Investigations on III-nitrides nanostructures: application to renewable energies and bio-sensing

Media type: E-Book

Title: Investigations on III-nitrides nanostructures: application to renewable energies and bio-sensing

Contributor: Soto Rodriguez, Paul Eduardo David [VerfasserIn]

imprint: [Erscheinungsort nicht ermittelbar]: E.T.S.I. Telecomunicación (UPM), 2016

Language: English

Origination:

University thesis: Dissertation, E.T.S.I. Telecomunicación (UPM), 2016

Footnote:

Description: This thesis, entitled Investigations on III-Nitrides Nanostructures: Application to Renewable Energies and Bio-Sensing", presents the work done at the "Instituto de Sistemas Optoelectrónicos y Microtecnología" (ISOM). The main objective of the presented work is: To investigate the potential of III-nitride (In(Ga)N, in particular) thin films/nanostructures for biosensors and water-splitting. The investigated structures have varying In contents (from medium to high) and varying morphologies, that are: thin compact InGaN films, InGaN nanowall networks, InGaN nanocolumns and InN quantum dots The thesis addresses: The molecular beam epitaxy growth of the mentioned thin films/nanostructures, on either GaN templates or Si(111) substrates, and their detailed morphological, structural, optical and electrochemical characterization. The insight and systematic evaluation of their electrochemical performance, for their final employment in bio-sensing and water-splitting applications. The work is presented as follows: Chapter I: The motivation for the work (including state of the art) and main goals of the thesis are explained. Chapter II: The fundamental properties of the employed material (III-nitrides) and employed nanostructures (nanocolumns and quantum dots (QDs)) are given. Due to their importance for the thesis development, the fundamental properties having a direct impact on the electrochemical activity of the employed material (III-nitrides). Chapter III: Details about experimental techniques used for the thesis realization are presented: epitaxial growth technique (MBE), morphological characterization (SEM and AFM), structural characterization (X-ray diffraction and TEM), optical characterization (PL, CL and SNOM), as well as chemical (GC) characterization. Chapter IV: Application related characterization of the structures, grown on both GaN templates and on Si(111), is addressed. For this, a general overview of electrochemistry for metals and (non degenerated n-type) semiconductors electrodes is provided after which a discussion on the (degenerated n-type semiconductor) high Incontent InGaN electrode is given. The biosensor concept is introduced as are the parameters that characterize its performance. A general introduction to water-splitting is given (both induced by electrolysis or with the aid of a non-degenerated semiconductor (photo)-electrode). Important parameters needed to fully characterize the water-splitting process/device will be highlighted. Chapter V: Specifications concerning the thin film/nanostructures growth. The samples fabricated and studied throughout this thesis, contain the following structures: (a) Grown on GaN templates: (i) high Indium (In) content InGaN single layers (ii) InN QDs on the top of (previously addressed) InGaN single layers (b) Grown on Si(111) substrate: (iii) high In-content InGaN single layers (iv) InGaN nanowall networks (v) InN QDs directly on top of the substrate, and also on the top of (previously addressed) InGaN single layers and nanowall networks (vi) InGaN nanocolumns This chapter provides a systematic analysis, regarding the control of the thin film/nanostructure morphology by the means of III/V flux ratio. As the III/V ratio changes from nearly stoichiometric (~1), to nitrogen rich (<1), and further, to highly nitrogen rich («1) one, the layer morphology evolves from compact to a nanowallnetwork morphology and further to a fully columnar morphology (nanocolumns). This chapter also provides insight into those morphological and structural properties of the grown thin films/nanostructures, which are relevant for the further development of the thesis. Chapter VI (divided in three parts): In the first part it presents results of potentiometric measurements of the structures grown on GaN templates, targeted for biosensing applications. Specifically, the response of the samples containing surface InN QDs on single InGaN layers is compared to their counterpart samples, consisting of bare single In(Ga)N layers. The measurements reveal that the sample containing surface QDs show higher and more stable (in time) responsivity (actually, the response of bare In(Ga)N films is found highly decreasing over time). We consequently show that the employment of surface InN QDs (on the top of thin InGaN layers) leads to a significantly improved performance of glucose and cholesterol biosensors. Nonnernstian behaviour is observed indicating that the InN QDs have a catalytic effect enhancing the redox reaction at the surface. All figures of merits are addressed and thoroughly discussed. In the second part it presents two comparative studies related to water-splitting applications. The first study involves two different structures (i) a thin InGaN single layer grown on GaN template substrate: and (ii) InGaN nanowall network grown on (a nitridated) Si(111). While excellent photocurrent and Hydrogen production efficiency are observed in both cases (with zero bias applied), somewhat better results are obtained for the latter structure. The second study involves two different structures grown on GaN templates: (i) a single InGaN layer and its (ii) InN QDs on InGaN layer counterpart. In this case, a considerable efficiency increase is observed by the inclusion of InN QDs. The background results for the observed tendencies are thoroughly discussed. The third and last part includes electrochemical analysis of the grown samples by cyclic voltammetry measurements. An extensive analysis of the redox reaction occurring at the interface of all the layers/nanostructures grown on Si(111) and, on the other hand, an analysis determining which parameters (redox potentials, shape, etc) in a typical CV scan are influenced by: (i) In content, (ii) surface area and (iii) presence of surface InN QDs. To conduct experiments, a redox potassium hexacyanoferrate (II) / potassium hexacyanoferrate (III) probe was used. The results show that an optimum balance between catalytic efficiency (which is increased by the addition of surface InN QDs),and (active) surface area (the free c- crystal plane (0001) is identified as the crystal plane inducing surface electrochemical activity), needs to be found, to further boost the efficiency of InN-QDs-on-InGaN-layer based biosensors and water-splitting electrodes. In this sense, the enhancement of catalytic efficiency and increase of electrochemically active surface area (that is, increase of free c-plane surface) are essential. The characterization by AFM, SEM, PL, CL, probe station and HRXRD was performed at ISOM´s facilities whereas the TEM analysis was performed externally at the "Universidad de Cádiz" (Spain) by the group of Prof. Dr. Francisco Miguel Morales Sánchez

Access State: Open Access

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