The electron energy‐loss near‐edge structure (ELNES) on the N K‐edges from the transition metal mononitrides with the rock‐salt structure and its comparison with that on the C K‐edges from the corresponding transition metal monocarbides
The electron energy‐loss near‐edge structure (ELNES) on the N K‐edges from the transition metal mononitrides with the rock‐salt structure and its comparison with that on the C K‐edges from the corresponding transition metal monocarbides
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岩盐结构过渡金属单氮化物 N K 边上的电子能量损失近边结构（ELNES）及其与相应过渡金属单碳化物 C K 边上的电子能量损失近边结构（ELNES）
DOI：
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发表时间：
1995
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通讯作者：
A. Craven
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作者：
A. Craven
本文给出了IVA族（Ti, Zr, Hf）和VA族（V, Nb, Ta）过渡金属单氮化物在N - K -边的电子能量损失近边结构（ELNES）的形状接近化学计量。除NbN和TaN外，这些化合物在接近化学计量时具有岩盐（B1）结构。NbN以岩盐结构和六边形结构存在。从它观察到两个不同的ELNES形状，其中一个与先前发表的岩盐结构数据密切相关。在正常条件下，TaN被认为只以六边形形式存在，岩盐形式是一个高温/高压相，尽管有报道称它是等离子体射流加热六边形形式的结果。再次观察到两个不同的ELNES形状，其中一个似乎符合其他具有岩盐结构的化合物的形状模式。所观察到的系统形状变化与在等效碳化物中观察到的非常相似，并且定性地遵循理论能带结构所期望的行为。从IVA族氮化物到VA族氮化物，N - K边的化学位移变化为~‐0.8 eV，而从IVA族碳化物到VA族碳化物的化学位移变化为~ + 0.8 eV。这种行为上的差异被解释为化合物在费米能级上的态密度不同的结果。ELNES中第一个峰的位置也显示出它相对于核心态的能量随着化合物中价电子数的增加以及金属种类的过渡系列的变化而系统变化。相对于阈值，ELNES中峰值的能量Er遵循与Natoli预测的类似的关系，即（Er‐V）a = const。其中V是“松饼锡”势，a是晶格参数。第一个峰给出了关系中的一个负常数。常数的值在随后的每一个峰中增加，直到第六个峰，在第四个和更高的峰中变为正值，但在从第六个峰到第七个峰时略有下降。在关系中，每个峰值给出了不同的V值。碳化物和氮化物的数据集在每个峰上都以类似的方式系统地不同，并且在每个集合内都存在线性偏差。如果用两个突出峰的能量差来代替Er，则系统差最小化，线性度显著提高。这种峰能随晶格参数的系统变化可以用来预测晶格参数。如果同时使用氮化物和碳化物的数据来计算相对于阈值的显著峰的能量，则会导致最大偏差为4%（或~ 0.02 nm）。然而，如果使用两个突出峰的能量差，并且单独处理碳化物和氮化物的数据，则最大偏差降至0.4%（或~ 0.002 nm）。在这个层面上，晶格参数本身的不确定性开始发挥作用，需要更好的表征材料来设定预测准确性的真正限制。最后简要介绍了该方法在材料微分析中的应用。
This paper presents the shapes of the electron energy‐loss near‐edges structure (ELNES) on the N K‐edge of the group IVA (Ti, Zr, Hf) and group VA (V, Nb, Ta) transition metal mononitrides close to stoichiometry. With the exceptions of NbN and TaN, these compounds have the rock‐salt (B1) structure when close to stoichiometry. NbN exists with both the rock‐salt structure and a hexagonal structure. Two distinct ELNES shapes were observed from it, one of which corresponds closely with previously published data from the rock‐salt structure. Under normal conditions, TaN is considered to exist only in the hexagonal form, the rock‐salt form being a high‐temperature/high‐pressure phase although it has been reported as the result of plasma jet heating of the hexagonal form. Again two distinct ELNES shapes were observed, one of which appeared to fit into the pattern of the shapes from the other compounds with the rock‐salt structure. The systematic changes of shape observed are very similar to those observed in the equivalent carbides and qualitatively follow the behaviour expected from theoretical band structures. The change in the chemical shift of the N K‐edge on going from a group IVA nitride to a group VA nitride is ∼‐0·8 eV while that on going from a group IVA carbide to a group VA carbide is ∼+0·8 eV. This difference in behaviour is explained as the result of differences in the densities of states at the Fermi levels of the compounds. The position of the first peak in the ELNES also shows a systematic change in its energy relative to the core state as the number of valence electrons in the compound increases and also as the transition series of the metal species changes. The energies, Er, of the peaks in the ELNES relative to the threshold follow a relationship similar to that predicted by Natoli, i.e. (Er ‐ V)a = const. where V is the ‘muffin tin’ potential and a is the lattice parameter. The first peak gives a negative constant in the relationship. The value of constant increases for each subsequent peak up to the sixth becoming positive for the fourth and higher peaks but drops slightly on going from the sixth to the seventh peak. Each peak gives a different value of V in the relationship. The data sets for the carbides and the nitrides are systematically different in a similar way for each peak and there are deviations from linearity within each set. The systematic difference is minimized and the linearity significantly improved if the difference in the energies of two prominent peaks is used instead of Er. This systematic variation of peak energy with lattice parameter can be used to predict the lattice parameter. If both the nitride and the carbide data for the energy of a prominent peak relative to the threshold are used, this results in a maximum deviation of 4% (or ∼0·02 nm). However, if the differences in the energies of two prominent peaks are used and the data for the carbides and the nitrides are treated independently, the maximum deviation drops to 0·4% (or ∼0·002 nm). At this level, uncertainties in the lattice parameters themselves come into play and better characterized materials are required to set true limits to the accuracy of the predictions. Finally some applications in the microanalysis of materials are outlined briefly.