Tungsten Boride and Boron Boron Nitride (WBN) Structures

(Tungsten Boride and Boron Boron Nitride (WBN) Structures)

Tungsten boride is a compound of tungsten and boron which has many properties, including high hardness (20 GPa), chemical inertness and electronic conductivity. It is also used as a coating for wear-resistant parts and in the semiconductor industry.

Typical applications of tungsten boride include the formation of a ternary tungsten boron nitride thin film with excellent thermal stability, tunable resistivity and good adhesion to oxides. The WBN films are prepared by thermal atomic layer deposition (ALD) processes that pulse boron-containing, nitrogen-containing and tungsten-containing reactants into a reaction chamber to deposit the WBN thin film.

The highest tungsten boride is a cI2-W structure (c-B-W) with a boron atom in a dyadic bond (D-B). It has a low shear modulus, which is attributed to the dyadic nature of the W-B system.

A body-centered cubic (cI2-W) structure with a boron atom in an a-rhombohedral bond (hR12-B) has a slightly higher shear modulus, indicating that the boron atoms in the a-rhombohedral structure are less tightly bound to the tungsten atoms in the cI2-W. Using a combination of theory and experiment, we have investigated the relative enthalpies of formation (DE) for structures with different boron atom contents.

The enthalpies of formation are determined by the relative position of the boron atoms in the crystal lattice. They are most closely aligned with the positions of tungsten atoms in a dyadic bond, which is the same for hP16-WB3 and cI2-W. However, it is not possible to find the exact positions of the boron atoms in a dyadic relationship with tungsten atoms in cI2-W and hR12-B because of the large mass difference between the W and B atoms.

(Tungsten Boride and Boron Boron Nitride (WBN) Structures)