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Electron Holography for Mapping Electric Fields and Charge
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
Martha R. McCartney, David J. Smith
The macroscopic behavior of many materials is closely interconnected with the presence of nanoscale electrostatic fields and the accumulation of electric charge. Measurement and control of these intrinsic materials properties, especially as a function of growth and treatment conditions, is often an essential step along the path towards realizing practical applications. The transmission electron microscope (TEM) is an indispensable tool for materials characterization at the nanoscale, but it cannot directly provide access to details about fields and charges within and surrounding the object under examination. The crux of the problem is that the electrostatic (and magnetic) fields cause phase changes to the incident electron beam which are not observable using conventional TEM imaging modes that only provide intensity information. Electron holography overcomes this fundamental limitation. By using a coherent source, electron holography interference techniques enable the phase change of the electron beam traversing the sample relative to a vacuum (reference) wave to be determined. Reconstruction of the complex electron wave function from the recorded electron hologram allows quantitative measurement of electric charge and electric fields to be made with nanoscale resolution, subject to certain requirements and limitations that are elaborated below.
Microstructure and Polarization Properties of III-Nitride Semiconductors
Published in Wengang (Wayne) Bi, Hao-chung (Henry) Kuo, Pei-Cheng Ku, Bo Shen, Handbook of GaN Semiconductor Materials and Devices, 2017
Electron holography is an electron-interference technique that makes the recovery of the phase information possible. A conducting filament that acts as an optical biprism is used to produce an interference pattern. The biprism is aligned manually so that its image matches the boundary of the specimen at the image plane. When a positive bias is applied to the biprism, the beams traveling through vacuum (reference) and the sample (object) overlap at the image plane, and their interference pattern is recorded. The geometric configuration around the biprism is depicted in Figure 2.16. The biprism filament is along the y-direction, and the beam propagates along the z-direction. The biprism is at a given potential, while the two plates are grounded. In some microscopes, these two plates are the edges of the selected area aperture.
Picometer Detection by Adaptive Holographic Interferometry
Published in Klaus D. Sattler, Fundamentals of PICOSCIENCE, 2013
Electron holography in its broadest sense is any technique that uses the interference patterns from coherent electron waves in order to extract the phase and amplitude information from the waves that have been scattered by a specimen. In traditional amplitude contrast transmission electron microscopy (TEM), two electron waves, A1eiϕ1 and A2eiϕ2, are detected incoherently, that is, Inc≈A1ei1ˆ2+A2eiϕ22=A12+A22
Most frequently asked questions about the coercivity of Nd-Fe-B permanent magnets
Published in Science and Technology of Advanced Materials, 2021
Jiangnan Li, Hossein Sepehri-Amin, Taisuke Sasaki, Tadakatsu Ohkubo, Kazuhiro Hono
The addition of a small amount of Ga to Nd-Fe-B sintered magnets has been known to increase the coercivity by improving the wettability of the intergranular phase during post-sinter annealing [30–33]. In earlier development of Nd-Fe-B sintered magnets, priority has been given to the achievement of high remanence. Then, part of Nd was replaced with Dy for increasing the coercivity. As a result, the chemical composition of the N50 type sintered magnet was around Nd13.9Fe79.5B6Cu0.1, which is slightly richer in Nd with respect to the stoichiometry of Nd2Fe14B, Nd11.7Fe82.4B5.8. In order to increase the coercivity of the Nd-Fe-B sintered magnet without using Dy, Nakajima et al. developed a Nd-rich and B-lean alloy with a trace Ga addition, i.e. Fe77.6RE14.8B5.1Cu0.1Ga0.5 as strip cast alloy for Nd-Fe-B sintered magnet with a substantially improved coercivity of 1.8 T for the grain size as large as ~5 µm [34]. Microstructure investigations by Sasaki et al. (Figure 6) showed the formation of three types of nonferromagnetic intergranular phases (Ia, amorphous Nd-rich, and Nd6Fe13Ga phases) are the main reason for the substantial enhancement of coercivity to 1.8 T upon post-sinter annealing [35]. Niitsu et al. also [36] also reported these three types of the intergranular phases are nonferromagnetic using electron holography. Magneto-optical Kerr effect microscopy by Soderznik et al. showed that the formation of thick non-ferromagnetic intergranular phase suppressed the cascade propagation of magnetic domains during the demagnetization process, which was considered to be responsible for the enhancement of coercivity [37].
Phase-field simulation of magnetic double-hole nanoring and its application in random storage
Published in International Journal of Smart and Nano Materials, 2021
Zengyao Lv, Xiaoyu Zhang, Honglong Zhang, Zhitao Zhou, Duo Xu, Yongmao Pei
For twin-vortex magnetization state, Nipun A [26] in 2007 demonstrated twin-vortex in 30-nm-thick Co nanopatterned double pac-man (DPM) elements (with Outer Diameter (OD): 400 nm, notch radius: 120 nm, and Slot Angle 60°), fabricated by electron-beam lithography (EBL) and liftoff processing, when the field is applied in an orthogonal direction, using Lorentz microscopy and off-axis electron holography.