Dagmar Chvostova

Ablation of organic polymers by 46.9-nm-laser radiation

We report results of the exposure of poly(tetrafluoroethylene) -(PTFE), poly(methyl methacrylate) -(PMMA), and polyimide -(PI) to intense 46.9-nm-laser pulses of 1.2-ns-duration at fluences ranging from ∼0.1 to ∼10J∕cm2. The ablation rates were found to be similar for all three materials, ∼80–90nm∕pulse at 1J∕cm2. The results suggest that the ablation of organic polymers induced by intense extreme ultraviolet laser radiation differs from that corresponding to irradiation with longer wavelengths.

ABLATION OF POLY(METHYL METHACRYLATE) BY A SINGLE PULSE OF SOFT X-RAYS EMITTED FROM Z-PINCH AND LASER-PRODUCED PLASMAS

The efficiency of ablation induced in poly(methyl methacrylate) (PMMA) by single soft X-ray pulses emitted from Z-pinch and laser-produced plasmas was determined. X-ray ablation of PMMA was found to be less efficient than that of teflon (PTFE). Nonthermal effects of the radiation on the polymer structure play a key role in the mechanisms of the ablation, i.e. the ablation can be explained by the formation of radiation-chemical scissions of the polymer chain followed by blowoff of low-molecular fragment fluid into the vacuum. The most promising application of this phenomenon seems to be micropatterning/micromachining.

Ablation of various materials with intense XUV radiation

Ablation behavior of organic polymer (polymethylmethacrylate) and elemental solid (silicon) irradiated by single pulses of XUV radiation emitted from Z-pinch, plasma-focus, and laser-produced plasmas was investigated. The ablation characteristics measured for these plasma-based sources will be compared with those obtained for irradiation of samples with XUV radiation generated by a free-electron laser.

Strain-controlled optical absorption in epitaxial ferroelectric BaTiO3 films

A lattice strain of 0.3%–1.3% is achieved in epitaxial tetragonal BaTiO3 films grown on (001)-oriented SrTiO3 single-crystal substrates. Our experimental studies of absorption spectra in the range of 0.74–9.0 eV demonstrate that epitaxy produces significant changes in the optical properties of the films compared with those of a reference polydomain BaTiO3 crystal: the absorption edge and the peak at 5 eV strongly blue-shift by 0.2–0.4 eV, the magnitude of the peak at 5 eV drops, and certain spectral features disappear, whereas the absorption peak at 8.5 eV remains unchanged. The observed behavior is attributed to ferroelectric polarization, which is enhanced by epitaxial strain in the films. Our results indicate that epitaxially induced variations of ferroelectric polarization may be used to tailor the optical properties of thin films for photonic and optoelectronic applications.

Deposition of InxOy and SnOx thin films on polymer substrate by means of atmospheric barrier-torch discharge

Abstract Barrier torch discharge was used for low temperature deposition of In x O y and SnO x thin films at atmospheric pressure on polymer substrates. Vapors of Sn- and In-acetylacetonat were used as growth precursors for the deposition process of SnO x and In x O y thin films. Transparent films of conductivity σ SnO ≈10 S/cm for SnO x and σ InO ≈10 2 S/cm for In x O y were deposited on polymer substrates under conditions when the atmospheric plasma jet directly interacted with the polymer substrate. Plasma jet excitation had to be pulse modulated in order to avoid thermal damages of the polymer substrate. SnO x and In x O y were also deposited in a different discharge mode, in which interaction of the light emitting plasma jet with the substrate did not directly occur. In this case, the films had pure adhesion and had electrical conductivity lower than σ −3 S/cm. The analysis by an electron microprobe system has shown that the films had chemical composition close to SnO 2 and In 2 O 3 , respectively. XRD diffraction did not confirm any crystalline phase in all the deposited samples.

CNx coatings deposited by pulsed RF supersonic plasma jet: hardness, nitrogenation and optical properties

Abstract A low pressure pulsed RF supersonic plasma jet system (RPJ) has been used for deposition of CN x thin films. The aim of the CN x thin films deposition was an application for tribological coatings. Chemical composition, mechanical and optical properties of deposited CN x films have been measured. The obtained parameters were found to be similar to those of CN x films prepared by DC magnetron sputtering. The deposition rate for the CN x films prepared in RPJ reactor was of approximately 2 μm/h. During the deposition process, the substrate temperature did not exceed 250°C, as required for certain kinds of machine tribological coatings. A strong correlation between DC bias magnitude, nitrogen concentration and mechanical properties was found. The value of the substrate bias V DC =−100 V was found to be optimal for deposition of hard CN x films with maximum microhardness H =22 GPa. The films with the highest microhardness had the lowest atomic concentration of nitrogen. Analogous correlation has been found in ‘Diamond Relat. Mater. 7 (1998) 417’, although the deposition method and conditions were quite different. The chemically active plasma has been investigated in the RF supersonic plasma jet channel during the deposition process by means of ‘in situ’ emission spectroscopy. The mechanism of CN x formation has been studied as well.

Influence of deposition parameters on laser ablation deposited amorphous carbon

Abstract Thin amorphous carbon films were deposited by KrF laser ablation from graphite and glassy carbon targets at different substrate temperatures with beam power density on the target of 3 × 108 W cm−2. The films were characterized by electrical resistivity, spectroscopic ellipsometry, ultraviolet transmission, visible and infrared spectra and Raman spectroscopy. The influence on film properties of substrate temperature during deposition varying from room temperature to 425°C was studied. The influence of the temperature and film thickness on the film buckling was also studied. A film resistivity of 108 Ω cm and an optical band gap energy of 1.9 eV was achieved. Raman spectra with low D band ( I D I G = 0.46 ) intensity were obtained.

Optical properties of reactively sputtered GeO2 in the vacuum ultraviolet region

Abstract Optical properties of sputtered GeO 2 films submitted to various heat treatments are investigated with measurements in the vacuum ultraviolet region by means of the multi-angle reflectivity method. A Kramers-Kronig analysis of the near-normal-incidence reflectivity is compared with previous results on glassy and polycrystalline GeO 2 . The films were sputtered from a germanium target (99.999%) in an argon + oxygen mixture at a total pressure of 0.6 Pa and oxygen pressure of 0.24 Pa, with a target power density of 1.6 W/cm 2 . The deposition rate was about 1.5 nm/min. The film density has been evaluated by X-ray total reflection measurements and used for the Penn gap model calculations. Using the density correlation in the f -sum rule, the Penn gap energies for hexagonal and glassy GeO 2 have been obtained and are compared with the average interband transition energy in GeO 2 spectra.

Optical properties of laser-prepared Er- and Er,Yb-doped LiNbO3 waveguiding layers

Doped LiNbO3 films were prepared from Er- and Er,Yb-doped monocrystalline targets using laser ablation. SiO2/Si was used as a substrate. Polycrystalline films were synthesized at substrate temperatures of 650–800 ° C. The influence of the deposition conditions on the film crystallinity, surface morphology, dopant concentration, optical properties (using the m-line technique and spectroscopic ellipsometry), and luminescence was studied. The films were luminescent at 1530 nm and were waveguiding.

Low-temperature enhancement of plasmonic performance in silver films

While plasmonic metals can manipulate optical energy at the nanoscale, they suffer from significant losses at visible wavelengths. We investigate the potential of low temperature to decrease such losses in optically thick Ag films. We extract the complex dielectric function (or relative permittivity) from spectroscopic ellipsometry measurements for smooth single-crystalline, smooth polycrystalline, and rough polycrystalline films down to liquid-helium temperatures and fit these data to a temperature-dependent Drude model. Smooth single-crystalline films exhibited the largest improvements relative to room temperature. Below 50 K, the surface plasmon polariton propagation lengths increased by ~50% at 650 nm. In rough polycrystalline films, improvements of 10% are expected.