The areal density of information stored on the hard disk has doubled every two years. This substantial increase in disk storage has resulted from the application of giant magnetoresistance heads, new thin film media, and better electronic recording channels. However, such an increase cannot be easily attained without reducing the separation between the magnetic read-write head and magnetic recording medium surfaces. This can be achieved by using a thinner protective overcoat. In this study, ultrathin tetrahedral amorphous carbon (ta-C) films were deposited on magnetic hard disks (CoCrTa/Cr/NiP/Al–Mg) by a magnetic filtered cathodic arc deposition under different substrate bias voltages. The obtained films exhibited smoother surfaces than the uncoated disks as indicated by the atomic force microscopic measurement. The Raman spectra acquired showed a single asymmetric Lorentzian curve shape. Tetrahedral amorphous carbon coatings were subjected to an accelerated corrosion test in vapors of concentrated hydrochloric acid for 24 h. The corrosion test demonstrated a reduced density of corrosion sites when compared to conventional diamond-like carbon films. Similarly, the scratch resistance of the ta-C coated disks, investigated by a nanoindenter, showed significant improvement in comparison to uncoated disks.
We present an optical study (photoluminescence and Raman scattering) of a GaAs/AlAs multiple quantum well structure doped n-type in the AlAs barriers. The photoluminescence shows that the Si donors of the barriers release their electrons in the GaAs wells, creating a dense quasi-two-dimensional electron gas. The Raman spectra contain a feature associated with the e1→e2 intersubband transition.
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