Albert L. Lipson

Seeding Atomic Layer Deposition of High-k Dielectrics on Epitaxial Graphene with Organic Self-Assembled Monolayers

The development of high-performance graphene-based nanoelectronics requires the integration of ultrathin and pinhole-free high-k dielectric films with graphene at the wafer scale. Here, we demonstrate that self-assembled monolayers of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) act as effective organic seeding layers for atomic layer deposition (ALD) of HfO(2) and Al(2)O(3) on epitaxial graphene on SiC(0001). The PTCDA is deposited via sublimation in ultrahigh vacuum and shown to be highly ordered with low defect density by molecular-resolution scanning tunneling microscopy. Whereas identical ALD conditions lead to incomplete and rough dielectric deposition on bare graphene, the chemical functionality provided by the PTCDA seeding layer yields highly uniform and conformal films. The morphology and chemistry of the dielectric films are characterized by atomic force microscopy, ellipsometry, cross-sectional scanning electron microscopy, and X-ray photoelectron spectroscopy, while high-resolution X-ray reflectivity measurements indicate that the underlying graphene remains intact following ALD. Using the PTCDA seeding layer, metal-oxide-graphene capacitors fabricated with a 3 nm Al(2)O(3) and 10 nm HfO(2) dielectric stack show high capacitance values of ∼700 nF/cm(2) and low leakage currents of ∼5 × 10(-9) A/cm(2) at 1 V applied bias. These results demonstrate the viability of sublimated organic self-assembled monolayers as seeding layers for high-k dielectric films in graphene-based nanoelectronics.

Nanoscale In Situ Characterization of Li‐ion Battery Electrochemistry Via Scanning Ion Conductance Microscopy

Scanning ion conductance microscopy imaging of battery electrodes, using the geometry shown in the figure, is a tool for in situ nanoscale mapping of surface topography and local ion current. Images of silicon and tin electrodes show that the combination of topography and ion current provides insight into the local electrochemical phenomena that govern the operation of lithium ion batteries.

Nanoporous templates and membranes formed by nanosphere lithography and aluminum anodization.

In recent years, ordered nanoporous anodized aluminum oxide (AAO) has emerged as an important template for parallel fabrication of nanostructures. For optimal performance in many applications, it is highly desirable to be able to independently control the width, height, and spacing of the pores in AAO. For instance, metallic films with holes templated by nanoporous AAO possess plasmonic properties that are related to the AAO pore spacing. Similarly, the diameter of palladium nanowires fabricated in AAO templates controls their sensitivity to hydrogen gas, and the sensor response time for palladium nanoparticles deposited into AAO is highly dependent on the pore depth. Pore diameter, length, and spacing are also expected to influence the performance of nanoporous membranes in applications such as biosensors, nanoscale filters, photovoltaics, and catalytic supports. AAO templates are typically fabricated through a two-step anodization process. In the first step, a disordered nanoporous alumina film is created following constant voltage anodization of aluminum. As the film grows, the pores self-order over a period of hours, leading to a hexagonally ordered arrangement at the subsurface growth front. When this initial alumina film is removed, the resulting aluminum surface possesses a hexagonally ordered arrangement of pits. These pits serve as porenucleation sites during the second anodization step, thus yielding a highly uniform and ordered nanoporous AAO film. This two-step procedure creates ordered nanoporous arrays in sulfuric, oxalic, malonic, and phosphoric acids at 25, 40, 130, and 195 V with interpore spacings of 63, 100, 250, and 500 nm, respectively. By modifying the anodization solution and using voltages higher than those used to achieve self-ordering, additional interpore spacings have been

Phase-Controlled Electrochemical Activity of Epitaxial Mg-Spinel Thin Films.

We report an approach to control the reversible electrochemical activity (i.e., extraction/insertion) of Mg(2+) in a cathode host through the use of phase-pure epitaxially stabilized thin film structures. The epitaxially stabilized MgMn2O4 (MMO) thin films in the distinct tetragonal and cubic phases are shown to exhibit dramatically different properties (in a nonaqueous electrolyte, Mg(TFSI)2 in propylene carbonate): tetragonal MMO shows negligible activity while the cubic MMO (normally found as polymorph at high temperature or high pressure) exhibits reversible Mg(2+) activity with associated changes in film structure and Mn oxidation state. These results demonstrate a novel strategy for identifying the factors that control multivalent cation mobility in next-generation battery materials.