Dissertations / Theses on the topic 'Cvd'

For the emerging semiconductor material silicon carbide (SiC) used in high power devices, chemical vapor deposition (CVD) is the most prominent method to create the electrically active SiC epitaxial layers in the device. The process of growing such epitaxial layers is to use a hydrocarbon and silane diluted in hydrogen flow through a hot chamber where chemical reactions take place in such manner that Si and C finally deposit on the surface creating epitaxial SiC. The addition of chlorine (Cl) to the process has been thoroughly investigated due to its ability to reduce homogeneous nucleation in the gas phase attributed to the stronger Si-Cl bond compared to the Si-Si bond. In this thesis the fluorinated chemistry has been investigated, since the Si-F bond is even stronger than the Si-Cl bond and the fluorinated chemistry for SiC CVD has remained poorly understood. Using SiF4 as Si precursor in growth experiments combined with thermal equilibrium calculations of gas phase composition and quantum chemical computations of the surface chemistry first the silicon chemistry in the CVD process has been probed. It is shown that while growth rates on the order of 35 µm/h can be achieved with a fluorinated chemistry, the deposition chemistry is very sensitive to the mass flows of the precursors and not as robust as the chlorinated CVD chemistry which routinely yields 100 µm/h over wide conditions. By using the position for the onset of epitaxial growth along the gas flow direction as a new measurable, together with modeling, it is conclude that SiF is the main Si growth species with SiHF as a minor Si species contributing to growth. The carbon chemistry in a fluorinated SiC CVD process has been probed by a similar approach. Here it is found that the slow kinetics of the SiF4 molecule needs to be matched by a carbon precursor with comparable slow kinetics. It is shown that methane is a suitable carbon precursor in combination with SiF4. Before a fluorinated CVD chemistry can be adopted in device processing, the effect of fluorine on the dopant incorporation must be understood since dopant incorporation is of paramount importance in semiconductor manufacturing. Dopant incorporation studies for n-type doping with N using N2 and p-type doping with Al using TMAl in fluorinated CVD of homoepitaxial SiC are presented. It is found to be possible to control the doping in SiC epitaxial layers when using a fluorinated CVD chemistry for both n- and p-type material using the C/Si ratio as in standard SiC CVD. However, large area doping uniformity seems to be a challenge for a fluorinated CVD chemistry, most likely due to the very strong Si-F and Al-F bonds. It is found that no additional optically or electrically active defects are created due to the use of fluorine in the CVD process. Finally, the fluorinated chemistry is compared to the chlorinated and brominated chemistries for SiC CVD and an overall model for halogen addition to SiC CVD is presented.

The aim of the thesis is to design, conduct and assess an experiment seeking to look into the utility properties of recent tools manufactured by HAM-FINAL. The tools include polycrystalline diamond (PCD) and CVD diamond cutting edges. In the theoretical part, the attention is devoted to cutting materials with an emphasis on diamond materials, as well as to issues associated with the wearing of the cutting tools, requirements specified for precision of bores and tools used in the manufacture of precision bores. The paper further provides an overview of a selection of world’s leading manufacturers of PCD blanks, CVD diamond coatings, CVD diamond layers and reamers with PCD cutting edges.

The research into the subject of graphene has soared over the past few years. Due to the exceptional nature of some of its properties, it has become ever popular in the field of nanotechnology. The use of graphene for various electronics applications have been displayed using graphene that can be exfoliated or grown via several techniques. However, the scalability of these methods do not allow for bulk synthesis, known in the case of other graphitic nanomaterials like fullerenes and carbon nanotubes. For realistic applications, graphene has to be made in large quantities at a reasonable cost for use in, for example, solar cells, FETs, chemical sensors and engineering composites. Here successful attempts have been made to synthesise few layer graphene via bulk methodologies commonly used in the manufacture of carbon nanotubes, using relatively inexpensive precursor materials. Spray pyrolysis, a simple and scalable technique for the manufacture of few layer graphene using ethanol and various sodium precursors was demonstrated, which showed polymer composite, electronic device and transparent thin film application. Few layer graphene was grown using a bimetallic catalyst of sodium and cobalt. Addition of the sodium caused a visual decrease in the amount of carbon deposited from ethanol chemical vapour deposition. The product when observed using the scanning and transmission electron microscope was shown to be made up of turbostatic few layer graphene platelets. Growth of single and few layer graphene was demonstrated using copper nanoribbons and cobalt nanosheets as catalyst templates. These when incorporated onto inert support material, produced single and few layer graphene in a process that is deemed scalable and compatible with present industrial CVD reactors used for making carbon nanotubes.

This diploma thesis is mainly focused on the fabrication of graphene layers on the copper foil by the Chemical Vapor Deposition (CVD). For this purpose the high-temperature chamber for the production of the graphene was completed and fully automated. The production of the high area graphene on the copper foil was experimentally achieved. The Raman microscopy and X-ray photoelectron spectroscopy measurements proved that the produced graphene is mostly a monolayer. Graphene layer was transferred on non-conductive substrate.

L'etude de depot d'oxyde de titane en couches minces par les deux techniques cvd et pacvd en vue de realisation des membranes inorganiques, necessite la maitrise de la texture des couches sur le support de membrane pour l'adapter aux conditions de fonctionnement. En cvd thermique, la texture des couches de tio#2 depend de la pression de travail et de la temperature du substrat. Cette texture est colonnaire a basse pression et granuleuse a des pressions plus elevees pour une temperature de 600c. En pacvd, les couches sont equivalentes au point de vue texture, elles sont amorphes et compactes. La morphologie des couches obtenues par pacvd est fonction de la nature de la surface du substrat. La puissance est un parametre qui peut etre responsable de la vitesse de depot en pacvd. Le domaine de la filtration de solution utilise est l'ultrafiltration et la nanofiltration

"Une étude des mécanismes de pyrolyse des hydrocarbures, conduisant au dépôt de pyrocarbone par CVD/CVI, a été menée suivant une double approche expérimentale/numérique. A partir du précurseur propane, la phase gazeuse a été analysée in-situ (spectroscopie IRTF) en cours d'infiltration et en ligne (CPG) en CVD ou CVI : le rôle des espèces en C2 dans la formation du pyrocarbone dit " faiblement anisotrope" et celui des espèces en C3 dans celle du pyrocarbone dit "laminaire colonnaire" ont été identifiés. Les caractérisations micro -et nano-texturales (MOLP, MET et spectroscopie Raman) des dépôts réalisés ont permis d'établir des mécanismes de croissance distincts pour chacune des formes de pyrocarbone laminaire. Des mécanismes homogènes détaillés décrivant la pyrolyse du propane et du méthane ont été introduits dans diverses modélisations numériques de réacteurs 0D et 1D. Ils ont été validés par confrontation avec différentes analyses expérimentales de la phase gazeuse. Des corrélations ont été établies entre la composition de la phase gazeuses déterminée par les modèles et le dépôt des microtextures principales. Les précurseurs effectifs à nombre impair de carbone semblent ainsi favoriser l'anisotropie du pyrocarbone, tandis qu'à l'inverse un précurseur effectif à nombre pair de carbone conduit à la formation de défauts et donc à une chute d'anisotropie. Sur cette base, des schémas réactionnels ont été pjroposés pour décrire la formation des microtextures principales déposées à partir de propane et de méthane. "

<p>Diamond is a promising material for high-power, high-frequency and hightemperatureelectronics applications, where its outstanding physical propertiescan be fully exploited. It exhibits an extremely high energy gap, veryhigh carrier mobilities, high breakdown field strength, and the highest thermalconductivity of any wide bandgap material. It could therefore producethe fastest switching, the highest power density, and the most efficient electronicdevices obtainable, with applications in the RF power, automotive andaerospace industries. Lightweight diamond devices, capable of high temperatureoperation in harsh environments, could also be used in radiationdetectors and particle physics applications where no other semiconductordevices would survive.The high defect and impurity concentration in natural diamond or polycrystallinehigh-pressure-high-temperature (HPHT) diamond substrates hasmade it difficult to establish reliable results when studying the electronicproperties of diamond. However, recent progress in the growth of high puritySingle-Crystal Chemical Vapor Deposited Diamond (SC-CVD) has openedthe perspective of applications under such extreme conditions based on thistype of artificial diamond.Despite the improvements, there are still many questions which must beanswered. This work will focus on electrical characterization of (SC-CVD)diamond by different measurements techniques such as internal photoemission,I-V, C-V, Hall and in particular, time-of-flight (TOF) carrier driftvelocity measurements. With the mentioned techniques, some importantproperties of diamond such as drift mobilities, lateral carrier transit velocities,compensation ratio and Schottky barrier heights have been investigated.Low compensation ratios (ND/NA) < 10-4 have been achieved in boron-dopeddiamond and a drift mobility of about 860 cm2 / V for the hole transit nearthe surface in a lateral TOF configuration could be measured.</p>

Silicon carbide (SiC) is a promising material for high power and high frequency devices due to its wide bandgap, high break down field and high thermal conductivity. The most established technique for growth ofepitaxial layers of SiC is chemical vapor deposition (CVD) at around 1550 °C using silane, SiH4, and lighthydrocarbons e g propane, C3H8, or ethylene, C2H4, as precursors heavily diluted in hydrogen. For high-voltagedevices made of SiC thick (&gt; 100 μm), low doped epilayers are needed. Normal growth rate in SiC epitaxy is~ 5 μm/h, rendering long growth times for such SiC device structures. The main problem when trying to achievehigher growth rate by increasing the precursor flows is the formation of aggregates in the gas phase; for SiCCVD these aggregates are mainly silicon droplets and their formation results in saturation of the growth ratesince if the gas flow does not manage to transport these droplets out of the growth zone, they will eventuallycome in contact with the crystal surface and thereby creating very large defects on the epilayer making theepilayer unusable. To overcome this problem, high temperature- as well as low pressure processes have beendeveloped where the droplets are either dissolved by the high temperature or transported out of the susceptor bythe higher gas flow. A different approach is to use chloride-based epitaxy that uses the idea that the silicondroplets can be dissolved by presence of species that bind stronger to silicon than silicon itself. An appropriatecandidate to use is chlorine since it forms strong bonds to silicon and chlorinated compounds of high purity canbe purchased. In this thesis the chloride-based CVD process is studied by using first a single molecule precursor,methyltrichlorosilane (MTS) that contributes with silicon, carbon and chlorine to the process. Growth of SiCepilayers from MTS is explored in Paper 1 where growth rates up to 104 μm/h are reported together withmorphology studies, doping dependence of growth rate and the influence of the C/Si- and Cl/Si-ratios on thegrowth rate and doping. In Paper 2 MTS is used for the growth of 200 μm thick epilayers at a growth rate of 100μm/h, the epilayers are shown to be of very high crystalline quality and the growth process stable. The growthcharacteristics of the chloride-based CVD process, is further studied in Paper 3, where the approach to add HClgas to the standard precursors silane and ethylene is used as well as the MTS approach. A comparison betweenliterature data of growth rates for different approaches is done and it is found that a precursor molecule withdirect Si-Cl bonds should be more efficient for the growth process. Also the process stability and growth ratedependence on C/Si- and Cl/Si are further studied. In Paper 4 the standard growth process for growth on 4° offaxis substrates is improved in order to get better morphology of the epilayers. It is also shown that the optimizedprocess conditions can be transferred to a chloride-based process and a high growth rate of 28 μm/h wasachieved, using the HCl-approach, while keeping the good morphology. In Paper 5 chloride-based CVD growthon on-axis substrates is explored using both the HCl- and MTS-approaches. The incorporation of dopants in SiCepilayers grown by the chloride-based CVD process is studied in Papers 6 and 7 using the HCl-approach. InPaper 6 the incorporation of the donor atoms nitrogen and phosphorus is studied and in Paper 7 theincorporation of the acceptor atoms boron and aluminum. The incorporation of dopants is found to follow thetrends seen in the standard growth process but it is also found that the Cl/Si-ratio can affect the amount ofincorporated dopants.<br>Kiselkarbid (SiC) är ett fascinerande material som samtidigt är mycket enkelt och mycketkomplicerat. Det är enkelt eftersom det byggs upp av bara två sorters atomer, kisel och kol.Atomerna bygger upp kristallens struktur genom att bilda Si-C bindningar och man kan beskrivakristallstrukturen som uppbyggd av tetraedrar med en kiselatom (eller kolatom) i mitten och enkolatom (eller kiselatom) i varje hörn på tetraedern. Samtidigt är SiC komplicerat eftersomberoende på hur man staplar dessa tetraedrar kan man få olika varianter på kristallstrukturen, såkallade polytyper. Det finns drygt 200 kända polytyper av kiselkarbid, men det är dock bara enhandfull av dessa polytyper som är tekniskt intressanta. Kiselkarbid är intressant eftersom det ärett hårt material som inte heller påverkas nämnvärt av kemiskt aggressiva miljöer ellertemperaturer upp till 2000 °C; dessutom är SiC en halvledare och tack vare dess tålighet är det ettmycket bra material för elektriska komponenter för högspänningselektronik eller för användningi aggressiva miljöer. För att kunna tillverka dessa komponenter måste man kunna odla kristaller av kiselkarbid. Detfinns i princip två typer av kristallodling; i) odling av bulkkristaller, där stora kristaller odlas föratt sedan kan skivas och poleras till kristallskivor (dessa skivor benämns oftast substrat), och ii)odling av epitaxiella skikt, där man odlar ett tunt lager kristall med mycket hög renhet ovanpå ettsubstrat (ordet epitaxi kommer från grekiskans epi = ovanpå och taxis = i ordning, epitaxiellaskikt odlas alltså ovanpå ett substrat och kopierar den kristallina ordningen hos substratet). I detepitaxiella skiktet, eller epilagret som det även kallas, kan man styra den elektriskaledningsförmågan med mycket hög precision genom att blanda in små mängder orenheter iepilagret, man pratar här om att dopa halvledarkristallen. För att odla epilager av SiC använderman CVD, CVD betyder Chemical Vapor Deposition, någon riktigt bra svensk översättningfinns inte men det är en teknik för att framställa ett tunt lager av ett material genom kemiskareaktioner med gaser som startmaterial. I standard CVD-processen för odling av SiC epilager använder man silan (SiH4) som kiselkälla och lätta kolväten som eten (C2H4) eller propan (C3H8) som kolkälla. Dessa gaser späds kraftigtut i vätgas och man odlar epilagret vid ungefär 1500-1600 °C. Med denna process kan man odlaca 5 mikrometer (mikrometer = miljondelsmeter) epilager på en timme. Men för vissakomponenter behöver man ett epilager som är över 100 mikrometer tjockt, vilket görtillverkningen av sådana komponenter både tidsödande och kostsam. Ett problem som manmåste lösa för att få högre tillväxthastighet i processen är att när man ökar mängden silan,kommer kiseldroppar att bildas i gasfasen och om de kommer i kontakt med substratet blirepilagret förstört. I denna avhandling undersöks ett sätt att lösa problemet med kiseldropparnaoch därmed kunna tillåta höga tillväxthastigheter för SiC epilager. Idén är att man kan lösa uppkiseldropparna genom att tillsätta något i gasblandningen som binder starkare till kisel än kisel.En mycket bra atom att använda för detta ändamål är klor eftersom klor binder mycket starkt tillkisel. Man kallar denna process för klorid-baserad CVD. Till att börja med använde vi molekylen metyltriklorsilan (MTS), som innehåller både kol, kiseloch klor, för klorid-baserad tillväxt av SiC epilager. Genom att använda MTS lyckades vi fåtillväxthastigheter mellan 2 och 104 mikrometer i timmen. Vi har även visat att det är möjligtanvända MTS för att odla 200 mikrometer tjocka epilager med en tillväxthastighet på 100mikrometer i timmen utan att den kristallina kvalitén på epilagren försämras. Ett alternativ till attanvända MTS är att addera saltsyra (HCl) i gasform till standard processen. För att förstå denklorid-baserade processen bättre, jämfördes de olika alternativen med litteraturdata från enprocess där man istället för vanlig silan hade använt triklorsilan (TCS) för att få en klorid-baserad process. Det visade sig att MTS- och TCS-processerna krävde mindre kiselhalt i gasfasen för attfå en hög tillväxthastighet, med andra ord var de mer effektiva. Vi förklarade detta med atteftersom dessa startmolekyler har tre kisel-kol bindningar är det enkelt att bilda SiCl2 molekylen,som har visat sig vara ett viktigt mellansteg i den klorid-baserade processen, eftersom man dåbara behöver bryta kemiska bindningar. Om man istället börjar från silan och saltsyra måstekemiska reaktioner ske för att skapa kisel-kol bindningar och därmed SiCl2. När man odlar kristaller underlättar man tillväxten genom att preparera ytan på substratet medatomära steg. Om man tittar på ytan med atomär förstoring kan säga att ytan liknar en trappa,detta är bra eftersom atomerna som bygger upp epilagret gärna fastnar vid atomära steg eftersomde kan binda in till kristallen både neråt och åt sidan. Vi har optimerat standard processen för attfå bättre morfologi, alltså en finare yta, när man odlar på substrat som har mindre andel atomärasteg på ytan och visat att denna optimering går att överföra till en klorid-baserad process medhög tillväxthastighet . Vi har även visat att man kan använda den klorid-baserade processen föratt odla epilager med hög tillväxthastighet på substrat helt utan atomära steg. Slutligen har vi studerat doping av kiselkarbid vid höga tillväxthastigheter med den kloridbaseradeprocessen, både n-typ doping (där man dopar med ämnen som har fler valenselektronerän kol och kisel så att man får ett överskott av elektroner i materialet) med kväve och fosfor, ochp-typ doping (där man dopar med ämnen som har färre valenselektroner än kol och kisel så attman får ett underskott av elektroner i materialet) med bor och aluminium.

Paramagnetic defects in free standing polycrystalline diamond films made by chemical vapour deposition (CVD) have been studied using electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR) and infrared absorption. EPR experiments at a range of frequencies (1-35 GHz) confirm the ¹H hyperfine parameters for the recently identified H1 defect (Zhou et al., Phys. Rev. B, 54:7881 (1996)). In the samples studied here, H1 is always accompanied by another defect at g=2.0028(1). Saturation recovery measurements are consistent with two defects centred on g=2.0028. The spin-lattice relaxation rate of H1 is a factor of 10-100 times more rapid than the single substitutional nitrogen centre (N⁰_S), which is known to be incorporated into the bulk diamond. ¹H matrix ENDOR measurements indicate that the H1 centre is in an environment with hydrogen atoms 2-10 A distant from the centre. The near neighbour hydrogen identified by the EPR was not detected in the ENDOR experiments. The concentration of H1 correlates with the total integrated C-H stretch absorption in the samples studied here. All the evidence is consistent with H1 being located at hydrogen decorated grain boundaries (or in intergranular material) rather than in the bulk diamond. The affect of annealing the films in vacuo up to 1900 K has been studied. On annealing at 1700 K it was found that some of the hydrogen on internal grain boundaries became mobile but was not lost from the sample, and the intensity of the EPR absorption at g=2.0028 decreased. Annealing at 1900 K severely degraded the optical properties of the samples, and a new defect with g=2.0035(2) was created. Infrared measurements show that hydrogen is lost from most CVD diamond samples when annealed to 1900 K for four hours. An EPR imaging (EPRI) probe was designed and built. This comprised a 3-loop, 2-gap loop-gap resonator and a pair of anti-Helmholtz coils providing a magnetic field gradient ∂B_z/∂z. Using this probe the distribution of N⁰_S was measured in the growth direction of four CVD diamonds to a resolution of 20 μm. The distribution of N⁰_S is shown to be different to the distribution of defects with g=2.0028. Two-dimensional images of the spin density of N⁰_S in single crystal type Ib diamonds made by the high temperature and pressure (HTP) method have been generated, demonstrating a resolution of 100 μm. A two-dimensional image of the spin density of g=2.0028 defects in a CVD sample is compared to a photograph of the same sample, showing the correlation between the distribution of the defects with the distribution of non-diamond material in the sample. The distribution of the [N-N]⁺ defect in a natural diamond has been examined using ∂B_z/∂B_ϰ field gradient coils.

This thesis presents a fundamental study on etching of diamond surfaces. Details of the growth by microwave plasma Chemical Vapour Deposition (CVD) and etching by microwave hydrogen plasma, oxygen reactive ion etching (RIE) and thermal oxidation are presented. Prolonged exposure of {100} diamond surfaces to microwave hydrogen plasma was investigated by atomic force microscopy (AFM). Reduction of surface roughness has been observed while formation of etch pits has not been detected. X-ray photoelectron spectroscopy (XPS) detected the removal of graphitic carbon and reduction of oxygen under hydrogen plasma etching. Electrical sheet resistivity has been observed to be depended on the texture of the CVD diamond films as well as on the ambient exposure time. Both the surface and electronic properties are shown to agree with theoretical models. Formation of columnar structures accompanied the oxygen RIE of CVD diamond films and cubo-octahedral crystallites. Using scanning electron microscopy (SEM) and AFM the preferential formation of columnar structures in the inter-granular area of the diamond films has been detected. Surface contamination by silicon oxide has been identified by EDAX on the diamond surface and specifically on the columnar structures. Analysis by XPS demonstrated that the RIE etched surfaces were oxygen terminated and also were partially graphitised. A discussion on the mechanism of columnar formation has been presented. From the thermal oxidation of cubo-octahedral CVD diamond crystallites the activation energies and pre-exponential factors of the {100} and {111} diamond surfaces were measured, using optical profilometry, to be 221 ± 34 kJ mol-1, 2.3 x 109 nm s-1 Pa-1 and 286 ± 29 kJ mol-1, 1.9 x 1014 nm s-1 Pa-1 over the temperature range 535oC to 600oC respectively. Thermal oxidation of {100} and {111} diamond surfaces was accompanied with the formation of etch pits, increase of surface roughness and the exposure of {113} diamond surfaces between the {100} and {111} surfaces. A mechanism for the thermal oxidation of the diamond surfaces has been proposed.

La thèse porte sur cette couche de nitrure ou d’oxynitrure de silicium. Le déroulé prévoit l’élaboration des deux types de dépôts par voie gazeuse (par Chemical Vapor Infiltration CVI), la caractérisation de ces dépôts (par tous les moyens scientifiques à disposition et jugés utiles), ainsi que des essais en conditions proches de l’application visée (haute température, présence de phases liquides) pour juger de l’efficacité de ces dépôts et notamment effectuer une comparaison entre le nitrure et l’oxynitrure. Une étude complète des paramètres modifiables lors de l’élaboration et de leur effet sur la chimie (et par conséquent l’influence sur le comportement du matériau en conditions d’utilisation) représente le cœur du travail considéré<br>Ceramics are usually used at high temperature because of their refractory nature. However, they are too brittle to be submitted to high stresses, such as in the rotating parts of aircraft engines. One way to reduce the brittleness of ceramics is to design them as composites. The fiber/matrix architecture displays a damageable character thanks to a suitable interfacial layer, which is deposited on the fiber cloths before the infiltration with molten silicon. The aim of the thesis is to propose and evaluate a solution to protect the fiber reinforcement during the impregnation step with liquid silicon. This solution involves the deposition of a protective layer made of silicon nitride or oxynitride

A novel CVD copper process is described using two new copper CVD precursors, KI3 and KI5, for the fabrication of IC or TSV (Through Silicon Via) copper interconnects. The highly conformal CVD copper can provide seed layers for subsequent copper electroplating or can be used to directly fabricate the interconnect in one step. These new precursors are thermally stable yet chemically reactive under CVD conditions, growing copper films of exceptionally high purity at high growth rates. Their thermal stability can allow for elevated evaporation temperatures to generate the high precursor vapor pressures needed for deep penetration into high aspect ratio TSV vias. Using formic acid vapor as a reducing gas with KI5, copper films of > 99.99 atomic % purity were grown at 250&deg;C on titanium nitride at a growth rate of > 1500 &Aring;/min. Using tantalum nitride coated TSV type wafers, ~ 1700 &Aring; of highly conformal copper was grown at 225&deg;C into 32 &mu;m × 5 &mu;m trenches with good adhesion. With ruthenium barriers we were able to grow copper at 125&deg;C at a rate of 20 &Aring;/min to give a continuous ~ 300 &Aring; copper film. In this respect, rapid low temperature CVD copper growth offers an alternative to the long cycle times associated with copper ALD which can contribute to copper agglomeration occurring. &copy; 2008 Elsevier B.V.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2009.<br>Includes bibliographical references (leaves 67-68).<br>In this thesis, we report transport studies performed on CVD-grown graphene. We perform resistivity and hall measurements on a large-area sample at 4' K. We measure the carrier mobility of the sample and find it to be on the order of 1000 cm2/Vs, whereas monolayer graphene regularly exhibits much higher mobilities. We also examine what we find to be weak signatures of Shubnikov-de Haas oscillations in magnetic field sweeps. Finally, we study magneto-resistance effects at low fields, and find that the sample exhibits weak-localization effects.<br>by Miriam Hanna Huntley.<br>S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2004.<br>Includes bibliographical references.<br>Ion implantation and diffusion couple experiments were used to study silver transport through and release from CVD silicon carbide. Results of these experiments show that silver does not migrate via classical diffusion in silicon carbide. Silver release is, however, likely dominated by vapor transport through cracks in SiC coatings. The results of silver ion implantation in silicon carbide and subsequent annealing at 1500ʻC place an upper limit on the silver diffusion coefficient in SiC of 5x10-21 m2/s, a value which is roughly 6 orders of magnitude less than the previous values reported in the literature. Silver diffusion should have been easily observable, but was not detected in SiC plates after heat treatments at 1500ʻC for times ranging between 200 h and 500 h. A detailed investigation of the silver morphology within the SiC both before and after heating showed that silver was immobilized at SiC grain boundaries and did not diffuse along them as expected. Novel spherical diffusion couples were fabricated containing silver inside shells of either graphite or SiC which were coated with CVD SiC. Mass measurements clearly revealed silver release from the diffusion couples after heating, but no silver was detected during concentration profile measurements in the SiC. Leak testing results, however, gave evidence of the presence of cracks in many of the SiC coatings, which may have provided pathways for silver escape. A simple vapor flow model was applied to estimate crack sizes that would account for silver release from SiC coatings in the current diffusion couples and coated fuel particle tests from the literature.<br>(cont.) These calculated crack sizes are small enough that they would not have been detected during normal investigation or post-irradiation examination. A diffusive mechanism has been assumed to control silver transport in silicon carbide based on silver release observations reported previously in the literature, but no direct evidence of silver diffusion has been offered. Additionally, variations in silver release from particle to particle indicate that silver transport does not occur equally in all silicon carbide samples and is not consistent with diffusion. The findings presented in this dissertation are important to coated particle fuel design and fabrication because they indicate that SiC can successfully retain silver but that some SiC coatings permit silver release. Future work must be directed at identifying the pathways for silver release and their root causes in order to prevent silver release from coated fuel particles.<br>by Heather J. MacLean.<br>Ph.D.

Chemical vapour deposition (CVD) diamond is a very interesting material for the fabrication of radiation detectors, particularly for X-ray dosimetry. CVD diamond could potentially be used for large-area X-ray sensors, it is extremely radiation hard, can withstand high temperatures and highly corrosive environments, and is also "tissue-equivalent" in regard to X-ray absorption. In fact, there exist several applications where other standard semiconductor detectors do not fulfil those specific requirements. In this work we report on the fabrication and characterisation of CVD diamond radiation detectors and we describe how this material, even though of a polycrystalline nature, is readily of great interest for applications as a solid state X-ray dosimeter and alpha particle sensor. We have characterised the detectors using I-V measurements, photo current response to 30 KV(peak) X-ray pulses and their response to 241Am alpha particles. Ion beam induced current (rnIC) studies have also been used to investigate charge transport within single diamond crystallites. Ion implanted ohmic contacts have also been developed using boron to graphitise the diamond surface and produce high-quality non-metalised ohmic contacts.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico<br>O avanÃo e o aperfeiÃoamento das tÃcnicas de sÃntese e manipulaÃÃo de materiais sÃo fundamentais para o entendimento de suas propriedades e das possÃveis formas de produÃÃo e utilizaÃÃo. PorÃm, no caso dos nanomateriais, principalmente, cujas extraordinÃrias capacidades sÃo bastante celebradas, problemas como defeitos estruturais, alto custo de obtenÃÃo e dificuldade de produÃÃo em larga escala ainda necessitam ser solucionados. Inserido neste panorama està o grafeno, um nanomaterial cuja morfologia bidimensional, constituÃda por Ãtomos de carbono dispostos de forma hexagonal, à responsÃvel por propriedades sem precedentes que apresentam revolucionÃria relevÃncia, tanto para a pesquisa bÃsica quanto para a pesquisa aplicada. Neste sentido, existem diferentes mÃtodos de sÃntese de grafeno, estando entre os mais vantajosos o mÃtodo de deposiÃÃo quÃmica em fase de vapor (Chemical Vapor Deposition - CVD). Este mÃtodo consiste na quebra das ligaÃÃes das molÃculas de um gÃs submetido a altas temperaturas de modo que os Ãtomos provenientes do gÃs sejam depositados sobre um determinado substrato. Neste trabalho, utilizou-se o mÃtodo CVD para a sÃntese de grafeno sobre substratos de silÃcio oxidado (Si/SiO2) recobertos por filmes de nÃquel (Ni) com, aproximadamente, 500nm de espessura, os quais funcionaram como catalisadores. O gÃs metano (CH4) foi utilizado como a fonte dos Ãtomos de carbono depositados e os processos de sÃntese tiveram diferentes conjuntos de parÃmetros executados. A sÃntese de grafeno pelo mÃtodo CVD teve como objetivo geral verificar os resultados divulgados na literatura e aperfeiÃoÃ-los, relacionando os parÃmetros utilizados nas sÃnteses e as caracterÃsticas dos filmes de Ni catalisadores com aquelas apresentadas pelos filmes de grafeno obtidos nos experimentos. As amostras foram caracterizadas por meio de Microscopia EletrÃnica de Varredura, Microscopia Ãptica e Raman Confocal e Microscopia de ForÃa AtÃmica. Em consistÃncia com os resultados publicados na literatura, observou-se que sÃo sintetizados filmes finos compostos por flakes de material grafÃtico com espessura nÃo uniforme, e que a obtenÃÃo de filmes mais uniformes à fortemente dependente da morfologia do filme catalisador. RegiÃes apresentando espectro Raman caracterÃstico de monocamadas de grafeno e de grafeno de poucas camadas foram maiores quando combinados o tratamento tÃrmico do filme de Ni com o baixo fluxo e menor tempo de exposiÃÃo ao CH4. Verificaram-se, ainda, variaÃÃes nos espectros Raman dos flakes. Estas variaÃÃes apresentaram-se mais intensas, quanto mais reduzido à o nÃmero de camadas de grafeno e incluem o aparecimento da banda D, alÃm do deslocamento dos picos, revelando a influÃncia dos substratos sobre os filmes sintetizados. Esta pesquisa considerou mÃtodos de estimativa do nÃmero de camadas por caracterÃsticas do espectro Raman, divulgados na literatura, aliados à anÃlise da espessura por AFM que mostraram ser possÃvel a sÃntese de monocamadas de grafeno.<br>The advancement and improvement of synthesis techniques and handling of materials are fundamental to understand their properties and possible forms of production and use. However, in the case of nanomaterials, problems such as structural defects, high cost and difficulty of achieving production on a large scale have yet to be solved. Inserted in this panorama is graphene, a two-dimensional nanomaterial whose morphology, consisting of carbon atoms arranged in hexagonal form, is responsible for unprecedented properties that have revolutionary relevance for both basic and applied research. There are different methods of synthesis of graphene. The method of Chemical Vapor Deposition (CVD) is among the most advantageous ones. This method consists in breaking the bonds of the molecules of a gas subjected to high temperatures so that the atoms from the gas are deposited on a given substrate. In this work, we used the CVD method for the synthesis of graphene on oxidized silicon substrates (Si/SiO2) coated with a 500 nm thick film of nickel (Ni), which served as the catalyst. Methane gas (CH4) was used as the source of the carbon atoms and the synthesis was carried out using different sets of parameters. Experiments were performed, firstly, using parameters es-tablished in the literature and the results were compared with those obtained by other authors. The influence of the synthesis parameters and the characteristics of the films of Ni catalysts on the properties of the graphene films was studied. The samples were characterized using Scanning Electron Microscopy, Confocal Raman and Optical Microscopy, and Atomic Force Microscopy. In agreement with results from the literature, it could be observed that thin films are synthesized and they are composed of graphitic flakes with a non-uniform thickness, which is strongly dependent of the morphology of catalyst film. Larger regions with characteristic Raman spectra of monolayer and few layer graphene could be obtained by combining thermal treatment of Ni film during the sputtering process with low gas flow and time of exposure to CH4 in the CVD experiment. Variations in the Raman spectra of the flakes could be observed, including the emergence of the D-band and the displacement of the peaks. These variations, which reveal the influence of substrates on the synthesized films, were more intense the smaller the number of graphene layers. Next, we combined methods reported in the literature for estimating the number of layers on the basis of the characteristics of the Raman spectra with AFM analysis to obtain the thickness of the graphene layer. The results obtained from our analysis show that monolayer graphene could be successfully synthesized in the experiments.

CASTRO, Manuela Oliveira de. Síntese de grafeno pelo método CVD. 2011. 84 f. Dissertação (Mestrado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2011.<br>Submitted by Edvander Pires (edvanderpires@gmail.com) on 2014-11-13T20:03:00Z No. of bitstreams: 1 2011_dis_mocastro.pdf: 3411512 bytes, checksum: 64f6579c926c263cd9391dfb058954bb (MD5)<br>Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2014-11-13T20:35:29Z (GMT) No. of bitstreams: 1 2011_dis_mocastro.pdf: 3411512 bytes, checksum: 64f6579c926c263cd9391dfb058954bb (MD5)<br>Made available in DSpace on 2014-11-13T20:35:29Z (GMT). No. of bitstreams: 1 2011_dis_mocastro.pdf: 3411512 bytes, checksum: 64f6579c926c263cd9391dfb058954bb (MD5) Previous issue date: 2011<br>The advancement and improvement of synthesis techniques and handling of materials are fundamental to understand their properties and possible forms of production and use. However, in the case of nanomaterials, problems such as structural defects, high cost and difficulty of achieving production on a large scale have yet to be solved. Inserted in this panorama is graphene, a two-dimensional nanomaterial whose morphology, consisting of carbon atoms arranged in hexagonal form, is responsible for unprecedented properties that have revolutionary relevance for both basic and applied research. There are different methods of synthesis of graphene. The method of Chemical Vapor Deposition (CVD) is among the most advantageous ones. This method consists in breaking the bonds of the molecules of a gas subjected to high temperatures so that the atoms from the gas are deposited on a given substrate. In this work, we used the CVD method for the synthesis of graphene on oxidized silicon substrates (Si/SiO2) coated with a 500 nm thick film of nickel (Ni), which served as the catalyst. Methane gas (CH4) was used as the source of the carbon atoms and the synthesis was carried out using different sets of parameters. Experiments were performed, firstly, using parameters es-tablished in the literature and the results were compared with those obtained by other authors. The influence of the synthesis parameters and the characteristics of the films of Ni catalysts on the properties of the graphene films was studied. The samples were characterized using Scanning Electron Microscopy, Confocal Raman and Optical Microscopy, and Atomic Force Microscopy. In agreement with results from the literature, it could be observed that thin films are synthesized and they are composed of graphitic flakes with a non-uniform thickness, which is strongly dependent of the morphology of catalyst film. Larger regions with characteristic Raman spectra of monolayer and few layer graphene could be obtained by combining thermal treatment of Ni film during the sputtering process with low gas flow and time of exposure to CH4 in the CVD experiment. Variations in the Raman spectra of the flakes could be observed, including the emergence of the D-band and the displacement of the peaks. These variations, which reveal the influence of substrates on the synthesized films, were more intense the smaller the number of graphene layers. Next, we combined methods reported in the literature for estimating the number of layers on the basis of the characteristics of the Raman spectra with AFM analysis to obtain the thickness of the graphene layer. The results obtained from our analysis show that monolayer graphene could be successfully synthesized in the experiments.<br>O avanço e o aperfeiçoamento das técnicas de síntese e manipulação de materiais são fundamentais para o entendimento de suas propriedades e das possíveis formas de produção e utilização. Porém, no caso dos nanomateriais, principalmente, cujas extraordinárias capacidades são bastante celebradas, problemas como defeitos estruturais, alto custo de obtenção e dificuldade de produção em larga escala ainda necessitam ser solucionados. Inserido neste panorama está o grafeno, um nanomaterial cuja morfologia bidimensional, constituída por átomos de carbono dispostos de forma hexagonal, é responsável por propriedades sem precedentes que apresentam revolucionária relevância, tanto para a pesquisa básica quanto para a pesquisa aplicada. Neste sentido, existem diferentes métodos de síntese de grafeno, estando entre os mais vantajosos o método de deposição química em fase de vapor (Chemical Vapor Deposition - CVD). Este método consiste na quebra das ligações das moléculas de um gás submetido a altas temperaturas de modo que os átomos provenientes do gás sejam depositados sobre um determinado substrato. Neste trabalho, utilizou-se o método CVD para a síntese de grafeno sobre substratos de silício oxidado (Si/SiO2) recobertos por filmes de níquel (Ni) com, aproximadamente, 500nm de espessura, os quais funcionaram como catalisadores. O gás metano (CH4) foi utilizado como a fonte dos átomos de carbono depositados e os processos de síntese tiveram diferentes conjuntos de parâmetros executados. A síntese de grafeno pelo método CVD teve como objetivo geral verificar os resultados divulgados na literatura e aperfeiçoá-los, relacionando os parâmetros utilizados nas sínteses e as características dos filmes de Ni catalisadores com aquelas apresentadas pelos filmes de grafeno obtidos nos experimentos. As amostras foram caracterizadas por meio de Microscopia Eletrônica de Varredura, Microscopia Óptica e Raman Confocal e Microscopia de Força Atômica. Em consistência com os resultados publicados na literatura, observou-se que são sintetizados filmes finos compostos por flakes de material grafítico com espessura não uniforme, e que a obtenção de filmes mais uniformes é fortemente dependente da morfologia do filme catalisador. Regiões apresentando espectro Raman característico de monocamadas de grafeno e de grafeno de poucas camadas foram maiores quando combinados o tratamento térmico do filme de Ni com o baixo fluxo e menor tempo de exposição ao CH4. Verificaram-se, ainda, variações nos espectros Raman dos flakes. Estas variações apresentaram-se mais intensas, quanto mais reduzido é o número de camadas de grafeno e incluem o aparecimento da banda D, além do deslocamento dos picos, revelando a influência dos substratos sobre os filmes sintetizados. Esta pesquisa considerou métodos de estimativa do número de camadas por características do espectro Raman, divulgados na literatura, aliados à análise da espessura por AFM que mostraram ser possível a síntese de monocamadas de grafeno.

The work is aimed at preparation and characterization of thin films deposited by Plasma-Enhanced Chemical Vapor Deposition (PE-CVD) on silicon wafers. A comprehensive characterization of the deposition system in order to determine the range of deposition conditions was a part of the study. Subsequently, the single and multi-layers were deposited from tetravinylsilane monomer. The deposition process was monitored by spectroscopic ellipsometry and mass spectroscopy. Layers and layered structures were characterized by microscopic and spectroscopic techniques. The physical and chemical properties of deposited films were studied with respect to the deposition conditions and monomer fragmentation in low-temperature plasma.

La société ESSILOR est à l’origine d’un nouveau concept ophtalmique : « l’optique digitale ». Ce concept s’appuie sur la discrétisation du verre en pixels et l’introduction, dans ces structures micrométriques, de liquides fonctionnels. Les axes de recherche de cette thèse sont issus des besoins et contraintes de cette thématique et ils concernent principalement : l’élaboration de couches minces polymères par un procédé CVD (Chemical Vapor Deposition) et les dépôts de films sur des substrats liquides. Un bâti commercial de CVD avec un mode d’activation thermique a permis la réalisation contrôlée et la caractérisation de couches minces conformes d’un matériau polymère aux propriétés en adéquation avec le cahier des charges industriel : le parylène. Des études sur le mécanisme mis en jeu ont révélé un mode de croissance original de ce matériau et pouvant être décrit par différents modèles complémentaires dans les informations qu’ils apportent. Nous avons également imaginé un dispositif de modulation des propriétés surfaciques des films de parylène par une fonctionnalisation en voie sèche. Le second procédé CVD qui a été étudié met en œuvre l’activation photonique. Il s’agit d’un bâti de photo-CVD innovant et très modulable, développé au CIRIMAT, pour répondre au mieux aux besoins de ce projet « verre digital » et en particulier à la nécessité de déposer des couches de divers polymères sur des liquides fonctionnels à une pression se rapprochant de la pression atmosphérique<br>ESSILOR society is investigating a new ophthalmologic concept: “the digital optic”. This concept is based on the discretization of the ocular glass in pixels, and the insertion, in those micrometric structures, of functional liquids. The research work of this PhD thesis aims to satisfy the requirements and constraints of this topic. They principally concerns: the elaboration of thin polymeric films by a CVD (Chemical Vapor Deposition) process and the deposition on liquid substrates. A commercial CVD reactor thermally activated has permitted the controlled production and the characterization of conform polymeric thin films whose properties are in good adequacy with the industrial specifications: the parylene. Studies on the mechanism have revealed an original growth mechanism of this material which can be described with some complementary and informative models. We also have developed a functionalization method by a dry process to modulate the surface properties of parylene films. The second CVD process studied uses a photonic activation. It is an innovative and very flexible photo-CVD process designed in the CIRIMAT in order to satisfy the “digital glass” project and in particular the necessity to deposit various polymer films on functional liquids at a pressure near the atmospheric pressure

Nanoscience and Nanotechnology have experienced a tremendous growth in few years. Nanotechnologies are the design, characterization, production and application of structures, devices and systems by controlling shape and size at nanometer scale. Carbon exists in several forms, depending on how the carbon atoms are arranged, their properties vary. One of the carbon forms is carbon nanotubes, which are capped at each end by half of a fullerene, and have aroused great interest in the research community because of their exotic electrical, thermal and mechanical properties. MWCNTs and SWCNTs were discovered in 1991 and 1993, respectively, by Ijima. A single-wall carbon nanotube can be described as a graphene sheet rolled into a cylindrical shape so that the structure has one-dimensional axial symmetry. Carbon nanotubes (CNTs) have unique characteristics that allow them to act as electrodes in charge storage devices, sensors and traps for pollutants, among others. On the one hand, for applications that require a certain amount of energy in pulse form, the traditional capacitors used in electronic circuits are not suitable because they cannot store enough energy in the volume and weight available. However, given the characteristics of CNTs that have a narrow size distribution, large specific surface area, low resistivity and high stability, CNTs have been regarded as a suitable material for electrodes in supercapacitors. On the other hand, the development of new systems, based in CNTs, which could overcome some of the current limitations in the capture of emerging pollutants in fluids, such as nanometric particles (being, moreover, difficult to detect) and organic pollutants at very low concentrations, is an additional objective of the present thesis. Water plasma and nitrogen plasma treatments were performed to remove amorphous carbon and to functionalize the surface of CNTs with different oxygen or nitrogen groups. Conditions of plasma treatments were optimized by adopting a Box-Wilson experimental design. Various microscopic and spectroscopic techniques were used to characterize the morphology, structure and elemental compositions before and after the plasma treatments. Electrochemical measurements show that water plasma treatment significantly increases the active surface area of CNTs, and nitrogen plasma is more effective to improve the charge transfer. Both nitrogen and water plasma raise the capacitance of CNTs notably in comparison to untreated CNTs. Manganese dioxide was deposited by galvanostatic method on untreated CNTs and plasma treated nanotubes. The MnO2 structure changes from nanoflower (as deposited) to needle like or to a layer coating on the surface of CNTs depending on the voltage applied during the cycling measurements. CNTs treated with 75 W plasma power and 10 Pa nitrogen pressure, and further functionalized with MnO2, exhibit the highest specific capacitance obtained in this thesis; 955 Fg-1 at 10 mVs-1. This value is almost 87% of the theoretical value for MnO2. The structural evolution of CNTs during water assisted growth has also been studied. The obtained length of CNTs was ~ 800 µm on silicon wafer. Transfer of ultralong CNTs on conductive adhesive aluminum tape was carried out using a novel methodology that lowers the series resistance of the electrode. The specific capacitance of CNTs/Al increases from 87 to 148 Fg-1 for untreated and water plasma treated CNTs/Al, respectively. In addition, we found that for a successful and faster growth of CNTs on copper substrate, strong adhesion of the buffer layer (Al2O3) is essential. A multilayered setup (Cu/Ni/Ti/Al2O3) prior to catalyst deposition boosts the growth rate and quality of CNTs. Vertically-aligned CNTs were synthesized on quartz fiber filters for environmental applications. Three chlorinated VOCs; trichloroethylene, chloroform and 1,2-dichlorobenzene were used to study the adsorption/desorption properties of CNTs/QF. The ability to detect or remove organic pollutants increases after the water plasma treatment, which functionalizes the CNTs surface and removes the catalyst from the top of CNTs (inner cavities are available for use). We found that molecules with aromatic rings present stronger interactions with CNTs (Phi-stacking).<br>La nanociencia y la nanotecnología han experimentado un enorme crecimiento en pocos años. Una de las formas del carbono son los nanotubos de carbono, que están limitados en cada extremo por medio fulereno, y que han despertado un gran interés en la comunidad científica debido a sus exóticas propiedades eléctricas, térmicas y mecánicas. Un nanotubo de carbono de pared simple puede ser descrito como una hoja de grafeno enrollada en forma cilíndrica de modo que la estructura tiene una simetría axial. Los nanotubos de carbono (CNTs) tienen características únicas que les permiten actuar como electrodos en dispositivos de almacenamiento de carga, sensores y adsorción de contaminantes, entre otros. Los principales objetivos de esta tesis son la síntesis de CNTs sobre los diversos sustratos para aplicaciones de almacenamiento de carga (supercondensadores) y ambientales. Tratamientos de plasma de agua y nitrógeno se realizaron para eliminar el carbono amorfo y funcionalizar la superficie de los CNTs con diferentes grupos de oxígeno o nitrógeno. Las condiciones de los tratamientos de plasma fueron optimizados mediante la utilización de un diseño experimental de Box-Wilson. Las medidas electroquímicas muestran que el tratamiento con plasma de agua aumenta significativamente el área superficial activa de los CNTs, y el plasma de nitrógeno es más eficaz para mejorar la transferencia de carga. Tanto el plasma de nitrógeno como el de agua aumentan la capacidad de los nanotubos de carbono en comparación con los CNTs no tratados. El dióxido de manganeso se depositó electroquímicamente mediante el método galvanostático sobre los nanotubos de carbono sin tratar y tratados con plasma. La estructura de MnO2 cambia de una estructura de “nanoflor” (inicialmente) a una en forma tipo aguja o de capa superficial en función del voltaje aplicado durante los experimentos de ciclado. Los CNTs tratados con 75 W de potencia de plasma y 10 Pa de presión de nitrógeno, y posteriormente funcionalizados con MnO2, exhiben la capacitancia específica más alta obtenida en esta tesis; 955 Fg-1 a 10 mVs-1. Este valor es aproximadamente el 87% del valor teórico para MnO2. La evolución estructural de los nanotubos de carbono durante su crecimiento asistido por agua ha sido estudiada. La longitud obtenida de los CNTs es de ~ 800 micras sobre una oblea de silicio. La transferencia de CNTs ultralargos a una cinta adhesiva de aluminio conductor se llevó a cabo utilizando una metodología novedosa que reduce la resistencia en serie del electrodo. La capacidad específica de los CNTs / Al aumenta de 87 a 148 Fg-1 para los CNTs / Al sin y con tratamiento de plasma de agua, respectivamente. Una configuración de múltiples capas (Cu/Ni/Ti/Al2O3) antes de depositar el catalizador aumenta la velocidad de crecimiento y la calidad de los CNTs. CNTs verticalmente alineados se sintetizaron sobre filtros de fibra de cuarzo para aplicaciones ambientales. Tres compuestos orgánicos volátiles clorados; tricloroetileno, cloroformo y 1,2 diclorobenceno se utilizaron para estudiar las propiedades de adsorción / desorción de CNTs / QF. Se vio que las moléculas con anillos aromáticos presentan interacciones más fuertes con los nanotubos de carbono (apilamiento de tipo pi).

O crescimento de filmes de diamante nanocristalino (NCD - Nanocrystalline Diamond) obtido através da infiltração nos poros do silício poroso (PS - Porous Silicon) foi estudado utilizando microscopia eletrônica de alta resolução, difração de raios-x de alta resolução, espectroscopia de fotoelétrons de raios-x e espectroscopia de espalhamento Raman. Os filmes de NCD/PS resultaram em um material compósito, com grande potencial de aplicação eletroquímica, principalmente devida à sua grande área supercial ativa. Utilizando o processo de anodização com ácido fluorídrico e acetonitrila foram produzidas camadas de PS com poros em microescala, do tipo pirâmide invertida, adequados para a deposição e infiltração dos filmes NCD. Para otimizar o processo de crescimento o reator de deposição química a partir da fase vapor (HFCVD - Hot Filament Chemical Vapor Deposition) foi adaptado para um reator de infiltração química a partir da fase vapor (HFCVI - Hot Filament Chemical Vapor Infiltration). Este procedimento permitiu que os gases reagentes infiltrassem na estrutura porosa onde a nucleação é iniciada, seguida da coalescência e formação do filme tanto nas paredes como no fundo dos poros. Nesta configuração uma entrada adicional de CH4 foi posicionada próxima ao PS que permitiu mudar a posição do fluxo em relação à amostra e possibilitou a utilização do fluxo adicional exatamente abaixo da amostra ou acima desta, porém ambas as entradas foram abaixo dos filamentos. Este sistema permitiu ainda combinações na variação das concentrações de CH4 nas duas entradas no intervalo entre 0,5 e 1,0 vol %. Os filmes obtidos com entrada de gás acima da amostra apresentaram as melhores características de NCD em todo o intervalo de variação de metano estudado. Numa segunda configuração, para melhorar a infiltração do NCD no PS foi utilizado carbono vítreo reticulado (CVR) como fonte adicional de carbono. Nestes experimentos, enquanto o fluxo principal de metano variou entre 0 e 1,0 vol. %, foram utilizados CVR obtidos com três índices de grafitização diferentes, tratados termicamente em 1300, 1500 e 2000°C. A amostra de PS foi posicionada sobre o CVR permitindo que o hidrogênio atômico atacasse a superfície do mesmo durante o processo de crescimento do filme, retirando desta estrutura o carbono que participa das reações de crescimento do NCD. Foi observada uma forte dependência no crescimento do filme em função do CVR utilizado, devido às variações das propriedades físico-químicas deste material com sua temperatura de obtenção. Particularmente, os filmes obtidos a partir do CRV 2000 e concentração de metano de 1,0 vol. % apresentaram a melhor morfologia com cobertura total das paredes e dos poros, seguindo a morfologia do substrato, cuja qualidade e cristalinidade foram confirmadas pelos espectros Raman e de raios-x, respectivamente. De maneira geral, as duas configurações utilizando fontes adicionais de carbono produziram com sucesso filmes de NCD infiltrados nos poros do Si com apenas 60 min de crescimento.<br>The growth of nanocrystalline diamond films (NCD) on porous silicon (PS) substrate was studied using high resolution scanning electron microscopy, high resolution X-ray diffraction, X-ray photoelectron spectroscopy and Raman scattering spectroscopy. The NCD/PS films resulted in a composite material, with great potential for electrochemical application, mainly due to its high active surface area. The morphology of PS pores in microscale, which looks like an inverted pyramid, was produced in a suitable way for the deposition and infiltration of NCD films, from anodization process, using the solution of fluoridric acid dissolved in acetonitrile additive. To optimize the process a Hot Filament Chemical Vapor Deposition reactor was changed for a Hot Filament Chemical Vapor Infiltration reactor. This procedure allowed the infiltration of the reacting gases into the porous structure where the nucleation takes place, followed by the coalescence and the film formation into pore bottoms and walls. In this configuration an additional entrance of CH4 was located next to the PS substrate using two distinct positions. These positions concerned the NCD films obtained with the use of the additional flow accurately underneath of the sample or above it, nonetheless both entrance were located below the filaments. This system still allowed combinations in CH4 concentrations for the two entrances in the range between 0.5 and 1.0 vol %. The films produced using the above gas entrance, presented the best NCD characteristics, in the whole range of methane variation. In the second configuration, to improve the NCD infiltration in the PS substrate, a piece of reticulated vitreous carbon (RVC) was used as an additional carbon source. In these experiments, while the main methane flow varied between 0 and 1.0 vol. %, RVC produced at three different graphitization index, treated thermally at 1300, 1500 and 2000 °C, were used as a second carbon source. The PS sample was placed in the center of RVC piece allowing the atomic hydrogen attack on its surface during the film growth, removing from its structure the necessary carbon to promote the reactions to form the NCD layer. The strong dependence in the film growth as a function of the RVC treated at different temperatures was observed, due to the physical-chemical property variations of this material with its graphitization index. Particularly, the films obtained from the RVC-2000 and 1.0 vol. % of methane concentration presented the best morphology with a continuous NCD film covering the pore wall and bottom following the substrate morphology, with high quality and crystallinity, confirmed from its Raman and X-ray spectra, respectively. In general, the two used configurations for additional carbon sources provided NCD film infiltration in PS substrate with success for only 60 min of growth time.

Dans le cadre de la determination des mecanismes du depot chimique en phase vapeur des pyrocarbones laminaires, une etude experimentale a ete conduite. Celle-ci comprend (i) l'analyse de la composition de la phase gazeuse (par spectrometrie infrarouge a transformee de fourier in-situ et par spectrometrie de masse), (ii) l'etude cinetique in-situ de la formation du pyrocarbone (microbalance) et (iii) l'analyse de la structure du carbone depose (microscopie optique en lumiere polarisee et microscopie electronique en transmission). Les parametres experimentaux etudies sont la temperature et le temps de sejour, afin de mettre en evidence l'effet de l'avancement des reactions homogenes (maturation) sur la vitesse de depot et sur la structure du carbone. Les experimentations concernent essentiellement le depot (cvd) dans le cas de la pyrolyse du propane. Cependant d'autres systemes gazeux (benzene, methane / tetrachlorure de carbone) ont egalement ete examines et les aspects lies a l'infiltration (cvi) ont ete pris en compte. Les correlations qui s'etablissent notamment entre les etudes cinetique et structurale realisees avec le precurseur propane, ont conduit a la proposition d'un modele qualitatif qui explique les transitions entre regimes cinetiques et entre types microtexturaux par l'existence de deux voies paralleles pour la formation du pyrocarbone laminaire. Ces deux modes de depot impliqueraient deux familles d'especes gazeuses differentes et meneraient a la formation des deux types de pyrocarbone les plus frequemment rencontres en cvi, a savoir les carbones dits laminaire lisse et laminaire rugueux.

Dans le cadre de la recherche des mécanismes de dépôt chimique en phase gazeuse de pyrocarbones laminaires, une étude approfondie du passage d'une texture laminaire lisse (LL) à une texture laminaire rugueuse (LR) sous l'effet de la température T et du temps de séjour ts, à été réalisée à travers quatre approches expérimentales. (1) Une analyse par spectrométrie infrarouge et par couplage chromatographie en phase gazeuse / spectrométrie de masse a permis de corréler l'évolution de la composition de la phase gazeuse (e. G. Formation d'hydrocarbures aromatiques polycycliques HAP à T et ts croissant) avec la transition microtexturale LL-->LR. (2) Une étude sur substrat de pyrographite a mis en évidence une nucléation lente et localisée (liée à la présence de sites réactifs) du pyrocarbone LL et une nucléation rapide et uniforme (indépendante de la présence de sites réactifs) du pyrocarbone LR. (3) Une analyse de la composition et de la nanostructure ( par microscopie électronique en transmission) a conduit à décrire le pyrocarbone LL comme constitué de couches carbonées étendues mais très distordues et le pyrocarbone LR de couches carbonées parallèles au plan d'anisotropie mais peu étendues. (4) Enfin une étude de l'infiltration de préformes poreuses a permis de mettre en évidence les phénomènes de maturation et appauvrissement internes conduisant respectivement à des transitions LL->LR et LR-->LL au sein des préformes. L'ensemble des résultats obtenus permet de proposer une description nettement différenciée des processus chimiques mis en jeu lors de la formation des pyrocarbones LL et LR. Le pyrocarbone LL résulte majoritairement de processus de chimisorption d'espèces aliphatiques ou polycycliques issues d'une maturation limitée alors que le pyrocarbone LR résulte principalement de processus de physisorption de HAP issus d'une forte maturation.

The most relevant thermo-mechanical properties of SiC or C based CFCCs are high strength, high toughness, low weight, high reliability, thermal shock and fatigue resistance. Thanks to these special characteristics, the CFCCs are the best candidates to substitute metals and monolithic ceramics, traditionally employed to realize components in energy, aeronautic and nuclear fields. Among the commonly techniques for the CFCCs production, CVI still represents the most significant one. Its main advantages are the versatility, the high quality deposits and the fact that it is conducted under mild temperature conditions. On the other hand, this technique is quite complex, therefore the set up of all process parameters needs long development time. The main purpose of the present study was to analyze the parameters controlling the CVD and CVI processes. Specifically, deposition and infiltration of SiC and Py-C tests were conducted on non-porous and porous substrates. The experiments were performed with a pilot size Isothermal/Isobaric CVI plant, designed and developed by ENEA. To guarantee the control of the process parameters, a previously optimization of the plant was needed. Changing temperature, pressure, flow rates and methane/hydrogen ratio, the Py-C deposition rate value, for an optimal fibre/matrix interphase thickness, was determined. It was also underlined the hydrogen inhibiting effect over the Py-C deposition rate. Regarding SiC morphologies, a difference between the inner and outer substrate surfaces was observed, as a consequence of a flow rate non-uniformity. In the case of the Cf/C composites development, the key parameter of the CVI process was the gas residence time. In fact, the hydrogen inhibiting effect was evident only with high value of residence time. Furthermore, lower the residence time more homogeneous the Py-C deposition rate was obtained along the reaction chamber axis. Finally, a CVD and CVI theoretical modelling was performed.

The most relevant thermo-mechanical properties of SiC or C based CFCCs are high strength, high toughness, low weight, high reliability, thermal shock and fatigue resistance. Thanks to these special characteristics, the CFCCs are the best candidates to substitute metals and monolithic ceramics, traditionally employed to realize components in energy, aeronautic and nuclear fields. Among the commonly techniques for the CFCCs production, CVI still represents the most significant one. Its main advantages are the versatility, the high quality deposits and the fact that it is conducted under mild temperature conditions. On the other hand, this technique is quite complex, therefore the set up of all process parameters needs long development time. The main purpose of the present study was to analyze the parameters controlling the CVD and CVI processes. Specifically, deposition and infiltration of SiC and Py-C tests were conducted on non-porous and porous substrates. The experiments were performed with a pilot size Isothermal/Isobaric CVI plant, designed and developed by ENEA. To guarantee the control of the process parameters, a previously optimization of the plant was needed. Changing temperature, pressure, flow rates and methane/hydrogen ratio, the Py-C deposition rate value, for an optimal fibre/matrix interphase thickness, was determined. It was also underlined the hydrogen inhibiting effect over the Py-C deposition rate. Regarding SiC morphologies, a difference between the inner and outer substrate surfaces was observed, as a consequence of a flow rate non-uniformity. In the case of the Cf/C composites development, the key parameter of the CVI process was the gas residence time. In fact, the hydrogen inhibiting effect was evident only with high value of residence time. Furthermore, lower the residence time more homogeneous the Py-C deposition rate was obtained along the reaction chamber axis. Finally, a CVD and CVI theoretical modelling was performed.

Aquesta tesi s’ha basat en la síntesi i el processament del grafè per tal d’obtenir les condicions òptimes per a la seva utilització en aplicacions d’espintrònica. La tesi està emmarcada en dos camps de recerca punters: el món del grafè amb la seva riquesa de propietats úniques i el camp de l’espintrònica que explora el grau de llibertat de l’espí de l’electró de cara a noves aplicacions en informàtica i tecnologia de comunicacions (com és ara els dispositius de lògica i d’emmagatzematge d’informació). En aquest context, el grafè és un material prometedor de cara a transportar l’espí amb grans longituds de difusió. Per aconseguir-ho, és clau que el grafè sigui d’alta qualitat amb el mínim de centres de dispersió, tant en el moment de la seva producció com en el processat. Per tant, en aquesta tesi s’ha fet un gran esforç per optimitzar els paràmetres de creixement pel mètode de deposició química per vapor (CVD). S’han aconseguit vàries contribucions rellevants en aquest camp: -S’ha demostrat la importància de la reacció inversa del grafè (“gravat”) durant el creixement, la qual comença a dominar per a temps llarg de creixement, degut a un augment de la concentració d’hidrogen in-situ. Aquest és un fenomen que ha estat ignorat anteriorment però que és de gran rellevància degut al seu efecte sobre l’estructura i la morfologia del grafè. S’ha aconseguit una caracterització completa de l’evolució de la forma dels dominis de grafè ajustant el temps de creixement, el flux dels gasos precursors i el confinament del catalitzador, fet que permet identificar millor l’inici del procés de “gravat”. Controlar aquest efecte és molt important per minimitzar els defectes estructurals induïts per la reacció inversa ja que poden afectar el transport d’electrons/spins. -S’ha introduït un nou tractament previ del catalitzador de coure per reduir els punts de nucleació per al creixement del grafè. La supressió dels punts de nucleació és molt important per tal de promoure un creixement més monocristal&#8226;lí del grafè i així minimitzar la dispersió dels electrons en la frontera dels grans de cristall del grafè. El procediment es basa en un procés de curat tèrmic assistit per fotocatàlisi, que elimina eficaçment els contaminants de carboni que són punts actius per a la nucleació del grafè. -S’ha demostrat una distància de propagació d’espí rècord, superior als 30 micròmetres, en el canal de grafè. Aquest resultat s’ha obtingut utilitzant grafè CVD d’alta qualitat crescut sobre platí i una tècnica de fabricació de dispositius recentment desenvolupada que minimitza la contaminació/ els defectes estructurals durant el processament del grafè. La vida útil de l’espí i les longituds de relaxació obtingudes han resultat ser els valors més alts aconseguits a temperatura ambient en comparació amb previs resultats obtinguts en condicions similars, és a dir, amb grafè CVD sobre substrat estàndard de SiO2/Si.<br>Esta tesis se ha basado en ajustar la síntesis y el procesamiento de grafeno para el desarrollo de dispositivos espintrónicos optimizados. La tesis está enmarcada en dos temáticas punteras: el mundo del grafeno con su riqueza de propiedades únicas y el campo de la espintrónica que explora el grado de libertad del espín de los electrones para nuevas aplicaciones en tecnología de la información y la comunicación (por ejemplo, dispositivos de lógica y almacenamiento de información). En este contexto, el grafeno es un material muy prometedor para transportar el espín con longitud de difusión alta. Para lograr esto, un grafeno de alta calidad con mínimos centros de dispersión de electrones es un parámetro clave y debe asegurarse estas propiedades desde el momento de su crecimiento y durante su procesamiento. Por lo tanto, en esta tesis, se han invertido muchos esfuerzos para ajustar los parámetros de crecimiento del grafeno mediante la deposición química por vapor (CVD). Se han logrado varias contribuciones relevantes en el campo: - Se ha demostrado la importancia de la reacción inversa del grafeno (“etching”) durante el crecimiento, la cual comienza a dominar a tiempos largos de crecimiento debido a un aumento in-situ de la concentración de hidrógeno. Este es un fenómeno que se ha ignorado anteriormente pero que es muy importante a tener en cuenta ya que afecta la estructura y morfologia del grafeno. Se ha logrado una caracterización completa de la evolución de la forma de los dominios del grafeno ajustando el tiempo de crecimiento, el flujo de precursores de gases y el confinamiento del catalizador lo cual permite identificar mejor el inicio del proceso de “etching”. Controlar este efecto es muy relevante para minimizar los defectos estructurales inducidos por la reacción inversa ya que pueden afectar el transporte de electrones / espines. - Se ha introducido un nuevo pretratamiento del catalizador de cobre para reducir los sitios de nucleación para el crecimiento de grafeno. La supresión de los sitios de nucleación es muy importante para promover un crecimiento más monocristalino de grafeno y minimizar así la dispersión de electrones en las fronteras de los granos de cristal de grafeno. El procedimiento se basa en un proceso de curado térmico asistido por fotocatalisis que elimina eficientemente los contaminantes carbono que son sitios activos para la nucleación de grafeno. - Se ha demostrado una propagación récord de espín de más de 30 micrómetros en el canal de grafeno. Dicho resultado se logró utilizando grafeno CVD de alta calidad crecido sobre platino y una técnica de fabricación de dispositivos recientemente desarrollada que minimiza la contaminación / defectos estructurales durante el procesamiento de grafeno. La vida útil del espín y las longitudes de relajación resultaron ser los valores más altos en contrados a temperatura ambiente en comparación a resultados previos obtenidos en condiciones similares, es decir grafeno CVD sobre sustrato estándar de SiO2 / Si.<br>“This thesis has focused on tuning the synthesis and processing of graphene to achieve optimized spintronic applications. Thus the thesis is framed in two cut-edging topics: the graphene world with its richness of unique properties and the field of spintronics which explores the spin degree of freedom of the electrons for novel applications in information and communication technology (e.g. information storage and logic devices). Under this context graphene is a very promising spin channel material to transport spin with long spin diffusion lengths. To accomplish that, a high quality-graphene with minimum electron scattering centers is a key parameter and must be ensured from the moment of its production and during its processing. Accordingly, in this thesis, a lot of efforts have been invested to fine-tune the growth parameters of graphene by chemical vapor deposition (CVD). Several relevant contributions in the field have been achieved: -THE DEMONSTRATION of the importance of the graphene etching backreaction during growth which begins to dominate at long growth times due to an in-situ increase of hydrogen concentration. That is a phenomenon that has been previously ignored but very important to consider since it impacts on the graphene domain reshaping. A thorough characterization of the graphene domain shape evolution has been accomplished by tuning the growth time, the flow of gas precursors and the catalyst confinement which allows better identifying the onset of the etching process. Controlling this effect is very relevant to minimize structural defects induced by etching which can impact the electron/spin transport. -THE INTRODUCTION of a novel pretreatment of the copper catalyst to reduce nucleation sites for graphene growth. The suppression of nucleation sites is very important to promote a more single-crystalline growth of graphene and thus minimize electron scattering at the domain boundaries of the graphene crystal grains. The procedure is based on a photocatalyst-assisted thermal annealing process that efficiently removes carbonaceous contaminants which are active sites for graphene nucleation. -THE DEMONESTRATION of record-long propagation of spins over 30 micrometers at the graphene channel. Such output was achieved using high-quality CVD graphene grown on platinum foil and a newly developed device fabrication technique which minimizes contamination/structural defects during graphene processing. The spin lifetimes and relaxation lengths were the highest values reported at room temperature in CVD grown graphene on a standard substrate, SiO2/Si.

Diamond is a semiconductor with many superior material properties such as high breakdown field, high saturation velocity, high carrier mobilities and the highest thermal conductivity of all materials. These extreme properties, as compared to other (wide bandgap) semiconductors, make it desirable to develop single-crystalline epitaxial diamond films for electronic device and detector applications. Future diamond devices, such as power diodes, photoconductive switches and high-frequency field effect transistors, could in principle deliver outstanding performance due to diamond's excellent intrinsic properties. However, such electronic applications put severe demands on the crystalline quality of the material. Many fundamental electronic properties of diamond are still poorly understood, which severely holds back diamond-based electronic device and detector development. This problem is largely due to incomplete knowledge of the defects in the material and due to a lack of understanding of how these defects influence transport properties. Since diamond lacks a shallow dopant that is fully thermally activated at room temperature, the conventional silicon semiconductor technology cannot be transferred to diamond devices; instead, new concepts have to be developed. Some of the more promising device concepts contain thin delta-doped layers with a very high dopant concentration, which are fully activated in conjunction with undoped (intrinsic) layers where charges are transported. Thus, it is crucial to better understand transport in high-quality undoped layers with high carrier mobilities. The focus of this doctoral thesis is therefore the study of charge transport and related electronic properties of single-crystalline plasma-deposited (SC-CVD) diamond samples, in order to improve knowledge on charge creation and transport mechanisms. Fundamental characteristics such as drift mobilities, compensation ratios and average pair-creation energy were measured. Comparing them with theoretical predictions from simulations allows for verification of these models and improvement of the diamond deposition process.

The erosion rate of CVD diamond was ascertained using various sized erodents, impacting at different velocities. The relative sizes of the contact area and the size of the grains affected the erosion rate. Since the contact area increased with erodent size and impact velocity, both the sand size exponent and the velocity exponent were dependent upon the size of the grains. This result confirms that the ratio of the contact area to the microstructure is important. CVD diamonds often exhibit small fractures near to grain boundaries. These fractures usually contain graphitic or amorphous carbon that has become trapped during growth. These "micro-features" are discussed in Chapter 4, and the erosion rate of CVD diamond was obtained at regions of different micro-feature densities. The change in erosion rate caused by different micro-feature densities was small, much smaller than that caused by different grain sizes. This was because there were few micro-features, and even fewer that were close enough to the surface to have an affect. They are shown to contribute to fracture progress on the growth side, but have limited effect on the nucleation side. The erosion rate of the nucleation side is dominated by the more numerous grain boundaries. The erosion rate of mechanical grade CVD diamond is experimentally determined to be lower than optical grade CVD diamond. The main difference between the two grades is a higher concentration of dislocations in the mechanical grade. However, the erosion erosion rates of CVD diamonds with very different dislocation densities are shown to be similar. A four-point bend test is used to determine the fracture toughness of mechanical grade CVD diamond, and it is shown that this parameter is higher for the mechanical grade CVD diamond. The low erosion rate of mechanical grade CVD diamond results from higher fracture toughness, but the reason for this is yet to be understood. It is suggested that micro-features may play a significant part in the lower fracture toughness of optical grade CVD diamond. However, Raman spectroscopy has been used to show that non-diamond carbon is present in both grades of CVD diamond.

This thesis details the use of chemical vapour deposition (CVD) to deposit hydrophobic surfaces, in addition to this, the functional properties are investigated and further characterisation of the surfaces extreme water repulsion (superhydrophobicity) is made. The design and manufacture of surfaces that repel water (hydrophobic) draws much inspiration from the natural world, including examples of superhydrophobic leaves. The way water can interact with a surface is characterised, with many examples of superhydrophobic surface generation provided from the literature, along with general routes toward their formation. The main aspects of CVD depositions are addressed and examples of hydrophobic surfaces using this technique are cited. The novel deposition of thermosetting and thermosoftening polymers has been investigated, with the role of the CVD deposition mechanism emphasised. The deposition of the polymer occurs via the preformation of polymer particles, which is not typical in CVD, these were then deposited onto the substrate. The result was an easy-to-produce and robust superhydrophobic thin film, constructed from an inherently hydrophobic material. The same principle is then expanded to silica microparticles, films of the particles were deposited on to a substrate with hydrophilic surfaces originally deposited. The silica films were subsequently rendered exceptionally superhydrophobic by a simple post-treatment. The formation of copper films is then reported, using copper nitrate precursors a relatively flat metallic copper film was formed. The films were then roughened by reaction to form copper hydroxide nano-crystals, this hydrophilic surface is again functionalised to render it superhydrophobic. All films deposited were characterised using energy dispersive X-ray analysis, glancing angle X-ray diffraction, UV/Vis spectroscopy, infra-red/Raman spectroscopy and scanning electron and atomic force microscopy were used to study surface morphology, with the hydrophobicities of each surface quantified. The superhydrophobic elastomer films underwent microbiological testing in order to examine the adhesion of bacteria. A substantial reduction in the ability of bacteria to attach to the superhydrophobic surfaces was observed and rationalised through a reduction in available contact between the media of the bacteria (water) and the surface material. The dynamic interaction between water and surfaces was examined through water bouncing. The dependence of water bouncing on surface hydrophobicity and microstructure was studied, in addition to the effect of water droplet volume and impact velocity. A new definition and scale for superhydrophobicity is proposed, through the ability of water droplets to bounce on a surface. Finally the insight gained from previous work carried out is used in developing a device for separating mixtures of oil and water, through the use of superhydrophobic meshes.

This work studies the use of the novel electric field assisted chemical vapour deposition (EACVD) process in the production of thermochromic thin films of vanadium dioxide on glass substrates. The investigation studies the effects an applied electric field has on both aerosol assisted chemical vapour deposition (AACVD) and atmospheric pressure chemical vapour deposition (APCVD) reactions of vanadyl acetylacetonate. The electric field was generated by applying a potential difference between two transparent conducting oxide coated glass substrates. The electric field was varied between 0 – 3000 Vm-1. The deposited films were analysed and characterized using scanning electron microscopy, Raman spectroscopy, X-ray diffraction, atomic force microscopy and contact angle measurements. It was found that applying an electric field led to large changes in film microstructure, preferential orientation and changes in the film growth rate. This led to significant changes in materials properties such as increased surface roughness and enhanced wetting behaviour. Electric field assisted chemical vapour deposition shows great promise as a method for nano-structuring and tailoring the properties of metal oxide thin films. Further to the work carried out depositing thermochromic materials a computation building study is carried out to assess the energy saving potential of thermochromic thin films in as intelligent glazing. The building simulation is used to examine the effect of the thermochromic transition, hysteresis width and hysteresis gradient on the energy demand characteristics of a model system in a variety of climates. The results are also compared against current industry standard glazing products. The results suggest that ideal thermochromic systems can give potential savings between 20 – 50 % depending on the specific climate. The building model is also used to asses the energy saving potential of VO2 thin films prepared by electric field assisted atmospheric pressure chemical vapour deposition.

The extreme properties of diamond combined with the emergence of chemical vapour deposition (CVD) techniques for the growth of large area free standing diamond wafers has led to considerable interest in the use of this material for electronic applications. However, to date, the polycrystalline nature of the material grown by heteroepitaxy has hindered progress in this field leading to only niche applications for diamond electronics being identified. Whilst homoepitaxial growth seemed to be a solution to counter this issue, the substrate cost and the lack of a suitable dopant for -type conductivity together with the relatively large activation energy of p-type dopants reduced the effectiveness of electronic devices made from diamond. Finally, the low growth rates using standard microwave CVD techniques remains a problem. This thesis presents electronic characterisation of such homoepitaxial films using Hall effect measurements. The observation of p-type character of the surface conductivity due to hydrogen termination was confirmed and a correlation between the transport properties and the film thickness was demonstrated. In addition to Hall effect measurements, SEM/STM data are presented and the parameters for high growth rates of these overlayers are revealed. Passivation of these layers has also been investigated so that the p-type character and hence the device operation is not lost at higher temperatures when the devices are operated in air. A newly developed material, ultrananocrystalline diamond (UNCD), has been studied for its -type character. Hall effect measurements revealed the conductivity of this material is strongly influenced by the addition of nitrogen into the source gases and UNCD becomes conductive with low thermal activation energy. Finally, impedance spectroscopy measurements were taken on both UNCD and phosphorus doped material to investigate the conduction paths in both materials that lead to the -type conductivity observed in both kind of materials. The likely impact of the realisation of more effective processes for both growth and doping, described here, for the development of electronic devices from diamond is discussed.

Linear and nonlinear microwave properties of chemical vapor deposition (CVD)-grown graphene are characterized by incorporating a coplanar waveguide (CPW) transmission-line test structure. The intrinsic linear transport properties (S-parameters) of the graphene sample are measured and extracted via a deembedding procedure and then fitted with an equivalent circuit model up to 10 GHz. A statistical uncertainty analysis based on multiple measurements is implemented to esti- mate the error of the extracted graphene linear parameters as well. Nonlinear properties (second- and third-order harmonics as a function of fundamental input power) of the sample are also measured with a fundamental input signal of 1 GHz. Clear harmonics generated from graphene are observed, while no obvious fundamental power saturation is seen. The measured nonlinearity is applied in a graphene patch antenna case study to understand its influence on potential applications in terms of third-order intermodulation levels.

The thesis deals with mechanical properties of thin hard wear-resistant coatings. The work presents a method of dynamic testing of thin hard coatings on a newly constructed prototype of impact wear tester. It provides a comparison with standard methods of layer testing and presents new experimental results of dynamic impact wear test of the coatings. Finally, the thesis covers preparation techniques of thin film systems deposited on various substrates and their characterization using optical and electron microscopy.

La deposition chimique en phase vapeur concerne la croissance de films fins a partir de precurseurs solides en phase gazeuse. Un grand nombre de reactions chimiques se produisent dans le volume gazeux ainsi qu'a la surface de croissance : le substrat. La prediction des taux de croissance et de l'uniformite des films que l'on obtient sont des parametres industriellement importants. Nous avons mene une etude numerique sur des reacteurs cvd en 2d et 3d pour la croissance de films fins de silicium (si) a partir du silene (sih#4) et utilisant l'hydrogene comme gaz porteur. En particulier, nous avons considere le reacteur horizontal avec substrat circulaire en rotation et la prise en compte de deux reactions chimiques incluant les especes suivantes : h#2, sih#4, sih#2, si#2h#6. Cette etude a ete menee grace a un logiciel en volumes finis utilisant une methode de resolution collocative avec l'algorithme piso. Nous avons pu montrer l'influence des debits du gaz porteur, de la vitesse de rotation du substrat et de la concentration des precurseurs sur la croissance des films. Cette etude numerique permet dores et deja d'optimiser ce genre de reacteurs.