Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany;
FEI, 5651 GG Eindhoven, The Netherlands; and.
Proc Natl Acad Sci U S A. 2014 Nov 4;111(44):15635-40. doi: 10.1073/pnas.1418377111. Epub 2014 Oct 20.
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 ∼ 200 °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.
我们描述了一种利用尚未被发现的现象的透射电子显微镜相位板，即连续薄膜表面的束致伏特电势。该伏特电势为负，表明它不是由束致静电充电引起的。为了防止污染并使伏特电势效应能够发生，必须将薄膜加热到约 200°C。相位移动是通过中心衍射束“实时”产生的，无需精确的相位板对准。使用伏特相位板（VPP）获得的图像对比度更高，与泽尼克相位板图像不同，没有边缘伪影。VPP 安装到显微镜中后，大约需要一周的初始稳定时间，然后相位移动行为才变得稳定。VPP 的使用寿命长，已经使用了超过 6 个月，性能没有明显下降。VPP 的工作原理与薄膜泽尼克相位板性能随时间下降的原因相同，但在 VPP 中它被以建设性的方式使用。导致伏特电势的过程的确切物理和/或化学原理尚未完全理解，但实验证据表明，辐射诱导的表面改性以及表面与真空残余气体之间的化学平衡在其中起着重要作用。
