Strutural and Chemial Properties of ZnSe-Fe
Eletrodeposited Granular Films
A.R. de Moraes, D.H. Mosa, W.H. Shreiner,N. Mattoso, and E. Silveira
Departamento deFsia-UFPR,CentroPolitenio, CP19044
81531-990 Curitiba-PR,Brazil
Reeivedon23April,2001
PotentiostatieletrodepositionmethodshavebeenusedtogrowpolyrystallineZnSeandZnSe-Fe
granularthinlmsonstainlesssteelsubstratesfromaqueoussolutions. Theselmswere
harater-izedbyx-ray diration,transmission eletronmirosopy,x-ray photoeletronspetrosopy and
Ramanspetrosopy.
I Introdution
Hybridsemiondutor(SC)/ferromagneti(FM)
stru-tures have been investigated due to the possibility of
usingnotonlythehargebutalsothespinofeletrons
to oneive new eletroni devies [1-3℄. In
partiu-lar,ZnSehasbeenpointedoutasoneattrating
andi-date to ahievesuh goaldue totheir favorable
hem-ial stability in the presene of Fe [4℄ and theoretial
alulationssuggestingthatlargetunnel
magnetoresis-tane ouldbeattained[5℄. Currently, mostofhybrid
SC/FM systems are fabriated using moleular beam
epitaxy (MBE) [6,7℄. However, the simplerand
inex-pensiveeletrodeposition of II-VIsemiondutor
om-pounds suh asZnSe hasalreadybeenstudied for
ap-pliations in optoeletronis and solar ells [8-11℄. In
thisworkwereportforthersttimeonthefabriation
oftheZnSe-Fegranularthinlmsbyeletrodeposition
tehniques.
II Sample preparation
ZnSe-Fegranularthinlmswereeletrodepositedunder
potentiostationditionsonto mehaniallyand
hem-ially polished stainless steel substrates. All
deposi-tion experimentswere performedusing aEG&GPAR
273Agalvanostat/potentiostatwithastationary
paral-lelplateeletrodesystemonsistingofaplatinumdisk
ounter-eletrode and a saturated Ag/AgCl referene
eletrode. Platingsolutionswerepreparedwithreagent
grade hemials (ZnSO
4 , SeO
2
, and Fe(NH
4 )
2 (SO
4 )
2 )
immediatelypriortoeahexperimentsbydissolvingthe
requisiteamountofthemetalliomponentsindistilled
0
thodi potentials with pH valueadjusted between 2.0
and 2.5 byusing sulfuri aidas additive. PureZnSe
thinlmsweredepositedat-0.85Vfromsolutions
on-taining200mMZn and 1mMSe. Asreportedin the
literature[8-11℄,theZnSe thin lms obtainedin these
onditionsare metalli gray, rystallizedwith adense
morphology. InorporationofFeinthesolution(partial
onentration between 0.1to 10mM) does not
signif-iantly hange, suh physial and morphologial, the
depositsaordingtooptialandsanningeletron
mi-rosopyanalyses. All the lmsare mirometerthik.
Adetailed investigationof thesimultaneous
eletrode-position of the Zn, Se and Fe ions will be presented
elsewhere[12℄.
III Results and Disussion
X-ray Photoemission Spetrosopy (XPS) analyses
showthattheZnSethinlmsarefreeofontaminants
withinhemialsensibility(about1at. %)ofour
exper-imentsperformedin anESCA3000VG system. From
XPSprole analysesperformed by Ar +
ion
bombard-ment at 3 keV, an exess of Se is observed near the
surfae of the deposits. Sine the Ar +
ion
bombard-mentoftheZnSeis ongruent[13℄;i.e., the
stoiquiom-etryoftheZnSeompoundismaintained,weonlude
that the exessof Se is related to the eletrohemial
kinetis.XPSanalysesrevealsthatZnSelmsprepared
fromsolutionsontaininglowFeonentrationexhibits
similarSe exessat the surfae. After surfaeething
withAr +
ions, anoxygen-free surfaeis obtainedand
theZn2p andSe2pore-levelsignalstendtoZnSe
dira-solution. Togetherwiththeintensedirationpeaksof
thesubstrate,threedirationpeaksobservedat31.7 0
,
53.2 0
, and 63 0
are assoiated with ubi ZnSe with a
zinblendestruture[14℄. Thedirationpeaksaround
27.2 0
and 66.4 0
were identied as Se with an
hexag-onalstruture whereas another peak around34.6 0
re-veals the presene of the SeO
2
[14℄. The trigonal Se
formation annot be ruled out [15℄. Thus, the
sam-ple is polyrystallinewith a predominant ZnSe
(111)-texturealongthegrowthdiretion. Theabseneofthe
Fedirationpeaksareprobablydueto smallpartile
sizeandtheirintrinsistruturaldisordersinesomeFe
dirationringsarevisibleintheTransmissionEletron
Mirosopy(TEM) analyses. TEManalyseswere
per-formedusingaJEOLJEM1200IIeletronmirosope
operating at 120 kV. For TEM analyses the stainless
steel substratewere removedfrom thebakside ofthe
samples by ontrolled eletrohemial ething using a
diluted nitri aid solution. In Fig. 2(a) is shown a
brighteldimageofapureZnSedeposit. SeletedArea
eletronDiration(SAED)patternofthissameregion
isshowninFig. 2(b).Someeletrondirationringsof
theZnSe are identied. Fig. 2()shows abrighteld
imageofadeposit preparedwith1mMFe. Aording
to the eletroni density ontrast, the Fe-rih regions
(darkzones)aredispersed inaZnSetemplate. Fe-rih
partileshavingaveragediametersvaryingfrom20nm
to 100 nm are observed. The network of the Fe-rih
partiles exhibits abroadsize distribution. The same
eletrodeposit exhibit perolating regions (not shown)
with Fe-rih lusters having an average diameter size
aslarge as950nm. Fig. 2(d) shownsthe SAED
pat-ternofthesameregionofthesampleshownintheFig.
2(). Some dirationrings assoiatedwith ZnSe and
Feareidentied. Therefore,anetworkofFe-rih
gran-ulesalmostphysiallyunoupled betweenthemanbe
obtainedbyeletrohemialproessfromaqueous
solu-tionswithonentrationsmallerthan1mMFe. Using
aJobin-YvonT64000miro-Ramansystem,theRaman
satteringmeasurementswereperformedatroom
tem-perature in the baksattering onguration from the
sample growth surfae. After dispersed by the
spe-trometer the sattered light wasdeteted by a liquid
nitrogen ooled harge oupled devie. The Raman
spetra were exited by the 514.5 nm line of a Ar +
laser. The laserwasfoused to aspot size of about 2
mandthepowerdensitywaskeptunder104W/m 2
,
in ordertoavoiddamagetothesamples. No
polariza-tionanalyzerwasused inorder to seletthesattered
lightomingfromthe sample. The spetralresolution
was 4m 1
. Fig. 3depitstheRamanspetraoffour
samples grown under dierent onditions speied in
itsaption. Thespetrawereshiftedvertiallyforthe
Figure1. X-ray dirationpatternintheBragg-Brentano
geometry performed with Co K radiation for a ZnSe-Fe
eletrodeposit with100mMFeinthesolution.
Figure2.(a)and()BrighteldmirographsofpureZnSe
andZnSe-Fepreparedfromsolutions ontaining1mMFe,
respetively. (b)and (d)Seleted-areaeletron diration
patternofthesameregionsreportedin(a)and(),
respe-tively.Somedirationringsareidentied.
sakeoflarity. WeexpetaninreasingofFe
inorpo-ration in thesamples from (a) to (d), withpure ZnSe
beinglabeledas(a). Thespetrumof pureZnSe
on-sistsofalongitudinaloptial(LO)phononat252m 1
andthetransversemode(TO)atabout205m 1
[16℄.
For all the spetra showed in Fig. 3 we observe one
strutureat252m 1
andaweakleakagefromtheTO
at205m 1
. Thepronounedpeakatabout235m 1
anbeattributed to atrigonalSephase[17℄, sinean
exess of Seon top of astoihiometriZnSe template
was observed by XPS and x-ray diration analyses.
TheRamanspetrumtakenfromthesubstrateshowed
formationofintermediaryompounds isexpeted[16℄.
Theseondorderzone-boundary2TA(X)modeanbe
observed at about140m 1
. With theinrease ofFe
ontenttherange under 150m 1
beomesmore
pro-nouned indiatinganinreaseofdisorderin the
sam-ples. With inreaseofFeontentoneobservesalso an
inreaseinthesatteredintensityfortheZnSeLOand
theTOphonons, in omparisonwith themodeat 235
m 1
. As the Raman measurements, SAED pattern
and X-ray diration analyses showed no evidene of
intermediary ompounds of the type Zn
1 x Fe
x Se, we
do not expet hange in the gap of the material and
onsequentlyresonaneeets. Weattributethiseet
asomingfromsurfaeenhanedRamansatteringdue
to theformationofFegranulesinside thesample[18℄.
Inonlusion,wedemonstratethatispossiblethe
fab-riationofgranularZnSe-Fethinlmswitha
polyrys-tallinestrutureusingeletrohemialproesses.
Figure3.Ramanspetraof(a)pureZnSedepositedat-0.85
V; ZnSe-Fe deposited underperiodially pulsedpotentials
between-0.85V and-1.1 Vfor times(b)1sand0.1sfrom
solutionontaining1mMFe;()1sand0.1sfromsolution
ontaining100mMFeand(d)1sand1sfromsolution
on-taining100mMFe.
Aknowledgments
Theauthors aregrateful to Centrode Mirosopia
Eletr^onia (UFPR) for the tehnial support in the
TEM measurementsand to Group of Optial
Proper-ties(IFGW-UNICAMP)fortheirhelpwiththeRaman
measurements. This work was partially supported by
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