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Implementation of a state of the art data acquisition and analysis program for variable low energy positron beam using LabVIEW based automation software is described. The program does the following functions: (a) controlling the remote programmable high voltage–power supply to bias the sample negatively (i.e., to vary the positron beam energy), (b) control of Windows based PCI MCA card, (c) calculating the S, W, R and ortho-positronium self-annihilation fraction (fPs) parameters, errors, and other relevant parameters, (d) saving the raw spectra, results and log data file and (e) dynamic display of raw spectrum and S, W, fPs versus energy for easy visualization of progress of the experiment. The USB based interfacing standard of this design provides easy connectivity to the personal computers.

A signal tapping circuit has been designed to derive the fast timing signal from the Chevron type, 2 stage MCP having phosphor screen as a readout device. Using this, the timing property of the MCP-BaF2 system has been studied using the digital storage oscilloscope in which a timing resolution of ~ 500 ps has been obtained. The applicability of MCP with phosphor screen configuration for timing measurements has been demonstrated.

Positron beam measurements carried out on high temperature Ni+ implanted FeCrCoNi show no void formation but only presence of monovacancies. With thermal treatment, evidence for the formation of nano sized σ-CoCr are obtained from positron based ratio curve analysis in the temperature range 973–1123 K. Corroborative evidence for the presence of these precipitates are obtained from EBSD and GIXRD measurements. Further annealing beyond 1150 K leads to coarsening of these precipitates and they no longer trap the positrons.

Positron beam-based Doppler broadening results on He ion-implanted FeCrCoNi show distinct changes in defect-sensitive S-parameter corresponding to the formation of helium-vacancy complexes, nucleation/ growth of helium bubbles, and finally the helium bubble rupture, with isochronal annealing. Data analyses of the positron beam-based ratio curves provide clear information on the kinetics of bubble growth and rupture. The difference data in S-parameter (ΔS), which corresponds to the bubble growth, displays a maximum at 1123 K, with annealing temperature. Comparing the ΔS value to that reported for nickel, it is concluded that FeCrCoNi has higher bubble growth resistance than nickel.

Rethinking analog to digital conversion has become extremely crucial in the race towards aggressively scaled technology nodes with decaying signal swings. The concept of more recent TDCs, which are completely designed in digital domain, make them simpler, easier to manufacture and faster to market. In previous work, LUCOS J. Doge, G. Schonfelder, G. Streil, and A. Konig. An HDR CMOS image sensor with spiking pixels, pixel-level ADC, and linear characteristics. Circuits and Systems II: Analog and Digital Signal Processing, IEEE Transactions on, 49(2):155–158, Feb 2002. , a high dynamic range image sensor using spike based processing with high pixel uniformity had been designed. This motivated a generic ADC concept, which makes use of spike processing, to design a highly effective sensor signal processing system, which carries the promise of robustness to technology scaling, for effective use in IoT and Industrie 4.0. In this work, an ADC concept based on acoustic localization in biological sensory systems has been pursued. An ADC has been designed based on this concept using biological models of spiking neurons. The first proof-of-concept prototype chip SSDCα has been designed in ams 350 nm technology node with area of the chip is 8.5 mm2, sampling rate from DC to 150 kHz, resolution from 8-bit to 13-bit, with 28, 200 transistors, 263 neurons and 517 synapses. The future work will move from 350 nm to 90 nm technology node to show the improvement and robustness of the SSDC with technology scaling.

Defect characterization of room temperature 1.5 MeV Ni ion implanted high entropy FeCrCoNi alloy for two fluences (1 × 10 15 ions/cm 2 and 5 × 10 16 ions/cm 2 ) was carried out using the variable low energy positron beam. The FCC solid solution remains robust and stable under 100 dpa irradiation and high temperature annealing. The change in the defect sensitive S-parameter upon implantation reveals the presence of monovacancies for both the doses. The changes in the defect microstructure upon thermal annealing are found to be dose dependent. The high dose shows the formation of stable stacking fault tetrahedrons (SFT's) from the aggregates of monovacancies at higher annealing temperatures while the low dose shows the annealing of monovacancies with temperature.

Accurate prediction of pavement performance is important for efficient management of road infrastructure. Pavement performance prediction models developed for low-volume roads are mainly based on deterministic approach. The deterministic prediction models are inadequate to completely capture the deterioration mechanism. Uncertainties may occur in pavement behaviour under changing traffic loads and environment conditions, which may not be realistically represented by deterministic model. The objective of this paper is to develop pavement deterioration prediction models by probabilistic approach, for various distresses observed on low-volume roads in the state of Kerala in India, with the help of existing deterministic models. The major distresses observed on low-volume roads were ravelling, pothole and edge failure. Load-associated distresses were rarely observed on these roads as the maximum cumulative standard axle observed was only one million standard axle (msa). Hence, lack of proper drainage ...

Defect annealing in FeCrCoNi high entropy alloy is studied using positron lifetime and Doppler broadening spectroscopic techniques. Variation of positron lifetime with temperature show the annealing of defects beyond 770 K. Theoretical positron lifetime and electron momentum distributions were computed for the alloy to understand the nature of defects present in the arc melted alloy. X-ray diffraction measurements show that the arc melted alloy forms FCC solid solution and the phase remains stable even after annealing at 1373 K. Recrystallization assisted grain growth occurs beyond 973 K.

Structural stability studies of boron doped 40:60 iron phosphate glasses under humid storage conditions, using Raman spectroscopy is reported. Raman measurements indicate that increased boron doping in these glasses maintaining oxygen/phosphorous ratio constant serves to strengthen the iron phosphate glass network, while for samples with iron/phosphorous ratio a constant, a systematic weakening of the network was observed with increased boron content. Raman measurements on glasses exposed to ambient laboratory conditions (300 K; RH: 70 -80%) for three years reveal excellent structural stability against atmospheric corrosion. Incidentally the sample with the strongest network - 20 mol% boron doped iron phosphate glass with O/P constant, indicated devitrification of the glass surface on storage. Definitive evidence of attack by atmospheric water vapour on the glass surface leading to the above devitrification has been obtained using Raman spectroscopy. Possible pathways for the enhanced atmospheric corrosion of this glass are discussed that would help mitigate this detrimental degradation of boron doped iron phosphate base glasses.

Detailed Raman spectroscopic studies on 40:60 iron phosphate glasses (IPG) and cesium doped IPG under ambient conditions revealed an evident disproportionation of the pyrophosphate network beyond 18 mol% Cs doping. In situ high pressure Raman spectroscopic studies were carried out on IPG and Cs doped IPG up to 40 GPa for the first time in order to investigate the structural stability of these glasses under pressure. Although the parent glass is found to be robust to such high pressures, pressure quenched samples loaded with cesium beyond 18 mol% concentration were observed to permanently cross link leading to new high density forms of the glass. The extent of cross linking is observed to systematically increase with the cesium content in the parent matrix.

LiInSe2 polycrystalline material was successfully synthesized from melt and temperature oscillation method (MTOM). The crystalline phase was confirmed by powder X-ray diffraction pattern. Crack free LiInSe2 single crystal of size 12 mm diameter and 32 mm length was grown using two zone tubular resistive heated furnace by modified vertical Bridgman–Stockbarger method with steady ampoule rotation. The grown LiInSe2 crystal was subjected to single crystal XRD, inductively coupled plasma-optical emission spectroscopy (ICP-OES), positron annihilation spectroscopy (PAS), Hall effect and dielectric measurements. Single crystal XRD measurement confirms the orthorhombic crystal system. ICP-OES analysis gives the crystal composition as Li0.81In1.01Se2.18. The average lifetime 278.03 ps in PAS measurements corresponds to vacancy clusters present in LiInSe2 crystal. Hall effect measurement confirms the n-type semiconductor nature. The dielectric permittivity and dielectric loss were obtained to be 9.8 and 0.108 respectively by capacitance measurements at room temperature for the frequency of 2 MHz.

Fatigue crack growth behaviour of a near α titanium alloy Timetal 834 has been studied at maximum dynamic strain ageing temperature (450 °C) and at the service temperature (600 °C). Compact-tension type fracture mechanics specimens have been tested with stress ratio and frequency of 0.1 and 1 Hz, respectively, under constant amplitude loading. The alloy showed higher crack growth rate at 450 °C due to dynamic strain ageing which causes higher stress concentration at the crack tip as compared to 600 °C. The pronounced effect of oxide and roughness induced crack closure revealed from Auger electron spectroscopy and surface profiler, respectively, have been attributed to reduce the stage I as well as stage II fatigue crack growth rate at 600 °C. Fractographic and crack path observations confirmed that the crack growth mechanism remained highly faceted in nature at low ΔK levels which changes subsequently to striation mode of fracture at relatively higher ΔK levels.

Indian Reduced Activation Ferritic Martensitic steel is irradiated with 1.1 MeV Fe ions to a dose of 0.1 dpa at room temperature. The positron annihilation study showed a decrease in S-parameter with annealing temperature due to vacancy annealing. A complete defect recovery is observed beyond 1073 K. The linear nature of (S, W) correlation plot shows that only one kind of defect is present throughout the annealing temperature.

Depth resolved positron beam results of Si and metal silicides are highlighted in terms of identifying the nature of vacancy defects in amorphous and disordered Si and phase transformation and defect evolution as a consequence of silicide formation, respectively.

Raman and infrared spectroscopic measurements were carried out on 40 mol% Fe 2 O 3 :60 mol% P 2 O 5 iron phosphate glass samples to study the effect of increasing external pressure on the local structure of both anhydrous and water trapped glasses. In-situ high‐pressure Raman measurements, done up to 24.2 GPa on anhydrous samples, revealed hardening of the phonon modes accompanied by a loss of Raman intensity and ultimately leading to complete smearing of modes at very high pressures. These changes were found to be reversible upon quenching the sample back to ambient pressure. Raman and infrared spectroscopy of pressure quenched IPG samples containing trace amounts of water have revealed definite signatures of devitrification at room temperature.

Iron phosphate glasses have been investigated using positron lifetime and micro Raman spectroscopy to study the crystallization kinetics and defect evolution across the glass and crystallization transitions. Positron lifetime parameters show distinct changes at temperatures corresponding to both the transitions. These changes have been understood as the signature of the evolution of open volume defects and their clustering across the amorphous to crystalline interfaces. Micro Raman measurements on annealed samples have identified the crystalline phases as Fe3(P2O7)2 and FePO4. Ab-initio positron lifetime computations reveal that the positron probes the Fe/P sites in defect free crystals. The nature of open volume defects produced upon annealing is identified by computing positron lifetimes for various possible defect clusters. A combination of both experimental and theoretical techniques has provided insights in understanding the evolution of defects across the phase transition in these glasses.

Bulk cobalt silicides Co2Si, CoSi and CoSi2 have been investigated using experimental positron lifetime, coincidence Doppler broadening and depth-resolved positron beam studies. Psitron lifetime and coincidence Doppler ratio curves have shown distinct features for the silicides as compared to that of pure Co and Si. Ab-initio calculations of positron life time have been carried out using the DOPPLER program. The experimental positron lifetime values are higher than the theoretical estimates for Co2Si and CoSi2, suggesting that these silicides contain vacancy defects. This is further supported by positron diffusion lengths deduced from the VEPFIT analysis of positron beam results. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The void swelling behaviour of (15Ni–14Cr) Ti-modified steels simulated by heavy ion irradiation, has been investigated using step height measurements and positron annihilation spectroscopy. 18% cold-worked samples were pre-implanted with helium at 170 keV and 275 keV energies so as to create a uniform helium concentration of 100 appm around the 588 nm depth region. This was followed by a 2.5 MeV Ni ion irradiation to create a peak damage of ~ 84 dpa (displacement per atom) at various irradiation temperatures between 700 and 970 K. The gross swelling which has occurred throughout the ion range is determined by step height measurements. Defect-sensitive positron annihilation lineshape S-parameter measurements show clear changes consequently to void formation as a function of sample depth. From the variation of the average S-parameter as a function of irradiation temperature, the peak swelling temperature has been deduced. The changes observed in step height measurements are compared with positron annihilation measurements and the results are discussed.

Positron annihilation spectroscopy along with glancing incidence X-ray diffraction have been used to investigate tin oxide thin films grown on Si by pulsed laser deposition. The films were prepared at room temperature and at 670 K under oxygen partial pressure. As-grown samples are amorphous and are found to contain large concentration of open volume sites (vacancy defects). Post-deposition annealing of as-grown samples at 970 K is found to drastically reduce the number of open volume sites and the film becomes crystalline. However, film grown under elevated temperature and under partial pressure of oxygen is found to exhibit a lower S -parameter, indicating lower defect concentration. Based on the analysis of experimental positron annihilation results, the defect-sensitive S -parameter and the overlayer thickness of tin oxide thin films are deduced. S – W correlation plots exhibit distinct positron trapping defect states in three samples.

The defect recovery in proton irradiated Ti-modified D9 steel has been studied by positron annihilation isochronal and isothermal annealing measurements. D9 samples have been irradiated with 3 MeV protons followed by isochronal annealing at various temperatures in the range of 323 to 1273 K. The dramatic decrease in positron annihilation parameters, viz. positron lifetime and Doppler S-parameter, around 500 K indicates the recovery of vacancy-defects. A clear difference in the recovery beyond 700 K is observed between solution annealed and cold worked state of D9 steel due to the precipitation of TiC in the latter. Isothermal annealing studies have been carried out at the temperature wherein vacancies distinctly migrate. Assuming a singly activated process for defect annealing, the effective activation energy for vacancy migration is estimated to be 1.13 ± 0.08 eV.

Automation of positron beam experiment with a single chip embedded design using a programmable system on chip (PSoC) which provides easy interfacing of the high-voltage DC power supply is reported. Virtual Instrument (VI) control program written in Visual Basic 6.0 ensures the following functions (i) adjusting of sample high voltage by interacting with the programmed PSoC hardware, (ii) control of personal computer (PC) based multi channel analyzer (MCA) card for energy spectroscopy, (iii) analysis of the obtained spectrum to extract the relevant line shape parameters, (iv) plotting of relevant parameters and (v) saving the file in the appropriate format. The present study highlights the hardware features of the PSoC hardware module as well as the control of MCA and other units through programming in Visual Basic.

Silicide formation in Co/Si thin structures synthesized using thermal evaporation, sputter deposition and ion implantation, has been investigated using depth-resolved positron annihilation spectroscopy (PAS) together with other corroborative experimental techniques. S vs. E p curves and S – W correlation plots have revealed important processes such as defect annealing, interdiffusion, silicide formation and recrystallization of amorphous Si. These studies have shown that there exist differences in the formation temperature of the silicide phases, the sequence of silicide phase formation and defect generation owing to the nature of the deposition methods employed.

Germanium atomic (Ge1) and molecular ions (Ge2) of equivalent energy are implanted in silicon at an elevated temperature. The ion induced damage has been characterized by RBS channeling (RBS/C) and positron annihilation spectroscopy. The RBS/C studies indicate that the molecular ion implantation has produced more defects in the near surface regions compared to the atomic ion implantation. This paper reports a first time observation of an enhanced production of vacancy related defects in silicon implanted with molecular ions.

Formation of CoSi 2 in Co implanted Si sample has been studied using glancing incidence X-ray diffraction and depth resolved positron annihilation techniques. The implanted sample exhibits near-surface amorphization in the temperature range between 300 K and 670 K. It is found that recrystallization of Si occurs at 870 K which inturn, triggers the formation of the CoSi 2 phase at lower temperatures as compared to that obtained in thin film systems. The results are discussed in the light of enhanced intermixing brought by defect migration, associated with recrystallization.

Depth resolved positron annihilation studies on Pd/Si thin film system have been carried out to investigate silicide phase formation and vacancy defect production induced by thermal annealing. The evolution of defect sensitive S-parameter clearly indicates the presence of divacancy defects across the interface, due to enhanced Si diffusion beyond 870 K consequent to silicide formation. Corroborative glancing incidence X-ray diffraction (GIXRD), Auger electron spectroscopy (AES) and Rutherford backscattering spectrometry (RBS) have elucidated the aspects related to silicide phase formation and Si surface segregation.

Silicide formation induced by thermal annealing in Ni/Si thin film system has been investigated using glancing incidence X-ray diffraction (GIXRD) and Auger electron spectroscopy (AES). Silicide formation takes place at 870 K with Ni 2 Si, NiSi and NiSi 2 phases co-existing with Ni. Complete conversion of intermediate silicide phases to the final NiSi 2 phase takes place at 1170 K. Atomic force microscopy measurements have revealed the coalescence of pillar-like structures to ridge-like structures upon silicidation. A comparison of the experimental results in terms of the evolution of various silicide phases is presented.

Pore structure in polypropylene membranes has been investigated using slow positron beam and small-angle X-ray scattering (SAXS) studies. The pore structure has been modified by chemically grafting methylmethacrylate in polypropylene. Depth-resolved Doppler lineshape S-parameter and positronium (Ps) fraction (3γ/2γ ratio) measurements have been carried out using a variable low energy positron beam. Lineshape S-parameter and Ps fraction are found to decrease with the extent of grafting. The deduced positron diffusion length is also seen to decrease with the extent of pore grafting. The power law dependence of SAXS intensity over a wide range of the wave vector transfer reveals the fractal nature of the pore–membrane surface and, the surface fractal dimensions are seen to increase with amount of pore grafting. The value of the negative exponent of the power law size distribution of the pores has been found to be increasing with increase in grafting revealing reduction in the pore size and narrower pore size distribution. The deduced pore size from SAXS measurements is correlated with positron diffusion length and S-parameter from the positron beam measurements.

The transformation of Co/Si to CoSi 2 /Si in the temperature range of 300–1170 K has been investigated using depth-resolved positron annihilation and Glancing incidence X-ray diffraction (GIXRD). The different silicide phases formed are identified from the experimental positron annihilation characteristics, which are consistent with the GIXRD results. The present study clearly indicates the absence of vacancy defects in the silicide overlayer.

GaN epilayer grown on Sapphire by MOCVD technique has been irradiated with 75 MeV Sn 5+ ions to a fluence of 1×10 11 , 10 12 , 10 13 and 10 14 cm −2 and studied using depth-resolved positron annihilation spectroscopy. High-energy ion-induced defects are found to be Ga mono vacancies, which have been identified from the defect sensitive S -parameter values as well as from R -parameter values, for all fluence beyond 10 11 cm −2 . It is also found that the concentration of vacancy defects increases with ion fluence.

Depth resolved positron annihilation measurements were carried out on 85?keV and 1?MeV nitrogen ion implanted InP samples. The defect sensitive S-parameter and R-parameter values for the low energy implantations confirm the presence of monovacancies up to a dose of 1015?cm?2 and coexistence of monovacancies and divacancies for 1016?cm?2 dose sample. Corroborative glancing incidence x-ray diffraction measurements on the highest dose sample revealed that the sample is amorphized. For high energy implantation, it is found that vacancy-defects are present right from the near-surface region and these defects are identified to be monovancancies, based on the observed S- and R-parameters. A comparison of the results for the low and high energy implantations is made.

The transformation of Pd/Si to Pd2Si/Si is studied using Auger electron spectroscopy over a wide temperature range of 370–1020 K. The Pd film gets totally converted to Pd2Si upon annealing at 520 K, and beyond 570 K, Si starts segregating on the surface of silicide. It is found that the presence of surface oxygen influences the segregation of Si. The time evolution study of Si segregation reveals that segregation kinetics is very fast and the segregated Si concentration increases as the temperature is increased. Scanning electron microscopy measurements show that Pd2Si is formed in the form of islands, which grow as the annealing temperature is increased.

The transformation of Pd/Si to Pd2Si/Si is investigated using depth-resolved positron annihilation, x-ray diffraction and Auger electron spectroscopy studies. The observed defect-sensitive positron S-parameter value of 1.022–1.054 indicates the existence of divacancies across the silicide/silicon interface and Si substrate region. Our experimental observation of vacancy defects is consistent with the model proposed for excess vacancy generation across the interface consequent to Si diffusion.

Effect of titanium concentration in the D9 composition on the defect recovery has been investigated using positron lifetime measurements. As-received and creep-tested samples of 20% cold-worked D9 having different weight percent of titanium namely, 0.18, 0.23, 0.25 and 0.36 have been investigated. As-received Ti variants of D9 have also been isothermally annealed at 973 K and positron lifetime studies have been carried out to confirm the evolution of TiC precipitates during the initial annealing stages. These results are discussed in the light of TiC precipitation with our earlier work on isochronal annealing of cold-worked D9. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of doping of the polyaniline emeraldine base (PEB), with Ni as well as Ni over layer coating has been investigated using variable low energy positron beam. Depth-resolved Doppler S-parameter measurements have been performed on undoped, Ni-doped polyaniline (PANI), and Ag (40 nm) film deposited PANI samples. Significant variation in S-parameter is observed for undoped and Ni-doped PANI. The size of the free volume hole has shifted to lower values upon doping with Ni as compared to that of undoped PANI, which is consistent with the conductivity measurements. For Ag-coated PANI systems, the S vs. Ep curves show distinct changes at the surface and interior regions. These results are discussed in the light of changes in free volume hole size distribution.

The void swelling behavior of heavy ion irradiated D9 steel has been investigated using variable low energy positron beam. The normalized defect-sensitive S-parameter shows up a large increase in the depth region corresponding to the maximum radiation damage as a function of irradiation temperature. From the variation of S-parameter as a function of irradiation temperature, the peak swelling temperature has been deduced and the results are discussed.

Bulk nickel silicides (NiSi and NiSi2) have been studied using the experimental positron lifetime and depth-resolved positron beam measurements. Ab-initio calculations of positron lifetime for the silicides have also been carried out using the atomic superposition method. For NiSi phase, it is found that the theoretically computed positron lifetime compares favourably with the experimentally deduced value indicating that NiSi is defect free. However, for NiSi2, the experimental positron lifetime does not compare well with the theoretical value suggesting that NiSi2 contains vacancy defects. This is further supported by the positron diffusion lengths deduced from the VEPFIT analysis of the positron beam results.

In spite of the large amount of tribological work carried out to explain the friction and wear mechanism in diamond-like carbon (DLC) films, some of the core issues relating to the evolution of reactive species across sliding interfaces and their role on the friction and wear mechanism remain unclear. The phase composition, film density and hydrogen content present in a DLC film can be tailored by substrate biasing during film deposition to achieve a nearly vanishing friction coefficient. Furthermore, nitrogen doping in DLC films significantly improves wear resistance, and sliding occurs in a nearly wearless regime. Undoped and nitrogen-doped DLC films exhibit a nearly frictionless value with ultra-low wear behavior when tests are performed in argon, nitrogen and methane atmospheres. The antifriction and antiwear properties of the DLC films were improved with the reduction of adsorbed oxygen impurities on the film surface. This behavior was understood by correlating the oxygen impurities present at the surface/subsurface region of the DLC film while using x-ray photoelectron spectroscopy and depth-resolved Auger electron spectroscopy.

We report here the design of ultra high vacuum (UHV) compatible pulsed positron beam lifetime system, which combines the principles of a conventional slow positron beam and RF based pulsing scheme. The mechanical design and construction of the UHV system to house the beam has been completed and it has been tested for a vacuum of ∼ 10−10 mbar. The voltages applied to the drift tube as a function of positron energies have been optimized using SIMION.

The scaling behavior of hardness with ligament diameter and vacancy defect concentration in nanoporous Au (np-Au) has been investigated using a combination of Vickers Hardness, Scanning electron microscopy, and positron lifetime measurements. It is shown that for np-Au, the hardness scales with the ligament diameter with an exponent of −0.3, that is, at variance with the conventional Hall-Petch exponent of −0.5 for bulk systems, as seen in the controlled experiments on cold worked Au with varying grain size. The hardness of np-Au correlates with the vacancy concentration CV within the ligaments, as estimated from positron lifetime experiments, and scales as CV1/2, pointing to the interaction of dislocations with vacancies. The distinctive Hall-Petch exponent of −0.3 seen for np-Au, with ligament diameters in the range of 5–150 nm, is rationalized by invoking the constrained motion of dislocations along the ligaments.

Positron beam studies on the silicidation in Pd/Si, Ni/Si and Co implanted Si thin film systems are presented. In the case of Pd/Si, the evidence for the occurrence of divacancies across the Pd2Si/Si interface consequent to Pd2Si formation is shown. In Ni/Si system, the identification of a multitude of silicide phases of Ni2Si, NiSi and NiSi2 is obtained from depth-resolved S-parameter, which is corroborated with GIXRD and AES results. In the case of the Co implanted Si, the recrystallization of amorphized silicon and the formation of CoSi2 precipitates in Si are brought out clearly.