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Annealing Effect on the Structural, Magnetic, Electrical, Optic Property, Nanomechanical, and Adhesive Characteristics of Co60Fe20Yb20 Thin Films on Glass Substrate

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Wen-Jen Liu
Wen-Jen Liu
Wen-Jen Liu
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Yung-Huang Chang
Yung-Huang Chang
Yung-Huang Chang
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Yuan-Tsung Chen at National Yunlin University of Science and Technology
Yuan-Tsung Chen
Po-Chun Chiu
Po-Chun Chiu
Po-Chun Chiu
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Abstract and Figures

In this study, X-ray diffraction (XRD) analysis showed the amorphous nature of the Co60Fe20Yb20 films deposited at room temperature (RT), 100 °C, and 200 °C. The body-centered cubic (BCC) CoFe (110) characteristic peak was visible at 44.7° after annealing films of 40 nm and 50 nm at 300 °C. The highest alternating current magnetic susceptibility (χac) value was 0.21 at 50 Hz in a 50 nm, and the lowest resistivity value was 1.02 (×10−2 Ω.cm) in a 50 nm. In terms of nano-indication measurement, the highest value of hardness was 9.29 GPa at 300 °C in a 50 nm. When the thickness increased from 10 nm to 50 nm, the hardness and Young’s modulus of the Co60Fe20Yb20 film also showed a saturation trend. The Co60Fe20Yb20 film had the maximum surface energy at 50 nm after 300 °C annealing. The transmittance of Co60Fe20Yb20 films decreased when the thickness was increased because the thickness effect suppresses the photon signal. Due to high χac, low electrical performance, strong nano-mechanical properties, and high adhesion, it was discovered in this work that 50 nm with annealing at 300 °C was the ideal condition for the magnetic and adhesive capabilities of Co60Fe20Yb20 film. More importantly, replacing the CoFeB seed or buffer layer with a thin CoFeYb film improved the thermal stability, making CoFeYb films attractive for practical magnetic tunnel junction (MTJ) applications. Furthermore, the specific properties of Co60Fe20Yb20 films were compared to those of Co60Fe20Y20 films, demonstrating that the specific properties of these two materials may be compared.
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Coatings2022,12,1753.https://doi.org/10.3390/coatings12111753www.mdpi.com/journal/coatings
Article
AnnealingEffectontheStructural,Magnetic,Electrical,Optic
Property,Nanomechanical,andAdhesiveCharacteristicsof
Co
60
Fe
20
Yb
20
ThinFilmsonGlassSubstrate
Wen‐JenLiu
1
,Yung‐HuangChang
2
,Yuan‐TsungChen
3,
*,Po‐ChunChiu
3
,Yu‐ZhiWang
3
,Shih‐HungLin
4
and
Po‐WeiChi
5
1
DepartmentofMaterialsScienceandEngineering,I‐ShouUniversity,
Kaohsiung840,Taiwan
2
BachelorPrograminInterdisciplinaryStudies,NationalYunlinUniversityofScienceandTechnology,123
UniversityRoad,Section3,Douliou64002,Taiwan
3
GraduateSchoolofMaterialsScience,NationalYunlinUniversityofScienceandTechnology,
123UniversityRoad,Section3,Douliou64002,Taiwan
4
DepartmentofElectronicEngineering,NationalYunlinUniversityofScienceandTechnology,
123UniversityRoad,Section3,Douliou64002,Taiwan
5
InstituteofPhysics,AcademiaSinica,Nankang,Taipei11529,Taiwan
*Correspondence:ytchen@yuntech.edu.tw;Tel.:+886‐5‐534‐2601
Abstract:Inthisstudy,X‐raydiffraction(XRD)analysisshowedtheamorphousnatureofthe
Co
60
Fe
20
Yb
20
filmsdepositedatroomtemperature(RT),100°C,and200°C.Thebody‐centeredcubic
(BCC)CoFe(110)characteristicpeakwasvisibleat44.7°afterannealingfilmsof40nmand50nm
at300°C.Thehighestalternatingcurrentmagneticsusceptibility(χ
ac
)valuewas0.21at50Hzina
50nm,andthelowestresistivityvaluewas1.02(10
−2
Ω.cm)ina50nm.Intermsofnano‐indication
measurement,thehighestvalueofhardnesswas9.29GPaat300°Cina50nm.Whenthethickness
increasedfrom10nmto50nm,thehardnessandYoung’smodulusoftheCo
60
Fe
20
Yb
20
filmalso
showedasaturationtrend.The
Co
60
Fe
20
Yb
20
filmhadthemaximumsurfaceenergyat50nmafter
300°Cannealing.ThetransmittanceofCo
60
Fe
20
Yb
20
filmsdecreasedwhenthethicknesswasin‐
creasedbecausethethicknesseffectsuppressesthephotonsignal.Duetohighχ
ac
,lowelectrical
performance,strongnano‐mechanicalproperties,andhighadhesion,itwasdiscoveredinthiswork
that50nmwithannealingat300°Cwastheidealconditionforthemagneticandadhesivecapabil‐
itiesofCo
60
Fe
20
Yb
20
film.Moreimportantly,replacingtheCoFeBseedorbufferlayerwithathin
CoFeYbfilmimprovedthethermalstability,makingCoFeYbfilmsattractiveforpracticalmagnetic
tunneljunction(MTJ)applications.Furthermore,thespecificpropertiesofCo
60
Fe
20
Yb
20
filmswere
comparedtothoseofCo
60
Fe
20
Y
20
films,demonstratingthatthespecificpropertiesofthesetwoma‐
terialsmaybecompared.
Keywords:annealedCo
60
Fe
20
Yb
20
thinfilms;X‐raydiffraction(XRD);low‐frequencyalternating
currentmagneticsusceptibility(χ
ac
);optimalresonancefrequency(f
res
);surfaceenergy;adhesion;
magnetictunneljunction(MTJ);electricalproperties;nanomechanicalproperties;transmittance
1.Introduction
Nowadays,thetechnologyiswelldevelopedandisusedinsomecommonlyseen
devices,suchasgenerators,semiconductorcomponents,andmagneticrecordingmedia.
Highperformancepermanentmagnetsmadeofoneormorerareearthelementsareused
inthesedevices.Thepriceofrareearthmaterialswasroughly10timeshigherfrom2010
to2011levels,sparkinginvestigationonsubstitutepermanentmagnetsdevoidofrare
earthelements.Permanentmagnetsmusthaveahighmagnetization,ahighcurietem‐
perature(Tc),ahighmagneticanisotropy,andahighcoercivity(Hc)[1–5].AddingBto
Citation:Liu,W.‐J.;Chang,Y.‐H.;
Chen,Y.‐T.;Chiu,P.‐C.;Wang,Y.‐Z.;
Lin,S.‐H.;Chi,P.‐W.Annealing
EffectontheStructural,Magnetic,
Electrical,OpticProperty,
Nanomechanical,andAdhesive
CharacteristicsofCo60Fe20Yb20Thin
FilmsonGlassSubstrate.
Coatings2022,12,1753.
https://doi.org/10.3390/
coatings12111753
AcademicEditor:AndreyV.Osipov
Received:22October2022
Accepted:13November2022
Published:15November2022
Publisher’sNote:MDPIstaysneu‐
tralwithregardtojurisdictional
claimsinpublishedmapsandinstitu‐
tionalaffiliations.
Copyright:©2022bytheauthors.Li‐
censeeMDPI,Basel,Switzerland.
Thisarticleisanopenaccessarticle
distributedunderthetermsandcon‐
ditionsoftheCreativeCommonsAt‐
tribution(CCBY)license(https://cre‐
ativecommons.org/licenses/by/4.0/).
Coatings2022,12,17532of11
theCoFealloymatrixanddepositingtheferromagneticCoFeBalloyonthemagnetictun‐
neljunction(MTJ)structure,resultinginafreeorpinnedlayer,istypicalmethodforcre‐
atingCoFeBalloy[6–8].Co60Fe20Yb20wasanewsubstanceintherealmofmagneticmate‐
rialsinthisstudy.CoFeYbfilmcanbeusedtoreplacetheCoFeBalloylayerintheMTJ
structure.ByaddingYb,thecrystallinityisimproved,anditsheatresistanceisincreased.
Althoughdynamicrandomaccessmemory(DRAM)andflashmemorystillmaintainthe
dominantpositioninthecurrentmarketinthenextfewyears,intheeraofrapidtechno‐
logicaldevelopment,drivenbythedemandforartificialintelligence(AI),Internetof
Things(loT),fifthgenerationwirelesssystems(5G),andemergingmemorymagnetore‐
sistancerandomaccessmemory(MRAM)willdeveloprapidlyinthenextfewyears,and
graduallybecomeamainstreamproduct.MRAMusesmagneticforcetostoredata[9–15].
Whenthecomputeristurnedoff,themagneticforceofitsmemorychipstillexists,soit
stillretainsthedatainthememory.TherareearthelementYbhasphysicochemicalprop‐
ertiescomparabletoCa.BothYbandCa,forexample,aredivalentionswithidentical
atomicsizesandelasticmoduli.Theyaremisciblenotonlyinliquids,butalsoincrystals
andsolids.CorrosionresistanceishigherinYb‐containingMg‐basedamorphousalloys
thaninCa‐containingmagnesium‐basedamorphousalloys[16–18].Becausetheaddition
ofYbnotonlyimprovestheplasticityofthealloyanditalsoimprovesitsthermalstability,
theclassicamorphousalloyMg‐Zn‐CaisreplacedbyrareearthYb[19,20].Co60Fe20B20thin
filmiscommonlyusedinMTJstructureasafreeorpinnedlayer,andcanachieveahigh
tunnelingmagnetoresistance(TMR)ratio.ThisstudyprimarilyusedthesameYb/Bratio
toformCoFeYbfilmsinordertoinvestigatesomespecificproperties.Thenoveltyofthis
researchistoinvestigatethestructureandmagneticpropertiesofCoFeYbthinfilmsasa
functionofthickness,aswellastoinvestigateannealedCoFeYbthinfilmstoseeifthey
willchangeinhightemperatureenvironments.However,followingaseriesofsample
testingandanalysis,itwasdiscoveredthatincreasingtheannealingtemperaturedidnot
causeanydamagetothesample.Thestructure,magneticproperties,electricalproperties,
mechanicalproperties,contactangleadhesionefficiency,andopticalcharacteristicsof
Co60Fe20Yb20thinfilmswithvaryingthicknessesandheattreatmentswereallmeasuredin
thiswork.Inpreviousresearch,theas‐depositedandpost‐annealingCo60Fe20Y20films
werecomparedwithCo60Fe20Yb20filmsfortheirmagnetic,optic,andadhesiveproperties,
asmentionedinTable1[21].
Table1.SignificantpropertiesforCo60Fe20Y20andCo60Fe20Yb20materials.
TypeofFilmMaximumχac
(a.u.)
MaximumSur‐
faceEnergy
(mJ/mm2)
Transmittance
(%)
Glass/Co60Fe20Y20[21]0.2331.8458
Glass/Co60Fe20Yb20
10–50nmatas‐depositedandan‐
nealedconditions
(Currentresearch)
0.2131.354
2.MaterialsandMethods
CoFeYbthinfilmswiththicknessesrangingfrom10to50nmwerecreatedonglass
substratesusingdirect‐current(DC)magnetronsputtering.Thefilmswerecreatedinfour
differentways:(a)atroomtemperature(RT),(b)annealedforanhourat100°C,(c)an‐
nealedforanhourat200°C,and(d)annealedforanhourat300°C.Theoperatingpres‐
sureforArwas3×10−3Torr,basepressurewas3×10−7Torr,andex‐situannealedpressure
was2.5×10−3TorrinparticularArgas.ThetargetcompositionofCoFeYballoyis60%Co,
20%Fe,and20%Yb.Additionally,grazingincidenceX‐raydiffraction(GIXRD)patterns
producedwithCuKα1(PANanalyticalX’pertPROMRD,MalvernPanalyticalLtd.,Cam‐
bridge,U.K.)andalowanglediffractionincidenceatatwo‐degreeanglewereusedto
Coatings2022,12,17533of11
analyzethestructureoftheCoFeYbfilms.Alow‐frequencyalternate‐currentmagnetic
susceptibility(χac)instrument(XacQuan,MagQuCo.Ltd.NewTaipei,Taiwan)with
measuredfrequencyrangesof10to25,000HzwasusedtostudyCo60Fe20Yb20thinfilms.
Theresistivityandsheetresistance(Rs)valuesofCo60Fe20Yb20filmsweremeasuredusing
astandardfour‐pointapproachforelectricalproperties.ThehardnessandYoung’smod‐
ulusweremeasuredusingtheMTSNanoIndenterXPwithaBerkovichtip(MTS,Minne‐
apolis,StateofMinnesota,USA)andcontinuousstiffnessmeasurement(CSM)methodol‐
ogy.Theloadingwasthendecreasedto10%ofthemaximumloadbeforetheindenter
wasgraduallyremovedfromthesurface.Theindentertookmeasurementsforeachsam‐
pleat10differentpoints.Thedepthoftheindentationwasmeasuredateachofthe40
stepsthatincreasedtheindentationload.Sixindentationsineachsamplewereexamined,
andthestandarddeviationwasaveragedtogeneratemoretrustworthyresults.Thecon‐
tactanglewasdeterminedusingdeionized(DI)waterandglycerol(CAM‐110,Creating
NanoTechnologies,Tainan,Taiwan).Whenthesamplewasremoved,thecontactangle
wasmeasured.Finally,thesurfaceenergywascalculatedusingthecontactangle[22–24].
TheopticalcharacteristicswereassessedusingaSpectroSmartAnalyzer(Collimage,Tai‐
pei,Taiwan)withvisiblelightwithawavelengthrangeof500–800nm.
3.Results
3.1.X‐rayDiffraction
XRDpatternsofas‐depositedandannealedCoFeYbthinfilmswiththicknessesvar‐
yingfrom10to50nmareshowninFigure1a–d.Figure1aexhibitsas‐depositedthinfilm
patterns,whereasthosegeneratedafterannealingat100°C,200°C,and300°Careillus‐
tratedinFigure1b–d.Figure1a–cindicatethatCoFeYbfilmsdepositedatRTandpost‐
annealedat100°Cand200°Careamorphousstatus.However,Figure1dshowsthatwhen
CoFeYbthinfilmsare40nmand50nmat300°C,thecharacteristicpeakCoFe(110)ap‐
pearsat44.7°,whichincreaseswiththethickness.Itscharacteristicpeakintensityhasa
tendencytoincrease.Fromtheaboveresults,itcanbespeculatedthattheCoFeYbthin
filmneedstobeannealedatatemperatureofatleast300°Candathicknessof40nmor
morebeforecrystallizationoccurs.
(a)(b)
Coatings2022,12,17534of11
(c)(d)
Figure1.ThinfilmsofCoFeYbwithXRDpatterns.(a)RT,(b)followingannealingat100°C,(c)
followingannealingat200°C,and(d)followingannealingat300°C.
3.2.MagneticProperty
Figure2a–dshowtheχacforfourdistinctpreparationcircumstances,withthicknesses
rangingfrom10to50nmatRTandannealedtemperaturesof100°C,200°C,and300°C,
respectively.Inthelow‐frequencyrangeof50–100Hz,thevalueofχacdecreaseswithfre‐
quency.Theoutcomesalsodemonstratethatthecorrespondingχacvalueriseswhenthick‐
nessisbetween10nmand50nm.ThesefindingsshowthatallCoFeYbsamplesexhibit
magneto–nanocrystallineanisotropyandthethicknesseffect.Agreaterannealingtemper‐
atureresultedinahigherχ
acvaluethanalowerannealingtemperature.Ingeneral,
strongercrystallizationandgraindevelopmentweregeneratedbythehigherannealing
temperatureandthickerthickness.Magneto–nanocrystallineanisotropycausedtheχ
ac
valueofCoFeYbtorise[25,26].
(a)(b)
Coatings2022,12,17535of11

(c)(d)
Figure2.Therelationshipbetweenthelow‐frequencyalternate‐currentmagneticsusceptibility(χac)
andfrequency,from50to25,000Hz.(a)RT,(b)followingannealingat100°C,(c)followinganneal‐
ingat200°C,and(d)followingannealingat300°C.
Figure3displaysthematchingmaximumχacfordifferentCoFeYbthicknessesunder
fourpreparationconditions.ThehighestχacofannealedCoFeYbthinfilmwasat300°C,
andatthattemperature,thethicknesswas50nm,whichismorethanitwasatotherin‐
vestigationalsettings.Thesefindingsclearlydemonstratedthethicknesseffectofχacin
CoFeYbfilms.Thethicknesseffectcausesariseinχacasthicknessincreases.Themaxi‐
mumχacofannealedCoFeYbthinfilmswaslargerthanthatatRT.Table2showsthe
maximumχacfortheidealresonancefrequency(fres)underfourdifferentsituations.The
greatestχachadthehighestspinsensitivityatthefres[27,28].Atdifferentthicknesses,fres
valuewaslessthan100Hz.Thefreswasdeterminedtobelessthan500Hz,makingit
suitableforusageintransformers,magneticcomponents,andlow‐frequencysensors.
Figure3.MaximumχacfortheCoFeYbthinfilms.
Table2.Theoptimalresonantfrequencyforvariousthicknesses.
ThicknessRTAnnealingat
100°C
Annealingat
200°C
Annealingat
300°C
10nm501005050
20nm50505050
30nm50505050
40nm50505050
Coatings2022,12,17536of11
50nm50505050
3.3.ElectricalProperties
Theresistivityandsheetresistance(Rs)withvariousthicknessesandtemperature
conditionsareshowninFigure4.Accordingtothefindingsofthisinvestigation,resistiv‐
ityandsheetresistance(Rs)bothreducedwithincreasingthicknessandannealedtem‐
peratures.Thesheetresistancedecreasedastheannealingtemperatureincreasedinterms
oftemperature.Itishypothesizedthatgrainaggregationinthefilmincreaseswithin‐
creasingannealingtemperature.Inthecaseoflargergrains,theconductivitywillalsobe
easier[29,30].
(a)(b)
Figure4.(a)TheresistivityofCoFeYbthinfilms,(b)thesheetresistanceofCoFeYbfilms.
3.4.Nano‐Indentation
ThehardnessandYoung’smodulusoftheCoFeYbthinfilmsareshowntoincrease
withthicknessinFigure5a,b.ThePharr–Olivermethodiswidelyusedtodeterminethe
hardnessofanano‐indentationbasedontheloadingandunloadingcurve,whichexposes
thecombinedhardnessoftheglasssubstrateandtheCoFeYbthinfilm[31].Because
CoFeYbthinfilmissothin,itisreasonabletoexpectasubstrateeffectinthenano‐inden‐
tationmeasurement.AccordingtoFigure5,thehardnessandYoung’smodulusoftheas‐
depositedCoFeYbthinfilmsincreasedfrom8.35GPato8.94GPaand89.3GPato100
GPa,respectively.ThehardnessandYoung’smodulusoftheannealed100°CCoFeYb
thinfilmsincreasedfrom8.52GPato8.84Gpaand90.2Gpato98.2Gpa,respectively.The
hardnessandYoung’smodulusoftheannealed200°CCoFeYbthinfilmsincreasedfrom
8.68Gpato9.08Gpaand94.1Gpato100.1Gpa,respectively.ThehardnessandYoung’s
modulusoftheannealed300°CCoFeYbthinfilmsincreasedfrom8.63GPato9.29GPa
and94.8GPato104.2GPa,respectively.Thefindingsoftheexperimentshowthatalt‐
houghtemperaturehaslittleimpactonhardnessandYoung’smodulus,thicknesshasa
majorimpact.Asthicknessincreased,bothhardnessandYoung’smodulussignificantly
increased[32,33].
Coatings2022,12,17537of11
(a)(b)
Figure5.Nano‐indentationofCoFeYbthinfilms.(a)Hardnessand(b)Young’smodulus.
3.5.SurfaceEnergyandAdhesionAnalysis
Figure6a–ddepictthecontactangles(θ)ofCo60Fe20Yb20thinfilmsunderfourdiffer‐
entconditionswhileutilizingDIwaterandglycerol.Inparticular,Co60Fe20Yb20thinfilms
werefoundtohavecontactanglesthatwereconsistentlylessthan90degreesanddrops
thatwerealmostspherical,showingthatthefilmsexhibitedgoodhydrophilicityandwet‐
tability.Asaresult,itispossibletoconcludethatthecontactangledecreasesasthean‐
nealedtemperaturerises.Thisismostlyduetotheheattreatmentincreasingthesizeof
thegrainsinthefilm.Highergrainsizeleadstoadecreaseinthesupportforcebetween
thegrains.SurfaceenergyandadhesionareimportantfactorsforCoFeYbfilmsinceitcan
beusedasaseedorbufferlayer.Liquidabsorptionisstrongandthecontactangleismin‐
imalwhenthesurfaceenergyislarge.Surfaceenergyiscalculatedusingthecontactangle
andYoung’sequation[22–24].
(A)(B)
Coatings2022,12,17538of11
(C)(D)
Figure6.Contactanglesoffourconditions:(A)RT,(B)followingannealingat100°C,(C)following
annealingat200°C,and(D)followingannealingat300°C.DIwater:(a)10nm,(b)20nm,(c)30
nm,(d)40nm,and(e)50nm.Glycerol:(f)10nm,(g)20nm,(h)30nm,(i)40nm,and(j)50nm.
Figure7showsthesurfaceenergyofCoFeYbfilmsunderallconditions,including
thethicknessincreasefrom10nmto50nmatRTafterannealingat100°C,200°C,and
300°C.Thesurfaceenergyrangedfrom22.3to31.3mJ/mm2,withpost‐annealedfilms
havingahighersurfaceenergythantheas‐depositedfilms.Inthisexperiment,thesurface
energyofthe50nmfilmafter300°Cannealingwasthehighest.Becauseofthecrystalli‐
zationeffect,theannealingtemperaturerises,increasingsurfaceenergyandadhesion.
Thecapacityofthesurfacetoabsorbliquidincreasedassurfacefreeenergyincreased.The
contactanglewouldalsobereducedasasizeableportionoftheliquidwouldbeabsorbed
[34].Weakadhesionandlowsurfaceenergyareassociatedwiththis[35].Whenthefilms’
surfaceenergieswerehigher,theadhesionwasstrongest.Theseresultsimplythatitis
easiertocombinewiththelayeroftheMTJstructure.
Figure7.SurfaceenergyofCoFeYbthinfilms.
3.6.AnalysisofOpticalProperty
Figure8a–dshowthetransmittance(%)forCoFeYbthinfilmsatvisiblewavelengths
rangingfrom500nmto800nm(d).Figure8aindicatesthatwhenthethicknessincreased
from10to50nmatRT,thetransmittance(%)decreasedfrom48%to14%.Figure8bshows
thatfollowing100°Cannealing,thetransmittance(%)decreasedfrom54%to14%asthe
thicknesschangedfrom10to50nm.Figure8cindicatesthatasthethicknessincreased
Coatings2022,12,17539of11
from10to50nm,thetransmittance(%)decreasedfrom52%to11%followingannealing
at200°C.Figure8ddemonstratesthatfollowingannealingat300°C,thetransmittance
(%)decreasedfrom54%to14%asthicknessvariedfrom10to50nm.Thefindingsdemon‐
stratethatthethicknessandinterfaceeffectsattenuatethephotonsignal,decreasingtrans‐
mittanceandhavinganimpactontheoverallfilmoptictransmittanceproperties[36,37].
(a)(b)
(c)(d)
Figure8.TransmittanceofCoFeYbthinfilms.(a)RT,(b)followingannealingat100°C,(c)following
annealingat200°C,and(d)followingannealingat300°C.
4.Conclusions
Thisstudyfocusedonthestructure,magneticproperties,electricalproperties,nano‐
mechanicalcharacteristics,adhesionefficiency,andopticalpropertiesofCo60Fe20Yb20thin
films.XRDanalysisrevealedthattheCo60Fe20Yb20filmsdepositedatRT,100°C,and200
°Cwereamorphous.However,40nmand50nmCoFeYbthinfilmsat300°Cexhibited
thecharacteristicpeakCoFe(110)at44.7°,whichincreasedwiththethickness.Themag‐
neticcharacteristicsexhibitedathicknesseffect:asthethicknessincreased,theinduced
saturationmagnetizationofχacincreased.Theelectricalpropertiesrevealedthatasthick‐
nessandannealedtemperaturesincreased,resistivityandsheetresistance(Rs)decreased.
Thenano‐mechanicalcharacteristicsroseinhardnessandYoung’smodulusasthethick‐
nessoftheCoFeYbfilmincreased,andtherewasasubstrateeffectinthenano‐indentation
test.ThesurfaceenergyoftheannealedCoFeYbthinfilmswasgreaterthanthatoftheas‐
depositedfilm.Intermsofopticalqualities,asthicknessincreased,transmittancefell,
whilethethicknesseffectandtheinterfaceeffectsuppressedthephotonsignal,causing
Coatings2022,12,175310of11
thetransmittancetodecrease.Asaresultofthisresearch,thefilmisappropriateforusage
asafreelayerofMTJandcanbeusedinMRAMandrecordingheads.
AuthorContributions:Conceptualization,W.‐J.L.,Y.‐H.C.,andY.‐T.C.;methodology,Y.‐T.C.,P.‐
C.C.,andY.‐Z.W.;validation,Y.‐T.C.;formalanalysis,Y.‐T.C.andP.‐W.C.;investigation,Y.‐T.C.
andW.‐J.L.;resources,Y.‐T.C.;writing—originaldraft,Y.‐T.C.andW.‐J.L.;writing—reviewand
editing,Y.‐T.C.;supervision,Y.‐T.C.andY.‐H.C.;projectadministration,Y.‐T.C.;fundingacquisi‐
tion,W.‐J.L.,Y.‐H.C.,andS.‐H.L.Allauthorshavereadandagreedtothepublishedversionofthe
manuscript.
Funding:ThisworkwassupportedbytheMinistryofScienceandTechnology(GrantNos.
MOST108‐2221‐E‐224‐015‐MY3andMOST105‐2112‐M‐224‐001),andtheNationalYunlinUniversity
ofScienceandTechnology(GrantNo.112T01).
InstitutionalReviewBoardStatement:Notapplicable.
InformedConsentStatement:Notapplicable.
DataAvailabilityStatement:Notapplicable.
Acknowledgments:ThisworkwassupportedbytheMinistryofScienceandTechnology,under
GrantNo.MOST108‐2221‐E‐224‐015‐MY3,MOST105‐2112‐M‐224‐001,andNationalYunlinUniver‐
sityofScienceandTechnology,underGrantNo.112T01.
ConflictsofInterest:Theauthorsdeclarethatthereisnoconflictofinterestsregardingthepublica‐
tionofthispaper.
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Annealing Effect on the Contact Angle, Surface Energy, Electric Property, and Nanomechanical Characteristics of Co40Fe40W20 Thin Films
Article
Full-text available
  • Oct 2021
This study investigated Co40Fe40W20 single-layer thin films according to their corresponding structure, grain size, contact angle, and surface energy characteristics. Co40Fe40W20 alloy thin films of different thicknesses, ranging from 10 to 50 nm, were sputtered on Si(100) substrates by DC magnetron sputtering. The thin films were annealed under three conditions: as-deposited, 250 °C, and 350 °C temperatures, respectively. The Scherrer equation was applied to calculate the grain size of Co40Fe40W20 thin films. The results show that the grain size of CoFe(110) increased simultaneously with the increase of post-annealing temperature, suggesting that the crystallinity of Co40Fe40W20 thin films increased with the post-annealing temperature. Moreover, the contact angles of all Co40Fe40W20 thin films were all less than 90°, suggesting that Co40Fe40W20 thin films show changes in the direction of higher hydrophilicity. However, we found that their contact angles decreased as the grain size of CoFe increased. Finally, the Young equation was applied to calculate the surface energy of Co40Fe40W20 thin films. After post-annealing, the surface energy of Co40Fe40W20 thin films increased with the rising post-annealing temperature. This is the highest value of surface energy observed for 350 °C. In addition, the surface energy increased as the contact angle of Co40Fe40W20 thin films decreased. The high surface energy means stronger adhesion, allowing the formation of multilayer thin films with magnetic tunneling junctions (MTJs). The sheet resistance of the as-deposited and thinner CoFeW films is larger than annealed and thicker CoFeW films. When the thickness is from 10 nm to 50 nm, the hardness and Young’s modulus of the CoFeW film also show a saturation trend.
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New resorbable Ca-Mg-Zn-Yb-B-Au alloys: Structural and corrosion resistance characterization
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  • Dec 2021
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New resorbable Ca32Mg12Zn38Yb18-2xBxAux (x=1,2) alloys were designed and prepared in order to verify their use for medical applications as potential short-term implants. Their amorphous structure containing some crystalline phases (CaZn, CaZn2 and MgZn) was determined by X-ray and neutron diffraction and electron microscopy methods. The biocorrosion behavior of the plates was tested by hydrogen evolution measurements, electrochemical polarization tests, and electrochemical impedance spectroscopy in Ringer's solution at 37 °C. The corrosion analysis was also supplemented by X-ray diffraction, photoelectron, and ICP-AES spectroscopy. The corrosion resistivity measurements revealed that the alloys manifest enhanced corrosion resistance. The corrosion current density for Ca32Mg12Zn38Yb18-2xBxAux (x=1, 2) alloys were 18.46 and 8.79 μA/cm², which is lower than for pure Mg (47.85 μA/cm²) and Zn (33.96 μA/cm²). A decreasing tendency for hydrogen to evolve as a function of time was noted. The hydrogen evolution did not exceed 1 ml/cm² over 1 h and average corrosion rate is calculated as 0.32 g/m2 . h for Ca32Mg12Zn38Yb14B2Au2 alloy after 312 h. The corrosion mechanism of the alloys includes an anodic dissolution, a hydroxide precipitation, corrosion product layer formation and corrosion propagation stage.
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Yttrium addition and Annealing Effect on the Structural, Magnetic, Adhesive, and Optical properties of CoFeY Thin Films on Glass Substrate
Article
  • Nov 2021
  • OPTIK
Co60Fe20Y20 film was sputtered on glass substrate with a 10 nm to 50 nm under four annealed conditions and the structure, magnetic properties, surface energy, and optical property were examined. An amorphous structure of CoFeY films was revealed by an X-ray diffraction analyzer, suggesting that the addition of yttrium (Y) refined the grain size and the annealing temperatures were insufficient to support grain growth. The saturation magnetization (Ms) and low-frequency alternate-current magnetic susceptibility (χac) increased with the increase in the thicknesses and annealing temperatures, suggesting that the thickness effect and Y can refine grain size and induce ferromagnetic spin exchange coupling. The highest Ms and χac of Co60Fe20Y20 film were 735 emu/cm³ and 0.23 at an annealing temperature of 300°C and 50 nm. The χac value of CoFeY film decreased significantly with the increase in measured frequency, while the maximum χac value increased significantly after heat treatment. The optimal resonance frequency (fres) corresponding to the maximum χac was 50 Hz, indicating the applicability of the film in a low-frequency range. The highest surface energy of the 50 nm was 31.84 mJ/mm² at 300 °C, while the highest transmittance 58% was observed in as-deposited 10 nm film. The transmittance decreased with the increase in annealing temperatures and thickness. A higher thickness may inhibit photon signal transfer through the film, causing a low transmittance. Moreover, the specific properties of Co60Fe20Y20 films are compared with Co40Fe40B10Y10 films, which indicate that Co60Fe20Y20 films have high maximum χac, surface energy, and transmittance than Co40Fe40B10Y10 films.
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Electronic and optical properties of Yb/Al/P co-doped silica optical fiber
Article
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The corresponding relationship between energy levels and absorption spectra of Yb³⁺ ion in Yb/Al/P co-doped silica fiber is obtained by first-principle methods. Based on the calculation result that the ortho-position (OP) substitution model has the lowest average formation energy, Yb-OP substitution model with six coordination of Yb³⁺ is constructed, which is a possible local microstructure in Yb/Al/P co-doped silica fiber. Due to the spin-orbital coupling effect, two occupied impurity levels are introduced into the band gap located at 2.72 eV and 4.06 eV, representing ²F5/2 and ²F7/2 manifolds respectively. The absorption peaks of 971 nm, 922 nm and 881 nm are fitted by Gaussian decomposition, corresponding to the transition ²F7/2-1 - ²F5/2-5, ²F7/2-1 - ²F5/2-6 and ²F7/2-1 -²F5/2-7. We construct the local environment model of Yb³⁺ ion and provide the relationship between energy levels and optical absorption of Yb³⁺ ion from the perspective of theoretical calculation, which is helpful to understand the Yb/Al/P co-doped silica fiber theoretically.
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Ductile behavior and excellent corrosion resistance of Mg-Zn-Yb-Ag Metallic Glasses
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  • Aug 2021
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Magnesium-based metal glasses (MMGs) have broad application potential as bio-implant materials because of their disordered atomic structure, fine degradability, low elasticity modulus, and high strength. However, their low plasticity and poor corrosion resistance limit their application. In the present study, Mg-Zn-Yb-Ag metallic glasses were fabricated by injecting into a copper roller. The addition of trace amounts of ytterbium (Yb) and precious metal silver significantly improved the ductility of MMGs under bending and tensile loading. The results show that the amorphous alloy with 4 at% of Yb exhibits optimum specific strength mainly because of high-density coarsening shear bands. Electrochemical experiments, immersion test, and analysis of corrosion products by XPS and EDS after immersion showed that the amorphous alloy with 4 at% of Yb exhibits the greatest corrosion resistance among the four samples because of rare earth (Yb) oxide film. The addition of the appropriate amount of the rare-earth element Yb to amorphous Mg-based alloys can not only remarkably influence the alloy plasticity but also improve the alloy corrosion resistance, thereby increasing the alloy application prospects.
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Thermodynamic properties of the Yb-Sb system predicted from first-principles calculations
Article
  • Jul 2021
  • ACTA MATER
In the present work, thermodynamic properties of the Yb-Sb system have been studied by first-principles based quasiharmonic phonon approach, reporting the temperature-dependent isobaric heat capacity, entropy, formation enthalpy, isothermal bulk modulus, and thermal expansion. The effects by using different exchange-correlation functionals and the pseudopotentials on thermodynamic properties are examined. The results reveal that the combined Perdew-Burker-Ernzerhof functional revised for solids (PBEsol) together with the pseudopotential with all f-electrons frozen in the core is the best choice. This combination leads to an overall good description of the relative phase stabilities and thermodynamic properties, except for the rocksalt YbSb compound which is calculated to have an energy of ∼25 kJ/mol-atom above the convex hull. The discrepancy is due probably to the change of the Yb valence states between the rocksalt YbSb structure and the other Yb-Sb compounds. Furthermore, the present calculations show that the Yb16Sb11 compound is stable. The analysis of stretching force constants demonstrates that the extremely strong Yb-Sb bonding is responsible for the stabilities of Yb11Sb10, Yb16Sb11, h-Yb5Sb3, and Yb4Sb3 at high temperatures.
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Texture development and tensile properties of Mg–Yb binary alloys during hot extrusion and subsequent annealing
Article
  • Jun 2021
Ytterbium (Yb) containing magnesium alloys have aroused extensive interest due to their excellent mechanical properties after thermomechanical processing and heat treatment. Unfortunately, the sole effect of Yb addition on the microstructure and mechanical properties of pure Mg matrix remains uncertain to date. In this work, the effects of Yb concentration on the texture development and tensile properties of pure Mg matrix during hot extrusion and the subsequent annealing were systematically investigated. The results revealed that the constitutional supercooling induced by Yb addition refined the as-cast microstructure but exerted a negligible effect on the original columnar grain morphology. When extruded at 300 °C, the dynamic recrystallization (DRX) process was considerably retarded. The in-grain misorientation axes (IGMA) analysis combined with TEM observation indicated that non-basal slips operated with increasing Yb concentration. Specifically, the prismatic 〈a〉 slip should be robustly activated in Mg–1.0 Yb extrudate, promoting the formation of the texture with {10–10} plane normal to the extrusion direction (ED), while for the Mg–2.0 Yb counterpart, the increased activity of pyramidal 〈c + a〉 slip and the relaxation of basal/<c + a> dislocations generated an ED-tilted texture component. The preferential grain growth dominated the subsequent annealing texture development at 400 °C when a comparable grain size was achieved. An obvious ED-tilted texture intensity with the peak around 〈–12–13〉 was observed in Mg–2.0 Yb alloy, which was primarily caused by grains with the basal orientation vanished and with the non-basal orientations intensified due to a higher concentration of Yb solute. Favored by the grain refinement, the Mg–2.0 Yb extrudate exhibited a high tensile yield strength of 304 ± 3.5 MPa, while the subsequently annealed counterpart presented a favorable elongation to failure of 14.8 ± 1.2%, which mainly due to the homogeneous grain structure, weak ED-tilted texture, and dissolution of coarse phases after high-temperature annealing.
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Rare-Earth-Free Magnets: Enhancing Magnetic Anisotropy and Spin Exchange Toward High- T C Hf 2 M Ir 5 B 2 ( M = Mn, Fe)
Article
  • Mar 2021
Designing new rare-earth-free (REF) permanent magnetic materials (PMM) to replace the high performing but critically restrained rare-earth-based PMM remains a great challenge to the scientific community. Here, we report on the rational design of new REF PMM, Hf2MIr5B2 (M = Fe, Mn) via a theory-experiment combined approach. Density functional theory (DFT) predicted strong interchain M-M spin-exchange coupling and large magnetocrystalline anisotropy energies (EMAE) for the new compounds, suggesting potential intrinsic PMM properties. Subsequent experimental bulk syntheses and magnetic characterizations established the highest ordering temperature (TC ∼ 900 K) for Hf2FeIr5B2 and the highest intrinsic coercivity (HC) value for Hf2MnIr5B2 (HC = 62.1 kA/m) reported to date for Ti3Co5B2-type compounds. Importantly, at room temperature both phases show significant coercivities due to intrinsic factors only, hinting at their huge potential to create REF PMM by improving extrinsic factors such as controlling the microstructure and the domain orientation.
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Transparent Films Made of Highly Scattering Particles
Article
  • Jan 2020
Today colloids are widely employed in various products from creams and coatings to electronics. The ability to control their chemical, optical, or electronic features by controlling their size and shape explains why these materials are so widely preferred. Nevertheless, altering some of these properties may also lead to some undesired side effects, one of which is an increase in optical scattering upon concentration. Here, we address this strong scattering issue in films made of binary colloidal suspensions. In particular, we focus on raspberry type polymeric particles made of a spherical polystyrene core decorated by small hemispherical domains of acrylate with an overall positive charge, which display an unusual stability against aggregation in aqueous solutions. Their solid films display a brilliant red colour due to Bragg scattering but appear completely white on account of strong scattering otherwise. To suppress the scattering and induce transparency, we prepared films by hybridizing them either with oppositely-charged PS particles with a size similar to that of the bumps on the raspberries. We report that the smaller PS-particles prevent raspberry-particle aggregation in solid films and suppress scattering by decreasing the spatial variation of the refractive index inside the film. We believe that the results presented here provide a simple strategy to suppress strong scattering of larger particles to be used in optical coatings.
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