Kiril Petkov

Photoinduced changes in the linear and non-linear optical properties of chalcogenide glasses

Abstract The linear refractive index, n, and the position of the absorption edge for thin chalcogenide/chalcohalide films from the systems As–S, As–S–X (X=Bi, Tl or I), and Ge–S–Me (Me=Bi, Tl, As) have been measured before and after exposure to above-bandgap illumination. For compositions containing either As or Ge, the absorption edge was shifted to longer wavelengths (i.e. photodarkening occurred) for As-containing films, and to shorter wavelengths (i.e. photobleaching occurred) for Ge-containing films. As–S–Ge films exhibit either photodarkening or photobleaching, depending on Ge content. The largest values of these edge shifts ranged from 20 up to 60 nm, in the case of Ge31S63Tl6. The conditions for synthesizing the glasses studied are reported. A formula for predicting the non-linear refractive index, n2, for chalcogenide/chalcohalide glasses from the dispersion of n, and which enables n2 to be related to structural parameters, has been developed and compared with existing formulae for other types of glass and crystals. Using the various formulae and the measured values of n, n2 for these materials has been predicted. The results indicate that glasses with compositions near As42S58 or As2S3Tl0.13 may, after UV exposure, exhibit significantly larger values of n2 than as-deposited As40S60.

Light-induced changes in the optical properties of thin films of Ge–S–Bi(Tl, In) chalcogenides

Abstract In this paper, we report some results from the study of changes in transmittance, reflectance and optical band gap of thin Ge–S–Bi(Tl, In) thin layers depending on the composition and the conditions of evaporation and illumination. Using two triple, TR f R m and TR b R m methods, the optical constants ( n and k ), and the thickness ( d ) of very thin layers from the Ge–S system have been determined to an accuracy of ±2 nm. R f , R b and R m is the reflection from the film side, from the glass substrate and that of 100 nm thick film deposited on Si substrate, respectively. The calculated values of the optical constants of the ternary chalcogenide films were compared with those obtained from the ellipsometric measurements and some conclusions for their practical applications were done.

Selective dissolution of thin AsxS100−x films

Abstract 3he changes in the dissolution rates of exposed (Vexp) and unexposed (Vunexp) areas of thin AsxS100−x films as well as the selectivity of the system (γ = Vexp/Vunexp) are studied as a function of the arsenic content. Aqueous solutions of K2CO3, Na2CO3, Na3PO4 and surfactants are used for dissolution. The arsenic content in amorphous bulk materials and in thin films is determined iodometrically. It is demonstrated that the alkaline stability of the layers increases and the surfactant acts more efficiently at higher arsenic content. Thin films consisting of As42S58 or As45S55 may be employed successfully as an inorganic photoresist, to reproduce accurately details with an edge width of 0.1 μm.

X-ray microanalysis and optical properties of thin As–S–Bi (Tl) films

Abstract Chalcogenide glasses are an important class of materials because of their wide range of applications in infrared optics, infrared detectors, electronic and optical switching devices and phase optical recording. In this paper, we discuss the results obtained studying the influence of the conditions of deposition (temperature and rate of evaporation), thin film concentration and light exposure on the optical properties of thin As-containing chalcogenide films. A technique named “phase contribution method” (PCM) is used for quantitative elemental analysis of thin layers from the system As–S–Bi (Tl) deposited on soda-lime glass substrates. The method has been tested with thin chalcogenide films with different thicknesses deposited on glass and graphite substrates. The relationship between the changes in the composition and optical properties has been derived. The changes allow the practical application of thin-layered information recording media and high-resolution inorganic photoresists.

Piezoelectric Crystal Sensor for Ammonia Detection

Piezoelectric quartz sensors (AT-cut, 5 MHz) with vacuum evaporated electrodes (Cr, Ni and Ag) were developed. Active NiCl2 and AgCl films were chemically deposited onto the Ni//quartz//Ni/Ag structures. The sensors were tested at ammonia concentrations of 6.63; 31.32; 99.73 and 320.47 μgcm−3 and their calibration functions were taken. It could be established that the sensor with an active Ag film deposited on a Ni electrode is most suitable for the detection of high ammonia concentrations (≥ 30 μgcm−3), while the NiCl2/Ni//quartz//Ni/AgCl structure shows the best characteristics for the detection of low NH3 concentrations (≤ 30 μgcm−3).

New Chalcohalide Glasses from the GeSe2–Ag2Se–AgI System for Nanostructured Sensors

New chalcohalide glasses from the GeSe2–Ag2Se–AgI system with potential application as active materials for sensor elements have been synthesized. The glass forming region was determined by means of XRD and electron microscopic analyses. The main physicochemical properties, the density d, Vickers microhardness HV and the temperatures of glass-transition Tg, crystallization Tcr and melting Tm were determined. A correlation between these properties and the composition of the investigated glasses is established and discussed.

Auger-electron spectroscopy investigation of thin Ag-As-S-Se films

The photoinduced changes in the refractive index and optical band-gap of thin As32S34Se34 films photodoped with silver were studied using spectrophotometric methods. The compositional profile of the films was revealed by means of Auger-electron spectroscopy.

Dry etching of thin chalcogenide films

Fluorocarbon plasmas (pure and mixtures with Ar) were used to investigate the changes in the etching rate depending on the chalcogenide glasses composition and light exposure. The experiments were performed on modified commercial HZM-4 vacuum equipment in a diode electrode configuration. The surface microstructure of thin chalcogenide layers and its change after etching in CCl2F2 and CF4 plasmas were studied by SEM. The dependence of the composition of As-S-Ge, As-Se and multicomponent Ge-Se-Sb-Ag-I layers on the etching rate was discussed. The selective etching of some glasses observed after light exposure opens opportunities for deep structure processing applications.