Photoemission studies of polythiophene and polyphenyl films produced via surface polymerization by ion-assisted deposition

Conducting polymer films are grown by mass-selected, hyperthermal thiophene ions coincident on a surface with a thermal beam of organic monomers of either alpha-terthiophene (3T) or p-terphenyl (3P) neutrals. Mass spectrometry and X-ray photoelectron spectroscopy previously verified polymerization of both 3T and 3P by 200 eV C(4)H(4)S(+) during surface polymerization by ion-assisted deposition (SPIAD). The electronic structure of these films are probed here by ultraviolet photoelectron spectroscopy (UPS) and polarized near-edge X-ray absorption fine structure spectroscopy (NEXAFS) and compared with similar spectra of evaporated films. The conducting polymer films formed by SPIAD display new valence band features resulting from a reduction in both their band gap and barrier to hole injection, which are calculated from the occupied and unoccupied valence band states measured by UPS and NEXAFS. These changes in film electronic structure result from an increase in the electron conjugation length and other changes in film structure induced by SPIAD.     

Growth of novel polythiophene and polyphenyl films via surface polymerization by ion-assisted deposition

Surface polymerization by ion-assisted deposition (SPIAD) is used here to grow novel polythiophene and polyphenyl thin films on a silicon surface by hyperthermal, mass-selected thiophene cations coincident with a thermal beam of alpha-terthiophene or p-terphenyl neutrals. X-ray photoelectron spectroscopy (XPS) observes a large enhancement in film growth for SPIAD compared with either thiophene ions or alpha-terthiophene exposure alone. Changes in S/Si and C/Si ratios from XPS, direct observation of higher polymerization products by mass spectrometry, characteristic vibrations in the Raman data, and enhanced stability in a vacuum all indicate that 200 eV SPIAD polythiophene films are most efficiently polymerized at a 1/150 ion/neutral ratio. Other ion/neutral ratios are less efficient at film growth, in the order 1/150 > 1/450 > 1/900 > direct ion deposition > 1/50. Changes in C/Si ratios and higher polymerization products indicate polymerization occurs in SPIAD polyphenyl films grown with a 1/100 ion/neutral ratio. Furthermore, thiophene ions are found to incorporate into some, but not all, of the polymerization products observed in mass spectrometry.     

Surface polymerization by ion-assisted deposition for polythiophene film growth

Cationic polymerization is induced at the gas-solid interface by hyperthermal organic cations coincident on a surface with a thermal beam of organic monomers. This process, termed surface polymerization by ion-assisted deposition (SPIAD), produces films that maintain the chemical structure of the monomer. A polythiophene film is produced here by SPIAD with 100 eV thiophene ions and terthiophene monomers coincident on Si and indium tin oxide (ITO) substrates held under vacuum. X-ray photoelectron spectroscopy observes enhancement in film growth for SPIAD compared with either thiophene ion or terthiophene exposure alone. Polythiophene films grown by both mass-selected and nonmass-selected ions with coincident terthiophene dosing both display similar fluorescence intensities at two wavelengths characteristic of emission from films of the terthiophene monomer. Raman spectra of films from nonmass-selected ions display several vibrations also observed in terthiophene films. Ions therefore play a critical role in film growth from nonmass-selected ions, in addition to any radical or photochemically driven processes that may also occur.     

Structural variety of CdS in films synthesized by vapor deposition polymerization

Poly(p-xylylene)—CdS (PPX—CdS) nanocomposite films with different thicknesses (～0.2, ～0.5, ～1, and ～1.5 μm) and concentrations of CdS from 5 to 90 vol.%, as well as single-component CdS and PPX films with various thicknesses were studied by X-ray diffraction. The films were synthesized on polished silicon or quartz substrates by low-temperature vapor deposition method. It was shown that CdS nanoparticles in PPX—CdS films, depending on their thickness and CdS content, can have an X-ray amorphous structure, a defect crystal structure (RCP structure), or a wurtzite-type crystal structure. Similar structures were observed for single-component CdS films of the corresponding thickness. The sizes of the coherent scattering regions of CdS were determined for some nanocomposite and single-component films. Poly(p-xylylene) in the studied nanocomposite films was characterized by an X-ray amorphous structure.

     

Surface analysis of films and film systems produced by pulsed laser deposition

Ceramic films and film systems (ZrO₂ films, ZrO₂/Ti multilayers, and BN films) are deposited by pulsed laser deposition (PLD) and analyzed using X-ray photoelectron (XPS), Auger electron (AES), and micro-Raman spectroscopies. The electron spectroscopies are used to determine the film stoichiometry, the nature of the bonding, and to specify contaminant species. The micro-Raman spectroscopy gives information on crystal structure, grain size, and mechanical stress within the films. In ZrO₂ films a stoichiometry is achieved with typically 5%, with only weak dependencies on processing variables. The only contaminants are a small amount of water from the ambient gas and a carbonaceous surface layer. Multilayers consisting of alternating ZrO₂ and Ti layers exhibit a TiC contamination within the Ti layers. Depending on the processing variables, BN films may be nearly stoichiometric or may have significant, even dominant contaminations throughout the film from elemental B, B₂O₃, and/or a boron-oxynitride species. The first component is due to the non-stoichiometric material removal from the target (N-depletion) at low laser fluences, as confirmed by XPS measurements on irradiated targets. The second and third arise from H₂O in the ambient, and exhibit a complex dependence on processing variables. Micro-Raman spectra show only amorphous or hexagonalphase BN. Depending on the position on the substrate relative to the laser-induced vapour/plasma plume, there may be a particle deposition or mechanical stress within the films, as evidenced from large shifts (up to 15 cm^–1) of the Raman spectral peaks.     

Colloid surface engineering via deposition of multilayered thin films from polyelectrolyte blend solutions

Multilayer thin films were constructed on polystyrene colloidal particles by depositing alternating layers of poly(allylamine hydrochloride) (PAH) at pH 7.5 and varying composition blends of poly(acrylic acid) (PAA) and poly(styrenesulfonate) (PSS) at pH 3.5. Following the deposition of each layer, microelectrophoresis experiments showed alternating zeta-potentials, suggesting the formation of multilayered films on the particles. Scanning and transmission electron microscopy were used to examine the surface morphology of the colloidal particles, with homogeneous surface coatings apparent for films deposited from PAA/PSS blend solutions containing up to 90 wt % PAA. The colloidal stability of these particles is greater than those coated with individual PAH and PAA layers. In the case of the blend PAA/PSS = 25:75 wt %, up to 20 layers were assembled without compromising the colloidal stability of the dispersion. The results demonstrate that the deposition of layers from PE blend solutions containing a strong and weak PE can be used as a facile method for controlling the surface properties and hence the colloidal stability of core-shell particles, as well as the thickness and morphology of the coatings. Control of these parameters is important for subsequent processing and application of these particles in controlled delivery, photonics, catalytic, and separation applications.     

Surface morphology and biological activity of protein thin films produced by electrospray deposition

Protein thin films were prepared by the electrospray deposition (ESD) method from aqueous solutions of alpha-lactalbumin (alpha-LA) at different concentrations, and their surface morphologies and biological activities were characterized. The surface morphologies of the deposited films were observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The SEM and AFM images showed that the film surfaces had a fine porous structure, in which the pore diameters ranged from 40 to 600 nm. The biological activities of the cross-linked protein films were tested by the mechanochemical method. The response to calcium ion (Ca(2+)) demonstrated that the biological activity of the films was preserved. These results indicate that the ESD method is potentially useful for the fabrication of active protein thin films. The freestanding protein thin films prepared by ESD and postdeposition cross-linking provide novel options for protein-based biomaterials.     

Redox active surface films produced by electrooxidation of substituted indolysines

The electrochemical oxidation of substituted mono-and 3,3′-biindolysines is studied by methods of cyclic voltammetry and electron spin resonance (ESR) combined with in situ electrolysis. In acetonitrile, there occurs easy irreversible electrochemical oxidation and proceed processes of association of generated radical cations via unsubstituted positions of five-membered cycles. Polymeric products of oxidation of 2-arylindolysines, 3-indolysine-2-yl-quinoxalines, and 2,2′-diaryl-3,3′-biindolysines are obtained when cycling potential in the interval ?0.3 V → +0.8 V → ?1.3 V → ?0.3 V (Fc/Fc⁺). The products deposit on the electrode with the formation of redox-active films that are capable of undergoing reversible oxidation with the formation of stable paramagnetic states registered by the ESR method.     

Morphology of anomalous polystyrene/ polybutyl acrylate composite particles produced by seeded emulsion polymerization

 Recently, we found that “golf ball”-like polystyrene (PS)/polybutyl acrylate (PBA) composite particles could be produced by seeded emulsion polymerization of butyl acrylate (BA) with PS seed particles. In this article, the effects of the polymerization temperature, BA monomer concentration, and the presence of 1-octanol, which is a good solvent for PBA and a poor solvent for PS in the polymerization, on the morphology was studied. Received: 25 February 1997 Accepted: 4 October 1997     

Chemical composition and properties of films produced from hexamethyldisilazane by plasma-enhanced chemical vapor deposition

Relationships between the chemical composition of the gas phase and the properties of SiC_xN_yH_z films produced from hexamethyldisilazane by plasma-enhanced chemical vapor deposition have been studied. The plasma composition has been examined by optical emission spectroscopy. Thermal analysis of the films with simultaneous mass spectrometric detection of released gases has been performed. On the basis of the results and published data, mechanisms for the formation of films by plasma polymerization have been proposed and the film growth at a low plasma power and high reactor temperatures has been found to follow the heterogeneous mechanism.     

QCM sensing of a chemical nerve agent analog via electropolymerized molecularly imprinted polythiophene films

The highly selective and sensitive detection of a chemical nerve agent analog pinacolyl methylphosphonate (PMP) was demonstrated using an electrochemically molecularly imprinted polymer (MIP) polythiophene film onto a quartz crystal microbalance (QCM) transducer surface. The fabrication and optimization of the sensor film was monitored by in situ electrochemistry‐QCM (EC‐QCM) measurements, which determined the change in mass and simultaneous change in redox properties of the polymer film. The film deposition, template loading, and template removal were evidenced by a combination of surface characterization techniques such as the attenuated total reflection infrared spectroscopy and high‐resolution X‐ray photoelectron spectroscopy. The fabricated MIP film demonstrated a limit of detection and a limit of quantification of ～60 and ～197 μM, respectively. The linear sensing range is between 125 and 250 μM concentration of PMP. Finally, theoretical modeling (AM1 semiempirical quantum calculations) studies revealed that a stable prepolymerization complex is formed in solution with the existence of H‐bonding interactions using the 2:1 monomer‐to‐template ratio. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Titanate nanotube thin films via alternate layer deposition

Layer-by-layer growth of titanate nanotubes on glass substrates was achieved by alternate layer deposition using an aqueous solution of colloidal titanate nanotubes and that of a polycation. Even a single layer thin film of titanate nanotube shows high photoinduced hydrophilicity.     

Synthesis and photoresponsive behavior of azobenzene-functionalized polythiophene films

In this paper, two kinds of azobenzene-functionalized polythiophene liquid-crystalline (LC) polymers with different spacer lengths (n = 6 and 11) were synthesized. The photochromic behaviors and photoresponsive property of these polymer films were investigated by means of spectrofluorophotometer, polarized optical microscope and ARC UV lamp. The results have shown that these liquid-crystalline polythiophene films exhibit a quite fast photochemical phase transition speed and a better opticalswitching property. Furthermore, the existence of the azobenzene moiety in the side chain has also rendered the polythiophene some interesting optical properties that can be modulated by UV light irradiation, e.g., the intensity of photoluminescent emission associated with the conjugated polythiophene main chain was found to decrease upon UV irradiation and the effect becomes more prominent when shorter spacers are used in between the azobenzene group and the main chain.     

Perhydridosilicone films produced by IR laser‐induced chemical vapour deposition from disiloxane

Solid perhydridosilicone films have been produced by transversely excited atmospheric (TEA) and continuous‐wave CO₂ laser‐induced gas‐phase decompositions of H₃SiOSiH₃ controlled by elimination and polymerization of transient silanone H₂SiO and affording silane and hydrogen as side products. The decomposition mechanism is supported by evidence of scavenged intermediates and minor volatile products. The films are characterized by FT infrared and x‐ray photoelectron spectroscopy and by scanning electron microscopy and shown to undergo facile oxidation of the topmost layers in air and chemical changes upon argon ion sputtering. Copyright © 2000 John Wiley & Sons, Ltd.     

Chemical surface deposition and growth rate of thin CdSe films

Chemical surface deposition of thin CdSe films was studied. The conditions for preparing thin films were examined, the degrees of Cd conversion in the starting compounds were determined, and the film thicknesses were measured.     

Chemical vapor deposition synthesis of tunable unsubstituted polythiophene

Despite having exceptional electroactive properties, applications of unsubstituted polythiophene (PTh) have been limited due to its insolubility. To overcome this challenge, we have employed oxidative chemical vapor deposition (oCVD) as a unique liquid-free technique to enable the oxidative polymerization of PTh using thiophene as the starting monomer and vanadium oxytrichloride as an effective vaporizable oxidant initiator. Vibrational and phototelectron spectroscopy indicated the formation of unsubstituted polythiophene. Cyclic voltammetry revealed its electrochromic behavior in solution. Significantly, polymer conjugation length and electrical conductivity can be tuned by controlling oCVD process variables. Polymerization is found to be adsorption-limited, so by providing sufficient monomer and limiting the amount of initiator at the growth surface, PTh is believed to be formed through α-α thiophene linkages.     

Control of surface properties using fluorinated polymer brushes produced by surface-initiated controlled radical polymerization

Surface-grafted styrene-based homopolymer and diblock copolymer brushes bearing semifluorinated alkyl side groups were synthesized by nitroxide-mediated controlled radical polymerization on planar silicon oxide surfaces. The polymer brushes were characterized by X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and time-dependent water contact angle measurements. Angle-resolved XPS studies and water contact angle measurements showed that, in the case of the diblock copolymer brushes, the second block to be added was always exposed at the polymer-air interface regardless of its surface energy. Values of z*/Rg were estimated based on the radius of gyration, Rg, of the grafted homopolymer or block copolymer chains for the grafted brushes and thickness of the brush, z*. The fact that z*/Rg > 1 suggests that all these brushes are stretched. These results support the idea that after grafting the first block onto the surface the nitroxide-end capped polymer chains were able to polymerize the second block in a "living" fashion and the stretched brush so formed was dense enough that the outermost block in all cases completely covers the surface. NEXAFS analysis showed a relationship between the surface orientation of the fluorinated side chains and brush thickness with thicker brushes having more oriented side chains. Time-dependent water contact angle measurements revealed that the orientation of the side chains of the brush improved the surface stability toward reconstruction upon prolonged exposure to water.     

Extractive-scintillating resin produced by radiation polymerization

The characterization of a resin material is presented, which contains selective complexing and scintillating molecules in chemically bound form. The resin material is produced via radiation polymerization of the solution of 2-(4-allyloxy-phenyl)-5-phenyl oxazole, 5-(allyloxy-phenyl)-2-[4-(5-phenyl-oxazole-2-il)-phenyl] oxazole, diethylene glycol dimethacrylate (DEGMA), styrene and the allyl derivative of a 18C6 crown ether-dicarbolic acid complexing agent. The product is a macroporous polymer matrix, which shows both excellent scintillation properties and ion binding capacity for radioanalytical purposes.     

Morphology of micron-sized monodispersed poly(butyl methacrylate)/polystyrene composite particles produced by seeded dispersion polymerization

In order to develop the seeded dispersion polymerization technique for the production of micron-sized monodispersed core/shell composite polymer particles the effect of polymerization temperature on the core/shell morphology was examined. Micron-sized monodispersed composite particles were produced by seeded dispersion polymerizations of styrene with about 1.4-μm-sized monodispersed poly(n-butyl methacrylate) (Pn-BMA) and poly(i-butyl methacrylate) (Pi-BMA) particles in a methanol/water (4/1, w/w) medium in the temperature range from 20 to 90 °C. The composite particles, PBMA/polystyrene (PS) (2/1, w/w), consisting of a PBMA core and a PS shell were produced with 2,2′-azobis(4-methoxy-2,4-dimethyl valeronitrile) initiator at 30 °C for Pn-BMA seed and with 2,2′-azobis(isobutyronitrile) initiator at 60 °C for Pi-BMA seed. The polymerization temperatures were a little above the glass-transition temperatures (T _g) of both Pn-BMA (20 °C) and Pi-BMA (40 °C). On the other hand, when the seeded dispersion polymerizations were carried out at much higher temperatures than the T _g of the seed polymers, composite particles having a polymeric oil-in-oil structure were produced. Received: 14 October 1998 Accepted in revised form: 2 June 1999     

Nucleation and growtn of polythiophene films on gold electrodes

The nucleation and growth of polythiophene films on gold electrodes has been studied using potentiostatic steps. The mechanism has been deduced and estimates made of the kinetic parameters. Dissolution of the gold substrate at potentials where thiophene polymerisation occurs is suppressed by the initial rapid formation of a monolayer of polymer. The data indicate that formation of bulk film occurs by the instantaneous nucleation and three-dimensional growth of polymer on top of this monolayer. Rate constants for growth parallel to the surface on the bare gold substrate and the covering polymer layer are surprisingly very similar. Growth perpendicular to the surface is slightly more rapid, typically by a factor of 1.5–3, although it is less dependent on potential. The high density of nuclei results in their overlap at an early stage, after which growth is only possible perpendicular to the surface. Within a narrow potential range, the observation of maxima and minima in current-time transients is interpreted in terms of the “death” and “rebirth” of growing centres.