Silicide formation and particle size growth in high temperature annealed, self- assembled

L1(0) FePt nanoparticle assemblies consisting of a few layers of 4-nm-diameter particles, are a potential data storage medium beyond 1 Tbit/in(2). However, annealing at temperatures &gt;500 degreesC is required to form the high anisotropy L1(0) phase. Recent studies have shown a substantial drop in magnetization for T-anneal&gt;650 degreesC. We show that this reduction in magnetization is due to silicide formation as a result of a chemical reaction with the native oxide or Si substrate. We also show that full L1(0) ordering is established only after annealing at 725 degreesC for 60 min and note that particle agglomeration occurs under these conditions. (C) 2004 American Institute of Physics.</p

Universal roles of hydrogen in electrochemical performance of graphene: high rate capacity and atomistic origins

Atomic hydrogen exists ubiquitously in graphene materials made by chemical methods. Yet determining the effect of hydrogen on the electrochemical performance of graphene remains a significant challenge. Here we report the experimental observations of high rate capacity in hydrogen-treated 3-dimensional (3D) graphene nanofoam electrodes for lithium ion batteries. Structural and electronic characterization suggests that defect sites and hydrogen play synergistic roles in disrupting sp(2) graphene to facilitate fast lithium transport and reversible surface binding, as evidenced by the fast charge-transfer kinetics and increased capacitive contribution in hydrogen-treated 3D graphene. In concert with experiments, multiscale calculations reveal that defect complexes in graphene are prerequisite for low-temperature hydrogenation, and that the hydrogenation of defective or functionalized sites at strained domain boundaries plays a beneficial role in improving rate capacity by opening gaps to facilitate easier Li penetration. Additional reversible capacity is provided by enhanced lithium binding near hydrogen-terminated edge sites. These findings provide qualitative insights in helping the design of graphene-based materials for high-power electrodes