Studies in atomic-scale control of functional titanium nitride thin films by reflection high energy electron diffraction

氮化钛，TiN，具有共价以及金属和离子性质，这使得它在微电路中的扩散屏障等技术应用和基础研究方面都很有吸引力。为了研究TiN薄膜有趣的物理性质，原位观察TiN薄膜的生长是更可行的。虽然最近有报道，在非原位实验中，TiN膜可以通过N-注入到在室温下蒸发在NaCl衬底上的Ti膜中来外延生长，但是氮化Ti膜期间的晶体结构和电子结构的变化的知识是不完整的。在400 kV分析和高分辨透射电子显微镜（TEM）结合离子加速器的条件下，用62 keV的氮离子（N2 ^+）注入蒸镀的Ti膜。通过原位TEM、电子能量损失谱和反射高能电子衍射的观察，沿着Xα分子轨道的离散变分计算，揭示了N离子注入引起的蒸发Ti膜的晶体结构和电子结构的变化。（001）取向的NaCl型TiN y是由（035）取向的hcp Ti向（001）取向的fcc Ti转变和N占据八面体（O-）位外延形成的，而（110）取向的TiN y是由（110）取向的TiH x氮化形成的。在fcc-Ti亚晶格的O位上，H优先从TiH_x中释放，而不是N优先占据O位。随着注入N剂量的增加，Ti膜中TiH_x生长区的体等离子体激元损耗峰向低能方向移动，而hcp-Ti生长区的体等离子体激元损耗峰逐渐向高能方向移动。Mulliken键重叠的人口分析确定，在O-位的N的占领引起削弱Ti-Ti键和Ti-N共价键的形成。

Titanium nitride, TiN, has covalent as well as metallic and ionic properties, which make it fascinating for both technological applications such as diffusion barriers in microcircuits, and fundamental research. In order to investigate the interesting physical properties of TiN films, in-situ observations of the growth of TiN films are more feasible. Although it has been recently reported in light of ex-situ experiments that TiN films could be epitaxially grown by N-implantation into Ti films evaporated on NaCl substrates at room temperature, knowledge of changes in the crystallographic and electronic structures during nitriding Ti films, is incomplete. Thus, nitrogen ions (N_2^+) with 62 keV were implanted into evaporated-Ti films in the 400 kV analytical and high resolution transmission electron microscopy (TEM) combined with ion accelerators. Observations by in-situ TEM equipped with electron energy loss spectroscopy and reflection high energy electron diffraction, along with the discrete variational Xα molecular orbital calculations, revealed changes in the crystallographic and electronic structures of evaporated-Ti films due to N-implantation. A (001)-oriented NaCl-type TiN_y is epitaxially formed by the transformation of (03 5)-oriented hcp-Ti to (001)-oriented fcc-Ti and by the occupation of N in the octahedral (O-) sites, whereas a (110)-oriented TiN_y is formed by nitriding a (110)-oriented TiH_x. The release of H from the TiH_x occurs preferentially rather than the occupation of N in the O-sites of fcc-Ti sublattice. The loss peak due to volume plasmon of areas where TiH_x has grown in the as-grown Ti film shifts to lower loss energy in the early N-implanting stage, while that of areas, where hcp-Ti has grown, gradually shifts to higher loss energies with increasing N dose. Analysis of Mulliken bond overlap populations determines that occupation of N in the O-sites gives rise to weakening Ti-Ti bonds and formation of Ti-N covalent bonds.