Search

Abstract: TiO2 thin films deposited by electron beam evaporation technique annealed in either O2 or Ar atmosphere showed ferromagnetism at room temperature. The pristine amorphous film demonstrates anatase phase after annealing under Ar/O2 atmosphere. While the pristine film shows a super-paramagnetic behavior, both O2 and Ar annealed films display hysteresis at 300K. X-ray photo emission spectroscopy (XPS), Raman spectroscopy, Rutherford’s backscattering spectroscopy (RBS), cross-sectional transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) were used to refute the possible role of impurities/contaminants in magnetic properties of the films. The saturation magnetization of the O2 annealed film is found to be higher than the Ar annealed one. It is revealed from shifting of O 1s and Ti 2p core level spectra as well as from the enhancement of high binding energy component of O 1s spectra that the higher magnetic moment is associated with higher oxygen vacancies. In addition, O2 annealed film demonstrates better crystallinity, uniform deposition and smoother surface than that of the Ar annealed one from glancing angle X-ray diffraction (GAXRD) and atomic force microscopy (AFM). We conclude that although ferromagnetism is due to oxygen vacancies, the higher magnetization in O2 annealed film could be due to crystallinity, which has been observed earlier in Co doped TiO2 film deposited by pulsed laser deposition (Mohanty et al., 2012 [10]). [Copyright &y& Elsevier]

Thin films of carbon-containing Au nanoparticles (NPs), prepared by the co-sputtering using a neutral Ar atom beam, were irradiated by 120 MeV Ag ions and also annealed, separately, at increasing temperatures in inert atmosphere. The surface plasmon resonance (SPR) band of the nanocomposite film was observed to be blue shifted (∼50 nm) in both cases, with increasing fluence and temperature. The structural changes of Au NPs embedded in amorphous carbon matrix were investigated using X-ray diffraction and transmission electron microscopy. A growth of Au NPs was observed with increasing fluence and also with increasing temperature. A percolation of Au NPs was observed at 500 °C. A growth of Au NPs with ion irradiation is explained in the framework of a thermal spike model. Raman spectroscopy revealed the ordering of a-C thin films with increasing fluence and temperature, which is ascribed to a change of refractive index and the blue shift of the SPR band. [ABSTRACT FROM AUTHOR]

Abstract: We report on room temperature MeV Au ion induced modifications at the Co/Si interfaces. Nanometers size thin film of Co and Si were grown by ultra high vacuum (UHV) electron beam evaporation technique on Si(111) surface and were irradiated by 1.5MeV Au2+ ions at a fluence of 5×1014 ionscm−2. High-resolution transmission electron microscopy (HRTEM) along with energy filter imaging technique has been employed to study the formation of Co–Si alloy at the interface. Formation of such surface alloy has been discussed in the light of ion-matter interaction in nanometer scale regime. [Copyright &y& Elsevier]

We have prepared germanium nanoparticles embedded in SiO2 matrix by atom beam co-sputtering (ABS) of Ge+SiO2 on Si substrate. The as-deposited films were annealed at various temperatures in Ar+H2 atmosphere and irradiated with various energies with fixed fluence. The pristine and irradiated samples were characterized by Raman, X-ray diffraction and atomic force microscopy (AFM). Rutherford back scattering (RBS) was used to quantify the concentration of Ge in the SiO2 matrix and the film thickness. Raman studies of the films indicate the formation of Ge crystallites as a result of swift heavy ion (SHI) irradiation. Moreover, the crystalline nature of Ge improves with an increase in energy. Glancing angle X-ray diffraction and Raman results also confirm the presence of Ge crystallites in the irradiated samples. Similarly, 400 keV Ge+ ions implanted into silicon substrate at higher fluence at 573 K have been irradiated with 100 MeV Au8+ions at RT. These irradiated implanted samples were subsequently characterized by XRD and Raman to understand the crystallization behavior. We also studied the surface morphology of a high-energy irradiated sample by AFM. The irradiation results were compared with those obtained by thermal annealing in ABS. The basic mechanism for crystallization induced by SHI in these films has been investigated. [ABSTRACT FROM AUTHOR]

Abstract: In the present work, we report the formation of SiGe nanoparticles embedded in SiO2 film by atom beam sputtering method in conjunction with Rapid Thermal Annealing (RTA). Crystalline SiGe nanoparticles in the co-sputtered films are formed after rapid thermal annealing at 900 °C and 1000 °C for 1 min in N2 gas ambient. These nanoparticles were characterized using UV–vis absorption, GXRD, FTIR and Raman measurements. UV–vis spectra show blue shift of absorption edge with the increase in annealing temperature. GXRD pattern shows that particles formed are crystalline. The average size of the nanoparticle estimated from GXRD is 15 nm to 30 nm for the films annealed at temperatures 800 °C and 1000 °C respectively. FTIR spectra show the phase separation between SiGe nanoparticles and SiO2 matrix after RTA. Raman spectra show that SiGe phase is formed with c-Ge as core and c-SiGe as shell in the SiO2 matrix. [Copyright &y& Elsevier]

Abstract: We report here the synthesis of silicon-nanoclusters embedded in SiO2 by atom beam co-sputtering technique. A sputtering target consisted of 40% and 60% area of Si pieces glued on a fused silica plate. A co-sputtered film containing Si embedded in SiO2 having different compositional fractions of Si was deposited on fused silica and c-Si substrates. Annealing was done in N2 atmosphere for 1 min at temperatures ranging from 700–900 °C to precipitate silicon nanoclusters. Samples were characterized using Raman and FTIR spectroscopy. In IR absorption spectra, the blue shift of the Si–O–Si asymmetric stretching band, from 1017 cm−1 for as-deposited samples, to 1070 cm−1 for samples annealed at 900 °C, indicates that phase separation of Si and SiO2 has been completed and films consist of Si particles embedded in an SiO2 matrix. Raman spectrum showed the emergence of 513 cm−1 due to nanocrystalline silicon after RTA at 900 °C. [Copyright &y& Elsevier]

Abstract: Using atom beam co-sputtering of SiO2, Ge and Si targets, composite films containing Si, Ge and SiOx at different compositions were prepared and annealed at different temperatures. The influence of annealing temperatures on phase formation in the composite films was studied. The films were characterized using UV–vis absorption spectroscopy, FTIR, and GXRD. GXRD plots show diffraction peaks due to SiGe alloy nanoparticles and no peaks due to elemental Si or Ge. The nanoparticle size estimated from GXRD is 4.7 nm. UV–visible spectra show the red shift in absorption edge as the annealing temperature is increased. FTIR spectra reveal phase separation of SiGe alloy from SiOx matrix, upon annealing. [Copyright &y& Elsevier]

The effect of high electronic energy deposition on the structure, surface topography, optical properties, and electronic structure of cadmium sulfide (CdS) thin films have been investigated by irradiating the films with 100 MeV Ag+7 ions at different ion fluences in the range of 1012–1013 ions/cm2. The CdS films were deposited on glass substrate by thermal evaporation, and the films studied in the present work are polycrystalline with crystallites preferentially oriented along (002)-H direction. It is shown that swift heavy ion (SHI) irradiation leads to grain agglomeration and hence an increase in the grain size at low ion fluences. The observed lattice compaction was related to irradiation induced polygonization. The optical band gap energy decreased after irradiation, possibly due to the combined effect of change in the grain size and in the creation of intermediate energy levels. Enhanced nonradiative recombination via additional deep levels, introduced by SHI irradiation was noticed from photoluminescence (PL) analysis. A shift in the core levels associated with the change in Fermi level position was realized from XPS analysis. The chemistry of CdS film surface was studied which showed profound chemisorption of oxygen on the surface of CdS. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) and Ni-doped zinc oxide (ZnO:Ni) films are prepared by atom beam sputtering with an intent of growing transparent conducting oxide (TCO) material and understanding its physical properties. The crystalline phases of the films are identified by the grazing angle X-ray diffraction (GAXRD) technique. Thicknesses of the films are measured by ellipsometry. Chemical states of the elements present in the films are investigated by X-ray photoelectron spectroscopy (XPS), which indicates the presence of Ni in the ZnO environment in a divalent state. Average transmission across the ZnO:Ni film was determined to be ∼83% in the visible region, which is less than that (∼90%) of undoped ZnO films. The resistivity measured by van der Pauw technique of the ZnO:Ni film (∼9×10-3 Ω cm) is two orders of magnitude smaller as compared to its undoped counterpart (1 Ω cm). For ZnO:Ni film an average carrier concentration of ∼1.4×1019 cm-3 was observed by Hall measurements. Two important mechanisms reported in the literature viz. influence of d–d transition bands and electron scattering from crystallites/grains are discussed as the possible causes for the increase in conductivity on Ni doping in ZnO. [ABSTRACT FROM AUTHOR]

Abstract: The effect of crystallinity of Ge nanocrystals on the charge storage properties of the metal oxide semiconductor (MOS) structure has been investigated. MOS structure with Ge nanocrystals embedded in the oxide has been fabricated by using atom beam sputtering technique. After annealing at 600°C in Ar+H2 atmosphere, capacitance–voltage (C–V) measurements show flat band voltage shift of ∼0.9V. It which is a clear indication of the memory effect of Ge nanocrystals, while unannealed structure doesnot show any hysteresis in the C–V curve. Micro Raman spectroscopy and X-ray diffraction (XRD) analyses show that crystalline content of Ge nanoparticles in the MOS structure has increased after annealing. [Copyright &y& Elsevier]

Impact of ion irradiation on thin films is an emerging area for materials modification. CdTe thin films grown by thermal evaporation on flexible molybdenum (Mo) substrate were irradiated with Swift (100 MeV) Ag+7 ions for various ion fluence in the range 1012–1013 ions/cm2. The modifications in the composition, structure and surface morphology have been studied as a function of ion fluence. The Energy Dispersive X-ray Analysis (EDS) shows slightly Te-rich composition for both as-grown and irradiated films with no significant change after irradiation. X-ray diffraction (XRD) analysis indicates a consistent shift in the (111) peak position towards higher diffraction angle and an increase in the full width at half maximum (FWHM) with increase in ion fluence. The change in the residual stress during irradiation has been evaluated and is related to the corresponding microstructural changes in the films. The initial tensile stress is found to be relaxed after irradiation. Atomic Force Microscopy (AFM) studies revealed significant grain splitting after irradiation and formation of hillocks at higher ion fluence. The surface roughness was significantly increased at higher ion fluence. [ABSTRACT FROM AUTHOR]

Abstract: Ge oxide films were irradiated with 150MeV Ag ions at fluences varying between 1012 and 1014 ions/cm2. The irradiation-induced changes were monitored by FT-IR spectroscopy, atomic force microscopy, X-ray diffraction and photoluminescence spectroscopy. The FT-IR spectra indicate stoichiometric changes and an increase in Ge content on irradiation. X-ray diffraction shows a crystallization of the irradiated films and presence of both Ge and GeO2 phases. The Ge nanocrystal size, as calculated from Scherrer’s formula, was around 30nm. The morphological changes, observed in atomic force microscopy, also indicate formation of nanostructures upon ion irradiation and a uniform growth is observed for a fluence of 1×1014 ions/cm2. [Copyright &y& Elsevier]

Polycrystalline CdTe thin films were irradiated with 80 MeV oxygen (O6+) ions for various fluences and its effect on the composition, structure, surface topography and optical properties have been investigated. The as-grown films are found to be slightly Te-rich in composition and there is no significant change in the composition after irradiation. X-ray diffraction analysis shows a high degree of crystallite orientation along the (111) plane of cubic phase CdTe. Upon irradiation a large decrease in intensity of the (111) plane and a small shift in the peak position has been resulted. The shift in the peak position is correlated with the change in the residual stress. The surface roughness of the films get increased after irradiation. A decrease in the grain size was observed after irradiation due to ion-induced recrystallization. The optical band gap energy decreased from 1.53 eV for as-grown film to 1.46 eV upon irradiation. The photoluminescence (PL) spectrum is dominated by the defect band and the effect of irradiation has been discussed and correlated with the observed change in the XRD peak position and optical band gap. [ABSTRACT FROM AUTHOR]

Abstract: Germanium (Ge) nanocrystals (NCs) have attracted a lot of attention due to their excellent optical properties. In this paper we report on the formation of Ge nanoparticles embedded in GeO2 matrix by electron beam evaporation and subsequent annealing. Charge retention properties of Ge NCs thus synthesized are also investigated. Fourier transform infrared (FTIR) spectroscopic studies are carried out to verify the evolution of the NCs. Micro-Raman analysis also confirms the formation of Ge nanoparticles in the annealed films. Development of Ge nanoparticles is established by photoluminescence (PL) analysis. The memory effect of Ge NCs is revealed by the hysteresis in the capacitance–voltage () curves of the fabricated metal-oxide-semiconductor (MOS) structure containing Ge NCs. [Copyright &y& Elsevier]

Heavy ion elastic recoil detection analysis (ERDA) set up with a large solid angle (∼⃒4.8 msr) Δ E - E position-sensitive telescope detector is developed at Inter University Accelerator Centre as a dedicated facility for the study of electronic sputtering of thin films under swift heavy ion (SHI) irradiation. The detector consists of a gas ionization chamber (Δ E ) and a solid-state surface barrier detector ( E ) housed in a same assembly. The electronic sputtering yield (atoms/ion) is determined by analyzing on-line fluence-dependent ERDA data obtained from a variety of thin films. Large erosion (>10 5 atoms/ion) of carbon from a-C:H by 150 MeV Ag 13+ ions, evolution of nitrogen (∼⃒880 atoms/ion) from copper nitride and depletion of oxygen (∼⃒1000 atoms/ion) from copper oxide film under 200 MeV Au 15+ ion impact are studied and reported in this work. The electronic sputtering of these materials is discussed on the basis of the thermal spike model of SHI and solid interaction. [ABSTRACT FROM AUTHOR]

Abstract: The irradiation effect of 350MeV Au+ ions on Ti/Si multilayers has been studied using Rutherford backscattering spectroscopy, X-ray reflectivity (XRR) and grazing incidence X-ray diffraction (GIXRD). Intermixing effects have been studied as a function of fluences of 0.46×1014, 1.82×1014 and 4.62×1014 cm−2. Rutherford backscattering spectra (RBS) confirm mixing at the interface. X-ray reflectivity patterns show damage at the interfaces with the absence of a continuous fringe pattern at high fluence doses in comparison to the pristine interface. Mixing leads to titanium di-silicide (TiSi2) phase formation as a shown by grazing incidence X-ray diffraction patterns. The observed intermixing is attributed to energy deposited by the incident ions in the electronic system of the target. Swift heavy ion irradiation induced intermixing increases with fluence. [Copyright &y& Elsevier]

Abstract: A fast atom source has been installed for the synthesis of metal particles in insulating matrix. The source delivers current density of 30μA/cm2 on the target placed at a distance of 10cm and with variable energy ranging from 0.8 to 2.0keV. The area of the beam is approximately 50mm diameter. Using the setup, particles of Ag and Cu have been grown in silica matrix. The sputtered species were deposited on quartz and silicon substrate. These composite films were also prepared by co-evaporation of SiO2 and metal. The samples were annealed at different temperatures and growth of metal particles in silica matrix was investigated by the optical absorption spectrometry. Distinct surface plasma resonance peaks have been observed both from Ag and Cu particles. Mie’s theory is used to estimate the particle size. Rutherford backscattering spectrometry was used to quantify the concentration of metal fraction in the silica matrix of the composite thin films. [Copyright &y& Elsevier]

Abstract: The changes in behaviour of mixing at the interface of Si/Me/Si (Me=V, Fe, Co) due to irradiation by swift heavy ions of Au at 120MeV with respect to the ion dose is reported here. The fluences were varied from 1×1013 to 1×1014 ions/cm2 on the bi-layers of Si/Me/Si (Me=V, Fe, Co). The interface of Si/Me (Me=V, Fe, Co) was characterized using Rutherford backscattering spectroscopy (RBS) and secondary ion mass spectrometry (SIMS). In all the three cases, the atomic mixing width was found to be increasing monotonically with ion fluence. The mixing rate calculations were made and the diffusivity values thus obtained suggested a transient melt phase at the interface according to thermal spike model. Further work on the irradiated samples for characterizing the buried layers and formation of stable silicide phases by annealing are being carried out. [Copyright &y& Elsevier]

In this paper a correlation is made between the interface chemistry and electrical properties of Ni Schottky barrier contacts to silicon using Current–Voltage technique. Single crystal n-Si substrate of 〈1 0 0〉 orientation with thin Ni layer were irradiated by Au at 95 MeV and annealed at 300 °C. The data suggests the formation of an interface layer due to swift heavy ion irradiation that contains crystalline NiSi phase. The room temperature I–V curves for different samples and their resistance values are estimated. [Copyright &y& Elsevier]

Ion beam mixing with low energy ions has been well studied and understood. Ion beam mixing with high energy heavy ions was initiated in the early nineties. The present experiment is carried out for investigation of ion beam mixing in V/Si system induced by electronic excitation. Au ions of 120 MeV were taken at different fluences upto 1014 ions/cm2 for this purpose. The mixing at the interface was investigated by secondary ion mass spectroscopy and Rutherford backscattering spectroscopy. We observe a linear dependence of the atomic mixing on the fluence. A mixed region of about ∼26 nm was observed at the fluence of 1014 ions/cm2. Possible mechanisms of swift heavy ion induced mixing in the present case are discussed. [Copyright &y& Elsevier]

Carbon foils produced by electron beam evaporation of approximately 5 μg/cm2 thickness are regularly in use as stripper foils in the 15UD Pelletron Accelerator at Nuclear Science Centre. This report examines the role of defects produced by the ion beams in influencing usable life of these carbon foils. The life of the foils has been estimated by measuring the transmitted ion current at the high-energy end of the 15UD Pelletron. The lifetime of carbon stripper foils entirely depend on the defects produced by the ions. A relation between the onset of the degradation of current transmission and the accumulated defects has been established. An improved type of carbon stripper foils might be obtained by the introduction of thin C60 layers. [Copyright &y& Elsevier]

The intrinsic deep donor level, known as EL2, is responsible for semi-insulating behavior of undoped GaAs. EL2 is the most extensively studied point defect in GaAs. The most important property related to EL2 is the metastability under sub-bandgap light exposure at low temperature. The microscopic origin of EL2 and its photo-induced metastability is still under debate. We present an experimental investigation on unirradiated and irradiated semi-insulating GaAs using thermally stimulated current spectroscopy and photo-current quenching. In addition to EL2, we have discovered some other metastable defects in semi-insulating GaAs. Li ions of 48 MeV were used to irradiate semi-insulating GaAs with fluences between 1011 and 1013 ions/cm2. The energy loss of 48 MeV Li ions in GaAs is dominantly due to electronic processes because the energy loss due to nuclear collision processes is much less than the lattice binding energy of GaAs. Extended range of 48 MeV Li ions in GaAs has been used to modify the defect levels by electronic energy loss processes. Several modifications of defect levels, including the metastable levels in semi-insulating GaAs observed after irradiation, are discussed. [Copyright &y& Elsevier]

The effect of MeV and low energy nitrogen implantation on the electrical properties of metal semiconductor junctions is studied. It is found that MeV implantation has better contact performance is comparison to keV nitrogen implantation. The defects introduced due to MeV implantation have very little effect on contact formation. [ABSTRACT FROM AUTHOR]

Higher cost and lower availability of enriched isotopic materials are the major constraints in targets fabrication of isotopes. If the distribution of the vapor flux is not controlled in the evaporation, large amount of material is wasted. Minimizing the material wastage is important in the fabrication of targets of expensive isotopes. Evaporation sources have been designed and machined at Inter-University Accelerator Centre (IUAC) for minimizing the consumption of materials in evaporation. Details of different types evaporation sources used in Target development laboratory at IUAC for minimizing the wastage of target material in target fabrication is discussed in this report. [ABSTRACT FROM AUTHOR]

Targets of isotopically enriched Er (erbium) were prepared on 45 μg/cm carbon backing using the method of vacuum evaporation. Another layer of carbon with thickness 23 μg/cm was deposited on it as a protective cap with the help of an electron gun. Carbon backing, Er and the capping carbon layer were deposited using resistive heating and electron gun deposition without disturbing the vacuum. The thickness of Er was measured by X-ray fluorescence analysis as well as with Rutherford backscattering spectrometry and it was found to be 150 μg/cm. Successful preparation of sandwiched targets was very sensitive to substrate temperature, deposition rate, duration of in situ annealing, cooling rate etc. [ABSTRACT FROM AUTHOR]

The authors investigate the formation of Ge nanocrystals by thermal annealing of substoichiometric GeOx films fabricated by electron-beam evaporation. At the same time, they also monitor the evolution of the GeOx matrix. The phase separation into semiconductor and oxide phases and the evolution of Ge nanocrystals were monitored by a combination of x-ray diffraction (XRD), Raman, and transmission electron microscopy (TEM) measurements. TEM shows spherical particles of sizes in the range of 2–9 nm. They infer that an annealing temperature of 500 °C is sufficient to generate a reasonable density of Ge nanocrystals in an amorphous GeOx matrix. Both XRD and Raman measurements suggest a simultaneous crystallization of the matrix at an annealing temperature of 600 °C. [ABSTRACT FROM AUTHOR]

Abstract: Formation of Ge crystallites in GeOx matrix as a result of heavy ion irradiation is reported. Micro-Raman spectra of the films show the evolution of Ge crystallite regions in GeOx thin films upon ion irradiation with 100 MeV Au. Transmission electron microscopic studies of the irradiated films revealed the presence of Ge crystallites. Crystallinity of the Ge nanoparticles was confirmed by high-resolution electron microscope images. Atomic force microscopy was employed to study the modifications in surface morphology of GeOx films before and after irradiation. Formation of Ge nanocrystallites has been explained on the basis of phenomenon of ion beam induced phase separation. [Copyright &y& Elsevier]

Films of C70 fullerene containing silver nanoparticles were synthesized by thermal codeposition. Optical absorption studies revealed that surface plasmon resonance of Ag nanoparticles occurs at unusually large wavelength, which showed a regular redshift from 521 to 581 nm with increase in metal content from 4.5% to 28%. It is explained by the Maxwell–Garnett theory considering the absorbing nature of fullerene matrix. Rutherford backscattering and transmission electron microscopy were performed to quantify metal content and the particle size, respectively. A better detection of low intensity vibrational modes of C70 in Raman scattering is observed due to surface enhanced Raman scattering. [ABSTRACT FROM AUTHOR]

By using a combination of detailed experimental studies, we identify the metastable and stable energy levels of EL2 in semi-insulating GaAs. These results are discussed in light of the recently proposed models for EL2 in GaAs. [ABSTRACT FROM AUTHOR]