Temperature stability of the pentacene thin-film phase

Moser, A.; Novák, Jiřı́; Flesch, Heinz-Georg; Djuric, Tatjana; Werzer, Oliver; Haase, A.; Resel, Roland

doi:10.1063/1.3665188

Cited by 22 publications

(29 citation statements)

References 19 publications

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“…When solved by a combination of first‐principles calculations and grazing incidence X‐ray diffraction (GIXD) (Figure ), the crystal structure of the SIP showed a reduced tilt of the long molecular axis compared with the bulk polymorphs and an interlayer packing closer to the HT phase than the LT phase (Figure b) . Crucially, the 15.4 Å SIP is found to be relatively unstable, converting to the HT bulk phase at elevated temperatures and with film aging; various methods have been employed to attempt to understand and control the phase formation by solvent and postannealing, controlling film thickness, limiting the conversion of the SIP to the bulk phase using capping layers or deposition of films on rough surfaces to preferentially form the bulk phase …”

Section: Experimentally Observed Sipsmentioning

confidence: 99%

“…A similar transformation is also observed for C 8 O‐BTBT‐OC 8 ( 12 ) films if the sample is stored for a period of over 6 months or if it is subjected to solvent vapor annealing, which serves as a catalyst to accelerate the transformation to the bulk phase . A transformation from the SIP to the bulk phase of 1 is also observed on heating above ≈400 K …”

Section: Growth and Evolution Of Sipsmentioning

confidence: 99%

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Substrate‐Induced and Thin‐Film Phases: Polymorphism of Organic Materials on Surfaces

Jones

Chattopadhyay

Geerts

et al. 2016

Adv Funct Materials

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231

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2233wileyonlinelibrary.com to that of the bulk liquid; [ 7 ] order typically exists over a few molecular layers before rapidly decaying to bulk behavior as the distance from the wall increases. [ 8 ] Similar ordering effects can also be observed in the quasiliquids which form on the surface of many solids due to surface melting (also known as premelting): [ 9,10 ] the existence of a liquid-like layer a few molecules thick on the surface of a solid below the melting point of the bulk material. [ 11 ] The structure within this layer is also found to be different to that of the bulk isotropic liquid, [ 12 ] highlighting the ordering occurring at the interface. A converse effect, surface freezing, is also observed in some liquids (primarily n -alkanes with 16 ≤ n ≤ 50), where a solid monolayer may exist at an interface up to ≈30 °C above the bulk melting point while the rest of the compound is molten. [13][14][15] Such phase behavior is strongly dependent on molecular shape and has only been observed for chain molecules, which then form layers similar to self-assembled monolayers (SAMs) at the interface with the liquid bulk. [ 16 ] Further examples of molecular ordering at interfaces can be seen in materials which display liquid crystal (LC) phases, a phase behavior also dependent on molecular shape and generally observed for molecules with a highly anisotropic shape (e.g., rod-like, disc-like or bowl-like molecules). [ 17 ] LCs have properties of both solids and liquids and display long range order which may be orientational and/or positional; various types of LC phases (mesophases) are possible and normally exist only over a certain temperature range (i.e., they are thermotropic); a further property of LCs is that they generally reach thermodynamic equilibrium in the bulk and at interfaces as a result of their short relaxation time. Nematic (N) phases of calamitic LCs (rod-like molecules with cylindrical symmetry) have no positional order but an orientational order which can be described by a unit vector, n , known as the director, which represents the preferred molecular orientation ( Figure 1 , left). A scalar order parameter can also be defi ned which is related to the average angle the long molecular axes make to the director, n .Increased order is seen in smetic phases (Sm) which have both orientational and positional order; for example in a smetic A phase (SmA) molecules form layers (positional ordering of the molecular mass centers) which are oriented normal to the plane of the layers (orientational order), while smetic C phases (SmC) form layers where molecules are oriented with the long molecular axes tilted at an angle to the molecular layer normal However, the factors that drive such a process are not clearly understood or studied in depth. In this feature article, we review the current state of understanding concerning SIPs, giving examples of systems where SIPs have been observed, discussing their origins, and which questions remain to be answered. The role of the substrate in controlling the growth a...

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Section: Experimentally Observed Sipsmentioning

confidence: 99%

Section: Growth and Evolution Of Sipsmentioning

confidence: 99%

Substrate‐Induced and Thin‐Film Phases: Polymorphism of Organic Materials on Surfaces

Jones

Chattopadhyay

Geerts

et al. 2016

Adv Funct Materials

Self Cite

231

280

View full text Add to dashboard Cite

show abstract

“…[15][16][17][18][19] Due to the similar packing motif, bulk and TF phase can coexist in the film, and transitions from TF to bulk phase can be induced via temperature and aging. 10,20,21 0021-9606/2018/149(14)/144701/5/$30.00…”

Section: Introductionmentioning

confidence: 99%

Molecular structure of the substrate-induced thin-film phase of tetracene

Pithan

Nabok

Cocchi

et al. 2018

The Journal of Chemical Physics

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We present a combined experimental and theoretical study to solve the unit-cell and molecular arrangement of the tetracene thin film (TF) phase. TF phases, also known as substrate induced phases (SIPs), are polymorphs that exist at interfaces and decisively impact the functionality of organic thin films, e.g., in a transistor channel, but also change the optical spectra due to the different molecular packing. As SIPs only exist in textured ultrathin films, their structure determination remains challenging compared to bulk materials. Here, we use grazing incidence X-ray diffraction and atomistic simulations to extract the TF unit-cell parameters of tetracene together with the atomic positions within the unit-cell.

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“…18,19 The metastable thin-film phase can be transformed into the Campbell phase by either heat treatment, solvent treatment, or aging, which is evident from experimental studies and molecular dynamics calculations. 20−23 Moreover, some recent results show that Campbell phase crystallites not only grow with their 001 contact plane parallel to the thin film polymorph, but additionally with their 001 contact plane inclined by well-defined angles of 5°, 10°, or 13°. 24−26 While homoepitaxy between the 001 TF (thin film) and 001 C (Campbell) planes might appear obvious, the appearance of inclined structures on the terraced 3D islands is surprising, and the mechanisms behind their formation remain unresolved.…”

Section: Introductionmentioning

confidence: 99%

Self-Limited Growth in Pentacene Thin Films

Pachmajer

Jones

Truger

et al. 2017

ACS Appl. Mater. Interfaces

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Pentacene is one of the most studied organic semiconducting materials. While many aspects of the film formation have already been identified in very thin films, this study provides new insight into the transition from the metastable thin-film phase to bulk phase polymorphs. This study focuses on the growth behavior of pentacene within thin films as a function of film thickness ranging from 20 to 300 nm. By employing various X-ray diffraction methods, combined with supporting atomic force microscopy investigations, one crystalline orientation for the thin-film phase is observed, while three differently tilted bulk phase orientations are found. First, bulk phase crystallites grow with their 00L planes parallel to the substrate surface; second, however, crystallites tilted by 0.75° with respect to the substrate are found, which clearly dominate the former in ratio; third, a different bulk phase polymorph with crystallites tilted by 21° is found. The transition from the thin-film phase to the bulk phase is rationalized by the nucleation of the latter at crystal facets of the thin-film-phase crystallites. This leads to a self-limiting growth of the thin-film phase and explains the thickness-dependent phase behavior observed in pentacene thin films, showing that a large amount of material is present in the bulk phase much earlier during the film growth than previously thought.

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Temperature stability of the pentacene thin-film phase

Cited by 22 publications

References 19 publications

Substrate‐Induced and Thin‐Film Phases: Polymorphism of Organic Materials on Surfaces

Substrate‐Induced and Thin‐Film Phases: Polymorphism of Organic Materials on Surfaces

Molecular structure of the substrate-induced thin-film phase of tetracene

Self-Limited Growth in Pentacene Thin Films

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