The 16th International Symposium on Small Particles and Inorganic Clusters (ISSPIC XVI) took place in Leuven July 8-13, 2012.
Atomic scale dynamics of ultrasmall germanium clusters
Controlled nanostructuring of a gold film covered with alkanethiol SAM by low energy cluster implantation
Size matters in scandium doped copper clusters
Ostwald ripening - Movie
Doped AunX+ clustersMaster Theses
Clusters and Laser Spectroscopy
Magnetic coupling in chromium oxide clusters
Clusters are small particles composed of a countable amount of atoms. Small metal clusters exhibit magnetic properties that are very different from the corresponding bulk materials. In addition, the magnetic properties can dramatically change by addition of oxygen atoms. It is theoretically predicted that the exchange coupling between the local magnetic moments in small CrnOm clusters depends strongly on the oxygen content. Specifically the antiferromagnetic chromium dimer, Cr2, may be turned into a ferromagnetic, or non-magnetic system by successive oxygen addition.
In this thesis project you will measure the total magnetic moment of CrnOm clusters (n = 2-4, m = 0-6) as function of the number of chromium atoms and the oxidation state using a magnetic deflection experiment. Hereto, a home-built high vacuum cluster beam setup will be used and the deflection of a particle ensemble in a strong inhomogeneous magnetic field (Stern-Gerlach magnet) will be recorded by a position sensitive detector. The unusual magnetic properties of unsupported clusters will be determined as function of the temperature of the clusters.
The change of exchange coupling between the local magnetic moments in Cr2Om clusters with the increasing of O atoms predicted by density functional theory. The magnetic moment on the Cr sites are marked within the parentheses. (Figure taken from B. V. Reddy et al 86, 3170, 1999)
Promoter: Prof. Peter Lievens, Prof. Ewald Janssens
Daily supervision: Yejun Li, Thanh Tung Nguyen
Type of work: experimental
Number of students: 1
Design of a new magnetic deflection system for atomic clusters
Figure 1: Stern-Gerlach experiment.
Stern and Gerlach developed in 1922 an experiment to deflect particles to illustrate basic principles of quantum mechanics. They were able to demonstrate that electrons and atoms have intrinsically quantum properties. The Stern-Gerlach experiment involves sending a beam of particles through an inhomogeneous magnetic field and observing their deflection (Fig. 1) [1]. In 2012, a Rabi-type magnet was designed, built and installed at the Clusters and Laser Spectroscopy research group for the deflection of atomic clusters (http://fys.kuleuven.be/vsm/class/research/magdef.php). The system will be operational one of the next months.
Figure 2: 3D simulation of a Rabi-type magnet.
In this thesis proposal, alternative designs for the Rabi-type Stern-Gerlach magnet will be considered. The design suffers from the contradictory requirement to provide both a high magnetic field and a high magnetic field gradient. The conception of alternative design will be carried out by making extensive use of 2D and 3D magnetic field simulation tools as available and developed in the Wave Propagation and Signal Processing research group at the KU Leuven – Kulak
Promoter: Prof. Ewald Janssens, Prof. Herbert De Gersem
Daily supervision: Prof. Ewald Janssens, Prof. Herbert De Gersem
Type of work: simulations
Number of students: 1
Metallic nanoclusters for the spatially-controlled attachment of proteins and cells
Immobilization of biomolecules on substrates is required in many different academic as well as industrial areas (e.g. biosensing, catalysis, bioseparation or bioelectronics). Since biomolecules are usually attached to surfaces different from their native environment, maintaining their biological activity remains challenging. As it is well known that the micro- and nano-environment of immobilized molecules and cells plays an important role for the function and specific properties of the biomolecules [1], different approaches have been proposed and used to selectively immobilize biomolecules onto various substrates. Recently, bare metallic nanoclusters deposited on a solid substrate have been used as specific binding site for protein adsorption [2].
The aim of this project is to analyze the influence of the size and the density of the deposited clusters on the immobilization of proteins. Vacuum-deposited platinum nanoclusters [3] will be produced with a size range of 1nm – 5nm (matching the size of a single protein molecule) and with different densities. These clusters, deposited on a biocompatible, protein-repellent substrate [4], function as specific binding sites for biomolecules. Proteins will be attached to the clusters, either directly or via a linker molecule[5].
You will use atomic force microscopy (AFM) techniques to investigate the cluster sizes and densities after the deposition as well as after their bio-functionalization. With atomic force spectroscopy you will probe the interaction between the immobilized molecule and its complementary molecule (e.g. using receptor-ligand system). Quantitative as well as structural information about the immobilized molecules will be obtained by quartz crystal microbalance experiments. Using these complementary analysis techniques, you are aiming to determine to what extend the spacing and size of the clusters can be changed in order to control qualitatively and quantitatively the immobilization of biomolecules at the nanoscale.
AFM image of surface deposited Au nanoclusters.
Schematic illustration of functionalized Au nanoclusters.
References
[1] Lee, Y.-S. & Mrksich, M. (2002), Trends in Biotechnology, 20 (12), S14-S18.
[2] Palmer, R. E. & Leung, C. (2007), Trends in Biotechnology, 25 (2), 48-55.
[3] Vandamme, N., et al. (2003), Journal of Physics: Condensed Matter, 15, 2983-2999.
[4] Alcantar, N. A., et al. (2000). Journal of Biomedical Materials Research, 51, 343–351.
[5] Rusmini, F., et al. (2007), Biomacromolecules, 8, 1775-1789.
Promoter: Prof. C. Bartic, Prof. Margriet Van Bael
Daily supervision: T. Peissker
Type of work: experimental
Number of students: 1
Quantum dots interaction with enzymes
Quantum dots (QDs) are semiconductor nanocrystals with sizes between 2 and 10 nm. In a QD, the free charge carriers are confined in all three dimensions. This quantum confinement gives rise to size-dependent properties. An example is the decreasing bandgap as the dot gets smaller. As a consequence, QDs can be engineered to emit light over the entire visible range by varying their size. Another aspect of quantum dots is their large surface-to-volume ratio, which makes them very sensitive to the environment. For quantum dots suspended in solutions, a small pH variation pH can cause huge changes in the light emission intensity. Coupling QDs with biological molecules opens new possibilities in biosensing and bioimaging[1,2]. One interesting class of biomolecules are enzymes, proteins that catalyze biochemical reactions. A quantum dot may sense these reactions, because they generate reactions products that locally alter the environment (e.g. local pH changes). In the case of redox-active enzymes, also direct transfer of electrons from the reaction site to a nanoparticle has been illustrated[3]. The goal of this project will be to study the interaction between QDs and enzymes. Fluorescence microscopy, photoluminescence spectroscopy and conducting AFM will be used to assess the mechanisms through which the enzymatic reaction influences the optical properties of QDs.
Left: QD with hydrophobic coating. Right: Addition of glucose to a solution containing quantum dots and glucose oxidase enzyme (GOX) causes a decrease in optical emission intensity due to acid production. The average energy of the photons increases.
References
[1] Willner et al. The FEBS Journal 2007, 274, 302-309.
[2] Alexson et al. J. Phys.: Condens. Matter 2005, 17, 637-656.
[3] Lioubashevski et al. JACS. 2004, 126, 7133-7143.
Promoter: Prof. C. Bartic, Prof. Margriet Van Bael
Daily supervision: D. Debruyne, O. Deschaume
Type of work: experimental
Number of students: 1
Magnetic properties of small atomic clusters
Atomic clusters constituted of a few atoms display uncommon properties very different from single atoms and bulk materials resulting from the large fraction of surface atoms and the discrete nature of the energy level spectrum. In particular, magnetic properties of small clusters are expected to display strong oscillations of their magnetic moment and magnetic anisotropy as a function of their size, geometry, and composition. Investigation of such small clusters is of high fundamental interest and is moreover very relevant for future applications as it could lead to the ultimate memory bit of information in magnetic storage devices.
In this thesis, you will produce small magnetic clusters using a plasma magnetron sputtering cluster source allowing to control their mass to atomic precision using a high resolution RF quadrupole mass filter. Clusters of different sizes will be deposited on a substrate using different deposition parameters. The resulting cluster shape and size distribution will be studied in detail by scanning probe microscopy. The atomic structure of individual clusters will be investigated using scanning tunneling microscopy measurements while the magnetic properties of ensembles of clusters will be characterized using measurements of the magneto-optical Kerr effect (MOKE).
Magnetron sputtering cluster source
STM image of Co clusters on a Au(111) surface
Promoter: Prof. Ewald Janssens, Prof. Peter Lievens, Prof. Margriet Van Bael
Daily supervision: : Dr. Arnaud Hillion, Dr. Thomas Picot, Dr. Koen Schouteden
Type of work: experimental
Number of students: 1
Superconductivity in nanostructured tin
α and β tin (Sn) are two stable phases of tin: α-Sn is a semiconductor with quasi zero bandgap, β-Sn is a low temperature superconductor with a bulk transition temperature of 3.7K. Several studies have reported that Sn deposited on a Si(111) surface undergoes a phase transition from the α to the β phase for increasing layer thickness. β-Sn belongs to the group of weakly-coupled superconductors. Strong phonon confinement effects are believed to be the main cause for the increase of the critical transition temperature that is observed in very thin Sn layers and Sn nanostructures.
In this master-thesis project, you will use cluster deposition and molecular beam deposition in UHV to produce nanostructured Sn. You will study the structural properties and possible phase transition by x-ray scattering and scanning probe microscopy. A unique opportunity for this year’s master thesis will be the first use of Mössbauer spectroscopy on the 119Sn isotope as a local nuclear probe for a detailed characterization of the structure and chemical environment. The superconducting properties will be measured by cryogenic electrical transport and SQUID-based magnetization experiments.
Depending on beamtime allocation, also synchrotron-based nuclear methods to measure the phonon density of states in the nanostructured Sn samples can be part of this master thesis.
Atomic force microscopy image of a cluster-assembled Sn film (top) grown by cluster deposition and of a collection of larger Sn islands (bottom) grown by molecular beam deposition.
Promoter: Prof. Margriet Van Bael, Prof. André Vantomme, Prof. Kristiaan Temst
Daily supervision: Kelly Houben, Dr. Thomas Picot
Type of work: experimental
Number of students: 1
Unraveling the quantum mechanical properties of nanoparticles with scanning tunneling microscopy
Nanoparticles, providing the bridge between the atomic and the bulk level, attract a lot of attention in solid state physics. Their properties do not simply scale with their size and cannot be readily predicted. A profound knowledge of their behavior is of crucial importance for fundamental physics, but also, e.g., for the operation of future nanoelectronic circuits and data storage media. Controlled preparation of nanoparticles on a substrate allows probing their physical properties with high spatial and energy resolution by means of scanning tunneling microscopy (STM) and spectroscopy (STS).
For this thesis project, you will create nanoparticles (clusters) in the gas phase by means of condensation of evaporated atoms, and deposit them on atomically flat substrates. The central goal of this research project is a systematic investigation of the size dependence of the electronic properties of these deposited clusters by STS.
More precisely, you will study the properties of individual nanoclusters for which the interaction with the substrate is minimized. This can be achieved by depositing the nanoclusters on metallic substrates that are covered with a thin NaCl layer that acts as a tunnel barrier and basically eliminates the interaction with the underlying substrate. You will investigate electron quantum-mechanical confinement phenomena and Coulomb charging effects that are expected because of the finite size of the nanoclusters.
Left: 80 x 80 nm2 STM image of
deposited Co clusters on the herringbone
reconstructed Au(111) surface.
Right: STS spectra of Au nanoparticles
reveal the quantized band structure as
well as Coulomb charging of the
nanoparticles.
Promoter: Dr. Koen Schouteden, Prof. Ewald Janssens, Prof. Peter Lievens, Prof. Chris Van Haesendonck
Daily supervision: Dr. Koen Schouteden, Zhe Li
Type of work: experimental
Number of students: 1
The structure and hydrogen storage capacity of transition metal doped aluminum clusters
Safe and efficient hydrogen storage remains one of the main challenges on the way of implementation of hydrogen fuel cells on an industrial scale. With the aim to find alternative solutions for gaseous hydrogen technology, light solid-state materials with high hydrogen storage capacity are considered. In this context small aluminum clusters are prospective. However, pure aluminum particles show relatively high activation barriers (0.7-1 eV) to dissociative chemisorption of hydrogen molecules, whereas low hydrogen adsorption/desorption energy barriers are needed for hydrogen regeneration at room temperature. Theory predicts that adding low concentrations of Ti, V, or Cr might lower the hydrogen adsorption/desorption energy barriers.
In this thesis work you will produce beams of transition metal doped aluminum clusters, AlnTM (n = 2-30, TM = Ti, V, Cr) using a laser vaporization cluster source. The ability of the clusters to absorb hydrogen will be investigated in the gas phase (i.e. unsupported) mass spectrometry. The saturation regime for hydrogen adsorption of bare and doped aluminum clusters will be examined.
In addition the structure of size selected bare and doped hydrogenated aluminum clusters will be determined by combining multiphoton infrared spectroscopy with density functional theory calculations. With infrared spectroscopy one can identify vibrational transitions that are characteristic for the cluster geometry. These measurements require an intense infrared laser source and will be carried out at the free electron laser FELIX (Free Electron Laser for Infrared eXperiments) at the Radboud University in Nijmegen, the Netherlands. The density functional theory calculations are no part of the thesis work and are available via collaborations with theory groups.
Mass spectra of AlnDm+ (D = deuterium) showing the ability of aluminum clusters in the gas phase to absorb hydrogenen.
Promoter: Prof. Ewald Janssens, Prof. Peter Lievens
Daily supervision: Dr. Vladimir Kaydashev
Type of work: experimental
Number of students: 1
Thesisonderwerpen: Vaste-stoffysica op nanometerschaal
