Low temperature growth of nanocrystalline diamond: Insight thermal property

One of the limitations of materials for high-power devices and structural coatings applications is heat dissipation. Diamond is a suitable material for heat distribution due to its high thermal conductivity. Nevertheless, it is usually grown at high temperature (800–1200 ◦C), which limits its use as a coating for substrates vulnerable to degradation at high temperatures. In this work, it is studied the effect of the distance between the plasma source and substrate on the growth of nanocrystalline diamond layers on silicon substrates at low temperature (<450 ◦C) by microwave linear antenna plasma enhanced chemical vapour deposition (MW-LA-PECVD) in pulse mode. The nanocrystalline diamond films have been analysed by scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman spectroscopy. Finally, the superficial thermal conductivity of the diamond layers was determined by scanning thermal microscopy-AFM (SThM-AFM).6 página

Synthesis, characterization and tribological behavior of nitrogen-doped chromium-diamond-like carbon nanocomposite thin films

Diamond-like carbon (DLC) films have been extensively studied for more than two decades due to their highly attractive properties. These films exhibit unique mechanical, chemical and electronic properties and thus, possess great potential for applications in tribology. However, two drawbacks in the DLC films are high level of internal stress developed during growth preventing deposition of thick films and low thermal stability. Synthesis of Me-DLC (Cr-DLC and N-doped Cr-DLC) presents a way to overcome these drawbacks. In the present study, DLC, Cr-DLC and N-doped Cr-DLC films were deposited on Si substrate using a hybrid Plasma assisted CVD/PVD process. Film characterization in terms of microstructure, structure, composition and chemical state of components was carried out by transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) of the Cr-DLC as well as N-doped Cr-DLC films. Mechanical properties of the films were characterized by microhardness testing. The tribological properties were studied by conducting pin-on-disc experiments. Optical profilometry was used to analyze intrinsic stress in the films and the wear profiles and wear rate. TEM and XPS showed that N-doping results in formation of CrN along with Cr carbide in the film. N-doped Cr-DLC films were found to possess higher hardness than the Cr-DLC and DLC films. N-doped Cr-DLC exhibited lower intrinsic stresses while maintaining a comparable friction coefficient and wear rate as well as higher microhardness. The low intrinsic stresses of N-doped Cr-DLC show promise for the deposition of thicker coatings, while maintaining desirable mechanical and tribological properties

Synthesis, structure and properties of zirconium-based binary alloy thin films

In this thesis, we demonstrate that original nanostructures can be obtained by working around the crystalline-to-amorphous transition in sputter-deposited thin films. In particular, we study two systems, Zr-Mo and Zr-W, in which such transition occurs. By decreasing the Mo content in the Zr-Mo system, a structural transition from a nanocrystalline solid solution of Zr in the bcc lattice of Mo to an amorphous structure can be achieved around 60 at% Mo. The films obtained present high hardness H, low Young's modulus E and, consequently, high H/E ratio compared with bulk Zr and Mo. Furthermore, we demonstrate that a self-separation of the nanocrystalline and the amorphous phases occurs at the composition intermediate to those necessary to form single-phased amorphous and nanocrystalline films. The particular geometry in which the nanocrystalline phase grows in competition with the amorphous phase is exploited to achieve a thickness-controlled surface morphology which allows to tune the film reflectance. A model was developed to describe the kinetics of the competitive growth between the nanocrystalline and the amorphous phases. Furthermore, it allows to construct a thickness-composition phase diagram evidencing that the nanocrystalline/amorphous competitive growth is easily hidden experimentally. Finally, we demonstrate that massive monocrystalline grains with lateral size larger than 1 µm can be obtained by working at low Ar pressure if the composition of the films approaches to the edge of the amorphous transition. Our results suggest that the phenomena reported here for Zr-Mo and Zr-W can be extended to other systems.In dieser Arbeit zeigen wir, dass originelle Nanostrukturen durch Umgehen des Übergangs von kristallin zu amorph in aufgesputterten dünnen Schichten erhalten werden können. Insbesondere untersuchen wir zwei Systeme in denen ein solcher Übergang stattfindet, Zr-Mo und Zr-W. Durch Verringerung des Mo-Gehalts im Zr-Mo-System kann ein struktureller Übergang von einer nanokristallinen festen Lösung von Zr im bcc-Gitter von Mo zu einer amorphen Struktur um 60 Atom-% Mo erreicht werden. Die erhaltenen Filme zeigen eine hohe Härte H, einen niedrigen Elastizitätsmodul E und folglich ein hohes H/E-Verhältnis im Vergleich zu massiven Zr und Mo. Des Weiteren zeigen wir, dass eine Selbsttrennung der nanokristallinen und der amorphen Phase bei einer bestimmten Zusammensetzung auftritt. Die besondere Geometrie, in der die nanokristalline Phase im Wettbewerb mit der amorphen Phase wächst, wird ausgenutzt, um eine dickengesteuerte Oberflächenmorphologie zu erreichen, die es erlaubt, die Filmreflexion einzustellen. Ein Modell wurde entwickelt, um die Kinetik des kompetitiven Wachstums zwischen der nanokristallinen und der amorphen Phase zu beschreiben. Schließlich zeigen wir, dass massive einkristalline Körner mit einer lateralen Größe von mehr als 1 µm bei niedrigem Ar-Druck bei einer Filmzusammensetzung am Rand des amorphen Übergangs erhalten werden können. Unsere Ergebnisse legen nahe, dass die hier beschriebenen Phänomene für Zr-Mo und Zr-W auf andere Systeme ausgedehnt werden können.Dans cette thèse, nous démontrons que des nanostructures originales peuvent être obtenues en travaillant autour de la transition cristallin/amorphe dans des films minces déposés par pulvérisation cathodique. En particulier, nous étudions deux systèmes, Zr-Mo et Zr-W, dans lesquels une telle transition se produit. Dans ce système, lorsque la teneur en Mo est réduite, une transition structurale d’une solution solide nanocristalline de Zr dans le réseau bbc de Mo à une structure amorphe peut être obtenue autour de 60 at % de Mo. Les films obtenus présentent une dureté H élevée, un faible module de Young E et, par conséquent, un ratio H/E élevé par rapport à celui de Zr et Mo. Par ailleurs, nous démontrons qu'une auto-séparation des phases nanocristalline et amorphe se produit à une composition spécifique. La géométrie particulière dans laquelle la phase nanocristalline se développe en concurrence avec la phase amorphe est exploitée pour contrôler la morphologie de surface et, par conséquence, la réflectance par l’intermédiaire de l’épaisseur. Un modèle a été développé pour décrire la cinétique de la croissance compétitive entre les phases nanocristalline et amorphe. De plus, cela permet de construire un diagramme de phase épaisseur-composition qui montre que la croissance compétitive nanocristalline/amorphe est facilement dissimulée expérimentalement. Finalement, nous démontrons que des grains monocristallins massifs de taille latérale supérieure à 1 µm peuvent être obtenus en travaillant à basse pression d’Ar si la composition des films se rapproche du bord de la transition amorphe. Nos résultats suggèrent que les phénomènes observés pour les systèmes Zr-Mo et Zr-W peuvent être étendus à d'autres systèmes

Deposição de filmes do diamante para dispositivos electrónicos

This PhD thesis presents details about the usage of diamond in electronics. It presents a review of the properties of diamond and the mechanisms of its growth using hot filament chemical vapour deposition (HFCVD). Presented in the thesis are the experimental details and discussions that follow from it about the optimization of the deposition technique and the growth of diamond on various electronically relevant substrates. The discussions present an analysis of the parameters typically involved in the HFCVD, particularly the pre-treatment that the substrates receive- namely, the novel nucleation procedure (NNP), as well as growth temperatures and plasma chemistry and how they affect the characteristics of the thus-grown films. Extensive morphological and spectroscopic analysis has been made in order to characterise these films.Este trabalho discute a utilização de diamante em aplicações electrónicas. É apresentada uma revisão detalhada das propriedades de diamante e dos respectivos mecanismos de crescimento utilizando deposição química a partir da fase vapor com filament quente (hot filament chemical vapour deposition - HFCVD). Os detalhes experimentais relativos à otimização desta técnica tendo em vista o crescimento de diamante em vários substratos com relevância em eletrónica são apresentados e discutidos com detalhe. A discussão inclui a análise dos parâmetros tipicamente envolvidos em HFCVD, em particular do pré-tratamento que o substrato recebe e que é conhecido na literatura como "novel nucleation procedure" (NNP), assim como das temperaturas de crescimento e da química do plasma, bem como a influência de todos estes parâmetros nas características finais dos filmes. A caracterização morfológica dos filmes envolveu técnicas de microscopia e espetroscopia.Programa Doutoral em Engenharia Eletrotécnic

Tailoring magnetic and mechanical properties of mesoporous single-phase Ni-Pt films by electrodeposition

Homogeneous mesoporous Ni-rich Ni-Pt thin films with adjustable composition have been synthesised by one-step micelle-assisted electrodeposition. The films exhibit a face-centred cubic solid solution (single phase) and their magnetic and mechanical properties can be tuned by varying the alloy composition. In particular, the Curie temperature (TC) is shown to decrease with the Pt content and thin films with a TC close to room temperature (i.e. Ni58Pt42) and below can be produced. Hysteresis loops show a decrease of saturation magnetisation (Ms) and coercivity (Hc) with decreasing Ni content. A comparison of porous and dense films reveals significantly lower saturation magnetic field strength for porous films. Concerning mechanical properties, mainly two trends can be observed: a decrease of the Young's modulus of the nanoporous films with respect to dense films by 10% in average and a progressive increase of Young's modulus with the Ni content from 4.2 GPa to 5.7 GPa in both types of films. The tunability of properties and facility of synthesis make this alloy a promising material for microelectromechanical systems (MEMS)