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DOE OSTI2020

Materials Data on Hf3N2 by Materials Project

Hf3N2 is MAX Phase-derived structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three Hf3N2 sheets oriented in the (0, 0, 1) direction. there are two inequivalent Hf sites. In the first Hf site, Hf is bonded in a distorted T-shaped geometry to three equivalent N atoms. All Hf–N bond lengths are 2.29 Å. In the second Hf site, Hf is bonded to six equivalent N atoms to form edge-sharing HfN6 octahedra. All Hf–N bond lengths are 2.26 Å. N is bonded to six Hf atoms to form a mixture of edge and corner-sharing NHf6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Hf3N2 by Materials Project

Hf3N2 crystallizes in the trigonal R3m space group. The structure is two-dimensional and consists of three Hf3N2 sheets oriented in the (0, 0, 1) direction. there are three inequivalent Hf sites. In the first Hf site, Hf is bonded in a distorted T-shaped geometry to three equivalent N atoms. All Hf–N bond lengths are 2.26 Å. In the second Hf site, Hf is bonded to six N atoms to form distorted edge-sharing HfN6 pentagonal pyramids. There are three shorter (2.28 Å) and three longer (2.32 Å) Hf–N bond lengths. In the third Hf site, Hf is bonded in a distorted T-shaped geometry to three equivalent N atoms. All Hf–N bond lengths are 2.24 Å. There are two inequivalent N sites. In the first N site, N is bonded to six Hf atoms to form a mixture of face, edge, and corner-sharing NHf6 octahedra. The corner-sharing octahedral tilt angles are 47°. In the second N site, N is bonded to six Hf atoms to form a mixture of face, edge, and corner-sharing NHf6 octahedra. The corner-sharing octahedral tilt angles are 47°.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Phase composition of polycrystalline HfNx (0.45 ≤ x ≤ 1.60) and effects of low-energy ion irradiation on microstructure, texture, and physical properties

We have investigated the phase composition of HfNx as a function of x and the effects of low-energy ion irradiation on the microstructure and physical properties of polycrystalline layers grown on SiO2 at 350 °C by ultrahigh vacuum reactive dc magnetron sputtering of Hf in mixed N2/Ar discharges. X-ray diffraction and Rutherford backscattering spectrometry results show that the phases obtained in polycrystalline HfNx layers with increasing x are hcp-structure α-Hf:N (x ≲ 0.6); multiphase mixtures consisting of α-Hf, NaCl-structure δ-HfN, rhombohedral ɛ-Hf3N2, and/or ζ-Hf4N3 (0.6 ≲ x ≲ 0.9); δ-HfN single phase (0.9 ≲ x ≲ 1.3); and mixtures of δ-HfN and higher nitrides (x ≳ 1.3). HfNx layers with 0.9 ≲ x ≲ 1.2 grown under mild ion irradiation (incident ion energy Ei ≃ 7 eV and ion-to-Hf flux ratios Ji/JHf = 1−3) are underdense with mixed orientation, low in-plane stress, and rough surface morphology due to limited adatom mobilities resulting in kinetic roughening and atomic shadowing during film growth. However, the use of intense ion irradiation (Ei = 25 eV and Ji/JHf = 4−20) results in HfNx layers, which are fully dense with strongly 111-oriented texture, compressive in-plane stress, and smooth surfaces due to ion irradiation enhanced adatom surface mobilities. In addition, the latter films have lower resistivity and higher hardness. For stoichiometric δ-HfN layers, ρ decreases from 69.7 to 35.2 μΩ cm and H increases from 22.1 to 27.4 GPa, with increasing ion-irradiation intensity. However, for HfNx layers with 1.2 ≲ x ≲ 1.6, the correspondingly higher steady state atomic N surface coverages during deposition alter growth kinetics in favor of 001 texture with a fully dense structure and compressive in-plane stress.

Materials Science↗