Structural analysis of Ti-Fe thin films prepared by pulsed laser deposition

Titanium iron oxide (Ti-Fe-O) thin films have been successfully deposited by pulsed laser deposition (PLD). Experiments were carried out by using some targets. One was a Ti-50 at.% Fe-sintered target, while the others were Ti and Fe plates with various surface area ratio [S_R=S_Fe/(S_Fe+S_Ti)] from 30 to 70%. The thin films were analyzed by X-ray diffractometry, Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy (TEM). From XRD analysis, the main phase in the thin films deposited at S_R=30 and 50% was β-Ti (Fe). By increasing S_R to 70%, the main phase of the thin film changed to TiFe. By phase diagram, composition of TiFe must be between Ti-47.5-50.3 at.% Fe at a temperature of 1085 °C. However, the composition of the thin film deposited at S_R=70% was found to be Ti_0.15Fe_0.62O_0.23. Thus, the composition of Fe in the thin film was much greater than the solubility limit. This fact suggests two possibilities. One is that the thin films, which we have deposited, were in a metastable state. The other is that metal oxides of amorphous state could be contained in the thin film.     

Synthesis of ZnFe2O4 nanosized powders by pulsed wire discharge

Nanocrystalline zinc ferrite (ZnFe₂O₄) powders have been synthesized successfully by high-power short-pulse electric discharge of Fe and Zn wires in oxygen gas. The powders were characterized by X-ray diffraction and transmission electron microscopy (TEM). Mean size of the obtained particles determined by both BET and TEM was 12 to 56 nm depending on the oxygen pressure. X-ray analysis showed that the zinc ferrite spinel was clearly obtained. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(450), pp. 3–6, July–August, 2006.     

Demonstration of a 77-GHz heterojunction bipolar transferredelectron device

We demonstrate for the first time a heterojunction bipolar transferred electron device (HBTED), a device with a bipolar transistor-like structure in which Gunn oscillations occur. The use of a graded doping profile in the collector region is, we believe, a key factor in the device design. AlGaAs/GaAs HBTEDs fabricated on semi-insulating GaAs substrates exhibit free-running oscillations at a frequency of around 77 GHz. The third (emitter) terminal enables this device to be injection-locked and to function as a self-oscillating mixer     

Room temperature operation of GaInAs-GaInAsP-InP SCH multiquantum-film laser with narrow wire-like active region

GaInAs-GaInAsP-InP SCH (separate-confinement heterostructure) multiquantum-film lasers with approximately 100-nm-wide wirelike active regions were fabricated by two-step low-pressure organometallic vapor-phase epitaxy (LP-OMVPE) growth and wet chemical etching and operated at room temperature. An increase in the threshold current density in such lasers was drastically reduced by using a preheating process in hydrogen atmosphere and a thin InP cover layer growth prior to the regrowth of a GaInAsP optical confinement layer. The fabrication processes presented can be very effective for realization of room-temperature operation of long-wavelength quantum-wire and quantum-box lasers based on GaInAs-InP materials.<>     

Advanced semiconductor lasers

Recent research activities in the field of advanced semiconductor lasers are reviewed with emphasis on highly stable single-wavelength lasers and surface-emitting (SE) lasers for wideband lightwave communication systems and optical parallel information processing. The operational characteristics of DSM (dynamic single-mode) lasers are summarized and requirements for high-performance operation as light sources for high-speed transmission or coherent communications are described. A type of DSM laser called the distributed-reflector (DR) laser is described as an advanced DSM laser which enables high efficiency, high power, and narrow linewidth operations. Specific features and the potential of SE lasers are summarized. Research activities and remaining problems to be solved for a breakthrough in optical parallel information processing are presented. The potential of multidimensional quantum-well structures, such as QW lasers and quantum-box lasers, is discussed in terms of superior characteristics in both stationary and dynamic operations. The present fabrication technologies for realizing high-performance lasers based on multidimensional QW structures are also presented     

Low-threshold-current CW operation of 1.5 ?m GaInAsP/InP bundle-integrated-guide distributed-Bragg-reflector (BIG-DBR) lasers

Low-threshold-current and high-power operation of 1.5 ?m GaInAsP/InP bundle-integrated-guide (BIG) DBR lasers were obtained. A single-mode operation temperature range of more than 70 deg was demonstrated around room temperature by shortening the active region to 100 ?m. The modulation characteristic was measured up to 2 GHz with a modulation depth of 100%. A maximum value of dynamic wavelength shift was 2 ? at 1.2 times threshold current.     

Gain and the threshold of three-dimensional quantum-box lasers

Gain and threshold current density are analyzed for quantum-box lasers where electrons are confined in quantum well three-dimensionally, based on the density-matrix theory of semiconductor lasers with relaxation broadening. The electronic dipole moment and its polarization dependence are first analyzed, and it is shown that the gain becomes maximum when the electric field of light is parallel to the longest side of the quantum box. Calculated gain is about 10 times that of bulk crystal for 100 Å × 100 Å × 100 Å GaAs/Ga0.8Al0.2As quantum box, and 15 times for Ga0.47In0.53As/InP quantum box with the same size, respectively. The threshold current density are 45 A/cm²and 62 A/cm²for GRINSCH GaAs/(Ga0.8Al0.2As-Ga0.4Al0.6As) and Ga0.47In0.53As/(Ga0.28In0.72As0.6P0.4-InP), respectively, where for the GaInAs/ GaInAsP/InP system the intervalence band absorption and nonradiative recombinations have been assumed to be the same as those obtained for bulk crystals experimentally. These results show the possibility of remarkable reduction in the laser threshold by the quantum-box structures.     

One-pot synthesis of hierarchically macro/mesoporous Al2O3 monoliths from a facile sol–gel process

Based on the preparation of ordered mesoporous Al₂O₃ powder using P123/isopropoxide aluminum/HNO₃ reaction system, hierarchically macro/mesoporous alumina monoliths were successfully fabricated by introducing PEG8000 as the phase-segregation initiator to generate macropores. The effects of PEG8000 and P123 contents on the monolithic and hierarchical morphology were investigated systematically. With appropriate selection of the starting composition, monolithic skeletons with bimodal macropores interconnected by mesostructured walls can be synthesized in both the dried gels and calcined samples. The well-defined macropores are in close-celled structure dispersed in large-sized mesoporous matrix. The mesopore size can be regulated by adjusting the PEG8000 content while its shape is governed by P123 content. The well-developed alumina monolith, MMA-P20, exhibits high surface area of 287 m²/g and narrowly distributed mesopores with median size of 13 nm after calcinaton.