Dense Rotational Twins in Superconducting (111)-orientated δ-NbN Epitaxial Films on 4H-SiC Substrates.

Hsiao Wen Chang^1*, Vankayala Krishna Ranganayakulu^2,3,4, Syu-You Guan², Peng-Jen Chen², Min-Nan Ou², Yang-Yuan Chen², Tien-Ming Chuang², Chia-Seng Chang², Maw-Kuen Wu², Ming-Jye Wang^1,2

¹Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan
²Institute of Physics, Academia Sinica, Taipei, Taiwan
³Department of Engineering and System Science, National Tsing-Hua University, Hsinchu, Taiwan
⁴Taiwan International Graduate Program, Academia Sinica, Taipei, Taiwan

* Presenter:Hsiao Wen Chang, email:hwchang@asiaa.sinica.edu.tw

In order to confirm the superconductivity observed in hexagonal ε-NbN reported recently, we have deposited NbN film on (0001) 4H-SiC substrate, with good lattice match, intentionally to grow hexagonal NbN phase. The detailed structural analysis show that the deposited films are (111)-orientated δ-NbN phase with dense rotational (60°) twins. Double diffraction effect in SAED (selected area electron diffraction) and Moiré fringes in HRTEM (high resolution transmission electron microscope) images confirm the existence of rotational twins in nanometer scale. The growth of highly twined film results from no energy preference for the two rotational twins of (111)-orientated δ-NbN to bond with the Si-faced (0001) 4H-SiC substrate. These highly twined δ-NbN epitaxial films exhibit high normal state resistivity, lower Tc, but good spatial uniformity of superconducting energy gap. No ε-NbN phase was observed in this study which is might due to a low growth temperature of thin film.

Keywords: magnetron sputtering, epitaxial growth, superconducting ultrathin film, niobium-nitride, dense twins