Interfaces between materials can have properties that differ greatly from the bulk state. In classical materials only a tiny fraction of atoms are at the interface while the vast majority is in the bulk of the material. The capability to engineer materials with an artificially high amount of interfaces opens up a pathway to amplify the interface effects and tailor the material properties by controlling the amount of interfaces. This approach to engineer materials step by step or layer by layer also allows for a controlled combination of very different materials into a hybrid material that would not form naturally and which can show fundamentally different and new properties.

In this thesis atomic layer deposition (ALD), molecular layer deposition (MLD) and pulsed laser deposition (PLD) are utilized to engineer ZnO-based thin films with high interface densities. The films are analysed with x-ray reflectivity (XRR), x-ray diffraction (XRD) and transmission electron microscopy (TEM) in regards to their internal structure. Time domain thermoreflectance (TDTR) is utilized to measure the thermal conductivity, the electrical properties are measured with a hall measurement setup. The latter is the focus in layered thin films of polycrystalline ZnO and amorphous InGaZnO4 in which a considerable increase in the charge carrier concentration following the interface density could be demonstrated.

The interfaces between a ZnO matrix, ZnO-benzene and AlOx layers are studied in detail in a hybrid ZnO/ZnO-benzene/AlOx system in which this work demonstrates, that these layers in ZnO can be as thin as a single atom/molecule, yet still form distinctive layers. However, these very thin layers of ZnO-benzene and AlOx are found to have little impact on the crystal growth of ZnO, but can act as effective barriers for ZnO crystal growth when 10 or more consecutive ALD/MLD cycles are utilized for each AlOx/benzene layer respectively. Finally the thermal conductivity in ZnO/benzene thin films is characterised, the database for the thermal conductivity in that system is significantly extended and thermal conductivities for irregularly layered structures are reported for the first time in ZnO/ZnO-benzene hybrid thin films. Analysis with multivariate data analysis of the database confirms that the interface density has the most pronounced effect on the thermal conductivity.

Nanopores have emerged as a special class of single-molecule analytical tool that offers immense potential for sensing and characterizing biomolecules such as nucleic acids and proteins. As an alternative to biological nanopores, solid-state nanopores present remarkable versatility due to their wide-range tunability in pore geometry and dimension as well as their excellent mechanical robustness and stability. However, being intrinsically incompatible with biomolecules, surfaces of inorganic solids need be modified to provide desired functionalities for real-life sensing purposes. In this thesis, we presented an exploration of various surface engineering strategies and an examination of several surface associated phenomena pertaining specifically to solid-state nanopores. Based on the parallel sensing concept using arrayed pores, optical readout is mainly employed throughout the whole study.
For the surface engineering aspect, a list of approaches was explored. A versatile surface patterning strategy for immobilization of biomolecules was developed based on selective poly(vinylphosphonic acid) passivation and electron beam induced deposition technique. This scheme was then implemented on nanopore arrays for nanoparticle localization. In addition, vesicle rupture-based lipid bilayer coating was adapted to truncated-pyramidal nanopores, which was shown to be effective for the minimizing DNA-pore interaction. Further, HfO2 coating by means of atomic layer deposition was employed to prevent the erosion of Si-based pores and to shrink the pore diameter, which enabled reliable investigations of DNA clogging and DNA polymerase docking.
For the surface associated phenomena, several findings were made. The lipid bilayer formation on truncated pyramidal nanopores via instantaneous rupture of individual vesicles was quantified based on combined ionic current monitoring and optical observation.  The probability of pore clogging appeared to linearly increase with the length of DNA strands and applied bias voltage, which could be attributed a higher probability of knotting and/or folding of longer DNA strands and more frequent translocation events at higher voltage. A free-energy based analytical model was proposed to evaluate the DNA-pore interaction and to interpret observed clogging behavior. Finally, docking of DNA polymerase on nanopore arrays was demonstrated using label-free optical method based on Ca2+ indicator dyes, which may open the avenue to sequencing-by-synthesis enabled by the docked polymerase.
 

Future trends in materials and devices are strongly based on novel fabrication methods that allow for mass production with low cost and high throughput. Such methods must be finely optimized to achieve nanometric control without incurring in high costs. This can be achieved by developing a process that reduces the number of steps required, as well as by reducing the amount of human involvement in the process, which would increase the quality and reproducibility of the output. But the improvement of fabrication technologies cannot be optimized without considering the materials desired, along with its most fundamental chemical and physical properties. Hence, to successfully design the instrumentation needed for novel fabrication technologies with nanometric precision, the design methodology must consider multiple different subjects related to the chemistry, physics, mechanics, electronics and automation, all working together to achieve the desired objective. In this doctoral work, such design methodology was implemented with a diverse number of tools and approaches to successfully optimize a nanofabrication method called Spatial Atomic Layer Deposition (SALD) to deposit thin films of a material that has potential applications as a component of non-silicon solar energy devices, photoelectrochemical water splitting devices, and thin film transparent electronics, among others: cuprous oxide (Cu2O ). Regarding the fabrication technology and the mechatronic design, SALD is a promising fabrication technique that allows fabrication of thin films with nanometric precision and with the ability to control their mechanical, electrical and crystallographic properties. Furthermore, the SALD approach used in this thesis and in the Laboratoire des Matériaux et du Génie Physique (LMGP) works in the open-air (no deposition chamber), and thus is potentially an industrial-compatible approach for large area, homogeneous thin film fabrication with a high throughput. Additionally, SALD can be used with conditions that make it compatible with flexible substrates and with rollto- roll (R2R) approaches. Finally, SALD provides flexibility on the deposition process so that it can be tuned to obtain different properties on the films fabricated with minimal change in the instrumentation. In this thesis, some of the potential benefits of the flexible parameters of the SALD system are explored and the impact of some of them on fabricated films is presented. Using Computational Fluid Dynamics (CFD) simulations, the fluid mechanics phenomena that occur during the deposition process in the SALD system were analyzed for different configurations of the reactor. The influence on the film properties were studied and validation with experimental depositions were performed. Afterwards, using the knowledge and guidelines obtained with the CFD simulations, and in order to lower the cost and complexity of modifying some of the mechanical components of the system, a workflow including Computer Aided Design (CAD) and additive manufacturing (also known as 3D printing) was established at the LMGP for the fabrication of one of the main components of the SALD system at LMGP: the deposition head. The use of additive manufacturing has followed a rapid increase on applications, and, in this work, it is the first time that such innovative fabrication technique is applied to thin-film nanofabrication processes, providing numerous potential applications in the field. In this thesis, such workflow is shown and explained, and the guidelines learned, and limitations discovered are presented as well. Finally, after making some modifications on the system and adding the necessary components such as new heating systems and containers for the needed precursor, Cu2O was successfully deposited with the SALD method. Cu2O is one of the few materials with promising electronic properties as a p-type transparent semiconductor. It is also a material that allows for mass production, if coupled with an industrial-compatible fabrication method (such as SALD), thanks to its non-toxicity, its chemical and environmental stability and its earth abundance. Here, the fabricated Cu2O films using the SALD system at LMGP are reported, and their p-type conductivity and crystallography are analyzed. In the work done during this doctoral project, a systematic approach was used to analyze, adapt and optimize the SALD system at LMGP for the deposition of Cu2O. Using CFD simulations, CAD tools, 3D printing and automation, the whole process was successfully installed in the system and highly conductive Cu2O films can be now deposited their further study or for their integration in numerous types of devices. Furthermore, the results of this work provide initial guidelines for the industrial design of an SALD-based high-throughput fabrication system, in which the design of its components is optimized for each material desired. Such design approach, combined with the flexibility and low cost of the SALD, the flexibility of the mechanical design and fabrication of some of its components, and the speed of the deposition procedure, make this work also useful to further increase the amount of materials compatible with SALD, as well as to further develop the SALD methodology into innovative fabrication processes of materials and devices. 

Atomic layer deposition (ALD) is a thin film growth technique which deposits conformal, pin-hole free films with sub-nanometer precision. Molecular layer deposition (MLD) is an analogous process to ALD where molecular fragments are used to deposit all-organic or organic-inorganic hybrid films. Both ALD and MLD have been employed in numerous industries to advance technologies, notably in the semiconductor, energy storage, display and optics industries. In this thesis, I present three projects which utilize ALD and MLD processes for industrial applications in semiconductors, drug delivery and optical devices. The first project describes a study of the conversion of ZnO to Al₂O₃ using trimethylaluminum. Past instances of conversion are introduced, a number of analytical techniques are used to show evidence of the conversion mechanism and the generality of exchange reactions is discussed. Exchange reactions are becoming important to consider during ALD processes and as a processing tool in the semiconductor industry. The second project develops low-temperature MLD and ALD processes to coat nanoparticles. The construction of a new reactor built specifically for particle MLD is presented. Evidence of controlled polyamide MLD coatings is shown and we demonstrate MLD and ALD films may be used to modulate the release of pharmaceutical powders. The third project uses ALD to smooth surface roughness and improve the optical performance of Ag mirrors. Current smoothing techniques are abrasive and detrimental to mirror performance. The ALD process shows significant smoothing capabilities of both nano and microscale roughness and dramatically recovers reflectance performance lost due to optical scatter. These projects demonstrate the versatility of ALD and MLD processes and show precise thin film deposition techniques will continue to find use in numerous semiconductor and non-semiconductor industries.

Lithium-ion batteries (LIBs) have become reliable electrochemical energy storage systems due to their relative high energy and power density, in comparison to alternative battery chemistries. The energy density of current LIBs is limited by the average operating voltage and capacity of oxide-based cathode materials containing a variety of transition metals (TM). Furthermore, the low anodic stability of "conventional" carbonate-based electrolytes limits further extension of the LIBs voltage window. Here, ageing mechanisms of cathodes are investigated, with a main focus on TM dissolution and on strategies to tailor the cathode surface and the electrolyte composition to mitigate TM dissolution.
Atomic layer deposition (ALD) coatings of the cathode surface with electrically insulating Al2O3 and TiO2 coatings is employed and investigated as a method to stabilize the cathode/electrolyte interface and minimize TM dissolution. The thesis illustrates both the advantages and limitations of amorphous oxide coating materials during electrochemical cycling. The protective oxide layer restricts auto-catalytic salt degradation and the consequent propagation of acidic species in the electrolyte. However, a suboptimal coating contributes to a nonhomogeneous cathode surface ageing during electrochemical cycling. Furthermore, the widely accepted concept of charge disproportionation as the fundamental cause of TM dissolution is demonstrated to be a minor factor. Rather, a chemical dissolution mechanism based on acid-base/electrolyte-cathode interaction underlies substantial TM dissolution.
The thesis demonstrates LiPF6, and by implication HF, as the principal source of TM dissolution. In addition, the oxidative degradation of ethylene carbonate (EC) solvent contributes indirectly to generation of HF. Thus, an increase in electrolyte oxidative degradation products accelerates TM dissolution. Substituting EC and LiPF6 with a more anodically stable solvent (e.g., tetra-methylene sulfone) and a non-fluorinated salt (e.g., LiBOB or LiClO4) or addition of TM scavenging additives like lithium difluorophosphate (LiPO2F2) are here investigated as strategies to either i) mitigate TM dissolution, ii) supress TM migration and deposition on the anode surface, or iii) supress formation of acidic electrolyte degradation products and thereby TM dissolution. The thesis also highlights the necessity of taking precautions when attempting to replace the components, as reducing TM dissolution may come at the expense of electrochemical cycling performance.
 

Perovskite (Pvk) solar cells and Pvk/silicon (Si) tandem solar cells are emerging photovoltaics (PV) technologies. In the last decade, their power conversion efficiency have reached 25.7 % and 31.3% respectively [1,2]. However, these PV technologies still show a large size difference between high efficiency cells, which have an area below the order of the cm2, and industry-viable cells. Hence, the ability to fabricate large area Pvk and Pvk/Si tandem cells showing high efficiency is crucial for industrial development of such technologies. This goal requires deposition process adaptation for every constitutive material layer in these solar cells. Particularly, the electron selective layer deposition is mostly performed by spin-coating, which is a non-adapted process for tens of nanometres-thick films on top of large area and possibly textured substrates. Atomic Layer Deposition (ALD) on the contrary appears to be very attractive for such thin film growth, especially in the tandem cells case, for which the Si bottom cell surface is usually textured.The work realized during this experimental thesis focuses on the study of the influence of integrating an ALD-grown tin dioxide (SnO2) electron selective layer in Pvk-based solar cells.First, ALD-grown SnO2 thin films properties are investigated and compared to the properties of reference spin-coated SnO2 layers. Some differences, notably in their optical and electrical properties, have been identified. The formation of a Pvk film on top of an ALD-grown SnO2 layer is then also analysed and compared to the one of a reference Pvk film, without arising significant differences.With the knowledge of the previous comparisons results in mind, a second part of the work is dedicated to studying the performance of ALD-grown SnO2 electron selective layer by analysing Pvk-based solar cells behaviour. Strong limitations are highlighted, which points out the SnO2/Pvk interface as the probable main limiting region.In a third part, the SnO2/Pvk interface is more precisely investigated thanks to chemical and energetics characterisation techniques. Notably, a work function difference and an ionization energy difference are observed between the ALD-grown SnO2 and the spin-coated SnO2 as well as a difference in the net effective contact area at the SnO2/Pvk interface depending on the SnO2 nature. These results make possible to draw several hypothesis concerning the causes of performance limitations in devices.Finally, the influence of the ALD process modification over SnO2 thin films properties and Pvk-based solar cells behaviour is examined. This study shows that diverse SnO2 thin films annealing as well as a change in ALD growth temperature can affect SnO2 thin films properties with sometimes inducing a modification of solar cells behaviour.The performed studies and their respective results improve the overall understanding of the mechanisms that hinder electron selective layers efficiency in Pvk-based solar cells. This allows the assumption of news ways to integrate successfully an ALD-grown SnO2 electron selective layer in such solar cells, which will participate in the development of Pvk and Pvk/Si tandem solar cells. 

Over the years, depositing metal oxides onto the surface of organic substances has been favored by a lot of industries to create products with a longer life cycle. The renewable energy sector has seen a lot of improvement in their power conversion efficiency (PCE) of perovskite solar cells (PSC) through the incorporation of metal oxides either through atomic layer deposition (ALD) or vapor phase infiltration (VPI). ALD has also supported the structural modification and pore selectivity of synthetic membranes used in water filtration systems, catalytic reactors, gas and liquid purification systems, batteries, sensors, fuel cells, and barrier layers. Among all the possible thin film oxides that can be deposited through ALD, aluminum oxide (or “alumina”) is a popular choice for moisture and chemical barrier applications. It is often chosen as a thin film oxide due to its film thickness uniformity, lack of pinhole defects, and transparency (ALD-alumina is a colorless thin film oxide). Depositing ALD-alumina on a substrate surface will prevent the said material to oxidize future, allowing it to preserve its natural surface chemistry and all the optomechanical properties that come with it. However, the behavior of ALDalumina in various aqueous solutions are still contested in the field, with various researchers reporting different trends of ALD-alumina behavior in solution. This can pose a problem, as a lot of applications that utilize ALD-alumina are immersed in water, or other liquids, for extended periods of time. Due to a lack of understanding of the ALD-alumina degradation behavior, this factor is often ignored in applications. This could be a problem that affects the accuracy in other fields of research. ix The purpose of this thesis is to study and determine factors that affect ALD-alumina film chemistry in aqueous solutions. A set of dissolution trials have been setup with solutions of different volumes, concentration, and pH. ALD-alumina, synthesized through the reaction of trimethylaluminum (TMA) and water (H2O), is deposited on an air-plasma cleaned silicon substrate. The deposition temperature is kept at 150 °C for 400 cycles of ALD, resulting in ~48 nm of alumina thin film oxide. These samples will then be immersed in different volumes of Type 1 DI water (DIW) and different moles of NaCl solution. This is done to understand the impact of water volume and salt concentration on the degradation rate of ALD-alumina. To eliminate other factors that could affect the thin film behavior, the samples are kept in tightly sealed vials that are stored in a dark space at room temperature. Throughout this project, the specific film thicknesses of our ALD-alumina samples will be tracked across time in days. The surface chemistry will also be analyzed to XPS deconvolution of the oxygen and aluminum spectra peaks. As an extension of ALD applications as a protective coating, this thesis will also investigate the effect of VPI on the PCE stability of PSCs. The charge transport layer, Spiro-OMeTAD, will be infiltrated by TiCl4 to create a hybrid organic-inorganic layer that prevents degradation due to Au diffusion into the layer or crystallization effects when exposed to high heat. By introducing TiOx into the layer, the Spiro-OMeTAD layer will have better thermal stability and have an improved PCE stability under high illumination and humidity. 

In this thesis, the growth of the semiconducting material ZnO by two methods - plasmaenhanced atomic layer deposition and vapor phase infiltration - is investigated. As ZnO is utilized in diverse applications such as UV-protection, gas sensors, or piezoelectrics, precise knowledge about the characteristics of the growth process is needed to obtain the desired properties for a specific application. Plasma-enhanced atomic layer deposition (PE-ALD) is a thin film technique which can deposit uniformal and conformal films with high thickness control at low temperatures. The presented studies show that PE-ALD is able to deposit ZnO with small amount of impurities as low as room temperature. Furthermore, by variation of the substrate temperature, ideal temperature regions for specific applications and the relationship between growth and resulting properties could be identified. In the beginning of the deposition, deviations from the ideal growth occur, which are identified as substrateenhanced island growth. The formation of crystallites is found to occur after this initial growth periode. The obtained knowledge about these growth characteristics is furthermore applied to piezoelectric devices. The piezoresponse of ZnO, sandwiched between electrodes, is hereby studied on both flexible and rigid substrates with a combination of macroscopic and scanning probe techniques. Vapor phase infiltration (VPI) is a technique for transforming polymers into hybrid organic/inorganic materials. It often uses the same precursors as ALD but instead of growing a thin film on a substrate, the polymer free volume is infiltrated with the precursors. In the thesis, the successfull infiltration of ZnO into polyisoprene is presented. Polyisoprene is an elastomeric polymer, a class of polymers which has not been widely studied as a substrate for VPI. The infiltration kinetics and the chemical mechanisms of this system are presented and it is shown that pre-heating of the polymer largely affects these due to changes in thickness and chemical structure. Concluding, the thesis gives fundamental insights into the growth characteristics for a future application of ZnO thin films or polymer/ZnO hybrids in diverse fields as well as a demonstration of ZnO in a piezoelectric device. 

Atomic Layer Deposition (ALD) is a cyclic process in which volatile precursors are reacted with a surface to generate a single layer of atoms or molecules and this process can be repeated to tune the thickness of these layers. Currently ALD is used in the manufacturing of silicon-based semiconductors, but the process faces reactivity issues that hinder its efficiency. A new set of precursors of the form X3SiCo(CO)4 have been proposed to fix these reactivity issues. In order to study the mechanistics of this process, analysis of the interaction between the X3SiCo(CO)4 compounds and the surface must be observed. Due to heterogeneity of the surface and the small number of atoms involved model systems can be a powerful tool to better understand the chemistry occurring at the surface. The model system chosen for this experiment is a compound called silsesquioxane that mimics the silicon surfaces reactivity, but also is available in the aqueous form. The experiment will be analyzed using electrospray ionization mass spectrometry (ESI-MS) coupled with a sample acquisition technique called pressurized sample infusion (PSI). These techniques were chosen because of their ability to handle highly air- and moisture-sensitive compounds as well as their ability to acquire data in real time. In order for mass spectrometry to be used, the precursors had to be charged and this was done by reacting the precursors with phosphine charged tags which generated charged analogues of the ALD precursors. These techniques were also used in a collaboration project to examine the reduction of bis(cyclopendadienyl)titanium(IV) dichloride (Cp2TiCl2) with manganese dust in dry THF with the manual addition of deoxygenated water. This reaction undergoes colour change from the initial red titanium species to the green reduced species and finally deep blue once the deoxygenated water is introduced to solution. ESI-MS was used at each of these colour changes to observe the reaction intermediates and help elucidate the reaction mechanism. 

Nickel oxide and palladium are used within various device heterostructures for chemical sensing, solar cells, batteries, etc. There is increasing interest in realizing flexible, low-cost, wearable electronics to enable ubiquitous sensors, next-generation displays, and improved human-machine interfaces. A major hurdle for flexible technology is the development of low temperature fabrication processes for the integration of inorganic devices with polymeric substrates. Here we investigate area-selective atomic layer deposition of NiO performed at 100 °C using bis(N,N'-di-tert-butylacetamidinato)nickel(II) and water on SiO2 and polystyrene. NiO grows two dimensionally and without nucleation delay on oxide substrates but not on SiNx or polystyrene, which require surface treatments such as an Al2O3 buffer layer or O2 plasma treatment to promote NiO nucleation. Additionally, prepatterned sp2 carbon-rich resists inhibit the nucleation of NiO. This way, carbon-free NiO may be patterned. A NiO grid pattern is fabricated as a demonstration. 10 Additionally, thermal reduction of NiO to Ni was explored using H2 (50-300 mTorr) and thermally generated H-atoms (3×10-5 Torr chamber pressure). Due to the relatively high free surface energy of metals, Ni films undergo dewetting at elevated temperatures when solid-state transport is enabled. Reduction of NiO to Ni is demonstrated at 100 °C and below using atomic hydrogen, a temperature low enough to be compatible with organic substrate temperature constraints as well as to avoid significant dewetting. Finally, the area-selective atomic layer deposition of Pd by area-activation is studied. Thermal atomic layer deposition of Pd can only proceed at low temperatures on surfaces that can dissociate the coreactant, H2. Prepatterned Ni functions to catalyze the nucleation of Pd at 100 °C. H-atom reduction of NiO grown by atomic layer deposition can generate an atomically smooth Ni surface, which allows the growth of void-free Pd films. Finally, the area-selective atomic layer deposition of Pd on patterned Ni grid lines is explored 

Abstract Chemical vapor deposition (CVD) and atomic layer deposition (ALD) are corner-stone techniques for depositing thin films in semi-conductor manufacturing. To deposit semiconductor grade materials, these techniques rely on high-performance precursors. This thesis covers synthesis, characterization, and evaluation of 1,3-dialkyltriazenides of group 11–14 metals as precursors for CVD and ALD. Triazenides had previously not been used as precursors for ALD, nor any other CVD process. The gallium and indium triazenides were used for ALD of indium- and gallium nitride and yielded materials of superior quality over other precursors. The success of these precursors sparked subsequent investigation into triazenides of zinc, and the group 11- and 14 metals. These triazenides showed high volatility and thermal stability making them highly interesting as CVD and ALD precursors. 

Hydrogen is considered a promising energy source with zero emission of CO2; it can provide higher energy density compared to other sources of energy. The amount at which H2 is produced, and the method of production need further improvement for the advancement of hydrogen energy technologies. Water electrolysis using renewable energy sources such as electrical, solar, and wind energy is one of the alternative technologies that can produce pure H2. However, water electrolysis itself is not an easy process, it requires a highly active catalyst capable of converting water into hydrogen, and oxygen.
This Ph.D. dissertation mainly focuses on developing efficient, robust, and low-cost catalysts for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and Oxygen reduction reaction (ORR). The work describes different strategies for improving the performance of the catalyst, such as creating nanocomposite, Nobel metal decoration, core-shell structures, hierarchical nanostructure, and cocatalyst and protective layers, which are vital for improving the efficiency of the catalyst. Consequently :
Nanocomposites composed of Ag2S nanoparticle, MoS2, and reduced graphene oxide (RGO) flake, with a 0D/2D/2D interface were synthesized. Ag2S nanoparticles were homogeneously distributed and embedded in a layer of semi-crystalline MoS2 nanosheets. The ternary catalyst results in a superior performance due to the intimate contact created by the 2D-2D interface (MoS2/RGO) and due to the uniformly grown Ag2S nanoparticles, which provides the ease of hydrogen adsorption by modulating the electronic properties, and exposure of highly rich active sites
Nobel metal decorated (Ag-decorated vertically aligned MoS2 nanoflakes) were developed and investigated for OER and ORR. Results of this work revealed that, due to the presence of silver, the catalyst shows more than 1.5 times an increase in the roughness-normalized rate of OER. Based on the rate constant values obtained during the ORR test, Ag-MoS2 proceeds through a mixed 4 electron and a 2 + 2 serial route reduction mechanism, suggesting that the presence of silver decreases the electron transfer number and increases the peroxide yield. 
A core-shell structure of hydrous NiMoO4 micro rods conformally covered by Co3O4 nanoparticles was developed and employed as an OER catalyst, showing a remarkable catalytic activity towards OER with a record low overpotential of 120 mV at 10 mA/cm2. Here, the strong interactions between core (hydrated NiMoO4) and shell (Co3O4) help to tune the electronic properties by modifying the active sites densities of the surface.
A hierarchical nanostructure composed of NiMoO4 nanorods and MoS2 nanosheets was synthesized on interconnected nickel foam substrates. The as-prepared hierarchical structure exhibits excellent OER performance due to its numerous exposed active sites for adsorbing oxygen intermediates which are beneficial for promoting the enhancement of the OER catalytic performance
Cu2O photocathode protected by a very thin layer of TiO2 and an amorphous Vox were synthesized and used for HER, with aim of improving the photostability of Cu2O. Photooxidation of Cu2O nanowires are minimized by growing TiO2 protective layer and an amorphous VOx cocatalyst. After optimization of the overlayer and the cocatalyst, the photoelectrode exhibits a stable photocurrent density for an extended illumination time. 
Besides, advanced characterization tools were used for tracking ORR reaction intermediates and OER active sites. RRDE, Operando Raman, and synchrotron-based photoemission spectroscopy analysis were utilized together with Post OER characterization tools to reveal the reason behind the higher catalytic activity of the catalyst. 
In summary, the presented outcomes can significantly contribute to the fundamental insight towards improving the efficiency of HER, OER, and ORR catalyst, by offering a clear and in-depth understanding of the preparation and characterization of cheap and efficient catalysts.
 

Enabling self-healing of materials is crucially important for saving resources and energy in numerous emerging applications. A plethora of recently published research works is dedicated to the development of strategies which allow for self-healing of materials, especially of those with certain technological importance. Given that most of the approaches are based on chemical processes, the vast majority of these works focus on the self-healing of organic materials, specifically polymers. At the same time, there is a growing demand for adapting such functionality to inorganic materials due to their importance in most developed electronics, including flexible electronics. The few existent examples of self-healing of inorganic materials rely on the incorporation of liquid healing agents, such as liquid metals or liquid precursors, into the devices. However, the development is in its infancy and further progress remains very challenging, mainly because of a lack of feasible healing agents and suitable ways to supply them to the damaged site.

In this thesis we have developed a concept for the self-healing of metal oxides, which is the most challenging type of material in this research area. This concept consists of growing metal oxide nanoparticles inside the bulk of halogenated polymers via vapor phase infiltration and their subsequent entropy-driven migration to externally induced defect sites, which eventually leads to the recovery of the defect. The hybrid material, i.e., the polymer matrix with dispersed NPs, can serve as a reservoir with healing agents for the repair of a cracked MeO film. The self-healing of inorganic materials and structures was realized also without liquid agents by making use of the mobility of inorganic NPs within polymers, as the spatial distribution of NPs can be tuned by means of harnessing both enthalpy and entropy.

Herein we present an expansion of the pool of self-healing materials to semiconductors such as indium, zinc, indium tin and zinc indium oxides, thereby allowing to increase the reliability and sustainability of future functional materials. We revealed that not only the morphology, but also the electrical properties of ITO can be largely restored upon healing. Such properties are of immediate interest for the further development of transparent flexible electrodes.
 

Two-dimensional (2D) materials rank among the most scientifically exciting materials of the early 21st century. Transition metal dichalcogenides (TMDCs) have emerged into the spotlight due to the semiconducting nature of many TMDCs, which is in contrast to the most actively studied 2D material, semimetallic graphene. Research on the basic properties of TMDCs has been very active and fruitful, resulting in unveiling of many new phenomena and properties. Furthermore, there is a strong drive to realize the technological potential of TMDCs. For use in practical applications, TMDCs need to be synthesized as uniform films of controlled thickness on large and complex substrates. In order to realize cost-effective industrial production, the synthesis needs to be done at low temperatures using methods that are highly controllable, scalable, and repeatable. Atomic layer deposition (ALD) is an advanced gas-phase thin film deposition technique capable of fulfilling the requirements of many demanding applications. ALD has already proven its industrial applicability in fields ranging from electroluminescent displays to microelectronics, photovoltaics, and corrosion protection. To realize the potential of ALD in the deposition of TMDCs, suitable ALD precursors possessing adequate reactivity, volatility, and thermal stability have to be identified and evaluated. In this thesis, 29 precursor candidates were tested for seven metals. Successful ALD processes were developed for five 2D sulfides: MoS2, SnS2, WS2, HfS2, and ZrS2. In addition, ALD processes were developed for oxides of molybdenum and tungsten. The oxides may be converted into the respective 2D sulfides. Furthermore, α-MoO3 is a 2D material by itself. The sulfide processes varied in terms of their growth behavior and morphology of the films. All of the films crystallized in 2D structures. In the case of SnS2 and WS2, crystallization required mild post-deposition annealing, which preserves the smooth morphology of the as-deposited amorphous films and gives an additional degree of freedom in processing. Particular attention was paid to the role of the substrate in the growth of TMDCs in tuning the film growth, morphology, and crystallinity. HfS2, MoS2, SnS2, and ZrS2 films were observed to grow in a van der Waals epitaxial manner on mica, which is a promising approach to achieve high film quality under mild conditions. Once the deposition processes are developed, the produced films should be evaluated for the target applications. A major challenge is to improve the performance of large-area TMDC films grown under application-relevant conditions up to the level of TMDC flakes that have been manually exfoliated from bulk crystals. The possible applications of ALD TMDCs are comprehensively reviewed in the literature part of the thesis. In the experimental part, results on photodetector (HfS2, SnS2, and ZrS2), field-effect transistor (SnS2), and hydrogen gas sensor (MoOx) devices are shown. It is anticipated that the processes developed in this thesis can be used also for other applications. For example, the rough MoS2 and disordered WS2 films should be promising for energy storage and conversion applications. 

Atomic Layer Deposition (ALD) is a promising method to deposit thin films on 3D−substrates without compromising high uniformity and conformality. In ALD, the substrate is repeatedly exposed to a sequence of reactive gases. Between each gas exposure, a pump/purge step is implemented to reach very low pressure in the ALD chamber (typically in the order of 10−6 mbar). The gases will react with the available surface groups of the substrate, adding atomic amounts of material to the substrate. A distinct feature that sets ALD superior to other methods is its self-limiting character. This means, when all the surface groups have been reacted with the introduced gas, the reaction stops. The high conformality and uniformity of ALD are benefited from its self-limiting character. Another gas exposure is followed after the pump/purge step to refresh the surface before the growth can continue. One ALD cycle will thus consist of a loop of alternated exposures of the two reactive gases. Often, the reactant in the first half cycle is called precursor, which is the source of metal. The reactant in the second half cycle is called the co−reactant, which assists the transformation of the precursor adsorbed on the substrate into the target material. The ALD cycles can be repeated until the desired thickness of the material has been achieved. Thanks to these unique features, ALD finds a lot of commercial applications including microelectronics, photovoltaics, and batteries. It is possible to deposit a wide variety of materials, including oxides, nitrides, sulphides, phosphates, and (noble) metals via different ALD chemistries. The first part of this thesis deals with the development of a novel ALD chemistry for deposition of ruthenium dioxide (RuO2) which is an interesting material for several applications, including (electro)catalysis and microelectronics. A new thermal ALD process for RuO2 deposition was developed and its ALD characteristics were determined. The process uti[1]lizes ruthenium tetroxide (RuO4) as the precursor and alcohols as a (mild) reductant to deposit RuO2. The deposition was feasible at temperatures as low as 60 ◦C and had a temperature window from 60−120 ◦C. The growth per cycle (GPC) of the process can be tuned by changing the alcohol counterpart. For instance, the use of methanol resulted in a GPC of 1 Å/cycle, ethanol in 1.5 Å/cycle, while in the case of 1−propanol and 2−propanol it was around 2 Å/cycle. The films were as−deposited amorphous from lab−based XRD. An anneal in helium or in air transformed the films into crystalline rutile RuO2 around 420 ◦C. The process also allowed for the deposition of smooth and conductive RuO2 films. Insights into the reaction mechanism were obtained by using several in situ techniques including in situ Fourier transform infrared spectroscopy (FTIR), mass spectrometry, and in vacuo X−ray photoelectron spectroscopy (XPS). Hence, we put forward the following mechanism. During the alcohol-containing pulse, the top RuO2 layer is partially reduced to RuOx (x<2), and consequently the alcohol is oxidized on the RuO2 surface into CO2 and H2O. The alcohol pulse also leaves carbon monoxide (CO) residues on the surface. During the RuO4 pulse two reactions occur: 1) oxidative removal of CO to CO2, 2) surface oxidation back to RuO2. In this reaction additional RuO2 is deposited on the surface. As discussed before, ALD offers conformal coatings on the substrate, however, for certain applications including the creation of nanostructures, (nanoparticles, nano lines etc.) limiting ALD growth in the lateral direction is very important. In this aspect, we show the potential of area−selective atomic layer deposition (AS−ALD) to derive nanostructures in a bottom[1]up fashion. Area-selective deposition takes place during the initial ALD cycles if an ALD process induces immediate growth on the surface of one particular material while there is a delay before the growth commences on the surfaces of other materials that are present on the same sample. This results in the formation of nanostructures that resemble the pattern of the growth surface. In this work, area−selective ALD of RuO2 is demonstrated using the ALD process consisting of RuO4 and alcohols as discussed before. Selective RuO2 deposition was achieved on SiO2 with inhibition on poly methyl methacrylate (PMMA). There was no deposition on PMMA blanket films even up to 200 ALD cycles, resulting in around 25 nm of selective RuO2 deposition on SiO2. Different parameters affecting the selectivity of the process were studied, including polymer thickness and deposition temperature during ALD. The feasibility of selective deposition with other co-reactants such as ethanol and iso-propanol was investigated, and we found that the growth per cycle can be increased by using a higher chain alcohol without compromising the selectivity. Other polymer layers were also studied as potential inhibition layers for AS−ALD of RuO2. Polymers with C=O functional groups effectively inhibit RuO2 growth. The developed area selective method was demonstrated by selectively depositing RuO2 on patterned SiO2/PMMA samples, followed by PMMA removal, resulting in RuO2 nanopatterns on the surface as demonstrated by transmission electron microscopy (TEM), and scanning electron microscopy with energy dispersive X−ray spectroscopy (SEM/EDX). Furthermore, we demonstrate sequential infiltration synthesis (SIS), an[1]other ALD−derived method that is quite promising for synthesizing inor ganic nanopatterns. This technique is based on the block selective infiltra[1]tion of ALD precursors and reactants to one of the blocks of a di−block copolymer (di−BCP) template. This results in inorganic material growth inside one of the domains of the di-BCP. The polymer template can be re[1]moved by appropriate post-treatments to generate the desired nanopattern. In this work, Ru and RuO2 nanostructures are prepared by SIS. Using a self assembled polystyrene−block−polymethylmethacrylate (PS−b−PMMA) template, Ru and RuO2 nanostructures resembling the PS domain have been synthesized. RuO4 and H2 gas were used as reactants for Ru SIS and RuO4 and methanol for RuO2 SIS. Selective and strong interaction of RuO4 molecules with PS domains has been achieved, without affecting the PMMA domains. The aromatic C=C and C-H bonds present in the PS domain were consumed as a result of RuO4 infiltration. Density functional theory calculations also supported the favorable interaction with PS and a plausible mechanism for Ru infiltration was put forward. A single SIS cycle was found to considerably enhance the contrast of the PS domain in the template as found from morphological assessments. Finally, infiltrated PS−b−PMMA was subjected to an H2 plasma treatment to remove the organic template and to generate Ru nanopatterns. The crystalline nature of the samples was confirmed by grazing incidence wide angle X−ray scattering measurements and the samples after plasma showed a superior crystallinity to the as−infiltrated samples. Finally, we show a novel selective decomposition strategy to obtain BMNPs, exemplified for Pt-Sn BMNPs. Monometallic nanoparticles with ALD are typically obtained by exploiting the island growth mode during the initial stages of metal ALD growth. In island growth, the deposited material tends to settle on the grown material, resulting in island like particles. With subsequent ALD cycles, the particles grow big enough to coalesce, resulting in a closed or continuous metal layer. Therefore, one can limit the number of ALD cycles before a closed layer is formed if the goal is to deposit metal nanoparticles. However, it is more challenging to deposit bimetallic nanoparticles and regulate their composition using ALD.In this thesis, Pt-Sn bimetallic nanoparticles (BMNPs) are prepared by the selective doping of Pt NPs with Sn. This is based on the selective de[1]composition of tetrakis(dimethylamino)tin (TDMASn), a Sn ALD precursor on Pt. There was no decomposition observed on other substrates such as SiO2, Al2O3 and TiN. Although the selective decomposition on Pt resulted in Pt-Sn BMNPs, the morphology revealed significant coarsening after BMNP formation. The original size of the Pt NPs was preserved by the introduction of an extra H2 pulse after each TDMASn pulse, resulting in a cyclic TDMASn-H2 process. The differences between the TDMASn only and TDAMSn-H2 process were investigated using in situ characterizations. The H2 pulse performs a dual role in the process: removing the NCH3CH3 ligands from the TDMASn precursor on the Pt surface by the fromation of volatile NHCH3CH3 and removing superflous Sn from the Pt surface. The Sn uptake showed saturation as a function of TDMASn-H2 cycles, and the Sn content in the BMNPs was tuned by changing the substrate temperature. The formation of Pt-Sn BMNPs using the TDMASn-H2 process was also shown on high surface area SiO2 supports. In summary, creating nanostructures by ALD requires limiting the lateral growth of the ALD process. There are several ALD−related techniques that can be exploited for the synthesis of such structures. In the framework of this thesis, the potential of three different routes such as selective deposition, selective infiltration, and selective decomposition, is exploited for the tailored synthesis of nanostructured materials 

Desert sand acoustic emissions are produced when a “sonic sand” is sheared locally or by a natural dune slipface avalanche, resulting in a brassy sound between 50 and 400 Hz. This type of sediment exhibits particular granulometric, shape and surface characteristics, due to the grains’ erosion and transport history, and emits sounds when the sheared grain layer vibrates in a synchronized manner, much like the membrane of a speaker. Recording such sand acoustic emissions on Mars (and perhaps other planetary environments) using rover microphones could thus become a new form of observable for scientists to estimate the surface sediment’s characteristics and history from a distance, but also the granular flow dynamics taking place. To determine whether this approach could be viable in the future, it is essential to evaluate how the Martian environment may affect sand acoustic emissions differently than on Earth. After showing that the muted Martian soundscape would likely allow rovers to detect such signals from a few tens of meters, the present thesis studies the impact of the interstitial air pressure within the sand bed on the sound emission mechanism of such sonic desert sands.

In this project, silent and sonic desert sand shear flows are induced under a range of pressure levels, from terrestrial ambient pressure to Mars-like pressure, within two separate, manually operated vacuum chamber setups: a smaller chamber shaken to create the sounds, and another longer chamber that better replicates avalanche-like sand flows. The motion applied and sound produced are measured using an accelerometer and a microphone inside the chamber. Metrics in the time and frequency domains are defined to analyse the changes in sound energy, amplitude, and frequency components produced at different pressure levels. Firstly, the silent sand tests are used to establish how the air pressure level within the experimental setup affects the regular sound of sheared sand (i.e. grains impacting one another) and more generally the sound emission of “normal” sounds, whose emission mechanisms do not depend on grain packing and synchronized motion. Then, a simplified theoretical model of how the sound pressure level (SPL) of a sound evolves with decreasing acoustic impedance, is derived and validated using the silent sand measurements performed. Finally, the sonic sand measurements are compared to the SPL model and silent sand measurement results, which are used as a baseline for nominal sound production behavior, to evaluate how the interstitial air pressure affects the amplitude and signal energy of the sheared sonic sand emissions. Furthermore, differences in the sand acoustic emissions’ frequency spectra and time duration across pressure levels provide information about the possible physical changes occurring in the granular flow dynamics of the sheared sonic sand.

In both experiments, the dominant frequency very closely follows the trend of the motion metrics used, as described in the literature, and remains very consistent across pressure levels. This suggests that the maximum sheared sonic sand layer thickness is independent of the interstitial air pressure. Then, the sonic sand emissions see an increase in the sound amplitude and signal energy related metrics from ambient pressure to 413.25 mbar, unlike the gradual decrease predicted by the SPL model and the trend of silent sand measurements with decreasing pressure. Below 413.25 mbar, the results suggest a stabilized behavior, with the acoustic metrics of the emissions following the model. Furthermore, in the avalanche-like emissions, a new frequency component slightly higher than the dominant frequency emerges as the chamber pressure decreases. These observations are evidenced in the time-domain, where the sand acoustic emissions seem to initiate earlier in the granular flow at 413.25 mbar and below, resulting in greater acoustic pressure levels being produced, compared to those at terrestrial pressure. It is hypothesized that more sheared sonic sand grains synchronize at 413.25 mbar and below (compared to terrestrial air pressure), and thus increase the amplitude of the sound wave produced. For avalanche-like flows, the new frequency component that appears with decreasing pressure level seems to suggest that the minimum sheared layer thickness threshold required to produce an emission is lowered at lower pressure, which leads to a higher frequency produced initially until the full layer forms, ultimately decreasing the frequency. Further research is required to confirm these preliminary findings and theories. 

Thin films are at the core of a variety of applications. In that, hybrid films are unique as they combine the properties of their inorganic and organic constituents in the same film. To synthesize thin, conformal and uniform hybrid films with controlled composition, molecular layer deposition (MLD) is a familiar and accomplished technique. The general aim of this dissertation is to investigate routes to realize high-throughput, reproducible processing of hybrid films using MLD where the following chapter serves to lay the foundation and discuss the outline. Firstly, the chapter introduces the technique of molecular layer deposition (MLD) as a part of the well-established atomic layer deposition (ALD) and chemical vapor deposition (CVD) family. Further introduced is an ALD processing scheme called spatial ALD that can be used for high throughput MLD. Lastly, few challenges and research questions related to the upscaling of hybrid MLD using spatial MLD that this dissertation aims to answer are laid out.

In the trend of Internet of Things (IoT), technologies that integrate CMOS (complementary metal-oxide-semiconductor) electronics with MEMS (microelectromechanical systems) exhibit a promising way to fulfill ever smaller, more power-efficient, and more customized and intelligent devices through system integration and miniaturization. To enable the nextgeneration micro-sensors and other micro-devices, micromechanical structures made from the CMOS back-end-of-line dielectric and metal layers provide for low-cost monolithic integration of MEMS with circuits. One issue with this CMOS MEMS technology is the dielectric sidewalls on the released structures and the resulting charging phenomena that degrade the performance. The dielectric sidewalls also prevent the electrical conduction under the mechanical forces after the MEMS structure is released. To solve these issues, this work develops a novel CMOS MEMS postprocessing technique by integrating a selective atomic layer deposition (ALD) coating over the microstructural sidewalls of interest. A conductive ALD layer, such as Pt, is applied to the capacitor sidewalls to eliminate the dielectric charging phenomenon. Moreover, CMOS MEMS metal-metal contact switch is demonstrated by coating ALD metal on contact sidewalls. This work successfully demonstrates the implementation of the ALD sidewall patterning technique and validation through multiple CMOS MEMS devices and applications, including resonator oscillators, switches, and accelerometers. A generalized lift-off-based ALD sidewall patterning process is implemented, which can support the high-aspect-ratio MEMS structure (at least > 10:1). The process is able to coat a conformal ALD film on the selected sidewalls of interest without causing a short circuit. A conductive ALD film is patterned on the capacitor sidewalls of a resonator oscillator to eliminate dielectric charging phenomena that cause the resonant frequency drift. TiO2-coated and Pt-coated devices are fabricated, measured, and compared with the uncoated counterparts. The charging time constant is reduced by over three orders of magnitude. Without the drift from charging, the instability at room temperature of 1.3 ppm is demonstrated computed from Allan deviation analysis at the averaging time of 300 s. Benefiting from the ALD sidewall patterning process, a lateral metal-metal contact switch is implemented in CMOS MEMS by patterning Pt ALD metal on the sidewalls and interconnecting to metal layers on the structural area of the contact. The lateral motional configuration allows the design of different tips and flexural springs as compliant blocking VI contacts with an intent to reduce the contact resistance. The results show that the lateral switches with a spring contact design provide the capability to lower the overall contact resistance. In this thesis, we develop a generalized ALD sidewall patterning process to eliminate the dielectric charging effect, explore the lateral ohmic contact switch, and study the benefits provided in this post-processing. This technique opens a way in CMOS MEMS for higher performance and wider application by modifying its dielectric sidewalls by coating with a conductive ALD film. 

This thesis presents a collection of work investigating the application of hafnium oxide (HfO₂) thin films as both wet-chemical and surface-state passivation layers for photovoltaic (PV) and electronic devices. Surface-state passivation layers are an essential aspect of silicon (Si) based PV devices, preventing carrier recombination that would otherwise occur for direct metal-Si contacts; thus increasing conversion efficiency. Such layers – often dielectric thin films – can either be used as ‘passivation layers’ whereby the films are regionally etched to allow direct metal-Si contact, as in the case of Passivated Emitter and Rear Contact (PERC) cells, or ‘passivation interlayers’ where the dielectric is kept in place between the metal and Si in a passivating contact structure, with the Tunnel Oxide Passivated Contact (TOPCon) cell. 

HfO₂ is shown to have excellent potential as a passivation layer, producing surface recombination velocities (SRVs) <1 cm/s with just 2.5 nm of material, which is competitive with current commercially used dielectric passivation layers. However, the conflicting annealing temperature dependence of passivation and conductance suggests that the use of HfO₂ as a passivating interlayer is limited. A novel form of passivating contact structure is introduced, that utilises dielectric stacks with HfO2, which could provide a low-temperature alternative to the current silicon dioxide (SiO_x)/poly-Si passivating contact structure used in TOPCon. 

This novel structure relies upon the unique etching characteristics of HfO₂ when combined with an aluminium oxide (Al₂O₃) layer, which results in pinhole formation. HfO₂ is found to be highly resistant to HF etching when crystallised, but etches rapidly whilst in an amorphous state. This varying etch resistance could potentially provide a route to wafer patterning, through a combination of laser annealing and a simple HF dip. This technique is more easily scaled-up for industrial application than existing photolithography processes. This strong etch resistance suggests great potential for HfO₂ thin films to be utilised as protective barrier layers in complex device fabrication for both electronic and photovoltaic applications

In the last two decades, light-emitting diodes (LEDs) and organic light-emitting diodes (OLEDs) have driven the development of lighting technology and systems in terms of efficiency, performance and new applications. The market for these technologies is expected to keep rising in the next decades as a result of the large energy and climate crisis that our modern society is facing. However, the possibilities of integration of LED sources are very limited, because OLEDs rely on an expensive fabrication process, consisting of multiple low-pressure and high-temperature sequential layers.  Light-emitting electrochemical cells (LECs) are another class of thin film light-emitting devices based on the same type of organic semiconductors as those used in OLEDs but with a fundamentally different working mechanism. The simultaneous presence of electronic and ionic charge carriers makes LECs independent of the work function of the electrodes and can consist, in their simplest form, in a single active layer sandwiched between two electrodes. Thanks to these properties, LECs truly represent a promising alternative as cost-effective sources for general lighting applications.  In this thesis, various novelties are introduced in LEC devices and in their fabrication such as a new ionic transporting polymer, new emitters, and finally the use of novel characterization methods new to the field of LECs, that give important insight in the functioning and shortcomings of these devices. In this Thesis, we demonstrate the introduction of a new ionic transporting polymer for polymer LECs. The concentration of the ionic transporting polymer and salt were optimized allowing to obtain state-of-the-art devices with long lifetime and brightness (over 1600 operational hours above 300 cd/m2). A new characterization tool was also used to probe the photoluminescence signal under electrical bias of a device. Thanks to this setup, it was possible to link the photoluminescence decay with the different phases of the turn-on and the recovery after turn-off.  Secondly, in the field of semitransparent optoelectronics, we also developed efficient semitransparent LECs with a unique SnO2/ITO-based top cathode fabricated with atomic layer deposition and pulsed laser deposition techniques. The high transparency of the cathode resulted in a peak transmission of 82% corresponding at the electroluminescence peak (563 nm). Interestignly, the two sides of the devices show a different luminance response to the electrical bias. The down side (anode side) shows higher luminance and longer lifetime than the up side (cathode side). We concluded that few possible reasons of this behavior can be associated with the different refractive indices of the substrate/anode and cathode, internal reflections and electroluminescence quenching. To prove this, photoluminescence measurements were done by irradiating either the down or up sides. The results indicate that the photoluminescence intensity is lower when measured exciting from the top side, suggesting that anode and cathode quench the photoluminescence by non-radiative recombination in different levels and that the additional damage might be caused by the cathode deposition techniques.  Finally, a series of copper(I) and platinum(II) complexes are used into working LECs. New emitters for light-emitting devices are necessary in order to mitigate the high costs of the most common iridium(III) compounds. In the last few years, Cu(I) complexes have rapidly grown in interest inside the LEC field showing fast progresses, on the other hand, Pt(II) complexes have only found application in LECs only very recently. Here, first we focus on how different anions affects copper(I)-LECs and second, on the fine-tuning of the ligands to achieve for the first time blue/green electroluminescence from platinum(II)-LECs.  In summary, supported by comprehensive electrical device characterization and photoluminescence studies, this work demonstrates the applicability of these novelties to LECs and more in general to solid-state light-emitting devices. 

The aim of this study is to advance the technique of fluorescent assays by using metallic nanostructures, which can enhance the fluorescence of molecules placed at nanometric distances. Enhancing fluorescence signals while keeping a good signal-to-noise ratio is very important for detection of low amounts of analytes in diagnosis of infectious diseases and cancer cells; and in monitoring of healthy, food and environment. For reproducibility reasons, a choice was made to work with structures constructed by electron-beam lithography in conjunction with atomic layer deposition and thermal evaporation. The structures consisted of two-dimensional periodic arrays of silver nanocylinders and dimers with and without an underlying thin silver layer. The reported investigations comprised three parts: fluorescence bead assays for RNA detection, a study of the optical/plasmonic properties of the nanostructures, and fluorescence experiments on these nanostructures.  Before entering in the plasmonics field, we explored a fluorescence-based technique for detection of labelled RNA of a specific pathogen using microspheres ow cytometry. We used a 2100 Bioanalyzer (Agilent Technologies), a commercially available desktop lab-on-a-chip ow cytometer. We demonstrated the detection down to 125 ng of RNA, 16 times less than previously reported.  Subsequently, we studied the plasmonic properties of specific electron-beam fabricated nanostructures, and to this aim we examined the dispersion relations of nanoscale planar multilayer metallic-dielectric films. For the first time, to our knowledge, it was obtained a solution for an IIMI (insulator-insulator-metal-insulator) configuration, using metal permittivity given by the lossless Drude's model as well as tabulated in the literature. This IIMI geometry is related to the fabricated nanostructures with an underlying silver layer. We showed that the studied structures and excitation can match the wave vectors required for excitation of propagating surface plasmons on the planar metal layer. We also showed that an extraordinary transmission achieved for the nanoparticles over that metal layer is due to the periodic array, but it cannot be attributed to propagating surface plasmons.  Further, a thorough study of the optical/plasmonic properties on the nanostructures was performed by finite element method (FEM) using the software COMSOL Multiphysics 3.5a with the RF module. We found that clear dipolar and quadrupolar resonant modes of localised surface plasmons were excited on the nanoparticles. These modes can be tuned by controlling some parameters, such as nanoparticles-metal layer thickness, refractive index of dielectric layer, the thickness of a cap dielectric layer and the cylinder diameter. The structure can also be applied in SPR sensing based on wavelength interrogation. The near-_eld of the metals enhances the second power of the electric _eld averaged over the top surface of the structure, where a fluorescence assay can be performed. The presence of the underlying silver layer red shifts the resonances and provides further enhancement to the squared electric _eld. The highest enhancement was achieved by a dimer in longitudinal polarisation. The factor was about 21.8 times higher than the one obtained by a simple dielectric substrate.  The fluorescence experiments were carried out on 55 to 60nm layers of polyvinyl alcohol (PVA) embedded with fluorochromes over the nanostructures. Fluorescence enhancement of up to 30.8 times, compared to bare dielectric substrate, was achieved on experiments with a homogeneous silver layer without nanoparticles. Most experiments with the nanocylinders over a planar silver layer showed reduced enhancement compared to structure with just the silver layer. This can be explained by modifications in the non-radiative routes, quenching the fluorescence.  In conclusion, we investigated the properties of a periodic array of silver cylinders and dimers, and the effects of an underlying thin silver layer. We showed how to tune the surface plasmon resonances by varying material and geometric parameters. The enhanced electric near-field provided by these structures can be applied in surface-enhanced fluorescence. Experiments showed fluorescence enhancement factors up to 20 times. With further numerical studies of electric field and modifications of radiative and non-radiative decay routes, it is possible to offer a complete description of fluorescence enhancement and to optimise it. 

This thesis presents a series of experiments into improved surface passivation of monocrystalline silicon, with a focus on chemical treatments and thin-film growth. A series of studies have been designed and performed for both passivation approaches.

Superacid chemical treatments offer excellent passivation of silicon (and of other electronic materials such as transition metal dichalcogenides - TMDCs), and the factors contributing to this are explored herein. A multi-material study is conducted into the behaviour of the superacid bis(trifluoromethanesulfonyl)imide (TFSA), using species with key chemical substitutions to assess the impact of functionality on passivation. The best silicon passivation is achieved by chemical treatments which introduce charge to the surface and those chemicals with CF₃SO₂ functionality, although an alternative mechanism for TMDCs must apply, as the trends observed with silicon are not consistent with those observed for TMDCs.

Superacid treatments can also be used to identify and diagnose degradation in silicon through re-passivation. The optimisation of sample processing for re-passivation is discussed, and subsequently three examples of re-passivation studies are presented. A particular focus is paid to temperature-induced degradation of Si/HfO₂ and Si/Al₂O₃, along an example of muon-induced degradation.

The latter half of this thesis focuses on silicon passivation via thin films. Ultra-thin SiO₂, Al₂O₃ and HfO₂ films are developed, with HfO₂ appearing a particularly promising ultra-thin passivation layer due to its passivation quality and negative fixed charge. Importantly, at nanoscale thicknesses, HfO₂ outperforms Al₂O₃, suggesting it is a promising alternative material for passivating interlayers of the kind which are needed for carrier selective contacts for solar cells.

Subsequently, two means to improve the passivation quality of ultra-thin HfO₂ are identified, namely the use of capping layers and chemical treatments to form chemically-enhanced passivating stacks. The improved passivation is found to be temporally stable, and resistant to further solution and thermal processing.

Flexible electronic circuits require thin conductive layers to act as contacts and interconnections. When using polymeric substrates, these layers must be deposited by low-temperature processes, which are essential to maintain the substrate’s original properties. With the purpose of achieving low resistivity and high confor-mality to polyimide step structures, thin films consisting of titanium nitride (TiN) and aluminium-doped zinc oxide (AZO) were grown by plasma enhanced atomic layer deposition (PEALD), and thermal atomic layer deposition (ALD) respectively. The optimized process conditions included temperature, plasma composition, and duration for the TiN, and doping concentration for the AZO. The precursors/co-reactants used were tetrakis(dimethylamino)titanium (IV), Ti[N(CH₃)₂]₄ and N₂ or H₂/N₂ plasma for the TiN, and diethyl-zinc, Zn(C₂H₅)₂ and water for the ZnO, doped with cycles of trimethyl-aluminium, Al(CH₃)₃ and water for the AZO. The TiN depositions were performed at Tyndall National Institute, while the AZO was produced at CENIMAT.
The samples were characterized by Hall effect measurements, profilometry, X-ray photoelectron spec-troscopy, X-ray diffraction, electron dispersive spectroscopy, transmission and scanning electron microscopy, and Raman spectroscopy. The best resistivities obtained were 1.67×10^-3 Ω.cm for an AZO sample deposited at 180 ºC, with 1.94% atomic Al, and 3.07×10^-3 Ω.cm for a TiN film produced at 300 ºC, with a 20 s H₂/N₂ plasma. TiN and AZO films grown on patterned polyimide over glass step structures at 250 ºC and 150/180 ºC respectively exhibited above 90% conformality, opening the possibility of their application in polymeric flexible electronic devices.

Molybdenum disulfide (MoS₂) has emerged as a semiconducting alternative to graphene for nanoscale optoelectronics, exhibiting novel optical and electronic properties at single-layer thickness. The scalable integration of monolayer MoS₂ (1L MoS₂) in mass-produced devices requires large-area monolayer films, typically grown via chemical vapour deposition (CVD). Despite favourable photoluminescence, the emission efficiency from untreated 1L MoS₂ is poor, limiting its practical optoelectronic suitability. Moreover, the realisation of MoS₂-based field-effect transistors demands the deposition of high dielectric constant (high-κ) materials. Growth of uniform high-κ layers on 1L MoS₂ via traditional thermal atomic layer deposition (ALD) is challenging, and the dielectric growth characteristics on CVD-1L MoS₂ are not well understood. 

Here, the characterisation and treatment of commercially available CVD-grown 1L MoS₂ films are investigated. Spatial variability in the structural and optical properties of CVD-1L MoS₂ is revealed, and a robust characterisation process for assessment of treatment-induced modifications is developed. Two general treatments of 1L MoS₂ are explored and are found to have opposing effects on the optical performance: immersion in the superacid bis(trifluoromethanesulfonyl)amide (TFSA) and ALD of either aluminium oxide (Al₂O₃) or hafnium dioxide (HfO₂) films via water (H₂O) co-reactant. Tuneability of the optical properties of CVD-1L MoS₂ is demonstrated via selection of the applied treatment. 

Alternative co-reactants for ALD of high-κ dielectrics on CVD-1L MoS₂, namely oxygen (O₂) plasma and ozone (O₃), are explored, and the impacts on MoS₂ are evaluated. Plasma-enhanced ALD (PEALD) with O₂ plasma is found to oxidise MoS₂ to MoO₃, but successful growth of HfO₂ via O₃-based ALD is demonstrated. The nucleation and growth behaviours of Al₂O₃ and HfO₂ films grown on CVD-1L MoS₂ via H₂O-based thermal ALD are also studied. 

This thesis highlights various external treatments that can modify the optical, electronic, and structural properties of CVD-1L MoS₂ films for optoelectronic applications

This doctoral thesis belongs to the field of electrical engineering, materials science and nanotechnology, with a focus on thin-film deposition and semiconductor device fabrication. The work centers on the development, optimization, and application of atomic layer deposition (ALD) processes for hafnium dioxide (HfO₂) as a high-k gate dielectric in indium oxide (In₂O₃)-based thin-film transistors (TFTs). HfO₂ was selected for its high permittivity, thermal stability, and compatibility with low-temperature processing, making it well-suited for emerging applications in flexible and transparent electronics.
The research includes three main components: (i) precursor selection and ALD recipe development for HfO₂ deposition, (ii) integration of the optimized dielectric into In₂O₃ TFTs fabricated on both rigid and flexible substrates, and (iii) demonstration of area-selective ALD (ASALD) using Kapton tape masking to enable additive patterning without conventional lithography. Extensive material characterization was performed using spectroscopic ellipsometry, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) to evaluate film thickness, composition, and surface morphology. Electrical characterization of the TFTs included transfer and output measurements, revealing consistent device performance with subthreshold swings as low as ~140 mV/dec and on/off ratios exceeding 10⁵, performance metrics that approach the upper range reported for solutionprocessed In₂O₃ devices using comparable fabrication approaches.
A hybrid ALD process was systematically developed to improve HfO₂ film quality at substrate temperatures below 150 °C, addressing key challenges in process conformality and interface quality. The incorporation of these optimized dielectrics into In₂O₃ TFTs resulted in enhanced switching behavior and reduced hysteresis, particularly on flexible polyimide substrates. Furthermore, the ASALD technique was employed to fabricate patterned dielectric with micrometer-scale resolution.
As a functional demonstration of the developed materials and processes, a novel inverter circuit was designed by integrating an ALD-based In₂O₃ TFT with a temperature-sensitive resistor. This circuit was combined with a printed energy storage module and an irreversible optical indicator to create a fully thin-film, CMOS-chip-free temperature sensor. The device provides a permanent visual output upon crossing a critical thermal threshold, highlighting a rare example of a monolithically integrated, selfpowered, disposable electronic label.
The findings demonstrate the viability of thermal ALD for high-performance oxide TFTs and the potential of ASALD as a lithography-free patterning technique for large-area, flexible electronics. This work contributes to the advancement of sustainable and scalable fabrication methods for nextgeneration electronic systems.