Yörük Emre, Klein Holger, Kodjikian Stéphanie
Institut Néel, Université Grenoble-Alpes and CNRS, Grenoble 38000, France.
Institut Néel, Université Grenoble-Alpes and CNRS, Grenoble 38000, France.
Ultramicroscopy. 2024 Jan;255:113857. doi: 10.1016/j.ultramic.2023.113857. Epub 2023 Sep 16.
Beam sensitive nanomaterials such as zeolites or metal-organic frameworks (MOF) represent a great challenge for crystallographic structure determination and refinement. The strong electron-matter interaction and the high spatial resolution achievable make electron diffraction the technique of choice for particles of sizes below a micrometer and many different 3-dimensional electron diffraction (3D ED) techniques have been developed in recent years. Nevertheless, beam sensitivity of the samples can lead to the crystal structure being damaged during the data acquisition impeding the determination of its structure. A simple way to reduce beam damage is to lower the dose during the experiment. However, this implies weaker diffraction intensities which can become problematic for the exploitation of the data. In order to obtain complete data sets with strong intensities without damaging the crystals, we developed the dose symmetric electron diffraction tomography (DS-EDT) method, combining the low-dose electron diffraction tomography (LD-EDT) technique with the dose-symmetric tomography scheme known from cryo-EM. In order to reduce the dose on an individual crystal and still obtain enough data for a structure solution and refinement, we partition the dose over several crystals. The individual datasets are then merged in order to achieve the necessary completeness. On two test structures we first show that merging of data from small domains of the reciprocal space is indeed sufficient to obtain reliable data for structure solution and refinement. Second, we show on the beam sensitive manganese formate that high-quality data can be obtained on a few frames while the frames that have suffered from beam damage can still be used to determine the orientation matrix and the unit cell of the crystals. The results from the dynamical refinement on the obtained data show a high accuracy of the atom positions. In this way, DS-EDT can reduce the total dose on an individual crystal by an order of magnitude with respect to the already very dose-efficient LD-EDT.
诸如沸石或金属有机框架（MOF）等对电子束敏感的纳米材料，给晶体结构的测定和精修带来了巨大挑战。强大的电子与物质相互作用以及可实现的高空间分辨率，使得电子衍射成为尺寸小于一微米的颗粒的首选技术，并且近年来已经开发出许多不同的三维电子衍射（3D ED）技术。然而，样品对电子束的敏感性可能导致在数据采集过程中晶体结构受损，从而阻碍其结构的确定。降低束流损伤的一种简单方法是在实验过程中降低剂量。然而，这意味着衍射强度较弱，这对于数据的利用可能会成为问题。为了在不损坏晶体的情况下获得具有强强度的完整数据集，我们开发了剂量对称电子衍射断层扫描（DS-EDT）方法，将低剂量电子衍射断层扫描（LD-EDT）技术与冷冻电镜中已知的剂量对称断层扫描方案相结合。为了降低单个晶体上的剂量，同时仍能获得足够的数据用于结构解析和精修，我们将剂量分配到多个晶体上。然后将各个数据集合并，以实现必要的完整性。在两个测试结构上，我们首先表明，合并来自倒易空间小区域的数据确实足以获得用于结构解析和精修的可靠数据。其次，我们在对电子束敏感甲酸锰上表明，可以在几帧上获得高质量数据，而遭受电子束损伤的帧仍可用于确定晶体的取向矩阵和晶胞。对所得数据进行动态精修的结果显示原子位置具有很高的准确性。通过这种方式，相对于已经非常高效的低剂量电子衍射断层扫描（LD-EDT），DS-EDT可以将单个晶体上的总剂量降低一个数量级。
