<p>Ion soft landing is a preparative mass spectrometry technique that enables intact deposition of polyatomic ions onto surfaces. The ability to select ions with well-defined mass, charge, and kinetic energy, along with precise control over size, shape, and position of the ion beam in the deposition process distinguishes ion soft landing from traditional synthetic and surface preparation approaches. A wide range of projectile ions including molecular ions, non-covalent complexes, clusters, and ionic fragments generated in the gas phase have been used in soft-landing studies to address both the fundamental questions related to ion-surface interactions and enable applications of hyperthermal beams.</p> <p>Since the first soft landing instrument was implemented by Cooks and co-workers in 1977, significant advances have been achieved in preparative mass spectrometry instrumentation. Current instrument development efforts are focused on obtaining high ion currents, increasing the experimental throughput, and developing capabilities for layer-by-layer deposition. In chapter 2 and 3, two novel instrumentation approaches are introduced, which improve the ion flux and experimental throughput of ion soft landing research. In particular, soft landing of ions of both polarities enables the bottom-up construction of ionic materials. Meanwhile, a rotating wall mass analyzer substantially increases the mass range of mass-selective deposition and disperses multiple species on the same surface thereby increasing the experimental throughput. These instrumentation developments open up the opportunities to explore research topics in the field of catalysis, energy storage and production, biology, and quantum sciences.</p> <p>In chapter 4, I describe a novel <i>in situ</i> spectroelectrochemistry approach for studying structural changes of electroactive species during electrochemical processes. In these experiments, ion soft landing is used to prepare well-defined ions at electrochemical interfaces. In addition, understanding of the gas-phase properties of cluster ions is important for their application in ion soft landing research. Ions can be prepared in the proper physical and chemical state via gas-phase chemistry approaches, and the favorable properties and reactivities of ions can thereby be harnessed using ion soft landing. In chapter 5 and 6, gas phase properties of host-guest complexes of cyclodextrins and polyoxometalates and molybdenum halide clusters are discussed.</p>

<p dir="ltr">Interfaces play an important role in a broad range of physical, chemical, and biochemical processes. For example, nutrient transport from and to cells happens at the cellular membrane interface, the corrosion of metals occurs due to chemical reactions at the solid/air interface, and the development of waterproof clothing relies on the modification of the clothing surface with hydrophobic species. The importance and complexity of interfaces make a detailed understanding of the interfacial physicochemical processes central to both the fundamental science and the development of new technologies. Specifically in the fields of energy storage/production and heterogeneous catalysis, understanding the transformations of the active species on surfaces leads to the development of high-performance, stable interfaces. In the thesis presented herein, ion soft landing was used as a preparative technique to understand the chemical changes that ions undergo on surfaces. Ion soft landing is a mass spectrometry technique in which polyatomic ions are deposited onto surfaces while preserving their chemical structure and charge state. The advantage of using ion soft landing to study interfaces is that it enables the preparation of well-defined ionic interfaces by the deposition of mass-selected ions on a defined surface area with high control over the amount of deposited material. Because ion soft landing uses purified ion beams formed in the gas phase, it also allows to study the chemical properties of the analytes in the absence of counterions or solvent molecules. Collectively, these capabilities make ion soft landing a powerful approach for preparing ionic interfaces and studying their chemical properties. A new direction in ion soft landing research takes advantage of gas phase ion chemistry techniques, such as collision-induced dissociation, to generate well-defined reactive fragment ions as unique building blocks for studying chemistry at interfaces. <b>Chapter 2 </b>of this thesis discusses the development of an ion soft landing instrument that enables high transmission of fragment ions for their deposition onto surfaces. Ion soft landing of reactive fragment ions opens up possibilities for studying their stability and reactivity on surfaces providing a path to the controlled preparation of unique ionic interfaces. <b>Chapters 3 </b>and <b>4 </b>describe an unusual spontaneous ligand loss observed for soft landed [Ni(bpy)₃]²⁺⁰, an ion of interest in the field of catalysis, and its stabilization by codeposition with anions. We compared the reactivity of [Ni(bpy)₃]²⁺on surfaces against that of [Ni(bpy)₂]²⁺and [Ni(bpy)]⁺species (both formed by ligand removal in the gas phase). This comparison indicates that the dissociation of [Ni(bpy)₃]²⁺ occurs both due to its reorganization on a surface and by charge-reduction. Both processes substantially reduce ligand binding energy and facilitate ligand loss from the complex.</p><p dir="ltr"><b>Chapter 5 </b>diverges from ion soft landing and instead presents a gas-phase ion chemistry study on the stability of cucurbituril-viologen host-guest complexes to better understand the intrinsic properties that influence the strength of their interaction. We found that there is a “perfect fit” size of the host that maximizes interactions with the guest thus increasing its stability. In addition, guests of smaller sizes that are better incorporated into the host have a substantial stability compared to those that have functional groups extending outside of the protecting cavity of the host. The results of this work reveal a strategy to stabilize viologens in the gas phase for the preparation of functional interfaces using ion soft landing.</p><p dir="ltr">Finally, <b>Chapter 6 </b>shows the results of a work at the teaching/learning interface, specifically regarding an undergraduate research project developed for the Analytical Chemistry I course (CHM323) at Purdue University. The goal of this project was to further develop students’ scientific skills on planning, problem-solving, and critical thinking to assess the performance of two analytical techniques. Specifically, the project described in <b>Chapter 6 </b>was designed in such a way that students had to do research on appropriate analytical techniques to quantify ascorbic acid in an unknown sample, propose an experimental protocol, perform it in the laboratory, and concisely summarize the results of their work in a lab report.</p><p dir="ltr">In summary, the work presented in this thesis encompasses three areas. First, it shows the advantages of using fragment ions produced in the gas phase to study the complex physicochemical processes occurring at interfaces. Second, it presents a study on the gas-phase stability of viologen-based host-guest complexes with the prospect of making viologens accessible for the preparation of functional interfaces using ion soft landing. Finally, it describes an undergraduate laboratory project aimed at developing the scientific skills of students in an analytical chemistry course.</p>