We report THz emission from lead zirconate-titanate (PZT) nanotube arrays, which is totally absent in flat films or bulk PZT; hence the effect is due to the nano-scale geometry of the tubes, which are 1 mu m in total diameter, 40 nm in wall thickness and standing normal to the Si substrates. The THz radiation is emitted within 0.2 ps and the spectrum exhibits a broad peak from 2 to 8 THz due to the abnormally large carrier concentration gradient and large piezoelectric coefficient in PZT; the inferred mechanism is optical rectification within a surface accumulation layer, rather than the Dember effect.
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