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Surface Modification of Etched Ion-Track Polymer Membranes by Atomic Layer Deposition

Spende, Anne (2016)
Surface Modification of Etched Ion-Track Polymer Membranes by Atomic Layer Deposition.
Technische Universität Darmstadt
Ph.D. Thesis, Primary publication

Abstract

Inorganic nanochannels integrated in solid state membranes as well as nanotubes are of high relevance for fundamental research and industrial applications in catalysis, filtration, sensorics, solar energy harvesting, biomedicine, and nanofluidics. Currently, lots of effects are being devoted to develop reproducible and efficient fabrication techniques that enable the precise tailoring of geometry, dimensions, and properties of the nanochannels. This thesis presents the combination of ion-track technology with low-temperature atomic layer deposition (ALD). Cylindrical and conical nanotubes as well as highly-ordered nanotube networks exhibiting aspect ratios above 3000 were synthesized. 30-μm thick polycarbonate membranes were irradiated with ∼GeV swift heavy ions at the UNILAC accelerator of GSI under normal or tilted beam incidence. By subsequent wet-chemical etching, each individual ion track was dissolved and thus converted into an open nanochannel. The length of the nanochannel was determined by the thickness of the polymer, whereas geometry and diameter (≥ 18 nm) were controlled by the etching parameters. To reduce the channel diameter further and modify the surface of the channel walls without affecting the channel shape, titania (TiO2), silicon dioxide (SiO2), and alumina (Al2O3) were deposited onto the templates by ALD. This sequential and self-limiting surface modification technique provided the precise control of the deposited thickness due to layer-by-layer growth. From small angle X-ray scattering (SAXS) analysis average channel diameter, diameter distribution before and after ALD as well as coating thickness were deduced. The results demonstrated homogeneous and conformal deposition along the entire cylindrical nanochannels down to inner diameters below 10 nm. For these samples, X-ray photoelectron spectroscopy (XPS) evidenced almost stoichiometric composition of the ALD layers deposited onto the membrane surface. For all investigated nanostructures, the dissolution of the supporting polymer template by wet-chemical methods and the following visualization of the resulting structures by electron microscope (SEM) in scanning and transmission mode revealed exactly defined geometries, diameters, and wall thicknesses. The preparation of arrays of free-standing conical nanotubes from multichannel membranes and the novel alike preparation of free-standing single tubular nanocones from single channel membranes enabled the comparison between the asymmetric etching process in single and multichannel membranes that resulted in the agreement of the radial base etching rates whereas the tip etching was by a factor of ∼ 2 faster for single channels. In addition, the base diameter was determined at the replica of the single channel itself, which enabled precise computation of the tip diameter. The homogeneity of the ALD processes inside the nanochannels was confirmed by energy dispersive X-ray spectroscopy (EDX) of the released nanotubes. In addition, ionic conductance (I-V) studies of cylindrical and conical single nanochannels before and after ALD demonstrated conformal deposition processes inside the single channels in polycarbonate. Surface charges induced by variation of the pH value of the electrolyte influenced the recorded ionic currents in agreement with the theory of nanofludics for channel diameters up to 100 nm. Furthermore, the gating of single conical nanochannels in polycarbonate membranes surface modified with a 5 nm thick TiO2 film was enabled by a straight-forward set-up comparable to n-type JFETs.

Item Type: Ph.D. Thesis
Erschienen: 2016
Creators: Spende, Anne
Type of entry: Primary publication
Title: Surface Modification of Etched Ion-Track Polymer Membranes by Atomic Layer Deposition
Language: English
Referees: Trautmann, Prof. Dr. Christina ; Ensinger, Prof. Dr. Wolfgang
Date: 17 May 2016
Place of Publication: Darmstadt
Refereed: 6 July 2016
URL / URN: http://tuprints.ulb.tu-darmstadt.de/5613
Abstract:

Inorganic nanochannels integrated in solid state membranes as well as nanotubes are of high relevance for fundamental research and industrial applications in catalysis, filtration, sensorics, solar energy harvesting, biomedicine, and nanofluidics. Currently, lots of effects are being devoted to develop reproducible and efficient fabrication techniques that enable the precise tailoring of geometry, dimensions, and properties of the nanochannels. This thesis presents the combination of ion-track technology with low-temperature atomic layer deposition (ALD). Cylindrical and conical nanotubes as well as highly-ordered nanotube networks exhibiting aspect ratios above 3000 were synthesized. 30-μm thick polycarbonate membranes were irradiated with ∼GeV swift heavy ions at the UNILAC accelerator of GSI under normal or tilted beam incidence. By subsequent wet-chemical etching, each individual ion track was dissolved and thus converted into an open nanochannel. The length of the nanochannel was determined by the thickness of the polymer, whereas geometry and diameter (≥ 18 nm) were controlled by the etching parameters. To reduce the channel diameter further and modify the surface of the channel walls without affecting the channel shape, titania (TiO2), silicon dioxide (SiO2), and alumina (Al2O3) were deposited onto the templates by ALD. This sequential and self-limiting surface modification technique provided the precise control of the deposited thickness due to layer-by-layer growth. From small angle X-ray scattering (SAXS) analysis average channel diameter, diameter distribution before and after ALD as well as coating thickness were deduced. The results demonstrated homogeneous and conformal deposition along the entire cylindrical nanochannels down to inner diameters below 10 nm. For these samples, X-ray photoelectron spectroscopy (XPS) evidenced almost stoichiometric composition of the ALD layers deposited onto the membrane surface. For all investigated nanostructures, the dissolution of the supporting polymer template by wet-chemical methods and the following visualization of the resulting structures by electron microscope (SEM) in scanning and transmission mode revealed exactly defined geometries, diameters, and wall thicknesses. The preparation of arrays of free-standing conical nanotubes from multichannel membranes and the novel alike preparation of free-standing single tubular nanocones from single channel membranes enabled the comparison between the asymmetric etching process in single and multichannel membranes that resulted in the agreement of the radial base etching rates whereas the tip etching was by a factor of ∼ 2 faster for single channels. In addition, the base diameter was determined at the replica of the single channel itself, which enabled precise computation of the tip diameter. The homogeneity of the ALD processes inside the nanochannels was confirmed by energy dispersive X-ray spectroscopy (EDX) of the released nanotubes. In addition, ionic conductance (I-V) studies of cylindrical and conical single nanochannels before and after ALD demonstrated conformal deposition processes inside the single channels in polycarbonate. Surface charges induced by variation of the pH value of the electrolyte influenced the recorded ionic currents in agreement with the theory of nanofludics for channel diameters up to 100 nm. Furthermore, the gating of single conical nanochannels in polycarbonate membranes surface modified with a 5 nm thick TiO2 film was enabled by a straight-forward set-up comparable to n-type JFETs.

Alternative Abstract:
Alternative abstract Language

Anorganische Nanokanäle integriert in Festkörpermembranen und Nanoröhren sind von großer Bedeutung für Grundlagenforschung und industrielle Anwendungen in den Bereichen Katalyse, Filtration, Sensorik, Solarenergiegewinnung, Biomedizin und Nanofluidik. Zur Zeit werden viele Prozesse untersucht, um eine reproduzierbare und effiziente Herstellung zu gewährleisten, die zudem die genaue Einstellung der Geometrie, der Dimensionen und der Eigenschaften der Nanokanäle ermöglicht. Diese Dissertation präsentiert die Kombination der Ionenspurtechnologie mit der Tieftemperatur-Atomlagenabscheidung (engl. atomic layer deposition, ALD). Zylindrische und konische Nanoröhren sowie geordnete Nanoröhren-Netzwerke mit Aspektverhältnissen über 3000 wurden hergestellt. 30-μm dicke Polycarbonatfolien wurden mit schweren Ionen, die kinetische Energien im Bereich ∼GeV aufwiesen, am UNILAC Beschleuniger der GSI unter senkrechtem und gekipptem Einfallswinkel bestrahlt. Durch nachfolgendes nasschemisches Ätzen wurde jede einzelne Ionenspur aufgelöst und in einen offenen Nanokanal transformiert. Die Länge des Nanokanals war durch die Dicke des Polymers bestimmt, wohingegen die Geometrie und der Durchmesser (≥ 18 nm) durch die Ätzparameter kontrolliert wurden. Um den Kanaldurchmesser weiter zu reduzieren und die Oberfläche der Kanalwände zu modifizieren ohne die Form des Kanals zu verändern, wurden Titandioxid (TiO2), Siliziumdioxid (SiO2) und Aluminiumoxid (Al2O3) mittels ALD auf die Template abgeschieden. Diese sequentielle und selbst-limitierende Oberflächenmodifikationstechnik ermöglichte die präzise Kontrolle der abgeschiedenen Schichtdicke durch Schicht-für-Schicht Wachstum. Aus Kleinwinkelröntgenstreuungsanalysen (engl. small angle X-ray scattering, SAXS) wurden der durchschnittliche Kanaldurchmesser, die Durchmesserverteilung vor und nach der ALD-Beschichtung sowie die Dicke der Beschichtung abgeleitet. Die Ergebnisse zeigten homogene und konformale Beschichtung entlang der gesamten Kanallänge für innere Durchmesser unter 10 nm. Für diese Proben wurde mittels Röntgenphotoelektronenspektroskopie (engl. X-ray photoelectron spectroscopy, XPS) eine fast stöchiometrische Zusammensetzung der ALD-Beschichtung an der Membranoberfläche nachgewiesen. In allen Fällen führte die Auflösung des Polymertemplats mittels nasschemischer Methoden zu selbsttragenden Nanostrukturen. Visualisierung dieser mittels Rasterelektronenmikroskopie (engl. scanning electron microscopy, SEM) zeigte exakt definierte Geometrien, Durchmesser und Wandstärken der Nanoröhren. Die Präparierung von Arrays freistehender konischer Nanoröhren aus Vielkanalmembranen und dieselbe neuartige Präparation freistehender einzelner röhrenförmiger Nanokegel aus Einzelkanalmembranen erlaubte den Vergleich des asymmetrischen Ätzprozesses in Einzel- und Vielkanalmembranen. Die radialen Ätzraten für die Basis der Kegel stimmten überein, während das radiale Ätzen der Kegelspitzen für Einzelkanäle doppelt so schnell war. Zudem wurde der Basisdurchmesser an der Replik des Einzelkanals gemessen, was die genaue Berechnung des Spitzendurchmessers ermöglichte. Die Homogenität der ALD-Prozesse in den Kanälen wurde durch energiedispersive Röntgenspektroskopie (engl. energy dispersive X-ray spectroscopy, EDX) nachgewiesen. Ionische Leitfähigkeitsuntersuchungen (I-V) zylindrischer und konischer Einzelkanäle vor und nach ALD-Beschichtungen bewiesen die konformale Beschichtung von Einzelkanälen in Polycarbonatmembranen. Durch Variation des pH Wertes des Elektrolyten induzierte Oberflächenladungen beeinflussten die gemessenen ionischen Ströme für Kanaldurchmesser bis zu 100 nm in Übereinstimmung mit der Nanofluidiktheorie. Desweiteren wurden mit einem unkomplizierten Aufbau vergleichbar mit einem n-Kanal JFET konische Einzelkanäle in Polycarbonatmembranen gesperrt, welche mit 5 nm TiO2 oberflächenmodifiziert waren.

German
Uncontrolled Keywords: Nanoconfinement, Nanotube, Nanocone, Nanotube Network, Atomic Layer Deposition, Ion-Track Technology, Polycarbonate, Ionic Conductance, Nanofluidic Transistor, TiO2, SiO2, Al2O3
Alternative keywords:
Alternative keywordsLanguage
Nanoconfinement, Nanoröhre, Nanokegel, Nanoröhren-Netzwerk, Atomlagenabscheidung, Ionenspurtechnologie, Polycarbonat, Ionische Leitfähigkeit, Nanofluidischer Transistor, TiO2, SiO2, Al2O3German
URN: urn:nbn:de:tuda-tuprints-56135
Classification DDC: 500 Science and mathematics > 500 Science
500 Science and mathematics > 530 Physics
500 Science and mathematics > 540 Chemistry
600 Technology, medicine, applied sciences > 660 Chemical engineering
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Ion-Beam-Modified Materials
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 14 Aug 2016 19:55
Last Modified: 14 Aug 2016 19:55
PPN:
Referees: Trautmann, Prof. Dr. Christina ; Ensinger, Prof. Dr. Wolfgang
Refereed / Verteidigung / mdl. Prüfung: 6 July 2016
Alternative keywords:
Alternative keywordsLanguage
Nanoconfinement, Nanoröhre, Nanokegel, Nanoröhren-Netzwerk, Atomlagenabscheidung, Ionenspurtechnologie, Polycarbonat, Ionische Leitfähigkeit, Nanofluidischer Transistor, TiO2, SiO2, Al2O3German
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