Note: Descriptions are shown in the official language in which they were submitted.
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NANOMETR1C STRUCTURES
Description
The present invention relates to structuring and decorating substrates on the
n~axiret~ic
scale. In particular, the present invention relates to surface-decorated
substrates comprising
nanometrically ordered surface structures of metal andlor metal-oxide clusters
and/or
semiconductor clusters, and further to a method for the ~att~rs~ mar~aca~e
arr~ y icatirn of
said method to epoxidate C, - C, alkenes or to oxidize from CO into CO,. The
present
invention also relates to surface-structured substrates, in which case the
structuring runs
nanometrically across macroscopic zones, In particular Pt, Au, GaAs, (n,,GaAs,
RIYGaAs, Si,
SiO,, Ge, Si"GaAs, InP, InPSi, GalnAsP, glass, graphite, diamond, mica, SrTi(~
or their doped
modifications, and a method for their preparation. The invention is based on
the film formation
of corc~shell polymer systems of which the core zones are modifred, i.e.
charged selectively in
solution with corresponding metal compounds. These films, which are
precipitated on the
structure's surface, may be selectively etched in such a manner that the
organic polymer
component will be wholly removed, and in the process the substrate will be
decorated by means
of the inorganic residues, resulting in a regular configuration. Furthermore
the structured films
may be used as masks, allowing selective substrate etching, and hence to
transfer a structure,
which is predetermined by the film, into the substrate.
Fine ly dispersed precious-metal catalysts are the basis of important chemical
processes
such as hydration, selective oxidation of alkenes, alkynes and aromatics to
form alcohols,
epoxies, ketones, aldehydes and carboxylic acids, oxidation of CO,
decomposition of nitrous
oxides (N~ into nitrogen and a corresponding oxidation product (H,O, COz), and
reaction of
methane and carbon dioxide to form a synthesis gas (COIN,).
An irnportant crlter(on for the activity and selectivity of catalysts is that
metal particles are
deposited on an appropriate, and usually oxidic, support. For instance, while
pure gold is, in
contrast to members of the platinum group, catalytically inert, in conjunction
with an oxidlc
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52960-014
support, it provides a highly active catalytic system. The selection of
anoxidic support assumes
a determinant role in activating and restructuring acatalytically active
particulate surface during
a catalytic cycle. The support's structure, and its chemical interaction with
the precious metal,
degrade the activity and selectivity of the catalyst. The ptecipitation of
platinum layers onto
su~dic or oxidic supports of well-defined surface stnrctures leads to custom-
made, highly active
catalytic systems. Zeblites of variable but well-defined pore structures cause
an increase in
active surface and, in conjunction with the "right" precious metal, also to an
increase both in
selectivity artd in activity. In the case of modem three~vay catalysts, CeQ is
used as a prorlnoter
along w'tth the precious metal (Pt, Pd, Rh) and the support (S'~, AhO~, ),
said CeC~ storing and
releasing the oxygen needed for the reaction. The catalytic process is
deasively improved
(hereby relative to those using catalysts lacking promoters.
t3esides the topography and kind of the support, the sizes, and the
mutualspacings, of
the precious-metal particles also are critical in regard to the stability and
effectiveness of the
catalysts.
Hoanrever, high catalytic activity is attained in particular with particles
smaller than 5nrn.
An important objective in the further development of heterogeneous catalyst
systems relates
to the regut~r corr~guration of precious-metal particles that are 1 to 3 nm in
size.
Periodic and aperiodic microstructures from several microns to several 100 nm
are
prepared for electronic and optical components, sensors, and in micro-
engin~ering, by mearts
of lithography.
Heretofore optical lithography has been very successful in making structures
larger than
180 nm. l~s this procedure is a parallel one, which moreover allows high
production flow, it has
been the unambiguously predominant process for producing microelectronic
cirouits. The
attainable t7n)nlmum structural size.is dictated by a technical tradeoff
between the physically
possible resolution and the depth of field required by the equipment. Standard
production
dimensions of integrated circuits already are less than 350nm. Utilization of
X-ray radiation
under technically rigorous cond'ttions results in dimensions of about 90 nm.
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3
For some time it has been feasible, using electron or ion beam lithography, to
attain
nanometric structures, and corresponding equipment is commercially available.
Atom beam
frthography controls the interaction of the atom beams with the optical masks,
and allows
production of large-scale line patterns and various 2D periodic structures
with a resolution less
than 100 nm. In this procedure atoms are directly d~posited on a substrate, or
ate used to
modrty organic resists.
This further reduction of geometric dimensions permits not only further
mlnialurization,
but also permits utilization of dimension-dependent physical properties, such
as quantum effects,
supertemomagneticproperties, or electron plasma-ion resonance. However, the
conversion Into
mactoscopic effects or test values requires high uniformity of an ensemble of
microscopic
structures.
For structures smaller than 1 d0 nm that are of interest in this connection,
conventional
lithographic procedures are exceedingly difficult and nakedly economical. New
procedures must
be developed, complementary to the conventional ones, which will depend either
on size-
controlled growth of inorganic structures or on molecular concepts of organic
and
macromotecular chemistry. Only a few Implementations are known:
(1) Making use of crystal growth ors GaAs (311 )8 oriented substrates, not
only small
units, but also well-ordered quantum-dot structures can be prepared. Following
the
growth of a thin film of InGaAs above a buffet layer ofAIGaAs, the stressed
InGaASs ~Im
breaks up into small pieces which are spontaneously buried underAIGaAs. In
this
manner ordered rows of AIGaAs microcrystals with a core of planar InGaAs dots
are
formed naturally. The sizes and distances between the dots can be
independently
controlled solely by means of growth parameters. The photoluminescence spectra
of
the dots are characterized by high efficiency and narrow line widths.
(2) A two- or muki-block copolymer consists of chemically different
macromolecular
chains, which are covalently connected at the ends or another molecular
position (for
Instance in the Base of star or graft block copolymers). In most cases
different blocks
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52960-074
do not mix with one another, and separate themselves into so-called micro-
domains.
The size and morphological order of said microdomains is determined in part by
the
proportions by volume of the individual blocks and by the molecular weight
distribution.
Changing the volume proportion of the polymer blocks allows adjustment of
different
microdomain structures such as spheres, cylinders and lamellas. Typically the
periods
so attained run between 10 and 200 nm.
Because it is possible to chemically and physically distinguish the ~connecfed
macromol~acular blocks, the chemically differentmicrodomains can be
selectively charged of
marked. This result is far instance attained by absorbing solvents or by a
selective reaction with
a transition metal. The transition metal frequently is used to achieve polymer
contrast in
electron microscopy.
Microphase separation also can be observed in ultra-thin films. The critical
factortherein
is tine extent to which the microdomain structure, and its organization, are
affected by the surface
and boundary-surface energies and by geometric constriction.
Park et al., in Science 189y, 276, 7401 and also inAppl. Phys. Lett. 1896, 68,
2586),
describe transferring the microdomain structure of a two-block copolymer to a
silicon nitride
substrate beneath. Two distinct techniques based on reactive ion etching allow
making holes
20 nm in diameterwith a periodicity of 40nm, and also the corresponding
inverse structure. In
the same way related ducts 30 nm in diameter and spaced by 15 nm could be
transferred to a
substrate. In this process, the microdomain, Consisting of the polybutadiene
of a polystyrene-b-
polybutadiene two-block copolymer, were reacted with ozone gas and dissolved
out of the
polystyrene matrix or marked with osmium atoms. Hoth procedures resulted in
local
inhomogeneitieswith respect to etching resistance, thereby in the end allowing
use of two-block
copolymer patterns as masks for nanometric surface structures. Such patterns,
when in the
range of a few nanometers, can be used in principle in engineering for making
nanometric
structures and as lithographic masks.
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However the procedures described in the state of the art incur the drawback
that they
are economically prohibiYrve and/or are restricted to very special systems.
Accordingly it is the objective of the present invention to develop a
versatile concept,
based on organic or macromolecular chemistry, which allows nanometric
structuring and
decoration of substrates. In particular, the Invention makes available a
method that allows
nanometric surface decoration of substrates by means of ordered deposition of
defined metal
or metahoxide Clusters on a substrate, and furthermore substrates of which the
surfaces are
decorated with said defined metal or metal-oxide clusters that are suitable as
catalysts In the
epoxidation of C, - CB or in the oxidation of CO to COs. Such a method in
particular allows for
the controlled preparation of compound clusters from acatalytically active
metal component and
a metal oxide, the relative proportions being systematicallyvariable.
Furthermore an economic,
i.e. an efficient method of the invention based on the molecular concepts of
organic or
macromolecul8rchemistry, is provided, which allowsrtanorrietric surface
structuring substrates,
that is preferably in the range under 20 nm, preferably lass than 5 nm, across
macroscopic
zones. The invention also offers structur~d substrates in the lowemanometric
range that are
characterized by a large depth to-width ratio, that is, the heights and depths
of these structures
are many times larger than the lateral dimensions_
This problem is solved by the invention by the embodiments set forth in the
claims.
tn particular, in a first aspect of !he invention, a method is created to
manufacture
surface-decorated substrates, comprising the following stages:
(a) introducing a polymer into an appropriate solvent, while forming a
dissolved core-
shell polymer system,
(b) charging at least part of the polymer cores with one or more identical or
different
metal compounds,
(c) depositing the charged tote-shell polymer system prepar~i in stage (b) in
the
form of a film on at least one side of a substrate in such manner that said
core-shell
polymer system is corr~gured in a regular structure in the film, and
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52960.014
(d) removing th8 polymer, producing the core-shell polymer system, while
generating
metal clusters and/or clusters of metal compounds on the substrate surface,
w'tthout
significant changes in the structure produced by the core-shell polymer
system.
In a preferred embodiment of this method for surface-decorating substances in
the
nanometer range, and before stage c), metal compounds) contained in the
pohymer core is (are)
chemically treated and/or irradiated by high-energy u.v., x-rays or electron
beams, whether in
solution or in the film, and are converted into metal or a metal oxide. !n the
course of stage (d)
of this method of the invention, the polymer is removed preferably by etching,
reduction or
oxidation. Etching by means of a reactive plasma, preferably an oxygen plasma,
is especially
preferred.
This method of the first embodiment of the invention surprisingly allows
orderly
precipitation, in art orderly and very simple manner, of discrete metal
clusters or metal-oxide
dusters onto different substrates, while forming regular, i,e.
ordered,nanometric structures.
Even semiconducting clusters, such as Si and Ge, can be prepared in very
simple manner by
the method of the invention. Moreoverthe method of the invention,
usingmicellarsystems from
amphiphilic block copolymers, allows oldered deposition of minute,
catalytically highly active
metal particles on nearly arbitrary substrates.
A second embodiment of the present invention relates to a method for preparing
surface-
structured substrates, which comprises the following stages:
(a) irrtroduclng a polymer lrrtcs an appropriate solvent, while forming a
dissolved care-
shell polymer system,
(b) charging at least some of the polymer cores with one or several, identical
or
different metal compounds,
(c) depositing the core-shell polymer system prepared in stage (b) in the form
of a
film on at feast one side of a substrate in such a manner that the core~shell
polymer
system is configured as a regular structure irt the film, and
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52980-014
(d) subJecfing the substrate prepared in stage (c) to a reactive ion etching
procedure,
to art ion sputtering procedure, or to a wet chemical procedure, or a
combination thereof,
the film deposited on the substrate being removed and the regular structure
produced
by the core-shell polymer system being converted as a function of the-kind of
Charge of
the polymer cores as well as of the duration of the reactiv~ ion etching
and/or ion
sputtering andlor the wet-chemical procedure into substrate relief structure.
In a preferred embodiment of this method of the invention tonanometrically
surf8ce-
structure substrates, at least part of the metal compounds contained in the
polymer cores is
inverted, before film deposition or following film formation, by
chemicaltreatment and/or high-
energy irradiation such as u.v., x-rays or electron beams, into one or more
metal particles and/or
metal-oxide particles in each polymer core.
This method of the irtVention allows manufacturing of such surface structures
as holes,
strips, troughs and dot-IiKe elevations of a width or diameter preferably
between 1~ and lOQnm,
and a depth, or height that may be a multiple of the lateral dimensions, in a
corresponding
substrate. These surface structures also are called relief structures of the
substrate.
The expression "core-Shell polymer system" herein denotes for instance
macromolecular
amphphile$ which associate in aqueous or organic solution and may form well-
defined spherical
or rod-shaped micelles, lamellas, vesicles or complex aggregates.
Consequently, the invention
also includes systems generally called host/guest systems wherein a moleurtar
cavity, i.e. a
molecule inner space, namely tf~e polymer core, generated by the polymer (host
compound), can
be charged, i.e. complexed with a guest compound, that is a particular metal
compound.
The polymer used )n the method of the invention, which is produced in solution
of such
a core-shell-polymer system, preferably is selected from block copolymers,
graft copolymers,
mil~oa~n st~l~xs, , star polymers with different branches,dendritic polymers,
micro gel-
particles, star block copolymers and core-shell latex polymers.
More preferred are the following polymers, namely polystyrene-b-
polyethyleneoxide,
polysfyrenez-b-poly(2-vinylpyridine), polystyrene-b-poly(4 vinylpyridine)
polymer or a mixture
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8
thereof. The polystyrene block therein however mgy be replaced also by other
non-polar
polymers, for instance polyisopropene, polybutadiene, polymethylmethacrylate
or other
polymethacrylates. The second, or polar block in such a two-block copolymer
may be one ~nrhieh
interacts as strongly as possible with the particular metal compound being
used. Illustrati~rely
such are polyacrylic acid, polymethacrylic acid, amino-substituted
polystyrenes, polyacrylates
or polymethacrylates, amino-substituted polydienes, polyethylene-imines,
saponified
polyoxazolines or hydrogenatedpolyacrylonitrile. The first block also may he a
polar polymer,
provided howevet than then the metal compound is selected in such manner that
foremost , i.e,
selectively, it interacts with the second polar block.
Typically the above polymer systems are dissolved in a selective solvent, fot
instance
toluene, ai a rate from about 10'~ to about 100 mg/ml, preferably about 5
mg/ml. Following
several, for instance 12 hours approximately, the solution is reacted w'tth
one or more metal
compound$ in stage (b) of the method of the invention and then is strongly
agitated, for instance
for about 24 h, in order to charge at least some of the polymer cores, formed
by the core-shell
polymer system, with the metal compound(s).
For example, such metal compounds are compounds of Au, Pt, Pd,Ag, In, Fe, Zr,
AI, Co,
Ni, Ga, Sn, zn, Ti, 8i and Ge in the corresponding oxidation stages or
mixtures thereof. Specific
examples are HAuCI,, MeAuCI,, where Me denotes an alkali metal, HzPtCh ,
Pd(Ac)a,Ag(Ac),
AgNO,, InCI, , FeCI, , Ti(OR),, TiCI,, Ti CI, , CoCI, , I~iCtZ, SiCI,, GeCI,,
GaH, , ZnEt,, AI(OR), ,
zr(OR)~, where R is a straight-chain or a branched-C~ - C8 alkyt
residue,ferrocene, Zeise salt
or SnBu,H or mixtures thereof. Preferably the metal compound is HAuCI,,
Typical inputs are
0,01 to 2.0 molecular precursor units per monomer unit of the polar polymer
block.
In stage (c) of the method of the invention, the deposition of the film is
carried out in
single or multiple layers onto at least one side of a substrate, preferably by
dipping, pouring,
SPA coating or by adsorption from a diluted solution. Mare preferably however
the deposition of
single or mukiple layers is carried out by dipping inta dilute solutions. For
example the films are
produced by drawing a substrate out of the solution at speeds, for instance
from 0.007 mmlmin
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52980-014
to 2 m/min. Such macroscopically covering films have a layer thickness of, for
instance, one or
more charged two-block copolymer_micelles, that is from 5 to 800nm. An
exemplary mono-
micellar film is therefore as thick as a micelle. The polymer cores, that is
for instance the
micelles or corresponding molecule cavities, charged with the metal compound
and/or the metal
particles, are in the process precipitated substantially intact, while a
regular structure Is being
formed in the film. The polymer cores, which are charged either with a metal
compound as a
precursor for the reduction to the corresponding metal, or already are charged
with the
corresponding metal particles or rhetal-oxide particles, arrange themselves in
this process on
their own into a regular structure on the substrate surface.
Rpplicable substrates are precious metals, oxidic glasses, monocrystalline or
mutticrystalline substrates, semiconductors, metals with or without a
inactivated surface,
insulators or in general substrates that are highly resistant to the etching
procedures below. In
particularthese are Pt, Au, GaAs, InyGaAs, A~GaAs, Sl, SiO~, Ge, Si~NY,
SixGaA,s, lnp, GaInAsP,
glass, graphite, diamond, mica, SrTICI~, and their doped modifiCCaations_ The
applicable sub$trates
may be flat, laminar (far instance mica flakes of a length < 15p. ) and also
those with laminar,
curved (convex or concave) surfaces (for instance microglass balls or
mlcroquarta balls of
diameters fot instance 1 to 80 ~).
The coating thickness is adjusted in a metallic precursor stage in solution by
means of
the molecular weight of the amphiphilic block Copolymers, by the size of the
particles and also
by the degree of polymerization of the (for instance micelle-forming) block,
forming a regular
structure, also by the magnitude of the charge, the particle size for instance
being 1 !0 20nm
and the inter particle distance being 20 to 400 nm, preferably 20 to 200 nm.
The cluster
uniformity attained by the method of the first embodiment of the present
Invention, and ifs regular
configuration, is achieved by means of the homogeneous distributicins of the
salts in solution on
the micelles and by the uniform size distribution of the two-block copolymer
micelles (Fig. 1 ).
This structure, i.e. the ordering, produced by the core-shell polymer system,
with at least some
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52980.014
of the polymer cores being selectiv~ly marked or charged by one or more metal
compound(s),
is not degraded in the particular ensuing stage (d).
A9 already discussed above, the polymer produdng the care-shell polymer system
in the
manner of step (d) of the method of the first aspect of this invention, with
concomitant
generation of metal clusters and/or clusters or metal compounds on the
substrate surface, is
completely removed without significantly changing the structure or
configuration pf the dusters
on the substrate surface as erected by the core-shell polymer system, In the
process, the
polymer Is removed, for instance by etching, reductioh or oxidation. These
procedures also may
be carried out at higher temperatures; especially etching is carried out using
a reactive plasma,
preferably an oxygen plasma. Furthermore, reactive gas plasma procedures (CFA,
H~ SF~ or
oxidation in an oxidizing atmosphere at raised temperatute, etching by high-
energy irradiation,
in particular by electromagnetic beams or partide beams such as electron
beams, orpyrolysis,
also may be used to remove the polymer enclosure.
The above techniques used in step (d) of the first embodiment of the method of
the
invention remove, In a residue-free manner, the organic polymer enclosure at
the desired site
or in the desired zone, and convert the metallic precursor stage into its
crystalline Me orMeO"
modifications In the form of agglomerates of small Me arMeO, particles, the so-
called clusters.
Depending on the metal compounds used in stage (b), the precipitated dusters
are, in
particular, oxygen-resistant precious metals such as Au, Pt, Pd or oxides, for
instance
semicondueting oxides such as TiOZ, or magnetic particles such as certain
modigcativns of
Fe,O" Fe, !vo or Ni.
The precipitation of metallic mixed systems such as Ru/Fe20, , AuICoO, AulCo,
O,,
AuIZnO, AuITiO,, AuIZrO~, Au/A~O, , Aulln=O, , PdIAl,O, , PdlZrO=, Pt/Al=CJ~
and Pt/graphite will
succeed by mixing a solution of a polymer system used in the manner of the
invention with a
mixture of the particular metal compounds.
For example, to separate "naked" metal/metal-oxide clusters, the micelles
containing
metal Baits produced by one of the above polymer systems are deposited in the
form of an
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5298Q014
ultrathin film on the selected substrate and thereupon the polymer sheath is
selectively removed
by oxygen-plasma treatment, bum-off in an oxygen rich atmosphere, pyrolysls or
by other
reducing conditions such as in a hydrogen plasma.
In this treatment, the transition-metal compound is converted into the
elemental metal
or, under oxidizing conditions, into metal-oxide particles. The thermal
reduction or the
conversion of precious-metal compounds in an oxygen atmosphere produces a
narrow particle
distribution similar to that resulting from burning the polymer by means of
the above described
plasma process (F)g. 2).
The above described method allows preparing clusters of various sites in
particular of
gold, platinum, pa~t(adium, nickel, titanium dioxide, iron oxide and cobalt
oxide.
SurPaoetaste corroborate the preCipltationfor instance of Au, Pt, In, Co, Pd,
TiQ Fe,g
as well as of the particular mixed systems, in particularAu/F~O, , AulCoO,
AuCo, 04, ~r~n0,
AuTiO" I~u2rQ,, Au/Al=O, , Au/In,O, , Pd/AIxO, , PdZrO,, Pt/Al=O, and
Pt/graphite. The cluster
diameters can be adjusted for instance to be between 4.5 and 9 00 nm by
varying the input
weights of the carrespondingmetal compound as precursorto the
correspondingsoluliori of the
core-sell polymer system. The periodicity, that Is the surface configuration
of the MeJMeO~
clusters regularly arrayed on the substrate surface can be adjusted to be
between approximately
nm, preferably 20 nm and 400 nm, by the degree of polymerization of the
initially used
polymer sy.$tem.
Surprisingly the method of the invention, which Is based on the self-
organization of a
core-shell polymer system acting as a template for the regular precipitation
of Me clusters and/or
MeOx, clusters, allows manufacturing in vent' simple and economical manner
nanometric
surface-decorated substrates.
Nanometric, surface-deeoratedsubstrates, containing metal clusters and/or
metal-oxide
clusters and produced by the method of the invention comprise at least on one
side clusters of
metal atoms and/or metal compounds of a diameter preferably 0.5 to 1 OOnm and
mutually apart
preferably up to 400 nm which are regularly arrayed on the substrate surface.
In particular these
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5296014
nanometric clusters may be clusters of gold, platinum, palladium, titanium
dioxide, iron oxide and
cobalt oxide. Furthermore the surface-decorated substrates of the invention
may contain
clusters of, for instance, Au/FeZO, , AuICoO, Au/Co, 0,,, AuIZnO, AuITi4,,
Au/ZrOZ, Au/A1,0, ,
Au/1n,0, , Pd/AlsO, , PdIZrO~ Pt/graphite, or Pt/A1,0, . Preferred substrates
are Pt, Au~aAs,
In"GaAs, AIxGaAs, S1, SiOb Ge, Si"N~,. S~,GaAs, InP, InPSi, GaInAsP, glass,
graphite, diamond,
mica, SrTiO, or their doped modifications.
The substrates prepared by the method of the invention and decorated
withnanometric
mefial clusters and/or metal-oxide cluster, that is, nanometric particles, are
characterized by
their high uniformity and also by their high heal resistance. When annealing
gold particles 7.5
nm high, only a slight decrease in height was observed even after prolonged
thermal loading.
This condition is shown in Fig. 3. The slight decrease .above 400°C can
be explained by the
conversion of primarily formed gold oxide into gold.
After i 2 hour annealing at T = 800'C, the ordering remains preserved, as can
be seen
in ~t (atxmic force microscope) pictures (Fig. 4).
Besides high thermal strength, the nanometric particles also show high
resistance to
chemicals. Once particle formation has been completed, the nanometric clusters
ate stable
relative to solutions containing sulfuric acid and chlorides, allowing
advantageous chemical
reactions at these nanometric precious-metal clusters.
In one implementation of the rt~ethod of the Invention, the block-copolymer
micelles are
also charged with different metal salts in solution. As shown by spectroscopic
electron-energy
losses, these mixed systems are incorporated into the micelles in a nighty
dispersed manner.
Each micelle also is homogeneously charged with both inorganic components. The
precipitation of the invention of the hybrid systems and the ensuing gas-
plasmatreatment res111t
in "naked" highly disperse mixed clusters such as Au/Ti0" AuIFes4, or AuICo,O,
on different
substrates_ Fig. 5 reproduces high-power pictures of manoftticellar films
following gas-plasma
treatment, and shows regularly arrayed nanometric clusters of identical sizes.
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52980-014
Another object of the present invention relates to using the above defined
aurfac~
decorated substrates In the epoxidation of C, - Cdalkenes or in the oxidation
of CO to COs.
As already mentioned, catalytic oxidation of CO into COZ is an important field
of
application for precious metals deposited on metal oxides (Au/T i0~, Au/Fe,O,
, or AuICo,O,)_
This process is significant, tot instance, in the field of fuel cells.
Catalysis cakes place at the
boundary surface df precious-metaflsupport. In particular as regards methanol-
driven fuel cells,
hydrogen is obtained by means of the so-.called steam-reforming process. The
generated
products are 75 % hydrogen, 25 % carbon dioxide and traces of carbon monoxide.
However
the carbon-.monoxide residue poisons the anode catalysts. Therefore the CO
content must be
decreased by selective oxidation into COs
In general, high catalytic activity at love consumption of precious metal is
desired. This
goal is attained in the invention by using the smallest possible particles and
hence increased
active surface and maximal boundary surface in heterogeneous catalysis between
precious
metal and metal oXide.
As shown in Table 1 below, the specific catalyst strongly affects the
activation energy of
oxidation.
Table 1: activation energy for the CO -,~ CO, for heterogeneous systems
Precious metal Support Activation Temperature
C
Pd Al,O3 or ZrO, .._ 150 -200
graphite or Als O, 150 - 200
Au AlZ O, 150 - 200
Au TiO, about 80
Au/Fez O, or AulfiO, at 80°C are about as catalytically active and
selecfive as PtlAI,O,
at 154-200°C. As regards methanol fuel cells in particular, an
activation temperature less than
100°C is fundamental.
Besides hydrogenation, precious-metal particles also are significant as
oxidation
catalysts. Ethylene oxidation by molecular oxygen at silver colloids is used
industrially to
CA 02308302 2000-04-28
14 5~~14
manufacture ethylene oxide. Salts of alkali -(preferably) cesium compounds or
alkaline earth
metals are used as promoters. However, this procedure is restricted to the
ethylene-
ethylaneoxide system and so far has not been applicable to longer-chain
alkenes, In this
respect the European patent application 0 709 360 A1 describes metaUmetal-
oxide- catalysts
prepared by the conventional co-precipitation method and used in the
epoxidation of higher
alkenes.
Within the Scope of the above defined method of the invention in its first
embodiment,
heterogeneous catalysts are manufactured by depositing the micelle-stabif~d
precious-metal
particles on an oxidic su~ort (for instance SiO~, said catalysis being
characterized, r~lative to
homogeneous systems, by high stabif~ty, activity and selectivity and by
requiring little
consumption of precious metals while offering high catalytic activity. By
using the block
copolymer micelles of the above-defined method of the invention, the particle
size and the inter-
particle distance and the ensuing active surface may be accurately adjusted.
On account of the
residue-fnae removal of the polymer and the simultaneous conversion of the
Metal salts by the
gas plasma procedure, there result well-defined metaUmetal-oxide compound
systems on
different substrates such as mica, glass or quartz.
(n order to attain good film formation, the Iniceltes are for instance
deposited on a planar
substrate (Fig. 6). I=of example the supports used may bemicroglass balls or
microquartz balls
or mica flakes having a smooth surfiace, because the speck surface of the
support and the
quantity of precious metal can be accurately computed for such micro-balls.
The ptoportion by
weight of precious metal in this procedure is less than in conventional powder
catalysts.
Table 2; charging Pd clusters (5 nm size) on glass balls-
Glass balls (~,) m(Pd)/m(ball) [mglg) % Pdlcatalysx
1000 0.0027 0.00027
100 0.027 0.0027
0.27 0.027
5 ~ 0.5 0.05
CA 02308302 2000-04-28
15 52960-014
,-
o.~r
2.7 0.27
The quantities of precious metals available for catalysis depend on the size
of the glass
balls. Typical catalysts based on palladium/supports have values of 1-10 %
precious metal.
When using block copolymer micelles, Such a high content in precious metals
cannot be
attained, however it is not absolutely required because the size and inter
particle distances can
be exactly adjusted using this concept. As a result, even a lov~ler quantity
of precious metals Will
resuk in the same or similar catalytic activity.
As regards the second embodiment of the method of the invention, the input,
which is
uniformly distributed on the polymer cores, can be converted in solution by
reduction or
oxidation and/or by high-energy radiation, into each single polymer core, into
single or several
metal particles or metal-oxide particles, or may be precipitated by adding an
appropriate
component in the polymer core, the particular core-shell structure of the
polymer system directly
affecting the size of the particles formed in the core-shell polymer systems.
In this procedure at least part of the metal compounds contained in the
polymer cores
are converted in solution by reduction or oxidation into one or several metal
particles) andlor
metal-oxide particles) in each single polymer core to such an extent that part
of the charged
polymer cores contain one or several metal atoms arldlot one or several metal
compounds. If,
for instance, HAuCI, is used as the metal compound, then the Au~' ions
charging the polymer
cores of the particular core-shell polymer system can be reduced in solution
by reduction or
oxidation to such an extent that some of the charged polymer cores contain one
or more gold
atoms and one or more Au~ ions. If such a reduction of the metal compounds
charging the
polymer cores is carried out in solution, then the reducing agent is
preferably hydrazine.
In stage (d) of the second embodiment of the method of the invention, the film
together
uv'tth the substrate at least partly covered by the film is subjected to
reactive ion etching, to ion
sputtering, or to a wet-chemical procedure or a combination thereof. The
sttuctures precipitated
CA 02308302 2000-04-28
16
5298Q014
onto the substrate surface act as masks, which are transferred into the
corresponding substrate
by etching, the film deposited on the substrate being removed in residue-free
manner at the
desired site or zone, and the regular structure produced by the core-shell
polymer systerrl being
converted into a substrate topographical structure because of, and as a
function of, the kind
of charge on the polymer core and the duration of r~active ion etching and/or
ion sputtering
andlor the wet-chemical procedure. Preferably ion etching is used with argon,
ozone, oxygen
and their mixtures, and even more preferred is ion sputtering_
Depending on the duration of etching, and as a function of the polymer core
charges, the
film deposited on the substrate is etched away In such manner that as a result
the substrate
being used also is removed, as a result of which surface-structured substrates
produced by the
second aspect of the method of the invention, which have a relief structure of
lateral dimensions
between preferably 1 and 100 nm across macroscopic zones, and in particular
holes, troughs,
strips, dot heights as well as their inverse structures with lateral
dimensions illustratively between
1 and 100 nm, also may be produced in the substrates across macroscopic zones.
The
structures' heights and depths so attained may be a multiple, for instance 20-
fold to 100-fold, of
the lateral dimensions.
If for instance, on the one hand micelles charged with gold-atoms, and on the
other hand
micelles or molecular cavities charged with gold-compounds, are present in
precipitated form
on the substrate next to uACharged micelles, then, depending on charge, and in
selective
manner, first the gold-atom charged micelles will be etched away, far instance
byAr sputtering,
while for instance forming holes. Then the uncharged micelles, and lastly the
gold-compound
charged micelles will be etched away. The result is formation of, for
instance, islands, as a result
of which the predetermined, regular stnrcture present in the precipitated
film, and acting as a
mask, are transferred by etching into the corresponding substrate in the form
of a relief
topography.
BELIEF DESCRIPTION OF THE DRAWINGS
The Figures are as follows:
CA 02308302 2000-04-28
17
$296-pia
Fig. 1 shows scanning force microscope pictures of substrates of the invention
decorated in the nanometric range: (a) Pt diameter = 7nm on vitreous silica;
(b) pd diameter =
nm on mica; (c) gold diameter = 8 nm on glass.
Flg. 2 shows a scanning force microscope picture of 8nm high nanodusters on
glass
following treat treatment in an oxygen atmosphere (T = 2000, p(~) = 0.5 bar, t
=120 min). The
length of an image edge is 1 p.
Fig. 3 shows the dependence of 7.5 nrn high gold clusters on glass on the
duration of
annealing at three different temperature.
Pig, 4 shows a scanning force microscope picture ofnanometrically decorated
surface
struduree of the irnrer,tion, where, following oxygen plasma treatment, the
gold clusters on glass
were annealed for 12 h at T = 800°C at standard atmosphere.
Flg. 5 shows scanning force microscope pictures of gold/metal-oxide hybrid
systems on
glass: (a) 5 nm high gold/titanium-oxide clusters; (b) 5 nm high gold/cobalt-
oxide clusters; (c) 5
nm high gold lronroxide clusters following oxygen plasma treatment; the length
of an image side
Isle.
Flg. 6 schematically shows the micelle (metal clusters) dimensions vs
microglass
spheres (upper sphere: before removing the polymer enclosure; lower sphere:
following removal
of the polymer enclosure).
Fig. 7 shows scanning force microscope pictures of nanometrically surface-
decorated
substrates of the invention according to Example 1, where naked gold clusters
are precipitated
on mica: (a)Audiameter= l2nm, periodicity=80nm; (b) Au diameter=3nm;
periodicity=28
nm; (c) Au diameter = 1 nm, periodicity = 140 nm,
Ft9~ 8 shows a scanning force microscope picture of xnanometricallysurface-
decorated
substrate of the invention according to Example 2, where naked gold clusters
were precipitated
on a Si wafer, Au diameter = 3 nm, periodicity = 120 nm.
CA 02308302 2000-04-28
52960-014
18
Fig. 9 shows a scanning force microscope of a nanometrically surface decorated
substrate of the invention according to Example 3, where naked gold ctuaters
were precipitated
on GaAs; Au diameter = 3 nm, periodicity ~ 70 nm.
Fig.10 shows scanning force microscope pictures ofnanometricallysurface
decorated
substrates of the invention according to Example 4, where naked gold Clusters
were precipitated
on SrTiO; ; Au diameter= 3 nm, periodicity = 120 nm: (a) before annealing; (b)
after annealing
at 800°C in an Ar/0= atmosphere.
Fig. 11 shows a scanning force microscope picture of a nanometrically surface~-
decorated substrate of the invention according to F~cample 5, where naked gold
clusters were
precipitated on a diamond film: Au diameter = 3 nm, periodicity =120 nm.
Fig.12 shows transmission electron microscope (TEM) pictures of mono,micellar
films
according to Example 8, consisting of (a) polystyrene - b-
poly[ethyleneoxide)(LiAuCl,~osj~
micelles, where the Au~ ions were reduced by electron beams into the film, and
(b)
poly[styrene]~ - b-. poly((2-vinylpyridine)(HAuCI,)o~, where the Au~" ion in
solution was
converted into Au and the growth of an approximately 6nrn diameter crystal was
induced in
each micelle before film formation; the particular TEM pictures are followed
by schematics of the
particular films.
Fiig.13 shows a scanning force microscope picture of a mono-micellar polymer
film of
poly(styrene)~~ -b- poly[(2-vinylpyridine)(HAuCh)o,~]4~ micelles on a Si wafer
according to
Example 9; the length of an image side Js 2.5 p.
Fig.14 shows scanning force microscope pictures of theGaAs wafer structured by
the
method of the invention according to Example 10. (a) 400 holes and (b) 400
Islands; the length
of an image side Is 1.25 u.
Fig, 95 shows the 3-D structure of 400 hales in theGaAs wafer structured by
the method
of the invention according to Example 10.
CA 02308302 2000-04-28
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52980-014
Fig. 18 shows scanning force microscope pictures of a GaAs relief structured
by the
method of the invention according to. Example 11: (a) = topography and (b) =
friction; the length
of an image side Is 2 w.
Fig. 17 sh~nrs further scanning force microscope pictures of a GaAs topography
structured by the method of the invention according to Example 11: (a) =
topography and (b) _
deviatwns of the amplitude signal; the length of an image side Is 1.25 ~.
I=ig. 18 shows the sectional height function of an etched GaAs wafer according
to
Example 11.
Fiig.19 shows a high-resolution scanning electron microscope picture of
anartometric
surface-decorated substrate of the invention according to Example 12, naked
cobalt clusters
having been precipitated on a Si wafer Co diameter = 12 nm, periodicity = 80
nm; the cobalt
duster's magnetic moment as a function of the magnetic field at T = 50 K is
also shown.
Fig. 20 shows a scanning force microscope picture of a nanometric surface-
decorated
substrate of the invention according to Example 13, where naked nickel
clusters were
precipitated onto a mica substrate: Ni diameter = 8 nm; periodicity = 140 nm.
Fig. 21 shows a scanning force microscope picture of ananometric, surface-
decorated
substrate of the Invention according to Example 14, where naked gold clusters
were precipitated
on a Ei-wafer; Au diameter = 8 nm; periodicity =100 nnl.
Fig. ZZ shows a scanning force microscope picture of a nanometric surface-
decorated
substrate of the invention according to F_xample 15, where naked platinum
dusters were
precipitated on a gold monocrystal substrate (100): Pt diameter = 4 nm;
periodicity = 40 nm.
IFig. 23 shows a 3-D plot of InGaAs quantum dots on a GaAs wafer structured by
the
method of the invention and according to Example 16.
The present invention is elucidated by the Examples below.
EXAMPLE 1:
The precipitation in the manner of the invention of regularly ordered gold
clusters on a
mica substrate across macroscopic zones having a diameter of 12 nm, 3 nm or 1
nm and a
CA 02308302 2000-04-28
52880.014
periodiaty resp. of 80 nrn, 25 nm or 140 nm is successfully carried out In
each case using a 5
mg/ml polyatyreneJ~ brpoly((2-vinylpyridine)(HAuCl4)aoleso toluene solution, a
S mglml
polyjsturene]~- b- polyj2 vinylpyrjdine)(HAuCl4)oshs toluene solution, or a 5
mg/ml
poly(styr'ene]~~oo .b.po,lyj(2-vinylpyridine)(HAuCI,,)o,~]~ toluene solution
by drawing a freshly
cleaved mica substrate at a draw speed of 13 mmlmin and subsequentlytreating
it in a 200 watt
oxygen plasma for 20 min. Fig. 7 shows scanning force microscope pictures of
the nanometric
surface-decorated substrates of the invention.
EXAMPLE 2:
The precipitation of the method of the invention of regularly ordered gold
clusters on a
Si substrate with thermally grown oxide or thin natural oxide across
macroscopic zones having
a diameter or 3 nm and a peridodicity of 120 nm is implemented using a 5 mg/ml
poly jstyrene],.,~
- b-poly j(2 vinylpyridine)(HAuCI,)o.~O toluene solution by drawing anSi wafer
at a draw speed
of 12 mm/min (Si wafer with thermal oxide) or at 6 mmlmin (Si wafer with oxide
coating) and
subsequently treating it in a 240 w oxygen plasma for 20 min. Fig. 8 shows a
scanning force
microscopic picture of the nanometric surface decorated substrate of the
invention.
E3(AMPLE 3:
The precipitation in the manner of the method of the invention of regularly
ordered gold
clusters on a GaAs substrate ac~oas macroscopic zones having a diameter of 3
nm and a
periodicity of TD nm is implemented using a 5 mg/m1 poly(styrene],~oo -b-
polyj(2-
vinylpyridine)(HAuCh)o,],~ toluene solution by drawing a freshly cleaved mica
substrate at a
draw speed of 18 mm/min and then treating it in a 200 w oxygen plasma for 2D
min. Fig. 9
shows a s canning force microscope picture of the nanometric surtace-decorated
substrat~.
CA 02308302 2000-04-28
21
EXAMPLE 4:
52880.014
The precipitation in the manner of the method of the irwention of regularly
ordered gold
clusters on an SrTiO, substrate across macroscopic zones having a diameter of
3nm and a
periodicity of 120 nm is implemented using a 5 mg/ml poly jstyrene]"~ -b-
poly[(2-
vinylpyridine)(HAuCI,~,~ toluene solution by drawing an SrTi01 monocrystal
substrate (104)
at a draw rate of 4 mmlmin and subsequently treating it in a 200 w oxygen
plasma for 20 min.
Subsequent annealing in an argon/oxygen atmosphere at 80Q'C for 15 irlin
proved the structure
is stable under these conditions, F.ig. 10 shows scanning force microscope
pictures of the
nanometrlc surface-decorated substrate of the invention before and after
annealing.
EJ(AMPLE 5:
The precipitation in the manner of the method of !he invention of regularly
ordered gold
clusters on a diamond substrate across macroscopic zones having a diameter of
3nm and a
periodicity of 120 nm is implemented using a 5 rriglml poly[styrene]~» -b-
polyj(2-
vinylpyridlne)(HAuCL,)a,~],,~ toluene solution by drawing a freshly cleaved
mica substrate at a
draw rate of 4 mm/min and then treating it In a 150 w oxyg~n plasma for 10
min. Fig_ 11 shows
a scanning fotce microscope picture of the nanometric surface-decorated
substrate of the
invention.
FrXANIPLE 6:
The epoxidation of 1-octane was investigated in ~ mini-reactor. Block
copolymer
micelles filled with gold-chloride/titanium-tetrachloridewere precipitated as
catalyst on deaved
pieces of mica. The coating of the cleaved pieces of mica 10 to 50p in size
was carried out
using a solution of 5 mg/ml of polyjstyrenej~ -b-poly[2-vinylpyridine)(HAuCI,b
~ (TiCI, )o,,]~ in
toluene. The cleaved pieces of mica were dried.on a cellulose web. Then the
polymer was
decomposed in a tubular heater in an oxygen atmosphere (T = 200C, p(O~ = 0.5
bar, t = 120
min), the metal components being precipitated in the form of small mixed
clusters on the mica.
CA 02308302 2000-04-28
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52960-01R
The cleaved pieces of mica were scurried in octane and following octane
addition molecular
oxygen was directly blown into the solution. The yield of 1-octane oxide at
1Q0°C was 38°k.
EXAI~I1PLE 7:
The oxidation catalysis of CO into CO= was investigated on block-copolymer
micelles
containing gpi~chloridetron-trichloride deposited on cleaved pieces of mica.
Tlte coating of the
to 50 ~ size cleaved pieces of mica was implemented using a solution of 5
mglml
poly[styreneJ~ -b-poly[(2-vinylpyridine)(HAuCI,~o., (FeCi, )a~,~ in toluene.
The cleaved pieces
of mica were dried on a cellulose web. Thereupon and in the manner described
in Example 8,
the polymer was decomposed in a tubular oven in an oxygen atmosphere (T =
200°C, p(Os) =
0.5 bar, t = 120 min). The catalyst was enclosed in athermostatted glass tube
and the reaction
gas (1 % CO,1 % f~, 75 % f-1z, 23 % N, was made to flow by. In the reaction of
CO into Cq the
CO was converted by half.
EXAMPLE 8:
Mono-micellar films composed of (a) poly[at~rreneJ,s,a -b- poly[ethyleneoxide)-
(~A~rCI,)a~ micelles, where the Atr~' ions are reduced in the film by electron
beams and hence
the precipitation of many Au crystals in a micelle was attained, and
(b)poly[styrene]~ -b-
poly((2-vinylpyridine)(HAuCI,)°~j~, where the Au~' in solution is
converted into Au and the
gtowth of a crystal about B nm in diameter is induced in each micelle for film
formation, are
prepared by drawing a carbon-coated Cu grid each time using a 5 mg/ml toluene
solution and
a draw speed of 7 mmlmin. Fig.12 shows TEM (transmission electron microscope)
pictures as
well as the particular films in schematic form.
CA 02308302 2000-04-28
23
EXAMPLE 9:
52960.014
A mono-micellar polymer film ofpoty[stytene],~~ -b- poly[(2-
vinylpyridine)(HAuCl4)o,,],,so
micelles on a Si wafer was prepared by drawing the substrate from a 5 mglml
concentrated
solution of toluene at a draw speed of 10 mmlmin. Fig. 13 shows the force
microscope picture.
F~KAMPLE 10:
A mono-micellar polymer film consisting of poly[styrene],.,oo -b-poly[(2-
vinylpyridine)],,~
micelles on a GaAs wafer was etched withAr ions (1.1 Kev, 12 pa/cm~ for 15
min, and, in the
case of the holes, each micelle was charged with one Au particle 1 Onm in
diameter and in case
of islands, 4 out of 10 of the 2-~inylpyridine units were neutralized with one
HAuCI, in solution.
Fig. 74 shows a force microscope picture of a GaAs wafer of such a structure.
EXAMPLE 11:
A micellar film Consisting of polyjstyrene]"oo -b-poly[(2-
vlnylpyridine)(I~AuCI')o,d]~so
micelles was precipitated by drawing a GaAs substrate at a speed of 2 mm/min
from a 5 mglml
concentration solution. The non-covering micetlar film acting as an etching
mask was etched
for 15 min by means ofAr ions (1_1 hfev,12 palcm2.). Fig.16 shows no relative
contrast of the
coefficient of friction at the surface. OnIyGaAs could be detected after
etching. Fig_ 17 shows
another segment of the same film and Fig. 17b shows the deflection
perpendicularto the surface
of the scanning force microscope needle. The two-siepGaAs relief so produced
is shown in
profile in Fig. 18.
E?4AMPt~ 12:
The precipitation by the method' of the invention of regularly ordered cobalt
clusters on
a silicon substrate with thermally grown oxide or thin natural oxide across
macroscopic zones
12 nm in diameter and a periodicity of 80 nm is imple~rnented using a 5 mg/ml
poly jstyrene]~~
-b- poly[(2-vinyipyridine)(CoCt~~,4]~~o toluene solution by drawing a Si wafer
at a dravy speed of
CA 02308302 2000-04-28
5298p.p14
24
13 mm/min (Si wafer with thermal oxide) or of 6 mm/min (Si wafer with thin
oxide coating) and
ensuing treatment in a TO w oxygen plasma for 15 min. Fig. 19 shows a scanning
force
microscope picture of the nanometric surface-decorated substrate of the
invention and the
associated magnetization curve at T = 50K. The ab~ene~ of hysteresis indicates
super
'ferromagnetic properties of the cobalt clusters.
EXAMPLE 13:
The precipitation of the method of the invention of regularly ordered nickel
clusters on
a mica substrate across macroscopic zones 6 nm in diameter and with a
periodicity of 'l40nm
is implemented by a 5 mg/rnl poly(styrene,y"~-~~iyj(2-vinylpyridine)(l~liC~
)off toluene solution
by drawing a freshly cleaved mica substrate at a draw speed of 12 mm/min for 5
rnin. Fig. 20
shows a scanning force mictoscope picture of thenanometriC, surface-decorated
strbsttate of
the invention.
E3CAM1PLE 74:
The precipitation of the method of the invention of regularly ordered gold
clusters on a
silicon substrate with thermally grown oxide or this natural oxide across
macroscopic zones
havinrg a diameter of 8 nm and a periodicity of 100 nm is implemented using a
5 mg/ml
polystyrene]"~ -b-poly((2_yinylpyrtdine)(i-IAuC4)a.~ toluene solution by
drawing anSi wafer
at a speed of 15 mm/min ~Si wafer with thermal oxide) or 10 mm/rriin (Si wafer
with 'thin oxide
coating) and ensuing treatment in a 100 w trifluoromethane plasma for 10 min.
Fig. 21 shows
a scanning force microscope picture of the nanometric, surface-decorated
substrate of the
invention.
CA 02308302 2000-04-28
EXAMPLE 15:
52960-01<
The precipitation of the method of the invention of regularly ordered platinum
clusters on
a gold substrate across mactoscopic zones 4 nm in diameter and having a
periodicity of 40nm
is implerne~ed using a 5 mg/ml polyjstyrene],~ -b-poly[(2-
vinylpyridine)(K[PtGI, C=H,~)o,,l,~
toluene solution by drawing a gold monoctystai substrate (100) at a speed of
12 mmlmin and
by ensuing treatment in a 120 w oxygen plasma for 10 min. Fig. 22 shows a
scanning force
microscope picture of the nanometric, surface decorated substrate of the
invention.
EXAMPLE 18:
A mono-micellar polymer film consisting of poly[styrene]~~ -b-poly j(2-
yinylpyridine)(HAuCI,)o,,),,~ micelles was precipitated by drawing a
semiconductlng-layer
substrate jGaAs, 3 nm); InGaAs (10 nm) and GaAs (substrate)] at a speed of 10
mm/min out of
a 5 mg/ml solution. The micellar film as etching mask was etched 15 min byAr'
ions (1.1 Kev,
12 y~alcm2). Fig. 23 shows a 3D structure of the quantum dtsts so prepared.
Photoluminescence
test corroborate that the islands in Fig. 23 are indeed "quantum dots°.
