In this thesis, we investigated the surface composition and orientation of both pure room-temperature ionic liquids (Ils) and binary mixtures of the ILs of the type consisting of the 1-alkyl-3-methylimidazolium ([C[subscropt n]mim]���, n=4, 8, and 12) cation coupled with either [PF���]���, [BF���]���, [Cl]���, or [Br]���. The surfaces of the ILs were examined using both direct recoil spectrometry (DRS) and surface tension measurements. With DRS, a spectral signal produced by a recoiled surface atom indicates the existence of a particular molecular or ionic species at the interface. Derived from the signal are the atomic ratios, which are strongly dependent on the surface orientation of the surface species. The DRS findings are complimented with surface tension measurements, and the thermodynamics properties (surface enthalpy and entropy) derived from such measurements are related to the surface composition and orientation. From the experiments on the neat ILs, the surface compositions of the imidazolium-based ILs were determined. Furthermore, the effects of systematic variations of the cation size (the length of the 1-alkyl chain) and anion identity on the surface orientation of the organic cation were also examined. The surfaces of binary mixtures containing ~25 mol % of [C������mim][PF���] or [C������mim][BF���] in [C���mim}[BF���] were also investigated. The DRS and surface tension data of the mixtures were compared to those of the pure components to determine the composition and any changes in the orientations of the cations upon mixing. / Graduation date: 2004