Access and use of this website and the material on it are subject to the Terms and Conditions set forth at Gold cluster carbonyls: saturated adsorption of CO on gold cluster cations, vibrational spectroscopy, and implications for their structures Fielicke, A.; vonHelden, G.; Meijer, G Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Questions? Contact the NRC Publications Archive team atPublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information. NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. For the publisher's version, please access the DOI link below./ Pour consulter la version de l'éditeur, utilisez le lien DOI ci-dessous.http://doi.org/10.1021/ja0509230Journal of the American Chemical Society, 127, 23, pp. 8416-8423, 2005-06- Abstract:We report on the interaction of carbon monoxide with cationic gold clusters in the gas phase. Successive adsorption of CO molecules on the Aun + clusters proceeds until a cluster size specific saturation coverage is reached. Structural information for the bare gold clusters is obtained by comparing the saturation stoichiometry with the number of available equivalent sites presented by candidate structures of Au n + . Our findings are in agreement with the planar structures of the Aun + cluster cations with n e 7 that are suggested by ion mobility experiments [Gilb, S.; Weis, P.; Furche, F.; Ahlrichs, R.; Kappes, M. M. J. Chem. Phys. 2001, 116, 4094]. By inference we also establish the structure of the saturated Aun(CO)m + complexes. In certain cases we find evidence suggesting that successive adsorption of CO can distort the metal cluster framework. In addition, the vibrational spectra of the Au n(CO)m + complexes in both the CO stretching region and in the region of the Au-C stretch and the Au-C-O bend are measured using infrared photodepletion spectroscopy. The spectra further aid in the structure determination of Aun + , provide information on the structure of the Aun + -CO complexes, and can be compared with spectra of CO adsorbates on deposited clusters or surfaces.

The adsorption of carbon monoxide on rhodium clusters in the size range of 3-15 atoms is studied in the gas phase using the frequency of the internal CO stretch, ν(CO), to probe the bonding situation of the CO. The IR absorption spectra of neutral, cationic, and anionic Rh n CO complexes are measured in the frequency range of ν(CO), between 1650 and 2200 cm -1 , using IR multiple photon dissociation spectroscopy. We find that for most clusters adsorption in an atop position (µ 1 ) is preferred; however, for some clusters, CO in bridging (µ 2 ) or hollow (µ 3 ) sites can be identified as well. Comparison with DFT calculations carried out for the smallest cluster complexes Rh n CO +/0/-(n ) 3 and 4) shows that the experimentally identified CO adsorption sites correspond to the energetically favored positions.

Simulations of the material deposition in extrusion-based additive manufacturing Prediction of the strand cross-section as function of the processing parameters Negative linear relationship between the printing force and the printing speed Abstract We propose a numerical model to simulate the extrusion of a strand of semi-molten material on a moving substrate, within the computation fluid dynamics paradigm. According to the literature, the deposition flow of the strands has an impact on the inter-layer bond formation in extrusion-based additive manufacturing, as well as the surface roughness of the fabricated part. Under the assumptions of an isothermal Newtonian fluid and a creeping laminar flow, the deposition flow is controlled by two parameters: the gap distance between the extrusion nozzle and the substrate, and the velocity ratio of the substrate to the average velocity of the flow inside the nozzle. The numerical simulation fully resolves the deposition flow and provides the cross-section of the printed strand. For the first time, we have quantified the effect of the gap distance and the velocity ratio on the size and the shape of the strand. The cross-section of the strand ranges from being almost cylindrical (for a fast printing and with a large gap) to a flat cuboid with rounded edges (for a slow printing and with a small gap), which substantially differs from the idealized cross-section typically assumed in the literature. Finally, we found that the printing force applied by the extruded material on the substrate has a negative linear relationship with the velocity ratio, for a constant gap.

We investigate experimentally and numerically the influence of the processing conditions on the cross-section of a strand printed by material extrusion additive manufacturing. The parts manufactured by this method generally suffer from a poor surface finish and a low dimensional accuracy, coming from the lack of control over the shape of the printed strands. Using optical microscopy, we have measured the cross-sections of the extruded strands, for different layer heights and printing speeds. Depending on the processing conditions, the cross-section of the strand can vary from being almost circular to an elongated rectangular shape with rounded edges. For the first time, we have compared the measurements of strands' cross-sections to the numerical results of a three-dimensional computational fluid dynamics model of the deposition flow. The proposed numerical model shows good agreement with the experimental results and is able to capture the changes of the strand morphology observed for the different processing conditions.

We report on the size and charge dependence of the C-O stretching frequency, ͑CO͒, in complexes of CO with gas phase anionic, neutral, and cationic cobalt clusters ͑Co n CO −/0/+ ͒, anionic, neutral, and cationic rhodium clusters ͑Rh n CO −/0/+ ͒, and cationic nickel clusters ͑Ni n CO + ͒ for n up to 37. We develop models, based on the established vibrational spectroscopy of organometallic carbonyl compounds, to understand how cluster size and charge relate to ͑CO͒ in these complexes. The dominating factor is the available electron density for backdonation from the metal to the CO * orbital. Electrostatic effects play a significant but minor role. For the charged clusters, the size trends are related to the dilution of the charge density at the binding site on the cluster as n increases. At large n, ͑CO͒ approaches asymptotes that are not the same as found for ͑CO͒ on the single crystal metal surfaces, reflecting differences between binding sites on medium sized clusters and the more highly coordinated metal surface sites.

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Copper nanoparticles with a diameter of 3.0 ± 0.3 nm were generated under vacuum, using a sputtering−aggregation source, and deposited onto glass or highly ordered pyrolytic graphite substrates. Upon exposure to room-temperature air, core−shell particles formed, as determined by surface plasmon resonance spectroscopy, high resolution X-ray photoelectron spectroscopy, and quartz crystal microgravimetry. At 160 °C in air, the core−shell particles converted predominantly to Cu2O. At 220 °C, they converted to CuO almost exclusively. The maximum oxide shell thickness attainable at room temperature was 0.56 nm, as determined by quartz crystal microgravimetry and scanning tunnelling microscope imaging. The shell thicknesses formed are compatible with a simple charge-transfer-based model akin to Mott and Fromhold−Cook theories of metal oxidation processes. The model, which yields the change in the height of the energy barrier to diffusion as a function of shell thickness, is found to be consistent with many adsorbate-induced diffusion processes involving core−shell nanoparticles.

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