The atomic layer deposition (ALD) growth of titania thin films was studied for the infiltration of silica photonic crystals. Titania thin films were grown in a custom-built ALD reactor by the alternating pulsing and purging of TiCl4 and water vapor. The conformal nature of ALD growth makes it an ideal candidate for the infiltration of the complex opal structure. Titania is a high refractive index material, which makes it a popular material for use in photonic crystal (PC) applications. Photonic crystals are periodic dielectric structures that forbid the propagation of light in a certain wavelength range. This forbidden range is known as the photonic band gap (PBG). A refractive index contrast of at least 2.8 is required for a complete PBG in an inverted opal structure. Therefore, the rutile structure of titania is more desirable for use in PCs due to its higher index of refraction than the anatase or brookite structure. The growth mechanisms and film properties of the TiO2 thin films were studied. Investigation of the growth mechanisms revealed saturated growth rate conditions for multiple temperature regions. Film characterization techniques included XRD, SEM/EDS, XPS, AFM, reflectivity, and index of refraction measurements. Post growth heat treatment was performed to study the conversion from the as-deposited crystal structure to the rutile structure. After optimization of the deposition process, the infiltration of silica opals for PC applications was attempted. The filling fraction was optimized by increasing the pulse and purge lengths at a deposition temperature of 100oC. Although the silica opals were successfully infiltrated using ALD of TiO2, the long range order of the PC was destroyed after the heat treatment step required to achieve the high index rutile structure.

In the late eighties, a new class of materials, known as photonic crystals (PCs), emerged enabling the propagation and generation of light to be potentially manipulated with unprecedented control. PCs consist of a periodic modulation of dielectric constant in one, two, or three dimensions, which can result in the formation of directional or omni-directional photonic band gaps (PBGs), spectral regions where light propagation is forbidden, and more remarkably, novel dispersion characteristics. Since PC properties scale with the dimension of the wavelength of interest, significant technological constraints must be fully addressed to manufacture 3D PBG materials for optical or infrared applications such as displays, lightning, and communications. PCs enable the unraveling of unique optical phenomena such as PBGs, spontaneous emission rate manipulation, sub-wavelength focusing, and superprism effects. This research focuses on the feasibility to achieve omni-directional PBGs in synthetic opal-based 3D PCs through precise nanoscale control to the original dielectric architecture. In particular, the optical response to the conformal deposition of dielectric layers using atomic layer deposition (ALD) within the porous template is strongly emphasized. Geometrical models were developed to faithfully model the manipulation of the synthetic opal architecture by ALD and then used in electromagnetic algorithms to predict the resulting optical properties. From these results, this research presents and investigates a scheme used to greatly enhance and adjust the PBG width and position, as well as simultaneously reducing the dielectric contrast threshold at which the PBG forms. This Thesis demonstrates that the unique opal architectures offered by ALD not only supports the formation of larger PBGs with high index materials; but also enables the use of optically transparent materials with reduced refractive index. Additionally, slight alteration of these structures facilitates the incorporation of non-linear (NL) electro-optical (EO) material for dynamic tuning capabilities and potentially offers a pathway for fabricating multi-functional photonic devices. Finally, low-temperature ALD was investigated as a means to manipulate band gaps and dispersion effects in 2D PC silicon slab waveguides and 3D organic biologically-derived templates. The results indicate the unique ability of ALD to achieve composite structures with desirable (large PBGs) or novel (slow light) optical properties.

Vor dem Hintergrund der in der Mikroelektronik-Fertigung heute verbreiteten Kupfertechnologie werden in der vorliegenden Arbeit drei neuartige metallorganische Verbindungen, nämlich phosphitstabilisierte Kupfer(I)-Trifluoracetat-Komplexe vorgestellt und hinsichtlich ihrer Anwendbarkeit für die chemische Gasphasenabscheidung (CVD) von Kupfer untersucht. Im einzelnen handelt es ich um die Substanzen Tris(trimethylphosphit)kupfer(I)trifluoracetat (METFA), Tris(triethylphosphit)kupfer(I)trifluoracetat (ETTFA) und Tri(tris(trifluorethyl)phosphit)kupfer(I)trifluoracetat (CFTFA). Mit den Substanzen erfolgen CVD-Experimente auf TiN und Cu bei Temperaturen <400°C. Die Precursoren werden dabei mittels eines Flüssigdosiersystems mit Verdampfereinheit der Reaktionskammer zugeführt. Während METFA wegen seiner ausreichend geringen Viskosität unverdünnt verwendet werden kann, kommen für ETTFA und CFTFA jeweils Precursor-Acetonitril-Gemische zum Einsatz. Mit keinem der Neustoffe können auf TiN geschlossene Kupferschichten erzeugt werden, während dies auf Kupferunterlagen in Verbindung mit Wasserstoff als Reduktionsmittel gelingt. Die Abscheiderate beträgt hierbei 2-3nm/min; der spezifische Widerstand der Schichten bewegt sich zwischen 4μΩcm und 5μΩcm. Mit allen Substanzen werden besonders an dünnen, gesputterten Kupferschichten Agglomerationserscheinungen und Lochbildung beobachtet. Im Fall von CFTFA treten zusätzlich Schäden am darunterliegenden TiN/SiO₂-Schichtstapel auf. Vergleichende Untersuchungen mit der für die Cu-CVD etablierten Substanz (TMVS)Cu(hfac) ergeben sowohl auf Cu als auch auf TiN geschlossene Kupferschichten. Dabei liegen die Abscheideraten bei Temperaturen zwischen 180°C und 200°C im allgemeinen deutlich über 100nm/min. Ein Vergleich dieser Resultate mit den Ergebnissen für die Neustoffe legt nahe, dass den untersuchten Kupfer(I)-Trifluoracetaten keine ausreichende Tauglichkeit für Cu-CVD-Prozesse in der Mikroelektronik-Technologie bescheinigt werden kann. Die im Vergleich zu (TMVS)Cu(hfac) höhere thermische Stabilität der Precursoren und ihre Fähigkeit, mit Wasserstoff als Reaktionspartner auf Cu geschlossene Kupferschichten erzeugen zu können, deutet jedoch auf ihre eventuelle Eignung für ALD-Prozesse hin. Daher widmet sich die Arbeit in einem abschließenden Kapitel dem Thema der Atomic Layer Deposition (ALD), wobei nach einem allgemeinen Überblick besonders auf für die Mikroelektronik relevante ALD-Prozesse eingegangen wird.

To sustain future civilization, the development of alternative clean-energy technologies to replace fossil fuels has become one of the most crucial and challenging problems of the last few decades. The thin film solar cell is one of the major photovoltaic technologies that is promising for renewable energy. The current commercial thin film PV technologies are based on \(Cu(In,Ga)Se_2\) and CdTe. Despite their success in reducing the module cost below $1/Wp, these absorber materials face limitations due to their use of scarce (In and Te) and toxic (Cd) elements. One promising candidate for an alternative absorber material is tin monosulfide (SnS). Composed of cheap, non-toxic and earth-abundant elemental constituents, SnS can potentially provide inexpensive PV modules to reach the global energy demand in TW levels. Because of the high volatility of sulfur and various oxidation states of tin, non- stoichiometric chemical composition, traces of other phases \((i.e. Sn, Sn_2S_3, and SnS_2)\), and elemental impurities (e.g. oxygen) are usually observed in SnS films obtained from various reported deposition techniques. First, we present a process to prepare pure, stoichiometric, single-phase SnS films from atomic layer deposition (ALD). The as-deposited SnS films exhibit several attractive properties, including suitable energy band gaps \((E_{g,}~ 1.1 – 1.3 eV)\), a large absorption coefficient \((\alpha > 10^4 cm^{˗1})\), and a proper carrier concentration \(([p] ~ 10^{15} – 10^{16} cm^{˗3})\). Then, heterojunction solar cells were fabricated from p-type SnS and n-type zinc oxysulfide (Zn(O,S)). A record high active-area efficiency of 2.46 % was achieved via conduction band offset engineering by varying the oxygen-to-sulfur ratio in Zn(O,S). Finally, we address two approaches potentially used for improving a device efficiency of the SnS solar cell. First, via doping to create an n-type SnS, a p-n homojunction device could be made. We present the processes and the results of doping SnS films with antimony and chlorine, potential n-type dopants. Second, by post-deposition heat treatment, an improvement in the transport properties of SnS film can be achieved. We discuss the effect of temperature and an annealing ambient \((N_2, H_2S\), and sulfur) on grain growth and the electrical properties of annealed SnS films. / Chemistry and Chemical Biology

Tin(II) sulfide (SnS) is an earth-abundant, inexpensive, and non-toxic absorber material for thin film solar cells. SnS films are deposited by atomic layer deposition (ALD) through the reaction of a tin precursor, bis(N,N'-diisopropylacetamidinato)tin(II), and hydrogen sulfide. The SnS films demonstrate excellent surface morphology, crystal structure, phase purity, stoichiometry, elemental purity, and optical and electrical properties. / Engineering and Applied Sciences

Für die Beschichtung von Bauelementen im Bereich der Elektronik erlangt das Beschichtungsverfahren der Atomlagenabscheidung zunehmend an Bedeutung. Dieses Verfahren überzeugt hier durch seine Fähigkeit sehr homogene Schichten mit einer Dicke von wenigen nm auch auf Strukturen mit hohen Aspektverhältnissen zu erzeugen. Diese Arbeit beschäftigt sich mit der Atomlagenabscheidung von Aluminiumoxid unter Verwendung der Präkursoren Trimethylaluminium und Wasser. Hauptaufgabe dieser Arbeit ist die Modellierung eines experimentellen Prozessaufbaus mit kommerzieller Simulationssoftware. Anhand der Simulationsergebnisse können Aussagen zur Optimierung des ALD-Prozesses getroffen werden. Die durchgeführten Untersuchungen zeigen, dass für die Simulation eines ALD-Prozesses sehr lange Rechenzeiten erforderlich sind. Insbesondere konnte ein tieferes Verständnis der automatischen Zeitschrittweitenregulierung der Software bei transienten Simulationen gewonnen werden. Die Dauer der Spülschritte wurde durch die Simulationsergebnisse als ausreichend bestätigt. Des Weiteren kann die Verwendung der zur Anlage gehörigen Gasdusche anhand der Simulationsergebnisse nicht empfohlen werden.

This thesis describes studies of materials which can be exploited for hydrogen production from water and sunlight. The materials investigated are maghemite (γ-Fe2O3), magnetite (Fe3O4) and especially hematite (α-Fe2O3), which is an iron oxide with most promising properties in this field. Hematite has been deposited using Atomic Layer Deposition (ALD) - a thin-film technique facilitating layer-by-layer growth with excellent thickness control and step coverage. The iron oxides were deposited using bis-cyclopentadienyl iron (Fe(Cp)2) or iron pentacarbonyl (Fe(CO)5) in combination with an O2 precursor. Since it is crucial to have good control of the deposition process, the influence of substrate, process temperature, precursor and carrier gas have been investigated systematically. By careful control of these deposition parameters, three polymorphs of iron oxide could be deposited: hematite (α-Fe2O3), maghemite (γ-Fe2O3) and magnetite (Fe3O4). The deposited materials were characterized using X-ray Diffraction, Raman and UV-VIS Spectroscopy, and Scanning Electron Microscopy. Hard X-ray Photoelectron Spectroscopy (HAXPES) was also used, since it is a non-destructive, chemically specific, surface sensitive technique – the surface sensitivity resulting from the short mean escape depth of the photoelectrons. The depth probed can be controlled by varying the excitation energy; higher photoelectron energies increasing the inelastic mean-free-path in the material. HAXPES studies of atomic diffusion from F-doped SnO2 substrates showed increased doping levels of Sn, Si and F in the deposited films. Diffusion from the substrate was detected at annealing temperatures between 550 °C and 800 °C. Films annealed in air exhibited improved photocatalytic behavior; a photocurrent of 0.23 mA/cm2 was observed for those films, while the as-deposited hematite films showed no photo-activity whatsoever. The optical properties of low-dimensional hematite were studied in a series of ultra-thin films (thicknesses in the 2-70 nm range). The absorption maxima were shifted to higher energies for films thinner than 20 nm, revealing a different electronic structure in thin films.

Electrochemical capacitors, now often termed supercapacitors, are high power electrochemical energy storage devices that complement or replace high power batteries in applications ranging from wind turbines to hybrid engines to uninterruptable power supplies to electronic devices. My dissertation explores the applications of relatively uncommon techniques for both supercapacitor material syntheses and gaining better mechanistic understanding of factors impacting electrochemical performance of supercapacitors. From fundamental ion electroadsorption studies made possible by using small angle neutron scattering (SANS), to the systematic investigations of coating thickness and microstructure in metal oxide / carbon nanocomposite electrodes realized through the novel use of the atomic layer deposition (ALD) technique, new avenues of material characterization and fabrication have been studied. In this dissertation I first present the motivation to expand the knowledge of supercapacitor science and technology, and follow with an in-depth literature review of the state of the art. The literature review covers different types of supercapacitors, the materials used in the construction of commercial and exploratory devices, an exploration of the numerous factors which affect supercapacitor performance, and an overview of relevant materials synthesis and characterization techniques The technical objectives for the work performed in this dissertation are then presented, followed by the contributions that I made in this field in my two primary research thrusts: advances to the understanding of ion electroadsorption theory in both aqueous and organic electrolytes through the development of a SANS-based methodology, and advances to metal-oxide carbon nanocomposites as electrodes through the use of ALD. The understanding of ion electro-adsorption on the surface of microporous (pores < 2 nm) solids is largely hindered by the lack of experimental techniques capable of identifying the sites of ion adsorption and the concentration of ions at the nanoscale. In the first research thrust of my dissertation, I harness the high penetrating power and sensitivity of neutron scattering to isotope substitution to directly observe changes in the ion concentration as a function of the applied potential and the pore size. I have conducted initial studies in selected aqueous and organic electrolytes and outlined the guidelines for conducting such experiments for the broad range of electrode-ions-solvent combinations. I unambiguously demonstrate that depending on the solvent properties and the solvent-pore wall interactions, either enhanced or reduced ion electro-adsorption may take place in sub-nanometer pores. More importantly, for the first time I demonstrate the route to identify the critical pore size below which either enhanced or reduced electrosorption of ions takes place. My studies experimentally demonstrate that poor electrolyte wetting in the smallest pores may indeed limit device performance. The proposed methodology opens new avenues for systematic in-situ studies of complex structure-property relationships governing adsorption of ions under applied potential, critical for rational optimization of device performance. In addition to enhancing our understanding of ion sorption, there is a critical need to develop novel supercapacitor electrode materials with improved high-energy and high-power characteristics. The formation of carbon-transition metal oxide nanocomposites may offer unique benefits for such applications. Broadly available transition metal oxides, such as vanadium oxide, offer high ion storage capabilities due to the broad range of their oxidation states, but suffer from high resistivities. Carbon nanomaterials, such as carbon nanotubes (CNT), in contrast are not capable to store high ion content, but offer high and readily accessible surface area and high electrical conductivity. In the second research thrust of my thesis, by exploiting the ability of atomic layer deposition (ALD) to produce uniform coatings of metal oxides on CNT electrodes, I demonstrated an effective way to produce high power supercapacitor electrodes with ultra-high energy capability. The electrodes I developed showed stable performance with excellent capacitance retention at high current densities and sweep rates. Electrochemical performance of the oxide layers were found to strongly depend on the coating thickness. Decreasing the vanadium oxide coating thickness to ~10 nm resulted in some of the highest values of capacitance reported to date (~1550 F·g⁻¹VOx at 1 A·g⁻¹ current density). Similar methodology was utilized for the deposition of thin vanadium oxide coatings on other substrates, such as aluminum (Al) nanowires. In this case the VOₓ coated Al nanowire electrodes with 30-50% of the pore volume available for electrolyte access show volumetric capacitance of 1390-1950 F cc⁻¹, which exceeds the volumetric capacitance of porous carbons and many carbon-metal oxide composites by more than an order of magnitude. These results indicated the importance of electrode uniformity and precise control over conformity and thickness for the optimization of supercapacitor electrodes.

No description available.

Conception de nanomatériaux à base d'oxyde par ALD : de la détection aux membranes / In this context, the aim of this PhD work is the synthesis of different nanostructured materials based on ALD oxide thin film (Al2O3, ZnO and Al2O3/ZnO nanolaminates) deposited on different types of substrates such as silicon substrate, glass, nanofibers, multipores and monopores membranes, PET and gold coated nickel dogbones. ALD deposition was performed on those substrates with changing the film thickness (number of cycles), the deposition temperature, and the film composition (doping, multilayers etc.). After the ALD deposition chemical, structural, optical, electrical and mechanical characterization were performed on the ALD deposited layer in order to study the influence of the deposition parameters on the thin film properties. The deposited and characterized ALD films were investigated on different fields:• Optical properties for solar cell applications (Chapter 2) • UV detection (Chapter 3)• Protective coating and gas barrier (chapter 4)• Ionic transport, water desalination, Mass spectrometry, DNA sequencing and Gas purification (chapter 5)The atomic layer deposition technique combined with nanostructured templates show several advantages on several application fields that will be reported on this thesis. The structural and properties evolution of the ALD thin film with the deposition parameter evolution leaded to a doped ZnO layer and Al2O3/ZnO multilayer with tunable optical, electrical and mechanical properties that can be interesting for different applications such as solar cell and UV detection. The conformal coating on high aspect ratio template with the angstrom range thickness control offered by the atomic layer deposition technique meted our target on nanopores diameter tuning for different applications on the nanometeric range such as gas purification. Moreover the compatibility of the deposited materials with some biological function leaded to a combination between nanostructure materials and biological function that shows promising results for different applications such as ionic transport, water desalination, mass spectrometry and DNA sequencing.