| We have systematically studied the performance and I-V characteristics of Self-Assembling Tunnel Junctions (SATJ's) as a new configuration of inelastic electron tunneling spectroscopy (IETS) for measuring vibrational spectra of molecules on metal surfaces. In a SATJ, the oxide layer associated with metal-insulator-impurity-metal junctions in a typical IETS configuration is replaced by an inert gas film. One advantage of the SATJ configuration is that the junction barrier is truly adjustable. The resistance of the junction can be adjusted over four orders of magnitude and yet the SATJ is observed to have enough stability to perform IETS in a point-contact geometry.;We have measured the vibrational spectra of both inert barrier junctions and those doped with hydrogen and acetylene. "Clean" junctions in which the barrier consists of a pure rare-gas (neon) film show, as expected, no significant peaks in the spectrum. Acetylene doped junctions exhibit peaks corresponding to vibrational modes of the acetylene molecules. In addition, a zero-bias feature (ZBF), typical in double junctions, appears to be a universal feature of the SATJ, although its presence is not understood in our single junction geometry. |
