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New perspectives to save cultural heritage
Altan, M. Orhan

CIP A 2003 XIX th International Symposium, 30 September - 04 October, 2003, Antalya, Turkey
After the chemical etching of a photoresist layer, in the process of
which is formed a relief image, and the subsequent metallization
in the disk glass substrate is grown a nickel carrier by using
electroforming process.
The information on metal carriers can be represented both in an
analog form as microtexts (or microimages) (HD-Rosetta, 2001)
and in a digital form (Kryuchyn, 2002). The information recorded
on a metal carrier as a change of the surface relief can be read by
optical methods (projection methods or by using the focussed laser
radiation), by a scanning electron beam or tunnel microscopy
techniques. We offer to use for recording information on metal
carriers the data representation formats used at arrangement of
information on CDs. The capacity of carrier is from 650 MB up to
4.7 MB depending on the recording method. The information can
be reproduced on CD players after a minor modification of the
optical scheme. The modification lies in the introduction into the
optical channel of a 1.2-mm thick plane-parallel plate (for CD
carriers) or 0.6-mm thick one (for DVD carriers).
The choice of nickel as a carrier material for long-term storage is
conditioned by the following reasons:
-nickel has a high melting temperature T M =1450 °C what provides
the safety of information at temperature rise up to 400-500 °C;
-the high corrosion resistance of nickel guarantees the safety of
information recorded on a metal carrier at storing it at moist
conditions and even at falling of moisture on its surface;
-the high mechanical strength and plasticity allow the nickel metal
carrier to withstand considerable impact loads.
The manufacture of an information carrier of nickel guarantees its
safety in case of fire or inundation.
There are straight corroborations of an opportunity to create long
term storage carriers on the basis of thin (0,3-1,0) mm metal films.
The copper-nickel stampers for replication of gramophone records
were kept perfectly well. Sound from them can be reproduced on
special devices with piezoelectric pickups with sufficiently high
quality. The nickel stampers have kept high optical reflection
(60%), on their surface there are no traces of corrosion. The
ellipsometric investigations of the surface of nickel stampers,
manufactured in the 30s of the last century, have shown, that on
their information surface there are no continuous oxide films and
only in separate areas they are available no more than 10 Â in
thickness. The appearance of such oxide films can be bound up
with the presence of impurities in a stamper. The further
investigations pursued by using techniques of Auger-electron
microscopy, micro-X-ray spectral analysis, secondary ion mass-
spectrometry, have shown necessary distribution of oxygen in a
surface layer of the nickel stamper. The zones with the increased
content of oxygen have coincide with the arrangement of
impurities such as aluminium, manganese, iron.
During 70 years the electroforming technology was improved
significantly, the purity of electrolytes for growing nickel plates
has increased by a factor of a few tens, that allowed on the modern
equipment to manufacture metal nickel carriers with the content of
impurities no more than 0,01 wt. %. In modem stampers for CD
replication the impurity content is smaller by a factor of 50-60
than in stampers, that were used in the past century for replication
of gramophone records. This allows to make the most optimistic
estimations on determining the terms of storage of metal nickel
On the information reproduction process at the long-term storage
the greatest effect can have the changes in the length of bumps,
by which the information is coded. The length of bumps can be
changed at the expense of oxide layers formation, organic
substances contamination. The organic impurities from the nickel
carriers surface can be removed by the electrochemical cleaning
methods which are widely used in the CD production technology.
Some increasing of bumps sizes can occur at the metal oxidation.
Such increasing of linear dimensions for nickel makes 15 A by
formation of a 100 A-thick oxide layer. At this case the change of
the signal reproduction duration (at the one-fold reproduction
velocity) will not exceed 35 ns what makes 4,2 % of the shortest
signal duration. The change of pits geometrical sizes influences
most the signals reproduction of the shortest bumps, the length of
which is about 1 pm. The allowable length increase of a bump can
be 420 A. The choice of corrosion-resistant metals such as nickel,
noble metals permits to forecast, that the allowable extensions of
bumps (4-5 %) owing to the formation of oxides or sulphides can
occur within 300-400 years. Thus, the metal carriers can provide a
reliable long-term storage of digital content recorded with high
density. The intrinsic decay of the images on the metal carriers
due to aging cannot be stopped totally, but only be slowed down.
As demonstrate the conducted experiments by electroforming
techniques one can create the relief microstructures on metal
substrates with the size of elements 0,01-0,02 pm, that are smaller
by a factor of a few tens of sizes of elements on the surface of
DVD carriers (Todorovic, 1999).
One of the main problems at development of long-term storage
carriers consists in choosing a method of information
representation. As demonstrates experience, the highest long-term
reliability of information storage have carriers with a relief form
of information presentation. Such a form of representation was
used on Edison phonograph cylinders, gramophone records etc.
The devices of information reproduction from such carriers
created in the time of manufacturing carriers, cannot be used for
qualitative sound reproduction any more, however, the carriers
have ensured safety of the recorded information. The reproducing
devices, constructed on new physical principles of reading, allow
to obtain the phonograms with sound quality, which is superior to
the sound quality, that existed 80-100 years ago. It is possible to
forecast, that more effective methods will be created and the
devices, realizing these methods for information reproduction
from CDs and carriers, on which a similar form of information
representation is used, will be designed.
File formats used for long-term information storage should be
widely used, be open and completely documented, have a high
flexibility to integrate multimedia information (Buchel, 2002).
The formats used for the information representation on CD and
DVD carriers meet these requirements.
By using metal carriers it is necessary to take additional care to
protect the information surface against contamination by dust
particles and mechanical damages. Coating the metal carrier
surface by a 0,2-0,3 pm-thick polymer film allows to solve this
problem partially. The polymer film can be replaced periodically.
A more effective protection of information can be ensured on
carriers made in the form of a transparent high-stability substrate
with a relief microstructure. Material for such carriers can be
shock-proof glass beads, quartz etc.