Pressure-induced phase transition in pentacene

Farina, Luca; Brillante, Aldo; Valle, Raffaele Guido Della; Venuti, Elisabetta; Amboage, M.; Syassen, K.

doi:10.1016/s0009-2614(03)00931-x

Cited by 56 publications

(71 citation statements)

References 12 publications

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“…Powder X-ray diffraction measurements confirmed this assignment. [16] The middle part of Figure 2 shows that domains of a different polymorph might be present in the crystal of either structure as a physical impurity. However, most commonly, the C phase is found as the phase impurity of the H phase and is most likely the metastable phase at ambient conditions.…”

Section: Methodsmentioning

confidence: 99%

Characterization of Phase Purity in Organic Semiconductors by Lattice‐Phonon Confocal Raman Mapping: Application to Pentacene

et al. 2005

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propagation geometry, we have performed the retrieval [7,9] of the effective magnetic permeability l and the effective electric permittivity e on the basis of calculated optical spectra. Generally, the shape of the retrieved spectra of e and l are similar to those, e.g., shown in Figure 4 of our recent publication. [7] Thus, the retrieved spectra are not shown here. For the SRR parameters of the first row of Figure 4 we find a resonance in l with l < 0 around a wavelength of 2.4 lm. For the SRR parameters of the second row of Figure 4 we find a resonance in l around 1.7 lm with reduced oscillator strength, thus l > 0, but still with a negative magnetic susceptibility. The oscillator strength is yet further reduced for the SRR parameters of the third row of Figure 4, corresponding to a magnetic resonance around a wavelength of 1.2 lm.In conclusion, we have designed and realized a variety of different metamaterials, taking advantage of the rapid prototyping capabilities of FIB nanofabrication. In particular, we have demonstrated a continuous transition from squareshaped metallic pads that exhibit a twofold degenerate Mie (electric dipole) resonance to SRRs with a red-shifted fundamental magnetic-dipole response and one remaining Mie resonance. The retrieval of the corresponding calculated optical spectra reveals a magnetic response with a negative magnetic susceptibility (although l > 0) at a wavelength of 1.7 lm and a negative permeability (i.e., l < 0) at a wavelength of 2.4 lm for propagation in the split-ring array plane. Overall, our results show the robustness of the SRR concept. Such robustness is especially important for nanometer-sized SRR arrays where fabrication tolerances are much more of an issue than for microwave structures. Combined with metallic nanowires leading to a negative permittivity, our findings on magnetic split rings pave the road for left-handed metamaterials at telecommunication wavelengths. ExperimentalThe starting point of our nanofabrication process is a glass substrate, coated with a 5 nm thin film of indium tin oxide (ITO) and a 20 nm film of gold. The ITO acts as an adhesion promoter and enhances the quality of the gold film. Both films are deposited by electron-beam evaporation under high vacuum (10 -4 Pa). The FIB writing corresponds to an inverse process in the sense that the FIB removes material. We use a dual-beam FIB/SEM (scanning electron microscopy) system (Zeiss 1540 XB) and Ga + ions accelerated by a voltage of 30 kV. Typical FIB currents are 5 pA, typical exposure doses are 2900 lA s cm -2. Each SRR consists of a square with a side length of 280 nm in which a notch of depth u is cut. The arms of the resulting "U" have a typical width of 75 nm. All structures discussed here consist of an array of 35 × 35 SRRs with a lattice constant of 450 nm (total area of 16 lm × 16 lm). The exposure of one array like the one shown in Figure 2 takes approximately 20 min. Afterwards, the structure can be immediately inspected by the SEM of the dual-beam system and no further post-proce...

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Section: Methodsmentioning

confidence: 99%

Characterization of Phase Purity in Organic Semiconductors by Lattice‐Phonon Confocal Raman Mapping: Application to Pentacene

et al. 2005

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“…This limits predictive power because experimental lattice parameters can be scarce or conflicting. In particular, different polymorphs of the same material may exist, sometimes even coexisting in the same sample [22,[26][27][28][29][30][31][32][33].…”

Section: Introductionmentioning

confidence: 99%

Structural and excited-state properties of oligoacene crystals from first principles

et al. 2016

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Molecular crystals are a prototypical class of van der Waals (vdW) bound organic materials with excitedstate properties relevant for optoelectronics applications. Predicting the structure and excited-state properties of molecular crystals presents a challenge for electronic structure theory, as standard approximations to density functional theory (DFT) do not capture long-range vdW dispersion interactions and do not yield excited-state properties. In this work, we use a combination of DFT including vdW forces, using both nonlocal correlation functionals and pairwise correction methods, together with many-body perturbation theory (MBPT) to study the geometry and excited states, respectively, of the entire series of oligoacene crystals, from benzene to hexacene. We find that vdW methods can predict lattice constants within 1% of the experimental measurements, on par with the previously reported accuracy of pairwise approximations for the same systems. We further find that excitation energies are sensitive to geometry, but if optimized geometries are used MBPT can yield excited-state properties within a few tenths of an eV from experiment. We elucidate trends in MBPT-computed charged and neutral excitation energies across the acene series and discuss the role of common approximations used in MBPT.

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“…Polymorphism in pentacene, on the other hand, has been observed in as-prepared powders [10] and thin-film growth experiments. For thin films, four different crystalline phases have been identified by using X-ray diffraction.…”

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“…X-ray powder diffraction and Raman scattering allow identification of the two polymorphic forms, [16] and pressure experiments have revealed that the 14.5 Å polymorph irreversibly transforms into the 14.1 Å polymorph at elevated pressures. [10,17,18] Energy-minimization using quasi-Monte-Carlo sampling have been employed to study the stability of polymorphs of pentacene: the two observed phases (14.1 Å and 14.5 Å) represent the deepest energy minima, [19] that is, the most stable forms of pentacene. Despite interest in the use of pentacene as an organicsemiconductor material, and the continuing efforts to characterize the various crystal forms, doubts have remained until now about both the existence of a high-temperature polymorph of pentacene and its structure and thermal-expansion properties.…”

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A Polymorph Lost and Found: The High‐Temperature Crystal Structure of Pentacene

Siegrist¹,

et al. 2007

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A well‐defined structural phase transformation is observed in bulk single crystals of pentacene, whereas pentacene powders heated above the phase‐transformation temperature do not always fully convert, and upon cooling, coexistence of the two polymorphs is observed down to room temperature. The first‐order phase transformation is isostructural: the close‐packed herringbone‐type layers shift against each other, keeping the same symmetry.

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Pressure-induced phase transition in pentacene

Cited by 56 publications

References 12 publications

Characterization of Phase Purity in Organic Semiconductors by Lattice‐Phonon Confocal Raman Mapping: Application to Pentacene

Characterization of Phase Purity in Organic Semiconductors by Lattice‐Phonon Confocal Raman Mapping: Application to Pentacene

Structural and excited-state properties of oligoacene crystals from first principles

A Polymorph Lost and Found: The High‐Temperature Crystal Structure of Pentacene

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