Manipulating the Assembly of Spray-deposited Nano-colloids: in situ Study and Monolayer Film Preparation

Fabrication of nanoparticle arrays on a substrate is one of the most concerned aspects for manipulating assembly of nanoparticles and preparing functional nanocomposites. Here, we studied in situ the assembly kinetics of polystyrene nanocolloids by using grazing incidence small-angle X-ray scattering. The structure formation of the nanoparticle film is monitored during air-brush spraying, which provides a rapid and scalable preparation. By optimizing the substrate temperature, the dispersion of the nanocolloids can be tailored to prepare monolayer film. The success of the monolayer preparations is attributed to the fast solvent evaporation which inhibits the aggregation of the nanocolloids. The present study may open a new avenue for the manufacture-friendly preparation of well-dispersed nanoparticle thin films.S.Y. acknowledges the kind financial support from Knut and Alice Wallenberg Foundation

Electronic excitation induced structural modification of FeCo nanoparticles embedded in silica matrix

Electronic excitation mediated energy loss by 120 MeV Au9+ swift heavy ions (SHIs) results in significant structural modifications of FeCo nanoparticles embedded in thin SiO2 matrix. The variations in local atomic structure and particle size/shape at different irradiation fluences are probed by extended x-ray absorption fine structure spectroscopy (EXAFS) and grazing incidence small angle x-ray scattering (GISAXS). The crystallinity and ordering of the films are found to first decrease and then increase with fluence. The observed alterations in co-ordination number of Fe/Co from EXAFS are correlated primarily with particle size modifications due to a transient thermal spike generated in the embedded nanoparticles by SHIs. The role of hydrogen desorption from nanoparticles is also highlighted

Tailoring of uniaxial magnetic anisotropy in Permalloy thin films using nanorippled Si substrates

In this work the investigation of in-plane uniaxial magnetic anisotropy induced by the morphology due to ion beam erosion of Si(1 0 0) has been done. Ion beam erosion at an oblique angle of incidence generates a well-ordered nanoripple structure on the Si surface and ripple propagates in a direction normal to ion beam erosion. Permalloy thin films grown on such periodic nanopatterns show a strong uniaxial magnetic anisotropy with easy axis of magnetization in a direction normal to the ripple wave vector. The strength of uniaxial magnetic anisotropy is found to be high for the low value of ripple wavelength; it is decreasing with increasing value of ripple wavelength. Similarly, the strength of uniaxial magnetic anisotropy decreases with increasing Permalloy film thickness. Grazing incidence small angle x-ray scattering data reveals an anisotropic growth of Permalloy thin films with preferential orientation of grains in the direction normal to the ripple wave vector. Permalloy thin film growth is highly conformal with the film surface replicating the substrate ripple morphology up to a film thickness of 50 nm has been observed. Correlation between observed uniaxial magnetic anisotropy to surface modification has been addressed

Direct Observation of Crystallization through Surface Wrinkling in Polymer Thin Film

Poster presented at the DGP Verhandlungen, held in Berlin (Germany) on March 15-20th, 2015.Polymer crystallization is a well concerned and yet unclear phase transition from amorphous coils to well organized nanoscale lamellae. Among the research areas of interest are fundamental issues relating to the early stages of polymer crystallization.1,2 Here we explore the structural transition at the early stages of ordering towards crystallization in diblock copolymer thin films. The structure change at early stages of crystallization is unraveled from a perspective of cooling induced density change. The diblock copolymer thin film offers a well confined crystallization case where the density change can be linked with the lateral molecular diffusion. Moreover, the cooling induced surface wrinkling promotes the nucleation and crystal growth in polymer. These findings provide us a new perspective to understand the whole scenario of polymer crystallization

Enhancement in field emission current density of Ni nanoparticles embedded in thin silica matrix by swift heavy ion irradiation

The field emission (FE) properties of nickel nanoparticles embedded in thin silica matrix irradiated with 100 MeV Au+7 ions at various fluences are studied here. A large increase in FE current density is observed in the irradiated films as compared to their as deposited counterpart. The dependence of FE properties on irradiation fluence is correlated with surface roughness, density of states of valence band and size distribution of nanoparticles as examined with atomic force microscope, X-ray photoelectron spectroscopy, and grazing incidence small angle x-ray scattering. A current density as high as 0.48 mA/cm2 at an applied field 15 V/μm has been found for the first time for planar field emitters in the film irradiated with fluence of 5.0 × 1013 ions/cm2. This significant enhancement in the current density is attributed to an optimized size distribution along with highest surface roughness of the same. This new member of field emission family meets most of the requirements of cold cathodes for vacuum micro/nanoelectronic device

Manipulating the Assembly of Spray-Deposited Nanocolloids: <i>In Situ</i> Study and Monolayer Film Preparation

Fabrication of nanoparticle arrays on a substrate is one of the most concerned aspects for manipulating assembly of nanoparticles and preparing functional nanocomposites. Here, we studied <i>in situ</i> the assembly kinetics of polystyrene nanocolloids by using grazing incidence small-angle X-ray scattering. The structure formation of the nanoparticle film is monitored during air-brush spraying, which provides a rapid and scalable preparation. By optimizing the substrate temperature, the dispersion of the nanocolloids can be tailored to prepare monolayer film. The success of the monolayer preparations is attributed to the fast solvent evaporation which inhibits the aggregation of the nanocolloids. The present study may open a new avenue for the manufacture-friendly preparation of well-dispersed nanoparticle thin films

Preparation of long-range ordered nanostructures in semicrystalline diblock copolymer thin films using micromolding

Long-range ordered nanostructures are prepared in the poly(styrene)-block-poly(ɛ-caprolactone) diblock copolymer thin films using micromolding. We evaluated the change in crystallinity based on grazing-incidence X-ray diffraction and proved that the crystallinity increased with the decrease of the mold size. This means that ordered nanostructures with atomic length scale order can be adjusted by tuning the mesoscale confinement. The inherent mechanism was the cooperation of geometric confinement, microphase structure and surface-induced ordering of PS-b-PCL in the melt, which paved the way for the subsequent crystal growth. These findings establish a route to promote the cost-effective nanofabrication by combining the mature microfabrication technique with the emerging directed self-assembly of block copolymers

Preparation of long-range ordered nanostructures in semicrystalline diblock copolymer thin films using micromolding

Long-range ordered nanostructures are prepared in the poly(styrene)-block-poly(ɛ-caprolactone) diblock copolymer thin films using micromolding. We evaluated the change in crystallinity based on grazing-incidence X-ray diffraction and proved that the crystallinity increased with the decrease of the mold size. This means that ordered nanostructures with atomic length scale order can be adjusted by tuning the mesoscale confinement. The inherent mechanism was the cooperation of geometric confinement, microphase structure and surface-induced ordering of PS-b-PCL in the melt, which paved the way for the subsequent crystal growth. These findings establish a route to promote the cost-effective nanofabrication by combining the mature microfabrication technique with the emerging directed self-assembly of block copolymers