Scanning Electron Microscopy
NREL uses field-emission scanning electron microscopy (SEM) to analyze the morphology/microstructure of materials with high-spatial resolution up to 1.2 nanometers.
How It Works
With basic SEM, a beam of highly energetic (0.1-50 keV) electrons is focused on a sample surface. This can produce several interactions including the emission of secondary electrons, backscattered electrons, photons, and X-rays; excitation of phonons; and diffraction under specific conditions.
Because the bombarding electron beam is scanned in the X-Y plane, an image for each of these different processes can be mapped with a suitable detector. A detector for secondary electrons, standard to all basic SEMs, records topography of the surface under observation with resolution on the order of 1-2 nanometers and magnification range from 10x to 500,000x. In addition, information on composition, phase, electrical, optical, thermal, and other properties can be mapped with excellent resolution with appropriate detectors.
The basic SEM is probably the most versatile instrument in materials science. Beyond being an isolated instrument, it also represents a platform. When combined with scanning probe microscopy, the electron microscope can be used to further control manipulation of nanostructures or select an area for observation with high precision. In situ phase transitions can be seen when cryogenic or heating stages are installed in the chamber. The combination with a focused ion beam is used for specimen preparation in transmission electron microscopy.
Equipment and Instrumentation
NREL is equipped with a JEOL 6320F for very high-resolution imaging provided by a combination of its cold field-emission source, advanced electron-optics and in-lens detector, a variable-pressure Hitachi S-3400N, and a JEOL JSM-5800, equipped with spectrum imaging for cathodoluminescence and a scanning probe microscopy platform. The electron microprobe JEOL 8900L is the preference when quantitative composition of specimens is required.
The following table provides a condensed listing of the systems, techniques, applications, and resolutions of the major SEM instrumentation.
|System||Analytical Technique||Typical Applications||Lateral Resolution||Special Features|
|JEOL 6320F||Field-emission scanning electron microscopy||Micro- and nanoscale characterization of topography, composition and phases||1.2 nm @ 1.5 kV
2.5 nm @ 1 kV
|THERMO EDX, EBIC
THERMO EDX, EBIC
|Scanning electron microscopy||Microstructure, EBSD||3.0 nm (HV)
4.0 nm (VP)
|Variable pressure (VP), HKL NORDLYS II EBSD|
|JEOL JSM-5800||Scanning electron microscopy||Microstructure, EBIC, cathodoluminescence||3.5 nm||Cathodoluminescence spectrum imaging, cryostage (15 to 300 K), CCD, InGaAs PDA|
|Customized SPM platform||Scanning tunneling microscopy, Atomic force microscopy, Near-field scanning optical microscopy||Nanoscale characterization and manipulation of nanostructures||< 1 nm||Scanning tunneling luminescence, electroluminescence, lateral transport measurements, NFCL|
|JEOL JXA-8900L||Electron probe microanalysis||Quantitative compositional analysis||100 nm to 5 mm||± 0.2 at.%|
Main Characteristics of Scanning Electron Microscopy
- High-resolution imaging (1-2 nm), high-speed acquisition (30-60 s)
- Live observation of the specimen in 5-6 orders of magnification (10x to 500,000x)
- Vacuum compatibility required. Vacuum chamber accommodates specimens up to 4 inches in diameter
- Versatility: multiple modes of operation available
- Readily accessible cross-sectional measurements
Scanning Electron Microscopy Techniques
High-resolution field-emission basic SEM image of germanium nanowires embedded in gallium indium phosphide matrix (after etching).