Control of surface functionalization of MXenes holds great potential, and in particular, may lead to tuning of magnetic and electronic order in the recently reported magnetic Cr2TiC2T
- Award ID(s):
- 1806147
- NSF-PAR ID:
- 10227641
- Date Published:
- Journal Name:
- Nano Letters
- ISSN:
- 1530-6984
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract x . Here, vacuum annealing experiments of Cr2TiC2Tx are reported with in situ electron energy loss spectroscopy and novel in situ Cr K‐edge extended energy loss fine structure analysis, which directly tracks the evolution of the MXene surface coordination environment. These in situ probes are accompanied by benchmarking synchrotron X‐ray absorption fine structure measurements and density functional theory calculations. With the etching method used here, the MXene has an initial termination chemistry of Cr2TiC2O1.3F0.8. Annealing to 600 °C results in the complete loss of F, but O termination is thermally stable up to (at least) 700 °C. These findings demonstrate thermal control of F termination in Cr2TiC2Tx and offer a first step toward termination engineering this MXene for magnetic applications. Moreover, this work demonstrates high energy electron spectroscopy as a powerful approach for surface characterization in 2D materials. -
more » « less
Abstract In quantum materials, macroscopic behavior is governed in nontrivial ways by quantum phenomena. This is usually achieved by exquisite control over atomic positions in crystalline solids. Here, it is demonstrated that the use of disordered glassy materials provides unique opportunities to tailor quantum material properties. By borrowing ideas from single‐molecule spectroscopy, single delocalized π‐electron dye systems are isolated in relatively rigid ultrasmall (<10 nm diameter) amorphous silica nanoparticles. It is demonstrated that chemically tuning the local amorphous silica environment around the dye over a range of compositions enables exquisite control over dye quantum behavior, leading to efficient probes for photodynamic therapy (PDT) and stochastic optical reconstruction microscopy (STORM). The results suggest that efficient fine‐tuning of light‐induced quantum behavior mediated via effects like spin‐orbit coupling can be effectively achieved by systematically varying averaged local environments in glassy amorphous materials as opposed to tailoring well‐defined neighboring atomic lattice positions in crystalline solids. The resulting nanoprobes exhibit features proven to enable clinical translation.
-
more » « less
Abstract Topological spin/polarization structures in ferroic materials continue to draw great attention as a result of their fascinating physical behaviors and promising applications in the field of high‐density nonvolatile memories as well as future energy‐efficient nanoelectronic and spintronic devices. Such developments have been made, in part, based on recent advances in theoretical calculations, the synthesis of high‐quality thin films, and the characterization of their emergent phenomena and exotic phases. Herein, progress over the last decade in the study of topological structures in ferroic thin films and heterostructures is explored, including the observation of topological structures and control of their structures and emergent physical phenomena through epitaxial strain, layer thickness, electric, magnetic fields, etc. First, the evolution of topological spin structures (e.g., magnetic skyrmions) and associated functionalities (e.g., topological Hall effect) in magnetic thin films and heterostructures is discussed. Then, the exotic polar topologies (e.g., domain walls, closure domains, polar vortices, bubble domains, and polar skyrmions) and their emergent physical properties in ferroelectric oxide films and heterostructures are explored. Finally, a brief overview and prospectus of how the field may evolve in the coming years is provided.
-
more » « less
Abstract Van der Waals (vdW) heterostructures that pair materials with diverse properties enable various quantum phenomena. However, the direct growth of vdW heterostructures is challenging. Modification of the surface layer of quantum materials to introduce new properties is an alternative process akin to solid state reaction. Here, vapor deposited transition metals (TMs), Cr and Mn, are reacted with Bi2Se3with the goal to transform the surface layer to XBi2Se4(X = Cr, Mn). Experiments and ab initio MD simulations demonstrate that the TMs have a high selenium affinity driving Se diffusion toward the TM. For monolayer Cr, the surface Bi2Se3is reduced to Bi2‐layer and a stable (pseudo) 2D Cr1+δSe2layer is formed. In contrast, monolayer Mn can transform upon mild annealing into MnBi2Se4. This phase only forms for a precise amount of initial Mn deposition. Sub‐monolayer amounts dissolve into the bulk, and multilayers form stable MnSe adlayers. This study highlights the delicate energy balance between adlayers and desired surface modified layers that governs the interface reactions and that the formation of stable adlayers can prevent the reaction with the substrate. The success of obtaining MnBi2Se4points toward an approach for the engineering of other multicomponent vdW materials by surface reactions.
-
more » « less
Abstract The ability to dynamically reconfigure superlattices in response to external stimuli is an intriguing prospect for programmable DNA‐guided nanoparticle (NP) assemblies, which promises the realization of “smart” materials with dynamically adjustable interparticle spacing and real‐time tunable properties. Existing in situ probes of reconfiguration processes have been limited mostly to reciprocal space methods, which can follow larger ordered ensembles but do not provide access to real‐space pathways and dynamics. Here, in situ atomic force microscopy is used to investigate DNA‐linked NP assemblies and their response to external stimuli, specifically the contraction and expansion of on‐surface self‐assembled monolayer superlattices upon reversible DNA condensation induced by ethanol. In situ microscopy allows observation and quantification of key processes in solution, e.g., lattice parameter changes, defects, and monomer displacements in small groups of NPs. The analysis of imaging data uncovers important boundary conditions due to DNA bonding of NP superlattices to a substrate. Tension in the NP–substrate DNA bonds, which can elastically extend, break, and re‐form during contraction/expansion cycles, counteracts the changes in lattice parameter and causes hysteresis in the response of the system. The results provide insight into the behavior of supported DNA‐linked NP superlattices and establish a foundation for designing and probing tunable nanocrystal‐based materials in solution.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.nanolett.0c04818
