In recent years the properties and applications of ZnO nanomaterials has been extensively examined, partly due to the potential of ZnO as UV and visible light emitter and detector. Much of the previous work concern synthesis and growth of ZnO in different forms. In this survey, we have primarily studied commercially available nanoparticles and how they can be distributed on surfaces, aiming for future applications in e.g. photovoltaic devices. Later custom synthesised ZnO particles will be used in collaboration with Prof. Gunnar Westin at Uppsala University.
ZnO nanoparticles, non-coated and organo-silane coated, with an average size of 70 nm from Alfa Aesar GmbH & Co KG, Germany, have been used in different dispersions for application on surfaces and the aim has been to achieve a controllable distribution of particles. In order to achieve this, different substrate preparations, solvents for dispersion and application methods have been used. Characterisation of the particle distribution has been done with Optical Microscopy (OM), Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The chemical and the crystallographic properties of the particles have also been investigated using Auger Electron Spectroscopy (AES) and X-ray Diffraction (XRD).
The substrates used are Si(001) with different preparations to create hydrophobic or hydrophilic surfaces. Nanoparticles were applied to the substrates using drop-coating and spin-coating. Several different solvents, including water, 1,2-PMA and chloroform, have been used for dispersions, yielding the possibility to use vapour pressure and solubility parameters to control the distribution.
Separated particles are observed in all of the examined samples below a certain ZnO concentration. The amount of separated particles is dependent on the surface used, the solvent and the preparation procedure. A trend that can be followed from micro-scale to nano-scale is that smaller agglomerates correspond to more separated particles. Particles of different forms have been identified for later characterization. |