Luận án Tiến sĩ: Tương tác Quang và Điện trong các Siêu cấu trúc Nano Kim loại Tự lắp ráp của Päivi Ahonen

TKK Dissertations 120 Espoo 2008 OPTICAL AND ELECTRICAL INTERACTIONS IN SELF-ASSEMBLED METAL NANOPARTICLE SUPERSTRUCTURES Doctoral Dissertation Päivi Ahonen Helsinki University of Technology Faculty of Chemistry and Materials Sciences Department of Chemistry TKK Dissertations 120 Espoo 2008 OPTICAL AND ELECTRICAL INTERACTIONS IN SELF-ASSEMBLED METAL NANOPARTICLE SUPERSTRUCTURES Doctoral Dissertation Päivi Ahonen Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Chemistry and Materials Sciences for public examination and debate in Auditorium KE2 (Komppa Auditorium) at Helsinki University of Technology (Espoo, Finland) on the 23rd of May, 2008, at 12 noon. Helsinki University of Technology Faculty of Chemistry and Materials Sciences Department of Chemistry Teknillinen korkeakoulu Kemian ja materiaalitieteiden tiedekunta Kemian laitos Distribution: Helsinki University of Technology Faculty of Chemistry and Materials Sciences Department of Chemistry P. Box 6100 FI - 02015 TKK FINLAND URL: http://www.fi/Units/PhysicalChemistry/ Tel. +358-9-451 2572 Fax +358-9-451 2580 E-mail: Paivi.fi © 2008 Päivi Ahonen ISBN 978-951-22-9361-2 ISBN 978-951-22-9362-9 (PDF) ISSN 1795-2239 ISSN 1795-4584 (PDF) URL: http://lib.fi/Diss/2008/isbn9789512293629/ TKK-DISS-2467 Multiprint Oy Espoo 2008 AB ABSTRACT OF DOCTORAL DISSERTATION HELSINKI UNIVERSITY OF TECHNOLOGY P.

BOX 1000, FI-02015 TKK http://www.fi Author Päivi Ahonen Name of the dissertation Optical and Electrical Interactions in Self-Assembled Metal Nanoparticle Superstructures Manuscript submitted 12.2008 Manuscript revised Date of the defence 23.2008 Monograph X Article dissertation (summary + original articles) Faculty Faculty of Chemistry and Materials Science Department Department of Chemistry Field of research Physical Chemistry Opponent(s) Professor Jens Ulstrup Supervisor Professor Kyösti Kontturi (Instructor) Abstract Self-assembly of molecules and supramolecules is one of the fundamental phenomena in chemistry, physics, biology and material science. For example biological systems, like lipid bilayers of cell membranes and tertiary protein structures are formed by spontaneous self-assembly. Conformation and properties of these assemblies can be affected by changing the local environment of the structures. In the case of biological molecules, such an example would be protonation or deprotonation by changes in pH.

When changing the conformation, one often changes the collective properties of the molecular assemblies. In this thesis, the formation of functional nanoscale devices is approached from the self-assembly of molecules and metallic monolayer capped nanoparticles into superstructures consisting of numerous nanoparticles. Stabilisation of the individual nanosized particles is based on bonding between noble metals and thiol ligands. The desired chemical characteristics and functionality of the nanoparticles is achieved by choosing the capping ligand layer and thus, directing the interactions between the nanoparticles.

Both formation and functionality of the superstructures are studied in this thesis. Syntheses of silver and gold nanoparticles capped with different ligands are included. Both the individual nanoparticles and the colloidal superstructures formed by them were characterised by transmission electron microscopy (TEM), dynamic light scattering (DLS), zeta-potential measurements and UV-vis spectroscopy. Characterisation of the electrical properties of the self-assembled structures were carried out by scanning electrochemical microscopy (SECM).

The thesis is divided in three parts, considering first the formation of colloidal nanoparticle superstructures in solution, then a photoresponsive switching nanoparticle structure and finally electron transport processes in nanoscale films. In the first part, formation of nanoparticle aggregates via chemical and electrostatic interactions are studied. The second part consists of assembly and characterisation of a nanoswitch built from nanoparticles and photoisomerisable azobenzene molecules. In the last section of the thesis, electron transport processes in two self-assembled nanoscale films are studied with SECM.

The first system is a molecular self-assembled monolayer and the second a film consisting of gold nanoparticles. Keywords Nanoparticles, self-assembled monolayers, SECM, molecular switches ISBN (printed) 978-951-22-9361-2 ISSN (printed) 1795-2239 ISBN (pdf) 978-951-22-9362-9 ISSN (pdf) 1795-4584 Language English Number of pages 68 p. Publisher Department of Chemistry Print distribution Department of Chemistry X The dissertation can be read at http://lib.fi/Diss/2008/isbn9789512293629/ AB VÄITÖSKIRJAN TIIVISTELMÄ TEKNILLINEN KORKEAKOULU PL 1000, 02015 TKK http://www.fi Tekijä Päivi Ahonen Väitöskirjan nimi Optiset ja sähköiset vuorovaikutukset itsejärjestäytyneissä nanopartikkelirakenteissa Käsikirjoituksen päivämäärä 12.2008 Korjatun käsikirjoituksen päivämäärä Väitöstilaisuuden ajankohta 23.2008 Monografia X Yhdistelmäväitöskirja (yhteenveto + erillisartikkelit) Tiedekunta Kemian ja materiaalitieteiden tiedekunta Laitos Kemian laitos Tutkimusala Fysikaalinen kemia Vastaväittäjä(t) Professori Jens Ulstrup Työn valvoja Professori Kyösti Kontturi (Työn ohjaaja) Tiivistelmä Molekyylien itsejärjestäytyminen eli molekyylirakenteiden spontaani muodostuminen on hyvin keskeinen luonnontieteilijöitä kiinnostava ilmiö. Itsejärjestymistä esiintyy muun muassa biologisissa systeemeissä, esimerkkeinä voidaan pitää vaikkapa lipidien asettumista levymäiseksi kaksikerrosrakenteeksi solukalvon muodostuessa sekä proteiinien tertiäärisiä rakenteita.

Muuttamalla tällaisten molekyylirakenteiden ympäristöä, biologisissa systeemeissä esimerkiksi pH:ta, voidaan molekyylien konformaatiota eli avaruusrakennetta muuttaa. Konformaationmuutokset johtavat tyypillisesti myös molekyylirakenteen kollektiivisten ominaisuuksien muuttumiseen. Tässä väitöskirjassa tutkitaan toiminnallisten nanomittakaavan rakenteiden muodostamista itsejärjestäytymisen avulla. Tutkitut systeemit ovat metallisista, orgaanisella ligandikerroksella stabiloiduista nanopartikkeleista muodostuneita rakenteita.

Ligandikerroksen kemiallinen luonne vaikuttaa rakenteiden muodostumiseen ja toiminnallisuuteen ja se voidaan valita sovellukseen riippuen tilanteeseen sopivaksi. Tutkimuksessa käsitellään sekä yo. rakenteiden muodostumista että niiden toiminnallisia ominaisuuksia. Menetelminä itsejärjestäytyneiden yksikerrosten sekä nanopartikkelisysteemien sähköisten ominaisuuksien tutkimisessa käytettiin sähkökemiallista pyyhkäisymikroskopiaa (SECM).

Optisten ominaisuuksien tutkimisessa käytettiin spektrofotometriaa sekä valonsirontamittauksia (DLS). Sekä yksittäisten nanopartikkelien että niistä muodostuneiden rakenteiden muodosta ja koosta saatiin tietoa transmissioelektronimikroskopian (TEM) ja valonsironnan avulla. Väitöskirjan ensimmäinen osa käsittelee kolloidisten nanopartikkelirakenteiden muodostumista, kun nanopartikkelien välillä on kemiallisia tai sähköstaattisia vuorovaikutuksia. Yhteenvedon toisessa osassa keskitytään optiseen nanokytkimeen, joka on muodostettu sitomalla nanopartikkeleita toisiinsa fotoisomeroituvan atsobentseenijohdannaisen avulla.

Isomeroitumisreaktiossa partikkeleja sitovan molekyylin avaruusrakenne muuttuu, jolloin myös partikkelien välinen etäisyys muuttuu. Väitöskirjan kolmannessa osassa tutkitaan elektroninsiirtoprosesseja kahdessa erityyppisessä nanorakenteessa; atsobentseenijohdannaisen muodostamassa molekulaarisessa yksikerroksessa sekä yksikerroksella stabiloiduista kultaklustereista muodostetussa kerroksessa. Asiasanat Nanopartikkelit, itsejärjestäytyneet yksikerrokset, SECM, molekyylikytkimet ISBN (painettu) 978-951-22-9361-2 ISSN (painettu) 1795-2239 ISBN (pdf) 978-951-22-9362-9 ISSN (pdf) 1795-4584 Kieli Englanti Sivumäärä 68 s. Julkaisija Kemian laitos Painetun väitöskirjan jakelu Kemian laitos X Luettavissa verkossa osoitteessa http://lib.fi/Diss/2008/isbn9789512293629/ Preface The research presented in this doctoral thesis was carried out at the Laboratory of Physical Chemistry and Electrochemistry, Helsinki University of Technology be- tween January 2005 and February 2008.

A period of four months in spring 2005 was spent at the University of Valencia. The work was financially supported by the Kemira foundation and the European Commission. First, I would like to express my gratitude to my supervisor Prof. Kyösti Kontturi and all the co-authors of the publications included in this thesis.

Special acknowledgements go to Prof. Schiffrin for sharing priceless pieces of his experience and to Dr. Timo Laaksonen for giving his great support during this time. Virginia Ruiz, Dr.

Peter Liljeroth, Dr. Christoffer Johans, Antti Nykänen, Prof. Janne Ruokolainen and Dr. Jerzy Paprotny are to be acknowledged for their contribution to this thesis.

I would like to thank Dr. Lasse Murtomäki for teaching me the basic knowledge on physical chemistry, Prof. José Manzanares for hosting my stay in Valencia, Hannu Revitzer for making the chemical analysis in some of the studies and Dr. Benjamin Wilson for proof-reading the manuscript of the thesis.

The whole group of researchers, teachers, students and other members of FyKe have earned my compliments for the atmosphere they have created to the laboratory. The discussions and support from the fellow members of FyKe has really made the time spent at the Laboratory of Physical Chemistry and Electrochemistry worth remembering. Finally, I thank my family and friends for supporting me in my choices and their endless patience with me. This thesis was made out of enthusiasm for research and science.

Päivi Ahonen Espoo, February 12th, 2008 i ii Table of Contents List of Abbreviations vi List of Symbols vii 1 Introduction 1 2 Colloidal nanoparticle superstructures via self-assembly 4 2.1 Dithiol induced nanoparticle cluster formation .2 Enhancing the stability of aqueous nanoparticle colloids. 9 3 Building a nanoswitch via self-assembly of nanoparticles 14 3.1 Photoisomerisation of azobenzene derivatised silver nanoparticles .2 Optical properties of nanoparticle clusters at quasi-static region .3 Optical switching of coupled plasmons of Ag-nanoparticles by pho- toisomerisation of an azobenzene ligand. 23 4 Electron transport processes in nano-scale films - characterisation with SECM 26 4.1 Photoswitching electron transport properties of an azobenzene con- taining self-assembled monolayer .2 Electrochemical gating in scanning electrochemical microscopy. 34 5 Conclusions 42 References 44 iii List of Publications This thesis consists of an overview and the following publications which are referred to in the text by their Roman numerals.

Kontturi, Formation of Stable Ag-Nanoparticle Aggregates Induced by Dithiol Cross- Linking, Journal of Physical Chemistry B, 2006, 110(26), 12954-12958. Kontturi, Stability and Elec- trostatics of Mercaptoundecanoic Acid Capped Gold Nanoparticles with Varying Counter-Ion Sizes, ChemPhysChem, 2006, 7(10), 2143-2149. Kontturi, Optical Switch- ing of Coupled Plasmons of Ag-Nanoparticles by Photoisomerisation of an Azobenzene Ligand, Physical Chemistry Chemical Physics, 2007, 9(5), 651-658. Kontturi, Photoswitching Electron Transport Properties of an Azobenzene Containing Thiol-SAM, Physical Chemistry Chemical Physics, 2007, 9(35), 4898-4901.

Quinn, Elec- trochemical Gating in Scanning Electrochemical Microscopy, Journal of Physical Chemistry C, 2008,112(7), 2724-2728. iv Author’s contribution Päivi Ahonen has planned and carried out all the experimental work in publications I, III and IV, apart from the synthesis of azobenzene derivatives. Ahonen corre- sponded also for all theoretical work in publications III and IV. Publication II was planned in collaboration with T.

In publication V, Ahonen carried out the experimental work planned in collaboration with the other authors. Ahonen was actively involved in preparation and writing of each manuscript. Professor Kyösti Kontturi Espoo, February 12th, 2008 v List of Abbreviations CCC Critical coagulation concentration DLS Dynamic light scattering DLVO Derjaguin-Landau-Verwey-Overbeek theory DNA Deoxyribonucleic acid FcMeOH Ferrocenemethanol FcTMA+ Ferrocenetrimethylammonium MPC Monolayer protected cluster MSA Mercaptosuccinic acid MUA Mercaptoundecanoic acid NC Nanocluster NP Nanoparticle PET 2-phenylethylthiol SAM Self-assembled monolayer SECM Scanning electrochemical microscopy SERS Surface enhanced Raman scattering STM Scanning tunneling microscopy TBA Tetrabutylammonium TEA Tetraethylammonium TMA Tetramethylammonium UME Ultramicroelectrode UV-vis Ultraviolet and visible light vi List of Symbols αi Polarisability of species i β Decay constant Γ(r) Radius dependant relaxation constant Γ∞ Bulk relaxation constant Γ+/− Eigenvalue of the aggregate mode ∆z Thickness of the film ε(ω) Dielectric function ε0 Permittivity of vacuum, 8.854 × 10−12 Fm−1 ε1 (ω) Real part of the dielectric function ε2 (ω) Imaginary part of the dielectric function εbulk (ω) Bulk dielectric function εm Dielectric constant of the embedding medium η Viscosity; polarisability of a nanoparticle κ Inverse Debye length Λ Dimensionless kinetic parameter λ Wavelength of light µ Electrochemical potential µ̃ Dimensionless electrochemical potential µeq Equilibrium electrochemical potential µ0 Standard electrochemical potential Σ Dimensionless conductivity σ Conductivity σ∆z Conductance ψ0 Surface potential ωp Plasmon frequency A Correction factor for relaxation constant a Nanoparticle radius AH Hamaker’s constant vii Ci Dimensionless concentration of species i Cabs Absorption cross-section Cext Extinction cross-section Csca Scattering cross-section Cib Dimensionless bulk concentration of species i ci Concentration of species i cb Total bulk concentration cbi Bulk concentration of species i D Nanoparticle diameter Di Diffusion coefficient of species i d Center-to-center particle separation e Elementary charge, 1.602 × 10−19 C E0 Standard potential Eeq Equilibrium potential F Faraday constant, 96485 Cmol−1 h Surface-to-surface particle separation I Current i Dimensionless current Ilim Limiting current ITC Tip current for a conductive substrate ITins Tip current for an insulating substrate ITk Tip current Ji Diffusion flux of species i kB Boltzmann constant, 1.381 × 10−23 JK−1 kET Rate constant of electron transfer Keff Dimensionless effective rate constant keff Effective rate constant K0 Dimensionless standard rate constant k0 Standard rate constant L Dimensionless tip-substrate separation viii me Effective mass of electron N Density of electrons Ñ (ω) Complex refraction index NA Avogadro’s number, 6.022 × 1023 mol−1 nm Refractive index of the embedding medium R Ideal gas constant, 8.314 Jmol−1 K−1 ; dimensionless radial distance RG Dimensionless electrode shape factor r Radius; radial variable re Radius of the electrode rg Total radius of the electrode including the glass sheath T Temperature; dimensionless time t Time Vattr Attractive potential Vrep Repulsive potential vF Fermi velocity Z Dimensionless distance normal to the electrode surface z Distance normal to the electrode surface; number of electrical charges ix 1 Introduction Self-assembly of chemical structures has attracted a great interest throughout the history of nanotechnology. Good examples of self-assembled systems are biological forms like cell membranes where the lipids assemble due to amphiphilic and steric interactions and form a bilayer able to support the interiors of the cell.

Similar spontaneous self-assembly has been applied in nanotechnology to form new struc- tures and the principle is commonly called the ’bottom-up’ approach.