Wen‐Yaung Lee

Electrochemistry of conducting polypyrrole films

Polypyrrole, poly-N-methylpyrrole and poly-N-phenylpyrrole polymers are prepared by the electropolymerization of the corresponding pyrrole monomer. Films of these polymers on platinum when mounted in a acetonitrile/Et4NBF4 solution can be electrochemically driven between the oxidized (conducting) form and the neutral (insulating) form. The measured E0 values are equal to −220, +480 and +600 mV vs. SSCE for polypyrrole, poly-N-methylpyrrole and poly-N-phenylpyrrole, respectively. The films are stable to this reaction and can be cycled repeatedly without evidence of decomposition. The cyclic voltammograms show that the reactions are not electrochemically reversible and the kinetic limitations of the reactions depend on the nature of the electrolyte salt. This reaction involves the oxidation of the extended π-system of the polymers and produces a color change in the film from yellow when neutral to black when oxidized.

X‐ray photoelectron spectroscopy and Auger electron spectroscopy studies of glow discharge Si1−xCx:H films

X‐ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were used to characterize the air‐exposed and sputter‐cleaned surfaces of glow‐discharge‐produced Si1−xCx:H (x=0.05 to 0.90) films. On the air‐exposed surfaces, silicon was preferentially oxidized with the enriched carbon existing as graphite or hydrocarbon. Signal intensities obtained from the surfaces sputter cleaned with 1 keV Ar+ ion beams indicated no significant preferential sputtering of C to Si for these films. The values of the carbon 1s and silicon 2p and 2s binding energies as well as the valence band spectra suggested a significant change in the local atomic configurations at x∼0.6–0.7. Based on these XPS and AES results and the reported IR absorption data, a slightly cross‐linked, carbon and hydrogen substituted polysilicon and an almost fully cross‐linked, silicon and hydrogen substituted polycarbon were proposed to describe the structure of films below and above x∼0.6–0.7, respectively.

Thickness and Growth Temperature Dependence of Structure and Magnetism in FePt Thin Films

We describe structural and magnetic measurements of polycrystalline, L10 chemically ordered Fe(55–60)Pt(45–40) films as a function of film thickness (from 3 to 13 nm) and growth temperature (270–370 °C). With increasing film thickness, the coercivity increases from about 1 kOe up to 11 kOe (growth at 400 °C), while for increasing growth temperature, the coercivity grows from 0.2 to 6 kOe for 4.3 nm thick films and 1.6 to 10 kOe for 8.5 nm thick films. There is a strong, nearly linear correlation between coercivity and the extent of L10 chemical order. In all the films there is a mixture of L10 and chemically disordered, fcc phases. The grain size in the L10 phase increases with both film thickness and growth temperature (increasing chemical order), while in the fcc phase the grain size remains nearly constant and is smaller than in the L10 phase. The films all contain twins and stacking faults. The relationship between the coercivity and the film structure is discussed and we give a possible mechanism for...

Reactive ion etching induced corrosion of Al and Al‐Cu films

Aluminum and Al‐Cu conductor lines etched with a Cl containing plasma in low‐pressure diode systems corroded rapidly upon atmospheric exposure. The mechanisms underlying this corrosion problem were investigated using Auger electron and x‐ray photoelectron spectroscopies. Reactive ion etching resulted in a nonprotective oxide layer and thus rendered the etched samples more susceptible to atmospheric corrosion. Factors contributing to the increased reactivity of etched samples includes C and Cl contamination, radiation damage, and for Al‐Cu alloys, Cu enrichment. A thermal oxidation treatment at temperatures of ∼300–350 °C and l atm O2 pressure for ≳30–45 min was found to be effective in restoring the protective oxide layer and thus improving the corrosion resistance of etched samples.

High magnetoresistance in sputtered Permalloy thin films through growth on seed layers of (Ni/sub 0.81/Fe/sub 0.19/)/sub 1-x/Cr/sub x/

The use of thin (Ni/sub 0.81/Fe/sub 0.19/)/sub 1-x/Cr/sub x/ seed layer for obtaining high anisotropic magnetoresistance in Permalloy (Ni/sub 0.81/Fe/sub 0.19/) films is reported. The process yields a high /spl Delta/R/R of for example, 3.2% for 120-/spl Aring/-thick NiFe, without high-temperature deposition or annealing. X-ray diffraction shows that the NiFeCr seed layer causes the formation of large [111] textured grains in the Permalloy film, and that the interface between these two layers is quite smooth. These both increase the /spl Delta/R and reduce the resistance R in the film, which lead to the high /spl Delta/R/R. Also discussed is the enhanced /spl Delta/R/R and thermal stability trilayer magnetoresistive sensors using this NiFeCr instead of Ta as a spacer.

High magnetoresistance permalloy films deposited on a thin NiFeCr or NiCr underlayer

Significantly enhanced anisotropic magnetoresistance (MR) in permalloy (Ni0.81Fe0.19) films deposited on a thin (Ni0.81Fe0.19)1−xCrx or Ni1−xCrx underlayer is reported. The maximum ΔR/R enhancement was observed using the underlayer with x≈0.44 at an optimum thickness of ≈30–45 A, depending on the deposition technique. An enhancement of 75%–150% was observed for 45–430 A thick permalloy films, compared to the films deposited without this underlayer. The ΔR/R enhancement is attributed to the decrease in the resistivity ρ and the increase in Δρ of the permalloy film due to the formation of large (111) textured crystal grains in the permalloy films deposited on this underlayer, as revealed by the x-ray diffraction results obtained using synchrotron radiation.Significantly enhanced anisotropic magnetoresistance (MR) in permalloy (Ni0.81Fe0.19) films deposited on a thin (Ni0.81Fe0.19)1−xCrx or Ni1−xCrx underlayer is reported. The maximum ΔR/R enhancement was observed using the underlayer with x≈0.44 at an optimum thickness of ≈30–45 A, depending on the deposition technique. An enhancement of 75%–150% was observed for 45–430 A thick permalloy films, compared to the films deposited without this underlayer. The ΔR/R enhancement is attributed to the decrease in the resistivity ρ and the increase in Δρ of the permalloy film due to the formation of large (111) textured crystal grains in the permalloy films deposited on this underlayer, as revealed by the x-ray diffraction results obtained using synchrotron radiation.

Degradation of thin tellurium films

Changes in electrical resistance, light transmission, and mass were used to monitor the in‐situ degradation rate of thin Te films in room air and in an accelerated temperature‐humidity environment. The degradation resistance of Te films was found to depend strongly on the film deposition rate, film thickness, and the presence of a surface oxide layer. It was shown that, in addition to oxidation, weight loss through the formation of some unidentified volatile products also contributed to the degradation of thin Te films. The effects of deposition rate and film thickness were attributed to their influence on the film microstructure.

Sputter etching studies of Fe–Ni and Fe–Pd films

Sputtering studies of Fe1−x–Nix (x=0.05 to 0.95) films were made and compared with those of Fe1−x–Pdx (x=0.06 to 0.7) films. Plots of steady‐state AES and ESCA signal intensity ratios versus bulk composition ratios for the Fe–Pd system gave two straight lines intersecting near x=0.38, where a bcc to fcc phase transition occurs. Similar plots for the Fe–Ni system showed a single straight line across the whole composition range although a similar phase transition occurs at x∠0.4. Values of slopes obtained from normalized AES and ESCA data were similar for the Fe–Ni but differed by a factor of 3 for the Fe–Pd system. Since ESCA has a larger sampling depth than AES for both alloy systems, these differences are attributed to the presence of a significant altered layer on the sputtered Fe–Pd surface, which is absent on sputtered surfaces of Fe–Ni films. This result is compared to the different diffusion rates of these two systems: (1) Depth profiles for air‐exposed and deliberately oxidized (160°–250 °C) films ...

Thin films for optical data storage

The most important requirements of thin film media for optical data storage applications as well as the most commonly studied write‐once and erasable optical recording media were reviewed. Detailed optical properties and degradation characteristics of thin Te films were presented to illustrate some of these requirements. Both of these two material properties were shown to be strongly influenced by the film thickness, film deposition rate, and substrate due to their influence on the microstructure of the film. The degradation mechanism and the effects of humidity and temperature on the degradation rate of thin Te films were also reported and discussed.

The stability of thin tellurium and tellurium alloy films for optical data storage: II☆

The chemical and physical degradation and the effects of the substrate and a low surface energy subbing layer on the stability of thin tellurium and tellurium alloy films for optical data storage are reported. Chemically, thin tellurium films degrade mainly through the uniform oxidation of tellurium to TeO2. In addition, localized degradation occurs at regions where initial defects on the substrate are present. Thin tellurium and tellurium alloy films can also degrade physically through crystal growth for an initially polycrystalline film and phase transformation for an initially amorphous film. While no significant difference in the uniform degradation rate is observed between films deposited onto poly(methyl methacrylate) (PMMA) and those deposited onto glass substrates, more localized degradation is detected for the films deposited onto PMMA substrates because of the higher initial defects of the substrate. The presence of a low surface energy subbing layer tends to degrade both the chemical and physical stability of these films. The degradation in the chemical stability is attributed to the change in the microstructure or thickness of the film due to the presence of the low surface energy subbing layer.