Synthesis and Characterization of [(PbSe)][TiSe] Isomers.

This work presents the preparation of a series of [(PbSe)][TiSe] isomers via a low temperature synthesis approach that exploits precursor nanoarchitecture to direct formation of specific isomers. The targeted isomers formed even when the precursors did not have the correct amount of each element to make a unit cell from each repeating sequence of elemental layers deposited. This suggests that the exact composition of the precursors is less important than the nanoarchitecture in directing the formation of the compounds.

Crystallography at the nanoscale: planar defects in ZnO nanospikes.

The examination of anisotropic nanostructures, such as wires, platelets or spikes, inside a transmission electron microscope is normally performed only in plan view. However, intrinsic defects such as growth twin interfaces could occasionally be concealed from direct observation for geometric reasons, leading to superposition. This article presents the shadow-focused ion-beam technique to prepare multiple electron-beam-transparent cross-section specimens of ZnO nanospikes, via a procedure which could be readily extended to other anisotropic structures.

Kinetics of the Topochemical Transformation of (PbSe) (TiSe) (SnSe) (TiSe) to (PbSnSe) (TiSe) .

Solid-state reaction kinetics on atomic length scales have not been heavily investigated due to the long times, high reaction temperatures, and small reaction volumes at interfaces in solid-state reactions. All of these conditions present significant analytical challenges in following reaction pathways. Herein we use in situ and ex situ X-ray diffraction, in situ X-ray reflectivity, high-angle annular dark field scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy to investigate the mechanistic pathways for the formation of a layered (PbSnSe)(TiSe) heterostructure, where m is the varying number of TiSe layers in the repeating structure.

Kinetically Controlled Formation and Decomposition of Metastable [(BiSe)] [TiSe] Compounds.

Preparing homologous series of compounds allows chemists to rapidly discover new compounds with predictable structure and properties. Synthesizing compounds within such a series involves navigating a free energy landscape defined by the interactions within and between constituent atoms. Historically, synthesis approaches are typically limited to forming only the most thermodynamically stable compound under the reaction conditions.

Structural Changes as a Function of Thickness in [(SnSe)]TiSe Heterostructures.

Single- and few-layer metal chalcogenide compounds are of significant interest due to structural changes and emergent electronic properties on reducing dimensionality from three to two dimensions. To explore dimensionality effects in SnSe, a series of [(SnSe)]TiSe intergrowth structures with increasing SnSe layer thickness (m = 1-4) were prepared from designed thin-film precursors. In-plane diffraction patterns indicated that significant structural changes occurred in the basal plane of the SnSe constituent as m is increased.

Interface-Driven Structural Distortions and Composition Segregation in Two-Dimensional Heterostructures.

The discovery of emergent phenomena in 2D materials has sparked substantial research efforts in the materials community. A significant experimental challenge for this field is exerting atomistic control over the structure and composition of the constituent 2D layers and understanding how the interactions between layers drive both structure and properties. While no segregation for single bilayers was observed, segregation of Pb to the surface of three bilayer thick PbSe-SnSe alloy layers was discovered within [(Pb Sn Se) ] (TiSe ) heterostructures using electron microscopy.

Long-Range Order in [(SnSe)][TiSe] Prepared from Designed Precursors.

Self-assembly of designed precursors has enabled the synthesis of novel heterostructures that exhibit extensive rotational disorder between constituents. In (SnSe)TiSe nanoscale regions of long-range order were observed in scanning transmission electron microscopy (STEM) cross sectional images. Here a combination of techniques are used to determine the structure of this compound, and the information is used to infer the origin of the order.

Amorphous Mixed-Metal Oxide Thin Films from Aqueous Solution Precursors with Near-Atomic Smoothness.

Thin films with tunable and homogeneous composition are required for many applications. We report the synthesis and characterization of a new class of compositionally homogeneous thin films that are amorphous solid solutions of AlO and transition metal oxides (TMO) including VO, CrO, MnO, FeO, CoO, NiO, CuO, and ZnO. The synthesis is enabled by the rapid decomposition of molecular transition-metal nitrates TM(NO) at low temperature along with precondensed oligomeric Al(OH)(NO) cluster species, both of which can be processed from aq solution.

Structural Changes in 2D BiSe Bilayers as n Increases in (BiSe)(NbSe) (n = 1-4) Heterostructures.

(BiSe)(NbSe) heterostructures with n = 1-4 were synthesized using modulated elemental reactants. The BiSe bilayer structure changed from a rectangular basal plane with n = 1 to a square basal plane for n = 2-4. The BiSe in-plane structure was also influenced by small changes in the structure of the precursor, without significantly changing the out-of-plane diffraction pattern or value of the misfit parameter, δ.

The synthesis of [(PbSe)1+δ]m(TiSe2)n[(SnSe2)1+γ]m(TiSe2)n heterostructures with designed nanoarchitectures by self assembly of amorphous precursors.

Targeted heterostructures containing intergrown two dimensional (2D) layers of 3 different constituent layers, SnSe2, PbSe and TiSe2, were prepared by controlling the composition and sequence of elemental bilayers within a designed precursor. Varying the structure of the precursor enabled the number of structural units of each constituent and the sequence of crystalline 2D layers to be precisely controlled. The stacking of the 2D layers, their structures, and the segregation of the elements between them were determined using X-ray diffraction and electron microscopy techniques, with the observed sequence of the 2D layers consistent with the targeted intergrowth.

Rational design of efficient electrode-electrolyte interfaces for solid-state energy storage using ion soft landing.

The rational design of improved electrode-electrolyte interfaces (EEI) for energy storage is critically dependent on a molecular-level understanding of ionic interactions and nanoscale phenomena. The presence of non-redox active species at EEI has been shown to strongly influence Faradaic efficiency and long-term operational stability during energy storage processes. Herein, we achieve substantially higher performance and long-term stability of EEI prepared with highly dispersed discrete redox-active cluster anions (50 ng of pure ∼0.

Non-uniform Composition Profiles in Inorganic Thin Films from Aqueous Solutions.

A variety of metal oxide films (InGaOx, AlOx, "HafSOx") prepared from aqueous solutions were found to have non-uniform electron density profiles using X-ray reflectivity. The inhomogeneity in HafSOx films (Hf(OH)4-2x-2y(O2)x(SO4)y·zH2O), which are currently under investigation as inorganic resists, were studied in more detail by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and medium-energy ion scattering (MEIS). The HAADF-STEM images show a greater concentration of heavy atoms near the surface of a single-layer film.

Designed Synthesis of van der Waals Heterostructures: The Power of Kinetic Control.

Selecting specific 2D building blocks and specific layering sequences of van der Waals heterostructures should allow the formation of new materials with designed properties for specific applications. Unfortunately, the synthetic ability to prepare such structures at will, especially in a manner that can be manufactured, does not exist. Herein, we report the targeted synthesis of new metal-semiconductor heterostructures using the modulated elemental-reactant technique to nucleate specific 2D building blocks, control their thickness, and avoid epitaxial structures with long-range order.

Antiphase Boundaries in the Turbostratically Disordered Misfit Compound (BiSe)(1+δ)NbSe2.

(BiSe)(1+δ)NbSe2 ferecrystals were synthesized in order to determine whether structural modulation in BiSe layers, characterized by periodic antiphase boundaries and Bi-Bi bonding, occurs. Specular X-ray diffraction revealed the formation of the desired compound with a c-axis lattice parameter of 1.21 nm from precursors with a range of initial compositions and initial periodicities.

Influence of Defects on the Charge Density Wave of ([SnSe](1+δ))1(VSe2)1 Ferecrystals.

A series of ferecrystalline compounds ([SnSe]1+δ)1(VSe2)1 with varying Sn/V ratios were synthesized using the modulated elemental reactant technique. Temperature-dependent specific heat data reveal a phase transition at 102 K, where the heat capacity changes abruptly. An abrupt increase in electrical resistivity occurs at the same temperature, correlated with an abrupt increase in the Hall coefficient.

Localized grounding, excavation, and dissection using in-situ probe techniques for focused ion beam and scanning electron microscopy: experiments with rock varnish.

While investigating rock varnish, we explored novel uses for an in-situ micromanipulator, including charge collection, sample manipulation, as well as digging and dissection at the micron level. Dual-beam focused ion beam microscopes (DB-FIB or FIBSEM) equipped with micromanipulators have proven to be valuable tools for material science, semiconductor research, and product failure analysis. Researchers in many other disciplines utilize the DB-FIB and micromanipulator for site-specific transmission electron microscope (TEM) foil preparation.