Growth and physical properties of crystalline rubrene - BOA Bicocca ...

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32 Experimental techniques 3.2 Sample characterization To carry out the work described in this thesis different characterization techniques have been used. Most measurements have been carried out either using an atomic force microscope (AFM) in one of its various working modes, or X-ray diffraction techniques (both with standard and synchrotron X-rays sources). These two techniques will thus be thoroughly described in the following paragraphs, along with the presentation of the relevant theoretical background. Other characterization techniques used for smaller parts of this work include electrical and optical measurements, whose experimental setup will be presented in the corresponding chapters. 3.2.1 Atomic Force Microscopy AFM is one of the so-called Scanning Probe Microscopes (SPM), which also comprise Scanning Tunnel Microscope (STM) and Scanning Near-field Optical Microscope (SNOM). Its invention dates back to 1986; it is an instrument characterized by a great versatility, in that it presents a wide range of different operating modes[81, 82]. Unlike STM, its use is not limited to conductive materials, and can also be used in liquid environments. This makes the AFM a particularly useful instrument for the study of organic or even biological samples, which are often poorly conducting or insulating and may need to be kept in an aqueous environment[83–85]. A simple scheme of a generic AFM, showing all its fundamental components, is reported in figure 3.4. The probe used to image the surface of a sample is a tip, generally made of silicon or silicon nitride, with a curvature radius at the apex which is generally the order of tens of nm and a height of the order of tens of µm. The tip is placed on a flexible cantilever, which can bend both in vertical and horizontal directions and which are usually in a triangular or rectangular shape. Given the physical properties of the cantilever it is possible to extract the force acting on the tip from a measure of the deflection of the cantilever itself. In figure 3.5 the images taken with a scanning electron microscope (SEM) of a triangular cantilever along with the tip mounted on it are reported. The deflection of the cantilever is measured through a laser beam impinging on the back of the cantilever and reflected toward a photodiode divided into four quadrants. Measuring the difference in the signal intensity between the top and bottom parts of the diode or between the left and the
3.2 Sample characterization 33 Laser Cantilever Scanner Photodiode Sample Feedback Figure 3.4: Schematic representation of a generic AFM with all its fundamental components. Figure 3.5: (a)SEM image of a triangular shaped cantilever and of the tip mounted on it. (b) Detail of the tip from image (a).
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Page 4 and 5: iv Contents 4 Rubrene thin films 47
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Page 8 and 9: viii Introduction ties of these mat
Page 10 and 11: x Introduction molecular oxygen inc
Page 12 and 13: 2 Organic semiconductors Figure 1.1
Page 14 and 15: 4 Organic semiconductors 1.3.1 Opti
Page 16 and 17: 6 Organic semiconductors Figure 1.2
Page 18 and 19: 8 Organic semiconductors 1.3.2 Elec
Page 20 and 21: 10 Organic semiconductors
Page 22 and 23: 12 Rubrene: physical and chemical p
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Page 60 and 61: 50 Rubrene thin films Parameter Val
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82 Oxidation dynamics of rubrene ep
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118 Conclusions and Perspectives On
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120 Conclusions and Perspectives
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122 Bibliography [13] D. A. Bernard
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124 Bibliography [41] V. Coropceanu
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126 Bibliography [71] A. J. Maliaka
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128 Bibliography [101] C. Kittel, I
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130 Bibliography [130] D. Beljonne,
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132 Bibliography
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134 PhD activity Attended courses
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