Jiri Zavadil

Heavy metal oxide glasses: preparation and physical properties

Abstract Heavy metal oxide glasses have been investigated in the following systems: TeO2–PbO–PbCl2, TeO2–ZnO, Ga2O3–PbO–Bi2O3 glasses with low OH concentration were prepared. The influence of the processing conditions on the color, the structure and the optical properties of the prepared samples was also assessed. Mixtures of starting oxides were melted in various reactive conditions using Pt, Au, SiO2 and alumina crucibles. A set of physical measurements including chemical and X-ray analysis, scanning electron microscopy, absorption spectroscopy, ultraviolet and infrared absorption edges and thermo-physical properties, were carried out. Samples were doped with Nd, Pr and Er rare earth ions. Low temperature photoluminescence spectra show the expected rare earth transitions and the broad band emission of the base glass.

Layers of Metal Nanoparticles on Semiconductors Deposited by Electrophoresis from Solutions with Reverse Micelles

Pd nanoparticles were prepared with reverse micelles of water/AOT/isooctane solution and deposited onto silicon or InP substrates by electrophoresis. A large change of capacitance-voltage characteristics of mercury contacts on a semiconductor was found after Pd deposition. This change could be modified when the Pd deposition is followed by a partial removal of the deposited AOT. The deposited Pd nanoparticles were investigated by optical mictroscopy, SIMS and SEM. Finally, Schottky diodes with barrier height as high as 1.07 eV were prepared by deposition of Pd nanoparticles on n-type InP and by a partial removal of superfluous AOT. These diodes are prospective structures for further testing as hydrogen sensors.

Chalcogenide glasses and fibers for applications in medicine

Chalcogenide glasses based on suplhides and selenides are very promising materials for various photonic applications, particularly for applications in medicine. Most of current optical fibers have been developed form ultrapure silica. While silica glasses are suitable for optical components in telecommunications they exhibit high losses beyond 2 micrometers - a wavelength range important for clinical practice. Thus special glass materials 9from which fibers could be drawn) should be developed for optical power transmission beyond 2 micrometers . The investigation and preparation of vitreous materials that include sulphide, selenide and selenide- tellurite glass systems together with fluoride and heavy metal oxide glasses on the base of ZrF4, HfF4 and GeO2, TeO2, PbO, respectively are being pursued in our laboratory. This research is aimed at the development of both passive and active (rare-earth doped) optical fibers. In this contribution we concentrate on the doping of chalcogenide glasses by rare earth elements (Er, Pr, Nd). Although the major role of these glasses is assumed in the development of laser power delivery systems for applications in surgery, dentistry, dermatology and ophthalmology, they can equally be used for the diagnostics of human tissues. An example of colon tissue autofluorescence will be given.

Electrophoresis deposition of metal nanoparticles with reverse micelles onto InP

Abstract Nanolayers were deposited onto surfaces of n-type InP single crystal wafers by electrophoresis from reverse micelle colloid solutions containing palladium nanoparticles. Two types of nanolayers were deposited, by applying a positive potential or a negative potential on the InP wafer. Further, wafers with nanolayers were annealed in high vacuum at 400 °C. The nanolayers were studied using capacitance–voltage characteristics on a mercury probe, by atomic force microscopy and by secondary-ion mass spectroscopy. Two types of Schottky-like diodes were prepared on wafers with the two types of nanolayers and studied by current–voltage characteristics. The diodes with nanolayers deposited by applying the positive potential, which contained Pd nanolayers, showed characteristics with better rectifying properties than the other type of diodes. Correlations among measured characterizations were found.

Palladium nanoparticles on InP for hydrogen detection

Layers of palladium (Pd) nanoparticles on indium phosphide (InP) were prepared by electrophoretic deposition from the colloid solution of Pd nanoparticles. Layers prepared by an opposite polarity of deposition showed different physical and morphological properties. Particles in solution are separated and, after deposition onto the InP surface, they form small aggregates. The size of the aggregates is dependent on the time of deposition. If the aggregates are small, the layer has no lateral conductance. Forward and reverse I-V characteristics showed a high rectification ratio with a high Schottky barrier height. The response of the structure on the presence of hydrogen was monitored.

Role of Rare-Earth Elements in the Technology of III-V Semiconductors Prepared by Liquid Phase Epitaxy

First applications of rare-earth (RE) elements in semiconductor technology are rooted in radiation tolerance improvements of silicon solar cells and purification of GaP crystals. The idea was later adopted in the technology of germanium and compound semiconductors. Since the 1980’s, considerable attention has been directed towards REs applications in III-V compounds both for epitaxial films and bulk crystals (Zakharenkov et al., 1997). The uniqueness of REs arises from the fact that the lowest-energy electrons are not spatially the outermost electrons of the ion, and thus have a limited direct interaction with the ion’s environment. The shielding of the 4f electrons by the outer filled shells of 5p and 5s electrons prevents the 4f electrons from directly participating in bonding (Thiel et al., 2002). The RE ions maintain much of the character exhibited by a free ion. This non-bonding property of the 4f electrons is responsible for the well-known chemical similarity of different REs. Since transitions between the electronic states of the shielded 4f electrons give rise to spectrally narrow electronic transitions, materials containing REs exhibit unique optical properties. By careful selection of the appropriate ion, intense, narrow-band emission can be gained across much of the visible region and into the near-infrared (Kenyon, 2002). Inspired by the striking results accomplished in the field of optical amplifiers and lasers based on REdoped fibres (Simpson, 2001), substantial research activity has been recently carried out on RE-doped semiconductor materials for optoelectronics (Klik et al., 2001). In most cases, however, achieving effective doping of III-V compounds by REs during growth from the liquid phase has proven difficult; the high chemical reactivity and the low solid solubility are the main restrictions on introducing RE atoms into the crystal lattices (Kozanecki & Groetzschel, 1990). On the other hand, the enhanced chemical affinity of REs towards most species of the shallow impurities leads to the formation of insoluble aggregates in the melt. Under suitable growth conditions, these aggregates are rejected by the growth front and are not incorporated into the grown layer: gettering of impurities takes place. Especially Si and main group-six elements acting as shallow donors in III-V semiconductors are effectively gettered due to REs high affinity towards them (Wu et al., 1992). Removal of detrimental impurities is of vital importance in applications such as PIN 13

Autofluorescence spectroscopy of colorectal carcinoma: ex vivo study

Diagnosis established by means of fluorescence spectroscopy is currently used in the field of urology and bronchology. Its major advantage is that it allows the diagnosis of epithelial dysplasia or malignant proliferation even if routine diagnostic endoscopy fails to reveal any macroscopic changes. The authors present results of their observations that deal with fluorescence diagnosis of colorectal carcinoma. They examined the wet microscopic mounts of healthy colon mucosa and compared them to that prepared from colon mucosa affected by adenocarcinoma. The diagnosis of adenocarcinoma was verified by using clinical and histology means. Fluorescence spectra of tissue samples, excited by means of 488 and 514.5 nm lines of Ar ion laser and/or by He-Ne laser line 632.8 nm, have been studied. This study demonstrated differences in both the spectral shape and in the signal intensity (at unchanged spectral shape) of photoluminescence spectra emitted from tissue affected by adenocarcinoma as compared to that of healthy colon mucosa. The results encourage us to continue the study aimed at development of the diagnostic system usable in the clinical practice.

Optical characterization of glass materials doped with rare-earth elements

Sulphide glasses of GeGaS and GeGaAsS systems doped with rare earth ions are promising materials for various photonic applications. Because the solubility of rare earth elements ins influenced by the purity of host glass, namely by OH group concentration, the attention has been paid to the preparation of highly pure and homogeneous undoped and rare earth doped glasses. Particularly the systems Ge0.25Ga0.1-xS0.65Prx and Ge0.25Ga0.05- xAs0.05S0.65Prx with x equals 500, 1000, 3000, 6000 wt. ppm have been prepared. Synthesized materials system have been characterized by Raman and low-temperature photoluminescence spectroscopies. The optical Pr concentration has been found to be around 1000 wt.ppm. The appearance of temperature induced radiative transitions have been observed on GeGaS:Er samples.

Characterization of chalcogenide glasses for optoelectronics

Chalcogenide glasses - Ge25Ga10S65 , Ge25Ga5As5S65 , As2S3 , As2S2Se , As25e3 — have been synthesized and doped with ions of rare earth RE3 , in the concentration range of 500 to 6000 wt.ppm. Special processing makes possible to reduce the hydroxyle content and to incorporate rare earth ions without phase separation. Various physical measurements, including photoluminescence have been implemented. Main observations and results may be summurized as follows: -OHgroup concentration could be lowered below 5x105 mol.% in pure chalcogenide glasses - Rare earth ions are introduced into sulfide glasses at concentrations ranging from 500 to 6000.ppm. Homogeneous and clear samples are obtained up to 3000wt.ppm Pr3+. - Clusters and defects are observed when RE and OH concentrations increases,. -Abackground photoluminescence in based glasses and it depends on temperature.

Special glasses for passive and active IR fibers for medical and biomedical applications

General chemical compositions of prepared glasses with low OH group concentrations are Ge0.25Ga0.10S0.65, Ge0.25Ga0.05As0.05S0.65, (TeO2)x - (PbCl2)1-x with x equals 0.4 to 0.6 and (TeO2)x - (ZnO)1-x with x equals 0.75 to 0.80. Samples doped with 500 to 12000 ppm rare earth in weight were prepared. Rare earth doped glasses are homogeneous when RE concentration is less than 3000 ppm. Heterogeneous inclusions arise beyond 1000 ppm RE when doping is made with chloride or oxide. Electron microscopy, absorption and fluorescence measurements have been made. YAG:Nd. Ar, He-Ne lasers were used for excitation of photoluminescence. The color and optic quality of the tellurite glasses depend on crucible materials. Rare earth doping results in visible defects or inhomogeneities when concentration is larger than 1000 ppm. The chemical composition and the optical absorption of doped and undoped samples was examined. Fluorescence intensity of Pr and Dy is smaller in these HMO glasses than in the sulfide glasses, which results from higher phonon energy and higher OH concentration. Further development is required for future applications.