Interface chemistry and thermoelectric characterization of Ti and TiO_x contacts to MBE-grown WSe₂

Abstract

WSe2 has demonstrated potential for applications in thermoelectric energy conversion. Optimization of such devices requires control over interfacial thermal and electrical transport properties. Ti, TiOx, and Ti/TiOx contacts to the MBE-grown WSe2 are characterized by XPS and transport measurements. The deposition of Ti is found to result in W-Se bond scission yielding metallic W and Ti-Se chemical states. The deposition of Ti on WSe2 in the presence of a partial pressure of O2, which yields a TiOx overlayer, results in the formation of substoichiometric WSex (x < 2) as well as WOx. The thermal boundary conductance at Ti/WSe2 contacts is found to be reduced for greater WSe2 film thickness or when Au/TiOx interface is present at the contact. Electrical resistance of Au/Ti contacts is found to be higher than that of Au/TiOx contacts with no significant difference in the Seebeck coefficient between the two types of contact structures. This report documents the first experimental study of Ti/WSe2 interface chemistry and thermoelectric properties.

Electron–phonon relaxation at the Au/WSe2 interface is significantly accelerated by a Ti adhesion layer: time-domain ab initio analysis

“…The initial conditions are chosen to match the experiments. 28,29 The electronic subsystem is pumped at 400 nm, corresponding to ∼3.1 eV. The 3.1 eV of energy is distributed between the electron and the hole.…”

“…2, majority of the carriers are excited from around this energy, and the symmetrical initial condition provides a better representation of the experiments. 28,29…”

“…26 A transition metal film, usually Ti, is often inserted at the interface to alter the electronic and optical response, as well as increase the adhesion of poorly bonded layers. 27–30 Giri et al demonstrated that on incorporation of a thin Ti adhesion layer between an Au slab and a non-metal substrate, the electron–phonon coupling is enhanced resulting in accelerated energy relaxation. 31 The increase in energy exchange near the interface is rationalized by the strengthened bonding between Au and the non-metal substrate when a Ti layer is included.…”

Unraveling the Mechanism of Remote Scavenging Effect at the InP/Al2O3 Interface Induced by Titanium Layer

“…The base pressure during the sputtering process (≈10 −3 mbar) is actually resulting in Ti metal and TiO x deposition, instead of pure Ti metal. [ 20 ] The P and In atoms are seen diffused into the Al 2 O 3 layer slightly after PMA at 400 °C, resulting in an intermixing region near the InP/Al 2 O 3 interface. Besides, the intermixing region is also seen at the Ti/Al 2 O 3 interface.…”

Nanostructured and Heterostructured 2D Materials for Thermoelectrics

“…It is shown that the TBC depends on the details of the contact, and the level of oxidization of titanium and is in the range of 6 to 22 MW/m 2 K. Despite the small thermal conductance values, the studied interface has a low ZT due to the dominance of the electronic tunneling transport. [247] A few experiments have been conducted to measure the cross-plane Seebeck coefficient of 2D heterostructures. Chen et al [215] stacked a Gr/hBN/Gr heterostructure and patterned electrodes on the top and bottom graphene sheets.…”