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

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24 Rubrene: physical and chemical properties grown in a reproducible way and with high structural quality. Nonetheless, in order to exploit rubrene in the fabrication of electronic devices, it is neces- sary to grow it in the thin film form, in order to meet the current industrial standards for device miniaturization. Moreover, the large anisotropy in the optical end electrical properties of crystalline rubrene requires a high control over the crystalline structure of the thin films, possibly with a single orientation. Despite this, up to now only few attempts to grow crystalline rubrene thin films have succeeded. Most of the times the attempts to grow rubrene thin films with standard solution or evaporation methods led only to amorphous films[20,21]. In particular there have been several attempts to grow rubrene thin films on SiO 2 , which is a standard dielectric for most electronic appli- cations, but up to now it has been possible to grow high quality crystalline thin films only by previously depositing a pentacene buffer layer on top of the bare SiO 2 substrate[19, 25, 72]. Other successful attempts to obtain rubrene crystalline thin films on SiO 2 substrates are based on the abrupt heating at 100 ◦ C of previously deposited amorphous films[26]. By these means it has been possible to obtain highly crystalline thin films with their a axis normal to the substrate surface, but constituted by grains of about 80 µm in size and with a random in-plane orientation of their b and c axes. Other successful attempts of rubrene crystalline thin films growth have exploited epitaxial growth on other inorganic substrates such as Au or Bi or on organic single crystals like tetracene[27, 73, 74]. By these means it is generally possible to have a greater control over the structural properties of the grown film, but the presence of an interface with another organic semiconducting material generally leads to complications in interpreting the results of optical and electrical measurements carried out on these systems. 2.8 Conclusions As discussed in the previous sections there are still several open prob- lems regarding both the intrinsic properties of rubrene and the preparation of working devices. In the next chapters we will thus describe both the results of our work aimed at growing crystalline rubrene thin films and of our experiments aimed a deeper understanding of the process of oxidation of crystalline rubrene; in addition, we will focus on the effects of this oxidation
2.8 Conclusions 25 process over rubrene optical and electrical transport properties.
Page 1: Università degli Studi di Milano-B
Page 4 and 5: iv Contents 4 Rubrene thin films 47
Page 6 and 7: vi Contents
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
Page 38 and 39: 28 Experimental techniques Figure 3
Page 42 and 43: 32 Experimental techniques 3.2 Samp
Page 46 and 47: 36 Experimental techniques the scan
Page 48 and 49: 38 Experimental techniques by repre
Page 50 and 51: 40 Experimental techniques Fω =
Page 52 and 53: 42 Experimental techniques In order
Page 56 and 57: 46 Experimental techniques whole di
Page 58 and 59: 48 Rubrene thin films for a long ti
Page 60 and 61: 50 Rubrene thin films Parameter Val
Page 62 and 63: 52 Rubrene thin films Figure 4.3: M
Page 64 and 65: 54 Rubrene thin films series of dif
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Page 68 and 69: 58 Rubrene thin films Figure 4.6: T
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74 Rubrene thin films present. Sinc
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76 Rubrene thin films ≈ −33.5 k
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78 Rubrene thin films
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80 Oxidation dynamics of rubrene ep
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100 Oxidation dynamics of rubrene e
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102 Influence of oxygen on electric
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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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