Superconductivity in MoN films with NaCl structure

Molybdenum Nitride Films: Crystal Structures, Synthesis, Mechanical, Electrical and Some Other Properties

“…Saito et al [26] have reported a continuous transformation of the γ-Mo2N phase to the stoichiometric B1-MoN phase by increasing nitrogen incorporation in the structure. The lattice parameter of 0.420-0.422 nm is close to the value equal to 0.425 nm calculated by Papaconstantopoulos et al [42] and to the experimental value of 0.4212 nm reported in the paper of Linker et al [40], which corresponds to the exact stoichiometry.…”

“…The films are deposited under two conditions: at 250 W with a total pressure of 0.93 Pa and at 300 W with a total pressure of 1. Linker et al [40] and Ihara et al [25] have performed reactive sputtering process with high nitrogen partial pressure to synthesize stoichiometric MoN films of B1-NaCl-type cubic structure because this compound has been predicted to have a higher superconducting transition temperature than NbN (17 K) on the basis of electronic band calculations (Section 7.3). The films 150-400 nm thick have been deposited onto sapphire and glassy carbon substrates in (Ar-N2) gas mixture at partial pressures of 2.66 and 6.65 Pa, respectively, or in pure nitrogen gas at a pressure of about 20 Pa by using a RF system at a total power of 500 W in [40].…”

“…Linker et al [40] and Ihara et al [25] have performed reactive sputtering process with high nitrogen partial pressure to synthesize stoichiometric MoN films of B1-NaCl-type cubic structure because this compound has been predicted to have a higher superconducting transition temperature than NbN (17 K) on the basis of electronic band calculations (Section 7.3). The films 150-400 nm thick have been deposited onto sapphire and glassy carbon substrates in (Ar-N2) gas mixture at partial pressures of 2.66 and 6.65 Pa, respectively, or in pure nitrogen gas at a pressure of about 20 Pa by using a RF system at a total power of 500 W in [40]. The substrate temperature was varied between room temperature and 1173 K. The stoichiometric MoN films are synthesized at a substrate temperature of 773 K. The resistivity of films has been studied as well as the superconducting temperature (Sections 6 and 7).…”

“…Linker et al [40] have carried out implantation of nitrogen into evaporated Mo films and Mo single-crystal surfaces using multiple ion energies and fluences. They found similar results to those previously described in Section 4.1.2.…”

“…Among all molybdenum nitride phases, γ-Mo2N can be synthesized over a large range of nitrogen pressure from some thousandths of Pascal in (Ar-N2) gas mixture [29] to dozens of Pascal in pure N2 gas [25,40]. Hence, depending on the range of pressure, an increase of pressure leads to contrasting results: A transition from γ-Mo2N to stoichiometric MoN phases occurs at large nitrogen partial pressure in (Ar-N2) gas mixture [40] or in pure N2 gas [25,40], whereas transitions from randomly oriented crystallites to oriented crystallites [29] or amorphous structures [31,32] occur at low nitrogen partial pressure. Such phenomena are related to an excess of nitrogen in the lattice and/or the occurrence of stresses during the film growth and so, discrepancies in the values of lattice parameters corresponding to γ-Mo2N are clearly seen in Table 1 compared with the bulk and theoretical values.…”