Progress toward an aberration-corrected low energy electron microscope for DNA sequencing and surface analysis
Progress toward an aberration-corrected low energy electron microscope for DNA sequencing and surface analysis
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DOI：
10.1116/1.4764095
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发表时间：
2012-11-01
影响因子：
1.4
通讯作者：
Davis, Ronald W.
中科院分区：
文献类型：
--
作者：
Mankos, Marian;Shadman, Khashayar;Davis, Ronald W.
单色、像差校正、双束低能电子显微镜（MAD-LEEM）是一种新型的成像技术，旨在对大分子、纳米颗粒和表面进行高分辨率成像。MAD-LEEM在一个工具中结合了三个创新的电子光学概念：单色器，镜面像差校正器和双电子束照明。单色器降低了照明电子束的能量扩散，这显著地提高了光谱和空间分辨率。需要像差校正器以在几百电子伏的着陆能量下实现亚纳米分辨率。双泛光照明方法消除了传统的单光束LEEM用于绝缘样品成像时产生的充电效应。在0到几百电子伏范围内的电子的低着陆能量对于避免辐射损伤也是至关重要的，因为具有千电子伏动能的高能电子对许多样品，特别是生物分子造成不可逆的损伤。对MAD-LEEM的关键电子光学器件--物镜透镜和磁束分离器组合的像差校正器的性能进行了仿真研究。初步结果表明，静电电子镜具有负的球差和色差系数，可以在很大的参数范围内进行调整。由电子镜产生的负像差可用于补偿LEEM物镜透镜对于一定范围的电子能量的像差，并提供实现亚纳米空间分辨率的路径。给出了在LEEM中表征固定在Au基底上的DNA分子的第一个实验结果。在自旋极化LEEM中获得的图像表明，在1-10 eV的范围内的低电子能量下可实现高对比度，并且显示着陆能量的微小变化对可实现的对比度具有强烈影响。MAD-LEEM方法有望显着提高LEEM的性能，用于生物科学，材料科学和纳米技术中需要纳米级分辨率和分析能力的广泛应用。特别是，显微镜具有提供具有核苷酸特异性对比度的未标记DNA链的图像的潜力。这简化了样本制备，并显著降低了从单个读段组装DNA序列所需的计算复杂性。(C)2012年美国真空学会。[http：//dx.doi.org/10.1116/1.4764095]
Monochromatic, aberration-corrected, dual-beam low energy electron microscopy (MAD-LEEM) is a novel imaging technique aimed at high resolution imaging of macromolecules, nanoparticles, and surfaces. MAD-LEEM combines three innovative electron-optical concepts in a single tool: a monochromator, a mirror aberration corrector, and dual electron beam illumination. The monochromator reduces the energy spread of the illuminating electron beam, which significantly improves spectroscopic and spatial resolution. The aberration corrector is needed to achieve subnanometer resolution at landing energies of a few hundred electronvolts. The dual flood illumination approach eliminates charging effects generated when a conventional, single-beam LEEM is used to image insulating specimens. The low landing energy of electrons in the range of 0 to a few hundred electronvolts is also critical for avoiding radiation damage, as high energy electrons with kilo-electron-volt kinetic energies cause irreversible damage to many specimens, in particular biological molecules. The performance of the key electron-optical components of MAD-LEEM, the aberration corrector combined with the objective lens and a magnetic beam separator, was simulated. Initial results indicate that an electrostatic electron mirror has negative spherical and chromatic aberration coefficients that can be tuned over a large parameter range. The negative aberrations generated by the electron mirror can be used to compensate the aberrations of the LEEM objective lens for a range of electron energies and provide a path to achieving subnanometer spatial resolution. First experimental results on characterizing DNA molecules immobilized on Au substrates in a LEEM are presented. Images obtained in a spin-polarized LEEM demonstrate that high contrast is achievable at low electron energies in the range of 1-10 eV and show that small changes in landing energy have a strong impact on the achievable contrast. The MAD-LEEM approach promises to significantly improve the performance of a LEEM for a wide range of applications in the biosciences, material sciences, and nanotechnology where nanometer scale resolution and analytical capabilities are required. In particular, the microscope has the potential of delivering images of unlabeled DNA strands with nucleotide-specific contrast. This simplifies specimen preparation and significantly eases the computational complexity needed to assemble the DNA sequence from individual reads. (C) 2012 American Vacuum Society. [http://dx.doi.org/10.1116/1.4764095]