Aligned MoO₂/MoS₂ and MoO₂/MoTe₂ 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 MoO₂/MoS₂ and MoO₂/MoTe₂ 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 MoO₂/MoS₂ nanoplates are composed of co-localized MoO₂ and MoS₂, and transmission electron microscopy confirms that the nanoplates feature MoO₂ cores with 2D MoS₂ coatings. Locked-coupled X-ray diffraction shows that the interfacial planes of the MoO₂ 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