Synthetic Metals (v.148, #1)

Fundamental research needs in organic electronic materials by Z. Valy Vardeny; Alan J. Heeger; Ananth Dodabalapur (1-3).
The workshop, Fundamental Research Needs in Organic Electronic Materials, jointly sponsored by DOE Basic Energy Sciences (BES) and EERE/BT was held on May 23–25, 2003 at the University of Utah Campus in Salt Lake City, Utah for the purpose of identifying key scientific issues enabling the technological success of these materials. Approximately 30 key experts and world leaders in organic materials chemistry, transport physics, time-resolved and steady-stated optical processes, organic spintronics, and device technology, gathered to stimulate new and revolutionary sciences.
Keywords: Organic; OLED; Spintronics; Organic FET; Organic PV;

Preface by José Antonio De Saja (5).

Magnetic Langmuir–Blodgett films of ferritin with different iron loadings by Alejandra Soriano-Portillo; Miguel Clemente-León; Carlos J. Gómez-García; Eugenio Coronado; Natividad Gálvez; Enrique Colacio; José M. Domínguez-Vera (7-10).
Magnetic Langmuir–Blodgett multilayers of two ferritin molecules 1 and 2, containing, respectively, 4220 and 3062 Fe atoms have been prepared by using the adsorption properties of a 6/1 mixed monolayer of dioctadecyldimethylammonium bromide (DODABr) and methyl stearate (SME). Transfer ratios close to unity were reached giving rise to LB films with a strong red colour. Infrared and UV–vis spectroscopy indicates that ferritin molecules are incorporated within the LB films. Magnetic measurements show that the superparamagnetic properties of these molecules are preserved. Thus, a marked hysteresis loop of magnetisation is obtained for LB films of 1 and 2 with a coercive field of 3400 and 2400 G, respectively.
Keywords: Langmuir–Blodgett films; Ferritin; Magnetic properties; Monolayers; Thin films;

Studies have been made of alternate layer (ABABA superlattices) multilayer Langmuir–Blodgett (LB) films using a cyclic polysiloxane (A) and an iridium(I) polyalkoxystilbazole metallo-organic complex (B). The electrically polar nature of the molecules studied suggests that they may be suitable candidates for new pyroelectric materials. The pyroelectric coefficient has been measured for alternate layer multilayer LB films built with various number of layers of the iridium(I) complex. We investigate the effect of chain length of the substitution and position of the substitution on the pyroelectric coefficient, capacitance and dielectric loss.
Keywords: Langmuir–Blodgett; Metallo-organic; Stilbazole; Pyroelectricity; Dielectric constant;

Hydrogen sensors based on carbon nanotubes thin films by I. Sayago; E. Terrado; E. Lafuente; M.C. Horrillo; W.K. Maser; A.M. Benito; R. Navarro; E.P. Urriolabeitia; M.T. Martinez; J. Gutierrez (15-19).
Single-walled carbon nanotubes (SWNTs) produced by arc-discharge have been researched as resistive gas sensors for H2 detection. Raw as well as modified single-walled carbon nanotubes were utilised as sensor material. Two types of modification treatments were carried out on the as grown SWNT material; chemical functionalization with palladium and doping with palladium by sputtering.CNTs were deposited on alumina substrates by airbrush. Two different alumina substrates (with and without heater element) were used to obtain the sensor devices.Conductance measurements were carried out in a N2 constant flow for H2 detection. The results demonstrate that the CNTs are p-type semiconductor materials, increasing their resistance with reducing gases. SWNTs functionalized with Pd show the best response when exposed to H2 at room temperature.
Keywords: Carbon nanotubes; Gas sensor; Functionalization; Hydrogen;

The use of Langmuir–Blodgett films of a perylene derivative and polypyrrole in the detection of trace levels of Cu2+ ions by P.A. Antunes; C.M. Santana; R.F. Aroca; O.N. Oliveira; C.J.L. Constantino; A. Riul (21-24).
Langmuir films of a tetracarboxylic perylene derivative and polypyrrole display condensed surface pressure isotherms that are shifted when Cu2+ ions are added to the ultrapure water subphase. These films were transferred onto interdigitated gold electrodes leading to Y-type Langmuir–Blodgett (LB) films. The electrodes modified with 5-layer LB films were immersed into a flask with ultrapure water and water containing Cu2+ ions at concentrations ranging from mM to μM. Impedance measurements indicated a distinct electrical response for the two types of films. Although the materials chosen have no specificity for ionic metals, they can be combined for detecting trace levels of Cu2+, which may be exploited in water quality monitoring.
Keywords: Langmuir–Blodgett films; BuPTCD; Ppy;

TiO2 nanocrystal films for sensing applications based on surface plasmon resonance by M.G. Manera; P.D. Cozzoli; M.L. Curri; G. Leo; R. Rella; A. Agostiano; L. Vasanelli (25-29).
Spherical and rod shaped organic-capped TiO2 nanocrystals (NCs), prepared by a hydrolytic route, were deposited as thin films and characterized by means of atomic force microscopy (AFM), X-ray diffraction (XRD) and surface plasmon resonance (SPR). SPR was assessed as transduction technique in order to test the sensing ability of the prepared films for detection of alcohol vapours as a function of NC shape and thermal treatment. The performances of the TiO2 nanocrystals were found to be dependent on the titania nanocrystal morphology and thermal treatment conditions, pointing to the beneficial effect of a rod-like shape as compared to a spherical one, and to a possible role of the titania surface organic coating in enhancing the sensor response.
Keywords: TiO2; Colloidal nanocrystals; Nanoparticle morphology; SPR; Sensing;

Nano-structured Langmuir–Blodgett mixed films of titanyl(IV) phthalocyanine and bis(neopentylimido)perylene by T. Del Caño; P.J.G. Goulet; N.P.W. Pieczonka; R.F. Aroca; J.A. De Saja (31-35).
Langmuir and Langmuir–Blodgett (LB) films of mixed titanyl(IV) phthalocyanine (TiOPc)–bis (neopentylimido)perylene (BNPTCD) were fabricated and characterized. The surface pressure–area isotherms (πA) of the mixed Langmuir films were recorded and revealed an unusual expansion of the surface area per molecule. The expansion is attributed to the interpenetration of the BNPTCD in the space available between adjacent Pc macrocycles preventing molecular stacking and forcing the expansion. This effect is a result of the high degree of mixing between species in the floating monolayer. This assumption was further supported by means of surface enhanced Raman scattering (SERS) mapping technique that proved the absence of large segregated domains in the LB film, in other words, the absence of phase separated regions, in agreement with a unique degree of miscibility.
Keywords: Perylenediimide; Phthalocyanine; LB film; Mixing;

Structural studies of zinc oxide films grown by RF magnetron sputtering by I. Sayago; M. Aleixandre; A. Martínez; M.J. Fernández; J.P. Santos; J. Gutiérrez; I. Gràcia; M.C. Horrillo (37-41).
The main purpose of this study consists of researching the piezoelectric characteristics of ZnO films grown by RF magnetron sputtering in reactive plasma. In this way the influence of deposition parameters, such as RF power and plasma oxygen content, on the structural and morphological properties of the films are analyzed.ZnO films are grown on SiO2/Si(1 0 0) substrate using a zinc oxide target. Different RF powers (from 50 to 200 W) and reactive plasmas (from 5 to 15% of oxygen content) have been tested and optimized to produce good quality films suitable for fabricating surface acoustic wave (SAW) devices.Crystalline structures and morphological characteristics of the films are investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively.SAW devices are fabricated with “IDT(Al)/ZnO/SiO2 ―Si” configuration. The frequency response of these devices is measured for their characterization.
Keywords: SAW; ZnO; Piezoelectric material; Sputtering;

Cyclodextrin mediated phase transfer in water of organic capped CdS nanocrystals by N. Depalo; R. Comparelli; M.L. Curri; M. Striccoli; A. Agostiano (43-46).
In this work the phase transfer of blue emitting CdS nanocrystals (NCs) from organic solvent to water is reported. Oleic acid capped CdS NCs were synthesized in non-coordinating solvents and effectively transferred from organic phase, i.e. hexane, in aqueous solution. The transfer was mediated by the formation of an inclusion complex between NC surfactant and α-cyclodextrin (αCD). Effect of αCD concentration and NC size on the phase transfer process was evaluated. No NC aggregation in the phase transfer and long stability in time were observed. The spectroscopic properties of the resulting solution were investigated. Finally a supramolecular hierarchical multilayer system with high level of structural complexity was fabricated by using a layer-by-layer assembling procedure of CdS-NC/αCD inclusion complex in multilayered films.
Keywords: Colloidal CdS nanocrystals; Cyclodextrins; Spectroscopical characterization; Host–guest chemistry; Polyelectrolytes;

Photophysics, electrochemistry and structure of a pyrazolino[60]fullerene dendrimer in solid molecular films by Vicente Parra; Teodosio del Caño; María José Gómez-Escalonilla; Fernando Langa; María Luz Rodríguez-Méndez; José Antonio De Saja (47-52).
A novel pyrazolino[60]fullerene dendrimer is studied in solid molecular films. Orientated monolayers of this donor–acceptor system are formed by means of the Langmuir–Blodgett (LB) technique. The fullerodendrimer exhibits high collapse pressures but a tendency to aggregate at the air–water interface. Nonetheless, the subsequent LB deposition process shows a good transfer behaviour onto a variety of substrates. Concurrently, cast dropped films are prepared to compare particular properties respect to those of the LB films. Steady-state absorption spectra imply J-aggregation through solution–LB–cast films. The photoinduced outcomes suggest an enhanced charge transfer between donor–acceptor in thin films via intermolecular effects, although an energy transfer process may coexists. Therefore, square wave voltammetry (SWV) is applied to study the electronic behaviour of the C60-dyad. The results are qualitatively correlated with the photophysics. Further, reflection–absorption infrared spectroscopy (RAIRS) and atomic force microscopy (AFM) are applied to analyse the structure of the films, which is the main responsible of their properties. In this regard, it can be distinguished the preferential intermolecular arrangement in LB films with respect to cast film, and an aggregation growing with increasing number of transferred monolayers in case of LB films, but upholding homogeneity all along the surface's coating, contrary to the cast heterogeneousness.
Keywords: Fullerene; Thin film; Langmuir–Blodgett; Energy and electron transfer; Reflection–absorption infrared spectroscopy;

The principle of photobleaching in the conjugated polymer material didodecylstilbenevinylene (didodecyl-PSV) was used as a built-in photoresist property to control the extent of the emissive layer in polymer light emitting devices (PLEDs). Illumination of thin films of the conjugated polymer material on optically transparent conducting substrates through a positive mask with short exposure times (20–60 s) using a 150 W Xenon lamp and subsequent application of the and the second electrode enabled the formation of an electroluminescent image of the mask. We demonstrate a direct method where no photoresist, intermediate steps or mechanical manipulation is required to generate a complex emissive pattern employing a homogenous film and homogenous electrodes. The fluorescence of the film showed complex lifetime decays. We found that the lifetime increased with emission wavelength indicating the presence of energetically disordered excitons. The fine structure observed in the solution emission is absent in the film emission. However, after photobleaching the film emission becomes very similar to the solution emission. The appearance of fine structure could indicate that only one state became responsible for the photoluminescence spectrum. Infrared spectroscopy was used to confirm the presence of a degradation route similar to that reported for dialkoxypolyphenylenevinylene materials where the vinylene bonds are react with molecular oxygen and form carboxylic acid groups. Finally the effect of using different electrode metals was established and a comparison made between the photoluminescence and electroluminescence properties. The electroluminescence emission maximum (580 nm) of didodecyl-PSV light emitting devices was found to be redshifted by 20 nm compared to the photoluminescence, exhibited turn-on voltages below 3 V and reached a luminance of 100 cd m−2 at current densities below 10 mA cm−2.
Keywords: PPV-type polymer; Light emitting device; Photobleaching;

Polycyclotrimerization of aromatic dicyanate monomers yields polycyanate (PCn) resin with s-triazine ring as the crosslinking points. This inherent s-traizine ring in PCn resin can function as hydrogen-bond (H-bond) acceptor; therefore, an H-bond donor, 9-anthracenecarboxylic acid (ACA), was used in this study to mix with the starting aromatic dicyanate monomer and the whole mixtures were further cured to prepare miscible ACA/PCn blends with inherent H-bond interactions. The resulting ACA/PCn blends show their absorption and emission patterns characteristic of the photoluminescent (PL) ACA and PCn components. An energy-transfer process from the PCn matrix to the included ACA operates, resulting in the increase of the PL quantum yield in the ACA/PCn blends as compared to pure PCn resin.
Keywords: Polycyanate; Anthracenecarboxylic acid; Hydrogen-bond; Photoluminescence;

Dual polymer electrochromic devices (ECDs) composed of electrochemically deposited conducting copolymers of thiophene-functionalized monomers, 2-[(3-thienylcarbonyl)oxy] ethyl 3-thiophene carboxylate (TOET), 2,3-bis-[(3-thienylcarbonyl)oxy]propyl 3-thiophene carboxylate (TOPT), and 3-[(3-thienylcarbonyl)oxy]-2,2-bis-[(3-thienylcarbonyl)oxy]propyl 3-thiophene carboxylate (TOTPT), and polyethylene dioxythiophene (PEDOT) as the counter part were constructed with tetrabutylammonium tetrafluoroborate (TBAFB) doped gelled poly(methyl methacrylate) (PMMA) and evaluated. An electrochromic device with the following configuration was assembled — indium tin oxide (ITO)-coated glass /conducting copolymer || gel electrolyte || PEDOT/ITO. Spectroelectrochemistry, electrochromic switching, stability and open-circuit memory of the devices were examined.
Keywords: Electrochromic devices; Electrochemical deposition; Conducting copolymers; Poly(3,4-ethylenedioxythiophene);

Micromorphology and conductivity of the vacuum-deposited polyaniline films by Hong Qiu; Hui Li; Kun Fang; Jing Li; Weimin Mao; Sheng Luo (71-74).
Polyaniline films with thickness of about 200 nm were deposited on unheated glass substrates by using a vacuum evaporation either HCl-doped or intrinsic polyaniline pellets. Micromorphology and electrical property of the films were studied by using scanning electron microscopy and by measuring their conductivity at room temperature. The films prepared by the HCl-doped polyaniline pellets grow with granular particles whereas those prepared by the intrinsic polyaniline pellets consist of long fibrils as well as granular particles. The micromorphology of the polyaniline films is determined by that of their initial pellets. The conductivity of the films prepared by the HCl-doped polyaniline pellets is 1.5 × 10−5  S/cm, which is much smaller than that of their initial pellets. The conductivity of the films prepared by the intrinsic polyaniline pellets is 2.3 × 10−5  S/cm, which is almost equal to that of the intrinsic polyaniline pellets.
Keywords: Polyaniline film; Vacuum evaporation; Micromorphology; Conductivity;

Surface-treatment effects on organic thin-film transistors by Sang Chul Lim; Seong Hyun Kim; Jung Hun Lee; Mi Kyung Kim; Do Jin Kim; Taehyoung Zyung (75-79).
We have fabricated organic thin-film transistors (OTFTs) using pentacene as an active layer with chemically modified SiO2 gate dielectrics. The effects of the surface treatment of SiO2 on the electric characteristics of OTFTs were investigated. The SiO2 gate dielectric surfaces were treated by normal wet-cleaning process, O2-plasma treatment, hexamethyldisilazane (HMDS), and octadecyltrichlorosilane (OTS) treatment. After the surface treatments, the contact angle and surface free energy were measured in order to analyze the surface state changes.From the electrical measurements, typical IV characteristics of TFTs were observed. The field effect mobility, μ, was calculated to be 0.29 cm2  V−1  s−1 for OTS-treated sample, while those of the HMDS, O2-plasma treated, and wet-cleaned samples to be 0.16, 0.1, and 0.04 cm2  V−1  s−1, respectively.
Keywords: Organic thin-film transistors; O2-plasma treatment; HMDS treatment; OTS treatment; Semiconductors;

The electrochemical co-polymerization of p-aminodiphenylamine and aniline: effect of pH by M.A. Cotarelo; F. Huerta; C. Quijada; F. Cases; J.L. Vázquez (81-85).
The electrochemical oxidation of p-aminodiphenylamine (4ADPA) in the presence of aniline in phosphate medium of pH ranging from 1 to 10.5 has been investigated. Mixtures of both monomers can be co-polymerized to produce electroactive poly aniline-co-4ADPA (Pan-4adpa) films if the pH of the medium is kept, approximately, within 3 and 9 and the upper potential limit is lower than the oxidation potential of aniline. Pan-4adpa growth rates are pH dependent and are also affected by the amount of polymeric material deposited on the electrode surface. It has been suggested the existence of a certain inhibition effect of both H+ and OH on the polymerization reaction. Contrary to what is observed for those films synthesized at pH 5 and 7, the growth of Pan-4adpa at pH 8 seems to be an autocatalytic process until the inhibition of the polymerization reaction takes place.
Keywords: Aniline; 4-ADPA; Cyclic voltammetry; Co-polymerization;

Towards all-polymer field-effect transistors with solution processable materials by Tomas G. Bäcklund; Henrik G.O. Sandberg; Ronald Österbacka; Henrik Stubb; Tapio Mäkelä; Salme Jussila (87-91).
We have fabricated polymer field-effect transistors (FET) from solution processable polymers. Starting with an inorganic structure using only an organic semiconductor (regio-regular poly(3-hexylthiophene)), the transistor performance was studied as the inorganic materials were replaced with polymeric alternatives one at a time. We see a gradual increase in subthreshold swing and off-currents and an increased threshold voltage when substituting the inorganic materials with polymer materials. The small reduction in transistor performance when going from inorganic substrate and insulator to polymeric materials indicates that it is possible to make flexible polymer devices from solution processed materials suitable for roll-to-roll processing. The all-polymer FET was realized using two different conducting polymers, polyaniline for the source and drain electrodes and poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate), PEDOT:PSS, for the gate electrode.
Keywords: Field-effect transistor; Organic; Solution process; Polymer insulator; All-polymer;

Spontaneously formed polypyrrole microtubes: incandescence and graphitization by Hu Yan; Makoto Inokuchi; Minoru Kinoshita; Naoki Toshima (93-98).
Emission of strong visible light from the polypyrrole microtube, spontaneously formed during electrochemical polymerization of pyrrole, was observed by applying voltage between the two ends of a single microtube. The molecular structure of the microtube gradually changes into that of graphite during the light emission or the incandescence, which is shown by the data of elemental analysis and Raman spectra as well as temperature dependence of electrical resistance at low temperature.
Keywords: Conductive polymer; Polypyrrole; Microtube; Incandescence; Graphitization; Spontaneous formation;

Patterned polymer photonic crystals using soft lithography and holographic lithography by Jun Hyuk Moon; Alex Small; Gi-Ra Yi; Seung-Kon Lee; Won-Seok Chang; David J. Pine; Seung-Man Yang (99-102).
We fabricated patterned polymer photonic crystals by holographic lithography in conjunction with soft lithography. A patterned SU-8 photoresist film was created by preformed pattern of a hard-baked SU-8 photoresist, transferred by a PDMS mold. Then, four-beam holographic exposure carved 3D photonic crystal structures onto the patterned photoresist. Because of refractive index matching of the photoresist and the hard-baked photoresist, scattering, which might have caused a distortion of interference pattern, did not occur. Eventually, an f.c.c. polymer structure with a line pattern was successfully created after development.
Keywords: Holographic lithography; Soft lithography; SU-8 photoresist; Photonic crystals; Scattering;

Corrigendum to “Conducting blends of poly(o-toluidine) and poly(ester)urathane” [Synth. Met. 144 (2004) 241–247] by Premamoy Ghosh; Amit Chakrabarti; Swarnendu B. Kar; Rajesh Chowdhury (103).