Electron beam lithography for nanofabrication

Consultable des del TDXTítol obtingut de la portada digitalitzadaLa litografía por haz de electrones (Electron Beam Lithography, EBL) se ha consolidado como una de las técnicas más eficaces que permiten definir motivos en el rango nanométrico. Su implantación ha permitido la nanofabricación de estructuras y dispositivos para su uso en el campo de la nanotecnología y la nanociencia. La EBL se basa en la definición de motivos submicrónicos mediante el rastreo de un haz energético de electrones sobre una resina. La naturaleza de los electrones y el desarrollo the haces extremadamente finos y su control preciso establecen la plataforma ideal para los requerimientos de la Nanofabricación. El uso de la EBL para el desarrollo de un gran número de nanoestructuras, nanodispositivos y nanosistemas ha sido, y continúa siendo, crucial para las aplicaciones de producción de máscaras, prototipaje o dispositivos discretos para la investigación fundamental. Su éxito radica en la alta resolución, flexibilidad y compatibilidad de la EBL con otros procesos de fabricación convencionales. El objetivo de esta tesis es el avance en el conocimiento, desarrollo y aplicación de la EBL en las areas de los micro/nanosistemas y la nanoelectrónica. El presente documento refleja parte del trabajo realizado en el Laboratorio de Nanofabricación del Instituto de Microelectrónica de Barcelona IMB-CNM-CSIC durante los últimos cinco años. Debido a la falta de experiencia previa en el IMB en la utilización de la EBL, ha sido necesario el desarrollo y consolidación de una serie de procesos, lo que ha condicionado parcialmente la investigación, tal y como recoge la memoria. Entre los aspectos relevantes compilados en esta tesis, en cuanto a innovación tecnológica, cabe destacar diversos avances en procesos tecnológicos basados en la EBL. Una nueva resina de tono negativo ha sido caracterizada y disponible para su uso en nanofabricación. La optimización de la EBL se ha llevado a cabo mediante métodos de corrección del efecto de proximidad. Se ha establecido el proceso de integración de estructuras nanomecánicas en circuitos CMOS, así como la fabricación de dispositivos basados en nanotubos de carbono. En concreto, el primer FET basado en un sólo nanotubo de carbono fabricado en España. Finalmente, la compatibilidad y viabilidad de los métodos de fabricación basados en haces de partículas se ha estudiado mediante el análisis del efecto de los haces de partículas cargadas sobre dispositivos. Por otro lado, esta memoria no sólo contiene la descripción de los principales resultados obtenidos, sinó que pretende aportar información general sobre procesos de nanofabricación basados en haces de electrones para ser utilizados en futuras investigaciones de este area.Electron beam lithography (EBL) has consolidated as one of the most common techniques for patterning at the nanoscale meter range. It has enabled the nanofabrication of structures and devices within the research field of nanotechnology and nanoscience. EBL is based on the definition of submicronic features by the scanning of a focused energetic beam of electrons on a resist. The nature of electrons and the development of extremely fine beams and its flexible control provide the platform to satisfy the requirements of Nanofabrication. Use of EBL for the development of a wide range of nanostructures, nanodevices and nanosystems has been, and continues to be, crucial for the applications of mask production, prototyping and discrete devices for fundamental research and it relies on its high resolution, flexibility and compatibility with other conventional fabrication processes. The purpose of this thesis is to advance in the knowledge, development and application of electron beam lithography in the areas of micro/nano systems and nanoelectronics. In this direction, this memory reflects part of the work performed at the Nanofabrication Laboratory of the IMB-CNM. Since there was no previous experience on EBL at CNM, the need for developing a set of processes has determined partially the work. The variety of topics that concern to nanoscience and nanotechnology is enormous. Chapter 1 briefly sintetizes nanoscale related aspects. This section aims to frame the contents of this thesis, coherently. Also for completeness, it is intended to address the specific subjects under discussion or contained in the following chapters and it is based or oriented to the experimental results that will be presented. Chapter 2 is a general overview of the EBL technique from the point of view of the system and the physical interaction of the process. In particular, the characteristics of the SEM and specifications of the lithographic capabilities of the system that is used are presented. In chapter 3, irradiation effect on resists is studied. The chemical behaviour of different polymeric materials is correlated with theoretical simulations for two types of resists: methacrylic based positive resists and epoxy based negative resists. The first is used for validation of the modelization and to describe the general performance of EBL on different conditions. The second covers the experiments oriented to establish the performance parameters of a new resist and comparison with another existing negative electron beam resist. Proximity effect correction concludes with the correlation of theory and experimental results for both types of resists, positive and negative. Chapter 4 is an example of the fabrication and optimization of a micro/nanosystem for sensing at the nanoscale. In particular, nanoresonators are developed with two approaches (EBL and FIB) and enhanced response is achieved by their integration on CMOS circuitry. Chapter 5 presents carbon nanotube (CNT) based devices that are realized and implemented for applications in nanoelectronics and sensing. First, different fabrication approaches for contacting CNTs are discussed. Then, the results of electrical characterization of the devices are presented. Finally, technology development for the use of these devices for sensing is established. The last chapter embraces all the previous sections and pays attention to the effect of electron beam on the devices. In particular, electron induced effect is studied on nanomechanical structures integrated in circuits and CNT based devices, in order to evaluate EBL based fabrication, SEM characterization or more fundamental aspects. Advanced characterization techniques are used together with simulations, both assessing a deeper understanding of the results. Electrical measurements and AFM based techniques are used to characterise the effect of the electron irradiation by changes in their performance characteristics, charging, surface potential imaging, etc. Main results and solved challenges are summarized in the conclusive chapter 7 that finishes with this document

Boosting the local anodic oxidation of silicon through carbon nanofiber atomic force microscopy probes

Many nanofabrication methods based on scanning probe microscopy have been developed during the last decades. Local anodic oxidation (LAO) is one of such methods: Upon application of an electric field between tip and surface under ambient conditions, oxide patterning with nanometer-scale resolution can be performed with good control of dimensions and placement. LAO through the non-contact mode of atomic force microscopy (AFM) has proven to yield a better resolution and tip preservation than the contact mode and it can be effectively performed in the dynamic mode of AFM. The tip plays a crucial role for the LAO-AFM, because it regulates the minimum feature size and the electric field. For instance, the feasibility of carbon nanotube (CNT)-functionalized tips showed great promise for LAO-AFM, yet, the fabrication of CNT tips presents difficulties. Here, we explore the use of a carbon nanofiber (CNF) as the tip apex of AFM probes for the application of LAO on silicon substrates in the AFM amplitude modulation dynamic mode of operation. We show the good performance of CNF-AFM probes in terms of resolution and reproducibility, as well as demonstration that the CNF apex provides enhanced conditions in terms of field-induced, chemical process efficiency

Tailoring Carbon Nanostructure for High Frequency Supercapacitor Operation

The possibility of enhancing the frequency performance of electrochemical capacitors by tailoring the nanostructure of the carbon electrode to increase electrolyte permeability is demonstrated. Highly porous, vertically oriented carbon electrodes which are in direct electrical contact with the metallic current collector are produced via MPECVD growth on metal foils. The resulting structure has a capacitance and frequency performance between that of an electrolytic capacitor and an electrochemical capacitor. Fully packaged devices are produced on Ni and Cu current collectors and performance compared to state-of-the-art electrochemical capacitors and electrolytic capacitors. The extension of capacitive behavior to the AC regime (~100 Hz) opens up an avenue for a number of new applications where physical volume of the capacitor may be significantly reduced

Nanomechanical properties of solvent cast polystyrene and poly(methyl methacrylate) polymer blends and self-assembled block copolymers

© 2015 Society of Photo-Optical Instrumentation Engineers (SPIE). The nanomechanical properties of solvent-cast polymer thin films have been investigated using PeakForce™ Quantitative Nanomechanical Mapping. The samples consisted of films of polystyrene (PS) and poly(methyl methacrylate) (PMMA) obtained after the dewetting of toluene solution on a polymeric brush layer. Additionally, we have probed the mechanical properties of poly(styrene-b-methyl methacrylate) block copolymers (BCP) as randomly oriented thin films. The probed films have a critical thickness <50 nm and present features to be resolved <42 nm. The Young's modulus values obtained through several nanoindentation experiments present a good agreement with previous literature, suggesting that the PeakForce™ technique could be crucial for BCP investigations, e.g., as a predictor of the mechanical stability of the different phases.This work was partially funded by the projects SNM (FP7-ICT-2011-8) and FORCE-for-FUTURE (CSD2010-00024).Peer Reviewe

Extended use of dual antiplatelet therapy among older adults with acute coronary syndromes and associated variables: a cohort study

Acute coronary syndromes; Dual antiplatelet therapy; ElderlySíndromes coronàries agudes; Teràpia antiplaquetària dual; Gent granSíndromes coronarios agudos; Terapia antiplaquetaria dual; Personas mayoresBackground Current guidelines recommend extending the use of dual antiplatelet therapy (DAPT) beyond 1 year in patients with an acute coronary syndrome (ACS) and a high risk of ischaemia and low risk of bleeding. No data exist about the implementation of this strategy in older adults from routine clinical practice. Methods We conducted a Spanish multicentre, retrospective, observational registry-based study that included patients with ACS but no thrombotic or bleeding events during the first year of DAPT after discharge and no indication for oral anticoagulants. High bleeding risk was defined according to the Academic Research Consortium definition. We assessed the proportion of cases of extended DAPT among patients 65 ≥ years that went beyond 1 year after hospitalisation for ACS and the variables associated with the strategy. Results We found that 48.1% (928/1,928) of patients were aged ≥ 65 years. DAPT was continued beyond 1 year in 32.1% (298/928) of patients ≥ 65; which was a similar proportion as with their younger counterparts. There was no significant correlation between a high bleeding risk and DAPT duration. Contrastingly, there was a strong correlation between the extent of coronary disease and DAPT duration (p < 0.001). Other variables associated with extended DAPT were a higher left ventricle ejection fraction, a history of heart failure and a prior stent thrombosis. Conclusion There was no correlation between age and extended use of DAPT beyond 1 year in older patients with ACS. DAPT was extended in about one-third of patients ≥ 65 years. The severity of the coronary disease, prior heart failure, left ventricle ejection fraction and prior stent thrombosis all correlated with extended DAPT.This work was supported by the “Instituto de Salud Carlos III” and “Fondos Europeos de Desarrollo Regional FEDER” [grant numbers JR/21/00041, PI20/00637 and CIBERCV16/11/00486] and by Conselleria de Educación – Generalitat Valenciana (PROMETEO/2021/008)

Voltage control of magnetism with magneto-ionic approaches : beyond voltage-driven oxygen ion migration

Magneto-ionics is an emerging field in materials science where voltage is used as an energy-efficient means to tune magnetic properties, such as magnetization, coercive field, or exchange bias, by voltage-driven ion transport. We first discuss the emergence of magneto-ionics in the last decade, its core aspects, and key avenues of research. We also highlight recent progress in materials and approaches made during the past few years. We then focus on the "structural-ion"approach as developed in our research group in which the mobile ions are already present in the target material and discuss its potential advantages and challenges. Particular emphasis is given to the energetic and structural benefits of using nitrogen as the mobile ion, as well as on the unique manner in which ionic motion occurs in CoN and FeN systems. Extensions into patterned systems and textures to generate imprinted magnetic structures are also presented. Finally, we comment on the prospects and future directions of magneto-ionics and its potential for practical realizations in emerging fields, such as neuromorphic computing, magnetic random-access memory, or micro- and nano-electromechanical systems

Bidirectional Modulation of Neuronal Cells Electrical and Mechanical Properties Through Pristine and Functionalized Graphene Substrates

[Abstract] In recent years, the quest for surface modifications to promote neuronal cell interfacing and modulation has risen. This course is justified by the requirements of emerging technological and medical approaches attempting to effectively interact with central nervous system cells, as in the case of brain-machine interfaces or neuroprosthetic. In that regard, the remarkable cytocompatibility and ease of chemical functionalization characterizing surface-immobilized graphene-based nanomaterials (GBNs) make them increasingly appealing for these purposes. Here, we compared the (morpho)mechanical and functional adaptation of rat primary hippocampal neurons when interfaced with surfaces covered with pristine single-layer graphene (pSLG) and phenylacetic acid-functionalized single-layer graphene (fSLG). Our results confirmed the intrinsic ability of glass-supported single-layer graphene to boost neuronal activity highlighting, conversely, the downturn inducible by the surface insertion of phenylacetic acid moieties. fSLG-interfaced neurons showed a significant reduction in spontaneous postsynaptic currents (PSCs), coupled to reduced cell stiffness and altered focal adhesion organization compared to control samples. Overall, we have here demonstrated that graphene substrates, both pristine and functionalized, could be alternatively used to intrinsically promote or depress neuronal activity in primary hippocampal cultures.This work was funded by the European Union’s Horizon 2020 Research and Innovation Program under the Grant Agreements 785219 and 881603 of the Graphene Flagship. DS acknowledges the support of the European Union’s Horizon 2020 Research and Innovation Program under the Marie Skłodowska-Curie grant agreement no. 838902. MP as the recipient of the AXA Bionanotechnology Chair, is grateful to the AXA Research Fund for financial support. This work was performed under the Maria de Maeztu Units of Excellence Program from the Spanish State Research Agency-grant no. MDM-2017- 0720. AC thanks Xunta de Galicia for his research grant Atracción de Talento (no. ED431H 2020/17). GR acknowledges funding from RYC-2016-21412. HH acknowledges funding from Juan de la Cierva – Incorporación no. IJC-2018-037396-IXunta de Galicia; ED431H 2020/1

Challenge 6: Open Science: reproducibility, transparency and reliability

Open Science is becoming a new paradigm in scientific research and complex changes are being done. This new way in knowledge development requires a great transformation that will allow science to adapt efficiently and effectively to the urgency of the problems to be solved while ensuring the reproducibility, transparency and reliability of scientific results. This chapter analyzes the impact of this change of model, the challenges to be addressed and the expected benefits.Peer reviewe

Pushing the Limits of Space Technology

Coordinators: Philippe Godignon; Gustavo Liñán.Peer reviewe