Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: This study developed and optimised zinc oxide (ZnO) nanowire-based nanogenerator.
The nanogenerator works on the piezoelectric effect that is, a mechanical
force is converted to an electrical voltage. The ZnO nanowires are piezoelectric
and when any force is applied to the nanowires an output voltage is generated.
This ZnO nanowire-based nanogenerator can be used to power small electronic
devices, such as pacemakers. The nanogenerator can also be incorporated into
clothes and shoes to generate electricity to charge a cell phone for example. The
problem experienced currently is that the nanogenerator does not generate enough
electricity to be of practical use and needs to be further optimised. Simulations and
mathematical models were used to identify areas where the nanogenerator could
be optimised in order to increase the output voltage. It is shown that the morphology
of the nanowires can have a considerable effect on the output voltage. For this
reason the growth of the nanowires was investigated first. Different methods were
used to propagate the nanowires in order to select the method that, on average,
has the highest output voltage. Accordingly, one parameter at a time and design of
experiments were used to optimise the nanowire growth. Consequently, these two
methods were used to optimise the growth parameters with the respect to the output
voltage. The aqueous solution method was found to yield nanowires that give
the highest generated output voltage. After growing over 600 nanowire samples,
optimal growth parameters for this method were found. These optimal growth parameters
were subsequently used to grow nanowires that were used to manufacture
the nanogenerator. The nanowires were grown on a solid substrate and hence
the nanogenerator was also manufactured on the solid substrate. Through various
optimisations of the manufacturing process the maximum output voltage achieved
was about 500 mV. However, this output voltage is too low to be of practical use,
even though the output has been raised considerably. The main problem was found
to be the fact that the contact between the nanowires and the electrode was weak
due to contamination. A new method was therefore required where the electrode
and the nanowires would be in proper contact to ensure that higher output voltages
were achieved. Subsequently, a flexible nanogenerator was manufactured in order to solve this problem. Accordingly, the nanowires were grown on the flexible
polyimide film and a buffer layer was then spun onto the flexible substrate, leaving
only the nanowire tips exposed. The electrode was then sputtered on top of this
buffer layer, covering the nanowire tips. This ensured proper contact between the
nanowires and the electrode. The nanogenerator, which was manufactured with
non-optimal growth parameters, gives a maximum voltage output of 1 V, double
the maximum achieved with the solid nanogenerator. When the optimal growth
parameters were used the output voltage was raised to 2 V. Various optimisation
techniques were performed on the nanogenerator, including plasma treatment and
annealing and the use of various materials in the buffer layer. Combining these
optimisation methods subsequently led to an optimised nanogenerator that can
generate an output voltage of over 5 V. This was achieved after over 1200 nanogenerators
had been manufactured. However, the output voltage was not in a usable
form. Circuitry was therefore developed to transform the voltage generated by the
nanogenerator to a useable form. The best circuit, the LTC3588, was used to power
an LED for 10 seconds. The completed device was found to achieve a power output
of 0.3 mW, enough for small electronic devices. / AFRIKAANSE OPSOMMING: ‘n Sink-oksied (ZnO) nanodraad gebaseerde nanogenerator is ontwikkeld en geöptimeer.
Die nanogenerator werk met behulp van die piezoelektriese effek - meganiese
krag work omgesit in ‘n elektriese spanning. Die ZnO nanodrade is piezoelektries
en wanneer ‘n krag op die drade aangewend word, word ‘n uittree spanning
gegenereer. Die nanogenerator kan gebruik word om klein elektroniese toestelle,
soos ‘n pasaangeër, van krag te voorsien. Die nanogenerator kan in klere en skoene
geïnkorporeer word om elektrisiteit op te wek vir die laai van ‘n selfoon. Die probleem
is egter dat die nanogenerator tans nie genoeg krag opwek om prakties van
nut te wees nie en verdere optimasie word benodig. Simulasies en wikundige modelle
work gebruik om areas te identifiseer waar die nanogenerator geöptimeer kan
word, met die doel om die uittreespanning te verhoog. Dit word bewys dat die
morfologie van die nanodrade ‘n groot effek het op die uittreespanning. Dus word
die groei van die nanodrade eerste ondersoek. Verskillende metodes word gebruik
om die nanodrade te groei en die beste metode, wat die hoogste uittreespanning op
gemiddeld verskaf, word gekies. Een parameter op ‘n slag en ontwerp van eksperimente
word gebruik om die nanodraad groei te optimeer. Die groei parameters
word geöptimeer deur van die twee metodes gebruik te maak, en die optimeering
word gedoen in terme van die uittreespanning. Die oplossing groei metode lei tot
nanodrade wat die hoogste uittreespanning verskaf. Na oor die 600 nanodraad
monsters gegroei is, is die optimale parameters gevind. Hierdie optimale parameters
word uitsluitlik gebruik om die nanogenerator te vervaardig. Die nanodrade
word op ‘n soliede substraat gegroei en dus word die nanogenerator op dieselfde
soliede substraat vervaardig. Verskeie metodes is gebruik om die vervaardiging te
optimeer en die hoogste uittreespanning wat bereik is, is 500 mV. Die uittreespanning
is te laag om van praktiese nut te wees alhoewel dit heelwat verhoog is. Die
grootste probleem is die swak kontak tussen die nanodrade en die elektrode, wat
veroorsaak word deur kontaminasie. ‘n Nuwe metode word verlang wat beter
kontak tussen die nanodrade en elektrode sal verseker. ‘n Buigbare nanogenerator
is vervaardig om die probleem op te los. Die nanodrade word nou op ‘n buigbare
film gegroei. ‘n Bufferlaag word tussen die nanodrade in gedraai, tot net die punte van die nanodrade nog sigbaar is. Die elektrode word bo-op die bufferlaag
gedeponeer, wat behoorlike kontak tussen die nanodrade en elektrode verseker.
Die nanogenerator wat met nie-optimale groei parameters vervaardig is, bereik ‘n
uittreespanning van 1 V, dubbel die soliede nanogenerator. Met optimale groei parameters
word die uittreespanning tot 2 V verhoog. Verskeie optimasie tegnieke
word op die nanogenerator toegepas. Die metodes sluit in suurstof plasma behandeling,
verhitting en die inkorporasie van verskillende materiale in die bufferlaag.
‘n Kombinasie van die metodes geïnkorporeer in een nanogenerator lei tot ‘n uittreespanning
van 5 V. Die uittreespanning is bereik na oor die 1200 nanogenerators
vervaardig is. The uittreespanning is nog nie in ‘n bruikbare vorm nie. Spesiale
stroombane is ontwikkel wat die nanogenerator spanning omskakel na ‘n bruikbare
vorm. Die beste stroombaan, die LTC3588, kan ‘n LED aanskakel vir 10 sekondes.
The toestel kan ook 0.3mWuittreekrag voorsien, genoeg vir klein elektroniese
toestelle om te werk.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/85781 |
| Date | 12 1900 |
| Creators | Van den Heever, Thomas Stanley |
| Contributors | Perold, W. J., Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xxvi, 230 p. : ill. |
| Rights | Stellenbosch University |
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