Nan Shao

Mutual promotion effect of crystal growth in TiN/SiC nanomultilayers

The mutual promotion effect of crystal growth in TiN∕SiC nanomultilayers is described in this letter. TiN, SiC single layers and a series of TiN∕SiC multilayers with different thickness of SiC and TiN layers were prepared using magnetron sputtering. Microstructure analysis shows that TiN and SiC single layers exist as nanocrystal and amorphous, respectively. However, in the alternately deposited nanomultilayers of TiN and SiC, due to the influence of crystal structure of TiN layer, SiC layer forms a B1-cubic phase when its thickness is less than 0.6nm. At the same time, the formation of SiC crystal promotes the growth of TiN layer and greatly improves its integrity when the thickness of the TiN layer is less than 4.3nm. Due to this effect, TiN∕SiC multilayers form a coherent epitaxial grown superlattice within a certain thickness range of TiN and SiC layers. Correspondingly, the multilayers show a superhardness effect which presents an anomalous enhancement of hardness and elastic modulus. The highest har...

Template-induced crystallization of amorphous SiO2 and its effects on the mechanical properties of TiN∕SiO2 nanomultilayers

TiN∕SiO2 nanomultilayers with various thicknesses of the SiO2 layer have been prepared by multi-target magnetron sputtering. Studies show that amorphous SiO2, which is more favorable under sputtering condition, crystallizes at smaller layer thickness (0.45–0.9nm) due to the template effect of TiN layers. Correspondingly, multilayers exhibit coherent epitaxial growth with intensive (111) texture, and show significant hardness enhancement with maximum hardness of 44.5GPa. Further increase in the SiO2 layer thickness (≳1nm) leads to the formation of amorphous SiO2 which blocks the coherent growth of the films, and thus decreases the multilayer hardness gradually.

Coherent epitaxial growth and superhardness effects of c‐TiN∕h‐TiB2 nanomultilayers

TiN∕TiB2 nanomultilayers with different TiB2 layer thicknesses were deposited by the multitarget magnetron sputtering method. Studies show that because of the template effects of the cubic TiN layer, the normally amorphous TiB2 layer crystallizes into a compact hexagonal structure when its thickness is less than 2.9 nm. As a result, the multilayers form a c‐TiN∕h‐TiB2 coherent epitaxial structure with the orientation relationship of {111}TiN∕∕{0001}TiB2,⟨110⟩TiN∕∕⟨112¯0⟩TiB2. Correspondingly, the multilayers show a significant hardness enhancement with a maximum hardness of 46.9 GPa. Further increase in TiB2 layer thickness leads to the formation of amorphous TiB2 that blocks the coherent growth of the films, and thus the hardness of the multilayers decreases gradually.

Effect of CH4 partial pressure on the microstructure and mechanical properties of magnetron sputtered TiC films

TiC thin film has become one of the most frequently used hard coatings because of its high hardness (26– 31 GPa), good wear resistance, low coefficient of friction against steel, and other excellent properties [1]. It can be deposited by chemical or physical vapor deposition (CVD or PVD). TiC films manufactured by PVD have the advantages of low deposition temperature, high quality, and high deposition speed, etc. [2]. Reactively sputtered TiC films are deposited by using gases which contain carbon such as CH4 and C2H2. Compared with using highly active C2H2, the processing is better controlled by using CH4. In this paper, TiC thin films were deposited with reactive magnetron sputtering method at different CH4 partial pressures and the effect of CH4 on their phase, microstructure, and mechanical properties was investigated. TiC films were deposited on silicon substrates by using radio frequency (RF) magnetron sputtering at room temperature. The substrates were ultrasonically cleaned in acetone and alcohol and then mounted on the substrate holder in the vacuum chamber. To improve the adhesion, a metallic Ti layer with a thickness of approximate 200 nm was deposited prior to the deposition of the ceramic TiC films. The TiC films were deposited from a pure Ti target (99.99%) in an Ar and CH4 mixture atmosphere. The Ar partial pressure was kept at 0.3 Pa, while the CH4 partial pressure varied from 0.01 to 0.08 Pa. (The CH4 partial pressure was 0.01, 0.02, 0.04, 0.06 and 0.08 Pa; specimens were numbered from 1 to 5 respectively). During this study, the target power was kept at 200 W and the deposition time was 120 min for each specimen. The phase formation and microstructure of films were investigated by X-ray diffraction (XRD) using a Dmax-rC diffractor and transmission electron microscopy (TEM) using a JEM-100CX TEM. The morphology of films was observed using a Nanoscope IIIa atomic force microscope (AFM). Mechanical property measurements of TiC thin films were carried out using a Fischerscope HV100 microhardness tester and the results were checked by AFM. The XRD spectra of the TiC films deposited at different CH4 partial pressures are shown in Fig. 1. It can be seen that at the CH4 partial pressure of 0.01 Pa, the film mainly contains metallic Ti. When CH4 pressure increases from 0.02 to 0.04 Pa, the films are single phase fcc TiC. When the CH4 partial pressure is higher than