2 research outputs found
Thickness-Dependent Hydrophobicity of Epitaxial Graphene
This article addresses the much debated question whether the degree of hydrophobicity of single-layer graphene (1LG) is different from that of double-layer graphene (2LG). Knowledge of the water affinity of graphene and its spatial variations is critically important as it can affect the graphene properties as well as the performance of graphene devices exposed to humidity. By employing chemical force microscopy with a probe rendered hydrophobic by functionalization with octadecyltrichlorosilane (OTS), the adhesion force between the probe and epitaxial graphene on SiC has been measured in deionized water. Owing to the hydrophobic attraction, a larger adhesion force was measured on 2LG Bernal-stacked domains of graphene surfaces, thus showing that 2LG is more hydrophobic than 1LG. Identification of 1LG and 2LG domains was achieved through Kelvin probe force microscopy and Raman spectral mapping. Approximate values of the adhesion force per OTS molecule have been calculated through contact area analysis. Furthermore, the contrast of friction force images measured in contact mode was reversed to the 1LG/2LG adhesion contrast, and its origin was discussed in terms of the likely water depletion over hydrophobic domains as well as deformation in the contact area between the atomic force microscope tip and 1LG
Confined Crystals of the Smallest Phase-Change Material
The demand for high-density memory
in tandem with limitations imposed
by the minimum feature size of current storage devices has created
a need for new materials that can store information in smaller volumes
than currently possible. Successfully employed in commercial optical
data storage products, phase-change materials, that can reversibly
and rapidly change from an amorphous phase to a crystalline phase
when subject to heating or cooling have been identified for the development
of the next generation electronic memories. There are limitations
to the miniaturization of these devices due to current synthesis and
theoretical considerations that place a lower limit of 2 nm on the
minimum bit size, below which the material does not transform in the
structural phase. We show here that by using carbon nanotubes of less
than 2 nm diameter as templates phase-change nanowires confined to
their smallest conceivable scale are obtained. Contrary to previous
experimental evidence and theoretical expectations, the nanowires
are found to crystallize at this scale and display amorphous-to-crystalline
phase changes, fulfilling an important prerequisite of a memory element.
We show evidence for the smallest phase-change material, extending
thus the size limit to explore phase-change memory devices at extreme
scales