We report results of a comprehensive study of the phase transition at T N (~643 K) as a function of particle size in multiferroic BiFeO 3 system. We employed electrical, thermal, and temperature dependent X -ray diffraction (XRD) studies in order to characterize the transition in a host of samples. We also carried out detailed magnetic measurements over a temperature regime 2-300 K under a magnetic field 100-10000 Oe both on bulk and nano-crystalline systems. While in the bulk system a sharp endothermic peak at T N together with a broad feature, ranging over nearly ~150 K (∆T), could be observed in calorimetry, the nanoscale systems exhibit only the broad feature. The characteristic dielectric anomaly, expected at T N , is found to occur both at T O and T N across ∆T in the bulk sample. The Maxwell-Wagner component due to interfaces between heterogenous regions with different conductivities is also present. The magnetic properties, measured at lower temperature, corroborate our observations in calorimetry. The metastability increases in the nanoscale BiFeO 3 with divergence between zero-field cooled (ZFC) and field cooled (FC) magnetization below ~100 K and faster magnetic relaxation. Interestingly, in nanoscale BiFeO 3 , one also observes finite coercivity at lower temperature which points out that suitable design of particle size and shape may induce ferromagnetism. The inhomogeneous distribution of Bi/Fe-ions and/or oxygen nonstoichiometry seems to be giving rise to broad features in thermal, magnetic as well as in electrical responses.

Fano resonance is reported here to be playing a dual role by amplifying or compensating for the quantum confinement effect induced asymmetry in Raman line-shape in silicon (Si) nanowires (NWs) obtained from heavily doped n- and p-type Si wafers respectively. The compensatory nature results in a near symmetric Raman line-shape from heavily doped p-type Si nanowires (NWs) as both the components almost cancel each other. On the other hand, the expected asymmetry, rather with enhancement, has been observed from heavily doped n-type SiNWs. Such a system (p- & n-) dependent Raman line-shape study has been carried out by theoretical line-shape analysis followed by experimental validation through suitably designed experiments. A dual role of Fano resonance in n- and p-type nano systems has been observed to modulate Raman spectra differently and reconcile accordingly to enhance and cease the Raman spectral asymmetry respectively. The present analysis will enable one to be more careful while analyzing a symmetric Raman line-shape from semiconductor nanostructures.

Uniform nanoneedles of binary oxide (Ni and Co) were synthesized on appropriate conducting substrates [fluorine-doped tin oxide (FTO) coated glass and carbon cloth (CC)] and investigated for dual application in electrochromism and glucose sensing. The prepared samples were characterized using electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy to reveal the presence of a NiCo 2 O 4 phase. Porosity analysis was carried to assign the microporous nature of the prepared sample. Detailed electrochemical and in situ bias-dependent optical spectroscopy studies were carried out to understand various aspects related to electrochromism and glucose sensing. A low-operating-voltage (∼2 V) color modulation with 50% contrast between the whitish translucent and dark-brown colors was achieved from the nanoneedle grown on a transparent FTO substrate. Furthermore, additionally, NiCo 2 O 4 nanoneedles grown on a CC substrate, with an enhanced exposed surface area, showed selective glucose-sensing properties with a very high sensitivity of 3000 μA/mM/cm 2 , as revealed using detailed electrochemical and impedance spectroscopic measurements.

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β-Ga2O3 nanostructures (nanowires, nanoribbons, and nanosheets) were synthesized via vapor transport method on gold coated silicon substrate in N2 ambient and these β-Ga2O3 nanostructures grown on silicon substrates were taken as the starting material to study the effect of annealing in the different environments (oxygen, water vapour, and ammonia solution) on the structural front and photoluminescence (PL) properties. The PL spectra of β-Ga2O3 nanostructures exhibit a UV-blue emission band whose intensity is strongly affected by the annealing in different environments. Annealing modifies the surface of the nanostructures by creating surface states which quench the PL by creating competitive nonradiative paths. This study also indicates the dominance of the formation of water induced surface states over ammonia induced surface states. The irreversible nature of these defects significantly affects the applicability of this system in moist high temperature environments.

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The growth and solid-state dewetting behavior of Au thin films (0.7 to 8.4 nm) deposited on the formvar film (substrate) by sputtering technique have been studied using transmission electron microscopy. The size and number density of the Au nanoparticles (NPs) change with an increase in the film thickness (0.7 to 2.8 nm). Nearly spherical Au NPs are obtained for <3 nm thickness films whereas percolated nanostructures are observed for ≥3 nm thickness films as a consequence of the interfacial interaction of Au and formvar film. The covered area fraction (CAF) increases from ∼13 to 75 % with the change in film thickness from 0.7 to 8.4 nm. In-situ annealing of ≤3 nm film produces comparatively bigger size and better sphericity Au NPs along with their narrow distributions, whereas just percolated film produces broad distribution in size having spherical as well as elongated Au NPs. The films with thickness ≤3 nm show excellent thermal stability. The films having thickness >6 nm show capability to be used as an irreversible temperature sensor with a sensitivity of ∼0.1 CAF/°C. It is observed that annealing affects the crystallinity of the Au grains in the films. The electron diffraction measurement also shows annealing induced morphological evolution in the percolated Au thin films (≥3 nm) during solid-state dewetting and recrystallization of the grains.