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000827183 0247_ $$2doi$$a10.1002/9783527808465.EMC2016.6252
000827183 037__ $$aFZJ-2017-01381
000827183 041__ $$aEnglish
000827183 1001_ $$0P:(DE-Juel1)165965$$aZheng, Fengshan$$b0$$eCorresponding author
000827183 1112_ $$a16th European Microscopy Congress (EMC 2016)$$cLyon$$d2016-08-28 - 2016-09-02$$wFrance
000827183 245__ $$aQuantitative measurement of the charge distribution along a tungsten nanotip using transmission electron holography
000827183 260__ $$aWeinheim, Germany$$bWiley-VCH Verlag GmbH & Co. KGaA$$c2016
000827183 300__ $$a737 - 738
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000827183 520__ $$aOff-axis electron holography can be used to measure the electron-optical phase shift associated with a charge density distribution in the transmission electron microscope (TEM). The charge density can then be recovered either by integrating the Laplacian of the reconstructed phase1 or, equivalently, by applying a loop integral2. Whichever approach is used, the perturbed reference wave3 does not affect the measurement of the projected charge density inside the specimen so long as it does not itself contain any charges. Here, we study a W nanotip, in which the charge density distribution is of interest for applications in field emission and atom probe tomography. We assess artefacts and noise in the measurements.Figure 1(a) shows an off-axis electron hologram of a W nanotip recorded at 300 kV using an FEI Titan 60-300 TEM. The interference fringe spacing is 0.318 nm, the nominal magnification is 140 000 and the voltage applied to the electrostatic biprism is 90 V. The apex of the nanotip has a diameter of approximately 5 nm and is covered with a layer of tungsten oxide. A voltage of 50 V was applied between the nanotip and a flat electrode positioned approximately 3 µm away from it. In order to remove the contribution to the phase shift from the mean inner potential, two holograms with and without a voltage applied to the nanotip were recorded. The difference between the two phase images was then evaluated after sub-pixel alignment. Figures 1(b) and (c) show the resulting unwrapped phase before and after adding phase contours of spacing 2π/3 radians. Figure 1(d) shows the charge distribution calculated by applying a Laplacian operator to a median-filtered version of the phase image. Figure 1(e) shows cumulative charge profiles along the nanotip determined both using a loop integral and by applying a Laplacian operator to either an unwrapped phase image or the original complex image wave. The integration region is marked by a green dashed rectangle in Fig. 1 (b). The measured charge profile is consistent between the three approaches. Figure 1(f) shows an evaluation of noise in the measurement obtained by performing a similar integration in a region of vacuum indicated by the red dashed rectangle in Fig. 1(b). Results such as those shown in Figs. 1(d) and (e) can be used to infer the electric field and electrostatic potential around the tip. Future work will involve comparing the present approaches with using a model-based technique for determining the charge density from a recorded phase image.
000827183 536__ $$0G:(DE-HGF)POF3-143$$a143 - Controlling Configuration-Based Phenomena (POF3-143)$$cPOF3-143$$fPOF III$$x0
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000827183 7001_ $$0P:(DE-Juel1)159136$$aMigunov, Vadim$$b1
000827183 7001_ $$0P:(DE-HGF)0$$aRamsperger, Urs$$b2
000827183 7001_ $$0P:(DE-HGF)0$$aPescia, Danilo$$b3
000827183 7001_ $$0P:(DE-Juel1)144121$$aDunin-Borkowski, Rafal$$b4
000827183 773__ $$a10.1002/9783527808465.EMC2016.6252
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000827183 9201_ $$0I:(DE-Juel1)ER-C-1-20170209$$kER-C-1$$lPhysik Nanoskaliger Systeme$$x1
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