M.B. Kurup

Ion beam mixing studies in the Sn-Si system

Abstract The process of ion beam mixing in the Sn-Si system is investigated by varying both the incident Ar+ ion energy (100–220 keV) at a fixed dose (2 × 1016/cm2) and the fluence (5 × 1015/cm2− 5 × 1016/cm2) at a constant energy (130 keV). The analyses of the spectra. obtained from Rutherford backscattering (RBS) of 3 MeV alpha particles, have shown that, in these samples (i) the width of the intermixed Sn-Si region increases as the Ar+ energy or fluence is increased (ii) the number of Si atoms/cm2 increases linearly with Ar+ dose and (iii) no significant penetrating tail is present in the Sn profile. From conversion electron Mossbauer (CEM) studies of these systems, it is observed that, at the most, about 40% of Sn in the intermixed layer contributes to form the Sn(1−x)Six compound. It is deduced from these results that x is in the range 0.5 ≦ x ≦ 0.8. These observations also suggest a large transport of Si atoms into the Sn layer, possibly due to radiation damage effects caused by Ar+ ion bombardment.

Investigations of Ar+ implantation and proton irradiation of amorphous Fe40Ni40B20 samples by Mössbauer techniques

The effect of the implantation of 150 keV Ar+ ions at different doses on the surface of amorphous Fe40Ni40B20 and the changes in the bulk properties following proton irradiations are investigated by conversion electron and transmission Mössbauer spectroscopy respectively. In the former case a correlation between the total Mössbauer absorption and the total energy deposited by incident Ar+ ions is established, indicating the development of certain stresses in the material, affecting the inter and intra molecular bonding in the near surface region. On the other hand, the proton irradiation seems to cause a reorientation of the atomic spins and also the formation of an additional Fe or Fe−Ni rich phase in the sample. Also the low field A.C. susceptibility is found to decrease as a function of the dose of incident protons. Possible reasons for the above behaviour are discussed.

Investigation of ion beam induced mixing in PdSi, SnSi and WSi systems

Abstract Systematic studies of the ion beam mixing are carried out with 70–250 keV Ar+ ions in the dose range 5 × 1015 to 5 × 1016 ions/cm2 in Pd Si , Sn Si and W Si systems. Rutherford back scattering measurements with 2–3 MeV a-particles have shown that (i) the formation of Pd silicide is dominated by a cascade mixing process (ii) the Sn Si system is more complex and a composition like SixSn(1−x) is formed in the intermixed region with 0.5 Si system for room temperature Ar+-bombardments.

Estimation of oxygen content in high Tc superconductors: An accelerator based method☆

Abstract It is now well known that the role played by oxygen is very important for the occurrence of superconductivity in the 1-2-3 type YBa 2 Cu 3 O 7−x compounds. We have made an attempt to estimate the oxygen content relative to that of Ba in these compounds after various types of heat treatments, using the resonance elastic scattering and Rutherford backscattering of 3.01 MeV alpha particles. It is consistently observed that those samples, which show good superconducting properties, also contain relatively higher oxygen content (6–16%) as compared to non-superconducting ones. However, it is difficult to make absolute determinations of the oxygen content by this technique. The oxygen content in these samples has also been determined by a chemical method. The two results are compared and their relative merits and disadvantages are discussed.

Electrical conduction in ion implanted Nylon-6 films

Abstract The changes in the electrical properties of Nylon-6 films after implantation with both alkali ions (Li + , Na + and K + ) and an inert ion (Ar + ) have been investigated for different implantation fluences and energies. A decrease in the resistivity of the sample by about six orders of magnitude is observed in many of the implanted samples. The ESR signals from these samples show the formation of free radicals dependent on ion fluence and energy. The temperature dependence of the resistivity is consistent with a model of carrier transport due to carriers hopping between electrically isolated conducting islands produced by ion implantation. No systematic and significant difference was observed in the behaviour of samples due to implantation with alkali ions vis-a-vis the inert ion.

Lattice location of Hf implanted in cubic Al, Cu and Ag host metals

Abstract Investigations regarding the location of implanted 178 Hf at 110 keV in Al, Cu and Ag single crystals by the channeling technique have revealed that in Al and Ag the Hf ions occupy substitutional sites. The effect of a large disparity in the masses of the impurity Hf and the host Al is reflected in a 15% lower minimum yield and a 5% larger width of the channeling dip for the Hf as compared to Al. In Cu the substitutionality is only 61%, at the same time the impurity ions are displaced by 0.05 to 0.07 A from a truly substitutional site. These results are discussed in terms of the differences in electronegativities and atomic radii of the impurity and the host atoms.

Electric quadrupole interaction at181Ta in RNi5 compounds

The time differential perturbed angular correlation measurements in PrNi5, NdNi5, GdNi5, DyNi5 and ErNi5 rare-earth intermetallics with181Ta as probe nuclei have revealed that these impurity nuclei experience a non-axial electric quadrupole interaction. In all the cases, except in GdNi5, the interaction frequency has a single value in the range 15–20 MHz with asymmetry parameterη ∼ 0.98. In GdNi5, however, there are two interaction frequencies (13.61 MHz and 26.89 MHz), the former being the dominant one (90%) withη ∼ 0.35 and the latter (10%) withη ∼ 0.98. It is concluded that in all cases the probe nuclei experiencing the highly asymmetric electric field gradient (efg) occupy the unique Ni(3g) site. Annealing studies have shown that in the case of GdNi5 the interaction gets highly damped, while there is negligible effect in the other cases. The temperature variation of the efg in all cases seems to follow the empiricalT3/2 relation.

A versatile PC based control system for channeling experiments

Abstract A PC based control system for aligning the low index directions of a single crystal target with that of a charged particle beam from an accelerator has been designed. Two stepper motors are employed to control the tilt (θ) and rotation (φ) of the target mounted on a double axis high precision goniometer. A user friendly software using BASIC language is developed for controlling the motors and acquiring data with two detectors simultaneously. Many additional features are also included in the design of the system.

L X-RAYS FROM 64 MEV IODINE PROJECTILES IN COLLISION WITH VARIOUS GAS TARGETS

L x-rays from 64 MeV iodine projectiles in collision with various gas targets, , have been studied. The x-ray intensity ratio is found to be weakly dependent on between and Ar, in contrast to a sharp decrease between C and Al, reported by Datz et al using thick solid targets. Differences in the measured intensity ratio of iodine with 7+ and 24+ charge states impinging on Kr target establishes the minor role of the electrons in the N shell of the projectile in the x-ray production mechanism. The data also support the MO correlation rule of Eichler et al for the asymmetric collision systems.

Electrical and structural properties of Ar+ implanted nylon-6 films

The changes in the structural and electrical properties of nylon-6 films after implantation with an inert gas ion such as Ar + , with energy of 285 keV and at different dose rates (10 14 to 10 17 ions cm -2 ), have been investigated. The conductivity, calculated using the projected range as the thickness of the implanted layer, increases by about four to five orders of magnitude for a dose rate of 5 x 10 15 ions cm -2 . This is the result of the formation of dangling bonds and free radicals due to implantation. The concentration of free radicals at room temperature measured using an electron spin resonance spectrometer shows that it is proportional to the dose rate up to a certain value, beyond which irradiation-induced damage sets in. The Fourier transform infra-red absorption spectra of the samples indicate certain structural changes due to ion implantation.