Glass Ge Research Articles

Electro-optical characterization of Ge–Se–Te glasses

Chalcogenide bulk glasses Ge 20Se 80− x Te x for xϵ(0,15) have been prepared by systematic replacement of Se by Te. Selected glasses have been doped with Ho, Er and Pr, and samples have been characterized by transmission spectroscopy, measurements of dc electrical conductivity and low-temperature photoluminescence. Absorption coefficients have been derived from measured transmittance and estimated reflectance. Arrhenius plots of dc electrical conductivity, in the measured temperature range 300–460 K, are characterized by single activation energies roughly equal to the half of the optical gap. Activation energies deduced from Arrhenius plots reveal a systematic decrease with increasing Te content. Similarly, both absorption and low-temperature photoluminescence spectra reveal shifts of absorption edge and/or dominant luminescence band to longer wavelength due to Te → Se substitution. Samples doped with Ho and Er exhibit a strong luminescence at 1200 and 1540 nm due to 5I 6 → 5I 8 and 4I 13/2 → 4I 15/2 transitions of Ho 3+ and Er 3+ ions, respectively. Pr doped samples exhibit only a relatively weak luminescence peak at 1590 nm, which we tentatively assign to 3F 3 → 3H 4 transition of Pr 3+ ions. Absorption of the base glass luminescence at 1460 and 1520 nm has been observed at low temperature on samples doped with Pr and Er, respectively.

Compositional dependence of the optical properties of new quaternary chalcogenide glasses of Ge–Sb–(S,Te) system

New quaternary telluride glassy materials with composition of Ge x Sb 40− x S 50 Te 10 and Ge x Sb 40− x S 55 Te 5 ( x = 10, 20, and 27) have been synthesized and their optical properties have been studied by means of spectroscopic ellipsometry in the range of 400–820 nm. The optical constants, i.e. the refractive index, extinction coefficient, absorption coefficient, and the optical band gap energy are determined and their compositional dependence is considered. These parameters are characteristics for amorphous structure of the synthesized glasses, revealed from the neutron diffraction measurements.

Acute Respiratory Infections in a Recently Arrived Traveler to Your Part of the World*

Many acute infectious pulmonary diseases have incubation periods that are long enough for travelers to have symptoms after returning home to a health-care system that is not familiar with “foreign” infections. Respiratory infections have a relatively limited repertoire of clinical manifestations, so that there is often nothing characteristic enough about a specific infection to make the diagnosis obvious. Thus, the pathway to the diagnosis of infections that are not endemic in a region relies heavily on taking a thorough history of both itinerary and of specific exposures. One important caveat is that on occasion, the history of a recent trip creates an element of “tunnel vision” in the evaluating health-care provider. It is tempting to relate a person's problem to that recent trip; however, when evaluating recent returnees, it is always important to remember that the travel may have nothing to do with the patient's presentation. Recent travel may add diagnostic considerations to the list of possibilities, but an astute clinician must not disregard the possibility that the patient's illness has nothing to do with the recent trip.

Solvent Effect on Deprotonation Equilibria of Acids of Various Charge Types in Non-aqueous Isodielectric Mixtures of Protic Ethylene Glycol and Dipolar Aprotic N,N-Dimethylformamide at 298.15 K

Deprotonation constants of phthalic (H2A) and biphthalic (HA−) acids and of mono-protonated (BH+) and di-protonated (BH 2 2+ ) piperazine acids have been determined at 25 °C by measuring the Emf of galvanic cells comprising H+-sensitive glass GE(H+) and Ag,AgCl electrodes in non-aqueous isodielectric mixtures of protic ethylene glycol (EG) and dipolar aprotic N,N-dimethylformamide (DMF). Solvent effects on deprotonation of the acids: ∂(ΔG diss o )=2.303RT[p(s K a)−p(R K a)], have been dissected into transfer Gibbs energies, ΔG t o , of the species involved by evaluating ΔG t o of the uncharged phthalic acid and base piperazine (B) from the measured solubilities of the acid and base, respectively, and using ΔG t o of H+ based on the TATB reference electrolyte assumptions, as evaluated earlier. The contributions of the different species involved in the protolytic equilibria i.e., H+,H2A,HA−,BH 2 2+ and BH+ and their respective conjugate bases HA−,A2−,BH+ and B have been discussed in terms of their solvation behavior as guided by the ‘acid-base’, dispersion, structural and electronic characteristics of the acid-base species and of the co-solvent molecules and binary mixtures, ignoring the Born-type electrostatic interactions on the ionic species as the solvent system is quasi isodielectric.

Tight-Binding Theory of Phase-Change Materials

ABSTRACTA simple theory of Ge, Sb, and Te crystals and glasses, based upon atomic valence orbitals with coupling given by universal parameters, is outlined. It is seen how dangling hybrids from Ge atoms can behave as negative U centers. In contrast, in Sb the nonbonding s orbitals play essentially no role, except to produce three-fold coordination and 90° bond angles. Te also has nonbonding s states, but also nonbonding p states causing two-fold coordination. These nonbonding p states form the top of the valence band, rather than the bond orbitals which formed the valence-band in Ge. We argue against lumping these totally different behaviors together as “lone pairs”. In the glass, bonds can form between all atom types, but bonds between different elements are energetically favored. Further, when Sb or Te atoms are involved, bonds can switch between neighbors with small energy change, in a manner suggested by Kastner, Adler and Fritsche. It is seen how to estimate the energy for these various different geometric configurations.

Vibrational spectroscopy study of niobium germanosilicate glasses

A series of glasses in the (Ge,Si)O 2–Nb 2O 5–(Na,K) 2O system were prepared by melting and casting. Their density and characteristic temperatures were determined by Differential Thermal Analysis (DTA) and their structure was analyzed by infrared and polarized Raman spectroscopies. DTA data have indicated an increased glass thermal stability with the replacement of GeO 2 by SiO 2. Kramers–Kronig analysis of the infrared specular reflectance data indicated a strong ionic character for the germanosilicate glasses. The Raman spectra of germanosilicate compositions were generally dominated by an intense Boson peak at ∼72 cm −1 and a high frequency, polarised peak at ∼880 cm −1, related to NbO 6 octahedra with at least one non-bridging oxygen. The germanosilicate structure appears to be formed by alternating GeO 4 tetrahedra and NbO 6 octahedra, in addition to SiO 4 tetrahedra.

Optical study of Ge 10Se 90− xTe x glassy semiconductors

Chalcogenide glasses are interesting materials from their infrared transmitting properties and photo-induced effects exhibited by them. Thin films of the glasses Ge 10Se 90− x Te x ( x = 0, 10, 20, 30, 40, 50) prepared by melt quench technique were evaporated at a pressure of ~ 10 − 4 Pa. The amorphous nature of bulk as well as thin films was detected by X-ray diffraction. Optical transmission spectra of thin films were obtained in the range 400–2400 nm. The optical constants i.e. optical band gap, absorption coefficient and refractive index are calculated using the Swanepoel method. The optical band gap is found to decrease with the increase of Te content. The absorption coefficient and refractive index decrease with the increase of wavelength. The refractive index first decreases (up to 30 at.%) and thereafter increase with Te content.

High refractive index chalcogenide glass for photonic crystal applications

A high refractive index Te-enriched bulk chalcogenide glass Ge(20)As(20)Se(14)Te(46) (n approximately 3.3) has been patterned by ablation using four- and two-beam interference femto-second laser setups operating at 800 nm. The regular arrays of 0.8 mum diameter and more than 0.8 mum depth holes and/or grooves of typical size of 1x1 mm(2) have been written on the surface of the glass in a time-scale of 1 second with 50 femtosecond pulses. The high photosensitivity of this narrow-gap semiconductor glass to the femtosecond irradiation is ascribed to a free electron absorption typical of metals, which is caused by laser-induced heating of the glass.

PAL spectroscopy as experimental probe for extended free-volume defects in inorganic glasses and ceramics

Extended free-volume defects trapping positrons are studied in inorganic glasses and functional ceramics using positron annihilation lifetime spectroscopy. Obtained results are treated in terms of general macroscopic approach grounded on physical–chemical properties of the tested materials which depend on the value of free volume content. At the example of chalcogenide glasses of ternary Ge–Sb–S system and spinel-type mixed transition-metal manganite Cu 0.4Co 0.4Ni 0.4Mn 1.8O 4 and magnesium aluminate MgAl 2O 4 ceramics, it is shown that strict correlation exists between numerical values of free volumes of potential positron traps and lifetime parameters determined within two-state positron trapping model.

CHALCOGENIDE INVERTED OPAL PHOTONIC CRYSTAL AS INFRARED PIGMENTS

Large surface infrared photonic crystals with reflectance higher than 90% have successfully been synthesized by self-assembling large size SiO 2 spheres, of 0.8-4.5 μm diameters, followed by melt infiltration with the chalcogenide glass Ge 33 As 12 Se 55 and the removal of the SiO 2 spheres by chemical etching. The sphere size and the periodicity of the templates were chosen to guarantee the formation of photonic band gaps of the inverted opals in the targeted IR regions of 3-5 μm and 8-12 μm. Fabrication, structural features and spectral behavior of the reflectance peaks of these chalcogenide glass inverse opals are presented.

Correlation between physical, optical and structural properties of sulfide glasses in the system Ge–Sb–S

Germanium-based sulfide glasses in the Ge–Sb–S system have been elaborated and studied. A relationship between the structure, the composition and the linear optical properties of the glass has been established. The effects of the introduction of Sb on the structure using IR and Raman spectroscopies and on the linear refractive index have been discussed. We have shown that the progressive introduction of Sb 2S 3 in the glass system (1 − x)GeS 2– xSb 2S 3 (with x = 0.10, 0.20, 0.40, 0.62 and 0.80) decreases the number of GeS 4 units in the glass network. As results, the glass transition temperature, the Vicker's microhardness and the stability of the glass against crystallization decrease dramatically. An increase in the density and the linear refractive index as well as shift of the absorption bandgap to infrared have also been observed. Similar behavior has been observed for the glasses of composition Ge 0.23Sb y S 0.77− y with an increase of y, except in the material's Vicker's microhardness, which increases with an increasing Sb content. This latter result indicates that the microhardness also depends on Sb 2S 3 content but seems to be more sensitive to GeS 2 content variation.

Threshold restoration effects in γ-irradiated chalcogenide glasses

The influence of annealing temperature Ta on the optical absorption edge in the previously γ-irradiated glasses of Ge–Sb(As)–S ternaries of pseudobinary ‘stoichiometric’ Sb(As)2S3–GeS2 and non-stoichiometric Sb(As)2S3–Ge2S3 cut-sections is studied. It is established that the post-irradiation thermally produced changes of the optical absorption edge differ in various Ta regions. Threshold restoration effects are found beginning from some intermediate onset temperature Ton for all investigated glasses. Compositional features of the apparent activation energies determined in corresponding Ta regions are analyzed. A possible mechanism for the observed effects is discussed.

Up-conversion luminescence efficiency in Er-doped chalcogenide glasses

The efficiency of up-conversion luminescence of Er3+ ions (excited by laser light operating at 810 nm) in the GeS2–Ga2S3:Er2S3 system strongly depends on the energy position of the fundamental absorption edge. This dependence is due to non-radiative energy exchange between the electronic subsystem of the glassy matrix and excited levels of Er3+ ions. In chalcogenide glasses Ge and Ga atoms are fourfold coordinated. Except for the M (M=Ge, Ga)–S heterobonds, the rest are M–M homobonds. These homobonds can be detected with Raman spectroscopy. The energy position of the absorption tail of the fundamental band depends on the concentration of M–M homobonds. When the concentration of these bonds increases the absorption edge shifts to longer wavelengths and the intensity of up-conversion luminescence decreases. The relative concentration of M–M bonds depends not only on composition of the glassy matrix but also on the synthesis and on concentration of extrinsic impurities such as OH−, SH− and –CH2–. Another cause of reduction of up-conversion luminescence intensity is the inhomogeneous distribution of REI in the Ga2S3–GeS2 glasses. The simple model describing dependence of luminescence intensity on type of REI distribution in the glassy matrix is discussed.

Preparation and characterization of glasses in the Ag 2S + B 2S 3 + GeS 2 system

The glass forming range of the Ag 2S + B 2S 3 + GeS 2 ternary system was investigated for the first time and a wide range of ternary glasses were obtained. The Archimedes’ method was used to determine the densities of the Ag–B–Ge glasses. The thermal properties of these thioborogermanate glasses were studied by DSC and TMA. The Raman, IR and NMR spectroscopy were used to explore the short-range order structure of the binary (Ag–B) and (Ag–Ge) and ternary (Ag–B–Ge) glasses. The results show the presence of bridging sulfur tetrahedral units, GeS 4/2 and AgBS 4/2, and trigonal units, BS 3/2, in the ternary glasses. Non-bridging sulfur units, AgSGeS 3/2 and Ag 3B 3S 3S 3/2 six membered rings, are also observed in these glasses at higher Ag 2S modification levels because the further addition of Ag 2S results in the degradation of the bridging structures to form non-bridging structures. The NMR studies show that Ag 2S goes into the GeS 2 subnetwork to form Ag 3S 3GeS 1/2 groups before going to the B 2S 3 subnetwork. In doing so, it is suggested that B 10S 20 supertetrahedra exist in Ag 2S + B 2S 3 and Ag 2S + B 2S 3 + GeS 2 glasses. Significantly B–S–Ge bonds form in the B 2S 3 + GeS 2 glasses, whereas they appear to be absent in the ternary glasses. From these observations, a structural model for these glasses has been developed and proposed.

Interpretation of Radiation-Induced Phenomena in Chalcogenide Glasses of Ge–Sb–S System Using Free Volume and Covalent Chemical Bonds Concepts

Interpretation of Radiation-Induced Phenomena in Chalcogenide Glasses of Ge–Sb–S System Using Free Volume and Covalent Chemical Bonds Concepts

Multiphonon energy gap law in rare-earth doped chalcogenide glass

The parameters for multiphonon relaxation of rare earth (RE) ions in the sulfide glass Ge 25As 8.33Ga 1.67S 65 have been re-evaluated using the temperature dependence of the fluorescence lifetime to separate out true multiphonon decay from other non-radiative processes. It is found that for energy gaps to the next lowest level greater than 2500 cm −1, other non-radiative processes become dominant over multiphonon decay. The most likely process for this additional non-radiative decay is energy transfer to vibrational impurities such as OH and SH. The newly derived parameters lead to an electron–phonon coupling parameter ϵ=0.058, which is more in line with other glass types than the previously accepted value of ϵ=0.36. These new multiphonon relaxation parameters and the existence of additional non-radiative decay mechanisms has implications for the modeling of chalcogenide-based active devices.

XPS and ionic conductivity studies on Li 2O–Al 2O 3–(TiO 2 or GeO 2)–P 2O 5 glass–ceramics

Lithium ion conducting glass–ceramics composed of the crystalline conducting phase LiM 2(PO 4) 3 (M=Ti and Ge) in which the M 4+ ions are partially substituted by Al 3+ ions (Li-analogue of NASICON) have been synthesized by heat-treatment of Li 2O–Al 2O 3–MO 2–P 2O 5 (M=Ti and Ge) glasses. The as-prepared and annealed glasses and glass–ceramics have been characterized by XRD, DSC, XPS and conductivity techniques. The glass transition temperature, T g of the annealed glasses was found to be 601°C and 474°C for the M=Ti and Ge glass systems whereas the crystallization temperature, T c of the annealed glasses are 644°C and 578°C respectively. XPS studies show that the O 1s spectra for all the glasses and glass–ceramics could be deconvoluted into two peaks corresponding to the non-bridging (NBO) and bridging oxygen (BO) atoms. The binding energies (BE) of Li, Ti, Ge, Al and P have also been listed. In the Li 2O–Al 2O 3–TiO 2–P 2O 5 system, the deconvoluted Ti 2p XPS spectra indicate the existence of two oxidation states of titanium, 3+ and 4+. The Ti 2p and Ge 3d core levels are characterized by high BEs, suggesting that Ti 4+–O and Ge 4+–O bonds are highly ionic in character. The glass–ceramics show fast ion conduction ( σ 303 K=6.53×10 −4 (M=Ti) and 3.99×10 −4 S cm −1 (M=Ge)) and low E a value (0.31 eV). These σ values are slightly higher than the corresponding crystalline Li 1+ x M 2− x Al x P 3O 12 (M=Ti and Ge) phases and four to five orders of magnitude higher than the respective glassy phases. Plausible explanation for the enhancement of σ in glass–ceramics is given. It is suggested that the M=Ge glass–ceramics can be used as a solid electrolyte in the all-solid state Li-ion rechargeable battery.

Chalcogenide glasses with large non-linear refractive indices

Non-linear refractive indices and non-linear absorptions of several chalcogenide glasses have been measured by the z-scan method at 1.06 μm, to evaluate their potential use in telecommunication as all optical ultra-fast switching devices. The index obtained for the reference glass As 2S 3 (2.5 × 10 −18 m 2/W) agrees with that found in the literature. Glasses in Ge–Se and Ge–Se–As systems have been measured. Non-linear refractive indices four times larger (10.2 × 10 −18 m 2/W) than that of As 2S 3 have been obtained for a Ge–Se–As glass.

Photoinduced anisotropy in chalcogenide glasses in a wide spectral range studied by reflectance difference spectroscopy

We present the results of an investigation of photoinduced anisotropy in films and bulk samples of chalcogenide glasses As 50Se 50 and Ge 20As 20S 60 using reflectance difference spectroscopy. Anisotropy in a wide spectral range (1.5–5.5 eV) can be generated and reorientated many times by linearly polarized light. We conclude that possibility of orientation and reorientation with the linearly polarized light not only of defects and scattering centers but also of the interatomic covalent bonds is characteristic for different chalcogenide glasses. We have found that doping of a chalcogenide glass Ge 20As 20S 60 by rare earths does not change the parameters and characteristics of photoinduced anisotropy.

Calorimetric studies of the glassy alloys in the GeSeTe system

Calorimetric studies of chalcogenide alloy glasses Ge 50 − x Se 50Te x ( x = 10, 20, 40 at%) have been performed by continuous heating rates. The crystallization mechanism has been studied by differential scanning calorimeter (DSC), scanning electron microscopy (SEM) and X-ray diffraction. From the heating rate dependence of the glass transition temperature T g and the crystallization peak temperature T p, the kinetic parameters of crystallization were calculated and their composition dependence were discussed. The kinetic parameters determined have made it possible to discuss the glass forming ability as well as the different types of nucleation and crystal growth exhibited by the studied chalcogenide glasses.