Crystal Growth, Structure, and Electronic Band Structure of α-4T Polymorphs

Siegrist, T.; Kloc, Christian; Laudise, R.A.; Katz, Howard E.; Haddon, Robert C.

doi:10.1002/(sici)1521-4095(199803)10:5<379::aid-adma379>3.0.co;2-a

Cited by 268 publications

(230 citation statements)

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“…The band line shape reflects the anisotropy of the known optical absorption of ͑001͒-oriented single crystalline thin films of ␣-4T with the structure of the low temperature ͑␣-4T / LT͒ polymorph having a monoclinic unit cell with parameters a = 6.09 Å, b = 7.86 Å, c = 30.48 Å, and ␤ = 91.8°. 5,[23][24][25] Indeed, the difference A ʈa ␣-4T − A Ќa ␣-4T between the absorbance for polarized light with the electric field parallel ͑ ʈ a ␣-4T ͒ and perpendicular ͑Ќa ␣-4T ͒ to the a ␣-4T axis, reported for such a single crystalline ␣-4T film in Fig. 2͑b͒, shows a positive band due to the strong absorption feature under ʈ a ␣-4T polarized light, negligible under Ќa ␣-4T polarized light; 24,25 hence, by the comparison between Figs.…”

Section: Dipartimento DI Scienza Dei Materiali and Cnism Università mentioning

confidence: 81%

“…It originates from the interference due to the crystal finite thickness ͑as indeed checked by measuring different TEN samples, not shown here͒. In the case under analysis this phenomenon is strongly limited due to a suitable choice of the TEN crystal substrate so thin that any complete fringes cannot be observed; in this way, after deposition of ␣-4T the anisotropy 23 of the film can be detected, if any.…”

Section: Dipartimento DI Scienza Dei Materiali and Cnism Università mentioning

confidence: 99%

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Pseudomorphic growth of organic semiconductor thin films driven by incommensurate epitaxy

Sassella

Campione

Raimondo

et al. 2009

Applied Physics Letters

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A stable pseudomorphic phase of ␣-quaterthiophene, a well known organic semiconductor, is obtained by growing films with organic molecular beam epitaxy ͑OMBE͒ on a single crystal of another organic semiconductor, namely, tetracene. The structural characteristics of the new phase are investigated by monitoring in situ the OMBE process by reflectance anisotropy spectroscopy; thus assessing that incommensurate epitaxy is in this case, the driving force for tuning the molecular packing in organic molecular films and in turn, their solid state properties. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3081413͔The key factor improving the performances of thin film devices based on organic semiconductors is the achievement of high charge mobility through the control of growth mechanisms aimed at improving the structural quality and morphology of the thin films. 1 The fine tuning of the material properties by a suitable modification of the molecular orientation and packing ͑crucial for determining the electronic band structure of the solid film and its charge-transport properties͒ 2 represents an alternative experimental opportunity. The arrangement of different organic semiconductors in multilayer architectures, including semiconductor junctions, gives further beneficial effects in thin film devices. 1 In this framework, organic molecular beam epitaxy ͑OMBE͒ represents the best choice among the growth techniques, assuring high quality films and controlled interfaces in organic heterostructures in view of both fundamental studies and applications. 3,4 Among the strategies for growing samples with designed properties, one of the most promising is the use of organic substrates 5-7 whose effect in tuning the molecular orientation of the overlayer has been already demonstrated. In particular, when organic single crystals are used as substrates, highly oriented organic heterostructures are grown even in the absence of any geometric coincidence between substrate and overlayer ͑incommensurate epitaxy͒. 5,[8][9][10][11][12][13] In this letter, we investigate the properties of an organic-organic heterostructure by demonstrating the OMBE growth of an epitaxial pseudomorphic phase of the ␣-quaterthiophene ͑␣-4T͒ film on tetracene ͑TEN͒ single crystals. By means of reflectance anisotropy spectroscopy ͑RAS͒, we monitored in situ the OMBE process, showing that the ␣-4T overlayer grows with a distorted lattice structure with respect to the bulk crystal, which results in incommensurate epitaxy. In addition, the full ex situ stability of this new phase is demonstrated so that organic-organic epitaxy is definitely assessed as a powerful tool for tuning the properties of the growing films. 14 ␣-4T was synthesized and purified according to Ref. 15, while commercial TEN was purified by several sublimation steps before use. TEN single crystals were grown by physical vapor transport. 16 Its crystal structure belongs to the triclinic system, with unit cell parameters a = 6.06 Å, b = 7.84 Å, c = 13.01 Å, ␣ = 77.13°, ␤ = 72.12°, ␥ = 85.79...

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Section: Dipartimento DI Scienza Dei Materiali and Cnism Università mentioning

confidence: 81%

Section: Dipartimento DI Scienza Dei Materiali and Cnism Università mentioning

confidence: 99%

Pseudomorphic growth of organic semiconductor thin films driven by incommensurate epitaxy

Sassella

Campione

Raimondo

et al. 2009

Applied Physics Letters

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show abstract

“…The electronic band structure calculation methods were successfully applied to a number of organic semiconductor materials. 10,[24][25][26] Prior to the band structure calculations, the atomic positions obtained from X-ray diffraction measurement were optimized with a force tolerance of 10 meV/ Å. Some of the interatomic distances are listed in Table 3.…”

Section: Resultsmentioning

confidence: 99%

Crystal Growth, Structure, and Electronic Band Structure of Tetracene−TCNQ

et al. 2007

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Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. September 12, 2006; In Final Form: December 6, 2006 We have grown the charge-transfer salt of the electron acceptor 7,7,8, and the electron donor tetracene using physical vapor transport. The crystal structure was solved by singlecrystal X-ray diffraction and the symmetry was found to be triclinic (space group P1 h). The 1:1 complex grows by alternating face to face stacking of tetracene and TCNQ molecules. Calculations on the electronic band structure show that the tetracene-TCNQ complex is an indirect band gap semiconductor and provide insight in the conductive properties of tetracene-TCNQ.

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“…2 has been measured after 8 nm of 4T were deposited on KAP (in two steps, 4 nm each). It clearly shows the structure at about 3.6 eV characteristic of the 4T film grown on KAP at low substrate temperature [9] (close to that of the low temperature polymorph [10]), with (001) as contact plane. The dielectric response of crystalline 4T [9,11] permits assignment of this peak to a contribution of the dielectric function of mixed transversal-longitudinal character, while its negative sign suggests that the a 4T (b 4T ) axis of the 4T crystal in the film is aligned with the β(α) reference direction of the RAS apparatus.…”

Section: Resultsmentioning

confidence: 99%