Today’s electronic society relies on the functionality of electrical contacts. To achieve good contact properties, surface coatings are normally applied. Such coatings should ideally fulfill a combination of different properties, like high electrical conductivity, high corrosion resistance, high wear resistance and low cost. A common coating strategy is to use noble metals since these do not form insulating surface oxides. However, such coatings are expensive, have poor wear resistance and they are often applied by electroplating, which poses environmental and human health hazards. In this thesis, nanocomposite carbide-based coatings were studied and the aim was to evaluate if they could exhibit properties that were suitable for electrical contacts. Coatings in the Cr-C, Cr-C-Ag and Nb-C systems were deposited by magnetron sputtering using research-based equipment as well as industrial-based equipment designed for high-volume production. To achieve the aim, the microstructure and composition of the coatings were characterized, whereas mechanical, tribological, electrical, electrochemical and optical properties were evaluated. A method to optically measure the amount of carbon was developed. In the Cr-C system, a variety of deposition conditions were explored and amorphous carbide/amorphous carbon (a-C) nanocomposite coatings could be obtained at substrate temperatures up to 500 °C. The amount of a-C was highly dependent on the total carbon content. By co-sputtering with Ag, coatings comprising an amorphous carbide/carbon matrix, with embedded Ag nanoclusters, were obtained. Large numbers of Ag nanoparticles were also found on the surfaces. In the Nb-C system, nanocrystalline carbide/a-C coatings could be deposited. It was found that the nanocomposite coatings formed very thin passive films, consisting of both oxide and a-C. The Cr-C coatings exhibited low hardness and low-friction properties. In electrochemical experiments, the Cr-C coatings exhibited high oxidation resistance. For the Cr-C-Ag coatings, the Ag nanoparticles oxidized at much lower potentials than bulk Ag. Overall, electrical contact resistances for optimized samples were close to noble metal references at low contact load. Thus, the studied coatings were found to have properties that make them suitable for electrical contact applications.

With growing demand for cardiovascular implants, improving the performance of artificial blood-contacting devices is a task that deserves close attention. Current prostheses made of fluorocarbon polymers such as expanded polytetrafluoroethylene (ePTFE) suffer from early thrombosis and require periodic replacement. A great number of attempts have already been made to improve blood compatibility of artificial surfaces, but only few of them found commercial implementation. One of the surfaces under intensive research for cardiovascular use is amorphous carbon-based coatings produced by means of the plasma-assisted deposition. However, this class of coatings can be produced using various techniques leading to a number of coatings with different properties. Carbon coatings produced in different plasmas may be of hard diamond-like type or soft graphite-like type, doping with different elements also changes the surface structure and properties. Taking this into account, the search for blood-compatible coating requires the understanding of surface composition and structure and its influence on blood-compatibility. This work attempts to advance our knowledge of this field. Here, commercial PTFE thin film was used as a working material, which composition corresponds to the composition of modern ePTFE vascular grafts and which compatibility with blood we tried to improve by deposition of nitrogenated amorphous carbon (a-CN) coatings in the plasma. Biocompatibility was assessed by a number of tests including the interaction with whole blood and various cells such as platelets, endothelial cells, neutrophils, and fibroblasts. Most of tests showed the blood compatibility of coated surface is better than that of untreated PTFE. Physico-chemical and morphological properties of coated surfaces were studied in parallel using x-ray photoemission spectroscopy (XPS), electron energy loss spectroscopy (EELS), x-ray absorption spectroscopy (XAS), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM). Some correlation between the structure of coatings and blood compatibility was inferred. It was found that at first nitrogen incorporation into amorphous carbon film stimulates blood compatibility. However, when nitrogen fraction increases over 23-25 %, no further improvement but reduction of blood compatibility was observed. Conclusion is made that for best biomedical performance, nitrogen percentage in a-CN coatings must be adjusted to the optimum value.

Analysis of the electronic structures of nitrogen-doped, amorphous carbon samples and of nanodiamond films are carried out in order to determine their sp2 bonding concentration. The amorphous carbon samples under consideration are deposited onto polytetrafluoroethylene (PTFE) polymer substrates by hot wire plasma sputtering of graphite in varying nitrogen concentration atmospheres. The deposition or modification of the substrates surface may lend itself to increasing hardness and wear resistance. Eventually these polymer substrates may be used for applications in the field of biomaterials, focusing on cardiovascular surgery, where a low blood/surface interaction is important. The primary technique used in this study is x-ray absorption spectroscopy, measured at the Advanced Light Source synchrotron at the Lawrence Berkeley National Laboratory, Berkeley, USA. A method of analyzing these spectra was then developed to determine the sp2 bonding concentrations in carbon films. Through this newly developed analysis method, the sp2 bonding concentrations in these samples increases from 74 to 93% with growing nitrogen doping. The diamond films presented here are deposited on silicon wafer substrates in a methane atmosphere by microwave plasma deposition. Various deposition conditions, such as bias voltage and methane atmosphere concentration, affect the purity of the diamond film. This analysis reveals sp2 bonding concentrations in these samples from, typically, a few percent to 25%.

Analysis of the electronic structures of nitrogen-doped, amorphous carbon samples and of nanodiamond films are carried out in order to determine their sp2 bonding concentration. The amorphous carbon samples under consideration are deposited onto polytetrafluoroethylene (PTFE) polymer substrates by hot wire plasma sputtering of graphite in varying nitrogen concentration atmospheres. The deposition or modification of the substrates surface may lend itself to increasing hardness and wear resistance. Eventually these polymer substrates may be used for applications in the field of biomaterials, focusing on cardiovascular surgery, where a low blood/surface interaction is important. The primary technique used in this study is x-ray absorption spectroscopy, measured at the Advanced Light Source synchrotron at the Lawrence Berkeley National Laboratory, Berkeley, USA. A method of analyzing these spectra was then developed to determine the sp2 bonding concentrations in carbon films. Through this newly developed analysis method, the sp2 bonding concentrations in these samples increases from 74 to 93% with growing nitrogen doping. The diamond films presented here are deposited on silicon wafer substrates in a methane atmosphere by microwave plasma deposition. Various deposition conditions, such as bias voltage and methane atmosphere concentration, affect the purity of the diamond film. This analysis reveals sp2 bonding concentrations in these samples from, typically, a few percent to 25%.

With growing demand for cardiovascular implants, improving the performance of artificial blood-contacting devices is a task that deserves close attention. Current prostheses made of fluorocarbon polymers such as expanded polytetrafluoroethylene (ePTFE) suffer from early thrombosis and require periodic replacement. A great number of attempts have already been made to improve blood compatibility of artificial surfaces, but only few of them found commercial implementation. One of the surfaces under intensive research for cardiovascular use is amorphous carbon-based coatings produced by means of the plasma-assisted deposition. However, this class of coatings can be produced using various techniques leading to a number of coatings with different properties. Carbon coatings produced in different plasmas may be of hard diamond-like type or soft graphite-like type, doping with different elements also changes the surface structure and properties. Taking this into account, the search for blood-compatible coating requires the understanding of surface composition and structure and its influence on blood-compatibility. This work attempts to advance our knowledge of this field. Here, commercial PTFE thin film was used as a working material, which composition corresponds to the composition of modern ePTFE vascular grafts and which compatibility with blood we tried to improve by deposition of nitrogenated amorphous carbon (a-CN) coatings in the plasma. Biocompatibility was assessed by a number of tests including the interaction with whole blood and various cells such as platelets, endothelial cells, neutrophils, and fibroblasts. Most of tests showed the blood compatibility of coated surface is better than that of untreated PTFE. Physico-chemical and morphological properties of coated surfaces were studied in parallel using x-ray photoemission spectroscopy (XPS), electron energy loss spectroscopy (EELS), x-ray absorption spectroscopy (XAS), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM). Some correlation between the structure of coatings and blood compatibility was inferred. It was found that at first nitrogen incorporation into amorphous carbon film stimulates blood compatibility. However, when nitrogen fraction increases over 23-25 %, no further improvement but reduction of blood compatibility was observed. Conclusion is made that for best biomedical performance, nitrogen percentage in a-CN coatings must be adjusted to the optimum value.

The UV-Visible spectra of a-C composites and nano composites have provided a very useful information about the electronic states and band structure. The UV-Visible spectra of a-C as well as nanoparticle are qualitatively similar. They do not show any absorption cutoff in wavelength (_max). In fact they are good absorbers of UV-Visible light in whole range. Composites show some absorptions which could be the combined effect of filler as we as host matrix. Since there is no _max, hence it is very unlikely to define any optical band gap. The nanoparticle is a good absorber in midinfrared compared to a-C. That may be due to presence of complicated kind of vibrational modes of carbon cased nanoparticle.Besides Fe3C also produces some additional modes. With kind of spectrum we have it is difficult to identify the different modes unambiguously for nanoparticle. The combined effects of filler as well as host polymer are reflected in both sets of composites. A new absorption is observed in a-C as well as in nanoparticle composites at 2370 cm−1 and 3462 cm−1 respectively. This peak may arise in composites due to interaction between filler and host matrix. The thermo gravimetric analysis is a useful characterization techniques for polymer and composites. It gives the information about the stability, phase change, degradation, chemical reaction and many more. The a-C composites as well as nano composites are stable up to 200_ C. These composites can be safely used for any practical purpose below this temperature. During the synthesis of composites the filler does not take part in any reaction. This fact is reflected in the DTG curve. The composites degrade in the way host polymer degrades.

Following the first report on electronic transport measurements of graphene, an atom-thick carbon material, many scientists have devoted effort to understand its fundamental properties. In this work, the mechanical properties of graphene-based materials, including monolayer graphene oxide and chemical vapor deposition (CVD) grown graphene, were determined using membrane structures. Furthermore, a membrane structure was used to demonstrate thermoacoustic sound generation from monolayer graphene. In order to realize the mechanical characterization, reproducible methods to fabricate graphene membranes were developed using dry and wet transfer techniques. A novel dry transfer technique produced graphene-sealed microchambers without trapping liquid inside. An improved wet transfer technique enabled the transfer of graphene onto perforated substrates. Monolayer graphene oxide was mechanically tested using scanning atomic force microscopy (AFM) combined with finite element analysis of the data. The mechanical deformation was measured by scanning AFM tips over the suspended graphene oxide membranes. The Young’s modulus of the membranes was obtained by analyzing the deformation using finite element analysis together with a mapping technique. In addition, membranes with 2 and 3 layers of graphene oxide were identified using transmission electron microscopy and mechanically characterized. Moreover, these same methods were used for measuring mechanical properties of ultra-thin amorphous carbon membranes. Bulge tests, which apply uniform pressure on the suspended membrane, revealed the mechanical behavior of polycrystalline graphene grown on copper foils by chemical vapor deposition. In particular, the effect of grain boundaries on the elastic properties of polycrystalline graphene was studied by correlating its Young’s modulus with the density of grain boundaries within the membranes. It was observed that a large number of grain boundaries softened the graphene membranes. Graphene, along with monolayer hexagonal boron nitride, is the ultimate limit of thin materials. Thus, it is an ideal candidate as a thermoacoustic sound source because of its low heat capacity per unit area. The work presented here provides the first demonstration of thermoacoustic sound generation from large-area monolayer graphene. A fundamental understanding of the influence of the underlying substrates was achieved by comparing the acoustic performance of graphene membranes on various patterned substrates with different porosities. / text

Per paskutinį dešimtmetį anglies nanostuktūros – amorfinės anglies plėvelės, fulerenai, o ypač nanovamzdeliai patraukė daugelio tyrėjų dėmesį. Šios struktūros yra daug žadančios puslaidininkių pramonėje, dėl galimybių prietaisų miniatiūrizavimui. Šiuo metu nanotechnologija patraukia vis didesnį dėmesį. Neabejojama anglies ir kitų nanostruktūrų išskirtinėmis savybėmis ir bandoma jas pritaikyti įvairiose srityse, tačiau šių struktūrų įdiegimą riboja tai, kad sunku pagaminti norimų struktūrų ir išmatavimų anglies nanodarinius, nes būtent anglies nanodarinių struktūra nulemia šių darinių fizikines savybes, taipogi ir laidumą. / Carbon nanodivices have attracted the attention of many researchers since their discovery last decade. These carbon molecules are tiny tubes with diameters down to 0.4 nm, while their lengths can grow up to a million times their diameter. Using their remarkable electrical properties, simple electronic logic circuits have been built. These structures are promising for the semiconductor industry which is leading the search of miniaturization. They are not only very good conductors, but they also appear to be the yet found material with the biggest specific stiffness, having half the density of aluminium. They also have great active surface. The aim of this work is to analyse the variable range hopping ( VRH ) conduction, which can describe conduction mechanism in carbon films. Also, to find conduction parameters, whish describe the conduction mechanism in carbon films and carbon nanotubes networks. In that work was analysed impacts of photon – assisted tunneling on electrical conductivity in carbon nanotubes networks mechanism.

Orientador: Francisco das Chagas Marques / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-14T14:37:10Z (GMT). No. of bitstreams: 1 OliveiraJunior_MyrianoHenriquesde_D.pdf: 13534676 bytes, checksum: 4da81eaf9a2b22721528c9804801a446 (MD5) Previous issue date: 2009 / Resumo: Neste trabalho desenvolvemos um sistema de deposição de filmes finos pela técnica de arco catódico filtrado (FCVA- Filtered Cathodic Vacuum Arc), que possibilita o desenvolvimento de ligas metálicas e, sobretudo, a deposição de filmes de carbono amorfo altamente tetraédrico. Utilizando este sistema desenvolvemos filmes de carbono amorfo (a-C) com elevada dureza (estimado em cerca de 50 a 60GPa) e alta concentração de ligações sp3 C-C em função da polarização do substrato. Estudamos as propriedades ópticas, mecânicas (stress e dureza), estruturais (Raman e RBS) e a estabilidade térmica (efusão de gases) destes filmes em função da energia de deposição. Também desenvolvemos e caracterizamos filmes de carbono crescidos por FCVA assistido por um feixe de íons secundário de Ar e Kr com diferentes energias, onde analisamos os efeitos da energia deste feixe sobre as propriedades físicas do material resultante. Além das estruturas de carbono intrínseco realizamos um estudo sobre filmes de carbono amorfo hidrogenado depositados por PECVD (plasma enhanced chemical vapor deposition) com diferentes tensões de bias (de 60 à 550V) e atmosferas mistas de CH4/Kr, onde variamos a pressão parcial deste gás nobre entre 0 e 50%. Estudamos a influência deste gás nobre sobre as propriedades estruturais do material assim como a forma como os átomos deste elemento se distribuem dentro da rede amorfa. Esta última análise foi baseada em estudos conduzidos a partir da absorção de raios-x na borda K do átomo de criptônio, onde verificamos a aglomeração destes átomos na forma de estruturas solidas. Também investigamos os processos de transformações estruturais ocorridas em estruturas a-C:H e ta-C com a temperatura baseadas na efusão de gases. Para este estudo construímos um sistema que funciona em ultra-alto vácuo, com temperatura controlada variando de ambiente até cerca de 1000 graus. Os estudos sobre as propriedades estruturais foram baseados, sobretudo, em medidas de espectroscopia de espalhamento Raman com radiação de excitação na região do visível e do ultravioleta, o que possibilita a obtenção de informações mais detalhadas sobre a forma como os átomos sp2 e sp3 distribuem-se no material. Por fim, exploramos o potencial de aplicação de três tipos de carbono amorfo; tipo polimérico (PLC), tipo diamante (DLC) e tetraédrico (ta-C) como monocamadas antirefletoras para células solares de silício cristalino e comparamos com o desempenho obtido com camadas fabricadas com materiais usualmente empregados na indústria para tal aplicação. Os resultados mostraram que filmes de carbono amorfo podem ser utilizados como camada anti-refletora. Os filmes de carbono tipo polimérico apresentaram resultados muito semelhantes aos obtidos com camadas convencionais de dióxido de estanho / Abstract: In this work we designed, manufactured and characterized a Filtered Cathodic Vacuum Arc (FCVA) deposition system. This technique is usually applied in the preparation of metallic alloys and highly sp3 - hybridized amorphous carbon thin films. By using this system we prepared a series of amorphous carbon films (a-C) with high hardness (up to ~60GPa) and high concentration of sp3 C-C bonds varying the deposition energy of the C+ ions. Mechanical (hardness and intrinsic stress) and structural (Raman, RBS and gas effusion) were investigated. Another series of a-C was developed by FCVA, but using an assisted beam of Ar or Kr as a function of the ion energy. The main purpose of this work is to understand of the effects of the bombardment of an energetic ion beam on the physical properties of the films. Another study performed on hydrogenated amorphous carbon films (a-C:H) were carried out on samples deposited by plasma enhanced chemical vapor deposition (PECVD). The films were prepared with different self-bias, varying from 60 up to 550V, and different mixed atmospheres of methane and krypton gases, varying the partial pressure of krypton from 0 to 50%. Films prepared at low bias are polymeric-like (PLC), while films prepared at high bias are diamond-like (DLC). We had performed investigations on the influence of this noble gas on the structural properties of the a-C:H films and how the Kr atoms are arranged within the amorphous matrix. The distribution of Kr atoms was studied mainly by x-ray absorption on the krypton absorption K-edge. Due to the absence of EXAFS oscillations the spectra were interpreted using the XANES region, which gave us evidences of clustering of Kr atoms. The processes involved in the a-C:H nd ta-C structural transformations during the thermal annealing were analyzed by means of thermal gas effusion measurements (using a quadrupole spectrometer) in a system developed in our laboratory. Raman scattering spectroscopy measurements were carried out with excitation radiation in the visible and ultraviolet ranges. This choice is justified due to the more detailed information obtained by multiwavelength Raman spectroscopy on the distribution of sp2and sp3sites within the amorphous carbon matrix. Finally, we had evaluated the possibility of the application of three types of amorphous carbon structures, the diamond-like and polymeric-like carbon, and the ta-C as antireflective coating on crystalline silicon solar cells. We observed that all amorphous carbon structures (DLC, PLC and ta-C) increase the short-circuit current of the solar cells. In the case of PLC films, the result is comparable to that obtained with conventional antireflective coating such as tin dioxide (SnO2) / Doutorado / Física da Matéria Condensada / Doutor em Ciências

[pt] Este trabalho teve como objetivos o estudo das modificações nas propriedades de filmes de carbono amorfo hidrogenado (a-C:H) através do tratamento da sua superfície com plasma de tetrafluoreto de carbono (CF4) e Argônio e a deposição e estudo das propriedades tribológicas de filmes de carbono amorfo fluorado e hidrogenado (a-C:F:H) sobre substrato de aço inoxidável 316L. A primeira parte da tese descreve a funcionalização por plasma da superfície com flúor de filmes previamente depositados de a-C:H sobre silício cristalino 100 pela técnica da deposição química na fase vapor assistido por plasma PECVD. Esta funcionalização foi feita pelo emprego de plasma de uma mistura dos gases CF4 e Argônio em diferentes proporções. Estes filmes tiveram a sua superfície analisada por espectroscopia de fotoelétrons, microscopia de força atômica e tiveram a sua energia superficial avaliadas por medidas de ângulo de contato de três diferentes líquidos (água deionizada, glicerol e bromonaftaleno). A funcionalização com Flúor tornou a superfície superhidrofóbica, atingindo valores em torno de 140 graus. Na segunda parte da tese descrevemos com sucesso a deposição por PECVD de filmes de carbono amorfo fluorados sobre substratos de aço inoxidável 316L. Para melhorar a adesão, os substratos foram submetidos a tratamento com nitretação e carbonitretação por plasma e a posterior deposição de um filme de titânio e de a-C:H. Nestes filmes foram realizadas medidas de microscopia de força atômica, dureza, espectroscopia de fotoelétrons e tribometria para determinar o coeficiente de atrito e resistência ao desgaste mecânico. Os resultados obtidos mostraram que a incorporação de CF4, produz filmes com propriedades semelhantes às propriedades do Teflon. Obtivemos filmes com dureza em torno de 11Gpa, mais duro que o aço inoxidável 316L, cuja dureza é de aproximadamente 4,5 GPa, porém menor que a medida em aço nitretado. Com relação ao coeficiente de atrito, o filme de a-C:F:H apresentou uma redução significativa em relação ao aço e ao aço nitretado. As medidas de tribometria também mostraram que o filme ficou bem aderido e apresenta boa resistência ao desgaste mecânico, resistindo a centenas de ciclos com a ponta do tribometro arrastando sobre a superfície com forças aplicadas de 10N. Como resultado conseguimos depositar filmes sobre aço inoxidável 316L com baixo coeficiente de atrito, dureza elevada e boa resistência ao desgaste mecânico. / [en] This work aimed to the study of the modifications of the properties of carbon amorphous hydrogenated films (a-C:H) trough the treatment of the surface film with plasma of carbon tetra fluoride (CF4) and Argon. Another object has been the study of the tribological properties of carbon amorphous fluorinated and hydrogenated (a-C:F:H) deposited on substrates of stainless steel 316L. The first part of the these describes the functionalization by plasma of the surfaces with fluorine of films previously deposited of a-C:H on crystalline silicon 100 by the technique of plasma enhanced chemical vapor deposition PECVD. This functionalization was made by the use of plasma of a mixture of CF4 and Argon gases in different proportions. The films had their surfaces analyzed by photoelectron spectroscopy, atomic force microscopy and their surface energies calculates by measurement of the angle contact of three different liquids (water, glycerol and bromonaphthalene). The functionalization with Fluorine made the surface super hydrophobic, reaching values for the contact angle around 140 degrees. In the second part of the these we describe the successful deposition by PECVD of films of carbon amorphous fluorinated on stainless steel 316L. In order to improve the adhesion, the substrates were submitted to treatment with nitriding and carbonitriding by plasma and the subsequent deposition of a film of titanium and a-C:H. In these films were realized measurements of atomic force microscopy, hardness, photoelectron spectroscopy and tribometry to determine the friction coefficient and the resistance to mechanical wastage. The results obtained showed that an incorporation of CF4, produces films with properties similar to teflon properties. We obtained films with hardness around 11 Gpa, harder than stainless steel 316L, whose hardness is approximately 4,5 Gpa, but smaller than the measure in nitrated steel. In relation to the friction coefficient, the film of a-C:F:H presented a significant reduction in relation to the steel and nitrated steel. The tribometry measurements also showed that the film was well adhered and present good resistance to mechanical wear, resisting to hundreds of cycles with the point of the tribometry dragging on the surface with applied force of 10N. As result we get to deposit films on stainless steel 316L with low friction coefficient, elevated hardness and good resistance to mechanical wear.