Structural analysis of molecular nanostructures and thin films

Phthalocyanines (Pcs) form crystals whose structure and morphology depend on the growth conditions, leading to changes in the physical properties which are still little understood. Pc thin films and nanostructures have already been exploited in optoelectronic applications and could form the basis of spintronic devices but little or contradictory structural information is available because they are challenging systems to study. Hence the precise determination of the molecular order in these systems is of considerable interest both from a fundamental and technological point of view but requires a combination of complementary techniques. Crystalline powders of α-copper phthalocyanine (CuPc), α-metal-free phthalocyanine (H2Pc) and their mixtures are studied using powder X-ray diffraction (XRD) and found to be isomorphous and adopt a triclinic structure first proposed for α-CuPc (Hoshino et al., 2003). This information is used to study highly textured crystalline α-Pc thin films. The texture reduces the available crystallographic information but allows for the manipulation of the anisotropic physical properties. The Pc molecular plane lies 82±11° to the substrate when deposited on a weakly interacting substrate but at 7 or 9±5° when templated by a layer of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA). Such an interpretation is different to all those previously given. The change in the texture is confirmed by high resolution transmission electron microscopy (HRTEM) of ultramicrotomed cross-sections of the films. The optimum TEM operating conditions were first determined on sections of CuPc single crystals which demonstrated an information limit of ~5Å with HRTEM. The technique was then applied to the films and the morphology, crystallinity and texturing of the layers is largely retained by the sectioning process. With further refinements it is hoped that this technique could be used to study the properties of interfaces and individual domains in multilayers and blends of organic thin films. Lastly the crystal structure of a new CuPc phase designated as η which forms nanowires as thin as 10nm and shows enhanced absorption in the infra-red (IR) is proposed. XRD, transmission electron diffraction (TED) and lattice potential energy (LPE) minimisation were used to determine the crystal structure: monoclinic P21/a, Z = 2, a = 24.8±0.2Å, b = 3.77±0.02Å, c = 13.2±0.1Å and β = 106±1°. The LPE minimisation was validated by correctly predicting the atomic coordinates of β-CuPc to within 0.05Å

Structural analysis of molecular nanostructures and thin films

Phthalocyanines (Pcs) form crystals whose structure and morphology depend on the growth conditions, leading to changes in the physical properties which are still little understood. Pc thin films and nanostructures have already been exploited in optoelectronic applications and could form the basis of spintronic devices but little or contradictory structural information is available because they are challenging systems to study. Hence the precise determination of the molecular order in these systems is of considerable interest both from a fundamental and technological point of view but requires a combination of complementary techniques. Crystalline powders of α-copper phthalocyanine (CuPc), α-metal-free phthalocyanine (H2Pc) and their mixtures are studied using powder X-ray diffraction (XRD) and found to be isomorphous and adopt a triclinic structure first proposed for α-CuPc (Hoshino et al., 2003). This information is used to study highly textured crystalline α-Pc thin films. The texture reduces the available crystallographic information but allows for the manipulation of the anisotropic physical properties. The Pc molecular plane lies 82±11° to the substrate when deposited on a weakly interacting substrate but at 7 or 9±5° when templated by a layer of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA). Such an interpretation is different to all those previously given. The change in the texture is confirmed by high resolution transmission electron microscopy (HRTEM) of ultramicrotomed cross-sections of the films. The optimum TEM operating conditions were first determined on sections of CuPc single crystals which demonstrated an information limit of ~5Å with HRTEM. The technique was then applied to the films and the morphology, crystallinity and texturing of the layers is largely retained by the sectioning process. With further refinements it is hoped that this technique could be used to study the properties of interfaces and individual domains in multilayers and blends of organic thin films. Lastly the crystal structure of a new CuPc phase designated as η which forms nanowires as thin as 10nm and shows enhanced absorption in the infra-red (IR) is proposed. XRD, transmission electron diffraction (TED) and lattice potential energy (LPE) minimisation were used to determine the crystal structure: monoclinic P21/a, Z = 2, a = 24.8±0.2Å, b = 3.77±0.02Å, c = 13.2±0.1Å and β = 106±1°. The LPE minimisation was validated by correctly predicting the atomic coordinates of β-CuPc to within 0.05Å.EThOS - Electronic Theses Online ServiceEPSRCGBUnited Kingdo

Orientation effects in copper phthalocyanine films studied by electron paramagnetic resonance spectroscopy

This article performs an analysis of current limitations regarding the extraction of parallel behavioral models to reproduce the power amplifier (PA) nonlinear behavior and its dynamics. To overcome these limitations, a general preprocessing block that clearly improves the identification capabilities shown by classical parallel structures is proposed. It follows the principle of separating both static and dynamic nonlinear behavior of the PA to obtain a better identification performance. A comparison with common parallel configurations using linear estimation is performed, to highlight the benefits of using the preprocessing structure. Furthermore, a new nonlinear parallel structure using sub-band filtering techniques is also proposed. For the models extraction and comparison, four types of noise-free simulated data presenting different levels of nonlinearities and memory, as well as a measured signal obtained from a laboratory amplifier have been considered.TARGET - IST-1-507893-NOECAPES-BrazilSpanish Government (MICINN) - TEC2008-06684-C03-0

Spin-Based Diagnostic of Nanostructure in Copper Phthalocyanine–C₆₀ Solar Cell Blends

Nanostructure and molecular orientation play a crucial role in determining the functionality of organic thin films. In practical devices, such as organic solar cells consisting of donor–acceptor mixtures, crystallinity is poor and these qualities cannot be readily determined by conventional diffraction techniques, while common microscopy only reveals surface morphology. Using a simple nondestructive technique, namely, continuous-wave electron paramagnetic resonance spectroscopy, which exploits the well-understood angular dependence of the <i>g</i>-factor and hyperfine tensors, we show that in the solar cell blend of C₆₀ and copper phthalocyanine (CuPc)for which X-ray diffraction gives no informationthe CuPc, and by implication the C₆₀, molecules form nanoclusters, with the planes of the CuPc molecules oriented perpendicular to the film surface. This information demonstrates that the current nanostructure in CuPc:C₆₀ solar cells is far from optimal and suggests that their efficiency could be considerably increased by alternative film growth algorithms

Spin-Based Diagnostic of Nanostructure in Copper Phthalocyanine-C-60 Solar Cell Blends

For the first time, two types of the metallofullerene Nd@C82 have been isolated and characterized. HPLC was used to isolate Nd@C82(I, II). The two isomers were characterized by mass spectrometry and UV‐Vis‐NIR absorption spectroscopy. Nd@C82(I) was found to be similar in structure to the main isomer of other lanthanofullerenes such as La@C82, as was previously reported. We assign Nd@C82(I) to have a C2v cage symmetry. Nd@C82(II) showed a markedly different UV‐Vis‐NIR absorption spectrum to Nd@C82(I). Its spectrum is in good agreement with that of the minor isomer of metallofullerenes such as Pr@C82. We therefore assign Nd@C82(II) to have a Cs cage symmetry. In contrast to other metallofullerenes, both isomers appear to be equally abundant