Dynamic electrostatic force microscopy technique for the study of electrical properties with improved spatial resolution

Abstract

The need to resolve the electrical properties of confined structures (CNTs, quantum dots, nanorods, etc) is becoming increasingly important in the field of electronic and optoelectronic devices. Here we propose an approach based on amplitude modulated electrostatic force microscopy to obtain measurements at small tip-sample distances, where highly nonlinear forces are present. We discuss how this improves the lateral resolution of the technique and allows probing of the electrical and surface properties. The complete force field at different tip biases is employed to derive the local work function difference. Then, by appropriately biasing the tip-sample system, short-range forces are reconstructed. The short-range component is then separated from the generic tip-sample force in order to recover the pure electrostatic contribution. This data can be employed to derive the tip-sample capacitance curve and the sample dielectric constant. After presenting a theoretical model that justifies the need for probing the electrical properties of the sample in the vicinity of the surface, the methodology is presented in detail and verified experimentally.

Interface-Induced Enhancement of Ferromagnetism in Insulating LaMnO3 Ultrathin Films

“…The LMO with the LAO capping layer possesses a slightly larger resistivity than bare LMO, demonstrating that the capping of LAO sustains the insulating nature of LMO, even the enhancement of the resistivity is not clear yet. We further investigate the homogeneity of the insulating property of LMO via the electrostatic force microscopy (EFM) with a lateral resolution of dozens of nanometers . When patterning a film using EFM, one can expect that the EFM signal of a uniform conductor should not show any apparent contrast due to the screening effect, while an insulator surface could show some contrast if the ability of holding charges is not uniform, although the contrast can also be influenced by oxygen migration, redox processes, and so forth .…”

Quantifying charge carrier concentration in ZnO thin films by Scanning Kelvin Probe Microscopy

“…Semenikhin 34 reported evidence of local doping inhomogeneity on conducting polybithiophene, while Koren 35 measured the doping distribution along single phosphorous-doped silicon nanowires. Although compared with Scanning Capacitance Microscopy (SCP) this technique presents some limitations in terms of accuracy 36 37 , previously mentioned and other reports 38 demonstrate that SKPM can be used to quantitatively measure the doping concentration in semiconductors with high spatial resolution 31 33 39 . Attempts to correlate SKPM measurements with charge carriers concentration in ZnO have been reported 40 41 .…”

“…SKPM is an AFM based technique developed by Nonnemacher et al in 1991 27 30 . As other electrostatic force microscopy techniques 39 46 , it measures the contact potential difference V CPD between a conductive tip and a sample. The V CPD is defined as: where q is the electronic charge, while ϕ tip and ϕ sample are the work functions of the tip and the sample respectively.…”

EFM data mapped into 2D images of tip-sample contact potential difference and capacitance second derivative

“…If the tip-sample distance is such that the sole effect of the electrostatic force is probed by the biased tip, then the force field can be approximated as f S ( z ) ≈ f el ( z ). Force-curve based techniques for the exact local separation of f S ( z ) into f el ( z ) and short-range forces have been recently proposed by Maragliano et al27. However, the implementation of these methods to obtain simultaneous 2D images of electrostatic force, short-range forces, capacitance and height, would require complex, expensive and fast analogic/digital circuitry, able to perform force-distance curve scans at different biases, point-by-point, in the 2D raster scan.…”

“…This technique282930 can be concisely indicated as EFM-sweep. In the case of EFM-sweep, the scan size is localized to a small area of the surface, which depends on the tip-sample distance and on the tip radius (in the order of tens of nanometers)27. With this local method, information on sample morphology is lost.…”