Inelastic tunneling spectroscopy using scanning tunneling microscopy on trans-2-butene molecule: spectroscopy and mapping of vibrational feature.

Inelastic tunneling spectroscopy (IETS) measurement using scanning tunneling microscopy (STM) with a commercially available STM set up is presented. The STM-IETS spectrum measured on an isolated trans-2-butene molecule on the Pd(110) shows a clear vibrational feature in d2I/dV2 at the bias voltage of 360 mV and -363 mV, which corresponds to the nu(C-H) mode (d2I/dV2 approximately 10 nA/V2). In addition, we have obtained an image by mapping the vibrational feature of nu(C-H) in d2I/dV2. The image is obtained by scanning the tip on the surface with the feedback loop activated while the modulation voltage is superimposed on the sample voltage. With the method that is readily performable with conventional software, we have clearly differentiated the molecules of trans-2-butene and butadiene through the mapping of the vibrational feature, demonstrating its capability of chemical identification in atomic scale.