An official website of the United States government
Perovskite SrIrO3 films and its heterostructures are very promising, yet less researched, avenues to explore interesting physics originating from the interplay between strong spin–orbit coupling and electron correlations. Elemental iridium is a commonly used source for molecular beam epitaxy (MBE) synthesis of SrIrO3 films. However, elemental iridium is extremely difficult to oxidize and evaporate while maintaining an ultra-high vacuum and a long mean free path. Here, we calculated a thermodynamic phase diagram to highlight these synthesis challenges for phase-pure SrIrO3 and other iridium-based oxides. We addressed these challenges using a novel solid-source metal-organic MBE approach that rests on the idea of modifying the metal-source chemistry. Phase-pure, single-crystalline, coherent, epitaxial (001)pc SrIrO3 films on (001) SrTiO3 substrate were grown. Films demonstrated semi-metallic behavior, Kondo scattering, and weak antilocalization. Our synthesis approach has the potential to facilitate research involving iridate heterostructures by enabling their atomically precise syntheses.
more »
« less
Synergistic roles of vapor- and liquid-phase epitaxy in the seed-mediated synthesis of substrate-based noble metal nanostructures
Colloidal growth modes reliant on the replication of the crystalline character of a preexisting seed through homoepitaxial or heteroepitaxial depositions have enriched both the architectural diversity and functionality of noble metal nanostructures. Equivalent syntheses, when practiced on seeds formed on a crystalline substrate, must reconcile with the fact that the substrate enters the syntheses as a chemically distinct bulk-scale component that has the potential to impose its own epitaxial influences. Herein, we provide an understanding of the formation of epitaxial interfaces within the context of a hybrid growth mode that sees substrate-based seeds fabricated at high temperatures in the vapor phase on single-crystal oxide substrates and then exposed to a low-temperature liquid-phase synthesis yielding highly faceted nanostructures with a single-crystal character. Using two representative syntheses in which gold nanoplates and silver–platinum core–shell structures are formed, it is shown that the hybrid system behaves unconventionally in terms of epitaxy in that the substrate imposes an epitaxial relationship on the seed but remains relatively inactive as the metal seed imposes an epitaxial relationship on the growing nanostructure. With epitaxy transduced from substrate to seed to nanostructure through what is, in essence, a relay system, all of the nanostructures formed in a given synthesis end up with the same crystallographic orientation relative to the underlying substrate. This work advances the use of substrate-induced epitaxy as a synthetic control in the fabrication of on-chip devices reliant on the collective response of identically aligned nanostructures.
more »
« less
- Award ID(s):
- 1911991
- PAR ID:
- 10308734
- Date Published:
- Journal Name:
- Nanoscale
- ISSN:
- 2040-3364
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Great opportunities emerge not only in the generation of anisotropic plasmonic nanostructures but also in controlling their orientation relative to incident light. Herein, a stepwise seeded growth method is reported for the synthesis of rod‐shaped plasmon nanostructures which are vertically self‐aligned with respect to the surface of colloidal substrates. Anisotropic growth of metal nanostructure is achieved by depositing metal seeds onto the surface of colloidal substrates and then selectively passivating the seed surface to induce symmetry breaking in the subsequent seed‐mediated growth process. The versatility of this method is demonstrated by producing nanoparticle dimers and linear trimers of Au, Au–Ag, Au–Pd, and Au–Cu2O. Further, this unique method enables the automatic vertical alignment of the resulting plasmonic nanostructures to the surface of the colloidal substrate, thereby making it possible to design magnetic/plasmonic nanocomposites that allow the dynamic tuning of the plasmon excitation by controlling their orientation using an external magnetic field. The controlled anisotropic growth of colloidal plasmonic nanostructures and their dynamic modulation of plasmon excitation further allow them to be conveniently fixed in a thin polymer film with a well‐controlled orientation to display polarization‐dependent patterns that may find important applications in information encryption.more » « less
-
Flexible electronics and mechanically bendable devices based on Group III-N semiconductor materials are emerging; however, there are several challenges in manufacturing, such as cost reduction, device stability and flexibility, and device-performance improvement. To overcome these limitations, it is necessary to replace the brittle and expensive semiconductor wafers with single-crystalline flexible templates for a new-bandgap semiconductor platform. The substrates in the new concept of semiconductor materials have a hybrid structure consisting of a single-crystalline III-N thin film on a flexible metal tape substrate which provides a convenient and scalable roll-to-roll deposition process. We present a detailed study of a unique and simple direct epitaxial growth technique for crystallinity transformation to deliver single-crystalline GaN thin film with highly oriented grains along both a -axis and c -axis directions on a flexible and polycrystalline copper tape. A 2-dimensional (2D) graphene having the same atomic configuration as the (0001) basal plane of wurtzite structure is employed as a seed layer which plays a key role in following the III-N epitaxy growth. The DC reactive magnetron sputtering method is then applied to deposit an AlN layer under optimized conditions to achieve preferred-orientation growth. Finally, single-crystalline GaN layers (∼1 μm) are epitaxially grown using metal organic chemical vapor deposition (MOCVD) on the biaxially-textured buffer layer. The flexible single-crystalline GaN film obtained using this method provides a new way for a wide-bandgap semiconductor platform pursuing flexible, high-performance, and versatile device technology.more » « less
-
Materials with metastable phases can exhibit vastly different properties from their thermodynamically favored counterparts. Methods to synthesize metastable phases without the need for high-temperature or high-pressure conditions would facilitate their widespread use. We report on the electrochemical growth of microcrystals of bismuth selenide, Bi2Se3, in the metastable orthorhombic phase at room temperature in aqueous solution. Rather than direct epitaxy with the growth substrate, the spontaneous formation of a seed layer containing nanocrystals of cubic BiSe enforces the metastable phase. We first used single-crystal silicon substrates with a range of resistivities and different orientations to identify the conditions needed to produce the metastable phase. When the applied potential during electrochemical growth is positive of the reduction potential of Bi3+, an initial, Bi-rich seed layer forms. Electron microscopy imaging and diffraction reveal that the seed layer consists of nanocrystals of cubic BiSe embedded within an amorphous matrix of Bi and Se. Using density functional theory calculations, we show that epitaxial matching between cubic BiSe and orthorhombic Bi2Se3 can help stabilize the metastable orthorhombic phase over the thermodynamically stable rhombohedral phase. The spontaneous formation of the seed layer enables us to grow orthorhombic Bi2Se3 on a variety of substrates including single-crystal silicon with different orientations, polycrystalline fluorine-doped tin oxide, and polycrystalline gold. The ability to stabilize the metastable phase through room-temperature electrodeposition in aqueous solution without requiring a single-crystal substrate broadens the range of applications for this semiconductor in optoelectronic and electrochemical devices.more » « less
-
Substrate-immobilized noble metal nanoplates: a review of their synthesis, assembly, and applicationnull (Ed.)Noble metal nanoplates are a unique class of two-dimensional (2D) nanomaterials whose planar geometry serves as one of the most important nanoscale building blocks. Referred to by names such as nanoplates, nanodisks, nanoprisms, and nanotriangles, they offer a distinct and compelling set of physicochemical properties renowned for their plasmonic response and catalytic activity. When immobilized on substrates, these same structures are empowered with new capabilities triggered by synergistic interactions with their support and coupling phenomena activated when adjacent nanostructures are held in place with nanometer-scale spacings. In this review, we bring together an impressive literature dedicated to the synthesis, assembly, and application of substrate-immobilized noble metal nanoplates where we highlight the interplay between the nanostructures and their support as a means for deriving a distinct and diverse product. Methods for obtaining substrate-bound nanoplates rely on colloid-to-substrate transfers or syntheses occurring directly on the substrate-surface and span a wide range of techniques including chemisorption, solvent evaporation assembly, air–liquid interfacial assembly, substrate- and seed-mediated syntheses, electrochemical syntheses, vapor-phase depositions, DNA-assisted assembly, and capillary assembly. Collectively, these techniques realize nanoplate formations that are random, close-packed assemblies, periodic arrays, and three-dimensional superlattices. Nanoplate functionality is demonstrated in sensor applications with a broad range of analytes that include explosives, environmentally persistent pollutants, illicit drugs, and microRNA biomarkers for cancer and cardiovascular disease, with proof-of-concept demonstrations as active plasmonics, skin-mountable sensors, point-of-care diagnostics, and electrochemical reactors. Together, this work demonstrates substrate-immobilized nanoplates as a powerful platform for realizing photo- and chemically-active surfaces of technological relevance.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d1nr07019c
