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New Generation Lithographic (NGL) techniques have been recently investigated in order to overcome the limitations of the long-used UV lithography. Several techniques have been proposed during the last decades, but the continued improvement of UV lithography rendered them useful only for a limited number of applications. More recently, nanoimprint lithography (NIL), invented in the nineties, has been considered as the new NGL due to its extreme simplicity and high resolution. Thermal NIL consists in the deformation of a thermoplastic under pressure and temperature by a nanostructured mold, while UV-NIL consists in the polymerization by UV light of a monomer at room temperature and under a lower pressure than Thermal NIL. One of the main problems of this technique is mold-polymer separation after the process. This problem is especially important for UV-NIL, because the working treatments for Thermal NIL degrade with UV light. In order to address this problem, thin diamond-like amorphous carbon films (DLC) have been proposed as an alternative to existing treatments for their low chemical reactivity and the possibility to incorporate other chemical elements to further reduce their surface energy.Amorphous carbon exists in different forms, depending on how it is grown. Its mechanical properties range from polymer or graphite-like to almost as resistant as diamond. Besides the excellent mechanical properties of DLC (high hardness, elasticity and wear resistance, and low dry friction), amorphous carbon has also been found useful in applications requiring inert and/or biocompatible surfaces.The project DPI2007-61349 of the Science and Innovation Department of Spain, named “Amorphous carbon molds for micro and nanoimprint of polymeric surfaces”, aims to study the effect of the incorporation of different elements in DLC films for the improvement of NIL molds.This thesis has focused on a series of objectives of this project: - Design and construction of a very high vacuum reactor for deposition processes and ionic etch - Incorporation of fluorine to amorphous carbon films and subseqüent characterization by different surface, mechanical and tribological techniques, as well as spectroscopy for the characterization of the plasma used for the process. - Set up and optimization of a deep ion etch technique with ion beam for the production of molds. - The use of different lithographic techniques oriented to the production in large scale of nanometric patterns. - The exploration of mold coating to increase its durability and antisticking properties in nanoimprint processes. The incorporation of fluorine in DLC films has demonstrated to be useful in the improvement of the properties of NIL molds, because it avoids the use of the current surface treatments, which in addition to being less durable, can react with polymers in presence of UV light.In this thesis, the influence of fluorine incorporation in the films has been studied. Fluorinated amorphous carbon films have been deposited by pulsed-DC plasma enhanced chemical vapor deposition, by progressively replacing methane by trifluoromethane. The experimental device used for deposition has been designed and built to allow a number of multiple processes in the same reactor. The results of the study demonstrate the feasibility of this technique, of easy industrial implementation, for the deposition of this type of coatings.The characterization of both the active species in the plasma and the groups incorporated into the deposited films has helped to understand the process of fluorine incorporation, as well as the change in the surface properties that it entails., Des techniques de lithographie de nouvelle génération (LNG) ont récemment été étudiées afin de surmonter les limites de la lithographie UV utilisée de longue date. Plusieurs techniques ont été proposées au cours des dernières décennies, mais l’amélioration continue de la lithographie UV ne les a rendues utiles que pour un nombre limité d’applications. Plus récemment, la lithographie par nanoimpression (NIL), inventée dans les années 90, a été considérée comme une nouvelle LNG en raison de son extrême simplicité et de sa haute résolution. La NIL thermique consiste en la déformation d'un thermoplastique sous pression et température par un moule nanostructuré, tandis que la UV-NIL consiste en la polymérisation par la lumière ultraviolette d'un monomère à température ambiante et sous une pression inférieure à celle de la NIL thermique.L'un des principaux problèmes de cette technique est la séparation moule-polymère après le processus. Ce problème est particulièrement important pour la UV-NIL, car les traitements utilisés pour la NIL thermique se dégradent avec la lumière UV. Afin de resoudre ce problème, des couches minces de carbone amorphe dites « type diamant » (DLC) ont été proposées comme alternative aux traitements existants pour leur faible réactivité chimique et la possibilité d’incorporer d’autres éléments chimiques pour réduire davantage leur énergie de surface.Le carbone amorphe existe sous différentes formes, en fonction de la façon dont il est cru. Ses propriétés mécaniques vont du polymère ou du graphite à presque aussi résistant que le diamant.Outre les excellentes propriétés mécaniques du DLC (haute dureté, élasticité et résistance à l'usure, et faible frottement à sec), le carbone amorphe s'est également révélé utile dans les applications nécessitant des surfaces inertes et / ou biocompatibles.Le projet DPI2007-61349 du département de la Science et de l’Innovation en Espagne, intitulé « Moules en carbone amorphe pour micro et nano-impressions de surfaces polymères », vise à étudier l’effet de l’incorporation de différents éléments dans des films DLC pour l’amélioration des moules NIL.Cette thèse s'est concentrée sur une série d'objectifs de ce projet : - Conception et construction d'un réacteur à très haut vide pour des procédés de dépôt et gravure ionique - Incorporation de fluor au carbone amorphe et caractérisation subséquente par différentes techniques superficielles, mécaniques et tribologiques, ainsi que spectroscopie pour la caractérisation du plasma utilisé pour le procédé. - Mise en place et optimisation d'une technique de gravure ionique profonde à faisceau ionique pour la production de moules. - L’utilisation de différentes techniques lithographiques orientées vers la production à grande échelle de motifs nanométriques. - L’exploration du revêtement de moules pour augmenter sa durabilité et ses propriétés anti-adhérentes dans les procédés de nano-impression.L'incorporation de fluor dans les films de DLC s'est avérée utile pour améliorer les propriétés des moules NIL, car elle évite l'utilisation des traitements de surface actuels, qui, en plus d'être moins durables, peuvent réagir avec les polymères en présence de rayons ultraviolets.Dans cette thèse, l'influence de l'incorporation de fluor dans les films a été étudiée. Des films de carbone amorphe fluorés ont été crus par dépôt chimique en phase vapeur assisté par plasma à courant continu pulsé, en remplaçant progressivement le méthane par du trifluorométhane. Le dispositif expérimental utilisé pour la croissance a été conçu et construit pour permettre plusieurs processus dans le même réacteur. Les résultats de l'étude démontrent la faisabilité de cette technique, de mise en œuvre industrielle facile, pour le dépôt de ce type de revêtements. La caractérisation à la fois des espèces actives dans le plasma et des groupes incorporés dans les films déposés a permis de comprendre le processus d’incorporation de fluor, ainsi que la modification des propriétés de surface qu’il entraîne.

Tribological Properties of Fluorinated Amorphous Carbon Thin Films

In contrast with PECVD technology, reactive sputtering of graphite allows an independent control of the substrate bias. This characteristic permits the modification of film properties without varying the plasma composition. In the present study, the characteristics of DLC films grown by pulsed-DC reactive sputtering were determined as a function of substrate bias. Asymmetric bipolar pulsed-DC in a gas mixture of Ar and 7.5% CH 4 with substrate bias in the range of − 300 V to 0 V, provided wear resistant a-C:H films with wear rate values in the range of 15 to 23 · 10 − 15 m 3 m − 1 N − 1 . DLC exhibit characteristics associated to hydrogenated DLC films (DLCH), namely: moderate sp 3 content and mass density (up to 1.8 g/cm 3 ), low hydrogen content (∼ 30%) and high transparency (> 90%) up to wavelengths of 700 nm with a Tauc gap energy up to 1.9 eV. Moreover, they also showed low stress values and moderate wear rates, as shown in previous studies.

Diamond like carbon (DLC) thin films have been deposited at room temperature from a graphite target by asymmetric bipolar pulsed-DC reactive magnetron sputtering. DC bias was applied to the substrate holder between 0 and −300 V. Pulsed-DC power density and pressure were fixed at 4.4 W/cm 2 and 1.3 Pa. Pulse frequency was kept constant at 150 kHz. The results have been discussed in terms of the effects induced by substrate bias voltage. Pulsed-DC power increases the ionization of the plasma compared to processes using RF power. The conditions during the process can be described by a higher ion and electron density, the existence of more energetic species and an intense ion bombardment of substrate during the negative pulse. The substrate bias voltage induces considerable effects on deposition rate, intrinsic compressive stress and abrasive wear of the films, but it has no appreciable effect on the surface water contact angle of DLC films. Intrinsic compressive stress is limited by the carbon surface ion implantation, which in turn is controlled by the bias voltage applied to the substrate. The Davis model fitting indicates an increase in the averaged growth rate to ion flux ratio which could justify the decrease of compressive stress of the studied samples. © 2007 Elsevier B.V. All rights reserved.

Asymmetric bipolar pulsed-DC plasmas have been recently applied as an industrial solution to the deposition of diamond-like carbon DLC films by plasma enhanced chemical vapour deposition (PECVD) and magnetron sputtering on large areas and with a high deposition rate. New applications of vertically aligned carbon nanotubes (VACNTs) require a suitable technology compatible with the industrial needs: large area and mass production. Among carbon nanotube production techniques, chemical vapour deposition (CVD) is one of the most widely used, specially for applications in which a high control over length, diameter and positioning of the CNTs is desired, as nanoelectronics, field emission displays (FEDs), gas sensors or functionalized CNTs arrays for biomedical and electrochemical applications. Particularly, plasma enhanced CVD (PECVD) favours a parallel growth of the CNTs to the electric field of the plasma sheath, which is of main interest in most of the applications mentioned above. In the present work, a comparative study between radiofrequency (RF) and pulsed-DC plasma sources for PECVD of CNTs is described. Pulsed-DC plasma conditions offer singular characteristics, over RF plasmas, such as: higher power density and electronic temperature inducing a higher ion density and enhancing ion bombardment on the substrate. Chemical species inside the plasma bulk were determined by optical emission spectroscopy (OES) during the growing process. Their concentration showed significant changes depending on the plasma excitation. CNTs were grown on c-Si (100) using Fe nanoislands (

The singular properties of hydrogenated amorphous carbon (a-C:H) thin filmsdeposited by pulsed DC plasma enhanced chemical vapor deposition (PECVD), such as hardness and wear resistance, make it suitable as protective coating with low surface energy for self-assembly applications. In this paper, we designed fluorine-containing a-C:H (a-C:H:F) nanostructured surfaces and we characterized them for self-assembly applications. Sub-micron patterns were generated on silicon through laser lithography while contact angle measurements, nanotribometer, atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to characterize the surface. a-C:H:F properties on lithographied surfaces such as hydrophobicity and friction were improved with the proper relative quantity of CH4 and CHF3 during deposition, resulting in ultrahydrophobic samples and low friction coefficients. Furthermore, these properties were enhanced along the direction of the lithographypatterns (in-plane anisotropy). Finally, self-assembly properties were tested with silicananoparticles, which were successfully assembled in linear arrays following the generated patterns. Among the main applications, these surfaces could be suitable as particle filter selector and cell colony substrate.

Diamond-like amorphous carbon (DLC) films have been grown by pulsed-dc plasma-enhanced chemical vapour deposition on silicon wafers, which were previously patterned by means of colloidal lithography. The substrate conditioning comprised two steps: first, deposition of a self-assembled monolayer of silica sub-micrometre spheres (∼300 nm) on monocrystalline silicon (∼5 cm2) by Langmuir–Blodgett technique, which acted as lithography template; second, substrate patterning via ion beam etching (argon) of the colloid samples (550 eV) at different incidence angles. The plasma deposition of a DLC thin film on the nanotextured substrates resulted in hard coatings with distinctly different surface properties compared with planar DLC. Also, in-plane anisotropy was generated depending on the etching angle. The samples were morphologically characterized by scanning electron microscopy and atomic force microscopy. The anisotropy introduced by the texture was evidenced in the surface properties, as shown by the directional dependences of wettability (water contact angle) and friction coefficient. The latter was measured using a nanotribometer and a lateral force microscope. These two techniques showed how the nanopatterns influenced the tribological properties at different scales of load and contact area. This fabrication technique finds applications in the industry of microelectromechanical systems, anisotropic tribological coatings, nanoimprint lithography, microfluidics, photonic crystals, and patterned surfaces for biomedicine.

1.1 Amorphous carbon characteristics The peculiar electronic configuration of carbon atoms, 1s2 2s2 2p2, and the small energy difference between their 2p and 2s orbitals, compared to the binding energy of the carbon bonds, allow the electrons to rearrange in s and p mixed orbitals that enhance the binding energy with other atoms. This process is called hybridization and produces three different types of orbitals: sp = s + p, sp2 = s + p + p and sp3 = s + p + p + p. Each different bonding state corresponds to a certain structural arrangement: sp bonding gives rise to chain structures (with two σ bonds and two π bonds), sp2 bonding conforms onto planar structures (three σ bonds and one π bond) and finally sp3 bonding produces tetrahedrical structures (four σ bonds). The p orbitals that form π bonds overlap less than the orbitals forming σ bonds. The reduced overlapping makes π bonds weaker than σ bonds. However, a number of scenarios are possible. Sometimes, as in ethene (C2H4), a σ and π bond combine producing a stronger bond between carbon atoms. This is called a double bond: C=C. Triple bonds consist of a σ bond and two π bonds, as in ethyne (C2H2). Although chemically stronger thanks to double bonds, the mechanical stability obtained with sp2 hybridization in solids is limited, due to the planar geometry. Instead, sp3 hybridization allows the creation of a three dimensional network of σ bonds. Due to this variety of possible bonding configurations, carbon has a number of allotropes: graphene (sheet of sp2 bonded carbons: σ bonds plus delocalized π bonds), carbon nanotubes and fullerenes (graphene sheets rolled over themselves forming cylinders or spheres, respectively), graphite (Bernal stack of graphene sheets), diamond (network of sp3 bonded carbons) and amorphous carbon (cross-linked and non-organized carbon matrix with a mixture of sp2 and sp3 bonds). It is to the modification of the latter with fluorine that this chapter is devoted to. The International Union of Pure an Applied Chemistry (IUPAC) defines amorphous carbon as “A carbon material without long-range crystalline order”. It also states that “Short range order exists, but with deviations of the interatomic distances and/or interbonding angles with respect to the graphite lattice as well as to the diamond lattice.” Depending on the ratio of sp2 and sp3 bonds in the matrix, amorphous carbon (a-C) presents a variety of well-reviewed mechanical properties [Silva, 2003]. Tetrahedral amorphous carbon films (ta-C or TAC) present the highest hardness, with a high degree of sp3 bonding and without hydrogen. It is almost exclusively deposited by filtered cathodic vacuum arc

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Electronic quality epitaxial graphene has been selectively grown on silicon carbide capped with a patterned aluminum nitride layer, providing a pathway to produce device structures that avoid lithographic patterning of graphene itself. Patterning of the cap exposes SiC where graphene will grow. Capped areas inhibit graphene growth and withstand graphitization temperatures up to 1420°C under 100 Pa of argon pressure. Graphene Hall bars were fabricated and characterized by scanning Raman spectroscopy, ellipsometry, and transport measurements. Hall-mobility is about 600 cm2/V s and can be further enhanced by fine tuning the argon pressure and improving the quality of SiC surface prior to graphitization.

Here we approximate the plasma kinetics responsible for diamondlike carbon (DLC) depositions that result from pulsed-dc discharges. The DLC films were deposited at room temperature by plasma-enhanced chemical vapor deposition (PECVD) in a methane (CH4) atmosphere at 10 Pa. We compared the plasma characteristics of asymmetric bipolar pulsed-dc discharges at 100 kHz to those produced by a radio frequency (rf) source. The electrical discharges were monitored by a computer-controlled Langmuir probe operating in time-resolved mode. The acquisition system provided the intensity-voltage (I-V) characteristics with a time resolution of 1 μs. This facilitated the discussion of the variation in plasma parameters within a pulse cycle as a function of the pulse waveform and the peak voltage. The electron distribution was clearly divided into high- and low-energy Maxwellian populations of electrons (a bi-Maxwellian population) at the beginning of the negative voltage region of the pulse. We ascribe this to intense stoc...

The effects of environmental conditions and fluorine content on friction of diamond-like carbon (DLC) films are determined and discussed. Relative humidity (RH) has a considerable effect on friction values, modifying them up to a factor 2. Two regions of RH are found, depending on its effect over friction. From 20% to 60% of RH, friction decreases probably due to a better substitution of superficial atoms by hydrogen. From 60% to 80% friction remains stable and equal for almost all samples. A possible explanation would be the formation of a physisorbed layer of water on the surface, which would mask the relatively small chemical and structural variations of the films. Moreover, the different components of surface free energy (SFE) are determined using Van Oss–Chaudury–Good model. The results clearly indicate the importance of Lifshitz–Van der Waals component on SFE and the small correction that supposes acid-base interactions. According to this model, the studied DLC is a monopolar basic material. The basic component is reduced when F content is increased.

Chemical properties, stress and surface free energy of hydrogenated and fluorinated amorphous carbon thin films, deposited by pulsed-DC plasma enhanced chemical vapour, are determined and discussed as a function of the fluorine incorporation in the films. The optical emission spectra of the CH 4 + CHF 3 plasma used for the deposition are interpreted and compared to the chemical analysis of the films by X-Ray photoelectron spectroscopy. Both analyses reveal a continuous increase of the F content ([F]/[F + C] up to 30% in the film) and the fluorinated C bonds (C–CF x , CF, CF 2 and CF 3 ) with the CHF 3 :CH 4 flow ratio. Surface free energy of the films decreases as the F content is increased.

The ion fluxes and ion energy distributions (IED) corresponding to discharges in methane (CH4) were measured in time-averaged mode with a compact retarding field energy analyser (RFEA). The RFEA was placed on a biased electrode at room temperature, which was powered by either radiofrequency (13.56 MHz) or asymmetric bipolar pulsed-dc (250 kHz) signals. The shape of the resulting IED showed the relevant populations of ions bombarding the cathode at discharge parameters typical in the material processing technology: working pressures ranging from 1 to 10 Pa and cathode bias voltages between 100 and 200 V. High-energy peaks in the IED were detected at low pressures, whereas low-energy populations became progressively dominant at higher pressures. This effect is attributed to the transition from collisionless to collisional regimes of the cathode sheath as the pressure increases. On the other hand, pulsed-dc plasmas showed broader IED than RF discharges. This fact is connected to the different working frequencies and the intense peak voltages (up to 450 V) driven by the pulsed power supply. This work improves our understanding in plasma processes at the cathode level, which are of crucial importance for the growth and processing of materials requiring controlled ion bombardment. Examples of industrial applications with these requirements are plasma cleaning, ion etching processes during fabrication of microelectronic devices and plasma-enhanced chemical vapour deposition of hard coatings (diamond-like carbon, carbides and nitrides).

Diamond-like carbon (DLC) thin films have been prepared at room temperature by plasma-enhanced chemical vapour deposition (PECVD) using pulsed-DC power and CH 4 as precursor. Tribological tests of these DLC films have been carried out with a nanotribometer and a calotest instrument adapted for wear measurements. Friction coefficients ranged from 0.15 to 0.20, which differ from values obtained by other techniques. In this study we have systematically measured the abrasive wear rate and friction coefficient of DLC films deposited at different conditions (pulse frequency and peak voltage), and we have discussed the results in terms of DLC structure and surface morphology. These films could find application as ultrathin anti-friction and anti-wear protective coatings, hydrophobic coatings, gas diffusion barriers and dielectric layers in electronic devices.

Coupling magnetic materials to plasmonic structures provides a pathway to dramatically increase the magneto-optical response of the resulting composite architecture. Although such optical enhancement has been demonstrated in a variety of systems, some basic aspects are scarcely known. In particular, reflectance/transmission modulations and electromagnetic field intensification, both triggered by plasmon excitations, can contribute to the magneto-optical enhancement. However, a quantitative evaluation of the impact of both factors on the magneto-optical response is lacking. To address this issue, we have measured magneto-optical Kerr spectra on corrugated gold/dielectric interfaces with magnetic (nickel and iron oxide) nanoparticles. We find that the magneto-optical activity is enhanced by up to an order of magnitude for wavelengths that are correlated to the excitation of propagating or localized surface plasmons. Our work sheds light on the fundamental principles for the observed optical response and demonstrates that the outstanding magneto-optical performance is originated by the increase of the polarization conversion efficiency, whereas the contribution of reflectance modulations is negligible.

By combining colloidal lithography and pulsed-DC plasma deposition of diamond-like amorphous carbon films, we have fabricated sub-microstructures that modulate the surface properties of this material. A self-assembled monolayer of silica sub-micron spheres was deposited on monocrystalline silicon, which was patterned either by thermal annealing of the particles or by hole-mask lithography via ion beam etching with argon. The samples showed hemispherical close-packed topographies and micro-pillar networks. The coefficient of friction, measured with a nanotribometer, and the wettability were controlled through this special surface patterning. These structures are suitable for applications requiring protective coatings with large area showing hydrophobic properties.

Permalloy thin films were deposited on SrTiO"3 substrates by magnetron sputtering and patterned using a 30kV Ga^+ focused ion beam to fabricate narrow bridges with notches pointing perpendicular to the bridge. These notches were used to introduce geometrical nanoconstrictions in order to study the formation and pinning of magnetic domain walls. Notches were placed either along one side of the bridge or in opposite positions at both sides. Several milling conditions were tested to evaluate the patterning. Atomic and magnetic force microscopy were performed to study the effect of the introduced notches on the magnetization of the bridge. While a plain bridge shows no magnetic contrast, indicating a uniform magnetization, notched bridges clearly demonstrate that domain walls are pinned around the notches.