Synthesis, structure, and opto-electronic properties of organic-based nanoscale heterojunctions

Enormous research effort has been put into optimizing organic-based opto-electronic systems for efficient generation of free charge carriers. This optimization is mainly due to typically high dissociation energy (0.1-1 eV) and short diffusion length (10 nm) of excitons in organic materials. Inherently, interplay of microscopic structural, chemical, and opto-electronic properties plays crucial role. We show that employing and combining advanced scanning probe techniques can provide us significant insight into the correlation of these properties. By adjusting parameters of contact- and tapping-mode atomic force microscopy (AFM), we perform morphologic and mechanical characterizations (nanoshaving) of organic layers, measure their electrical conductivity by current-sensing AFM, and deduce work functions and surface photovoltage (SPV) effects by Kelvin force microscopy using high spatial resolution. These data are further correlated with local material composition detected using micro-Raman spectroscopy and with other electronic transport data. We demonstrate benefits of this multi-dimensional characterizations on (i) bulk heterojunction of fully organic composite films, indicating differences in blend quality and component segregation leading to local shunts of photovoltaic cell, and (ii) thin-film heterojunction of polypyrrole (PPy) electropolymerized on hydrogen-terminated diamond, indicating covalent bonding and transfer of charge carriers from PPy to diamond

Electronic transport in intrinsic H-terminated nanocrystaline diamond with various grain size

Both effective conductivity and Hall mobility of H-NCD were found to strongly decrease with the diminishing grain size. Effective Hall concentrations (to 1017 m-2) correspond to the true hole concentrations on the surface of the grain interiors. The effective Hall mobility is a robust parameter with respect to the surface conditions

Possible role of extracellular tissue in biological neural networks

In the present paper, we analyze the role of extracellular tissue (ECT) in signal transfer and information processing in biological neural networks. Our speculative approach, which is based mainly on the facts taken from the literature, is completed by simple original models and quantitative estimates. It is shown that the presence of ECT controls some fundamental parameters of immersed biological neural network, which are traditionally treated as intrinsic to neuron membranes. We then propose that the diffusive transfer of action potential via the nervous fiber together with processes induced in the surrounding ECT, is ultimately controlled, in contrast to the standard paradigm, by the quantum diffusion of $$\hbox {Na}^{{+}}$$ and $$\hbox {K}^{{+}}$$ ions, which minimizes the heat production in nervous tissue. Furthermore the diffusion of polarization wave along the axon membrane excites in surrounding ECT temporal potential distribution, which can bias the synapses and dendrites of all vicinal neurons. We claim that just this, so-called, ephaptic coupling between neighboring neurons, completes the local neural network and in fact is responsible for information processing there. Such an idea is obviously incompatible with current models of neural networks of McCulloch–Pitts’ and Rosenblatt’s type, which assume that the information processing takes place exclusively within the neuron soma, being thus convenient merely for the description of artificial neural networks

Diffusive propagation of nervous signals and their quantum control

The governing theory of electric signal transfer through nerve fibre, as established by Hodgkin and Huxley in the 1950s, uses for the description of action potential a clever combination of various concepts of electrochemistry and circuit theory; however, this theory neglects some fundamental features of charge transport through any conductor, e.g., the existence of a temporary charged layer on its boundary accompanied by an external electric field. The consequences of this fact are, among others, the introduction of a non-adequate concept of “conduction velocity” and the obscure idea of saltatory propagation of action potential in myelinaed nerve fibres. Our approach, based on standard transport theory and, particularly, on the submarine cable model, describes the movement of the front of the action potential as a diffusion process characterized by the diffusion constant DE. This process is physically realized by the redistribution of ions in the nervous fluid (axoplasm), which is controlled by another diffusion constant DΩ ≪ DE. Since the action bound with the movement of Na+ and K+ cations prevailing in the axoplasm is comparable with the Planck constant ℏ (i.e. DΩ → ℏ∕2M, where M is ion mass), signal transfer is actually a quantum process. This fact accounts for the astonishing universality of the transfer of action potential, which is proper to quite different species of animals. As is further shown, the observed diversity in the behaviour of nerve tissues is controlled by the scaling factor \sqrt{(D_{\UpOmega} / D_E)}, where DΩ is of a quantum nature and DE of an essentially geometric one

On Expansion of a Spherical Enclosure Bathed in Zero-Point Radiation

Abstract: In the present contribution a simple thought experiment made with an idealized spherical enclosure bathed in zero-point (ZP) electromagnetic radiation and having walls made of a material with an upper frequency cut-off has been qualitatively analysed. As a result, a possible mechanism of filling real cavities with ZP radiation based on Doppler’s effect has been suggested and corresponding entropy changes have been discussed

Room Temperature Reactive Deposition of InGaZnO and ZnSnO Amorphous Oxide Semiconductors for Flexible Electronics

Amorphous oxide semiconductors (AOSs) are interesting materials which combine optical transparency with high electron mobility. AOSs can be prepared at low temperatures by high throughput deposition techniques such as magnetron sputtering and are thus suitable for flexible transparent electronics such as flexible displays, thin-film transistors, and sensors. In magnetron sputtering the energy input into the growing film can be controlled by the plasma conditions instead of the substrate temperature. Here, we report on magnetron sputtering of InGaZnO (IGZO) and ZnSnO (ZTO) with a focus on the e ect of deposition conditions on the film properties. IGZO films were deposited by radio-frequency (RF) sputtering from an oxide target while for ZTO, reactive sputtering from an alloy target was used. All films were deposited without substrate heating and characterized with respect to microstructure, electron mobility, and resistivity. The best as-deposited IGZO films exhibited a resistivity of about 2 102 Ohmcm and an electron mobility of 18 cm2V1s1. The lateral distribution of the electrical properties in such films is mainly related to the activity and amount of oxygen reaching the substrate surface as well as its spatial distribution. The lateral uniformity is strongly influenced by the composition and energy of the material flux towards the substrate

Electrical and optical properties of scandium nitride nanolayers on MgO (100) substrate

Scandium nitride (ScN) is a rocksalt-structure semiconductor that has attracted attention for its potential applications in thermoelectric energy conversion devices, as a semiconducting component in epitaxial metal/semiconductor superlattices. ScN nanolayers of 30 nm thickness were deposited on MgO (001) substrate by reactive sputtering. Epitaxial growth of ScN(002) was observed with a mosaicity between grains around the {002} growth axis. Both direct band gaps theoretically predicted were measured at 2.59 eV and 4.25 eV for the energy gaps between the valence band and the conductance band at the X point and the Γ point respectively. Electrical and optical properties were observed to be strongly influenced by the crystalline order and the carrier concentration

Large area heavily boron doped nano-crystalline diamond growth by MW-LA-PECVD [Póster]

Diamond is a unique semiconductor with a wide bandgap which usually is easily doped with boron and is acknowledged as one of the best materials for electrochemical applications. Heavily boron doped, high quality single crystal synthetic diamond can reach electrical conductivity as high as 103 S.cm, whereas polycrystalline material usually reaches c.a. 102 S.cm. However, many potential applications are restricted by the deposition temperature and limited coating area of conventional MW PECVD systems. Deposition of boron doped nano-crystalline diamond (BNCD) layers using a microwave PECVD system with linear antenna delivery (MW-LA-PECVD), enabling large area coating, was first reported in 2014 [1]. However, layers showed lower electrical conductivity in comparison to BNCD layers deposited using conventional PECVD systems. In addition, deposition of BNCD by MW-LA-PECVD is complicated by the necessity for the addition of oxygen species, which are known to limit boron incorporation and the competitive growth of silicon carbide at low CO2 concentrations [2, 3]. In this work, we further study the effect of deposition conditions on the synthesis of BNCD using the MW-LA-PECVD technique. In order to produce highly conductive BNCD with a low sp2 fraction, we have investigated in greater detail the effect of deposition temperature, from 250 °C up to 750 °C, using temperature controlled substrate stages and the effect of precursor gas compositions