The current status of knowledge regarding the surfaces of the iron oxides, magnetite (Fe₃O₄), maghemite (γ-Fe₂O₃), haematite (α-Fe₂O₃), and wüstite (Fe_1−xO) is reviewed. The paper starts with a summary of applications where iron oxide surfaces play a major role, including corrosion, catalysis, spintronics, magnetic nanoparticles (MNPs), biomedicine, photoelectrochemical water splitting and groundwater remediation. The bulk structure and properties are then briefly presented; each compound is based on a close-packed anion lattice, with a different distribution and oxidation state of the Fe cations in interstitial sites. The bulk defect chemistry is dominated by cation vacancies and interstitials (not oxygen vacancies) and this provides the context to understand iron oxide surfaces, which represent the front line in reduction and oxidation processes. Fe diffuses in and out from the bulk in response to the O₂ chemical potential, forming sometimes complex intermediate phases at the surface. For example, α-Fe₂O₃ adopts Fe₃O₄-like surfaces in reducing conditions, and Fe₃O₄ adopts Fe_1−xO-like structures in further reducing conditions still. It is argued that known bulk defect structures are an excellent starting point in building models for iron oxide surfaces.

The atomic-scale structure of the low-index surfaces of iron oxides is the major focus of this review. Fe₃O₄ is the most studied iron oxide in surface science, primarily because its stability range corresponds nicely to the ultra-high vacuum environment. It is also an electrical conductor, which makes it straightforward to study with the most commonly used surface science methods such as photoemission spectroscopies (XPS, UPS) and scanning tunneling microscopy (STM). The impact of the surfaces on the measurement of bulk properties such as magnetism, the Verwey transition and the (predicted) half-metallicity is discussed.

The best understood iron oxide surface at present is probably Fe₃O₄(100); the structure is known with a high degree of precision and the major defects and properties are well characterised. A major factor in this is that a termination at the Fe_oct–O plane can be reproducibly prepared by a variety of methods, as long as the surface is annealed in 10⁻⁷−10⁻⁵ mbar O₂ in the final stage of preparation. Such straightforward preparation of a monophase termination is generally not the case for iron oxide surfaces. All available evidence suggests the oft-studied (√2×√2)R45° reconstruction results from a rearrangement of the cation lattice in the outermost unit cell in which two octahedral cations are replaced by one tetrahedral interstitial, a motif conceptually similar to well-known Koch–Cohen defects in Fe_1−xO. The cation deficiency results in Fe₁₁O₁₆ stoichiometry, which is in line with the chemical potential in ultra-high vacuum (UHV), which is close to the border between the Fe₃O₄ and Fe₂O₃ phases. The Fe₃O₄(111) surface is also much studied, but two different surface terminations exist close in energy and can coexist, which makes sample preparation and data interpretation somewhat tricky. Both the Fe₃O₄(100) and Fe₃O₄(111) surfaces exhibit Fe-rich terminations as the sample selvedge becomes reduced. The Fe₃O₄(110) surface forms a one-dimensional (1×3) reconstruction linked to nanofaceting, which exposes the more stable Fe₃O₄(111) surface. α-Fe₂O₃(0001) is the most studied haematite surface, but difficulties preparing stoichiometric surfaces under UHV conditions have hampered a definitive determination of the structure. There is evidence for at least three terminations: a bulk-like termination at the oxygen plane, a termination with half of the cation layer, and a termination with ferryl groups. When the surface is reduced the so-called “bi-phase” structure is formed, which eventually transforms to a Fe₃O₄(111)-like termination. The structure of the bi-phase surface is controversial; a largely accepted model of coexisting Fe_1−xO and α-Fe₂O₃(0001) islands was recently challenged and a new structure based on a thin film of Fe₃O₄(111) on α-Fe₂O₃(0001) was proposed. The merits of the competing models are discussed. The α-Fe₂O₃(1$\overline{1}$02) “R-cut” surface is recommended as an excellent prospect for future study given its apparent ease of preparation and its prevalence in nanomaterial.

In the latter sections the literature regarding adsorption on iron oxides is reviewed. First, the adsorption of molecules (H₂, H₂O, CO, CO₂, O₂, HCOOH, CH₃OH, CCl₄, CH₃I, C₆H₆, SO₂, H₂S, ethylbenzene, styrene, and Alq₃) is discussed, and an attempt is made to relate this information to the reactions in which iron oxides are utilized as a catalyst (water–gas shift, Fischer–Tropsch, dehydrogenation of ethylbenzene to styrene) or catalyst supports (CO oxidation). The known interactions of iron oxide surfaces with metals are described, and it is shown that the behaviour is determined by whether the metal forms a stable ternary phase with the iron oxide. Those that do not, (e.g. Au, Pt, Ag, Pd) prefer to form three-dimensional particles, while the remainder (Ni, Co, Mn, Cr, V, Cu, Ti, Zr, Sn, Li, K, Na, Ca, Rb, Cs, Mg, Ca) incorporate within the oxide lattice. The incorporation temperature scales with the heat of formation of the most stable metal oxide. A particular effort is made to underline the mechanisms responsible for the extraordinary thermal stability of isolated metal adatoms on Fe₃O₄ surfaces, and the potential application of this model system to understand single atom catalysis and sub-nano cluster catalysis is discussed. The review ends with a brief summary, and a perspective is offered including exciting lines of future research.

知识的关于氧化铁，磁铁矿的表面的当前状态（铁₃ Ò ₄），磁赤铁矿（γ-的Fe ₂ ö ₃），赤铁矿（α-的Fe ₂ ö ₃），和方铁矿（铁_{1- X}O）被审查。本文首先概述了氧化铁表面起主要作用的应用，包括腐蚀，催化，自旋电子学，磁性纳米颗粒（MNP），生物医学，光电化学水分解和地下水修复。然后简要介绍了其整体结构和性能。每种化合物都基于紧密堆积的阴离子晶格，在间隙位置中Fe阳离子的分布和氧化态不同。整体缺陷化学主要由阳离子空位和间隙（不是氧空位）主导，这为理解氧化铁表面提供了背景，氧化铁表面代表了还原和氧化过程中的第一线。Fe随O _2的扩散从主体中扩散进出化学势，有时在表面形成复杂的中间相。例如，的α-Fe ₂ ö ₃采用的Fe ₃ ö ₄样面在还原条件下，和Fe ₃ ö ₄采用的Fe _{1- X} O形状中进一步还原条件仍然结构。有人认为，已知的整体缺陷结构是氧化铁表面构建模型的绝佳起点。

氧化铁低折射率表面的原子尺度结构是本综述的主要重点。Fe ₃ O ₄是表面科学中研究最多的氧化铁，主要是因为其稳定性范围恰好与超高真空环境相对应。它也是一种电导体，可以直接使用最常用的表面科学方法进行研究，例如光发射光谱法（XPS，UPS）和扫描隧道显微镜（STM）。讨论了表面对整体性质（如磁性，Verwey跃迁和（预测的）半金属性）的测量的影响。

目前，人们最了解的氧化铁表面可能是Fe ₃ O ₄（100）。该结构是众所周知的，具有很高的精确度，并且主要缺陷和特性也得到了很好的表征。一个主要因素是，只要表面在10 ^-7 -10 ^-5  mbar O _2中进行退火，就可以通过多种方法可重复地制备在Fe _oct -O平面上的端接。在准备的最后阶段。对于铁氧化物表面，单相端接的这种直接制备通常不是这种情况。所有可用的证据表明，经常研究的（√2×√2）R45°重建是由于最外面的晶胞中阳离子晶格的重排而导致的，其中两个八面体阳离子被一个四面体间隙代替，该构想在概念上类似于井孔结构。 Fe _{1- x} O中已知的Koch-Cohen缺陷。阳离子缺陷导致Fe ₁₁ O ₁₆化学计量，这与超高真空（UHV）中的化学势一致，超高真空接近Fe ₃之间的边界O ₄和Fe ₂ O ₃相。铁_对3 O ₄（111）表面的研究也很深入，但是两个不同的表面终结点在能量上存在紧密并且可以共存，这使得样品制备和数据解释有些棘手。随着样品边缘的减少，Fe ₃ O ₄（100）和Fe ₃ O ₄（111）表面均显示富铁端接。Fe ₃ O ₄（110）表面形成与纳米刻面相关的一维（1×3）重建，从而露出更稳定的Fe ₃ O ₄（111）表面。的α-Fe ₂ ö ₃（0001）是研究最多的赤铁矿表面，但在特高压条件下制备化学计量表面的困难阻碍了对结构的确定。有证据表明至少存在三个末端：在氧平面上的块状末端，具有一半阳离子层的末端和具有亚丙基的末端。当表面被还原时，形成所谓的“双相”结构，该结构最终转变为Fe ₃ O ₄（111）状的末端。两相表面的结构是有争议的。共存的基本上接受模型的Fe _{1- X} O和的α-Fe ₂ ö ₃（0001）岛屿最近挑战和基于Fe的薄膜的新结构₃Ò ₄上（111）的α-Fe ₂ ö ₃（0001）中提出的。讨论了竞争模型的优点。所述的α-Fe ₂ ö ₃（1$\overline{\mathrm{1个}}$02）“ R形”表面由于其易于制备且在纳米材料中盛行，因此被推荐作为未来研究的极好前景。

在后面的部分中，回顾了有关在氧化铁上吸附的文献。首先，吸附分子（H ₂，H ₂ O，CO，CO ₂，O ₂，HCOOH，CH ₃ OH，CCl ₄，CH ₃ I，C ₆ H ₆，SO ₂，H ₂ S，乙苯，苯乙烯和Alq ₃）进行了讨论，并尝试将此信息与使用氧化铁作为催化剂（水-煤气变换，费-托，乙苯脱氢成苯乙烯）或催化剂载体（CO氧化）的反应相关。描述了氧化铁表面与金属的已知相互作用，并且表明其行为取决于金属是否与氧化铁形成稳定的三元相。那些没有的（例如金，铂，银，钯）倾向于形成三维粒子，而其余的（镍，钴，锰，铬，钒，铜，钛，锆，锡，锂，钾，钠，Ca，Rb，Cs，Mg，Ca）并入氧化物晶格中。结合温度随最稳定的金属氧化物的形成热量而定。_讨论了3 O ₄表面，并讨论了该模型系统在理解单原子催化和亚纳米簇催化方面的潜在应用。回顾以一个简短的总结结束，并提供了一个包括令人兴奋的未来研究思路的观点。