Phase manipulation of terahertz waves by work function engineering in metal-graphite structures

TL;DR

This study demonstrates control over the phase of emitted terahertz waves from metal-graphite interfaces by engineering work function differences, revealing how metal choice influences THz phase and amplitude through band bending and doping effects.

Contribution

It introduces a method to manipulate THz wave phase via work function engineering in metal-graphite structures, a novel approach in THz wave control.

Findings

Opposite THz phase responses for metals with higher and lower work functions than graphite.

THz amplitude correlates with work function differences and carrier mobilities.

Interfacial band bending affects the phase and amplitude of emitted THz waves.

Abstract

We manipulate the transient terahertz (THz) waves emitted from metal-graphite interfaces, where potential barriers were formed because of work function differences. To adaptively control the phase of the THz waves, two distinct groups of metals were evaporated on n-type doped highly oriented pyrolytic graphite (HOPG): group A, which consisted of Pt, Au, and Ag with work functions larger than that of HOPG and group B, which consisted of Al and Ti with work functions smaller than that of HOPG. The phase of the transient THz lineshapes from group A was opposite to that of group B under infrared laser excitation, which is indicative of opposite band bending and concomitant interfacial doping for ambipolar transport at the metal-graphite junctions. The amplitude of the THz waves could be further substantiated by the work function differences and modified minority carrier mobilities at the depletion regions.