Optical Properties of Quantum-sized Gold and Silver Nanoclusters PDF Download
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Author: Viraj Dhanushka Thanthirige
Publisher:
ISBN:
Category : Metal clusters
Languages : en
Pages : 270
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Book Description
Atomically precise quantum-sized gold and silver nanoclusters have gained enormous research attention as they show unique properties like discrete electronic transitions, superparamagnetism, greater catalytic activity, and enhanced linear and non-linear optical properties. These characteristics make them viable for applications in molecular electronics, catalysis and biological imaging. Among several characteristics, optical properties like electronic absorption, photoluminescence (PL) and exciton dynamics have been the focus of intense research in recent years. Although progress has been made exploring the optical properties, several important questions are yet to be understood, which include the influence of ligands, metal atom doping, mechanism of PL etc. To gain further insights into these phenomena, in this study, we used the power of temperature-dependent absorption, PL and ultrafast time-resolved spectroscopy. Firstly, core-gold/shell-gold electron-phonon interactions in bi-icosahedral Au25 clusters were studied via the use of temperature-dependent absorption and ultrafast time-resolved PL. The results show that the staple shell motif structure is important for understanding the electron phonon interaction and the coupling of core and shell-gold. The ligands that make up the shell-gold were altered and their influence on optical properties were studied; the results show that the chemical nature of ligands has minor effect on both steady-state and time-resolved optical properties. The influence of solvent on bi-Au25 clusters was studied and the results revealed that in protic solvents, solvent hydrogen bonds with axial Cl atoms and it alters the absorption at low temperatures. This result proves that the optical properties of quantum-sized gold clusters are similar to that of molecules, with subtle differences. Secondly, we focused on understanding the origins of PL in gold clusters. Our efforts revealed that the ligand to metal-metal charge transfer state is the reason for greater PL in glutathione-protected Au22 clusters. The results demonstrate that the rigidification of shell-gold enhances PL quantum yield as high as 60% was realized for tetraoctylammonium-passivated Au22 clusters. Rigidification of the shell-gold was shown to be the reason for enhancing PL in protein-passivated gold clusters. Another strategy involving fluorescence resonance energy-transfer from the dye to Au22 cluster was demonstrated as a viable path for achieving highly luminescent gold clusters in water. Detailed time-resolved measurements demonstrated that both energy and electron transfer pathways are prevalent in dye-functionalized gold clusters and it is important to overcome electron transfer deactivation to achieve enhanced energy transfer-assisted PL. Temperature-dependent and ultrafast time-resolved optical measurements on metal-doped gold and silver clusters revealed that the central metal atom alters both electron-phonon interactions as well as exciton lifetimes. Interestingly, the results of this study provided support for an Energy Gap Law developed to describe the non-radiative deactivation pathways in organometallics. Systematic size-dependence measurements were carried out on hexane-thiolate protected gold clusters and the energy gap law successfully predicted the dependence of exciton dynamics on the HOMO-LUMO energy gap. Moreover, optical measurements reveal the unique behavior of highly symmetric icosahedral Au144 clusters.
Author: Viraj Dhanushka Thanthirige
Publisher:
ISBN:
Category : Metal clusters
Languages : en
Pages : 270
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Book Description
Atomically precise quantum-sized gold and silver nanoclusters have gained enormous research attention as they show unique properties like discrete electronic transitions, superparamagnetism, greater catalytic activity, and enhanced linear and non-linear optical properties. These characteristics make them viable for applications in molecular electronics, catalysis and biological imaging. Among several characteristics, optical properties like electronic absorption, photoluminescence (PL) and exciton dynamics have been the focus of intense research in recent years. Although progress has been made exploring the optical properties, several important questions are yet to be understood, which include the influence of ligands, metal atom doping, mechanism of PL etc. To gain further insights into these phenomena, in this study, we used the power of temperature-dependent absorption, PL and ultrafast time-resolved spectroscopy. Firstly, core-gold/shell-gold electron-phonon interactions in bi-icosahedral Au25 clusters were studied via the use of temperature-dependent absorption and ultrafast time-resolved PL. The results show that the staple shell motif structure is important for understanding the electron phonon interaction and the coupling of core and shell-gold. The ligands that make up the shell-gold were altered and their influence on optical properties were studied; the results show that the chemical nature of ligands has minor effect on both steady-state and time-resolved optical properties. The influence of solvent on bi-Au25 clusters was studied and the results revealed that in protic solvents, solvent hydrogen bonds with axial Cl atoms and it alters the absorption at low temperatures. This result proves that the optical properties of quantum-sized gold clusters are similar to that of molecules, with subtle differences. Secondly, we focused on understanding the origins of PL in gold clusters. Our efforts revealed that the ligand to metal-metal charge transfer state is the reason for greater PL in glutathione-protected Au22 clusters. The results demonstrate that the rigidification of shell-gold enhances PL quantum yield as high as 60% was realized for tetraoctylammonium-passivated Au22 clusters. Rigidification of the shell-gold was shown to be the reason for enhancing PL in protein-passivated gold clusters. Another strategy involving fluorescence resonance energy-transfer from the dye to Au22 cluster was demonstrated as a viable path for achieving highly luminescent gold clusters in water. Detailed time-resolved measurements demonstrated that both energy and electron transfer pathways are prevalent in dye-functionalized gold clusters and it is important to overcome electron transfer deactivation to achieve enhanced energy transfer-assisted PL. Temperature-dependent and ultrafast time-resolved optical measurements on metal-doped gold and silver clusters revealed that the central metal atom alters both electron-phonon interactions as well as exciton lifetimes. Interestingly, the results of this study provided support for an Energy Gap Law developed to describe the non-radiative deactivation pathways in organometallics. Systematic size-dependence measurements were carried out on hexane-thiolate protected gold clusters and the energy gap law successfully predicted the dependence of exciton dynamics on the HOMO-LUMO energy gap. Moreover, optical measurements reveal the unique behavior of highly symmetric icosahedral Au144 clusters.
Author: Rodolphe Antoine
Publisher: Springer
ISBN: 3319647431
Category : Technology & Engineering
Languages : en
Pages : 89
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Book Description
Metallic quantum clusters belonging to intermediate size regime between two and few hundred of atoms, represent unique building blocks of new materials. Nonlinear optical (NLO) characteristics of liganded silver and gold quantum clusters reveal remarkable features which can be tuned by size, structure and composition. The two-photon absorption cross sections of liganded noble metal quantum clusters are several orders of magnitude larger than that of commercially-available dyes. Therefore, the fundamental photophysical understanding of those two-photon processes in liganded clusters with few metal atoms deserve special attention, in particularly in context of finding the mechanisms responsible for these properties. A broad range of state-of-the-art experimental methods to determine nonlinear optical properties (i.e. two-photon absorption, two-photon excited fluorescence and second harmonic generation) of quantum clusters are presented. The experimental setup and underlying physical concepts are described. Furthermore, the theoretical models and corresponding approaches are used allowing to explain the experimental observations and simultaneously offering the possibility to deduce the key factors necessary to design new classes of nanoclusters with large NLO properties. Additionally, selected studied cases of liganded silver and gold quantum clusters with focus on their NLO properties will be presented as promising candidates for applications in imaging techniques such as fluorescence microscopy or Second-Harmonic Generation microscopy.
Author: Alfredo Campos Otero
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
It is well known that the optical properties of nanoparticles of noble metals, in particular gold and silver, deviate strongly from those of macroscopic metals. For sizes between ten and a few hundred nanometers, they are dominated by surface plasmons (SPs) described by purely classical models. On the other hand, clusters of a few tens of atoms behave like quantum systems inducing new optical behaviors. The structure of the nanoparticles and the dielectric environment can affect the optical properties. In this thesis I used a scanning transmission electron microscope (STEM) fitted with an electron energy loss spectrometer (EELS) to measure, in parallel, the optical and structural properties of individual nanoparticles. I present how complementary experiments (STEM-EELS and optical absorption) on sizeselected small silver nanoparticles embedded in silica yield at first inconsistent results: while optical absorption shows no size-effect in the range between only a few atoms and ~10 nm, a clear spectral shift is observed in STEM-EELS technique. Our quantitative interpretation, based on a mixed classical/quantum model which takes into account all the relevant quantum effects, resolves the apparent contradictions, not only within our experimental data, but also in the literature. Our comprehensive model describes how the local environment is the crucial parameter controlling the manifestation or absence of quantum size effects. Secondly, I was interested in the purely classical region through lithographed structures of a few hundred nanometers. Although triangular plasmonic cavities have been widely studied in the literature, a classification in terms of plasmonic modes of breathing and edge was missing. In this study, experimental STEM-EELS results, analytical models and classical simulations enabled us to describe the nature of the different modes.
Author: Khan Maaz
Publisher:
ISBN: 1789234786
Category :
Languages : en
Pages : 290
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Book Description
Author: Giuseppe Palumbo
Publisher: Royal Society of Chemistry
ISBN: 9780854043217
Category : Medical
Languages : en
Pages : 688
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Book Description
The wide range of topics covered make this book of interest to a diverse range of scientific communities.
Author: Susie Eustis
Publisher:
ISBN:
Category : Gold
Languages : en
Pages :
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Book Description
A new method is developed referred to as Gold Nanorod Optical Modeling Equations (GNOME) for determining the average aspect ratio of gold nanorods in solution. In this method, the observed inhomogeneously broadened optical spectrum is fitted to a number of calculated homogeneously broadened spectra with different aspect ratios having different contributions. From this method, the average aspect ratio is determined. This is a more accurate than the presently used method of TEM. The surface plasmon enhanced fluorescence spectra of gold nanorods are calculated as a function of the aspect ratio and compared to experimental spectra. In this calculation, the inclusion of both the aspect ratio distribution calculated from the GNOME method as well as the incorporation of the intrinsic fluorescence of bulk gold are found necessary to model the enhanced fluorescence spectrum of gold nanorods using previously published equations. The enhanced spectrum decreases rapidly as the aspect ratio increases and the surface plasmon band shift away from the gold interband absorption. Photochemical methods are used to synthesize silver nanoparticles on silica surfaces and gold nanoparticles in solution. The formation silver nanoparticles utilizes benzophenone as a photosensitizing agent to initiate the reaction. The effects of the light source and irradiation time are investigated. The presence of different forms of silica are investigated in the formation of metal nanoparticles. This method produced silver nanoparticles on silica that can be in the form of film or powder that are useful in heterogeneous catalysis. Direct photochemical methods are applied to generate gold nanoparticles from chloroauoroic acid in ethylene glycol in the presence of polyvinylpyrrolidone as a capping material. A detailed mechanism of the formation of the gold nanoparticle is determined. This is done by following the kinetics of formation of the gold nanoparticles after irradiation under different conditions. The disproportionation of the gold ions as well as their reduction by ethylene glycol is found to be important in the formation of the nanoparticles. Photochemical synthesis provides room temperature techniques to generate metal nanoparticles in a variety of environments.
Author: Catherine Louis
Publisher: World Scientific
ISBN: 1786341263
Category : Science
Languages : en
Pages : 681
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Book Description
Gold Nanoparticles for Physics, Chemistry and Biology offers an overview of recent research into gold nanoparticles, covering their discovery, usage and contemporary practical applications.This Second Edition begins with a history of over 2000 years of the use of gold nanoparticles, with a review of the specific properties which make gold unique. Updated chapters include gold nanoparticle preparation methods, their plasmon resonance and thermo-optical properties, their catalytic properties and their future technological applications. New chapters have been included, and reveal the growing impact of plasmonics in research, with an introduction to quantum plasmonics, plasmon assisted catalysis and electro-photon conversion. The growing field of nanoparticles for health is also addressed with a study of gold nanoparticles as radiosensibiliser for radiotherapy, and of gold nanoparticle functionalisation. This new edition also considers the relevance of bimetallic nanoparticles for specific applications.World-class scientists provide the most up-to-date findings for an introduction to gold nanoparticles within the related areas of chemistry, biology, material science, optics and physics. It is perfectly suited to advanced level students and researchers looking to enhance their knowledge in the study of gold nanoparticles.
Author: Benedetto Corain
Publisher: Elsevier
ISBN: 0080555004
Category : Technology & Engineering
Languages : en
Pages : 471
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Book Description
Metal Nanoclusters in Catalysis and Materials Science: The Issue of Size Control deals with the synthesis of metal nanoclusters along all known methodologies. Physical and chemical properties of metal nanoclusters relevant to their applications in chemical processing and materials science are covered thoroughly. Special attention is given to the role of metal nanoclusters size and shape in catalytic processes and catalytic applications relevant to industrial chemical processing.An excellent text for expanding the knowledge on the chemistry and physics of metal nanoclusters. Divided in two parts; Part I deals with general aspects of the matter and Part II has to be considered a useful handbook dealing with the production of metal nanoclusters, especially from their size-control point of view. * Divided into two parts for ease of reference: general and operational * Separation of synthetic aspects, physical properties and applications* Specific attention is given to the task of metal nanoclusters size-control
Author: Aditya Kumar Sahu
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 0
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Book Description
Materials on a scale of 1 - 100 nm have demonstrated that the properties are dependent on their size and shape. [1-3] The non-existence of symmetry at the interface or electron confinement, which is not linear in size, contributes to the creation of new properties on a nanoscale. [1] Thus, the materials at the nanometer scale (1 - 100 nm) contain a cluster of atoms or molecules whose properties are neither of their constituents nor that of the bulk. Noble metal nanoparticles have bright colors due to the surface plasmon resonance absorption. [2] Examination of the absorption of surface plasmon resonance is part of a broad ongoing area of research to investigate properties on the nanometer scale. The color of metal nanoparticles is found to depend on the size and shape of the nanoparticles and the surrounding medium dielectric constant, leading to numerous studies of their synthesis and applications. [3, 4] The complexity of producing the desired size, shape, and monodispersity of nanoparticles continues to press for new and improved synthesis techniques. The development of the required chemical and physical interfaces for interacting with target molecules also involves the need for several different techniques for the synthesis of metal nanoparticles. The increase in the number of available nanoparticles and nanotechnology creates lots of applications and significant advancements in everyday life. Studies attempt to define the features of nanoparticles, contributing to the basic science in a way that provides possibilities for other applications to use nanoparticles.
Author: Brian E. Conn
Publisher:
ISBN:
Category : Nanoparticles
Languages : en
Pages : 163
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Book Description
Nanoclusters are finite aggregations of 2-10,000 atoms that interact through synergistic effects to form materials with unique chemical and physical properties. The properties of nanoclusters have been shown to be size-dependent, and to have incongruous chemical and physical properties from the constituent bulk material. In recent years there has been an extraordinary scientific effort to establish size-evolutionary patterns to provide a fundamental understanding of the size-dependent properties of nanoclusters. The current size-evolutionary patterns for nanoclusters have yielded theoretical and synthetic models that have begun to rationalize and explain the origin of nanocluster properties. The size-evolutionary models have shown that large surface-to-volume ratios, quantum confinement, and structural and energetic size effects are the dominating factors that influence the properties of nanoclusters. However, there is an obligation to continually revise and improve the current size-evolutionary models to provide a more accurate theory to bridge the understanding between atomic/molecular states, structural motifs at the metal surface interface, and condensed-phase physics. M4Ag44(p-MBA)30 nanoclusters, where M is an alkali metal, have recently been shown to have exceptional stability, which confers unique traits to this molecule. In particular, the synthesis is straightforward, produces a truly single-sized molecular product, and has a quantitative yield. Here, we describe in detail the results of experimental and theoretical studies on the synthesis, structure, stability, and electronic and optical properties of M4Ag44(p-MBA)30, including ESI-MS, NMR, optical absorption, IR, TGA, and other measurements as well as DFT and TDDFT calculations. Additionally, the structure and facile synthesis of M4Ag44(p-MBA)30 has provided a "golden" opportunity to explore the effects of doping M4Ag44(p-MBA)30 with gold. This work has deepened our understanding of this important Ag molecule, which should facilitate its use in a wide range of fundamental studies, applications, and size-evolutionary models. Understanding the fundamental principles of structure formation of monolayer-coated nanoclusters remains an enduring challenge. Although with the advances recent in X-ray determinations monolayer-coated nanoclusters, accurate de novo structural predictions still remain scarce. Building on recent syntheses and de novo structure predictions of M3AuxAg17-x(TBBT)12, where M is a countercation, x = 0 or 1, and TBBT is 4-tert-butylbenzenethiol, we report an X-ray determined structure that authenticates an a priori prediction, and in conjunction with first-principles theoretical analysis, lends force to the underlying forecasting methodology. The predicted and verified Ag(SR)3 monomer, together with the recently discovered Ag2(SR)5 dimer and Ag3(SR)6 trimer, establishes a family of unique mount motifs for silver thiolate nanoparticles, expanding knowledge beyond the earlier-known Au-S staples in thiol-capped gold nanoclusters. These findings demonstrate key principles underlying ligand-shell anchoring to the metal core, as well as unique T-like benzene dimer and cyclic benzene trimer ligand bundling configurations, opening vistas for rational design of metal and alloy nanoparticles.
