Biennial Report 2005-2007 - Saha Institute of Nuclear Physics

154 Biennial Report 2005-075.1.2.8 Rare earth implatation in polymeric thin films deposited on silicon substarteErbium ion implantation in polystyrene thin films has been performed with 40 and 60 keV ions to adose range between 1 × 10 14 and 1 × 10 16 ions/cm 2 . The X-ray reflectivity technique was appliedto determine the ion-induced eroded layer thickness and interestingly, the erosion rate is found todecrease with increasing ion doses exhibiting simple power law behavior of the form (dose) −b . Wepropose the formation of a carbonaceous network at the top surface, which seems to prevent furthererosion of the polymer with increasing the duration of implantation time. These findings mayopen up a possibility of loading a large amount of erbium in a polymer matrix by the implantationtechnique to make it suitable for various optoelectronic applications.M Bhattacharyya, MK Sanyal, TK Chini, P ChakrabortySP5.1.2.9 Morphology of Au nanoparticles formed by magnetron sputtering: ellipsoidsand ringsUltraviolet (UV) visible spectroscopy, atomic force microscopy and grazing incidence X-ray reflectivityhave been used to study morphology of Au nanoparticles grown by direct current (DC)magnetron sputter deposition on hard (glass) and soft amorphous (polystyrene films on quartz)substrates. Au nanoparticles are found to be ellipsoidal showing an increase in ellipticity ǫ [= a/b,a(b)= semimajor (semiminor) axis] with decrease in polystyrene film thickness from 250 to 20 nm,where b remains almost invariant around 3 nm. They sit on top of the film with the semimajor axesroughly parallel to film surface. On glass, the Au film was probed at different stages of growth.After an initial period (1 min) of spheroid nanoparticle formation by dewetting, the coverage wascomplete (as observed from Au optical spectra) and partially wetting islands appeared after 2 minon the Au covered glass surface. After 5 min, these islands formed rings resembling quantum rings.The rings broke up again into islands after 10 min.Sudeshna Chattopadhyay, Subhendu Sarkar, Alokmay Datta, Purushottam ChakrabortySP5.1.2.10 Effect of Polymer Confinement: Tuning Self-Assembled Growth of MonodisperseAu Nanoparticles on Polystyrene FilmsX-ray reflectivity and tapping mode atomic force microscopy reveal that, Au, sputter-depositedon polystyrene films for film thickness ≤ R g (R g being unperturbed polymer gyration radius), diffuseand coalesce slowly, under ambient conditions and predominantly along the polymer surface,to form nanoparticles. The nanoparticles are highly monodisperse, and their in-plane dimensionsincrease with decrease in polystyrene film thickness. The observed directed coalescence is causedby sharply defined, higher surface energy zones ortraps, corresponding to lower cohesion, betweengyration spheres on polystyrene film surface. Lowering of in-plane cohesion and coalescence arefound only when gyration spheres are layered along film depth due to thinning of the polystyrenefilm. The coalescing potential of these traps is given by the spatially localized increase in surface