Development of Capacitive Electrodes Biomedical Engineering

90 Pages·2014·2.52 MB·English

by  Andre C. Marta

Development of Capacitive Electrodes
Ana Teresa Ramalho Cordeiro
Thesis to obtain the Master of Science Degree in
Biomedical Engineering
Supervisors: Professor Jorge Manuel Ferreira Morgado
Professor Maria Isabel de Sousa Rocha
Examination Committee
Chairperson: Professor João Pedro Estrela Rodrigues Conde
Supervisor: Professor Jorge Manuel Ferreira Morgado
Member of the Committee: Professor Francisco André Corrêa Alegria
September 2014
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Acknowledgments
I would like to express my sincere gratitude to my supervisor Professor Jorge Morgado for the useful
comments and remarks, his enormous patience and motivation through the learning process of this
master thesis, as well as to Professor Isabel Rocha. Furthermore, I would like to thank Professor Rau´l
Martinsforhisguidance,enthusiasm,immenseknowledgeaswellforthecontinoussupportontheway.
Also, I would like to thank my lab mates who willingly shared their precious time whenever I needed
somehelp. Iwouldliketothanktomyfamilyandfriendswhohavealwayssupportedme,whetherwhen
makingfunofmystressfulpersonalityorjustbybeingthere.
Thankyou
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Resumo
Opresentetrabalhoabordaaimplementac¸a˜odeumprocessoparaafabricac¸a˜odeele´ctrodoscapaci-
tivos.
O procedimento usa moldes de o´xido de alum´ınio (OA) nanoporosos preenchidos com n´ıquel. Apo´s
a remoc¸a˜o do molde de alumina, os ele´ctrodos de n´ıquel tem a superf´ıcie coberta com nanofios. Por
cima,doismateriaisdiele´ctricos,a´lcoolpolivin´ılicoedio´xidodetitaˆnio,foramdepositadosparaaumentar
aindamaisasuacapacidade.
No desenvolvimento dos moldes de alumina nanoporosa, os estudos iniciais focaram-se no controle
da morfologia. De seguida, os ele´ctrodos nanoestruturados (Ele´ctrodos I) foram caracterizados em
termosdacapacidadeele´ctrica. Omaioraumentodacapacidadefoiparaosele´ctrodosfabricadoscom
um molde de OA poroso obtido atrave´s de dupla anodizac¸a˜o com corrente constante de 70 mA. Este
aumento variou com a frequeˆncia, sugerindo a existeˆncia de um sistema de dispersivo. O aumento foi
de25.29%e32.73%para100Hze1kHz,respectivamente,emrelac¸a˜oaumele´ctrododerefereˆncia
(a1mm).
Um segundo tipo de ele´ctrodos (Ele´ctrodos II) foi desenvolvido por um processo mais simples que
consistenumfilmedeumadispersa˜odenanotubosdecarbononopol´ımerocondutorPEDOT:PSSnum
contactodealum´ınio. Oobjectivoeraverificarseestaabordagemresultavanoaumentodarugosidade
para que a a´rea superficial aumentasse, uma vez que seria mais simples do que o processo anterior
usado para Ele´ctrodos I. A sua capacidade foi medida. Na˜o se verificou um aumento significativo,
sugerindoqueoconteu´dodenanotubosdecarbonoerademasiadobaixo.
Palavras-chave:
Ele´ctrodoscapacitivos,aluminaanodizadaporosa
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Abstract
Thepresentworkaddressestheimplementationofaprocedureforthemanufactureofcapacitiveelec-
trodes.
That procedure used anodized aluminum oxide (AAO) porous templates with an electrochemical nickel
filler. After removal from the alumina template, the nickel electrodes have the surface covered with
nanowires. On the top of this, two dielectric materials, polyvinyl alcohol and titanium dioxide, were
depositedtofurtherincreasetheircapacitance.
Inthedevelopmentoftheanodizedporousaluminatemplates, thestudieswereinitiallyfocusedonthe
morphologycontrol. Afterwards,nanostructuredelectrodes(ElectrodesI)werepreparedandcharacter-
ized in terms of capacitance. The highest increase of the capacitance value was found for electrodes
fabricated with a nanoporous AAO template obtained through double-step anodization at constant cur-
rentof70mA.Thiscapacitanceincreasevariedwiththefrequency,suggestingtheexistenceofadisper-
sivesystem,andtheincreasewasa25.29%and32.73%increasefor100Hzand1kHz,respectively,
withrespecttoareferenceelectrode,attheminimumdistance.
Another type of electrodes (Electrode II) was developed by a simpler process consisting in depositing
a dispersion of carbon nanotubes in a conducting polymer PEDOT:PSS on an aluminum contact. The
objective was to verify if this approach resulted in yielded roughness so that the surface area would
significantly increase, since it would be simpler than the development process used for Electrodes I.
Their electric capacitance was measured. It was not found a significant increase of the capacitance
suggestingthatthecarbonnanotubescontentwastoolow.
Keywords:
Capacitiveelectrodes,anodizedaluminumoxide
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Contents
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
Resumo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
ListofTables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi
ListofFigures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv
Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1 Motivation 1
2 TheoreticalFoundationsandLiteratureReview 5
2.1 AnodicAluminumOxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1 Aluminumanodizationstructures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.2 AAOElectrochemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.3 KineticsofAnodicAluminumOxideFormation . . . . . . . . . . . . . . . . . . . . 12
2.1.4 Double-stepAnodizationofAluminum . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.1.5 Pre-texturedPorousAAOvsSelf-organizedPorousAAOtemplates . . . . . . . . 19
2.2 FillingoftheAAOtemplate-Electrodeposition . . . . . . . . . . . . . . . . . . . . . . . . 20
2.2.1 Nickelelectrodeposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.3 High-kDielectrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3 ExperimentalProcedures: methodsandmaterials 23
3.1 ElectrodesI-ManufactureoftheAAOtemplatesbyaluminumanodization. . . . . . . . . 24
3.1.1 AnnealingProcess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.1.2 DegreasingProcess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.1.3 Electropolishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.1.4 Anodization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.1.5 Pore-wideningandbarrierlayerdestruction . . . . . . . . . . . . . . . . . . . . . . 31
3.2 ElectrodesI-Electrodepositionofnickeltofillthetemplates . . . . . . . . . . . . . . . . . 32
3.3 ElectrodesI-Cleaningandassembling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.3.1 MetalliccontactandPolymericlayer . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.3.2 Cleaningoftheremainingaluminumsubstrateandaluminumoxide . . . . . . . . 35
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3.4 ElectrodesI-Depositionofthedielectric(spincoating). . . . . . . . . . . . . . . . . . . . 36
3.5 AtomicForceMicroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.6 ElectrodesII-Evaporationofthealuminumcontact. . . . . . . . . . . . . . . . . . . . . . 38
3.7 ElectrodesII-DepositionofthePEDOT:PSSandMultiwallCarbonNanotubescomposite
film . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.8 ElectrodesII-Depositionofthedielectric(spincoating) . . . . . . . . . . . . . . . . . . . 40
3.9 ConductanceandCapacitancemeasurements . . . . . . . . . . . . . . . . . . . . . . . . 40
4 ResultsandDiscussion 45
4.1 AnodizationResults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
4.1.1 Nanoporousstructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
4.1.2 PoreDensity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.1.3 Meanporediameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
4.1.4 SurfaceAreaandPoreLength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
4.2 ElectrodepositionResults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.3 ConductanceandCapacitanceResults . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.3.1 Dielectricmaterialinfluence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.3.2 ElectrodesI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4.3.3 ElectrodesII . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
5 Conclusions 67
5.1 Achievements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
5.2 FutureWork. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Bibliography 74
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