Correlated growth in ultrathin pentacene films on silicon oxide: Effect of deposition rate

Abstract

Understanding the growth mechanism in molecular organic thin films is fundamental to their applications in organic electronics. We present an extensive study of the growth mechanism of pentacene thin films on silicon dioxide (SiO 2 ) using atomic force microscopy. For a fixed substrate temperature T s , the deposition rate is found to be a key parameter in controlling the nucleation density in the submonolayer regime and hence transport properties in the first layer of the organic field effect transistors. At a fixed T s ϭ338 K the maximum number of pentacene islands per unit area N follows the scaling law Nϰ ␦ with ␦ϭ1.16Ϯ0.10. A mechanism of homogeneous nucleation followed by diffusive growth accounts for this behavior and allows us to estimate the critical nucleus size of the pentacene islands. The results obtained from a statistical analysis of the island size distribution are fully consistent with a phenomenological capture zone model. The validity of this model depends on the extent of reevaporation of pentacene admolecules during deposition, which is moderated by the deposition rate. We demonstrate that the rate dependence of island nucleation has important implications for the density of grain boundaries, which may play an important role in the transport mechanism.

Percolative effects on noise in pentacene transistors

“…The averaged transfer curves for films ranging in thickness from 40nm to 7nm and a set of 10nm devices with a deposition rate of 3.6 Å/s are shown in Figure 2a. As has been reported previously 16 , an optimum mobility is obtained for intermediate thicknesses of [15][16][17][18][19][20][21][22][23][24][25] nm.…”

“…2b. Deviations from the typical α =1 behavior for organics usually result from a far from equilibrium growth rate 18,19 as can be seen in the upper curve in Figure 2b.…”

Key role of molecular kinetic energy in early stages of pentacene island growth

“…2 one infers that the island size distribution becomes narrower and peaked at smaller values as E k increases. This trend towards a more uniform island size is characteristic of a changeover towards correlated island growth as proposed by Pratontep et al [28,29], where the overlap area of the capture zones of neighboring islands is large.…”

Pentacene thin films on ferromagnetic oxide: Growth mechanism and spintronic devices

“…30 The analysis of the effective coverage, obtained by measuring the volume of the islands, 15 shows that it decreases from 75% at a substrate temperature of 45 C to 55% at 75 C: at this temperature desorption could start to play a significant role. 31 All together, data in Figure 3 demonstrate that the molecule-substrate interaction is weak when pentacene grows on LSMO.…”

“…At higher growth rates (0.03 nm/s) P i à m¼2 E m þ i à E D ¼ 1.13 6 0.04 eV and i* ¼ 3 were reported, 36 hence E N ¼ 0.23 6 0.01 eV. Considering that E N varies with the growth rate, 31 the value we extracted for pentacene on LSMO is compatible with the one for SiO 2 substrates (Figure 4(b)), assuming that at lower rates E N levels off rather than diverging. 35,37 Pentacene nucleation and growth on LSMO are much closer to those on SiO 2 than those on Co. 34 The diffusion mechanism was analysed in order to disentangle the contributions of diffusion and nucleation in E N .…”