79 results found
Attwood M, Kim DK, Hadden JHL, et al., 2021, Asymmetric N-heteroacene tetracene analogues as potential n-type semiconductors, Journal of Materials Chemistry C, Vol: 9, Pages: 17073-17083, ISSN: 2050-7526
In the search for high performance n-type organic semiconductors (OSCs) a simple strategy might be substitution of aromatic CH groups for nitrogen heteroatoms. Here, we report the synthesis and characterisation of two novel N-heteroacene compounds, namely, 1,5,12-triazatetracene (TrAT1) and 2,5,12-triazatetracene (TrAT2). Their potential as n-type materials is evaluated against 5,12-diazatetracene (DAT) by UV/vis and EPR spectroscopy, cyclic voltammetry, DFT, single crystal X-ray diffraction and thin film characterisation. Increasing the number of N-heteroatoms was found to stabilise the HOMO and LUMO leading to electron affinities for TrAT1 and TrAT2 of ca. −4 eV. Both compounds were found to exhibit columns of co-facial π-stacked molecules. For TrAT1, molecules are also linked by hydrogen bonding, while the crystal structure of TrAT2 was found to be inherently disordered. Thin films of DAT, TrAT1 and TrAT2 were grown by organic molecular beam deposition (OMBD) and found to form discontinuous films, where TrAT1 exhibited a preferential orientation.
Wade J, Higgins SG, Heutz S, et al., 2021, In memoriam Alasdair James Campbell (11 May 1961-27 February 2021), Journal of Materials Chemistry C, Vol: 9, Pages: 6100-6102, ISSN: 2050-7526
Lubert-Perquel D, Szumska AA, Azzouzi M, et al., 2020, Structure dependence of kinetic and thermodynamic parameters in singlet fission processes., Journal of Physical Chemistry Letters, Vol: 11, Pages: 9557-9565, ISSN: 1948-7185
Singlet fission-whereby one absorbed photon generates two coupled triplet excitons-is a key process for increasing the efficiency of optoelectronic devices by overcoming the Shockley-Queisser limit. A crucial parameter is the rate of dissociation of the coupled triplets, as this limits the number of free triplets subsequently available for harvesting and ultimately the overall efficiency of the device. Here we present an analysis of the thermodynamic and kinetic parameters for this process in parallel and herringbone dimers measured by electron paramagnetic resonance spectroscopy in coevaporated films of pentacene in p-terphenyl. The rate of dissociation is higher for parallel dimers than for their herringbone counterparts, as is the rate of recombination to the ground state. DFT calculations, which provide the magnitude of the electronic coupling as well as the distribution of molecular orbitals for each geometry, suggest that weaker triplet coupling in the parallel dimer is the driving force for faster dissociation. Conversely, localization of the molecular orbitals and a stronger triplet-triplet interaction result in slower dissociation and recombination. The identification and understanding of how the intermolecular geometry promotes efficient triplet dissociation provide the basis for control of triplet coupling and thereby the optimization of one important parameter of device performance.
Abdelghany TM, Leitch AC, Nevjestic I, et al., 2020, Emerging risk from "environmentally-friendly" solvents: Interaction of methylimidazolium ionic liquids with the mitochondrial electron transport chain is a key initiation event in their mammalian toxicity, FOOD AND CHEMICAL TOXICOLOGY, Vol: 145, ISSN: 0278-6915
Antonio EN, Wicking C, Filip S, et al., 2020, Role of iron speciation in oxidation and deposition at the hexadecane-iron interface, ACS Applied Materials and Interfaces, Vol: 12, Pages: 19140-19152, ISSN: 1944-8244
Interactions between iron surfaces and hydrocarbons are the basis for a wide range of materials synthesis processes and novel applications, including sensing. However, in diesel engines these interactions can lead to deposit formation that reduces performance, lowers efficiency, and increases emissions. Here, we present a global study to understand deposition at iron-hexadecane interfaces. We use a combination of spectroscopy, microscopy, and mass spectrometry to investigate surface reactions, bulk chemistry, and deposition processes. A dynamic equilibrium between the oxidation products, both at the surface and in solution, determines the deposition at the surface. Considering the solution and the surface in parallel, we find that the iron speciation affects the morphology, composition, and quantity of the deposit at the surface, as well as the oxidation of hexadecane. Fe(II) and Fe(III) both promote the decomposition of peroxides-intermediates in the oxidation of hexadecane-but through noncatalytic and catalytic mechanisms, respectively. In contrast, Fe(0) is proposed to initiate hexadecane autoxidation during its oxidation to Fe(III). We find that in all cases, the surfaces exclusively contain Fe(III) following heat treatment with hexadecane. Upon subsequent exposure at room temperature, Fe(III) species are found to promote oxidation; this finding is particularly concerning for hybrid vehicles where longer time periods are expected between engine operation. Our work provides a foundation for the development of strategies that disrupt the role of iron in the degradation of hexadecane to ultimately reduce oxidation and deposition in diesel engines.
Kim DK, Lubert-Perquel D, Heutz S, 2020, Correction: Comparison of organic and inorganic layers for structural templating of pentacene thin films, Materials Horizons, Vol: 7, Pages: 299-299, ISSN: 2051-6355
Correction for ‘Comparison of organic and inorganic layers for structural templating of pentacene thin films’ by Dong Kuk Kim et al., Mater. Horiz., 2019, DOI: 10.1039/c9mh00355j.The authors wish to amend the Acknowledgements section of the originally published manuscript. The correct Acknowledgements section is shown below.
Tseng HH, Serri M, Harrison N, et al., 2020, Properties and degradation of manganese(III) porphyrin thin films formed by high vacuum sublimation, Porphyrin Science By Women (In 3 Volumes), Pages: 924-931, ISBN: 9789811223556
Manganese porphyrins are of interest due to the optical, electronic and magnetic properties of the central metal ion, coupled to the low bandgap of the polyaromatic ring. These attractive characteristics are harnessed in solutions or in ultra-thin films, such as, for example, self-assembled monolayers. However, for devices, thicker films deposited using a controlled and reproducible method are required. Here we present the morphological, structural, chemical and optical properties of manganese(III) tetraphenylporphyrin chloride (MnTPPCl) thin films deposited using organic molecular beam deposition, typically employed to process analogue molecules for applications such as organic photovoltaics. We find, using a combination of UV-vis and X-ray photoelectron spectroscopies, that the sublimation process leads to the scission of the Mn-Cl bond. The resultant film is a Mn(II)TPP:Mn(III)TPPCl blend where approximately half the molecules have been reduced. Following growth, exposure to air oxidizes the Mn(II)TPP molecule. Through quantitative analysis of the time-dependent optical properties, the oxygen diffusion coefficient (D) ~1.9 × 10-17 cm2/s is obtained, corresponding to a slow bulk oxidation following fast oxidation of a 8-nm-thick surface layer. The bulk diffusion D is lower than for analogous polycrystalline films, suggestion that grain boundaries, rather than molecular packing, are the rate-limiting steps in oxidation of molecular films. Our results highlight that the stability of the axial ligands should be considered when depositing metal porphyrins from the vapor phase, and offer a solvent-free route to obtain reproducible and smooth thin films of complex materials for engineering film functionalities.
Kim DK, Lubert-Perquel D, Heutz S, 2020, Comparison of organic and inorganic layers for structural templating of pentacene thin films, Materials Horizons, Vol: 7, Pages: 289-298, ISSN: 2051-6355
Pentacene is a key organic semiconductor, which has achieved prominence in transistor applications and as an archetypal material for singlet fission, the process whereby the absorption of one photon leads to the formation of two triplet states. Functional properties of molecules are highly anisotropic, and control over the molecular orientation in thin films with structural templating is commonly implemented as a route for governing the morphology and structure of organic films. Among the structural templating layers, 3, 4, 9, 10 perylenetetracarboxylic dianhydride (PTCDA) and copper (I) iodide (CuI) have been shown to effectively template aromatic systems such as phthalocyanines. Here, we extend their use to pentacene thin films and find that a successful transition to a flat-lying arrangement is achieved with CuI films grown at high temperatures, but not with PTCDA. As a result, we postulate a model based on quadrupole interactions as the driving force behind the molecular orientation of pentacene. A 0.25 eV increase in work function and a two-fold increase in absorption are recorded for the induced flat-lying orientation. Therefore, our templating methodology provides design opportunities for optoelectronic devices that require a predominantly flat-lying orientation.
Tseng H-H, Serri M, Harrison N, et al., 2019, Properties and degradation of manganese(III) porphyrin thin films formed by high vacuum sublimation, Journal of Porphyrins and Phthalocyanines, Vol: 23, Pages: 1515-1522, ISSN: 1088-4246
Manganese porphyrins are of interest due to the optical, electronic and magnetic properties of the central metal ion, coupled to the low bandgap of the polyaromatic ring. These attractive characteristics are harnessed in solutions or in ultra-thin films, such as, for example, self-assembled monolayers. However, for devices, thicker films deposited using a controlled and reproducible method are required. Here we present the morphological, structural, chemical and optical properties of manganese(III) tetraphenylporphyrin chloride (MnTPPCl) thin films deposited using organic molecular beam deposition, typically employed to process analogue molecules for applications such as organic photovoltaics. We find, using a combination of UV-vis and X-ray photoelectron spectroscopies, that the sublimation process leads to the scission of the Mn–Cl bond. The resultant film is a Mn(II)TPP:Mn(III)TPPCl blend where approximately half the molecules have been reduced. Following growth, exposure to air oxidizes the Mn(II)TPP molecule. Through quantitative analysis of the time-dependent optical properties, the oxygen diffusion coefficient (D) ∼1.9×10−17cm2/s is obtained, corresponding to a slow bulk oxidation following fast oxidation of a 8-nm-thick surface layer. The bulk diffusion D is lower than for analogous polycrystalline films, suggestion that grain boundaries, rather than molecular packing, are the rate-limiting steps in oxidation of molecular films. Our results highlight that the stability of the axial ligands should be considered when depositing metal porphyrins from the vapor phase, and offer a solvent-free route to obtain reproducible and smooth thin films of complex materials for engineering film functionalities.
Wu Z, Robaschik P, Fleet L, et al., 2019, Controlling ferromagnetic ground states and solitons in thin films and nanowires built from iron phthalocyanine chains, Advanced Functional Materials, Vol: 29, ISSN: 1616-301X
Iron phthalocyanine (FePc) is a molecular semiconductor whose building blocks are one-dimensional ferromagnetic chains. We show that its optical and magnetic properties are controlled by the growth strategy, obtaining extremely high coercivities of over 1 T and modulating the exchange constant between 15 and 29 K through tuning the crystal phase by switching from thin films with controlled orientations, to ultralong nanowires. Magnetisation measurements are analysed using concepts and formulas with broad applicability to all one-dimensional ferromagnetic chains. They show that FePc is best described by a Heisenberg model with moments preferentially lying in the molecular planes. The chain Hamiltonian is very similar to that for the classic inorganic magnet CsNiF3, but with ferromagnetic rather than antiferromagnetic interchain interactions. The data at large magnetic fields are well-described by the soliton picture, where the dominant degrees of freedom are moving one-dimensional magnetic domain walls and at low temperatures and fields by the “super-Curie-Weiss” law characteristic of nearly one-dimensional xy and Heisenberg ferromagnets. The ability to control the molecular orientation and ferromagnetism of FePc systems, and produce them on flexible substrates, together with excellent transistor characteristics reported previously for phthalocyanine analogues, makes them potentially useful for magneto-optical and spintronic devices.
Leber R, Wilson L, Robaschik P, et al., 2019, Vacuum deposition of biferrocene thin films: growth strategies for stability and tuneable magnetism, 257th National Meeting of the American-Chemical-Society (ACS), Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Lubert-Perquel D, Kim DK, Kay C, et al., 2019, Growth, morphology and structure of mixed pentacene films, Journal of Materials Chemistry C, Vol: 7, Pages: 289-296, ISSN: 2050-7526
Thin films of pentacene and p-terphenyl were grown via organic molecular beam deposition to enable solid-state dilution of functional molecules (pentacene) in an inert matrix (p-terphenyl) at higher concentrations than permitted by traditional crystal growth methods, such as melts. Growth rates were first optimised for single component films to ensure a precise control over the dopant/host concentrations when the mixed films were deposited. Both thin film and bulk phases can be identified in pentacene growths, with the precise lattice parameters dependent on the deposition rates. The effect on the microstructure, resulting from progressive dilution of pentacene in a p-terphenyl host, was then investigated. Although disorder increases and the crystallite size decreases in the mixture, with a minimum at a 1 : 1 ratio, phase segregation is not observed on the length scale (limit) that can be probed in our measurements. This indicates that the mixed films form homogeneous solid-solutions that may be employed for the investigation of solid-state phenomena. Our methodology can be extended to other compatible host-dopant systems used in optoelectronic and spintronic devices.
Lubert-Perquel D, Salvadori E, Dyson M, et al., 2018, Identifying triplet pathways in dilute pentacene films, NATURE COMMUNICATIONS, Vol: 9, ISSN: 2041-1723
Leber R, Wilson LE, Robaschik P, et al., 2017, High Vacuum Deposition of Biferrocene Thin Films on Room Temperature Substrates, Chemistry of Materials, Vol: 29, Pages: 8663-8669, ISSN: 0897-4756
Metallocenes are a promising candidate for future spintronic devices due to their versatile and tunable magnetic properties. However, single metallocenes, e.g., ferrocene, sublimate below room temperature, and therefore the implementation for future applications is challenging. Here, a method to prepare biferrocene thin films using organic molecular beam deposition (OMBD) is presented, and the effect of substrate and deposition rate on the film structure and morphology as well as its chemical and magnetic properties is investigated. On Kapton and Si substrates, biferrocene interacts only weakly with the substrate, and distinct grains scattered over the surface are observed. By incorporating a 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) seeding layer and depositing biferrocene at high deposition rates of 1.0 Å s–1, it is possible to achieve a well-ordered densely packed film. With spintronic applications in mind, the magnetic properties of the thin films are characterized using superconducting quantum interference device (SQUID) magnetometry. Whereas initial SQUID measurements show weak ferromagnetic behavior up to room temperature due to oxidized molecule fragments, measurements of biferrocene on PTCDA capped with LiF show the diamagnetic behavior expected of biferrocene. Through the successful deposition of biferrocene thin films and the ability to control the spin state, these results demonstrate a first step toward metallocene-based spintronics.
Robaschik P, Ma Y, Din S, et al., 2017, Formation of ferromagnetic molecular thin films from blends by annealing, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, Vol: 8, Pages: 1469-1475, ISSN: 2190-4286
We report on a new approach for the fabrication of ferromagnetic molecular thin films. Co-evaporated films of manganese phthalocyanine (MnPc) and tetracyanoquinodimethane (TCNQ) have been produced by organic molecular beam deposition (OMBD) on rigid (glass, silicon) and flexible (Kapton) substrates kept at room temperature. The MnPc:TCNQ films are found to be entirely amorphous due to the size mismatch of the molecules. However, by annealing while covering the samples highly crystalline MnPc films in the β-polymorph can be obtained at 60 °C lower than when starting with pure MnPc films. The resulting films exhibit substantial coercivity (13 mT) at 2 K and a Curie temperature of 11.5 K.
Alexander JA, Scheltens FJ, Drummy LF, et al., 2017, Measuring Optical Absorption in Organic Photovoltaics Using Monochromated Electron Energy-Loss Spectroscopy, IEEE 44th Photovoltaic Specialist Conference (PVSC), Publisher: IEEE, Pages: 966-969, ISSN: 0160-8371
Fleet LR, Stott J, Villis B, et al., 2017, Self-Assembled Molecular Nanowires for High-Performance Organic Transistors, ACS Applied Materials and Interfaces, Vol: 9, Pages: 20686-20695, ISSN: 1944-8244
While organic semiconductors provide tantalizing possibilities for low-cost, light-weight, flexible electronic devices, their current use in transistors—the fundamental building block—is rather limited as their speed and reliability are not competitive with those of their inorganic counterparts and are simply too poor for many practical applications. Through self-assembly, highly ordered nanostructures can be prepared that have more competitive transport characteristics; however, no simple, scalable method has been discovered that can produce devices on the basis of such nanostructures. Here, we show how transistors of self-assembled molecular nanowires can be fabricated using a scalable, gradient sublimation technique, which have dramatically improved characteristics compared to those of their thin-film counterparts, both in terms of performance and stability. Nanowire devices based on copper phthalocyanine have been fabricated with threshold voltages as low as −2.1 V, high on/off ratios of 105, small subthreshold swings of 0.9 V/decade, and mobilities of 0.6 cm2/V s, and lower trap energies as deduced from temperature-dependent properties, in line with leading organic semiconductors involving more complex fabrication. High-performance transistors manufactured using our scalable deposition technique, compatible with flexible substrates, could enable integrated all-organic chips implementing conventional as well as neuromorphic computation and combining sensors, logic, data storage, drivers, and displays.
Gilchrist JB, Heutz S, McComb DW, 2017, Revealing structure and electronic properties at organic interfaces using TEM, Current Opinion in Solid State and Materials Science, Vol: 21, Pages: 68-76, ISSN: 1359-0286
Molecules and atoms at material interfaces have properties that are distinct from those found in the bulk. Distinguishing the interfacial species from the bulk species is the inherent difficulty of interfacial analysis. For organic photovoltaic devices, the interface between the donor and acceptor materials is the location for exciton dissociation. Dissociation is thought to occur via a complex route effected by microstructure and the electronic energy levels. The scale of these devices and the soft nature of these materials create an additional level of difficulty for identification and analysis at these interfaces. The transmission electron microscope (TEM) and the spectroscopic techniques it incorporates can allow the properties of the donor-acceptor interfaces to be revealed. Cross-sectional sample preparation, using modern focused ion beam instruments, enables these buried interfaces to be uncovered with minimal damage for high resolution analysis. This powerful instrument combination has the ability to draw conclusions about interface morphology, structure and electronic properties of organic donor-acceptor interfaces at the molecular scale. Recent publications have demonstrated these abilities, and this article aims to summarise some of that work and provide scope for the future.
Eguchi K, Heutz S, Awaga K, 2017, Templating effects of tetrakis(thiadiazole) porphyrazine on the structure and optical properties of copper phthalocyanine thin films, Journal of Porphyrins and Phthalocyanines, Vol: 21, Pages: 322-326, ISSN: 1088-4246
Molecular templating is an attractive method to improve the crystallinity and control the molecular orientations of organic thin films. Here, we report on the templating effects of an organic nn-type semiconductor, tetrakis(thiadiazole)porphyrazine (H2TTDPz), on the structure and optical absorption of a pp-type semiconductor, copper phthalocyanine (CuPc). X-ray diffraction measurements for the double layer thin films, CuPc/H2TTDPz, indicate a face-on orientation of CuPc, which is replicating the structure of the H2TTDPz thin films, even though the CuPc thin films usually form edge-on-type thin films. The optical absorption measurements show new low-energy transitions in the templated CuPc films.
Gonzalez Arellano DL, Bhamrah Harley J, Yang J, et al., 2017, Room temperature routes towards the creation of zinc oxide films from molecular precursors, ACS Omega, Vol: 2, Pages: 98-104, ISSN: 2470-1343
The advent of “flexible” electronics on plastic substrates with low melting points requires the development of thin film deposition techniques that operate at low temperatures. This is easily achieved with vacuum or solution-processed molecular or polymeric semiconductors, but oxide materials remain a significant challenge. Here we show that zinc oxide (ZnO) can be prepared using only room-temperature processes, using the molecular thin film precursor zinc phthalocyanine (ZnPc), followed by vacuum ultra-violet light treatment to elicit degradation of the organic components and transformation of the deposited film to oxide material. The degradation mechanism was assessed by studying the influence of the atmosphere during the reaction: it was particularly sensitive to oxygen pressure in the chamber and optimal degradation conditions were established as 3 mbar with 40% oxygen in nitrogen. The morphology of the film was relatively unchanged during the reaction, but detailed analysis of itscomposition using both scanning transmission electron microscopy (STEM) and secondary ion mass spectrometry (SIMS) revealed that a 40 nm thick layer containingZnO results from the 100 nm thick precursor after complete reaction. Our methodology represents a simple route for the fabrication of oxides and multilayer structuresthat can be easily integrated into current molecular thin film growth setups,without the need for a high temperature step.
Alexandra J Ramadan, Fearn S, Tim Jones, et al., 2016, Film Formation of Non-Planar Phthalocyanines on Copper (I) Iodide, RSC Advances, Vol: 6, Pages: 95227-95231, ISSN: 2046-2069
Structural templating is frequently used in organic photovoltaic devices to control the properties of the functional layersand therefore improve efficiencies. Modification of the substrate temperatures has also been shown to impact thestructure and morphology of phthalocyanine thin films. Here we combine templating by copper iodide and high substratetemperature growth and study its effect on the structure and morphology of two different non-planar phthalocyanines,chloroaluminium (ClAlPc) and vanadyl (VOPc) phthalocyanine. X-ray diffraction, atomic force microscopy and low energyion scattering show that both the morphology and the structure of the films are starkly different in every case, highlightingthe versatility of phthalocyanine film growth.
Alexander JA, Scheltens FJ, Drummy LF, et al., 2016, Measurement of optical properties in organic photovoltaic materials using monochromated electron energy-loss spectroscopy, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 4, Pages: 13636-13645, ISSN: 2050-7488
Perfetti M, Serri M, Poggini L, et al., 2016, Molecular order in buried layers of TbPc2 Single-Molecule Magnets detected by torque magnetometry, Advanced Materials, Vol: 28, Pages: 6946-6951, ISSN: 1521-4095
Cantilever torque magnetometry is used to elucidate the orientation of magnetic molecules in thin films. The technique allows depth-resolved investigations by intercalating a layer of anisotropic magnetic molecules in a film of its isotropic analogues. The proof-of-concept is here demonstrated with the single-molecule magnet TbPc2 evidencing also an exceptional long-range templating effect on substrates coated by the organic molecule perylene-3,4,9,10-tetracarboxylic dianhydride.
Heutz SEM, Eguchi K, Ono Y, et al., 2016, Highly-Oriented Molecular Arrangements and Enhanced Magnetic Interactions in Thin Films of CoTTDPz using PTCDA Templates, Physical Chemistry Chemical Physics, Vol: 18, Pages: 17360-17365, ISSN: 1463-9084
In the present work, the templating effect of thin layers of perylene-3,4,9,10-tetracarboxylic dianhydride(PTCDA) on the growth of cobalt tetrakis(thiadiazole)porphyrazine (CoTTDPz) thin films was examined.X-ray diffraction and optical absorption spectra indicate that while CoTTDPz forms amorphous thin filmson the bare substrates, it forms crystalline thin films on the PTCDA templates, in which the molecularplanes of CoTTDPz are considered to be parallel to the substrates. Magnetic measurements reveal asignificantly enhanced antiferromagnetic interaction of CoTTDPz in the templated thin films, with valuesreaching over 13 K. The ability to generate crystalline films and to control their orientation usingmolecular templates is an important strategy in the fields of organic electronics and spintronics in orderto tailor the physical properties of organic thin films to suit their intended application.
Goode AE, Porter AE, Kłosowski MM, et al., 2016, Analytical transmission electron microscopy at organic interfaces, Current Opinion in Solid State and Materials Science, Vol: 21, Pages: 55-67, ISSN: 1359-0286
Organic materials are ubiquitous in all aspects of our daily lives. Increasingly there is a need to understand interactions between different organic phases, or between organic and inorganic materials (hybrid interfaces), in order to gain fundamental knowledge about the origin of their structural and functional properties. In order to understand the complex structure–property–processing relationships in (and between) these materials, we need tools that combine high chemical sensitivity with high spatial resolution to allow detailed interfacial characterisation. Analytical transmission electron microscopy (TEM) is a powerful and versatile technique that can fulfil both criteria. However, the application of analytical TEM to organic systems presents some unique challenges, such as low contrast between phases, and electron beam sensitivity. In this review recent analytical TEM approaches to the nanoscale characterisation of two systems will be discussed: the hybrid collagen/mineral interface in bone, and the all-organic donor/acceptor interface in OPV devices.
Tay SER, Goode AE, Weker JN, et al., 2016, Direct in situ observation of ZnO nucleation and growth via transmission X-ray microscopy, Nanoscale, Vol: 8, Pages: 1849-1853, ISSN: 2040-3364
The nucleation and growth of a nanostructure controls its size and morphology, and ultimately its functional properties. Hence it is crucial to investigate growth mechanisms under relevant growth conditions at the nanometer length scale. Here we image the nucleation and growth of electrodeposited ZnO nanostructures in situ, using a transmission X-ray microscope and specially designed electrochemical cell. We show that this imaging technique leads to new insights into the nucleation and growth mechanisms in electrodeposited ZnO including direct, in situ observations of instantaneous versus delayed nucleation.
Ramadan AJ, Rochford LA, Moffat J, et al., 2016, The morphology and structure of vanadyl phthalocyanine thin films on lithium niobate single crystals, Journal of Materials Chemistry C, Vol: 4, Pages: 348-351, ISSN: 2050-7534
The electric field of ferroelectric materials has been used as a driving force to promote molecular adsorption and control the orientation of small dipolar molecules. This approach has not been investigated on larger polyaromatic molecules, such as those used in organic electronic devices, even though the physical and electronic properties of thin films are strongly dependent on molecular structure and orientation, ultimately affecting device performance. Here we investigate the effects of model ferroelectric surfaces on a dipolar organic semiconducting molecule. Thin films of vanadyl phthalocyanine (VOPc) deposited on to (0001) and (2[1 with combining macron][1 with combining macron]0) lithium niobate were subjected to structural and morphological analysis. Whilst thin films could be grown on these surfaces, no obvious change to their structure or morphology was observed suggesting there was no influence of a surface electrical field or surface chemistry on the film structure, and that the substrate is more complex than previously thought.
Rochford LA, Ramadan AJ, Woodruff DP, et al., 2015, Ordered growth of vanadyl phthalocyanine (VOPc) on an iron phthalocyanine (FePc) monolayer, Physical Chemistry Chemical Physics, Vol: 17, Pages: 29747-29752, ISSN: 1463-9084
The growth and characterisation of a non-planar phthalocyanine (vanadyl phthalocyanine, VOPc) on a complete monolayer (ML) of a planar phthalocyanine (Iron(II) phthalocyanine, FePc) on an Au(111) surface, has been investigated using ultra-high vacuum (UHV) scanning tunnelling microscopy (STM) and low energy electron diffraction (LEED). The surface mesh of the initial FePc monolayer has been determined and shown to correspond to an incommensurate overlayer, not commensurate as previously reported. Ordered islands of VOPc, with (1 × 1) epitaxy, grow on the FePc layer at submonolayer coverages. The individual VOPc molecules occupy sites directly atop the underlying FePc molecules, indicating that significant intermolecular bonding must occur. It is proposed that this interaction implies that the V[double bond, length as m-dash]O points down into the surface, allowing a Fe–O bond to form. The detailed appearance of the STM images of the VOPc molecules is consistent with previous studies in other VOPc growth studies in which this molecular orientation has been proposed.
Heutz S, 2015, MOLECULAR SPINTRONICS A warm exchange, NATURE MATERIALS, Vol: 14, Pages: 967-968, ISSN: 1476-1122
Ramadan AJ, Rochford LA, Ryan MP, et al., 2015, The influence of polar (0001) zinc oxide (ZnO) on the structure and morphology of vanadyl phthalocyanine (VOPc), RSC Advances, Vol: 5, Pages: 65949-65952, ISSN: 2046-2069
Metal oxide thin films are increasingly utilized in small molecular organic photovoltaic devices to facilitate electron transport and injection. Despite this there is little understanding of the influence these layers have on the structure of adjacent organic semiconductor layers. Here we use both O- and Zn- terminated (0001) single crystal zinc oxide (ZnO) as a model system to investigate the effect of a metal oxide surface on the growth of a molecular semiconductor, vanadyl phthalocyanine (VOPc). The surface reconstructions of these model surfaces are determined and the properties of thin films of VOPc deposited atop are investigated. The nature of the bulk truncation of the surface is found to have pronounced effects on both the morphology and crystal structure of these molecular films. This work highlights the importance of considering the effects of the chemical composition and surface termination of metal oxide films on the structure of adjacent molecular semiconductor films.
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.