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Dielectric Engineering for Manipulating Exciton Transport in Semiconductor Monolayers
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Understanding and Manipulating Helical Nanofilaments in Binary Systems with Achiral Dopants
Here, in this paper, we report the relationship between helical pitch of the helical nanofilament (HNF) phase formed by bent-core molecule NOBOW and the concentration of achiral dopants 5CB and octane, using linearly polarized resonant soft X-ray scattering (RSoXS). Utilizing theory-based simulation, which fits well with the experiments, the molecular helices in the filament were probed and the superstructure of helical 5CB directed by groove of HNFs was observed. Quantitative pitch determination with RSoXS reveals that helical pitch variation is related to 5CB concentration with no temperature dependence. Doping rodlike immiscible 5CB led to a pitch shortening of up to 30%, which was attributed to a change in interfacial tension. By shedding light not only on phase behavior of binary systems but also enabling control over pitch length, our work may benefit various applications of HNF-containing binary systems, including optical rotation devices, circularly polarized light emitters, and chirality transfer agents.
Light-Driven Ultrafast Polarization Manipulation in a Relaxor Ferroelectric
Relaxor ferroelectrics have been intensely studied for decades based on their unique electromechanical responses which arise from local structural heterogeneity involving polar nanoregions or domains. Here, we report first studies of the ultrafast dynamics and reconfigurability of the polarization in freestanding films of the prototypical relaxor 0.68PbMg 1/3 Nb 2/3 O 3 -0.32PbTiO 3 (PMN-0.32PT) by probing its atomic-scale response via femtosecond-resolution, electron-scattering approaches. By combining these structural measurements with dynamic phase-field simulations, we show that femtosecond light pulses drive a change in both the magnitude and direction of the polarization vector within polar nanodomains on few-picosecond time scales. This study defines new opportunities for dynamic reconfigurable control of the polarization in nanoscale relaxor ferroelectrics.
Manipulating Interlayer Excitons for Near-Infrared Quantum Light Generation
Interlayer excitons (IXs) formed at the interface of van der Waals materials possess various novel properties. In parallel development, strain engineering has emerged as an effective means for creating 2D quantum emitters. Here, exploring the intersection of these two exciting areas, we use MoS2/WSe2 heterostructure as a model system and demonstrate how strain, defects, and layering can be utilized to create defect-bound IXs capable of bright, robust, and tunable quantum light emission in the technologically important near-infrared spectral range. Our work presents defect-bound IXs as a promising platform for pushing the performance of 2D quantum emitters beyond their current limitations.
Nanorod Pair Complexes Manipulated via Magnetic Casimir Forces
Here, we demonstrate a route to modulate Casmir–Lifshitz interactions between anisotropic nanoparticles and magnetic fluids. By semiclassical quantum electrodynamics, we study ground state dispersion forces for cylindrical dielectric nanorods made of polystyrene (PS) and zinc oxide (ZnO) embedded in toluene-based host media with gold-coated magnetite nanoparticles and also predict magnetic contributions to the fully retarded excited state interaction. The variation in magnetic permeability enables tuning between repulsive and attractive interactions, and measurable magnetic Casimir traps are predicted between a pair of ZnO–PS nanoparticles whose equilibrium position can be modulated over an order of magnitude with a small variation in the size of the magnetite nanoparticle. This provides an alternative magnetic Casimir-effect pathway to reversibly tune quantum electromagnetic forces at the nanoscale for the assembly and enhancement of colloidal stability.
Dynamic Manipulation of DNA-Programmed Crystals Embedded in a Polyelectrolyte Hydrogel
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Selected Area Manipulation of MoS 2 via Focused Electron Beam-Induced Etching for Nanoscale Device Editing
Here we demonstrate direct-write patterning of single and multilayer MoS 2 via a focused electron beam-induced etching (FEBIE) process mediated with the XeF 2 precursor. MoS 2 etching is performed at various currents, areal doses, on different substrates, and characterized using scanning electron and atomic force microscopies as well as Raman and photoluminescence spectroscopies. Scanning transmission electron microscopy reveals a sub-40 nm etching resolution and the progression of point defects and lateral etching of the consequent unsaturated bonds. The results confirm that the electron beam-induced etching process is minimally invasive to the underlying material in comparison to ion beam techniques, which damage the subsurface material. Single-layer MoS 2 field-effect transistors are fabricated, and device characteristics are compared for channels that are edited via the selected area etching process. The source–drain current at constant gate and source–drain voltage scale linearly with the edited channel width. Moreover, the mobility of the narrowest channel width decreases, suggesting that backscattered and secondary electrons collaterally affect the periphery of the removed area. Focused electron beam doses on single-layer transistors below the etching threshold were also explored as a means to modify/thin the channel layer. The FEBIE exposures showed demonstrative effects via the transistor transfer characteristics, photoluminescence spectroscopy, and Raman spectroscopy. While strategies to minimize backscattered and secondary electron interactions outside of the scanned regions require further investigation, here, we show that FEBIE is a viable approach for selective nanoscale editing of MoS 2 devices.
Dimolybdenum Paddlewheel Complexes with Cation Binding Sites as Electrolyte Additives to Manipulate the Solid-Electrolyte Interphase at Lithium Metal Anodes
The use of electrolyte additives at millimolar loadings to control the surface chemistry of lithium metal anodes (LMAs) is a leading strategy to improve lithium metal batteries and promote electrosynthetic reactions. Whereas previous studies employed either inorganic or organic additives, in this study, we report the first organometallic additive, Mo 2 (mea) 4 [1, mea = 2-(2-methoxyethoxy)acetate], a dimolybdenum paddlewheel complex that is stable under Li plating conditions and features cation binding sites in the second coordination sphere that promote reversible Li + coordination. Binding of Li + ions to 1 induces immobilization of cationically charged aggregates (or products thereof) into the solid electrolyte interphase (SEI), imparting multiple beneficial functions. The modified SEI was found to protect the LMA against parasitic side reactions, produce modest but measurable improvements to Li plating properties (e.g., overpotential, surface structure, and Coulombic efficiency), and improve interfacial charge transport properties. Furthermore, the most notable benefit to battery cycling performance appears in calendar aging tests, which show that the presence of the additive protects the LMA from parasitic side reactions that would otherwise decrease overall cell cycling efficiency over time. Collectively, these data disclose a tactic for designing electrolyte additives using principles of organometallic synthesis.
Doping of Cr in Graphene Using Electron Beam Manipulation for Functional Defect Engineering
Chromium atoms in graphene have been proposed to exhibit magnetic moments and spin-selective conducting states depending on the local bonding geometry within the graphene structure, which could lead to interesting applications in spintronics. Despite this interest, there are few direct experimental reports of Cr dopants in graphene even though it is theorized to be stable. Here, we demonstrate the introduction of single Cr dopant atoms into the graphene lattice and onto graphene edges through the controlled use of a focused electron beam in a scanning transmission electron microscope. Here, we show local control of doping locations, and when coupled with targeted in situ milling during scanning of the e-beam, these strategies demonstrate an important component of the fabrication of tailored nanostructured devices in the electron microscope. The approach is validated with first-principles calculations to understand synthesis pathways during fabrication and reveal the energetics and local properties of Cr atoms embedded in graphene; for example, Cr doping can convert graphene into a magnetic and semiconducting material, which suggests Cr-doped graphene can be used as a building block for potential electronic devices and a means to construct them.
Manipulating Coordination Structures of Mixed-Valence Copper Single Atoms on 1T-MoS[subscript 2] for
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Interfacial Water Manipulation with Ionic Liquids for the Oxygen Reduction Reaction
The role that interfacial water plays in both promoting and inhibiting the electrochemical oxygen reduction reaction (ORR) remains somewhat unclear and controversial. Here, we use electroanalytical chemistry, spectroscopy, and microkinetic modeling to probe the impact of hydrophobic ionic liquid (IL) thin films on interfacial water structure and its role in promoting or inhibiting the ORR. Through the use of in situ ATR-SEIRAS, we find that the IL thin films limit the content of water at the interface and prevent the formation of hydrogen bond stabilized water organization. The impact of this exclusion of water on the promotion of the ORR is through the reduced coverage of OH ad spectator species. The decreased solvation of “active” OH ad species weakens its interaction with the catalyst surface, lowering the barrier to the last step in the ORR mechanism. This “destabilized” OH ad impact on ORR kinetics is confirmed through a microkinetic model. Furthermore, the results presented here highlight the mechanistic pathway through which hydrophobic ILs enhance ORR kinetics and point to pathways to both further improve this performance enhancement and the potential for integration of hydrophobic ILs into other technologically relevant elementary electrochemical reactions.
Dynamic Manipulation in Piezoresponse Force Microscopy: Creating Nonequilibrium Phases with Large Electromechanical Response
We discuss how domain walls and topological defects in ferroelectric materials have emerged as a powerful tool for functional electronic devices including memory and logic. Similarly, wall interactions and dynamics underpin a broad range of mesoscale phenomena ranging from giant electromechanical responses to memory effects. Exploring the functionalities of individual domain walls, their interactions, and controlled modifications of the domain structures is crucial for applications and fundamental physical studies. However, the dynamic nature of these features severely limits studies of their local physics since application of local biases or pressures in piezoresponse force microscopy induce wall displacement as a primary response. Here, we introduce an approach for the control and modification of domain structures based on automated experimentation, whereby real-space image-based feedback is used to control the tip bias during ferroelectric switching, allowing for modification routes conditioned on domain states under the tip. This automated experiment approach is demonstrated for the exploration of domain wall dynamics and creation of metastable phases with large electromechanical response.
Manipulating Excitonic Quantum Droplets in Two-Dimensional CdSe Nanoplatelets via Thickness and Core/Shell Morphology
Recently, photoexcitation of high-density 4 or 5 monolayer (ML) thick CdSe nanoplatelet films at temperatures below ~200K was observed to produce pump-intensitydependent, superlinear, progressively red-shifted light output due to amplified spontaneous emission (ASE) from polyexcitonic species, distinct from biexcitonic ASE. These polyexcitonic species comprise Coulombically bound multiexciton states, termed “quantum droplets”, that form when multiexciton binding energy exceeds thermal energy fluctuations. In this work, we investigate thinner samples as well as core/shell nanoplatelet films and find that the 3 ML sample supports quantum droplet ASE up to higher temperatures than the 4 or 5 ML whereas core/shell structures suppress this form of ASE even at very low sample temperatures despite observable biexcitonic ASE, suggesting that the reduced or repulsive Coulomb binding energy of multiple excitons suppresses quantum droplets. These findings help to add understanding of routes to harness quantum droplet optical nonlinearities.