Cu-W Films Research Articles

A new Cu-W bionic shell pearl multilayer structure

Different microstructure Cu-W films can satisfy various properties requirements. In this current work, a new Cu-W bionic shell pearl multilayer structure films were prepared by the DC dual-target magnetron co-deposition method. The connections between the multilayer films are formed by the regular zigzag weaving of slender filamentary structures in the Cu-W bionic shell pearl structure. We discovered that the influence of atomic diffusion resulted in the construction of a bionic shell pearl multilayer structure under the combined effect of W content and uphill diffusion of Cu. The Cu-10.7 at.%W films with this structure consist mainly of the face center cubic(fcc) structure of Cu and a small amount of stacking faults, but its mechanical properties are better than those of the same composition film prepared by other methods. This method can be extended to a general strategy for manufacturing other immiscible systems.

Effects of periods on the evolution of microstructure and mechanical properties of multilayered Cu-W films during thermal annealing

Benefiting from the unique structure, the copper‑tungsten (Cu-W) multilayered film is attractive due to its high strength and fracture toughness, diffusion barrier effects and radiation tolerance. However, the influence of period on the interfacial stability and strengthening mechanism during annealing has seldom been touched. Hence, the Cu-W multilayers with the periods from 1.6 to 27 nm were synthesized by altering substrate rotation speed using co-sputtering. In contrast to the findings in literature by sequential sputtering, kinetically constrained deposited atoms contribute to the more amorphous phase near interface in the films with smaller periods and result in the reduced hardness. During annealing, Cu and W atoms are thermal-activated and up-hill diffuse towards Cu- and W-rich layers, respectively, which can not only eliminate the amorphous phases but also enlarge the concentration ratio and result in the spinodal decomposition. In turn, the films with larger periods present higher thermal resistibility against phase separation due to the stronger diffusion barrier effect of thicker W-rich layers. The mechanical properties of the annealed films generally increase with the temperature up to 400 °C due to the reduced amorphous phases and the enhanced interfacial strengthening. At 500 °C, the separation of soft Cu phase and the loss of coherency mainly lead to the reduced mechanical properties. It is striking that the Cu-W film with the moderate thickness exhibits the highest hardness at higher temperature of 500 °C, indicating the significant importance of period to control their high temperature mechanical properties.

Thermal stability of nanocrystalline grains in Cu-W films

It has been hypothesized that introduction of proper solute atoms, which preferentially segregates to grain boundaries, can stabilize the nanoscale grain size at elevated temperatures. To explore this possibility, we synthesized pure Cu and Cu-3 at. % W nanocrystalline films using magnetron sputtering. Scanning electron microscopy and x-ray diffraction showed that while grains in pure Cu coarsen rapidly when annealed at 673 K, Cu-3% W maintains a stable microstructure when annealed at the same temperature, achieving grain size of 37 nm after 120 min annealing. Nanoindentation measurements gave results consistent with the grain size evolution: upon annealing at 673 K, the hardness of the pure Cu film decreases to 40% of its initial value after 20 min, while the Cu-3% W film retains more than 90% of its initial hardness even after 120 min. Atom probe analysis shows W segregation in the Cu-3% W film. Results of this study indicate that solute segregation can be used as a method to fabricate nanocrystalline materials that are stable against grain coarsening at elevated temperatures.

The evolution of hardness in Cu-W alloy thin films

A series of Cu-W films with the W content higher than 17.2 at% were prepared by magnetron sputtering focused co-deposition technology. The micro-structures and nanoidentation hardness of the films were investigated. Except for the fcc, amorphous and bcc phases, a novel multilayered structure has been observed at the range of about 17.2–90 at% W. Within the multilayered structure, the high-density interfaces can inhibit the motion of dislocations, which resulted in the hardness at least 2 GPa higher than that of the mixing rule. Depending on different microstructures, the hardness curve of the Cu-W films can be divided into three regions instead of the linear increase with the W content. From 17.2–40 at% W, the hardness increased slowly due to lots of amorphous phase. Within 40–65 at% W, the hardness increased linearly, which was caused by the gradually obvious multilayered structure and decreasing amorphous content. Above 65 at% W, single-phase body-centered cubic (bcc) films were observed. In this region, the upward trend of hardness slowed down due to the porous columnar structure and gradually disappeared multilayered structure.

Preparation of Cu-W film by ion beam sputtering and characterization

This works aims at exploring the effects of dual ion beam sputtering-assembled W-rich copper-tungsten films. The film characterization was performed by means of X-ray diffraction and magnetic coating thickness testing. Our results indicate a gradual change in the tungsten structure—from approximately metastable and amorphous to crystalline—as the Ar+ ion energy increases during the sputtering process. Due to the reflection effect, an increase in film thickness was also observed with increasing energy. At lower energies, the film deposition become very difficult due to the atomic shot peening effect.

Cu-W thin film structure influenced by Ar+ energy and beam flow during preparation by ion beam sputtering

This article focuses on the effects of Ar+ and beam flow on Cu-W film structure produced using dual ion beam sputtering. The testing method is analysis through XRD. The results show that increasing Ar+ energy and beam flow causes the Cu-W film to crystalize. The Cu-W film deposition speed is primarily determined by Ar+ energy and beam flow.

Structure characteristic and its evolution of Cu-W films prepared by dual-target magnetron sputtering deposition

Immiscible Cu-W alloy thin films were prepared using dual-target magnetron sputtering deposition process. The structure evolution of Cu-W thin films during preparation was investigated by X-ray diffraction, transmission electron microscopy and high resolution transmission electron microscopy. In the initial stage of dual-target magnetron sputtering deposition process, an amorphous phase formed; then it crystallized and the analogy spinodal structure formed due to the bombardment of the sputtered particles during sputtering deposition process, the surface structure of the film without the bombardment of the sputtered particles was the amorphous one, the distribution of the crystalline and amorphous phase showed layer structure. The solid solubility with the analogy spinodal structure was calculated using the Vegard law. For Cu-13.7%W (mole fraction) film, its structure was composed of Cu-11%W solution, Cu-37%W solution and pure Cu; for Cu-14.3%W film, it was composed of Cu-15%W solution, Cu-38%W solution, and pure Cu; for Cu-18.1%W film, it was composed of Cu-19%W solution, Cu-36% W solution and pure Cu.

Influence of Ar+ Energy of Bombardment Cu Target and Low Energy Assisted Bombardment on Cu-W Thin Film Structure by Ion Beam Sputtering

This paper is to study the influence of Ar+ energy of bombardment Cu target and low energy assisted bombardment on Cu-W film structure in the preparation of Cu-W thin film by dual ion beam sputtering technique with iron as the substrate and argon as ion source. The results shown : when Ar+ energy of bombardment tungsten target is about 3keV, the beam of copper target is 20mA, Ar+ energy of bombardment Cu target is 1kev, 1.5kev and 2keV respectively, Cu-W thin film prepared by ion beam sputtering exists with the skeleton of tungsten in amorphous phase mixing with copper grains; with the increase of Ar+ energy of of bombardment copper target, the grain size of copper increases slightly; influenced by crystal defects and lattice distortion, copper diffraction peak offsets a little. Low energy assisted bombardment helps to increase grain growth of copper and can decrease crystal defects and lattice distortion. But with excessive energy, thin film fails to deposit.

Enhanced adhesion of Cu-W thin films by ion beam assisting bombardment implanting

Cu-W thin film with high W content was deposited by dual-target DC-magnetron co-sputtering technology. Effects of the substrates surface treating technique on the adhesive strength of Cu-W thin films were studied. It is found that the technique of ion beam assisting bombardment implanting of W particles can remarkably improve the adhesive property of Cu-W thin films. Indentation and scratching test show that, the critical load is doubled over than the sample only sputter-cleaned by ion beam. The enhancing mechanism of ion beam assisting bombardment implanting of Cu-W thin films was analyzed. With the help of mid-energy Ar + ion beam, W atoms can diffuse into the Fe-substrate surface layer; Fe atoms in the substrate surface layer and W atoms interlace with one another; and microcosmic mechanical meshing and diffusing combination on atom-scale among the Fe and W atoms through the film/substrate interface can be formed. The wettability and thermal expansion properties of the W atoms diffusion zone containing plentiful W atoms are close to those of pure W or W-based Cu-W film.

Characterization of surface morphology of copper tungsten thin film by surface fractal geometry and resistivity

Thin films of copper-tungsten (Cu-W) deposited on silicon wafers by magnetron sputtering were characterized by Atomic Force Microscopy (AFM). X-ray diffraction (XRD) and transmission electron microscopy (TEM) and four-point probe method were employed to characterize the microstructure and properties of Cu-W films. Power spectra density (PSD) was used to calculate the fractal dimension of AFM images. The results show that the fractal dimension values increase with the film thickness. A positive correlation between fractal dimension and resistivity of the film was also demonstrated for amorphous films. Changes in the relationship between the resistivity and the fractal dimension are observed for films with possible crystalline structures.

95/00331 Pore size distribution of coals and chars from western Canada

A backscattered electron image detector has been used in a scanning electron microscope to study simultaneously the image intensity If of thin sputtered films of copper-aluminium alloys on single-crystal silicon substrates and the image intensity Ir of an adjacent, bulk copper reference specimen. The contrast ratio k = If/Ir for a given film and the reference sample depends on the energy E of the incident electrons. A graph of k vs. 1/E is used to obtain a characteristic energy Ei called the intercept energy which, in agreement with previous work, depends on the thickness of the film but not on its composition. Another feature of a curve of k vs.1E is that k tends to a limit as 1/E increases. This limit depends on the composition of the film to which the curve applies, and thus both thickness and composition can be obtained from a given curve. The present results which cover the low range of atomic numbers (Z = 13−29) are compared with the results obtained for Cu-W films which cover the atomic number range from Z = 29 to Z = 74. It is confirmed that the thicknesses of the light Cu-Al alloys studied in the present experiments and of Cu-W films can be obtained from a single curve of ln(thickness) vs. ln(Ei) and therefore that the method of using electron image contrast to measure thickness is applicable over a wide range of atomic numbers.

The use of electron image contrast to measure the thickness and composition of thin films of light binary alloys

A backscattered electron image detector has been used in a scanning electron microscope to study simultaneously the image intensity I f of thin sputtered films of copper-aluminium alloys on single-crystal silicon substrates and the image intensity I r of an adjacent, bulk copper reference specimen. The contrast ratio k = I f/ I r for a given film and the reference sample depends on the energy E of the incident electrons. A graph of k vs. 1/ E is used to obtain a characteristic energy E i called the intercept energy which, in agreement with previous work, depends on the thickness of the film but not on its composition. Another feature of a curve of k vs. 1 E is that k tends to a limit as 1/ E increases. This limit depends on the composition of the film to which the curve applies, and thus both thickness and composition can be obtained from a given curve. The present results which cover the low range of atomic numbers ( Z = 13−29) are compared with the results obtained for Cu-W films which cover the atomic number range from Z = 29 to Z = 74. It is confirmed that the thicknesses of the light Cu-Al alloys studied in the present experiments and of Cu-W films can be obtained from a single curve of ln(thickness) vs. ln( E i) and therefore that the method of using electron image contrast to measure thickness is applicable over a wide range of atomic numbers.