Broad-band light-emitting diode for 1.4-2.0 μm usingvariable-composition InGaAs quantum wells

We describe a novel broad-band light-emitting diode employing InGaAs quantum wells with different bandgaps. The device structures were grown by molecular-beam epitaxy on InP substrates and consist of three In_xGa_1-xAs quantum wells (x=0.4, 0.53, and 0.66) imbedded in the p-doped region of an InAlAs p-n junction diode. Electrons injected into the p-region are captured into the wells and recombine with holes to produce radiation at the three bandgap wavelengths. Broad-band emission over a large wavelength range (1.4-2.0 μm) is easily achieved with this approach. These novel solid-state sources have a variety of potential applications, for example, in miniature spectrometer and sensor systems     

Bnfluß des Kohlenstoffgehaltes von 0,015 bis 1 % und der Gefügestruktur auf das Hochtemperaturfestigkeits- und -zähigkeitsverhalten von Baustählen nach der Erstarrung aus der Schmelze

Bestimmung der Festigkeit und Brucheinschnürung sowie der Gefügestruktur an Baustählen mit Kohlenstoffgehalten zwischen 0,015 und 1 % im Temperaturbereich von Liquidustemperatur bis 900 °C. Aufnahme von Kenngrößen zur Beurteilung der Innenrißanfälligkeit beim Stranggießen. Ursachen für das unterschiedliche Verformungsverhalten.     

Molecular beam epitaxy and characterization of Al x Ga1-x As y Sb1-y (0.0 ≤x ≤ 1.0) lattice matched to InAs substrates

We report the molecular beam epitaxial growth of Al _x Ga_1-x As _y Sb_1-y (0.0 ≤ x ≤ 1.0) on undoped, liquid-encapsulated Czochralski, (100) oriented InAs substrates. The degree of lattice mismatch was determined by x-ray diffraction. The lattice matched materials (y ≈ 0.08 + 0.08x) were characterized by low temperature photoluminescence, electro-reflectance, and capacitance-voltage measurements. The experimental bandgap energies agree with earlier experimental results for Al _x Ga_1-x Sb, and also with a self-consistent first principles pseudopotential model. The capacitance-voltage measurements indicate background acceptor concentrations for the unintentionally-doped epitaxial layers of about 2 × 10¹⁵ cm^-3 atx = 1.0 to 5 × 10¹⁶ cm^-3 atx ≈ 0.0.     

Corrosion of synthetic metals

Intrinsically conducting polymers as polypyrrole or polythiophene are new materials which have found widespread interest in the last ten years. Acceptor type doping leads to a solid, which is well comparable to graphite salts. For any kind of practical application of these polymers, the problem of adequate long term stability under environmental conditions must be solved. There are only a few measurements of conductivity vs. time in the air to derive conclusions in this direction, e.g. for polypyrrole. For the first time we present results of a systematic research into the understanding of corrosion phenomena, which occur in aqueous eletrolytes at different pH. Polypyrrole is selected as a well established candidate for a synthetic metal. Layers at a nominal thickness of 10μm on platinum, doped with BF₄^? anions, were investigated in aqueous buffers in the pH-range of 1–13. Corrosion was determined via the measurement of the residual redox capacities. The material corroded after a rapid electrochemical mechanism and a relatively slow chemical mechanism. Both processes involve the radical cationic centers (polarons) in the solid. The time constants varied from 10² to > 10⁸ s. Our findings allow for a better understanding of corrosion and selfdischarge of polypyrrole. Other conducting polymers were found to corrode after the same mechanism.     

Einfluß der Austenitausscheidung auf die Sensibilisierung eines Duplexstahls gegenüber interkristalliner Korrosion

Der Einfluß der Austenitausscheidung auf die Sensibilisierung gegenüber interkristalliner Korrosion wird an einem Duplexstahl Cr-Ni (24,4–7,4 %) untersucht. Zuvor wurden die Walzzustandsmorphologie des Duplexstahles durch thermische Behandlung zerstört und die Carbidausscheidungen in Lösung gebracht. Elektronenmikroskopie und Huey-Versuche verifizierten die Ergebnisse.