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、金属和离子性质，这使得它对微电路中的扩散屏障等技术应用和基础研究都很有吸引力。为了研究TiN薄膜有趣的物理性质，原位观察TiN薄膜的生长更为可行。虽然最近有报道称，在室温下，通过在NaCl基底上蒸发的Ti薄膜中植入n，可以外延生长TiN薄膜，但对Ti薄膜氮化过程中晶体结构和电子结构的变化的了解尚不完整。在400 kV高分辨透射电子显微镜（TEM）下，结合离子加速器，将62 keV的氮离子（N_2^+）注入蒸发ti薄膜。利用原位透射电子能谱和反射高能电子衍射观察，结合离散变分Xα分子轨道计算，揭示了氮注入后蒸发ti薄膜的晶体结构和电子结构的变化。A（001）取向的nacl型TiN_y是通过（03 - 5）取向的hcp-Ti向（001）取向的fcc-Ti的转变以及在八面体（O-）位上占据N而形成的，而（110）取向的TiN_y是通过氮化（110）取向的TiH_x形成的。在fcc-Ti亚晶格的o位上，H优先从TiH_x中释放出来，而N则优先被占据。生长Ti膜中TiH_x生长区域的体积等离激元损失峰在氮注入初期向低损失能转移，而hcp-Ti生长区域的体积等离激元损失峰随着N剂量的增加逐渐向高损失能转移。对Mulliken键重叠居群的分析表明，N在o位上的占据会导致Ti-Ti键的减弱和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.