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The influence of the transition metals on the molecular orientation and molecule-substrate interaction has been investigated by angular dependent NEXAFS spectroscopy for the recently synthesised dialkynyl bridged complexes M-2-DEBP (Cl(PBu3)(2)M-C equivalent to C-C6H4[4 C6H4-C equivalent to CM(PBu3)(2)Cl, M = Pt, Pd; DEBP = diethynyl-biphenyl, i.e. C equivalent to C-C6H4-C6H4-C equivalent to C-). Thin films of both samples have been deposited on Au/Si(111), and the angular dependent analysis of the main pi* feature deriving by the superimposition of the resonances due to benzene and acetylene carbon orbitals showed a polarisation effect for Pd-2-DEBP only. A tendency to a preferential molecular orientation at nearly 50 degrees to the surface was calculated. Furthermore, for Pd2-DEBP, the two pi* resonances already assigned to benzene and acetylene carbon atoms showed different angular effects; a likely explanation for this behaviour bear in mind the interaction between sp and sp 2 carbons of the organic DEBP moieties with Pd centres of neighbouring macromolecules, giving rise to interchain interactions then leading to an enhancement of the already assessed self-assembling properties.

The sensitivity to relative humidity of a sensor based on I2-doped polyphenylacetylene thin film membranes has been investigated. The sensor geometry allows its application in miniature devices. The response to humidity variations (20%–80%) is fast and reproducible for long times (months). The I/V characteristics suggest that ionic type conductivity is prevailing. Current intensity measurements performed on films of different thicknesses show that surface conductivity is mainly responsible for the sensor's electrical response.

A new surface acoustic wave humidity sensor has been developed and tested. It is based on the use of a polyphenylacetylene (PPA) membrane which has already been utilized in the I 2 -doped form for the study of humidity sensors based on electrical conductivity responses. PPA shows physical properties which make it an almost ideal membrane for acoustic wave type sensors. Measurements performed on both Rayleigh and surface transverse waves have shown a high sensitivity of the device over a wide range of relative humidity values, a reversible behaviour together with a fairly fast response time.

The electrical properties of iodine-doped poly(phenylacetylene) [PPA] solutions have been studied by means of low-frequency electrical conductivity and dielectric measurements in the frequency range 1 MHz-1 GHz. These data show that, in these systems, the conducting mechanism is different and more complicated than the typical additive behaviour of diluted ionic solutions. The high-frequency dielectric measurements display a pronounced dielectric dispersion characterized by a single Debye-type relaxation process. This dielectric behaviour can be attributed to the dipolar character of PPA, enhanced when the polymer interacts with the iodine doping species.

A near-edge x-ray absorption fine structure (NEXAFS) spectroscopy investigation on the electronic structure of some novel pi-conjugated organometallic polymers is presented. The investigated materials consist of Pt and Pd(II) complex units linked together through sigma-bonded organic spacers of ethynyl-thiophene type in a polymeric array. The C K-edge NEXAFS spectra were interpreted by comparison with literature data and with the spectra of reference samples. The linking between the thiophene rings and alkyne groups produces a splitting of the C1s --> pi* peak observed in the spectra of the thiophene systems. Angle-dependent measurements, performed at normal and grazing incidence of the linearly polarized photons, evidenced a preferential orientation of the polymer chains with an average tilt angle of 45 degrees for the thiophene moieties

The structure of some novel oligomeric thiophene-containing pi-conjugated Pd(II) complexes, recently prepared in our laboratory, Cl-Pd(PBu3)(2)-C=C-C4H2S-C=C-C4H2S-C=C-C4H2S-C=C-Pd(PBu3)(2)Cl or Pd-TRI and Cl[-Pd(PBu3)(2)-C=C-C4H2S-C=C-](3)-Pd(PBu3)(2)Cl Or Pd-DET, were studied by means of x-ray photoelectron spectroscopy. The interface formation between chromium and the organometallic rr-conjugated polymer films was also investigated. Chromium was evaporated stepwise in situ onto the surface of the polymer films and the XPS core-level spectra of the polymer and of the metal overlayer were studied as a function of Cr coverage. A charge-transfer reaction from the deposited metal atoms to the substrate material was evidenced by the modifications taking place in the polymer spectra upon Cr deposition. A comparison with the surface reactivity towards chromium of [-Pd(PBu3)(2)-C=C-C6H4-C6H4-C=C-](n), Pd-DEBP, a related polymer where benzene groups replace thiophene in the organic conjugated moiety, will be discussed.

X-ray photoelectron spectroscopy was used in order to investigate the interface formation between chromium and thin films of a newly synthesised π-conjugated polymer P(PA- p NO 2 PA); the investigated material is a block copolymer consisting of phenylacetylene (PA) and para -nitro phenylacetylene ( p NO 2 PA) units {[–(CHC–R) n –(CHC–R′) m –] N ; RC 6 H 5 , R′C 6 H 4 NO 2 }. Chromium was evaporated stepwise in situ onto the polymer surface and the XPS spectra of the substrate polymer and of the metal overlayer were studied as a function of increasing chromium thickness. In the early stages of the interface formation, chromium was found to interact mainly with the nitrogen atoms of the –NO 2 groups, that are reduced to nitride-like species; the N–O bond is broken, as evidenced by the modifications occurring in the N1s and O1s spectra. The changes in the C1s spectra upon increasing metal deposition suggest the formation of a chromium–arene π-complex at low chromium coverage and of carbide-like species at higher chromium thickness.

The electrical conductivity of poly(phenylacetylene)-iodine in tetrahydrofuran solution has been measured at the frequency of 10 kHz, in the temperature range from −15 to 40 °C as a function of iodine concentration. The data have been analysed on the basis of the counterion fluctuation model developed for highly charged polyelectrolyte aqueous solutions. The dependence of the electrical conductivity on the iodine concentration suggests that the conduction mechanism is governed by the interaction of the polymer with iodine molecules, resulting in a charge-transfer complex in solution, the effectiveness of which is maximum at some well-defined concentrations corresponding to six polymer units for each I5− ion.

The electrical conductivity of poly(phenylacetylene)-iodine in tetrahydrofuran solutions has been measured at the frequency of 10 kHz, in the temperature range from − 15 to 40 °C. The data have been analysed in the light of current theories of polyelectrolyte solutions, considering the effect of counterions along the charged polymer chain. Our results show a linear dependence of electrical conductivity on the polymer concentration at an I 2 doping concentration of 10 mg/ml. These data can be accounted for by considering an electronic charge distributed over, on average, a polymer segment containing six monomers.

A device for surface acoustic wave (SAW) measurements, based on a polymeric sensitive membrane, that is polyethynylfluorenol (PEFl), has been realized. The SAW/PEFl sensor shows relatively fast and highly sensitive responses in the range of relative humidity 0–60%. The enhanced sensitivity of the SAW/PEFl device, in comparison with that of a SAW sensor which utilized a polyphenylacetylene film, may be attributed to the presence of OH groups belonging to the polymer repeat unit.

A coverage-dependent XPS investigation of the early stages of interaction between evaporated Cu and polyphenylacetylene (PPA) has been carried out. Copper films have been deposited at 300 K to a final thickness of about 5 monolayers. Overlayer and substrate core-level emission behaviour indicates the layer-by-layer growth of Cu on the PPA surface without interdiffusion. At low copper coverages a chemical interaction between the Cu adatoms and the substrate is observed by monitoring the changes occurring at the pi --> pi * satellite feature of the C1s core-level line. We observe a decrease of intensity for this satellite as the copper coverage increases, interpreted in terms of the formation of a Cu-pi complex with the phenyl ring. The Cu Auger spectra demonstrate the presence of positively charged metal atoms up to a coverage of approximately 5 angstrom. In the submonolayer region the occurrence of broadening of the C1s core level on the low binding energy side is observed together with a positive shift for the Cu2p3/2 emission. Upon completion of the first copper monolayer these phenomena are removed. The observed behaviour can be accounted for in terms of differential charging with injection and trapping of charge into the PPA film from the Cu atoms that have not yet completed the first monolayer.

XPS investigation of the early stages of Cu/PPA interface formation has been performed in the range of coverage 0.5 A 13 A Cu . Copper is found to grow in a layer-by-layer mode without interdiffusion with the substrate. Weak chemical interaction between Cu and the π ring electrons of the phenyl groups is evidenced by monitoring the changes occuring at the C 1s secondary structure π→π ∗ shake up transition.

A humidity sensor has been fabricated by using thin films of iodine-doped polyphenylacetylene. The electrical response of the sensor towards relative humidity variations is fast and reversible during long working periods. The investigated sensor is also sensitive to the vapours of other chemical substances.

Thin films of iodine-doped polyphenylacetylene (PPA) have been investigated and used as humidity sensors. Measurements of resistance variations of a PPA/I2 system, induced by relative humidity variations ranging from 10 to 90%, have been performed at constant temperatures (25 and 30 °C). The behaviour of the resistance versus relative humidity is found to be approximately exponential. Our samples show a good reversibility during humidity cycles and a relatively fast response time (a few seconds).

A new material, polyethynylfluorenol (PEFl), has been prepared and characterized, either undoped or homogeneously doped with SnCl 2 . We have chosen as basic device for the sensor a simple humistor (humidity sensor resistor) since we have observed that the PEFl conductivity varies with the environmental relative humidity (r.h.). This behaviour is completely reversible without any noticeable 'memory effect'. PEFl can be considered a promising material for the fabrication of humidity sensors.