Synthesis of a 3D network of Pt nanowires by atomic layer deposition on carbonaceous template

The formation of a 3D network composed of free standing and interconnected Pt nanowires is achieved by a two-step method, consisting of conformal deposition of Pt by atomic layer deposition (ALD) on a forest of carbon nanotubes and subsequent removal of the carbonaceous template. Detailed characterization of this novel 3D nanostructure was carried out by transmission electron microscopy (TEM) and electrochemical impedance spectroscopy (EIS). These characterizations showed that this pure 3D nanostructure of platinum is self-supported and offers an enhancement of the electrochemically active surface area by a factor of 50

Electrodeposition of adherent submicron to micron thick manganese dioxide films with optimized current collector interface for 3D Li-ion electrodes

Three-dimensional (3D) configuration of high-performance energy storage devices has been the subject of ongoing investigations targeting their integration in autonomous microelectronic systems. In this study we demonstrate a route toward the realization of high capacity cathode material for 3D thin-film lithium-ion (Li-ion) batteries. Electrolytic manganese dioxide (EMD) film can be applied as a Li-ion intercalation electrode upon its conversion to lithium manganese dioxide (LiMn2O4 or LMO) by solid-state reaction. The main challenges of depositing thicker EMD film directly on the current collector often lay in achieving a good film adhesion and preventing oxidation of non-noble current collectors such as TiN, Ni. To improve the adhesion of the EMD films we modify the surface of the current collector by means of thin-film or seed layer coatings, which also prevent the oxidation of the underlying current collector substrate during the anodic deposition process. As a result submicron to micron thick EMD films with good adhesion were deposited on various current collectors. The acidity of the electrolyte solutions was varied depending on the type of the surface coating or current collector used. The mechanism of the EMD film growth and morphology on different substrates was examined. Compatibility of the proposed current collector interface modification for the electrodeposition of conformal thick EMD films on high-aspect ratio microstructures was demonstrated. A method of EMD film conversion to LMO at low-temperature on different substrates was shown as the path toward their application in 3D Li-ion batteries

Local solid-state modification of nanopore surface charges

The last decade, nanopores have emerged as a new and interesting tool for the study of biological macromolecules like proteins and DNA. While biological pores, especially alpha-hemolysin, have been promising for the detection of DNA, their poor chemical stability limits their use. For this reason, researchers are trying to mimic their behaviour using more stable, solid-state nanopores. The most successful tools to fabricate such nanopores use high energy electron or ions beams to drill or reshape holes in very thin membranes. While the resolution of these methods can be very good, they require tools that are not commonly available and tend to damage and charge the nanopore surface. In this work, we show nanopores that have been fabricated using standard micromachning techniques together with EBID, and present a simple model that is used to estimate the surface charge. The results show that EBID with a silicon oxide precursor can be used to tune the nanopore surface and that the surface charge is stable over a wide range of concentrations.Comment: 10 pages, 6 figure

Carbon nanostructures for enabling microstructured energy storage devices

Commercial Li_ion batteries are based on liquid electrolytes which are considered unsafe as the organic solvents they contain are volatile and flammable. As an alternative, Li_ion batteries with solid electrolytes are proposed. Solid-state batteries need to be made in form of a thin-film stack to compensate for the low ion conductivity through the solid electrolyte. However, these batteries in their current planar format have low energy density. Solid-state batteries with higher energy density and similar power density are possible, if the architecture of the thin film battery is changed from planar to microstructured. This can be achieved by depositing the active materials as a thin-film stack with sub-micrometer thicknesses over these microstructured surfaces. To this date no commercial battery of this type is available. In this thesis, several challenges regarding the fabrication of this type of batteries were investigated. In particular, nanostructured graphitic carbon layers where explored. High aspect-ratio carbon nanosheets (CNS) were used as model material to study conformal deposition of pinhole free thin electrolyte films by electrodeposition. Thin planar graphitic carbon films with nano roughness were investigated as adhesion promotor for nanoporous electrolytic manganese dioxide films to be used as cathode in our 3D Li-ion thin-film batteries. Carbon nanosheets (CNS) layers were used as high surface area carbon nanostructures. The CNS consist of a maze of electrically interconnected thin graphitic carbon sheets which are oriented vertically with respect to the substrate. CNS form a self-supported, high aspect ratio network with a sheet thickness ranging from a few nanometers to tens of nanometer and with sheet heights up to 2 micrometer. The planar graphitic carbon layers were obtained with process of growing CNS, however, in this case, the process was interrupted right after the nucleation stage, providing graphitic carbon films with few tens of nanometers. In the first part of thesis an extensive electrochemical characterization of CNS layers with different morphology and surface area (height) in aqueous and non- aqueous electrolyte solutions was performed. During this investigation a direct correlation between electrochemical capacitance, wettablity and functional surface groups on CNS sheets was determined. Moreover, the electrochemical capacitance of the CNS layers was used to determine the area enhancement of these structures. An area enhancement 120x per micrometer of CNS was found. One of the biggest challenges in the fabrication of a microstructured battery is the ability to conformally coat high aspect ratio microstructures with active battery materials. This is especially difficult for the solid electrolyte. As the solid electrolyte is directly sandwiched between two active electrodes, it is required to be electronically insulating. Hence, the electrolyte film needs to be pinhole free. In this thesis we have used the high aspect ratio CNS layer as a template to investigate the conformal deposition of electrically insulating poly(phenylene oxide) or PPO films. So far, PPO films had only been electrodeposited on planar surfaces. According to literature, these films were electrically insulating but ionically conductive. In this thesis we were able to conformally coat about 10nm thin PPO films over the CNS layers. The as-deposited PPO films were pinhole-free, electrically insulating and showed some ionic conductivity. The planar graphitic carbon film was used as a conductive seed layer to investigate the growth and electrochemical properties of electrolytic manganese dioxide (EMD) battery electrode. The graphitic carbon coating provided an excellent adhesion between the TiN substrate and EMD which significantly improved the electrochemical performance compared to EMD layers for example grown on platinum seed. Moreover, with the help of these graphitic carbon films, up to 500 nm thick EMD films could be grown, which was not possible neither with Pt nor TiN current collectors. Finally, a working half-cell was composed based on the developed graphitic carbon adhesion layer, EMD thin-film cathode and thin PPO as solid Li-ion electrolyte. However, due to the ultrathin thickness of PPO, the attempts to build full battery were unsuccessful. It is suggested that the PPO can serve as ion conductive buffer or protective layer rather than the main solid electrolyte in the stack. Even though the half-cell materials and processes are fully transferable to a microstructured substrate, further research will be required to build a full 3D thin-film battery.status: publishe

Electrolytic Manganese Dioxide Coatings on High Aspect Ratio Micro-Pillar Arrays for 3D Thin Film Lithium Ion Batteries

In this work, we present the electrochemical deposition of manganese dioxide (MnO2) thin films on carbon-coated TiN/Si micro-pillars. The carbon buffer layer, grown by plasma enhanced chemical vapor deposition (PECVD), is used as a protective coating for the underlying TiN current collector from oxidation, during the film deposition, while improving the electrical conductivity of the stack. A conformal electrolytic MnO2 (EMD) coating is successfully achieved on high aspect ratio C/TiN/Si pillar arrays by tailoring the deposition process. Lithiation/Delithiation cycling tests have been performed. Reversible insertion and extraction of Li+ through EMD structure are observed. The fabricated stack is thus considered as a good candidate not only for 3D micorbatteries but also for other energy storage applications

Electrolytic Manganese Dioxide Coatings on High Aspect Ratio Micro-Pillar Arrays for 3D Thin Film Lithium Ion Batteries

In this work, we present the electrochemical deposition of manganese dioxide (MnO₂) thin films on carbon-coated TiN/Si micro-pillars. The carbon buffer layer, grown by plasma enhanced chemical vapor deposition (PECVD), is used as a protective coating for the underlying TiN current collector from oxidation, during the film deposition, while improving the electrical conductivity of the stack. A conformal electrolytic MnO₂ (EMD) coating is successfully achieved on high aspect ratio C/TiN/Si pillar arrays by tailoring the deposition process. Lithiation/Delithiation cycling tests have been performed. Reversible insertion and extraction of Li⁺ through EMD structure are observed. The fabricated stack is thus considered as a good candidate not only for 3D microbatteries but also for other energy storage applications.status: publishe

Direct correlation between the measured electrochemical capacitance, wettability and surface functional groups of CarbonNanosheets

In this work, we studied the interfaces formed between Carbon Nanosheets (CNS) with ranging height and morphology in combination with aqueous and non-aqueous electrolyte solutions. The study concentrates on the influence of CNS wettability and surface functional groups on the electrochemical capacitance measured by Electrochemical Impedance Spectroscopy (EIS). Capacitance values at point of zero charge(pzc) were used as a reference point to compare CNS structures with different heights. A correlation was found between electrochemical capacitance values determined in water based electrolyte solution and the wettability of CNS. For example, CNS with the same height of 1.1 μm but grown from different precursors had contact angles of 16 and 141° and respective capacitance densities of 922 and 167 μF/cm2. The CNS capacitance was normalized to the capacitance of planar Highly Oriented Pyrolytic Graphite (HOPG) electrode to estimate the area enhancement of the various CNS samples. Surface area enhancement of 120x per micrometer of CNS layer was found. © 2014 Elsevier Ltd.publisher: Elsevier articletitle: Direct correlation between the measured electrochemical capacitance, wettability and surface functional groups of CarbonNanosheets journaltitle: Electrochimica Acta articlelink: http://dx.doi.org/10.1016/j.electacta.2014.03.148 content_type: article copyright: Copyright © 2014 Elsevier Ltd. All rights reserved.status: publishe

Self-limiting electropolymerization of ultrathin, pinhole-free poly(phenylene oxide) films on carbon nanosheets

Poly(phenylene oxide) (PPO) is an electronically insulating, solid polymer film which can be prepared via electropolymerization of phenol on electronically conductive surfaces. The self-limiting nature of this reaction allows the formation of pinhole-free films with nanometer thickness on high aspect ratio micro- and nano-structured substrates. In this work, we investigated the electrodeposition of PPO on carbon nanosheets (CNS). The highly corrugated CNS morphology makes a perfect model substrate to study the conformal electrodeposition of PPO films for advanced energy storage devices based on three-dimensional large-area surfaces. Uniform PPO films of about 8 nm were successfully coated over CNS layers with area enhancements of over 200x. The films uniformly covered the CNS petals and were electronically insulating as confirmed from cyclic voltammetry tests in redox electrolyte solutions. These thin conformal PPO films are of interest for blockage of electronic leakage in supercapacitor applications or even as ion conducting buffer layers in lithium ion batteries. (c) 2015 Elsevier Ltd. All rights reserved.publisher: Elsevier articletitle: Self-limiting electropolymerization of ultrathin, pinhole-free poly(phenylene oxide) films on carbon nanosheets journaltitle: Carbon articlelink: http://dx.doi.org/10.1016/j.carbon.2015.02.059 content_type: article copyright: Copyright © 2015 Elsevier Ltd. All rights reserved.status: publishe

Nanometer-thin graphitic carbon buffer layers for electrolytic MnO₂ for thin-film energy storage devices

In this study, nanometer thin graphitic carbon coatings were applied as an adhesion layer for the growth of submicron to micron thick electrolytic manganese dioxide (EMD) films for thin-film energy storage devices. The graphitic carbon coating served not only as current collector and adhesion layer between the EMD and the substrate, but also prevented the oxidation of the non-noble TiN substrate during the anodic deposition process. The EMD films consisted of a network of interconnected nanometer-size particles with around 50% porosity. The ability to grow a few hundred nanometer thick EMD film with good adhesion to the current collector is critical for reliable thin-film batteries on high aspect ratio microstructured surfaces. Thin EMD films grown on our graphitic carbon coated TiN substrates showed improved reversible Li-ion intercalation kinetics and increased cycle life compared to similar films deposited on noble metal platinum substrates, thus demonstrating the improved interface properties using the graphitic carbon buffer layer.status: publishe