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Transition metal nitrides are being widely applied, as durable sensors, semiconductor and superconductor devices, their electrical conductivity and wear resistance having a significant influence on these applications. However, there are few reports about how to improve above properties. In this paper, tantalum was incorporated into hafnium nitride films through Hf 1- x Ta x N y [ x =Ta/(Hf+Ta), y =N/(Hf+Ta)] solid solution. The electrical conductivity and wear resistance of the films were significantly improved, due to the increase of the electron concentration (tantalum has one more valence electron than hafnium) and the increase in H/E and H 3 /E 2 ratios caused by the effect of solid solution hardening, respectively. The highest electrical conductivity of Hf 1- x Ta x N y films is 8.3×10 5 S m −1 , which is 1.7 times and 5.2 times of that of hafnium nitride and tantalum nitride films, respectively. In addition, the lowest wear rate of films is 1.2×10 −6 mm 3 /N m, which is only 10% and 48% of that of hafnium nitride and tantalum nitride films, respectively. These results indicate that alloying with another transition metal is an effective method to improve electrical conductivity and wear resistance of transition metal nitrides. [ABSTRACT FROM AUTHOR]

Although surface roughening of films holds an important role in determining the final surface morphologies and properties, how to control it is not yet well explored. Here, we report that the surface roughening of hafnium nitride films varies significantly as a stoichiometry-driven phase transformation takes place. Through a combination of surface morphological measurements and simulations, we demonstrate that the variation of roughening mechanisms arises from the changes in diffusion behavior during growth. This study shows that the phase transformation can induce surface roughening transition, thus providing a new handle in controlling the morphologies and physical properties of thin films. [ABSTRACT FROM AUTHOR]

Although vacancies exist commonly in nonstoichiometric transition metal nitrides, their roles on structure and properties are not yet well explored. We show that in rocksalt hafnium nitride films creation of nitrogen and hafnium vacancies leads to an asymmetrical lattice contraction and distortion from cubic to rhombohedral structure owing to the presence of strong texture and compressive stress, and also causes decrease in hardness because of reduction in bulk modulus and decrease in electrical conductivity due to reduction in electron relaxation time. This new insight into vacancy-induced “negative effect” is demonstrated through good matches between our experiments and theoretical calculations. [ABSTRACT FROM AUTHOR]

A stoichiometry-driven phase transition from rocksalt to “nitrogen-rich” structure exists in group-IVB transition metal nitride films. As this phase transition is critical in controlling the film properties it has attracted numerous studies. However, researchers are still divided with regard to the structural identity of this “nitrogen-rich” phase, not to mention detailed exploration of the phase transition mechanisms. In this study, we confirmed that the “nitrogen-rich” phase in hafnium nitride (HfN x ) films had a cubic Th 3 P 4 structure of space group symmetry of I- 43 d (220), namely c -Hf 3 N 4 . The confirmation was obtained by combining the first-principle calculations with a series of experiments: Selected Area Electron Diffraction, High Resolution Transmission Electron Microscopy, Raman, Gracing Incident X-ray Diffraction and X-ray Photoelectron Spectroscopy. The mechanisms of the phase transition were elucidated through calculations on enthalpy of formation ( EOF ). The experimental results agree well with the theoretical calculations. We conclude that with increasing nitrogen, phase transition takes place from rocksalt ( δ -HfN) to c -Hf 3 N 4 through three stages of structural evolution: δ -HfN (containing Hf vacancies) → mixture of ( δ -HfN + c -Hf 3 N 4 ) → c -Hf 3 N 4 . The driving force of the phase transition is energy minimization. The three stages of structural evolution are explained by comparing the EOF of the δ -HfN and c -Hf 3 N 4 phases. As the phase transition takes place, the hafnium nitride film morphs from a conductive and opaque metal into an insulating and transparent semiconductor. [ABSTRACT FROM AUTHOR]