Response of a YBaCuO/MgO bolometer structure at high levels of laser excitation. Nonlinear model and experiment

A nonlinear model is developed for the photoresponse of a bolometric structure taking into account the temperature dependences of the thermal constants of the YBaCuO/MgO structure and its boundary thermal resistance. The model also allows for the specific form of the currentvoltage characteristic of YBaCuO and the heat release from the transport current flow. A comparison between the experimental data and the model showed that the nonlinear thermal model accurately describes the temporal characteristics of the photoresponse. Fiz. Tverd. Tela (St. Petersburg) 40, 191–194 (February 1998)     

Narrowband ultraviolet photodetector based on MgZnO and NPB heterojunction

An ultraviolet photodetector was fabricated based on Mg_0.07Zn_0.93O heterojunction. N, N'-bis (naphthalen-1-y1)-N, N'-bis(pheny) benzidine was selected as the hole transporting layer. I-V characteristic curves of the device were measured in the dark and under the illumination of 340?nm UV light with density of 1.33 mW/cm². The device showed a low dark current of about 3×10^-10 A and a high photo-dark current ratio of 1×10⁵ at -2 V bias. A narrowband photoresponse was observed from 300 to 400?nm and centered at 340?nm with a full width at half-maximum of only 30?nm. The maximum peak response is at 340?nm, which is 0.192 A/W at the bias of -1 V.     

Structure and transport properties of ultrathin YBa2Cu3O7−x films

The crystal structure and transport properties of epitaxial c-oriented YBa₂Cu₃O_7−x films are investigated for high-T _c layer thicknesses from 5 to 300 nm. The films were prepared by laser deposition. Films less than 30 nm thick become predominantly single-domain in the direction of the c axis. As the thickness decreases, the orthorhombicity parameter of the YBaCuO lattice decreases, which correlates with the critical temperature degradation observed in films less than 9 nm thick. The obtained thickness dependence of the effective microwave surface resistance of a YBaCuO film agrees well with the computational result obtained in the framework of local electrodynamics for samples with a constant microwave conductance. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 8, 608–613 (25 April 1996)     

Surface resistance of an YBaCuO film in the megahertz range determined from the Q factor of a planar inductance coil: Effect of extrinsic factors

High-quality YBaCuO films are used to sequentially prepare a 10-GHz disk resonator and a planar inductance coil. The Q factor of the planar inductance coil at its resonance frequency (64 MHz) is much higher than the values reported for analogous structures. The measurement results are used to estimate the surface resistance of the films at frequencies of 10 GHz and 64 MHz. The surface resistance measured at 64 MHz is more than fourfold of that calculated from the surface resistance measured at 10 GHz by the dependence R _sur ∼ ω². Our analysis demonstrates that extrinsic factors cannot substantially affect the measurement results; therefore, the deviation from the R _sur ∼ ω² dependence in the megahertz range is determined by the intrinsic properties of the superconducting strip.     

Measurement of the impedance of very thin superconducting YBaCuO films at 10 GHz with a cavity perturbation method between 4 and 300 K

We have measured the complex film impedance 1/σd (σ conductivity, d film thickness) of three YBaCuO thin films with d = 44, 115, and 168 nm on MgO substrates at 10.2 GHz in the temperature range between 300 and 4 K. Below T_c, the experimental results are discussed in terms of the two-fluid model and the BCS theory. The residual resistance decreases with the film thickness. The thinnest film has a residual surface resistance of 3 · 10^?4 Ω. For this film, the complex microwave conductivity is calculated and compared with the models. Apart from the residual resistance, the measured conductivity is in agreement with the peak caused by the energy gap of the BCS theory. All measurements were performed with a cavity perturbation method which we have to our knowledge applied for the first time to superconducting thin films. The method allows to determine the complex impedance of films with arbitrary thickness. In particular, films with thicknesses small compared to the skin depth δ or the London penetration depth λ can be measured. Therefore, we are able to measure the impedance both in the normal and superconducting state.     

Critical thickness and stress relaxation in YBaCuO (123) strained epitaxial layers and YBaCuO based strained superlattices

An energy model has been used to calculate the critical thickness h _c of YBaCuO thin films and YBaCuO based superlattices within an isotropic or anisotropic approximation. The critical thickness of single layers calculated from the anisotropic model (16 nm) is in good agreement with the previously published experimental values which are spread out from 4 to 20 nm. In the case of superlattices, relaxation appears to be governed by the critical thickness of the elementary sub-layers and is then better evaluated through the calculation performed for YBaCuO single layers. XRD measurements on YBa₂Cu₃O₇/PrBa₂Cu_3?xGa_xO₇ superlattices grown on {100{ SrTiO₃ have evidenced a tetragonal stress in the YBaCuO ab plane which remains expanded when the YBaCuO elementary layer thickness is lower than 4.8 nm (4 YBaCuO cells). However the critical temperature of the shortest period superlattices is only slightly affected by this expanded stress in contrast to the effect of an elastic stress externally applied along the ab plane of YBaCuO thin films.     

Sub-doppler laser cooling of thulium atoms in a magneto-optical trap

Sub-Doppler laser cooling in a magneto-optical trap for thulium atoms at a wavelength of 410.6 nm has been experimentally studied. Without any dedicated molasses period of sub-Doppler cooling, the cloud of 3 × 10⁶ atoms at a temperature of 25(5) μK was observed. The measured temperature is significantly lower than the Doppler limit of 240 μK for the cooling transition at 410.6 nm. The high efficiency of the sub-Doppler cooling process is due to a near-degeneracy of the Landé g-factors of the lower 4f ¹³6s ² (J = 7/2) and the upper 4f ¹²5d _3/26s ² (J = 9/2) cooling levels.     

Quenching of SO2 phosphorescence by a magnetic field

Phosphorescence excitation spectra of the ã³B₁← [Xtilde]¹A₁ transition of SO₂ were measured in the absence and presence of a magnetic field (B = 0?44 T², P(SO₂) = 0?7 Torr). The absorption and phosphorescence excitation spectra of the ã³B₁← [Xtilde]¹A₁ transition of SO₂ measured in the absence of a magnetic field show that the relative intensity of the bands of the phosphorescence excitation spectrum is smaller than the relative intensity of the corresponding bands of the absorption spectrum beginning with the (0, 2, 0) band. In the presence of a magnetic field, the intensity of the phosphorescence excitation band falls, for ν_exc> 26400 cm^-1. Under the direct excitation of the ã³B₁← [Xtilde]¹A₁ transition, the dependence of the magnetic quenching of the SO₂ phosphorescence on the excitation frequency (ν_exc) was studied at P(SO₂) = 0?7 Torr and B = 0?44 T. The dependence of the magnetic field effect on ν_excshows that only the vibrationally excited levels of the ã³B₁ state are sensitive to an external magnetic field. The magnetic field strength and the pressure dependence of the magnetic field effects were studied under indirect excitation of the ã³B₁← [Xtilde]¹A₁ transition at λ_exc = 308 nm. The magnetic field and the pressure dependence were investigated for pure SO₂ and for SO₂ + RH (RH n-C₅H₁₂) mixtures. It was found that the magnetic field effect was saturated at B ? 0?25 T. The saturation value (Gr = l(0?3 T)/l(0)) increases with increasing gas pressure. The magnetic field, the pressure and the excess vibrational energy (ν_excess) dependence of the magnetic quenching of SO2 phosphorescence show that the data observed can be explained by an indirect mechanism within the framework of a low level density approximation.     

Study of highT c superconductivity in Y1Ba2Cu3O7−x by PAC

HighT _c superconductivity in the YBaCuO superconductor has been investigated through the quadrupole interaction of the probe nuclei⁹⁹Tc. The quadrupole interactions were measured by the TDPAC method from 77 to 296 K. The probe nuclei⁹⁹Tc were introduced into the YBaCuO superconducting specimen by diffusion. The derived electric quadrupole interaction parameters show that the probe nuclei are subject to a unique EFG interaction and occupy a substitutional lattice site in the YBaCuO superconductor. A strong EFG of 10¹⁹ V/cm² was observed. The temperature dependence of the EFG exhibits a linear decrease with temperature increase. Anomalies of both EFG and ν were found in the superconducting transition temperature region. The role of the oxygen vacancies in the Cu−O chains is discussed.     

Thermal diffusivity of MORB-composition rocks to 15 GPa: implications for triggering of deep seismicity

We have measured the thermal diffusivity of eclogite and majorite with a model MORB composition at pressures of 3 and 15 GPa, respectively. Both phase assemblages show inverse dependences of their thermal diffusivities on temperature: D _eclogite=9(10)×10^?10+7(1)×10^?4/T(K) m ²/s and D _majorite=6.2(5)×10^?7+3.0(5)×10^?4/T(K) m ²/s. The values for majorite are in good agreement with previous measurements for other garnets and are considerably lower than thermal diffusivities of wadsleyite and ringwoodite, which are the main components of the mantle transition zone. We discuss the implications of the low thermal conductivity of subducted oceanic crust in the transition zone for the triggering of deep seismicity.     

Effect of laser irradiation on the electrical properties of dysprosium doped LiCo-Ferrite

The effect of laser irradiation on the electrical properties of Li_0.5+z Co _z Dy _x Fe_2.5?2z?x O₄ ferrite (0.0 ≤ x ≤ 0.2, z = 0.1) has been studied in the temperature range 300 K ≤ T ≤ 750 K at frequencies of 10 kHz?5 MHz, using a LIMO-IR laser diode, at a wavelength of 808 nm. It was found that laser irradiation increases the polarization, the resistivity and the paramagnetic region. As the result of electronic rearrangement and lattice defects, small polorons and clusters were created. The doping of LiCo-Ferrite by Dy³⁺ increases both the AC and DC resistance of the investigated material. The variation of the AC and DC resistance with the Dy-content (x) obeys the following correlations R _ac/100 = 50x ²+4x+0.005 and R _dc/1000 = 31x ²+0.099x+0.09, respectively. A peculiar behaviour was obtained for the sample with Dy-content x = 0.075, as the resistance notably decreases. The applicable result is that laser irradiation increases the resistance of LiCo-ferrite by about 17% while its doping by dysprosium at x = 0.15 increases the resistance by about 23%. Its value is nearly stable for the temperature range from 340 to 480 K.     

Transient grating measurements of refractive-index changes in intensively pumped Yb-doped laser crystals

Mechanisms of transient light-induced refractive-index changes in Yb-doped crystals Yb:KYW, Yb:KGW and Yb:YVO₄ were studied. Relative amplitudes and lifetimes of the electronic component of phase gratings caused by the polarizability difference of the excited and unexcited Yb³⁺ ions and the thermal component arising from thermalization of the pump energy were measured. Polarizability difference values of the ground ² F _7/2 and the excited metastable ² F _5/2 levels at the testing wavelength of 633 nm were determined for all crystals. The thermal diffusivity of the samples was estimated for selected directions of the thermal gradient. An athermal direction, along which the thermal component of refraction disappears, was found in Yb:KYW crystal under specific experimental conditions. PACS 42.70.Hj; 42.65.An; 66.30.Xj     

The perpendicular fundamental v5 of chloroform 12CH35Cl3: high resolution infrared study of the v5 band together with the millimetre-wave rotational spectrum

The infrared spectrum of the perpendicular fundamental v₅ of chloroform around 776 cm^?1 has been studied by applying two high resolution methods. A short range from the central part of the spectrum was measured with a diode laser by using a cold jet sample including chloroform in natural isotopic abundancies. More than 100 rotational lines of ¹²CH³⁵Cl₃ could be assigned. The whole band region was measured by a Fourier transform spectrometer at a resolution of 0.0010cm^?1. In this case an isotopically pure sample of ¹²CH³⁵Cl₃ was used. Starting from the results of the diode laser investigation more than 2000 lines could be assigned with J_max = 91 and K_max = 58. In addition to the infrared spectra, millimetre-wave lines also were measured. A total of 58 lines corresponding to J values 22, 23 and 35 at the excited vibration state v₅ = 1 were assigned and analysed. All the data from three different spectra were simultaneously fitted and, for example, the results v₀ = 775.961 50(3) cm^?1, 98, B₅-B₀ = ?0.180171(22) × 10^?3cm^?1, C₅ ? C₀ = ?0.170 57(15) × 10^?3cm^?1, and (Cζ)₅ = 0.047 5294(11) cm^?1 were obtained.     

Short pulse width UV laser at 355 nm based on pulse LD side-pumped ceramic Nd:YAG and BBO electro-optical Q-switched

355 nm UV laser was obtained with a pulse width of less than 5 ns and a peak power at megawatt level by adopting the 808 nm pulse laser diode (LD) side-pumped ceramic Nd:YAG and BBO crystal electrooptical Q-switched. The single-pulse energy was measured to be 24.3 mJ with 4.86 ns pulse width and 5.11 MW peak power at a repetition rate of 1Hz under a 120 A pump current. Using a volume of beam splitting mirrors, wavelength outputs at 1064, 532, and 355 nm pulse laser was obtained simultaneously with a respective average output power of 656.6, 357.1, and 260.5 mW, the beam quality factor M ₂ are (M _{x − 1064}² = 5.83, M _{y − 1064}² = 5.61), (M _{x − 532}² = 4.25, M _{y − 532}² = 4.08) and (M _{x − 355}² = 6.32, M _{y − 355}² = 6.15), corresponding to a conversion efficiency at 11% from 1064 to 355 nm.     

Persistent Luminescence of Eu2☎ and Na☎ Doped Alkaline Earth Aluminates

The luminescence and afterglow properties of the Eu^2? and Na^? doped alkaline earth aluminales, stoichiometric and non-stoichiometric (M_x Al₂O₄:Eu^2?, Na^?; M = Ca or Sr, x = 0.97, 1.00 or 1.03, X_Na, = 0.02), were studied. Broad band luminescence and afterglow of the Eu^2? ion were observed in the blue (λ_max = 440nm) and green (λ_max = 520nm) region for the calcium and strontium aluminates, respectively. Both Na^? co-doping and strontium excess quenched the afterglow efficiently. The results supported the mechanism of the persistent luminescence where the cation vacancies act as traps. The results for the calcium aluminates were ambiguous, probably due to the slightly larger ionic radius of the Na^? with respect to that of Ca^2?. The sodium ions may not fit into the calcium sites and thus form (an) independent compound(s).     

Abscheidung von Glimmpolymerschichten in einem weiten Metallrezipienten und Untersuchungen zur Struktur

Investigations are reported of growth rate, chemical structure (IR-spectroscopy, mass-spectrometry), thermal stability, surface structure (scanning electron microscopy) of thin polymeric films grown in a gas (Ar-hexamethyldisiloxane-mixture) discharge with a heated cathode, which is situated in the centre of a cylindrical metallic vessel (l = 50 cm, 2r = 30 cm). The discharge conditions are the following: I = 0,25 – 4 A, U = 30 – 100 V, p = 6 – 40 Pa, argon flow rate = 3,8 · 10^?5 mol/min, Ar/HMDS = 1 : 0,7 – 1 : 2,4. The growth rate changes from 2 to 18 nm/min, depending on the discharge conditions. The reproducibility of the growth rate shows deviations smaller than 10%. The films consist of a highly cross linked polymeric material and are stable up to 260°C, the solubility in n-hexane being smaller than 2%. The surface of the thin film (d ～ 10² nm) is smooth. Corrosion resistance to soda lye (0,2% NaOH) has been proved.     

Study on electrical conductivity and phase transition in singly doped BIPBVOX (Bi2V1−xPbxO5.5−x/2) solid electrolyte

Samples of bismuth lead vanadium oxide (BIPBVOX) (Bi₂V_1–xPb_xO_5.5–x/2) singly substituted system in the composition range 0.05 ≤ x ≤ 0.20 were prepared by sol–gel synthesis route. Structural investigations were carried out by using a combination of differential thermal analysis (DTA) and powder X-ray diffraction (PXRD) technique. Energy dispersive X-ray spectroscopy analysis (EDXA) of doped samples was carried out to predict the sample purity and doping concentration. Transitions, α?β, β?γ and γ′?γ were detected by XRD, DTA and variation in the Arrhenius plots of conductivity. The ionic conductivity was measured by AC impedance spectroscopy. The solid solutions with composition x ≤ 0.07 undergo α?β phase transition, at 329 °C and β?γ phase transition at 419 °C. The highly conducting γ′-phase was effectively stabilized at room temperature for compositions with x ≥ 0.17 whose thermal stability increases with Pb content. At 300 °C, the highest value of conductivity 6.234 × 10^?5 S cm^?1 was obtained for composition x = 0.15 and at 600 °C the highest value of conductivity 0.65 S cm^?1 is observed for x = 0.17. AC impedance plots reveal that the conductivity is mainly due to the grain contribution to oxide ion conductivity.     

Emission analysis of RE3+ (Eu3+, Tb3+ & Ho3+): B2O3-BaO-LiF/AIF3 glasses

We report here the luminescence spectra of certain rare earth ions (Eu³⁺, Tb³⁺ & Ho³⁺) doped B₂O₃-BaO-LiF/AiF₃ based on the measurements of emission and decay curves of prominent emission transitions. For both the reference host glasses, FTIR, XRD, DTA-TG profiles have been recorded to understand their structural and thermal properties. Eu³⁺ doped glasses have shown five emission transitions of ⁵D₀ → ⁷F_{01,2,3 & 4} located at 580nm, 593nm, 615nm, 655nm and 704nm respectively with an excitation at λ_exci = 392 nm (⁷F₀ → ⁵L₆). Also under an UV source, these europium glasses have displayed a bright red emission from their surfaces. Tb³⁺ glasses have exhibited four emission bands of ⁵D₄ → ⁷F_6,5,4,3 at 491nm, 547nm, 588nm and 625nm respectively with an excitation at λ_exci = 376 nm (⁷F₆ → ⁵G₆). Intense green emission from the glass surfaces has been noticed upon exposure to the UV source. Prominently bluish-green emission has been noticed from the surfaces of the holmium glasses under an UV source and same emission transition (⁵F₄ → ⁵I₈) at 519 nm with an excitation at λ_exci = 389 nm (⁵I₈ − ⁵G₄) has also been obtained from their measured emission spectra. For all the prominent emissions of the rare earth glasses, decay curves have been measured to compute their lifetimes.     

Macrostructure of high-temperature superconducting YBaCuO thin films grown by laser ablation

The superconducting parameters and macrostructure of YBaCuO thin films grown by laser ablation on SrTiO₃ substrates are influenced by the substrate temperature during growth. In a study of this influence it is found that the macrostructure has significant bearing on the superconducting parameters of the films and on the critical current, in particular. For J _c⩽10⁵ A/cm² the films have a distinctly pronounced granular structure, while for J _c>10⁵ A/cm² the films do not have any kind of block structure. Zh. Tekh. Fiz. 68, 48–51 (February 1998)     

Correlation between phase structure and electrical conduction in BISNVOX system for intermediate temperature solid oxide fuel cells (IT-SOFC)

Samples of Sn⁴⁺-substituted bismuth vanadate, formulated as Bi₄Sn _x V_{2? x} O_{11?( x /2)? δ} in the composition range 0.07 ≤ x ≤ 0.30, were prepared by standard solid-state reactions. Sample characterization and the principal phase transitions (α ? β, β ? γ and γ′ ? γ) were investigated by FT-IR spectroscopy, X-ray powder diffraction, differential thermal analysis (DTA) and AC impedance spectroscopy. For composition x = 0.07, the α ? β and β ? γ phase transitions were observed at temperatures of 451 and 536°C, respectively. DTA thermograms and Arrhenius plots of conductivities revealed the γ′ ? γ phase transition at 411 and 423°C for x = 0.20 and 0.30, respectively. AC impedance plots showed that conductivity is mainly due to the grain contribution, which is evident in the enhanced short-range diffusion of oxide ion vacancy in the grains with increasing temperature. The highest ionic conductivity (5.03 × 10^?5 S cm^?1 at 300°C) was observed for the x = 0.17 solid solution with less pronounced thermal hysteresis.