| 1. |
- Ekström, Erik, et al.
(author)
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Microstructure control and property switching in stress-free van der Waals epitaxial VO2 films on mica
- 2023
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In: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 229
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Journal article (peer-reviewed)abstract
- Realizing stress-free inorganic epitaxial films on weakly bonding substrates is of importance for applications that require film transfer onto surfaces that do not seed epitaxy. Film-substrate bonding is usually weakened by harnessing natural van der Waals layers (e.g., graphene) on substrate surfaces, but this is difficult to achieve in non-layered materials. Here, we demonstrate van der Waals epitaxy of stress-free films of a non-layered material VO2 on mica. The films exhibit out-of-plane 010 texture with three in-plane orientations inherited from the crystallographic domains of the substrate. The lattice parameters are invariant with film thickness, indicating weak film-substrate bonding and complete interfacial stress relaxation. The out-of-plane domain size scales monotonically with film thickness, but the in-plane domain size exhibits a minimum, indicating that the nucleation of large in-plane domains supports subsequent island growth. Complementary ab initio investigations suggest that VO2 nucleation and van der Waals epitaxy involves subtle polarization effects around, and the active participation of, surface potassium atoms on the mica surface. The VO2 films show a narrow domain-size-sensitive electrical-conductivity-temperature hysteresis. These results offer promise for tuning the properties of stress-free van der Waals epitaxial films of non-layered materials such as VO2 through microstructure control.
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| 2. |
- Ramanath, Ganpati, et al.
(author)
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Engineering inorganic interfaces using molecular nanolayers
- 2023
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 122:26
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Journal article (peer-reviewed)abstract
- Advances in interface science over the last 20 years have demonstrated the use of molecular nanolayers (MNLs) at inorganic interfaces to access emergent phenomena and enhance a variety of interfacial properties. Here, we capture important aspects of how a MNL can induce multifold enhancements and tune multiple interfacial properties, including chemical stability, fracture energy, thermal and electrical transport, and electronic structure. Key challenges that need to be addressed for the maturation of this emerging field are described and discussed. MNL-induced interfacial engineering has opened up attractive opportunities for designing organic-inorganic hybrid nanomaterials with high interface fractions, where properties are determined predominantly by MNL-induced interfacial effects for applications.
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| 3. |
- Rowe, Collin, et al.
(author)
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Nanomolecularly-induced Effects at Titania/Organo-Diphosphonate Interfaces for Stable Hybrid Multilayers with Emergent Properties
- 2024
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In: ACS Applied Nano Materials. - : AMER CHEMICAL SOC. - 2574-0970.
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Journal article (peer-reviewed)abstract
- Nanoscale hybrid inorganic-organic multilayers are attractive for accessing emergent phenomena and properties through superposition of nanomolecularly-induced interface effects for diverse applications. Here, we demonstrate the effects of interfacial molecular nanolayers (MNLs) of organo-diphosphonates on the growth and stability of titania nanolayers during the synthesis of titania/MNL multilayers by sequential atomic layer deposition and single-cycle molecular layer deposition. Interfacial organo-diphosphonate MNLs result in similar to 20-40% slower growth of amorphous titania nanolayers and inhibit anatase nanocrystal formation from them when compared to amorphous titania grown without MNLs. Both these effects are more pronounced in multilayers with aliphatic backbone-MNLs and likely related to impurity incorporation and incomplete reduction of the titania precursor indicated by our spectroscopic analyses. In contrast, both MNLs result in two-fold higher titania nanolayer roughness, suggesting that roughening is primarily due to MNL bonding chemistry. Such MNL-induced effects on inorganic nanolayer growth rate, roughening, and stability are germane to realizing high-interface-fraction hybrid nanolaminate multilayers.
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| 4. |
- Sangiovanni, Davide G., et al.
(author)
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Strain hardening and toughening in metal/molecular nanolayer/metal nanosandwiches
- 2024
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 124:26
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Journal article (peer-reviewed)abstract
- Introducing molecular nanolayers (MNLs) is attractive for enhancing the stability of, and inducing unusual properties at, inorganic thin film interfaces. Although organic molecules anchored to inorganic surfaces have been studied extensively, property enhancement mechanisms underpinned by molecular assemblies at inorganic thin film interfaces are yet to be revealed and understood. Here, ab initio molecular dynamics simulations of tensile strain of Au/MNL/Au thin film nanosandwich models provide insights into molecularly induced strain hardening and toughening. Au/MNL/Au nanosandwiches support up to approximate to 30% higher stresses and exhibit up to approximate to 140% higher toughness than pure Au slab models. Both hardening and toughening are governed by molecular length and terminal chemistry in the MNL. Strong Au/MNL interface bonding and greater molecular length promote defect creation in Au, which results in strain hardening. Accommodation of increasing post-hardening strains in the MNL mitigates the stress increase in the Au slabs, delays interface fracture, and contributes to toughening. Remarkably, toughening correlates with equilibrium interface strain, which could be used as a proxy for efficiently identifying promising inorganic/MNL combinations that provide toughening. Our findings are important for the discovery and design of inorganic-organic interfaces, nanomaterials, and composites.
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