Thallium Vapor Research Articles

Gas-discharge laser on a self-terminating thallium transition

We report an experimental study of the performance parameters of a gas discharge pumped thallium vapour laser operating on the 7s2S1/2 - 6p2P3/2o self-terminating transition at 535 nm. The switch we used, a TPI3-10k/25 cold-cathode thyratron, ensures a rise time of the load voltage pulse less than 15 ns. The laser output power is shown to increase in proportion to the energy stored in the discharge capacitor (up to the maximum voltage of the thyratron). The optimal pump pulse repetition rate for He(Ne)—Tl mixtures is ∼1.75 kHz. Even small hydrogen additions reduce the lasing energy and average output power. The addition of bismuth vapour increases the optimal pulse repetition rate (up to 3 kHz) and average output power. The factors responsible for the lower lasing efficiency in comparison with the copper vapour laser are analysed.

MOCVD Growth, Micro‐Structural, and Superconducting Properties of a‐Axis Oriented TlBaCaCuO Thin Films.

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MOCVD Growth, Micro-Structural, and Superconducting Properties of a-Axis Oriented TlBaCaCuO Thin Films

The fabrication of pure a-axis oriented Tl2Ba2Ca1Cu2O8 (Tl-2212) superconducting thin films, prepared ex-situ by a combined approach of metal−organic chemical vapor deposition (MOCVD) and thallium vapor diffusion, is reported. The unusual orientation has been obtained by depositing the superconducting films on LaAlO3 (100) buffer layers grown on SrTiO3 (100) substrates. The micro-structural and superconducting properties of a-axis oriented films have been investigated and compared with those of the c-axis oriented samples simultaneously deposited.

A metal-organic chemical vapor deposition approach to double-sided Tl2Ba2Ca1Cu2O8superconducting films on LaAlO3(100) substrates

Double-sided Tl2Ba2CaCu2O8 (Tl-2212) films for device applications have been fabricated through thallium vapor diffusion into BaCaCuOF matrices deposited by a novel metal-organic chemical vapor deposition (MOCVD) process onto 10 × 10 mm2 LaAlO3 (100) substrates. The present approach uses a multimetal molten single source in a monocomponent hot-wall MOCVD reactor whose geometry allows simultaneous and uniform film growth on both sides of the substrate. Both sides are epitaxially coated by homogeneous and monophasic Tl-2212 films, which, even more importantly, have comparable superconducting and transport properties.

The study of critical current density of superconducting thallium oxide films from spray-deposited precursors

Spray deposition is a promising and economic approach for fabricating high-temperature superconducting films for the Tl-oxide superconductors. The Tl-oxides provide the potential for operation at 77 K in practical magnetic fields of 3– 5 T , which has been demonstrated by measurements on the irreversibility behavior of the Tl-1223 single layer compound with Bi and Sr substitution. In this report, we present the preparation and characterization of Tl 0.78Bi 0.22Sr 1.6Ba 0.4Ca 2Cu 3O 9 superconducting films fabricated from spray-deposited Tl-free, Ag-containing and Cu-rich precursors and reacted with thallium vapor using a two-step crucible process at 650°C/815°C in flowing argon for only 10/10 min . An epitaxial superconducting film was synthesized successfully and critical current densities of 8×10 5 A/ cm 2 at 77 K in zero-field were obtained with excellent in-field performance.

Dual mode cross slotted filter realized with double-sidedTl2Ba2CaCu2O8 films grown by MOCVD

We report on the realization of dual mode microwave filters based onTl2Ba2Ca1Cu2O8 (Tl-2212) double-sided superconducting films.The Tl-2212 samples have been grown ex situ on 10×10 mm2LaAlO3 (100) substrates by a combined approach of metal-organic chemicalvapour deposition (MOCVD) and thallium vapour diffusion. Their morphological,compositional and structural natures have been investigated by scanningelectron microscopy, energy dispersive x-ray analyses and x-ray diffractioncharacterization. Both sides of the films are smooth, homogeneous in thicknessand composition and show epitaxially-grown Tl-2212 phases. Typical values ofTc = 100 K and Jc = 0.05 MA cm-2 at 77 K have been inductively measuredfor both sides. Microwave measurements have been performed at 20 GHz by usinga dielectric resonator.Two planar superconducting single-stage dual mode filters operating in theC-band with 1% and 10% fractional bandwidth have been realized. The basicelement of the device is a square patch resonator diagonally crossed byunequal slots providing both a size reduction and a simple and controllableway to couple the two degenerate modes. Device response has been studied atdifferent temperatures, performing power and intermodulation measurements. Inview of practical applications, the results are compared with those obtainedby a filter based on high-quality YBCO films.

Synthesis and microwave properties of TI2Ba2CaCu2O8 superconducting films grown by MOCVD

We report on the synthesis, structural and electrical characterization of high quality Tl2Ba2Ca1Cu2O8 (Tl-2212) superconducting films. The samples have been grown ex-situ on mm2 LaAlO3 (100) substrates by a combined approach of metal-organic chemical vapor deposition (MOCVD) and thallium vapor diffusion. The morphological and compositional nature of the c-axis oriented films has been investigated by SEM and X-ray analyses. Typical values of K and MA/cm2 at 77 K have been measured. Microwave measurements have been performed at f = 87 GHz inserting the film in a copper cavity and at f =1.5 GHz on patterned samples using a microstrip resonator technique. A penetration depth nm is evaluated by fitting the microwave data with phenomenological equations. The minimum value of the surface resistance measured at 4.2 K is 60 and 6 m at 1.5 GHz and 87 GHz respectively. The microwave data are described in the context of a modified two fluid model. An evaluation of the temperature dependence of the scattering rate has been performed through the simultaneous measurement of the surface resistance and the penetration depth.

Properties of single- and double-sided Tl 2Ba 2CaCu 2O 8 films grown by MOCVD and their potential applications to microwave devices

The synthesis of high quality single- and double-sided Tl 2Ba 2Ca 1Cu 2O 8 (Tl-2212) superconducting thin films, prepared ex-situ by a combined approach of metal-organic chemical vapor deposition (MOCVD) and thallium vapor diffusion, is reported. The structural and transport properties of samples grown on 10×10×0.5 mm 3 (100) LaAlO 3 substrates have been measured. The study of the microwave response shows that MOCVD may be a very promising technique for large-scale production of films suitable for microwave applications.

Properties of TBCCO 2212 Thin Films for Electronic Applications

We report on the synthesis and structural and electrical characterization of high quality Tl 2 Ba 2 Ca 1 Cu 2 O x superconducting thin films. The samples have been prepared ex-situ by a combined approach of Metal-Organic Chemical Vapor Deposition (MOCVD) and thallium vapor diffusion. The films have been grown on 10×10 mm 2 (100) LaAlO 3 substrates. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray analyses (EDX) have investigated the morphological and compositional nature of the films. The transport properties have been measured using both a four-probes and an inductive method. The highest critical temperature and critical current density are 104 K and 1 × 106A/cm2 respectively. The microwave response of two samples has been studied using a microstrip resonator technique. The best surface resistance values are below 200 μΩ at 1.2 GHz and 4.2 K. Measurements of the field dependence of the surface resistance have been performed.

Studies of Electromagnetically Induced Transparency in Thallium Vapor and Possible Utility for Measuring Atomic Parity Nonconservation

Motivated by the potential use of electromagnetically induced transparency (EIT) to measure atomic parity nonconservation (PNC), we have studied EIT and associated optical rotation for a three-level system in thallium vapor. EIT allows sub-Doppler resolution of the ${6P}_{1/2}\ensuremath{\rightarrow}{6P}_{3/2}$ mixed magnetic dipole, electric quadrupole transition at $1.28\ensuremath{\mu}\mathrm{m}$ when $0.535\ensuremath{-}\ensuremath{\mu}\mathrm{m}$ radiation acts on the ${6P}_{3/2}\ensuremath{\rightarrow}{7S}_{1/2}$ transition. Our measurements include rotation due to electromagnetically induced birefringence and Faraday rotation perturbed by EIT. We also identify a new method for determining the amplitude ratio $E2/M1$ for the $1.28\ensuremath{-}\ensuremath{\mu}\mathrm{m}$ transition. The possible advantages of an EIT technique for measuring atomic PNC are discussed in the context of our results.

Correlation between the Tl concentration depth profiles and the thallination time in TlBaCaCuO superconducting films

The elemental composition and depth profiles of superconducting TlBaCaCuO (TBCCO) films deposited on yttrium-stabilized zirconia (YSZ) substrates were studied by IBA techniques such as RBS and NRA. The TBCCO films were prepared by annealing in thallium vapour a series of spray deposited Ba 2Ca 2Cu 3O x precursor films with crude Tl 2Ba 2Ca 2Cu 3O x pellets at 850°C for various times of thallination in s single-zone reaction chamber. Synthesized TBCCO films, 3–4 μm thick, were characterized by resistivity and XRD measurements. The zero resistance T c values ranged from 87 to 97 K, depending on the time of thallination. IBA studies revealed a correlation between the Tl concentration depth profiles and the thallination time. The highest T c value, 97 K, was obtained after a relatively short thallination time of 5 min, leading also to the best crystallographic orientation. The physical implications of these results are discussed.

A-axis-oriented TlBaCaCuO films by a two step route involving MOCVD and thallium vapour diffusion on LaAlO3 buffer layers grown on SrTiO3 (100) substrates

TlBaCaCuO superconducting films have been fabricated on LaAlO3 (100) buffer layers, grown by metal-organic chemical vapour deposition (MOCVD) on SrTiO3 (100) substrates. The usual two step procedure, involving the MOCVD deposition of BaCaCuO(F) matrices and a thallium vapour diffusion process, has been adopted for the preparation of the TlBaCaCuO films. The films grown on the LaAlO3 (100)/SrTiO3 (100) substrates area-axis oriented as indicated by both X-ray diffraction measurements and scanning electron micrographs. The morphological nature of the LaAlO3 buffer layer seems to be responsible for the formation ofa-axis-oriented domains, since simultaneous fabrications of TlBaCaCuO films on commercial LaAlO3 (100) and LaAlO3 (100)/SrTiO3 (100) substrates givec-axis anda-axis-oriented films, respectively. The MOCVD grown LaAlO3 buffer layers are highly (100) oriented, the full width at half maximum (FWHM) of the rocking curve of the (100) peak being as small as 0.16°.

Growth of epitaxial TlBaCaCuO a-axis oriented films on LaAlO 3 buffer layers grown on SrTiO 3 (100) substrates

a-Axis oriented films of the TlBaCaCuO family have been grown on LaAlO 3 (100) buffer layers on SrTiO 3 (100) substrates. The two step fabrication procedure involves the deposition of BaCaCuO(F) matrices through metal-organic chemical vapour deposition (MOCVD) and their annealing to yield the TlBaCaCuO phase through a thallium vapour diffusion process. The present unusual orientation, which to our knowledge is the first example of an a-axis orientation for this class of superconductors, is due to the nature of the LaAlO 3 buffer layers deposited on SrTiO 3 (100) substrates. The LaAlO 3 films deposited in-situ via MOCVD from the new generation precursor La(hfa) 3·diglyme (hfa=1,1,1,5,5,5-hexafluoro-2,4-pentanedione, diglyme=bis(2-methoxyethyl)ether) and Al(acac) 3 (acac=acetylacetone) are highly (100) oriented. The full widths at half maximum (FWHM) of the rocking curve of the (100) peak as small as 0.16° have been observed.

Effect of BaCaCu precursor matrix on the formation and properties of superconducting Tl 2Ba 2Ca n−1 Cu nO x films A combined metalorganic chemical vapour deposition and thallium vapour diffusion approach

Superconducting thin films of the Tl 2Ba 2CaCu 2O x (2212) and Tl 2Ba 2Ca 2Cu 3O x (2223) phases have been prepared through a combined approach of MOCVD and thallium vapour diffusion. The effects due to the nature of the BaCaCuO(F) precursor matrix on the formation of the TlBaCaCuO phase film have been investigated. Fluorinated [BaCaCuO(F)] matrices have been deposited from Ba(hfa) 2·tetraglyme, Ca(hfa) 2·tetraglyme and Cu(acac) 2 via metalorganic chemical vapour deposition (MOCVD) on yttria-stabilized zirconia (YSZ) substrates. Both fluorinated [BaCaCuO(F)] and unfluorinated (BaCaCuO) matrices proved suitable for vapour diffusion thallium incorporation using selected Tl 2O 3:BaO:CaO:CuO mixtures. The formation of the superconducting 2212 and 2223 films is discussed depending upon the fluorinated and unfluorinated nature of the precursor matrices.

Superradiance at a wavelength of 535 nm in a mixture of calcium and thallium vapors

The results of the first experiments in which the superradiance in Tl vapors on the transition with green wavelength 5350 A (a resonance transition 3D 2−4F 3 in calcium) are presented. The dependence of pulse peak intensity on thallium vapor density is investigated. A computer simulation is performed showing the possibility of a substansial decrease in duration of superradiance pulses in a mixture of thallium and calcium vapors.

Reproducible synthesis by metal-organic chemical vapour deposition and thallium vapour diffusion of oriented thin-films : intergrowth of and structures

Superconducting thin-films containing randomly disordered layers of and have been synthesized through a combined approach of metal-organic chemical vapour deposition (MOCVD) and thallium vapour diffusion. The BaCaCu matrices have been deposited onto yttria stabilized zirconia (YSZ) substrates using the second generation tetraglyme and tetraglyme (hfa denotes hexafluoroacetylacetonate), and the (acac denotes acetylacetonate) as volatile metal-organic precursors. BaCaCu precursor films of composition 2:2:3 were annealed in the presence of a mixture of thallium (III), barium, calcium and copper oxides at temperatures of 840 - and oxygen partial pressure varying from 0.04 - 0.5 atm. The formation of an oriented () intergrowth structure has been observed in narrow temperature and oxygen partial pressure ranges. The electrical resistivity data show which, in accordance with the scanning electron microscopy image, appears indicative of a material with weakly linked grains.

Optical characterization of Tl-based superconducting films deposited from aerosol

Superconducting Tl-based films were prepared by deposition of precursor Ba-Ca-Cu films from an aerosol generated ultrasonically, followed by an annealing in a thallium vapour. As substrates we used single crystalline yttrium-stabilized zirconia (YSZ). The prepared films were about 3 μm thick. Annealed films consisted of 2212 and 2223 phases and partially of an amorphous phase, as revealed by X-ray and Raman spectroscopy. Hence, lower T c values were obtained, from the interval 85–105 K. The Raman spectra measurements show the presence of peaks similar to those previously reported for the 2212 phase, with, however, some shifts in energy, which could be related to the presence of the 2223 phase and thus to the strengthening of the chemical bonds.

Properties of Tl-1223 superconducting thick films fabricated from precursor inks using a thallium vapor transport process

Using a two-zone thallium vapor transport furnace and a thick film ink process, we have successfully made superconducting films 10 to 50 /spl mu/m thick on a variety of substrates. Ba/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ and Bi/sub 0.22/Sr/sub 1.6/Ba/sub 0.4/Ca/sub 2/Cu/sub 3/O/sub x/ precursor films with and without Ag additions were made by mixing powders in an organic vehicle, painting a substrate and burning the vehicle off. Films were converted to the superconducting phase by passing an O/sub 2/ carrier gas over a Tl/sub 2/O/sub 3/ source and then the sample. TBCCO 1223 films generally form over a narrow sample temperature range near 860/spl deg/C, whereas TBSBCCO films form 1213, 1223 or a mixture of these phases depending on sample annealing temperature and O/sub 2/ partial pressure. TBCCO T/sub c/'s average 104 K with zero-field J/sub c/ (77 K) /spl ap/3500 A/cm/sup 2/ while TBSBCCO T/sub c/'s are higher at 110 K with J/sub c//spl ap/6800 A/cm2. Both compounds show weak-link behavior in a magnetic field.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

TlBaCaCuO superconducting thin films via metal-organic chemical vapour deposition (MOCVD) and thallium vapour diffusion

Superconducting thin films of the TlBaCaCuO family have been prepared through a combined approach of MOCVD and thallium vapour diffusion. A three-step process has been adopted involving i) the synthesis of Ba−Ca−Cu−O films by MOCVD using «second-generation» barium and calcium sources, ii) the hydrolysis of the fluoride phases by annealing in water vapour-saturated oxygen and iii) the annealing in the presence of a thallium source. Reproducible results, in terms of phase formation, are discussed depending on the different conditions of the preannealing process. The superconducting films consist predominantly of single-phase Tl2Ba2Ca2Cu3Ox(2223). Preferential orientation of the crystallitec-axes perpendicular to the substrate surface has been observed. The films exhibit superconducting onset temperatures of 115–120 K with zero resistance higher than 100 K.

Fabrication and properties of TBCCO films via air-atomising spray deposition of thallium-free precursors

The high-field properties of polycrystalline superconducting TlBaCaCuO films fabricated by the incorporation of thallium vapour into air-atomised BaCaCuO precursors are described. Thick films with T c values in the range 106–111 K have been prepared on polycrystalline yttria-stabilised zirconia substrates. The surface morphology, crystal structure and composition of the films are related to their high-field transport and magnetisation properties. Typical 10 mm × 9 mm films show J c values > 1×10 4 A/cm 2 at 77 K (0 T). The best film has a J c=1.3×10 4 A/cm 2 ( I c=3.6 A) at 77 K (0 T). Films prepared on 26 mm×9 mm substrates show typical large-area J c values > 0.5×10 4 A/cm 2 (77 K, 0 T). A square planar specimen of dimensions 4.3 mm ×4.3 mm exhibited magnetisation J c values=1.2×10 5 A/cm 2 at 4.2 K (0.1 T), 9.3×10 4 A/cm 2 at 10 K (0.1 T), 3.3×10 4 A/ cm 2 at 4 K (8 T), and 1.6×10 4 A/cm 2 at 10 K (8 T).