Ratiometric Alcohol Sensor based on a Polymeric Nile Blue

We present a sterilizable ratiometric fluorescent ethanol sensor with sensitivity over a wide range (0-100%) of ethanol concentration v/v. The sensor is composed of a near infra red fluorescent solvatochromic dye, nile blue methacrylamide polymerized into a polyethylene (glycol) dimethacrylate matrix. The dye can typically exhibit two or more wavelength dependent shifts in the fluorescence intensities based on its different micropolar environments. Two different concentrations of the nile blue methacrylamide dye were prepared and polymerized into homogenous films. The fluorescence properties of the two different films were investigated with a view to determining their ethanol sensing capabilities. The sensor was immersed in a water-ethanol solvent mixture. Excitation of the dye was performed at 470 nm. The range of emission wavelengths was 480-800 nm. The ratio of the fluorescence intensities at 620 nm and 554 nm was obtained for ethanol concentrations varying from 0-100% and the calibration curve of the ratiometric fluorescence intensities over the entire concentration range of ethanol was plotted. A ratiometric intensity change of over 33% has been obtained for pure ethanol compared to that obtained for pure water. The sensor response was rapid (≤10 minutes). The sterilizable ethanol sensor exhibits good potential for on-line monitoring of the ethanol generated in an LB fermentation chamber

Electronic structure of NiS1−x_{1-x}Sex_x across the phase transition

We report very highly resolved photoemission spectra of NiS(1-x)Se(x) across the so-called metal-insulator transition as a function of temperature as well as composition. The present results convincingly demonstrate that the low temperature, antiferromagnetic phase is metallic, with a reduced density of states at E$_F$. This decrease is possibly due to the opening of gaps along specific directions in the Brillouin zone caused by the antiferromagnetic ordering.Comment: Revtex, 4 pages, 3 postscript figure

Magnetism and exchange in the layered antiferromagnet NiPS3NiPS_3

The anisotropic susceptibility of the layered antifemomagnet $NiPS_3(T_N = 155 K)$ has been measured between 45 K and 650 K. The system may be described by the effective spin Hamiltonian $H = DS^2_{iz}-\sum_{ij} J_{ij}S_i . S_j$, with the quadratic single-ion anisotropy terms introducing anisotropy in an otherwise isotropic situation. The exchange I and single-ion anisotropy parameter D were determined from an analysis of the anistropic susceptibility data for two different models: (i) the Oguchi model, in which a pair of spins chosen at random is treated exactly while its interactions with the rest of the crystal are approximated by a mean field and (ii) the correlated effective field (CEF) approximation developed by Lines, which reduces the many-body problem to a single-particle, non-interacting ensemble form, by the introduction of static temperature-dependent correlation parameter, which are evduated by forcing consistency with the fluctuation-dissipation theorem. It is found that the CEF approximation is superior to the Ognchi model in describing the susceptibility of $NIPS_3$. The exchange and crystal field parameters for the CEF approximation are J / k = -58.0 K; D / k = 16.1 K; g_l_l = 2.05 and $g_\perp =2.13$

Dilution of a layered antiferromagnet: Magnetism in MnxZn1−xPS3Mn_xZn_{1-x}PS_3

The magnetic properties of the layered antiferromagnet $MnPS_3$ have been studied as a function of dilution with zinc. The magnetic susceptibility of $Mn_xZn_{1-x}PS_3$can be accounted for reasonably well by a randomly diluted antiferromagnetic honeycomb lattice. For compositions above the percolation threshold the suceptibility was calculated using the high-temperature series expansion (HTSE) for a dilute magnetic lattice. For compositions below the percolation threshold uncompensated spins of the finite Mn clusters give rise to an additional Curie correction to the HTSE which is maximum near the $p_c$

Magnetism, exchange and crystal field parameters in the orbitally unquenched Ising antiferromagnet FePS3

FePS3 is a layered antiferromagnet (T N=123 K) with a marked Ising anisotropy in magnetic properties. The anisotropy arises from the combined effect of the trigonal distortion from octahedral symmetry and spin-orbit coupling on the orbitally degenerate5 T 2g ground state of the Fe2+ ion. The anisotropic paramagnetic susceptibilities are interpreted in terms of the zero field Hamiltonian, ?=?i [?(L iz 2 ?2)+|?|L i .S i ]?? ij J ij S i .S j . The crystal field trigonal distortion parameter ?, the spin-orbit coupling ? and the isotropic Heisenberg exchange,J ij, were evaluated from an analysis of the high temperature paramagnetic susceptibility data using the Correlated Effective Field (CEF) theory for many-body magnetism developed by Lines. Good agreement with experiment were obtained for ?/k=215.5 K; ?/k=166.5 K;J nn k=27.7 K; andJ nnn k=?2.3 K. Using these values of the crystal field and exchange parameters the CEF predicts aT N=122 K for FePS3, which is remarkably close to the observed value of theT N. The accuracy of the CEF approximation was also ascertained by comparing the calculated susceptibilities in the CEF with the experimental susceptibility for the isotropic Heisenberg layered antiferromagnet MnPS3, for which the high temperature series expansion susceptibility is available

Size-Selected Zinc Sulfide Nanocrystallites: Synthesis, Structure, and Optical Studies

We report the synthesis of three sizes of thioglycerol- apped precipitated ZnS nanocrystallites with relatively narrow size distributions, having average sizes of 1.8, 2.5, and 3.5 nm, respectively. These crystallites were extracted as free-standing powders which remain stable under normal atmospheric conditions and can be redispersed in suitable solvents. The nanocrystallite powders were characterized using X-ray diffraction (XRD), highresolution transmission electron microscopy (HRTEM), electron diffraction (ED), energy dispersive analysis of X-rays (EDAX), and UV-vis optical absorption. The synthesized nanocrystallites show typical lattice spacings corresponding to the cubic phase of ZnS, as confirmed from HRTEM, ED, and XRD. The lattice-resolved structures within a single nanocrystallite show characteristic defects such as twinning and dislocations. We present a comparative analysis of the size of nanocrystallites obtained from X- ay diffraction and TEM. The position of the excitonic transitions as seen in the optical absorption spectrum of the nanocrystallites was compared with the predictions of various models that correlate the size versus band gap of these nanocrystallites

Size-selected zinc sulfide nanocrystallites: synthesis, structure, and optical studies

We report the synthesis of three sizes of thioglycerol-capped precipitated ZnS nanocrystallites with relatively narrow size distributions, having average sizes of 1.8, 2.5, and 3.5 nm, respectively. These crystallites were extracted as free-standing powders which remain stable under normal atmospheric conditions and can be redispersed in suitable solvents. The nanocrystallite powders were characterized using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), energy dispersive analysis of X-rays (EDAX), and UV-vis optical absorption. The synthesized nanocrystallites show typical lattice spacings corresponding to the cubic phase of ZnS, as confirmed from HRTEM, ED, and XRD. The lattice-resolved structures within a single nanocrystallite show characteristic defects such as twinning and dislocations. We present a comparative analysis of the size of nanocrystallites obtained from X-ray diffraction and TEM. The position of the excitonic transitions as seen in the optical absorption spectrum of the nanocrystallites was compared with the predictions of various models that correlate the size versus band gap of these nanocrystallites