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Identification of Different Isomers of Reacted Transition Metal Clusters
Young Dok Kim,Gerd Gantefor 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.3
When gas molecules adsorb on clusters, dissociative or non-dissociative chemisorption can take place. For some cases, both takes place at the same time, leading to the formation of two different isomers. With conventional methods, it is difficult to identify various isomers. In the present work, a novel method to identify isomers of a reacted cluster is presented. Using atomic and molecular reagents, one can obtain various isomers at different concentrations, and these isomers can be identified using ultraviolet photoelectron spectroscopy. Several examples for the identification of different isomers will be presented here.gf
Chemical properties of size-selected Au clusters treated under ambient conditions
Lim, D.C.,Dietsche, R.,Gantefor, G.,Kim, Y.D. North Holland ; Elsevier Science Ltd 2008 Chemical physics letters Vol.457 No.4
Non-scalable chemical behaviors of deposited size-selected clusters under realistic conditions.
Lim, D.C.,Dietsche, R.,Gantefor, G.,Kim, Y.D. Elsevier Science Publishers [etc.] 2009 Chemical Physics Vol. No.
Au cluster anions consisting of 2-13 atoms were soft-landed on native-oxide-covered Si wafers. Reaction of soft-landed clusters with an atomic oxygen atmosphere was studied using X-ray photoelectron spectroscopy (XPS). Au<SUB>5</SUB>, Au<SUB>7</SUB>, and Au<SUB>13</SUB> turned out to show pronounced inertness for Au-oxide formation. When the samples with deposited Au clusters were treated with aqueous NaOH, the inert Au<SUB>5</SUB>, Au<SUB>7</SUB>, and Au<SUB>13</SUB> clusters became reactive towards Au-oxide formation, whereas the other originally reactive clusters became inert. This result can be interpreted in terms of electronic modification of Au clusters by Na, which was also evidenced by Au 4f and Na 1s core level shifts.
Braun, C.,Proch, S.,Seo, H.O.,Kim, Y.D.,Gantefor, G. North Holland ; Elsevier Science Ltd 2012 Chemical physics letters Vol.530 No.-
Relaxation dynamics of optically excited states of Au<SUB>3</SUB><SUP>-</SUP> and Au<SUB>3</SUB><SUP>-</SUP>(H<SUB>2</SUB>O)<SUB>m</SUB> were studied via femtosecond time-resolved photoelectron spectroscopy (fsTRPES). Au<SUB>3</SUB><SUP>-</SUP> exhibits photo-dissociation into either (Au<SUB>2</SUB><SUP>-</SUP>+Au<SUB>1</SUB>) or (Au<SUB>2</SUB>+Au<SUB>1</SUB><SUP>-</SUP>) with a time constant of 1.6ns. One water molecule adsorbed on Au<SUB>3</SUB><SUP>-</SUP> opened new photo-induced dissociation channel with a much shorter time constant. More than one water molecule on Au<SUB>3</SUB><SUP>-</SUP> inhibited photo-dissociation, most likely as a result of facile dissipation of excess energy of optically excited states by nuclear motions of clusters. The photochemical pathway can be controlled by adjusting the number of water molecules interacting with the ionic species.
Lopez Salido, Ignacio,Bertram, Nils,Lim, Dong-Chan,Gantefor, Gerd,Kim, Young-Dok Korean Chemical Society 2006 Bulletin of the Korean Chemical Society Vol.27 No.4
Studies on Ag nanoparticles grown on Highly Ordered Pyrolytic Graphite (HOPG) using HREELS provide different results for smaller and larger particle sizes corresponding to Ag coverages below and above 4 monolayers, respectively. For the larger particles, a positive frequency shift with decreasing particle size and a broadening of the plasmon resonance were observed with decreasing particle size, in line with previous studies on Ag on alumina. For the smaller particles, in contrast, a shift to lower energy with decreasing particle size, and a narrowing of the plasmon resonance with decreasing particle size can be found. The asymmetry of the Ag-features present for Ag coverages above 4 monolayers disappears for Ag coverages below 4 monolayers. The result for the smaller particles can be rationalized in terms of change of the particle growth mode with increasing particle size, which corroborates our STM data, as well as electronic effects due to the metal/support charge transfer.
Electronic relaxation in lead clusters: An indicator of non-metallic behavior
Heinzelmann, J.,Kruppa, P.,Proch, S.,Kim, Y.D.,Gantefor, G. North Holland ; Elsevier Science Ltd 2014 Chemical physics letters Vol.603 No.-
Time-resolved photoemission spectroscopy was used to shed light on the relaxation dynamics of optically excited states of mass-selected Pb<SUB>n</SUB> cluster anions. For clusters with 9-21 atoms, relaxation times were estimated to be several picoseconds as expected for non-metallic species. For Pb<SUB>12</SUB><SUP>-</SUP> and Pb<SUB>13</SUB><SUP>-</SUP>, it was possible to observe photo-excited electrons hopping down the ladder of excited states back to the ground state. For Pb<SUB>28</SUB><SUP>-</SUP>, a long relaxation time of 15ps was found, i.e., although the density of states increased considerably with increasing cluster size, electronic relaxation was still very slow at this cluster size due to its non-metallic nature.
Dollinger, A.,Strobel, C.H.,Bleuel, H.,Seo, H.O.,Park, E.J.,Kim, Y.D.,Gantefor, G. Elsevier 2015 CURRENT APPLIED PHYSICS Vol.15 No.9
Mass-selected W cluster anions in the size range of 20-3500 are deposited on highly ordered pyrolytic graphite (HOPG) surfaces. The structures of resulting thin films are studied using atomic force microscopy. Clusters with more than ~600 atoms form thin films, in which the clusters are not completely merged but survive as individual species to a certain extent. The new class of materials fabricated here (cluster-assemblies) has a potential for applications in heterogeneous catalysis and in optoelectronic devices. In addition, they are interesting from the perspective of basic research.