An important direction in nanoscale science is to synthesize materials whereby atomic clusters serve as the building blocks. Properties of these clusters can be controlled through size and composition, and such an approach offers a pathway toward designing larger, customized materials. One way to stabilize such materials is through the use of ligated clusters. Ag4Ni2(DMSA)4 is one such cluster, the first with a bimetallic core, and has been stabilized by the experimental group of A. Sen at The Pennsylvania State University. The theoretical studies undertaken in this thesis were directed toward providing information on the atomic structure, nature of electronic states, optical spectra, and any magnetic information of this new species. Theoretical studies have also been carried out on various clusters to provide input into the fragmentation data obtained through MS/MS experiments.

Nanoclusters a base de platina vêm sendo amplamente estudados devido à possibilidade de ajustar suas propriedades físicas e químicas através da manipulação de seu tamanho, forma e composição. No entanto, nossa compreensão em nível atomístico dos mecanismos que determinam a estabilidade desses sistemas está longe de ser ideal. Nesta dissertação de mestrado, utilizamos a teoria do funcional da densidade, empregando o método de projeção de onda aumentada com a aproximação do gradiente generalizado, para investigar as propriedades enérgicas, estruturais e eletrônicas de nanoligas PtnMT55-n (MT = Fe, Co, Ni, Cu, Zn). Usando uma energia relativa (energia excedente) para medir a estabilidade de uma nanoliga, sendo obtidas as seguintes composições de menor energia: Pt35Fe20, Pt42Co13, Pt28Ni27, Pt20Cu35 e Pt20Zn35. Com exceção da estrutura do tipo caroço-casca Pt42Co13 icosaedrica (ICO), os demais sistemas possuem ambos os átomos Pt e MT expostos diretamente à região de vácuo, o que é interessante para reações químicas. Das análises estruturais, obtivemos a relação entre tamanho, ordem de ligação e tendência de segregação. Para Zn55 e Pt55, as estruturas de caroço reduzido (RCORE) são preferidas, enquanto para MTs como Fe, Co, Ni e Cu que são menores do que a Pt em 10.6, 11.3, 11.3 e 8,5%, a geometria icosaedrica é favorecida. Portanto, a combinação de Pt com átomos de MT em uma nanoliga (PtMT) favorece a configuração ICO para átomos de MT pequenos (Fe, Co, Ni e Cu), devido a grande liberação de tensão. Já PtnZn55-n que apresentam pequena diferença de tamanho (Zn é menor do que a Pt em apenas 2,1%), consequentemente, a estabilização de estrutura ICO não é possível e uma estrutura RCORE é obtida para todas as composições analisadas. A posição do centro de gravidade dos estados-d ocupados em relação ao nível de Fermi pode ser ajustada em função da composição de Pt. Assim, a energia de adsorção do adsorbato para o nanoligas pode ser alterada, o que afeta a reatividade das nanoligas PtnMT55-n. / Platinum-based nanoclusters have been widely studied due to the possibility to tune their physical and chemical properties through size, shape, and composition. However, our atom-level understanding of the mechanisms that determines the stability of those systems is far from ideal. In this dissertation, we use the density functional theory, using the projected augmented wave method with the generalized gradient approximation, to investigate the energetic, structural, and electronic properties of the PtnTM55-n (TM = Fe, Co, Ni, Cu, Zn) nanoclusters. Using a relative energy (excess energy) to measure the stability of a nanoalloy, we have obtained the lowest energy compositions Pt20Fe35, Pt42Co13, Pt28Ni27, Pt20Cu35, and Pt20Zn35. Except for the core-shell Pt42Co13 icosahedron (ICO) structure, the other systems have both Pt and TM atoms exposed directly to the vacuum region, which is interesting for chemical reactions. From structural analyses we have obtained an interplay of size mismatch, bond-order parameter, and the segregation tendency. For Zn55 and Pt55, the reduced-core (RCORE) structures are preferred, while for small size TMs, like Fe, Co, Ni, and Cu that are smaller than Pt by 10.6, 11.3, 11.3, and 8.5%, the icosahedral geometry is stabilized. The combination of Pt with TM atoms in a nanoalloy (PtTM) favors the ICO configuration for small TM atoms (Fe, Co, Ni, and Cu), because of the larger release of the strain energy. PtnZn55-n presents a small size mismatch (Zn is smaller than Pt by only 2.1%), consequently, the ICO stabilization is not possible and RCORE structure is obtained for all compositions. The position of the center of the gravity of the occupied d -states in relation to the Fermi level can be tuned as a function of the Pt composition. Thus, the adsorption energy of adsorbate to the nanoalloys can be changed, which can affect the reactivity of the PtnTM55-n nanoclusters.

Gold monolayer-protected nanoclusters (MPCs) with average diameters of 1-5 nm protected by alkane- and arenethiolates were synthesized. Mixed-monolayer protected nanoparticles (MMPCs) were prepared by functionalizing hexanethiolate-protected MPCs with either 11-mercaptoundecanoic acid (MUA-MMPC), 11-mercaptoundecanol (MUO-MMPC), or 4-aminothiophenol (ATP-MMPC) using ligand place exchange. Presentation of various chemical reagents such as nucleophile, acid, or base and change in physical environment through ultrasonic and thermal irradiation resulted in changes to particles and their physical properties. Thermogravimetric analysis (TGA) was used to measure maximum temperature of the derivated thermogravimetric peaks (Tmax,DTG) as a means of comparing temperature dependence of mass loss. The absorption spectrum within the surface plasmon resonance (SPR) band was monitored over time throughout chemical and ultrasonic treatments to assess stability of these particles in solution. MUA-MMPCs and ATP-MMPCs were self-assembled with Cu2+, poly(sodium 4- styrenesufonate), poly(allylamine hydrochloride), generation 2 polyamidoamine dendrimer, and C60 fullerene as linking molecules on functionalized glass substrates using a layer-by-layer approach resulting in nanoparticle multi-layer films. The thin films were characterized using UV-vis spectroscopy during deposition, and then before and after chemical treatment, and thermal and ultrasonic irradiation to assess stability of nanocomposites. Finally, an in-situ cross-linking approach was used to deposit gold MPC-C60 thin film nanocomposite on functionalized glass substrate. UV-vis spectroscopy was used to monitor deposition rates of the resulting film in comparison with the MPC-C60 multilayer film assembled layer-by-layer. These MPC-C60 nanocomposites were also characterized using conductive atomic force microscopy (C-AFM).

In this study, we used the Density functional theory (DFT) and Molecular dynamics (MD) to obtain the suitable hydrogen storage structure of Rh nanoclusters on the boron nitride sheet and Li atoms on the graphene. The reason of studying two type of nanoparticles is that there are two adsorption method in hydrogen storage, such as the adsorption of hydrogen molecules and hydrogen atoms. Using Rh nanoclusters on the boron nitride sheet to store hydrogen belong to the adsorption of hydrogen atoms. Using Li atoms on the graphene to store hydrogen belong to the adsorption of hydrogen molecules. We use these two models to simulate the hydrogen storage in this study. There were four parts in this study: The first part: The Density functional theory is utilized to obtain the configuration and corresponding energy of Rh nanoclusters, boron nitride sheet, Rh nanoclusters adsorbed on the boron nitride sheet, Li atoms adsorbed on the graphene, hydrogen adsorbed on the graphene and hydrogen adsorbed on the Li atoms. Then, we use the Force-matching method (FMM) to modify the parameters of potential function by the reference data which are obtained by Density functional theory. Finally, we use the modified parameters of potential function to perform Molecular dynamics in this study. The second part: In this part, the dynamical behavior of Rh nanoclusters with different sizes on the boron nitride sheet are investigated in temperature-rise period. The migration trajectory, square displacement and mean square displacement of the mass center of the Rh nanoclusters are used to analyze the dynamics behavior of Rh nanoclusters on the boron nitride sheet. The third part: In this part, the pristine graphene and graphen with Li atoms are investigated the efficiency of hydrogen storage at different temperature and pressure. In order to obtain the temperature (77K and 300K) and pressure effect of hydrogen storage, the densimetric distribution and gravimetric capacity (wt%) are analyzed. The fourth part: The Molecular dynamics is utilized to study the hydrogen storage and delivery when the distance between two graphene is different. Then, the temperature effect (77K and 300K) of hydrogen storage, the gravimetric capacity (wt%) are analyzed. In addition, the gravimetric capacity (wt%) of hydrogen delivery are also analyzed in the larger system space at 300K.

This paper, contain three parts, focus on develop synthesis method for novel functional nanocluster, base on its special optical and reactive property. In the first part, lysozyme VI was mixed with HAuCl4 under acidic condition(pH~3) and yield blue fluorescent Au8 nanocluster. When this Au8 cluster was incubate under alkaline condition (pH~12) a size evolution from Au8 to Au25 took place and monitored with fluorescence spectrum, MALDI MS, DLS. On the other hand, on the role of structural characteristic, fluorescence of Au8 cluster can be quenched by GSH as GSH induced core-etching reaction took place. Take advantage of this reaction, GSH in RBC can be quantitatively analysis by Au8 cluster. Compare with standard medical analysis method, this assay got comparable quantitative result and advantage in environmental friendly, low cost and low sample demand. Follow the first part, it was knowing that Hg2+quench fluorescence of Au25 but Au8 cluster. The second part of research development a ratiometric fluorescence assay for Hg2+ in drinking water sample, by control size evolution of nanocluster mentioned in first part by adding Ag+ into protein direct synthesis nanocluter process. Under optimize condition of bimetallic nanocluster synthesis, two separately fluorescence peak locate under 613 nm and 471 nm represent bigger size and smaller nanoclusters. Using fluorescence intensity ratio of two wavelength, concentration of Hg2+ in water sample can be determined by standard addition method with high reproducibility. Limit of detection was determined to be 0.1 and 0.4 nM, both lower than EPA permitted level in drinking water. On the third part, SA and HAuCl4 was mixed under water contained acetonitrile solution and SA caped nanocluster was form. This nanocluster after self essemble possess special crystalline and surface phenomenon and fit matrix for high reproducible laser desorption/ionization mass spectrometry. Compare with traditional matrix SA, the cluster matrix show 6.6% in RSD with 33%. And the desorption/ionization efficiency of nanocluster matrix is also much higher. Insulin, myoglobin and HSA sample can be quantitative with this matrix with mean RSD lower than 10%.

Ethylene adsorption was studied by use of DFT/B3LYP with basis set 6-31G(d,p) in Gaussian&lsquo / 03 software. It was found that ethylene adsorbs molecularly on the Ni13 nanocluster with &amp / #960 / adsorption mode. &amp / #960 / adsorption mode is studied for the Ni10 (1 1 1), Ni13 (1 0 0) and Ni10 (1 1 0) surface cluster as well. Relative energy values were calculated as &amp / #8722 / 50.86 kcal/mol, &amp / #8722 / 20.48 kcal/mol, &amp / #8722 / 32.44 kcal/mol and &amp / #8722 / 39.27 kcal/mol for Ni13 nanocluster, Ni10 (1 1 1), Ni13 (1 0 0) and Ni10 (1 1 0) surface cluster models, respectively. Ethylene adsorption energy was found inversely proportional to Ni coordination number when Ni10 (1 1 1), Ni13 (1 0 0) and Ni10 (1 1 0) cluster models and Ni13 nanocluster were compared with each other. DFT/B3LYP and basis set of 86-411(41d)G in Gaussian&lsquo / 03 was used to investigate Ni55 nanocluster. Ethylene adsorption on Ni55 nanocluster was studied by means of equilibrium geometry calculations with &amp / #960 / adsorption modes for two different coordination numbers as 6 and 8. The related adsorption energies were approximately found as -22.07 and -14.82 kcal/mol for these coordination numbers of surfaces, respectively. In addition, the binding energies stated in literature that are for Ni2 dimer and Ni13 nanoclusters were considered together with our binding energy results for Ni55 nanocluster. Accordingly, when a correlation line was drawn and the intercept of binding energies was obtained against the value of &amp / #8213 / n&amp / #8722 / 1/3&amp / #8214 / where n is the number of atoms in the cluster / the result of interception gives a good estimation for bulk nickel binding energy at infinite &amp / #8213 / n&amp / #8214 / . This interception result was found as 4.58 eV/atom where the experimental value is reported as 4.45 eV/atom for bulk in the literature. Ehtylene hydrogenation mechanisms were also investigated in terms of the resultant geometries and total energy required for the related mechanism steps.

This diploma thesis presents experimental evidence of a theoretical concept which predicts the self-organization of delta-layers of silicon nanoclusters in the buried oxide of a MOS-like structure. This approach of "bottom-up" structuring might be of eminent importance in view of future semiconductor memory devices. Unconventionally, a 15nm thin SiO2 layer, which is enclosed by a 50nm poly-Si capping layer and the Si substrate, is irradiated with Si+ ions. Ion impact drives the system to a state far from thermodynamic equilibrium, i.e. the local composition of the target is modified to a degree unattainable in common processes. A region of SiOx (x<2) - where x is a function of depth - is formed which is not stable. During annealing, the system relaxes towards equilibrium, i.e. phase separation (via spinodal decomposition and nucleation) sets in. Within a certain time window of annealing, the structure of the system matches with a structure similar to the multidot non-volatile memory device, the principal character of which is a 2D layer of Si nanoclusters of ~3nm in diameter which is embedded in a 3D SiO2 matrix at a distance of ~3nm from the Si substrate. The physical mechanisms of ion mixing of the two Si-SiOx interfaces and subsequent phase separation, which result in the desired sample structure, are elucidated from the viewpoint of computer simulation. In addition, experimental evidence is presented based on various methods, including TEM, RBS, and SIMS. Of particular importance is a novel method of Si nanocluster decoration which applies Ge as contrast enhancing element in TEM studies of tiny Si nanoclusters.

The ability of sub 100 nm nanoparticles to target and modulate the biology of cells will enable major advancements in cellular imaging and therapy in cancer and atherosclerosis. A key challenge is to load an extremely high degree of targeting, imaging, and therapeutic functionality into small, yet stable particles. A general mechanism is presented for thin autocatalytic growth on nanoparticle substrates (TAGS), as demonstrated for a homologous series of < 5 nm textured Au coatings on < 42 nm iron oxide cluster cores. Very low Au supersaturation levels are utilized to prevent commonly encountered excessive autocatalytic growth that otherwise produce thick shells. The degree of separation of nucleation to form the seeds from growth is utilized to control the morphology and uniformity of the thin Au coatings. The thin and asymmetric Au shells produce strong near infrared (NIR) absorbance with a cross section of ~10⁻¹⁴ m², whereas the high magnetic content per particles provides strong r2 spin-spin magnetic relaxivity of 200 mM⁻¹s⁻¹. TAGS may be generalized to a wide variety of substrates and high energy coatings to form core-shell nanoparticles of interest in a variety of applications as diverse as catalysis and bionanotechnology. High uptake of the nanoclusters by macrophages is facilitated by the dextran coating, producing intense NIR contrast both in cell culture and an in vivo rabbit model of atherosclerosis. A novel conjugation technique further allows covalent binding of anti-epidermal growth factor receptor (EGFR) monoclonal antibody (Ab) to the nanoclusters for highly selective targeting to EGFR over expressing cancer cells. AlexaFluor 488 tagged Ab nanocluster conjugates were prepared to correlate the number of conjugated Abs with the hydrodynamic diameter. The high targeting efficacy was evaluated by dark field reflectance imaging and atomic absorbance spectrometry (AAS). Colocalization of the nanoparticles by dual mode in-vitro imaging with dark field and fluorescence microscopy demonstrates the Abs remained attached to the Au surfaces. The extremely high curvature of the Au shells with features below 5 nm influence the spacing and orientations of the Abs on the surface, which has the potential to have a marked effect on biological pathways within cells. These targeted small multifunctional nanoclusters may solve some key molecular imaging challenges for cancer and atherosclerosis. / text

Nanoclusters a base de platina vêm sendo amplamente estudados devido à possibilidade de ajustar suas propriedades físicas e químicas através da manipulação de seu tamanho, forma e composição. No entanto, nossa compreensão em nível atomístico dos mecanismos que determinam a estabilidade desses sistemas está longe de ser ideal. Nesta dissertação de mestrado, utilizamos a teoria do funcional da densidade, empregando o método de projeção de onda aumentada com a aproximação do gradiente generalizado, para investigar as propriedades enérgicas, estruturais e eletrônicas de nanoligas PtnMT55-n (MT = Fe, Co, Ni, Cu, Zn). Usando uma energia relativa (energia excedente) para medir a estabilidade de uma nanoliga, sendo obtidas as seguintes composições de menor energia: Pt35Fe20, Pt42Co13, Pt28Ni27, Pt20Cu35 e Pt20Zn35. Com exceção da estrutura do tipo caroço-casca Pt42Co13 icosaedrica (ICO), os demais sistemas possuem ambos os átomos Pt e MT expostos diretamente à região de vácuo, o que é interessante para reações químicas. Das análises estruturais, obtivemos a relação entre tamanho, ordem de ligação e tendência de segregação. Para Zn55 e Pt55, as estruturas de caroço reduzido (RCORE) são preferidas, enquanto para MTs como Fe, Co, Ni e Cu que são menores do que a Pt em 10.6, 11.3, 11.3 e 8,5%, a geometria icosaedrica é favorecida. Portanto, a combinação de Pt com átomos de MT em uma nanoliga (PtMT) favorece a configuração ICO para átomos de MT pequenos (Fe, Co, Ni e Cu), devido a grande liberação de tensão. Já PtnZn55-n que apresentam pequena diferença de tamanho (Zn é menor do que a Pt em apenas 2,1%), consequentemente, a estabilização de estrutura ICO não é possível e uma estrutura RCORE é obtida para todas as composições analisadas. A posição do centro de gravidade dos estados-d ocupados em relação ao nível de Fermi pode ser ajustada em função da composição de Pt. Assim, a energia de adsorção do adsorbato para o nanoligas pode ser alterada, o que afeta a reatividade das nanoligas PtnMT55-n. / Platinum-based nanoclusters have been widely studied due to the possibility to tune their physical and chemical properties through size, shape, and composition. However, our atom-level understanding of the mechanisms that determines the stability of those systems is far from ideal. In this dissertation, we use the density functional theory, using the projected augmented wave method with the generalized gradient approximation, to investigate the energetic, structural, and electronic properties of the PtnTM55-n (TM = Fe, Co, Ni, Cu, Zn) nanoclusters. Using a relative energy (excess energy) to measure the stability of a nanoalloy, we have obtained the lowest energy compositions Pt20Fe35, Pt42Co13, Pt28Ni27, Pt20Cu35, and Pt20Zn35. Except for the core-shell Pt42Co13 icosahedron (ICO) structure, the other systems have both Pt and TM atoms exposed directly to the vacuum region, which is interesting for chemical reactions. From structural analyses we have obtained an interplay of size mismatch, bond-order parameter, and the segregation tendency. For Zn55 and Pt55, the reduced-core (RCORE) structures are preferred, while for small size TMs, like Fe, Co, Ni, and Cu that are smaller than Pt by 10.6, 11.3, 11.3, and 8.5%, the icosahedral geometry is stabilized. The combination of Pt with TM atoms in a nanoalloy (PtTM) favors the ICO configuration for small TM atoms (Fe, Co, Ni, and Cu), because of the larger release of the strain energy. PtnZn55-n presents a small size mismatch (Zn is smaller than Pt by only 2.1%), consequently, the ICO stabilization is not possible and RCORE structure is obtained for all compositions. The position of the center of the gravity of the occupied d -states in relation to the Fermi level can be tuned as a function of the Pt composition. Thus, the adsorption energy of adsorbate to the nanoalloys can be changed, which can affect the reactivity of the PtnTM55-n nanoclusters.

The worldwide growing demand for clean energy leads to necessity for new energy generation methods. Nuclear power generators are an excellent solution for these demands. The feasibility of nuclear power production depends on the performance of structural materials under the harsh conditions in nuclear reactors such as high radiation flux and high temperature. The development of structural materials to withstand such conditions is a big challenge and crucial for advanced nuclear fission and fusion reactors. Several materials are developed, amongst them Oxide Dispersion Strengthened (ODS) steels also called Nanostructured Ferritic Alloys (NFA). NFA consist of Fe-Cr based ferritic/martensitic steels that contain highly dispersed nanometer-size Y-Ti-O nanoclusters, and are manufactured via powder metallurgy. The presence of nanoclusters leads to high temperature stability and radiation resistance. Despite many research activities using advanced analytical techniques such as Transmission Electron Microscopy and Atom Probe Tomography as well as theoretical calculations many properties of the nanoclusters, such as the detailed atomic structure and composition as well as their efficiency for trapping He, vacancies and self-interstitial atoms (SIA), are still not completely understood. In the first part of this thesis work, six different structural models for atomic clusters in bcc Fe which may contain O, Y, Ti, and vacancies (v) are investigated by Density Functional Theory (DFT) calculations. Results for clusters with identical numbers of constituents (O, Y, Ti, and v) are compared. The most important finding consists in the statement that the data on the stability or energetics of the relaxed clusters are comparable although their atomic configurations are often different. This contradicts the prevailing opinion in the related theoretical literature that favors the so-called structure-matching model, which is also investigated in this work. In all studied cases, the absolute value of the total binding energy per cluster constituent becomes lower if Y is partially replaced by Ti, i.e. the driving force for the growth of O-Y clusters is higher than that of O-Y-Ti clusters. This may be correlated with the experimental observation that the presence of Ti leads to a reduction of the size of the oxide clusters in NFA and to a higher dispersion. A further major result is the finding that cage-like (CL) clusters and clusters with an oxygen atom in the center (cage) have a similar total binding energy. If Ti is not present such clusters are slightly more stable than the corresponding CL clusters. The opposite holds for clusters with Ti. It is also shown that adding O atoms to CL cluster leads to structures with O in the center. Vacancies are an important for the stabilization of the cluster due to the very strong binding with O. We infer that the Ov pair may be the origin for cluster nucleation growth. Because of limited computational resources, the dimension of clusters investigated by DFT is still below or close to the limit of the experimental resolution of methods allowing for a simultaneous determination of atomic structure and composition of the clusters. These small clusters may be considered as nuclei for further structural evolution and growth during which a selection of the most favored cluster structures could occur. In the second part of the work four different cluster structures are used to investigate their ability to trap irradiation defects He, v and SIA. These defects are inserted on different positions inside and in the environment of the clusters, the total energy of the corresponding supercell is minimized by DFT, and the binding and incorporation energy of the three kinds of defects is determined. He in the center of a CL cluster is more stable than on interfacial vacant sites (IVS). In CL O-Y clusters, He on an IVS is more stable than in clusters with oxygen in the center, whereas there is no significant difference between the two kinds for clusters with Ti. Up to a distance of 1.5 times the iron lattice constant from the cluster center He is not stable on most of the octahedral and tetrahedral interstitial sites in the Fe matrix. Instead, He is shifted towards positions closer to the cluster. Relaxation occurs to known IVS as well as to previously unknown interfacial interstitial sites (IIS). Moreover, two or three He atoms are placed on sites found to be stable after adding a single He. The corresponding binding and incorporation energies obtained after relaxation are nearly equal to the sum of the values for the interaction with a single He atom. However, placing He dimers or trimers in the environment of a vacancy that belongs to the cluster may also lead to relatively low values of the incorporation energy. Also, He jump barriers between interfacial sites and the center of CL clusters are determined. In the CL O-Y cluster, the barriers are lower than in the CL O-Y-Ti cluster, i.e. trapping and release of He is easier in the former than in the latter. The main reason for the high He trapping efficiency is the low electron density in the empty regions of the oxide-like structure of the clusters. Vacancy and SIA interaction with the clusters is also attractive. The binding energy of a vacancy strongly depends on the site where the vacancy is inserted while in all the studied cases the SIA is annihilated at the cluster-iron interface. Present results clearly demonstrate that the oxide-based nanoclusters are strong traps for irradiation-induced defects, which is in agreement with experimental findings.