Fabrication and Characterization of Macroscopic Graphene Layers on Metallic Substrates

[spa] En 2004, A. Geim y K. Novoselov (Universidad de Manchester, UK), aislaron por primera vez una capa atómica de carbono (la estructura más fina hasta la fecha), más conocido como grafeno, cuyas propiedades mecánicas y electrónicas extremas permanecen por encima de todos los materiales conocidos: la más alta movilidad electrónica, ambipolaridad, soporta grandes densidades de corriente, el más alto módulo elástico, más conductividad térmica, alta impermeabilidad, y reconcilia fragilidad y ductilidad. El estudio del grafeno estaba a punto de ser el siguiente paso en el boom de la Nanotecnología cuando en 2010, este descubrimiento recibió el Premio Nobel. El objetivo de la tesis es superar las limitaciones de las técnicas actuales en cuanto a la superficie de crecimiento del grafeno (de algunas micras) y extender las posibles aplicaciones a sistemas y dispositivos que requieran de superficies macroscópicas. Para este propósito, esta tesis tuvo diferentes fases que consistieron en: a) El diseño y construcción de un nuevo reactor de alto vacío, que lleva a cabo procesos de Depósito Químico de Vapor (CVD) a altas temperaturas y pulverización catódica. b) Estudio de los principios del crecimiento del grafeno en metales, y desarrollo de un método CVD modificado basado en pulsos de gas (metano), que reduce el tiempo de depósito a 1-10 s, presión de 10-4 Pa, cantidad de gas precursor necesario, y la temperatura (900-1000 °C). c) Fabricación de grafeno de gran área y alta calidad en sustratos metálicos, cobre/níquel depositado y láminas de cobre, mediante este CVD modificado. d) Caracterización del grafeno obtenido mediante diferentes técnicas con el fin de optimizar sus propiedades físicas y superficiales, así como el método CVD; estudios estructurales y morfológicos con espectroscopia Raman, microscopía electrónica y óptica. Además de un proceso de transferencia de cobre a silicio. e) Fabricación y caracterización de grafeno obtenido mediante exfoliación mecánica de grafito sobre silicio para caracterizarlo eléctricamente y fabricar un transistor de Efecto Campo. Las muestras exfoliadas fueron usadas también para estudiar el efecto de la radiación de SHI rasante sobre la superficie.[eng] In 2004 there were newly conditions for a scientific revolution, with very important technology implications and yet to be completely developed. It is the isolation of atomic carbon layers, better known as graphene, whose extreme mechanical and electronic properties stand out above all known materials: it presents the highest electron mobility, ambipolarity, it supports large current densities, the highest elastic modulus, increased thermal conductivity, it shows high impermeability, and reconciles fragility and ductility. The study of graphene was about to be the next step to the boom in nanotechnology. In this case, the system to consider is purely two-dimensional, being the thinnest structure known to date. In 2010, this discovery was acknowledged with the Nobel Prize to the scientists A. Geim and K. Novoselov from the Manchester University (UK). The goal of the project, in which this thesis was framed, is to develop new materials in ultrathin structures of few monoatomic layers, based on graphene, with extreme surface properties (very high wear resistance, ultra low friction and surface energy, extreme chemical resistance, biocompatibility) for biomedical applications. The scope of this objective is to overcome the limitations of current techniques in terms of the growth surface of graphene (of some .m2) and to extend the possible applications of graphene to systems and devices requiring macroscopic size surfaces. For this purpose, the thesis had different tasks consisting of: a) The design and construction of a new high vacuum reactor in the Clean Room of the Universitat de Barcelona that works with high-temperature chemical vapor deposition (CVD) and magnetron sputtering. b) Study of the principles of a CVD process of graphene on metals, and development of a modified CVD method based on pulses of gas (methane), which will reduce the current deposition times to 1-10 s, pressure of 10-4 Pa, quantity of precursor gas needed, and temperature (900-1000 °C), to grow high quality graphene. c) Fabrication of graphene layers on metal substrates, sputtered copper/nickel and copper foils, of large area and high quality by this modified CVD technique, focusing on obtaining the material as effectively as possible towards an implementation on applications. d) Characterization of the graphene obtained through different techniques in order to optimize its physical and surface properties, as well as the CVD method; such as structural and morphological studies by Raman spectroscopy, SEM and Optical Microscopy. In addition to a transfer process from copper to silicon. e) Fabrication and characterization of graphene layers by means of mechanical exfoliation of graphite on silicon in order to characterize the electrical properties to fabricate a graphene-based FET. Exfoliated samples were also used to study the effect of the SHI irradiation with glancing angles on the surface. The thesis is then, divided into four main parts. The Part I will introduce the state of the art of graphene as novel material and its outstanding properties, its discovery, and all the technologies that triggered its development during these years until the first applications. The Part II will describe the experimental setups used throughout this work, regarding the fabrication and characterization of substrates by magnetron sputtering, the growth mechanisms of the new developed CVD system, and a brief explanation of the fundamentals of each technique. In the part III, a complete review of all the results of the samples obtained by mechanical exfoliation of graphite and CVD on copper will be exposed; together with their characterization. Part IV includes the main conclusions of the work, which are summarized. Afterwards, a list of the scientific results published is shown, as well as the contributions in conferences and meetings. In the end of the manuscript, an Appendix with three sections is shown: a complete CVD review, the abstract of the patent developed during this thesis, and a complete list of all the samples produced

Anisotropic surface properties of micro/nanostructured a-C:H:F thin films with self-assembly applications

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

Nanostructured DLC coatings for self-assembly applications

The singular characteristics of diamond-like carbon (DLC) thin films, concerning tribological and surfaces properties, are suitable for self-assembly applications. Usually, DLC thin films have been developed as protective coatings for sliding surfaces with relative motion. But, DLC coatings deposited on nanostructured surfaces also provide new potential for self-assembly applications. In particular, the addition of fluorine during the deposition of DLC deposited by pulsed DC plasma enhanced chemical vapor deposition (PECVD) has a significant effect on the surface energy and tribological characteristics, which accelerates the mechanisms involved in self-assembly processes. Among the multiple applications of DLC coatings we also found their biocompatibility and antithrombogenicity. Such properties make them candidates for a number of medical applications where wear-resistant coatings, such as prosthesis, or simply biocompatible parts are required

Nanostructured DLC coatings for selfassembly applications

Màster en Nanociència i NanotecnologiaThe special characteristics and singular properties of diamond-like carbon (DLC) thin films deposited by pulsed DC plasma enhanced chemical vapor deposition (PECVD), such as hardness and wear resistance, are suitable for self assembly applications as protective coating and as nanostructured surfaces. In this master thesis project, nanostructured DLC surfaces will be designed and characterized for self-assembly applications. Submicron patterns were lithographed on silicon through laser lithography while contact angle, nanotribometer, atomic force microscopy (AFM) and scanning electron miscroscopy (SEM) were used to characterize the surface. DLC properties on lithographed surfaces such as hydrophobicity and hardness were improved with the proper relative quantity of CHF3, resulting in very high contact angles and low friction coefficients. Self assembly properties were tested with silica nanoparticles which were prepared with a sol-gel solution

Anisotropic surface properties of micro/nanostructured a-C:H:F thin films with self-assembly applications

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

Nanostructured DLC coatings for self-assembly applications

The singular characteristics of diamond-like carbon (DLC) thin films, concerning tribological and surfaces properties, are suitable for self-assembly applications. Usually, DLC thin films have been developed as protective coatings for sliding surfaces with relative motion. But, DLC coatings deposited on nanostructured surfaces also provide new potential for self-assembly applications. In particular, the addition of fluorine during the deposition of DLC deposited by pulsed DC plasma enhanced chemical vapor deposition (PECVD) has a significant effect on the surface energy and tribological characteristics, which accelerates the mechanisms involved in self-assembly processes. Among the multiple applications of DLC coatings we also found their biocompatibility and antithrombogenicity. Such properties make them candidates for a number of medical applications where wear-resistant coatings, such as prosthesis, or simply biocompatible parts are required

Central nervous system involvement in systemic lupus erythematosus: Data from the Spanish Society of Rheumatology Lupus Register (RELESSER)

Objectives To analyze the prevalence, incidence, survival and contribution on mortality of major central nervous system (CNS) involvement in systemic lupus erythematosus (SLE). Methods Patients fulfilling the SLE 1997 ACR classification criteria from the multicentre, retrospective RELESSER-TRANS (Spanish Society of Rheumatology Lupus Register) were included. Prevalence, incidence and survival rates of major CNS neuropsychiatric (NP)-SLE as a group and the individual NP manifestations cerebrovascular disease (CVD), seizure, psychosis, organic brain syndrome and transverse myelitis were calculated. Furthermore, the contribution of these manifestations on mortality was analysed in Cox regression models adjusted for confounders. Results A total of 3591 SLE patients were included. Of them, 412 (11.5%) developed a total of 522 major CNS NP-SLE manifestations. 61 patients (12%) with major CNS NP-SLE died. The annual mortality rate for patients with and without ever major CNS NP-SLE was 10.8% vs 3.8%, respectively. Individually, CVD (14%) and organic brain syndrome (15.5%) showed the highest mortality rates. The 10% mortality rate for patients with and without ever major CNS NP-SLE was reached after 12.3?vs 22.8 years, respectively. CVD (9.8 years) and organic brain syndrome (7.1 years) reached the 10% mortality rate earlier than other major CNS NP-SLE manifestations. Major CNS NP-SLE (HR 1.85, 1.29?2.67) and more specifically CVD (HR 2.17, 1.41?3.33) and organic brain syndrome (HR 2.11, 1.19?3.74) accounted as independent prognostic factors for poor survival. Conclusion The presentation of major CNS NP-SLE during the disease course contributes to a higher mortality, which may differ depending on the individual NP manifestation. CVD and organic brain syndrome are associated with the highest mortality rates.Systemic lupus erythematosusNP-SLECentral nervous systemSurvivalMortalit

Relationship between damage clustering and mortality in systemic lupus erythematosus in early and late stages of the disease: cluster analyses in a large cohort from the Spanish Society of Rheumatology Lupus Registry.

To identify patterns (clusters) of damage manifestations within a large cohort of SLE patients and evaluate the potential association of these clusters with a higher risk of mortality. This is a multicentre, descriptive, cross-sectional study of a cohort of 3656 SLE patients from the Spanish Society of Rheumatology Lupus Registry. Organ damage was ascertained using the Systemic Lupus International Collaborating Clinics Damage Index. Using cluster analysis, groups of patients with similar patterns of damage manifestations were identified. Then, overall clusters were compared as well as the subgroup of patients within every cluster with disease duration shorter than 5 years. Three damage clusters were identified. Cluster 1 (80.6% of patients) presented a lower amount of individuals with damage (23.2 vs 100% in clusters 2 and 3, P In a large cohort of SLE patients, cardiovascular and musculoskeletal damage manifestations were the two dominant forms of damage to sort patients into clinically meaningful clusters. Both in early and late stages of the disease, there was a significant association of these clusters with an increased risk of mortality. Physicians should pay special attention to the early prevention of damage in these two systems