Ravikiran Late

Study of Porous Silicon Prepared Using Metal-Induced Etching (MIE): a Comparison with Laser-Induced Etching (LIE)

Porous silicon (p-Si), prepared by two routes (metal induced etching (MIE) and laser induced etching (LIE)) have been studied by comparing the observed surface morphologies using SEM. A uniformly distributed smaller (submicron sized) pores are formed when MIE technique is used because the pore formation is driven by uniformly distributed metal (silver in present case) nanoparticles, deposited prior to the porosification step. Whereas in p-Si, prepared by LIE technique, wider pores with some variation in pore size as compared to MIE technique is observed because a laser having gaussian profile of intensity is used for porosification. Uniformly distribute well-aligned Si nanowires are observed in samples prepared by MIE method as seen using cross-sectional SEM imaging. A single photoluminescence (PL) peak at 1.96 eV corresponding to red emission at room temperature is observed which reveals that the Si nanowires, present in p-Si prepared by MIE, show quantum confinement effect. The single PL peak confirms the presence of uniform sized nanowires in MIE samples. These vertically aligned Si nanowires can be used for field emission application.

Observation of large dielectric permittivity and dielectric relaxation phenomenon in Mn-doped lanthanum gallate

Polycrystalline LaGa1−xMnxO3 (x = 0, 0.05, 0.1, 0.15, 0.2 and 0.3) samples were prepared via the solid-state reaction method. These samples were characterized using synchrotron-based X-ray diffraction (XRD) and the X-ray absorption near edge structure (XANES). XRD studies confirm the orthorhombic structure for the prepared samples whereas XANES analysis reveals the co-existence of Mn3+ and Mn4+ in all Mn-doped samples. Dielectric relaxation is observed for all Mn-doped samples whereas a large dielectric constant (e′) is perceived in samples with higher Mn doping (x = 0.2 and x = 0.3). Occurrence of a large e′ is attributed to the huge decrease in impedance with increasing Mn doping which is governed by the hopping charge transport and extrinsic interface effects, whereas at high frequencies, this effect is observed possibly due to dipolar effects associated with the possible off-centrosymmetry of the MnO6 octahedron which is indicated by the pre-edge feature (Mn K-edge) in XANES and validated through P–E measurements. The appearance of dielectric relaxation was credited to the dipolar effects associated with the flipping of the Mn3+/Mn4+ dipole i.e., with the hopping of charge carriers between Mn3+ and Mn4+ under an external electric field. The value of activation energy (Ea = 0.36 eV), extracted from temperature-dependent dielectric data, reveals the polaron hopping mechanism.

Room temperature magnetodielectric studies on Mn-doped LaGaO3

Polycrystalline samples of LaGa1−xMnxO3 (0 ≤ x ≤ 0.3) were prepared by the solid-state reaction route. The phase purity of these samples was confirmed by powder x-ray diffraction experiments carried out on BL-12 at the Indus-2 synchrotron radiation source. The sample with x = 0.2 shows significant change in the value of capacitance with the application of a magnetic field. The observed results were understood by systematically analyzing magnetocapacitance (MC), magnetoresistance (MR), and dielectric loss as a function of frequency. Our results and analysis suggest that the observed magnetodielectric (MD) coupling may be due to the MR effect of the Maxwell–Wagner type and/or field-induced dipolar relaxation. Further, it is observed that oxygen stoichiometry plays a very crucial role in the observed MD coupling.

Interplay between phonon confinement and Fano effect on Raman line shape for semiconductor nanostructures: Analytical study

Abstract Theoretical Raman line shape functions have been studied to take care of quantum confinement effect and Fano effect individually and jointly. The characteristics of various Raman line shapes have been studied in terms of the broadening and asymmetry of Raman line shapes. It is shown that the asymmetry in the Raman line-shape function caused by these two effects individually does not add linearly to give asymmetry of line-shape generated by considering the combined effect. This indicates existence of interplay between the two effects. The origin of interplay lies in the fact that Fano effect itself depends on quantum confinement effect and in turn provides an asymmetry. This can not be explained by considering the two effects contribution independent of each other.

Possibility of spin-polarized transport in edge fluorinated armchair boron nitride nanoribbons

We predict the possibility of spin based electronic transport in edge fluorinated armchair boron nitride nanoribbons (ABNNRs). The structural stability, electronic and magnetic properties of these edge fluorinated ABNNRs have been systematically analyzed by means of first-principles calculations within the local spin-density approximation (LSDA). Regardless of their width, ABNNRs with F-passivation at only the edge-B atoms are found to be thermodynamically stable and half-metallic in nature. The spin polarized states are found to be ∼0.4 eV more stable than that of spin compensated states. Further, upto 100% spin polarization is expected in ABNNRs with F-passivation at only the edge-B atoms as indicated by the giant splitting of spin states which is observed in the corresponding band structures, DOS and transmission spectrum. The existence of half-metallicity is attributed to the localization of electronic charge at unpassivated edge-N atoms as revealed from the analysis of Bloch states and projected density of states (PDOS). Importantly, present stability analysis suggests that the possibility of experimental realization of spin polarized transport in ABNNRs is more promising via F-passivation of ribbon edges than that of H-passivation. The observed half-metallic nature and large difference in the energies (∼0.4 eV) of spin polarized and spin compensated states projects these half-metallic ABNNRs as potential candidates for inorganic spintronic applications.

Origin of photoluminescence from silicon nanowires prepared by metal induced etching (MIE)

In this present study the origin of luminescence from silicon nanowires (SiNws) has been studied. SiNWs are fabricated on Si substrate by metal induced chemical etching (MIE). Here it is found that the band gap of SiNWs is higher than the gap of luminescent states in SiNWs which leads to the effect of Si=O bond. The band gap is estimated from diffuse reflectance analysis. Here we observe that band gap can be tailored depending on size (quantum confinement) but photoluminescence (PL) from all the sample is found to be fixed at 1.91 eV. This study is important for the understanding of origin of photoluminescence.

Intrinsic Half-metallicity in Edge Fluorinated Armchair Boron Nitride Nanoribbons

We predict intrinsic half-metallicity in armchair boron nitride nanoribbons (ABNNRs) via edge fluorination. The stability, electronic and magnetic properties of bare and edge fluorinated ABNNRs have been systematically analyzed by means of first-principles calculations within the local spin-density approximation (LSDA). The ribbons whose only edge-B atoms passivated with F atoms (i.e., edge-N atoms are un-passivated), regardless of width, are found half-metallic with a half-metal gap of 0.3 eV. A 100 \% spin polarized charge transport across the Fermi level is expected for such ribbons as the spin polarized states are

Effect of hafnium substitution on the dielectric properties of CaCu3Ti4O12

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Stability analysis of zigzag boron nitride nanoribbons

0.4 eV more stable than the spin un-polarized states and only single-spin conducting channels are present across the Fermi level owing to the gigantic spin splitting. The existence of half-metallicity is attributed to the localization of electronic charge at bare edge-N atoms as revealed from the analysis of Bloch states and projected density of states (PDOS).The sufficiently large half-metal gap (0.3 eV) with huge difference in the energies (

Raman spectroscopy for study of interplay between phonon confinement and Fano effect in silicon nanowires

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