Infrared dielectric function spectra and phonon modes of high-quality, single crystalline, and highly resistive wurtzite ZnO films were obtained from infrared (300–1200 cm−1) spectroscopic ellipsometry and Raman scattering studies. The ZnO films were deposited by pulsed-laser deposition on c-plane sapphire substrates and investigated by high-resolution x-ray diffraction, high-resolution transmission electron microscopy, and Rutherford backscattering experiments. The crystal structure, phonon modes, and dielectric functions are compared to those obtained from a single-crystal ZnO bulk sample. The film ZnO phonon mode frequencies are highly consistent with those of the bulk material. A small redshift of the longitudinal optical phonon mode frequencies of the ZnO films with respect to the bulk material is observed. This is tentatively assigned to the existence of vacancy point defects within the films. Accurate long-wavelength dielectric constant limits of ZnO are obtained from the infrared ellipsometry analysis and compared with previously measured near-band-gap index-of-refraction data using the Lyddane–Sachs–Teller relation. The ZnO model dielectric function spectra will become useful for future infrared ellipsometry analysis of free-carrier parameters in complex ZnO-based heterostructures.

Due to the fine-tuning possibilities of the building blocks and demands for environmental protection, organic molecular magnetic materials composed only of light elements (C,H,N,O,S) are considered potential candidates for magnetic applications. However, for these applications it is necessary that the magnetic state (ferromagnetism or ferrimagnetism) is stable at room temperature. This was believed to be only possible in materials containing metallic 3-d or 4-f elements. As a matter of fact, recording media are in general polycrystalline, granular or amorphous ferromagnetic metals, alloys and oxides. Recent reports, however, showed weak ferromagnetic signals at room temperature and above in highly oriented pyrolytic graphite [1] (HOPG) and in polymerized fullerene. [2,3] Nevertheless, magnetism experts are highly skeptical about room-temperature ferromagnetism in carbon-based materials without magnetic ions. Recently, unusually large ferromagnetic signals were found in meteoritic graphite. [4] This large ferromagnetic signal was interpreted as induced by magnetite (Fe 3 O 4 ) inclusions in the graphite structure by a magnetic proximity effect. [4] It is interesting to note that in spite of some reports in the pastÐcasting doubts on simple interpretations of ferromagnetism in carbon-based materials in terms of ferromagnetic impurities [5] Ðit appears that prejudices against a possible intrinsic origin of the observed ferromagnetism hindered a broad and rush development of these organic ferromagnets. In this work, we produced localized ferro-or ferrimagnetic spots (a few micrometers in diameter) on clean HOPG surfaces using a proton microbeam. Our results rule out the influence of ferromagnetic impurities and open up a new field of investigation with clear implications for future applications of metal-free carbon ferromagnets.Clean surfaces of a HOPG sample (Advanced Ceramic, Fe content < 0.3 ppm, rocking-curve width= 0.4) were irradiated by 2.25 MeV protons using a microbeam applied parallel to the c-axis. Beam diameters between 1 and 2 lm, separated by 20 lm, and at different fluences and doses were chosen. The total deposited electric charge (areal) density was between 0.05 and 50 nC lm ±2 . The irradiated areas and surroundings were characterized simultaneously by atomic force (AFM) and magnetic force microscopy (MFM) at room temperature, operating in the ªTapping/Liftº scanning mode, using Si cantilevers with pyramidal tips coated with a magnetic CoCr film alloy magnetized perpendicular to the sample surface. MicroRaman characterization of the spot areas was used to determine the degree of disorder. Figure 1a shows the MFM images and Figure 1b the line scans of the topography and MFM signals obtained in three areas of the HOPG sample before irradiation. For virgin graphite samples, even though the changes in topography are significant, one obtains in general a MFM signal with a phase shift of the order of ± 0.1, which corresponds to the noise of COMMUNICATIONS

The band gap energies EG of the lithium compounds have been measured by transmittance and reflectivity measurements as well as measurements of the diffuse reflectivity. At room temperature EG=2.83 eV (LiInSe2), EG=3.56 eV (LiInS2), EG=3.13 eV (LiGaSe2) and EG=3.62 eV (LiGaS2) have been obtained presupposing a direct interband transition. In a first attempt the birefringence of LiInS2 was studied by transmittance measurements. Using infrared and Raman spectroscopy the lattice vibrational properties have been investigated.

Composite polyaniline−silica films produced on glass surfaces during the dispersion polymerization of aniline in the presence of colloidal silica were investigated. The film morphology and composition were characterized by FTIR, UV−vis, and X-ray photoelectron spectroscopies. Compared with pure polyaniline films produced under similar conditions, the composite films are thinner and smoother, and their surface is silica rich. The film thickness of both pure and composite films decreased as the polymerization temperature increased from 0 to 50 °C. To determine the particle size of polyaniline-silica dispersion particles, which are formed at the same time as the films, dynamic light scattering was used. The correlation between the particle size and film thickness is discussed. The electrical conductivity of composite polyaniline films was only a little affected by the presence of silica.

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