Page 43 - Synthesis of Functional Nanoparticles Using an Atmospheric Pressure Microplasma Process - LiangLiang Lin
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Multiphase Operational Microplasma Setup and the Involved Instrumentation Techniques
sample surface, with exceptional depth of field. When the electrons of primary beam interact with the sample, energetic electrons are released from the sample surface, which contain information such as size, shape, texture and composition. The electron beam is scanned in a raster pattern, and a variety of detectors are used to detect the scattered electrons to produce an image. In addition to morphological, topographical and compositional information, SEM also can detect and analyze surface fractures, examine surface contaminations, reveal spatial element variations, identify crystalline structures and provide qualitative chemical analyses.25,26 As to the sample preparation, it is commonly prepared by scattering the solid particles on a carbon tape and mounted on a stub of metal.
Figure 2.3 The instrument fundament of scanning electron microscope
Atomic force microscopy(AFM) is another popular technique for the morphology characterization, with demonstrated resolution on the order of ~0.1 nm. It uses a cantilever with an extremely sharp tip to scan over the sample surface. As the tip approaches the surface, the attractive force causes the cantilever to deflect towards the surface. With the closer distance to the surface, increasing repulsive force takes over and causes the cantilever to deflect away. Meanwhile, the deflections towards or away from the surface is detected by a laser beam and tracked by a position-sensitive photo diode. In this way the surface feature is reflected by moving the AFM tip over sample surface. Compared to the SEM, AFM has a higher resolution and images in three-dimensional topography instead of two-dimensional projection. The major advantage of AFM is in providing direct quantitative topological information. Moreover, the samples do not require any special treatments (such as metal/carbon coatings) which may damage the sample and does not suffer from charging
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