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Self-LimitedGrowth in Pentacene Thin Films

View Article: PubMed Central - PubMed

ABSTRACT

Pentaceneis one of the most studied organic semiconducting materials. Whilemany aspects of the film formation have already been identified invery thin films, this study provides new insight into the transitionfrom the metastable thin-film phase to bulk phase polymorphs. Thisstudy focuses on the growth behavior of pentacene within thin filmsas a function of film thickness ranging from 20 to 300 nm. By employingvarious X-ray diffraction methods, combined with supporting atomicforce microscopy investigations, one crystalline orientation for thethin-film phase is observed, while three differently tilted bulk phaseorientations are found. First, bulk phase crystallites grow with their00L planes parallel to the substrate surface; second,however, crystallites tilted by 0.75° with respect to the substrateare found, which clearly dominate the former in ratio; third, a differentbulk phase polymorph with crystallites tilted by 21° is found.The transition from the thin-film phase to the bulk phase is rationalizedby the nucleation of the latter at crystal facets of the thin-film-phasecrystallites. This leads to a self-limiting growth of the thin-filmphase and explains the thickness-dependent phase behavior observedin pentacene thin films, showing that a large amount of material ispresent in the bulk phase much earlier during the film growth thanpreviously thought.

No MeSH data available.


AFM height micrographs of pentacene samplesof 20 nm (A), 100 nm (B), and 300 nm (C) nominal thicknesses. (D)shows the incline distribution for the samples presented in (A–C).(E) depicts detailed information on the boxed area in (B). (F) showsline scans along marked areas in (C).
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fig4: AFM height micrographs of pentacene samplesof 20 nm (A), 100 nm (B), and 300 nm (C) nominal thicknesses. (D)shows the incline distribution for the samples presented in (A–C).(E) depicts detailed information on the boxed area in (B). (F) showsline scans along marked areas in (C).

Mentions: For theinvestigation of the surface topography, AFM height scan measurementshave been performed; representative AFM micrographs of the varioussamples are depicted in Figure 4. Starting with the sample of 20 nm nominal thickness (cf. Figure 4A), this shows clearthree-dimensional island structures. Similar to the case of a pentacenemonolayer,42 these structures are of dendriticshape. Furthermore, the terraces are preserved, resulting in a steplikeincrease of the structure height in the image, as frequently reportedfor pentacene thin films.43,44 The step height isin the range of 14–16 Å, as expected for pentacene grownwith a 00L orientation, which means each step correspondsto a single pentacene layer. Note that polymorph determination fromthe step height lies beyond the resolution of the AFM setup. The roughness,σRMS, of the film is determined to be 2.5 nm, andthe incline distribution shows a maximum at a slope angle of 0.3°(cf. Figure 4D, redline). A closer look at a pentacene island in the 20 nm film revealsthat the dendritic branches grow nearly independently to adjacentones. Although the terrace height seems to be constant throughoutdifferent branches, cracks are formed and adjacent branches, evenwithin one island, do not coalesce.


Self-LimitedGrowth in Pentacene Thin Films
AFM height micrographs of pentacene samplesof 20 nm (A), 100 nm (B), and 300 nm (C) nominal thicknesses. (D)shows the incline distribution for the samples presented in (A–C).(E) depicts detailed information on the boxed area in (B). (F) showsline scans along marked areas in (C).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5384045&req=5

fig4: AFM height micrographs of pentacene samplesof 20 nm (A), 100 nm (B), and 300 nm (C) nominal thicknesses. (D)shows the incline distribution for the samples presented in (A–C).(E) depicts detailed information on the boxed area in (B). (F) showsline scans along marked areas in (C).
Mentions: For theinvestigation of the surface topography, AFM height scan measurementshave been performed; representative AFM micrographs of the varioussamples are depicted in Figure 4. Starting with the sample of 20 nm nominal thickness (cf. Figure 4A), this shows clearthree-dimensional island structures. Similar to the case of a pentacenemonolayer,42 these structures are of dendriticshape. Furthermore, the terraces are preserved, resulting in a steplikeincrease of the structure height in the image, as frequently reportedfor pentacene thin films.43,44 The step height isin the range of 14–16 Å, as expected for pentacene grownwith a 00L orientation, which means each step correspondsto a single pentacene layer. Note that polymorph determination fromthe step height lies beyond the resolution of the AFM setup. The roughness,σRMS, of the film is determined to be 2.5 nm, andthe incline distribution shows a maximum at a slope angle of 0.3°(cf. Figure 4D, redline). A closer look at a pentacene island in the 20 nm film revealsthat the dendritic branches grow nearly independently to adjacentones. Although the terrace height seems to be constant throughoutdifferent branches, cracks are formed and adjacent branches, evenwithin one island, do not coalesce.

View Article: PubMed Central - PubMed

ABSTRACT

Pentaceneis one of the most studied organic semiconducting materials. Whilemany aspects of the film formation have already been identified invery thin films, this study provides new insight into the transitionfrom the metastable thin-film phase to bulk phase polymorphs. Thisstudy focuses on the growth behavior of pentacene within thin filmsas a function of film thickness ranging from 20 to 300 nm. By employingvarious X-ray diffraction methods, combined with supporting atomicforce microscopy investigations, one crystalline orientation for thethin-film phase is observed, while three differently tilted bulk phaseorientations are found. First, bulk phase crystallites grow with their00L planes parallel to the substrate surface; second,however, crystallites tilted by 0.75° with respect to the substrateare found, which clearly dominate the former in ratio; third, a differentbulk phase polymorph with crystallites tilted by 21° is found.The transition from the thin-film phase to the bulk phase is rationalizedby the nucleation of the latter at crystal facets of the thin-film-phasecrystallites. This leads to a self-limiting growth of the thin-filmphase and explains the thickness-dependent phase behavior observedin pentacene thin films, showing that a large amount of material ispresent in the bulk phase much earlier during the film growth thanpreviously thought.

No MeSH data available.