PHI 700Xi Auger nanoprobe
Auger electron spectroscopy (AES) is a surface characterization technique based on using an incident electron beam with typically 3-20keV energy and collecting the Auger electrons emitted by the extreme surface of the sample (∼3nm). Localized elemental analyses can be performed by pointing a specific area using secondary electron microscopy (SEM) and selecting specific Auger peaks. Scanning Auger microscopy (SAM) produces elemental maps of the surface by scanning the electron beam over the sample. It provides the spatial distribution of each element at the sample surface with high lateral resolution (∼50nm). AES can also be run in the depth profiling mode using an Ar+ sputter gun. In-depth elemental distributions are obtained through measurements of concentration profiles.
The Auger nanoprobe available at the NanoCaracterization Platform (PFNC) is the PHI700Xi from ULVAC-PHI. This system is equipped with an analyser mounted coaxially with respect to the electron column and thus collecting electrons constantly around the 360° azimuth. This specific geometry offers high and uniform sensitivity (0.5 at.%) and reduces topographic shadowing effects. The instrument design provides high long term stability and thermal drift correction for efficient chemical imaging.
- Sample size <1cm2, sample height <1cm, insulating samples cannot be analysed, no in-situ sample preparation
- Source: Electron beam (FEG), maximum target current = 25 nA, Zr/W tip, Energy range = 1–25keV, SAM resolution = 8 nm at 20keV 1nA
- Auger analyser: Cylindrical Mirror Analyzer (CMA), operating in Constant Retard Ratio (CRR) mode, Energy resolution ΔE/E = 0.5 %, channels plates for detection
- SEM: Field of View below 3×2.5mm2, resolution = 5 nm at 20keV 1nA
- In-situ argon sputtering for surface cleaning, depth profiling or charge compensation: Energy range = 10-5000 eV, maximum beam current >10µA
- Base pressure: 5×10-9 mbar, differential pumping during in-situ argon sputtering (P < 2×10-8mbar), specific pumping of the electron gun (P = 10-10mbar)
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- Metrology / Characterisation: Physical
A typical case study could be the analysis of the surface elemental distribution of silicon nanowires (NW) deposited by Chemical Vapor deposition (CVD) using Cu nanoparticles as catalysts . SAM was used to characterize such nanowires to reveal the spatial distribution of elements. The resulting SEM image and elemental maps of copper and silicon are presented in figure 1. The Auger measurements confirm that Cu is only located at the catalyst and not dispersed all along the Si NW.
The use of our Auger nanoprobe is illustrated on several typical cases in the following papers: