This research focuses on how the structure of modified interfaces influence the behavior of the interface. Two groups of dialkyl sulfides are prepared and studied: a purely hydrocarbon dialkyl sulfide with the structure CH₃(CH₂)₁₇S(CH₂)_nCH₃, where n=7, 9, and 17, and a carboxylic acid containing dialkyl sulfide with the structure CH3₃(CH₂)₁₇S(CH₂)_mCOOH, where m=7, 10, and 15. The structure and the permeability of these monolayers are characterized by <i>ex situ</i> and <i>in situ</i> FTIR, contact angle measurements, and electrochemistry. It is found that the two groups of dialkyl sulfides have different surface structures and different monolayer-solution interfacial behaviors. The presence of a polar group, such as -COOH, within the monolayer structure is found to increase the charge transfer properties of the modified electrode by influencing the interfacial structure. The structure and permeability of monolayers prepared from 15-mercaptopentadecanoic acid, 16-mercaptohexadecanoic acid, and their corresponding ethyl esters are also studied. Infrared spectroscopy and electrochemical permeability measurements indicate that the ester monolayers are ordered and have few differences in their structural and physical properties. Monolayers prepared from 15-mercaptopentadecanoic acid and 16-mercaptohexadecanoic acid, however, are structurally and physically different from the esters and each other. The IR and contact angle results indicate that hydrogen bonding interactions between the terminal groups of the monolayers influence the structural organization and physical properties of the monolayer. The extent of the hydrogen bonding interactions within the ω-mercaptoalkanoic acid monolayers appear to be related to the structure of the interface, suggesting that the orientation of the terminal functional group influences its ability to interact within the monolayer. / Master of Science