Transient absorption spectroscopy of noble metal nanoparticles

TRANSIENT ABSORPTION SPECTROSCOPY OF NOBLE METAL NANOPARTICLES YU KUAI NATIONAL UNIVERSITY OF SINGAPORE 2013 TRANSIENT ABSORPTION SPECTROSCOPY OF NOBLE METAL NANOPARTICLES YU KUAI A THESIS SUBMITTED FOR THE DEGREE OF PHILOSOPHY IN SCIENCE NUS GRADUATE SCHOOL FOR INTEGRATIVE SCIENCES AND ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2013 Declaration I hereby declare that the thesis is my original work and it has been written by me in its entirety I have duly acknowledged all the sources of information which have been used in the thesis This thesis has also not been submitted for any degree in any university previously YU KUAI i | P a g e     ii | P a g e     Acknowledgments Although the cover on this thesis bears only my name, it would not have been possible to complete this thesis without the help and support of all kind people around me, to only some of whom it is possible to give particular mention here I would like to express my sincere gratitude to my supervisor, Prof Qing-Hua Xu (Department of Chemistry, NUS) for his support, encouragement and guidance through out the course He exposed me to a whole new world of research involving ultrafast optical spectroscopy that subsequently became my research interests I was given a lot of freedom to fill in my project as I wished, for which I am grateful to him I would also like to express my warm and sincere thanks to my supervisor, Prof MingHui Hong (Department of Electrical and Computer Engineering, NUS) for the opportunities I have been given in the lab I have learned a lot from his dedication and hard work My association with him has been a wonderful experience I am also very grateful to Prof Michel Orrit (Department of Physics, Leiden University) for having me in Leiden I thank Michel for the stimulating scientific discussions and continued support I have great times in the lab of working together with a postdoctoral researcher, Dr Peter Zijlstra I am grateful to him for never getting impatient with my relentless questioning on the technical and fundamental aspects of research For the rest of the group, I am grateful for all the wonderful times we had I always appreciated the working atmosphere in different labs where hard work was possible in a relaxed environment It played an important role in ensuring that the four years of research did not drive me crazy For this, thank you to all fellow colleagues I had wonderful time in Singapore and the Netherlands with my friends and colleagues The NUS Graduate School for Integrative Sciences and Engineering (NGS) is a wonderful program The financial support provided by NGS is a very critical factor ensuring a smooth completion of my candidature iii | P a g e     I would like to acknowledge the support from my family and friends To my family, mum, dad, and brother, for their encouragement during the past years, I always appreciate your continuing support and allowing me to pursue my interests all the times Finally, I would like to thank Yingmei for her encouragement and friendship To all my close friends, I am indebted to all the support that you have provided all these while iv | P a g e     Table of Contents Declaration i Acknowledgments iii  Table of Contents v  Summary ix  List of Tables xi List of Figures xiii List of Publications xix Introduction of Optical Properties of Noble Metal Nanoparticles 1.1 Noble Metal Nanoparticles 1.2 Optical Properties 1.3 Excitation Dynamics 14 1.4 Detection Techniques 28 1.5 Thesis Outline 34  References 37  Electron Dynamics of Gold Nanorods 2.1 Introduction 43 2.2 Experimental Section 45 2.3 Intraband Excitation 47 v | P a g e     2.4 Interband Excitation 51 2.5 Conclusion 58 References 59 Transient Absorption Spectroscopy of Single Gold Nanorods 3.1 Imaging of Single Gold Nanorods 64 3.2 Scattering Spectrum of Single Gold Nanorods 67 3.3 Transient Absorption Spectrum of Single Gold Nanorods 69 3.4 Cooling Dynamics in Single Gold Nanorods 71 3.5 Conclusion 73 References 74 Damping of Acoustic Vibrations of Single Gold Nanorods 4.1 Introduction 77 4.2 Experimental Setup 79 4.3 Acoustic Vibrations of Single Gold Nanorods in Air and Water 82 4.4 Theoretical Analysis of Vibrational Modes 87 4.5 Water Layer Thickness Dependent Acoustic Vibrations 90 4.6 Discussions of Acoustic Vibrations 96 4.7 Conclusion 97 References 99 Acoustic Vibrations of Single Gold Nanorods upon Ag Deposition 5.1 Introduction 105 vi | P a g e     5.2 Experimental Section 107 5.3 Estimation of the Silver Shell Thickness 109 5.4 Acoustic Vibrations of Au/Ag Core-Shell Nanorods 111 5.5 Monitoring the Atomic Layer of Silver Deposition 115 5.6 Conclusion 117 References 119 Conclusions and Perspectives 6.1 Thesis Conclusions 123 6.2 Perspectives 125   vii | P a g e         viii | P a g e     lattice The delay traces were fitted with an exponential decay superposed on a sum of two damped oscillating terms:21,25 δ T (t ) / T = Ac exp(−t / τ cool ) + ∑ k = ( ext ,br ) Ak exp( −t / τ k ) cos(2πν k t − φk ) where the first term represents the cooling of the particle and (1)   τ cool is the characteristic time for heat exchange between the crystal lattice and the environment The oscillating term corresponds to two damped oscillation modes, with k = extension (ext) or breathing (br), each one with its own characteristic decay time τ k , frequency ν k , phase φk Ac and Ak are proportionality constants Fitting eq to the vibrational trace gives the extension and breathing frequencies The power spectral density of the traces is shown in Figure 5.4b, which exhibits two peaks due to the breathing and the extension modes The frequency of the extensional mode is relatively constant, while the breathing mode shifts from 102 GHz to 79 GHz as the silver shell thickness increases from nm to nm a)250 Spectral Density (a.u.) b) δ Τ/Τ (a.u.) 200 150 100 50 0 100 200 300 400 Time delay (ps) 500 Au nanorod 0.8 nm 1.5 nm 2.2 nm 2.8 nm 3.3 nm 4.3 nm 0 20 40 60 80 100 Frequency (GHz) 120 Figure 5.4: (a) Acoustic vibrations of a single gold nanorod coated with silver shell with thickness varying from nm (bottom) to 4.3 nm (upper), corresponding white-light spectra are shown in Figure 5.2a All the curves display both the breathing mode and the extensional mode The red lines are fits to the experimental data using eq (b) Power spectral density of the oscillatory part of the traces in (a) The extensional mode at low frequency hardly changes with increasing silver thickness up to nm, while the frequency of the breathing mode decreases as indicated by the arrow Figure 5.5a and 5.5b show the measured frequencies of the extensional and breathing modes of several gold nanorods as functions of the deposited silver layer thickness The 112 | P a g e     frequency of the extensional mode does not change significantly for silver layer thickness up to nm However, the frequency of the breathing mode decreases gradually with increasing silver shell thickness for all the particles we studied b)120 Breathing νbr (GHz) Extensional νext (GHz) a) 17 16 15 14 13 110 100 90 80 70 c) 6 Ag shell thickness (nm) Ag shell thickness (nm) d) 10 40 30 Qbr Qext 20 10 0 Ag shell thickness (nm) 0 Ag shell thickness (nm) Figure 5.5: Vibrational frequencies and damping times of gold nanorods coated with various amount of silver shell Experimental data of the vibrational frequencies of extensional mode (a) and breathing mode (b) of gold nanorods upon a gradual increase of the silver shell thickness up to nm Quality factors of the extensional mode (c) and the breathing mode (d) of gold nanorods coated with various amount of silver shell The exact calculation of the vibrational behaviour of a core-shell nanorod supported on a substrate requires extensive modelling and is beyond the scope of the current work Instead, we will use a simple model to provide a qualitative understanding of the observed behaviour Hu et al employed continuum mechanics to derive expressions for the breathing and extensional vibrational frequencies of a mono-metallic, slender nanorod.22 For a cylindrical rod with a length L and radius R, the vibrational frequencies were expressed in terms of the elastic moduli and dimensions of the nanorod as: 113 | P a g e     ϕ n cl( s ) 2π R (n vbr ) = (2) where the non-negative integer n indicates the radial mode number (for the fundamental breathing mode, n = ), and (m vext ) = 2m + E ρ (s) 2L (3) where the non-negative integer m indicates the extension mode number (for the fundamental extension mode m = ), cl( s ) is the longitudinal speed of sound in the metal E is the Young’s modulus along the long particle axis, and ρ eigenvalue ϕn for the breathing mode of (s) a is the density of the metal The slender rod is given by ϕn J (ϕn ) = (1 − 2σ ) J1 (ϕn ) / (1 − σ ) , where σ is Poisson’s ratio.31  For the fundamental breathing mode, ϕ0 = 2.28 To qualitatively understand the vibration frequencies of gold nanorods upon silver deposition, Au/Ag core-shell bimetallic nanorod was also applied to the continuum mechanics which was developed for a monometallic cylinder nanorod as an approximation Gold nanorods synthesized by seed-mediated growth in the presence of silver ions are known to be single crystals with a growth direction along the [1 0] direction.32-34 Silver-coated gold nanorods synthesized according to literature by adding a coating solution containing silver ions to preformed gold nanorods are maintained monocrystallinity of the particle, where the epitaxial growths of silver shell on the gold particles.10-11,35 The silver is assumed to be uniformly deposited onto the particle The detailed calculation results are shown in Figure 5.6 The vibrational frequencies of the breathing mode decreased with increasing the silver shell deposition, whereas the vibrational frequencies of the extensional mode hardly changed 114 | P a g e     a) 120 b) νext (GHz) νbr (GHz) 16 100 80 14 12 Ag shell thickness (nm) 6 Ag shell thickness (nm) Figure 5.6: Calculated vibrational frequencies of the breathing mode (a) and the extensional mode (b) of gold nanorods with size 25 nm × 54 nm versus the uniformly coating of a silver shell Figure 5.5c and 5.5d show the quality factors of extensional mode and breathing mode of gold nanorods with coating of different amounts of silver The quality factors of bare gold nanorods deposited on glass substrate and immersed in water are Qext = 5.6 ± 0.7 and Qbr = 23.5 ± 2.0 for the extensional mode and breathing mode, respectively The values are slightly larger than what we have recently measured which probably due to the less surfactant on gold nanorods The quality factors of the extensional mode and the breathing mode after continuously coating a silver shell up to nm were relatively constant The introduced interface between metal-metal and defects not give extra damping to the vibrational energy loss 5.5 Monitoring the Atomic Layer of Silver Deposition In order to know the setup stability and measurement accuracy, we continuously measured the pump-probe signal of one particle for ten times, while maintaining other conditions unchanged The obtained vibrational frequencies of the extensional mode and the breathing mode are shown in Figure 5.7a The vibrational frequencies of the extensional mode and breathing mode are 17.11 ± 0.33 GHz and 102.92 ± 0.23 GHz, respectively During the 115 | P a g e     measurements, the solvent in the flow cell (growth solution or ascorbic acid) was pumped in and pumped out for many times depending on the growth steps The absorbed molecules on the gold nanorods could be washed away In order to know the recycling solvent effect, we measured the pump-probe signal of another single gold nanorod for ten times after each recycle The obtained vibrational frequencies of the extensional mode and the breathing mode are shown in Figure 5.7b The vibrational frequencies of the extensional mode and breathing mode are 16.46 ± 0.09 GHz and 102.65 ± 0.25 GHz, respectively The standard deviation of the extensional mode and the breathing mode owning to the experimental setup is relatively small and less than 0.3 GHz, which makes it accurate to determine the silver deposition effects on the acoustic vibrations of single gold nanorods The high accuracy in frequency measurements should enable us to detect very thin layers of silver by the acoustic vibrations To verify this dependence, we measured the vibrations of gold nanorods with very thin layer of silver deposited (less than nm) The silver deposition was controlled by the reaction time and estimated by measuring the white-light spectrum The detailed results are shown in Figure 5.8 a) 104.0 Measurements error b) 104.0 103.2 Recycling error 103.6 103.2 νbr (GHz) νbr (GHz) 103.6 102.8 102.4 102.4 102.0 16.0 102.8 16.4 16.8 17.2 νext (GHz) 17.6 18.0 102.0 16.0 16.4 16.8 17.2 17.6 18.0 νext (GHz) Figure 5.7: The vibrational frequencies of the extensional mode and the breathing mode of a single gold nanorod in repeated measurements (a) and of another single gold nanorod in recycling measurements (b) 116 | P a g e     b)130 18 Breathing νbr (GHz) Extensional νext (GHz) a) 17 16 15 14 110 100 90 80 13 0.0 0.5 1.0 0.0 1.5 Ag shell thickness (nm) c) 40 0.5 1.0 1.5 Ag shell thickness (nm) d) 40 30 30 Qbr Qext 120 20 10 20 10 0 0.0 0.5 1.0 Ag shell thickness (nm) 1.5 0.0 0.5 1.0 1.5 Ag shell thickness (nm) Figure 5.8: Measured vibrational frequencies of the extensional mode (a) and the breathing mode (b) of particles with different silver shell thicknesses up to nm (thickness estimated from shifts in the white-light spectra) The measured vibrational frequencies of several gold nanorods with a thin layer of silver are shown in Figure 5.8a and 5.8b and the corresponding quality factors are shown in Figure 5.8c and 5.8d The breathing frequencies decrease upon deposition of a few atomic layers of silver, whereas the extensional frequencies not show an obvious trend Therefore, it is feasible to detect only a few atomic layers silver deposition on gold nanorods with all optical methods while it is even hard to be distinguished by transmission electron microscopy The current all optical methods make it possible to in-situ quantitatively detect the mass deposition in various environments 5.6 Conclusion The acoustic vibrations of Au/Ag core-shell nanorods were investigated for varying amounts of deposited silver using single-particle pump-probe spectroscopy Continuous silver coating 117 | P a g e     of single gold nanorods was achieved by carefully control the synthesis parameters We determined the silver thickness by combining the single-particle absorption spectroscopy and acoustic vibrations of Au/Ag core-shell nanorods Starting from single bare gold nanorods, the vibrational frequency of the breathing mode was found to decrease with increasing the silver thickness, whereas the changes of the extensional mode are much weaker The measured vibrational frequencies are consistent with a simple model based on continuum mechanics The deposited silver on gold nanorods did not give significant damping to the breathing mode and the extensional mode We demonstrated that the all optical methods are possible to quantitatively detect an atomic layer of mass deposition 118 | P a g e     References (1) Lee, K S.; El-Sayed, M A Gold and Silver Nanoparticles in Sensing and Imaging: Sensitivity of Plasmon Response to Size, Shape, and Metal Composition J Phys Chem B 2006, 110, 19220 (2) Willets, K A.; Van Duyne, R P Localized Surface Plasmon Resonance Spectroscopy and Sensing Annu Rev Phys Chem 2007, 58, 267 (3) Zijlstra, P.; Orrit, M Single Metal Nanoparticles: Optical Detection, Spectroscopy and Applications Rep Prog Phys 2011, 74, 106401 (4) Zijlstra, P.; Paulo, P M R.; Orrit, M Optical Detection of Single Non- Absorbing Molecules Using the Surface Plasmon Resonance of a Gold Nanorod Nat Nanotechnol 2012, 7, 379 (5) Pearce, M.; Melanko, J.; Salem, A Multifunctional Nanorods for Biomedical Applications Pharm Res 2007, 24, 2335 (6) Huang, Y.-F.; Lin, Y.-W.; Chang, H.-T Control of the Surface Charges of Au−Ag Nanorods:  Selective Detection of Iron in the Presence of Poly(Sodium 4Styrenesulfonate) Langmuir 2007, 23, 12777 (7) Cortie, M B.; McDonagh, A M Synthesis and Optical Properties of Hybrid and Alloy Plasmonic Nanoparticles Chem Rev 2011, 111, 3713 (8) Toshima, N.; Yonezawa, T Bimetallic Nanoparticles - Novel Materials for Chemical and Physical Applications New J Chem 1998, 22, 1179 (9) Huang, C C.; Yang, Z S.; Chang, H T Synthesis of Dumbbell-Shaped Au- Ag Core-Shell Nanorods by Seed-Mediated Growth under Alkaline Conditions Langmuir 2004, 20, 6089 (10) Liu, M.; Guyot-Sionnest, P Synthesis and Optical Characterization of Au/Ag Core/Shell Nanorods J Phys Chem B 2004, 108, 5882 119 | P a g e     (11) Becker, J.; Zins, I.; Jakab, A.; Khalavka, Y.; Schubert, O.; Soennichsen, C Plasmonic Focusing Reduces Ensemble Linewidth of Silver-Coated Gold Nanorods Nano Lett 2008, 8, 1719 (12) Duan, J S.; Park, K.; MacCuspie, R I.; Vaia, R A.; Pachter, R Optical Properties of Rodlike Metallic Nanostructures: Insight from Theory and Experiment J Phys Chem C 2009, 113, 15524 (13) Hodak, J H.; Henglein, A.; Hartland, G V Coherent Excitation of Acoustic Breathing Modes in Bimetallic Core−Shell Nanoparticles J Phys Chem B 2000, 104, 5053 (14) Hodak, J H.; Henglein, A.; Hartland, G V Tuning the Spectral and Temporal Response in Ptau Core Shell Nanoparticles J Chem Phys 2001, 114, 2760 (15) Petrova, H.; Lin, C.-H.; Hu, M.; Chen, J.; Siekkinen, A R.; Xia, Y.; Sader, J E.; Hartland, G V Vibrational Response of Au−Ag Nanoboxes and Nanocages to Ultrafast Laser-Induced Heating Nano Lett 2007, 7, 1059 (16) Kirakosyan, A S.; Shahbazyan, T V Vibrational Modes of Metal Nanoshells and Bimetallic Core-Shell Nanoparticles J Chem Phys 2008, 129, 034708 (17) Crut, A.; Juvé, V.; Mongin, D.; Maioli, P.; Del Fatti, N.; Vallée, F Vibrations of Spherical Core-Shell Nanoparticles Phys Rev B 2011, 83, 205430 (18) Wang, L.; Kiya, A.; Okuno, Y.; Niidome, Y.; Tamai, N Ultrafast Spectroscopy and Coherent Acoustic Phonons of Au Ag Core Shell Nanorods J Chem Phys 2011, 134, 054501 (19) Cardinal, M F.; Mongin, D.; Crut, A.; Maioli, P.; Rodríguez-González, B.; Pérez-Juste, J.; Liz-Marzán, L M.; Del Fatti, N.; Vallée, F Acoustic Vibrations in Bimetallic Au@Pd Core–Shell Nanorods J Phys Chem Lett 2012, 3, 613 (20) Mahmoud, M A.; Szymanski, P.; El-Sayed, M A Different Methods of Increasing the Mechanical Strength of Gold Nanocages J Phys Chem Lett 2012, 3527 (21) Zijlstra, P.; Tchebotareva, A L.; Chon, J W M.; Gu, M.; Orrit, M Acoustic Oscillations and Elastic Moduli of Single Gold Nanorods Nano Lett 2008, 8, 3493 120 | P a g e     (22) Hu, M.; Wang, X.; Hartland, G V.; Mulvaney, P.; Juste, J P.; Sader, J E Vibrational Response of Nanorods to Ultrafast Laser Induced Heating: Theoretical and Experimental Analysis J Am Chem Soc 2003, 125, 14925 (23) Nikoobakht, B.; El-Sayed, M A Preparation and Growth Mechanism of Gold Nanorods (Nrs) Using Seed-Mediated Growth Method Chem Mater 2003, 15, 1957 (24) Tchebotareva, A L.; Ruijgrok, P V.; Zijlstra, P.; Orrit, M Probing the Acoustic Vibrations of Single Metal Nanoparticles by Ultrashort Laser Pulses Laser & Photonics Rev 2010, 4, 581 (25) Ruijgrok, P V.; Zijlstra, P.; Tchebotareva, A L.; Orrit, M Damping of Acoustic Vibrations of Single Gold Nanoparticles Optically Trapped in Water Nano Lett 2012, 12, 1063 (26) Zijlstra, P.; Orrit, M Single Metal Nanoparticles: Optical Detection, Spectroscopy and Applications Reports on Progress in Physics 2011, 74, 106401 (27) Lindfors, K.; Kalkbrenner, T.; Stoller, P.; Sandoghdar, V Detection and Spectroscopy of Gold Nanoparticles Using Supercontinuum White Light Confocal Microscopy Phys Rev Lett 2004, 93, 037401 (28) Yu, K.; You, G.; Polavarapu, L.; Xu, Q.-H Bimetallic Au/Ag Core–Shell Nanorods Studied by Ultrafast Transient Absorption Spectroscopy under Selective Excitation J Phys Chem C 2011, 115, 14000 (29) Brioude, A.; Jiang, X C.; Pileni, M P Optical Properties of Gold Nanorods:  Dda Simulations Supported by Experiments J Phys Chem B 2005, 109, 13138 (30) Prescott, S W.; Mulvaney, P Gold Nanorod Extinction Spectra J Appl Phys 2006, 99, 123504 (31) Tchebotareva, A L.; Ruijgrok, P V.; Zijlstra, P.; Orrit, M Probing the Acoustic Vibrations of Single Metal Nanoparticles by Ultrashort Laser Pulses Laser Photonics Rev 2010, 4, 581 121 | P a g e     (32) Wang, Z L.; Gao, R P.; Nikoobakht, B.; El-Sayed, M A Surface Reconstruction of the Unstable {110} Surface in Gold Nanorods J Phys Chem B 2000, 104, 5417 (33) Katz-Boon, H.; Rossouw, C J.; Weyland, M.; Funston, A M.; Mulvaney, P.; Etheridge, J Three-Dimensional Morphology and Crystallography of Gold Nanorods Nano Lett 2010, 11, 273 (34) Carbó-Argibay, E.; Rodríguez-González, B.; Gómez-Gra, S.; Guerrero- Martínez, A.; Pastoriza-Santos, I.; Pérez-Juste, J.; Liz-Marzán, L M The Crystalline Structure of Gold Nanorods Revisited: Evidence for Higher-Index Lateral Facets Angew Chem 2010, 122, 9587 (35) Ahn, S.-H.; Kim, D.-S.; Seo, D.; Choi, W.; Yi, G.-R.; Song, H.; Park, Q H.; Kim, Z H Localized Plasmon Resonances of Bimetallic Agauag Nanorods Phys Chem Chem Phys 2013, 15, 4190 122 | P a g e     Chapter Conclusions and Perspectives   In this thesis we have investigated the nonlinear optical properties of gold nanorods with both ensemble measurements and single-particle studies by using transient absorption spectroscopy and we have also investigated the nonlinear spectra changes of gold nanorods after coating with another silver shell Here we conclude the thesis and reviewing the main results and providing a perspective on future work 6.1 Thesis conclusions The unique optical properties of metal nanoparticle which derive from the localized surface plasmon resonance (SPR), are the main aspects to inspire the tremendous investigations in the past two decades In Chapter 1, we calculate the extinction spectra of metal nanoparticles, such as gold spheres, nanorods, Au/Ag core-shell nanorods, based on Mie’s theory The SPRs are sensitive to the size, shape and composition of the particles We also calculate the transient absorption spectra and plasmon dynamics of metal nanoparticles after pulsed laser excitation by using Rosei model and two-temperature model The excitation dynamics of metal nanoparticles are thus well theoretically described Finally, the experimental setups which used for ensemble measurements and single-particle studies are elaborated An investigation of the electron dynamics of gold nanorods under different excitation wavelength are presented in Chapter Under different excitation conditions, we observed different bleaching saturation behavior of transverse and longitudinal plasmon bands under high excitation pump fluences We have tried to explain the results with a consistent picture: the bleaching amplitude and electron-phonon relaxation time are directly related to energy distribution into different modes, which are excitation wavelength and fluence dependent Because of the well developed laser sources and the wide range of probing wavelength which covering the plasmon resonance spectra, the measurements in solution provide an easy 123 | P a g e     way to study the nonlinear optical properties of metal nanoparticles However, the samples studied are inhomogeneous including the size, shape by chemical synthesis methods It makes it very difficult to understand of the transient absorption spectrum of metal nanoparticles Furthermore, by eliminating the inhomogeneous effect, more information about the oscillation frequency, damping of the plasmons can be accessed Therefore, it is also important to study the nonlinear optical properties of single particles In Chapter 3, we conducted the two-colour pump-probe spectroscopy of a single gold nanorod on glass substrate By correlating the scattering spectra with the transient absorption spectra, we can identify the same particle with the linear properties to its nonlinear optical properties The transient absorption spectra of a single gold nanorod are quantitatively described via the transient electron temperature and density in gold considering both intraband and interband transitions From the electron-phonon decay time we found an electron phonon coupling constant in single gold nanorods which is in good agreement with the ensemble measurements as reported in Chapter and also consistent with previous studies Although the plasmon dynamics have been extensively investigated by ensemble measurements and single-particles studies, interactions between the particles and the environment remains to be done Having a quantitatively understanding for energy dissipation to the environment would allow more practical applications, such as controlling the energy flow and allowing single particle transient absorption experiments to be used as a probe of the microenvironment, etc In Chapter 4, we conducted the damping measurements of immobilized single gold nanorods in different environments When immersed in water, the decrease of the quality factor of the breathing mode is in good agreement with a model that takes into account viscous damping and radiation of sound waves into the medium For the extension mode however we observe an extremely low quality factor when the particles are immersed in water The effect is much stronger than expected from viscous damping, and is attributed to hydrodynamic lubrication forces in a thin water layer between the nanoparticle and the glass substrate 124 | P a g e     In Chapter 5, the acoustic vibrations of gold nanorods coated with silver were investigated as a function of silver amount deposition using single-particle pump-probe spectroscopy Both the extensional and breathing vibrational modes of the nanorods were coherently excited and detected This permits precise determination of their periods The period of extensional mode does not change obviously when silver thickness coating up to nm in our studies However, the frequencies of the breathing mode were found to decrease with increasing the silver deposition Those behaviours reflect the changes of nanoparticle size, in agreement with numerical simulations The acoustic vibrations of the particles allowed us to detect even one layer of silver atoms deposited on gold nanorods The sensitive response of breathing mode provides a novel tool to characterize the small amount of mass deposition on gold nanorods The pump-probe spectroscopy for small metal nanoparticles could be even improved to detect the single bio-molecular attachment 6.2 Perspectives Ultrafast spectroscopy is an interdisciplinary area of research that spans various disciplines for physics, chemistry to life sciences With the help of pulsed lasers, it is possible to study processes that occur on time scales as short as 10-15 seconds Transient absorption spectroscopy is an extension of absorption spectroscopy As we have already known, the metal nanoparticles exhibit spectacular optical properties in the visible range, and also the coupling between nanoparticles gives more interesting optical phenomenon Generally, most studies are focused on their linear optical properties, however, the nonlinear optical properties are rarely discussed, especially on ordered metal nanostructures Single-particle studies have developed into a mature and powerful research approach that is adding new insights into many different areas within the physical and life sciences The ability to detect and perform experiments on single particle opens up new experimental approaches for investigating the physical world One is no longer limited by ensemble averaging, making it possible to detect intrinsic phenomenon, to visualize rare events and to 125 | P a g e     gather information over the heterogeneity of the sample The single-particle studies are especially important for metal nanoparticles which the optical properties are well related with the size and shape of the particles It is very important to correlate the structure of metal nanoparticles to the optical properties and theory, which will pave the way for us to utilize the linear optical properties of metal structures Although the ways of the different dynamical process in metal nanoparticle, including electron-electron, electron-phonon coupling, particle cooling and coherent excitation and damping of acoustic vibrations in metal nanoparticles are reasonably well-known, transient absorption studies of single metal nanoparticles is a relatively unexplored area of research at present As the laser sources for the single particle measurements improves, it is possible to study the particles with relatively small sizes even down to the clusters, which will bring us the information to bridge the molecular dynamics to particles dynamics This will yield a molecular-level understanding of the metal dynamics and finally can be used as a molecular detection in microenvironment In this thesis, we try to understand the transient absorption spectroscopy of gold nanorods, and Au/Ag core-shell nanorods in solution and single particle measurements No doubt, there are still lots of rooms to study the transient absorption changes through the interactions between metal nanoparticle and semiconductor, molecular etc which will benefit the various kinds of applications from solar cell to bioengineering Our vision, perhaps rather naive, is to design and predict a certain structure with specific transient absorption spectrum and electron dynamics We anticipate that the well understood nonlinear spectroscopy will help us to control the physical processes in ultra-short time scales 126 | P a g e     ... University on the study of nonlinear optical properties of metal nanoparticles This thesis entitled: ? ?Transient absorption spectroscopy of noble metal nanoparticles? ?? is my own work and has not been submitted... electronic dynamics of metal nanoparticles With the theoretical and experimental studies, we hope you will understand the transient absorption spectroscopy of noble metal nanoparticles after... xi List of Figures xiii List of Publications xix Introduction of Optical Properties of Noble Metal Nanoparticles 1.1 Noble Metal Nanoparticles 1.2 Optical Properties