Sudesh Sharma

Room temperature ferromagnetism in Mn doped TiO2 thin films: Electronic structure and Raman investigations

In this work dc-magnetization, electronic structural, and Raman investigations of Ti1−xMnxO2 (x = 0.00, 0.05, 0.10, and 0.15) thin films deposited on fused-quartz substrate by a simple and cost effective spray pyrolysis technique have been reported. X-ray diffraction revealed the formation of pure anatase TiO2 phase devoid of elemental Mn clusters in all the Mn incorporated TiO2 films. It is established by x-ray photoelectron spectroscopic (XPS) measurements that Ti ions substituted by Mn ions in both divalent and trivalent states in the TiO2 matrix. No peak corresponding to Mn+4 could be evidenced by XPS. The Raman study has further established the formation of TiO2 in anatase structure in both pure TiO2 and Mn-doped TiO2 films. The Ti1−xMnxO2 films with x ≥ 0.05 exhibit ferromagnetic ordering at room temperature which arises most likely due to formation of bound magnetic polarons.

Observation of room temperature ferromagnetism in spray pyrolyzed polycrystalline Ti1−xCoxO2 thin films

We report here the room temperature ferromagnetic ordering in spray-pyrolized polycrystalline thin films of Ti1−xCoxO2 (x = 0, 0.025, 0.05 and 0.10). The saturation magnetic moment in these films with x = 0.05 and 0.10 is estimated to be of 0.28 and 0.38µB/Co, respectively. The ambient air employed in the present case of the spray pyrolysis process resulted in ferromagnetic films possessing very high resistivity values (∼10 7 � cm). This is in contrast to Ti1−xCoxO2 films deposited by vacuum based techniques, which are relatively conducting. While pristine TiO2 film exhibited the anatase phase, the rutile phase of TiO2 also evolved with an increase in Co concentration in these films. X-ray diffractograms could not reveal segregation of Co atoms in the TiO2 matrix; also, no formation of any oxide of cobalt was detected. X-ray photoelectron spectroscopic investigation established the Co cations to be bivalent, and suggests that Co +2 is substituting Ti +4 in the TiO2 matrix. Due to the highly resistive nature of these films, the observed room temperature ferromagnetism could be attributed either to the formation of bound magnetic polarons or to defect mediated ordering.

Raman study of the structure of ferric chloride in frozen aqueous solutions

Abstract A comparison of the Raman spectra of ferric chloride hexahydrate (FCHH) in 11·5M HCl solution at 298 and 165K has shown that the FeCl 4 − ions, which are the most prominent species in the highly acidic FCHH solution, get converted into polymeric species, composed of higher chloro-ferrate octahedral groups of the type FeCl 5 2− ·H 2 O and FeCl 6 3− . The Raman spectra of the frozen FCHH in 11·5M HCl and in 3M HCl are similar, indicating the similarity of structures of the polymeric species present in the two frozen solutions. The observed similarity between the Raman spectrum of FCHH in 3M HCl at 298 and 165K suggests that on freezing the solution transforms into glass without any appreciable structural changes.

On the growth of single crystals of ammonium chloride from vapor‐phase techniques

Kinetics of growth of ammonium chloride single crystals have been studied employing vapor‐phase techniques. The crystals grown by the Piper‐Polich technique were found polycrystalline in nature. Single crystals of ammonium chloride 1–2 mm wide and 5–7 mm long have been grown below its transformation temperature employing sublimation techniques. A possible growth mechanism has been suggested.

Plasmonic ladder–like structure and graphene assisted high surface enhanced Raman scattering detection

Surface enhanced Raman scattering (SERS) study is an interesting active area of research, where periodically patterned plasmonic substrates play a key role in SERS enhancement. Surface plasmon resonance excitation generates tremendous electromagnetic near-fields (E) in the form of localized or propagating near-fields contributing to the Raman signal (E4 process) to a great extent and overall enhancement is reported to be as high as 1010 or even more. Independently, graphene alone can enhance the Raman signal due to chemical enhancement. In the present study, we have attempted to achieve high SERS from the R6G Raman active probe using plasmonic patterned substrates in the presence and absence of graphene oxide. Plasmonic ladder-like patterned substrates are fabricated using laser interference lithography, which is cost effective, simple to operate, and has potential for large scale nanofabrication. By combining graphene oxide with R6G, we have found additional two time enhancement compared to that obtain f...