Title Promoter Affiliations Abstract "Dynamics of Quantum Correlations" "Mark Fannes" "Theoretical Physics" "The main aim of this thesis is to study quantum dynamics, with a focus on irreversible, dissipative dynamics, by collecting repeated observations and arranging them to form a process. This leads to quantum states of extended models with some simplifying features. The models explored here are quantum spins on Fermionic lattices and chains of quantum spins. We focus in particular on the randomising properties of the dynamics.The thesis begins by exploring the relation between the average von Neumann and Rényi entropies of integer orders for shift-invariant quasi-free Fermionic lattice systems. This then leads to an investigation into approximating the von Neumann entropy in terms of a combination of integer-order Rényi entropies and an estimate for the quality of such an approximation is given.Later, a rather general technique is introduced to model a quantum system’s dynamics on a semi-infinite half-chain of quantum spins. Here, bounds are given for the average entropy of the model system as well as a general scheme for computing the average Rényi entropy of integer order of such models.Finally, the half-chain model is made explicit with the example of a simple qubit evolving under a thermalising dissipative dynamics. With this example, the integer-order Rényi entropies are explicitly calculated. By optimising over all possible choices of models, a model-independent expression for the average Rényi entropies is derived." "Non-noble metal catalysis for Cross-coupling reactions: Computational insights" "Jeremy Harvey" "Quantum Chemistry and Physical Chemistry" "Catalysis plays a pivotal role in our society since we are critically dependent on plastic materials and pharmaceutical products of which many steps of their industrial production are led by catalyzed processes.Accordingly, the development of a new catalytic systems based on transition metals is very active.However, catalysts are, nowadays, mainly made by organometallic complexes based on rare and precious noble metals such as Pd, Pt, Ir.These types of catalysts made out of noble metals are very efficient, however, they carry with their performances the drawback of being highly toxic, scarce, and expensive.This aspect is forcing the catalysis field to move on to the development of catalysts based on non-noble metals such as Fe, Ni, and Co.The aim of this thesis and the related results are contained in these statements.By the use of computation, we tried to get some advances in the understanding of some reaction mechanisms of non-noble metal-catalyzed processes.We used density functional theory (DFT) to study some challenging chemical reactivity and complicated reaction mechanisms.Specifically, we focused on three processes: two cross-coupling reactions catalyzed by either iron or nickel complexes and an amidation reaction catalyzed by Ni complexes. Generally, we were able to provide some insights into the reaction mechanisms involved during these reactions. We could also suggest and rule out some intermediates and reaction steps of which it is difficult to account for experimentally.In summary, the first project is about an iron-catalyzed reductive coupling of which we were not able to draw a definitive reaction mechanism, however, we provided some insights, such as ruling out the presence of a discrete Fe(I) reduced species, and suggesting that a halogen transfer reaction carried out by solid zinc might be important.In the second project, we collaborate with the group of Prof. Hu in EPFL providing a suitable reaction mechanism for the amidation reaction of esters catalyzed by Ni complexes. In this project with the use of computation, we could suggest a NiZn-heterodimer as the potential nucleophile of the reaction. The third and last project is about the Negishi arylation of propargyl bromides catalyzed by Ni complexes.In this project, we were able to rule out the presence of a Ni(I) species and also able to suggest that a previously unidentified halogen transfer step plays an important role in catalyst pre-activation.In conclusion, with the use of computation, we were able to tackle some challenges in the reaction mechanisms of the processes under study." "Security of Cryptographic Implementations" "Bart Preneel" "ESAT - COSIC, Computer Security and Industrial Cryptography" "This thesis focuses on issues arising when implementing cryptography, specificallyperformance, side-channels and integration. All these issues must be addressedto turn a cryptographic algorithm into a practical system which can providesecurity properties such as confidentiality or authenticity.Considering the potential threat by quantum computers we deal withperformance optimizations for supersingular isogeny Diffie-Hellman (SIDH).We compare different approaches for modular multiplication and show thatMontgomery multiplication is theoretically the fastest and that product scanningis the fastest implementation. We also propose 2^391 19^88 − 1 and other primessuitable for SIDH which give an additional 12% speed-up. Further, we extendthis comparison to Twisted Edwards curves with optimized addition chains andshow that the increased flexibility in creating addition chains cannot compensatefor the slower operations. Afterwards, practical performance improvements byusing special multiplication instructions on ARM platforms are shown. Usingthese and an extended set of suitable primes gives a speed-up of 50%.We then consider a complete cryptographic system. We provide a securityanalysis of end-to-end encrypted email. It is shown how the complex behaviorsof the components, when integrated into a single system, compromise or weakensecurity. Vulnerabilities are presented for 23 out of 35 tested S/MIME clientsand 10 out of 28 tested OpenPGP clients.Finally, a side-channel attack on the Frodo scheme is presented. The attack canbe performed with a single trace due to the reuse of secret values at multipletimes during the algorithm. The attack extracts the key with probability 50%and 99% for parameter sets NIST1 and NIST2 respectively, also showing thatit is more effective for supposedly more secure parameters. We also propose amitigation with only minor impact on performance." "Synthesis and characterization of polyoligosiloxysilicones" "Johan Martens" "Centre for Surface Chemistry and Catalysis" "Silicon-based materials are of vital importance in today’s society. From the sand and clay dug up from the Earth to be used in construction, to the highly purified forms used in the production of electronics, computers and medical implants, the chemical element Si has found its way into nearly every aspect of our lives. Nevertheless, our highly technological world is fueled by an ever-lasting quest for progress. This search continuously increases the demand for new materials with improved or new properties. One imaginative approach towards novel material design and synthesis starts from relatively small supramolecular building blocks that can be combined in ingenious ways to create highly specialized compounds. Within the world of silicon-based materials the octameric oligomer [Si8O12], also known as the double four ring (D4R), is seen by many as such a potential building block. Considering its highly symmetrical near-cubic shape and the possibility to attach functional groups to each of its eight corners, one can imagine many different structures based on this versatile building unit.Up until now some attempts have been made in connecting D4R units in a controllable fashion, one of which by the connection with silicone linkers. Some of the reported materials were synthesized by reacting bifunctional silanes with the D4R units of a cyclosilicate hydrate. The large amounts of water molecules present in previously available D4R sources, however, rendered controlling the length of the silicone linkers very difficult, due to undesired oligomerization side reactions of the silane reagent. Alternative synthesis pathways suffer from a similar lack of control. Cyclosilicate hydrate chemistry does, however, provide hints at lowering the water content in the precursor material. Cyclosilicate hydrate structures made in the presence of hexamethyleneimine or tetrabutylammonium hydroxide both consist out of hydrogen bonded D4R units and contain much less water compared to conventionally used D4R sources. In this doctoral research, the possibility of using these alternative precursor materials as D4R source to synthesize D4R-silicone copolymers while exerting some control on the length of the connecting silicone linkers, was investigated. The resulting copolymers are referred to as polyoligosiloxysilicones, or POSiSils in short.This approach was proven successful as a first POSiSil material was synthesized from the hexamethyleneimine cyclosilicate hydrate and dimethyldichlorosilane. The resulting copolymer, which was given the code PSS-1 after polyoligosiloxysilicone number 1, was shown to consist out of alternating D4R units connected solely by dimethylsilicone monomers. Electron microscopy imaging indicated preferential unidirectional growth of the copolymer. A model of PSS-1 is proposed consistent with all experimental data, having an arrangement of D4R units in similar columnar structures as in the parent material with the columns being connected either by strong Van der Waals forces or by sporadic crosslinking. The synthesis of PSS-1 would then be the first case of silicone-like materials wherein zero dimensional building blocks (D4R) from an already pre-organized structure are permanently fixed by the direct insertion of reactive linkers.A second member of the POSiSil family, referred to as PSS-2, was made by reacting tetrabutylammonium cyclosilicate hydrate with dimethyldichlorosilane. PSS-2 appeared to be a dense, amorphous material consisting of a network of D4R units systematically connected by short silicone chains. These chains are most likely composed of a roughly equal amount of dimeric and trimeric dimethylsilicone linkers. Permanent porosity of PSS-2 was achieved by eliminating residual tetrabutylammonium cyclosilicate hydrate embedded inside partially transformed PSS-2 polymer, by calcination. The collapse of the sacrificial parent material leaves nanovoids inside PSS-2, which theoretically should be both flexible and hydrophobic.As the composition of PSS-2 is far more complex than PSS-1, the further development of such a challenging class of materials demanded greater insight in their structure. The Silicon connectivity of PSS-2 was thus investigated at a deeper level using more advanced solid-state 29Si NMR methods. In a first part 1Hà29Si multiple contact cross polarization (MC-CP) was shown to provide quantitative data in a much shorter time frame compared to traditional single pulse experiments. In a second part, the ensemble of NMR data, including challenging 29Si-29Si double quantum – single quantum (DQ-SQ) MAS NMR experiments was used to gain more precise information about the surprisingly organized structure of PSS-2. In future work this insight will prove indispensable for the further development of the POSiSil family.In the final part a new synthesis pathway to D4R-based spherosilicates with the synthesis of the previously inaccessible and highly reactive [Si8O12][OSi(CH3)2Cl]8 spherosilicate suited for derivatization or hybrid material synthesis, is achieved. The minimal water content in this new elegant pathway not only enables the use of bifunctional silanes for functionalization, it also limits wasting silylating agents to unwanted side reactions. By altering the silylating agent the new synthesis pathway enables the quantitative synthesis of other spherosilicates such as the commonly used [Si8O12][OSi(CH3)2H]8 spherosilicate with high yield and purity.This work has opened the way to the new family of POSiSil materials, situated next to existing families of nanoporous materials such as zeolites and metalorganic frameworks (MOFs). The variability of cyclosilicate and linkers makes the POSiSil family potentially as large as the latter families. By applying the principles of network design, a near infinite amount of members of this new class of materials can in principle be made available for application. " "TiO2 Gas Phase Photocatalysis from Morphological Design to Plasmonic Enhancement" "Johan Martens" "Centre for Surface Chemistry and Catalysis" "The past decades, photocatalysis has emerged as a powerful technology for pollution abatement and energy applications, but its use in gaseous environment is less obvious than in water borne applications. Therefore this thesis specifically aims at understanding and improving TiO2-based photocatalysis in all its facets towards gas phase processes.In first instance a suitable photoreactor is developed and validated. A simple suspension-based coating strategy enables to immobilize powderous photocatalytic materials onto glass bead supports that are packed around a light source in a cylindrical glass reactor tube. The presented design offers several advantages such as good catalyst immobilization, efficientlight utilization, intimate contact with gaseous pollutants and a catalyst weight gain by a factor of 25 compared to self-supporting pellets. This glass bead photoreactor is used in a comparative study on TiO2-basedphotocatalytic materials, in which both technological and economical parameters are considered. By performing a cost effectiveness analysis, PC500 (Cristal Global) is determined to be a very active and cost efficient photocatalyst in the degradation of gaseous acetaldehyde and even outperforms the typical benchmark Aeroxide P25 catalyst (Evonik).In the next part of the work, fundamental insight is gathered in the driving factors for gas phase photocatalytic reactions by investigating the different nature of the P25 and PC500 catalysts. The high surface area andsophisticated yet accessible pore system of PC500 seem to dominate overthe superior electronic efficiency of P25. These findings are supportedby photocatalytic gas phase experiments, photocurrent measurements, N2-sorption data, X-ray diffraction patterns, UV-VIS spectroscopy, thermo-gravimetric analysis and acetaldehyde adsorption measurements, amongst others.The dominating effect of surface area on gas phase photocatalytic activity is exploited in the development of well-immobilized, spacious TiO2 thin films. These films are prepared by depositing a thin, conformal layer of TiO2 onto sacrificial carbonaceous templates by means of atomic layer deposition. The carbonaceous templates are either carbon nanosheets or multi-walled carbon nanotubes, both grown on silicon wafers. After application of a calcination step, the sacrificial template is removed, TiO2 is crystallized into the anatase phase and the as-deposited continuous TiO2 layer has transformed into an interconnected network of nanoparticles. Electron microscopy images show that the overall appearance of the films is entirely commensurate to the original template morphologies. The employed strategy allows to fabricate spacious thin films with surface area enhancement factors of up to 260 with regard to a dense, flat TiO2 film. Thus obtained thin films exhibit superior photocatalytic activity compared to a reference film consisting of the photoactive PC500 catalyst. For the testing of these thin films another type of photoreactor was developed. The use of the constructed single pass flow through, slit-shaped, flat bed photoreactor is visualized by computational fluid dynamic simulations.As an intermission the use of surface photovoltage measurements is discussed in relation to photocatalytic activity. The research question is simply whether surface photovoltage measurements can be used as a quick screening tool for assessing photocatalytic performance. The answer is less straightforward. Based on several practical case studies, the trend between photovoltage and photoactivity isinvestigated using a custom-made photovoltage set-up. For TiO2-based materials with variable anatase/rutile ratios, catalytic activity is determined to be proportional to photovoltage readings. In contrast, in the case of variable amounts of silver nanoparticles deposited on the TiO2 surface that act as electron traps under UV illumination, an inverse relation is observed. Furthermore, a significant effect of the catalyst humidity is detected, but the most important conclusion to be drawn from thisstudy is that surface photovoltage measurements can only probe electronic properties. The vast impact of morphological parameters on photocatalytic activity is not accounted for by this technique. Therefore care should be taken when interpreting surface photovoltage data in relation to photocatalysis. Finally, successful attempts have been madeto extend the TiO2 photoactivity window towards the visible light region of the spectrum. This is achieved by exploiting surface plasmon resonance effects of gold-silver alloy nanoparticles. In the first part of theresearch a theoretical, predictive model is established that enables topredict the plasmon resonance wavelength of such alloy nanoparticles, based on the combined effect of particle size and alloy composition. The model is developed using theoretical simulations of extinction spectra based on Mie theory and dielectric data from literature. The proposed model indicates that mainly the alloy composition determines the resonance wavelength, while particle size is of minor importance. In the second part of the investigation, gold-silver alloy nanoparticles are deposited on the TiO2 surface. By merely altering the alloy composition of the deposited nanoparticles, plasmonic photocatalysts can be prepared that display surface plasmon resonance in a 70 nm broad window in the visible light wavelength range that is roughly centered at the maximum intensity wavelength of solar radiation. Thus obtained plasmonic photocatalysts are tested towards their self-cleaning performance in the degradation of a solid layer of stearic acid located at the catalyst-air interface. The highest quantum efficiency is obtained when the resonance wavelength of theplasmonic catalyst exactly matches that of the incident light. This is demonstrated for the case of Au0.3Ag0.7 nanoparticles on TiO2 under 490 nm illumination, provided by a custom-made LED array. In conclusion, in this work TiO2 gas phase photocatalysis is investigated in its broadest sense. Different aspects are discussed ranging from reactordevelopment, over techno-economic analysis, morphological catalyst design, characterization, structure-activity relation, interpretation of photovoltage measurements, to visible light activity using plasmonics. We are hopeful that this altogether leads to better understanding and novel insight into this fascinating research domain."