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

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.In the field of terahertz (THz) science and technology, engineering the functionalities of THz waves such as the amplitude, phase, spectrum and directionality is of great importance for various potential applications such as THz imaging 1 , coherent control of molecular dynamics 2 and remote sensing. 3 The emitted THz waves from different materials, which yields information not only on the amplitude but also on the phase, provides insight into the ultrafast dynamics of non-equilibrium carrier transport with a femtosecond time scale e.g., direction of band bending and surge currents as compared to conventional methods. 4,5 A rich variety of approaches have been demonstrated by changing material parameters and ambient conditions. Early studies indicated that polarity reversal of THz radiation could be achieved as a function of pump laser wavelength around the band edge in bulk a) Electronic

Semiconducting Conjugated Microporous Polymer: An Electrode Material for Photoelectrochemical Water Splitting and Oxygen Reduction

“…Work function of the HOPG and the polymer are found to be lower than that of the probe by 225±10 meV and 175±10 meV, respectively (Figure S10, Supporting Information). Freshly cleaved HOPG is known to have a work function of around 4.6 eV . Therefore, work function of PTEB is calculated to be around 4.65±0.02 eV.…”