Molecular dynamics simulations of pentacene thin films: The effect of surface on polymorph selection

Yoneya, Makoto; Kawasaki, Masahiro; Ando, Masahiko

doi:10.1039/c0jm01577f

Cited by 49 publications

(67 citation statements)

References 25 publications

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“…According to the work of Yoneya et al on pentacene, 22 the thin film phase is favored close to the substrate surface as the packing arrangement of pentacene molecules induces a flatter interface between molecular lamellae. This is practically achieved by a "shifted structure" whereby the positions of pentacene molecules of a given lamella are shifted within the (a, b) plane (contact plane of the lamellae) with respect to pentacene molecules of the subsequent lamella.…”

Section: Discussionmentioning

confidence: 99%

“…11,12 Subsequently, numerous studies have been undertaken to investigate the crystal structure 13−17 and the origin 18−23 of these thin film phases considering the high relevance of pentacene for thin film organic electronic applications. 2−4 Surface energy 18,19 and structure, 20,21 substrate roughness, 22,23 as well as processing conditions 24−26 have been reported to play a role in the preferential crystallization of a given structural organization close to the substrate. Remarkably, recent theoretical studies based on Molecular Dynamics (MD) simulations 20−23 brought significant insight on the influence of substrate/molecules and molecules/molecules interactions on polymorph selection close to the substrate−molecule interface.…”

Section: Introductionmentioning

confidence: 99%

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X-ray Structural Investigation of Nonsymmetrically and Symmetrically Alkylated [1]Benzothieno[3,2-b]benzothiophene Derivatives in Bulk and Thin Films

Gbabode

Dohr

Niebel

et al. 2014

ACS Appl. Mater. Interfaces

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A detailed structural study of the bulk and thin film phases observed for two potential high performance organic semi conductors has been carried out. The molecules are based on [1]benzothieno[3,2 b]benzothiophene (BTBT) as conjugated core and octyl side groups, which are anchored either symmetrically at both sides of the BTBT core (C 8 −BTBT−C 8 ) or nonsymmetrically at one side only (C 8 −BTBT). Thin films of different thickness (8−85 nm) have been prepared by spin coating for both systems and analyzed by combining specular and grazing incidence X ray diffraction. In the case of C 8 −BTBT−C 8 , the known crystal structure obtained from single crystal investigations is observed within all thin films, down to a film thickness of 9 nm. In the case of C 8 −BTBT, the crystal structure of the bulk phase has been determined from X ray powder diffraction data with a consistent matching of experimental and calculated X ray diffraction patterns (Rwp = 5.8%). The packing arrangement of C 8 −BTBT is similar to that of C 8 −BTBT−C 8 , that is, consisting of a lamellar structure with molecules arranged in a "herringbone" fashion, yet with lamellae composed of two head to head (or tail to tail as the structure is periodic) superimposed molecules instead of only one molecule for C 8 −BTBT−C 8 . As for C 8 −BTBT−C 8 ,we demonstrate that the same phase is observed in bulk and thin films for C 8 −BTBT whatever the film thickness investigated.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

X-ray Structural Investigation of Nonsymmetrically and Symmetrically Alkylated [1]Benzothieno[3,2-b]benzothiophene Derivatives in Bulk and Thin Films

Gbabode

Dohr

Niebel

et al. 2014

ACS Appl. Mater. Interfaces

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“…There is a report that focused on the adsorption and packing of 6T molecules on Ag(111) surfaces by MD simulations, 18) but the simulations were largely different from the present case where many 6T molecules are standing on inert surfaces and form a bulklike crystal structure. In the case of pentacene, many papers on MD simulations have been published, [12][13][14][15] but the force field model used was caseby-case; the MM3 potential was used in Refs. 12 and 15, the Buckingham potential model with a Coulombic contribution for the interaction between rigid pentacene molecules (and DREIDING parameters for the interactions between pentacene molecules and silica substrates) was used in Ref.…”

Section: Interactions Between Atoms and Moleculesmentioning

confidence: 99%

“…In previous papers, there seems to have been a tendency to use the Buckingham potential more frequently than the Lennard-Jones potential for describing the van der Waals interactions in molecular crystalline systems. 13,14) In this study, both the Buckingham potential and Lennard-Jones potential were used and results were compared (the results were not very different from each other). The Si and O atoms in amorphous SiO 2 substrates were not moved during all the simulations carried out in this study, by fixing the velocity of these atoms as zero.…”

Section: Interactions Between Atoms and Moleculesmentioning

confidence: 99%

“…MD simulations have already been applied to organic semiconductors, mainly to the research on pentacene (C 22 H 14 ). [12][13][14][15] However, they have not been applied to the study of "graphoepitaxy" of organic semiconductors, to the best of the author's knowledge. First, in this study, MD simulations of orientation adjustment at the groove edge were carried out.…”

Section: Introductionmentioning

confidence: 99%

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Molecular dynamics simulations of graphoepitaxy of organic semiconductors, sexithiophene, and pentacene: Molecular-scale mechanisms of organic graphoepitaxy

Ikeda

2018

Jpn. J. Appl. Phys.

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Molecular dynamics (MD) simulations of the organic semiconductors α-sexithiophene (6T) and pentacene were carried out to clarify the mechanism of organic graphoepitaxy at the molecular level. First, the models of the grooved substrates were made and the surfaces of the inside of the grooves were modified with -OH or -OSi(CH 3 ) 3 , making the surfaces hydrophilic or hydrophobic. By the MD simulations of 6T, it was found that three stable azimuthal directions exist (0, >45, and 90°; the angle that the c-axis makes with the groove), being consistent with experimental results. MD simulations of deposition processes of 6T and pentacene were also carried out, and pentacene molecules showed the spontaneous formation of herringbone packing during deposition. Some pentacene molecules stood on the surface and formed a cluster whose a-axis was parallel to the groove. It is expected that a deep understanding of the molecular-scale mechanisms will lead graphoepitaxy to practical applications, improving the performance of organic devices.

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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

231

280

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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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Molecular dynamics simulations of pentacene thin films: The effect of surface on polymorph selection

Cited by 49 publications

References 25 publications

X-ray Structural Investigation of Nonsymmetrically and Symmetrically Alkylated [1]Benzothieno[3,2-b]benzothiophene Derivatives in Bulk and Thin Films

X-ray Structural Investigation of Nonsymmetrically and Symmetrically Alkylated [1]Benzothieno[3,2-b]benzothiophene Derivatives in Bulk and Thin Films

Molecular dynamics simulations of graphoepitaxy of organic semiconductors, sexithiophene, and pentacene: Molecular-scale mechanisms of organic graphoepitaxy

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

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