Polycrystalline domain structure of pentacene thin films epitaxially grown on a hydrogen-terminated Si(111) surface

Nishikata, Susumu; Sazaki, Gen; Sadowski, Jerzy; Abdullah, Amir; Nishihara, Takaharu; Fujikawa, Y.; Suto, Shozo; Sakurai, Takeshi; Nakajima, Kazuo

doi:10.1103/physrevb.76.165424

Cited by 23 publications

(47 citation statements)

References 27 publications

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“…The calculations were performed for bilayer Pn with a vacuum slab. We considered various in‐plane lattice parameters to account for thin film phases,6 a ML Pn on SiO 2 ,35 a ML Pn on H‐Si(111),14 and the bulk phase (Holmes) 36. According to previous studies, the in‐plane lattice parameters vary little between different thin film phases and the magnitude of in‐plane lattice vectors, as well as molecular tilt at (001) plane increase from a thin film phase Pn to a bulk‐terminated Pn 6, 37.…”

Section: Resultsmentioning

confidence: 99%

“…The schematic of the Pn unit cell with the outlay of the in‐plane lattice vectors is shown in Figure . When deposited on noble metals,8–11 Pn adsorbs in a lying‐down configuration, whereas on insulating,12 or semiconducting/semimetallic inorganic surfaces,13–16 Pn films are terminated with a standing‐up molecular orientation (the ab ‐plane being parallel to the substrate surface). In bottom‐contact FET structures containing both, metallic and insulating surfaces, such substrate‐dependent molecular ordering often leads to growth defects at the boundary between metal contacts and the dielectric.…”

Section: Introductionmentioning

confidence: 99%

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Real‐Time Microscopy of Reorientation Driven Nucleation and Growth in Pentacene Thin Films on Silicon Dioxide

Abdullah

Fujikawa

Sakurai

et al. 2013

Adv Funct Materials

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The role of molecular reorientation processes in the self‐assembly of anisotropic molecules, such as pentacene (Pn) is studied utilizing a unique capability of low‐energy electron microscopy (LEEM) for the real‐time investigation of the film growth. In Pn film on SiO2, a layer‐by‐layer growth is observed, albeit different from the expected Volmer–Weber growth mode typical for the systems with lower adhesion (weak interfacial interaction). The observed growth mechanism is also different than conventional concept of layer‐by‐layer, or Frank van der Merwe growth. In the Pn/SiO2 system the nucleation density decreases in each consecutive layer, at least up to four monolayers. This growth mechanism is hereafter named inverse Stranski‐Krastanov growth. Furthermore, in this growth system the second layer islands nucleate preferentially at the domain boundaries formed by the interconnections of the bottom (first layer) domains. The top layer overgrows bottom layer with its own, initial in‐plane crystal orientation, regardless of the in‐plane orientations in underlying Pn domains. The dark‐field LEEM imaging allows us to distinguish between Pn domains having different azimuthal direction of molecular tilt. LEEM intensity versus start voltage (LEEM I–V) curves taken in the vicinity of mirror potential from the first and second layer Pn islands show that the surface potential of the second layer is higher by about 0.05 eV than that of the first layer, while the surface potentials for the epitaxial and non‐epitaxial parts of the second layer island are identical.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Real‐Time Microscopy of Reorientation Driven Nucleation and Growth in Pentacene Thin Films on Silicon Dioxide

Abdullah

Fujikawa

Sakurai

et al. 2013

Adv Funct Materials

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“…When deposited on graphene or metals, such as Au or Cu, pentacene molecules generally lie flat on the substrate surface, while edge‐on configurations may also be observed under specific conditions . In contrast, when deposited on polymer surfaces, self‐assembled monolayers or amorphous silica (SiO x ), the molecules stand approximately upright, with a slight tilt of the long molecular axis away from the surface normal depending on which polymorph is present . An alternative arrangement occurs in submonolayer and monolayer films, where molecules stand vertically on the substrate surface with no tilt away from the surface normal; it should emphasized here that the monolayer structure of pentacene does not constitute a SIP as it does not extend over multiple molecular dimensions and the same is true for other monolayer structures.…”

Section: Experimentally Observed Sipsmentioning

confidence: 99%

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

Jones

Chattopadhyay

Geerts

et al. 2016

Adv Funct Materials

228

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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“…Moreover, the use of low energy electrons minimizes damage to the organic films. The Pn grown on various substrates such as metallic, semiconducting and modified ones [5][6][7][8] has been investigated by LEEM. In anisotropic systems like Pn, the molecular orientation and crystalline structure critically depend on the competition of the intermolecular and the moleculesubstrate interactions.…”

Section: Introductionmentioning

confidence: 99%

Pentacene growth on graphite investigated by low-energy electron microscope

Liu¹,

Abdullah²,

Fujikawa³

et al. 2010

Journal of Crystal Growth

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Polycrystalline domain structure of pentacene thin films epitaxially grown on a hydrogen-terminated Si(111) surface

Cited by 23 publications

References 27 publications

Real‐Time Microscopy of Reorientation Driven Nucleation and Growth in Pentacene Thin Films on Silicon Dioxide

Real‐Time Microscopy of Reorientation Driven Nucleation and Growth in Pentacene Thin Films on Silicon Dioxide

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

Pentacene growth on graphite investigated by low-energy electron microscope

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