By Goerg H. Michler
There are many books on electron microscopy, although, the learn of polymers utilizing EM necessitates specific concepts, precautions and training equipment, together with ultramicrotomy. This booklet discusses the overall features of some of the strategies of EM, together with scanning strength microscopy (AFM). the applying of those concepts to the research of morphology and houses, fairly micromechanical homes, is defined intimately. Examples from all periods of polymers are presented.
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As well as a cathode with a sharpened tip, an arrangement of two anodes is used in a FEG, as illustrated in Fig. e. The ﬁrst anode is positively biased by several kV with respect to the cathode. This extraction voltage V generates the ﬁeld strength at the cathode that pull electrons out of the tip. The second anode accelerates the electrons to the ﬁnal energy determined by the voltage V between the cathode tip and the grounded second anode. A cold FEG is an excellent point source of illumination, and may not even require demagniﬁcation action from the ﬁrst condenser lens.
Although one can in principle use either electrostatic or magnetic lenses to focus a beam of electrons, magnetic rather than electrostatic lenses are preferred because they are more convenient to use and have lower aberrations, so only magnetic 22 2 Transmission Electron Microscopy: Fundamentals of Methods and Instrumentation lenses will be considered here. A homogeneous magnetic ﬁeld already acts as a weak electron lens for rays with a small inclination with respect to the ﬁeld direction. For practical purposes, however, magnetic lenses with short focal lengths are obtained by concentrating the magnetic ﬁeld by means of pole pieces.
An image rotation (marked by the angle ϕ in Fig. ) caused by the helical paths of the electrons within the focussing magnetic ﬁeld is a typical feature of the action of a magnetic lens. 3 Electron-Optical Aberrations and Resolution In addition to the simple image formation discussed before, a more realistic one must take into account electron-optical aberrations. Unfortunately it is not possible to can- Fig. 3. 2 Fundamentals of Electron Optics and Instrumentation 23 cel out or correct aberrations in electron optics simply by combining positive and negative elements of diﬀerent refractive indices, as is done in light optics.