Ján Lančok

The response of tin acetylacetonate and tin dioxide-based gas sensors to hydrogen and alcohol vapours

The aim of this work is to investigate the properties of gas sensors with active layers prepared by pulsed laser deposition (PLD) technology. The active layers were deposited on planar sensor chips with interdigital platinum electrodes. The deposition was carried out from tin dioxide and tin acetylacetonate (SnAcAc) targets by KrF excimer laser. In some cases Pd catalyst was sputtered on the surface of the active layer. The ‘as-deposited’ sensors were submitted to heat treatment. The chemical composition of heat treated active layers was studied by XPS method. This method revealed the oxidation state of palladium and the distribution between organic and inorganic phase during the deposition of SnAcAc. The DC responses of the sensors to a reducing atmosphere containing 1000 ppm of hydrogen, methanol, ethanol, n-propanol and n-butanol were also measured. The maximum sensitivity S (ratio of sensor resistances SaRair/Rgas) achieved 67 for hydrogen, 21 for methanol, 50 for ethanol, 71 for n-propanol and 44 for n-butanol. The temperature of maximum sensitivity (Tmax )t o distinct gases, the influence of molecular weight of detected gas on Tmax and the influence of molecular weight on the sensor response speed are also discussed. # 2000 Elsevier Science B.V. All rights reserved.

CNx films created by combined laser deposition and r.f. discharge: XPS, FTIR and Raman analysis

Abstract Thin CNx films were deposited by combination of KrF pulse laser deposition with additional radio frequency discharge (13.56 MHz). Nitrogen pressure was changed from 1 to 40 Pa and the r.f. power was adjusted to 100 W. N/C ratio in films higher than 1.1 was measured by wavelength dispersive X-ray analysis. Films were amorphous. Microhardness from 2 to 9 GPa and adhesion to silicon substrate from 5 to 19 N were found. The X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and Raman spectral studies indicate N-sp3 C, N-sp2 C and N-sp C bondings of nitrogen atoms with respect to carbon and the presence of NH groups. The presence of different amorphous, crystalline and polymer-like phases is discussed.

Planar laser waveguides of Ti:sapphire, Nd:GGG and Nd:YAG grown by pulsed laser deposition

Highly efficient laser action is demonstrated in epitaxially grown Nd:GGG and Ti:sapphire layers. Waveguide losses as low as 0.5 dB/cm are achieved in films of low particulate content, high homogeneity and improved surface morphology obtained by optimized pulsed laser deposition (PLD) configurations. Low threshold laser emission is observed at 800 nm for Ti:sapphire, and at 1060 nm and 937 nm for Nd:GGG waveguides, with slope efficiencies of 26% and 20% respectively. These results verify the versatility of PLD schemes in the fabrication of novel optoelectronic structures.

Preparation of nitrogen-rich CNx films with inductively coupled plasma CVD and pulsed laser deposition

Abstract Nitrogen-rich amorphous carbon nitride films with N/(N+C)≥0.5 have been deposited with three different methods, namely: (i) inductively coupled plasma CVD utilizing chemical transport reactions (ICP–CTR); (ii) inductively coupled plasma CVD with gaseous precursors (ICP–GP) and (iii) pulsed laser deposition (PLD) with additional r.f. plasma discharge. By means of plasma diagnostic measurements it is shown that in each case high concentrations of active radical species (e.g. CN and N ) are necessary to obtain high nitrogen concentrations. On the other hand, these nitrogen-rich films turned out to be mainly sp2 bonded having rather low densities of 1.8–2.0 g cm−3 only, irrespective of the method. From a comparison of the three techniques, and of further literature data, conclusions are drawn regarding the conditions necessary to obtain high N/(N+C) ratios, and regarding the deposition of superhard, crystalline sp3 bonded carbon nitride modifications.

PLANAR WAVEGUIDE LASERS AND STRUCTURES CREATED BY LASER ABLATION : AN OVERVIEW

The parameters of planar and channel waveguide lasers fabricated by different techniques are reviewed. Materials and properties of thin films used for creation of planar waveguide lasers are summarized. The parameters of active and passive planar waveguides created by the method of pulsed laser deposition and problems of laser deposition are described. The aspects of laser generation of planar waveguide lasers, resonators and channel waveguides are presented. The results of our experiments of laser deposition of thin Ti:sapphire layers and thin layers of Nd:YAG and Nd:YAP are briefly discussed.

Investigation of the thermal stability of nitrogen-rich amorphous carbon nitride films

Abstract The thermal stability of nitrogen-rich amorphous carbon nitride films (N/C≥1) is investigated from room temperature up to 600°C. The films were deposited by three different methods, namely pulsed laser deposition (PLD), inductively coupled plasma chemical vapour deposition (ICP-CVD) with gaseous precursors, and ICP-CVD utilizing transport reactions. As-deposited and annealed films were characterized with respect to their thickness, composition and bonding structure by a variety of methods including wavelength dispersive X-ray analysis (WDX), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). Annealing at 200°C leads to desorption of surface contaminants while in the range between 200 and 400°C a significant densification is observed. Above 400°C a drastic loss of film material, especially nitrogen-rich groups, sets on, leading to the total destruction of the films at 600–700°C. These observations are compared with the annealing behaviour of films with lower nitrogen content.

Carbon nitride layers created by laser deposition combined with RF discharge

Abstract The structure, composition and bonding of carbon nitride films created by pulsed laser deposition in combination with radio-frequency discharge for nitrogen activation were studied by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and by Raman spectroscopy for various deposition conditions. XPS measurements revealed a maximum N/C of ∼0.5 and an increased number of N-sp 3 C bonds for lower N/C values. FTIR and Raman spectra indicate the presence of a polymeric phase.

Structural and optical characterisation of Nd doped YAlO3 films deposited on sapphire substrate by pulsed laser deposition

Abstract The textured and amorphous thin waveguiding films of Nd/YAlO3 (Nd/YAP), were directly deposited on (0001) and (1102) sapphire substrates by a pulse laser ablation technique. The structural properties of the samples were characterised by X-ray diffraction and electron microprobe analyses. A strong dependence of crystalline structure and stoichiometry of the films on oxygen pressure was found. Luminescence around 1070 nm wavelength region was observed. Further excitation spectra were measured by means of a tuneable Ti-sapphire laser with a wavelength of approximately 800 nm and the fluorescence was observed at 1070 nm. The fluorescence decay constant was determined as 185 ±5 μs. The refractive indices of the film in the range 1.8134–1.8244 at 1064 nm have been measured by the m-line technique. The increase of the films refractive index by Δn = 8 × 10−3 at 1064 nm wavelength was observed with the change of dopant Nd concentration of 0.16%. Waveguiding losses lower than l dB/cm have been demonstrated at 1.06 μm wavelength.

Waveguiding pulsed laser deposited Ti:sapphire layers on quartz

Waveguiding thin films of Ti:sapphire were successfully grown on quartz. substrates by the technique of pulsed laser deposition from crystalline targets of various Ti,O, concentrations. The XRD spectra, titanium concentration, index of refraction, waveguiding properties and losses, and luminescence spectrum of films were studied. The refractive index of the films increases by 0.002 with change of dopant concentration of 0.37 wt.% of Ti,O,. The waveguide losses of a value of - 6.5 dB/cm for I pm film thickness were measured. 0 1998 Elsevier Science S.A. All rights reserved.

In-situ monitoring of the growth of nanostructured aluminum thin film

Metal thin film functional properties depend strongly on its nanostructure, which can be manipulated by varying nucleation and growth conditions. Hence, in order to control the nanostructure of aluminum thin films fabricated by RF magnetron sputtering, we made use of in-situ monitoring of electrical and optical properties of the growing layer as well as plasma characterization by mass and optical emission spectroscopy. The electrical conductivity and I-V characteristics were measured. The optical constants were obtained from optical monitoring basedonspectralellipsometry.Therelevantmodels(basedononeortwoLorentzoscillatorsand B-splinefunctions)weresuggestedtoevaluatethedataobtainedfromthemonitoringtechniques. Theresultsofthein-situmonitoringwerecorrelatedwithscanningelectronmicroscopeanalyses. Wedemonstratedthemonitoringwasabletodistinguishthegrowthmodeinreal-time.Wecould estimate the percolation threshold of the growing layer and control layer nanostructure. The nanostructure was effectively manipulated by RF power variation. Optical functions exhibiting plasmonic behavior in the UV range and a strong nonlinear character of I-V curves were obtained for an ultrathin Al film deposited at a lower growth rate. C 2011 Society of Photo-Optical