Production, Deposition & Characterization Of Metal Nanoclusters Using a Gas Aggregation Source

1. Production, Deposition & Characterization Of Metal Nanoclusters Using a Gas Aggregation Source I. Shyjumon Institut für Physik Supervisor : Prof. Dr. Rainer Hippler I.Shyjumon

2. Outline • Introduction • Materials & Methods • Nanocluster source • Characterization techniques (AFM, GIXD, XPS) • Results & Discussion • Characterization of Ti/Ti – Oxide Clusters • Structural deformation and Lattice parameter studies of Ag - nanoclusters • Summary & Outlook I.Shyjumon

3. Introduction – What is a cluster ? Clusters – Intermediate range between atoms and bulk matter Aggregates of 2–10n particles (n  6 or 7) I.Shyjumon

4. Types of Clusters - 1 Based on the type of constituent particles & type of bonding Semiconductor Clusters Rare gas Clusters Metal Clusters S block – Metallic bond (e.g. alkali & alkaline earth) SP metals – Covalent bond (e.g. Al) Bonding -Van der Waals Inter-atomic attraction increases with increasing atomic mass (HeRn). Bonding – Covalent e.g. C, Si & Ge http://www.tc.bham.ac.uk/~roy/Teaching/CHM3T1 I.Shyjumon

5. Types of Clusters - 2 Ionic Clusters Molecular Clusters Cluster molecules thermodynamically and/or kinetically stable with respect to coalescence e.g. Al13MgAl13 atoms with large difference in electronegativity Bonding – Ionic e.g. (NaCl)n, [MgxOy]2(xy)+ van der Waals, dipole-dipole interactions, and hydrogen bonding e.g. (N2)n, (C6H6)n, (H2O)n I.Shyjumon

6. Why clusters ? - Applications • Clusters are of fundamental interest: • due to their intrinsic properties and reduced size • because of their central position between molecular and condensed matter science. Technical Importance due to the unique electronic & optical properties • Basic use in the fabrication of thin films • They have potential as a catalyst in certain chemical reactions. • Ag clusters used in photography • Ag nanoclusters are used in electronic devices • Energetic cluster interaction on surface surface cleaningsurface metallization, precision machining I.Shyjumon

7. Materials & Methods – I • Nanocluster source • Cluster formation • Cluster growth I.Shyjumon

8. Nanocluster source • Fast metal atoms are formed by the cathode bombardment of ions • A part of thermalized atoms are transferred into clusters I.Shyjumon

9. G = ko /(KNa) Growth parameter Cluster formation Cluster formation byGas aggregation Mk+M  Mk+1 2M+A  M2+A, M, A – metal and buffer gas atoms Size of formed cluster n  G3/4 I.Shyjumon

10. Mechanisms of cluster growth If free atoms (or molecules) dominates Mn + Mq Mn+q Takes place at high temperature I.Shyjumon

11. Materials & Methods – II • Characterization techniques • Atomic force microscopy (AFM) • X-ray diffraction (XRD) & X-ray photoelectron spectroscopy (XPS) I.Shyjumon

12. Atomic force microscopy (AFM) Tapping mode Width = w+2d I.Shyjumon

13. e- Ekin(e-) = hν- Ebin hν E Ebin e- XRD & XPS • X-ray Diffraction: Diffraction volume can be increased by decreasing the angle of incidence • X-ray Photoelectron Spectroscopy: I.Shyjumon

14. Results & Discussion – I Characterization of Ti/Ti-oxide clusters I.Shyjumon

15. Cluster size dependence on temperature time of deposition:- 15 s, P = 100 W, at 0.1 mbar • the temperature dependence of size is due to cluster-Ar interaction, that increases the coagulation processes I.Shyjumon

16. Cluster size dependence on time wall temperature, T = 148 K t = 120 s N/µm2 - 280 to 390 h – 14 to 24 nm Around 30 s, the second layer growth - starts before the first layer is completed I.Shyjumon

17. Ti2p3/2 – 458.8 eV TiO2 Chemical composition • Chemical composition analysed by XPS Ti/O - 1:2 • Clusters on the surface are fully oxidised TiO2 I.Shyjumon

18. Results & Discussion – II Structurual deformation & lattice Parameter studies of size selected Ag clusters I.Shyjumon

19. Size selection of Ag nanoclusters • Mass selection by mass filter • Clusters are selected according to M/e • Size selection is also possible by varying the aggregation tube length I.Shyjumon

20. Cluster Flattening • deconvolution by Au colloidal particles, d ~ 4 nm m = 2.3×105 amu, size ~ 4.1 nm, N ~2131 atoms t = 240 sT = 198 K I.Shyjumon

21. Cluster Flattening mechanism • Cluster surface collision mechanisms depend on different parameters Cluster size, N E = 0.1 to 1 eV/atom Impact energy, E • Front atoms are stopped due to collision I.Shyjumon

22. Size effect on melting point • expt. with = 0.5°, 2Θ = 36° to 46°; Heating : 373K up to 973K t = 15 min bulk Ag,M.P 1230 K • Small melting temperature due to small cluster size • Theoretical Gibbs-Thomson equation I.Shyjumon

23. Lattice constant change with size • Strain due to residual tensile stress t = 15 min, Vs = -1.5 KV • Strain as a result of lattice disorders & structural disorders • influence of local melting reduced with increase in size I.Shyjumon

24. Summary & Outlook • Strong dependence of size on cluster forming chamber temperature • Second layer growth observed far before the first layer is completed • Ti clusters on the surface exists as TiO2 • Flattening of clusters occurs with increase in substrate bias. • A proportional increase of cluster melting point with size is observed • Lattice constant increases at small cluster sizes and decreases after a a size of 12 nm. • Better understanding on cluster growth & production of nanocluster films with noval application I.Shyjumon

25. Acknowledgement Thanks to: Prof. Rainer Hippler Prof. Christiane A. Helm & Manesh Gopinadhan, Prof. B.M. Smirnov & Prof: Bharracharya Dr. Harm Wulff & Dr. Marion Quaas, Dr. Hartmut Steffen, Vasile Vartolomei, Stefan Wrehde... Thank you all…….. I.Shyjumon

26. Size selection of Ag nanoclusters-II • Size selection by varying the aggregation tube length t = 10 s, T = 148 K • Aggregated clusters are omitted in AFM height analysis I.Shyjumon

27. Cluster - surface collision In general collision processes can be of 3 types Low energy, Medium energy & High energy The important parameters that control the process are, Cluster sizeN (2  N  105), Impact energyE (10-2 to 108 eV) Impact angleΦin, charge state, cluster & surface temperature Cohesive energies of clusterEclcohand surfaceEscoh I.Shyjumon

28. Processes in cluster-surface collision W. Harbich, in Metal Clusters at Surfaces, edited by K.H. Meiwes-Broer(Springer, Berlin, 2000). I.Shyjumon

29. Size selection without & with mass filter aggregation tube length = 16 cm t = 55 s t = 25 s Aggregated clusters were omitted in AFM height analysis I.Shyjumon

30. Quadrupole mass filter V- voltage (1-250 Volt) f – frequency (3-100 kHz) d=25.4 mm, diameter of poles K – Mass calibration factor (0.5 to 2) – calibration of cluster mass with other characterization techniques I.Shyjumon

31. M ~ 1.2×105 amu Quadrupole mass filter Clusters are mass selected by quadrupole mass filter Expected height & measured heights fits well- shows the perfect working of the mass filter I.Shyjumon

32. Rp+RT RT –h/2 w/2 cluster tip 4 3 w Height [nm] 2 1 0 0 10 20 30 40 50 60 70 X[nm] M= 3 10 Comparison –spherical clusters Si tip (RT~ 6nm) J.Vesenka (et.al), BioPhy.J. 65, 992 (1993) I.Shyjumon

33. 10 nm Si tip 6 nm Hi‘ res tip 100nm 100nm - 50 nm - - 50 nm - Nioprobe sample With HI’RES tip 15 nm Sharp peaks of less than 12nm Determine the shape of the tip apex 0 nm 250 nm TEM image of Nioprobe AFM analysis (HI’ RES Tip Geometry) Scanning Probe Image Processor (SPIP) I.Shyjumon

34. Size determination by XRD mean effective particle sizes in direction of the diffraction vector Scherrer equation diffraction line is convolution of physical line profile & instrumental profile L is the domain of definition of the experimental line profile http://www.uni-leipzig.de/~iom/muehlleithen/2003/2003_wulff.pdf I.Shyjumon

35. GIXD measurements Step size of heating reduced to 20 K/min near the melting temperature I.Shyjumon

36. Cluster catalysts Supported [Ru6C] cluster catylysts on TiO2 – ammonia synthesis, decomposition of NOx Clusters of Ru3(Co)12 – assymetric transfer hydrogenation of ketones Small Ti clusters for catalysis of hydrogen exchange in NaAlH4 nanoscale silver oxide (Ag2O) - strong photoactivated emission for excitation wavelengths shorter than 520 nm I.Shyjumon

37. Chemical composition of Ag clusters Ag clusters on Si(100); t = 5 min Ag(111) is the most intensive peak in randomly oriented polycrystalline Ag I.Shyjumon

38. Comparison of Ti & Ag clusters Sputtering yeild Ti - 0.37 & Ag -1.4 Larger surface coverage of Ag clusters due to high sputter yeild Larger mean size for Ti clusters are due to oxidation I.Shyjumon

39. The Magnetron • A planar magnetron is a system of ring-magnets, placed under the target • The additional magnetic field causes a Lorentz-force which is forcing the electrons on a circular „race track“ • Advantage: a high sputter-rate even in very low pressure conditions • Disadvantage: the target material is sputtered only in the „race track“-region I.Shyjumon

40. Magnetron Plasma- balanced mode Inner magnet up Outer magnet down • Electrons are trapped above the race track region by the filed. • The field lines are well confined around the target racetrack and electron loss is reduced to minimum. S.wrehde I.Shyjumon

41. Extraction of +ve & -ve clusters • +ve clusters are found to have more in numbers than –ve ones I.Shyjumon

42. X-ray reflectivity results Ti (Oxide) clusters on Si wafer Dimater, d = 2π / ΔQ I.Shyjumon

43. UV-visible spectra of TiO2 in quartz No peak observed at 410 nm – characteristic absorption peak for Ti Concludes that the nanoparticles are fully oxidised (no free electron present) I.Shyjumon