The structural and electrical properties of thermally grown TiO2 thin films

We studied the structural and electrical properties of TiO2 thin films grown by thermal oxidation of e-beam evaporated Ti layers on Si substrates. Time of flight secondary ion mass spectroscopy (TOF-SIMS) was used to analyse the interfacial and chemical composition of the TiO2 thin films. Metal oxide semiconductor (MOS) capacitors with Pt or Al as the top electrode were fabricated to analyse electrical properties of the TiO2 thin films. We show that the reactivity of the Al top contact affects electrical properties of the oxide layers. The current transport mechanism in the TiO2 thin films is shown to be Poole–Frenkel (P–F) emission at room temperature. At 84 K, Fowler– Nordheim (F–N) tunnelling and trap-assisted tunnelling are observed. By comparing the electrical characteristics of thermally grown TiO2 thin films with the properties of those grown by other techniques reported in the literature, we suggest that, irrespective of the deposition technique, annealing of as-deposited TiO2 in O2 is a similar process to thermal oxidation of Ti thin films

Factors of Influence on the Performance of a Short-Latency Non-Invasive Brain Switch: Evidence in Healthy Individuals and Implication for Motor Function Rehabilitation.

Brain-computer interfacing (BCI) has recently been applied as a rehabilitation approach for patients with motor disorders, such as stroke. In these closed-loop applications, a brain switch detects the motor intention from brain signals, e.g., scalp EEG, and triggers a neuroprosthetic device, either to deliver sensory feedback or to mimic real movements, thus re-establishing the compromised sensory-motor control loop and promoting neural plasticity. In this context, single trial detection of motor intention with short latency is a prerequisite. The performance of the event detection from EEG recordings is mainly determined by three factors: the type of motor imagery (e.g., repetitive, ballistic), the frequency band (or signal modality) used for discrimination (e.g., alpha, beta, gamma, and MRCP, i.e., movement-related cortical potential), and the processing technique (e.g., time-series analysis, sub-band power estimation). In this study, we investigated single trial EEG traces during movement imagination on healthy individuals, and provided a comprehensive analysis of the performance of a short-latency brain switch when varying these three factors. The morphological investigation showed a cross-subject consistency of a prolonged negative phase in MRCP, and a delayed beta rebound in sensory-motor rhythms during repetitive tasks. The detection performance had the greatest accuracy when using ballistic MRCP with time-series analysis. In this case, the true positive rate (TPR) was ~70% for a detection latency of ~200 ms. The results presented here are of practical relevance for designing BCI systems for motor function rehabilitation

Morphological and molecular variability in some Iranian almond genotypes and related Prunus species and their potentials for rootstock breeding

41 Pag., 6 Fig., 5 Tabl. The definitive version is available at: http://www.sciencedirect.com/science/journal/03044238In this study, in order to know the variability for a rootstock breeding program genetic diversity and relationships among 55 Iranian almond genotypes and seven related Prunus species were investigated. Morphological and molecular analyses were used. Principal component analysis showed that three components explained 67.6% of the total morphological variation for the first year and 68.06% for the second year of the study. Leaf traits were predominant in the first component and contributed most of the total variation. Leaf length and width, as well as, leaf area were highly correlated with each other and correlated to vigor. Also a negative correlation was found between leaf length/width ratio and vigor. Ward’s method was used to construct cluster from morphological data which allocated individuals into their respective species. Out of 100 pre-screened RAPD primers, 16 with reproducible bands and maximum polymorphism were selected. Two-hundred and sixty bands were scored of which 250 of them were polymorphic. Average value of polymorphism per primer was 95.81% and maximum value for polymorphism (100%) was obtained from TIBMBA-14, TIBMBA-17, TIBMBB-05, TIBMBB-08, TIBMBD-09, and TIBMBD-10. On the other hand, the minimum value was obtained from TIBMBB-16 (86%). Primer TIBMBB-5 gave the maximum number of bands (25 fragments) and the minimum obtained from TIBMBE-18 (11 fragments). Genetic similarity based on Jaccard’s coefficient ranged from 0.28 to 0.79 with an average of 0.53. Molecular analysis revealed a high degree of separation among samples regarding their geographical origin. Correlation between two approaches was low (R =−0.38). High molecular and morphological variability indicated that this collection includes rich and valuable plant materials for almond rootstock breeding.We are grateful for the financial supports provided by the Center of Excellence for stone fruits root stock breeding program of the University of Tehran.Peer reviewe

Terahertz electromodulation spectroscopy of electron transport in GaN

Time-resolved terahertz (THz) electromodulation spectroscopy is applied to investigate the high-frequency transport of electrons in gallium nitride at different doping concentrations and densities of threading dislocations. At THz frequencies, all structures reveal Drude transport. The analysis of the spectral response provides the fundamental transport properties, such as the electron scattering time and the electrons’ conductivity effective mass. We observe the expected impact of ionized-impurity scattering and that scattering at threading dislocations only marginally affects the high-frequency mobility.The research was supported by the German Science Foundation DFG under grants Ke 516/1-2 and Ke 516/6- 1.This is the accepted manuscript. The final version is available at http://scitation.aip.org/content/aip/journal/apl/106/9/10.1063/1.4914326

Theory of Exciton Migration and Field-Induced Dissociation in Conjugated Polymers

The interplay of migration, recombination, and dissociation of excitons in disordered media is studied theoretically in the low temperature regime. An exact expression for the photoluminescence spectrum is obtained. The theory is applied to describe the electric field-induced photoluminescence-quenching experiments by Kersting et al. [Phys. Rev. Lett. 73, 1440 (1994)] and Deussen et al. [Synth. Met. 73, 123 (1995)] on conjugated polymer systems. Good agreement with experiment is obtained using an on-chain dissociation mechanism, which implies a separation of the electron-hole pair along the polymer chain.Comment: 4 pages, RevTeX, 2 Postscript figure

Enhancement of the ferromagnetic order of graphite after sulphuric acid treatment

We have studied the changes in the ferromagnetic behavior of graphite powder and graphite flakes after treatment with diluted sulphuric acid. We show that this kind of acid treatment enhances substantially the ferromagnetic magnetization of virgin graphite micrometer size powder as well as in graphite flakes. The anisotropic magnetoresistance (AMR) amplitude at 300 K measured in a micrometer size thin graphite flake after acid treatment reaches values comparable to polycrystalline cobalt.Comment: 3.2 pages, 4 figure

Environmental drivers of distribution and reef development of the Mediterranean coral Cladocora caespitosa

Cladocora caespitosa is the only Mediterranean scleractinian similar to tropical reef-building corals. While this species is part of the recent fossil history of the Mediterranean Sea, it is currently considered endangered due to its decline during the last decades. Environmental factors affecting the distribution and persistence of extensive bank reefs of this endemic species across its whole geographic range are poorly understood. In this study, we examined the environmental response of C. caespitosa and its main types of assemblages using ecological niche modeling and ordination analysis. We also predicted other suitable areas for the occurrence of the species and assessed the conservation effectiveness of Mediterranean marine protected areas (MPAs) for this coral. We found that phosphate concentration and wave height were factors affecting both the occurrence of this versatile species and the distribution of its extensive bioconstructions in the Mediterranean Sea. A set of factors (diffuse attenuation coefficient, calcite and nitrate concentrations, mean wave height, sea surface temperature, and shape of the coast) likely act as environmental barriers preventing the species from expansion to the Atlantic Ocean and the Black Sea. Uncertainties in our large-scale statistical results and departures from previous physiological and ecological studies are also discussed under an integrative perspective. This study reveals that Mediterranean MPAs encompass eight of the ten banks and 16 of the 21 beds of C. caespitosa. Preservation of water clarity by avoiding phosphate discharges may improve the protection of this emblematic species.Spanish Ministry of Economy and Competitiveness [CTM2014-57949-R]info:eu-repo/semantics/publishedVersio

Defect distribution in a-plane GaN on Al2O3

The authors studied the structural and point defect distributions of hydride vapor phase epitaxial GaN film grown in the [11−20] a direction on (1−102) r-plane sapphire with metal-organic vapor phase deposited a-GaN template using transmission electron microscopy, secondary ion mass spectrometry, and positron annihilation spectroscopy. Grown-in extended and point defects show constant behavior as a function of thickness, contrary to the strong nonuniform defect distribution observed in GaN grown along the [0001] direction. The observed differences are explained by orientation-dependent and kinetics related defect incorporation.Peer reviewe

Ferromagnetic coupling and magnetic anisotropy in molecular Ni(II) squares

We investigated the magnetic properties of two isostructural Ni(II) metal complexes [Ni4Lb8] and [Ni4Lc8]. In each molecule the four Ni(II) centers form almost perfect regular squares. Magnetic coupling and anisotropy of single crystals were examined by magnetization measurements and in particular by high-field torque magnetometry at low temperatures. The data were analyzed in terms of an effective spin Hamiltonian appropriate for Ni(II) centers. For both compounds, we found a weak intramolecular ferromagnetic coupling of the four Ni(II) spins and sizable single-ion anisotropies of the easy-axis type. The coupling strengths are roughly identical for both compounds, whereas the zero-field-splitting parameters are significantly different. Possible reasons for this observation are discussed.Comment: 7 pages, 7 figure