Scanning Auger Microscopy

Characterisation Installation 5
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Auger electron spectroscopy (AES) and SAM are electron beam techniques based on the Auger effect. An electron beam with typically 3-25 keV energy impinges the sample surface and causes the emission of Auger electrons. This is a non-radiative decay process following the ionization of atoms by the incident electrons. Auger electrons energies are characteristic of the probed elements and thus allow the analysis of the elemental composition of materials. Inelastic mean free paths are very short, of the order of one nanometer, thus making AES and SAM extremely surface sensitive (sampling depth ~ 3-5 nm).

Secondary electron microscopy (SEM) is used to localize the area of interest before Auger analysis. Localized elemental analyses can thus be performed by pointing this area. Scanning Auger microscopy produces elemental maps of the surface by scanning the electron beam over the sample and selecting specific Auger peaks. It provides the spatial distribution of each element at the sample surface with high lateral resolution (~50 nm). 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. Auger depth profiling allows revealing ultra-thin layers and quantifying their elemental composition. In-depth information can also be obtained by analysing a cross-sectional sample. Compared to transmission electron microscopy, SAM does not need any complex sample preparation and bring complementary data at a larger scale. It is thus of real interest to investigate nanostructures for technological applications. Surface sensitivity makes it complementary to electron microscopy techniques (EDX and EELS) and higher spatial resolution offers an alternative to photoelectron spectromicroscopy (XPEEM).

          provided at NFFA-Europe laboratories by:

PHI 700Xi Auger nanoprobe

Chemical composition of heterogeneous surfaces at the 10 nm to 10-100 µm scale

Prototypical devices

In-depth chemical composition by argon sputtering or cross-section analysis

Electron beam (FEG), maximum target current = 25 nA, Zr/W tip

Energy range = 1 – 25 keV

Auger analyzer: Cylindrical Mirror Analyzer (CMA), operating in Constant Retard Ratio (CRR) mode, channels plates for detection  

SEM detector: Field of View below 3×2.5 mm2, spatial resolution = 5 nm at 20keV 1nA                

Scanning Auger Microscopy (SAM) : energy resolution DE/E = 0.5 %, spatial resolution = 8 nm at 20keV 1nA

Scanning Electron Microscopy (SEM) : spatial resolution = 5 nm at 20keV 1nA

5 degrees of freedom : x, y, z, θ, φ

Ranges : 0 < x< 3 mm, 0 < y < 2.5 mm, 8 < z < 15 mm, 0 < θ < 360°, 0 < φ < 30°

Solids and powders, bulk materials, multi-layers, nanostructures (nanowires, nanoparticles), size: 0.5×0.5 mm2, measurements at ambient temperature, no in-situ sample preparation but ex-situ capabilities are available (see other capabilities)

In-situ argon sputtering for surface cleaning, depth profiling or charge compensation: energy range = 10-5000 eV, maximum beam current > 10 µA

Base pressure = 5 10-9 mbar, differential pumping during in-situ argon sputtering (P < 2 10-8 mbar), specific pumping of the electron gun (P = 10-10 mbar)

Ex-situ surface cleaning with heating or Gas Cluster Ion Source possible, with subsequent transfer in inert/UHV atmosphere using transfer vessel or UHV suitcase

XPS and ToF-SIMS tools in close connection with transfer in inert/UHV atmosphere using transfer vessel