In this work, physical phenomena related to the growth and phase formation of alumina, Al2O3, are investigated by experiments and computer calculations. Alumina finds applications in a wide variety of areas, due to many beneficial properties and several existing crystalline phases. For example, the α and κ phases are widely used as wear-resistant coatings due to their hardness and thermal stability, while, e.g., the metastable γ and θ phases find applications as catalysts or catalyst supports, since their surface energies are low and, hence, they have large surface areas available for catalytic reactions. The metastable phases are involved in transition sequences, which all irreversibly end in the transformation to the stable α phase at about 1050 °C. As a consequence, the metastable aluminas, which can be grown at low temperatures, cannot be used in high temperature applications, since they are destroyed by the transformation into α. In contrast, α-alumina, which is the only thermodynamically stable phase, typically require high growth temperatures (~1000 °C), prohibiting the use of temperature sensitive substrates. Thus, there is a need for increasing the thermal stability of metastable alumina and decreasing the growth temperature of the α phase. In the experimental part of this work, hard and single-phased α-alumina thin films were grown by magnetron sputtering at temperatures down to 280 °C. This dramaticdecrease in growth temperature was achieved by two main factors. Firstly, the nucleation stage of growth was controlled by pre-depositing a chromia “template” layer, which is demonstrated to promote nucleation of α-alumina. Secondly, it is shown that energetic bombardment was needed to sustain growth of the α phase. Energy-resolved mass spectrometry measurements demonstrate that the likely source of energetic bombardment, in the present case, was oxygen ions/atoms originating from the target surface. Overall, these results demonstrate that low-temperature α-alumina growth is possible by controlling both the nucleation step of growth as well as the energetic bombardment of the growing film. In addition, the mass spectrometry studies showed that a large fraction of the deposition flux consisted of AlO molecules, which were sputtered from the target. Since the film is formed by chemical bonding between the depositing species, this observation is important for the fundamental understanding of alumina thin film growth. In the computational part of the work, the effect of additives on the phase stability of α- and θ-alumina was investigated by density functional theory calculations. A systematic study was performed of a large number of substitutional dopants in the alumina lattices. Most tested dopants tended to reverse the stability between α- and θ-alumina; so that, e.g., Modoping made the θ phase energetically favored. Thus, it is possible to stabilize the metastable phases by additives. An important reason for this is the physical size of the dopant ions with respect to the space available within the alumina lattices. For example, large ions induced θ stabilization, while ions only slightly larger than Al, e.g., Co and Cu, gave a slight increase in the relative stability of the α phase. We also studied the stability of some of these compounds with respect to pure alumina and other phases, containing the dopants, with the result that phase separations are energetically favored and will most likely occur at elevated temperatures.

The work presented in this thesis deals with experimental and theoretical studies related to the growth of crystalline alumina thin films. Alumina, Al2O3, is a polymorphic material utilized in a variety of applications, e.g., in the form of thin films. Many of the possibilities of alumina, and the problems associated with thin film synthesis of the material, are due to the existence of a range of different crystalline phases. Controlling the formation of the desired phase and the transformations between the polymorphs is often difficult. In the experimental part of this work, it was shown that the thermodynamically stable alpha phase, which normally is synthesized at substrate temperatures of around 1000 °C, can be grown using reactive sputtering at a substrate temperature of 500 °C by controlling the nucleation surface. This was done by predepositing a Cr2O3 nucleation layer. Moreover, it was found that an additional requirement for the formation of the α phase is that the depositions are carried out at low enough total pressure and high enough oxygen partial pressure. Based on these observations, it was concluded that energetic bombardment, plausibly originating from energetic oxygen, is necessary for the formation of α alumina (in addition to the effect of the chromia nucleation layer). Further, the effects of impurities, especially residual water, on the growth of crystalline films were investigated by varying the partial pressure of water in the ultra high vacuum (UHV) chamber. Films deposited onto chromia nucleation layers exhibited a columnar structure and consisted of crystalline α-alumina if deposited under UHV conditions. However, as water to a partial pressure of 1x10-5 Torr was introduced, the columnar growth was interrupted. Instead, a microstructure consisting of small, equiaxed grains was formed, and the gamma-alumina content was found to increase with increasing film thickness. When gamma-alumina was formed under UHV conditions, no effects of residual water on the phase formation was observed. Moreover, the H content was found to be low (< 1 at. %) in all films. Consequently, this shows that effects of residual gases during sputter deposition of oxides can be considerable, also in cases where the impurity incorporation in the films is found to be low. In the modeling part of the thesis, density functional theory based computational studies of adsorption of Al, O, AlO, and O2 on different alpha-alumina (0001) surfaces have been performed. The results give possible reasons for the difficulties in growing the α phase at low temperatures through the identification of several metastable adsorption sites, and also provide insights related to the effects of hydrogen on alumina growth. / Report code: LiU-TEK-LIC-2007:1.

<p>Thermistor material can be used to fabricate un-cooled IR detectors their figure of merit is the Temperature Coefficient of Resistance (TCR). Ge dots in Si can act as a thermistor material and they have a theoretical TCR higher than for SiGe layers but they suffer from intermixing of Si into the Ge dots. Ge dots were grown on unstrained or strained Si layers and relaxed or strained SiGe layers at temperatures of 550 and 600°C by reduced pressure chemical vapor deposition (RPCVD). Both single and multilayer structures where grown and characterized. To achieve a strong signal in a thermal detector a uniform shape and size distribution of the dots is desired. In this thesis work, an endeavor has been to grow uniform Ge dots with small standard deviation of their size. Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) have been used to characterize the size and shape distribution of Ge dots. Ge contents measured with Raman spectroscopy are higher at lower growth temperatures. Simulation of TCR for the most uniform sample grown at 600°C give 4.43%/K compared to 3.85%/K for samples grown at 650°C in a previous thesis work.</p><p>Strained surfaces increases dot sizes and make dots align in crosshatched pattern resulting in smaller density, this effect increases with increasing strain.</p><p>Strain from buried layers of Ge dots in a multilayer structure make dots align vertically. This alignment of Ge dots was very sensitive to the thickness of the Si barrier layer. The diameter of dots increase for each period in a multilayer structure. When dots are capped by a Si layer at the temperature of 600°C intermixing of Si into the Ge dot occurs and the dot height decrease.</p>

<p>The work presented in this thesis deals with experimental and theoretical studies related to the growth of crystalline alumina thin films. Alumina, Al₂O₃, is a polymorphic material utilized in a variety of applications, e.g., in the form of thin films. Many of the possibilities of alumina, and the problems associated with thin film synthesis of the material, are due to the existence of a range of different crystalline phases. Controlling the formation of the desired phase and the transformations between the polymorphs is often difficult.</p><p>In the experimental part of this work, it was shown that the thermodynamically stable alpha phase, which normally is synthesized at substrate temperatures of around 1000 °C, can be grown using reactive sputtering at a substrate temperature of 500 °C by controlling the nucleation surface. This was done by predepositing a Cr₂O₃ nucleation layer. Moreover, it was found that an additional requirement for the formation of the <em>α</em> phase is that the depositions are carried out at low enough total pressure and high enough oxygen partial pressure. Based on these observations, it was concluded that energetic bombardment, plausibly originating from energetic oxygen, is necessary for the formation of <em>α</em> alumina (in addition to the effect of the chromia nucleation layer). Further, the effects of impurities, especially residual water, on the growth of crystalline films were investigated by varying the partial pressure of water in the ultra high vacuum (UHV) chamber. Films deposited onto chromia nucleation layers exhibited a columnar structure and consisted of crystalline <em>α</em>-alumina if deposited under UHV conditions. However, as water to a partial pressure of 1x10^-5 Torr was introduced, the columnar growth was interrupted. Instead, a microstructure consisting of small, equiaxed grains was formed, and the gamma-alumina content was found to increase with increasing film thickness. When gamma-alumina was formed under UHV conditions, no effects of residual water on the phase formation was observed. Moreover, the H content was found to be low (< 1 at. %) in all films. Consequently, this shows that effects of residual gases during sputter deposition of oxides can be considerable, also in cases where the impurity incorporation in the films is found to be low.</p><p>In the modeling part of the thesis, density functional theory based computational studies of adsorption of Al, O, AlO, and O2 on different alpha-alumina (0001) surfaces have been performed. The results give possible reasons for the difficulties in growing the <em>α</em> phase at low temperatures through the identification of several metastable adsorption sites, and also provide insights related to the effects of hydrogen on alumina growth.</p> / Report code: LiU-TEK-LIC-2007:1.

Organic molecules adsorbed on inorganic substrates are the topics of interest in this thesis. Interfaces of this kind are found in dye sensitized solar cells that convert solar energy to electricity, a promising environmentally friendly energy source which might provide a route to replace fossil fuels. Another field where these interfaces play a role is in molecular electronics, an approach to solve the down scaling in the ever increasing hunt for miniaturized electronic devices. The motivation for this work lies among other in these applications and surface science is a suitable approach to investigate the electronic and morphologic properties of the interfaces as it provides detailed knowledge on an atomic level. Phthalocyanines are the organic molecules investigated and the inorganic substrates range from wide band gap via narrow band gap semiconductors to metals. Photoelectron and X-ray spectroscopy experiments are performed to shed light on the electronic properties of the adsorbed molecules and the substrate, as well as the chemical interaction between adsorbate and substrate at the interface. The ordering of the adsorbate at the interface is important as ordered molecular thin films may have other properties than amorphous films due to the anisotropic electronic properties of the organic molecules; this is investigated using scanning tunneling microscopy. We find that the phthalocyanines are affected by adsorption when the substrate is TiO2 or Ag, where charge transfer from the molecule occurs or an interface state is formed respectively. The molecules are adsorbed flat on these surfaces giving a large contact area and a relatively strong bond. On Ag, ordered structures appear with different symmetry depending on initial coverage. The reactivity of the TiO2 surface is not ideal in the solar cell application and by modifying the surface with a thin organic layer, the negative influence on the adsorbed phthalocyanine is reduced. ZnO is not as reactive as TiO2, thanks maybe to the upright adsorption mode of the phthalocyanines. The semiconductor InSb is less reactive leading to self-assembled molecular structures on the (001) surface, either homogenously distributed in a one monolayer thick film or in strands along the reconstruction rows. InAs on the other hand has a larger influence on the adsorbed molecules resulting in a metallic film upon thermal treatment. / QC 20100812

Quasicrystals is a new kind of material that have several interesting aspects to it. The unusual atomic structure entails many anomalous and unique physical properties, for example, high hardness, and extremely low electrical and thermal conductivity. In thin films quasicrystals would enable new functional materials with a combination of attractive properties.In this work, AlCuFe and Nanoflex steel, materials that are known to form quasicrystals in bulk, have been deposited as thin films on Si and Al2O3 substrates using DC magnetron sputtering. These thin films were heat treated, and the formation and growth of different phases, among other approximant and quasicrystalline phases, were studied using mainly in-situ X-ray diffraction.During the project several problems with the formation of quasicrystals were encountered, and it is proposed how to overcome these problems, or even how to make use of them. Finally, the quasicrystalline phase was realized, although it was not completely pure. In the end some suggestions for future work is presented.

Thermistor material can be used to fabricate un-cooled IR detectors their figure of merit is the Temperature Coefficient of Resistance (TCR). Ge dots in Si can act as a thermistor material and they have a theoretical TCR higher than for SiGe layers but they suffer from intermixing of Si into the Ge dots. Ge dots were grown on unstrained or strained Si layers and relaxed or strained SiGe layers at temperatures of 550 and 600°C by reduced pressure chemical vapor deposition (RPCVD). Both single and multilayer structures where grown and characterized. To achieve a strong signal in a thermal detector a uniform shape and size distribution of the dots is desired. In this thesis work, an endeavor has been to grow uniform Ge dots with small standard deviation of their size. Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) have been used to characterize the size and shape distribution of Ge dots. Ge contents measured with Raman spectroscopy are higher at lower growth temperatures. Simulation of TCR for the most uniform sample grown at 600°C give 4.43%/K compared to 3.85%/K for samples grown at 650°C in a previous thesis work. Strained surfaces increases dot sizes and make dots align in crosshatched pattern resulting in smaller density, this effect increases with increasing strain. Strain from buried layers of Ge dots in a multilayer structure make dots align vertically. This alignment of Ge dots was very sensitive to the thickness of the Si barrier layer. The diameter of dots increase for each period in a multilayer structure. When dots are capped by a Si layer at the temperature of 600°C intermixing of Si into the Ge dot occurs and the dot height decrease.

<p>Quasicrystals is a new kind of material that have several interesting aspects to it. The unusual atomic structure entails many anomalous and unique physical properties, for example, high hardness, and extremely low electrical and thermal conductivity. In thin films quasicrystals would enable new functional materials with a combination of attractive properties.In this work, AlCuFe and Nanoflex steel, materials that are known to form quasicrystals in bulk, have been deposited as thin films on Si and Al2O3 substrates using DC magnetron sputtering. These thin films were heat treated, and the formation and growth of different phases, among other approximant and quasicrystalline phases, were studied using mainly in-situ X-ray diffraction.During the project several problems with the formation of quasicrystals were encountered, and it is proposed how to overcome these problems, or even how to make use of them. Finally, the quasicrystalline phase was realized, although it was not completely pure. In the end some suggestions for future work is presented.</p>

This Thesis concerns the development of fullerene-like (FL) carbon nitride (CNx) thin films and the discovery of phosphorus-carbide (CPx) compounds. The work dedicated to CPx include first-principles theoretical simulations of the growth and properties of FL-CPx structures. I have employed DC magnetron sputtering methods to synthesize both CNx and CPx thin films. The deposition conditions for CPx films were chosen on the basis of the theoretical results as well as from the experience from the deposition of FL-CNx thin films. The characterization of the CPx films is divided into three main directions: structural characterization by transmission electron microscopyand scanning electron microscopy, analysis of the amount of elements and chemical bonds presentin the structure by X-ray photoelectron spectroscopy and Auger spectroscopy, and mechanicalproperty analysis by nanoindentation. The CPx films exhibit a short range orderedstructure with FL characteristics for substrate temperature of 300 °C and for a phosphorus content of 10-15 at.%, which isconsistent with the theoretical findings. These films also displayed the best mechanical properties in terms of hardness and resiliency, which are better than those of the corresponding FL-CNx films. For the FL-CNx thin film material, I find that the surface water adsorption is lower compared to commercial computer hard disk top coatings. Following that line the dangling bonds in FL-CNx coatings have been investigated  by electron spin resonance (ESR). The absence of ESR signal for FL-CNx indicates very low density of dangling bonds in the material, which explains the low water adsorption tendency. The potential for using highly elastic FL-CNx coatings in an automotive valve-train environment has also been investigated. CNx coatings of different nitrogen content were investigated using microscopy, wear testing, nanoindentation testing, and in an experimental cam-tappet testing rig. The FL-CNx coating with the higher value of hardness/elastic modulus showed greater durability in cam-tappet wear testing.

Metastable (Ti,Si)N alloy and TiN/SiNx multilayer thin solid films as well as SiNx/TiN surfaces have been explored. Cubic Ti1-xSixN (0≤x≤0.14) films deposited onto cemented carbide (WC-Co) substrates by arc evaporation exhibited a competitive columnar growth mode where the structure transforms to a feather-like nanostructure with increasing Si content as revealed by x-ray diffraction and transmission electron microscopy. X-ray photoelectron spectroscopy revealed the presence of Ti-N and Si-N bonding, but no amorphous Si3N4. Band structure calculations showed that phase separation of NaClstructure Ti1-xSixN solid solution into cubic SiN and TiN phases is energetically favorable. The metastable microstructure, however, was maintained for the Ti0.86Si0.14N film annealed at 900°C, while recrystallization in the cubic state took place at 1100°C annealing during 2h. The Si content influenced the film hardness close to linearly, by combination of solid-solution hardening in the cubic state and defect hardening. For x=0 and x=0.14, nanoindentation gave a hardness of 29.9±3.4 GPa and 44.7±1.9 GPa, respectively. The hardness was retained during annealing at 900°C. Nanostructured materials, e.g., nanocomposites and nanolaminates, are defined by internal interfaces, of which the nature is still under debate. In this work two-phase model systems were explored by depositing SiNx/TiN nanolaminate films, including superlattices containing cubic SiNx, by dual target reactive magnetron sputtering. It is demonstrated that the interfacial phase of SiNx onto TiN(001) and TiN(111) can be crystalline, and even epitaxial with complex surface reconstructions. Using in situ structural analyses combined with ab initio calculations, it is found that SiNx layers grow epitaxially, giving rise to strong interfacial bonding, on both TiN(001) and TiN(111) surfaces. In addition, TiN overlayers grow epitaxially on SiNx/TiN(001) bilayers in nanolaminate structures. These results provide insight into the development of design rules for novel nanostructured materials. / Report code: LiU-TEK-LIC-2006:51.