In situ monitoring of Joule heating effects in germanium nanowires by µ-Raman spectroscopy.

We explored a noninvasive optical method to determine the Joule heating of individual germanium nanowires. Using confocal µ-Raman spectroscopy, variations in the optical phonon frequency, in detail the downshifting of the first-order Stokes Raman band, are correlated to the temperature increase of vapor-liquid-solid grown germanium nanowires under an applied electrical bias. The germanium nanowires were found to handle high threshold current densities of more than 10(6) A cm(-2) before sustaining immediate deterioration. Failure of single crystalline germanium nanowires was directly observed when the applied electric field reached the breakdown point of 1.25 × 10(5) V cm(-1).