Salvatore Scaglione

Evaluation of the sp2/sp3 ratio in amorphous carbon structure by XPS and XAES

A comparison among XPS and XAES spectra features of graphite (sp2 bonding), diamond (sp3 bonding), amorphous carbon (i-C) and several hydrogenated amorphous carbon samples (i-C:H) has been carried out. XAES derivative spectra of graphite, i-C and i-C:H samples show a fine structure (275–280 eV) which is assigned to KVV transitions involving pπ electrons. An estimate of the sp2/sp3 ratio on the basis of the presence of such structures in the spectra has been attempted. Values of the sp2/sp3 ratio between 0.5 and 1.5 have been found for hydrogenated samples, whereas for amorphous carbon a value of 3 has been obtained.

Comparison among XAES, PELS and XPS techniques for evaluation of Sp2 percentage in a-C:H

The ratio R of Sp3 to Sp2 in hydrogenated amorphous carbon (a-C:H) has been evaluated by X-ray Auger electron spectroscopy (XAES), photoelectron energy loss spectroscopy (PELS) and X-ray photoelectron spectroscopy (XPS). Hydrogenated amorphous carbon samples have been deposited by dual ion beam sputtering technique (DIBS). Percentages of Sp2 sites are in the range of 45% to 70% for all analyzed samples. Values measured by XAES are about 10% greater than values measured by PELS and the XPS evaluation appears in agreement with them. Besides, R values seem to be influenced not only by hydrogen contents but even by parameters of deposition (i.e. energy of hydrogen ion beam and growth rate).

Structural and optical modification in hafnium oxide thin films related to the momentum parameter transferred by ion beam assistance

Abstract Hafnium oxide (HfO2) films were deposited on silica and glass substrates by ion (Xe+) assisted deposition with increasing ion momentum transfer to the growing film. The relationship among the ion momentum values, the crystalline phase and the refractive index (packing density) has been worked out by means of X-ray diffraction and spectrophotometric analysis. Compaction of the films by ion beam assistance is clearly evidenced by the changes in their microstructure. A three steps transition from a random monoclinic phase, via amorphous phase, up to an highly phase oriented (fiber texture), as a function of ion momentum, has been found.

On the super-Gaussian unstable resonators for high-gain short-pulse laser media

High-mode-volume, high-energy (70-mJ), high-brightness (1.6*10/sup 14/ W cm/sup -2/ Sr/sup -1/) laser beams have been extracted from a high-gain short-pulse XeCl laser with a super-Gaussian unstable resonator. These results are obtained by increasing the cavity magnification factor to 6.6 and the output mirror peak reflectivity to 78%. The output beam divergence is seen to decrease from an initial value of approximately 0.2 mrad down to nearly diffraction limited after 6 ns for the short gain build-up time of the active medium. >

The influence of the momentum transfer on the structural and optical properties of ZnSe thin films prepared by r.f. magnetron sputtering

Abstract ZnSe films were deposited at room temperature by radio frequency magnetron sputtering onto [100] oriented silicon substrates. Under the same deposition conditions three sets of samples were produced by varying the sputtering pressure (0.4, 0.5 and 0.9 Pa), and changing the sputtering power supply in the range 25–150 W. The effect of the different growth conditions on the structural and optical properties was investigated by using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) Spectroscopy. In particular, the dependence of the coatings residual strain, texture, refractive index and extinction coefficient on the parameter β, proportional to the momentum transfer was studied. According to the results, the ZnSe coatings were grown almost exclusively in the cubic phase with a small percentage of very disordered ZnSe hexagonal phases. At low β values, the films were found in a tensile in-plane stress state, then a stress inversion from tensile to compressive occurred at β=27 a.u. and the films remained in a compressive state for momentum values β>27 a.u.

Structural and optical properties of silver thin films deposited by RF magnetron sputtering

Abstract In this work, we investigate the optical and the structural properties of Ag films by means of spectrophotometric techniques and X-ray diffraction methods in the low- and high-angle regimes. The coatings were grown by radio frequency magnetron sputtering on (100)-oriented silicon substrates. Several sets of samples were produced by varying the sputtering pressure (0.15–0.9 Pa) and changing the sputtering power supply in the range of 25–100 W. In particular, the dependence of the coating optical features, surface roughness, texture and residual stress on the parameter β, proportional to the momentum transferred to the growing film from the energetic particles bombarding it, was pointed out. The results indicate that the Ag films are polycrystalline with a moderate [111] texture and compressive in-plane stress was measured for all the investigated samples. The behavior of the stress with the momentum parameter can be summarized as follows: (i) the compressive stress increases in the range 0 1000 V2s/A.

Laser damage dependence on structural and optical properties of ion-assisted HfO2 thin films

Abstract Laser damage studies at 248 nm (KrF excimer laser) have been performed on HfO 2 films of 300 nm thickness deposited on silica substrates by the Xe ion-assisted electron beam evaporation technique. The assistance parameters (ion mass, energy and current density) have been adjusted to investigate the effect of the Xe-ion momentum transfer parameter P on the film optical and structural properties. Then, the dependence of laser damage fluence on film properties has been studied. Higher laser damage fluences have been found for the HfO 2 films deposited at lower P values and characterized by a fully crystalline structure with the grain of smaller size and randomly oriented.

Adhesion enhancement of optical coatings on plastic substrate via ion treatment

The main limitation in using plastics for optical components is the softness of their surface, which is responsible for low impact and abrasion resistance and for weak adhesion between the film and the substrate. Protecting the substrate with a hard film can increase the impact resistance of polymeric lenses. However, deposition of thin films on chemically cleaned plastic substrates has resulted in fast delamination of the coating. This paper discusses the problems associated with coated plastics, it presents the ion assistance as one of the solutions and it finally identifies the relevant parameters. A hard oxide layer with additional ion pre-treatment is proposed as protection for plastic optics. The adhesion between the film and the substrate has been evaluated by a scratch-test and the hardness has been calculated by measuring the radius of the stylus track.

Laser optical coatings produced by ion beam assisted deposition

Abstract A general requirement of optical coatings for lasers is low absorption combined with good mechanical behaviour. Ion beam assisted deposition is recognized to be a technique that gives high density and durable coatings but frequently with unacceptably high absorption. In this work the influence of ion assistance on optical and mechanical properties of films of interest for CO 2 laser and excimer laser coatings (MgF 2 , BaF 2 , Y 2 O 3 , ZrO 2 , ZnSe) has been investigated. Ion assisted deposited fluorides exhibit a large improvement in hardness and density and at the same time their absorption is low at the wavelengths of interest. The mechanical properties of the other materials are also improved by the ion assistance and, for oxide films, the absorption is lowered by using an oxygen ion beam. Antireflection and partially reflecting coatings for pulsed XeCl (308 nm) and CO 2 (10.6μm) lasers have been produced and tested in the operating conditions of the laser resonators where they will be employed.

Narrowband filter radiometer for ground-based measurements of global ultraviolet solar irradiance and total ozone

The ultraviolet narrowband filter radiometer (UV-RAD) designed by the authors to take ground-based measurements of UV solar irradiance, total ozone, and biological dose rate is described, together with the main characteristics of the seven blocked filters mounted on it, all of which have full widths at half maxima that range 0.67 to 0.98 nm. We have analyzed the causes of cosine response and calibration errors carefully to define the corresponding correction terms, paying particular attention to those that are due to the spectral displacements of the filter transmittance peaks from the integer wavelength values. The influence of the ozone profile on the retrieved ozone at large solar zenith angles has also been examined by means of field measurements. The opportunity of carrying out nearly monochromatic irradiance measurements offered by the UV-RAD allowed us to improve the procedure usually followed to reconstruct the solar spectrum at the surface by fitting the computed results, using radiative transfer models with field measurements of irradiance. Two long-term comparison campaigns took place, showing that a mean discrepancy of +0.3% exists between the UV-RAD total ozone values and those given by the Brewer #63 spectroradiometer and that mean differences of +0.3% and -0.9% exist between the erythemal dose rates determined with the UV-RAD and those obtained with the Brewer #63 and the Brewer #104 spectroradiometers, respectively.