Feb 27, 2009
Nanostar tips light up in SPM
Surface probe microscopy is typically used to capture topographical data on the nanoscale. However, a large amount of additional information can be obtained by exploiting electrostatic or magnetic interactions between the cantilever tip and the scanned surfaces. Striking examples are the identification of inert coating layers and morphological effects.
Researchers at the University of Vigo, Spain, have been using colloid chemistry for years to synthesize various types of nanoparticles with controlled size, morphology and surface properties. Although several standard techniques have been used to characterize the nanoparticles, certain properties require more sophisticated imaging methods, such as those provided by scanning probe microscopy.
For example, using both magnetic force microscopy (MFM) and electrostatic force microscopy (EFM), it is possible to identify magnetic or conducting regions within nanoscale materials. This has been shown nicely in the latest study on iron oxide and gold particles with various geometries, encapsulated by uniform silica shells. Careful adjustment of the lift height has been essential to account for the insulating effect of the silica shells.
Additionally, and probably more importantly, application of a controlled bias on the surface during EFM imaging of anisotropic gold nanoparticles with sharp tips and edges allows the identification of areas with higher charge localization. This is particularly important in nanostars, where sharp tips provide excellent localization sites. This may have important implications regarding the use of such nanostars as surface enhanced Raman scattering substrates with intrinsic hot spots, as has been recently suggested.
The researchers presented their work in Nanotechnology.
About the author
The work was performed at the Colloid Chemistry Group, University of Vigo, Spain. Dr Jessica Pacifico has been a postdoctoral researcher for two years, funded by the Spanish Ministry of Science, and is working on SPM and SNOM imaging of nanoparticles and their assemblies. Prof. Luis M Liz-Marz´n is head of the Colloid Chemistry Group and his current research interests include the synthesis of metal, semiconductor and magnetic nanoparticles with controlled composition, size and morphology, as well as the creation of colloidal composites and nanoparticle arrays in two and three dimensions, and their applications in biosensing and ultrasensitive detection.