Ph. D. THESIS 2009

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Figure 15. a Optical image of gold wires network in polymer matrix, b) SEM image of two double wires after removing the unreacted matrix There are two main aspects which allow a clear description of a “double-wire” characteristic: the size of the wire, denoted wire width, and the double-wire separation distance, denoted distance between lines. For comparison, atomic force microscopy (AFM) measurements were performed in order to establish the 3D aspect of the metallic wires (Figure 16). 2.0µm Z[nm] z [nm] 600 500 400 300 200 100 0 0 0.5 1 1.5 2 2.5 3 3.5 4 5 x[m] X[µm] 11 Distance between lines Wire width Figure 16. AFM measurements of a typical gold double-wire: a) topographic view, b) cross-section along the double wire, c) 3D view A topographic AFM view is shown in the left images of Figure 16a) and a cross section along them is plotted at the centre, in Figure 16b). Each metallic wire has a full width at half maximum of 600 nm with a height of 500 nm. A 3D view is shown on the right images. As it can be seen, regular and continuous metallic wires can be fabricate, their walls being almost vertical [10]. At the first estimation it can be assumed that the metal deposition does not occur at the center of the laser beam, but on its outer diameter. In fact, there is about more complex phenomena that occur during the gold wires fabrication. How can we control the cluster generation, and further the growth of metallic structures, when the energy provided by laser irradiation is considerably lower than the UV one but highly localized within the gold salt- doped matrix? The fabricated lines are very sensitive to the writing conditions. At low laser power the lines are thin and show granular structure, as shown in Figure 17(a). On the contrary, at higher power the lines are regular, but exhibit a double-wire shape due to the ablation process, which occurs immediately after laser interaction with gold nanoparticles previously formed – Figure 17(b). We may admit that the size of nanoparticles that act as nucleation centres is another parameter which influences the evolution of fabrication process. The morphology of patterns undergoes a spectacular change if the laser power and the critical exposure time are oversized, due to a novel ablation process.
In fact, this unusual phenomenon is caused by the collective action of multiple pulses. Nucleation 10 mW 20 mW 12 40 mW Growth a b Nucleation 40 mW Figure 17. Competition between (a)nucleation and (b) growth processes during the gold fabrication at different laser power 4.3.3. The influence of the operating parameters The deposition of gold nanowires is performed at the active layersubstrate interface in order to recover the metallic deposit at the substrate surface after removing the unreacted matrix. The chemical reaction path of the salt-PSS-ferric citrate system is expected to be dependent on the initial molar ratios between reactants and on viscosity of solutions, on the reaction parameters, such as laser power and nature of the substrate used for the active layer deposition. 4.3.3.1. The laser power The delivered power of femtosecond laser was varyed in order to establish how it can modify the characteristics of double nanowire. Typical laser powers are in the tens of milliwats, measured at the laser output. Under our experimental conditions, no gold lines were observed for laser powers below 10 mW. Higher laser powers, ranging from 30 to 40 mW, are required to initiate the process for other metals such as silver, copper or nickel. This can be attributed to a higher reactivity of gold (III) ions (oxidative power) when compared to others metallic ions. There were obtained similar structures as shape, but various as size, at two different powers of the laser (80 mW and 120 mW), the results suggesting that
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“BABES-BOLYAI” UNIVERSITY CLUJ-
Page 3 and 4:
General Introduction OUTLINE Part A
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3.6.1. Dots 188 3.6.2. 3D structure
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Part A: Synthesis and Structural An
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Page 19 and 20: 1.5.1. Tetramethyl 3,7-dihydroxybic
Page 21 and 22: Table 7. The selected molecular par
Page 23 and 24: a b Figure 14. 1 H NMR spectrum (CD
Page 25 and 26: Figure 16. 13 C NMR spectrum APT (C
Page 27 and 28: Absorbance (a. u.) Absorbance (a.u.
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Page 31 and 32: m u lt ip let a t a t δ ==1 .7 6 p
Page 33 and 34: Figure 22. 13 C NMR APT spectrum of
Page 35 and 36: Figure 24. NMR investigation of the
Page 37 and 38: (mol·l -1 ) syn 8.8 x10 -3 1.4373
Page 39 and 40: a b Figure 29. 3D FTIR spectra in s
Page 41 and 42: Figure 32. ORTEP diagram for the cy
Page 43 and 44: H2 … N3 = 1.839 Å H5 … N6 = 1.
Page 45 and 46: 2. Conclusions of the part A Differ
Page 47: 20. L. J. Bellamy, “Advanced in I
Page 50 and 51: 2. Experimental part: fabrication a
Page 52 and 53: 3 m 30 m a b Figure 4. Optical imag
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Page 64 and 65: a b Figure 21 a) Optical image of g
Page 66: 4.5.3. 3D structures The 3D structu
Page 69 and 70: Selected References 1. E. S. Wu, J.
Page 71: VIII. J. Bosson-Ehoomann, A. Mihut,
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Ph. D. THESIS 2009

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