Direct imaging and manipulation of ionic diffusion in mixed electronic-ionic conductors.

Next generation Li-ion batteries require improved energy densities, power output and safety to satisfy the demands of emerging technologies. All solid state 3D thin-film batteries (ASB) based on nanoionics are considered as frontrunners to enable all this. In order to facilitate the introduction of this new architecture, a homogeneous electrochemical activity and a high ionic diffusivity of the electrodes is key. However, nanometer-resolved techniques to probe structural, electrical and electrochemical properties of the battery components are still limited. Here we propose a study that combines conductive atomic force microscopy (C-AFM) and secondary ion mass spectrometry (SIMS) for structural and electrical characterization. In addition, a novel concept called ion-modulated C-AFM (imC-AFM) is introduced to also sense the electrochemical activity of ions in confined volumes. Using the aforementioned methodologies, LixMn2O4 thin film cathodes are studied observing: (1) a direct correlation between electrical conductivity and local chemistry. (2) A non-uniform Li-ion electrochemical activity (i.e. ionic conductivity) on the cathode's surface with a clear enhancement in grain boundaries (GBs). Finally, (3) imC-AFM observes a high volume expansion associated with high Li incorporation. This work introduces a novel pathway for the rapid analysis of materials to be used in ASB.

Towards metal-organic framework based field effect chemical sensors: UiO-66-NH2 for nerve agent detection.

We present a highly sensitive gas detection approach for the infamous 'nerve agent' group of alkyl phosphonate compounds. Signal transduction is achieved by monitoring the work function shift of metal-organic framework UiO-66-NH2 coated electrodes upon exposure to ppb-level concentrations of a target simulant. Using the Kelvin probe technique, we demonstrate the potential of electrically insulating MOFs for integration in field effect devices such as ChemFETs: a three orders of magnitude improvement over previous work function-based detection of nerve agent simulants. Moreover, the signal is fully reversible both in dry and humid conditions, down to low ppb concentrations. Comprehensive investigation of the interactions that lead towards this high sensitivity points towards a series of confined interactions between the analyte and the pore interior of UiO-66-NH2.

Nanostructured TiO2/carbon nanosheet hybrid electrode for high-rate thin-film lithium-ion batteries.

Heterogeneous nanostructured electrodes using carbon nanosheets (CNS) and TiO2 exhibit high electronic and ionic conductivity. In order to realize the chip level power sources, it is necessary to employ microelectronic compatible techniques for the fabrication and characterization of TiO2-CNS thin-film electrodes. To achieve this, vertically standing CNS grown through a catalytic free approach on a TiN/SiO2/Si substrate by plasma enhanced chemical vapour deposition (PECVD) was used. The substrate-attached CNS is responsible for the sufficient electronic conduction and increased surface-to-volume ratio due to its unique morphology. Atomic layer deposition (ALD) of nanostructured amorphous TiO2 on CNS provides enhanced Li storage capacity, high rate performance and stable cycling. The amount of deposited TiO2 masks the underlying CNS, thereby controlling the accessibility of CNS, which gets reflected in the total electrochemical performance, as revealed by the cyclic voltammetry and charge/discharge measurements. TiO2 thin-films deposited with 300, 400 and 500 ALD cycles on CNS have been studied to understand the kinetics of Li insertion/extraction. A large potential window of operation (3-0.01 V); the excellent cyclic stability, with a capacity retention of 98% of the initial value; and the remarkable rate capability (up to 100 C) are the highlights of TiO2/CNS thin-film anode structures. CNS with an optimum amount of TiO2 coating is proposed as a promising approach for the fabrication of electrodes for chip compatible thin-film Li-ion batteries.

A study of Joule heating-induced breakdown of carbon nanotube interconnects.

We investigate breakdown of carbon nanotube (CNT) interconnects induced by Joule heating in air and under high vacuum conditions (10(-5) mbar). A CNT with a diameter of 18 nm, which is grown by chemical vapor deposition to connect opposing titanium nitride (TiN) electrodes, is able to carry an electrical power up to 0.6 mW before breaking down under vacuum, with a corresponding maximum current density up to 8 × 10(7) A cm(-2) (compared to 0.16 mW and 2 × 10(7) A cm(-2) in air). Decoration with electrochemically deposited Ni particles allows protection of the CNT interconnect against oxidation and improvement of the heat release through the surrounding environment. A CNT decorated with Ni particles is able to carry an increased electrical power of about 1.5 mW before breaking down under vacuum, with a corresponding maximum current density as high as 1.2 × 10(8) A cm(-2). The Joule heating produced along the current carrying CNT interconnect is able to melt the Ni particles and promotes the formation of titanium carbon nitride which improves the electrical contact between the CNT and the TiN electrodes.

Dynamic microscopy of nanoscale cluster growth at the solid-liquid interface.

Dynamic processes at the solid-liquid interface are of key importance across broad areas of science and technology. Electrochemical deposition of copper, for example, is used for metallization in integrated circuits, and a detailed understanding of nucleation, growth and coalescence is essential in optimizing the final microstructure. Our understanding of processes at the solid-vapour interface has advanced tremendously over the past decade due to the routine availability of real-time, high-resolution imaging techniques yielding data that can be compared quantitatively with theory. However, the difficulty of studying the solid-liquid interface leaves our understanding of processes there less complete. Here we analyse dynamic observations--recorded in situ using a novel transmission electron microscopy technique--of the nucleation and growth of nanoscale copper clusters during electrodeposition. We follow in real time the evolution of individual clusters, and compare their development with simulations incorporating the basic physics of electrodeposition during the early stages of growth. The experimental technique developed here is applicable to a broad range of dynamic phenomena at the solid-liquid interface.