Application of surface analysis methods to nanomaterials: summary of ISO/TC 201 technical report: ISO 14187:2011 – surface chemical analysis – characterization of nanomaterials

The ISO technical report 14187 provides an introduction to (and examples of) the information that can be obtained about nanostructured materials by using surface analysis tools. In addition, both general issues and challenges associated with characterizing nanostructured materials and the specific opportunities and challenges associated with individual analytical methods are identified. As the size of objects or components of materials approaches a few nanometers, the distinctions among ‘bulk’, ‘surface’, and ‘particle’ analysis blur. This technical report focuses on issues specifically relevant to surface chemical analysis of nanostructured materials. The report considers a variety of analysis methods but focuses on techniques that are in the domain of ISO/TC 201 including Auger electron spectroscopy, X‐ray photoelectron spectroscopy, secondary ion mass spectrometry, and scanning probe microscopy. Measurements of nanoparticle surface properties such as surface potential that are often made in a solution are not discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Analytical Potential of EDS at low Voltages

 This paper addresses some of the principles underpinning chemical microanalysis of bulk specimens in the scanning electron microscope using low beam voltages ( ≤5 kV) and energy dispersive x-ray spectrometry. The advantages of this relatively new method lie primarily in the strong dependence of the sample penetration range on the electron beam energy (∼10x from 5 kV to 20 kV). This directly yields superior spatial resolution and sensitivity for the analysis of sub-micron particles, surface films and at interfaces. The correspondingly shorter x-ray escape range reduces the importance of the complex matrix absorption and fluorescence terms; the parameters for which may not always be known accurately. A useful x-ray signal can only be generated with a beam energy which is at least 1.3x the excitation energy for the relevant characteristic x-rays. Low voltage fluorescent yields are relatively low and depend strongly on overvoltage (U < 3) and low voltage x-ray signals are relatively weak. These considerations lead to the development of a radical new instrument which produces 9000 counts per second from an Aluminium target with a < 2 nm probe containing 0.2 nA of current at 5 kV, fast submicron resolution x-ray maps ( < 0.1 μm is possible), and close to 1 nm electron image resolution at 1 kV. The greatly improved (15x) EDS sensitivity and superior electron and x-ray imaging are being used to extend, to explore and to exploit more fully the superior performance envelope of the SEM with EDS at low voltages.     

Electron energy loss spectrometry mapping

Among electron beam microanalytical techniques, electron energy loss spectrometry (EELS) offers unique advantages in terms of information content, sensitivity, limits of detection. This paper describes new methods and tools for acquiring families of spectra over many pixels on the specimen, i.e. spectrumimages, and for processing them. Applications in different fields of research, both in materials science and in life sciences, demonstrate the potential impact of the technique for characterizing nano-sized structures.