• D K Avasthi

      Articles written in Bulletin of Materials Science

    • Foreword

      D K Avasthi E S Dwarakadasa

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    • Developments in nuclear techniques for hydrogen depth profiling

      D K Avasthi

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      Hydrogen plays a crucial role in the properties of various materials, devices and in growth of hydrogenated amorphous materials. Therefore, its quantification and determination of concentration at various depths is of immense interest. Among various techniques of hydrogen depth profiling, the nuclear techniques being non-destructive in nature are widely used. Elastic recoil detection analysis (ERDA) with helium ions was first used for hydrogen depth profiling. Later on, the heavy ions were utilised due to certain advantages. It has been shown recently by us that H alongwith other elements in thin film up to Ca can be detected simultaneously with heavy ion ERDA, if the elements being detected are well separated in masses. It also has been shown that even the neighbouring elements such as C, N, O alongwith H can be detected provided a ΔE-E detector telescope is used in ERDA. The time of flight (TOF) with ERDA, nuclear reaction analysis (NRA), neutron TOF are other nuclear techniques such as hydrogen loss during the measurement, which must be taken into account for accurate and reliable results. A scenario of developments in nuclear techniques with suitable examples is given in this brief review.

    • Effect of heavy-ion irradiation on dielectric constant and electrical conductivity of doped and undoped nonlinear substance

      K Somashekhara Udupa P Mohan Rao Sriramana Aithal A P Bhat D K Avasthi

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      Implantations were carried out on gel-grown potassium dihydrogen orthophosphate (KDP) and those doped with magnesium oxide (MgO) single crystals using 100 MeV Ag+ heavy-ion beam of 15 UD 16 MV pelletron accelerator. To conduct a comparative study, measurements were carried out in the temperature range 243 K-403 K at frequencies ranging from 1 kHz-1 MHz on irradiated and nonirradiated nonlinear samples. It was observed that the mechanism of dielectric behaviour varied with frequency, temperature and ion irradiation. Further, implantation produced erratic variation in the conductivity both in the intrinsic and extrinsic regions, and also in the dielectric behaviour of the substance. The property of sensitive dependence on initial conditions, namely, chaos had set in after ion irradiation. However, the doping effect had not completely terminated the above transition, leading to chaos in the nonlinear medium.

    • 12C5+ radiation effects in SR-86 track recording polymer

      H S Virk G S Randhawa R Thangaraj D K Avasthi K Asokan

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      The samples of SR-86 polymer were irradiated with12C5+ ions of energy 5·0 MeV/u using fluences of 1011−1014 ions/cm2 at NSC Pelletron in a high vacuum scattering chamber. The optical studies show an increase in absorption of UV or IR in the shorter wavelength region (250–500 nm). The study also reveals that the increase in radiation dose extends the optical absorption region to longer wavelengths. It is observed that the bulk etch rate of this polymer is enhanced after heavy ion irradiation.

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