ChemInform Abstract: Synthesis of [(SnSe)_1.15]_m(TaSe₂)_n Ferecrystals: Structurally Tunable Metallic Compounds.

Abstract

Compounds. -The title ferecrystals (fere: Latin, almost) with 1 ≤ n,m ≤ 6 and n and m varied independently are prepared by physical vapor deposition of the elements followed by annealing at 400°C for 30 min. The samples are characterized by XRD, HRTEM, and electrical measurements. Each of the intergrowth compounds contains highly oriented intergrowths of SnSe bilayers and TaSe 2 monolayers with a square in-plane structure of the SnSe constituent, a hexagonal in-plane structure for the TaSe2 constituent, and rotational disorder between the constituent layers. Temperature dependent electrical resistivity reveals metallic behavior for all compounds. A simple model explains the difference in resistivity as a function of m and n. -(ATKINS, R.; WILSON, J.; ZSCHACK, P.; GROSSE, C.; NEUMANN, W.; JOHNSON*, D. C.; Chem. Mater. 24 (2012) 23, 4594-4599, http://dx.

Charge Density Wave Transition in (PbSe)1+δ(VSe2)n Compounds with n = 1, 2, and 3

“…These precursors were annealed at 250 °C to self-assembly of the targeted products. This temperature was determined using the approach of Atkins et al 34 perpendicular to the substrate. Using Bragg's Law, the c-axis lattice parameters were determined to be 1.225(1), 1.835(3), and 2.445(4) nm for n = 1, 2, and 3, respectively.…”

“…The last step was to hold the Pb|Se, V|Se, and Pb|Se/V|Se ratios constant while scaling the total thickness, using the quality of the resulting annealed sample diffraction patterns to determine the thickness such that each Pb|Se bilayer forms two (001) planes of rock salt structured PbSe and the V|Se layer forms a single Se−V−Se dichalcogenide structured trilayer. X-ray diffraction (XRD) scans were taken on the annealed precursors in order to determine the total thickness that yields maximum peak intensity and minimum peak fwhm in the resulting product, as described previously by Atkins et al 34 Sequences with the nanoarchitecture of the desired products, for example, the sequence of layers Pb|Se−V|Se−V|Se for (PbSe) 1+δ (VSe 2 ) 2 , were repeatedly deposited until the desired total sample thickness of about 45 nm was reached. These precursors were annealed at 250 °C to self-assembly of the targeted products.…”

Structural Changes as a Function of Thickness in [(SnSe)1+δ]mTiSe2 Heterostructures

“…This involved preparing a series of precursors of the sequence {1 × [Ti|Se] + m × [Sn|Se]} with varying m and n values, measuring their compositions via electron probe microanalysis (EPMA), measuring the thickness of the repeating amorphous sequence via X-ray reflectivity (XRR), and interpolating to obtain desired compositions and thicknesses as described previously. 24 Once the deposition was calibrated, precursors for each of the targeted [(SnSe) 1+δ ] m TiSe 2 compounds were prepared by depositing the {[Ti|Se] + m × [Sn|Se]} sequence the required number of times to obtain the desired total thickness. An annealing study was conducted to determine optimum annealing temperatures and times to transform the designed precursors into the targeted compounds.…”

Synthesis of Metastable Inorganic Solids with Extended Structures

“…For TaSe2, NbSe2, WSe2 and MoSe2, the different TSe2 units within a layer have different orientations, even in bilayers. [66,90,94] In special cases, where there is an accidental epitaxial relationship between the two constituents, preferred orientations over multiple unit cells can be observed, consistent with heterogeneous nucleation of subsequent layers off of an initially nucleated layer. [95] Figure 32 shows different STEM Controlling the extent and rate of diffusion in the deposition of the precursor and during the annealing process is also challenging.…”

“…Indeed, this approach works, producing heterostructures with amazing fidelity due to the large stability difference between the precursor and the targeted heterostructures. [65][66][67] Appropriately designed precursors have enabled the synthesis of compounds with specific sequences of layers as shown in Figure 25. [68] This approach enables the synthesis of extensive families of homologous compounds, because the criteria for formation is to be more stable than the precursor.…”