The electron beam (e-beam) in the scanning electron microscopy (SEM) provides an appealing mobile heating source for thermal metrology with spatial resolution of ∼1 nm but the lack of systematic quantification of the e-beam heating power limits such application development. Here, we systemically study ebeam heating in LPCVD silicon nitride (SiN x) thin-films with thickness ranging from 200 to 500 nm from both experiments and complementary Monte Carlo simulations using the CASINO software. There is good agreement about the thickness-dependent e-beam energy absorption of thin-film between modeling predictions and experiments. Using the absorption results we then demonstrate adapting e-beam as a quantitative heat source by measuring the thickness-dependent thermal conductivity of SiN x thin-films, with the results validated to within 7% by a separate Joule heating experiment. The results described here will open a new avenue to using SEM e-beams as a mobile heating source for advanced nanoscale thermal metrology development. The interaction between the high-kinetic energy electrons from an electron beam (e-beam) and a sample produces a wealth of signals which provide a variety of insights for scanning electron microscopy (SEM), such as analyzing composition, imaging surface morphology, and investigating the crystalline structures. During the electron−substrate interaction, heat is also generated and this makes it possible to apply the e-beam as a high-quality mobile heat source for generating nanoscale thermal hotspots but also for thermal studies in SEM and transmission electron microscopy (TEM). 1−6 E-beams have several unique characteristics which are appealing for nanoscale thermal metrology. First, an e-beam's potential spatial resolution of ∼1 nm is appealing compared to that of alternate techniques for nanoscale thermal measurements, such as the 3ω method, time/frequency-domain thermoreflectance, and Raman/luminescence-based methods, which are generally limited by the microfabrication length scale or optical diffraction limit. 7−9 Similarly, focusing a high-energy e-beam into such a small area results in nanoscale heat sources with extraordinarily high heat fluxes, easily exceeding ∼1 MW cm −2. This is valuable for the study of heat dissipation from nanoscale hotspots, which is important for both fundamental understanding and engineering design in micro-and nanoelectronics, because nanometer-scale hotspots of up to hundreds of degrees Celsius are believed to influence device performance and reliability. 10 Furthermore, compared to Joule heating by microfabricated heater lines or scanning with a 48 heated atomic force microscope tip, 11,12 the e-beam's 49 dynamically controllable shape and position makes it a more 50 nimble heat source for precise manufacturing and thermal 51 studies.
The suspended micro-thermometry measurement technique is one of the most prominent methods for probing the in-plane thermal conductance of low dimensional materials, where a suspended microdevice containing two built-in platinum resistors that serve as both heater and thermometer is used to measure the temperature and heat flow across a sample. The presence of temperature fluctuations in the sample chamber and background thermal conductance through the device, residual gases, and radiation are dominant sources of error when the sample thermal conductance is comparable to or smaller than the background thermal conductance, on the order of 300 pW/K at room temperature. In this work, we present a high resolution thermal conductance measurement scheme in which a bipolar direct current reversal technique is adopted to replace the lock-in technique. We have demonstrated temperature resolution of 1.0–2.6 mK and thermal conductance resolution of 1.7–26 pW/K over a temperature range of 30–375 K. The background thermal conductance of the suspended microdevice is determined accurately by our method and allows for straightforward isolation of this parasitic signal. This simple and high-throughput measurement technique yields an order of magnitude improvement in resolution over similarly configured lock-in amplifier techniques, allowing for more accurate investigation of fundamental phonon transport mechanisms in individual nanomaterials.
Invited for this month′s cover is the group of Alexis T. Bell at The University of California, Berkeley in Berkeley, California. The image shows the utility of gold nanoparticles deposited on hydrotalcite (Au/HT) for the continuous gas‐phase non‐ oxidative dehydrogenation reaction of bioderived C2–C4 alcohols to the respective carbonyl compounds and hydrogen. The Communication itself is available at 10.1002/cssc.201500786.
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