Ag Alloy Thin Films Research Articles

Fabrication of highly electrically conductive Ti/Ag/Ti tri-layer and Ti–Ag alloy thin films on PET fabrics by multi-target magnetron sputtering

In this study Ti/Ag/Ti tri-layer and Ti–Ag alloy films were deposited on the surfaces of polyethylene terephthalate (PET) fabrics by multi-target magnetron sputtering system to fabricate highly electro-conductive textiles. Before sputtering, the fabric was treated by polyacrylic acid ester (PA) to form a continuous surface on the surface of PET fabric by padding method. The as-fabricated fabrics were characterized by scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectrometer. And the physical properties of the coated fabrics were evaluated by electrical conductivity, contact angle (CA), flexibility and adhesion. At last, a simple electric circuit was made with the as-treated fabric to evaluate the electrical property and explore its application further. The results of the study revealed that pretreatment with PA could form a continuous film on the surface of PET fabric. The PA-coated PET fabric with Ti/Ag/Ti fabric exhibited excellent electrical property whose electrical resistivity was only 5.1 × 10−7 Ω m, CA of 137°. The PA-coated PET fabric with Ti–Ag alloy film exhibited a rather lower electrical resistivity of 3.4 × 10−7 Ω m, CA of about 130°. Moreover, the samples retain ideal flexibility and adhesion. Therefore this study can broaden the application area of magnetron sputtering on discontinuous surface to fabricate electrical conductive fabric. And due to the excellent electro-conductivity, this kind of fabric will be a promising material for smart textiles.

Low driving voltage indium–tin oxide/Al–Ni–Cu–La anode electrodes for top-emission organic light-emitting diodes

We have developed indium–tin oxide (ITO)/Al–Ni–Cu–La anode electrodes for cost-effective large top-emission organic light-emitting diode (OLED) displays. By combining alkaline cleaning with thermal annealing, the driving voltage of the OLED devices containing Al–Ni–Cu–La thin films was effectively reduced, becoming comparable to that for conventional Ag alloy thin films. Cross-sectional transmission electron microscopy (XTEM) observation revealed that the grains in the Al matrix and the precipitates on the Al–Ni–Cu–La surface were small, resulting in a low driving voltage and a high optical reflectivity. The Al–Ni–Cu–La thin films overcome the oxidation issues that cause an increase in contact resistance due to the formation of AlOx between the Al alloy and the ITO thin films, and could replace conventional anode electrodes having an ITO/Ag/ITO structure.

The Effect of Cu:Ag Atomic Ratio on the Properties of Sputtered Cu-Ag Alloy Thin Films.

Cu–Ag thin films with various atomic ratios were prepared using a co-sputtering technique, followed by rapid thermal annealing at various temperatures. The films’ structural, mechanical, and electrical properties were then characterized using X-ray diffractometry (XRD), atomic force microscopy (AFM), FESEM, nano-indentation, and TEM as functions of compositions and annealing conditions. In the as-deposited condition, the structure of these films transformed from a one-phase to a dual-phase state, and the resistivity shows a twin-peak pattern, which can be explained in part by Nordheim’s Rule and the miscibility gap of Cu–Ag alloy. After being annealed, the films’ resistivity followed the mixture rule in general, mainly due to the formation of a dual-phase structure containing Ag-rich and Cu-rich phases. The surface morphology and structure also varied as compositions and annealing conditions changed. The recrystallization of these films varied depending on Ag–Cu compositions. The annealed films composed of 40 at % to 60 at % Cu had higher hardness and lower roughness than those with other compositions. Particularly, the Cu50Ag50 film had the highest hardness after being annealed. From the dissolution testing, it was found that the Cu-ion concentration was about 40 times higher than that of Ag. The galvanic effect and over-saturated state could be the cause of the accelerated Cu dissolution and the reduced dissolution of the Ag.

Growth of nanocomposite in eutectic Cu–Ag films

Eutectic composition Cu–Ag alloy thin films were prepared by co-deposition at room temperature onto oxidized Si substrates by thermal evaporation. Morphological development, structure and phase state of the films were investigated by transmission electron microscopy. The films possess fibre morphology 10–30 nm in diameter and strong <111> texture is present. The fibres are nanocrystalline composed of 2–3 nm size zones of Cu and Ag rich solid solution phases and a model for morphological development and phase separation is described. In the early stages of growth phase separation occurs by nucleation in melted islands and a eutectic of randomly oriented crystallites forms. In later stages of growth the phase separation takes place by spinodal decomposition. It results in a strain stabilized unique morphology corresponding to an intermediate stage of phase separation.

Influence of synthesis conditions on the nanostructure of immiscible copper–silver alloy thin films

Far from equilibrium, immiscible nanocrystalline Cu–Ag alloy thin films of nominal composition Cu–30(±5) at.% Ag were deposited by co-sputtering. While films deposited at ∼300 K exhibit a two-phase mixture of face-centered cubic (fcc) Ag + fcc Cu, those deposited either at ∼100 K or at low power (∼40 W) exhibit an fcc Cu–25 at.% Ag solid solution, excess fcc Ag and small fractions of a metastable hexagonal (4H) Cu–Ag phase. Increasing the sputtering gas pressure leads to phase separation into fcc Cu, fcc Ag and metastable 4H Cu–Ag.

Fabrication of nanoporous superstructures through hierarchical self-assembly of nanoparticles

Highly-extended self-supporting nanoporous Au and Au–Ag alloy thin films can be successfully prepared by a self-assembly method with metal nanoparticles as starting building blocks. The size, structure, and composition distribution of the synthesized nanoporous films were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray diffraction. The experimental results revealed that thermal activation and photoinduced attractive force of nanoparticles cause the particles to be assembled at the air–water interface. The pore size of this new nanoporous material can be controlled by varying the nanoparticle size.

Novel technology for depositing a Pd–Ag alloy film on a tapered optical fibre for hydrogen sensing

Pd–Ag alloy thin films have attracted much attention in view of their potential applications in sensing hydrogen. In this paper we report on a new method of deposition of a high quality homogeneous Pd–Ag thin film on an optical fibre. The deposition method is used to fabricate sensors, which can detect hydrogen at very low concentrations (below 4%), by depositing a Pd–Ag thin film on tapered optical fibres. The deposition method and the complete method for fabrication of the tapered optical fibre sensors are presented in detail, as well as measurements of the hydrogen concentration in a nitrogen atmosphere made using the fabricated sensors. The sensors show good sensitivity and the optical responses of the sensors are in good agreement with theory.

High-power-density fault-current limiting devices using superconducting YBa2Cu3O7 films and high-resistivity alloy shunt layers

Switching of superconducting thin-film resistive fault-current limiting devices with alloy shunt layers was studied. Au–Ag alloy thin films, whose room-temperature resistivity is about six times higher than that of pure gold, were sputter deposited on YBa2Cu3O7 films on sapphire substrates with high critical current density of Jc=3.05±0.05MA∕cm2. A small sample, 5mm wide and 40mm long, had the capacity of a rated current of 32Arms in normal operation and withstood a high voltage of 107Vrms for 0.1s after switching, resulting in a very high switching power density of ∼1.7kVA∕cm2, which is more than four times higher than conventional devices using gold shunt layers.

The electromagnetic interference shielding effect of indium–zinc oxide/silver alloy multilayered thin films

A study was made to examine the electromagnetic interference (EMI) shielding effect of multilayered thin films in which indium–zinc oxide (IZO) thin films and Ag or Ag alloy thin films were deposited alternately at room temperature using a RF magnetron sputtering. The optical, electrical and morphological properties of the constituent layers were analyzed using an ultraviolet-visible photospectrometer, a 4-point probe and an atomic force microscopy (AFM), respectively. The EMI shielding effect of the multilayered thin films was also measured using a coaxial transmission line method. A detailed analysis showed that the control of the film morphologies, i.e., the surface roughnesses of the constituent metal layers was essential to an accurate estimate of the electrical and optical properties of multilayered coatings. It was shown that properly designed IZO/Ag alloy multilayered thin films could yield a visible transmission of more than 70%, a sheet resistance of less than 1 Ω/sq., together with an EMI shielding effect larger than 45 dB in the range from 30 to 1000 MHz.

Improvement of the thermal stability of silver metallization

The thermal stability of Ag(Al) alloy thin films on SiO2 has been investigated and compared to pure Ag thin films on SiO2 substrates. The prevention of Ag agglomeration on the SiO2 layer is a critical issue to improve the thermal stability of Ag metallization. We deposited Ag(Al) alloy thin films on SiO2 and compared them to pure Ag thin films by performing various analyses: Rutherford backscattering spectrometry, x-ray diffractometry, optical microscope, and four-point probe. Ag(Al) thin films showed good thermal stability on the SiO2 layer without any diffusion barrier and the Ag alloy thin films were stable up to 600 °C for 1 h in vacuum. No agglomeration was found during annealing for 1 h at 600 °C in vacuum. The electrical resistivity of the as-deposited Ag (3.1 at. % Al) thin film is slightly higher than that of pure Ag thin film. However, the resistivity of Ag(Al) samples annealed at high temperatures (up to 600 °C for 1 h in vacuum) remained constant due to no occurrence of agglomeration. It is confirmed in this study that the thermal stability of Ag metallization on SiO2 substrates can be enhanced by using Ag(Al) alloy thin films.

Degradation of Ag and Ag-alloy mirrors sputtered on poly(ethylene terephthalate) substrates under visible light irradiation

Ag coated polymer film is widely used as the lamp reflector of backlights of liquid crystal displays (LCD). We investigated the degradation behavior of Ag and Ag alloy thin film mirrors sputtered on poly(ethylene terephthalate) (PET) substrates under intense visible light irradiation at elevated temperatures. Ag and Ag alloy thin films were prepared on PET substrates by DC magnetron sputtering at room temperature. The interface was exposed to visible light from a Xe lamp with an intensity of 500 mW/cm 2 through the PET substrate. In order to avoid the deterioration of PET itself, the component of the ultraviolet (UV) light was excluded by placing a UV cut filter between the light source and the specimen. The reflectance was measured with a light spectrometer with an integrating sphere. While deposition of 0.5 nm of metals such as Ti on PET before the deposition of Ag was found quite effective to maintain the high reflectance of the Ag thin film, the deposition of Al, Mg and Si accelerated the degradation. The alloys of Ag with Au, Pd or Pt were found to be not effective. Results of the observation of the initial growth of Ag thin films with and without Ti pre-deposition on PET with the use of atomic force microscope (AFM) will be also reported.

Effect of rare-earth-doping on the magnetoresistive properties of sputtered Co–Ag alloy thin films

Rare-earth (RE) doped Co 0.4Ag 0.6 thin films (≈40 nm) were deposited on glass substrates at room temperature by an rf-magnetron sputtering system. Co-sputtering was used to dope RE (Ce, Nd, Sm, Tb, Dy and Er) into the Ag region. The evolution of the magnetoresistance (MR) properties and the phase separation in this sputtered Co–Ag alloy system were investigated in relation to the annealing condition and the RE-doping. Experimental results showed that the doping of either Ce, Tb or Sm enhanced the MR response of the Co–Ag films, while Nd depressed the response.