Publications
86 results found
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.
Ramadan AJ, Rochford LA, Keeble DS, et al., 2015, Structural templating in a non-planar phthalocyanine using single crystal copper iodide, Advanced Materials Interfaces, ISSN: 2196-7350
Solution-grown copper iodide crystals are used as substrates for the templated growth of the nonplanar vanadyl phthalocyanine using organic molecular beam deposition. Structural characterization reveals a single molecular orientation produced by the (111) Miller plane of the copper iodide crystals. These fundamental measurements show the importance of morphology and structure in templating interactions for organic electronics applications.
Tseng H-H, Serri M, Harrison NM, et al., 2015, Thin film properties of tetracyanoquinodimethane (TCNQ) with novel templating effects, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 3, Pages: 8694-8699, ISSN: 2050-7526
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- Citations: 8
Ramadan AJ, Rochford LA, Keeble DS, et al., 2014, Exploring High Temperature Templating in Non-planar Phthalocyanine / Copper Iodide (111) Bilayers, Journal of Materials Chemistry C, ISSN: 2050-7526
Elevated substrate temperature growth of phthalocyanine thin films is known to influence film morphology and increase crystallinity. Structural templating offers another method through which the structure of phthalocyanine films can be controlled. Here we combine the use of copper iodide (CuI) and elevated substrate temperatures and investigate their effect on the growth of a non-planar phthalocyanine system. Employing x-ray diffraction and atomic force microscopy we present detailed surface and crystal structure information. Vanadyl phthalocyanine (VOPc) is shown to adopt an edge-on orientation on CuI at ambient substrate temperatures, a behavior in stark contrast to that of previously studied planar phthalocyanine molecules. Elevated substrate temperature is shown to result in changes in the surface morphology and structure demonstrating the versatility of the system. The crystal structure of VOPc was redetermined and used to infer the molecular orientation of the various VOPc/CuI bilayer structures.
Gilchrist JB, Basey-Fisher TH, Chang SC, et al., 2014, Uncovering buried structure and interfaces in molecular photovoltaics, Advanced Functional Materials, Vol: 24, Pages: 6473-6483, ISSN: 1616-301X
The processes that generate current in organic photovoltaics are highly dependent on the micro‐ and nano‐structure in the semiconductor layers, especially at the donor‐acceptor interface. Elucidating film properties throughout the thickness of the devices is therefore key to their further development. Here, a methodology is developed to gain unprecedented insights into the structure and composition of the molecular layers within the depth of device structure using high resolution transmission electron microscopy (HRTEM). The technique was applied to three archetypical solar cell configurations consisting of copper phthalocyanine (CuPc) and C60, which have been cross‐sectioned using a focused ion beam method optimized to minimize sample damage. The HRTEM images exhibit lattice fringes in both CuPc and C60, confirming the crystallinity and texture of both materials, and offering novel insight into the growth of C60 onto molecular materials. The donor‐acceptor interface morphology is further studied using scanning transmission electron microscopy (STEM) in combination with energy dispersive X‐ray (EDX) spectroscopy, extending the scope of our methodology to amorphous heterostructures.
Rochford LA, Ramadan AJ, Heutz S, et al., 2014, Selective nucleation of iron phthalocyanine crystals on micro-structured copper iodide, Physical Chemistry Chemical Physics, ISSN: 1463-9084
Morphological and structural control of organic semiconductors through structural templating is an efficient route by which to tune their physical properties. The preparation and characterisation of iron phthalocyanine (FePc) / copper iodide (CuI)bilayers at elevated substrate temperatures is presented. Thin CuI (111) layers are prepared which are composed of isolated islands rather than continuous films previously employed in device structures. Nucleation in the early stages of FePc growth is observed at the edges of islands rather than on the top (111) faces with the use of field emission scanning electron microscopy (FE-SEM ). Structural measurements show two distinct polymorphs of FePc, with CuI islands edgesnucleating high aspect ratio FePc crystallites with modified intermolecular spacing. By combining high substrate temperature growth and micro structuring of the templating CuI (111) layer structural and morphological control of the organic film is demonstrated.
Pilia L, Serri M, Matsushita MM, et al., 2014, Giant Magnetoresistance in a Molecular Thin Film as an Intrinsic Property, ADVANCED FUNCTIONAL MATERIALS, Vol: 24, Pages: 2383-2388, ISSN: 1616-301X
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- Citations: 10
Serri M, Wu W, Fleet LR, et al., 2014, High-temperature antiferromagnetism in molecular semiconductor thin films and nanostructures, Nature Communications, Vol: 5, Pages: 1-9, ISSN: 2041-1723
The viability of dilute magnetic semiconductors in applications is linked to the strength of the magnetic couplings, and room temperature operation is still elusive in standard inorganic systems. Molecular semiconductors are emerging as an alternative due to their long spin-relaxation times and ease of processing, but, with the notable exception of vanadium-tetracyanoethylene, magnetic transition temperatures remain well below the boiling point of liquid nitrogen. Here we show that thin films and powders of the molecular semiconductor cobalt phthalocyanine exhibit strong antiferromagnetic coupling, with an exchange energy reaching 100 K. This interaction is up to two orders of magnitude larger than in related phthalocyanines and can be obtained on flexible plastic substrates, under conditions compatible with routine organic electronic device fabrication. Ab initio calculations show that coupling is achieved via superexchange between the singly occupied a1g () orbitals. By reaching the key milestone of magnetic coupling above 77 K, these results establish quantum spin chains as a potentially useable feature of molecular films.
Warner M, Din S, Tupitsyn IS, et al., 2013, Potential for spin-based information processing in a thin-film molecular semiconductor, Nature, Vol: 503, Pages: 504-508, ISSN: 0028-0836
Organic semiconductors are studied intensively for applications in electronics and optics1, and even spin-based information technology, or spintronics2. Fundamental quantities in spintronics are the population relaxation time (T1) and the phase memory time (T2): T1 measures the lifetime of a classical bit, in this case embodied by a spin oriented either parallel or antiparallel to an external magnetic field, and T2 measures the corresponding lifetime of a quantum bit, encoded in the phase of the quantum state. Here we establish that these times are surprisingly long for a common, low-cost and chemically modifiable organic semiconductor, the blue pigment copper phthalocyanine3, in easily processed thin-film form of the type used for device fabrication. At 5 K, a temperature reachable using inexpensive closed-cycle refrigerators, T1 and T2 are respectively 59 ms and 2.6 μs, and at 80 K, which is just above the boiling point of liquid nitrogen, they are respectively 10 μs and 1 μs, demonstrating that the performance of thin-film copper phthalocyanine is superior to that of single-molecule magnets over the same temperature range4. T2 is more than two orders of magnitude greater than the duration of the spin manipulation pulses, which suggests that copper phthalocyanine holds promise for quantum information processing, and the long T1 indicates possibilities for medium-term storage of classical bits in all-organic devices on plastic substrates.
Hatch SM, Briscoe J, Sapelkin A, et al., 2013, Influence of anneal atmosphere on ZnO-nanorod photoluminescent and morphological properties with self-powered photodetector performance, JOURNAL OF APPLIED PHYSICS, Vol: 113, ISSN: 0021-8979
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- Citations: 50
Warner B, Oberg JC, Gill TG, et al., 2013, Temperature- and Light-Induced Spin Crossover Observed by X-ray Spectroscopy on Isolated Fe(II) Complexes on Gold, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, Vol: 4, Pages: 1546-1552, ISSN: 1948-7185
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- Citations: 130
Wu W, Rochford LA, Felton S, et al., 2013, Magnetic properties of copper hexadecaphthalocyanine (F<sub>16</sub>CuPc) thin films and powders, JOURNAL OF APPLIED PHYSICS, Vol: 113, ISSN: 0021-8979
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- Citations: 15
Westacott P, Tumbleston JR, Shoaee S, et al., 2013, On the role of intermixed phases in organic photovoltaic blends, Energy & Environmental Science, ISSN: 1754-5692
Warner M, Mauthoor S, Felton S, et al., 2012, Spin-Based Diagnostic of Nanostructure in Copper Phthalocyanine-C<sub>60</sub> Solar Cell Blends, ACS NANO, Vol: 6, Pages: 10808-10815, ISSN: 1936-0851
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- Citations: 28
Cruickshank AC, Dotzler CJ, Din S, et al., 2012, The Crystalline Structure of Copper Phthalocyanine Films on ZnO(1(1)over-bar00), JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 134, Pages: 14302-14305, ISSN: 0002-7863
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- Citations: 25
Gilchrist JB, Heutz S, McComb DW, 2012, Using TEM and XRD to probe crystal orientation in organic thin films grown with OMBD, Conference on Electron-Microscopy-and-Analysis-Group (EMAG), Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588
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- Citations: 7
Palamarciuc T, Oberg JC, El Hallak F, et al., 2012, Spin crossover materials evaporated under clean high vacuum and ultra-high vacuum conditions: from thin films to single molecules, JOURNAL OF MATERIALS CHEMISTRY, Vol: 22, Pages: 9690-9695, ISSN: 0959-9428
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- Citations: 91
Wu W, Fisher AJ, Harrison NM, et al., 2012, Theoretical modeling of the electronic structure and exchange interactions in Cu(II)Pc, International Conference on Strongly Correlated Electron Systems (SCES), Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588
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- Citations: 1
Illy BN, Cruickshank AC, Schumann S, et al., 2011, Electrodeposition of ZnO layers for photovoltaic applications: controlling film thickness and orientation, Journal of Materials Chemistry
Stott J, Kumatani A, Minari T, et al., 2011, Bottom-Contact Pentacene Thin-Film Transistors on Silicon Nitride, IEEE ELECTRON DEVICE LETTERS, Vol: 32, Pages: 1305-1307, ISSN: 0741-3106
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- Citations: 7
Illy BN, Cruickshank AC, Da Campo R, et al., 2011, Electrodeposition of ultrathin ZnO buffer layers with controllable orientation for photovoltaic applications, ISSN: 0065-7727
ZnO is one of the most promising materials for applications in nanotechnology due to its large band gap and high electron mobility. A large amount of work has focused on the study of nanostructured ZnO. However, two dimensional transparent compact layers are also of great interest as transparent conductive oxides in optoelectronic devices. Compact ZnO layers are usually deposited by methods which are generally costly thus significantly limiting their potential application. Electrodeposition is a low cost alternative, offering a high degree of control on the characteristics. In this work the effects of the deposition parameters on the film characteristics have been studied in order to fabricate the thinnest electrodeposited films ever reported and to tune the crystallographic orientation. Incorporation of the layer into an organic ZnO/P3HT:PCBM solar cell is used to demonstrate how a careful control of the orientation can dramatically improve the photovoltaic device efficiency.
Cruickshank A, Tay S, Illy B, et al., 2011, Electrodeposition of ZnO Nanostructures on Molecular Thin Films, Chemistry of Materials, Vol: 23, Pages: 3863-3870, ISSN: 1520-5002
Electrodeposition of highly crystalline ZnO nanostructures directly onto copper phthalocyanine and pentacene thin films, from aqueous solutions containing zinc nitrate and dissolved oxygen, has been successfully demonstrated for the first time using a two-step electrochemical deposition process. Importantly, surface activation of the molecular thin film substrates by depositing a thin layer of ZnO nanoparticles at high cathodic overpotentials prior to film growth was found to be crucial for achieving a dense coverage of ZnO nanostructures with uniform morphology. The mechanism for ZnO deposition via electroreduction of hydroxide precursor species (oxygen and NO3– ions) at the organic-electrolyte interface was shown to be analogous to that reported for conventional inorganic and metal electrodes. Comparison of cathodic current density-time curves, measured during deposition, with film orientation and morphology revealed that the cathodic current density and number of nucleation sites are key factors in determining the characteristics of ZnO film growth on organic substrates. Significantly, the CuPc and pentacene films are not damaged or degraded during this process.
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