The heart is one of the most important organs of the human body and cardiovascular diseases remain the biggest cause of deaths worldwide. Today, due to the aging of the population and the growing demand for cardiovascular implants, improving the performance of artificial surfaces of vascular prostheses is highly desired. The common material for fabricating prostheses, such as stents used to remedy narrow and weak arteries, is Fluorocarbon polymers or expanded Polytetrafluoroethylene (ePTFE, Gore-tex). Although these polymers are well known for chemical inertness, thermal stability and low friction, they can cause early thrombosis (forming clot) and coagulation in blood vessels and require periodic replacement. Modifying the surface properties of Polytetrafluoroethylene (PTFE) by coating with carbon-based materials may improve its blood compatibility. Carbon-based coatings have properties similar to biomedical components, such as low friction, bioinertness, high wear resistance and exceptional hardness. Plasma processing methods are commonly used for coating thin films on various materials including carbon-based components. Plasma-based processes are also widely used in the aerospace, automotive, steel and biomedical industries. For example, extending the lifetime of surgically implanted hip joints and cutting tools are biomedical and industrial applications of plasma-based material processing respectively. Plasma-assisted deposition techniques are commonly used for carbon-based coating including nitrogen-doped amorphous carbon (a-C) films. In this thesis, PTFE samples with different thickness and roughness characteristics are used as substrates and diamond-like carbon (DLC) is deposited on them by simultaneous plasma-assisted sputtering and chemical vapour deposition (CVD). Hot filament plasma and ICP (Inductively coupling plasma) are used to coat DLC on PTFE and silicon (Si) substrates under various plasma conditions. The latter is the first report on the techniques to coat DLC by ICP plasma sputtering. This new technique (ICP-sputtering) is developed to improve low deposition rate and high temperature deposition of previous method (Hot filament plasma sputtering). Advantageous of this new developed method (ICP-sputtering) are discussed and compared with the previous method in this thesis. Various amount of nitrogen is introduced to the plasma chambers and the effect of nitrogen dopant is also studied using different characterization techniques for chemical, electronic and morphological properties of coated films. sp2 and sp3 contents were also estimated in amorphous carbon (a-C) and nitrogenated amorphous carbon (a-CN) films. Characterization techniques used for in this thesis are including SEM (scanning electron microscopy), AFM (atomic force microscopy), Raman spectroscopy, XAS (x-ray absorption spectroscopy), XES (x-ray emission spectroscopy), XPS (x-ray photoelectron spectroscopy) and XRD (x-ray diffraction).

In this work columnar nanospirals of AlInN were grown on top of TiN-coated sapphire substrates by magnetron sputtering. A variety of samples with different growth parameters were fabricated and investigated. The main objectives in this work were to optimize the degree of circular polarization and to control the active wavelength region for where this polarization effect occurs. Attempts were made to achieve a high degree of circular polarization in both reflected and transmitted light. It is shown that for reflected light it is possible to achieve a high degree of circular polarization within the visible wavelength regions. For transmitted light the concept of achieving circularly polarized light is proven.

Darbe tiriamas magnetroniniu plazminiu būdu suformuotų Mg-Al-Zr lydinių anodinis tirpimas, bei antikorozinės savybės. Magnetroniniu plazminiu būdu buvo suformuotos dangos su skirtingu cirkonio kiekiu (t.y. 95%, 90,4%, 76,2%, 71% ir 67%). Dangos formuojamos ant stiklo paviršiaus. Voltamperiniais ir elektrocheminio impedanso metodais ištirtas Mg-Al-Zr lydinių anodinis atsparumas ir korozinė elgsena 0.1 M (NH4)3BO3 + 0.1 M NaCl tirpale, kurio pH 8,5. MP lydinių korozinis atsparumas didėja, didinant Zr koncentraciją lydinyje. Taip pat lydiniai, kuriuose didesnė Mg koncentracija, bet mažesnė Zr aktyviai anodiškai tirpsta. Atominės jėgos mikroskopo metodu (AJM) nustatyta lydinių morfologija, dangos su didesne Zr koncentracija charakterizuojamos mažesniais kristalitų dydžiais. Aptartos MP metodo pritaikymo galimybės. / The goal of this work was to study anodic dissolution and anticorrosion properties of Mg-Al-Zr alloys formed by magnetron sputtering. Magnetron sputtering technique was applied to deposit Mg-Al-Zr alloys with different amount of Zr, on glass substrates. Anodic dissolution and anticorrosive stability of the sputtered alloys were studied by voltammetric and electrochemical impedance spectroscopy methods in 0.1 M (NH4)3BO3 + 0.1 M NaCl solution (pH 8,5). EIS and voltammetric measurements indicated a lesser anodic dissolution and a superior anticorrosive resistance in Mg-Al-Zr alloys with higher Zr concentration. Atomic force microscopy demonstrated (AFM) that by increasing amount of Zr in sputtered samples the grain size decrease.

Darbe tiriamos magnetroniniu plazminiu (MP) būdu suformuotų Mg – Al – Zr lydinių morfologinės, korozinės ir puslaidininkinės savybės. Magnetroninio plazminio dulkinimo metodu buvo suformuotos 5Mg-Al-95Zr, 33Mg-Al-67Zr, 29Mg-Al-71Zr, 24Mg-Al-76Zr, 8Mg-Al-90Zr dangos ant stiklo paviršiaus. Atominės jėgos mikroskopo (AJM) metodu nustatyta, kad magnetroniniu plazminiu būdu suformuotos Mg – Al – Zr lydinių dangos charakterizuojamos mažesniais kristalitų dydžiais ir tolygesne mikrostruktūra. Fotoelektrocheminiais ir elektrocheminio impedanso spektroskopijos metodais ištirta lydinių korozinė elgsena 0,1 M (NH4)3BO3 + 0,1 M NaCl ( pH = 8,5) tirpale. Mott – Shottky analizės metodu nustatytas puslaidininkinių paviršiaus sluoksnių laidumo pobūdis: 5Mg-Al-95Zr, 33Mg-Al-67Zr, 29Mg-Al-71Zr, 24Mg-Al-76Zr, 8Mg-Al-90Zr dangų atveju jis donorinis (n – tipo). Aptartos Mott – Shottky metodo taikymo magnetroninėms dangoms tirti galimybės. / The aim of present work was to study corrosion properties of magnetron sputtered Mg – Al – Zr alloys and characterise semiconductor properties of the surface layers developed during corrosion. Atomic force microscopy (AFM) demonstrated, that sputtered alloys had a smaller grain size and a smoother surface. Fotocorrosion and electrochemical behaviour of tha alloys was studied in 0,1 M (NH4)3BO3 + 0,1 M NaCl ( pH = 8,5) solution. The Mott – Schottky plots of 5Mg-Al-95Zr, 33Mg-Al-67Zr, 29Mg-Al-71Zr, 24Mg-Al-76Zr, 8Mg-Al-90Zr electrodes showed a linear relationship between modified capacitance (C-2) on applied potential. It was concluded n – type semiconductivity for the layers on 5Mg-Al-95Zr, 33Mg-Al-67Zr, 29Mg-Al-71Zr, 24Mg-Al-76Zr, 8Mg-Al-90Zr alloys.

Recent studies of fcc metals with dense twins (~10 nm spacing) have revealed impressive mechanical properties, along with improved ductility and electrical conductivity in comparison to nanocrystalline metals with similar feature sizes. Many important fcc metals could benefit from these “nanotwinned” microstructures, however, not all fcc metals readily form such twins. The tendency of fcc metals to form twin boundaries is related to the twin boundary energy; those with low twin boundary energy, such as silver (Ag), easily form twins. Increasing twin boundary energy interferes with twin formation, to the point that in metals with high twin boundary energy, like aluminum (Al), twins are quite rare. This thesis focuses on the synthesis of nanotwinned Ag and Al via physical vapor deposition. Nanotwinned Ag is readily fabricated, however, a template approach had to be developed to induce twins in Al. The microstructures and their relationships to observed mechanical properties are also discussed. Grain boundaries interfere with dislocation transmission by posing a slip system discontinuity between grains. Twin boundaries are a special class of grain boundaries in which the grains on either side of the boundary are related by mirror symmetry. Twin boundaries inhibit dislocation transmission, providing strength in the same manner as grain boundaries. However, their symmetrical structure reduces the free volume and grain boundary energy. Accordingly, coherent twin boundaries are often more energetically stable than grain boundaries, and their coherency allows plasticity mechanisms to remain active under conditions where such mechanisms may be inhibited at grain boundaries. Hence, twin boundaries may provide a metal with unique combinations of high strength and good ductility, conductivity, and thermal stability.

No description available.

Solar cells based on CdTe absorbers are attractive due to the optimal direct band gap energy and large absorption coefficient of CdTe, however, their performance and commercialization is hindered by the lack of reliable p-type contacts. CdTe has a low carrier concentration and a large electron affinity, which results in a requirement of non-realistic work functions for metals to be used as back contacts in the solar cell. Even noble metals such as Ag present a significantly large potential barrier for holes, thereby reducing the hole current through the semiconductor/metal interface. Several attempts to resolve this challenge have been tried, however, many drawbacks have been encountered. Two particular systems, namely Cu2Te thin films and CdTe/ZnTe strained-layer superlattices, are investigated for their potential use as ohmic contacts in CdTe solar cells. A detailed analysis of the optical, electrical, and structural properties of Cu2Te thin films deposited by magnetron sputtering is presented. It is shown that these films have an indirect band gap and highly degenerate semiconductor behavior. The large p-type carrier concentration of Cu2Te films is highly desirable for the application of Cu2Te as a p-type contact to CdTe. In-depth studies of optical transitions and miniband transport in strained-layer CdTe/ZnTe superlattices are presented as well. The band offsets between CdTe and ZnTe were determined by comparison of measured and calculated optical transitions. Superlattice structures that offer best contact performance have been identified by use of tunneling probability simulations. Characterization of CdTe solar cells with above mentioned contacts indicated that contacts based on CdTe/ZnTe superlattices are a viable Cu free option for stable and reliable p-type contacts in CdTe solar cell. The contact performance of Cu2Te thin films was comparable to that of CdTe/ZnTe superlattices and both demonstrated an advantage over contacts based on ZnTe:N thin films which were used a standard.

This thesis present research on synthesis, microstructure, and properties of carbide- and boride- based thin films. The films have been synthesized by dc magnetron sputtering, and their microstructures have been characterized mainly by X-ray photoelectron spectroscopy (XPS), X-ray diffraction, and transmission electron microscopy.  One of the main objectives with this research has been to evaluate the thin films potential as materials for sliding electrical contact applications and this have influenced, which properties that have been evaluated. Co-sputtered Nb-C films have a microstructure comprising of nanocrystalline NbCx  (nc-NbCx) grains embedded in a matrix of amorphous C (a-C). A thinner a-C matrix form in the Nb-C films compared to the well-studied Ti-C system. As a consequence, the Nb-C films have a higher hardness and conductivity than previously studied Ti-C sputtered under similar conditions. The promising electrical contact properties are attained for reactively sputtered Nb-C films under industrial conditions, at deposition rates two orders of magnitude higher. A reduction in crystallinity is seen when Si is added to the Nb-C films and amorphous films forms at Si content > 25 at.%. The alloying of Si was however not beneficial for the electrical contact properties. Substoichiometric CrB2-x (B/Cr = 1.5) and NbB2-x (B/Nb = 1.8) films are achieved when deposited from MeB2 targets. Boron segregates to grain boundaries forming a B-rich tissue phase. This result in superhardness for the NbB2-x films (42 ± 4 GPa) as well as a low friction attributed to the formation of a boric acid film. Carbon forms a solid solution in the MeB2 grains as well as segregating to grain boundaries forming an amorphous BCx (a-BCx) phase when alloyed to CrB2-x and NbB2-x films. The formation of the a-BCx phase drastically improves the electrical contact resistance of the NbB2-x films. However, the mechanical properties are degraded, which result in a high friction and wear rate. It was in TEM studies of the metastable amorphous structures for the Nb-Si-C films found that the electron beam induces crystallization. Hence, great care is required when studying these types of metastable structures.

A totally new solid stationary phase deposition technique for micro machined gas chromatography (GC) columns fabrication was proposed: to overcome the limitations of conventional liquid (or occasionally solid) stationary phases in terms of very volatile compounds retention and/or clean room batch production, an approach consisting of the collective direct deposition of the adsorbent in micro columns channels by sputtering was performed. The process was fully compatible with clean room fabrication flow and industry-ready, with very good precision results. Silica, alumina, graphite and magnesia were proven able to separate volatile hydrocarbons. Various types of columns (structure, stationary phase) were fabricated in the form of 2x2 cm² silicon-Pyrex chips, and their thermodynamic and kinetic evaluations were reported. Retentions were observed to increase from magnesia to graphite through alumina and silica and with phase ratio decrease, as expected; very satisfying efficiencies were obtained: more than 5700 plates, and 250 µm-high plates. The possibility to use such columns for fast in-situ and autonomous monitoring of light hydrocarbons in oilfield environments was demonstrated by the implementation of a chip temperature-programming system and various versatility tests (high temperatures, carrier gas, humidity): a complete C1-C9 linear alkanes separation was performed in less than 15 seconds, as well as complex mixtures fast separations (isomers, unsaturated), and an industrial confidential application was developed and patented. Therefore, sputter-deposited stationary phase micro columns opened numerous perspectives for the developments of miniaturized GC apparatuses.

No description available.