Dissertations / Theses on the topic 'Nanocluster size'
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1
Conn, Brian E. "Revealing the Magic in Silver Magic Number Clusters: The Development of Size-Evolutionary Patterns for Monolayer Coated Silver-Thiolate Nanoclusters." University of Toledo / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1481294367098454.
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Cao, Lu. "Deposition of size-selected nanoclusters." Thesis, University of Birmingham, 2016. http://etheses.bham.ac.uk//id/eprint/6616/.
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The work presented in this thesis explores the production and the controlled deposition of size-selected nanoclusters. The size-dependent propagation of gold nanoclusters is investigated by depositing them through few-layer graphene (FLG) using a magnetron sputtering cluster source. Au55 nanoclusters penetrate through the FLG, however Au923 nanoclusters remain on the surface, as imaged by aberration corrected scanning transmission electron microscope (ac-STEM). The control of the atomic structure of gold nanoclusters (Au923) by systematically varying the gas-phase condensation parameters in the magnetron sputtering cluster source (e.g. magnetron power and condensation length) is also reported. Results show we have the ability to eliminate all icosahedral isomers by tuning the formation conditions. The biggest advance reported in the work concerns the new technology of the Matrix Assembly Cluster Source (MACS), which has the potential to increase the production rate of nanoclusters by 7 orders of magnitude from 0. 1-1 nA (from a magnetron source) to 1-1 Om A. The principle of the MACS is demonstrated by the production of Ag and Au clusters. The development of the latest MACS instrument is also described. An equivalent cluster beam current of ~ 1OOnA has been achieved. Gold and silver clusters produced under controlled experimental conditions show a relatively narrow size distribution even without mass selection (at best ±25% in the number of atoms). The mean cluster size can be controlled via the experimental parameters, especially the metal concentration in the matrix. STEM is again the principal tool employed characterize the number and structure of cluster produced by the MACS.
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Pratontep, Sirapat. "Production and characterisation of size-selected nanoclusters on surfaces." Thesis, University of Birmingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289304.
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Foster, Dawn Michelle. "Production and characterisation by scanning transmission electron microscopy of size-selected noble metal nanoclusters." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7902/.
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In this thesis aberration corrected scanning transmission electron microscopy is employed to study the atomic structure of size-selected nanoclusters. The nanoclusters are produced using a magnetron sputtering gas aggregation cluster source with lateral time of flight mass filter, which enables the deposition of high precision samples. For Au nanoclusters, the combination of these techniques is used to determine atomic structure as a function of size, elucidate cluster growth mechanisms, determine the lowest energy structural isomers and investigate control of atomic structure through growth conditions. To further investigate the atomic structure of Au nanoclusters, an in-situ heating holder for the ac-STEM is used to extract a quantitative value for the energy difference between competing structural isomers. A study of surface melting of Au clusters on amorphous-carbon is also presented and the results are discussed with reference to several models for nanoscale melting. Finally, ac-STEM and STEM EELS are used to study the atomic structure and ageing in air of size-selected Ag nanoclusters. It is shown that exposure to air induces a change in both atomic structure and chemical composition.
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Arredondo, Melissa Gayle. "Zero-Dimensional Magnetite." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/14151.
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Low-dimensional magnetic systems are of interest due to several new effects and modifications that occur at sizes below the average domain grain boundary within the bulk material. Molecule-like magnetite (Fe3O4) nanoparticles, with sizes ranging from one to two nm were synthesized and characterized in order to investigate new properties arising from quantum size effects. These small systems will provide opportunities to investigate magnetism of zero-dimension systems. A zero-dimensional object is usually called a quantum dot or artificial atom because its electronic states are few and sharply separated in energy, resembling those within an atom. Since the surface to volume ratio is the highest for zero-dimensional systems, most of the changes to magnetic behavior will be observed in ultra-fine magnetic particles. Chemically functional magnetic nanoparticles, comprised of a Fe3O4 magnetite core encased in a thin aliphatic carboxylate, have been prepared by sequential high temperature decomposition of organometallic compounds in a coordinating solvent. In this work, aliphatic carboxylic acid chain length, reaction temperature and duration were varied to produce small core diameters. In order to correlate size effects with changes in particle formation, it is important to have a through understanding of the structural components. This includes studies of the core size, surface effects, decomposition, electronic properties and magnetic behavior. Quantum size effects were observed in the (Fe3O4)X(carboxylate)Y monolayer protected clusters (MPCs) when the average core diameter was ≤ 2.0 nm, evidenced by a blue shifted absorbance band maxima, suggesting the onset of quantum confinement. These (Fe3O4)X(carboxylate)Y MPCs also posses a complex interplay between surface and finite size effects, which govern the magnetic properties of these zero-dimensional systems. These MPCs are all superparamagnetic above their blocking temperatures with total magnetic anisotropy values greater than the bulk value due to an increase in surface and magnetocrystalline anisotropy. A non-linear decrease in saturation magnetization (MS) [Bohr Magneton] per cluster) as a function of the reciprocal of core radius have been attributed to surface effects such as a magnetically inactive layer or an increase in spin disorder as core diameter decreases. The reduced core dimensions of these MPCs make them ideal candidates for further investigation of quantum magnetic systems.
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Cuko, Andi. "Modelling nano-oxide materials with technological and environmental relevance : silica, titania and titanosilicates Predicting size-dependent emergence of crystallinity in nanomaterials: titania nanoclusters versus nanocrystals Global optimisation of hydroxylated silica clusters: A cascade Monte Carlo Basin Hopping approach." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS368.
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Dans cette thèse, nous nous concentrons sur la modélisation des nano matériaux à base de titane, de silice et de titanosilicate en raison de leur importance technologique. Pour de tels systèmes, d'abord, nous avons identifiez les structures plus stables au moyen des méthodes d'optimisation global. Dans un deuxième temps, nous avons étudié les propriétés structurelles, énergétiques et électroniques de ces nanoparticules en fonction de leur taille, en extrapolant parfois jusqu'à l'échelle macroscopique. Pour une telle caractérisation, nous avons utilisé des méthodes quantiques basées sur la Théorie Fonctionnelle de la Densité. Des résultats obtenus, nous pouvons prédire que: (i) la cristallinité des nanoparticules d'oxyde de titane, qui est la propriété clé pour son activité photocatalytique, émergerait lorsque les nanoparticules atteignent une taille supérieure à 2,0-2,5 nm; (ii) le mélange d'oxyde de titane et de silice pour former des titanosilicates, se révèle thermodynamiquement favorable à l'échelle nanométrique, contrairement à l'échelle macroscopique; (iii) l'hydratation des nanoparticules de silice et de titane, qui joue un rôle important dans le processus d'agrégation et de nucléation pendant la synthèse de nanoparticules plus grandes, est contrôlée par les facteurs environnementaux tels que la température et la pression de vapeur d'eauIn this thesis we focus on modelling of titania, silica and titanosilicate based nano materials because of their technological importance as they are employed in heterogeneous (photo-)catalysis, in electronics gas-sensing etc. to cite a few. For such systems, we firstly performed global optimization studies in gas-phase and water containing environments in order to identify the structures of nanoparticles. Secondly, we studied structural, energetic and electronic size-dependent properties of such nanoparticles as well as their reducibility, extrapolating up to the bulk macroscopic level in some cases. For such characterization we use accurate quantum mechanical methods based on the Density Functional Theory (DFT). Our results point to a series of important predictions such us: i) the crystallinity of titania nanoparticles, which is the key property for the photoactivity, is predicted to emerge when nanoparticles become larger than 2.0-2.5 nm; ii) the mixing of titania and silica to form titanosilicates is found be thermodynamically favorable at the nanoscale, contrary to the bulk; iii) the hydration of silica and titania nanoclusters, which plays an important role in the aggregation and nucleation process during the synthesis of larger nanoparticles, is controlled by environmental factors such as temperature and water vapor pressure as predicted from calculated phase diagrams
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Li, Yu-Chi, and 李昱錡. "Size-tunable copper nanocluster aggregates and their application in hydrogen sulfide sensing on paper-based devices." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/91552947742911627223.
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碩士國立臺灣大學
化學研究所
104
An one-pot approach has been developed to control the size of penicillamine-copper nanocluster (PA-Cu NC) aggregates through the addition of different concentrations of polystyrene sulfonate (PSS). The PSS-PA-Cu NC aggregates are photoluminescent and have excellent water dispersity, better photostability under UV irradiation, and remarkable sensitivity towards H2S (limit of detection: 650 nM) compared to PA-Cu NC aggregates without PSS dispersion. The practicability of this probe was verified by determination of the H2S concentration in hot spring-water samples. The PSS-PA-Cu NCs were integrated into a portable microfluidic paper-based analytical device (μPAD) for the on/off determination of H2S in hot spring-water samples. This platform targets released H2S gas to avoid interference from other ions in water samples in contrast with conventional H2S detection methods which can only determine H2S directly from solution. The PSS-PA-Cu NC/μPADs use ultra-low sample volumes (5 μL) and feature shorter analysis times (~30 min) compared to conventional solution-based methods. The quantitative results not only can be seen by the naked-eye, as well as facilely recorded and transmitted using a smartphone but also can determined by microplate reader. The LOD of the PSS-PA-Cu NC/μPAD device was 1 μM. In conclusion the PSS-PA-Cu NC/μPADs have great potential to monitor H2S levels in gaseous and liquid samples.
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Yang, Sheng-Hui, and 楊勝輝. "Investigation into Temperature and Size Effects on Behaviors of Water Nanoclusters." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/25027517322540011509.
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碩士國立中山大學
機械與機電工程學系研究所
94
Structure properties of water clusters are investigated in this study by means of molecular dynamics simulations. The oxygen density profile, dipole moment and hydrogen bond properties of water clusters are all examined. The temperature dependence and size dependence of the structure properties are also explored in the present study. Upon the molecular dynamics simulations, the flexible three-centered (F3C) water potential is used to model the inter- and intra-actions of the water molecule. It is found that as the temperature rises, the density of the oxygen and the average number of hydrogen bonds per water molecule will decrease. The effect of cluster size, however, is less significant on the structure properties. The differences between the structural properties for the surface region and those for the interior region of the cluster are also investigated. It is found that as the temperature rises, the average number of hydrogen bonds per water molecule decreases, but the ratio of surface water molecules increases. After comparing the water densities in interior regions and the average number of hydrogen bonds in those regions, we find there is no apparent size effect on water molecules in the interior region, whereas the size of the water cluster has a significant influence on the behavior of water molecules at the surface region.
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Liu, Chien-Hung, and 劉健宏. "Study of site-selective photoluminescence in gold nanoclusters." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/14810902815242833948.
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碩士中原大學
物理研究所
100
Photoluminescence (PL) from the Au nanoclusters (NCs) has been investigated. Upon scanning the excitation light with energy below 2.1 eV down to 1.6 eV, the PL narrows and begins shifting linearly with excitation energy. The time-resolved PL was studied and the PL decay traces of Au NCs were found to depend on the excitation and emission energies. We observed absorption peak of site-selective PL from photoluminescence excitation (PLE). The effect of site-selective PL was found to depend on the capping molecules of Au NCs. In addition, we studied the PL in Au NCs in low temperatures, and found it involves different emission mechanism.
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Hsieh, Cheng-Yin, and 謝政穎. "Syntheses, Characterizations and Applications of CdSe Magic-Size Nanoclusters and 2D Nanosheets." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/41856149167442924022.
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Belomoin, Gennadiy A. "Effect of size and surface structure manipulation on the luminescent properties of silicon nanoclusters /." 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3242793.
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Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6455. Adviser: Munir Nayfeh. Includes bibliographical references (leaves 103-109) Available on microfilm from Pro Quest Information and Learning.
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Erickson, Nathan William. "Size distributions and nonlinear optical enhancement of silver nanoparticles produced by LAM." Thesis, 2011. http://hdl.handle.net/2152/ETD-UT-2011-05-3445.
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In this dissertation, I will look into the size distribution of silver nanoparticles produced by laser ablation of microparticles (LAM). I will investigate the role of both pulsed and continuously operating nozzles on the size distribution. In addition, I will examine any deviations from the previously observed log-normal size distribution for silver nanoparticles comparing previous collection techniques involving supersonic jet impaction with a current time of flight mass spectrometer (TOF-MS). These new observations will be made in situ using a Wiley-McLaren TOF-MS with a reflector and multiphoton ionization and will mainly focus on the smaller sized nanoparticles. An introduction to enhancing a second harmonic optically generated signal will also be investigated involving silver nanocomposites while utilizing a polarized crossed-beam femtosecond laser technique.text
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Lee, Kuo-Hao, and 李國豪. "Size and Photoluminescence Evolution of Gold Nanoclusters with Bovine Serum Albumin as Templates during X-ray Irradiation." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/49420083247112535407.
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碩士國立交通大學
電子物理系所
101
Gold nanoparticles were synthesized by intense X-ray irradiation in the presence of bovine serum albumin (BSA). By control the molar concentration between BSA and gold, we can adjust the gold nanoparticles size from 20 nm to 1.9 nm. The influence of these nanoparticles size on the optical properties of these ultra-small gold nanoclusters (<2 nm) was investigated. Our results show that the gold nanoclusters capped with bovine serum albumin (BSA) produced photoluminescent with two major emission wavelength from gold nanoclusters (635 nm and 710 nm). We confer the source of emission wavelength at 635 nm is core of gold nanoclusters band gaps by temperature dependent fluorescence spectroscopy. Simultaneously, we also try to synthesize gold/silver complex nanoclusters and measure their biocompatibility. The BSA coated gold nanoclusters, gold/silver complex nanoclusters and silver nanoclusters exhibit higher fluorescent intensity and good biocompatibility suitable for applications in bio-image and sensitive fluorescence sensors.
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Yang, Ta-Wei, and 楊大緯. "(I) A First-principles Investigation on the Structure and Physical Properties of the Magic-size (CdSe)13 Nanoclusters(II) Theoretical Study on the Decay Constant in Quantum Transport through Single Molecular Junctions." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/khv8py.
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碩士國立臺灣師範大學
化學系
105
This study includes two parts. The first-part is a first-principles investigation on the structure and physical properties of the magic-size (CdSe)13 nanoclusters, and the second part is a theoretical study on the decay constant in quantum transport through single molecular junctions. In first part, we investigated the structure and configuration of the experimentally synthesized CdSe nanoclusters using computational approaches. Based on previous literatures, we examined the C3-cage-core, the C1-cage, and the C3V-tubular structure for the (CdSe)13 nanoclusters. Both the bare and the ligated clusters were considered, using the methylamine and ethylamine to mimic the octylamine and oleylamine used in the experiment. Based on our calculation results, we propose a dimerized tubular model for the CdSe clusters, which is drastically different from the previous C3-cage-core model. This model not only matches well with the experimental SAXS result for the size and shape of the nanoclusters, but also shows a good correspondence to the absorbance and CD spectra. The underlying physical reason for the dimerization is also proposed. In second part, several theoretical methods were used to study the attenuation factor in the quantum transport of different molecular frameworks. In electron transport through single molecules, it is known that the quantum conductance decreases exponentially with increasing molecular length, and the extent of decrease is determined by the decay constant. Previous Hückel Model studies, suggested that the decay constant may be determined solely by the repeating unit of the molecular framework, and is not affected by the electrode or the linkage group, but a first-principles validation has not yet been performed. Here we investigated different molecules consisted of single, double, and triple-bond frameworks, and adopted three theoretical methods of different levels to calculate the molecular conductance. In the first method, an orthogonal Wannier basis set and a virtual electrode was adopted to study the central molecules. In the second method, we use the Green’s Function method to study the molecule linked to a nanographene electrode. In the third one, we apply the modular approach to the Hamiltonian of the repeating unit derived ab initially, and calculate the decay constant.
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Chang, Chun-Chih, and 張鈞智. "Theoertical Studies of Chemical Reactions on Rhodium Nano Clusters: I. Bond scission of NO over rhodium and nickel small-size clustersII. CO2 dissociation on various structures of rhodium nanoclusters (Rh13) supported on unzipped graphene oxide III. Dehydrogenation of ethane, propane and butane on Rh13 clusters supported on unzipped graphene oxide、IrO2 (110) and TiO2 (110)." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/84735474505585045774.
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博士國立臺灣師範大學
化學系
104
We applied density-functional theory (DFT) to investigate the adsorption and dissociation of NO on Rh19 and Ni19 clusters with a double-icosahedral (DI) structure. The transition structures of the NO dissociating on the potential-energy surfaces were derived with the nudged-elastic-band (NEB) method. The adsorption energies of NO molecules on the rhombus-center region of DI clusters are -2.53 eV and -2.78 eV with the N-O bond elongated to 1.33Å and 1.35 Å, respectively, on Ni19 and Rh19, compared to 1.16 Å of the gaseous NO counterpart. The barriers to the dissociation of N-O on both DI-Rh19 (Ea = 0.24 eV) and DI-Ni19 (Ea = 0.42 eV) clusters are small, indicating that the rhombus-center region of DI metal clusters might activate the scission of the N-O bond. To understand the size effects of the rhodium nanocluster, we first investigated the catalytic activity of various rhodium nanoclusters (Rhn, n = 1, 4, 5, 8, 13 amd 14) on unzipped graphene oxide (Rhn/UGO). The calculated result exhibited that the catalytic activity of CO2 dissociation on Rh13/UGO systems is better than other systems. The catalytic activity of various structures of Rh13 clusters on unzipped graphene oxide (Rh13/UGO) has been further investigated for comparison with Rh13 nanoclusters and Rh(111) surfaces. In, addition, the binding energy of Rh atoms on UGO is less than the cohesive energy (- 5.75 eV) of bulk Rh, indicating that the Rh atoms adsorbed on UGO tend to collect into clusters. We systematically calculated the energies of adsorption of CO2 on Rh13 nanoclusters in various stable shapes on unzipped graphene oxide; Rh13-Ih/UGO had the largest energy (where the Ih representing icosahedral shape), -1.18 eV, with the C–O bond being elongated from 1.17 to 1.29 Å; the barrier for dissociation of CO2 on Rh13-Ih/UGO is, accordingly, the smallest (Ea = 0.45 eV), indicating that Rh13-Ih/UGO might act as an effective catalyst to adsorb and to activate the scission of the C-O bond of CO2 . We finally discussed the adsorption and dehydrogenation of alkanes (CnH2n+2, n = 2, 3, 4) on a low-symmetry Rh13 cluster (Rh13-Ls) in comparing with the system of the same cluster (Rh13-Ls) but supported on either an unzipped graphene-oxide (UGO) sheet (Rh13-Ls/UGO), or an IrO2 (110) surface (Rh13-Ls/IrO2), or TiO2 (110) surface (Rh13-Ls/TiO2) to understand the different support effects between Rh13-Ls and the various supports. The adsorption energies, calculated with density-functional theory, of these alkanes follow the order Rh13-Ls/UGO ≈ Rh13-Ls/ TiO2 > Rh13-Ls > Rh13-Ls/ IrO2. Our proposed reaction path for the dehydrogenation of ethane, propane and butane on Rh13-Ls/UGO has the first barriers of height 0.21, 0.22 and 0.16 eV, respectively, to form -C2H5, -C3H7 and -C4H9. In comparing with the barriers on Rh13-Ls、Rh13-Ls/ TiO2 and Rh13-Ls/ IrO2, we found that the barrier on Rh13-Ls/UGO is the lowest for all alkanes. We also studied the electronic properties, such as charge differences, density of states, electron localization functions and interaction energies, to explain the interaction between adsorbates and substrates, using density-functional theory (DFT).