We report a detailed study of surface and interface properties of pulsed-laser-deposited NiMnSb f... more We report a detailed study of surface and interface properties of pulsed-laser-deposited NiMnSb films on a Si͑100͒ substrate as a function of film thickness. As the thickness of films is reduced below 35 nm, formation of a porous layer is observed. Porosity in this layer increases with decrease in NiMnSb film thickness. These morphological changes of the ultrathin films are reflected in the interesting transport and magnetic properties of these films. Compositional anomaly and surface and interface roughness are not the source of magnetic and transport properties of the films.
Using an indigenously built DC magnetron sputtering system short period (~ 42Å) Co/Ti multilayer ... more Using an indigenously built DC magnetron sputtering system short period (~ 42Å) Co/Ti multilayer and Co/Ti multilayer with ~ 4Å Cu buffer layer at both interfaces with 20 bilayers in each case have been prepared for use as reflecting optics in the water window soft X-ray regime of 23-44 Å. The samples have been subsequently characterized by specular and diffused grazing incidence X-ray reflectivity (GIXR) measurements as well as cross-sectional transmission electron microscopy (TEM) to carry out detail investigations on the interfaces. Analysis of GIXR data and TEM measurements clearly reveal that interface roughness is the major contributor to the interface imperfections in these short period multilayers and interface roughness in the multilayer are significantly reduced after the introduction of Cu barrier layers.
ABSTRACT Multilayer period thickness changes for various thickness ratios, Γ (ratio of W layer th... more ABSTRACT Multilayer period thickness changes for various thickness ratios, Γ (ratio of W layer thickness to period thickness) as a function of annealing temperatures were studied by grazing incidence x-ray reflectivity (GIXRR), and grazing incidence x-ray diffraction (GIXRD). Both period thickness expansion and compression were observed depending upon Γ and annealing temperatures. Multilayer with the W layer thickness close to the B4C layer has undergone less period thickness changes. Successive appearance and disappearance of multilayer Bragg maxima in GIXRR were observed. Such behavior suggested that redistribution of atomic density within bilayer, the displacement of interface and the multilayer period thickness changes as annealing proceeds. GIXRD measurements performed using synchrotron radiation suggested the formation of phases corresponding to tungsten boride and carbide.
The European Physical Journal Special Topics, Mar 28, 2009
NbC/Si multilayers grown on silicon substrates of different roughness have been used to study the... more NbC/Si multilayers grown on silicon substrates of different roughness have been used to study the influence of surface quality on growth characteristics. Surface morphology of substrate and multilayer film are characterized by topographic measurements using atomic force microscopy (AFM) technique and power spectral density analysis (PSD). Grazing incidence x-ray reflectivity (GIXR) technique in combination with PSD analysis reveals a growth characteristic of multilayer film on substrates of different roughness. It is revealed that the stochastic growth of NbC on rough substrate leads to formation of clusters of varying size depending on initial substrate roughness. Details of growth characteristic are discussed.
ABSTRACT In this paper, we report cleaning of carbon capped molybdenum (Mo) thin film by in-house... more ABSTRACT In this paper, we report cleaning of carbon capped molybdenum (Mo) thin film by in-house developed radio frequency (RF) plasma reactor, at different powers and exposure time. Carbon capped Mo films were exposed to oxygen plasma for different durations at three different power settings, at a constant pressure. After each exposure, the thickness of the carbon layer and the roughness of the film were determined by hard x-ray reflectivity measurements. It was observed that most of the carbon film got removed in first 15 minutes exposure. A high density layer formed on top of the Mo film was also observed and it was noted that this layer cannot be removed by successive exposures at different powers. A significant improvement in interface roughness with a slight improvement in top film roughness was observed. The surface roughness of the exposed and unexposed samples was also confirmed by atomic force microscopy measurements.
We present the results of a study of structural and superconducting properties of polycrystalline... more We present the results of a study of structural and superconducting properties of polycrystalline Nb thin films (200Å, 300Å, 400Å, 700Å and 1000Å) and Nb/Cu bilayers (300Å/300Å and 400Å/300Å) prepared on Si substrates by ion beam sputtering at room temperature. The thicknesses, roughnesses at the surfaces and interfaces were determined by X-ray reflectivity whereas the grain sizes were determined from grazing incidence X-ray diffraction and transmission electron microscopic studies. The superconducting transition temperature (TC) of Nb thin films are smaller than TC of bulk Nb. The Nb-200Å sample does not show TC down to 2.3K. The average size of the grains varies from 42Å for Nb-200Å sample to 69Å for Nb-1000Å sample. Our results show that the TC in these polycrystalline films is not only limited by its thickness but also by the size of the grains. The Nb films deposited in situ on the Cu layer (Nb/Cu) show a marginal increase in average sizes of the grains as compare to their resp...
ABSTRACT We studied localized surface plasmon resonances (LSPR) at different compositions, substr... more ABSTRACT We studied localized surface plasmon resonances (LSPR) at different compositions, substrate temperatures, and mass thicknesses of Ag-Au alloy nanoparticle films grown by sequential pulsed laser deposition. The LSPRs were pronounced at all compositions of the films grown at high substrate temperature of about 300 °C as compared to those grown at room temperature. The alloy formation and composition of the films were determined using X-ray photoelectron and energy dispersive spectroscopy. Films' mass thickness and compositional uniformity along the thickness were determined using X-ray reflectometry and secondary ion mass spectroscopy. Atomic force microscopic analysis revealed the formation of densely packed nanoparticles of increasing size with the number of laser ablation pulses. The LSPR wavelength red shifted with increasing either Au percentage or film mass thickness and corresponding LSPR tuning was obtained in the range of 450 to 690 nm. The alloy dielectric functions obtained from three different models were compared and the optical responses of the nanoparticle films were calculated from modified Yamaguchi effective medium theory. The tuning of LSPR was found to be due to combined effect of change in intrinsic and extrinsic parameters mainly the composition, morphology, particle-particle, and particle-substrate interactions.
ABSTRACT Cobalt thin films were deposited on GaAs, Si and Glass substrates by RF-magnetron sputte... more ABSTRACT Cobalt thin films were deposited on GaAs, Si and Glass substrates by RF-magnetron sputtering. The structure was studied using atomic force microscopy, X-ray reflectivity and grazing incidence X-ray diffraction. Magnetic properties were determined with the magneto-optic Kerr effect. The deposited films have in-plane uniaxial anisotropy and after annealing the anisotropy reduces. The reduction in anisotropy may be due to release of stress and the remaining anisotropy after annealing may be due to shape anisotropy of the particulates.
NbC films were prepared using Ion beam sputtering system at various discharges current from 0.4 a... more NbC films were prepared using Ion beam sputtering system at various discharges current from 0.4 amps to 1.2 amps at room temperature. Effect of temperature on NbC films were also studied by depositing NbC films at various temperatures from room temperature to 200,300,400 and 600˚C. X-ray reflectivity (XRR) study shows that surface roughness of the film decreases with decrease in discharge current .The optimum lowest roughness 3.2Ǻ having density 92% of bulk was achieved at discharge current 0.6 amps at 3.0 cm 3 /min Ar gas flow. X-ray study also shows that film roughness decreases with increase in temperature of the film and after a certain temperature it increases with increase in temperature. The lowest surface roughness 2.1Ǻ was achieved at 300˚C with density 83% of bulk NbC at constant discharge current 0.6 amps.
Thin films of 3 different thicknesses each of Ni83.2Fe3.3Mo13.5 and Ni83.1Fe6.0Mo10.9alloys have ... more Thin films of 3 different thicknesses each of Ni83.2Fe3.3Mo13.5 and Ni83.1Fe6.0Mo10.9alloys have been grown using Pulsed Laser Deposition (PLD) technique. Our motivation is to investigate the magnetic properties of a few nm thick Ni alloys with mostly Mo (4d element) addition since the corresponding soft ferromagnetic bulk alloys have shown very small coercivity of ˜ 0.1 Oe. Detailed structural characterization has been undertaken before probing the magnetic properties. Arc melted alloy buttons after homogenization are used directly as targets for the deposition. Films were deposited on single crystal Sapphire (0001) substrates using excimer laser. The structural characterization has been done by X-ray diffraction (XRD), X-ray reflectivity (XRR), Energy dispersive x-ray spectroscopy (EDS), and Atomic force microscopy (AFM). The X-ray diffraction pattern shows that the films are highly textured and grown along [111] direction of the alloys. They have high lattice strain which makes t...
We report a detailed study of surface and interface properties of pulsed-laser-deposited NiMnSb f... more We report a detailed study of surface and interface properties of pulsed-laser-deposited NiMnSb films on a Si͑100͒ substrate as a function of film thickness. As the thickness of films is reduced below 35 nm, formation of a porous layer is observed. Porosity in this layer increases with decrease in NiMnSb film thickness. These morphological changes of the ultrathin films are reflected in the interesting transport and magnetic properties of these films. Compositional anomaly and surface and interface roughness are not the source of magnetic and transport properties of the films.
Using an indigenously built DC magnetron sputtering system short period (~ 42Å) Co/Ti multilayer ... more Using an indigenously built DC magnetron sputtering system short period (~ 42Å) Co/Ti multilayer and Co/Ti multilayer with ~ 4Å Cu buffer layer at both interfaces with 20 bilayers in each case have been prepared for use as reflecting optics in the water window soft X-ray regime of 23-44 Å. The samples have been subsequently characterized by specular and diffused grazing incidence X-ray reflectivity (GIXR) measurements as well as cross-sectional transmission electron microscopy (TEM) to carry out detail investigations on the interfaces. Analysis of GIXR data and TEM measurements clearly reveal that interface roughness is the major contributor to the interface imperfections in these short period multilayers and interface roughness in the multilayer are significantly reduced after the introduction of Cu barrier layers.
ABSTRACT Multilayer period thickness changes for various thickness ratios, Γ (ratio of W layer th... more ABSTRACT Multilayer period thickness changes for various thickness ratios, Γ (ratio of W layer thickness to period thickness) as a function of annealing temperatures were studied by grazing incidence x-ray reflectivity (GIXRR), and grazing incidence x-ray diffraction (GIXRD). Both period thickness expansion and compression were observed depending upon Γ and annealing temperatures. Multilayer with the W layer thickness close to the B4C layer has undergone less period thickness changes. Successive appearance and disappearance of multilayer Bragg maxima in GIXRR were observed. Such behavior suggested that redistribution of atomic density within bilayer, the displacement of interface and the multilayer period thickness changes as annealing proceeds. GIXRD measurements performed using synchrotron radiation suggested the formation of phases corresponding to tungsten boride and carbide.
The European Physical Journal Special Topics, Mar 28, 2009
NbC/Si multilayers grown on silicon substrates of different roughness have been used to study the... more NbC/Si multilayers grown on silicon substrates of different roughness have been used to study the influence of surface quality on growth characteristics. Surface morphology of substrate and multilayer film are characterized by topographic measurements using atomic force microscopy (AFM) technique and power spectral density analysis (PSD). Grazing incidence x-ray reflectivity (GIXR) technique in combination with PSD analysis reveals a growth characteristic of multilayer film on substrates of different roughness. It is revealed that the stochastic growth of NbC on rough substrate leads to formation of clusters of varying size depending on initial substrate roughness. Details of growth characteristic are discussed.
ABSTRACT In this paper, we report cleaning of carbon capped molybdenum (Mo) thin film by in-house... more ABSTRACT In this paper, we report cleaning of carbon capped molybdenum (Mo) thin film by in-house developed radio frequency (RF) plasma reactor, at different powers and exposure time. Carbon capped Mo films were exposed to oxygen plasma for different durations at three different power settings, at a constant pressure. After each exposure, the thickness of the carbon layer and the roughness of the film were determined by hard x-ray reflectivity measurements. It was observed that most of the carbon film got removed in first 15 minutes exposure. A high density layer formed on top of the Mo film was also observed and it was noted that this layer cannot be removed by successive exposures at different powers. A significant improvement in interface roughness with a slight improvement in top film roughness was observed. The surface roughness of the exposed and unexposed samples was also confirmed by atomic force microscopy measurements.
We present the results of a study of structural and superconducting properties of polycrystalline... more We present the results of a study of structural and superconducting properties of polycrystalline Nb thin films (200Å, 300Å, 400Å, 700Å and 1000Å) and Nb/Cu bilayers (300Å/300Å and 400Å/300Å) prepared on Si substrates by ion beam sputtering at room temperature. The thicknesses, roughnesses at the surfaces and interfaces were determined by X-ray reflectivity whereas the grain sizes were determined from grazing incidence X-ray diffraction and transmission electron microscopic studies. The superconducting transition temperature (TC) of Nb thin films are smaller than TC of bulk Nb. The Nb-200Å sample does not show TC down to 2.3K. The average size of the grains varies from 42Å for Nb-200Å sample to 69Å for Nb-1000Å sample. Our results show that the TC in these polycrystalline films is not only limited by its thickness but also by the size of the grains. The Nb films deposited in situ on the Cu layer (Nb/Cu) show a marginal increase in average sizes of the grains as compare to their resp...
ABSTRACT We studied localized surface plasmon resonances (LSPR) at different compositions, substr... more ABSTRACT We studied localized surface plasmon resonances (LSPR) at different compositions, substrate temperatures, and mass thicknesses of Ag-Au alloy nanoparticle films grown by sequential pulsed laser deposition. The LSPRs were pronounced at all compositions of the films grown at high substrate temperature of about 300 °C as compared to those grown at room temperature. The alloy formation and composition of the films were determined using X-ray photoelectron and energy dispersive spectroscopy. Films' mass thickness and compositional uniformity along the thickness were determined using X-ray reflectometry and secondary ion mass spectroscopy. Atomic force microscopic analysis revealed the formation of densely packed nanoparticles of increasing size with the number of laser ablation pulses. The LSPR wavelength red shifted with increasing either Au percentage or film mass thickness and corresponding LSPR tuning was obtained in the range of 450 to 690 nm. The alloy dielectric functions obtained from three different models were compared and the optical responses of the nanoparticle films were calculated from modified Yamaguchi effective medium theory. The tuning of LSPR was found to be due to combined effect of change in intrinsic and extrinsic parameters mainly the composition, morphology, particle-particle, and particle-substrate interactions.
ABSTRACT Cobalt thin films were deposited on GaAs, Si and Glass substrates by RF-magnetron sputte... more ABSTRACT Cobalt thin films were deposited on GaAs, Si and Glass substrates by RF-magnetron sputtering. The structure was studied using atomic force microscopy, X-ray reflectivity and grazing incidence X-ray diffraction. Magnetic properties were determined with the magneto-optic Kerr effect. The deposited films have in-plane uniaxial anisotropy and after annealing the anisotropy reduces. The reduction in anisotropy may be due to release of stress and the remaining anisotropy after annealing may be due to shape anisotropy of the particulates.
NbC films were prepared using Ion beam sputtering system at various discharges current from 0.4 a... more NbC films were prepared using Ion beam sputtering system at various discharges current from 0.4 amps to 1.2 amps at room temperature. Effect of temperature on NbC films were also studied by depositing NbC films at various temperatures from room temperature to 200,300,400 and 600˚C. X-ray reflectivity (XRR) study shows that surface roughness of the film decreases with decrease in discharge current .The optimum lowest roughness 3.2Ǻ having density 92% of bulk was achieved at discharge current 0.6 amps at 3.0 cm 3 /min Ar gas flow. X-ray study also shows that film roughness decreases with increase in temperature of the film and after a certain temperature it increases with increase in temperature. The lowest surface roughness 2.1Ǻ was achieved at 300˚C with density 83% of bulk NbC at constant discharge current 0.6 amps.
Thin films of 3 different thicknesses each of Ni83.2Fe3.3Mo13.5 and Ni83.1Fe6.0Mo10.9alloys have ... more Thin films of 3 different thicknesses each of Ni83.2Fe3.3Mo13.5 and Ni83.1Fe6.0Mo10.9alloys have been grown using Pulsed Laser Deposition (PLD) technique. Our motivation is to investigate the magnetic properties of a few nm thick Ni alloys with mostly Mo (4d element) addition since the corresponding soft ferromagnetic bulk alloys have shown very small coercivity of ˜ 0.1 Oe. Detailed structural characterization has been undertaken before probing the magnetic properties. Arc melted alloy buttons after homogenization are used directly as targets for the deposition. Films were deposited on single crystal Sapphire (0001) substrates using excimer laser. The structural characterization has been done by X-ray diffraction (XRD), X-ray reflectivity (XRR), Energy dispersive x-ray spectroscopy (EDS), and Atomic force microscopy (AFM). The X-ray diffraction pattern shows that the films are highly textured and grown along [111] direction of the alloys. They have high lattice strain which makes t...
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Papers by Sanjay Rai