Gianantonio Della Mea

Glow discharge vapour deposition polymerisation of polyimide thin coatings

Abstract The glow discharge vapour deposition polymerisation method for the preparation of polyimide coatings is presented. This method involves the deposition of the monomer vapours onto a solid substrate in a vacuum chamber. The evaporation of the monomers is obtained by using standard radio frequency magnetron sputtering equipment: the monomer powders are placed on a sputtering source and bombarded by low energy He ions at pressures in the range of 10–20 Pa. By a momentum-transfer mechanism, the ions dissipate their energy causing target heating and sublimation of the monomer molecules. The emission of volatile species from the monomers target surface and their interactions with the plasma components are studied by mass spectrometry and optical emission spectroscopy. Polyimide coatings with thickness ranging from 200 nm to 3 μm have been deposited onto silicon single crystals, sapphire and polyimide substrates. SEM micrographs of these coatings show a homogeneous and crack-free surface. The as-deposited films are mainly made of a mixture of polyamic acid and non-reacted monomers, as revealed by Fourier transform infrared spectroscopy. The imide peaks clearly appear only after thermal treatment (typically 250°C, 1 h, in air or argon). The electrical properties of the polyimide coatings (i.e. bulk and sheet resistivity and dielectric breakdown voltage) are those typical of an insulating material and comparable with the commercial polyimide. These films are characterised by good adhesion to the silicon, sapphire and other polyimide substrates. Chemical resistance to some reagents (acetone, hydrogen peroxide, nitric and hydrofluoric acid) has also been tested.

Hydrogen detection in ruthenium oxide layers by means of the 1H(15N,αγ)12C nuclear reaction

Hydrogen in RuOx layers on quartz prepared by the thermal decomposition of RuCl3 has been detected by means of a nuclear technique. RuOx absorbs water rapidly from the liquid and a constant H/Ru ratio is found throughout the thickness of the layer. RuOx also absorbs water from the ambient moisture, but no saturation is observed even after several months. The permeability of RuOx to water is explained in terms of grain boundary diffusion.

Deposition of silica-silver nanocomposites by magnetron cosputtering

Thin films have been grown on silicon and silica substrates by cosputtering of silica and silver in Ar, Ar+2.5%O2, and Ar+5%O2 gas mixtures. Rutherford backscattering spectrometry showed that the films have Ag atomic fractions xAg in the range of ∼1to∼10at.%, and, by valence considerations, that the fraction of oxidized Ag in the films deposited in presence of oxygen is limited. Transmission electron microscopy images revealed the presence of Ag nanoclusters, with a mean size diameter not larger than 5nm. The clusters are preferentially arranged along columns. It is suggested that the columns are regions with diameter in the nanometer range in which the density of the dielectric matrix is lower, thus favoring the formation of metal clusters. In presence of O2, the clusters were observed to have a more regular spherical shape. The optical absorption spectra of films grown in presence of O2 are distinguished from those grown in Ar by specific features, which are attributed to oxidation at the cluster surface.

Structural and functional characterization of W-Si-N sputtered thin films for copper metallizations

Ternary W-Si-N thin films have been reactively sputter-deposited from a W5Si3 target at different nitrogen partial pressures. The composition has been determined by 2.2 MeV 4 He + beam, the structure by x-ray diffraction and transmission electron microscope, the chemical bonds by Fourier transform - infrared spectroscopy and the surface morphology by scanning electron microscopy. Electrical resistivity was measured by four point probe technique on the as grown films. The film as-deposited is amorphous with the Si/W ratio increasing from about 0.1 up to 0.55 with the nitrogen content going from 0 to 60 at%. The heat treatments up to 980 °C induce a loss of nitrogen in the nitrogen rich samples. Segregation of metallic tungsten occurs in the sample with low nitrogen content (W 58 Si 21 N 21 ). Samples with high nitrogen content preserve the amorphous structure, despite of the precipitation of a more ordered phase inferred by FT-IR absorbance spectrum of the layer treated at highest temperature. The surface morphology depends upon the nitrogen content; the loss of nitrogen induces the formation of blistering and in the most nitrogen rich sample the formation of holes. Electrical resistivity preliminary results on the as grown layers range between 500 and 4750 μωcm passing from the lowest to the highest N concentration.

Plasma Deposited Porphyrin/Phthalocyanine Films as Promising Optical Gas Sensing Materials

5,10,15,20 meso-tetraphenyl porphyrin (H 2 TPP) and copper phthalocyanine (CuPc) films have been deposited by means of a recently developed plasma based technique named glow discharge induced sublimation (GDS). The two macrocycles have been deposited by vacuum evaporation (VE) and H 2 TPP by spin coating (SPIN) as well for comparison. The physical properties of the films have been characterized by means of scanning electron microscopy (SEM) and nitrogen physisorption measurements. SEM images and physisorption isotherms highlight both the much higher surface roughness and specific surface area of GDS samples with respect to the VE and SPIN ones. Optical sensing measurements, performed in differently concentrated ethyl alcohol atmospheres, highlight that GDS samples yield much higher response intensities than SPIN and VE films, short response times and complete recovery.

Development of new H 2 TPP porphyrin films with improved optical sensing capabilities

In this work novel 5,10,15,20 meso-tetraphenyl porphyrin (H2TPP) films have been deposited by means of a new physical technique named glow discharge induced sublimation (GDS). A preliminary characterization has been performed by means of scanning electron microscopy (SEM) and Fourier transform infra-red (FT-IR) analyses. SEM images and infra-red analyses highlight the great surface roughness and the high purity of GDS films, respectively. For comparison, H2TPP films have been also deposited by means of spin coating (SPIN) technique. Optical sensing measurements, performed in differently concentrated ethyl alcohol (EtOH) atmospheres, highlight that GDS samples yield higher response intensities than SPIN films, very short response times and complete recovery.

Soluble phthalocyanines as optical gas sensing materials

A novel soluble phthalocyanine compound, i.e zinc phthalocyanine (sulfonamide) has been synthesized by chemical substitution of zinc phthalocyanine and used to produce thin solid films by means of the spin coating technique. The chemical structure of the spin coated films has been investigated by FT-IR analysis. Atomic Force Microscopy (AFM) has been used to characterize the film morphology and to measure the film thickness. The spin coated films have been tested as optical sensing materials of volatile organic compounds such as methanol, ethanol and 2-propanol. The change of optical reflectance of the films upon exposure to alcohol-vapour-containing atmospheres has been measured versus alcohol concentration and exposure time. The films exhibit a fast and reproducible response, with a complete and fast recovery in methanol and ethanol-containing atmospheres, while diffusion-driven effects appear during exposure to 2-propanol. The response and sensitivity of the films to ethanol vapour is higher than to methanol and 2-propanol.

Mo-W-O thin films for CO sensing

The Mo-W-O thin films were deposited by RF reactive sputtering from composite target of W and Mo (20:80 weight ratio). Structural characterisation was carried out by X-ray diffraction spectroscopy and the composition of the film was obtained by Rutherford backscattering analysis. The layers were investigated by volt-amperometric technique for electrical and gassensing properties. The films were capable of sensing CO. No effect of poisoning of the surface was recorded and recovery of the resistance was complete. A concentration of CO as low as 15 ppm produced a relative variation in the conductance of 390% with response and recovery times of about 2 minutes at a working temperature of 200°C.