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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.


Rocking curvesof the 001 reflection of the thin-film phase (A) and the 001 reflectionof the Campbell (bulk) phase (B) for films with nominal thicknessesranging from 50 to 300 nm; curves are vertically shifted for clarity.Dashed lines indicate satellite peaks at ±0.75° inclinedaround the specular peak position at Δω = 0°.
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fig2: Rocking curvesof the 001 reflection of the thin-film phase (A) and the 001 reflectionof the Campbell (bulk) phase (B) for films with nominal thicknessesranging from 50 to 300 nm; curves are vertically shifted for clarity.Dashed lines indicate satellite peaks at ±0.75° inclinedaround the specular peak position at Δω = 0°.

Mentions: The specular diffraction patterns presented in Figure 1 only provide information on the crystalnetplanes that are parallel to the substrate surface. As such, thereis no information on the degree of crystal alignment (mosaicity),i.e., if some of these netplanes also develop with an inclinationto the surface. To gather this information, rocking curves were recordedon the 001 peaks of both the thin-film and Campbell phase and compared;the data are depicted in Figure 2. Starting with the thin-film phase peaks, a very similarbehavior is observed independent of the layer thickness (Figure 2A): a strong specularpeak at Δω = 0° with a narrow fwhm of about 0.1°is observed. The maximum intensity of these curves increases withthe layer thickness. Additionally to the sharp peak, a broad diffusecontribution is present, which is commonly assigned to dislocationsbeing present in the films.38


Self-LimitedGrowth in Pentacene Thin Films
Rocking curvesof the 001 reflection of the thin-film phase (A) and the 001 reflectionof the Campbell (bulk) phase (B) for films with nominal thicknessesranging from 50 to 300 nm; curves are vertically shifted for clarity.Dashed lines indicate satellite peaks at ±0.75° inclinedaround the specular peak position at Δω = 0°.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384045&req=5

fig2: Rocking curvesof the 001 reflection of the thin-film phase (A) and the 001 reflectionof the Campbell (bulk) phase (B) for films with nominal thicknessesranging from 50 to 300 nm; curves are vertically shifted for clarity.Dashed lines indicate satellite peaks at ±0.75° inclinedaround the specular peak position at Δω = 0°.
Mentions: The specular diffraction patterns presented in Figure 1 only provide information on the crystalnetplanes that are parallel to the substrate surface. As such, thereis no information on the degree of crystal alignment (mosaicity),i.e., if some of these netplanes also develop with an inclinationto the surface. To gather this information, rocking curves were recordedon the 001 peaks of both the thin-film and Campbell phase and compared;the data are depicted in Figure 2. Starting with the thin-film phase peaks, a very similarbehavior is observed independent of the layer thickness (Figure 2A): a strong specularpeak at Δω = 0° with a narrow fwhm of about 0.1°is observed. The maximum intensity of these curves increases withthe layer thickness. Additionally to the sharp peak, a broad diffusecontribution is present, which is commonly assigned to dislocationsbeing present in the films.38

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.