A. K. Nigam

A study of blistering in Mylar due to H+ ion implantation

Abstract 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 CO 2 are found to be the main components resulting from radiolysis of the Mylar due to H + ion implantation. However, the emission of H 2 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.

Effects of hydrogen bombardment on Ni40Fe6Co20Cr12Mo6B16 amorphous alloy

Abstract The effect of H+ ion implantation at the energy level of 250 keV on the surface behaviour of an amorphous alloy, Ni40Fe6Co20Cr12Mo6B16, in three different conditions, namely the amorphous, crystallized by annealing at 460°C for 20 min and for 60 min, has been studied. It is observed that the material in the amorphous state is highly resistant to blistering in the fluence range 0.72 × 108 to 1.5 × 1019 ions/cm2; however, under identical conditions of irradiation, the material annealed for 20 min is relatively less resistant and the one annealed for 60 min is the least resistant to blistering. A typical surface feature consisting of fine nodules and pinholes is observed to develop due to irradiation, depending on the initial condition of the material and the dose level of implantation. The high resistance of the material against blistering in the amorphous state is explained in terms of a large solubility and low diffusivity of hydrogen, low probability of irradiation-induced disordering, and high strength combined with adequate ductility in the amorphous condition.

Sponge-like blisters on copper by H+-ion implantation at ambient temperatures

325 keV H+-ion implantation was done in annealed polycrystalline copper specimens in the fluence range 2.2-8.4*1018 ions cm-2 at ambient temperature. SEM examination of the surface topography showed the occurrence of blistering at 5.2*1018 ions cm-2. Blisters were observed to grow with increasing dose. At 8.4*1018 ions cm-2 severe sponginess localised only to blister skins, in contrast to the porous surface features developed on the whole implanted region by the high temperature (>or approximately=0.5 Tm) implantations, was observed. The present observations are explained in terms of the growth of bubbles contained within the blister skin at its ambient temperature.

Blistering observed in Mylar due to H+-ion bombardment☆☆☆

Abstract 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 CH bond breakage theory due to ion bombardment.

High fluence hydrogen implantation in copper: Blistering and grain boundary movement

Abstract Annealed polycrystalline copper samples are implanted with 325 keV H+ -ions at ambient temperature for total fluences of 2.2–8.4 × 1018 ions/cm2, and are examined using SEM and optical microscope. The critical fluence for blistering is about 5.2 × 1018 ions/cm2. The observations reported are (i) preferential decoration of grain boundaries with elongated blisters which have a tendency of interconnecting each other, (ii) irradiation induced grain boundary movement, (iii) onset of blistering only on few grains and tendency of coalescence, at the critical dose, (iv) spongy blister skins, and (v) simultaneous occurrence of blister exfoliation from the top and from the periphery. The observation (i) is attributed to preferential nucleation of gas bubbles along the grain boundaries and their successive coalescence; (ii) and (iii) are assigned to partial channelling; (iv) is understood to be a consequence of the growth and the coalescence of the bubbles within the skin: and (v) is considered to be the be...

Experimental CO2 evolution curve obtained during 250 keV D+ implantation on Mylar and its theoretical model

The partial pressure variation curve of the evolved CO2 during implantation of 250 keV D+ ion beam in Mylar has been experimentally measured and theoretically explained on the basis of a diffusion based model. Unlike the earlier percolation model, our model explains the rising portion of the curve (i.e. the pre-maximum portion) very satisfactorily. This pre-maximum portion is very important as most of the radiolytic processes take place during this short span, due to the high rate of energy deposition by the ion beam. The reasons for the failure of the percolation model in the pre-maximum portion are also explained.

Effect of Neutron and Proton Irradiation on Some Properties of Kapton

Photoacoustic, dielectric and surface-morphological properties of Kapton* were studied after exposing sheets (25 μm thick) separately to fast reactor neutrons (E>0.1 MeV) and to 250 keV protons up to doses 1.2×1018 (maximum)and 7.0×1015 cm−2, respectively. The photoacoustic spectrum (PAS) of the maximum neutron dose irradiated sample shows the red-shift of the absorption peak from 450 nm to 470 nm, whereas in the proton irradiated (7×1015 cm−2) sample, a new flattened absorption peak appears at λ ≃ 515 nm. There is a net enhancement in the D.C. dielectric constant of about 13% after the maximum neutron dose. It is attributed to the enhanced water absorptivity of the material due to neutron induced radiation damage.

Variation in the fluorine/carbon elemental ratio in PVDF due to 90 keV D+ implantation

Abstract The elemental ratio of fluorine and carbon (F/C) in Polyvinylidene fluoride (PVDF) has been measured using 360 keV D+ RBS with the varying 90 keV D+ ion dose. From a virgin value of 1, this ratio reduces sharply with ion dose and saturates at a value of 0·37 corresponding to a very high fluence of 3·58 × 1016 D+cm−2 (14·30 × 108 Gy). Radiolytically evolved gas analysis (REGA) employing residual gas analyser (RGA) shows radiolytical evolution of HF and H without any indication of carbonous species. A negligible depletion in carbon edge and nearly 60% depletion in the F edge clearly depicts the formation of double bonds in the C-C-C back-bone of the macromolecule without its scission. The depletion profile of F as observed on the edge of C in the RBS spectrum is nearly flat with a tendency to increase in depth. The radiation saturated PVDF having a different F/C ratio is thought to have some exotic physical and chemical properties.

A simple set-up for in-situ observation of the critical dose of blistering during ion implantation in polymers

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.

A modified diffusion-based model for radiolytically evolved gases during ion implantation in polymers

Abstract A refined theoretical model, based on 3-dimensional diffusion equation, has been proposed to explain our earlier experimental results of dynamic partial pressure variation of CO 2 evolved during 250 keV D + ion implantation in Mylar. This model gives a better fit with the experimental points than the percolation model in the pre-maximum as well as in the postmaximum region of the curve. The experimental H 2 evolution curve obtained by Davenas et al. in 500 keV Ar + implantation of PMMA, has also been explained by our model in a much better way than by the percolation model.