Substrate effects on Single-Layer Atomically Thin 2D Semiconductor Titanium Telluride

Fg.1: Semiconductor (purple), Substrate (green) Credit: Meng Kai Lin/University of Illinois at Urbana-Champaign

An atomically thin semiconductor layer, mostly used in electronics, are a single layer or more, transition metal dichalcogenides, which are just atoms sandwiched together in simple terms, and they are the part of a family called 2D materials, as their thickness approaches the 2D limit, which can be even thinner than 1nm. Such materials are quite useful in electronics, they tend to form weak bonds on the outside layer and are generally assumed to be unaffected by the substrate that provides the physical support. 

But to go further, scientists have tested this assumption to better understand the physics of a single layer, and also the effects of the substrate to fine-tune the substrate to characterize the layer.

As reported in the Physics Review Letters, a team led by Tai-Chang Chiang of the University of Illinois, Meng-Kai Linm used Berekely's Advanced Light Source (ALS) to study the changes in the electronic properties of titanium telluride, a 2D semiconductor. 

Titanium Telluride is very sensitive to a substrate, which makes it useful as a test case for the study. Single Layer titanium telluride was grown on platinum telluride, and the tests were conducted as the thickness of the substrate, PtTe₂, was increased, as shown in Fig.1. The results showed that as the thickness of the substrate increased, a systematic variation occurred in the single-layer titanium telluride. An electric phenomenon known as a Charge Density Wave (CDW), a static modulation of conduction electrons, a coupled charge, and lattice distortion characteristic of single-layer Titanium Telluride, was suppressed. 

“The experimental findings, combined with first-principles theoretical simulations, led to a detailed explanation of the results in terms of the basic quantum mechanical interactions between the single-layer and the tunable substrate,” said Lin.

And as the interfacial bond remains weak, the researchers concluded that the observed changes were correlated with the substrate's transformation from a semiconductor to a semimetal as it increased in thickness. 

“This systematic study illustrates the crucial role that substrate interactions play in the physics of ultrathin films,” said Lin. “The scientific understanding derived from our work also provides a framework for designing and engineering ultrathin films for useful and enhanced properties.”

Reference: DOI: 10.1103/PhysRevLett.125.176405