Thin-film phase

Examples of XRD Characterization of Thin Films Phase Identification... 

As described in Sect. 2.1.2, block copolymer thin film phase behavior can be controlled by the surface/interface energies as well as the interplay between the film thickness t and polymer natural period Lo. Depending on the nature of the surface interactions, block copolymer thin films can be separated into two general categories [14,41] ... 

Fig. 2.3. Five orders of reflection in a thin film results also show the presence of the two most X-ray diffraction scan, indicating the high level common polymorphs of pentacene, the bulk-of crystallinity often present in pentacene thin like phase and the thin-film phase [25]. films deposited on different dielectrics. These...

Danev R, Nagayama K (2006) Applicability of thin film phase plates in biological electron microscopy. Biophysics 2 35-43... 

Pc [14, 15]. The set marked by p originates from the (001) lattice planes of the thin film phase (TF-phase) of Pc which was characterised by several work groups [6, 16-20]. In both phases the long molecular axis are nearly perpendicular to the (001) lattice planes, and hence perpendicular to the substrate plane. Both phases are identified by their characteristic (001) lattice distances. The (001) lattice distance is 1.45 nm for the C-phase [15] and 1.54 nm for the TF phase [17], as calculated by using Bragg s law [13]. 

Figure 11.6 Evolution of pentacene films on Cu(l 10). After completion of the first monolayer revealing a predominant (6.5 X 2) phase and occasionally a coexisting c(13 X 2) phase (a) an intermediate phase A is formed whereas for thickness above 2 nm the molecules continue in an upright orientation a-dopting the well known thin film phase B (b).

Figure 11.10 Morphology and structure of thin pentacene films on a SAM pre-covered Au(l 11) substrate (a) SEM micrograph of a 2 nm film together with corresponding STM data (b), (c) showing a layered arrangement of upright standing molecules. XRD data recorded for a 30 nm film (d) clearly reveal the presence of (001) oriented films revealing the thin film phase while at larger thickness the bulk phase is adopted.

H. Yoshida, I. Katsuhiko, and N. Sato, X-ray diffraction reciprocal space mapping study of the thin film phase of pentacene, Appl. Phys. Lett. 90, 181930(2007). 

I. P. M. Bouchoms, W. A. Schoonveld, J. Vrijmoeth, and T. M. Klapwijk, Morphology identification of the thin film phases of vacuum evaporated pen-... 

As a result of the above, and of the direct competition between molecule-substrate and intermolecular interactions, the presence of the metal or insulator can induce interface polymorphs which do not exist in the bulk. Examples for this are the specific thin film phases of pentacene on insulators [16, 74, 75] or metals (e.g., Cu(llO) [16]), the a- and 3-phases of tetraeene on Ag(l 11) [69], or the square phases of PTCDA on Ag(l 11) [30] and Au(l 11) [84]. It is evident that the charge carrier mobilities of organic semiconductors will depend on the crystal phase. 

The reason for pentacene being superior for the production of TFT devices [7, 8] when compared with other molecules [9] is still not obvious. In this chapter, we will discuss to what extent the peculiar growth properties [10] of pentacene on metallic contacts and gate dielectrics contribute to the device performance. For this purpose, first the early growth state of pentacene films and the molecular structure of the so called thin film phase is reviewed. Then, major sources of crystal defects in thin films as determined by advanced synchrotron diffiaction techniques are discussed. The relation of these defects to the frequently discussed electronic traps that strongly influence transport properties of TFTs [6, 11, 12] is indicated. Finally, the spatially resolved photo response of pentacene OTFTs will be discussed in the context of injection barriers and contact homogeneity. 

In a recent study, the detailed molecular arrangement of the thin film phase was resolved by a grazing incidence truncation rod scattering study [25]. 

Surface energy calculations [28] reveal that the (001) cleaving plane is the surface with the lowest surface energy. In turn, the formation of (001) oriented films can be expected, if the interaction of the pentacene molecules with the surface is negligible to the pentacene-pentacene interaction. Experiments show that this condition apparently fulfilled for various inert substrates such as reduced and oxidised Si, as well as many polymeric films used as gate dielectric. Note that the surface energy of the thin film phase is rather isotropic... 

Figure 15.2 Thin film phase unit cell, (a) The side view illustrates the layered structure of the thin film phase, (b) The top view emphasises the herringbone ordering motive, which is a common feature of all pentacene polymorphs.

Another way to avoid dewetting is to passivate the metallic surface by a self assembled monolayer (SAM), e.g. an alkane thiol monolayer (C-18). After passivation, the growth structure resembles the growth mode on inert surfaces [33], the same holds for growth of pentacene on conducting polymers such as PEDOT PSS [poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)] [39]. It is interesting to note that on bare Si, pentacene initially forms a flat lying monolayer, but on-top of this monolayer, the thin film phase readily forms [16] without need for passivation. 

Bouchoms, I.P.M., Schoonveld, W.A., Vrijmoeth J., and Klapwijk, T.M., Morphology identification of the thin film phases of vacuum evaporated pentacene on Si02, Synth. Met. 104, 175, 1999 Knipp, D., Street, R.A., Volkel, A., and Ho, J., Pentacene thin film transistors on inorganic dielectrics Morphology, stmctural properties, and electronic transport, J. Appl. Phys. 93, 347, 2003. 

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