Browsing by Author "V. Shrinet"

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A simple set-up for in-situ observation of the critical dose of blistering during ion implantation in polymers
(1984) V. Shrinet; U.K. Chaturvedi; S.K. Agrawal; A.K. Nigam
A simple set-up was designed and fabricated for in-situ studies of the critical dose of blistering and changes on the surface morphology of the polymers during ion-implantation. Mylar, a very important polymer, stable at high temperatures, which shows severe blistering at dose level ∼- 7 × 1015, 250 keV H+ ions cm-2, was chosen for study with this set-up. The design of t some initial results are discussed here. Some major limitations are also described. © 1984.
A study of blistering in Mylar due to H+ ion implantation
(1986) V. Shrinet; U.K. Chaturvedi; A.K. Nigam
A comprehensive study of blistering of Mylar under 100 and 250 keV H+ -ion implantation has been made. The conversion of blisters to "Karnavalaya" and vice-versa due to electron beam excitation during scanning electron microscopy of the implanted sample is found to be an analog of similar events taking place during ion implantatio. This results in the development of complex blisters. The critical dose for blistering is found to be dependent on the residual surface stresses. It is higher when the stresses are compressive as when tensile. The gases emitted during ion implantation were analysed by a residual gas analyser. CO and CO2 are found to be the main components resulting from radiolysis of the Mylar due to H+ ion implantation. However, the emission of H2 in this case remains inconclusive due to various experimental limitations. Various observed features on the Mylar surface after ion implantation were successfully explained on the basis of a proposed model of blistering based on the micro-structure of semicrystalline polymers. © 1986.
Blistering observed in Mylar due to H+-ion bombardment
(1983) V. Shrinet; U.K. Chaturvedi; S.K. Agrawal; Vakil Singh; A.K. Nigam
So far the blistering phenomenon due to ion implantation has been observed in metals and alloys, but no blistering has been reported in polymers like Mylar etc. A severe blistering in Mylar (polyethylene teraphthalate) has been observed by us, due to 250 keV H+-ion bombardment up to a dose level of 7×1015 ions/cm2, at ambient temperature. In metals and alloys the blistering is due to the pressure built up by the coalescence of the implanted gaseous species. However, in Mylar the cause is entirely different. In fact, it is attributed to the hydrogen gas released on account of the breakage of aliphatic C-H bonds of monomer, due to ion implantation. Very interesting features, like uniform unexfoliated circular blisters, circular rings (Karnavalayas) and black dots of different sizes along with their development sequence, have been observed. The observed features are explained on the basis of the aliphatic CH bond breakage theory due to ion bombardment. © 1983.
Dynamic balancing of Wheatstone bridge with two thin-film arms: Theory and its experimental verification
(1986) U.K. Chaturvedi; V. Shrinet; A.K. Nigam
A theory for the dynamic balancing of the double thin-film arms Wheatstone bridge, when both of its sensor arms are growing in thickness in vacuum, has been developed. Rate of growth of the imbalancing signal, bridge sensitivity at the null balance, and its decay with the growth of the sensor arm thickness are derived and discussed. It is shown that as long as the bridge remains dynamically balanced, the ratio of the deposition rates of the films on the sensor arms R and S is proportional to the external resistance ratio P/Q. Hence, if the bridge is kept balanced by the feedback system, the composition of the film codeposited on a common substrate will remain constant which can, however, be varied by changing the ratio P/Q. An experiment was performed to test the validity of this theory by evaporating Cu and Cr separately on the two sensor arms of the bridge in the same vacuum chamber. The vapor pressures of both the metals were recorded simultaneously by a RGA scanning 50-70-amu range. It was found that as long as the bridge remains balanced, the ratio p Cu/pCr remains constant. In contrast, when the bridge is imbalanced with either polarity, pCu/pCr varied in either direction from this constant value. Further, for a ±10% deviation in the pCu/pCr from the constant ratio, the signal grows at a rate of ∼10 μV s-1. This signal is found to be capable of electronic feedback control of the evaporation system.
EFFECT OF NEUTRON AND PROTON IRRADIATION ON SOME PROPERTIES OF KAPTON.
(Plenum Press, 1984) V. Shrinet; U.K. Chaturvedi; S.K. Agrawal; V.N. Rai; A.K. Nigam
[No abstract available]
Formation of concentric rings on the flaked surface of Mylar due to 250-keV H+-ion implantation
(1986) U.K. Chaturvedi; V. Shrinet; A.K. Nigam
Concentric rings formed on the flaked surface of Mylar after 250-keV H+-ion implantation (fluence: 8×1015 cm-2) have been observed. Unlike those in metallic glasses and in Si single crystals where similar features have been observed due to MeV-energy He+ implantation, the number of these rings is very limited. In some cases, several groups of such rings have been observed in a single flaked blister. The cause of formation of such features is discussed in the light of existing theories. © 1986 The American Physical Society.
Recovery of the electrical insulation of a van de Graaff accelerator's charging belt by vacuum drying
(1985) V. Shrinet; N.L. Singh; S.K. Agrawal; G.P. Mishra; A.K. Nigam
The insulation of a moisture exposed “leaky” charging belt of AN-400 Van-de-Graaff Accelerator was successfully restored by vacuum drying. Although the drying time is of nearly one week, the technique is comparatively easy, risk free and superior to other alternative techniques and does not require dismantling of the belt. Copyright © 1986 by The Institute of Electrical and Electronics Engineers, Inc.
Role of local temperature rise in stress channel production due to ≥350 keV proton implantation on Mylar surface
(1986) V. Shrinet; U.K. Chaturvedi; A.K. Nigam
The production of radial stress channels in the unimplanted zone but along the boundary of the circular beam spot of Mylar surface implanted at H + ion energy >or=350 keV has been explained on the basis of severe local temperature rise due to beam heating. On account of this temperature rise the irradiated zone melts and the radial channels are generated due to radial compressive stress along the boundary on cooling. The sharp decrease in the critical dose for the onset of blistering with a beam energy is attributed to the increase in gaseous diffusivity of evolved gases with local temperature rise which results in a faster coalescence of gas and earlier blistering.