Synthesis of Inorganic Structural Isomers By Diffusion‐Constrained Self‐Assembly of Designed Precursors: A Novel Type of Isomerism

et al. 2016

Sci Rep

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Hybrid electronic heterostructure films of semi- and superconducting layers possess very different properties from their bulk counterparts. Here, we demonstrate superconductivity in ferecrystals: turbostratically disordered atomic-scale layered structures of single-, bi- and trilayers of NbSe2 separated by PbSe layers. The turbostratic (orientation) disorder between individual layers does not destroy superconductivity. Our method of fabricating artificial sequences of atomic-scale 2D layers, structurally independent of their neighbours in the growth direction, opens up new possibilities of stacking arbitrary numbers of hybrid layers which are not available otherwise, because epitaxial strain is avoided. The observation of superconductivity and systematic Tc changes with nanostructure make this synthesis approach of particular interest for realizing hybrid systems in the search of 2D superconductivity and the design of novel electronic heterostructures.

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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Superconducting ferecrystals: turbostratically disordered atomic-scale layered (PbSe)1.14(NbSe2)n thin films

Grosse

Alemayehu

et al. 2016

Sci Rep

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“…The thickness of each block can be individually controlled as well as the order of the layers, resulting in over 20,000 distinct nanoarchitectures for n and m less than 10. [36] The three constituents can also be combined into one heterostructure, either by alloying the constituents that have a common structure [37], to form a random (A,B)C alloy, or by preparing three component heterostructures with distinct layers of each constituent forming an ordered ABAC alloy. These two possibilities provide access to a large number of new compounds, many more than one would like to make, so the challenge is to understand how properties change as the constituent thicknesses, order, and composition are varied to accelerate the search for the optimum properties for a particular application.…”

Section: Modulated Elemental Reactantsmentioning

confidence: 99%

Self-assembly of designed precursors: A route to crystallographically aligned new materials with controlled nanoarchitecture

Westover

Atkins

Journal of Solid State Chemistry

et al. 2016

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Self-Assembly of designed precursors: a route to crystallographically aligned new materials with controlled na no a r c hi t e c t u r e , Journal of Solid State Chemistry, http://dx. ABSTRACTModulated elemental reactants is a method by which new and complex intergrowth compounds can be synthesized by the self-assembly of designed precursors prepared by physical vapor deposition. Careful calibration of the composition and thickness of the precursors ensures the formation of the desired product by precise control of local composition and diffusion lengths. Superstructures of increasing complexity can be realized using binary and ternary systems as starting points. The synthesis of systems based on three different binary compounds, either alloyed together or separated into distinct layers, expands the number of possible superstructures that can be formed using this technique, but provides analytical challenges. The synthesis of [(SnSe) 1.15 ] 1 ([Ta x V 1-x ]Se 2 ) 1 [(SnSe) 1.15 ] 1 ([V y Ta 1-y ]Se 2 ) 1 compound is used to illustrate the preparation of precursors and the challenges in both measuring and limiting the interdiffusion of layers during self-assembly. Systematic changes in the electrical properties of (SnSe) 1+δ (Ta x V 1-x )Se 2 alloys are observed as x is varied. The electrical resistivity of [(SnSe) 1.15 ] 1 ([Ta x V 1-x ]Se 2 ) 1 [(SnSe) 1.15 ] 1 ([V y Ta 1-y ]Se 2 ) 1 can be modeled as the two constituent layers in parallel. INTRODUCTIONNew synthetic methods have been critical both to advance scientific understanding as well as to advance technology. Traditional approaches have historically focused on using thermodynamic control to make desired products, for example growing doped silicon crystals from a melt of fixed composition. Phase diagrams were determined to understand the thermodynamic relationships between compounds. Kinetic control, typically achieved by controlling temperature as a function of time, was used to influence the microstructure. The search for new materials focused on finding reaction conditions where new compounds would be thermodynamically stable. High temperature synthesis and the growth of new materials from melts were commonly used to overcome slow solid state diffusion rates and to form single crystals for structure determination. New compounds and new phenomena are discovered whenever new approaches are developed, such as vapor transport reactions in the 1960's, [1,2] or new adaptations, such as the use of low temperature fluxes, [3,4] are explored. A grand challenge in the field of materials discovery is the development of approaches to predict new structures and the properties associated with specific compositions, and the development of approaches that will enable their synthesis. Historically, serendipity played a significant role in most new discoveries as unexpected compounds formed in reaction mixtures.

“…While thermodynamically stable misfit layer compounds can be prepared typically only when n = m = 1, ferecrystals can be synthesized with a wide range of m and n values . One can even prepare ferecrystals that are structural isomers, only distinguishable from one another by the number of interfaces between the different building blocks …”

Section: Introductionmentioning

confidence: 99%

Formation of a Selenide‐Based Heterostructure From a Designed Precursor†

Crystal Research and Technology

Esters

Johnson

2017

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The formation of the ferecrystalline compound (SnSe) 1.15 VSe 2 is studied utilizing complementary X-ray diffraction techniques, differential scanning calorimetry, compositional analysis, scanning transmission electron microscopy, and X-ray absorption spectroscopy. A careful analysis unravels the formation mechanism, where a simultaneous crystallization of the individual constituents goes hand in hand with the formation of the superlattice structure. SnSe 2 monolayers form along with SnSe and VSe 2 units in the superlattice during the formation of (SnSe) 1.15 VSe 2 , with the SnSe 2 monolayers coexisting up to 300°C. An annealing temperature of 400°C is required to fully self-assemble the ferecrystalline compound (SnSe) 1.15 VSe 2 , composed of alternating rocksalt-like SnSe bilayers and VSe 2 trilayers. These results demonstrate a complex pathway along a multi-valley energy landscape for these metastable compounds, which in turn offers a rich platform to synthesize targeted layering sequences by precisely controlling the composition of the precursors as well as the annealing conditions.