Schottky barrier heights of tantalum oxide, barium strontium titanate, lead titanate, and strontium bismuth tantalate

The Schottky barrier heights of various metals on the high permitivity oxides tantalum pentoxide, barium strontium titanate, lead zirconate titanate, and strontium bismuth tantalate have been calculated as a function of the metal work function. It is found that these oxides have a dimensionless Schottky barrier pinning factor S of 0.28-0.4 and not close to 1 because S is controlled by Ti-O-type bonds not Sr-O-type bonds, as assumed in earlier work. The band offsets on silicon are asymmetric with a much smaller offset at the conduction band, so that Ta2O5 and barium strontium titanate are relatively poor barriers to electrons on Si. © 1999 American Institute of Physics.

Schottky barrier heights of tantalum oxide, barium strontium titanate, lead zirconate titanate and strontium bismuth tantalate

Schottky barrier heights of various metals on tantalum pentoxide, barium strontium titanate, lead zirconate-titanate and strontium bismuth tantalate have been calculated as a function of metal work function. These oxides have a dimensionless Schottky barrier pinning factor, S, of 0.28 - 0.4 and not close to 1, because S is controlled by the Ti-O type bonds not Sr-O type bonds, as assumed previously. Band offsets on silicon are asymmetric with much smaller offset at the conduction band, so that Ta2O5 and barium strontium titanate (BST) are relatively poor barriers to electrons on Si.

Bismuth-doped fiber integrated ring laser mode-locked with a nanotube-based saturable absorber

We demonstrate passive mode-locking of a bismuth-doped fiber laser using a singlewall nanotube-based saturable absorber. Stable operation in the all-normal dispersion and average soliton regime is obtained, with an all-fiber integrated format. © 2010 Optical Society of America.

Infrared luminescence properties of bismuth-doped barium silicate glasses

Infrared (IR) luminescence covering 1.1 to similar to 1.6 mu m wavelength region was observed from bismuth-doped barium silicate glasses, excited by a laser diode at 808 nm wavelength region, at room temperature. The peak of the IR luminescence appears at 1325 nm. A full width half-maximum (FWHM) and the lifetime of the fluorescence is more than 200 nm and 400 mu s, respectively. The fluorescence intensity increases with Al2O3 content, but decreases with BaO content. We suggest that the IR luminescence should be ascribed to the low valence state of bismuth Bi2+ or Bi+, and Al3+ ions play an indirect dispersing role for the infrared luminescent centers.

Microstructure control and iodine doping of bismuth telluride

On the materials scale, thermoelectric efficiency is defined by the dimensionless figure of merit zT. This value is made up of three material components in the form zT = Tα²/ρκ, where α is the Seebeck coefficient, ρ is the electrical resistivity, and κ is the total thermal conductivity. Therefore, in order to improve zT would require the reduction of κ and ρ while increasing α. However due to the inter-relation of the electrical and thermal properties of materials, typical routes to thermoelectric enhancement come in one of two forms. The first is to isolate the electronic properties and increase α without negatively affecting ρ. Techniques like electron filtering, quantum confinement, and density of states distortions have been proposed to enhance the Seebeck coefficient in thermoelectric materials. However, it has been difficult to prove the efficacy of these techniques. More recently efforts to manipulate the band degeneracy in semiconductors has been explored as a means to enhance α.

The other route to thermoelectric enhancement is through minimizing the thermal conductivity, κ. More specifically, thermal conductivity can be broken into two parts, an electronic and lattice term, κ_e and κ_l respectively. From a functional materials standpoint, the reduction in lattice thermal conductivity should have a minimal effect on the electronic properties. Most routes incorporate techniques that focus on the reduction of the lattice thermal conductivity. The components that make up κ_l (κ_l = 1/3Cνl) are the heat capacity (C), phonon group velocity (ν), and phonon mean free path (l). Since the difficulty is extreme in altering the heat capacity and group velocity, the phonon mean free path is most often the source of reduction.

Past routes to decreasing the phonon mean free path has been by alloying and grain size reduction. However, in these techniques the electron mobility is often negatively affected because in alloying any perturbation to the periodic potential can cause additional adverse carrier scattering. Grain size reduction has been another successful route to enhancing zT because of the significant difference in electron and phonon mean free paths. However, grain size reduction is erratic in anisotropic materials due to the orientation dependent transport properties. However, microstructure formation in both equilibrium and nonequilibrium processing routines can be used to effectively reduce the phonon mean free path as a route to enhance the figure of merit.

This work starts with a discussion of several different deliberate microstructure varieties. Control of the morphology and finally structure size and spacing is discussed at length. Since the material example used throughout this thesis is anisotropic a short primer on zone melting is presented as an effective route to growing homogeneous and oriented polycrystalline material. The resulting microstructure formation and control is presented specifically in the case of In₂Te₃-Bi₂Te₃ composites and the transport properties pertinent to thermoelectric materials is presented. Finally, the transport and discussion of iodine doped Bi₂Te₃ is presented as a re-evaluation of the literature data and what is known today.

Frequency upconversion properties of Er3+/Yb3+-codoped lead-germanium-bismuth oxide glasses

The frequency upconversion properties of Er3+/Yb3+-codoped heavy metal oxide lead-germanium-bismuth oxide glasses under 975 mn excitation are investigated. Intense green and red emission bands centered at 536, 556 and 672 run, corresponding to the H-2(1/2) --> I-4(15/2), S-4(3/2) --> I-4(15/2) and F-4(9/2) -->I-4(15/2) transitions of Er3+, respectively, were simultaneously observed at room temperature. The influences of PbO on upconversion intensity for the green (536 and 556 nm) and red (672 nm) emissions were compared and discussed. The optimized rare earth doping ratio of Er3+ and Yb3+, is 1:5 for these glasses, which results in the stronger upconversion fluorescence intensities. The dependence of intensities of upconversion emission on excitation power and possible upconversion mechanisms were evaluated and analyzed. The structure of glass has been investigated by means of infrared (IR) spectral analysis. The results indicate that the Er3+/Yb3+-codoped heavy metal oxide lead-germanium-bismuth oxide glasses may be a potential materials for developing upconversion fiber optic devices. (C) 2006 Published by Elsevier Ltd.

Improved fluorescence from Tm3+/Er3+/Ce3+ triply doped bismuth-silicate glasses for S+C-bands amplifiers

Fluorescence of Tm3+/Er3+ codoped bismuth-silica (BS) glasses and the sensitization of Ce3+ are investigated. It shows that Ce3+ codoping with Tm3+/Er3+ in BS glasses results in a quenching of Tm3+ ion emission from F-3(4) to the H-3(6) level. Consequently, the 1.47 mu m emission occurs after the population inversion between the H-3(4) and F-3(4) levels. Furthermore, the codoped glasses show the broad emission spectra over the whole S and C bands with full-width at half-maximum (FWHM) up to about 119nm, as it combines 1.55 mu m emission band of Er3+ with 1.47 mu m emission band of Tm3+ under 800nm excitation.

Optical spectroscopy and energy transfer of Er3+/Ce3+ in B2O3-doped bismuth-silicate glasses

Ce3+ and B2O3 are introduced into erbium-doped Bi2O3-SiO2 glass to enhance the luminescence emission and optic spectra characters of Er3+. The energy transfer from Er3+ to Ce3+ will obviously be improved with the phonon energy increasing by the addition of B2O3. Here, the nonradiative rate, the lifetime of the I-4(11/2) -> I-4(3/2) transition, and the emission intensity and bandwidth of the 1.5 mu m luminescence with the I-4(13/2) -> I-4(5/2) transition of Er3+ are discussed in detail. The results show that the optical parameters of Er3+ in this bismuth-borate-silicate glass are nearly as good as that in tellurite glass, and the physical properties are similar to those in silicate glass. With the Judd-Ofelt and nonradiative theory analyses, the multiphonon decay and phonon-assisted energy-transfer (PAT) rates are calculated for the Er3+/Ce3+ codoped glasses. For the PAT process, an optimum value of the glass phonon energy is obtained after B2O3 is introduced into the Er3+/Ce3+ codoped bismuth-silicate glasses, and it much improves the energy-transfer rate between Er3+ I-4(11/2)-I-4(13/2) and Ce3+ F-2(5/2) -> F-2(7/2), although there is an energy mismatch. (c) 2007 Optical Society of America.

Metallogenic Provinces of the Southwestern United States and Northern Mexico

Some of the metallogenic provinces of the southwestern United States and northern Mexico are defined by the geographic distribution of trace elements in the primary sulfide minerals chalcopyrite and sphalerite. The elements investigated include antimony, arsenic, bismuth, cadmium, cobalt, gallium, germanium, indium, manganese, molybdenum, nickel, silver, tellurium, thallium, and tin. Of these elements, cobalt, gallium, germanium, indium, nickel, silver, and tin exhibit the best defined geographic distribution.

The data indicate that chalcopyrite is the preferred host for tin and perhaps molybdenum; sphalerite is the preferred host for cadmium, gallium, germanium, indium, and manganese; galena is the preferred host for antimony, bismuth, silver, tellurium, and thallium; and pyrite is the preferred host for cobalt, nickel, and perhaps arsenic. With respect to the two minerals chalcopyrite and sphalerite, antimony, arsenic, molybdenum, nickel, silver, and tin prefer chalcopyrite; and bismuth, cadmium, cobalt, gallium, germanium, indium, manganese, and thallium prefer sphalerite. This distribution probably is the result of the interaction of several factors, among which are these: the various radii of the elements, the association due to chemical similarities of the major and trace elements, and the degree of ionic versus covalent and metallic character of the metal-sulfur bonds in chalcopyrite and sphalerite. The type of deposit, according to a temperature classification, appears to be of minor importance in determining the trace element content of chalcopyrite and sphalerite.

A preliminary investigation of large single crystals of sphalerite and chalcopyrite indicates that the distribution within a single crystal of some elements such as cadmium in sphalerite and indium and silver in chalcopyrite is relatively uniform, whereas the distribution of some other elements such as cobalt and manganese in sphalerite is somewhat less uniform and the distribution of tin in sphalerite is extremely erratic. The variations in trace element content probably are due largely to variations in the composition of the fluids during the growth of the crystals, but the erratic behavior of tin in sphalerite perhaps is related to the presence of numerous cavities and inclusions in the crystal studied.

Maps of the geographic distribution of trace elements in chalcopyrite and sphalerite exhibit three main belts of greater than average trace element content, which are called the Eastern, Central, and Western belts. These belts are consistent in trend and position with a beltlike distribution of copper, gold, lead, zinc, silver, and tungsten deposits and with most of the major tectonic features. However, there appear to be no definite time relationships, for as many as four metallogenic epochs, from Precambrian to late Tertiary, are represented by ore deposits within the Central belt.

The evidence suggests that the beltlike features have a deep seated origin, perhaps in the sub-crust or outer parts of the mantle, and that the deposits within each belt might be genetically related through a beltlike compositional heterogeneity in the source regions of the ores. Hence, the belts are regarded as metallogenic provinces.

Low-Power Super-resolution Readout with Antimony Bismuth Alloy Film as Mask layer

Sb-Bi alloy films are proposed as a new kind of super-resolution mask layer with low readout threshold power. Using the Sb-Bi alloy film as a mask layer and SiN as a protective layer in a read-only memory disc, the super-resolution pits with diameters of 380 nm are read out by a dynamic setup, the laser wavelength is 780 nm and the numerical aperture of pickup lens is 0.45. The effects of the Sb-Bi thin film thickness, laser readout power and disc rotating velocity on the readout signal are investigated. The results show that the threshold laser power of super-resolution readout of the Sb-Bi mask layer is about 0.5 mW, and the corresponding carrier-to-noise ratio is about 20 dB at the film thickness of 50 nm. The super-resolution mechanism of the Sb-Bi alloy mask layer is discussed based on its temperature dependence of reflection.

Near infrared broadband emission from bismuth-dysprosium codoped chalcohalide glasses

We investigate the broadband infrared emission of bismuth doped and bismuth/dysprosium codoped chalcohalide glasses. It is found that the bismuth/dysprosium codoping can drastically enhance the fluorescence as compared with either bismuth or dysprosium doped glasses. Meanwhile, the full width at half maximum of bismuth/dysprosium codoped glasses is over 170 nm, which is the largest value among all the reported rare-earth doped chalcohalide glasses. An ideal way for energy consumption between bismuth and dysprosium ions is supposed. Such improved gain spectra of both bismuth and dysprosium ions may have potential applications in developing broadband fibre amplifiers.

Ultrabroadband infrared luminescence and optical amplification in bismuth-doped germanosilicate glass

This letter reports the ultrabroadband infrared luminescence from 1000- to 1700-nm wavelength range and demonstrate optical amplification at the second optical communication window in a novel bismuth-doped germanosilicate glass. The full-width at half-maximum of the luminescence is about 300 mn and the optical gain is larger than 1.37 within the wavelength region from 1272 to 1348 nm with pump power 0.97 W. This material could be useful to fabricate ultrabroadband optical fiber amplifiers.

Optical amplification near 1300 nm in bismuth-doped strontium germanate glass

We demonstrate the broadband optical amplification in bismuth-doped strontium germanate glass with 808 nm and 980 nm laser diodes (LDs) as excitation sources. The net optical gain has been obtained within the wavelength region of 1272 to 1348 nm with 808 nm laser diode under 0.97 W power. The maximum gain and gain coefficients are 1.23 and 1.03 cm(-1) at 1315 nm, respectively. The signal increment at 1300 nm is 2.8 times with 980 nm LD, under 3 W power. The differential thermal analysis measurement reveals the good thermal stability of the studied glass. This glass could be suggested as a promising gain medium for broadband optical amplifiers.