Contact Geometry-Dependent Excitonic Emission in Mixed-Dimensional van der Waals Heterostructures.

Manipulation of excitonic emission in two-dimensional (2D) materials via the assembly of van der Waals (vdW) heterostructures unlocks numerous opportunities for engineering their photonic and optoelectronic properties. In this work, we introduce a category of mixed-dimensional vdW heterostructures, integrating 2D materials with one-dimensional (1D) semiconductor nanowires composed of vdW layers. This configuration induces spatially distinct localized excitonic emissions through a tailored interfacial heterolayer atomic arrangement.

Optimized Substrate Orientations for Highly Uniform Metal Halide Perovskite Film Deposition.

Uniform optoelectronic quality of metal halide perovskite (MHP) films is critical for scalable production in large-area applications, such as photovoltaics and displays. While vapor-based MHP film deposition is advantageous for this purpose, achieving film uniformity can be challenging due to uneven temperature distribution and precursor concentration over the substrate. Here, we propose optimized substrate orientations for the vapor-based fabrication of homogeneous MAPbI thin films, involving a PbI primary layer deposition and subsequent conversion using vaporized methylammonium iodide (MAI).

Photoimageable Organic Coating Bearing Cyclic Dithiocarbonate for a Multifunctional Surface.

We report the fabrication of photocross-linkable and surface-functionalizable polymeric thin films using reactive cyclic dithiocarbonate (DTC)-containing copolymers. The chemical functionalities of these material surfaces were precisely defined with light illumination. The DTC copolymers, namely, poly(dithiocarbonate methylene methacrylate--alkyl methacrylate)s, were synthesized via reversible addition-fragmentation chain transfer polymerization, and the reaction kinetics was thoroughly analyzed.

Colloidal Synthesis of MoSe/WSe Heterostructure Nanoflowers via Two-Step Growth.

The ability to control the active edge sites of transition metal dichalcogenides (TMDs) is crucial for modulating their chemical activity for various electrochemical applications, including hydrogen evolution reactions. In this study, we demonstrate a colloidal synthetic method to prepare core-shell-like heterostructures composed of MoSe and WSe via a two-step sequential growth. By overgrowing WSe on the surface of preexisting MoSe nanosheet edges, MoSe-core/WSe-shell heterostructures were successfully obtained.

In Situ Vapor-Phase Halide Exchange of Patterned Perovskite Thin Films.

Metal halide perovskites (MHPs) exhibit optoelectronic properties that are dependent on their ionic composition, and the feasible exploitation of these properties for device applications requires the ability to control the ionic composition integrated with the patterning process. Herein, the halide exchange process of MHP thin films directly combined with the patterning process via a vapor transport method is demonstrated. Specifically, the patterned arrays of CH NH PbBr (MAPbBr ) are obtained by stepwise conversion from polymer-templated PbI thin films to CH NH PbI (MAPbI ), followed by halide exchange via precursor switching from CH NH I to CH NH Br.

Orientation-Dependent Conversion of VLS-Grown Lead Iodide Nanowires into Organic-Inorganic Hybrid Perovskites.

In this study, we demonstrate Sn-assisted vapor-liquid-solid (VLS) growth of lead iodide (PbI) nanowires with van der Waals layered crystal structure and subsequent vapor-phase conversion into methylammonium lead iodide (CHNHPbI) perovskites. Our systematic microscopic investigations confirmed that the VLS-grown PbI nanowires display two major growth orientations of [0001] and [1¯21¯0], corresponding to the stacking configurations of PbI layers to the nanowire axis (transverse for [0001] vs. parallel for [1¯21¯0]).

Inherent Resistance of Seed-Mediated Grown MoSe Monolayers to Defect Formation.

Recent progress in the chemical vapor deposition technique toward growing large-area and single-crystalline two-dimensional (2D) transition metal dichalcogenides (TMDs) has resulted in an electronic/optoelectronic device performance that rivals that of their top-down counterparts, despite the extensive use of hydrogen, a common reducing agent that readily generates defects in TMDs. Herein, we report that 2D MoSe domains containing oxide seeds are resistant to hydrogen-induced defect generation. Specifically, we observed that the etching of the edges of seed-containing MoSe was significantly less than that of pristine MoSe, without apparent seed particles, under the same H annealing conditions.

VLS Homoepitaxy of Lead Iodide Nanowires for Hybrid Perovskite Conversion.

Controlled fabrication of lead halide-based perovskite (LHP) nanostructures provides a new methodology for exploiting the excellent optoelectronic properties of the material. Here, we report the vapor-liquid-solid (VLS) growth of a highly uniform and dense array of [0001]-oriented PbI nanowires using PbI thin film as the epitaxial substrate layer. We show that reducing the lattice mismatch of the van der Waals epitaxial PbI substrate layer is necessary to accommodate the aligned nanowire growth.

Hydrogen-assisted step-edge nucleation of MoSe monolayers on sapphire substrates.

The fabrication of large-area single crystalline monolayer transition metal dichalcogenides (TMDs) is essential for a range of electric and optoelectronic applications. Chemical vapor deposition (CVD) is a promising method to achieve this goal by employing orientation control or alignment along the crystalline lattice of the substrate such as sapphire. On the other hand, a fundamental understanding of the aligned-growth mechanism of TMDs is limited.

Direct Observation of Transient Surface Species during Ge Nanowire Growth and Their Influence on Growth Stability.

Surface adsorbates are well-established choreographers of material synthesis, but the presence and impact of these short-lived species on semiconductor nanowire growth are largely unknown. Here, we use infrared spectroscopy to directly observe surface adsorbates, hydrogen atoms and methyl groups, chemisorbed to the nanowire sidewall and show they are essential for the stable growth of Ge nanowires via the vapor-liquid-solid mechanism. We quantitatively determine the surface coverage of hydrogen atoms during nanowire growth by comparing ν(Ge-H) absorption bands from operando measurements (i.

Interplay between defect propagation and surface hydrogen in silicon nanowire kinking superstructures.

Semiconductor nanowire kinking superstructures, particularly those with long-range structural coherence, remain difficult to fabricate. Here, we combine high-resolution electron microscopy with operando infrared spectroscopy to show why this is the case for Si nanowires and, in doing so, reveal the interplay between defect propagation and surface chemistry during ⟨211⟩ → ⟨111⟩ and ⟨211⟩ → ⟨211⟩ kinking. Our experiments show that adsorbed hydrogen atoms are responsible for selecting ⟨211⟩-oriented growth and indicate that a twin boundary imparts structural coherence.

Sidewall morphology-dependent formation of multiple twins in Si nanowires.

Precise placement of twin boundaries and stacking faults promises new opportunities to fundamentally manipulate the optical, electrical, and thermal properties of semiconductor nanowires. Here we report on the appearance of consecutive twin boundaries in Si nanowires and show that sidewall morphology governs their spacing. Detailed electron microscopy analysis reveals that thin {111} sidewall facets, which elongate following the first twin boundary (TB1), are responsible for deforming the triple-phase line and favoring the formation of the second twin boundary (TB2).

Rational defect introduction in silicon nanowires.

The controlled introduction of planar defects, particularly twin boundaries and stacking faults, in group IV nanowires remains challenging despite the prevalence of these structural features in other nanowire systems (e.g., II-VI and III-V).

Tunable mid-infrared localized surface plasmon resonances in silicon nanowires.

We observe and systematically tune an intense mid-infrared absorption mode that results from phosphorus doping in silicon nanowires synthesized via the vapor-liquid-solid technique. The angle- and shape-dependence of this spectral feature, as determined via in-situ transmission infrared spectroscopy, supports its assignment as a longitudinal localized surface plasmon resonance (LSPR). Modulation of resonant frequency (740-1620 cm(-1)) is accomplished by varying nanowire length (135-1160 nm).

Controlling silicon nanowire growth direction via surface chemistry.

We report on the first in situ chemical investigation of vapor-liquid-solid semiconductor nanowire growth and reveal the important, and previously unrecognized, role of transient surface chemistry near the triple-phase line. Real-time infrared spectroscopy measurements coupled with postgrowth electron microscopy demonstrate that covalently bonded hydrogen atoms are responsible for the (left angle bracket 111 right angle bracket) to (left angle bracket 112 right angle bracket) growth orientation transition commonly observed during Si nanowire growth. Our findings provide insight into the root cause of this well-known nanowire growth phenomenon and open a new route to rationally engineer the crystal structure of these nanoscale semi-conductors.