Note: Descriptions are shown in the official language in which they were submitted.
2 ~
O.Z. 0~50/41333
Stora¢e~of information units in the nanometer ranae
The pre~ent invention relates to a proces~ for
storing informa~ion unit~ in the nanome~er range by
modifying the shape of the ~urface of a ~emiconducting
laminate m~terial.
The storage of information, in particular image
and data signals, currently take~ place predominantly
u3ing magne~ic or optical recording carriers. The infor-
mation density which can be achieved using ~he latter is
detarmined by the s~nallest information units which can be
written and read again by the process. In conventional
magnetic s~orage media, these units are determined by the
si3e of ~he magnetic domains (Wei~ regions), from a
mechanical pOiIlt of view by the head gap o~ the
readJwrite head~ u~ed and by the distancs of the
read/write unit from the actual information carriex. In
information carri2rs where the ~tored information is
pxoduced by a change in optical properties, the limit i~
the wavelength of ligh~ usDd. The smalle~t information
2n units here can thus not be smaller than about half the
waveleng~h of the light. ~n increa~e in ~or~ge den~ity
in optical recording carriers of this type has in the
meantime al80 been achi ~ed ~hrough optical close-field
microscopy, whera the optical read unit i only a few
2S na~ometer3 abo~e the information-carrying surface. The
be~t informa~ion den~itieR achieved here are in the order
of about 20 nm.
A further increase in the information density i~
only pss~ibl2 by using close-field techniques with a
resolution in th~ ~ubnanometer range. Suitable me~hods
for thi~ purpo~e are scanning probe techniques, including
the scanning tunneling micro~cope and the atomic force
micro~cope. The~e methods allow Lmaging of surface0 on an
a~omic scale. It ha~ therefore been propo~ed to produce
information ~torage media having the highest pos~ible
denslty, namely in the range of the individual atoms or
molecules. Success in developing these media would resul~
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- 2 - O.Z. 0050/41333
in information densities in the terabyte/cm2 range.
A number of proposals have been made for ~oring
informa ion in the nanometer region on inorganic or
organic ~urfaces, including M.A. McCord et al., J.Yac~
5ci.~echnolO B4, (19B6), 86-88, R.M. Silver e~ al.,
Appl.Phyæ.Lett. 51 (1987), 247-249, and U. Staufer et
al., J.Vac.Sci.Tachnol. A6 ~1988), 537-539. The deposi-
tion of individual atoms has also been reported
(R.S. Becker et al., Nature 325 (1987), 415-4213.
However, all the propo~als hitherto ~or the
provi~ion of maximum-re~olution information storage media
which al~o have, in particular, long-term ~tability are
unsatisfactory. Whereas organic storage media are in-
capablo of producin~ linQ widths <10 nm, inorganic
~ystem~, which can repro~ucQ structures down to 3 nm, are
un~tabl* over relatively long periods, ie. from minute~
to hour~O In the ca~e of the stable structures in silicon
which have been disclo~ed hitherto (Van Loenen et al.,
Appl. Phy~.hettO 55 (1989~, 1312-1314), the atomic
~truc~ure i~, by contra~t, des~.royed, ie. the atomic
order i8 lost. ~ proces~ of this type i~ therefore only
suitable for producing non-era~ab:Le storage media.
It is th~rafore an ob~ect of the present inven-
tion to provide a proce 8 for ~torin~ information units
in the nanometar range which makes it possible, in
particular, to ~tore in~ormation or a long period
without deskroying the local lattice structure.
We havQ ~ound ~ha~ ~hi~ objeet i3 achieved by a
proce~ for the stable ~torag~ of information units in
the nanometer range, in which the ~urface of a ~emi-
conducting l~minate material i~ sub~ected to plastic
deformation by means of a ~urface-sensitive scanning
probe without modifying the atomic order.
Plastic deformation o~ the surface of the semi-
conducting laminata matarial by means of a surface-
~en~iti~e scanning probe without modifying the atomic
order can be achievad in one embodimant according to the
2~31819
- 3 ~ O.Z. 0050/41333
invention by the action of mechanical force or by apply-
ing a short-duration electrical field.
In a further embodiment, however, the information
units stored in accordance with the process according to
the invention in the form of a structured surface can be
converked back to the original state through relaxation
without modifying the atomic order by supplying energy,
ie. the in~ormation i~ erased. For this purpose, the
supply of thermal energy by heating the entire surface or
by la~er treatmen$ of the entire surface or of poin~s is
particularly ~uitable.
The proce~ according to the invention s~arts
from a semiconducting layer comprising, for e~ample, WSe2
or another conYentional ~emiconducting layer based on a
selenide, teluride or sulfide. The surface of a layer of
this type is sub~ected to plastic de ormation by a
~urface- en~i~ive scanning probe using the close-field
technique. The3e pitR, which are usually circular or
oval, are produced without the atomic oxder of the layer-
forming material being de~troyed. The plasticallydeformed surfac~ of the laminate material is then con-
verted very rapidly back into the original unstructured
form by, for example, thermal treatment, as is possible,
inter alia, by IR laser bombarc~en~. The clo~e-field
technique used for writing the informa~ion can be a
conventional Acanning tunneling microscopy or atomic
force micro~cop~ proce~ The arrangement of these close-
field technique~ for characterizing surfaces is known and
has been de~cribed (y. ~uk et 81., Rev.Sci.Instrum. 60(2)
3~ (1989)l 165-180).
The proce~ according ~o the invention is des-
cribed in illustrati~e term~ below:
A sample o~ a tungs~en dis~lenide layer was first
imaged on an atomic scale in a scanning tunneling micro-
scope under high-~acuum conditions. Figure 1 show~ such
an atomic arrangement of khe tungsten diselenide surface.
A defined, ~hort-duration movemen~ of the STN kip towards
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~ 4 - O.Z. 0050/41333
the sample surface (deflection 10 nm) was then used to
plastically deform the tungs~en diselenide surface. The
surface defect produced in this way was then observed
using the same tip. The modified surface is shown in
Figure 2. ~he essential feature of thiq structured
suxface is that the atomic clo~e-order of the pit has not
been des~royed. The pit has a diameter of about 2.5 nm
and a depth of about 7 A. This surface deformation i
stable and can only be returned to the original flat
shape by thermal treatmen~. The area represented in
Figure 2 is about 100 A2 and provides space for four of
the surface deformation~ indicated. This results in a
storage density of 4 104 bits ~4-103 bytes) per ~m2, or
4-109 bytes/mm2 and 4-1011 byte3/cm2 or 4 terabits/cm2.
