Inelastic electron tunneling spectroscopy for molecular detection

Inelastic electron tunneling spectroscopy (IETS) [R. C. Jaklevic and J. Lambe, Phys. Rev. Lett. 17, 1139 (1966); R. G. Keil et al., Appl. Spectrosc. 30, 1 (1976); K. W. Hipps and U. Mazur, J. Phys. Chem. 97, 7803 (1993); U. Mazur et al., Anal. Chem. 64, 1845 (1992); P. K. Hansma, Tunneling Spectroscopy (Plenum, New York, 1982)] measurements are performed on Si nanowire (NW)/SiO2/Al NW tunnel junctions. The tunnel junction area is similar to 50 x 120 nm and tunneling occurs across a 10 nm thick SiO2 layer. IETS measurements are performed at 300K for ammonium hydroxide (NH4OH), acetic acid (CH3COOH), and propionic acid (C3H6O2) molecules. The I-V, dI/dV-V, and d(2)I/dV(2)-V characteristics of the tunnel junction are measured before and after the adsorption of molecules on the junction using vapor treatment or immersion. Peaks can be observed in the d(2)I/dV(2)-V characteristics in all the cases following molecules adsorption. These peaks may be attributed to vibrational modes of N-H and C-H bonds. (C) 2014 American Vacuum Society.