Geyang Li

Effect of N2 partial pressure on the microstructure and mechanical properties of magnetron sputtered CrNx films

Abstract In this paper, Chromium nitride (CrN x ) thin films were deposited with reactive magnetron sputtering method. EDX, X-ray diffraction and transmission electronic microscopy were employed to characterize their chemical compositions, phases and microstructures. Microhardness and elastic modulus were evaluated using a microhardness tester and the effect of N 2 partial pressure on the composition, phases, microstructure and mechanical properties of CrN x thin films was investigated. The results show that the phase formation of CrN x thin films varies from Cr+Cr 2 N to single-phase Cr 2 N, and then Cr 2 N+CrN to nearly single-phase CrN with increasing N 2 partial pressure. The microhardness values of these films make a distribution ranging from HV 21.4 to 27.1 GPa, and when the atom ratio of Cr:N is 1:2 and 1:1, thin film reaches peak hardness values (HV 27.1 and HV 26.8 GPa, respectively), while the elastic modulus is maximal (350 GPa) when single-phase Cr 2 N films is formed.

Superhardness effects of heterostructure NbN/TaN nanostructured multilayers

Although superhardness effects have been extensively investigated for epitaxial ceramic nanomultilayer films with the same crystal structures in the last decade, those for multilayers with different crystal structures have been seldom studied. In this article, NbN/TaN nanomultilayers have been designed and deposited by reactive magnetron sputtering. The results showed that the crystal structures of NbN and TaN are face-centered cubic and hexagonal in superlattice films, respectively, and the lattice plane (111) of NbN is coherent with the (110) of TaN, i.e., {111}fcc-NbN∥{110}h-TaN. The results of microhardness measurement showed that the superhardness effects of NbN/TaN multilayers exist in a wide range of modulation period from 2.3 to 17.0 nm. This phenomenon is different from that of epitaxial ceramic multilayers where the maximum hardness usually takes place at a modulation period of 5.0–10.0 nm. It is proposed that the coherent stresses and the structural barriers (fcc/hexagonal) to dislocation motio...

Crystallization of Si3N4 layers and its influences on the microstructure and mechanical properties of ZrN∕Si3N4 nanomultilayers

ZrN∕Si3N4 nanomultilayers with different layer thicknesses of Si3N4 were synthesized to study the crystallization of Si3N4 and its effects on the microstructure and mechanical properties of multilayers. Results indicated that influenced by the template effects of crystalline ZrN layers, amorphous Si3N4 layers were crystallized into a rocksaltlike pseudocrystal structure when their thickness was less than 0.9nm. Then crystallized Si3N4 layers grew epitaxially with ZrN and formed strong columnar crystals, accompanied with a remarkable increase in hardness. When its thickness exceeds 1.1nm, the subsequently deposited Si3N4 grows as amorphous, blocking the epitaxial growth and leading to a quick decline of hardness.

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...

Microstructure and properties of Ti–Si–N nanocomposite films

Ti–Si–N nanocomposite films were deposited by multitarget reactive magnetron sputtering. Energy dispersive spectroscopy, X-ray diffraction, transmission electron microscopy, and x-ray photoelectron spectroscopy were employed to characterize their microstructure and a microhardness tester was used to measure their hardness. The influence of substrate temperature on these films was investigated, too. The results reveal that the films consist of TiN and Si3N4. Si3N4 exists as amorphous, which strongly prevents the growth of TiN grains and causes TiN to form a nanocrystalline or amorphous phase. The hardness of films deposited at room temperature reaches the peak value of 36 GPa at a Si content of 4.14 at. %, and then decreases gradually with the increase of Si content. The enhancement of the substrate temperature weakens the restraint effect of amorphous Si3N4 on the growth of TiN grains, which results in coarse TiN grains and subsequently leads to a lower peak value and a slower decrease of the hardness of ...

Microstructure and mechanical properties of boron carbide thin films

Abstract Boron carbide thin films were deposited on single-crystal silicon substrates with magnetron sputtering method at different temperatures using a sintered B 4 C target. Auger electron spectroscopy, Fourier transform infrared spectroscopy and transmission electronic microscopy were employed to characterize their chemical compositions and microstructure. Mechanical properties of the films were evaluated using a nanoindenter. The results show the as-deposited boron carbide films are amorphous or microcrystalline with high hardness and high modulus. With the increase of the substrate temperature, boron carbide films show a tendency of crystallization, and accordingly the hardness and modulus reach 50.4 and 420 GPa from 42.5 and 300 GPa, respectively.

Study on the superhardness mechanism of Ti-Si-N nanocomposite films: Influence of the thickness of the Si3N4 interfacial phase

The superhardness effect of Ti–Si–N nanocomposite films is closely related to the thickness of the interfacial phase, Si3N4. The influence of the thickness of Si3N4 on the growth structure and mechanical properties of Ti–Si–N nanocomposite films was determined by studying TiN∕Si3N4 multilayers with different thicknesses of Si3N4 layers to reveal the strengthening mechanism of the nanocomposite films. The results show that Si3N4, which is amorphous in single film, can exist as a crystalline structure in TiN∕Si3N4 multilayers when the thickness of the Si3N4 layers is less than 0.7nm because of the “template effect” of TiN. As a result, TiN and Si3N4 layers form a coherent epitaxial growth with a preferred orientation. As a result, the multilayers exhibit a superhardness effect. When the thickness is greater than 0.7nm, Si3N4 exists as an amorphous structure and prevents TiN from coherent epitaxial growth with it, resulting in the decrease of the hardness and elastic moduli of the multilayers. The experiment...

Magnetron sputtered NbN thin films and mechanical properties

Abstract In this study, NbN thin films were deposited by reactive magnetron sputtering at different N 2 partial pressures and at room temperature. X-Ray diffraction analysis, transmission electron microscopy and atomic force microscopy were employed to characterize their phases, microstructure and surface morphology. Their microhardness and elastic modulus were evaluated using a microhardness tester and the effects of N 2 partial pressure on the phase formation, microstructure and mechanical properties of NbN thin films were investigated. The results show that there are clear effects of N 2 partial pressure on the deposition rate, phases, hardness and elastic modulus of magnetron sputtered NbN films. At a low N 2 partial pressure, the deposition rate is higher, while hcp β-Nb 2 N and fcc δ-NbN coexist in NbN films. With the increase of N 2 pressure, the deposition rate decreases and the films are single-phase fcc δNbN; accordingly, the hardness and modulus reach peak values of 36.6 GPa and 457 GPa, respectively. A further increase of the N 2 partial pressure will cause hcp e-NbN to appear in NbN films and then the hardness and modulus of films decrease.

Coherent growth and mechanical properties of AlN/VN multilayers

The growth condition of metastable cubic AlN (c-AlN) in AlN/VN multilayers and the effect of c-AlN on the mechanical properties of multilayers were investigated. A series of AlN/VN multilayers with different modulation periods were prepared by reactive magnetron sputtering. The microstructure and mechanical properties of multilayers were characterized with low-angle x-ray diffraction, high-resolution transmission electron microscopy, and nanoindentation. The results show that AlN exists as a metastable cubic phase in multilayers at small modulation periods due to the “template effect” and forms a superlattice with VN through coherent epitaxial growth. Correspondingly, multilayers show the superhardness effect with the enhancement of hardness and elastic modulus. With the increase of modulation periods, c-AlN transforms to the stable hexagonal structure (h-AlN) and multilayers demonstrate a “brick-wall” structure with nanometer grains. The hardness and elastic modulus of multilayers with large modulation p...

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.