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Fabrication of metal nanoparticles and nanoparticle aggregates onto self-assembled monolayers via organometallic chemical vapor deposition


Aliganga,  Anne Kathrena A.
MPI for Polymer Research, Max Planck Society;

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Aliganga, A. K. A. (2004). Fabrication of metal nanoparticles and nanoparticle aggregates onto self-assembled monolayers via organometallic chemical vapor deposition. PhD Thesis, Johannes Gutenberg-Universität, Mainz.

Fabrication of Metal Nanoparticles and Nanoparticle Aggregates Onto Self-Assembled Monolayers via Organometallic Chemical Vapor Deposition Metal nanoparticles, gold in particular, have been the focus of numerous investigations because of promises offered by their optical, electronic, and chemical properties. Of particular interest are their tunable, electronic, magnetic, and photonic behaviors due to quantum confinement effects, with nanocluster-based devices being envisioned as the next generation in electronics miniaturization. One of the technological challenges is to fabricate robust and organized assemblies of these nanoscale building blocks where the collective structural properties and functions might be manipulated by the nature as well as the composition of the nanoparticles. Among the various techniques developed, self-assembly has been quite effective in creating ordered superlattices of nanoparticles by exploiting the molecular interactions such as van der Waals forces, chemisorptive bonding, electrostatic interactions, etc. A key structural element is the bifunctional bridges, which link the nanoparticles to the substrate surfaces and/or between layers of nanoparticles, such as aliphatic dithiols. This process can be achieved by simple beaker chemistry. In this work, SAMs of alkanedithiol are used as templates for nucleation and growth of nano-sized metal particles prepared via organometallic chemical vapor deposition (OMCVD). The OMCVD process offers an alternative method in the production of ultrathin metal layers and nanostructures. In comparison to the commonly employed colloidal methods, the OMCVD process offers a promising route in tailoring new generation of nanodevices particularly in the fabrication of gold nanoparticles. The OMCVD process provides a good control of the aggregation state of the nanoparticles because the particles are immobilized on the surface and fixed in their morphology. The OMCVD gold nanoparticles are free from encapsulating ligand, which would mean a good flexibility for further functionalization since there is no additional process needed. Thus, providing ease in the construction of electronic devices and sensing purposes. Another important feature the OMCVD gold posseses, is its non-sphericality, which results in more interesting and exciting plasmon resonances patterns than the spherical-shaped particles. This might give more tunability of the plasmon resonant particles with tailored properties for specific applications. In order to enhance the design and optimization of applications based on OMCVD gold nanoparticles, this study presents some basic properties of the particles prepared on self-assembled monolayers using the OMCVD process. In this study, a detailed investigation of the matrix of OMCVD gold, specifically, SAMs of 1-octanethiol (C8-T) and 1,8-octanedithiol and its binary mixtures was performed where two major issues are being addressed. Using SDMS, XPS, SPM and SPR techniques, first, the relationship between the mole ratio of C8-T and C8-DT molecules in solution versus their corresponding mole ratio in the binary mixed SAMs. And second, the distribution of C8-DT in the matrix of C8-T on the surface, wherein, phase separation was observed between C8-DT and C8-T SAMs. The fabrication of gold nanoparticles onto SH terminated SAMs via the OMCVD process using trimethylphosphinegoldmethyl ((CH3)3PAuCH3) as the volatile organometallic precursor was carried out successfully without contaminations of the phosphine ligand on the surface. This study mainly addresses the characterization of the OMCVD gold, e.g. control of growth, size distribution, and spectroscopic characterization, revealing the basic properties of gold, thus, opening new dimensions regarding to the gold's potential applications in the future. The technological prospects of OMCVD gold are enormous but at this point, there are still several things that need to be explored, e.g. its electrochemical properties, coulomb staircase, fluorescence enhancements and other optoelectronic properties that may pave a path towards the optimization of its potential applications. In the quest towards fabrication of molecular electronics, in which the three-dimensional positions of nanoparticles on surfaces must be controlled precisely, preferrably, at the level of individual particles, we were able to demonstrate for the first time the possibility of fabricating a well-defined alignment of the OMCVD gold nanoparticles onto patterned SAMs by employing the favoured bottom-up method of fabrication. The deposition of other metals like, mercury and palladium onto SAMs was also demonstrated in this study. In particular, in the OMCVD of palladium, results about further thiol functionalization of Pd was presented, which are helpful in employing the OMCVD Pd for the construction of a relatively cheap integrated optical sensor devices. In the emerging disciplines of nano-engineering, nano(bio)electronics, and nano-photonics, the OMCVD process proved promising and may offer new dimensions to these areas with particles possessing new opto-electronic properties.