edfas.org 7 ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 26 NO. 2 remains a challenge at the nanoscale, it is recommended to use the SThM method under vacuum conditions when quantitative measurements are expected. Moreover, it becomes difficult to characterize quantitatively, with low uncertainty, a physical phenomenon such as heat dissipation in a nanodevice or the thermal transport properties of nanostructures.[1] COMBINED SThM-SEM INSTRUMENT The combined SThM-SEM instrument (Fig. 5) developed at CETHIL is based on a compact AFM system designed to be inserted into a SEM for handling and metrological scanning.[5] The advantages of this instrument coupling is the ability to conduct experiments in vacuum conditions and perform correlative AFM, SThM, and SEM analysis. The equipment can simultaneously image the sample with high resolution, accurately measure heights, distances and thermophysical properties of the material or temperature field at the sample surface when active, while retaining the SEM’s large field of view to position the cantilever exactly where needed. The user can also observe in real time the shape and size of the tip, as well as the sample surface during thermal image acquisition and force spectroscopy measurements. The system improves workflow by saving time without having to move the sample between instruments. In addition, the combined instrument allows better knowledge of the geometry, size (radius of curvature) and surface condition of the tip, as well as better knowledge of physical contact (materials at the apex of the tip and at tip-sample contact). All these parameters are valuable inputs for modeling and quantitative thermal analysis at the nanoscale. ANALYSIS OF SUSPENDED NANOSTRUCTURES To demonstrate the capabilities of the combined setup, the heat transport within a 100 nm in diameter and 20 µm in length rough Si nanowire (NW) was analyzed.[2] The nanowire was suspended between two platforms. This work was carried out in collaboration with the Catalonia Institute for Energy Research. The experiments involved a series of approach curves measurements (in AFM’s force spectroscopy mode) along the suspended nanowire. A three-dimensional electrothermal model of the probe interacting with the nanowire, established by a finite element method, was used to calibrate the probe and to determine, from the experimental results, the local thermal conductance along the nanowire Gtip-NW(x) (Fig. 6, top). Fitting Gtip-NW(x) with an analytical model of heat dissipation in the nanowire enabled estimating the nanowire’s thermal conductivity at 13.7 ± 1.6 Wm-1K-1 (Fig. 6, bottom), which is in very good agreement with its values calculated elsewhere. This work highlights the capabilities of the combined SThM-SEM instrument, in particular the value of highly controlled probe positioning at the nanoscale. CONCLUSION This article presents the SThM technique, showing that this microscopy can be used not only to study the Fig. 5 Combined SThM-SEM instruments.
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