Ho Yin,
    CD-R disks like the one you have use an organic dye to do the actual
recording.  Data is recorded by exposing teh dye to a high power laser pulse
which alters the dye chemically, changing its reflectivity in a small spot.
This reflectivity change is what's being read by the player.  Similarly,
DVD-RW, uses a phase change alloy rather than a dye.  The tracks your friend
has found wiht AFM are not the data.  They are the servo pattern that is
read by the laser to determine where on the disc it is and to help it stay
on track.  These are embossed either in a resin or in the polycarobnate
itself before the coatings (dye, reflective layer - Aluminum or other, etc)
are applied.  Try google searching "phase change media" or something imilar
to learn more.

-Lou


>From: "Ho Yin Chan" 
>Reply-To: General MEMS discussion 
>To: [email protected]
>Subject: [mems-talk] Argument in CD writing process
>Date: Mon, 24 Oct 2005 13:48:43 -0400
>
>Hi all,
>
>There is an argument between me and my friend about the CD writing process.
>What I know is the data is written on the Aluminum layer inside the CD but
>not the bottom polycarbonate. I have searched information for that to
>confirm my point of view. However, my friend uses an AFM to scan the
>surface of the bottom CD surface. He can find some tracks pattern on it.
>So, he is pretty sure the data is written on the polycarbonate. But, I
>still can't believe it. Can someone figure out what's the point we overlook
>in this issue? We are using CDR for testing. Before and after pattern
>writting using computer, we compared the surface profile.