4 research outputs found
Aligned MoO<sub>2</sub>/MoS<sub>2</sub> and MoO<sub>2</sub>/MoTe<sub>2</sub> Freestanding Core/Shell Nanoplates Driven by Surface Interactions
Controlling
the growth of two-dimensional (2D) transition metal
dichalcogenides (TMDCs) is an important step toward utilizing these
materials for either electronics or catalysis. Here, we report a new
surface-templated growth method that enables the fabrication of MoO<sub>2</sub>/MoS<sub>2</sub> and MoO<sub>2</sub>/MoTe<sub>2</sub> core/shell
nanoplates epitaxially aligned on (0001)-oriented 4H-silicon carbide
and sapphire substrates. These heterostructures are characterized
by a variety of techniques to identify the chemical and structural
nature of the interface. Scanning electron microscopy shows that the
nanoplates feature 3-fold symmetry indicative of epitaxial growth.
Raman spectroscopy indicates that the MoO<sub>2</sub>/MoS<sub>2</sub> nanoplates are composed of co-localized MoO<sub>2</sub> and MoS<sub>2</sub>, and transmission electron microscopy confirms that the nanoplates
feature MoO<sub>2</sub> cores with 2D MoS<sub>2</sub> coatings. Locked-coupled
X-ray diffraction shows that the interfacial planes of the MoO<sub>2</sub> nanoplate cores belong to the {010} and {001} families. This
method may be further generalized to create novel nanostructured interfaces
with single-crystal substrates
Diameter Refinement of Semiconducting Arc Discharge Single-Walled Carbon Nanotubes via Density Gradient Ultracentrifugation
Arc
discharge single-walled carbon nanotubes (SWCNTs) possess superlative
optical and electronic properties that are of high interest for technologically
important applications including fiber optic communications, biomedical
imaging, and field-effect transistors. However, as-grown arc discharge
SWCNTs possess a mixture of metallic and semiconducting species in
addition to a wide diameter distribution (1.2 to 1.7 nm) that limit
their performance in devices. While previous postsynthetic sorting
efforts have achieved separation by electronic type and diameter refinement
for metallic arc discharge SWCNTs, tight diameter distributions of
semiconducting arc discharge SWCNTs have not yet been realized. Herein,
we present two advances in density gradient ultracentrifugation that
enable the isolation of high purity (>99%) semiconducting arc discharge
SWCNTs with narrow diameter distributions centered at ∼1.6
and ∼1.4 nm. The resulting diameter-refined populations of
semiconducting arc discharge SWCNTs possess monodisperse characteristics
that are well-suited for high-performance optical and electronic technologies
Templating Sub-10 nm Atomic Layer Deposited Oxide Nanostructures on Graphene via One-Dimensional Organic Self-Assembled Monolayers
Molecular-scale control over the
integration of disparate materials
on graphene is a critical step in the development of graphene-based
electronics and sensors. Here, we report that self-assembled monolayers
of 10,12-pentacosadiynoic acid (PCDA) on epitaxial graphene can be
used to template the reaction and directed growth of atomic layer
deposited (ALD) oxide nanostructures with sub-10 nm lateral resolution.
PCDA spontaneously assembles into well-ordered domains consisting
of one-dimensional molecular chains that coat the entire graphene
surface in a manner consistent with the symmetry of the underlying
graphene lattice. Subsequently, zinc oxide and alumina ALD precursors
are shown to preferentially react with the functional moieties of
PCDA, resulting in templated oxide nanostructures. The retention of
the original one-dimensional molecular ordering following ALD is dependent
on the chemical reaction pathway and the stability of the monolayer,
which can be enhanced via ultraviolet-induced molecular cross-linking
Graphene Oxide Interlayers for Robust, High-Efficiency Organic Photovoltaics
Organic photovoltaic (OPV) materials have recently garnered significant attention as enablers of high power conversion efficiency (PCE), low-cost, mechanically flexible solar cells. Nevertheless, further understanding-based materials developments will be required to achieve full commercial viability. In particular, the performance and durability of many current generation OPVs are limited by poorly understood interfacial phenomena. Careful analysis of typical OPV architectures reveals that the standard electron-blocking layer, poly-3,4-ethylenedioxy-thiophene:poly(styrene sulfonate) (PEDOT:PSS), is likely a major factor limiting the device durability and possibly performance. Here we report that a single layer of electronically tuned graphene oxide is an effective replacement for PEDOT:PSS and that it significantly enhances device durability while concurrently templating a performance-optimal active layer π-stacked face-on microstructure. Such OPVs based on graphene oxide exhibit PCEs as high as 7.5% while providing a 5× enhancement in thermal aging lifetime and a 20× enhancement in humid ambient lifetime versus analogous PEDOT:PSS-based devices