Growth of conjugated oligomer thin films studied by atomic-force microscopy

Biscarini, Fabio; Zamboni, R.; Samorı́, Paolo; Ostoja, P.; Taliani, C.

doi:10.1103/physrevb.52.14868

Cited by 146 publications

(139 citation statements)

References 30 publications

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“…A similar value being in order of few hundred meV has been found e.g. for sexithiophene islands on mica [164]. For homogeneous nucleation such a behavior has been predicted in the literature, with the activation energy E N being a function of characteristic energies like the energies for adsorption and diffusion and of the critical nucleus size of the system [165].…”

Section: 22supporting

confidence: 50%

“…These islands are non-fluorescent because they are formed of upright standing molecules on the surface. In the literature it has been discussed for αT6 [164], that two different types of island exist: Either islands consisting of a simple layer of upright standing molecules (refers to stepheight of 2.7 nm) or islands consisting of a layer of lying molecules with a layer of upright standing molecules on top (refers to stepheight of 3.0 nm). Sometimes tall aggregates with heights up to 200 nm grow on top of those islands, Fig.9.6(c), similar to PPTTPP, Fig.9.5(a).…”

Section: Growthmentioning

confidence: 99%

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Organic Molecular Nanotechnology

Schiek

Balzer

Al‐Shamery

et al. 2008

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Zur Homepage der Dissertation AbstractFormation of needle-like crystals from inorganic as well as from organic semiconductors such as para-phenylenes, α-thiophenes and phenyl-thiophene co-oligomers on dielectric surfaces has attracted increasing interest within the last years. The para-hexaphenylene has proven to be a versatile building block for generating long, parallely aligned organic nanofibers by a self-assembly process on a muscovite mica substrate via sublimation in high vacuum. These nanofibers possess outstanding optical properties like strong, polarised blue fluorescence in high quantum yields after unpolarised excitation with UV light, waveguiding and lasing features. Furthermore, they are chemically and thermically stable and can be easily detached from the growth substrate to serve as key elements in next generation optoelectronic and nanophotonic devices. Owing to their typical height and width on a nanometer scale and length up to one millimeter, the fibers bridge the gap between microscopic and macroscopic dimensions. The morphology of the nanofibers (length, height, width, aspect ratio, bending into rings) is susceptable to process parameters and pretreatment of the substrate. But chemically functionalisation of the molecular building block as key step of this thesis widens the scope of possibilities: Nanoaggregates with tailored morphology and optical properties are generated from designed functionalised molecular building blocks. Functional groups have been implemented at the 1,4´´´-para-positions of p-quaterphenylenes using a non-trivial Suzuki cross-coupling strategy. Symmetrically as well as non-symmetrically functionalised oligomers have been achieved in excellent yields and high purity. Additionally, the synthesis of phenyl-thiophene cooligomers and their acceptability for the nanofiber growth on muscovite mica via organic molecule deposition in high vacuum are presented. The fluorescence peak emission frequency of the nanostructures from the substituted p-quaterphenylenes shifts within the blue depending on the functionalisation. While dimensions are still influenced by the growth parameters, the overall shape (i.e. cross-section) of the aggregates alters significantly with the functional group. Even new properties like nonlinear optical activity are accessible. Due to intrinsic nonzero hyperpolarisability of push-pull functionalised oligomers, the respective nanofibers act as frequency doublers and emit strong second harmonic light after excitation with near infrared femtosecond laser pulses. Note that this design approach is possible while conserving the concept of highly crystalline nanofibers. Thus, a new route of bottom-up nanotechnology is presented starting from organic molecular synthesis towards generating of tailormade organic nanofibers opening new prospects for future nanotechnology. 3 ZusammenfassungDie Bildung von nadelförmigen Kristallen aus anorganischen und organischen Halbleitermolekülen wie zum Beispiel para-Phenylenen, α-Thiophenen und Phenylthiophen Co-oligomeren fa...

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Section: 22supporting

confidence: 50%

Section: Growthmentioning

confidence: 99%

Organic Molecular Nanotechnology

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Balzer

Al‐Shamery

et al. 2008

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“…We conclude that on increasing the thickness of deposited material the memory of the template effect given by the patterned electrodes is lost and T6 growth proceeds in a homo-epitaxial mode. [27] A closer look at Figure 8 points the attention to an intriguing feature present and reproduced in all reported maps: Raman maps have a larger lateral colour spread with respect to the electrode pattern obtained from optical microscopy. In order to clarify this feature we refer to a magnification of parallel gold electrodes, as in Figure 9.…”

Section: Confocal Raman Mapping Of T6-based Fet'smentioning

confidence: 99%

Confocal Raman Spectroscopy of α‐Sexithiophene: From Bulk Crystals to Field‐Effect Transistors

Brillante¹,

Bilotti²,

Albonetti³

et al. 2007

Adv Funct Materials

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We report confocal micro‐Raman spectra of the organic semiconductor α‐sexithiophene (T6) on bulk crystals and on thin films grown on technologically relevant substrates and devices. We show that the two polymorphs, which are clearly identified by their lattice phonon spectra, may coexist as physical impurities of one inside the other in the same crystallite. Spatial distribution of the two phases is monitored by Raman phonon mapping of crystals grown upon different conditions. Raman microscopy has then been extended to T6 thin films grown on silicon oxide wafers. We identify the crystal phase in thin films whose thickness is just 18 nm. The most intense total‐symmetric Raman vibration is still detectable for a two‐monolayer thick film. Comparative analysis between micro‐Raman and AFM of T6 thin films grown on field effect transistors shows that electrode‐channel steps favour the nucleation and growth of T6 molecules on the substrate, at least below 50 nm.

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“…A conjugated oligomer, such as a-sexithienyl (T 6 ), [13] is a prototype for the electro-optical properties of a polymer, but it has a well-defined composition, which makes it possible to compare films with single crystals, [14±17] and it can be purified and processed by clean techniques, such as sublimation in ultra-high vacuum, [18] in the absence of solvents and contaminants. The kinetics of the film growth by high vacuum sublimation is governed by parameters such as deposition rate, temperature of the substrate, and amount of deposited material, i.e., time of deposition or film thickness.…”

mentioning

confidence: 99%

Morphology Controlled Energy Transfer in Conjugated Molecular Thin Films

Muccini¹,

Murgia²,

Biscarini³

2001

Adv. Mater.

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In α‐sexithienyl (T6) molecular thin films the spectral features of photoluminescence can be correlated to precise structural topologies and the nature of photoluminescence can be controlled. AFM images show that the topological features of T6 films evolve progressively from 2D to 3D structures with film thickness. It is shown that coalescence between different domains results in photoluminescence spectra that are dominated by the aggregate emission. The Figure shows the photoluminescence spectra of submonolayer and lamellae architectures.

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Growth of conjugated oligomer thin films studied by atomic-force microscopy

Cited by 146 publications

References 30 publications

Organic Molecular Nanotechnology

Organic Molecular Nanotechnology

Confocal Raman Spectroscopy of α‐Sexithiophene: From Bulk Crystals to Field‐Effect Transistors

Morphology Controlled Energy Transfer in Conjugated Molecular Thin Films

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