Ex situ microscopic techniques electron microscopy

The resolution of the technique is limited by the size of the microelectrode tip, at present 200 nm. In the future, reduction of tip size to tens of nanometres by use of novel microelectrode fabrication procedures should increase the applicability of SECM. 

Electron microscopy56, most commonly employed as scanning electron microscopy (SEM), is now a widely used tool in examining the morphology of surfaces under vacuum conditions, and so in an electrochemical context electrode surfaces and corroded surfaces. Instruments also permit chemical microanalysis to be carried out. 

One of the reasons as to why we should use electron microscopy rather than optical microscopy to obtain topographical images is shown in Fig. 12.17 the resolution obtainable can reach almost atomic dimensions. The 

In electron microscopy a sample is bombarded with a finely focused beam of monochromatic electrons. Products of the interaction of the incident electron beam with the sample are detected. If the sample is sufficiently thin—up to 200 nm thickness—the beam is transmitted after interacting with the sample, leading to the technique of transmission electron microscopy (TEM). TEM is used to probe the existence of defects in crystals and phase distributions. Scanning TEM instruments have been recently developed to obtain images over a wider area and to minimize sample degradation from the high-intensity beams. 

If the sample is thicker, then interaction is with the surface of the sample and the products of this interaction follow trajectories away from the surface. In scanning electron microscopy (SEM), it is usually the secondary emitted electrons that are detected, the electron beam being scanned (rastered) across the sample surface. For reflection techniques non-metallic surfaces have to be coated with a thin metal film (about 

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