Structural studies of Copper Tetra-Tert-Butyl Phthalocyanine Langmuir-Blodgett and vacuum deposited films
The Langmuir-Blodgett (LB) technique was employed to fabricate thzn films of Copper-Tetra-Tert-Butyl Phthalacyanine (CuTTBPc). However, CuTTBPc has a strong tendency to aggregate and hence inhibit the synthesis of uniform layers. It has been found that the incorporation of Arachidic Aczd (AA) can reduce the aggregation effect A study of the isothernis produced for a variety of concentrations of CuTTBPc:AA showed a reduction in the aggregation as the amount of AA was increased. Transfer ratios for such films are predominately Y-type indicating that deposition occurred on both the up- and downstroke Atomic Force Microscopy (AFM) was used to image the CuTTBPc.AA LBfilms with a thickness of I - 21 MLs. Good surface coverage was observed. Hezght projile studies of the I ML film indicate that the layer is 1.7 nm in thickness. When the film thickness is increased the topography of the surface conszsts of clusters typically associated with aggregation. The uniforniity of the films was examined by spectroscopic ellipsometiy, whereby zt became evident that films were growing in a unlform layer-by-layer fashion desprte the obvious presence of aggregation. The average layer thzckness, deduced from the ellipsometrzc data, was 2.31nm. The uniform growth would suggest the layers were depositing on both the up- and downstroke making the films Y-type in configuration atid perhaps indicating that the films have a Stranski-Krastanov structure. Scannzng Tunnelling Microscope (STM) zmages of CuTiTPc on Ag/Si(lll)-(4 xJ3)R30° found the molecules to be flat lying. The sulface was htghly ordered aiid densely packed with molecules forming rows, which ran parallel to each other. Scanning Tunnelling Spectroscopy (STS) studies found that the Highest Occupzed Molecular Orbital (HOMO) zs a half-occupied MO of b1g symmetry with mired Cu 3d(x2-y2)and ligand 2p character. A study of the orientation and molecular ordering of the CurrBPc molecule in a pure CuTTBPc LB film (on SiO J and evaporated films of CuTTBPc(on Si02 and Si(l1 I)) and H,TTBPc (St03 was carrzed out uszng X-Ray Photoemission Spectroscopy (XPS) and Near Edge X-ray Absorption Fine Structure (NEX4FS) A strong angular dependence was found indzcatzng that the molecule was tilted on the surface. The tilt angle was calculated to be 18.5" to the su&ce normal XPS results revealed that the ordering was strongest in the CuTlBPc LB film, followed by the evaporated films of CuTTBPc and HzTl%Pc on SO2, followed by CuTTBPc on Si(ll1). A study of the electronzc structure of the copper atom in the CuTTBPc was also carried out and the found to be in good agreement with previously published work.
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