[en] This progress report gives an account of the various research and developmental activities carried out at the Materials Science Division of the Indira Gandhi Centre for Atomic Research, Kalpakkam during 1991-93. It also gives a summary of the results of the research activities, describes the experimental facilities and also list the publications

[en] Short communication

[en] By exploiting the special BIOS interrupt (INT 1CH) of PC in conjunction with a compatible high-voltage controller card and menu-driven control program, we report here the automation of variable low-energy positron beam experiments. The beam experiment consists of monitoring the Doppler broadening lineshape parameters corresponding to the annihilation 511 keV γ-ray at various positron beam implantation energies. The variation and monitoring of the sample high voltage, which determines positron beam energy, is carried out using a controller add-on card coupled to a 0-30 kV high-voltage unit. The design features of this controller card are discussed. This controller card is housed in a PC, which also houses a multichannel analyser (MCA) card. The MCA stores the Doppler energy spectrum of the annihilation γ-ray. The interactive control program, written in Turbo C, carries out the assigned tasks. The design features of the automation and results are presented

[en] Published in summary form only

[en] The role of Hf as an impurity on defect processes in Zr and its alloy forms is of technological importance in reactor environments. Positron lifetime measurements were done at room temperature after each step of isochronal annealing treatment of the irradiated sample from 323K to 1023K in steps of 50K

[en] Positron beam based Doppler broadening measurements have been carried out on Pd/Si thin film system to investigate various aspects of silicidation. Ab-inito calculations of the positron lifetime and Doppler lineshape parameters of Pd, Si and Pd₂Si were also carried out. A comparison of experimental and calculated positron annihilation parameters has been presented. (author)

[en] Depth-resolved positron beam studies have been carried out on Ar-irradiated Si using Doppler S parameter and lifetime measurements. Si samples have been irradiated with 140-keV Ar ions to a dose of 2x10¹³ and 5x10¹⁶ Ar/cm², respectively, so as to produce disordered and amorphous states in near-surface regions. The observed features of the defect sensitive line shape S parameter indicate the presence of small vacancylike defects in the disordered sample and higher-order vacancy clusters in an amorphous sample. Pulsed positron beam lifetime results indicate that the disordered Si sample exhibits lifetime distribution ascribable to mostly divacancies. In the case of an amorphous sample, the lifetime distribution is broad with larger lifetime values indicating the presence of a distribution of large vacancy clusters or nanovoids. By using theoretical lifetime values for Si reported in the literature, an empirical fit to the lifetime variation as a function of vacancy cluster size is obtained. By comparing the experimental lifetime distribution with this data, the vacancy cluster size distribution in disordered and amorphous Si is deduced. In disordered Si, divacancies are found to be the dominant defects species followed by small concentration of V₃. In amorphous Si, nanovoids in the size range of four to seven vacancy clusters are present with V₅ and V₆ clusters being the dominant defect species. The implication of these results is discussed in light of recent computer-simulation studies

[en] Short communication. 2 figs

[en] The ion-induced damage and its effects on amorphization in Si using low energy positron beam (LEPB), which is depth-selective and sensitive to defects have been studied. A Si(100) single crystal of 500 μ thickness has been implanted with 140 keV Ar⁺ ions over a dose range from 5 x 10¹⁴ to 5 x 10¹⁶ ions/cm² at room temperature using 150 keV ion implanter

[en] An ultra high vacuum compatible variable low energy positron beam system has been developed and commissioned. The UHV system consists of three interconnected main parts- a source chamber, a U-shaped beam transport tube and a target chamber. The extraction and focusing of re-emitted slow positrons is carried out in the source chamber. The elimination of fast positrons by velocity selection and transport of slow positrons are achieved by the U-shaped magnetic transport tube. The target chamber houses the target at variable negative voltage for beam energy variation. Various electrostatic lenses and magnetic coils for slow positron beam extraction, focusing and transport have been incorporated. The UHV performance of the system is found to be satisfactory. The functioning of entire positron beam system is checked by measuring the 511 keV annihilation γ-ray spectrum at the target. (author). 7 refs., 3 figs