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We report on the application of high energy light ions (Li and O) irradiation for modification of defects, in particular, for annihilation of point defects using electronic energy loss in GaAs to minimize the defects produced by nuclear collisions. The high resolution x-ray diffraction and micro-Raman spectroscopy have been used to monitor that no lattice damage or amorphization take place due to irradiating ions. The effects of irradiation on defects and their energy levels have been studied using thermally stimulated current spectroscopy. It has been observed that till an optimum irradiation fluence of 1013 ions/cm2 there is annihilation of native defects but further increase in irradiation fluence results in accumulation of defects, which scales with the nuclear energy loss process, indicating that the rate of defects produced by the binary collision process exceeds rate of defect annihilation. Defect annihilation due to electronic energy loss has been discussed on the basis of breaking of bonds and enhanced diffusivity of ionized native defects. [ABSTRACT FROM AUTHOR]

High energy light ion irradiation has been used to anneal H-related defect complexes and to modify the electronic properties of semi-insulating InP (SI-InP). Raman and infrared spectroscopic measurements have been used to investigate the annihilation of native defects in SI-InP irradiated with 85 MeV C. Irradiation resulted in a decrease in sample resistivity by four orders of magnitudes and a change in the type of conductivity. The Raman spectroscopic results indicate an improvement in the InP sample due to irradiation up to an optimum fluence. The role of high electronic energy loss in defect annealing, which includes modification of the electrical properties and crystal structure of irradiated SI-InP, is discussed. [ABSTRACT FROM AUTHOR]

High energy light ions have been used to engineer the electrical properties of semi-insulating InP and GaAs by creation and annihilation of native defects. Due to light mass, high energy ions lose most of their energy during flight inside the material by electronic excitation, which also modifies the charge states of the defect. Imbalance in charge compensation caused by irradiation induced defect engineering results in the modification of resistivity of the semi-insulating samples. The activation energies of the defect levels responsible for the modified resistivity have been estimated from the measurement of thermally activated currents. It is shown that the modified charge compensation is due to annihilation and/or creation of native defects depending on the material (GaAs or InP) and the fluence of irradiated ions. It has also been observed that annealing does not have any effect on modified compensation in InP, but in the case of GaAs, compensation recovers after thermal annealing. [ABSTRACT FROM AUTHOR]

Abstract The topographic evaluation of the nano-scale pattern, on ZnO (001) surface, and its scaling properties have been investigated here after low energy atom beam irradiation. Preferential sputtering promotes the formation of Zn-rich zones near the surface that serve as the nucleation centers for the spontaneous nanostructure growth. The rms roughness (σ) however increases with irradiation fluence and displays power law behaviour, σ ∼ t β , for t < t c (crossover time) but saturates at longer time scale. In the case of t > t c , σ is independent of irradiation time but interestingly follows the power law behaviour σ ∼ L α , where L is the size of image used in analysis. The morphology of the surfaces has also been investigated using the height-height correlation and power spectral density methods. The observed values of growth (β) and roughness (α) exponents indicate a scaling behavior that is induced by the disordered but well-defined geometry of the nanostructures. [ABSTRACT FROM AUTHOR]

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: The second-order transverse acoustic mode and amorphous Raman modes, originating from a continuous random network and medium range ordering (MRO), in high energy light ion (HELI) irradiated GaAs are investigated. The change in the phonon density of states of the transverse acoustic mode phonon distinguishes the effect of HELI irradiation on highly resistive undoped and chromium-doped GaAs. The boson mode, originating from the MRO of the system, has been identified and a model based on phonon-fracton scattering has been used for the explanation of this “boson mode”. The spectral dimension, correlation length and the scaling factor, with which the elastic constant varies with length in MRO regions in GaAs, are estimated. [Copyright &y& Elsevier]

Abstract: Potential fluctuations due to donor–acceptor compensation have been used to observe localization–delocalization transition in semi-insulating GaAs. Photoinduced transients, resulting from relaxation of stored charges in potential valleys, have two components. The long-lived power law decay at low temperature signifies a microscopically inhomogeneous disordered phase, and single exponential decay at a higher temperature signifies a homogeneous ordered phase. Temperature dependence of steady state photocurrent and kinetics of photocurrent decay suggest percolation as a possible mechanism for photoinduced transition in semi-insulating GaAs. [Copyright &y& Elsevier]

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]

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]

We report on the generation of radiative defects, the so-called color centres, in 25 keV He irradiated and thermally oxidized 4H–SiC < 0001 > surface investigated by photoluminescence spectroscopy utilizing 266 nm deep-UV excitation. Ion irradiation showed the generation of photoluminescent peaks ascribed to silicon vacancies (V Si) and unknown defect-related bands (UD 3 and UD 4). Thermal treatment (200–800 C) resulted in a significant increase of luminescence at an optimal temperature, depending on the initial density of emitters. While thermal oxidation resulted in several other high-brightness color centres, emitting photons even at room temperature. In addition to the defects in the crystalline 4H–SiC lattice, the difference in photoluminescence after oxidation indicates the presence of various other complex surface and interfacial defects. [Display omitted] • Generation of radiative defects: • Generation of silicon vacancies (V Si) and unknown defect-related bands (UD 3 and UD 4) in 4H–SiC after ion irradiation. • Thermal oxidation induced high-brightness room-temperature color centres. (including surface emitters from the oxide layer and oxide-bulk interface) • Role of ion fluence (He/cm2) on the emission intensities from the color centres. • Isochronal thermal annealing (200–800C) study of the color centres generated in ion irradiated 4H–SiC. • Temperature-dependent photoluminescence (77–300K): The effect of temperature in luminescence from the oxidation-induced color centres. [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]

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]

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]

We report the synthesis of Ag and Au nanoparticles embedded in various matrices (silica, PET and a-Si) by atom beam sputtering and thermal co-evaporation. We have also synthesized Au nanorings using electron beam evaporation followed by subsequent annealing in inert atmosphere. UV-Visible absorption, atomic force microscopy (AFM), X-ray diffraction (XRD) and transmission electron microscopy (TEM) have been used for characterization of metal nanostructures. UV-Visible spectra indicate the presence of metal nanoparticles by the surface plasmon resonance absorption peak at (∼400 nm for Ag and ∼520 nm for Au). XRD measurements reveal the average particle size that is confirmed by TEM and AFM. The work is in progress to use the prepared metal nanoparticles for (i) biomedical application such as detection of cancer cell (ii) detection of glucose (iii) surface enhanced Raman scattering (SERS) to enhance the characterization of biomolecules (iv) UV-filter and (v) broad absorption band extending to IR region. The broad absorption of Ag-polymer nanocomposites in infrared region shows the possibility of application of these nanocomposites in solar absorbers. Swift heavy ion (SHI) irradiation of the nanoparticles embedded in silica matrix shows the dissolution of nanoparticles. SHI irradiation can be used as a tool to tailor the optical properties of nanocomposites and also provides a fundamental understanding of the interactions of SHI with low dimensional materials. [ABSTRACT FROM AUTHOR]

Gold nanoparticles embedded in silica matrix were prepared by co-evaporation. After deposition, the samples were annealed at different temperatures in inert environment for 30 min. No signature of nanoparticle formation was found in case of as-deposited samples, while the annealed samples showed a clear signature of a surface plasmon resonance absorption peak around 520 nm, which indicated the formation of Au nanoparticles. The samples annealed at 900 °C were irradiated with 100 MeV Ag ions at fluences 2.5×1012 and 1×1013 ions/cm2. UV-visible absorption measurements of pristine and irradiated films showed a clear signature of dissolution of Au nanoparticles with ion beam fluence. X-ray diffraction studies of pristine and irradiated samples also supported the dissolution of Au nanoparticles with ion beam fluence. Rutherford backscattering spectrometry was used for quantification of gold. [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]

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]

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]

Thermally stimulated current spectroscopy, photoquenching, and photorecovery have been used to reveal the EL2-related metastable defect levels in semi-insulating GaAs. It has been found that one set of metastable levels is directly related to EL2 and the other set is indirectly related to EL2 defect through charge transfer. The origin of these EL2-related metastable levels has been discussed in the context of recently proposed three-center-complex model of EL2 in semi-insulating GaAs. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Investigates the depth profile of implanted species of light mass elements with a detector telescope. Description of the elastic recoil detection analysis (ERDA) technique; Reasons why the technique can lead to misleading results; Accurate profiling of implanted specimen.

Sub-stoichiometric GeOx films were fabricated by electron-beam evaporation method. The films were irradiated with 100 MeV Ag7+ ions at fluences between 1 × 1012 and 1 × 1014 ions-cm-2. Spectroscopic ellipsometric measurements were performed in air at room temperature. The values of the layer thickness and refractive index were extracted from ellipsometry using a multilayer analysis and the Tauc Lorentz model. The refractive index (at 633 nm) of the as-deposited GeOx film was estimated to be 1.860 and decreased to 1.823 for films irradiated at an ion fluence of 1 × 1014 ions-cm-2. The thickness of the films also decreased after irradiation and is due to a sputtering induced by the ion beam. The change in the refractive index with ion fluence is attributed to a stoichiometric change and structural transformation represented by GeOx→ Ge + GeOy (y > x) occurring due to a thermal spike induced by ion irradiation. Swift heavy ions thus provide a scope for modulating the refractive index of GeOx films. The thickness and stoichiometric changes are supported by Rutherford backscattering measurements. [ABSTRACT FROM AUTHOR]

We report on the formation of a-axis oriented Au[sub 0.6]Ge[sub 0.4] alloy on a Si(100) substrate on 120 MeV Au-ion irradiation of a Au/Ge bilayer and subsequent vacuum annealing at 360 °C. Irradiation-induced changes occurring across the Au/Ge interface were studied using Rutherford backscattering spectrometry. Phase identification was done by x-ray diffraction and the surface morphology of the samples was studied by scanning electron microscopy. Formation of oriented Au[sub 0.6]Ge[sub 0.4] alloy was confirmed by transmission electron microscopy and discussed on the basis of swift heavy ion induced effects followed by thermal annealing. [ABSTRACT FROM AUTHOR]

The recovery effect of isochronal thermal annealing and inelastic energy deposited during 100 MeV Ag swift heavy ion (SHI) irradiation is demonstrated in the case of 4H-SiC pre-damaged by elastic energy deposition of 300 keV Ar ion. The Ar-induced fractional disorder follows a nonlinear two-step damage build-up. The fractional disorder level of 0.3 displacements per atom (dpa) is established as the threshold above which the lattice rapidly enters the amorphous phase, characterized by the presence of highly photo-absorbing defects. The SHI-induced recovery suggests that the damage annealing, in the pre-damaged region (∼ 350 nm) where the S e for 100 MeV Ag is almost constant (∼ 16.21 keV/nm), is more pronounced than the damage creation by SHI. This allows the disorder values to saturate at a lower value than the present initial disorder. Furthermore, the thermal effect due to SHI irradiation of an amorphous nano-zone embedded in a crystalline host matrix has been evaluated using the 3D implementation of the thermal spike. The recovery process by SHI is ascribed to the thermal spike-induced atomic movements resulting from the melting and the resolidification of the crystalline–amorphous interface. [ABSTRACT FROM AUTHOR]

Defects in SiC have shown tremendous capabilities for quantum technology-based applications, making it necessary to achieve on-demand, high-concentration, and uniform-density defect ensembles. Here, we utilize 100 MeV Ag swift heavy ion irradiation on n-type and semi-insulating 4H-SiC for the controlled generation of the defects that have attracted a lot of attention. Photoluminescence spectroscopy shows strong evidence of V Si emitters in semi-insulating 4H-SiC. Additionally, irradiation generates photo-absorbing centers that enhance the optical absorption, suppressing the luminescence intensity at higher fluences (ions / cm 2). In n-type 4H-SiC, irradiation drastically increases the inter-conduction band transitions, attributed to absorption from trap centers. A clear correlation is found between (i) loss in the intensity of E 2 (TO) Raman signal and the enhancement in absorbance at 532 nm and (ii) decoupling of the longitudinal optical phonon–plasmon coupled Raman mode and the reduction in carrier concentration. The optical bandgap decreases with irradiation fluence for semi-insulating 4H-SiC. This is attributed to the formation of disorder and strain-induced localized electronic states near the band edges. [ABSTRACT FROM AUTHOR]

An ultrafast thermal spike within a time interval of a few pico-seconds generated by intense ionizing energy deposited using 100 MeV Ag ions is utilized to study the atomistic details of damage recovery in 4H-SiC. Sequential single ion irradiations were performed using 300 keV Ar and 100 MeV Ag in <0001> 4H-SiC to invoke swift heavy ion (SHI) beam induced epitaxial recrystallization in samples with different degrees of pre-damaged conditions. SHI irradiation was carried out at both room temperature and a low temperature of ~80 K. Low-temperature irradiation was carried out to arrest thermal diffusion of defects and to isolate ionization-induced defect migration in 4H-SiC. Insights into the thermal spike generated by ionizing events in crystalline and amorphous regions at both the temperatures predict a SiC response to SHI. The results emphasize the role of different degrees of pre-damage induced physico-chemical conditions and irradiation temperatures against SHI-induced recrystallization as evaluated by Rutherford backscattering/channeling, Raman spectroscopy, and hard x-ray photoelectron spectroscopy. Understanding the dependence of ion-beam damage accumulation and their recovery on the inelastic to elastic energy loss ratio is important for the performance prediction of SiC intended for extreme environments such as space, defense, and nuclear radiation. We report substantial damage recovery even at a near liquid nitrogen temperature of ~80 K. The recovery gets impeded mainly by the formation of complex defects having homonuclear bonds. The results are explained in the framework of the inelastic thermal spike model, and the role of phonon in the damage recovery process is emphasized. [ABSTRACT FROM AUTHOR]

Thin, durable, uniform, isotopic targets of 193 Ir, 187 Re, 182 W, 181 Ta, 175 Lu and 169 Tm of thicknesses ∼80 μ g/cm 2 , 60 μ g/cm 2 , 70 μ g/cm 2 , 175 μ g/cm 2 , 110 μ g/cm 2 and 270 μ g/cm 2 , respectively, have been fabricated on carbon backing by physical vapor deposition technique for nuclear reaction studies at Inter University Accelerator Centre (IUAC), New Delhi. Preparation of very thin self-supporting targets of these elements is non-reproducible. A carbon backing thickness of ∼22 μ g/cm 2 was achieved. For the targets of refractory metals ( 193 Ir, 187 Re, 182 W, 181 Ta) e-gun evaporation was used. The lanthanide targets ( 175 Lu, 169 Tm) were fabricated using: (a) e-gun (for nat C backing), (b) resistive heating (for source material deposition) and (c) e-gun evaporation (for nat C capping) methods successively, without breaking the vacuum. Fabrication details of these targets, with actions taken against the challenges (peeling off, heat damage etc.) experienced during fabrication, are reported. No high Z contamination is found in any of the targets by RBS and XRF analysis. [ABSTRACT FROM AUTHOR]

This article reports a comprehensive study on damage evolution in undoped InP due to 100 MeV silver (Ag 7+ ) ion irradiation. Raman and Rutherford back scattering channeling (c-RBS) measurements are employed to bring out two different aspects of disorder in the system. While Raman spectroscopy revealed a monotonic increase in sub-surface strain due to ion irradiation, the later detected heavy damage in the wafer at high fluences. Furthermore, we have estimated the lattice temperature under above irradiation conditions in InP using a unified thermal spike model. The model includes both inelastic thermal spike and elastic collision spike along with the effect of latent heat. This model explains the observed damage evolution of the target. Above experimental techniques in conjunction with the simulation model provides a qualitative explanation of the damage accumulation leading to structural modification in the Ag ion-irradiated InP wafer. [ABSTRACT FROM AUTHOR]

The self-supporting 206,208 Pb enriched isotopic targets of thicknesses varying from 500 μg/cm 2 to 800 μg/cm 2 have been prepared in the high vacuum environment at the target laboratory of Inter University Accelerator Centre (IUAC), by using the resistive heating method. The limited amount of the target material, selection of the parting agent, highly oxidizing tendency of the Pb in the atmosphere and the separation of the lead film from the glass slides were the few major challenges faced in the fabrication of the targets. A limited amount of isotopic material (100 mg) was utilized for the preparation of more than 20 thick self-supporting targets of 206 Pb and 208 Pb isotopes. Several attempts were made to overcome the difficulty of finding a suitable parting agent to avoid direct contact of water with the target material are discussed, along with the methods adopted for the fabrication of the targets. Further Energy Dispersive X-ray (EDX) analysis was performed to check the elemental purity of the foils. These targets have been successfully used for several nuclear physics experiments using the neutron detector setup known as National Array of Neutron Detectors (NAND) at IUAC, New Delhi. [ABSTRACT FROM AUTHOR]

In this study, the effect of irradiation temperature on microstructural evolution of Indian RPV steel is reported. This study, by virtue of helium ion irradiation at 77, 300 and 573 K, could bring out the effect of the irradiation induced defects on microstructural and mechanical property changes at different stages of their existence starting from the state of cascade damage till the point of their free migration. Irradiation experiments were performed with varying ion energies to achieve nearly uniform irradiation damage of 0.05, 0.2 and 3 dpa in a ~ 300 nm wide region. Irradiated samples were characterized using GIXRD, PAS, TEM and nanoindentation. Unirradiated samples showed predominant presence of a combination of di- and tri-vacancy type of defects. Most of the dislocations present in unirradiated samples were screw dislocations, while mixed type was noticed upon irradiation irrespective of the irradiation temperature. PAS study showed formation of distinct defect types at different irradiation temperatures. TEM study confirmed formation of dislocation loops and defect clusters on irradiation. Higher irradiation temperatures resulted in the extension of the width of the damage region owing to increased migration of defects. [ABSTRACT FROM AUTHOR]

Thin 160 Gd targets (enrichment 98.12%) in the thickness range of 45–55 μg/cm 2 have been prepared on carbon backing in the high vacuum environment using thermal evaporation technique. During the fabrication, a few of the challenges faced were the oxidizing tendency of Gd in the atmosphere, limited amount of enriched material and the peeling off problem during floating of the films. Several trials were first conducted with natural Gd to optimize different parameters of the fabrication process. By utilizing only 30 mg of enriched isotopic material, more than 25 targets of 160 Gd were fabricated successfully. The purity check and thickness measurement of the prepared targets were performed using Energy Dispersive X-Ray Fluorescence and Rutherford Back Scattering techniques. Absence of any heavy ions and presence of negligible amount of oxygen in the prepared films revealed the purity of the targets fabricated using thermal evaporation technique. [ABSTRACT FROM AUTHOR]

Thin films of amorphous alumina of thickness 350 nm were deposited on fused silica substrates by electron beam evaporation. Amorphous films were annealed at several temperatures in the range: 400–1130 °C and changes in film crystallinity, short-range structure, optical and mechanical properties were studied. X-ray diffraction studies found that crystallization starts at 800 °C and produces γ and δ-alumina, the latter phase grows with heat treatment and the sample was mostly δ and θ-alumina after annealing at 1130 °C. The as-deposited amorphous alumina films have low hardness of 5 to 8 GPa, which increases to 11 to 12 GPa in crystalline sample. 27 Al Magic Angle Spinning Nuclear Magnetic Resonance was used to study the short-range order of amorphous and crystalline alumina films and it was found that amorphous alumina film contains AlO 5 and AlO 4 structural units in the ratio of 1:2. The concentration of AlO 5 was significantly suppressed in crystalline film, which contains 48% of Al 3 + ions in AlO 6 , 7% in AlO 5 and 45% in AlO 4 units. [ABSTRACT FROM AUTHOR]

Abstract: Isotopic targets of 90,94Zr, with thickness of 280μg/cm2, have been prepared in ultra-high vacuum chamber by electron beam deposition method on carbon backing of 45μg/cm2 thickness at Inter University Accelerator Centre (IUAC), New Delhi. Amounts of 50.9 and 58mg isotopic materials were utilized for preparation of 90Zr and 94Zr targets, respectively. These targets have been successfully used in nuclear physics experiments at IUAC. [Copyright &y& Elsevier]

The reactivity of the Zr/Si interface induced by swift heavy ion beams of Au has been investigated in the present work. Zirconium was evaporated on a clean silicon substrate in ultra high vacuum (UHV) at a pressure of 10-8 Torr by the electron beam evaporation technique and the final layer was a thin film of Au to avoid oxidation of zirconium. The Zr/Si system was irradiated by 350 MeV Au26+ ions at liquid nitrogen temperature at different fluences (0.46×1014, 1.85×1014 and 4.62×1014 ions/cm2). Rutherford back scattering (RBS) spectroscopy using 2 MeV He ions was used to monitor the Zr and Si concentration profiles and interdiffusion at the interfaces. The irradiation at the Zr/Si interface showed mixing. X-ray diffraction measurements confirmed the formation of the ZrSi2 phase. Thermal spike formation and melting in the tracks was found to be the dominant process at the interfaces. [ABSTRACT FROM AUTHOR]

Abstract: 184W enriched isotopic target of 210μg/cm2 thickness on carbon backing of 100μg/cm2 thickness has been made in ultra-high vacuum environment by evaporation method using 6kW electron beam at Inter University Accelerator Centre (IUAC). Hundred and thirty milligrams of enriched 184W powder was used in this target preparation process. This target has been successfully used in two nuclear reaction experiments performed at IUAC. Methods adopted to convert the tungsten powder to a special pellet form in order to minimize the consumption of the expensive material, preparation of stress relieved carbon-backing foil, steps taken to make the carbon withstand the heat generated during the tungsten evaporation, the method of tungsten fabrication and details of ultra-high vacuum evaporator facility of IUAC are discussed. [Copyright &y& Elsevier]

Abstract: Elastic recoil detection (ERD) analysis of GeO x thin films was carried out to understand the mechanism of phase separation. Stoichiometry of the film was monitored on-line at various fluences of 100MeV Au ions. Although significant electronic sputtering of GeO x film was observed but the stoichiometry remained almost constant up to a fluence of 3×1012 ions/cm2. Structural modifications of the films after irradiation was studied by offline glancing angle X-ray diffraction (GAXRD), which showed the presence of Ge crystallites in the films. The results indicate that the phase separation does not occur because of preferential sputtering of oxygen but may occur as a result of rearrangement of Ge and O atoms within the films. The activation for rearrangement is provided by ion impact. [Copyright &y& Elsevier]

Silver nanoparticles (Ag NPs) embedded in silica were prepared by a novel process of atom beam sputtering (ABS). Optical and structural properties of Ag NPs were studied by using ultraviolet–visible absorption, transmission electron microscopy and X-ray diffraction. The processes involving nucleation and growth of Ag NPs are discussed. The superiority of the ABS over ion implantation and ion beam mixing is discussed. These Ag NPs are found to be glucose sensitive, indicating their possible application in medical diagnostics. [Copyright &y& Elsevier]

Abstract: The topography of Si(100) and Si(111) surfaces after irradiation with 1.5keV Ar atoms beam incident at 45° with respect to the surface normal has been studied as a function of atom fluence using atomic force microscopy. The sputtered silicon (100) samples exhibit ripple pattern, with the average value of the ripple wavelength increasing from 15nm to 19nm as fluence increases from 1.7×1017 atoms/cm2 to 5.1×1017 atoms/cm2, though the height of ripples remains same i.e. 1.02nm. On the other hand, in case of Si(111) samples, the average value of the ripple wavelength increases from 22nm to 40nm with fluence increasing from 1.7×1017 atoms/cm2 to 5.1×1017 atoms/cm2. A close view of the surface morphologies of Si(100) and Si(111) showed that the ripples on Si(111) surface are, more regular than Si(100). When the fluence is further increased, it is found that the wavelength of ripple tends to saturate and the height tends to decrease, as a result the surface becomes smooth at higher (∼6.8×1017 atoms/cm2) fluence. [Copyright &y& Elsevier]

Abstract: One hundred and twenty mega electron volts [120MeV] of Au ion irradiation induced increase in conductivity at ion impact sites in C60, has been observed using conducting atomic force microscope (C-AFM). The current image shows the formation of ion tracks having much larger conductivity as compared to surroundings in C60 films on Si substrate. The increase in conductivity is attributed to the electronic energy loss induced polymerization and transformation from insulating C60 to conducting graphite like carbon around ion path. The unirradiated sample has a semiconducting nature of I–V characteristic, which shows an increased ohmic behavior with increasing fluence. This effect has been attributed to simultaneous imaging of more than one track at sites where very close/overlapping ion impacts take place. [Copyright &y& Elsevier]