This thesis investigates the properties of ultra-thin layers of organic molecules deposited at or adsorbed onto thin films of gold. The two main experimental techniques used in this thesis work are Temperature Programmed Desorption-Infrared Reflection Absorption Spectroscopy (TPD-IRAS), an excellent technique to probe the structure and orientation of molecular layers on metallic substrates, and Temperature Programmed Desorption-Mass Spectroscopy (TPD-MS), a very useful tool to study the energetics of molecular layers and adsorbates on solid surfaces. The two techniques are especially powerful when used simultaneously because they can be used to 1) follow molecular rearrangement phenomena occurring prior and during desorption; 2) find correlations between such rearrangement phenomena and the ultimate binding strength of the molecules/adsorbates to the surface.

The TPD-IRAS and TPD-MS techniques have been used to study: I) the structure and desorption dynamics of DNA bases on gold; II) the phase behavior of oligo(ethylene glycol) (OEG)-terminated selfassembled monolayers (SAMs) on gold; and III) the nucleation, growth and structure of D₂O-ice on SAMsat liquid nitrogen temperatures in ultra high vacuum.

The first part investigates the orientation, structure and binding strength of DNA bases spontaneously adsorbed to gold. The four DNA bases interact very differently on and with the gold surface. Guanine and adenine interact strongly with the surface, and displays a series of complex structural transitions during the desorption event. Adenine form strong bonds with the gold surface, whereas cohesive interactions seem to dominate for guanine. Cytosine and thymine display a less complicated desorption behavior, and the corresponding desorption energies are lower/ much lower than those observed for adenine and guanine. These results are in qualitative agreement with recent studies of the activity of immobilized oligonucleotides on gold nanoparticles.

The second part is a study of SAMs of thiolated molecules on gold exposing OEG-tails in different conformations, all trans and helical, toward the ambient. The temperature dependence is investigated using TPD-IRAS, and it is found that the helical OEGs undergo a reversible phase transition into the all trans oramorphous states at approximately 60 °C, depending on chemical groups used to attach the OEG tail tothe alkyl thiol portion.

The third part focuses on ultra-thin ad-layers of D₂O deposited onto OEG substrates at low temperature in UHV. Extensive simulations of RA spectra of the D₂O-ice overlayers are performed using Maxwell Garnett effective medium theory to support the interpretation of the experimental data. These simulations reveal that the ice overlayers contain a significant and varying volume fraction of voids. Isothermal annealing ofthe ice overlayers shows that the kinetics of the amorphous to crystalline phase transition of ice, normally observed at about 140 K, is strongly dependent on the conformation of the OEG layer. The kinetics is fast on helical OEG SAMs most likely because of the existence of specific nucleation sites that governs the crystalline formation of ice.

The binding strength and structure of D₂O deposited to biomimetic phosphate SAMs with H⁺, Na⁺ and Ca2⁺ as counter-ions are also investigated. D₂O is tightly bound to Ca²⁺- and Na⁺- phosphate SAMs, affecting several ad-layers of D₂O. These results may have implication for the chemistry occurring at biomineral surfaces, and specifically for the role of water on the nucleation and growth of hydroxyapatite, the inorganic component in bone.

This thesis presents efforts to better understand and control the interfacial properties of oligo(ethylene glycol)-containing self-assembled monolayers (OEG SAMs) on gold. This has been done by means of molecular and interfacial design, followed by extensive characterization of the SAMs using a variety of surface analytical techniques. The OEG-terminated and amide group-containing alkylthiols were chosen for the study. The characterization of the OEG SAMs by contact angle goniometry, null ellipsometry, infrared reflection-absorption spectroscopy (IRAS) and X-ray photoelectron spectroscopy (XPS) revealed not only a high crystallinity and an excellent orientation of the constituent molecules in the SAMs, but also conformational differences between the investigated SAMs. It is, for example, shown that the observed all trans and helical OEG conformations depend on the oligomer chain length and/or on the lateral hydrogen bonding in the assembly. Further on, the thermal phase behavior of the OEG SAMs was investigated in ultra high vacuum by temperature programmed IRAS. This approach revealed a reversible helix-to-alltrans phase transition in the EG₆ SAMs occurring at approximately 60 °C. A detailed comparative spectroscopic investigation of several analogous OEG compounds proved that the OEG phase behavior, including the unusual helix-to all trans transition, depends on the linking group between the OEG and alkylthiol chains. It was thereby demonstrated that the selection of an appropriate linking group provided means to control the OEG conformation and phase behavior via intermolecular interactions, e.g. hydrogen bonding. In order to give a more exact account of the influence of lateral hydrogen bonding on the thermal stability of the SAMs, their temperature programmed desorption was analyzed by mass spectrometry and IRAS in parallel. The results from this study clearly showed an improved thermal stability of the hydrogen bonded SAMs.

Some preliminary results on the potential use of such hydrogen bonded OEG SAMs as templates for biomolecular architectures are also presented in this thesis. The amide-containing OEG compounds were chosen as a general strategy for further interfacial design and enabled the preparation of homogeneously mixed SAMs with a fixed hydrogen-bonded underlayer and a fine-tunable OEG portion. It is also shown that a spatially controlled functionalization of the SAMs can be done by incorporating compounds with terminal -COOH groups into the OEG assembly. Carboxy-derivatized molecules in OEG SAMs are expected to act as anchors for lipid bilayers, thus forming a template for supported lipid bilayer membranes. Alternatively, highly ordered SAMs can be prepared by self-assembly of extremely long compounds with the structure HSC₁₅-amide-EG₆-amide-C₁₆ for the integration and anchoring of lipid bilayers on gold.

The study thereby demonstrates a route to manipulate the interfacial properties of oligomer based SAMs on gold surfaces, by controlling the intermolecular interactions. The resulting OEG SAM interface not only enables the construction of templates for biosensors, but also novel molecular 2D and 3D architectures in general.