Site: Philips Research Laboratories
Prof. Holstlaan 4
5656 AA Eindhoven, The Netherlands
Date Visited: 16 October 1997
WTEC: D.T. Shaw (report author), H. Goronkin, M.C. Roco
Philips is one of the most important manufacturers of electronic consumer products in Europe, with annual sales of more than $40 billion. Roughly 70% of the Philips research comes from contracts from the company's product division; the rest is devoted to exploratory research, which typically does not lead to commercial products within three years. Among the exploratory research projects, an estimated 20% are related to nanoparticle/nanostructured materials. The laboratories have a wide spectrum of research activities that are of interest to this study, ranging from nanocrystalline materials synthesis, nanofabrication, and nanocrystal engineering to quantum transport in nanostructures and quantum theory of solids.
Dr. Mark J. VanBommel made a short presentation on nanoparticle coatings for consumer electronic applications (coatings for antiglare, antistatic, and antireflection uses). Depending on their specific applications, these nanoparticles need to have special properties (e.g., high electric conductivity, or low specular optical scattering). Antimony-doped tin dioxide (Sb:SnO2) particles have been used for these applications, as an example. These nanoparticle coatings are typically produced by physical or chemical wet deposition processes. Spray pyrolysis, spinning, or dip coating techniques are usually carried out in a controlled ambient environment. To avoid dull-looking surfaces, the primary particle diameter is usually less than 2 nm. Figure B.2 shows an electron micrograph of these particles. The electrical conductivity can be regulated by controlling the antimony concentration in SnO2.
Dr. A.W.M. (Ton) deLaat discussed briefly the production of nanometer-sized ceramic particles with very low sintering temperatures. Homogeneous green particles are important to prevent defects in sintered products; by using proper dispersants, dense and homogeneous layers have been obtained.
Dr. Erik A. Meulenkamp discussed size determination by absorbance measurements of ZnO nanoparticles and electrochemical properties of ZnO/ITO/glass electrode systems. ZnO nanoparticles produced by physical deposition are irradiated by light of various wavelengths. The shift of the absorbance peaks toward higher energy (or low wavelength) when the size of ZnO particles decreases (Figure B.3) clearly demonstrates the quantum size effect on bandgap energies. Figure B.4 shows the effects of electron accumulation for E < -0.5V in a ZnO/ITO/glass electrode system.
Dr. Bianca M.I. van der Zande, who is on leave from Utrecht University, discussed the generation and optical properties of rod-shaped gold particles with diameters ranging from 10 to 30 nm. Aqueous dispersion of rod-like gold particles is obtained by electrode position in nanopores of anodized alumina. In the VIS/NIR absorption spectra, two absorption maxima are observed: one corresponds to the transverse plasma resonance, and the other to the longitudinal plasmon resonance, which moves to higher wavelengths when the particle aspect ratio is increased (Figure B.4).
Electron micrograph of antimony-doped tin dioxide particles (primary particle size ~20 nm).
Quantum size effect on the absorbance of ZnO.
Normalized experimental VIS/NIR absorption spectra of rod dispersions with aspect ratio L/d = 1 (spherical gold sol), L/d = 4, L/d = 9, and L/d = 13.
From published papers, it is evident that Philips researchers are active in many other topics in nanostructures, including template synthesis of nanowires in porous polycarbonate membranes, self-assembled monolayers of metallic nanoparticles, and luminescence-tuning in semiconducting nanocrystallines.