Modeling the constant-current distance-voltage mode of scanning tunneling spectroscopy

Abstract

We demonstrate the relationship between sample density of electronic states and constant-current distancevoltage spectra starting from the usual expressions for tunneling current in scanning tunneling microscopy experiments. First-order differential equations are derived for the tip position as a function of voltage drop across the tunnel junction for both square and trapezoidal barrier transmission functions. Numerical solutions of the square barrier equation are carried out for different sample density of states and compared with self-consistent integration of the tunneling integral equation. It is shown that normalization of the distance vs voltage spectra by taking logarithmic derivatives reproduces the peak positions in the sample density of states usually to within 0.1 eV. The use of differential equations is proposed as an accurate method for analyzing experimental data and applied to the example case of the π * orbital of the c(8 × 2) phase of benzoate on Cu(110).

Multiple coexisting intercalation structures of sodium in epitaxial graphene-SiC interfaces

“…The junction voltage is swept in a positive large bias interval where high local density of states is observed as an increased rate of tip retraction. 27 This measurement is the most useful form of STS for studying high-energy IPS's, where normal STS in constant height mode leads to high currents and tip instability.…”

Superatom orbitals of C60on Ag(111): Two-photon photoemission and scanning tunneling spectroscopy

“…25 and Ref. 26. These procedures require knowledge of the absolute tip-sample distance and apparent tunneling barrier height, which can depend strongly on the bias and tip conditions.…”

“…The effect has been evaluated for constantcurrent differential conductance measurements 25 and for z-V measurements as performed in this work. 26 Reference 26 revealed that distortion arising from the transmission function background can be reliably corrected using the logarithmic derivative of the raw STS data, (d[ln z]/d[ln V]). This was found to reproduce peak positions in the density of states to better than 0.1 eV.…”

Electrochemical Scanning Tunneling Microscopy Analysis on Protein Based Electronic Devices

“…Scanning tunneling spectroscopy (STS) measurements enable to record the electronic properties of the sample on different surface sites. On the other hand, the current-distance (I -s) measurements 30 where the bias was kept constant and the tip-sample distance was varied and the current were measured. Therefore, in this analysis the current decay factor of the surface was analyzed.…”