RESUMEN
Mn2SnS4 belongs to the MII2AIVQ4 (M = transition metal; A = Si, Ge and Sn; Q = S, Se and Te) class of compounds that crystallizes in the orthorhombic space group Cmmm and shows complex magnetic properties. Here we report the synthesis and magnetic properties of Fe- and Cr-substituted Mn2SnS4 quaternary chalcogenides. All these compounds have been synthesized using a high-temperature solid-state route. Room temperature neutron diffraction studies on the specific compositions of chromium- and iron-substituted compounds were performed to obtain the site occupancy of different elements in the unit cell. The neutron diffraction analysis by employing the Rietveld refinement shows that for the Fe-substituted compound, most of the Fe goes to the Mn site with a small amount at the Sn site, while in the Cr-substituted sample, all the Cr occupy the Mn site. However, the Sn site almost remains intact in the case of the Fe-substituted compound, while it is significantly disordered for the Cr-substituted sample as a fraction of Mn occupies the Sn site and an equivalent amount of Sn occupies the Mn site. XPS study shows that both Cr and Fe exist in the +3 oxidation state, while Mn exists in the +2 state and Sn exists in a mixture of +2 and +4 oxidation states. Magnetic property study of these substituted compounds shows different types of magnetism, which is attributed to the variation of d-electrons of the substituent atom. The chromium-doped compounds show ferrimagnetic character along with two transitions: one transition at â¼37 K and another at â¼152 K. However, in Fe-substituted Mn2SnS4 samples, the low-temperature transition disappears and an increase in the high-temperature antiferromagnetic ordering temperature i.e. from 152 K (Mn2SnS4) to 174 K (Mn1.82Fe0.18SnS4) is observed. The increase in the antiferromagnetic ordering temperature in Mn2-xFexSnS4 may be attributed to the increase in the covalence of Mn/Fe-S-Mn/Fe bonds (shorter) with iron substitution.
RESUMEN
Creating a well-defined nanostructure through de-oxyribo nucleic acid (DNA)-nanotechnology, and specifically the development of metal/inorganic semiconductor junctions on DNA-assembled nanostructures, is an emerging research area. Herein, we investigate the electrical properties of biomolecule DNA-template based one-dimensional nanowires (NWs)-CdS/Au and without-template based nanoparticles (NPs)-CdS/Au devices grown on the Indium Tin Oxide (ITO) glass substrates. More importantly, the NWs-CdS/Au device displays a dramatic augmentation of current flow and also a striking change in threshold voltage (~55 mV) in comparison to NPs (~190 mV) and reported bulk-CdS/Au (~680 mV) devices. Albeit the manifestation of non-linear/asymmetric current-voltage (I-V) characteristic establishes the CdS/Au junction as Schottky device, but captivatingly, the large ideality factor of about 24 found in NWs-CdS/Au device could be due to the DNA-assembled based organic process CdS-semiconductor. Capacitance-voltage (C-V) measurements of the NWs-CdS/Au divulge a remarkable hump-like feature at lower frequency owing to the frequency dispersion effect. In contrast, the effect appears to be enfeebled with increasing frequency. We conjecture that the density of surface/interface traps materialises at the interface of nanostructures-CdS/metal-Au results in the changes in underlying electrical properties. The observation of significant differences in the electrical properties of DNA-assembled NWs-based Schottky junctions could possibly be helpful for the fabrication of more sophisticated and higher multispecificity biosensors for medical applications.
Asunto(s)
Técnicas Biosensibles , Nanoestructuras , ADN , Nanotecnología , SemiconductoresRESUMEN
Among MII2AIVQ4 (M = transition metal; A = Si, Ge, and Sn; Q = S, Se, and Te)-type compounds, most of which crystallize in an olivine or spinel structure, Mn2SnS4 is a unique compound that crystallizes in the orthorhombic space group Cmmm and exhibits complex magnetic properties. In this article, we report synthesis and study of the effect of Sb substitution (up to 20%) on the magnetic properties of Mn2SnS4. All the compounds were found to be in a single phase and indexed with the orthorhombic parent structure. Rietveld refinement of the room-temperature neutron diffraction data of Mn2Sn0.85Sb0.15S4 sample shows that Sb occupies the Mn site by replacing an equivalent amount of Mn. Subsequently, the replaced Mn occupies the Sn site causing disorder at both the Mn and the Sn sites, and the refined composition (Mn1.85(1)Sb0.15(1))(Sn0.85(1)Mn0.15(1))S4 is obtained. Although the purpose of incorporation of Sb(iii) was to create a mixed valence state at the Mn site, XPS study shows contrasting results. Sb exists in a mixed valence state, Sb(iii) and Sb(v), which balances the charge at the Sn(iv) site. Magnetic study of the compounds shows a very interesting trend. Pure Mn2SnS4 shows two magnetic transitions: one at 152 K that corresponds to antiferromagnetic ordering and other at 53 K corresponding to weak ferromagnetic ordering possibly due to spin canting. With antimony substitution, the temperature (152 K) of antiferromagnetic ordering remains unchanged, whereas the temperature of weak ferromagnetic ordering gradually increases with an increase in the Sb content from 53 K for the undoped compound to 88 K for 20% Sb-doped Mn2SnS4. The increase in the temperature of weak ferromagnetic ordering could be attributed to the incorporation of Sb, which induces more disorder at the Mn site, thereby making the magnetic lattice dilute with reduced frustration.
RESUMEN
The highly sensitive, interference-free and non-enzymatic optical sensing of glucose has been made possible for the first time using the hydrothermally synthesized ZnO nanorods. The UV irradiation of glucose-treated ZnO nanorods decomposes glucose into hydrogen peroxide (H2O2) and gluconic acid by UV oxidation. The ZnO nanorods play the role of a catalyst similar to the oxidase used in the enzymatic glucose sensors. The photoluminescence (PL) intensity of the near-band edge emission of the ZnO nanorods linearly decreased with the increased concentration of H2O2. Therefore, the glucose concentration is monitored over the wide range of 0.5-30 mM, corresponding to 9-540 mg/dL. The concentration range of the linear region in the calibration curve is suitable for its clinical use as a glucose sensor, because the glucose concentration of human serum is typically in the range of 80-120 mg/dL. In addition, the optical glucose sensor made of the ZnO nanorods is free from interference by bovin serum albumin, ascorbic acid or uric acid, which are also present in human blood. The non-enzymatic ZnO-nanorod sensor has been demonstrated with human serum samples from both normal persons and diabetic patients. There is a good agreement between the glucose concentrations measured by the PL quenching and standard clinical methods.