Characterization of ultrathin films of titanyl phthalocyanine on graphite: PIES and UPS study

Kera, Satoshi; Abduaini, A.; Aoki, Masaru; Okudaira, Koji K.; Ueno, Nobuo; Harada, Yoshiya; Shirota, Yasuhiko; Tsuzuki, Toshimitsu

doi:10.1016/s0040-6090(98)00644-0

Cited by 41 publications

(45 citation statements)

References 16 publications

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“…It can be hypothesized that the Fermi level being closer to the LUMO can result from the localized dipole moment at center of the TiOPc molecules, which has been confirmed in previous experimental and DFT calculation data. 41,42,44 It is noted that because of the existence of large After the deposition of additional TiOPc molecules onto the ML, flat-lying bilayer growth and island formation are observed resulting from "ML-by-ML" growth as shown in Figure 2. In Figure 2a, a 3D-rendered STM image shows BL growth on the TiOPc ML with a molecular ML-by-ML growth mode; after completion for the bottom face-up layer, each impinging molecule forms a new single molecule second-layer island or attaches to an existing island, instead of diffusing to a step edge or starting third layer growth.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Growth Mode Transition from Monolayer by Monolayer to Bilayer by Bilayer in Molecularly Flat Titanyl Phthalocyanine Film

et al. 2017

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To avoid defects associated with inhomogeneous crystallites and uneven morphology that degrade organic device performance, the deposition of ultraflat and homogeneous crystalline organic active layers is required. The growth mode transition of organic semiconducting titanyl phthalocyanine (TiOPc) molecule from monolayer-by-monolayer to bilayerby-bilayer can be observed on highly ordered pyrolytic graphic (HOPG), while maintaining large and molecularly flat domains. The first monolayer of TiOPc lies flat on HOPG with a ∼98% face-up orientation. However, as the thickness of the TiOPc increases to over 15 monolayers (ML), the growth mode transitions to bilayer-by-bilayer with the repeated stacking of bilayers (BL), each of which has face-to-face pairs. Density functional theory calculations reveal that the increasing of thickness induces weakening of the substrate effect on the deposited TiOPc layers, resulting in the growth mode transition to BL-by-BL. The asymmetric stacking provides the driving force to maintain nearly constant surface order during growth, allowing precise, subnanometer thickness control and large domain growth. ■ INTRODUCTIONAlthough inorganic Si and III-V materials have led the modern semiconductor industry for half a century, the integration of organic thin films has been expanded to microelectronics for displays, solar cells, and platforms for electronic skins. 1−8 These organic thin film transistors (OTFT) and organic photovoltaics (OPV) provide low cost, mechanical flexibility, and direct bandgap modulation for electroluminescence. In flexible organic electronics, molecular orientation, degree of crystallinity, and morphology govern carrier transport and injection between organic layers and electrodes; 9−14 therefore, the development of homogeneous crystalline organic channels on flexible electrodes is crucial. Taking advantage of its high strength and enhanced photovoltaic efficiency during deformation, graphene has recently been employed as a flexible electrode for OTFTs and OPV. 15−17 Therefore, to fabricate flexible organic devices integrated onto graphene electrodes, it is essential to deposit organic layers on graphene, while maintaining the growth of ultraflat large domains. Moreover, the growth of organic layers with nearly atomic flat surfaces and large domain sizes is not only required to template uniform deposition of organic heterostructures but may also enable bandgap engineering of the contacts.The growth of aromatic organic films relies on van der Waals interactions between organic molecules. 18−20 During the deposition of organic layers, the growth of the films can involve directional molecular packing, resulting from the shape anisotropy of molecules. In many cases, the molecule−substrate interaction is stronger than molecule−molecule interaction; therefore, the molecules form a flat monolayer on substrates in the initial growth stage. 20−22 However, upon additional organic molecular deposition, the molecule−substrate interaction can be overwhelmed by molecule−molecule inte...

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Section: ■ Results and Discussionmentioning

confidence: 99%

Growth Mode Transition from Monolayer by Monolayer to Bilayer by Bilayer in Molecularly Flat Titanyl Phthalocyanine Film

et al. 2017

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“…Assignments of the observed bands in the OTiPc spectra have been described in detail in the previous paper. 8) Briefly, band A is related to the π molecular orbital (MO) of the inner porphine- In the case of the as-grown 0.6-MLE film on the HOPG, the intensity of five bands A-D originating from OTiPc are weak, and, in particular, the band C 2 is scarcely seen, while features of the substrate are very strong. By considering that He * interacts effectively with an orbital extending outside the surface, it was concluded that (i) the HOPG surface is not fully covered by molecules, and (ii) molecules in the outermost layer are mainly oriented flat with the oxygen atom directed inward (downward orientation).…”

Section: Resultsmentioning

confidence: 99%

“…7) The molecular orientation in the 1-MLE film was determined by the method described in a previous paper. [7][8][9][11][12][13][14] For all spectra shown in this paper, the binding energy (E B ) and the kinetic energy (E K ) are scaled for the vacuum level (E vac ).…”

Section: Methodsmentioning

confidence: 99%

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Molecular Orientation and Aggregation of Titanyl Phthalocyanine Molecules on Graphite Substrates: Effects of Surface Topography of the Substrate

Kera

Okudaira

Harada

et al. 2001

Jpn. J. Appl. Phys.

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Penning ionization electron spectroscopy (PIES) was used to investigate the effects of crystallographic inperfection of the substrate surface on organic ultrathin-film growth. For titanyl phthalocyanine (OTiPc) evaporated on graphite, it was found that the molecular orientation and aggregation in the film depend significantly on the type of graphite substrate. On a highly oriented pyrolytic graphite (HOPG), OTiPc film prepared by 1-monolayer-equivalence (MLE) deposition consists of islands of double layers, while on Grafoil, the molecules do not aggregate as on the HOPG, and form a monolayer. This large difference originated from the surface topography of the two graphite substrates.

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“…The family of phthalocyanines (Pcs) represents one of the most promising candidates for ordered organic thin films in organic electronics due to their excellent film growth and electronic properties [18][19][20][21][22]. To date, a number of phthalocyanine adlayers have been investigated by STM and the reported topography appeared with fourfold shape independent of packing arrangements and imaging conditions [23][24][25][26][27][28].…”

Section: Introductionmentioning

confidence: 99%

On the topography multiplicity of non-planar titanyl (IV) phthalocyanine molecules and the STM imaging mechanism

et al. 2008

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Characterization of ultrathin films of titanyl phthalocyanine on graphite: PIES and UPS study

Cited by 41 publications

References 16 publications

Growth Mode Transition from Monolayer by Monolayer to Bilayer by Bilayer in Molecularly Flat Titanyl Phthalocyanine Film

Growth Mode Transition from Monolayer by Monolayer to Bilayer by Bilayer in Molecularly Flat Titanyl Phthalocyanine Film

Molecular Orientation and Aggregation of Titanyl Phthalocyanine Molecules on Graphite Substrates: Effects of Surface Topography of the Substrate

On the topography multiplicity of non-planar titanyl (IV) phthalocyanine molecules and the STM imaging mechanism

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