Analysis of current voltage characteristics of MWIR homojunction photodiodes for uncooled operation

Dark currents n⁺/ν/p⁺ Hg_0.69Cd_0.31Te mid wave infrared photodiodes were measured at room temperature. The diodes exhibited negative differential resistance at room-temperature, but with increasing leakage currents as a function of reverse bias. The current–voltage characteristics were simulated and fitted by incorporating trap assisted tunneling via traps and Shockley–Read–Hall generation recombination process due to dislocations in the carrier transport equations. The thermal suppression of carriers was simulated by taking energy level of trap (E_t), trap density (N_t) and the doping concentrations of n⁺ and ν regions as fitting parameters. Values of E_t and N_t were 0.78E_g and ～6–9 × 10¹⁴ cm^?3 respectively for most of the diodes. Variable temperature current voltage measurements on variable area diode array (VADA) structures confirmed the fact that variation in zero bias resistance area product (R₀A) is related to g–r processes originating from variation in concentration and kind of defects that intersect a junction area.     

The low frequency behaviour in high frequency capacitance–voltage characteristics due to contribution of band-to-band tunnelling and generation–recombination in Hg0.75Cd0.25Te MIS capacitors

Hg_1−xCd_xTe Metal–Insulator–Semiconductor (MIS) capacitors were studied both experimentally and theoretically to investigate the capacitance contributions due to band-to-band (btb) tunnelling and generation–recombination (gr) of carriers to inversion layer capacitance. A good fit to the data has been obtained by including the btb contributions rather than gr contributions.     

Study of spontaneous fission with EUROGAM

Prompt γ radiation following spontaneous fission has been measured using the EUROGAM 2 array. Using these data and newly developed analysis techniques a number of subjects were studied, which are briefly discussed. One of these subjects, shape transition in A≈100 Sr and Zr nuclei is discussed in more detail. Quadrupole moments were determined for rotational bands in the N=58,59,60,62 and 64 Sr and Zr isotopes. Deformation parameters, which increase from β₂ ≈ 0.1 at N=56 to β₂ ≈ 0.4 at N=64, suggest that in strontium and zirconium isotopes shape change happens gradually between N=56 and N=62 and is probably due to an occupancy of three or more deformation-driving orbitals of h_11/2 parentage.     

Host-guest complexation behaviour of emissive calix[3]naphthobipyrrole toward aromatic guests

A new hexapyrrolic macrocycle composed of three naphthobipyrrole units has been synthesized which exhibited different emission changes with hydrogen pyrophosphate and benzoate ions. Phosphate ions caused red shifting of the fluorescence band of calixnaphthobipyrrole while benzoate ions resulted in quenching of the same. The fluorescence quenching was further utilized for investigating binding preferences of the probe with neutral aromatic guest molecules substituted with groups having varied electron withdrawing abilities. The extent of quenching with the neutral guests increased with the increasing electron deficiency on the aromatic ring of the guest. The fluorescence quenching has been ascribed to electron transfer from the host to the guest species.     

Estimation of betulinic acid from wild fruit extracts of Ziziphus mauritiana and Ziziphus nummularia from different regions of North India by a validated high-performance thin-layer chromatography method

JPC – Journal of Planar Chromatography – Modern TLC - The Ziziphus fruits are recognized as a rich source of biologically active compounds, such as polysaccharides, phenolics,...     

Synthesis of Some New 2-(4-Methoxybenzothiazol-2′-yl amino)-4-(2-chloro-4-trifluoromethylanilino)-6-(substituted thioureido)-1,3,5-triazine as Antifungal Agents

2,4,6-Trichloro 1,3,5-triazine was selectively reacted with new nucleophilic reagents such as 4-methoxy-2-aminobenzothiazole, 2-chloro-4-trifluoromethyl-aniline, and phenylsubstituted thiourea in alkaline medium to give 2-(4-methoxybenzothiazol-2′-ylamino)-4-(phenylthioureido)-6-(substitutedthioureido)-1,3,5-triazines. The structures of these compounds were confirmed by IR, ¹H NMR, ¹⁹F NMR, mass spectral data, and elemental analysis. The compounds show fungicidal activity against Alternaria alternata, Aspergillus niger, and Macrofomina.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Surface structural,morphological, and catalytic studies of homogeneously dispersed anisotropic Ag nanostructures within mesoporous silica

Highly dispersed anisotropic Ag nanostructures were synthesized within the channels of 3-aminopropyltrimethoxysilane (APTMS)-modified mesoporous SBA-15 for catalyzing the reduction of p-dinitrobenzene, p-nitrophenol, and p-nitroacetophenone, respectively. A green templating process without involving any reducing agent, by varying the amount (1–10 wt.%) of Ag loading followed by calcination at 350 °C under H₂ led to change in the morphology of Ag nanoparticles from nanospheres (~7–8 nm) to nanorods (aspect ratio ~12–30 nm) without any deformation in mesoporous sieves. In comparison to white bare SBA-15, gray-colored samples were formed with Ag impregnation exhibiting absorption bands at 484 and 840 nm indicating the formation of anisotropic Ag nanostructures within mesoporous matrix. TEM and FE-SEM micrographs confirmed the presence of evenly dispersed Ag nanostructures within as well as on the surface of mesoporous matrix. AFM studies indicated a small decrease in the average roughness of SBA-15 from 20.59 to 19.21 nm for 4 wt.% Ag/m-SBA-15, illustrating the encapsulation of majority of Ag nanoparticles in the siliceous matrix and presence of small amount of Ag nanoparticles on the mesoporous support. Moreover, due to plugging of mesopores with Ag, a significant decrease in surface area from 680 m²/g of SBA-15 to 385 m²/g was observed. The Ag-impregnated SBA-15 catalyst displayed superior catalytic activity than did bare SBA-15 with 4 wt.% Ag-loaded catalyst exhibiting optimum activity for selective reduction of p-nitrophenol to p-aminophenol (100 %), p-nitroacetophenone to p-aminoacetophenone (100 %), and p-dinitrobenzene to p-nitroaniline (87 %), with a small amount of p-phenylenediamine formation.

Open image in new window

Graphical abstract This paper demonstrates the spontaneous formation of uniformly dispersed Ag nanospecies of various morphologies (nanospheres, size ~7–8 nm and nanorods, aspect ratio ~12–30 nm), both within as well as on the surface of the mesoporous SBA-15, as a function of increased Ag loading. Surface structural and other physiochemical properties of Ag/m-SBA-15 nanocomposites were considerably influenced w.r.t change in Ag loading. Ag/m-SBA-15 nanocomposites with 4 wt.% Ag loading exhibited the highest selectivity (87 %) for the selective reduction of p-dinitrobenzene to p-nitroaniline and 100 % selectivity for p-nitrophenol to p-aminophenol and p-nitroacetophenone to p-aminoacetophenone, respectively.

     

Aptamer based voltammetric biosensor for the detection of <Emphasis Type="Italic">Mycobacterium tuberculosis</Emphasis> antigen MPT64

The authors report an aptaelectrode based on graphene modified iron-oxide chitosan hybrid (CHIT-IO-GR) nanocomposite film deposited on fluorine tin oxide (FTO) for the detection of the Mycobacterium tuberculosis specific antigen MPT64. The biotinylated DNA aptamer sequence specific to the MPT64 was immobilized onto the CHIT-IO-GR/FTO electrode by using streptavidin-biotin interactions. XRD, FT-IR, FE-SEM and electrochemical studies were applied to monitor the steps of the fabrication. The aptaelectrode, operated best at typical voltage of 0.44 V, exhibited a limit of detection (LOD) of 0.9 fg?mL^?1 within 20 min. The biosensor retained about 80% of its initial activity after 10 uses. The potential application of the aptasensor was established by spike-in studies to obtain recoveries between 83 and 95%.

Open image in new window

Graphical abstract An electrochemical aptaelectrode based on nanocomposite consisting of chitosan (CHIT), iron-oxide nanoparticles (IO) and functionalized graphene (GR) has been fabricated to detect M. tb antigen MPT64 with an LOD of 0.9 fg?mL^?1 within 20 min.

     

Microwave enhanced Akabori reaction for peptide analysis

The Akabori reaction, devised in 1952 for the identification of C-terminus amino acids, involves the heating of a linear peptide in the presence of anhydrous hydrazine in a sealed tube for several hours. We report here a modified Akabori reaction that rapidly identifies the C-terminus amino acid in a polypeptide including its amino acid sequence information at both the C-terminus and the N-terminus. This modified methodology demonstrates the fundamentals of microwave chemistry applied to bioanalytical problems. In this modified process, hydrazinolysis has been accelerated by the application of microwave irradiation. In our reaction, the linear peptide and hydrazine solution, contained in a loosely covered conical flask, was exposed to a few minutes of irradiation using an unmodified domestic microwave oven. While the classical Akabori reaction required several hours, the microwave assisted reaction takes just minutes. If dimethyl sulfoxide is added to dilute the reaction mixture, the process is retarded enough to allow aliquots of the reaction mixture to be drawn every few minutes over a period of about an hour in order to study the progress of hydrazinolysis. Reaction products were monitored by mass spectrometry-primarily FAB-MS. In addition to providing sequence information, the microwave enhanced Akabori reaction quickly detects the presence of arginine (Arg) by converting each Arg to ornithine (Orn). Furthermore, certain amino acids, containing beta-SH, CO2H, and CONH2 groups in their side chain, are susceptible to modification by hydrazine, thereby, providing rapid confirmation of the presence of these amino acid residues. In these preliminary studies, the following oligopeptides were analyzed to demonstrate the effectiveness of our approach; the dipeptide (Trp-Phe), the tripeptide (Tyr-Gly-Gly), the tetrapeptide (Pro-Phe-Gly-Lys), the heptapeptide (Ala-Pro-Arg-Leu-Arg-Phe-Tyr), and a N-terminal blocked tripeptide (N-acetyl-Met-Leu-Phe).