Petr Nemec

Structure, nonlinear properties, and photosensitivity of (GeSe_2)_100-x(Sb_2Se_3)_x glasses

Chalcogenide glasses from (GeSe2)​100-​x(Sb2Se3)​x system were synthesized, with x varying from 5 to 70, in order to evaluate the influence of antimony selenide addn. on nonlinear optical properties and photosensitivity. Nonlinear refractive index and two photon absorption coeffs. were measured both at 1064 nm in picosecond regime using the Z-​scan technique and at 1.55 μm in femtosecond regime using an original method based on direct anal. of beam profile change while propagating in the chalcogenide glasses. The study of their photosensitivity at 1.55 μm revealed highly glass compn. dependent behavior and quasi-​photostable compns. have been identified in femtosecond regime. To better understand these characteristics, the evolution of the glass transition temp., d. and structure with the chem. compn. were detd.

Chalcogenide coatings of Ge15Sb20S65 and Te20As30Se50

Chalcogenide coatings are investigated to obtain either optical components for spectral applications or optochemical sensors in the mid-infrared. The deposition of Ge(15)Sb(20)S(65) and Te(20)As(30)Se(50) chalcogenide glasses is performed by two physical techniques: electron-beam and pulsed-laser deposition. The quality of the film is analyzed by scanning electron microscopy, atomic force microscopy, and energy dispersive spectroscopy to characterize the morphology, topography, and chemical composition. The optical properties and optical constants are also determined. A CF(4) dry etching is performed on these films to obtain a channeled optical waveguide. For a passband filter made by electron-beam deposition, cryolite as a low-refractive-index material and chalcogenide glasses as high-refractive-index materials are used to favor a large refractive-index contrast. A shift of a centered wavelength of a photosensitive passband filter is controlled by illumination time.

RF sputtered amorphous chalcogenide thin films for surface enhanced infrared absorption spectroscopy

The primary objective of this study is the development of transparent thin film materials in the IR enabling strong infrared absorption of organic compounds in the vicinity of metal nanoparticles by the surface plasmon effect. For developing these optical micro-sensors, hetero-structures combining gold nanoparticles and chalcogenide planar waveguides are fabricated and adequately characterized. Single As2S3 and Ge25Sb10Se65 amorphous chalcogenide thin films are prepared by radio-frequency magnetron sputtering. For the fabrication of gold nanoparticles on a chalcogenide planar waveguide, direct current sputtering is employed. Fabricated single layers or hetero-structures are characterized using various techniques to investigate the influence of deposition parameters. The nanoparticles of gold are functionalized by a self-assembled monolayer of 4-nitrothiophenol. Finally, the surface enhanced infrared absorption spectra of 4-nitrothiophenol self-assembled on fabricated Au/Ge-Sb-Se thin films hetero-structures are measured and analyzed. This optical component presents a ~24 enhancement factor for the detection of NO2 symmetric stretching vibration band of 4-nitrothiophenol at 1336 cm−1.

Laser desorption ionization time-of-flight mass spectrometric study of binary As-Se glasses.

Binary chalcogenide As-Se glasses and their thin films are important for optics, computers, materials science and technological applications. To increase understanding of the properties of thin films fabricated by plasma deposition techniques, more information concerning the physics of plasma plume is needed. In this study the formation of clusters in plasma plume from different As-Se glasses by laser desorption ionization (LDI) or laser ablation (LA) was studied by time-of-flight mass spectrometry (TOF MS) in positive and negative ion modes. Formation of a number of As(p)Se(q) singly charged clusters As(3)Se(q)(+) (q = 1-5), AsSe(q)(-) (q = 1-3), As(2)Se(q)(-) (q = 2-4), and As(3)Se(q)(-) (q = 2-5) was found from As-Se glasses with the molar ratio As:Se in the range from 1:2 to 7:3. The stoichiometry of the As(p)Se(q) clusters was determined via isotopic envelope analysis and computer modeling. The structure of the clusters is proposed and the relationship to the structure of the parent glasses, as also suggested by Raman scattering spectra, is discussed.

Selenide sputtered films development for MIR environmental sensor

A micro-sensor based on selenide glasses for evanescent wave detection in mid-infrared spectral range was designed and fabricated. Ge-Sb-Se thin films were successfully deposited by radio-frequency magnetron sputtering. In order to characterize them spectroscopic ellipsometry, atomic force microscopy and contact angle measurements were employed to study near and middle infrared refractive index, surface roughness and the wettability, respectively. Selenide sputtered films were micro-patterned by means of reactive ion etching with inductively coupled plasma process enabling single-mode propagation at a wavelength of 7.7 µm for a waveguide width between 8 and 12 µm. Finally, optical waveguide surface was functionalized by deposition of a hydrophobic polymer, which will permit detection of organic molecules in water. Thus, the optical transducer is a ridge waveguide composed by cladding and guiding Ge-Sb-Se sputtered layers exhibiting a tailored refractive index contrast and a polymer layer onto its surface ready for environmental detections in middle infrared.

Chalcogenide waveguide for IR optical range

Due to remarkable properties of the chalcogenide glasses, especially sulphide glasses, amorphous chalcogenide films should play a motivating role in the development of integrated planar optical circuits and their components. This paper describes the fabrication and properties of optical waveguides of pure and rare earth doped sulphide glass films prepared by two complementary techniques: RF magnetron sputtering and pulsed laser deposition (PLD). The deposition parameters were adjusted to obtain, from sulphide glass targets with a careful control of their purity, layers with appropriate compositional, morphological, structural characteristics and optical properties. These films have been characterized by micro-Raman spectroscopy, atomic force microscopy (AFM), X-ray diffraction technique (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive X-ray measurements (EDX). Their optical properties were measured thanks to m-lines prism coupling and near field methods. Rib waveguides were produced by dry etching under CF4, CHF3 and SF6 atmosphere. The photo-luminescence of rare earth doped GeGaSbS films were clearly observed in the n-IR spectral domain and the study of their decay lifetime will be presented. First tests were carried out to functionalise the films with the aim of using them as sensor.

Infrared optical sensor for CO2 detection

Among the measures to reduce CO2 emissions, capture and geological storage holds out promise for the future in the fight against climate change. The aim of this project is to develop a remote optical sensor working in the mid-infrared range which will be able to detect and monitor carbon dioxide gas. Thus, chalcogenide glasses, transmitting light in the 1-6 μm range, are matchless materials. The first of our optical device is based on the use of two GeSe4 chalcogenide optical fibers, connected to an FTIR spectrometer and where CO2 gas can flow freely through a 4 mm-spacing between fibers. Such sensor system is fully reversible and the sensitivity threshold is about 0.5 vol.%. Fiber Evanescent Wave Spectroscopy technology was also studied using a microstructured chalcogenide fiber and first tests led at 4.2 μm have provided very promising results. Finally, in order to explore the potentiality of integrated optical structures for microsensor, sulphide or selenide Ge25Sb10S(Se)65 rib waveguide were deposited on Si/SiO2 wafer substrates, using pulsed laser deposition and RF magnetron sputtering deposition methods. The final aim of this study is to develop a rib waveguide adapted for middle-IR including an Y-splitter with a reference beam and sensor beam targeting an accurate CO2 detection.

Fabrication and characterization of chalcogenide films

Amorphous chalcogenide films can play a motivating role in the development of integrated planar optical circuits and their components. The aim of the present investigation was to optimize deposition conditions of pure and Tm3+ or Er3+ doped sulphide films by PLD and rf magnetron sputtering system. The study of their compositional, morphological and structural characteristics was realized by MEB-EDS, atomic force, RBS, X-ray diffraction and Raman spectroscopy analyses. Some optical properties (transmittance, index of refraction, optical band gap, etc) of prepared chalcogenide films and the propagation modes measured at 633 nm, 1304 nm and 1540 nm by means of the m-lines prism-coupling configuration were investigated. The whole results point out hopeful perspectives strengthened by the clear observation of the photo-luminescence of erbium and thulium within doped sulphide films.

Dysprosium-doped chalcogenide films prepared by pulsed-laser deposition

The chalcogenide glasses possess interesting optical properties such as a good transmission in the nIR-mIR wavelength region, high linear and non-linear refractive index and photosensitivity, which allows holographic patterns writing. Moreover, their low-phonon energy makes them good candidates for optical amplification. In order to design an integrated circuit on chalcogenide glasses, the pulsed laser deposition (PLD) technique is a suitable method for deposition of glass with complex composition. Amorphous Ge-Ga-Sb-S films (pure and dysprosium doped) were prepared by PLD using different energy of the laser beam pulses. Compositional, morphological and structural characteristics of the films were studied by MEB-EDS, atomic force, scanning electron microscopy, X-ray diffraction and Raman spectroscopy analyses. The photo-luminescence of Dy doped Ge-Ga-Sb-S films was investigated. The emission band centered at 1340 nm corresponding to 6F11/2, 6H9/2-6H15/2 electron transitions of Dy3+ ions was identified in luminescence spectra of dysprosium doped thin films. A study of the optical properties and the effects of exposure and thermal annealing below the glass transition temperature on the optical parameters of thin films from the Ge-Ga-Sb-S system will be presented.

Optical absorption of sandwich structure (Ag3AsS3)0.6(As2S3)0.4 thin film-gold nanoparticles prepared by pulse laser deposition

Pulse laser deposition technique was used to deposite (Ag3AsS3)0.6(As2S3)0.4 thin films upon previously prepared gold nanoparticle layers. The optical transmission spectra of sandwich structure based on Ag3AsS3)0.6(As2S3)0.4 thin film and gold nanoparticles were studied in the temperature range 77-300 K. Temperature behaviour of the Urbach absorption edge as well as the temperature dependences of the energy pseudogap and Urbach energy were investigated. The effect of the order-disorder processes on the optical properties of sandwich structure was discussed. Optical parameters of Ag3AsS3)0.6(As2S3)0.4 thin film and sandwich structure based on (Ag3AsS3)0.6(As2S3)0.4 thin film and gold nanoparticles were compared.