Investigating the layer-by-layer growth of oriented multilayers of metal-bis(phosphonate): Structure, composition and nonlinear optical properties

The method of layer-by-layer growth is investigated as a route to thin films with second order NLO properties. To incorporate such properties into films, the organic molecules used must contain conjugated {dollar}pi{dollar} systems situated between electron donor and acceptor groups to fulfill the need for a polarizable moiety situated in an anharmonic potential. These systems must be oriented within the film such that the bulk structure is noncentrosymmetric. To accomplish this, {dollar}alpha,omega{dollar}-bis(phosphonate) molecules are used that have one terminal phosphonate group "protected" in ester form, while the other group is a free phosphonic acid which will bind to metal-primed Si. The ester must be hydrolyzed for layering to continue, and this is accomplished by heating the films in 0.5M HCl overnight. This "deprotection" method was shown to be efficient by growing films on Cab-O-Sil and determining the extent of hydrolysis through use of Solid State {dollar}sp{lcub}31{dollar}P NMR, as described in Chapter III.; This layering scheme was used to produce films of Hf and aryl-(4-diethylphosphonate)decylphosphonic acid ether on Si, as discussed in Chapter IV. The films produced had reasonable thicknesses and one film had a reasonable index of refraction. The other film was proposed to be less dense or patchy due to its smaller index of refraction. Second harmonic generation (SHG) indicated the signal from the films was destructively interfering with the signal from the substrate. The less dense film was also shown to be more disordered by SHG. Near field scanning optical microscopy (NSOM) showed large troughs with depths equivalent to the total thickness at places throughout the films. More of these troughs were observed on the less dense film.; Films of either Hf or Zr and bis(1-ethyl)3-(N-methyl((4-((4-phenylphosphonic acid)azo)-phenyl)amino)decyl)phosphonate on both Si and glass were also produced as discussed in Chapter V. UV-VIS spectroscopy indicated the deprotection method was protonating the azobenzene molecule which was preliminarily seen to adversely affect the SH response from these films. Measures were taken to minimize protonation of the chromophore, and although the resulting films were thinner than predicted, they were shown to produce the expected SH response of increasing intensity with increasing number of layers.; This dissertation work is summarized and future plans are proposed in Chapter VI.