Volta potential phase plate for in-focus phase contrast transmission electron microscopy
Volta potential phase plate for in-focus phase contrast transmission electron microscopy
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DOI：
10.1073/pnas.1418377111
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发表时间：
2014-11-04
影响因子：
11.1
通讯作者：
Baumeister, Wolfgang
中科院分区：
文献类型：
--
作者：
Danev, Radostin;Buijsse, Bart;Baumeister, Wolfgang
我们描述了一种用于透射电子显微镜的相板，利用了迄今为止未知的现象，即连续薄膜表面上的光束感应伏特电位。伏特电位为负，表明它不是由束致静电充电引起的。薄膜必须加热到接近200摄氏度，以防止污染，并使伏特电位的影响。相移是由中心衍射光束“在飞行中”产生的，消除了对精确相位板校准的需要。用Volta相板（VPP）获得的图像具有更高的对比度，并且与Zernike相板图像不同，没有边缘伪影。在安装到显微镜后，VPP有一个大约一周的初始沉淀时间，之后相移行为变得稳定。VPP使用寿命长，使用时间超过6个月，性能没有明显下降。VPP的基本机制与导致薄膜泽尼克相板性能随时间退化的机制相同，但在VPP中，它以建设性的方式使用。引起伏特电位的过程背后的确切物理和/或化学尚不完全清楚，但实验证据表明，辐射引起的表面修饰与真空中表面和残余气体之间的化学平衡起着重要作用。
We describe a phase plate for transmission electron microscopy taking advantage of a hitherto-unknown phenomenon, namely a beam-induced Volta potential on the surface of a continuous thin film. The Volta potential is negative, indicating that it is not caused by beam-induced electrostatic charging. The film must be heated to similar to 200 degrees C to prevent contamination and enable the Volta potential effect. The phase shift is created "on the fly" by the central diffraction beam eliminating the need for precise phase plate alignment. Images acquired with the Volta phase plate (VPP) show higher contrast and unlike Zernike phase plate images no fringing artifacts. Following installation into the microscope, the VPP has an initial settling time of about a week after which the phase shift behavior becomes stable. The VPP has a long service life and has been used for more than 6 mo without noticeable degradation in performance. The mechanism underlying the VPP is the same as the one responsible for the degradation over time of the performance of thin-film Zernike phase plates, but in the VPP it is used in a constructive way. The exact physics and/or chemistry behind the process causing the Volta potential are not fully understood, but experimental evidence suggests that radiation-induced surface modification combined with a chemical equilibrium between the surface and residual gases in the vacuum play an important role.