The electronic properties of metal complexed poly(3-alkylthiophene) films

Dielectric spectroscopy has been used to extract the AC and DC electrical conductivities of P3MT complexed with the paramagnetic ion Fe²⁺, and these were compared to data for uncomplexed P3MT in the frequency range of 1 Hz-10 MHz. The polymers were nominally undoped; however, the presence of residual Fe³⁺ ions from the polymerisation reaction renders the materials p-type semiconductors. Measurements were carried out over the temperature range 123-323 K. An analysis of the frequency-dependent complex conductivity together with the DC conductivity can be used to elucidate whether free charge conduction, charge hopping or quantum tunnelling is the dominant conduction mechanism. The results were compared to the predictions of a variety of theoretical conduction models. It was found that the presence of the Fe²⁺ ions produced greater long-range order at low temperatures by complexing between the sulphur heteroatoms of four 3-methylthiophene monomer units. This provided an additional barrier hopping conduction mechanism at low temperatures (183-243 K), and the hopping occurred over a barrier height within the range 0.45-0.6 eV.     

Nanostructural depth-profile and field-effect properties of poly(alkoxyphenylene-thienylene) Langmuir-Schäfer thin-films

The correlations between morphological features and field-effect properties of poly(alkoxyphenylene-thiophene) thin Langmuir-Schäfer film deposited on differently terminated gate dielectric surfaces, namely bare and methyl functionalized thermal silicon dioxide (t-SiO₂), have been systematically studied. The film morphology has been investigated at different film thickness by Scanning Force Microscopy. Films thicker than a few layers show comparable morphology on both dielectric surfaces while differences are seen for the ultra-thin polymer deposit in close proximity to the substrate. Such deposit is notably more heterogeneous on bare t-SiO₂, while a more compact and uniform nanogranular structure is observed on the silylated t-SiO₂. As to the field-effect properties, the methyl-terminated gate dielectric surface leads to a two order of magnitude mobility enhancement along with a field-effect thickness independent conductance.     

化学气相沉积聚合法制备聚丁酸酰基取代对亚苯基二亚甲基

合成了一种新的丁酸酰基取代对亚苯基二亚甲基二聚体,用化学气相沉积聚合法制备了聚丁酸酰基取代对亚苯基二亚甲基(PPX-COCH2CH2COOH)膜,采用FTIR、NMR的方法证实了其化学结构,采用元素分析方法测定苯环上丁酸酰基的取代程度为4.7%左右.对膜溶解性和抗化学氧化性能的研究表明,PPX-COCH2CH2COOH膜具有优异的耐溶剂性和抗化学氧化性能.丁酸酰基的引入使得薄膜的结晶度有所下降.含有丁酸酰基取代基的聚合物的热稳定性较好.PPX-COCH2CH2COOH膜可以和肝素等反应,甲苯胺蓝法测得肝素含量为15.8μg/cm2.     

Biomass-based composites from poly(lactic acid) and wood flour by vapor-phase assisted surface polymerization

To prepare biomass-based composites in an environmentally benign manner, vapor-phase assisted surface polymerization (VASP) was applied to prepare the composites from wood flour and poly(l-lactic acid) (PLLA) without solvent. VASP of l,l-lactide successfully proceeded on the wood flour surfaces, resulting in surface coverage by newly generated PLLA. For obtained PLLA/wood flour composites, it was clarified that grafting of PLLA on wood flour surfaces had occurred to form covalently bonded composites, with the accumulated PLLA layers having crystallized in situ during VASP. Resulting PLLA layers showed very high crystallinity of 79.2% and a high melting point close to the equilibrium melting point. Moreover, thermal degradation behavior of the composites suggested a cooperative degradation manner of the components.     

Formation kinetics and structure of self-assembled poly(3-alkylthiophene) films on gold surface

The self-assembly process of poly(3-dodecylthiophene) (PDT) on an Au(1 1 1) surface was revealed by Fourier transform infrared reflection absorption spectroscopy (FTIR-RAS). The adsorption kinetics of PDT obeys the time-dependent Langmuir adsorption isotherm. The SAM growth of PDT is accompanied by a transition of the molecular conformation. After the immersion of the gold substrate into the chloroform solution, the PDT coils adsorb on the surface. However, the coils are spread over the surface due to the attractive force between the sulfur atoms of the thiophene-rings and the Au atoms. Simultaneously, the alkyl chain moiety of PDT is provisionally oriented perpendicular to the surface. At equilibrium, the alkyl chain moiety adopts a flat-lying configuration with respect to the surface. The SAM technology allows well-defined film structures to be fabricated and the subtle molecular orientation to be controled, which is impossible by the conventional fabrication methods of thin films such as vacuum-deposited and cast films.     

Structures and electronic properties of thin-films of polycyclic aromatic hydrocarbons

We report the fabrication and characterization of organic thin-film transistors (TFTs) using several polycyclic aromatic hydrocarbons (PAHs). Pentacene, ovalene, dibenzocoronene and hexabenzocoronene were deposited as organic semiconductors on silicon wafers with gold electrodes as the bottom-contact configuration of the TFTs. The pentacene TFT showed the highest field-effect mobility of more than 0.1 cm²/Vs in comparison with the other PAHs. The results clarified that the high field-effect mobility of the pentacene thin film is due to large grain size and intrinsic electronic properties.     

Electronic properties of semiconducting poly(ferrocenylsilane) thin films with vapor-phase iodine diffusion doping

We report diffusion doping of the semiconducting polymer poly (ferrocenylsilanes), or PFS. We have obtained a steady-state conductivity change of greater than eight orders of magnitude effected through iodine vapor doping of PFS. The sign of thermoelectric power measurements indicates p-type conductivity. The conductivity exhibits an activation energy of E=(0.45–0.65) eV for moderately-doped samples and E=(0.8–0.99) eV for heavily-doped samples. We report sample photoconductivity, which we find to be principally of bolometric origin. We also study the evolution of electrical properties over time: during several days after fabrication, the samples exhibit an irreversible decrease in conductivity which may be attributable to partial iodine desorption. After this aging process, especially noticeable in heavily doped material, the sample properties stabilize, suggesting promise in a range of prospective device applications. © 2001 Kluwer Academic Publishers     

Bolometric properties of silicon thin-film structures fabricated by plasmachemical vapor-phase deposition

A method of fabricating uncooled thermally sensitive sandwich structures based on amorphous hydrated silicon films is discussed and experimental results are reported. The structures have an area of 10⁻⁴ cm², a resistance of ≅10 kΩ, and a temperature coefficient of resistance ≃2%/K. At 30 Hz and a current of ≃1 μA, the excess noise exceeds the thermal resistance noise by a factor of 1.7. Pis’ma Zh. Tekh. Fiz. 23, 63–68 (June 26, 1997)     

Photocurrent of regioregular poly(3-alkylthiophene)/fullerene composites in surface-type photocells

We have studied steady-state photocurrents of regioregular poly(3-alkylthiophene)/C₆₀ composite on surface-type photocells formed with Au electrodes. The photocurrent is observed above 1.4 eV, in agreement with the light-induced ESR measurements on the composite. The photocurrent is small up to 1.8 eV and then increases abruptly at 1.9 eV and keeps increasing up to 3 eV. The action spectra is not symbatic nor antibatic with the optical absorption spectra. The exponent n of the light intensity I dependence of the photocurrent P, P ∝ Iⁿ, is close to n = 0.5 above 1.9 eV, indicating the involvement of the bimolecular recombination. Below 1.9 eV, n is between 0.5 and 1, indicating the contribution of the monomolecular process. The change in the exponent is understood by a universal curve as a function of the photoexcitation density taking account of the fraction of the incident light absorbed and the optical penetration depth.     

Morphological analysis of poly(o-methoxyaniline) thin-films deposited by spin coating technique

Morphological study of conducting polymer thin films obtained by spin coating is reported. Poly(o-methoxyaniline) films were deposited onto glass substrates and analyzed by profilometry and atomic force microscopy (AFM). It is shown that final thickness is correlated by a power law with spin speed with a solution concentration varying coefficient and that surface roughness decreases with increasing spin speed.     

Synthesis and properties of diblock copolymers containing poly(3-hexylthiophene) and poly(fluorooctyl methacrylate)

This study reports the synthesis of regioregular poly(3-hexylthiophene)-b-poly(1H,1H-dihydro perfluorooctyl methacrylate) (P3HT-b-PFOMA) block copolymers by atom transfer radical polymerization of FOMA using P3HT macroinitiators. The P3HT macroinitiator was previously prepared by chemical modification of hydroxy terminated P3HT The block copolymers were characterized by 1H-NMR, 13C-NMR, GPC, DSC, TGA and TEM. The block copolymers are able to self-assemble into phase separated micellar thin film morphology from chloroform.     

Pore-bridging poly(dimethylsiloxane) membranes as selective interfaces for vapor-phase chemical sensing

A new kind of polymer-based sensor is described in which the experimental parameters controlling selectivity and sensitivity are decoupled. The sensor is based on a surface acoustic wave (SAW) gravimetric transducer modified with a high-surface-area, nanoporous alumina coating. A very thin ( approximately 40 nm) poly(dimethylsiloxane) (PDMS) coating resides atop the porous alumina structure. In this configuration, the total surface area of the nanoporous alumina coating controls the sensitivity of the device, while the chemical properties of the PDMS membrane control selectivity. In conventional polymer-based sensors, the polymer plays the dual role of controlling both selectivity (via the chemical composition of the coating) and sensitivity (via the volume of the film). In this paper, we show that PDMS acts as a chemically selective gate that absorbs polar and nonpolar VOCs but does not transport these analytes to the underlying pore volume. In contrast, water vapor is absorbed by the PDMS to a very minor extent but is easily transported through it to the underlying walls of the porous substructure. Specifically, there was little difference in the mass-loading response arising from polar and nonpolar VOCs dosed onto planar and nanoporous SAW devices modified with PDMS. In contrast, SAW devices having nanoporous coatings responded up to 24 times more selectively to water than planar sensors modified identically.     

In situ polymerization preparation of blends of poly(methyl methacrylate) and poly(styrene-co-acrylonitrile)

The in situ polymerization of methyl methacrylate (MMA) with poly(styrene-co-acrylonitrile) (SAN) was studied. The PMMA/SAN in situ polymerization blends obtained were examined by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), tensile tests and scanning electron microscopy (SEM). The blends with compositions of 95/5, 80/20, 70/30, and 60/40 in weight ratios were miscible and had a single phase structure. However, the 90/10 PMMA/SAN in situ polymerization blend obtained was inhomogeneous and had a two-phase structure; polymerization-induced phase separation occurred during the preparation process of the blend. Both tensile strength and elongation at break increase with increasing SAN content up to 30 wt%. The degradation temperature and thermal stability of PMMA increased remarkably on incorporation of SAN up to 30 wt%.