Structural Changes as a Function of Thickness in [(SnSe)_1+δ]_mTiSe₂ Heterostructures

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Single- and few-layer materials exhibit unique properties due to reduced dimensionality.
• Tin selenide (SnSe) and titanium diselenide (TiSe2) are layered chalcogenides with potential electronic applications.
• Understanding dimensionality effects is crucial for designing novel electronic materials.

Purpose of the Study:

• To investigate the impact of SnSe layer thickness on the structure and electronic properties of [(SnSe)1+δ]mTiSe2 intergrowth compounds.
• To explore the transition from 3D to 2D behavior in these layered structures.
• To identify potential applications of these tunable materials.

Main Methods:

• Synthesis of [(SnSe)1+δ]mTiSe2 thin films with varying SnSe layer thickness (m=1-4).
• Characterization using in-plane X-ray diffraction and scanning transmission electron microscopy (STEM).
• Theoretical analysis using density functional theory (DFT) calculations.

Main Results:

• Structural changes, including increased rotational disorder and varied stacking sequences in SnSe layers, were observed with increasing m.
• Unexpected p-type behavior was observed for the first time in (MSe)m(TiSe2)n compounds.
• Resistivity, Hall coefficient, and Seebeck coefficient showed complex dependencies on SnSe layer thickness, indicating non-single-band transport.

Conclusions:

• The intergrowth structures exhibit tunable electronic properties influenced by SnSe layer thickness and stacking.
• The observed transport properties suggest complex electronic interactions beyond simple composite behavior.
• These findings open avenues for designing novel thermoelectric and electronic materials with controlled dimensionality.