Abstract
Terahertz (THz) electromagnetic wave has been widely used as a spectroscopic probe to detect the collective vibrational mode in vast molecular systems and investigate dielectric properties of various materials. Recent technological advances in generating intense THz radiation and the emergence of THz plasmonics operating with nanoscale structures have opened up new pathways toward THz applications. Here, we present a new opportunity in engineering the state of matter at the atomic scale using THz wave and a metallic nanostructure. We show that a medium strength THz radiation of 22 kV/cm can induce ionization of ambient carbon atoms through interaction with a metallic nanostructure. The prepared structure, made of a nano slot antenna and a nano island located at the center, acts as a nanogap capacitor and enhances the local electric field by two orders of magnitudes thereby causing the ionization of ambient carbon atoms. Ionization and accumulation of carbon atoms are also observed through the change of the resonant condition of the nano slot antenna and the shift of the characteristic mode in the spectrum of the transmitted THz waves.
Highlights
Our uniquely designed nanostructure has a great advantage for engineering the THz field enhancement and the ability to trigger the ionization of ambient carbon atoms even under a medium strength THz radiation of 22 kV/cm, that has not be shown in earlier works
The nano island and slot antenna were defined by focused ion beam (FIB) after deposition of a 100-nm-thick gold layer and a 10-nm-thin Ti layer for adhesion on top of the Si substrate
In order to mimic the transition of the resonance depending on the degree of the charge transfer, we performed a finite-difference time-domain (FDTD) method based simulation[14]
Summary
A regenerative amplifier laser beam, with 1 kHz repetition rate providing 35 fs and 3 mJ pulses centered at 800 nm, is irradiated on a ZnTe crystal to produce intense THz radiation with the peak-to-peak power between 18.3 ~ 22 kV/cm using a variable filter. The generated THz wave with a horizontal polarization is focused by two Tsurupica lenses with a focal spot size of 2 mm and is incident on the slot antenna. The THz radiation is focused again onto the ZnTe crystal for detection. A focused electron beam examines the surface of the target sample and the emitted Auger electrons are collected in an electron energy analyzer. The electron beam energy is 5 kV and the target current is 10 nA (for mapping) with a 500 eV sputtering rate
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