We have investigated the influence of the interplay of the temperature and the water concentration in the adsorption solution on the growth of self-assembled monolayers on silicon using octadecyltrichlorosilane as the precursor. Toluene has been used as the solvent. The morphology of the submonolayer films has been investigated by atomic force microscopy (AFM). The surface coverages have been determined both with ellipsometry and through quantitative evaluation of AFM images. The size distribution of species in the precursor solution has been studied with dynamic light scattering. The influence of water concentrations between 8 and 18 mmol/L has been investigated in the temperature range from 2 to 35 degrees C. Dynamic light scattering revealed a unimodal size distribution of ordered aggregates in solution with a hydrodynamic radius of 200 nm regardless of the temperature and water concentration. However, formation of these features was faster at higher water contents and lower temperatures. Moreover, a characteristic temperature, which was higher for higher water concentrations, was found, above which such aggregates could not be detected anymore. Below this temperature an increase of the aggregate concentration has been observed until a plateau had been reached within a temperature range of approximately 5 degrees C. AFM measurements and ellipsometry on the corresponding submonolayer films showed that this temperature range is also associated with a transition from fast growth via characteristic fractally shaped islands to comparatively slow homogeneous growth via adsorption of individual molecules. The results are discussed in terms of diffusion and adsorption limitations.

The growth of self-assembled monolayers from octadecyltrichlorosilane (OTS) on modified silicon surfaces has been investigated. The influence of different immersion times in a deactivation reagent on the growth mechanism and the ordering of the films has been studied. Characterization of the films and the submonolayer coverage has been performed with tapping mode atomic force microscopy, ellipsometry, and infrared spectroscopy. We found that a deactivation of active sites led to a higher mobility of adsorbed molecules on the surface resulting in circular islands of highly ordered alkylsiloxane. However, upon prolonged immersion in OTS these ordered islands did not continue to grow and full monolayer coverage could not be obtained. Instead, an exchange reaction with the deactivation reagent leading to a disordered film between the ordered islands was observed. This was confirmed by external reflection infrared spectroscopy.

The growth of self-assembled monolayers of alkylsiloxanes on silicon surfaces through adsorption of alkyltrichlorosilanes at various concentrations in toluene has been investigated. The influence of high alkylsilane concentrations up to 50 mmol/L on the ordering of the films has been studied. Characterization of the films has been performed with tapping mode atomic force microscopy and ellipsometry. Different alkylsilanes have been used in order to study both the effect of the chain length and the age of the precursor solution on the ordering of the molecules in solution as well as on the substrate surface. For freshly prepared solutions with a high concentration of octadecyltrichlorosilane (OTS, C18), irregular rough films with a maximum surface coverage of 70% have been observed. For C10, C12, and C16 alkylsilanes, comparatively flat films have been obtained under the same conditions. For OTS, such flat films can only be achieved after prolonged aging of the precursor solution. The results are discussed in terms of ordering depending on different experimental parameters.

The growth behavior of self-assembled monolayer films strongly depends on parameters such as solvent, water concentration in the solvent, substrate type, and deposition method. A further parameter, the temperature, is of particular importance. It has been found that growth kinetics, size, and shape of the structures obtained strongly depend on the deposition temperature. Thus, exact adjustment and control of the solution temperature is of crucial importance for investigation of deposition mechanisms. The development of a temperature control unit has been the basis for a series of experiments on deposition of octadecyltrichlorosilane (OTS) on silicon wafers to study the influence of temperature on growth kinetics and film structure. Characterization of the films was performed with ellipsometry and atomic-force microscopy. It has been found that octadecylsiloxane (ODS) island sizes decrease with increasing temperature. Furthermore, a characteristic temperature exists above which increasingly disordered deposition occurs. At low temperatures (5-10 degrees C) smaller dot-like features are observed besides larger fractally shaped islands characteristic for self-assembly growth of ODS films. Our results indicate that these small dot-like features originate from ordered aggregates in the adsorption solution and that they are the precursors of the formation of larger islands. However, they can only be observed at low temperatures, because at room temperature they coalesce quickly to form larger units, due to the high surface mobility.

We have investigated the growth of octadecylsiloxane (ODS) self-assembled monolayers on mica. Freshly cleaved muscovite mica and octadecyltrichlorosilane (OTS) dissolved in toluene (c = 1.0 mmol/L) have been used as substrate and precursor, respectively. The water content of the adsorption solution was between 14.6 and 16.6 mmol/L. Adsorption experiments were carried out in a temperature range between 5 and 45 degrees C, and the obtained submonolayer ODS films were characterized with atomic force microscopy (AFM). Besides the morphology of the films, also information on the surface coverage has been obtained by quantitative evaluation of the AFM images. Depending on the temperature, evidence for both ordered and disordered expanded ODS phases has been found. The pronounced maximum in surface coverage--in contrast to adsorption on silicon substrates--at a temperature of about 27 degrees C and the different morphology of the submonolayer films as compared to silicon substrates could be explained in terms of a deposition, diffusion, and aggregation (DDA) model.