Thomas John Meurig, Simpson Edward T, Kasama Takeshi, Dunin-Borkowski Rafal E
Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, UK.
Acc Chem Res. 2008 May;41(5):665-74. doi: 10.1021/ar700225v. Epub 2008 May 7.
Transmission electron microscopes fitted with field-emission guns (to provide coherent electron waves) can be adapted to record the magnetic fields within and surrounding nanoparticles or metal clusters, for example, the lines of force of a nanoferromagnet encapsulated within a multiwalled carbon nanotube. Whereas most chemists are aware that electron microscopy readily identifies crystallographic symmetries and phases, solves structures, and, in conjunction with electron energy-loss spectroscopy, yields valence states and electronic information of materials, relatively few know that it can also provide important quantitative information, with nanometer-scale spatial resolution, pertaining to such materials' magnetic properties. In this Account, with the aid of representative examples embracing solid-state chemistry, geochemistry, and bio-inorganic phenomena, we illustrate how off-axis electron holography affords deep insight into magnetic phenomena on the nanoscale. Specifically, we describe the unprecedented level of information available regarding the magnetic nature of magnetotactic bacteria, magnetic nanoparticle chains and chiral bracelets, and geochemically relevant phenomena involving exsolution (the un-mixing of two mineral phases, as in the magnetite-ulvöspinel system). It is, for example, possible to reveal vortices and multidomain states that have no net magnetization in minute blocks of magnetite. With the current burgeoning interest and activity in nanoscience and nanotechnology, our Account concludes with examples of some existing enigmas that electron holography, especially when augmented by the related technique of electron tomography, might play an important experimental role in resolving, such as the occurrence of ferromagnetism in nanocrystals of silver within carbon tubes and in clusters of alkali metals incarcerated within zeolites.
配备场发射枪（以提供相干电子波）的透射电子显微镜可用于记录纳米颗粒或金属簇内部及周围的磁场，例如，记录封装在多壁碳纳米管内的纳米铁磁体的磁力线。大多数化学家都知道电子显微镜能够轻松识别晶体对称性和相、解析结构，并且与电子能量损失谱相结合，能够得出材料的价态和电子信息，但相对较少有人知道它还能以纳米级空间分辨率提供与这些材料磁性相关的重要定量信息。在本综述中，借助涵盖固态化学、地球化学和生物无机现象的代表性实例，我们阐述了离轴电子全息术如何能深入洞察纳米尺度上的磁现象。具体而言，我们描述了关于趋磁细菌、磁性纳米颗粒链和手性手镯的磁性本质以及涉及出溶作用（如磁铁矿 - 钛磁铁矿体系中两种矿物相的分离）的地球化学相关现象所获得的前所未有的信息水平。例如，有可能揭示在微小的磁铁矿块中没有净磁化的涡旋和多畴状态。鉴于当前纳米科学和纳米技术领域的蓬勃兴趣和活动，我们的综述最后列举了一些现有谜团的例子，电子全息术，特别是在与电子断层扫描这一相关技术相结合时，可能在解决这些谜团中发挥重要的实验作用，比如碳管内银纳米晶体以及沸石内捕获的碱金属簇中出现铁磁性的情况。
