STEM EBIC mapping of the metal-insulator transition in thin-film NbO2

STEM EBIC mapping of the metal-insulator transition in thin-film NbO

Charged Nanoparticle Dynamics in Water Induced by Scanning Transmission Electron Microscopy

Using scanning transmission electron microscopy we image ∼4 nm platinum nanoparticles deposited on an insulating membrane, where the membrane is one of two electron-transparent windows separating an aqueous environment from the microscope’s high vacuum. Upon receiving a relatively moderate dose of ∼10⁴<i>e</i>/nm², initially immobile nanoparticles begin to move along trajectories that are directed radially outward from the center of the field of view. With larger dose rates the particle motion becomes increasingly dramatic. These observations demonstrate that, even under mild imaging conditions, the <i>in situ</i> electron microscopy of aqueous environments can produce electrophoretic charging effects that dominate the dynamics of nanoparticles under observation

Charged Nanoparticle Dynamics in Water Induced by Scanning Transmission Electron Microscopy

Using scanning transmission electron microscopy we image ∼4 nm platinum nanoparticles deposited on an insulating membrane, where the membrane is one of two electron-transparent windows separating an aqueous environment from the microscope’s high vacuum. Upon receiving a relatively moderate dose of ∼10⁴<i>e</i>/nm², initially immobile nanoparticles begin to move along trajectories that are directed radially outward from the center of the field of view. With larger dose rates the particle motion becomes increasingly dramatic. These observations demonstrate that, even under mild imaging conditions, the <i>in situ</i> electron microscopy of aqueous environments can produce electrophoretic charging effects that dominate the dynamics of nanoparticles under observation

Charged Nanoparticle Dynamics in Water Induced by Scanning Transmission Electron Microscopy

Using scanning transmission electron microscopy we image ∼4 nm platinum nanoparticles deposited on an insulating membrane, where the membrane is one of two electron-transparent windows separating an aqueous environment from the microscope’s high vacuum. Upon receiving a relatively moderate dose of ∼10⁴<i>e</i>/nm², initially immobile nanoparticles begin to move along trajectories that are directed radially outward from the center of the field of view. With larger dose rates the particle motion becomes increasingly dramatic. These observations demonstrate that, even under mild imaging conditions, the <i>in situ</i> electron microscopy of aqueous environments can produce electrophoretic charging effects that dominate the dynamics of nanoparticles under observation

Charged Nanoparticle Dynamics in Water Induced by Scanning Transmission Electron Microscopy

Using scanning transmission electron microscopy we image ∼4 nm platinum nanoparticles deposited on an insulating membrane, where the membrane is one of two electron-transparent windows separating an aqueous environment from the microscope’s high vacuum. Upon receiving a relatively moderate dose of ∼10⁴<i>e</i>/nm², initially immobile nanoparticles begin to move along trajectories that are directed radially outward from the center of the field of view. With larger dose rates the particle motion becomes increasingly dramatic. These observations demonstrate that, even under mild imaging conditions, the <i>in situ</i> electron microscopy of aqueous environments can produce electrophoretic charging effects that dominate the dynamics of nanoparticles under observation

Large-Scale Fabrication, 3D Tomography, and Lithium-Ion Battery Application of Porous Silicon

Recently, silicon-based lithium-ion battery anodes have shown encouraging results, as they can offer high capacities and long cyclic lifetimes. The applications of this technology are largely impeded by the complicated and expensive approaches in producing Si with desired nanostructures. We report a cost-efficient method to produce nanoporous Si particles from metallurgical Si through ball-milling and inexpensive stain-etching. The porosity of porous Si is derived from particle’s three-dimensional reconstructions by scanning transmission electron microscopy (STEM) tomography, which shows the particles’ highly porous structure when etched under proper conditions. Nanoporous Si anodes with a reversible capacity of 2900 mAh/g was attained at a charging rate of 400 mA/g, and a stable capacity above 1100 mAh/g was retained for extended 600 cycles tested at 2000 mA/g. The synthetic route is low-cost and scalable for mass production, promising Si as a potential anode material for the next-generation lithium-ion batteries with enhanced capacity and energy density

Hydrothermal Preparation and Magnetic Properties of NaFeSi₂O₆: Nanowires vs Bulk Samples

A single-step hydrothermal route to the preparation of the pyroxene mineral, NaFeSi₂O₆, is reported. The as-prepared samples are found to adopt a nanowire morphology and can be made with a yield of several hundred milligrams at a time with high purity. Synchrotron X-ray diffraction, electron microscopy, and Mössbauer spectroscopy are employed to characterize the structure and morphology. A comparison of the temperature- and field-dependent magnetic properties between the nanowire and sintered phases shows substantial differences that can likely be attributed to the reduced particle size and increased number of spins on the surface of the nanowires

Aligned Epitaxial SnO₂ Nanowires on Sapphire: Growth and Device Applications

Semiconducting SnO₂ nanowires have been used to demonstrate high-quality field-effect transistors, optically transparent devices, photodetectors, and gas sensors. However, controllable assembly of rutile SnO₂ nanowires is necessary for scalable and practical device applications. Here, we demonstrate aligned, planar SnO₂ nanowires grown on A-plane, M-plane, and R-plane sapphire substrates. These parallel nanowires can reach 100 μm in length with sufficient density to be patterned photolithographically for field-effect transistors and sensor devices. As proof-of-concept, we show that transistors made this way can achieve on/off current ratios on the order of 10⁶, mobilities around 71.68 cm²/V·s, and sufficiently high currents to drive external organic light-emitting diode displays. Furthermore, the aligned SnO₂ nanowire devices are shown to be photosensitive to UV light with the capability to distinguish between 254 and 365 nm wavelengths. Their alignment is advantageous for polarized UV light detection; we have measured a polarization ratio of photoconductance (σ) of 0.3. Lastly, we show that the nanowires can detect NO₂ at a concentration of 0.2 ppb, making them a scalable, ultrasensitive gas sensing technology. Aligned SnO₂ nanowires offer a straightforward method to fabricate scalable SnO₂ nanodevices for a variety of future electronic applications

Nanofilament Formation and Regeneration During Cu/Al₂O₃ Resistive Memory Switching

Conductive bridge random access memory (CBRAM) is a leading candidate to supersede flash memory, but poor understanding of its switching process impedes widespread implementation. The underlying physics and basic, unresolved issues such as the connecting filament’s growth direction can be revealed with direct imaging, but the nanoscale target region is completely encased and thus difficult to access with real-time, high-resolution probes. In Pt/Al₂O₃/Cu CBRAM devices with a realistic topology, we find that the filament grows backward toward the source metal electrode. This observation, consistent over many cycles in different devices, corroborates the standard electrochemical metallization model of CBRAM operation. Time-resolved scanning transmission electron microscopy (STEM) reveals distinct nucleation-limited and potential-limited no-growth periods occurring before and after a connection is made, respectively. The subfemtoampere ionic currents visualized move some thousands of atoms during a switch and lag the nanoampere electronic currents

<i>In Situ</i> Transmission Electron Microscopy of Lead Dendrites and Lead Ions in Aqueous Solution

An ideal technique for observing nanoscale assembly would provide atomic-resolution images of both the products and the reactants in real time. Using a transmission electron microscope we image <i>in situ</i> the electrochemical deposition of lead from an aqueous solution of lead(II) nitrate. Both the lead deposits and the local Pb²⁺ concentration can be visualized. Depending on the rate of potential change and the potential history, lead deposits on the cathode in a structurally compact layer or in dendrites. In both cases the deposits can be removed and the process repeated. Asperities that persist through many plating and stripping cycles consistently nucleate larger dendrites. Quantitative digital image analysis reveals excellent correlation between changes in the Pb²⁺ concentration, the rate of lead deposition, and the current passed by the electrochemical cell. Real-time electron microscopy of dendritic growth dynamics and the associated local ionic concentrations can provide new insight into the functional electrochemistry of batteries and related energy storage technologies