Browsing by Author "T. Shripathi"

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Core level X-ray photoelectron spectroscopy study of exchange coupled Fe/NiO bilayer interfaced with Si substrate (Fe/NiO-nSi structure)
(2013) Neelabh Srivastava; T. Shripathi; P.C. Srivastava
The chemical interactions and surface chemical states of exchange coupled structures of Fe/NiO bilayer interfaced with silicon substrate has been studied from X-ray photoelectron spectroscopy (XPS) technique. The structure has been irradiated from swift (∼100 MeV) heavy ions (of Fe7+) with a fluence of ∼5 × 1012 ions/cm2. The surface of the samples has also been cleaned from ion beam etching for various durations to record the XPS spectra. On the irradiation, signals due to Fe2p and Ni2p are emerging along with the signal of Si2p whereas no signal of Si2p has been observed, prior to irradiation. The observation shows that the Si atoms are present within the probed surface layer due to irradiation induced interfacial intermixing. We also observed a shift in the binding energy position of Si2p which could be due to the formation of silicide phases as a result of irradiation induced interfacial intermixing. XPS results have indicated the presence of ionic Fe (Fe2+ or Fe3+) and metallic Ni at the Fe/NiO interface, which could be due to the different chemical reactions at the Fe/NiO interface. © 2013 Elsevier B.V.
Corrigendum to “Layered double hydroxides as effective carrier for anticancer drugs and tailoring of release rate through interlayer anions” [Journal of Controlled Release 224 (2106) 186–198] (Layered double hydroxides as effective carrier for anticancer drugs and tailoring of release rate through interlayer anions (2016) 224 (186–198), (S016836591630013X), (10.1016/j.jconrel.2016.01.016))
(Elsevier B.V., 2021) Sudipta Senapati; Ravi Thakur; Shiv Prakash Verma; Shivali Duggal; Durga Prasad Mishra; Parimal Das; T. Shripathi; Mohan Kumar; Dipak Rana; Pralay Maiti
The authors regret that the initial published version of this article an error in the assembly of Fig. 7b resulted in some image duplications. The corrected Fig. 7b includes the correct images of the experiment. This correction/omission doesn't alter any conclusion of the article as quantitative analysis of the experiment has been performed through MTT assay, presented in Fig. 7a. [Figure Presented] The figure legend remains the same. The corrections made in this corrigendum do not affect the original conclusions of the article. The author's apologies for any inconvenience caused. © 2016 Elsevier B.V.
Effect of ferrocene concentration on the synthesis of bamboo-shaped carbon-nitrogen nanotube bundles
(2005) Ram Manohar Yadav; T. Shripathi; Anchal Srivastava; O.N. Srivastava
We have investigated the effect of ferrocene concentration on the synthesis of carbon-nitrogen (C-N) nanotubes. The bamboo-shaped carbon-nitrogen nanotubes were synthesized by spray pyrolysis of Fe(C 5H 5) 2 and CH 3CN solution using argon as a carrier gas at the optimum temperature of ∼900°C. The effect of ferrocene concentration on the length and concentration of nitrogen in nanotubes was studied. Micro-structural features of the nanotubes were monitored employing scanning and transmission electron microscopic techniques. SEM studies reveal that with decreasing ferrocene concentration from 25 mg ml -1 to 5 mg ml -1, the length of the nanotubes vary from 80 μm to 430 μm. A feasible growth model has been described and discussed. X-ray photoelectron spectroscopic studies have confirmed the formation of nitrogen-doped carbon nanotubes. These studies reveal that the nitrogen concentration in the nanotubes decreases with the increase of ferrocene concentration. The present synthesis route also provides means of producing carbon nanotubes with different concentrations of nitrogen. Copyright © 2005 American Scientific Publishers All rights reserved.
Effect of growth temperature on bamboo-shaped carbon-nitrogen (C-N) nanotubes synthesized using ferrocene acetonitrile precursor
(2009) Ram Manohar Yadav; Pramod Singh Dobal; T. Shripathi; R.S. Katiyar; O.N. Srivastava
This investigation deals with the effect of growth temperature on the microstructure, nitrogen content, and crystallinity of C-N nanotubes. The X-ray photoelectron spectroscopic (XPS) study reveals that the atomic percentage of nitrogen content in nanotubes decreases with an increase in growth temperature. Transmission electron microscopic investigations indicate that the bamboo compartment distance increases with an increase in growth temperature. The diameter of the nanotubes also increases with increasing growth temperature. Raman modes sharpen while the normalized intensity of the defect mode decreases almost linearly with increasing growth temperature. These changes are attributed to the reduction of defect concentration due to an increase in crystal planar domain sizes in graphite sheets with increasing temperature. Both XPS and Raman spectral observations indicate that the C-N nanotubes grown at lower temperatures possess higher degree of disorder and higher N incorporation.
Effect of multielement doping on low-field magnetotransport in La0.7-xMmxCa0.3MnO3 (0.0≤x≤0.45) manganite
(2009) P.K. Siwach; Pankaj Srivastava; H.K. Singh; A. Asthana; Y. Matsui; T. Shripathi; O.N. Srivastava
We report the synthesis, structure and low-field magnetotransport properties of Mischmetal (Mm)-doped La0.7-xMmxCa0.3MnO3 (0≤x≤0.45) manganite. Mischmetal-Mm-is a natural mixture of rare earth elements La, Ce, Pr and Nd with ∼28%, 50%, 6% and 16% composition, respectively. All the samples crystallize in orthorhombic structure. Increasing x (Mm), corresponding to decreasing the La-site average ionic radii (〈rA〉) hence increasing the size mismatch (i.e. variance σ2), results in strong suppression of ferromagnetism (TC) and the associated metallicity (TIM). It may be pointed out that Mm (La, Ce, Pr and Nd) substitution has been done to create two effects. First, creation of multivalence of Mn (2+, 3+ and 4+) via Ce substitution and second to create higher degree of disorder due to size difference brought in not only by Ce but also by Pr and Nd. Evidences and arguments based on XPS analysis suggest that multivalent ions La, Mm and Ca, and the resulting presence of Mn2+, Mn3+ and Mn4+, causes the simultaneous operation of ferromagnetism-double exchange (Mn2+/Mn3+ and Mn3+/Mn4+) and antiferromagnetic-superexchange (Mn3+/Mn3+ and Mn2+/Mn2+) interaction. In addition, Mm doping also creates inhomogenities at La-as well as Mn-site due to size and valency difference. A curiously huge magnetoresistance as high as ∼63% for x=0.35, under a moderate magnetic field of ∼10 kOe has been observed and even at low magnetic field of ∼3 kOe MR is ∼30%. The competing double exchange and superexchange coupled with inhomogenities are the most likely cause for the occurrence of large ∼63% CMR in the Mm-doped LCMO. © 2008 Elsevier B.V. All rights reserved.
Electrical and XPS studies of 100 MeV Si 7+ ion irradiated Pd/n-GaAs devices
(Elsevier, 2004) O.P. Sinha; T. Shripathi; N.P. Lalla; P.C. Srivastava
The effect of Swift Heavy Ion (100MeV Si 7+ ) irradiation on electronic-transport of Pd/n-GaAs devices has been studied by I-V and C-V techniques. The chemical compositions of the interface have been studied by XPS/EDAX techniques. It is observed that the irradiated devices show a reduction in current and capacitance by few orders of magnitude. The C-V characteristics show a change in conductivity type from n- to p-type after the irradiation. On hydrogenation, the irradiated devices show a capacitance peak in C-V characteristics, which has been ascribed to As vacancies. The XPS studies of these devices, for various etching durations, show that the ratio of As:Ga has reduced after the irradiation, which indicates the formation of irradiation-induced As vacancies. This reduction in As:Ga ratio is also confirmed by EDAX measurement. The observed conductivity type change from n- to p-type (on the irradiation) seems to be due to the change of substitutional sites of dopant silicon atoms from Ga to As sites due to the irradiation-induced As vacancies. © 2004 Elsevier B.V. All rights reserved.
Layered double hydroxides as effective carrier for anticancer drugs and tailoring of release rate through interlayer anions
(Elsevier B.V., 2016) Sudipta Senapati; Ravi Thakur; Shiv Prakash Verma; Shivali Duggal; Durga Prasad Mishra; Parimal Das; T. Shripathi; Mohan Kumar; Dipak Rana; Pralay Maiti
Hydrophobic anticancer drug, raloxifene hydrochloride (RH) is intercalated into a series of magnesium aluminum layered double hydroxides (LDHs) with various charge density anions through ion exchange technique for controlled drug delivery. The particle nature of the LDH in presence of drug is determined through electron microscopy and surface morphology. The release of drug from the RH intercalated LDHs was made very fast or sustained by altering the exchangeable anions followed by the modified Freundlich and parabolic diffusion models. The drug release rate is explained from the interactions between the drug and LDHs along with order-disorder structure of drug intercalated LDHs. Nitrate bound LDH exhibits greater interaction with drug and sustained drug delivery against the loosely interacted phosphate bound LDH-drug, which shows fast release. Cell viability through MTT assay suggests drug intercalated LDHs as better drug delivery vehicle for cancer cell line against poor bioavailability of the pure drug. In vivo study with mice indicates the differential tumor healing which becomes fast for greater drug release system but the body weight index clearly hints at damaged organ in the case of fast release system. Histopathological experiment confirms the damaged liver of the mice treated either with pure drug or phosphate bound LDH-drug, fast release system, vis-à-vis normal liver cell morphology for sluggish drug release system with steady healing rate of tumor. These observations clearly demonstrate that nitrate bound LDH nanoparticle is a potential drug delivery vehicle for anticancer drugs without any side effect. © 2016 Elsevier B.V. All rights reserved.
New insights into CoFe/n-Si interfacial structure as probed by X-ray photoelectron spectroscopy
(Elsevier B.V., 2016) Arvind Kumar; T. Shripathi; P.C. Srivastava
X-ray photoelectron spectroscopy (XPS) is a well known tool in studying the physical and chemical properties of surface/interfaces which provides the element specific, non-destructive and quantitative information. In the present study, information about the surface chemical states of interfacial structure of CoFe thin films on n-Si substrates has been studied from XPS technique. The surface of the samples has also been cleaned from ion beam etching for 30 min with Ar+ ions to record the XPS spectra. The observation shows that the Si atoms are present within the probed surface layer due to interfacial intermixing across the interface which is due to strong chemical reactivity of n-Si substrate. A shift in the binding energy peaks of Fe2p and Co2p has also been observed which could be due to the formation of silicide phases as a result of interfacial intermixing. XPS results have indicated the formation of silicide phases across the interfaces which poses interfacial antiferromagnetic coupling across CoFe/n-Si interface to affect the magnetic behaviour. It has been found that the present XPS results are in well support with our earlier study. © 2016 The Authors
Photoelectron spectroscopy study of Mn/n-Si interfacial structure
(2013) M.K. Srivastava; T. Shripathi; P.C. Srivastava
The Mn/n-Si interfacial structure is susceptible to intermixing even at room temperature. To investigate the chemistry as a result of the intermixing, valence band and core level photoelectron spectroscopy of Mn/Si has been carried out using synchrotron radiation of 134 eV energy and Al Kα X-ray (λ = 1,486.6 Å) source. The fabricated structures have also been irradiated from swift heavy ions (Fe7+ of ∼100 MeV) to investigate the ion beam mixing in such structures. Valence band photoelectron spectroscopy with 134 eV photons shows the evolution of Mn3d, Mn3p and Si2p levels with a shifting towards lower binding energy side compared to their elemental values of the binding energy. This binding energy shift shows the formation of chemical compound of Si and Mn. Evolution of Si2p core level prior to and after the swift heavy ion irradiation shows strong chemical reactivity of manganese thin film with silicon. Deconvolution of Mn3d valence band has shown the formation of silicide phase due to the hybridization of Mn3d and Si3sp states. Mn2p core level study shows that the oxide and silicide formation takes place during the growth and for successive etching, oxide part is decreasing whereas silicide part is increasing. © 2013 Springer Science+Business Media New York.
Synthesis of C-N nanotube blocks and Y-junctions in bamboo-like C-N nanotubes
(2008) Ram Manohar Yadav; Dinesh Pratap Singh; T. Shripathi; O.N. Srivastava
We report the observations made on the synthesis and characterization of C-N nanotube blocks and Y-junctions in bamboo-like C-N nanotubes. The C-N nanotube Blocks have been synthesized by pyrolyzing the mixture of silver nitrate acetonitrile solution and ferrocene benzene solution. The structural/microstructural characterization of the as-synthesized material has been done using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray photoelectron spectroscopic (XPS) analysis has been carried out to confirm the presence of nitrogen in nanotubes. These investigations reveal the formation of blocks of bamboo-like nanotubes having the dimension 300 × 200 × 30 μm and the diameter is 20-50 nm. We also observe the formation of Y-junctions in bamboo-like nanotubes as we spray the acetonitrile ferrocene and AgNO3 mixture. The length of the synthesized Y-junction nanotube bundles is ∼2 μm. Some more complex Ψ-shaped junctions are also found to be present. The diameters of the Y-junction nanotubes is ∼80 nm at the junction and 25-50 nm at the branches. © 2008 Springer Science+Business Media B.V.
Synthesis of carbon and carbon-nitrogen nanotubes using green precursor: Jatropha-derived biodiesel
(2013) Rajesh Kumar; R.M. Yadav; K. Awasthi; T. Shripathi; A.S.K. Sinha; R.S. Tiwari; O.N. Srivastava
The jatropha-derived biodiesel, a green precursor was found to be a new and promising precursor for the synthesis of carbon nanotubes (CNTs) and carbon-nitrogen (C-N) nanotubes. The CNTs and C-N nanotubes have been synthesised by spray pyrolysis of biodiesel with ferrocene and ferrocene-acetonitrile, respectively, at elevated temperature under an argon atmosphere. The typical length and diameter of as-grown CNTs are 20 μm and 20-50 nm, respectively. The C-N nanotubes are found in bundles with effective length of ~30 μm and diameter ranging between 30 and 60 nm with bamboo-shaped morphology. The as-grown CNTs and C-N nanotubes were characterised through scanning and transmission electron microscopes, X-ray photoelectron, Raman and Fourier transform infrared spectroscopic techniques. These investigations revealed that the nanotubes synthesised by jatropha-derived biodiesel are clean from carbonaceous impurities and the bamboo compartment formations in C-N nanotubes are due to nitrogen incorporation. The nitrogen concentration in C-N nanotubes decreases with the increase in synthesis temperature. © 2013 Copyright Taylor and Francis Group, LLC.
X-ray diffraction and photoelectron spectroscopy study of swift heavy ion irradiated Mn/p-Si structure
(Elsevier, 2010) M.K. Srivastava; T. Shripathi; D.M. Phase; P.C. Srivastava
The electronic structure and interfacial chemistry of thin manganese films on p-Si (1 0 0) have been studied by photoelectron spectroscopy measurements using synchrotron radiation of 134 eV and from X-ray diffraction data. The Mn/p-Si structures have been irradiated from swift heavy ions (∼100 MeV) of Fe 7+ with a fluence of 1 × 10 14 ions/cm 2 . Evolution of valence band spectrum with a sharp Fermi edge has been obtained. The observed Mn 3d peak has been related to the bonding of Mn 3d-Si 3sp states. Mn 3p (46.4 eV), Mn 3s (81.4 eV) and Si 2p (99.5 eV) core levels have also been observed which show a binding energy shift towards lower side as compared to their corresponding elemental values. From the photoelectron spectroscopic and X-ray diffraction results, Mn 5 Si 3 metallic phase of manganese silicide has been found. The silicide phase has been found to grow on the irradiation. © 2009 Elsevier B.V. All rights reserved.