Simplified inelastic electron tunneling spectroscopy based on low-noise derivatives

A standard experimental setup for Inelastic Electron Tunneling Spectroscopy (IETS) performs the measurement of the second derivative of the current with respect to the voltage (d(2)I/ dV(2)) using a small AC signal and a lock-in based second harmonic detection. This avoids noise arising from direct differentiation of the current-voltage characteristics (I-V) by standard numerical methods. Here we demonstrate a noise-filtering algorithm based on Tikhonov Regularization to obtain IET spectra ( i.e. d(2)I/dV(2) vs. V) from measured DC I-V curves. This leads to a simple and effective numerical method for IETS extraction. We apply the algorithm to I-V data from a molecular junction and a metalinsulator-semiconductor tunneling device, demonstrating that the computed first/second derivatives have a workable match with those obtained from our lock-in measurements; the computed IET spectral peaks also correlate well with reported experimental ones. Finally, we present a scheme for automated tuning of the algorithm parameters well-suited for the use of this numerical protocol in real applications.

Automated summary

In this paper, a noise-filtering algorithm based on Tikhonov Regularization is proposed for extracting IET spectra from measured DC I-V curves. By applying this algorithm to experimental data, it is demonstrated that the computed derivatives match well with the measured values, and the computed IET spectral peaks correlate with the experimental results.