In situ observation of nanoparticle ordering at the air-water-substrate boundary in colloidal solutions using x-ray nanobeams

Abstract

The nanoscale structuring during evaporation of a droplet consisting of an aqueous colloidal solution of 2 nm gold nanoparticles in water on a silicon substrate is followed in real time. The authors investigated the transfer of lateral order and vertical layering as a function of time at the three-phase contact line air-solution substrate combining a nanometer-sized x-ray beam with a grazing incidence geometry. A pronounced retardation of vertical ordering is observed with respect to lateral ordering. While individual layers are deposited during evaporation of the solvent, the growth parallel to the substrate shows a strongly nondiffusive behavior. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2776850͔Large-scale arrays of ordered nanoparticles are fascinating materials for science and technology, e.g., data storage 1 or DNA sensoring, 2 due to their distinct optical properties. [2][3][4] To deposit the nanoparticle layer on top of the substrate, several methods are available, e.g., vacuum deposition 1,5 and solution casting. Solution casting allows nanostructuring of large-area two-dimensional ͑2D͒ thin films with specific morphology, offering the possibility to design 2D or threedimensional photonic crystals. This method is especially important and applicable in the field of colloidal particles, as colloidal particles are often suspended in aqueous solutions.Nanostructuring, however, is a very complex process involving several mechanisms. 6 The solvent evaporates and increases the concentration of the colloidal particles. The increased evaporation near the contact line drives a convective flow within the drop that transports material toward the periphery. 7 Additionally, an increased solute concentration and a decreased temperature near the three-phase contact line ͑TPCL͒ may trigger solutal 8 and thermocapillary 9 Marangoni flows. Furthermore, the interaction with the substrate 10 and transversal contact line instabilities 11 have to be taken into account. Finally, capillary forces come into play as soon as the solution film has a comparable thickness as the colloidal particles' diameter. 12 Previous studies addressed the ordering of nanoparticles at the liquid-air interface. 13 However, for technical applications it is of great importance to transfer this order to a solid substrate. 14 The interaction with the substrate allows for tuning the arrangement of the nanoparticles and thus the layers' optical properties. Hence, it is only natural to investigate in situ the evolution of ordering at the TPCL liquid-air substrate.Grazing incidence small angle x-ray scattering 5,6 ͑GISAXS͒ has proven to be a well suited technique for realtime studies. Here, the x-ray beam impinges under a small angle ␣ i Ͻ 1°on to the sample surface. 6 We combined a nanobeam small angle x-ray scattering ͑nano-SAXS͒ geometry of ID13 /ESRF with a grazing incidence setup, allowing for nanobeam-grazing incidence small angle x-ray scattering ͑nano-GISAXS͒ experiments. We used the extremely brilliant 300 nm size beam ͑full width at h...

Time-Resolved Ultrathin Cobalt Film Growth on a Colloidal Polymer Template

“…To name just a few, there are vacuum deposition, 9-12 molecular beam epitaxy, 13 pulsed laser deposition, 14,15 dip coating, [16][17][18] and solution casting. 19,20 In general, vacuum deposition of metallic material is the most widely used technique in industrial applications. 21 The aim of our study is to investigate in situ and in real time the growth of an ultrathin metallic layer on a colloidal polymer template.…”

Investigation of surface modification of casein films by rennin enzyme action using micro-beam grazing incidence small angle X-ray scattering

“…External forces or convective flows induced by temperature or pressure gradients could cause deviations from the square root law [24].…”

“…Scattering techniques with micrometer-sized X-ray beams can be combined with high-resolution scans of the sample relative to the X-ray beam. Scans across concentration gradients allow studying structure formation processes [24,26], e.g. structural changes of casein micelles have been investigated in a calcium gradient film by μGISAXS [5].…”

Determination of the local gold contact morphology on a photoactive polymer film using nanobeam GISAXS

“…In terms of using microbeam and sub-microbeam GISAXS experiments in the field of nano-technology, the possibility of having access to a local structure information becomes of increasing importance [52,53]. The availability of nanometer sized X-ray beams will be very beneficial for future developments in this direction.…”