We report a comprehensive study of the growth dynamics in highly periodic, composition tunable InAsSb nanowire (NW) arrays using catalyst-free selective area molecular beam epitaxy. Employing periodically patterned SiO2-masks on Si (111) with various mask opening sizes (20–150 nm) and pitches (0.25–2 μm), high NW yield of >90% (irrespective of the InAsSb alloy composition) is realized by the creation of an As-terminated 1 × 1-Si(111) surface prior to NW nucleation. While the NW aspect ratio decreases continually with increasing Sb content (x Sb from 0% to 30%), we find a remarkable dependence of the aspect ratio on the mask opening size yielding up to ∼8-fold increase for openings decreasing from 150 to 20 nm. The effects of the interwire separation (pitch) on the NW aspect ratio are strongest for pure InAs NWs and gradually vanish for increasing Sb content, suggesting that growth of InAsSb NW arrays is governed by an In surface diffusion limited regime even for the smallest investigated pitches. Compositional analysis using high-resolution x-ray diffraction reveals a substantial impact of the pitch on the alloy composition in homogeneous InAsSb NW arrays, leading to much larger x Sb as the pitch increases due to decreasing competition for Sb adatoms. Scanning transmission electron microscopy and associated energy-dispersive x-ray spectroscopy performed on the cross-sections of individual NWs reveal an interesting growth-axis dependent core–shell like structure with a discontinuous few-nm thick Sb-deficient coaxial boundary layer and six Sb-deficient corner bands. Further analysis evidences the presence of a nanoscale facet at the truncation of the (111)B growth front and {1-10} sidewall surfaces that is found responsible for the formation of the characteristic core–shell structure.

High and low molar mass compounds containing the 3-alkyl-1,4-diaryIpentazadiene group were synthesized in the reaction of aromatic diazonium salts with primary amines. These high nitrogen compounds are characterised by high photosensitivity and thermostability. The photolytic decomposition was studied in detail with respect to the substitution at the aromatic moieties and at N3 of the pentazadiene chromophore. Electron donating aromatic substituents were found to increase photosensitivity and decrease thermostability whereas electron withdrawing aromatic substituents cause higher photolytic and thermolytic stability. A little influence of the alkyl group at N3 on the photosensitivity of the pentazadiene group was observed. Photolysis was investigated by means of UV/Vis spectroscopy and obeys first order kinetics for some compounds under investigation. Gel permeation chromatography (GPC) measurements during photolysis of pentazadiene polymers prove that irradiation with UV light causes irreversible chain degradation. Thermolysis in bulk was studied for all compounds by differential scanning calorimetry (DSC). In contrast to the results of the photolysis the alkyl substituent at N3 has an effect on the thermostability of the pentazadiene chromophore.

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Dedicated to Prof. Dr. R. Kerber on the occasion of his 70th birthday SUMMARY:Poly(diary1 diazosu1fide)s and model diary1 diazosulfides of the general structure aryl-N = N-S-aryl' are tested for their thermostability. Thermolysis in solution is followed by means of UV spectroscopy. At the beginning of the decay most model diazosulfides follow first-order kinetics, but show an acceleration of the decay rate in the further course of the thermolysis. In contrast to the models the decomposition of the corresponding polymers cannot be described by first-order kinetics, except one example (P 1).Thermogravimetry studies show weight losses of 8 -12% in the range between 80 and 150 "C depending on the structure of the models and polymeric diazosulfides. These values correspond with the content of azo function in these compounds, therefore it is assumed that nitrogen is split off under these reaction conditions. ZUSAMMENFASSUNG:Die Thermostabilitat von Poly(diary1 diazosu1fid)en und Diaryldiazosulfid-Modellsubstanzen mit der allgemeinen Struktur Aryl-N=N-S-Aryl' wird untersucht. Die Thermolyse in Ldsung wird mit UV-Spektroskopie verfolgt. Die meisten Modell-Diazosulfide folgen zu Beginn des Abbaus einer Kinetik erster Ordnung, zeigen aber im weiteren Verlauf der Thermolyse eine Beschleunigung der Abbaugeschwindigkeit. Im Gegensatz dazu kann die Zersetzung der entsprechenden Polymeren (aul3er im Fall von P 1) nicht durch ein Geschwindigkeitsgesetz erster Ordnung beschrieben werden. Thermogravimetrische Untersuchungen zeigen im Temperaturbereich von 80 bis 150 "C Gewichtsverluste zwischen 8 und 12'70, abhhgig von der Struktur der Diazosulfid-Modellsubstanzen bzw. -Polymeren. Die Werte entsprechen den Gehalten an Azo-Gruppen der Verbindungen, so da8 angenommen wird, da8 unter diesen Reaktionsbedingungen Stickstoff abgespalten wird.