No description available.

Interest exists in the development of transparent conducting oxide materials, which have diverse applications in areas such as transparent coatings for display technologies, solar cells, and optoelectronics. Since many of the applications require the use of thin film forms, the need is to establish useful experimental approaches to the fabrication of such structures. One relatively new method in this area is oxygen-plasma assisted atomic beam epitaxy (OPABE) in which oxide layers are grown under normal molecular beam epitaxy (MBE) conditions with the addition of an oxygen atom beam to ensure full oxidation of the depositing metallic species. Work in this area has to date mainly focussed on the growth of relatively stable oxides such as ZnO, MgO and In₂O₃ which are the strongly thermodynamically favoured reaction products, across a broad range of reaction conditions. In contrast, the present work is concerned with the growth of Cu2O and a range of delafossite materials, namely CuInO₂, CuCrO₂ and CuGaO₂, which are expected to require much more sensitive control to achieve the desired reaction product. Studies of the OPABE growth of Cu₂O on MgO (100) and MgO (110) substrates have been carried out, using a broad range of physical techniques to characterise the grown Cu₂O deposits. It is demonstrated that CuO is the favoured reaction product at low growth temperatures, although Cu₂O becomes increasingly favoured as the growth temperature increases. Alternatively, it is also shown that a novel bilayer growth method, whereby some pure Cu is deposited prior to oxide growth, can be used to form the desired Cu (I) phase. Varying crystal orientations are seen, depending on the exact growth conditions; core level and valence band X-ray photoelectron spectroscopy (XPS), optical band gap and atomic force microscopy (AFM) measurements are used to characterise the deposits. Further growth investigations of the delafossite compounds CuInO₂, CuCrO₂ and CuGaO₂ using OPABE are also recorded, and for the case of CuInO₂, comparison is also made with the pulsed laser deposition approach. For all three materials systems, oriented crystal growth on basal planes sapphire substrates is seen, with either the (001) plane or the (015) plane orienting parallel to the substrate depending on the growth temperature, provided approximately correct metal fluxes are used as set by the Knudsen-cell temperatures. The typical valence band electronic structure of delafossite materials is observed in all three cases, and XPS peak shifts suggest that the layers can be electrically doped by adding appropriate metal fluxes during growth. AFM measurements show the grown films are relatively rough and it is suggested that the growth mode follows an island growth mechanism in which oriented three dimensional islands formed at the start of growth gradually enlarge and coalesce as the film thickens. Optical absorption measurements are consistent with the generally accepted optical band gaps of the materials concerned.

ABSTRACT PLASMA SURFACE MODIFICATION AND CHARACTERIZATION OF PMMA FILMS &Ouml / zgen, &Ouml / zge M.Sc., Department of Polymer Science and Technology Supervisor: Prof. Dr. Nesrin Hasirci Co-supervisor: Prof. Dr. Vasif Hasirci December 2011, 114 pages Surface properties play an essential role for determining the behavior of a material for many applications such as coating, printing, adhesion and prosthesis implanting since the surface is the first part that comes in contact with the environment. Although the bulk properties of some materials are at the desired level, the surface may need to be modified for a better compatibility with its surrounding. Plasma treatment is one generally preferred technique because of its high potential to create various functional groups on the surface of the sample by changing the applied plasma parameters. Some molecules can be successfully immobilized onto these surfaces using these specific chemical functional groups created by plasma. The type of the functional group is important for intended purpose of covalent binding of different molecules on the surface of a material. Present study offers important routes for optimization of the surface functionality of (PMMA) films by changing the plasma parameters. For this purpose, solvent casted polymethylmetacrylate PMMA films were modified by, nitrogen, argon and oxygen plasma by using a radiofrequency (RF) generator / and with various powers (10W, 50W, 100W) for different periods (5min, 15min and 30min). The effects of these plasma parameters (gas type, applied power, plasma time) on hydrophilicity, surface free energy, surface chemistry, and surface topography were investigated. Also, the types of surface free radicals created with oxygen plasma treatment were analysed and the decay of these radicals were examined by Electron Spin Resonance Spectroscopy (ESR). In general, plasma treatment reduced the contact angle of PMMA films where the most hydrophilic surface was obtained for 100W 30 min argon plasma treated sample showing superhydrophilic character with the water contact angle value of ~10&deg / . Surface free energy measurements were carried out according to Geometric Mean, Harmonic Mean, Acid-Base approach and it was found that oxygen, nitrogen and argon plasma treatments increased the surface free energy for all samples by increasing the polar components and introducing functional groups on the surface. X-Ray Photoelectron Spectroscopy (XPS) analysis results revealed that free carbonyl and carbonate groups were formed by oxygen plasma treatment, whereas carboxylic acid and free carbonyl groups were formed after argon plasma treatment, and imine, primary amine, amide and nitrozo groups were formed by nitrogen plasma. Atomic Force Microscopy (AFM) analysis revealed that the roughness of the surface increased considerably from ~2 nm to ~75 nm for the 100W 30 min oxygen plasma treated samples. ESR analysis indicated the presence of peroxy radicals on the surface of the oxygen plasma treated PMMA and the intensity of these radicals increased with increasing plasma power. Decay study of the newly created radicals demonstrated that after 1 month under the atmospheric conditions there were still peroxy radicals on the surface of PMMA. This functionality is important in leading time for further process for binding of different molecules to the surface of the materials for specific purposes. As a result, RF plasma was found to be an effective tool for modification of surface properties of materials with product diversity for intended purposes.

No description available.

Neste trabalho foram realizados e estudados tratamentos superficiais sobre óxidos transparentes condutivos (TCOs) depositados sobre vidro, cuja aplicação ou finalidade é a montagem de dispositivos poliméricos eletroluminescentes. A principal intenção da utilização destes processos é diminuir a tensão de limiar e também aumentar a luminância desses dispositivos, sem interferir na transmitância original dos filmes. Três diferentes técnicas de tratamentos superficiais foram utilizadas: (a) Plasma de oxigênio; (b) Água-régia e (c) UV-Ozônio. Neste último processo, um reator foi montado utilizando uma lâmpada de vapor de mercúrio a alta pressão (tipo alta intensidade de descarga), sem o bulbo externo para fornecer a disponibilidade de radiação UV para a obtenção de ozônio a partir do ar atmosférico. Este reator com baixo custo e fácil manuseio foi montado para realizar um processo alternativo comparado aos dois processos anteriormente citados (Plasma de oxigênio e Água-Régia) e constitui o principal foco, comparando a partir de resultados experimentais obtidos por dispositivos montados, utilizando diferentes TCOs. Foi possível confirmar que o procedimento a partir do UV-Ozônio é reprodutível, pois pode substituir com vantagens as outras duas técnicas que apresentam custo mais elevado ou que exige manuseio especial. Pela utilização de diferentes períodos de tratamento como a única variável, nas condições estabelecidas durante os experimentos, foi mantida uma amostra sem tratamento para comparação em cada resultado obtido. Em comparação aos outros tratamentos, a técnica de UV-ozônio apresentou reprodutibilidade. Neste caso, verificamos que houve eliminação de contaminantes indesejáveis como carbono e hidrocarbonetos detectadas pela técnica de DRIFT (Diffuse Reflectance Infra-Red Fourier Transformed) e melhor espalhamento de polímero (PEDOT:PSS) sobre a superfície através da técnica de ângulo de contato foi observado. Para os filmes de ITO e FTO o período ótimo foi observado durante 5 minutos e para o ZnO, durante 15 minutos. Os resultados das medições de resistência de folha, espessura e efeito Hall, não revelaram significantes modificações. Revelando que as superfícies foram influenciadas apenas atomicamente ou molecularmente. / In this work superficial treatment on transparent conductive oxides (TCOs) were carried out and studied by application or finality for the assembly of electroluminescent polymeric devices. The mean intention by use of these processes is to decrease the threshold voltage and also increase the luminance of the devices, without interfering in the original TCOs transmittances. Three different treatment techniques were used: (a) oxygen plasma; (b) aqua regia and (c) UV-ozozne. In the he last one, a reactor was assembled using a high-pressure mercury vapor lamp (high intensity discharge lamp type) without outer bulb to provide the available UV radiation to obtain ozone from atmospheric air. This reactor with low cost and easy handle was mounted to accomplish an alternative process compared by other (oxygen plasma and aqua regia) and it has the main focus of this work compared from experimental results obtained by mounted devices using different TCOs. It was possible to confirm that the procedure from the UV-Ozone is reproducible, because it can replaced with advantages the other techniques that have expansive costs or special handling. The use of different treatment times as only variable on the imposed condition in the experiments, a sample was reserved without treatment for comparison during each obtained result. In comparison with other treatments the UV-Ozônio presented reproducibility. In this case was verified the undesirable contaminants eliminated as carbon and hydrocarbon and detected by DRIFT (Diffuse Reflectance Infra-Red Fourier Transformed) technique and better scattering of polymer (PEDOT:PSS) on surface by contact angle was observed. For ITO and FTO films the optimum period was observed during 5 minutes and ZnO during 15 minutes. The measurements results of sheet resistance, thickness and Hall effect revealed no significant changes confirming that the surfaces were influenced only atomically or molecularly only.

Neste trabalho foram realizados e estudados tratamentos superficiais sobre óxidos transparentes condutivos (TCOs) depositados sobre vidro, cuja aplicação ou finalidade é a montagem de dispositivos poliméricos eletroluminescentes. A principal intenção da utilização destes processos é diminuir a tensão de limiar e também aumentar a luminância desses dispositivos, sem interferir na transmitância original dos filmes. Três diferentes técnicas de tratamentos superficiais foram utilizadas: (a) Plasma de oxigênio; (b) Água-régia e (c) UV-Ozônio. Neste último processo, um reator foi montado utilizando uma lâmpada de vapor de mercúrio a alta pressão (tipo alta intensidade de descarga), sem o bulbo externo para fornecer a disponibilidade de radiação UV para a obtenção de ozônio a partir do ar atmosférico. Este reator com baixo custo e fácil manuseio foi montado para realizar um processo alternativo comparado aos dois processos anteriormente citados (Plasma de oxigênio e Água-Régia) e constitui o principal foco, comparando a partir de resultados experimentais obtidos por dispositivos montados, utilizando diferentes TCOs. Foi possível confirmar que o procedimento a partir do UV-Ozônio é reprodutível, pois pode substituir com vantagens as outras duas técnicas que apresentam custo mais elevado ou que exige manuseio especial. Pela utilização de diferentes períodos de tratamento como a única variável, nas condições estabelecidas durante os experimentos, foi mantida uma amostra sem tratamento para comparação em cada resultado obtido. Em comparação aos outros tratamentos, a técnica de UV-ozônio apresentou reprodutibilidade. Neste caso, verificamos que houve eliminação de contaminantes indesejáveis como carbono e hidrocarbonetos detectadas pela técnica de DRIFT (Diffuse Reflectance Infra-Red Fourier Transformed) e melhor espalhamento de polímero (PEDOT:PSS) sobre a superfície através da técnica de ângulo de contato foi observado. Para os filmes de ITO e FTO o período ótimo foi observado durante 5 minutos e para o ZnO, durante 15 minutos. Os resultados das medições de resistência de folha, espessura e efeito Hall, não revelaram significantes modificações. Revelando que as superfícies foram influenciadas apenas atomicamente ou molecularmente. / In this work superficial treatment on transparent conductive oxides (TCOs) were carried out and studied by application or finality for the assembly of electroluminescent polymeric devices. The mean intention by use of these processes is to decrease the threshold voltage and also increase the luminance of the devices, without interfering in the original TCOs transmittances. Three different treatment techniques were used: (a) oxygen plasma; (b) aqua regia and (c) UV-ozozne. In the he last one, a reactor was assembled using a high-pressure mercury vapor lamp (high intensity discharge lamp type) without outer bulb to provide the available UV radiation to obtain ozone from atmospheric air. This reactor with low cost and easy handle was mounted to accomplish an alternative process compared by other (oxygen plasma and aqua regia) and it has the main focus of this work compared from experimental results obtained by mounted devices using different TCOs. It was possible to confirm that the procedure from the UV-Ozone is reproducible, because it can replaced with advantages the other techniques that have expansive costs or special handling. The use of different treatment times as only variable on the imposed condition in the experiments, a sample was reserved without treatment for comparison during each obtained result. In comparison with other treatments the UV-Ozônio presented reproducibility. In this case was verified the undesirable contaminants eliminated as carbon and hydrocarbon and detected by DRIFT (Diffuse Reflectance Infra-Red Fourier Transformed) technique and better scattering of polymer (PEDOT:PSS) on surface by contact angle was observed. For ITO and FTO films the optimum period was observed during 5 minutes and ZnO during 15 minutes. The measurements results of sheet resistance, thickness and Hall effect revealed no significant changes confirming that the surfaces were influenced only atomically or molecularly only.

The main objective of nanotechnology is to build self-powered nanosystems that are ultrasmall in size, exhibit super sensitivity, extraordinary multi functionality, and extremely low power consumption. As we all know that 21st century has brought two most important challenges for us. One is energy shortage and the other is global warming. Now to overcome these challenges, it is highly desirable to develop nanotechnology that harvests energy from the environment to fabricate self-power and low-carbon nanodevices. Therefore a self-power nanosystem that harvests its operating energy from the environment is an attractive proposition. This is also feasible for nanodevices owing to their extremely low power consumption. One advantageous approach towards harvesting energy from the environment is the utilization of semiconducting piezoelectric materials, which facilitate the conversion of mechanical energy into electrical energy. Among many piezoelectric materials ZnO has the rare attribute of possessing both piezoelectric and semiconducting properties. But most applications of ZnO utilize either the semiconducting or piezoelectric property, and now it’s time to fully employ the coupled semiconducting-piezoelectric properties to form  the basis for electromechanically coupled nanodevices. Since wurtzite zinc oxide (ZnO) is structurally noncentral symmetric and has the highest piezoelectric tensor among tetrahedrally bonded semiconductors, therefore it becomes a promising candidate for energy harvesting applications. ZnO is relatively biosafe and biocompatible as well, so it can be used at large scale without any harm to the living environment. The synthesis of another transition metal oxide known as Co3O4 is also important due to its potential usage in the material science, physics and chemistry fields. Co3O4 has been studied extensively due to low cost, low toxicity, the most naturally abundant, high surface area, good redox, easily tunable surface and structural properties. These significant properties enable Co3O4 fruitful for developing variety of nanodevices. Co3O4 nanostructures have been focused considerably in the past decade due to their high electro-chemical performance, which is essential for developing highly sensitive sensor devices. I started my work with the synthesis of ZnO nanostructures with a focus to improve the amount of harvested energy by utilizing oxygen plasma treatment. Then I grow ZnO nanorods on different flexible substrates, in order to observe the effect of substrate on the amount of harvested energy. After that I worked on understanding the mechanism and causes of variation in the resulting output potential generated from ZnO nanorods. My next target belongs to an innovative approach in which AFM tip decorated with ZnO nanorods was utilized to improve the output energy. Then I investigated Co3O4 nanostructures though the effect of anions and utilized one of the nanostructure to develop a fast and reliable pH sensor. Finally to take the advantage of higher degree of redox chemistry of NiCo0O4 compared to the single phase of nickel oxide and cobalt oxide, a sensitive glucose sensor is developed by immobilizing glucose oxidase. However, there were problems with the mechanical robustness, lifetime, output stability and environmental adaptability of such devices, therefore more work is going on to find out new ways and means in order to improve the performance of fabricated nanogenerators and sensors.

No description available.

This doctoral thesis concerns the preparation of porous cerium oxide/carbon bilayers on silicon substrates. In this regard, carbonaceous films in the form of amorphous carbon (a-C) and nitrogenated amorphous carbon (CNx) are considered. The influence of various process parameters of the cerium oxide deposition on the morphology of the final cerium oxide/carbon bilayer is investigated. A correlation could be found between the morphol- ogy of the bilayer and the stoichiometry of the cerium oxide film determined by means of XPS. Furthermore, a study regarding the chemical composition of the used carbonaceous films by means of various spectroscopic techniques is presented. It was found that the chemical composition of the carbonaceous films strongly depends on the deposition con- ditions of these films and influences the behaviour of these films during oxygen plasma treatment and cerium oxide deposition, respectively. 1

Les biocapteurs sont utilisés quotidiennement pour déterminer la présence de molécules biologiques dans une matrice complexe, comme l’urine pour les tests de grossesses ou le sang pour les glucomètres. Les techniques courantes pour la détection des autres maladies nécessitent fréquemment le marquage de l’analyte avec une autre molécule, ce qui est à éviter pour fin de simplicité d’analyse. Ces travaux ont pour but la maximisation de la sensibilité d’une surface d’or ou d’argent nanotrouée, afin de permettre la détection de la liaison de molécules biologiques par résonance des plasmons de surface localisés (LSPR), en utilisant la spectroscopie de transmission. Un biocapteur portable, rapide et sans marquage pour quantifier des analytes d’intérêt médical ou environnemental pourrait être construit à partir de ces travaux. Dans l’objectif d’étudier de nombreuses configurations pour maximiser la sensibilité, le temps et le coût des méthodes de fabrication de nanostructures habituelles auraient limité le nombre de surfaces nanotrouées pouvant être étudiées. Un autre objectif du projet consiste donc au développement d’une technique de fabrication rapide de réseaux de nanotrous, et à moindres coûts, basée sur la lithographie de nanosphères (NSL) et sur la gravure au plasma à l’oxygène (RIE). La sensibilité à la variation d’indice de réfraction associée aux liaisons de molécules sur la surface du métal noble et la longueur d’onde d’excitation du plasmon de surface sont influencées par les caractéristiques des réseaux de nanotrous. Dans les travaux rapportés ici, la nature du métal utilisé, le diamètre ainsi que la périodicité des trous sont variés pour étudier leur influence sur les bandes LSPR du spectre en transmission pour maximiser cette sensibilité, visant la fabrication d’un biocapteur. Les surfaces d’argent, ayant un diamètre de nanotrous inférieur à 200 nm pour une périodicité de 450 nm et les nanotrous d’une périodicité de 650 nm démontre un potentiel de sensibilité supérieur. / Biosensors are used daily to determine the presence of biomolecules in a complex matrix, like urine for pregnancy test or blood with a glucometer. The usual biodetection methods require the addition of a tag on the analyte, which is to be avoided to design a simple analytical method. The objective of this work is to maximize the sensitivity of a gold or silver nanohole arrays to detect the biomolecules liaisons close to the metal surface by localized surface plasmon resonance (LSPR) in transmission spectroscopy. A portable and effective biosensor to quantify analytes could be built based on this work, without a tagging step. To achieve the objective of evaluating numerous configurations for maximal sensitivity, the time and cost of the usual nanostructures fabrication methods would have limited the number of nanohole arrays in metal surface that could have been studied in this project. This fact motivated another objective of this project, the development of a fast and low cost fabrication method for nanohole arrays using nanospheres lithography (NSL) followed by reactive ions etching (RIE). The plasmon sensitivity and wavelength excitation are influenced by the nanohole arrays characteristics. In the work presented here, the chemical composition of the metal surface, the diameter and the periodicity of the nanohole arrays are shown to the influence the LSPR bands. The transmission maximum and minimum position of some LSPR bands are sensitive to refractive index change, which can be exploited in a biosensor format to detect biomolecules. The optimization of these nanohole arrays characteristics allows the maximization of this sensitivity to build a biosensor. The best index refraction sensitive results were with silver surfaces, with nanohole diameters smaller than 200 nm for a periodicity of 450 nm and the nanoholes with a periodicity of 650 nm show a potential for an increased sensitivity.