We report on the formation and properties of self-assembled monolayers (SAMs) prepared by depositing semifluorinated and hydrocarbon trichlorosilane precursors, F(CF2)(8)(CH2)(2)SiCl3 (F8H2) and H(CH2)(18)-SiCl3 (H18), respectively, from vapor, organic solvent, and liquid CO2 (1-CO2). Contact angle measurements of the SAM deposition kinetics reveal that regardless of the molecule type, the deposition rates from 1-CO2 exceed those from vapor or organic solvents by several orders of magnitude. We derive two different transport models describing the formation of SAMs. We show that while the diffusion-limited model is not capable of describing the experimental data, the adsorption-limited model captures the major features of the adsorption kinetics quite well. We apply the results of the adsorption-limited model to conclude that the observed behavior is a consequence of (i) a relatively high bulk concentration (1-CO2 VS vapor) and (ii) higher solution diffusivity (1-CO2 VS organic solvent) of the silanes in 1-CO2. Near-edge X-ray absorption fine structure (NEXAFS) is used to monitor the orientation of the F8H2 and H18 molecules in their corresponding SAMs as a function of time. Our NEXAFS data show that the F8H2 molecules adsorb initially from 1-CO2 without any molecular order in the monolayer. As more F8H2 molecules partition at the silicon oxide surface, they start to organize and orient. A complete monolayer order is achieved after approximate to30 min exposure to F8H2/1-CO2 solutions. The deposition kinetics and molecular behavior of the H18 moieties in the SAMs are found to be different, however. After a brief exposure (< 2 s) of the silica substrate to the H18/1-CO2 solution, the molecules adsorb and form an organized monolayer. Similar to the case of the semifluorinated species, the order in the H18 SAM increases with increasing time and saturates after approximate to5 min exposure to H18/1-CO2 solution. We attribute the difference in the orientation kinetics to the different solubilities of F8H2 and H18 in 1-CO2.