Investigation of Al diffusion in different oxide thin-film layers by SNMS/HFM method

Depth profiles of Ga₂O₃/a-SiO₂/Al₂O₃- substrate, Ga₂O₃/a-Si₃N₄/Al₂O₃- substrate, and Ga₂O₃/Al₂O₃ substrate thin layers were determined by the SNMS/HFM method. Al diffusion from the Al₂O₃ substrate was investigated after 50, and in some cases after 600 hours of heat treatment time at different temperatures (600 °C,850 °C,950 °C,1050 °C and 1150 °C). The diffusion coefficient of Al at 850 °C was found to be D _Al=8.7 * 10^–18 cm²/s in amorphous SiO₂; D _Al=1.5*10^–17 cm²/s in amorphous Si₃N₄ and D _Al=5.5* 10^–16 cm²/s in Ga₂O₃ at 600 °C, respectively. The possible diffusion mechanism is explained in terms of the metal-oxygen bond-strengths. Although the studied materials have high resistivity at room temperature, the applied SNMS/HFM method has proven to be an efficient surface analytical tool even in these cases.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Tetrachlorinated Tetraazaperopyrenes (TAPPs): Highly Fluorescent Dyes and Semiconductors for Air‐Stable Organic n‐Channel Transistors and Complementary Circuits

A range of 2,9‐perfluoroalkyl‐substituted tetraazaperopyrene (TAPP) derivatives ( 1 – 5 ) was synthesised by reacting 4,9‐diamino‐3,10‐perylenequinone diimine (DPDI) with the corresponding carboxylic acid chloride or anhydride in the presence of a base. The reaction of compounds 1 – 4 with dichloroisocyanuric acid (DIC) in concentrated sulphuric acid resulted in the fourfold substitution of the tetraazaperopyrene core, yielding the 2,9‐bisperfluoroalkyl‐4,7,11,14‐tetrachloro‐1,3,8,10‐tetraazaperopyrenes 6 – 9 , respectively. The optical and electrochemical data demonstrate the drastic influence of the core substitution on the properties. All compounds are highly luminescent (fluorescence quantum yields of up to Φ=0.8). The LUMO energies of the tetrachlorinated TAPP derivatives (determined by cyclic voltammetry and computed by DFT calulations) were found to be below ?4 eV. In the course of this work the performance of TAPP derivatives in organic thin‐film transistors (TFTs) was investigated, and their n‐channel characteristics with field‐effect mobilities of up to 0.14 cm² V^?1 s^?1 and an on/off current ratio of >10⁶ were confirmed. Long‐term stabilities of 3–4 months under ambient conditions of the devices were established. Complementary inverters and ring oscillators with n‐channel TFTs based on compound 8 and p‐channel TFTs based on dinaphtho‐[2,3‐b:2′,3′‐f]thieno[3,2‐b]thiophene (DNTT) were fabricated on a glass substrate.     

A New Approach for the Photosynthetic Antenna–Reaction Center Complex with a Model Organized Around an s‐Triazine Linker

Two new artificial mimics of the photosynthetic antenna‐reaction center complex have been designed and synthesized (BDP‐H₂P‐C₆₀ and BDP‐ZnP‐C₆₀). The resulting electron‐donor/acceptor conjugates contain a porphyrin (either in its free‐base form (H₂P) or as Zn‐metalated complex (ZnP)), a boron dipyrrin (BDP), and a fulleropyrrolidine possessing, as substituent of the pyrrolidine nitrogen, an ethylene glycol chain terminating in an amino group C₆₀‐X‐NH₂ (X=spacer). In both cases, the three different components were connected by s‐triazine through stepwise substitution reactions of cyanuric chloride. In addition to the facile synthesis, the star‐type arrangement of the three photo‐ and redox‐active components around the central s‐triazine unit permits direct interaction between one another, in contrast to reported examples in which the three components are arranged in a linear fashion. The energy‐ and electron‐transfer properties of the resulting electron‐donor/acceptor conjugates were investigated by using UV/Vis absorption and emission spectroscopy, cyclic voltammetry, and femtosecond transient absorption spectroscopy. Comparison of the absorption spectra and cyclic voltammograms of BDP‐H₂P‐C₆₀ and BDP‐ZnP‐C₆₀ with those of BDP‐H₂P, BDP‐ZnP and BDP‐C₆₀, which were used as references, showed that the spectroscopic and electrochemical properties of the individual constituents are basically retained, although some appreciable shifts in terms of absorption indicate some interactions in the ground state. Fluorescence lifetime measurements and transient absorption experiments helped to elucidate the antenna function of BDP, which upon selective excitation undergoes a rapid and efficient energy transfer from BDP to H₂P or ZnP. This is then followed by an electron transfer to C₆₀, yielding the formation of the singlet charge‐separated states, namely BDP‐H₂P ^.+‐ C₆₀ ^.? and BDP‐ZnP ^.+‐ C₆₀ ^{. ?}. As such, the sequence of energy transfer and electron transfer in the present models mimics the events of natural photosynthesis.     

Isolated and solvated thioxanthone: a photophysical study

Quantum chemical methods have been employed to study the photophysics of thioxanthone in vacuum and various solvents. Structurally, the solvation leads to a lengthening of the carbonyl bond, whereas the benzene skeleton is mostly unaffected. This is mirrored by the larger blue shift of the (n(O)π*) states as compared to the red shift which the (ππ*) states undergo. For a proper understanding of the radiative and radiationless processes occurring, the excitation energy profile along a linearly interpolated path has been determined in various cases. The interesting interplay of excited states thus revealed, has been investigated to qualitatively suggest the relaxation pathways available (or dominant) in the cases under study. Rates for these processes have also been computed wherever possible.     

Electron Transfer between Hydrogen‐Bonded Pyridylphenols and a Photoexcited Rhenium(I) Complex

Two pyridylphenols with intramolecular hydrogen bonds between the phenol and pyridine units have been synthesized, characterized crystallographically, and investigated by cyclic voltammetry and UV/Vis spectroscopy. Reductive quenching of the triplet metal‐to‐ligand charge‐transfer excited state of the [Re(CO)₃(phen)(py)]⁺ complex (phen=1,10‐phenanthroline, py=pyridine) by the two pyridylphenols and two reference phenol molecules is investigated by steady‐state and time‐resolved luminescence spectroscopy, as well as by transient absorption spectroscopy. Stern–Volmer analysis of the luminescence quenching data provides rate constants for the bimolecular excited‐state quenching reactions. H/D kinetic isotope effects for the pyridylphenols are on the order of 2.0, and the bimolecular quenching reactions are up to 100 times faster with the pyridylphenols than with the reference phenols. This observation is attributed to the markedly less positive oxidation potentials of the pyridylphenols with respect to the reference phenols (≈0.5 V), which in turn is caused by proton coupling of the phenol oxidation process. Transient absorption spectroscopy provides unambiguous evidence for the photogeneration of phenoxyl radicals, that is, the overall photoreaction is clearly a proton‐coupled electron‐transfer process.     

Acoustic Radiation Force Impulse-Imaging for the evaluation of the thyroid gland: a limited patient feasibility study

Purpose

Real-time tissue elastography, a qualitative elastography method, has shown promising results in the diagnostic work up of thyroid nodules. However, to our knowledge no study has evaluated a quantitative elastography method in the thyroid gland. The present study is a feasibility study evaluating Acoustic Radiation Force Impulse-Imaging, a novel quantitative elastography method in the thyroid gland.

Methods

ARFI-imaging involves the mechanical excitation of tissue using short-duration acoustic pulses to generate localized displacements in tissue. The displacements induce a lateral shear-wave propagation which is tracked using multiple laterally positioned ultrasound “tracking“ beams. Inclusion criteria were: thyroid nodules ?1 cm, non-functioning or hypo-functioning on radionuclide scanning, and cytological/histological assessment of thyroid nodule as reference method. All patients received conventional ultrasound, and examination of the thyroid gland including Power Doppler Ultrasound using a 9 MHz linear transducer, in addition real-time elastography (RTE) was performed at 9 MHz frequency and ARFI-imaging was performed at 4 MHz using Siemens (ACUSON S2000) B-mode-ARFI combination transducer.

Results

Sixty nodules in 55 patients were analyzed. Three nodules were papillary carcinoma. The stiffer the tissue the faster the shear wave propagates. The results obtained indicated that the shear wave velocity in thyroid lobes ranged between 0.5 and 4.9 m/s. The median velocity of ARFI-imaging in the healthy nodule-free thyroid gland, as well as in benign and malignant thyroid nodules was 1.98 m/s (range: 1.20-3.63 m/s), 2.02 m/s (range: 0.92-3.97 m/s), and 4.30 m/s (range: 2.40-4.50 m/s), respectively. While no significant difference in median velocity was found between healthy thyroid tissue and benign thyroid nodules, a significant difference was found between malignant thyroid nodules on the one hand and healthy thyroid tissue (p = 0.018) or benign thyroid nodules (p = 0.014) on the other hand. Specificity of ARFI-imaging for the differentiation of benign and malignant thyroid nodules was comparable with RTE (91-95%).

Conclusions

ARFI can be performed in the thyroid tissue with reliable results.     

Titanium-based molecular squares and rectangles: syntheses by self-assembly reactions of titanocene fragments and aromatic N-heterocycles

This paper reports on the potential of titanium compounds as building blocks for supramolecular polygons. Self-assembly reactions of low-valent titanocene units and N-heterocyclic bridging ligands lead to novel titanium-based supramolecular squares. Pyrazine (3), 4,4'-bipyridine (4), and tetrazine (5) were used as bridging ligands, and the acetylene complexes [Cp2Ti{eta2-C2(SiMe3)2}] (1) and [(tBuCp)2Ti{eta2-C2(SiMe3)2}] (2) as sources of titanocene fragments. Molecular rectangles can be synthesized by stepwise reduction of the titanocene dichlorides [Cp(2)TiCl2] and [(tBuCp)2TiCl2] and consecutive coordination of two different bridging ligands. The resulting complexes are the first examples of molecular rectangles containing bent metallocene corner units. Single-crystal X-ray analyses of the tetranuclear compounds revealed the geometric properties of the molecular polygons in the solid state. Comparison of bond lengths and angles in coordinated and free ligands reveals the reduced state of the bridging ligand in the low-valent titanium compounds. The syntheses and properties of these novel, highly air- and moisture-sensitive compounds are discussed.