Supriya Arora

Swift heavy ion irradiation effects on transport properties of epitaxial thin films of La1-xCaxMnO3

Abstract The influence of swift heavy ion (SHI) irradiation on transport properties of epitaxial thin films of La0.75Ca0.25MnO3 (LCMO) is studied. The films were irradiated with 90 MeV16O beams and 250 MeV107 Ag beams at different fluence values. In the case of 90 MeV16O ions LCMO specimens were irradiated to 1011-1014 ions/cm2 and for 250 MeV107Ag ions with 1010–1013 ions/cm2. A systematic variation in Curie temperature (T c) or resistivity peak temperature (T p) has been observed. It has been noted that for both types of ions the T p increased for the specimen irradiated at 1011 ions/cm2 fluence. Further increase of fluence decreased the T p value and at higher fluence (1014 ions/cm2 for 90 MeV16O and 1013 ions/cm2 for 250 MeV107 Ag ions) the specimens showed no metal-to-insulator transition even at low temperature down to 77K. They show completely semiconducting behavior with high resistance values. These results are discussed in terms of SHI irradiation-induced structural distrotion and strain on thin...

Study of columnar amorphization and structural symmetry changes produced by swift heavy ion irradiation in YBa2Cu3O7−y thin films using STM

Abstract Columnar amorphization and structural symmetry changes produced by 250 MeV Ag+17 ion irradiation in epitaxial thin films of YBa2Cu3O7−y were studied using scanning tunneling microscopy (STM). The columnar amorphized regions were found to have sizes between 2–3 nm and structural distortion up to 4–5 nm size around the ion tracks. The change in spacing between the nearest columnar defect as a function of ion fluence was studied. The observed columnar amorphization is discussed in the framework of electronic energy loss of swift heavy ions which excites the electronic system of the materials leading to the deterioration of structural symmetry due to energy transfer to lattice via electron-phonon interactions.

90 MeV 16O ion irradiation effects on transport and magnetization in epitaxial thin films of La0.75Ca0.25MnO3

The influence of 90 MeV 16O ion irradiation on the electric and magnetic properties of epitaxial thin films of La0.75Ca0.25MnO3 is studied. These films were deposited on LaAlO3(100) substrates by the pulsed excimer laser deposition technique. The thickness of each film was about 3000 A. The high quality of the films was ensured by x-ray diffraction and transport measurements. The films were irradiated with 90 MeV oxygen ions at different doses (1011–1014 ions/cm2). It is observed that at a low dose of 1011 ions/cm2 the resistivity peak temperature (Tp) and the Curie temperature (Tc) increase, however as the dose is increased further, the Tp and Tc decrease. At the higher dose of 1014 ions/cm2, the film becomes insulating and does not show any peak in the resistivity–temperature curve down to 60 K. These results are discussed in terms of the effects of ion induced compositional inhomogeneity and strain on the film properties.

In situ current-voltage characterization of swift heavy ion irradiated Au/n-GaAs Schottky diode at low temperature

A Au/n-GaAs(100) Schottky diode was irradiated at 80 r K by a 180 r MeV 107 Ag 14+ ion beam. In situ current-voltage (I--V) characterization of the diode was performed at various irradiation fluences ranging from 1 ‐ 10 10 to 1 ‐ 10 13 r ions r cm m 2 . The semiconductor was heavily doped (carrier concentration=1 ‐ 10 18 r cm m 3 ), hence thermionic field emission was assumed to be the dominant current transport mechanism in the diode. Systematic variations in various parameters of the Schottky diode like characteristic energy E 0 , ideality factor n , reverse saturation current I S , flatband barrier height K bf and reverse leakage current I R have been observed with respect to the irradiation fluence. The nuclear and electronic energy losses of the swift heavy ion affect the interface state density at the metal-semiconductor interface resulting in observed variations in Schottky diode parameters.

Electronic transport and 1/f noise studies in 250 MeV 107Ag ion irradiated La0.75Ca0.25MnO3 thin films

The influence of 250 MeV 107Ag ion irradiation on electrical transport and low frequency conduction noise properties of La0.75Ca0.25MnO3 (LCMO) thin films have been investigated. A systematic variation of metal–insulator transition temperature Tp and resistivity as a function of ion fluence has been observed. It has been noted that for the sample irradiated with 1011 ions/cm2, Tp increased by 10 K and the resistivity is decreased in the ferromagnetic metallic state from that of an unirradiated sample, whereas our noise results show a monotonic increase in the normalized noise Sv/V2, as a function of ion fluence. The observed modifications in the noise properties of the irradiated LCMO thin films are consistent with the general expectation concerning the effect of swift heavy ions irradiation induced lattice defects.

Structural, magnetic and x-ray absorption studies of NdCo1−xNixO3 (0 ≤ x ≤ 0.5)

We have systematically investigated the effect of Ni substitution on the structural and magnetic properties of NdCoO3. Single phase nature and orthorhombic Pbnm structure is confirmed by the Reitveld refinement of X-ray diffraction data in all samples. X-ray absorption near edge spectroscopy of Co and Ni K-edges reveals the presence of trivalent state of Ni and Co ions in all samples. Composition dependent crossover from canted antiferromagnetic (AFM) (for x < 0.3) to spin glass behavior (for x ≥ 0.3) is observed in magnetic measurements. Low temperature ferromagnetic (FM) component in doped samples is attributed to the stabilization of Co+3 ions in intermediate-spin (IS) state t52ge1g with S = 1 The FM and AFM are observed to coexist as confirmed by M-H hysteresis. Nd sublattice seems to inhibit the magnetic contribution from Co ions, and we ruled out the possibility of charge disproportion induced by Ni substitution leading to FM interactions in these systems as proposed in different reports.

1/f noise properties of a La1−xCaxMnO3 thin film

Abstract The voltage noise studies of the La0.75Ca0.25MnO3 (LCMO) thin film in the low frequency region are presented. The observed noise arises due to resistance fluctuations and its magnitude follows a power law of 1/f form. Magnitude of the 1/f noise and value of the Hooges parameter in the paramagnetic (PM) and ferromagnetic metallic states (FMM) are found to be much larger than that of metals and semiconductors. The large magnitude of the 1/f noise observed in the FMM state suggests that the contribution arising due to strong Jahn–Teller distortions is significant. Temperature dependence of the normalized noise shows a phase transformation from the PM state to FMM state.

COMPARATIVE EVALUATION OF SEQUENTIAL INTRAOPERATIVE USE OF WHOLE BLOOD FOLLOWED BY BRILLIANT BLUE VERSUS CONVENTIONAL BRILLIANT BLUE STAINING OF INTERNAL LIMITING MEMBRANE IN MACULAR HOLE SURGERY.

Purpose: To compare the structural and functional outcome of use of autologous heparinized whole blood before staining internal limiting membrane with brilliant blue (BB) versus conventional BB–assisted macular hole surgery. Methods: Sixty eyes of 60 patients were randomly divided equally in Group A (BB staining using whole blood) and Group B (conventional BB staining). Clinical assessment and spectral domain optical coherence tomography was done at baseline and 3 weeks, 6 weeks, 16 weeks, and 6 months postoperatively. Results: Group A eyes had a significantly higher best-corrected visual acuity as compared with Group B postoperatively (P < 0.001, <0.001, 0.004, 0.04 at 3, 6, 16 weeks, and 6 months). Inner segment/outer segment junction continuity was noted in greater number of eyes in Group A compared with Group B (P = 0.02, 0.002, 0.003, and 0.03 at 3, 6, 16 weeks, and 6 months). Eyes in Group A had significantly higher outer foveal thickness at 3 weeks (P = 0.001) and 6 weeks (P < 0.001) compared with Group B. Conclusion: Use of whole blood before staining internal limiting membrane with BB causes earlier and better visual rehabilitation postoperatively, which could be attributed to earlier photoreceptor regeneration as evidenced by inner segment/outer segment junction continuity and increase in outer foveal thickness.

Choroidal thickness evaluation of healthy eyes, central serous chorioretinopathy, and fellow eyes using spectral domain optical coherence tomography in Indian population

Aim: The purpose of this study is to establish a normative database of subfoveal choroidal thickness (CT) in healthy young Indians using spectral domain optical coherence tomography (SD OCT). Evaluation and comparison of CT of central serous chorioretinopathy (CSC) and fellow eyes were also performed. Materials and Methods: This was a prospective, cross-sectional, and observational study. It included 112 normal eyes of 112 healthy volunteers who had no evidence of ocular or systemic disease, 84 CSC eyes with acute, treatment-naïve CSC, and 69 fellow eyes with no evidence of neurosensory detachment or pigment epithelium detachment on SD OCT. Complete history, examination, and SD OCT were performed in all eyes. Results: The mean age of 81 patients (84 eyes) with CSC was 35.04 ± 8.86 years, 69 fellow eyes was 34.61 ± 8.71 years, and 112 healthy volunteers (112 eyes) was 33.16 ± 9.4 years (P < 0.05). The mean subfoveal CT of CSC eyes was 429 ± 74.18 μ, fellow eyes was 360 ± 57.99 μ, and normal eyes was 301.80 ± 46.59 μ (P < 0.001). Conclusion: CT varies not only with age, axial length, and refractive error but also with races. Therefore, it is important to establish a normative database in a particular population before carrying out further research in diseased states. CT in CSC eyes is significantly thicker than fellow eyes, and CT of fellow eyes is significantly thicker than normal eyes. This reinforces the fact that choroidal permeability is increased in both eyes of patients with CSC.

Evidence for spin glass state of NdCo1−xNixO3 (x = 0.3−0.5)

Low-temperature magnetic properties of single phase NdCo1−xNixO3(x = 0.3−0.5) have been studied using ac and dc magnetic susceptibility measurements. Nickel substituted samples have been found to exhibit a different magnetic state at low temperature as compared to pristine NdCoO3. The temperature dependent dc magnetization M (T) revealed the presence of a sharp cusp occurring at characteristic temperatures TP, for x = 0.3, 0.4, 0.5. Below TP, clear effect of magnetic field can be seen in M (T) curves and TP decreases with increasing magnetic field as well as Ni substitution content. The isothermal magnetization measurements at low temperatures shows small unsaturated hysteresis loop at lowest temperature (10 K). The ac susceptibility results show a clear frequency dependent feature. These results are analyzed to distinguish superparamagnetic and spin glass behavior by using Neel-Arrhennius, Vogel-Fulcher law, and power law fitting. This analysis ruled out the superparamagnet like state and suggests the pr...