Kutsch, Bernd

Mennig, Martin

Schmidt, Helmut K.

Schmitt, Mike

Acronym

FOURTH SAAR-LOR-LUX MEETINGon Funct ional  Advanced Mater ia lsßrß'E'ErE'Centre Lorrain d'Optrquc et Elcctro,tiquc dcs SotidcsPFROCEEEDII\TGiSatTECHNOPÖLE DE NIETZCLOESUNIVERSITE DE NIETZ-SUPE LECFRANCENOVEIVIBER 2-I-25 1994LuxembourgMetzNancvINTENSTVE COURSESsupported bythe European Community COMETTvia Euro MateriauxSm 1994126r- *1l \ 4t-____tUniversi te de IVIetz(--\ z I)L IDCICCICan tpus  de  MetzäPöle Universi ta i reEu ropöcn Na ncy-l\,I etzThe rneet ing is  he lc l  on thc  Canrpus o1 'supc lcc-Nlc tz  and is  inc l r rc lec l  in  thc  events  o f  i ts  Ccntcnary .,llIXPS-Investigations to the Influence of the Interface Colloid-Matrix on theElectronic Structure of Noble Metal Colloids in Organic/ Inorganic Sol-Gel-Coatings on a Glass SubstrateB. Kutsch, M. Schmitt, M. Mennig and H. SchmidtInst i tut  für Neue Mater ial ien gem. GmbH, lm Stadtwald,66123 Saarbrücken, GermanyAbstract1.  Introduct ionThe preparation of noble metal colloids in glass-like sol-gel-coatings on glass substrates isof interest because of their optical properties (high molar extinction coefficients, high tem-perature stability, non-linear optical properties, decorative applications). In recent publica-tions 11-41, the successful preparation and optical characterisation f such coatings hasbeen reported in case of Ag, Pd, Au and Cu. The colloid formation process is controlled bybifunctional l igands and thus the interface colloid to matrix that also has an influence on theoptical properties of the system, plays a very important role. A systematic investigation ofthe electronic structure of these colloids with special stress on the interface colloid to thesurrounding matrix has not been performed yet. Temperature and atmosphere during densi-fication of the coatings, composition of the matrix, composition of the substrate and shapeof the col loids are possible parameters which could change this interface.2. Results0,0Fig. 1:  calculated UV-VISspectra [5] using the Mie-theory within the model ofa metal l ic Cu nucleus coa-ted with a shel l  of  CUOwith var ious thickness in adielectric matrix (no= 1 ,52).ä6: s iz€ of  the metal l ic nu-cleus, äx.  s ize of  theox id ic  she l l ,  mean s ize o fthe co l lo ids :  15 nm,  ar row:experimental  resul t  [4] .4mETo give an example to one aspect of the enormous influence of the interface to the physicalproperties of the coatings, fig. 1 shows a theoretically calculated optical spectrum for a Cucolloids containing coating using the Mie-theory. In this model it is assumed, that a nucleusof metallic Cu colloids (mean size: -15 nm) is coated with a CuO shell with different thick-nesses.The spectra resulting from this calculation as a function of the thickness of the shellfit very good to the experimental UV-VIS and XPS data published in t4l and prove themodel proposed there i f  a mean thickness of the oxidic shel l  of about2 - 3 nm is assumed.The aim of this paper is to demonstrate hat the combination of UV-VIS spectroscopy andXPS offers a wide and detailed set of information about the electronic structure of thecolloids. Beneath a quantitative analysis of the composition of the coatings and thestructure of the valence band, XPS offers a direct account o the core binding energies andthus to a determination of the valences of the investigated elements. Fig. 2 shows a XPS4f-core spectrum of Au colloids in a sol-gel-matrix, prepared as described in [3] on a sodal ime glass.Fig. 2: XPS spectrum ofthe Au 4f l ines of  Au col-lo ids in a sol-gel-matr ixdensi f ied at  300'C on asoda-l ime glass sub-strate.  The binding ener-gies indicated were refer-red to C 1s=284.6 eVbinding energy [eV]Two components with a binding energy of  84,45 eV (1) and 83,48 eV (2) can be resolved.The first component is attributed to metall ic Au whereas the second component could beascr ibed to a formal ly negat ive valence of Au. As this component is not observed whenfused si l ica is used as a substrate instead of soda l ime glass i t  is  hypothesised that th iscomponent is due to an interaction of the surface of the Au colloids with Na* ions, which dif-fuse into the sol-gel-matr ix f rom the substrate as determined by SNMS. In detai l ,  i t  could beattributed to the formation of an Au-compound at the surface of the colloids or to a chargetransfer f rom the nucleus to the surface. Both assumptions would imply a di f ferent dielectr icfunct ion at  the surface of the col lo ids compared with the nucleus. The observed bindingenergy component (2) is much lower than in the case of metal l ic Au (84 eV) and can not beexplained only as a pure physical  ef fect  s imi lar to ref .  t6-Bl  in the case of smal l  Au-col lo idswhich showed a binding energy shi f t  of  about 0.25 eV to higher values due to f inal  stateeffects. In the contrary, such final state and size effects for small colloids probably contrib-ute to the energy difference of 0.45 eV of the "metallic" component (1) in fig. 2 to the bulkvatue for metallic gold at 84 eV. Bulk Au-compounds with such low Au 4f-core energies asin component (2) are not known in the literature. Any effect due to improper energy refer-ence can be excluded since the binding energies for the Si 2p l ines and the O 1s-l ine were102.88 eV and 532.32 eV respectively which are typical values for soda-lime glasses [9]. Atpresent HTEM and UV-VIS investigations are carried out to study these coatings in detail toget more information about the surface and shape of the Au colloids and to clarify whetherthis effect also can be explained by a nucleus-shell-model. Au colloids with surface layers ofdifferent electronic structure are very interesting for non-linear optical investigations as thedielectric function at the surface has a strong influence on the X,(t)-effect. Further work willbe concentrated in this field and in the systematic preparation of such effects.The authors thank the Deutsche Forschungsgemeinschaft nd the State of Saarland for f i-nancial support and J. Rostalski who performed the calculation of the spectra in f ig. 1.3. ReferencesA. Hinsch, A. Zastrow, J. Non-Cryst. Sol. 147&148 (1992), 579-581T. Burkhart ,  M.  Mennig,  H.  Schmidt ,  A.  L icc iu l l i ,  Proc.  MRS Spr ing Meet ingSan Francisco 1994M. Mennig,  M. Schmit t ,  U.  Becker,  G.  Jung,  H.  Schmidt ,  SPIE Meet ing Sol-Gel-  Opt ics l l l ,  San Diego 1994,  to be publ ishedM. Mennig,  M. Schmit t ,  B.  Kutsch,  H.  Schmidt ,  SPIE Meet ing Sol-Gel-Opt icsl l l ,  Dan Diego 1994,  to be publ ishedJ. Rostalski,  RWTH Aachen, private communicationM. Quinten,  l .  Sander,  P.  Ste iner ,  U.  Kreib ig,  K.  Fauth,  G.  Schmid,  Z. ' f  .  Phys.D ,  4 ,  ( 1991 ) ,377 -379S.  B .  D icenzo,  G.  K .  Wer the im,  Comm.  So l .  S ta te  Phys .11  (1985) ,  5 ,203-219P.  H.  C i t r in ,  G.  K .  Wer the im,  Phys .  Rev .  8 ,27  (1983) ,6 ,  3176-3200Th. Gross, Ramm, Sonntag, Unger, Weijers, Adem, Surf.  & Interf.  Anal. 18(1 992), 59-64t1lt2lt3lt4ltslt6lt7ltBltelru

XPS-investigations to the influence of the interface colloid-matrix on the electronic structure of noble metal colloids in organic/inorganic sol-gel coatings on a glass substrate

Scientific documents from the Saarland University,

FOURTH SAAR-LOR-LUX MEETING
on Funct ional  Advanced Mater ia ls
ßrß'E'ErE'
Centre Lorrain d'Optrquc et Elcctro,tiquc dcs Sotidcs
PFROCEEEDII\TGiS
at
TECHNOPÖLE DE NIETZ
CLOES
UNIVERSITE DE NIETZ-SUPE LEC
FRANCE
NOVEIVIBER 2-I-25 1994
Luxembourg
Metz
Nancv
INTENSTVE COURSES
supported by
the European Community COMETT
via Euro Materiaux
Sm 1994126
r
- *1
l \ 4t-____t
Universi te de IVIetz
(--\ z I)L IDCICCI
Can tpus  de  Metz
ä
Pöle Universi ta i re
Eu ropöcn Na ncy-l\,I etz
The rneet ing is  he lc l  on thc  Canrpus o1 'supc lcc-Nlc tz  and is  inc l r rc lec l  in  thc  events  o f  i ts  Ccntcnary .
,llI
XPS-Investigations to the Influence of the Interface Colloid-Matrix on the
Electronic Structure of Noble Metal Colloids in Organic/ Inorganic Sol-Gel-
Coatings on a Glass Substrate
B. Kutsch, M. Schmitt, M. Mennig and H. Schmidt
Inst i tut  für Neue Mater ial ien gem. GmbH, lm Stadtwald,66123 Saarbrücken, Germany
Abstract
1.  Introduct ion
The preparation of noble metal colloids in glass-like sol-gel-coatings on glass substrates is
of interest because of their optical properties (high molar extinction coefficients, high tem-
perature stability, non-linear optical properties, decorative applications). In recent publica-
tions 11-41, the successful preparation and optical characterisation f such coatings has
been reported in case of Ag, Pd, Au and Cu. The colloid formation process is controlled by
bifunctional l igands and thus the interface colloid to matrix that also has an influence on the
optical properties of the system, plays a very important role. A systematic investigation of
the electronic structure of these colloids with special stress on the interface colloid to the
surrounding matrix has not been performed yet. Temperature and atmosphere during densi-
fication of the coatings, composition of the matrix, composition of the substrate and shape
of the col loids are possible parameters which could change this interface.
2. Results
0,0
Fig. 1:  calculated UV-VIS
spectra [5] using the Mie-
theory within the model of
a metal l ic Cu nucleus coa-
ted with a shel l  of  CUO
with var ious thickness in a
dielectric matrix (no= 1 ,52).
ä6: s iz€ of  the metal l ic nu-
cleus, äx.  s ize of  the
ox id ic  she l l ,  mean s ize o f
the co l lo ids :  15 nm,  ar row:
experimental  resul t  [4] .4m
E
To give an example to one aspect of the enormous influence of the interface to the physical
properties of the coatings, fig. 1 shows a theoretically calculated optical spectrum for a Cu
colloids containing coating using the Mie-theory. In this model it is assumed, that a nucleus
of metallic Cu colloids (mean size: -15 nm) is coated with a CuO shell with different thick-
nesses.The spectra resulting from this calculation as a function of the thickness of the shell
fit very good to the experimental UV-VIS and XPS data published in t4l and prove the
model proposed there i f  a mean thickness of the oxidic shel l  of about2 - 3 nm is assumed.
The aim of this paper is to demonstrate hat the combination of UV-VIS spectroscopy and
XPS offers a wide and detailed set of information about the electronic structure of the
colloids. Beneath a quantitative analysis of the composition of the coatings and the
structure of the valence band, XPS offers a direct account o the core binding energies and
thus to a determination of the valences of the investigated elements. Fig. 2 shows a XPS
4f-core spectrum of Au colloids in a sol-gel-matrix, prepared as described in [3] on a soda
l ime glass.
Fig. 2: XPS spectrum of
the Au 4f l ines of  Au col-
lo ids in a sol-gel-matr ix
densi f ied at  300'C on a
soda-l ime glass sub-
strate.  The binding ener-
gies indicated were refer-
red to C 1s=284.6 eV
binding energy [eV]
Two components with a binding energy of  84,45 eV (1) and 83,48 eV (2) can be resolved.
The first component is attributed to metall ic Au whereas the second component could be
ascr ibed to a formal ly negat ive valence of Au. As this component is not observed when
fused si l ica is used as a substrate instead of soda l ime glass i t  is  hypothesised that th is
component is due to an interaction of the surface of the Au colloids with Na* ions, which dif-
fuse into the sol-gel-matr ix f rom the substrate as determined by SNMS. In detai l ,  i t  could be
attributed to the formation of an Au-compound at the surface of the colloids or to a charge
transfer f rom the nucleus to the surface. Both assumptions would imply a di f ferent dielectr ic
funct ion at  the surface of the col lo ids compared with the nucleus. The observed binding
energy component (2) is much lower than in the case of metal l ic Au (84 eV) and can not be
explained only as a pure physical  ef fect  s imi lar to ref .  t6-Bl  in the case of smal l  Au-col lo ids
which showed a binding energy shi f t  of  about 0.25 eV to higher values due to f inal  state
effects. In the contrary, such final state and size effects for small colloids probably contrib-
ute to the energy difference of 0.45 eV of the "metallic" component (1) in fig. 2 to the bulk
vatue for metallic gold at 84 eV. Bulk Au-compounds with such low Au 4f-core energies as
in component (2) are not known in the literature. Any effect due to improper energy refer-
ence can be excluded since the binding energies for the Si 2p l ines and the O 1s-l ine were
102.88 eV and 532.32 eV respectively which are typical values for soda-lime glasses [9]. At
present HTEM and UV-VIS investigations are carried out to study these coatings in detail to
get more information about the surface and shape of the Au colloids and to clarify whether
this effect also can be explained by a nucleus-shell-model. Au colloids with surface layers of
different electronic structure are very interesting for non-linear optical investigations as the
dielectric function at the surface has a strong influence on the X,(t)-effect. Further work will
be concentrated in this field and in the systematic preparation of such effects.
The authors thank the Deutsche Forschungsgemeinschaft nd the State of Saarland for f i-
nancial support and J. Rostalski who performed the calculation of the spectra in f ig. 1.
3. References
A. Hinsch, A. Zastrow, J. Non-Cryst. Sol. 147&148 (1992), 579-581
T. Burkhart ,  M.  Mennig,  H.  Schmidt ,  A.  L icc iu l l i ,  Proc.  MRS Spr ing Meet ing
San Francisco 1994
M. Mennig,  M. Schmit t ,  U.  Becker,  G.  Jung,  H.  Schmidt ,  SPIE Meet ing Sol-
Gel-  Opt ics l l l ,  San Diego 1994,  to be publ ished
M. Mennig,  M. Schmit t ,  B.  Kutsch,  H.  Schmidt ,  SPIE Meet ing Sol-Gel-Opt ics
l l l ,  Dan Diego 1994,  to be publ ished
J. Rostalski,  RWTH Aachen, private communication
M. Quinten,  l .  Sander,  P.  Ste iner ,  U.  Kreib ig,  K.  Fauth,  G.  Schmid,  Z. ' f  .  Phys.
D ,  4 ,  ( 1991 ) ,377 -379
S.  B .  D icenzo,  G.  K .  Wer the im,  Comm.  So l .  S ta te  Phys .11  (1985) ,  5 ,203-219
P.  H.  C i t r in ,  G.  K .  Wer the im,  Phys .  Rev .  8 ,27  (1983) ,6 ,  3176-3200
Th. Gross, Ramm, Sonntag, Unger, Weijers, Adem, Surf.  & Interf.  Anal. 18
(1 992), 59-64
t1l
t2l
t3l
t4l
tsl
t6l
t7l
tBl
tel
ru


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XPS-investigations to the influence of the interface colloid-matrix on the electronic structure of noble metal colloids in organic/inorganic sol-gel coatings on a glass substrate

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