Instrument: FEI Inspect S with Oxford Instruments EDX detector
A wide range of solid sample types can be used with SEM though all must be electrically-conductive either naturally or by pre-coating the sample with a conducting material (typically carbon or gold).
Following visualisation of a sample, features of interest can be quantified using software or the elemental composition of the sample may be determined by coupling the SEM to energy dispersive X-ray spectroscopy (EDX).
SEM is a powerful technique to support the characterisation of unknown samples or for sample confirmation.
An electron beam is generated from a thermionic gun, which is directed onto a sample placed in a vacuum chamber to prevent disruption of the beam.
Interaction of the primary electrons with the sample can generate secondary electrons (SE) from ionisation of the sample close to the sample surface. Detection of the SE pattern can then be resolved to reveal the surface of the image.
Since the SE are emitted from near the surface of the sample a near 3D image is produced.
SEM can be used to visualise and measure morphological aspects of a wide range of samples including biological samples. Since the technique reveals key physical features of a sample it can be useful to help determine the mineralogical composition of a sample as well as generating insight into the history of a sample, for example by revealing structural changes within the sample.
By linking the SEM to our EDX capability we can determine the elemental composition of specific areas of a sample of interest which can help to confirm the identity of unknown materials.
Application areas include geochemical analysis, forensics, materials analysis and analysing manufacturing quality.
Solid samples, which can be either organic and inorganic, are required for SEM. All samples need to be conductive for viewing. If samples are not naturally conducting then we would sputter-coat the sample with carbon or gold to achieve this.
Samples should be provided in a form such that they can be added to a carbon adhesive sticker which is then mounted on a stub for viewing. Samples which don’t adhere well to carbon adhesive stickers may need to be fixed in a resin to enable mounting.
Biological samples may need to be chemically fixed though the option of using a low vacuum setting can circumvent this.
Typical sample sizes for SEM is based more on area than weight of sample, and is of the order of 2 cm square. Smaller samples than this are also amenable provided thay can easily be handled.