Synthesis of [(VSe₂)_n]_1.06[(TaSe₂)_n] Superlattices Using a Hybrid Approach: Self‐Assembly of Amorphous Nanostructured Reactants

Abstract

The development of tools to predict both the properties and structures of unknown materials has created the growing field of crystal engineering-the rational optimization of properties based on structure-function relationships. [1][2][3][4][5] The great potential of crystal engineering has already been realized in ground-breaking studies of semiconductor superlattices, [6] nanostructured cuprate superconductors, [7,8] bismuth-antimony superlattice thermoelectrics, [9] and colossal magnetoresistant cation-ordered manganese oxides.[10] While epitaxialgrowth techniques were used to prepare most of these new materials, this field has been limited by the lack of alternate synthetic approaches that provide similar structural control. In this manuscript we report the preparation of a series of [(VSe 2 ) n ] 1.06 [(TaSe 2 ) n ] superlattices synthesized using a hybrid approach in which a nanostructured reactant prepared using vacuum deposition is subsequently annealed at low temperature. On annealing the initially non-crystalline reactant self-assembles into an ordered crystalline compound with unit-cell control of the desired nanostructure based on the design of the initial reactant. Opportunities enabled by this synthetic approach include the ability to prepare nanostructured materials containing elements with a wide range of vapor pressures and surface mobilities, and the ability to prepare nanostructured materials with large crystallographic misfit between the lattices of the components. The traditional method used in crystal engineering of nanostructured materials is epitaxial growth involving toggling sources to control the nanostructure period.[11] A variety of techniques (evaporation, [12] sputtering, [13] atomic layer deposition, [14] pulsed-laser deposition, [15] metal-organic vapor chemical deposition) [16] have been developed that utilize different sources or deposition techniques for the depositing species.The substrates are heated and the rates are controlled to balance the arrival rate of the depositing species, their evaporation, and their surface mobility to obtain epitaxial layer-bylayer growth. Exquisite control has been achieved in a wide variety of systems resulting in custom compounds with unexpected physical properties. [13,[15][16][17] The opportunities offered by crystal engineering have also encouraged the development of new synthetic approaches to designed solids. Many chemists and materials scientists have focused on self-assembly as a means to prepare ordered nanostructured materials and epitaxial interfaces.[18-22] Self-assembly techniques typically involve the deposition of films from solution, the removal of solvents and ligands, and the annealing of the resulting films to convert the amorphous precursor to the desired crystalline material. In contrast to epitaxialgrowth techniques, self-assembly is potentially scalable to produce materials in bulk and at low cost. The trade-off for these advantages is the loss of exquisite structural control possible with epitaxial-growth techniques.The a...

Charge Transfer between PbSe and NbSe2 in [(PbSe)1.14]m(NbSe2)1 Ferecrystalline Compounds

“…Other zone axis orientations are visible in the main image. The appearance of atomic columns localized within constituent layers with a coherence length of a few nanometers and the variation of this alignment between layers indicates a turbostratic disorder − between adjacent layers of PbSe-NbSe 2 .…”

Synthesis and Thermal Properties of Solid-State Structural Isomers: Ordered Intergrowths of SnSe and MoSe2

“…27,28 Tin granules of 99.5%+ purity from Aldrich Chemicals, molybdenum rods of 99.95% purity from Alfa Aesar and amorphous selenium shot of 99.999% purity from Alfa Aesar were used as purchased. Sn and Mo were evaporated using Thermionic TM electronbeam guns and Se was evaporated using a resistively heated Knudsen cell.…”

“…Ferecrystal thin films were prepared on ⟨100⟩ Si substrates in a deposition chamber evacuated to 10 –8 Torr using the modulated elemental reactants technique described previously. , Tin granules of 99.5%+ purity from Aldrich Chemicals, molybdenum rods of 99.95% purity from Alfa Aesar, and amorphous selenium shot of 99.999% purity from Alfa Aesar were used as purchased. Sn and Mo were evaporated using Thermionic electron-beam guns, and Se was evaporated using a resistively heated Knudsen cell.…”

Synthesis of Metastable Inorganic Solids with Extended Structures

“…New families of homologous compounds have been prepared by layering two different dichalcogenides, including SnSe2. [79][80][81][82][83][84] New families of homologous compounds (shown in Figure 26) have been prepared with transition metal dichalcogenide layers alternating with layers of Bi2Se3 and Bi2Te3, [85,86] GeSe2, [87] and V3Se4. [88] These metastable compounds are prepared using precursors as described for misfit layer homologs discussed previously.…”