Laboratoire des Sciences de l'Ingénieur, de l'Informatique et de l'Imagerie (ICube), CNRS and University of Strasbourg, 23 rue du Loess, 67037 Strasbourg, France.
Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), UMR7504 CNRS and University of Strasbourg, 23 rue du Loess, 67034 Strasbourg, France.
J Chem Phys. 2023 Apr 28;158(16). doi: 10.1063/5.0143828.
Type I and type II silicon clathrates are guest-host structures made of silicon polyhedral cages large enough to contain atoms that can be either inserted or evacuated with only a slight volume change of the structure. This feature is of interest not only for batteries or storage applications but also for tuning the properties of the silicon clathrate films. The thermal decomposition process can be tuned to obtain Na8Si46 and Na2<x<10Si136 silicon clathrate films on intrinsic and p-type c-Si (001) wafer. Here, from a unique synthesized NaxSi136 film, a range of resistivity of minimum four order of magnitude is possible by using post-synthesis treatments, switching from metallic to semiconductor behavior as the Na content is lowered. Extended exposition to sodium vapor allows us to obtain fully occupied Na24Si136 metallic films, and annealing under iodine vapor is a way to reach the guest-free Si136, a semiconducting metastable form of silicon with a 1.9 eV direct bandgap. Electrical measurements and resistance vs temperature measurements of the silicon clathrate films further discriminate the behavior of the various materials as the Na concentration is changing, additionally shouldered by density functional theory calculations for various guest occupations, further motivating the urge of an innovative pathway toward true guest-free type I and type II silicon clathrates.
I 型和 II 型硅笼合物是一种主体-客体结构，由足够大的硅多面体笼组成，可以容纳原子，这些原子可以通过结构的轻微体积变化插入或排出。这种特性不仅对电池或存储应用有兴趣，而且对调整硅笼合物薄膜的性质也有兴趣。可以通过调节热分解过程来获得 Na8Si46 和 Na2<x<10Si136 硅笼合物薄膜，这些薄膜沉积在本征和 p 型 c-Si（001）晶片上。在这里，从独特合成的 NaxSi136 薄膜中，可以通过后合成处理获得最小四个数量级的电阻率范围，从而实现从金属到半导体的转变，因为 Na 含量降低。将钠蒸气进一步暴露，可以获得完全占据的 Na24Si136 金属薄膜，而在碘蒸气中退火是获得无客硅笼合物 Si136 的一种方法，这是一种具有 1.9 eV 直接带隙的硅亚稳态半导体。硅笼合物薄膜的电测量和电阻与温度的测量进一步区分了各种材料的行为，因为随着 Na 浓度的变化，密度泛函理论计算也对各种客体占据进行了计算，这进一步激发了对真正无客体 I 型和 II 型硅笼合物的创新途径的渴望。
