Brian Zutter

Thermometry of Silicon Nanoparticles

Current thermometry techniques lack the spatial resolution required to see the temperature gradients in typical, highly-scaled modern transistors. As a step toward addressing this problem, we have measured the temperature dependence of the volume plasmon energy in silicon nanoparticles from room temperature to 1250

Temperature Dependence of the Silicon Nitride Volume Plasmon

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In Situ Scanning Transmission Electron Microscopy (STEM) of Individual Electrochemical Intercalation Events in Graphite

C, using a chip-style heating sample holder in a scanning transmission electron microscope (STEM) equipped with electron energy loss spectroscopy (EELS). The plasmon energy changes as expected for an electron gas subject to the thermal expansion of silicon. Reversing this reasoning, we find that measurements of the plasmon energy provide an independent measure of the nanoparticle temperature consistent with that of the heater chips macroscopic heater/thermometer to within the 5\% accuracy of the chip thermometers calibration. Thus silicon has the potential to provide its own, high-spatial-resolution thermometric readout signal via measurements of its volume plasmon energy. Furthermore, nanoparticles in general can serve as convenient nanothermometers for \emph{in situ} electron microscopy experiments.

STEM EBIC mapping of the metal-insulator transition in thin-film NbO2

Silicon nitride membranes are commonly used as electron transparent windows in transmission electron microscope (TEM) in situ experiments. A pair of silicon nitride membranes, each suspended over a hole in a silicon wafer and generally 10-100 nm thick, can enclose a liquid or gas and maintain a high vacuum outside the enclosed region [1]. In addition, microelectronic devices and MEMS-based heating holders are commonly microfabricated on top of silicon nitride membrane windows. In the TEM the beam electrons primarily lose energy in a thin silicon nitride membrane by inducing a volume plasmon. Thus in many in situ TEM experiments the silicon nitride plasmon has the potential to allow, without additional sample preparation, temperature mapping across the field of view through plasmon energy expansion thermometry (PEET) [2]. However, previously the silicon nitride plasmon’s temperature dependence has not been measured.

In Situ Observation of Cooling in a Bismuth Telluride and Bismuth-Antimony Telluride Nanoscale Heterojunction

Graphite intercalation compounds (GICs) are formed when ions or molecules (intercalants) are inserted between the carbon layers of a graphite host. With some electrolytes a reversible charge transfer process occurs during intercalation, making GICs attractive materials for batteries. The demand for improved batteries has highlighted the need for in situ measurements probing electrode-electrolyte interactions [1]. With in situ scanning transmission electron microscopy (STEM) we observe the reversible electrochemical intercalation of multi-layered (~20-100 layers) graphene in 96% sulfuric acid (H2SO4).

Plasmon Energy Mapping in Aluminum and Indium with Sub-Nanometer Resolution

This article has been published in a revised form in Microscopy and Microanalysis https://doi.org/10.1017/S1431927617007802. This version is free to view and download for private research and study only. Not for re-distribution, re-sale or use in derivative works.

Detailed In Situ Observations of Electromigration in Aluminum Wires

Thermoelectrics have a wide variety of applications, but their efficiency, typically stated in terms of the figure of merit ZT, must be improved before they become economical for non-niche applications. According to theory [1, 2], ZT can be improved relative to the bulk by constructing devices that feature nanometer-scale confinement in one or more dimensions. Here we describe transmission electron microscopy (TEM) observations of cooling in heterojunctions constructed from 2D flakes of exfoliated bismuth telluride and bismuth-antimony telluride.

Asymmetric Temperature Profiles in Joule-Heated in Aluminum Nanowires

In the free electron model, the plasmon energy is proportional to the square root of the valence electron density. Using scanning transmission electron microscopy (STEM) and electron-energy loss spectroscopy (EELS) to measure plasmon energies, one can generate electron density maps with sufficient resolution to reveal atomic-scale features [1]. We use STEM EELS to map the plasmon energy in aluminum and indium films on a 5 nm-thick silicon nitride membranes. Using an aberration-corrected STEM, we have acquired spectrum images with 80 pm spatial resolution. In both metals we see atomic periodicity in the plasmon energy signals.

Temperature Dependence of the Volume Plasmon in Silicon Nanoparticles

Atoms in a current-carrying metal wire can experience electromigration, where the electric field and associated electric current drive atomic diffusion [1]. Understanding this process is important for the successful very-large-scale integration (VLSI) of integrated circuits (ICs) [2], since each IC contains many small wires subject to large current densities. Using scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS), we have observed in situ electromigration in aluminum wires suspended on electron-transparent, 15 nm-thick silicon nitride membranes. In some cases, a void that forms with one sign of the electrical current will be subsequently filled when the current is reversed, indicating the existence of sites that are particularly disposed to both sourcing and sinking atoms (see Figure 1).

Aloof Beam Plasmons in Silver Nanoparticles

Subject to direct current (DC) Joule heating, a straight, suspended wire that is heat-sunk at its ends will produce a symmetric temperature distribution that peaks in the middle of the wire. This temperature distribution is independent of the sign of the DC current through the wire. We have observed asymmetric temperature profiles in Joule heated aluminum nanowires (60 nm thick by 30 nm wide): the location of the maximum temperature switches sides around the midpoint of the wire depending on the sign of the current through the wire. Simulations of the wire’s temperature profile indicate that the asymmetry could arise from an unexpectedly large value of the nanowire’s thermoelectric Thomson coefficient.