QWIP focal plane arrays on InP substrates for single and dual band thermal imagers

Alternative material systems on InP substrate provide certain advantages for mid-wavelength infrared (MWIR), long-wavelength infrared (LWIR) and dual band MWIR/LWIR quantum well infrared photodetector (QWIP) focal plane arrays (FPAs). While InP/InGaAs and InP/InGaAsP LWIR QWIPs provide much higher responsivity when compared to the AlGaAs/GaAs QWIPs, AlInAs/InGaAs system facilitates completely lattice matched single band MWIR and dual band MWIR/LWIR FPAs.We present an extensive review of the studies on InP based single and dual band QWIPs. While reviewing the characteristics of InP/InGaAs and InP/InGaAsP LWIR QWIPs at large format FPA level, we experimentally demonstrate that the cut-off wavelength of AlInAs/InGaAs QWIPs can be tuned in a sufficiently large range in the MWIR atmospheric window by only changing the quantum well (QW) width at the lattice matched composition. The cut-off wavelength can be shifted up to ～5.0 μm with a QW width of 22 Å in which case very broad spectral response (Δλ/λ_p = ～30%) and a reasonably high peak detectivity are achievable leading to a noise equivalent temperature difference as low as 14 mK (f/2) with 25 μm pitch in a 640 × 512 FPA. We also present the characteristics of InP based two-stack QWIPs with wavelengths properly tuned in the MWIR and LWIR bands for dual color detection. The results clearly demonstrate that InP based material systems display high potential for dual band MWIR/LWIR QWIP FPAs needed by third generation thermal imagers.     

Determination and analysis of the dispersive optical constants of the 5,5′,6,6′-tetraphenyl-2,2′-bi([1,3]dithiolo[4,5-b][1,4]dithiinylidene)–DDQ complex thin film

The synthesis and optical properties of the 5,5′,6,6′-tetraphenyl-2,2′-bi([1,3]dithiolo [4,5-b] [1,4]dithiinylidene)–2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) complex thin film were investigated by the optical characterization. The optical constants such as refractive index, extinction coefficient and absorption coefficient were determined using the transmittance T(λ) and reflectance R(λ) spectra and the refractive index dispersion was analyzed using single oscillator of Wemple–Didomenico model. The single oscillator energy E₀ and the dispersion energy E_d were calculated. The effect of temperature on refractive dispersion and optical band gap E_g is also discussed. As a result, the annealing temperatures have an important effect on refractive index of thin film.     

Three-dimensional seismic array characterization study: experiment and modeling

In the summer of 2003, the Littoral Acoustic Demonstration Center conducted an acoustic characterization experiment for a 21-element marine seismic exploration airgun array of total volume of 0.0588 m(3) (3590 in.(3)). Two Environmental Acoustic Recording System buoys, one with a desensitized hydrophone, were deployed at a depth of 758 m in a water depth of 990 m, near Green's Canyon in the Gulf of Mexico. Shots over a grid were recorded and calibrated to produce absolute broadband (up to 25 kHz) pressure-time dependencies for a wide range of offsets and arrival angles in the water column. Experimental data are analyzed to obtain maximum received zero-to-peak pressure levels, maximum received sound exposure levels, and pressure levels in 13-octave frequency bands for each shot. Experimental data are quantitatively modeled by using an upgraded version of an underwater acoustic propagation model and seismic source modeling packages for a variety of ranges and arrival angles. Experimental and modeled data show good agreement in absolute pressure amplitudes and frequency interference patterns for frequencies up to 1000 Hz. The analysis is important for investigating the potential impact on marine mammals and fish and predicting the exposure levels for newly planned seismic surveys in other geographic areas.     

Determination of trace elements in marine plankton by inductively coupled plasma mass spectrometry (ICP-MS)

A method has been developed for the determination of 23 elements in marine plankton in which inductively coupled plasma (ICP) source mass spectrometry (MS) was used to quantify the elements in the solution after digestion in a mixture of hydrofluoric and nitric acids in sealed PTFE vessels in a microwave field. The procedure was validated by the analysis of a standard reference soil (SRM 2709 San Joaquin Soil) and a standard reference fresh water plankton (CRM 414). The method was applied to the analysis of several marine plankton samples grown under controlled conditions including several whose growth media had been enriched with selenium. Matrix induced signal suppressions and instrumental drift were corrected by internal standardization. The suitabilities of germanium, indium, rhodium, scandium and yttrium as internal standard elements were evaluated. Neither scandium nor yttrium could be used due to the presence of these elements in the samples, germanium was used for the determination of As, Co, Cu, Fe, Ni, Se, Si and Zn, indium was used for Al, Ba, Ca, Eu, Sr, and Tl, and rhodium was used for Cd, Cr, Hg, Mg, Pb, Sb, Sn, and V. For Al, Ca, Cr, Cu, Fe, Mg, Mn, Ni, Si, Sr, V, and Zn internal standardization did not completely compensate for the suppressive effect of the heavier elements and the solutions were diluted. However, for As, Ba, Cd, Co, Eu, Hg, Pb, Sb, Se, Sn and Tl, it was possible to obtain accurate results despite the 35–¶40% suppression in the signals. Isobaric overlap was only a problem in the cases of ⁴²Ca and ⁷⁸Se; ⁴⁴Ca and ⁷⁷Se, respectively, were used. Memory effects were only observed with Hg for which a nitric acid-sodium chloride solution was the most effective wash-out solution. The marine plankton samples were able to tolerate a higher concentration of Hg as the selenium concentration increased.     

Electrochemical preparation of a soluble conducting aniline-thiophene copolymer

A new of soluble sulfonated conductive copolymer has been synthesized by electrochemical oxidation in the presence of anhydrous FSO₃H. The sulphur-to-nitrogen ratios indicated that copolymers were formed in addition to the incorporation of groups into polymeric backbone. The sulfonated copolymer films have better solubility in DMSO and KOH. The conductivity of the copolymer films increases with the increase in the number of thiophene rings in the polymeric backbone. Copolymer films synthesized were investigated by cyclic voltammetry, UV-visible, FT-IR and ¹H-NMR spectroscopy, dry conductivity and intrinsic viscosity measurements, elemental analysis and SEM pictures.     

Determination of the Absolute Configuration of Dimethyl (2S,3S)-2-Allyl-3-hydroxyglutarate: A Chiral Building Block for Preparing Branched-Chain Nucleoside Analogues

A yeast-catalyzed reduction of dimethyl (2S,3S)-2-allyl-3-hydroxyglutarate is the key step in the preparation of bis-homo, branched-chain nucleoside analogues. To establish unambiguously the stereochemical course of the microbial reaction, the product has been converted to a derivative esterified with camphanoyl chloride, and a crystal structure of the derivative solved.     

Vibrational spectrum and assignments of 2-(4-methoxyphenyl)-1H-benzo[d]imidazole by ab initio Hartree-Fock and density functional methods

The room temperature attenuated total reflection Fourier transform infrared spectrum of the 2-(4-methoxyphenyl)-1H-benzo[d]imidazole has been recorded with diamond/ZnSe prism. The conformational behaviour, structural stability of optimized geometry, frequency and intensity of the vibrational bands of the title compound were investigated by utilizing ab initio calculations with 6-311G** basis set at HF, B3LYP, BLYP, B3PW91 and mPW1PW91 levels. The harmonic vibrational frequencies were calculated and scaled values have been compared with experimental IR spectrum. The observed and the calculated frequencies are found to be in good agreement. The theoretical vibrational spectra of the title compound were interpreted by means of potential energy distributions using VEDA 4 program. Furthermore, the optimal uniform scaling factors calculated for the title compound are 0.9120, 0.9596, 0.9660, 0.9699, and 0.9993 for HF, mPW1PW91, B3PW91, B3LYP and BLYP methods, respectively.     

Determination of antimony by using tungsten trap atomic absorption spectrometry

An electrically heated tungsten coil was used as a trap in the determination of antimony. The technique consists of three steps. Initially, SbH₃ is formed by hydride generation procedure; then the analyte species in vapor form are transported to W-coil trap heated at 370 °C. Following the preconcentration step, the trap is heated to 895 °C; analyte species are revolatilized and transported to the flame-heated quartz atom cell where atomization and the formation of signal take place. The experimental parameters were optimized both for trap and no-trap studies. The most important experimental parameters are concentrations of HCl and NaBH₄ solutions, H₂ and Ar gas flow rates, and collection and revolatilization temperatures of W-coil. Accuracy was tested using a certified reference material, waste water EU-L-1. Limit of detection for the system is 16 ng l^− 1 using a sample of 36 ml collected in 4.0 min. Enhancement factor in sensitivity was 17.     

Distortion and segregation in a dislocation core region at atomic resolution

The structure of an isolated, Ga terminated, 30 degree partial dislocation in GaAs:Be is determined by high resolution transmission electron microscopes and focal series reconstruction. The positions of atomic columns in the core region are measured to an accuracy of better than 10 pm. A quantitative comparison of the structure predicted by an ab initio electronic structure total energy calculation to the experiment indicates that theory and experiment agree to within 20 pm. Further analysis shows the deviations between theory and experiment appear to be systematic. Electron energy loss spectroscopy establishes that defects segregate to the core region, thus accounting for the systematic deviations.     

Incorporation of different conjugated linkers into low band gap polymers based on 5,6‐Bis(octyloxy)‐2,1,3 benzooxadiazole for tuning optoelectronic properties

Four new 2,1,3‐benzooxadiazole‐based donor–acceptor conjugated polymers, namely poly{9‐(9‐heptadecanyl)‐9H‐carbazole‐alt‐5,6‐bis(octyloxy)‐4,7‐di(selenophen‐2‐yl)benzo[c][1,2,5]oxadiazole)}(PSBSC), poly{9‐(9‐heptadecanyl)‐9H‐carbazole‐alt‐5,6‐bis(octyloxy)‐4,7‐di(furan‐2‐yl)benzo[c][1,2,5]oxadiazole)}(PFBFC), poly{9,9‐dioctyl‐9H‐fluorene‐alt‐5,6‐bis(octyloxy)‐4,7‐di(selenophen‐2‐yl)benzo[c][1,2,5]oxadiazole)}(PSBSFL), and poly{9,9‐dioctyl‐9H‐fluorene‐alt‐5,6‐bis(octyloxy)‐4,7‐di(furan‐2‐yl)benzo[c][1,2,5]oxadiazole)}(PFBFFL), were synthesized via Stille polycondensation reaction. All polymers were found to be soluble in common organic solvents such as chloroform, tetrahydrofuran, and chlorobenzene. Their structures were verified by ¹H‐NMR and the molecular weights were determined by gel permeation chromatography (GPC). The polymer films exhibited broad absorption bands. Among all polymers, photovoltaic cells based on the device structure of ITO/PEDOT:PSS/PSBSC:PC₇₁BM(1:3, w/w)/LiF/Al revealed an open‐circuit voltage of 0.62 V, a short circuit current of 7.63 mA cm^?2 and a power conversion efficiency of 1.89%. This work demonstrates a good example for tuning absorption range, energy level, and photovoltaic properties of the polymers with different spacers and donor units can offer a simple and effective method to improve the efficiency of PSCs. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2459–2467