Growth model of pentacene on inorganic and organic dielectrics based on scaling and rate-equation theory

Abstract

We have fabricated a large body of pentacene thin films on different organic and inorganic dielectric materials at four substrate temperatures with different nominal film thicknesses ranging from the submonolayer over the multilayer to the "thick" film regime. These films were characterized by atomic force microscopy and analyzed quantitatively by means of scaling and rate equation theory in order to deduce the molecular growth dynamics of pentacene films on organic substrates that are used as gate dielectrics in organic thin film transistors. We found that on all substrates and in the substrate temperature range 25°C ഛ T s ഛ 70°C the growth can be well described as diffusion-limited aggregation. A critical island size of 3 ഛ i ഛ 4 was deduced from the scaling of the distribution density of the pentacene grain areas and the power-law dependence of the saturated nucleation density on the deposition rate. This is valid for all substrates in the investigated temperature regime and is also found to be true for 50 nm thick pentacene films thus emphasizing that the molecule-molecule interaction itself is independent of the underlying surface.

Nucleation and growth of thin films of rod-like conjugated molecules

“…Typically sizes between 2 and 4 are found for different rodlike molecules. For 5A on SiO 2 , a value of 3-4 is reported [9,63] similar to 2-3 reported for 6P on disordered mica(0001) substrates [62]. However, due to the large experimental data set necessary, in many studies also scaling laws are used to determine the critical nucleus size.…”

“…However, capture zone scaling [59][60][61] seems to provide more reliable results [64][65][66] for some cases. In agreement with rate theory, scaling laws typically yield values between 2 and 3 for 6P [62,64] and somewhat higher values between 3 and 6 for 5A [8,9,11] on SiO 2 or cyclohexane terminated Si{001} [67]. However, in particular for the growth of 5A care has to be taken with respect to the applicability of these single shot methods because of fractal growth morphologies [68].…”

“…Their use as organic semiconductors opens exiting new possibilities for electronic and optoelectronic devices, in particular flexible or stretchable [6] ones. There is ample of evidence that models used in inorganic epitaxy might also be applicable to this new class of materials [7][8][9]. However, on a molecular level these materials do not always follow the well established findings of classical epitaxy [10,11].…”

Arrays of Pentacene Single Crystals by Stencil Evaporation

“…This diffusion length is in the range of the value reported in the literature X S = 2.5 µm for pentacene on SiO 2 at 40°C. 26 X S was deduced from the inter-island distance of pentacene submonolayers grown in the complete condensation regime. X S is defined in the DLA regime as the mean diffusion length of molecules 13 before desorption.…”

Phthalocyanine‐Cored Star‐Shaped Polystyrene for Nano Floating Gate in Nonvolatile Organic Transistor Memory Device

“…Moreover, the surface free energy of the polymer surface was nearly identical to that of pentacene, 47.2 mJ m −2 , contributing to the growth of pentacene crystals via vacuum deposition under room temperature and resulting in relatively large grain sizes of pentacene crystals around 0.3-0.5 µm (Figure 5 c,d). [ 46 ] These deposited pentacene fi lms on the CuPC-PS 4 or PS 4 surface showed a clear diffraction signal at 2 θ = 5.71° with an interlayer spacing ( d 001 ) ≈15.5 Å in out-of-plane X-ray diffraction (XRD) profi les ( Figure S13, Supporting Information). This signal corresponded to a kinetically favored metastable structure, known as a "thin fi lm phase," where the long axis of pentacene molecules were perpendicularly aligned to the surface, achieving effi cient charge carrier transportation through overlapped π-orbitals.…”