The goal of this thesis work is to investigate the possibility to grow graphene by Chemical Vapor Deposition (CVD) on copper foil with acetylene as a precursor and varigon (5\% H$_2$ in Ar) as a carrier gas. The possibility of nitrogen doping by ammonia treatment during the growth process is also investigated. The possibility of graphene transfer, with the use of Poly(Methyl Metacrylate) (PMMA), from the copper onto another target substrate, Flourine doped Tin Oxide (FTO), is also explored. The main technique of characterization of the grown and transfered graphene is Raman spectroscopy, a great tool for investigating the number of graphene layers and amount of defects. Other characterization methods used are Scanning Electron Microscopy (SEM) X-ray Photoelectron Spectroscopy (XPS) to investigate morphology and elemental composition, respectively. The result of this thesis study is that graphene growth is entirely possible with acetylene as a precursor, as shown by the Raman spectroscopy, XPS and SEM. The grown graphene has a high quality with few layers and a low number of defects. The ammonia treatment, however, doesn't seem to have an immediate effect on the graphene growth. The XPS data indicates that there are no nitrogen doping in the graphene, though there might be a correlation between the ammonia and the number of layers, but further investigations has to be made. Transfer is also proven possible with the method developed. However, improvements to the transfer method can be done since there are both larger tares, caused by the transfer onto the FTO, as well as microscopic tares, possibly caused by thermal expansion of the PMMA.

Necessity is the mother of all inventions. With Si hitting the speed bottleneck, newer materials to replace Si are being sought out. The ex-foliation based experiments on graphene by Geim and Novoselov at this point was perfect as many of its physical properties were fascinating from an electronics standpoint and hence it was very soon projected as a Si replacement for logic applications. In addition, graphene is also an attractive alternative to applications such as radio frequency devices, ultra-sensitive mass/chemical sensing, high-speed optoelectronics and transparent conductors for photo-voltaic applications. While the widespread success and utility of Si can be attributed to easy availability of source material and the ability to synthesize large areas of ultra high quality material, chemical vapor deposition (CVD) is the only available method to controllably produce large area monolayer graphene. CVD graphene is however polycrystalline and therefore defective. Hence, in order to promote graphene towards large-scale commercialization, it is necessary to be able to grow spatially homogeneous graphene with tailored defect densities. Transfer of atomic layers of graphene from the substrate on which it is grown, a Cu foil typically, on to an insulating substrate for electrical measurements is typically a major defect inducing step. Hence, a direct transfer-free fabrication of suspended device using graphene grown on thin films of electro-deposited Cu was attempted and successfully reported for the first time. Though it was shown that the fabrication process itself did not introduce any additional defects, the maximum obtained mobility on such fabricated structures was 5200 cm2/V·s. This value is lower than reported values in literature and thus improvements for electronic applications warranted further optimization. However, limitations on ability of electro-deposited Cu films (melting point of 1083 ◦C) to withstand high temperatures, 1000 ◦C, impeded further optimizations. Hence, growth on Cu foils was taken up. On Cu foil, we were able to identify the roles of the growth kinetics and system thermodynamics on the final quality of graphene. Specifically, by carefully altering the conditions during appropriate growth phases, we were able to obtain graphene films of tunable defect densities with motilities ranging from 200 - 20000 cm2/V·s. Using a host of characterization Techniques like electrical transport, Raman spectroscopic measurements, TEM imaging and water permeation studies, we find that the defect densities in graphene are largely concentrated at the boundaries, while the bulk of the graphene grain remains pristine. Further investigations revealed a thermodynamic correlation between the growth conditions and quality of the grain boundary in terms of defect density and structure. In addition to the influence of defects in graphene on charge mobility as seen before, their impact on the device contact resistance and charge transport hysteresis in graphene field effect transistors were also investigated. With a careful control on the film defect density, we were able to demonstrate devices with low contact resistance (1000 Ωµm ) and tunable hysteresis behavior. Finally, alternate substrates for graphene and its impact on the carrier densities were explored. Non-polar substrate SiO2 and polar substrates such AlN and AlGaN were chosen. On AlN, we obtained higher carrier mobility due to reduced phonon-electron scattering and a higher ’P’ doping behavior due to piezo-electric effects. Hence, to leverage the previous observation, novel FET device architecture with a HEMT based substrate using AlGaN was demonstrated.

This thesis analyzes the chemical vapour deposition (CVD) growth of vertically aligned carbon nanotube (CNT) forests in order to understand how CNT forests grow, why they stop growing, and how to control the properties of the synthesized CNTs. In situ kinetics data of the growth of CNT forests are gathered by in situ optical microscopy. The overall morphology of the forests and the characteristics of the individual CNTs in the forests are investigated using scanning electron microscopy and Raman spectroscopy. The in situ data show that forest growth and termination are activated processes (with activation energies on the order of 1 eV), suggesting a possible chemical origin. The activation energy changes at a critical temperature for ethanol CVD (approximately 870°C). These activation energies and critical temperature are also seen in the temperature dependence of several important characteristics of the CNTs, including the defect density as determined by Raman spectroscopy. This observation is seen across several CVD processes and suggests a mechanism of defect healing. The CNT diameter also depends on the growth temperature. In this thesis, a thermodynamic model is proposed. This model predicts a temperature and pressure dependence of the CNT diameter from the thermodynamics of the synthesis reaction and the effect of strain on the enthalpy of formation of CNTs. The forest morphology suggests significant interaction between the constituent CNTs. These interactions may play a role in termination. The morphology, in particular a microscale rippling feature that is capable of diffracting light, suggest a non-uniform growth rate across the forest. A gas phase diffusion model predicts a non-uniform distribution of the source gas. This gas phase diffusion is suggested as a possible explanation for the non-uniform growth rate. The gas phase diffusion is important because growth by acetylene CVD is found to be very efficient (approximately 30% of the acetylene is converted to CNTs). It is seen that multiple mechanisms are active during CNT growth. The results of this thesis provide insight into both the basic understanding of the microscopic processes involved in CVD growth and how to control the properties of the synthesized CNTs.

L’élaboration par CVD (dépôt chimique en phase vapeur ou Chemical Vapor Deposition) de composites à matrices céramiques met en jeu de nombreux mécanismes physico chimiques en interaction les uns avec les autres. La maîtrise du procédé et son optimisation nécessitent une description précise de ces derniers et de leurs couplages, qui peut être réalisé dans un cadre de modélisation suffisamment global. Dans le cas des matériaux déposés dans un réacteur à parois chaudes, qui permet un bon contrôle de la qualité des matériaux, la décomposition des gaz précurseurs en phase gaz joue un rôle extrêmement important. Nous avons entrepris dans cette thèse la modélisation thermodynamique et cinétique de la phase gaz associée aux dépôts des carbures B-C et Si-B-C, systèmes encore mal maîtrisés. En se basant sur des calculs de chimie théorique, nous avons déterminé et caractérisé un ensemble de réactions chimiques d’importance cruciale dans ces systèmes. Nous sommes les premiers à étudier certaines d’entre elles. Un mécanisme réactionnel du système B-C-Cl-H (dépôt de carbure de bore) a été proposé puis utilisé avec un modèle de réacteur unidimensionnel. Des mesures IRTF, également réalisées au cours de cette thèse, permettent une validation du mécanisme réactionnel à différents niveaux. En particulier, la formation de l’espèce BCl2CH3 comme principal produit gazeux carboné a été clairement mise en évidence, ainsi que la température à laquelle BCl3 se décompose pour former BHCl2 et HCl. Les concentrations des espèces en zone chaude ont finalement été mises en relation avec les vitesses de prise de masse et une loi de dépôt a été proposée pour ce système. Dans le cas du système Si-B-C nous avons caractérisé certaines réactions de couplage entre les sous systèmes B-Cl-H et Si-C-Cl-H. Une modélisation globale de la cinétique homogène associée au dépôt de carbures Si-B-C est une perspective à court terme de ce travail. Enfin, l’étude rigoureuse de certaines réactions nous a amené à invoquer et/ou développer des méthodes théoriques spécifiques - et pour certaines non standard - telles que la théorie de l’état de transition, la théorie variationnelle de l’état de transition, la théorie variationnelle de l’état de transition à coordonnée de réaction variable et la théorie RRKM. En particulier, une approche unidimensionnelle du calcul des états propres des modes de vibration lâches a été développée. Sa validité a été confirmée par comparaison à d’autres modèles (oscillateur harmonique, rotation libre, etc …), valables dans des situations plus restreintes. / The Chemical Vapour Deposition of ceramics matrix composites involves many coupling physico-chemical mechanisms. The process control and optimization are allowed by precise description of these mechanisms and their interactions, witch can be realized through a global modelisation. In the case of hot wall reactors, witch allowed a good control of deposit properties, homogeneous gas phase decomposition play a crucial function. We have undertaken in this thesis a gas phase thermodynamic and kinetic studies associated to B-C and Si-B-C carbides elaboration, witch remains hard to control. By theoretical chemical calculations, we proposed a set containing crucial reactions for theses systems. We are the first to study some of them. A reaction mechanism of the B-C-Cl-H system (for the boron carbide deposition) have been proprosed and utilised with a one dimensional reactor model. Experimental IRTF spectrum, also investigated in our works, allow different validations of the reactional mechanism. In particular, BCl2CH3 is showed to be the main carbon product in the gas phase, and prediction of activation temperature of BCl3 to BHCl2 and HCl transformation is very good. Finally, hot zone concentration species have been related to the experimental deposition rate and a kinetic deposition law has been proposed for this system. In the case of Si-B-C system, some important coupling reactions between B-Cl-H and Si-C-Cl-H systems have been characterized. A global modelisation of the homogeneous gas phase kinetic for Si-B-C carbides is short-term perspective. At least, the rigorous study for some reactions have needed the use or the development of specific theoretical methodology – no standard for some of them – as the Transition State Theory (TST), the Variationnal Transition State Theory (VTST), the Variationnal Transition State Theory with Variable Reaction Coordinate (VTST-VRC) and the Rice–Ramsperger–Kassel–Marcus (RRKM) theory. In particular, we have developed a convenient way to compute the eigenvalues of low hindered one dimensional vibration modes. Validity of the approach has been assessed by comparisons with more specific model (harmonic oscillator, free and hindered rotation, etc …)

Metal chalcogenides (sulfides, selenides and tellurides) are materials of current interest due to their peculiar properties such as optoelectronic, magnetooptic, thermoelectric and piezoelectric displays. These semiconducting materials have potential applications in solar cell devices, infrared detectors and ambient thermoelectric generators. Previously, these materials have been deposited by multiple-source precursor route with several problems associated with this technique. This work describes the synthesis of metal complexes (Zn, Cd, Fe, Ni, Pd, Pt) using the imidodichalcogenodiphosphinate ligand (Woollins ligand). Their thermal decomposition together with structural and spectroscopy analysis was carried out. The complexes were used as single source precursors for the deposition of cadmium selenide, cadmium phosphide, cadmium sulfide, zinc selenide, iron selenide and the tellurides of nickel, palladium, platinum and iron as thin films and powders. These were deposited by AACVD and pyrolysis. The deposited thin films and powders were characterised by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy dispersive analysis of X-rays (EDAX), X-ray photoelectron spectroscopy (XPS) and superconducting quantum interference device (SQUID). The cadmium complexes [Cd{iPr2P(Se)NP(Se)iPr2}2] and [Cd{iPr2P(S)NP(Se)iPr2}2] deposited the mixture of hexagonal CdSe and monoclinic Cd2P3 films at the flow rate of 160 sccm at 475 and 500 °C. At the flow rate of 240 sccm, only hexagonal CdSe was deposited from [Cd{iPr2P(Se)NP(Se)iPr2}2] at all temperatures. Hexagonal CdS and the mixture of orthorhombic Cd6P7/cubic Cd7P10 were deposited from [Cd{iPr2P(S)NP(S)iPr2}2]. The zinc complexes [Zn{iPr2P(Se)NP(Se)iPr2}2] and [Zn{iPr2P(S)NP(Se)iPr2}2] both deposited cubic ZnSe at all temperatures with the flow rates of 160 and 240 sccm. The iron complexes [Fe{(SePPh2)2N}2] and [Fe{(SePPh2NPPh2S)2N}2] deposited orthorhombic FeSe2 mixed with monoclinic Fe3Se4 by pyrolysis at 500 and 550 °C. An unresolved pattern was observed from the complex [Fe{(SePPh2NPPh2S)2N}2] at 550 °C. XPS analysis of the deposited FeSe2 showed the surface oxidation of the material, while the magnetic measurements on the sample using SQUID confirmed its ferromagnetic properties. The telluride complexes of nickel, palladium, platinum and iron deposited the metal telluride respectively as: hexagonal NiTe, hexagonal PdTe, hexagonal PtTe2 (mixed with rhombohedral PtTe) and hexagonal FeTe2. Conductivity studies on NiTe and PdTe revealed them to be insulators, while the magnetic measurements on FeTe2 indicated its antiferromagnetic behaviour.

Novel carborane (B10C2H12) and aromatic compounds (benzene, pyridine, diaminobenzene) copolymers and composite materials have been fabricated by electron beam induced cross-linking and plasma enhanced chemical vapor deposition (PECVD) respectively. Chemical and electronic structure of these materials were studied using X-ray and ultra-violet photoelectron spectroscopy (XPS and UPS). UPS suggest that the systematic tuning of electronic structure can be achieved by using different aromatic compounds as co-precursors during the deposition. Furthermore, top of valence band is composed of states from the aromatic moieties implying that states near bottom of the conduction band is derived from carborane moieties. Current- voltage (I-V) measurements on the ebeam derived B10C2HX: Diaminobenzene films suggest that these films exhibit enhanced electron hole separation life time. Enhanced electron hole separation and charge transport are critical parameters in designing better neutron voltaic devices. Recently, PECVD composite films of ortho-carborane and pyridine exhibited enhanced neutron detection efficiency even under zero bias compared to the pure ortho-carborane derived films. This enhancement is most likely due to longer electron-hole separation, better charge transport or a combination of both. The studies determining the main factors for the observed enhanced neutron detection are in progress by fabricating composite films of carborane with other aromatic precursors and by altering the plasma deposition conditions. This research will facilitate the development of highly sensitive and cost effective neutron detectors, and has potential applications in spintronics and photo-catalysis.

Tato diplomová práce se zabývá dotováním grafenu nízkoenergiovými elektrony. Na křemíkový substrát pokrytý vrstvou SiO2 jsou pomocí litograficky vyrobené masky nadeponované kovové kontakty z titanu a zlata. Grafen vyrobený pomocí metody depozice z plynné fáze je přenesen na substrát a slouží jako vodivé spojení kovových elektrod, které vytvářejí kolektor a emitor. Na křemík je ze spodu přivedeno napětí, které tak vytváří spodní hradlo. Takto vytvořený grafenový tranzistor je ozařován nízkoenergiovými elektrony, které mění dotování grafenu. Z polohy maxima v závislosti odporu grafenu na hradlovém napětí lze vyčíst typ dotování. Toto maximum udává napětí, při kterém Fermiho meze grafenu prochází Diracovým bodem v pásové struktuře grafenu. Velikost hradlového napětí, primární energie elektronového svazku a proud svazku jsou tři parametry, které mají velký vliv na změny dotování. Při ozařování transistoru dochází ke změně typu dotování právě tehdy, když odpor grafenu v závislosti na hradlovém napětí dosáhne maxima. Vývoj této změny je zkoumán pro různé energie a proudy primárního svazku v závislosti na hradlovém napětí i v čase. Typ dotování je také prozkoumán při zastavení ozařování v různých fázích smyčky hradlového napětí. Dopování grafenu nízkoenergiovými elektrony je popsáno v teoretickém modelu.

This diploma thesis is focused on fabrication of graphene field-effect transistors, characterisation of their transport properties and investigation of low-energy electron beam influence on the devices' properties under UHV conditions. The theoretical part of this work describes graphene fabrication methods, options of graphene transfer onto the substrates for graphene field-effect transistor manufacture. Furthermore, model of graphene doping via electrostatic interaction or photon, resp. electron beam exposition is explained. The experimental part of this work consist of manufacture of the graphene field-effect transistor in order to examine the change of its transport properties induced by doping of the graphene via low-energy electron beam exposition.

Die plasmaunterstützte chemische Gasphasenabscheidung (PE-CVD) hat sich als eines der wichtigsten Dünnschichtverfahren etabliert. Für die Bearbeitung von Pulvern haben sich in der Technik Wirbelbettverfahren bewährt. Beide Verfahren sind an sich gut untersucht und verstanden. In der Arbeit wird ein Konzept zur Kombination dieser beiden Verfahren vorgestellt. Dabei zeigt sich, dass die einzelnen Modelle beider Verfahren durch experimentelle Untersuchungen ergänzt werden müssen, um das entsprechende Parameterfeld abzugrenzen. Durch die Untersuchung der Gasphase während der Abscheidung können Rückschlüsse auf die ablaufenden chemischen Reaktionen gezogen werden. Vergleichende ramanspektroskopische Untersuchungen, zwischen statischen Beschichtungen und Beschichtungen im Wirbelbett gestatteten es, den Einfluss der einzelnen Prozessparameter zu untersuchen. Mikroglaskugeln mit einem Durchmesser von ca. 160µm werden mittels Toluen als Precursor in einem Argon-Wasserstoff-Plasma beschichtet. Dazu werden als Prozessparameter die Mikrowellenleistung, die Zusammensetzung der Gasphase und das Precursorangebot variiert. Die durch die Oberflächenmodifizierung erreichten Änderungen der Eigenschaften der pulverförmigen Substrate können durch Oberflächenspannungsmessungen gezeigt werden. Es zeigt sich, dass vor allem die mechanische Beanspruchung im Wirbelbett und die Zusammensetzung der Reaktionsgasphase entscheidenden Einfluss auf die entstehende Schichtstruktur besitzen.

Vor dem Hintergrund der in der Mikroelektronik-Fertigung heute verbreiteten Kupfertechnologie werden in der vorliegenden Arbeit drei neuartige metallorganische Verbindungen, nämlich phosphitstabilisierte Kupfer(I)-Trifluoracetat-Komplexe vorgestellt und hinsichtlich ihrer Anwendbarkeit für die chemische Gasphasenabscheidung (CVD) von Kupfer untersucht. Im einzelnen handelt es ich um die Substanzen Tris(trimethylphosphit)kupfer(I)trifluoracetat (METFA), Tris(triethylphosphit)kupfer(I)trifluoracetat (ETTFA) und Tri(tris(trifluorethyl)phosphit)kupfer(I)trifluoracetat (CFTFA). Mit den Substanzen erfolgen CVD-Experimente auf TiN und Cu bei Temperaturen <400°C. Die Precursoren werden dabei mittels eines Flüssigdosiersystems mit Verdampfereinheit der Reaktionskammer zugeführt. Während METFA wegen seiner ausreichend geringen Viskosität unverdünnt verwendet werden kann, kommen für ETTFA und CFTFA jeweils Precursor-Acetonitril-Gemische zum Einsatz. Mit keinem der Neustoffe können auf TiN geschlossene Kupferschichten erzeugt werden, während dies auf Kupferunterlagen in Verbindung mit Wasserstoff als Reduktionsmittel gelingt. Die Abscheiderate beträgt hierbei 2-3nm/min; der spezifische Widerstand der Schichten bewegt sich zwischen 4μΩcm und 5μΩcm. Mit allen Substanzen werden besonders an dünnen, gesputterten Kupferschichten Agglomerationserscheinungen und Lochbildung beobachtet. Im Fall von CFTFA treten zusätzlich Schäden am darunterliegenden TiN/SiO₂-Schichtstapel auf. Vergleichende Untersuchungen mit der für die Cu-CVD etablierten Substanz (TMVS)Cu(hfac) ergeben sowohl auf Cu als auch auf TiN geschlossene Kupferschichten. Dabei liegen die Abscheideraten bei Temperaturen zwischen 180°C und 200°C im allgemeinen deutlich über 100nm/min. Ein Vergleich dieser Resultate mit den Ergebnissen für die Neustoffe legt nahe, dass den untersuchten Kupfer(I)-Trifluoracetaten keine ausreichende Tauglichkeit für Cu-CVD-Prozesse in der Mikroelektronik-Technologie bescheinigt werden kann. Die im Vergleich zu (TMVS)Cu(hfac) höhere thermische Stabilität der Precursoren und ihre Fähigkeit, mit Wasserstoff als Reaktionspartner auf Cu geschlossene Kupferschichten erzeugen zu können, deutet jedoch auf ihre eventuelle Eignung für ALD-Prozesse hin. Daher widmet sich die Arbeit in einem abschließenden Kapitel dem Thema der Atomic Layer Deposition (ALD), wobei nach einem allgemeinen Überblick besonders auf für die Mikroelektronik relevante ALD-Prozesse eingegangen wird.