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The tunneling current through an atomic force microscopy (AFM) tip is used to evaluate the effective electrical contact area, which exists between tip and sample in contact-AFM electrical measurements. A simple procedure for the evaluation of the effective electrical contact area is described using conductive atomic force microscopy (C-AFM) in combination with a thin dielectric. We characterize the electrical contact area for coated metal and doped-diamond tips operated at low force (<200 nN) in contact mode. In both cases, we observe that only a small fraction (<10 nm2) of the physical contact (~100 nm2) is effectively contributing to the transport phenomena. Assuming this reduced area is confined to the central area of the physical contact, these results explain the sub-10 nm electrical resolution observed in C-AFM measurements. [ABSTRACT FROM AUTHOR]

The ability to develop ferroelectric materials using binary oxides is critical to enable novel low-power, high-density non-volatile memory and fast switching logic. The discovery of ferroelectricity in hafnia-based thin films, has focused the hopes of the community on this class of materials to overcome the existing problems of perovskite-based integrated ferroelectrics. However, both the control of ferroelectricity in doped-HfO2 and the direct characterization at the nanoscale of ferroelectric phenomena, are increasingly difficult to achieve. The main limitations are imposed by the inherent intertwining of ferroelectric and dielectric properties, the role of strain, interfaces and electric field-mediated phase, and polarization changes. In this work, using Si-doped HfO2 as a material system, we performed a correlative study with four scanning probe techniques for the local sensing of intrinsic ferroelectricity on the oxide surface. Putting each technique in perspective, we demonstrated that different origins of spatially resolved contrast can be obtained, thus highlighting possible crosstalk not originated by a genuine ferroelectric response. By leveraging the strength of each method, we showed how intrinsic processes in ultrathin dielectrics, i.e., electronic leakage, existence and generation of energy states, charge trapping (de-trapping) phenomena, and electrochemical effects, can influence the sensed response. We then proceeded to initiate hysteresis loops by means of tip-induced spectroscopic cycling (i.e., "wake-up"), thus observing the onset of oxide degradation processes associated with this step. Finally, direct piezoelectric effects were studied using the high pressure resulting from the probe's confinement, noticing the absence of a net time-invariant piezo-generated charge. Our results are critical in providing a general framework of interpretation for multiple nanoscale processes impacting ferroelectricity in doped-hafnia and strategies for sensing it. [ABSTRACT FROM AUTHOR]

The basic unit of information infilamentary-based resistive switchingmemories is physically stored in a conductive filament. Therefore,the overall performance of the device is indissolubly related to theproperties of such filament. In this Letter, we report for the firsttime on the three-dimensional (3D) observation of the shape of theconductive filament. The observation of the filament is done in ananoscale conductive-bridging device, which is programmed under realoperative conditions. To obtain the 3D-information we developed adedicated tomography technique based on conductive atomic force microscopy.The shape and size of the conductive filament are obtained in three-dimensionswith nanometric resolution. The observed filament presents a conicalshape with the narrow part close to the inert-electrode. On the basisof this shape, we conclude that the dynamic filament-growth is limitedby the cation transport. In addition, we demonstrate the role of theprogramming current, which clearly influences the physical-volumeof the induced conductive filaments. [ABSTRACT FROM AUTHOR]