step annealing but the disappearance of the dots by three-step annealing. Comparing with the samples under only one-step annealing, we demonstrate a significant enhancement of the interdiffusion in the dot layer under multi-step annealing.     

Resistivity distribution of silicon single crystals using codoping

Numerous studies including continuous Czochralski method and double crucible technique have been reported on the control of macroscopic axial resistivity distribution in bulk crystal growth. The simple codoping method for improving the productivity of silicon single-crystal growth by controlling axial specific resistivity distribution was proposed by Wang [Jpn. J. Appl. Phys. 43 (2004) 4079]. Wang [J. Crystal Growth 275 (2005) e73] demonstrated using numerical analysis and by experimental results that the axial specific resistivity distribution can be modified in melt growth of silicon crystals and relatively uniform profile is possible by B–P codoping method. In this work, the basic characteristic of 8 in silicon single crystal grown using codoping method is studied and whether proposed method has advantage for the silicon crystal growth is discussed.     

The extraction of Cr(III) from aqueous thiocyanate solutions and its separation from Co(II) and Ni(II)

For the system liquid anion-exchanger—Cr(III)−NCS⁻, an investigation has been made of the dependence of the percentage extraction of Cr(III) on parameters such as standing time of the Cr(III)−NCS⁻ solution, temperature, pH and type of exchanger. Quantitative extraction of e.g. 4·10⁻⁴ M Cr(III) by 0.1M Aliquat in CCl₄ is easily achieved at room temperature, using 4.75M KNCS−0.05N HCl as aqueous phase. At high Cr(III) concentrations, the complex anion present in the organic phase is Cr(NCS) ₆ ³⁻ ; when working with dilute metal ion solutions, the species extracted is Cr(NCS)₄ (H₂O) ₂ ⁻ . Separations of mixtures containing 10⁻²−10⁻⁴ M Co(II), Ni(II) and Cr(III) have successfully been accomplished.     

Excretion of iodide in 24-h urine as determined by ion-pair reversed-phase liquid chromatography with electrochemical detection

A simple method is presented for the routine analysis of iodide in urine. After a one-step sample clean-up, iodide was separated by ion-pair reversed-phase liquid chromatography and detected electrochemically with a silver electrode. The coefficient of variation of a single analysis of iodide in a pooled urine sample (530 nmol/l) was 7.6%. The detection limit, derived from a signal-to-noise ratio of 3, was 3 pmol, corresponding to 0.06 mumol/l. The recovery of iodide added to urine was 96 +/- 7%. The accuracy of the method was assessed by analysing ten different samples with neutron activation analysis. The data obtained with the two methods showed a high correlation (r = 0.991) and did not differ significantly. Excretion of iodide in samples of 24-h urine from a free-living population was shown to have a log-normal distribution and to be higher in men than in women. The iodide/creatinine ratio was independent of sex and increased with age.     

CO2 laser induced reactions of trichloroethylene

The pressure and laser-power dependence of the product distributions in the TEA CO₂ laser induced decomposition of trichloroethylene were studied. At moderate pressures molecular elimination of HCl to give CClCCl via intermolecular energy transfer was found to be the major reaction path. At low pressures a pure laser-induced CCl bond fission to give CHCCl was found to be the primary, reaction step.     

Origin of Antibacterial Activity of ZnO Nanoparticles: The Roles of Protonic and Electronic Conductions

To elucidate the origin of antibacterial activity of ZnO nanoparticles, a reactive oxygen species (ROS) mechanism is systematically investigated based on electronic and protonic conductions. While the enhancement of antibacterial activity by an increase in electronic conductivity is marginal, an apparent improvement is observed by in the increase of protonic conductivity in terms of the surface basicity. This study first demonstrates that antibacterial activity can be enhanced by controlling the surface basicity of solid particles. The basicity of ZnO can be modulated by doping alkaline‐earth oxides such as MgO and CaO, and it results in the increase of hydroxyl defects on the surface of solid particles. The basicity shows a strong dependency on mobile OH concentrations. The increase of ROS hydroxyl radicals is confirmed by Mg (ZMO) or Ca‐doping (ZCO), which shows high antibacterial activity, and Ca‐doped ZnO exhibits the highest performance. It is clearly observed that the antibacterial activity is proportional to the basicity, which is controlled by the mobile OH formation. While both electrons and hydroxyl species are required for ROS reactions, it is concluded that the formation of hydroxyl species is a key factor in improving the antibacterial activity in ZnO.     

Modified Anti Snyder Model with Minimal Length,Momentum Cutoff and Convergent Partition Function

International Journal of Theoretical Physics - In this paper we consider the possible modification of the anti Snyder model so that it have the non-zero minimal length, momentum cutoff and the...     

Influence of sol-gel precursors on the electrochemical performance of NaMn<Subscript>0.33</Subscript>Ni<Subscript>0.33</Subscript>Co<Subscript>0.33</Subscript>O<Subscript>2</Subscript> positive electrode for sodium-ion battery

Among the various cathode materials explored for sodium-ion batteries (SIBs), NaMn_0.33Ni_0.33Co_0.33O₂, with a layered oxide structure, is a promising material due to its high theoretical capacity (240 mAhg^?1). We have synthesized NaMn_0.33Ni_0.33Co_0.33O₂ using two different types of precursors, namely metal acetates and metal nitrates by the sol-gel method. XRD patterns confirm the formation of a stable phase of the material at 900 °C. Coupled TGA-FTIR analysis was used to optimize the calcination conditions and to understand the hydrolysis and condensation mechanism of the sol-gel precursors. FTIR spectra extracted at different temperatures reveal the polymer network-forming tendency of the acetate ligands whereas the polymerization is inhibited in the nitrate precursors. SEM analysis shows spherical and platelet morphologies of samples synthesized from nitrate and acetate precursors, respectively. Using in situ impedance and galvanostatic charge/discharge studies, we observed that the precursors used to synthesize the cathode material influence the electrochemical properties of the material, as in this case, where we observe a 20 % improvement in terms of capacity by using acetate precursors instead of nitrate precursors.     

Optical access transmission with improved channel capacity using non-orthogonal frequency quadrature amplitude modulation

A new modulation scheme that improves the bandwidth efficiency of an optical access link is proposed in this paper. It is implemented using non-orthogonal frequency shift keying (FSK) and quadrature amplitude modulation (QAM) simultaneously. We call the proposed technique non-orthogonal frequency quadrature amplitude modulation (NOFQAM). Especially, non-orthogonal FSK based on digital signal processing (DSP) is proposed for the first time. DSP-aided non-orthogonal FSK allows us to select RF carrier frequency irrespective of the channel bandwidth to allocate FSK symbols, unlike the existing orthogonal FSK. The non-orthogonality is implemented using a sequential correlation, where a received NOFQAM signal is correlated with only one RF carrier at a time by using DSP. After the sequential correlation is completed, both the FSK and the QAM symbols are recovered successfully and merged to generate the NOFQAM symbols. For experimental verification, a 20-km optical access link, which can transmit a 64-NOFQAM signal sampled at 10 Gsample/s, is implemented. We observed no increase in occupied channel bandwidth and a power penalty <0.5 dB compared to the 16-QAM scheme. A bit error rate lower than 10^?11 was obtained for the frequency spacing considered herein, which corresponds to 3% of the used RF carrier (1.5 GHz) when there are 50 sampling points per 64-NOFQAM symbol.     

Timing jitter reduction of optical pulse source using unpumped erbium doped fiber

A technique to enhance the stability of optical pulse source has been proposed that employs a specific length of unpumped erbium doped fiber. Two types of pulse sources are used one after the other, one of them is a 10 GHz mode locked laser and the other is a gain switched DFB laser diode with the repetition rate of 2 GHz. A 3-m erbium doped fiber is consolidated outside the cavity of the pulse sources so as to form strong standing waves, resulting into enhanced spatial hole burning effect. As a result, the phase noise of the pulse source is suppressed, whereas the possible undesired changes in the attributes of the pulse source are also nullified because we have designed the setup outside the cavity of the pulse source. Consequently, the timing jitter of the pulse source is reduced significantly.