Maximum a posteriori estimation of activation energies that control silicon self-diffusion

Self-diffusion in crystalline silicon is controlled by a network of elementary steps whose activation energies are important to know in a variety of applications in microelectronic fabrication. The present work employs maximum a posteriori (MAP) estimation to improve existing values for these activation energies, based on self-diffusion data collected at different values of the loss rates for interstitial atoms to the surface. Parameter sensitivity analysis shows that for high surface loss fluxes, the energy for exchange between an interstitial and the lattice plays the leading role in determining the shape of diffusion profiles. At low surface loss fluxes, the dissociation energy of large-atom clusters plays a more important role. Subsequent MAP analysis provides significantly improved values for these parameters.     

Measurement method for carrier concentration in TiO2 via the Mott-Schottky approach

In direct contrast to the way in which silicon is precisely doped for integrated circuit applications in order to optimize device performance, there is little nuanced understanding of the correlation between TiO₂ doping level, charge carrier concentration, and the operation of TiO₂-based photocatalysts, dye-sensitized solar cells, and sensors. The present work outlines a rigorous methodology for the determination of free carrier concentration for doped metal oxide semiconductors such as TiO₂ that are not amenable to standard metrology methods. Undoped, Cr-, Mn-, and Nb-doped polycrystalline anatase TiO₂ are synthesized via atomic layer deposition (ALD) using Ti(OCH(CH₃)₂)₄, H₂O, Cr(C₅H₇O₂)₃, Mn(DPM)₃ (DPM = 2,2,6,6-tetramethyl-3, 5-heptanedionato), and Nb(OCH₂CH₃)₅ as the source materials for Ti, O, Cr, Mn, and Nb, respectively. Chemical composition and crystallinity are investigated and a thorough “device-like” characterization of TiO₂ Schottky diodes is carried out to justify the subsequent extraction of carrier concentration values from capacitance-voltage (C-V) measurements using the Mott-Schottky approach. The influence of factors such as substrate type, contact metal type, and surface and interface preparation are examined. Measurements of donor carrier concentration are obtained for undoped, Cr-, Mn-, and Nb-doped TiO₂ synthesized by ALD. Possible causes for the obtained carrier concentrations are discussed.     

Posterior shoulder joint instability. Classification, pathomechanism,diagnosis, conservative and surgical management

The posterior instability of the shoulder is a more difficult diagnostic and therapeutic challenge than the anterior instability. There are many etiologies and causes of posterior instability. Most studies in the literature are retrospective and yield a great variation in therapeutic recommendations. Generally it has to be separated in traumatic and atraumatic instabilities. Most of the traumatic dislocations are impaction fractures of the humeral head against the dorsal glenoid. Therapy is depending on the size of the humeral defect, the duration of dislocation and the functional demand of the patient. Therapeutic possibilities are closed reduction and fixation with a cast, open reduction and the transfer of the lower tubercule (McLaughlin's procedure), lifting of the defect and supporting with cancellous bone, subcapital rotational osteotomy or arthroplasty. The therapy of choice for atraumatic instability is a individualized rehabilitation program with strengthening and balancing of rotator cuff muscles and scapular stabilizers. Psychologic abnormalities and emotional problems have to be recognized prior to any operative procedure. These patients are no operative candidates. Operative treatment of choice is the posterior capsular shift addressing the causative redundancy or laxity of the postero-inferior capsule. Posterior bony procedures as glenoid osteotomy or bone block transfers are indicated, if the pathologic geometry of the glenoid is primarily responsible for posterior instability. It is strongly recommended to combine them with a capsular shift to address the secondary capsular redundancy.     

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Investigation of nanostructured TiO2 surface and interface electric fields with photoreflectance spectroscopy

The electrical properties of buried solid–solid interfaces are essential to the optimization of devices such as dye‐sensitized solar cells and photocatalysts. The degree of fixed charge buildup at these interfaces can be sample‐dependent, influenced by only a small fraction of total surface sites, and challenging to quantify. This work describes the applicability of photoreflectance spectroscopy (PR) to the characterization of thin film nanostructured TiO₂. The approach involves the synthesis of polycrystalline anatase TiO₂ on quartz and Si(100) by atomic layer deposition with Ti(OCH(CH₃)₂)₄ and H₂O as precursors. PR reveals negligible band bending at the TiO₂ free surface. A distinct spectral feature at 299.0 ± 0.3 kJ/mol (3.10 ± 0.0031 eV) is attributed to electronic states at the TiO₂‐Si interface. Temporal variations in the magnitude of this feature are discussed in the context of bulk carrier concentration, solid–solid interface chemical reactions, and charge exchange between interface and grain boundary states and the bulk bands. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1049–1055, 2013     

Directed self‐assembly by photostimulation of an amorphous semiconductor surface

A method for nanoscale directed self‐assembly is demonstrated that employs an amorphous semiconductor containing subcritical nuclei for crystallization. This strategy combines attractive features of top‐down and bottom‐up approaches by exploiting the self‐organization capabilities latent in amorphous materials, but in a way that can be controlled by optical or electron beam exposure tools. The method was demonstrated with amorphous TiO₂ deposited on silicon, heated to 270°C, and exposed to low‐level ultraviolet light. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Interaction of Alpha Synuclein and Microtubule Organization Is Linked to Impaired Neuritic Integrity in Parkinson’s Patient-Derived Neuronal Cells

Parkinson’s disease (PD) is neuropathologically characterized by the loss of dopaminergic neurons and the deposition of aggregated alpha synuclein (aSyn). Mounting evidence suggests that neuritic degeneration precedes neuronal loss in PD. A possible underlying mechanism could be the interference of aSyn with microtubule organization in the neuritic development, as implied by several studies using cell-free model systems. In this study, we investigate the impact of aSyn on microtubule organization in aSyn overexpressing H4 neuroglioma cells and midbrain dopaminergic neuronal cells (mDANs) generated from PD patient-derived human induced pluripotent stem cells (hiPSCs) carrying an aSyn gene duplication (SNCA^Dupl). An unbiased mass spectrometric analysis reveals a preferential binding of aggregated aSyn conformers to a number of microtubule elements. We confirm the interaction of aSyn with beta tubulin III in H4 and hiPSC-derived mDAN cell model systems, and demonstrate a remarkable redistribution of tubulin isoforms from the soluble to insoluble fraction, accompanied by a significantly increased insoluble aSyn level. Concordantly, SNCA^Dupl mDANs show impaired neuritic phenotypes characterized by perturbations in neurite initiation and outgrowth. In summary, our findings suggest a mechanistic pathway, through which aSyn aggregation interferes with microtubule organization and induces neurite impairments.     

A Priori Catalytic Activity Correlations: The Difficult Case of Hydrogen Production from Ammonia

The catalytic decomposition of ammonia has recently been proposed as a possible source of hydrogen for fuel cells. However, the ruthenium catalyst is costly. Although there exist several correlations for catalytic activity that suggest potentially useful alternatives, the particular candidates differ. The present work seeks to determine experimentally which, if any, of these correlations correctly predicts suitable substitutes. The experiments examine 13 different metallic catalysts from numerous places within the Periodic Table, and show that the activity varies in the order Ru>Ni>Rh>Co>Ir>Fe?Pt>Cr>Pd>Cu?Te, Se, Pb. The results suggest that nitrogen desorption limits the rate on Fe, Co, and Ni, whereas N–H bond scission limits the rate on other metals such as Rh, Ir, Pd, Pt, and Cu. Conventional single-parameter correlations of activity generally fail to predict the results because the rate-determining step changes across the data set.