Bhupendra N. Dev - Academia.edu (original) (raw)

Papers by Bhupendra N. Dev

AIP Conference Proceedings, 2008

ABSTRACT Ion irradiation of graphite and other carbon allotropes is a versatile tool for manipula... more ABSTRACT Ion irradiation of graphite and other carbon allotropes is a versatile tool for manipulating their physical, chemical and even magnetic properties. Fullerene films, when irradiated with 2 MeV protons, display soft‐ferromagnetic ordering at 5 K. At 300 K both pristine and irradiated films show diamagnetic behaviour.Magnetisation data in the temperature range of 2‐300 K, in 1 T applied field, for the irradiated film show much stronger temperature dependence compared to a pristine film. The ion irradiation study has been further extended to the graphite system. Poly‐crystalline graphite samples were irradiated with 2.25MeV protons at a fluence of 2×1017 ions∕cm2.Magnetic ordering in highly oriented pyrolytic graphite samples have been reported earlier under similar irradiation conditions [Esquinazi et. al. Phys. Rev. Lett. 91 (2003) 227201]. In that study, the authors attribute the observed irradiation induced magnetic ordering to the formation of a mixed sp2‐sp3 hybridized carbon atoms. Here we present Raman and X‐ray photoelectron spectroscopic studies on pristine and irradiated graphite samples. Irradiated samples are found to show an increased number of sp3 hybridized carbon atoms. However, the Raman spectrum, specially the second order data, do indicate that the nature of the graphene lattice structure has been preserved in the irradiated samples. The formation of a mixed sp2‐sp3 hybridization in graphite structure, which might be responsible for magnetism,will be discussed.

In earlier work(S. M. Mohapatra et al., Rev. Solid State Sci. 4), 873 (1990) and references there... more In earlier work(S. M. Mohapatra et al., Rev. Solid State Sci. 4), 873 (1990) and references therein. our group had evaluated the nuclear quadrupole coupling constants e^2qQ and asymmetry parameters eta for a number of adsorbed atoms of the first, third, sixth and seventh groups on unreconstructed silicon surfaces. Subsequently, Schatz(G. Krausch et al., Phys. Rev. Lett. 68), 377 (1992). and his group, in their pioneering experimental efforts, studied the e^2qQ and eta for the excited ^111Cd^* nucleus resulting from beta-decay of ^111In nucleus adsorbed on the 7× 7 reconstructed silicon surface. Two sets of e^2qQ and eta were observed with the values of e^2qQ quite close to our earlier predictions^1 but with eta of 0.20 and 0.25 in contrast to eta=0 for the unreconstructed (111) surface. The dimer-adatom-stacking-fault(DAS) model for indium sites on the (7× 7) was suggested as a likely candidate for explaining the observed eta. We have been recently involved in testing this suggestio...

Physics at Surfaces and Interfaces - Proceedings of the International Conference, 2003

AIP Conference Proceedings, 2013

ABSTRACT Ag/Si (111) interface has been investigated using first principles DFT approach, to esta... more ABSTRACT Ag/Si (111) interface has been investigated using first principles DFT approach, to establish the unique interplay between the structural and electronic properties. The interface induced properties, such as evolution of metal-induced gap states (MIGS), formation of Schottky barrier height (SBH), for this rectifying Ag/Si contact have been reported.

Applied Physics Letters, 2014

ABSTRACT Iron silicide (cubic FeSi2) nanowires have been grown on Si(110) by reactive deposition ... more ABSTRACT Iron silicide (cubic FeSi2) nanowires have been grown on Si(110) by reactive deposition epitaxy and investigated by scanning tunneling microscopy and scanning/transmission electron microscopy. On an otherwise uniform nanowire, a semi-periodic pattern along the edges of FeSi2 nanowires has been discovered. The origin of such growth patterns has been traced to initial growth of silicide nanodots with a pyramidal Si base at the chevron-like atomic arrangement of a clean reconstructed Si(110) surface. The pyramidal base evolves into a comb-like structure along the edges of the nanowires. This causes the semi-periodic structure of the iron silicide nanowires along their edges.

Thin Solid Films, 2011

Growth of Ag nanoislands on air-oxidized Si(001), (111) and (110) surfaces has been investigated ... more Growth of Ag nanoislands on air-oxidized Si(001), (111) and (110) surfaces has been investigated by reflection high energy electron diffraction (RHEED), scanning tunneling microscopy (STM) and cross-sectional transmission electron microscopy. We have shown that the ...

Thin Solid Films, 2012

ABSTRACT Growth of Ag films on Br- and H-passivated Si(111) surfaces and the annealing behaviour ... more ABSTRACT Growth of Ag films on Br- and H-passivated Si(111) surfaces and the annealing behaviour have been investigated by Rutherford backscattering spectrometry, scanning electron microscopy and photoemission electron microscopy techniques. Upon annealing the phenomenon of thermal grooving was observed in the Ag films. Depending on the annealing temperature, at an intermediate annealing time Ag depletion (evaporation) from the grain boundaries produces fractal patterns of Ag-depleted regions. Continued annealing eventually produces a percolated network of Ag-depleted regions (thermal grooves) along the grain boundaries and isolated Ag grains appear as the depth of the grooves reaches the substrate. For the fractal structures produced by thermal grooving, the fractal dimension has been estimated to be 1.60 ± 0.04. Observation of a fractal pattern in thermal grooving was not hitherto reported. A thorough analysis of the experimental results has been carried out in the context of current theories. These theories are inadequate to describe the experimental results.

Surface and Interface Analysis, 2011

... Anupam Roy 1 ,; JK Dash 2 ,; A. Rath 2 ,; BN Dev 1,*. Article first published online: 8 NOV 2... more ... Anupam Roy 1 ,; JK Dash 2 ,; A. Rath 2 ,; BN Dev 1,*. Article first published online: 8 NOV 2011. ... Correspondence: BN Dev, Department of Materials Science, Indian Association for the Cultivation of Science, Raja SC Mullick Road, Jadavpur, Kolkata-700 032, Inda. ...

Radiation Physics and Chemistry, 1998

Radiation Effects and Defects in Solids, 2007

Polycrystalline fullerene (C60) films prepared on hydrogen-passivated Si(1 1 1) substrates were i... more Polycrystalline fullerene (C60) films prepared on hydrogen-passivated Si(1 1 1) substrates were irradiated by 2 MeV protons with fluences ranging from 6×1015 to 1×1017 ions/cm2. Ferromagnetic-like ordering is reported for samples irradiated with a fluence of 6×1015 ions/cm2 [S. Mathew et al., arxive:cond-mat/0503315]. Raman spectroscopy results indicate an enhancement of the characteristic Ag and Hg modes of C60 after irradiation,

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1999

Epitaxial Ag(1 1 1) thin ®lms ($125 nm) have been grown on Br-passivated Si(1 1 1) surfaces under... more Epitaxial Ag(1 1 1) thin ®lms ($125 nm) have been grown on Br-passivated Si(1 1 1) surfaces under high vacuum. Growth features observed from XRD, RBS/channeling and TEM/TED experiments are comparable to those grown under UHV conditions. RBS/channeling measurements on the Ag layer showed a minimum yield (v min) of 62% indicating a poor crystalline quality. We irradiated the Ag(1 1 1) layer with 1 MeV Si at¯uences of 5 Â 10 15 and 1 Â 10 16 ionsacm 2 with the substrate at room temperature and an ion current density of 50 nA/cm 2. Following irradiation, the measured v min values are 40% and 38%, respectively, indicating an improvement in crystalline quality of the Ag layer. This behaviour is also seen in thermal annealing upto 500 C due to some grain boundary melting. In thermal annealing at P 600 C desorption of Ag occurs leaving holes in the Ag layer. Morphology of the annealed layer has been analyzed with RBS/PIXE studies with an ion microbeam of He ions.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1999

Radiation damage and Surface modi®cations of semi-insulating GaAs0 0 1 substrates upon 1 MeV C an... more Radiation damage and Surface modi®cations of semi-insulating GaAs0 0 1 substrates upon 1 MeV C and 2 MeV C 2 coimplantation with Ga 2 have been studied by X-ray re¯ectometry, combined Rutherford backscattering/channeling and transmission electron microscopy. Two disordered layers ± one near-surface and another deeper ± are formed. Additionally the electron density of the near-surface region has been found to be lower compared to bulk GaAs. This has been attributed to vacancy-enrichment in this region. The disorder caused by C 2 implantation is higher compared to C. Assuming that the near-surface disorder is partially caused by electronic excitation in the semi-insulating substrate, a possible reason for this dierence is the coherent dynamic response of the electrons in the target due to vicinage of C atoms in the C 2 cluster. In the deeper layer, overlap of damage cascades might be responsible for the higher damage caused in the cluster implantation.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2008

We have carried out scanning tunneling microscopy experiments under ultrahigh vacuum condition to... more We have carried out scanning tunneling microscopy experiments under ultrahigh vacuum condition to study the roughness of pristine as well as ion-bombarded Si(1 0 0) surfaces and of ultrathin Ge films deposited on them. One half of a Si(1 0 0) sample (with native oxide layer) was irradiated at room temperature using 45 keV Si À ions at a fluence of 4 Â 10 15 ions/cm 2 while the other half was masked. STM measurements were then carried out on the unirradiated as well as the irradiated half of the sample. Root-mean-square (rms) roughness of both the halves of the sample has been measured as a function of STM scan size. Below a length scale of 30nmweobservesurfacesmoothingandsurfacerougheningisobservedforlengthscalesabovethisvalue.However,thesurfaceisself−affineuptolengthscalesof30 nm we observe surface smoothing and surface roughening is observed for length scales above this value. However, the surface is self-affine up to length scales of 30nmweobservesurfacesmoothingandsurfacerougheningisobservedforlengthscalesabovethisvalue.However,thesurfaceisself−affineuptolengthscalesof200 nm and the observed roughness exponent of 0.46 ± 0.04 is comparable to earlier cases of ion sputtering studies where only roughening [

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2008

Poly-crystalline graphite samples were irradiated using 2.25 MeV H + ions with a fluence of 2 Â 1... more Poly-crystalline graphite samples were irradiated using 2.25 MeV H + ions with a fluence of 2 Â 10 17 ions/cm 2. Magnetic ordering in highly oriented pyrolytic graphite samples have been reported earlier under the similar irradiation conditions [Esquinazi et al., Phys. Rev. Lett. 91 (2003) 227201]. In that study, the authors attribute the observed irradiation induced magnetic ordering to the formation of a mixed sp 2-sp 3 hybridized carbon atoms. In the present study, we report the X-ray photoelectron and Raman spectroscopic studies on pristine and irradiated samples. Irradiated samples are found to show an increased number of sp 3 hybridized carbon atoms. However, the Raman spectrum, specially the second order data, do indicate that the nature of the graphene lattice structure has been preserved in the irradiated samples. The mechanisms for the irradiation induced enhancement in sp 3 hybridization are discussed.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2001

An ion microbeam facility has been set up at one of the beam lines of the 3 MV tandem Pelletron a... more An ion microbeam facility has been set up at one of the beam lines of the 3 MV tandem Pelletron accelerator facility at IOP, Bhubaneswar. This is the first facility of its kind in India, having potential applications in the growing fields involving semiconductors, materials science, biology, archeology and environmental science, from both scientific and industrial points of view. So

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2003

Very thin films of gold deposited on silicon substrates form isolated nano-island structures due ... more Very thin films of gold deposited on silicon substrates form isolated nano-island structures due to the non-wetting nature of gold. Thick films are more homogeneous and do not have the isolated island structures. Thin gold films of various thicknesses (%0.4-21.4 nm) are deposited under high vacuum condition and irradiated with 1.5 MeV Au 2þ ions. The sputtered particles are collected on catcher grids (carbon coated) during the irradiation and are analyzed with transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS). The average sputtered particle size is determined from TEM measurements, whereas the amount of gold on the catcher grid is found by RBS. The average sputtered particle size from thin (up to a thickness of %2 nm) discontinuous films is larger compared to the average particle size from thick continuous films. The coverage of the sputtered particles on the catcher grids is also discussed. Energy spike and its distribution in the nano-islands is proposed to be the main reason for the variation in the particle size and the coverage of the sputtered particles on the catcher grid.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2003

Transmission electron microscopy (TEM), atomic force microscopy (AFM) and Rutherford backscatteri... more Transmission electron microscopy (TEM), atomic force microscopy (AFM) and Rutherford backscattering spectrometry (RBS) have been used to study the modification of Au nanoislands, grown on silicon substrates under high vacuum condition by MeV self-ion irradiation. Upon irradiation with 1.5 MeV Au 2þ ions, interesting observations were found for the nanoislands in comparison with continuous films: (i) higher probability of crater formation, (ii) larger sputtered particle size as well as coverage and (iii) enhanced sputtering yield. Crater formation has been studied as a function of impact angle at a fluence of 1 • 10 14 ions cm À2 and we found that crater formation is prominent at high impact angles (i.e. at glancing angle geometry). AFM has been used to determine the crater formation, TEM to study the sputtered particles as well as craters and RBS has been used to determine the sputtering yield from the nanoisland and continuous films.

Journal of Physics: Conference Series, 2013

We employ XSW assisted XAFS at Ni K edge to characterize ion-irradiated Pt/Ni/C multilayer, parti... more We employ XSW assisted XAFS at Ni K edge to characterize ion-irradiated Pt/Ni/C multilayer, particularly the nanoclusters formed within C layer, revealed by X-TEM and angleresolved fluorescence studies. Retrieving the structural model from XAFS coordination results involved intriguing steps such as accounting for the intensity variation across the layers, determination of extra pre-diffused Ni into C layer (beyond the reflectivity determined roughness) and decoupling interfacial, layer and cluster coordination. The clusters are determined to be Ni centered Ni-Pt bimetallic nanoclusters (Ni:Pt = 60:40), formed due to irradiation induced diffusion of Pt atoms from the disrupted Pt/C interface towards prediffused Ni atoms present in C layer. They are highly disordered beyond nearest neighbor and resemble glassy structure which could find wide-scale applications in magnetic devices.

AIP Conference Proceedings, 2008

ABSTRACT Ion irradiation of graphite and other carbon allotropes is a versatile tool for manipula... more ABSTRACT Ion irradiation of graphite and other carbon allotropes is a versatile tool for manipulating their physical, chemical and even magnetic properties. Fullerene films, when irradiated with 2 MeV protons, display soft‐ferromagnetic ordering at 5 K. At 300 K both pristine and irradiated films show diamagnetic behaviour.Magnetisation data in the temperature range of 2‐300 K, in 1 T applied field, for the irradiated film show much stronger temperature dependence compared to a pristine film. The ion irradiation study has been further extended to the graphite system. Poly‐crystalline graphite samples were irradiated with 2.25MeV protons at a fluence of 2×1017 ions∕cm2.Magnetic ordering in highly oriented pyrolytic graphite samples have been reported earlier under similar irradiation conditions [Esquinazi et. al. Phys. Rev. Lett. 91 (2003) 227201]. In that study, the authors attribute the observed irradiation induced magnetic ordering to the formation of a mixed sp2‐sp3 hybridized carbon atoms. Here we present Raman and X‐ray photoelectron spectroscopic studies on pristine and irradiated graphite samples. Irradiated samples are found to show an increased number of sp3 hybridized carbon atoms. However, the Raman spectrum, specially the second order data, do indicate that the nature of the graphene lattice structure has been preserved in the irradiated samples. The formation of a mixed sp2‐sp3 hybridization in graphite structure, which might be responsible for magnetism,will be discussed.

In earlier work(S. M. Mohapatra et al., Rev. Solid State Sci. 4), 873 (1990) and references there... more In earlier work(S. M. Mohapatra et al., Rev. Solid State Sci. 4), 873 (1990) and references therein. our group had evaluated the nuclear quadrupole coupling constants e^2qQ and asymmetry parameters eta for a number of adsorbed atoms of the first, third, sixth and seventh groups on unreconstructed silicon surfaces. Subsequently, Schatz(G. Krausch et al., Phys. Rev. Lett. 68), 377 (1992). and his group, in their pioneering experimental efforts, studied the e^2qQ and eta for the excited ^111Cd^* nucleus resulting from beta-decay of ^111In nucleus adsorbed on the 7× 7 reconstructed silicon surface. Two sets of e^2qQ and eta were observed with the values of e^2qQ quite close to our earlier predictions^1 but with eta of 0.20 and 0.25 in contrast to eta=0 for the unreconstructed (111) surface. The dimer-adatom-stacking-fault(DAS) model for indium sites on the (7× 7) was suggested as a likely candidate for explaining the observed eta. We have been recently involved in testing this suggestio...

Physics at Surfaces and Interfaces - Proceedings of the International Conference, 2003

AIP Conference Proceedings, 2013

ABSTRACT Ag/Si (111) interface has been investigated using first principles DFT approach, to esta... more ABSTRACT Ag/Si (111) interface has been investigated using first principles DFT approach, to establish the unique interplay between the structural and electronic properties. The interface induced properties, such as evolution of metal-induced gap states (MIGS), formation of Schottky barrier height (SBH), for this rectifying Ag/Si contact have been reported.

Applied Physics Letters, 2014

ABSTRACT Iron silicide (cubic FeSi2) nanowires have been grown on Si(110) by reactive deposition ... more ABSTRACT Iron silicide (cubic FeSi2) nanowires have been grown on Si(110) by reactive deposition epitaxy and investigated by scanning tunneling microscopy and scanning/transmission electron microscopy. On an otherwise uniform nanowire, a semi-periodic pattern along the edges of FeSi2 nanowires has been discovered. The origin of such growth patterns has been traced to initial growth of silicide nanodots with a pyramidal Si base at the chevron-like atomic arrangement of a clean reconstructed Si(110) surface. The pyramidal base evolves into a comb-like structure along the edges of the nanowires. This causes the semi-periodic structure of the iron silicide nanowires along their edges.

Thin Solid Films, 2011

Growth of Ag nanoislands on air-oxidized Si(001), (111) and (110) surfaces has been investigated ... more Growth of Ag nanoislands on air-oxidized Si(001), (111) and (110) surfaces has been investigated by reflection high energy electron diffraction (RHEED), scanning tunneling microscopy (STM) and cross-sectional transmission electron microscopy. We have shown that the ...

Thin Solid Films, 2012

ABSTRACT Growth of Ag films on Br- and H-passivated Si(111) surfaces and the annealing behaviour ... more ABSTRACT Growth of Ag films on Br- and H-passivated Si(111) surfaces and the annealing behaviour have been investigated by Rutherford backscattering spectrometry, scanning electron microscopy and photoemission electron microscopy techniques. Upon annealing the phenomenon of thermal grooving was observed in the Ag films. Depending on the annealing temperature, at an intermediate annealing time Ag depletion (evaporation) from the grain boundaries produces fractal patterns of Ag-depleted regions. Continued annealing eventually produces a percolated network of Ag-depleted regions (thermal grooves) along the grain boundaries and isolated Ag grains appear as the depth of the grooves reaches the substrate. For the fractal structures produced by thermal grooving, the fractal dimension has been estimated to be 1.60 ± 0.04. Observation of a fractal pattern in thermal grooving was not hitherto reported. A thorough analysis of the experimental results has been carried out in the context of current theories. These theories are inadequate to describe the experimental results.

Surface and Interface Analysis, 2011

... Anupam Roy 1 ,; JK Dash 2 ,; A. Rath 2 ,; BN Dev 1,*. Article first published online: 8 NOV 2... more ... Anupam Roy 1 ,; JK Dash 2 ,; A. Rath 2 ,; BN Dev 1,*. Article first published online: 8 NOV 2011. ... Correspondence: BN Dev, Department of Materials Science, Indian Association for the Cultivation of Science, Raja SC Mullick Road, Jadavpur, Kolkata-700 032, Inda. ...

Radiation Physics and Chemistry, 1998

Radiation Effects and Defects in Solids, 2007

Polycrystalline fullerene (C60) films prepared on hydrogen-passivated Si(1 1 1) substrates were i... more Polycrystalline fullerene (C60) films prepared on hydrogen-passivated Si(1 1 1) substrates were irradiated by 2 MeV protons with fluences ranging from 6×1015 to 1×1017 ions/cm2. Ferromagnetic-like ordering is reported for samples irradiated with a fluence of 6×1015 ions/cm2 [S. Mathew et al., arxive:cond-mat/0503315]. Raman spectroscopy results indicate an enhancement of the characteristic Ag and Hg modes of C60 after irradiation,

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1999

Epitaxial Ag(1 1 1) thin ®lms ($125 nm) have been grown on Br-passivated Si(1 1 1) surfaces under... more Epitaxial Ag(1 1 1) thin ®lms ($125 nm) have been grown on Br-passivated Si(1 1 1) surfaces under high vacuum. Growth features observed from XRD, RBS/channeling and TEM/TED experiments are comparable to those grown under UHV conditions. RBS/channeling measurements on the Ag layer showed a minimum yield (v min) of 62% indicating a poor crystalline quality. We irradiated the Ag(1 1 1) layer with 1 MeV Si at¯uences of 5 Â 10 15 and 1 Â 10 16 ionsacm 2 with the substrate at room temperature and an ion current density of 50 nA/cm 2. Following irradiation, the measured v min values are 40% and 38%, respectively, indicating an improvement in crystalline quality of the Ag layer. This behaviour is also seen in thermal annealing upto 500 C due to some grain boundary melting. In thermal annealing at P 600 C desorption of Ag occurs leaving holes in the Ag layer. Morphology of the annealed layer has been analyzed with RBS/PIXE studies with an ion microbeam of He ions.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1999

Radiation damage and Surface modi®cations of semi-insulating GaAs0 0 1 substrates upon 1 MeV C an... more Radiation damage and Surface modi®cations of semi-insulating GaAs0 0 1 substrates upon 1 MeV C and 2 MeV C 2 coimplantation with Ga 2 have been studied by X-ray re¯ectometry, combined Rutherford backscattering/channeling and transmission electron microscopy. Two disordered layers ± one near-surface and another deeper ± are formed. Additionally the electron density of the near-surface region has been found to be lower compared to bulk GaAs. This has been attributed to vacancy-enrichment in this region. The disorder caused by C 2 implantation is higher compared to C. Assuming that the near-surface disorder is partially caused by electronic excitation in the semi-insulating substrate, a possible reason for this dierence is the coherent dynamic response of the electrons in the target due to vicinage of C atoms in the C 2 cluster. In the deeper layer, overlap of damage cascades might be responsible for the higher damage caused in the cluster implantation.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2008

We have carried out scanning tunneling microscopy experiments under ultrahigh vacuum condition to... more We have carried out scanning tunneling microscopy experiments under ultrahigh vacuum condition to study the roughness of pristine as well as ion-bombarded Si(1 0 0) surfaces and of ultrathin Ge films deposited on them. One half of a Si(1 0 0) sample (with native oxide layer) was irradiated at room temperature using 45 keV Si À ions at a fluence of 4 Â 10 15 ions/cm 2 while the other half was masked. STM measurements were then carried out on the unirradiated as well as the irradiated half of the sample. Root-mean-square (rms) roughness of both the halves of the sample has been measured as a function of STM scan size. Below a length scale of 30nmweobservesurfacesmoothingandsurfacerougheningisobservedforlengthscalesabovethisvalue.However,thesurfaceisself−affineuptolengthscalesof30 nm we observe surface smoothing and surface roughening is observed for length scales above this value. However, the surface is self-affine up to length scales of 30nmweobservesurfacesmoothingandsurfacerougheningisobservedforlengthscalesabovethisvalue.However,thesurfaceisself−affineuptolengthscalesof200 nm and the observed roughness exponent of 0.46 ± 0.04 is comparable to earlier cases of ion sputtering studies where only roughening [

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2008

Poly-crystalline graphite samples were irradiated using 2.25 MeV H + ions with a fluence of 2 Â 1... more Poly-crystalline graphite samples were irradiated using 2.25 MeV H + ions with a fluence of 2 Â 10 17 ions/cm 2. Magnetic ordering in highly oriented pyrolytic graphite samples have been reported earlier under the similar irradiation conditions [Esquinazi et al., Phys. Rev. Lett. 91 (2003) 227201]. In that study, the authors attribute the observed irradiation induced magnetic ordering to the formation of a mixed sp 2-sp 3 hybridized carbon atoms. In the present study, we report the X-ray photoelectron and Raman spectroscopic studies on pristine and irradiated samples. Irradiated samples are found to show an increased number of sp 3 hybridized carbon atoms. However, the Raman spectrum, specially the second order data, do indicate that the nature of the graphene lattice structure has been preserved in the irradiated samples. The mechanisms for the irradiation induced enhancement in sp 3 hybridization are discussed.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2001

An ion microbeam facility has been set up at one of the beam lines of the 3 MV tandem Pelletron a... more An ion microbeam facility has been set up at one of the beam lines of the 3 MV tandem Pelletron accelerator facility at IOP, Bhubaneswar. This is the first facility of its kind in India, having potential applications in the growing fields involving semiconductors, materials science, biology, archeology and environmental science, from both scientific and industrial points of view. So

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2003

Very thin films of gold deposited on silicon substrates form isolated nano-island structures due ... more Very thin films of gold deposited on silicon substrates form isolated nano-island structures due to the non-wetting nature of gold. Thick films are more homogeneous and do not have the isolated island structures. Thin gold films of various thicknesses (%0.4-21.4 nm) are deposited under high vacuum condition and irradiated with 1.5 MeV Au 2þ ions. The sputtered particles are collected on catcher grids (carbon coated) during the irradiation and are analyzed with transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS). The average sputtered particle size is determined from TEM measurements, whereas the amount of gold on the catcher grid is found by RBS. The average sputtered particle size from thin (up to a thickness of %2 nm) discontinuous films is larger compared to the average particle size from thick continuous films. The coverage of the sputtered particles on the catcher grids is also discussed. Energy spike and its distribution in the nano-islands is proposed to be the main reason for the variation in the particle size and the coverage of the sputtered particles on the catcher grid.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2003

Transmission electron microscopy (TEM), atomic force microscopy (AFM) and Rutherford backscatteri... more Transmission electron microscopy (TEM), atomic force microscopy (AFM) and Rutherford backscattering spectrometry (RBS) have been used to study the modification of Au nanoislands, grown on silicon substrates under high vacuum condition by MeV self-ion irradiation. Upon irradiation with 1.5 MeV Au 2þ ions, interesting observations were found for the nanoislands in comparison with continuous films: (i) higher probability of crater formation, (ii) larger sputtered particle size as well as coverage and (iii) enhanced sputtering yield. Crater formation has been studied as a function of impact angle at a fluence of 1 • 10 14 ions cm À2 and we found that crater formation is prominent at high impact angles (i.e. at glancing angle geometry). AFM has been used to determine the crater formation, TEM to study the sputtered particles as well as craters and RBS has been used to determine the sputtering yield from the nanoisland and continuous films.

Journal of Physics: Conference Series, 2013

We employ XSW assisted XAFS at Ni K edge to characterize ion-irradiated Pt/Ni/C multilayer, parti... more We employ XSW assisted XAFS at Ni K edge to characterize ion-irradiated Pt/Ni/C multilayer, particularly the nanoclusters formed within C layer, revealed by X-TEM and angleresolved fluorescence studies. Retrieving the structural model from XAFS coordination results involved intriguing steps such as accounting for the intensity variation across the layers, determination of extra pre-diffused Ni into C layer (beyond the reflectivity determined roughness) and decoupling interfacial, layer and cluster coordination. The clusters are determined to be Ni centered Ni-Pt bimetallic nanoclusters (Ni:Pt = 60:40), formed due to irradiation induced diffusion of Pt atoms from the disrupted Pt/C interface towards prediffused Ni atoms present in C layer. They are highly disordered beyond nearest neighbor and resemble glassy structure which could find wide-scale applications in magnetic devices.