Superhard Tungsten Tetraboride Films Prepared by Pulsed Laser Deposition Method

Abstract

Attempts to synthesize and/or theoretically predict new superhard materials are the subject of an intense research activity. The trials to deposit them in the form of films have just began. WB(2) (77 wt % WB(2) and 23 wt % WB(4)) and WB(4) (65 wt % WB(4) and 35 wt % WB(2)) polycrystalline bulk samples were obtained in this work via electron beam synthesis technique and, subsequently, used as targets for films preparation by the pulsed laser deposition method. The targets were irradiated by a frequency-doubled Nd:glass laser with a pulse duration of 250 fs. The films grown on SiO(2) substrates at 600 °C were characterized by X-ray diffraction, scanning electron and atomic force microscopies, and Vickers microhardness technique. The deposited films are composed of WB(4). The intrinsic film hardness, calculated according to the "law-of-mixtures" model, lies in the superhardness region 42-50 GPa.

Two-phase zirconium boride thin film obtained by ultra-short pulsed laser ablation of a ZrB12 target

“…In the ultra-short ablation of a large number of systems, as it is reported in literature [6][7][8]12,25], the presence of two different laser induced emissions can be distinguished: a first plasma (primary plume) lasting for few hundreds of nanosecond and characterized by the presence of electronic transitions of atomic and ionic emissions and a second one (secondary component or plume) starting after few microseconds and showing a typical black-body like emission spectrum. The emission produced by ultra-short laser ablation of the ZrB 12 target presents a particular characteristic, in fact, together with the primary and secondary plumes also a third emission of material is present.…”

“…Usually, thin films obtained by ultra-short PLD are formed by particles ranging from tens to hundreds of nanometers in diameter and no larger particles are present onto their surfaces [6][7][8]. Fig.…”

“…The expanding evaporated material is deposited on the surface of a suitable substrate to form a film. PLD is a versatile deposition technique, particularly well suited to grow thin films of a large number of materials with technological interest, such as oxides, nitrides, carbides, and borides [6][7][8][9][10]. Ultra-short PLD has been widely used for its capability to evaporate and to deposit refractory materials, transferring the target stoichiometry to the film, although the mechanism involved, in * Corresponding author.…”

WB2 to WB3 phase change during reactive spark plasma sintering and pulsed laser ablation/deposition processes

“…Deposited films may have a thickness from several nanometers to several micrometers. In the last years, certain success has been achieved in the pulsed laser deposition of superhard thin films of tungsten tetra-boride (WB 4 ) [28]. Obtained by the PLD method, thin films of WB 4 on the SiO 2 substrate, according to theoretical calculations, have very high Vickers hardness of 42-50 GPa [28].…”

Unexpectedly hard and highly stable WB3 with a noncompact structure

“…The early established hP14-W 2 B 5 [9] was recently identified as hP12-WB 2 [10], which has a maximum measured hardness of 42.2 GPa [11]. First-principles calculations suggested that hP6-WB 2 was energetically more stable than the experimentally reported hP3-WB 2 [12] and could have the high hardness with a value of 43.8-47.4 GPa [13,14].…”