Junhua Xu

Effect of deposition parameters on composition, structures, density and topography of CrN films deposited by r.f. magnetron sputtering

Abstract CrN thin films were fabricated on single crystal silicon substrates by using the reactive radio frequency magnetron sputtering. The effects of deposition parameters on the deposition rate, composition, microstructures, density, and surface roughness of the CrN films have been investigated by AES, XRD, XRR, and AFM. It is found that the cubic-CrN phase can be observed in films with a relatively wide range of nitrogen gas flows. The composition of CrN films was controlled by the gas flows of N 2 and the gas flow ratio (Ar/N 2 ). The density of CrN films decreases with the increase of gas flows at room temperature. It is considered that the observed density decrease of CrN films is due to an increasing number of collision between CrN particles with the increasing gas flows of Ar and N 2 . It is beneficial to produce dense films at high temperature of substrate. The effects of gas flows on the deposition rate showed that the deposition rate decreases with the increase of nitrogen gas flows. The surface roughness of the films increases with the increase of Ar and N 2 gas flows, and Ar gas flows play a main role in the surface roughening. It is suggested that the ion and particles bombardment at low gas pressures cause a smoother surface.

Thermal stress hardening of a-Si3N4/nc-TiN nanostructured multilayers

Amorphous/nanopolycrystalline Si3N4/TiN nanostructured multilayer films have been fabricated by radio-frequency reactive magnetron sputtering. The effects of deposition temperature, modulation period, and the layer thickness ratio on the hardness have been studied, in order to elucidate the hardening mechanisms in these multilayers. The hardness of the Si3N4/TiN multilayers is affected not only by the modulation periods, but also by the layer thickness ratio and deposition temperature. The hardness value is about 40% higher than the value calculated from the rule of mixtures at a deposition temperature of 500 °C and a modulation ratio (lSi3N4/lTiN) of 3/1. Based on the experimental results, it is suggested that the alternating stress field caused by thermal mismatch between Si3N4 and TiN is one of the main reasons for the superhardness effect in Si3N4/TiN nanostructured multilayers.

Surface evolution of nanostructured CrN and Si3N4 films

Comparative surface evolution of nanocrystalline (nc)-CrN and amorphous (a)-Si3N4 monolithic films and their alternative multilayer films has been studied in relation to film thickness in monolithic films, as well as to modulation periods in multilayers. Structural analysis was carried out using atomic force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM). The scaling behaviors of the AFM topographical profiles were analyzed using the one-dimensional power spectral density method (1DPSD). It is interesting to note that the growth exponents (β) of both CrN and Si3N4 films can be divided into two regions of β1=0.22±0.08 and β2=0.87±0.1 for CrN films and β1=0.09±0.01 and β2=0.24±0.03 for Si3N4 films. The critical transition thickness, where the roughness jumps, is about 16.0 for CrN films and 168.0 nm for Si3N4 films. The 1DPSD analysis showed that the dependence at high frequency can be fitted to f−4.3 and f−4.2 power law decays, since the film thickness is less than 16.0 for C...

Structure, hardness, and elastic modulus of Pd/Ti nanostructured multilayer films

The structure, hardness, and elastic modulus of Pd/Ti multilayers deposited by radio-frequency magnetron sputtering were investigated by x-ray diffraction, high-resolution transmission electron microscopy, and nanoindentation. Both the Ti and Pd layers were face-centered-cubic structures in all modulation periods from 2.8 nm to 90.0 nm in Pd/Ti multilayers. There are stacking faults in Ti layers at large modulation periods, where the crystal structure is hexagonal close packed. An anomalous hardness enhancement was observed. The hardness values of Pd/Ti multilayers are three times and two times the values measured in Pd films and as calculated by the rule of mixture for Pd and Ti films, respectively. The modulus values of Pd/Ti multilayers are between those of constituent single layer films at a larger modulation period, and increase slightly at a smaller modulation period. The elastic modulus difference model cannot explain this hardness enhancement, since the elastic modulus is almost the same for the c...

Interfacial intermixing of TiN/Si3N4 super-hard multilayer films studied by fluorescence x-ray absorption fine structure

Fluorescence x-ray absorption fine structure and x-ray diffraction are used to study the structures of super-hard TiN/Si3N4 multilayer films deposited by reactive magnetron sputtering at temperatures of 20, 200, 500 and 800 °C. The results clearly reveal the presence of interfacial intermixing between adjacent TiN and Si3N4 layers. And the interlayer is composed of TiSixN1−x solid solution with an NaCl-like structure. Increasing the growth temperature from 20 to 500 °C, the crystalline quality of the pure TiN layer improves significantly, and the thickness of the interlayer rises from 2.5 to 5.0 A. For the TiN/Si3N4 multilayer film grown at 500°C, the interfacial layer is composed of TiSi0.24N0.76 solid solution, where the Ti–N bond length (2.07 A) is largely shrunk as compared with the value (2.12 A) in the pure TiN layer. When growth temperature rises to 800°C, the composition of the interfacial layer becomes TiSi0.3N0.7 and reaches a thickness of 7.8 A. We propose that the TiSixN1−x interlayer with obviously contracted Ti–N bond length is an important hardening factor for the crystalline/amorphous TiN/Si3N4 multilayer films grown at high temperatures.

Enhancement in layer-by-layer growth in heteroepitaxial growth of Co on Au(111) surface by Bi surfactant

The surfactant effect of Bi on the heteroepitaxial growth of Co on the Au(111) surface has been studied. With the predeposition of submonolayer Bi on Au(111) prior to evaporation of Co, more long-lasting reflection high-energy electron diffraction intensity oscillations were observed at room temperature. This implied that Bi enhanced the layer-by-layer growth of Co on the Au(111) surface. The dependence of the Co film growth on the thickness of the Bi surfactant layer suggested that there existed a suitable amount of Bi surfactant that enhanced a smoother layer-by-layer growth. The Auger electron spectra revealed that Bi was segregated at the top of the surface. Therefore, Bi was concluded to be an effective surfactant to enhance the layer-by-layer growth of Co on Au(111).

EFFECT OF Bi SURFACTANT IN THE HETEROEPITAXIAL GROWTH OF Co ON Cu SURFACES

We have investigated the effect of Bi on the heteroepitaxial growth of Co on Cu by reflection high-energy electron diffraction (RHEED) measurements. It was found that Bi enhanced the layer-by-layer growth of Co on the Cu(111) surfaces at 100°C. The dependence of the growth on Bi layer thickness suggested that there existed a suitable amount of Bi surfactant layer that enhanced smoother layered growth. On the contrary, for the case of Co growth on Cu(100), Bi depressed the layer-by-layer growth of Co on Cu(100). The surface segregation effect of Bi was also studied by Auger electron spectroscopy (AES).

Bi-enhanced Heteroepitaxial Layered Growth of Cr on Fe(100)-c(2× 2)O Reconstruction Surfaces

We have investigated the effect of Bi on the homoepitaxial growth of Cr on Fe(100) by reflection high-energy electron diffraction (RHEED) measurements. It was found that Bi enhances the layered growth of Cr on Fe(100)-c(2× 2)O reconstruction surfaces. The dependence of the growth on Bi layer thickness suggests that there exists a suitable amount of Bi surfactant layer that enhances smoother layered growth. The surface segregation effect of Bi was studied by Auger electron spectroscopy.

Hardening Mechanisms of Amorphous / Polycrystalline Nanostructured Multilayer Films: Si3N4/CrN and Si3N4/TiN

The amorphous/polycrystalline Si 3 N 4 /CrN and Si 3 N 4 /TiN nano-structured multilayer films have been fabricated by RF reactive magnetron sputtering. The microstructure and properties of these films were measured by XRD, HRTEM and nano-indenter There is no superhardness effect in the Si 3 N 4 /CrN multilayers. The hardness values of Si 3 N 4 /CrN multilayers are between those of the constituent CrN and Si 3 N 4 films at a substrate temperature of 20∼C, and are a little higher than those of Si 3 N 4 films at a deposition temperature of 500°C. However, the superhardness effect was found in Si 3 N 4 / TiN multilayers. The hardness of Si 3 N 4 / TiN multilayers is affected not only by modulation periods, but also by layer thickness ratio and deposition temperature. The maximum hardness value is about 40% higher than the value calculated from the rule of mixtures at a deposition temperature of 500°C and a layer thickness ratio ( l Si3N4 / l TiN ) of 3 / 1. Based on experimental results, the hardening mechanisms in these multilayers have been discussed.