Crystal structure of aluminium containing superconducting oxides: single crystal study of GdBa2Cu3−x AL x O6.88 (x=0.28) and ErBa2Cu3−y Al y O6.6 (y=0.14)

Following the discovery of the high temperature super-conductivity in YBa₂Cu₃O_7– (T _c 93 K) [1] it has been found that Y atoms can be substituted entirely by almost all of the rare-earth elements, except for Ce, Pr, and Tb, without changing the superconducting properties appreciably [2, 3]. The magnetic moments carried by the rare-earth atoms have apparently no influence on the superconducting properties. In Nd-, Sm-, Gd-, Dy- and Er-based compounds the rare earth moments order at low temperatures (0.025–2.2 K) [4–8] and the ordered antiferromagnetic state coexists with the superconducting state. We have investigated the antiferromagnetic ordering of these compounds by neutron diffraction both on powder and single crystal samples obtained from several laboratories [8–10]. Magnetic structures of all these compounds consist of antiferromagnetic (001) planes stacked ferro- or antiferromagnetically. There have been some controversies as to the stacking of antiferromagnetic (001) planes in GdBa₂Cu₃O_7–.     

Defects in pulsed laser and thermal processed ion implanted silicon

The evolution of the nature and concentration of the defects produced by 100 or 300 keV As ions at fluences 1 to 4×10^–12 cm^–2 inn-type, Fz Silicon doped with 10¹⁵ to 10¹⁶ cm^–3 has been studied as function of thermal treatments (in the range 500°–900 °C) and of the energy density (in the range 0.3–0.6 J cm^–2) of a light pulse from a ruby laser (15 ns, 0.69 m). Deep-level transient spectroscopy (DLTS) combined with capacitance — voltage (C-V) measurements were used to get the characteristics (energy level, crosssection for the capture of majority carriers) of the defects and theirs profiles. The difficulties encountered in the analysis of the results, due to the large compensation of free carriers in the implanted region and to the abrupt defect and free carrier profiles, are discussed in detail and the corrections to apply on the C-V characteristics and the DLTS spectra are described. The defects resulting from the two types of treatments are found to be essentially the same. Only, for laser energies higher than 0.5 J cm^–2, the laser treatment appears to introduced new defects (atE0.32 eV) which should result from a quenching process. The fact that a laser energy smaller than the threshold energy for melting and recrystallization is able to anneal, at least partially, the defects produced by the implantation, demonstrates that the annealing process induced by the laser pulse is not a purely thermal process but is enhanced by a mechanism involving ionization.     

Bromoacyl Analogs of Pyrene–Containing Phosphatidylcholine as New Fluorescent Lipid Probes with Intramolecular Quenching

Two new derivatives of phosphatidylcholine with an intramolecularly quenched fluorescence, namely, 1––bromoundecanoyl–2–[4–(pyren–1–yl)butyroyl]–sn–glycero–3–phosphocholine (BPPhC) and 1–(9,10–dibromostearoyl)–2–[4–(pyren–1–yl)butyroyl]–sn–glycero–3–phosphocholine (DBPPhC), have been obtained by replacing acyl chains by residual pyrenebutyric and bromine–labeled fatty acids. Their structure has been verified by the ¹H–NMR method and the spectral properties have been characterized in media of different polarity with the aid of absorption and fluorescent spectroscopy. It has been established that when BPPhC and DBPPhC are included in liposomes, the intensity of their fluorescence changes markedly as a function of the physical state of the bilayer, which makes it possible to use the compounds obtained as lipid probes for investigating the properties of biological and artificial membranes.     

Generation of picosecond pulses in solid-state lasers using new active media

Results are reported of investigations aimed at generating nanosecond radiation pulses in solid-state lasers using new active media having broad gain lines. Passive mode locking is accomplished for the first time in a BeLa:Nd³⁺ laser at a wavelength 1.354 m, and in a YAG:Nd³⁺ laser on a 1.32–m transition. The free lasing and mode-locking regimes were investigated in an alexandrite (BeAl²O₄:Cr³⁺) laser in the 0.72–0.78–m range and in a synchronously pumped laser on F 2- centers in LiF in the 1.12–1.24–m region. The features of nonlinear perception of IR radiation by the eye, using a developed picosecond laser on F₂ ^– centers, are investigated for the first time.Translated from Lazernye Sistemy, pp. 67–86, 1982.     

Type N solutions of the vacuum scalar-tensor field equations

All solutions of the vacuum relativistic scalar-tensor field equations R=–,, are given in the case where the Weyl tensor is of Petrov-Penrose type N. These eight solutions are listed according to the Petrov-Plebaski classification of their trace-free Ricci tensor components and belong to the three classes[T–3S]_[1–1] (R,N), [3T–S]_[1–1](R,N) and [4N]_[2](O,N).     

Injection lasers in the 1.3–1.8 μm wavelength range

Conclusion There are developed techniques for the preparation of diode lasers in the 1.3 to 1.8 m range on the basis of quaternary epitaxial heterostructure. Devices for a particular wavelength of 1.3 m are now commercially available. The state of art in the laser studies with connection to lower room-temperature threshold and to higher operation temperature is illustrated in fig. 9. We feel that the laser system of InGaAsP, which is known since 1974 [1, 2], may be elaborated further for higher laser characteristics in spite of the fact that present state is quite acceptable for different applications. There are many fibre-optics projects based on the conception of laser optical communication with the use of diodes in the range of 1.3–1.8 m.Invited talk at the International Conference on Radiative Recombination and Related Phenomena in III–V Compound Semiconductors, Prague, 4–7 October, 1983.The author is indebted to Dr. L. M. Dolginov, B. N. Sverdlov, A. E. Drakin, P. A. Louk, E. G. Shevchenko for the help in this work.     

Thepin structure employed as current amplifier

Injection of excess carriers into thei region of a forward biasedpin diode diminishes proportionally its resistivity (primary circuit). Resistivity variations in thei region are used to control higher currents and powers in the secondary circuit. This basic idea is developed quantitatively for a simplified symmetrical model of thepin structure in a stationary regime and then generalized for the asymmetrical case. The frequency characteristics of the electronic device are studied. For demonstration of the theoretical results thepin structure in silicon with known parameters is used.Notation 2d [m] length ofi region - D [m² s^–1] ambipolar diffusion constant - e [C] electron charge - E ₂ [Vm^–1] electric field strength iny direction - i ₁ [Am^–2] current density inx direction - i ₂ [Am^–2] current density iny direction - i _m [Am^–2] current density due to recombination of carriers ini region - i _1ef ,i _2ef [Am^–2] effective values of currentsi ₁,i ₂ - i _ns ,i _ps [Am^–2] saturated current densities from the heavily dopedn, p regions - i intrinsic region - I [A] total current throughp-n junction - I ₁ [A] total current in pin diode - I ₂ [A] current in secondary circuit - k[J grad^–1] Boltzmann's constant - L=(D) [m] ambipolar diffusion length of carriers in middle region - n(x) [m^–3] excess electron concentration in middle region - ¯n [m^–3] average value of electron concentration in middle region - n _i [m^–3] intrinsic electron concentration - n _A [m^–3] acceptor concentration inp region - n _D [m^–3] donor concentration inn region - p(x) [m^–3] excess hole concentration in middle region - q [m²] area of electrodes 3 and 4 - Q [C] charge stored ini region - R [m^–3 s^–1] recombination rate - s [m] width of diode - t [m] thickness of diode - T [K] absolute temperature - U [V] voltage acrossp-n junction - U ₁ [V] voltage acrosspin diode - U ₂ [V] voltage across terminals of secondary circuit - U _m [V] voltage drop acrossi region - V _D [V] voltage drop acrossn — i andp — i junctions at zero load - W ₁ [W] power inpin diode circuit - W ₂ [W] power in secondary circuit - x [m] distance from center of diode - coefficient in current amplification factor - [rad] phase shift of diode current with respect to applied voltage - [s] life time of excess carriers ini region - [m² V^–1 s^–1] carrier mobility ini region in the symmetrical model - _n [m² V^–1 s^–1] electron mobility ini region - _p [m² V^–1 s^–1] hole mobility ini region - [^–1 m^–1] conductivity     

Low temperature magnetic ordering of a series of structurally characterized chloroferrates

Iron-57 Mössbauer spectroscopic results for a new series of related chloroferrate salts of complex ammonium cations are presented. In particular, spectra of materials based on FeCl ₄ ^– , FeCl ₅ ^2– , FeCl ₆ ^– , [FeCl₅(H₂O)]^2–, and [FeCl₅(CH₃OH)]^2– anions are discussed relative to the systematics of their isomer shifts, coordination numbers, and low temperature 3D critical ordering temperatures. The following specific systems have been studied by Mössbauer spectroscopy and definitively characterized by single-crystal X-ray analysis: [CH₃NH ₃ ⁺ ]₄[FeCl₆]^3–[Cl^–](A), [Me₂N(-CH₂CH₂)₂NMe ₂ ⁺ ][FeCl ₅ ^2– ] (B), [H₃NCH₂CH₂NH ₃ ²⁺ ][FeCl₅·H₂O^2–], (C), and [NH₃(CH₂)₆NH ₃ ²⁺ ]₄[(FeCl ₆ ^3– )(FeCl ₄ ^– )ClCl ₄ ^– ] (D). The spectral data for these complexes are considered in the light of results of previous studies for systems such as [K₂FeCl₅·H₂O], [Co(NH₃)₆][FeCl₆], diamethyltriethylenediammoniumpentachloroferrate (E), and the related [FeCl₅·CH₃OH]^2– salt (F). The critical 3D ordering temperatures are 1.45, 6.80, 3.45, and 1.22K forA, B, C, andD, respectively.     

Recent progress with the CO-overtone Δv=2 laser

We report the recent progress in the performance of the CO-overtone v=2 laser. We were able to increase both the number of lines and the output power by a significant amount. This laser is now a reliable source for spectroscopic applications in the spectral region from 2500–3800 cm^–1. The typical parameters of the laser plasma and a table with the observed laser transitions and their frequencies are given.     

Injection lasers based on AlGaAsSb/GaSb and InGaAsSb/GaSb heterostructures

The isoperiodic heterostructures AIGaAsSb/GaSb and InGaAsSb/GaSb and injection lasers based on them are investigated. It is shown that in the heterostructures of the first type it is possible to obtain very low threshold currents at room temperature at wavelengths 1.72–1.78 m. Analysis of the experimental data and interpolation characteristics show that considerable optical confinement in the investigated heterostructures of the first type. Estimates show that the minimum threshold current in heterolasers for the spectral range 1.75–1.78 m is approximately 1 kA/cm². An investigation of the InGaAsSb/GaSb heterostructures shows that a case unusual for heterostructures of III-V compounds is realized in them when the material indicated has a smaller refractive index than the wideband layers. The antiwaveguide anomaly may be useful for the development of laser structures of new types.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva, Vol. 141, pp. 46–61, 1983.     

Radiation of an electric dipole located on the “Coastline”

The radiation characteristics of a vertical electrical dipole located in a narrow transition domain with a different law of impedance variation, as calculated from [4] and [5], are compared with the results in [2]. The sense of the solutions formally obtained earlier is discussed [1, 2]. The process of radiowave propagation along tracks inclined slightly to the coastline is investigated numerically.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 91–95, September, 1972.     

Luminescence Properties of New Fused Benzothiophene Derivatives and Their Conductive Oligomers Structural and Solvent Effects

The structural and solvent effects on the electronic absorption and fluorescence spectra, and fluorescence quantum yields, of four new fused benzothiophene derivatives, including benzothieno[3,2b]-thiophene (BTT), benzothieno[3,2-b]benzothiophene (BTBT), 6-methoxy[1]benzothieno[3,2b]-thiophene (MeOBTT), and benzothieno[3,2-b]indole (BTI) were investigated at 295 K. The luminescence properties of the corresponding conductive oligomers, poly(BTT) and poly (MeOBTT), electrosynthesized in acetonitrile, were also studied. Satisfactory McRae, Suppan, and Kawski-Chamma-Viallet solvatochromic correlations were established for the four monomers in most solvents. A weak negative solvatochromic behavior was found for these compounds, indicating that their dipole moments are slightly lower in the excited singlet state than in the ground state. Kamlet-Abboud-Taft multiparametric correlations were also obtained for absorption and fluorescence wave numbers and quantum yields, demonstrating the existence of specific solute-solvent interactions. In the case of the oligomers, important red-shifts of the fluorescence emission maxima ( 90–110 nm) relative to the corresponding monomers were observed, which shows the extent of conjugated segments in the oligomer chains.     

Integration of GaN thin films to SiO2–Si(100) substrates by laser lift-off and wafer fusion method

A process methodology has been adopted to bond GaN thin films to Si(100) substrates using the combination of laser lift-off and direct wafer fusion. Using optimum excimer laser conditions, 2–10 μm of GaN is lifted-off from sapphire. The lifted-off thin film is cleared from gallium residual and then suitably treated in a hydrofluoric, nitric and acetic acid mixture to render the surface hydrophilic. This treatment provides van der Waals bonds to immediately contact bond with SiO₂–Si(100) substrate at room temperature. The bonds are further strengthened by a high temperature annealing at 650 C for 2 h. The structural and mechanical characteristics of the bonded structure reveal uniform and high quality bonding. The optical characteristics of the transferred bonded film on SiO₂–Si(100) substrate exhibit similar properties to that of GaN on sapphire. In a similar manner, high-brightness blue LEDs were transferred from sapphire to SiO₂–Si(100) substrate with no deterioration in the electrical and optical performance of the device.     

Tunable UV laser photolysis of organometallics with product detection by laser mass spectroscopy: Trimethylaluminum

We use tunable UV laser light in the region 200–320 nm, produced by frequency doubling the output of a dye laser, for the decomposition of organometallic compounds. This method has been applied to TMA, trimethylaluminum Al(CH₃)₃. Only the TMA monomer absorbs UV light for >220 nm. TMA decomposes by one-photon absorption mainly into two channels: aluminum atoms Al plus organic fragments, and aluminummonomethyl AlCH₃ molecules plus organic fragments. The ratio [Al]/[AlCH₃] is wavelength dependent. We present a mechanism to explain the photolysis of trimethyl compounds of group III elements (Al, Ga, In).     

Observation of sub-Poisson field in a gas laser with feedback

Conclusions The author's earlier work [6, 7] has demonstrated the feasibility in principle of controlling the statistics of laser emission using photoreceiver—pump feedback, and the photodetector photocurrent in the FB circuit was made lower than the SN level, i.e., sub-Poisson fields with values _in+ [6] and ₊ [7] was observed. The experimental results can be adequately described by using the balance equations.Presented at the International Workshop on Squeezed and Correlated States, Moscow, December 3–7, 1990.     

Synthesis and Reactivity of Mg(II)–Fe(II)–Fe(III) Hydroxycarbonates

Green rust-like compounds (GRs) were discovered as natural minerals in various hydromorphic soils, where anoxic conditions allow their stability. They may control some redox processes in aquifers and participate to the transformation of various pollutants. Since Mg(II) cations are present in the fields where GRs were discovered, a partial substitution of Mg(II) to Fe(II) leading to intermediate compounds between GRs and usual Mg(II)–Fe(III) hydroxysalts is suspected. Mg(II)–Fe(II)–Fe(II) hydroxycarbonates can be obtained as intermediate oxidation products of (Mg, Fe)(OH)₂ in carbonate-containing aqueous media obeying to [Fe^II _4(1–x)Mg^II _4x Fe^III ₂(OH)₁₂]²⁺ [CO₃ ^2– nH₂O]^–2. TMS spectra at 12 K are similar to those of GRs, i.e., two quadrupole doublets, one due to Fe(II) with a large isomer shift =1.29 mms^–1 (with respect to -iron at room temperature) and quadrupole splitting E _Q=2.76 mms^–1, the other one due to Fe(III) with smaller hyperfine parameters =0.49 mms^–1 and E _Q=0.44 mms^–1. Fe(II) ions oxidise rapidly into Fe(III) with dissolved O₂. The reactivity is similar to that of Fe(II)–Fe(III) hydroxysalts GR, and thus the potential of Mg(II)–Fe(II)–Fe(III) compounds for reducing pollutants.     

Improving the beam quality of solid-state systems using both outside and inside cavity devices with variable optical characteristics along the cross section

This paper presents the results of application to different laser installations of soft or apodized apertures (AA) [1–3] with smooth transmission profiles decreasing from center to edges. Two types of AA, which were made of CaF₂:Pr crystals, have been used: induced absorption (IA) AA and photooxidation (PhO) AA. The 3–45-mm-diameter IA and PhO AA with smooth monotonic flat-top profiles have been used in 1.06-m laser amplifier systems to suppress hard-edge Fresnel diffraction rings in beam cross section and to increase the second harmonic conversion efficiency. The 3–4-mm-diameter PhO AA with bell-like transmission profiles were placed inside the 2.94-m and 1.06-m resonators of master oscillators. The tendency of the output energy to increase by 1.3–1.8 times and the decrease in beam divergence in single-mode lasing as compared with a hard-edge aperture have been observed in the experiments described below.Institute of Radioengineering and Electronics, Academy of Sciences of the USSR. Institute of General Physics, Academy of Sciences of the USSR. Translated from Preprint No. 17 of the Institute of General Physics, Moscow, 1991.     

Submillimeter laser action of CW optically pumped CF2Cl2 (Fluorocarbon 12)

Eleven new CW far infrared (FIR) laser lines have been observed in the 600 m–1200 m range from the CF₂Cl₂ (Fluorocarbon 12) molecule optically pumped by a CO₂ laser. A 510^–4–10^–3 accuracy is achieved in the measurement of the FIR wavelengths.The frequency offset between the CO₂ pump center and the absorption line centers are measured using the transferred Lamb dip technique. Owing to a recent spectroscopic study of the CF₂ ³⁵Cl₂ molecule three lines may be assigned with great confidence as rotational transitions in thev ₆ vibrational band 923 cm^–1 of this main isotope.     

Some optimum parameters of golay detector of infra-red radiation

The relation for the sensitivity of the pneumatic detector based on the analysis of the thermal, pneumatic and optical parts of the instrument is derived. From this relation the optimum diameter of the flexible mirror and the optimum gas pressure in the detector cell are calculated.List of symbols used B brightness [sb] - C thermal capacity of absorbing membrane [cal cm^–2 grad^–1] - c specific heat of gas in cell [cal g^–1 grad^–1] - D diameter of grid [cm] - d diameter of flexible mirror [cm] - E illumination [ph] - F ₂ area of light spot [cm²] - F ₃ area of flexible mirror [cm²] - f,f ₁ focal distance [cm] - f ₀ chopping frequency of infra-red radiation [sec^–1] - h depth of cell [cm] - k radiation cooling constant [cal cm^–2 sec^–1 grad^–1] - k ₀ reflectivity of flexible mirror - k ₁,k ₂,k ₃,k ₄ constants - L total length of edge of half of grid [cm] - l distance between lens and flexible mirror [cm] - M, N constants - m refractive power of flexible mirror [cm^–1] - n number of grammolecules of gas in cell - P radiative power [cal sec^–1] - p,p ₀,p pressure, atmospheric pressure, change in pressure [dyne cm^–2] - R gas constant [erg grad^–1] - r coordinate - r ₀ radius of flexible mirror [cm] - r ₁,r ₂ radii of beam of rays [cm] - t tension of flexible mirror [dyne cm^–1] - , T, T _f absolute temperature and its change [grad] - V, V volume and increase in volume [cm³] - v coordinate - v ₀ maximum height of deflection of flexible mirror [cm] - x, x distance of object and image from focal planes [cm] - , angles - specific weight of gas at pressure of 1 atm. [g cm^–3] - absorption coefficient of infra-red radiation - thermal conductivity of gas [cal cm^–1 sec^–1 grad^–1] - v number of lines of grid per 1 cm [cm^–1] - radius of light spot on grid [cm] - T time constant [sec] - ₀, ₁, ₂, ₃ light flux and its change [lm]