Photoassisted growth and nitrogen doping of ZnSe

ZnSe was grown on GaAs(100) substrates by photoassisted MOVPE using the precursors dimethylzinc-triethylamine (DMZn-TEN) and ditertiarybutylselenide (DtBSe). The optimal growth temperature was T_g = 300°C. Above 300°C no enhancement of growth rate was observed under illumination. Furthermore, nitrogen doping experiments were performed using phenylhydrazine, allylamine and tert-butylamine as nitrogen precursors. Nitrogen concentrations up to 10¹⁹ cm⁻³ (SIMS) were achieved with input flow ratios as low as [PhHz]/[Se] = 4 × 10⁻⁴. All as-grown samples were highly compensated. Successful nitrogen incorporation was also observed with allylamine. However, the use of tert-butylamine together with the adduct compound DMZn-TEN showed no incorporation of nitrogen.     

In situ reflectance difference spectroscopy of ZnSe-based semiconductor surfaces

We will give a brief report on applications of reflectance difference spectroscopy (RDS) for in situ growth monitoring during MOVPE. The experiments were made on GaAs(001) substrates using dimethylzinc-triethylamine, ditbutylselenide and as metalorganic precursors in a laminar flow reactor. We analyzed the influence of the in situ GaAs-substrate preparation on the optical response of the surface. The growth of ZnSe was investigated and compared to data obtained in an MBE process. Spectra at various stages of growth and time-dependent kinetic RDS records were measured during deposition and fitted with a three-layer growth model. Furthermore we utilized the surface sensitivity of the RDS technique to demonstrate surface kinetic processes during p-doping with tbutylamine.     

Molecular‐Dynamics Studies of Single‐Stranded Hexitol,Altritol, Mannitol,and Ribose Nucleic Acids (HNA,MNA, ANA,and RNA,Resp.) and of the Stability of HNA⋅RNA,ANA⋅RNA,and MNA⋅RNA Duplexes

The influence of the orientation of a 3′‐OH group on the conformation and stability of hexitol oligonucleotides in complexes with RNA and as single strands in aqueous solution was investigated by molecular‐dynamics (MD) simulations with AMBER 4.1. The particle mesh Ewald (PME) method was used for the treatment of long‐range electrostatic interactions. An equatorial orientation of the 3′‐OH group in the single‐stranded D ‐mannitol nucleic acid (MNA) m(GCGTAGCG) and in the complex with the RNA r(CGCAUCGC) has an unfavorable influence on the helical stability. Frequent H‐bonds between the 3′‐OH group and the O−C(6′) of the phosphate backbone of the following nucleotide explain the distorted conformation of the MNA⋅RNA complex as well as that of the single MNA strand. This is consistent with experimental results that show lowered hybridization potentials for MNA⋅RNA complexes. An axial orientation of the 3′‐OH group in the D ‐altritol nucleic acid (ANA) a(GCGTAGCG) leads to a stable complex with the complementary RNA r(CGCAUCGC), as well as to a more highly preorganized single‐stranded ANA chain. The averaged conformation of the ANA⋅RNA complex is similar to that of A‐RNA, with only minor changes in groove width, helical curvature, and H‐bonding pattern. The relative stabilities of ANA⋅RNA vs. HNA⋅RNA (HNA=D ‐hexitol nucleic acid without 3′‐OH group) can be explained by differences in restricted movements, H‐bonds, and solvation effects.     

Interactive System for Similarity-Based Inspection and Assessment of the Well-Being of mHealth Users

Recent digitization technologies empower mHealth users to conveniently record their Ecological Momentary Assessments (EMA) through web applications, smartphones, and wearable devices. These recordings can help clinicians understand how the users’ condition changes, but appropriate learning and visualization mechanisms are required for this purpose. We propose a web-based visual analytics tool, which processes clinical data as well as EMAs that were recorded through a mHealth application. The goals we pursue are (1) to predict the condition of the user in the near and the far future, while also identifying the clinical data that mostly contribute to EMA predictions, (2) to identify users with outlier EMA, and (3) to show to what extent the EMAs of a user are in line with or diverge from those users similar to him/her. We report our findings based on a pilot study on patient empowerment, involving tinnitus patients who recorded EMAs with the mHealth app TinnitusTips. To validate our method, we also derived synthetic data from the same pilot study. Based on this setting, results for different use cases are reported.     

Selective RGD‐Mediated Adhesion of Osteoblasts at Surfaces of Implants

Osteoblasts: yes, platelets: no! Bone implants have to be integrated with the surrounding tissue to allow a smooth and stable connection. A new procedure is shown which is based on covalent linking of a highly selective RGD peptide to a poly(methyl methacrylate) (PMMA) material (see picture). Osteoblasts very effectively bind to the treated surface and are stimulated to proliferate.     

Thiolate-Bridged Diiron(III) Complex with Spin-Crossover Behaviour

The reaction of the ligand HL · (HCl)₂ (HL = 2,6-di(aminomethyl)-4-tert-butyl-thiophenol) with MCl₂ in methanol in the presence of sodium methanolate and air affords the dinuclear complexes [L₃M₂][ClO₄]₃ (M = Fe: 2 , Co: 3 ) in 85% and 68% yield, respectively. Both complexes were characterized by infrared spectroscopy, magnetic susceptibility measurements, and ¹H NMR spectroscopy. By temperature-variable ⁵⁷Fe Mössbauer spectroscopy diamagnetic 2 is shown to exhibit a gradual spin transition between the species [L₃(low-spin-Fe)₂]³⁺ ((ls,ls)- 2 ) and [L₃(high-spin-Fe)₂]³⁺ ((hs,hs)- 2 ). At room temperature the relative concentrations of both species are nearly equal. Well resolved quadrupole doublets at all temperatures for both (ls,ls)- 2 (γ in the range 0.22(1)–0.28(1) mm s^–1) and (hs,hs)- 2 (γ in the range 0.48(1)–0.53(2) mm s^–1) are indicative of a spin conversion time longer than the half-life of the I = ³/₂ state of ⁵⁷Fe. Cyclic voltammetry and square wave voltammetry of 2 in CH₃CN solution reveal four quasi-reversible one-electron transfer processes. The first two processes were assigned to metal-centered reductions of (hs,hs)- 2 and (ls,ls)- 2 , respectively, to yield the mixed-valent species [L₃Fe^IIFe^III]³⁺.     

Hydrierung aromatischer Nitrile auf dem Fe3(CO)9-Cluster

Hydrogenation of Aromatic Nitriles on the Fe₃(CO)₉ Cluster The μ₃-nitrile bridged clusters Fe₃(CO)₉(μ₃-η²-N≡CR) ( 3 , R = phenyl, p-tolyl, p-anisyl) consume hydrogen upon heating in solution with formation of the acimidoyl- and the alkylideneimido-bridged clusters HFe₃(CO)₉(μ₃-η²-HN=CR) ( 1 ) and HFe₃(CO)₉(μ₃-η²-N=CHR) ( 2 ). These can be obtained in a better way by successive H⁺ and H^– addition with NaBH₄ and H₃PO₄. HFe₃(CO)₉(μ₃-η²-N=CHR) ( 2 ) adds P(OMe)₃ with concomitant hydrogen migration to form Fe₃(CO)₉P(OMe)₃(μ₃-η¹-N–CH₂R) ( 6 ). The phosphite-substituted cluster Fe₃(CO)₈P(OMe)₃(μ₃-η²-N≡CPh) ( 5 a ) on the other hand is converted by the H⁺/H^– addition to the products HFe₃(CO)₈P(OMe)₃(μ₃-η²-HN=CPh) ( 7 a ) and HFe₃(CO)₈P(OMe)₃(μ₃-η²-N=CHPh) ( 8 a ).