Light‐induced degradation in indium‐doped silicon

Light‐induced degradation of charge carrier lifetime was observed in indium‐doped silicon. After defect formation, an annealing step at 200 °C for 10 min deactivates the defect and the initial charge carrier lifetime is fully recovered. The observed time range of the defect kinetics is similar to the well known defect kinetics of the light‐induced degradation in boron‐doped samples. Differences between defect formation in boron‐ and indium‐doped silicon are detected and discussed. A new model based on an acceptor self‐interstitial A_Si–Si_i defect is proposed and established with experimental findings and existing ab‐initio simulations.

     

Pure nuclear reflexes and combined hyperfine interactions in YIG

Mössbauer spectra of oriented YIG single crystals were taken and the numerical analysis using the transmission integral yielded a consistent set of hyperfine interaction parameters. They are in good agreement with theoretical values obtained by MO-calculations which included clusters up to 62 ions. Finally pure nuclear reflexes are predicted for single crystals and two theoretical spectra are given.Dedicated to U. Gonser on his 60. birthday     

Investigation of metallization schemes for high temperature devices based on silicon carbide

The suitability of several metallization schemes for high temperature sensors and devices based on silicon carbide was investigated. Auger electron spectroscopy (AES) depth profiling was used for the detection of possible interface reactions and thermal induced diffusion processes. Changes in the structure of the films under the influence of high temperature were observed by transmission electron microscopy (TEM). The maximum operation temperature for the metallization with aluminum as coverlayer was found at 450?°C. The ability of gold with underlying tungsten nitride as diffusion barrier to work at temperatures above 450?°C was shown.     

The precise compleximetric titration of uranium(vi)

The compleximetric reaction of uranium (VI) with EDTA has been studied. A method is described for determining uranium(VI) with PAN as an indicator and without an indicator by titration in the ultraviolet region. With the described technique, quantities of uranium varying from 12 μg to 9 mg can be determined. The coefficients of variation vary from 5 % to 0.1 %, respectively.     

Synthesis, spectroscopy, and theoretical calculations for a series of push-pull [14]-pyridoannulenes

Three new isomeric dipyridoannulenes were synthesized and characterized. These molecules possess differing conjugation pathways between the substituent alkoxy donating groups and the pyridyl acceptor groups. Optical absorption and emission properties of the dipyridoannulenes and their corresponding acyclic precursors were measured and correlated to structural differences and used to evaluate conjugation effectiveness and charge-transfer pathways. Optical properties of protonated dipyridoannulenes were also measured and found to be somewhat insensitive to the degree of protonation. Density functional studies of these systems at the B3LYP/6-31G* level provided insight into their stabilities, polarities, and quinoidal character. An analysis of the HOMO and LUMO molecular orbitals provided further information regarding charge-transfer behavior. These systems are good metal binding candidates, as the pyridine moiety can act as both an electron-acceptor and a site for metal coordination.     

RF artifacts caused by metallic implants or instruments which get more prominent at 3 T: an in vitro study

Metallic devices with high electrical conductivity inside or adjacent to the body might lead to marked alterations of the RF amplitude B1 in the tissue under investigation, especially at increased RF frequency, and if specific conditions for electromagnetic resonance are fulfilled. RF-metal interaction effects were investigated systematically at B0=0.2, 1.5 and 3 T analyzing correlated image artifacts for copper wires (d=1 mm, L=53 and 27 cm), and for following instruments and implants made of titanium or nitinol: biopsy needles, hip prostheses, vascular stents and aneurysm clips. The samples were examined in Gd-DTPA-doped 140 mM NaCl solution using spin-echo (SE) sequences with high readout bandwidth. Automatic transmitter adjustment V(T,auto) and manually reduced transmitter voltage VT were applied in order to detect B1 enhancement. At 0.2 T, beyond the shielding of the luminal region of the stents, no RF effects were observed. At 1.5 T, the copper wires caused distinct RF artifacts. At 3 T, RF artifacts also appeared for the hip prostheses and the biopsy needles. Stents with pronounced luminal shielding at lower field strength revealed marked B1 enhancement close to their outer surface.     

Assignment of the four lowest ionized states of p-benzoquinone and the question of “lone pair splitting” in this system

The lowest ionized states of p-benzoquinone are assigned to be n_/²B_3g, n₄/²B_2u, π₁/²B_3u, and π₂/²B_1g in order of increasing energy. This sequence of states confirms Turner's original assignment and invalidates subsequent proposals. The origin of the difficulties with these assignments are traced back to the non-validity of Koopmans' theorem for the “oxygen lone pair” ionizations (i.e., ionization to the n_/²B_3g and n₊/²B_2u states).     

Zur Kenntnis der Zellulosefasern

Zusammenfassung Bei Verwendung gereinigter, hochmolekularer Zellulosen wurde festgestellt, daß die Xanthogenierung in heterogener Phase höchstens bis zu einer-Zahl von 75–80 fortschreitet. Gegenwart überschüssiger flüssiger Phase läßt höhere Xanthogenierungsgrade erhalten.Zellulosen mit einem DP über 1000 sind erst dann zu klaren Viskosen löslich, wenn die-Zahl 50 überschreitet.Der erhaltene höchste Xanthogenierungsgrad ist abhängig vom Abpreßgrad, bzw. der Gegenwart genügender flüssiger Phase. Im Falle der Xanthogenierung in Emulsion genügt bereits eine Alkali-Konzentration von etwa 10%, bei der noch keine Alkali-Zellulose I gebildet wird, um klar lösliche Viskosen zu erhalten.Beim Waschen von Xanthogenaten mit Methanol bzw. Äthanol wird überschüssiges Alkali zurückgehalten. Vergleich der Werte zeigt, daß die Summe der durch Xanthogenierung und durch Alkali besetzten Stellungen des Moleküls etwa mit den erreichbaren-Zahlen übereinstimmen.Bis zu-Zahlen von etwa 75 erfolgt die Xanthogenierung, ohne daß zusätzliche kristalline Bereiche geöffnet werden, also intermizellar.