Both bi-stable memory and mono-stable threshold switching are observed in amorphous NbOx films. In addition, the transition between memory and threshold switching can be induced by changing external electrical stress. Raman spectroscopy and transmission electron microscope data show that the NbOx film is self-assembled into a layered structure consisting of a top metal-rich region and a bottom oxygen-rich region. The volume ratio of the two regions depends on the film thickness. Our experimental results suggest that different characteristics of conducting filaments in the two regions result in thickness dependence of switching types and the transition between memory and threshold switching.

The effect of metal particles on the photoluminescence (PL) and the Raman spectra of functionalized SWCNTs in aqueous solutions was systematically investigated by studying three different metal particles (gold, cobalt, and nickel) on three different SWCNT suspensions (DNA-, RNA-, and sodium deoxycholate salt (DOC)-functionalized SWCNTs). Substantial enhancement of the PL intensities was observed, while the Raman spectra remained unchanged, after gold, cobalt, or nickel particles were introduced into RNA-SWCNT aqueous suspensions. Almost the same results were obtained after the same metal particles were added to DNA-SWCNT aqueous suspensions. However, both the PL and the Raman spectra did not exhibit any change at all after the same metal particles were introduced into DOC-SWCNT aqueous suspensions. The unusual PL enhancements observed in this work cannot be accounted for by the three well-known mechanisms in the literature: surface-enhanced Raman scattering effect, Förster resonance energy transfer in a rebundling of isolated SWCNTs, and pH changes of the aqueous solutions.