On the use of high-Tc superconductors for Perot-Fabry mirrors coatings

In a very rough experiment using two MgO plates, coated with a 200 Å thick YBaCuO film to increase their reflectivity, and facing each other their YBaCuO films to make a Perot-Fabry (PF) interferometer, we have observed a 43% maximum transmission and a finesse around 33 at v=29 cm^?1, in good accordance with a new phenomenological model for YBaCuO. Much higher performances can be expected by optimizing the YBaCuO film thickness.     

Adaptation of the sheet resistance of an YBaCuO layer to the substrate impedance,applications

We have studied the Far Infrared transmission spectra of an MgO plate covered with an YBaCuO film of thickness t=200 Å, at different temperatures. By cooling from room temperature to temperatures Θ < 140 K, the Far Infrared interference fringes are displaced by half a period. Explanation in terms of different adaptations of the YBaCuO sheet resistance to the MgO substrate impedance during cooling.     

Surface resistance and far infrared absorptivity at T=7 K of highT c YBaCuO superconductors

A surface resistance as small as R_S=3×10^?2 Ohms has been computed at T=8 K, for v=0.6 Thz (v=20 cm^?1), for an YBaCuO film deposited on an MgO substrate. The calculations are made with the refractive index computed from the Far IR transmission spectra of a 400 Å thick film. Still lower values are obtained with another sample, 300 Å thick of exceptional quality (R_S=1.2×10^?2 Ohms).     

Si-YBaCuO intermixing and reactive patterning technique

A novel Si-YBaCuO intermixing technique has been developed for patterning YBaCuO superconducting thin films on both insulating oxide substrates (MgO) and semiconductor substrates (Si). The electrical, structural, and interfacial properties of the Si-YBaCuO intermixed system have been studied using resistivity, x-ray diffraction, scanning electron microscopy, x-ray photoelectron spectroscopy and Auger depth profiling measurements. The study showed that the reaction of Si with YBaCuO and formation of silicon oxides during a high temperature process destroyed superconductivity of the film and created an insulating film. On a MgO substrate, the patterning process was carried out by first patterning a silicon layer using photolithography or laser-direct-writing, followed by the deposition of YBaCuO film and annealing. For a silicon substrate, thin metal layers of Ag and Au were patterned as a buffer mask which defines the YBaCuO structures fabricated thereafter. Micron-sized (2-10 Μm) superconducting structures with zero resistance temperature above 77 K have been demonstrated. This technique has been used to fabricate current controlled HTS switches and interconnects.     

Do quasiparticles in high-T c superconductors condense like molecules of a perfect gas in the bose-Einstein condensation?

Far IR transmission spectra of very thin YBaCuO films in the 10–40 cm^?1 range have now sufficient accuracy and reproducibility to show that the number of quasiparticles at temperature Θ<Θ_c, Θ_c being the transition temperature, do not follow a Θ⁴ law, but rather a Θ^1.5 one.     

溶胶-凝胶法制备Zn2+掺杂MgO薄膜及光电性能表征

采用溶胶-凝胶(sol-gel)法,利用旋转涂覆技术在玻璃衬底及单晶Si(111)衬底上制备掺Zn2+的MgO薄膜。使用紫外可见光分光光度计测定掺杂薄膜的透过率,并采用XRD和EDS等测试手段研究薄膜的晶向结构和成分。结果表明,胶棉液的含量对成膜质量有重要的影响;随着Zn2+掺杂量的提高,薄膜透过率先增大后减小,在掺杂量为10%时,薄膜有最佳透过率;随着退火温度的升高,薄膜晶粒生长没有出现明显的择优取向。最后,对模拟放电单元进行放电测试,结果表明,在掺杂量为10%时,薄膜有最低着火电压和最高的记忆系数。     

中红外高激光破坏阈值薄膜的研究

针对中红外波段（尤其是2.94 μm波长），选择合适的薄膜材料并结合适当的制备工艺参数，优化制备出了几种高破坏阈值2.94 μm激光腔镜。使用了1.06 μm和2.94 μm两种波长的激光对样品进行了破坏阈值实验。通过实验结果进行对比，总结出该波段高破坏阈值光学薄膜的一些独特性质以及镀制要求，得出一套有效地镀制高激光破坏阈值中红外薄膜的方案。所镀腔镜经过自制的自由震荡式长脉宽2.94 μm Er:YAG激光器的使用检验，满足使用要求。     

Conical cavity for surface resistance measurements of hightemperature superconductors

A conically shaped cavity that intrinsically avoids mode-degeneration while maintaining the advantages of cylindrical resonators is presented. The cavity was applied to surface resistance measurements of YBaCuO thin films on MgO substrates at 18 GHz. The lowest measured value was 4.5 mΩ±2.1 mΩ for a 10 mm×10 mm laser ablated film at 77 K. An error analysis is carried out which leads to an accuracy of ±2.1 mΩ for samples with 9 mm diameter and an accuracy of ±0.5 mΩ for samples with 20 diameter     

A Far IR Study of NbN in the Normal and Superconductive State

A thin film of NbN (thickness t = 300 Å), has been deposited on an MgO and a Si wafer. Both samples have been studied by transmission from 10 or 20 to 120 cm^?1, and have exhibited one maximum of transmission at a given frequency like the classical superconductors as Pb, Sn or Hg in the superconductive state. From the Far IR experimental data, the characteristic temperature θ_c, and the gap frequency (ν_gap (θ) = 2 Δ (θ), Δ(θ) being the energy gap) are immediately obtained (for instance for the NbN / MgO sample, θ_c = 15.5 K; ν_g (5 K) = 39.7 cm^?1), and it is seen that $\frac{{{\text{2}}\vartriangle (4{\text{K)}}}}{{{\text{k}}_{\text{B}} \theta _c }} \approx 3.5$ as expected from the BCS theory for a weak coupling. To fit the data we had to adjust only two additionnal parameters: collision and plasma frequency, ν_c (θ) and ν_p (including all carriers). At θ = 5 K, thebest fit for the NbN / MgO sample is obtained with ν_c = 371 cm^?1 and ν_p = 12,600cm^?1.     

High brightness visible (660 nm) resonant-cavity light-emittingdiode

Visible (660 nm) resonant-cavity light-emitting (RCLEDs) have been fabricated. The top-emitting devices employed two AlGaAs-AlAs-Bragg mirrors and GaInP-AlGaInP quantum-well active layers. The device performance was characterized as a function of the device diameters, ranging from 24 to 202 μm. The larger devices exhibited a nearly linear increase of output power with injected current with 8.4-mW emission at 120 mA. A maximum external efficiency of 4.8% was measured at 4 mA on the 84-μm aperture devices. All devices exhibited a narrow emission at 659-661 nm with a linewidth around 3 nm. The results show that RCLED's are promising low-cost light sources for plastic fiber transmission as well as display applications     

Pigtailed high-finesse tunable fibre Fabry-Perot interferometers with large, medium and small free spectral ranges

We have made prototypes of three kinds of fibre Fabry-Perot (FFP) tunable filters, each of which can cover a separate free spectral range interval as determined by its resonator length. Free spectral ranges from hundreds of angstroms to tens of megahertz can be realised from the appropriate type. We have built FFPs with free spectral ranges of >1000 A, 25 GHz, 5 GHz and 2.5 GHz. Finesse up to 200 has been demonstrated. The devices are piezoelectrically tuned and are coupled to fibres in-line using standard rotary splices or ST connectors.     

Fabrication and Electrochemical Properties of Epitaxial Samarium‐Doped Ceria Films on SrTiO3‐Buffered MgO Substrates

Thin films of samarium‐oxide‐doped (20 mol%) ceria (SDC) are grown by pulsed‐laser deposition (PLD) on (001) MgO single‐crystal substrates. SrTiO₃ (STO) prepared by PLD is used as a buffer layer on the MgO substrates to enable epitaxial growth of the fluorite‐structured SDC film; the STO layer provides a proper crystalline match between SDC and MgO, resulting in highly crystalline, epitaxial SDC films grown in the (001) orientation. Film conductivity is evaluated by electrochemical impedance spectroscopy measurements, which are performed at various temperatures (400–775 °C) in a wide range of oxygen partial pressure (pO₂) values (10^?25?1 atm) in order to separate ionic and electronic conductivity contributions. At 700 °C, SDC/STO films on (100) MgO exhibit a dominant ionic conductivity of about 7 × 10^?2 S cm^?1, down to pO₂ values of about 10^?15 atm. The absence of grain boundaries make the SDC/STO/MgO heterostructures stable to oxidation‐reduction cycles at high temperatures, in contrast to that observed for the more disordered SDC/STO films, which degraded after hydrogen exposure.     

An experimental study of Josephson effect in bulk YBaCUO

We have observed Josephson effect in bulk YBaCuO. The size of bulk is 7.5×2.2×0.3 mm and the microwave frequency is 9.82 GHz in our experiment. Several microwave induced steps can easily be observed. When an external magnetic field is applied to the bulk, the critical supercurrent at zero voltage is suppressed significantly. It has been demonstrated that YBaCuO bulk can be seen as a network of Josephson junctions. An experimental study of Josephson effect in bulk YBaCuO at millimeter wave frquency is in progress.     

Noise figure of vertical-cavity semiconductor optical amplifiers

The noise figure of vertical-cavity semiconductor optical amplifiers (VCSOAs) is investigated theoretically and experimentally. Limitations on the noise figure set by the reflectivity of the mirrors are studied. Highly reflective mirrors lead to increased output noise as well as lasing at moderate carrier densities, which imposes a limit on the obtainable population inversion. Expressions for the excess noise coefficient, which governs signal-spontaneous beat noise enhancement due to finite mirror reflectivity, are presented for transmission and reflection-mode operation. Experimental results from a VCSOA operating in the reflection mode at 1.3 μm are presented. The results, from optical as well as electrical measurement techniques, are analyzed and compared to theoretical values     

Thin film encapsulation for organic light emitting diodes using a multi-barrier composed of MgO prepared by atomic layer deposition and hybrid materials

We demonstrated an organic/inorganic multi-barrier and encapsulation for flexible OLED devices. The multi-barrier consisted of a silica nanoparticle-embedded hybrid nanocomposite, in short, S-H nanocomposite, and MgO, which were used as organic and inorganic materials, respectively. The S-H nanocomposite was spin-coated followed by UV curing. The thickness of the S-H nanocomposite was 200 nm, and 40 nm of MgO was deposited by atomic layer deposition (ALD) using Mg(CpEt)₂ and H₂O at 70 °C. The results of a Ca test showed that the 4.5 dyads of the MgO/S-H nanocomposite had a low water vapor transmission rate (WVTR) of 4.33 × 10^?6 g/m²/day and an optical transmittance of 84%. The normalized luminance degradation of the thin film encapsulated OLED was also identical to that of glass-lid encapsulation after 1000 h of the real operation time. We proposed low temperature ALD as a deposition method to create relatively thin film for OLED passivation without degradation, such as creation of dark spots. The results confirmed that it may be feasible for our multi-barrier to passivate flexible OLEDs devices.     

Performance of waveguide-based two-dimensional photonic-crystalmirrors studied with Fabry-Perot resonators

As a step toward the use of photonic crystals in optoelectronic devices, we present a thorough study of 2-D photonic-crystal mirrors etched into a GaAs-AlGaAs planar waveguide. Fabry-Perot resonators are fabricated to deduce the reflectivity, transmission, losses, as well as the penetration lengths of these mirrors. The guided photoluminescence of InAs quantum dots embedded in GaAs is used to obtain the transmission spectra of these cavities. The varying thickness between the mirrors allows a scan across the whole bandgap spectral range. Quality factors (up to 200) and peak transmissions (up to 0.3) are measured showing that mirrors of four rows of holes have 88% reflectivity, 6% transmission and 6% losses. Losses are also related to a two-dimensional transfer matrix method calculation including a recently introduced scheme to account for losses     

Cubic HfN Thin Films with Low Resistivity on Si (001) and MgO (001) Substrates

We deposited epitaxial and highly textured cubic HfN (B1-NaCl) thin films on single-crystal MgO (001) and Si (001) substrates, respectively, using a pulsed laser deposition technique. The HfN thin films are around 100 nm thick. Detailed microstructural characterizations, including x-ray diffraction, transmission electron microscopy (TEM), and high-resolution TEM, were carried out. Resistivity as low as 40 μΩ cm was observed by standard four-point probe measurements. The low resistivity and good diffusion barrier properties demonstrated by our preliminary Cu-diffusion tests for HfN on Si suggest that HfN could be a promising candidate diffusion barrier for Cu interconnects.     

Comparison of radio-frequency and microwave superconductingproperties of YBaCuO dedicated to magnetic resonance imaging

Properties of YBaCuO thin films are evaluated in two distinct frequency ranges using different patterns made during the same process on LaAlO₃ substrate. Microwave superconducting properties in the range 1-45 GHz are determined by S-parameters measurement of a superconducting coplanar waveguide in the range 53-95 K. We obtain a surface resistance of 0.4 mΩ at 10.8 GHz and 77 K. Radio-frequency properties are obtained by measuring the Q-factor of a superconducting resonator (YBCO multiturn transmission lines separated by a sapphire sheet) dedicated to surface magnetic resonance imaging. At 52 MHz and 77 K we measure a Q-factor of 33180. The extraction of the radio-frequency surface resistance from Q-factor measurements in the 64-95 K range takes into account external loss mechanisms and nonuniform normal current distribution and leads to a 0.0093-μΩ surface resistance at 52 MHz and 77 K, in good agreement with the value extrapolated from microwave measurements assuming an ω² frequency dependence. The evaluation of λ₀ is carried out by using several models for X_L(t). Least squares fits to data in the microwave and radio-frequency domain are performed using the Gorter-Casimir expression for X_L(t) and give the same λ₀ value for both devices     

Analysis of a multiple-beam waveguide for free-space transmissionof microwaves

The transmission of several quasi-optical beams via one system of oversized focusing mirrors is discussed. The analysis of this multiple-beam waveguide shows that such a system can substantially reduce the total mirror surface compared to the corresponding number of individual lines. With the help of analytic coupling coefficients for Gaussian beam modes deduced from the coupling integrals, configurations of four mirrors are found, which give low losses due to the reconversion of spurious modes generated at the different mirrors. Optimization of the mirror surfaces as a function of system parameters is performed and expressions for the loss as a function of the number of transmission channels are deduced. The results are confirmed by diffraction calculations and laboratory scale experiments. The application to a high-power system promises a very efficient transmission with high mode purity     

In-situ nanoindentation of epitaxial TiN/MgO (001) in a transmission electron microscope

The deformation behavior of the epitaxial TiN/MgO (001) thin film/substrate system was studied through in-situ nanoindentation in a transmission electron microscope (TEM). The required sample geometry was prepared using Ga⁺ focused ion beam (FIB) etching. During room-temperature indentation, both the TiN film and the MgO substrate deformed through the motion of dislocations. The result was a localized hemispherical plastic zone in the TiN film directly under the indentation contact area, forming an 8° tilt boundary. These results show directly that small-scale plasticity in TiN can occur at room temperature through the motion of dislocations.