Facet-selective Growth Research Articles

Facet-selective growth of MOF-on-MOF heterostructures enables etching-free synthesis of highly-open Co/N-doped carbon nanoframes for efficient catalysis

Facet-selective growth of MOF-on-MOF heterostructures enables etching-free synthesis of highly-open Co/N-doped carbon nanoframes for efficient catalysis

Single-Crystalline Mesoporous Palladium and Palladium-Copper Nanocubes for Highly Efficient Electrochemical CO 2 Reduction

Single-Crystalline Mesoporous Palladium and Palladium-Copper Nanocubes for Highly Efficient Electrochemical CO ₂ Reduction

Seed shape-controlled, facet-selective growth of superspiky gold nanocrystals for biosensing applications

Seed shape-controlled synthesis of superspiky Au nanocrystals is reported using different shaped Au seeds, showing excellent plasmonic sensing and surface-enhanced Raman scattering sensing performances.

Crystal Facet Engineering of CoPt Quantum Dots for Diverse Colloidal Heterostructures.

Precise control of crystal orientation, and specifically the exposed surface, is critical for the engineering of heterostructures. Here, using CoPt as a model system, we explore the energetics to expose suitable facets to promote the required heterostructure formation. Different heterostructures are grown ranging from core/shell structure, diffused interface, dumbbell structured dimers, and embedded island structures wherein these hybrids are fabricated via micro/macrolevel facet-selective growth. The reaction conditions used to achieve such diversity starting from the same seed offer insights into the growth mechanisms of these heterostructures. Such a microscopic understanding of surface chemistry paves the way for the design of new heterostructures with exciting properties.

Facet-Selective Epitaxial Growth of δ-Bi2O3 on ZnO Nanowires

Integration of ZnO nanowires with Bi2O3 coating layers can modify their physicochemical properties and efficiently improve the performance of the resulting nanostructured composites for specific applications. The interfacial structures often control the properties of such nanocomposite systems. We report a novel approach to achieving selective epitaxial growth of δ-Bi2O3 layers onto the {11–20} nanoscale facets of ZnO nanowires. By detailed atomic scale characterization of the surfaces and interfaces of the Bi2O3/ZnO nanocomposites we proposed that growth of the δ-Bi2O3 species on ZnO {11–20} surfaces follows the Stranski–Krastanov mechanism with an epitaxial relationship of ZnO [10–10] (11–20)∥δ-Bi2O3 [001] (100). An atomic model is proposed to explain the epitaxial relationship, the interfacial atomic structure, and the facet-selective growth.

Promotion of the halide effect in the formation of shaped metal nanocrystals via a hybrid cationic, polymeric stabilizer: Octahedra, cubes, and anisotropic growth

To promote the effect of halide ions (Cl-, Br-, and I-) in facet-selective growth of {111} and {100} of shaped metal nanocrystals, we utilize PDADMAC, a hybrid cationic, polymeric stabilizer. SERS and synthesis experiments provide evidence supporting that the higher amount of PDADMA+ at surfaces promotes the local adsorption of halides, allowing the creation of Pd cubes, octahedra, and cuboctopods.

Facet-Selective Epitaxy of Compound Semiconductors on Faceted Silicon Nanowires.

Integration of compound semiconductors with silicon (Si) has been a long-standing goal for the semiconductor industry, as direct band gap compound semiconductors offer, for example, attractive photonic properties not possible with Si devices. However, mismatches in lattice constant, thermal expansion coefficient, and polarity between Si and compound semiconductors render growth of epitaxial heterostructures challenging. Nanowires (NWs) are a promising platform for the integration of Si and compound semiconductors since their limited surface area can alleviate such material mismatch issues. Here, we demonstrate facet-selective growth of cadmium sulfide (CdS) on Si NWs. Aberration-corrected transmission electron microscopy analysis shows that crystalline CdS is grown epitaxially on the {111} and {110} surface facets of the Si NWs but that the Si{113} facets remain bare. Further analysis of CdS on Si NWs grown at higher deposition rates to yield a conformal shell reveals a thin oxide layer on the Si{113} facet. This observation and control experiments suggest that facet-selective growth is enabled by the formation of an oxide, which prevents subsequent shell growth on the Si{113} NW facets. Further studies of facet-selective epitaxial growth of CdS shells on micro-to-mesoscale wires, which allows tuning of the lateral width of the compound semiconductor layer without lithographic patterning, and InP shell growth on Si NWs demonstrate the generality of our growth technique. In addition, photoluminescence imaging and spectroscopy show that the epitaxial shells display strong and clean band edge emission, confirming their high photonic quality, and thus suggesting that facet-selective epitaxy on NW substrates represents a promising route to integration of compound semiconductors on Si.

Shape-directional growth of Pt and Pd nanoparticles.

The design and synthesis of shape-directed nanoscale noble metal particles have attracted much attention due to their enhanced catalytic properties and the opportunities to study fundamental aspects of nanoscale systems. As such, numerous methods have been developed to synthesize crystals with tunable shapes, sizes, and facets by adding foreign species that promote or restrict growth on specific sites. Many hypotheses regarding how and why certain species direct growth have been put forward, however there has been no consensus on a unifying mechanism of nanocrystal growth. Herein, we develop and demonstrate the capabilities of a mathematical growth model for predicting metal nanoparticle shapes by studying a well known procedure that employs AgNO3 to produce {111} faceted Pt nanocrystals. The insight gained about the role of auxiliary species is then utilized to predict the shape of Pd nanocrystals and to corroborate other shape-directing syntheses reported in literature. The fundamental understanding obtained herein by combining modeling with experimentation is a step toward computationally guided syntheses and, in principle, applicable to predictive design of the growth of crystalline solids at all length scales (nano to bulk).

Fabrication of Regular ZnO/TiO2 Heterojunctions with Enhanced Photocatalytic Properties

Facet-selective growth: Regular ZnO/TiO2 heterojunctions have been successfully synthesized using a facile hydrothermal technique (see figure). Due to the interfacial lattice matching, wurtzite ZnO can only grow on the eight {101} facets of the anatase TiO2 single crystals, while the other two {001} facets are untouched. The as-prepared regular ZnO/TiO2 heterojunctions exhibited enhanced photocatalytic generation of (·)OH radicals and enhanced photodegradation of methyl orange when irradiated with UV light.

Facet-selective growth of Cu–Cu2O heterogeneous architectures

We have demonstrated a facile protocol for the synthesis of facet-selective growth of low-cost metal Cu nanoparticles on {111} facets of polyhedral 26-facet Cu2O architectures. The novel Cu–Cu2O heterogeneous architectures show better adsorption and photodegradation of methyl orange than those of the original Cu2O architectures.

Facet-selective growth and optical properties of CdTe/CdSe tetrapod-shaped nanocrystal heterostructures

Abstract

Facet-Selective Epitaxial Growth of Heterogeneous Nanostructures of Semiconductor and Metal: ZnO Nanorods on Ag Nanocrystals

We demonstrate a new approach for synthesizing Ag-ZnO heterogeneous nanostructures in which single-crystalline ZnO nanorods were selectively grown on {111} rather than {100} facets of single-crystalline Ag truncated nanocubes. We have identified the fine structure of the Ag-ZnO heterostructures and proposed a mechanism indicating that structure match plays a critically important role in this type of facet-selective growth. These heterogeneous nanostructures are of special interest and have potential applications in electrical contacts, functional devices, biological sensors, and catalysis.

Facet-Selective Growth Rates of Doped Diamond Crystals Prepared by Microwave Plasma-Assisted Chemical Vapor Deposition.

In order to produce a highly oriented diamond layer on a silicon (100) substrate, reaction conditions should be controlled so as to achieve an initial selective growth on the (111) face, followed by the (100) face. In the present study, cubo-octahedral diamond crystals were formed by the microwave plasma-assisted chemical vapor deposition of methane and hydrogen on a silicon (100) wafer. Trimethylboron and dimethylsulfur as the boron or sulfur sources, respectively, were added to the gas phase and diamond was homoepitaxially deposited on the {100} and {111} of the crystals. The growth rate determined from geometrical changes in the crystals, was affected by the type of diamond faces used, the boron to carbon (B/C) and sulfur to carbon (S/C) ratios in the gas phase, the methane concentration, and the substrate temperature. The growth rate decreased with increasing B/C and S/C ratios, but the relative growth rate of [100] to [111] remained nearly independent of the dopant concentration. The [111] preferred growth was realized under lower methane concentrations and higher substrate temperatures.

1.3-μm strained MQW-DFB lasers with extremely low intermodulation distortion for high-speed analog transmission

The intermodulation distortion and the noise characteristics of 1.3-/spl mu/m strained multiquantum-well distributed feedback (MQW-DFB) lasers have been investigated under the modulation frequency of 1.9 GHz in connection with the device structure. In this study, a strained MQW with strain-compensated layers has been introduced in order to increase in the quantum-well number and well width. This causes increase in the differential gain, resulting in increase of the resonance frequency (FR). The FR as high as 5.1 GHz/mW/sup 1/2/ has been obtained which is in good agreement with the theoretical calculation. In addition to the strained MQW structure, a new buried heterostructure entirely grown by MOCVD, named as FSBH (facet selective growth buried heterostructure), has been developed to minimize the leakage current which degrades L-I characteristics at high bias current causing the high distortion. The third-order-intermodulation distortion (IMD3) of -88 dBc and relative intensity noise (RIN) of -152 dB/Hz have been obtained under a two-tone test at 1.9 GHz. This suggests that this newly developed laser is quite suitable for high-speed-subcarrier multiplexing transmission.