Electronic properties and gap state defect passivation of Si SiO2 nanostructures

Bandgap control of silicon based material provides a promising way towards next generation photovoltaic devices such as tandem solar cells, what can be realized by nanostructures consisting of Si SiO2 quantum wells or superlattices. However, due to increased interface to volume ratios at reduced dimensions, charge carrier recombination and scattering at Si SiO2 interfaces might dominate the photoelectrical properties and gain critical impact on mobility lifetime products amp; 956; amp; 964; and thus internal quantum efficiencies [1]. To circumvent this drawback, the effect of hydrogen treatment on charge carrier recombination and electronic densities of states at the interface of ultrathin oxides layers is analyzed. Samples with structurally and chemically well defined interfaces were prepared by plasma oxidation of crystalline Si with atomic oxygen under ultrahigh vacuum conditions [2]. It is demonstrated, that Si SiO2 interface states can be passivated under appropriate conditions in forming gas H2 N2 and in hydrogen plasma. As a result, the photoelectrical performance of such structures is clearly improved. This is verified by i estimation of mobility lifetime products from photocurrent measurements, ii analysis of interface densities of states by means of surface photovoltage measurements SPV , and iii deducing densities of occupied states in the band gap as elucidated from UV excited constant final state yield spectroscopy CFSYS

Carbon nanotubes in neural interfacing applications

Carbon nanotubes (CNT) are remarkable materials with a simple and inert molecular structure that gives rise to a range of potentially valuable physical and electronic properties, including high aspect ratio, high mechanical strength and excellent electrical conductivity. This review summarizes recent research on the application of CNT-based materials to study and control cells of the nervous system. It includes the use of CNT as cell culture substrates, to create patterned surfaces and to study cell–matrix interactions. It also summarizes recent investigations of CNT toxicity, particularly as related to neural cells. The application of CNT-based materials to directing the differentiation of progenitor and stem cells toward neural lineages is also discussed. The emphasis is on how CNT surface chemistry and nanotopography can be altered, and how such changes can affect neural cell function. This knowledge can be applied to creating improved neural interfaces and devices, as well as providing new approaches to neural tissue engineering and regeneration.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90821/1/1741-2552_8_1_011001.pd

The influence of tDCS on perceived bouncing/streaming

Processing ambiguous situations is a constant challenge in everyday life and sensory input from different modalities needs to be integrated to form a coherent mental representation on the environment. The bouncing/streaming illusion can be studied to provide insights into the ambiguous perception and processing of multi-modal environments. In short, the likelihood of reporting bouncing rather than streaming impressions increases when a sound coincides with the moment of overlap between two moving disks. Neuroimaging studies revealed that the right posterior parietal cortex is crucial in cross-modal integration and is active during the bouncing/streaming illusion. Consequently, in the present study, we used transcranial direct current stimulation to stimulate this brain area. In the active stimulation conditions, a 9 cm2 electrode was positioned over the P4-EEG position and the 35 cm2 reference positioned over the left upper arm. The stimulation lasted 15 min. Each participant did the bouncing/streaming task three times: before, during and after anodal or sham stimulation. In a sample of N = 60 healthy, young adults, we found no influence of anodal tDCS. Bayesian analysis showed strong evidence against tDCS effects. There are two possible explanations for the finding that anodal tDCS over perceptual areas did not modulate multimodal integration. First, upregulation of multimodal integration is not possible using tDCS over the PPC as the integration process already functions at maximum capacity. Second, prefrontal decision-making areas may have overruled any modulated input from the PPC as it may not have matched their decision-making criterion and compensated for the modulation

Evolution of E2 transition strength in deformed hafnium isotopes from new measurements on 172^{172}Hf, 174^{174}Hf, and 176^{176}Hf

The available data for E2 transition strengths in the region between neutron-deficient Hf and Pt isotopes are far from complete. More and precise data are needed to enhance the picture of structure evolution in this region and to test state-of-the-art nuclear models. In a simple model, the maximum collectivity is expected at the middle of the major shell. However, for actual nuclei, this picture may no longer be the case, and one should use a more realistic nuclear-structure model. We address this point by studying the spectroscopy of Hf. We remeasure the 2^+_1 half-lives of 172,174,176Hf, for which there is some disagreement in the literature. The main goal is to measure, for the first time, the half-lives of higher-lying states of the rotational band. The new results are compared to a theoretical calculation for absolute transition strengths. The half-lives were measured using \gamma-\gamma and conversion-electron-\gamma delayed coincidences with the fast timing method. For the determination of half-lives in the picosecond region, the generalized centroid difference method was applied. For the theoretical calculation of the spectroscopic properties, the interacting boson model is employed, whose Hamiltonian is determined based on microscopic energy-density functional calculations. The measured 2^+_1 half-lives disagree with results from earlier \gamma-\gamma fast timing measurements, but are in agreement with data from Coulomb excitation experiments and other methods. Half-lives of the 4^+_1 and 6^+_1 states were measured, as well as a lower limit for the 8^+_1 states. We show the importance of the mass-dependence of effective boson charge in the description of E2 transition rates in chains of nuclei. It encourages further studies of the microscopic origin of this mass dependence. New data on transition rates in nuclei from neighboring isotopic chains could support these studies.Comment: 16 pages, 16 figures, 7 tables; Abstract shortened due to character limi

Collagen I-Matrigel Scaffolds for Enhanced Schwann Cell Survival and Control of Three-Dimensional Cell Morphology

We report on the ability to control three-dimensional Schwann cell (SC) morphology using collagen I Matrigel composite scaffolds for neural engineering applications. SCs are supportive of nerve regeneration after injury, and it has recently been reported that SCs embedded in collagen I, a material frequently used in guidance channel studies, do not readily extend processes, instead adopting a spherical morphology indicative of little interaction with the matrix. We have modified collagen I matrices by adding Matrigel to make them more supportive of SCs and characterized these matrices and SC morphology in vitro. Incorporation of 10%, 20%, 35%, and 50% Matrigel by volume resulted in 2.4, 3.5, 3.7, and 4.2 times longer average SC process length after 14 days in culture than with collagen I only controls. Additionally, only 35% and 50% Matrigel constructs were able to maintain SC number over 14 days, whereas an 88% decrease in cells from initial seeding density was observed in collagen-only constructs over the same time period. Mechanical testing revealed that the addition of 50% Matrigel increased matrix stiffness from 6.4kPa in collagen I only constructs to 9.8kPa. Furthermore, second harmonic generation imaging showed that the addition of Matrigel resulted in non-uniform distribution of collagen I, and scanning electron microscope imaging illustrated distinct differences in the fibrillar structure of the different constructs. Collectively, this work lays a foundation for developing scaffolding materials that are concurrently supportive of neurons and SCs for future neural engineering applications.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78114/1/ten.tea.2008.0406.pd

Nonuniform friction-area dependency for antimony oxide surfaces sliding on graphite

Cataloged from PDF version of article.We present frictional measurements involving controlled lateral manipulation of antimony nanoparticles on graphite featuring atomically smooth particle-substrate interfaces via tapping- and contact-mode atomic force microscopy. As expected from earlier studies, the power required for lateral manipulation as well as the frictional forces recorded during the manipulation events exhibit a linear dependence on the contact area over a wide size range from 2000 nm2 to 120 000 nm2. However, we observe a significant and abrupt increase in frictional force and dissipated power per contact area at a value of about 20 000 nm2, coinciding with a phase transition from amorphous to crystalline within the antimony particles. Our results suggest that variations in the structural arrangement and stoichiometry of antimony oxide at the interface between the particles and the substrate may be responsible for the observed effect. © 2013 American Physical Society

Erratum to: Design of pharmaceutical products to meet future patient needs requires modification of current development paradigms and business models

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