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How to do thermal chemistry between very thin layers?

How to do thermal chemistry between very thin layers? - Chemistry Forum

How to do thermal chemistry between very thin layers? - Chemistry Forum. Discuss chemical reactions, chemistry.


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Old 02-05-2004, 06:03 AM
raid517
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Default How to do thermal chemistry between very thin layers?



Hi I am currently considering a project that is inspired by DVD-R
recording technology.

To understand what I hope to achieve a small explanation of DVD-R
technology might be in order.

You see the primary layer of a DVD5 is sandwiched at the centerer of
two 0.6 mm plastic substrates. It stands to reason therefore that the
semi-transparent layer of the new soon to be released 'dual layered'
DVD (which at GB is twice the capacity of the old disks) is about
half that; 0.2 to 0.3 mm.

In human terms these layers are very close together, but in optical
terms they are not. The spot of heat generated by the laser is
microscopic and only present on any given location on the disk for a
tiny fraction of a second. Yes, the heat will dissipate to the other
layer - that's simple thermodynamics. But by the time it dissipates
over the 0.2-0.3 mm distance, the temperature will only be a tiny
fraction of what it was at the source.

There are several thought experiments you can perform to gain comfort
with this. For example, just think about the laser power (a few 10's
of milliwatts) applied to something 0.2-0.3 mm in size, even for an
extended period, let alone for a millisecond. It's just not going to
get that hot. You could easily apply the laser to the end of your
finger continuously and not even feel it.

So in effect you can imagine a circumstance where the heat from a
laser can be applied in a very specific way. Indeed so precisely can
the energy from a laser be applied that one could quite feasibly
focus the vast majority of that energy to a layer behind any other
layers and localize the heat source to that area alone. The true
amount of energy transferred between any layers is simply not
significant enough to warrant concern.

But what I want to do is a little different. What I would like to do
is some genuine thermal chemistry between very thin layers
constituted in a similar way to that describes above. Effectively
what I would like to do is change the chemical properties of a number
of very thin chemical layers using heat from a laser, so that I can
achieve a very specific chemical effect.

However as this is just a thought experiment at this time, I have to
confess that my chemical and physical skills are not yet quite where
I would like them to be.

You see if I have an unspecified optically transparent chemical
substance laid out on a flat surface that can react to the heat from
a laser and I then add other layers on top of this and separate them
in a similar way to that described above, then surely there must be
an exact calculation you can make which would consider the thermal
qualities of the layers you are using, how much energy would be
required to effect a specific chemical change, how much energy would
be transported to subsequent layers - and the width/frequency of the
laser you would need to perform this task. What you would then have
to do is begin to look for substances which fitted the qualities that
this equation described - and which also achieved the effect you were
looking for.

The question is, what would this equation look like in real terms?

I am certainly no scientific genius (indeed I am a humble musician by
profession) - but even to my simple mind, it seems that you should be
able to come up with an equation that was able to fit all the
variables in this situation.

It may seem odd, but I'm afraid I can't quite say why I am interested
in this subject, except that it is related to the field of computing
and my interest in data storage.

Can anybody here offer any useful insights into this subject - or
maybe someone here might even have experience in this specific area?

If so, your input would be very much appreciated.

Kind regards,

GJ



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Old 02-05-2004, 08:00 AM
raid517
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Default re:How to do thermal chemistry between very thin layers?

Mmm... Maybe this question is better suited to the physics section? If
the mods think it is, please feel free to move it there. Although
what it really is is a Chemical problem with physical qualities. So
it's a bit of both really...

GJ



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