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We propose a label-free biosensor concept based on the charge state manipulation of nitrogen-vacancy (NV) quantum color centers in diamond, combined with an electrochemical microfluidic flow cell sensor, constructed on boron-doped diamond. This device can be set at a defined electrochemical potential, locking onto the particular chemical reaction, whilst the NV center provides the sensing function. The NV charge state occupation is initially prepared by applying a bias voltage on a gate electrode and then subsequently altered by exposure to detected charged molecules. We demonstrate the functionality of the device by performing label-free optical detection of DNA molecules. In this experiment, a monolayer of strongly cationic charged polymer polyethylenimine is used to shift the charge state of near surface NV centers from negatively charged NV − to neutral NV 0 or dark positively charged NV +. Immobilization of negatively charged DNA molecules on the surface of the sensor restores the NV centers charge state back to the negatively charged NV − , which is detected using confocal photoluminescence microscopy. Biochemical reactions in the microfluidic channel are characterized by electrochemical impedance spectroscopy. The use of the developed electrochemical device can also be extended to nuclear magnetic resonance spin sensing. This research was funded by the [EU HORIZON Quantum Flagship Project ASTERIQS] grant number [820394], the [FWO (Flanders)] grant number [G.0.943.11.N.10.], the [CTU grant] grant number [SGS14/214/OHK4/3T/17], the [Czech Science Foundation (GACR)] grant numbers [GAČR 16-16336S] and [GA20-28980S], the [SAFMAT] grant numbers [LM2015088] and [LO1409], the institutional resources of the Department of Biomedical Technology FBMI CTU, the Erasmus Student Mobility Grant, and the J. E. Purkyněfellowship awarded by the Academy of Sciences of the Czech Republic.

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.

Although Raman spectroscopy is a good tool for effective assessment of atomic boron concentration in diamond, determination of further physical properties using this non-destructive approach requires advancement in Raman analysis. In this work, we present an extended study of the Raman spectrum of boron-doped diamond, over a broad boron doping range and at increasing measurement temperature, based on the interaction between phonon and electronic Raman scattering effects. The presented analysis demonstrates the considerable contribution of electronic Raman scattering to the Raman spectrum and opens a practical route toward determination of additional boron-doped diamond properties, such as carrier concentration and carrier mobility.

CuSCN thin films (optimized previously for perovskite photovoltaics) are deposited on glass, F:SnO2 (FTO), Au, glass-like carbon (GC), and reduced graphene oxide (rGO). They exhibit capacitive charging in an electrochemical window from ca. −0.3 to 0.2 V vs Ag/AgCl. Outside this window, CuSCN film is prone to chemical and structural changes. Anodic breakdown (at ca. 0.5 V) causes restructuring into submicrometer particles and denuding of the substrate. The natural p-doping is demonstrated by both the Hall effect and Mott–Schottky plots from electrochemical impedance. The corresponding flatband potentials (in V vs Ag/AgCl) varied with the substrate type as follows: 0.12 V (CuSCN@FTO), 0.08 V (CuSCN@Au), −0.02 V (CuSCN@GC), and 0.00 V (CuSCN@rGO). The acceptor concentrations determined from electrochemical impedance spectroscopy are by orders of magnitude larger than those from electrical conductivity and the Hall effect, the latter being regarded correct. Raman spectra confirm that thiocyanate is the domina...

We present an anomal current decrease for Mg contact on semi-insulating (SI) GaAs. The explanation of the observed effect is discussed within the light of the observed transport characteristics and XPS analysis.

Raman spectroscopy has been foreseen as a simple and non-destructive characterization method to determine the boron concentration in heavily boron-doped diamond with metallic conductivity. However, currently available empirical studies are not fully satisfactory for enabling accurate determination of the boron concentration in diamond. Here, we study Raman spectra of epitaxial boron-doped diamond as a function of the boron concentration and the excitation wavelength. The zone center phonon and the phonon density of state maximum (at ca. 1200 cm−1) lines are analyzed using a decoupled double Fano-function. This analysis method accurately describes the observed variation of the asymmetric parameters with atomic boron concentration and the photon excitation energy and enables the determination of the atomic boron concentration from the parameters of the examined Raman lines.

A comparative study of diode structures based on semi-insulating (SI) GaAs with evaporated Mg vs. Pt contacts is presented. Electric field strength in the vicinity of the contacts is inferred from the detection of α-particles emitted from 241Am radioisotope. It is shown that at zero bias, the structure with Mg-based contacts (MgO/SI GaAs) gives comparatively small signal implying an ohmic behaviour. Contrary, the structure with Pt contacts reveals presence of a non-negligible electric field near the contacts at zero bias voltage, thus indicating presence of a sizeable space charge region near the interface. The results are supplemented by insights from atomistic electronic structure modeling of idealized GaAs/Pt vs. GaAs/Mg and GaAs/MgO interfaces.

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 $$\sqrt{(D_{\Omega} / D_E)}$$ , where DΩ is of a quantum nature and DE of an essentially geometric one.

We report on the optimisation of precursor gas composition for the repeatable preparation of large area highly conductive boron doped nano-crystalline diamond layers with low sp 2 content using microwave plasma enhanced linear antenna chemical vapour deposition apparatus. The precursor gas composition parameter space was probed by varying the boron, oxygen and carbon atomic ratios whilst fixing all other parameters constant. By radically increasing the B content and careful consideration of the B and O content in the gas phase, thin B-NCD layers (∼300 nm) were prepared over large areas, repeatable, with high boron concentrations (∼2 × 10 21 at/cm 3 ) and electrical conductivity levels akin to B-NCD layers prepared in conventional MW PECVD systems (>35 S cm −1 ) with electrochemical properties suitable for industrial applications.

Gadolinium bisphthalocyanine (GdPc2) has been placed among the highest ranked molecular materials considered namely for modern optoelectronic applications including organic solar cells. To improve understanding of the correlation between GdPc2 magnetic properties and its electronic functionality, we experimentally and theoretically studied charge carrier concentration, charge mobility, and influence of local magnetic field on charge carrier transport. For better clearance, all the main studied properties of GdPc2 bisphthalocyanine were compared with Zn phthalocyanine (ZnPc) as a reference material. Conductivity and charge carrier mobility were measured in materials incorporated in FET active channels. UV Vis spectroscopy, Electron Paramagnetic Resonance Spectroscopy, and IR spectroscopy were also applied. The narrow band gap together with small ionization potential of GdPc2 lead to high free charge carrier concentration. Among parameters affecting charge carrier mobility, molecular arrangement and intermolecular and intramolecular charge carrier pathways were highlighted. The possibility that the interaction of the mobile charge carriers with the local magnetic field of GdPc2 molecules reduces charge carrier mobility is also discussed.

It is important for electro-optical applications of nanocrystalline diamond (NCD) films to achieve high optical transparency with low electrical resistivity. However, currently fabrication of highly transparent NCD films with reasonable electrical conductivity remains a challenge – any increase in conductivity simultaneously reduces transparency. Here, we report on fabrication of highly conductive and yet highly transparent electrodes based on boron-doped nanocrystalline diamond (B-NCD) films and Ti grids. We studied B-NCD films with variable boron content and thickness to determine preferable electrical and optical characteristics. Composite electrodes with a sheet resistance of 200 Ω/sq and optical transparency of 80% have been obtained by the integration of a thin nanostructured Ti-grid, sandwiched between the glass substrate and B-NCD layer.

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 effect 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 &times, 10&minus, 2 Ohm∙cm and an electron mobility of 18 cm2∙V&minus, 1∙s&minus, 1. 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.

In this work, we deal with a study of the electron-transport behavior of zirconium nitride RF magnetron sputtered films using Zr target in reactive nitrogen ambient. The films were grown on silica-coated silicon substrates at a substrate temperature of 300°C. The growth process was monitored using an in-situ spectral ellipsometer in a spectral range from 245 to 1690 nm. The ellipsometric data were analyzed using a dispersion model based on Drude-Lorentz oscillators. We estimated electron-transport properties at each stage of the deposition process by analysis of the model parameters. The mechanism of the thickness-dependent electron-transport phenomenon of the ZrN films is discussed in this work.

We present a comparative study of the symmetric metal-SI GaAs-metal (M-S-M) diodes with full-area contacts on both device sides, in order to demonstrate the effect of contact metal work function in a straightforward way. We compare the conventional high work function Pt contact versus the less explored low work function Mg contact. The Pt-S-Pt, Mg-S-Mg and mixed Mg-S-Pt structures are characterized by the current-voltage measurements, and individual Pt-S and Mg-S contacts are investigated by the X-ray photoelectron spectroscopy (XPS). The transport measurements of Mg-S-Pt structure show a significant current decrease at low bias while the Mg-S-Mg structure shows saturation current at high voltages more than an order of magnitude lower with respect to the Pt-S-Pt reference. The phenomena observed in Mg-containing samples are explained by the presence of insulating MgO layer at the M-S interface, instead of the elementary Mg, as confirmed by the XPS analysis. Alternative explanations of the influence of MgO layer on the effective resistance of the structures are presented. The reported findings have potential applications in M-S-M sensors and radiation detectors based on SI GaAs.

Although significant efforts have been dedicated to optimize the quality of epitaxial diamond layers, reported properties of diamond based electronic devices do not yet approach expected theoretical values. Recent works indicate that boron-doped and phosphorous-doped diamond can be grown on atomically stepped (113) surfaces (A. Tallaire et al., 2016; M.-A. Pinault-Thaury et al., 2019), however the electrical properties of these layers have not been studied in detail. In this work, we report on structural and electrical properties of boron-doped epitaxial diamond layers grown on (113) substrates. Properties of the diamond layers have been investigated by means of scanning electron microscopy, atomic force microscopy, Hall effect, secondary ion mass spectrometry and Raman spectroscopy. Our results show that boron-doped diamond layers can be grown on (113) substrates at high deposition rates with atomically flat surfaces, excellent electrical properties and high boron incorporation efficiency.

In this work, current multiplication at high electric field in epitaxial boron-doped diamond with high acceptor concentration is analyzed, including self-heating effect and impurity impact ionization. Quasi-static current-voltage (I-V) characteristics were measured using a transmission-line pulse setup with 100 ns pulse duration on samples with two Ohmic titanium/gold electrodes. Unambiguous exponential and super-exponential behaviors are observed in the I-V curves along with, in some cases, negative differential resistance. The self-heating effect is analyzed using transient interferometric mapping of the thermal energy distribution between electrodes with an ns time scale. Measured I-V characteristics are modelled by finite element method and by considering boron acceptor ionization due to self-heating effect and impurity impact ionization. Simulated I-V characteristics, in particular the appearance of the negative differential resistance region attributed to self-heating, are in good agreement with experimental data.

Transparent conductive electrodes are principal components in various optoelectronic devices and technologies. As such, diamond coatings in the form of electrically conductive thin films are envisioned to provide advantageous chemical and mechanical characteristics/stability in a variety of modern technologies including optoelectronics, biosensing, electrochemical and micromechanical systems. However, deposition of electrically conductive polycrystalline diamond coatings for such applications is currently a challenging task, since temperatures above 600 °C are usually required to ensure good diamond layer quality, which in turn limits the selection of substrates, to materials capable of withstanding exposure to high temperatures. In the present work, we investigate routes toward enhancement of electrical characteristics of nanocrystalline boron-doped diamond (BDD) films fabricated at low temperatures via chemical vapour deposition. We found that post-growth processing of BDD layers enhances their electrical properties, which otherwise are dependent on the employed deposition temperature regime. Finally, we show that integration of an electrically conductive Ti grid opens a route for fabrication of highly transparent and conductive composite nanocrystalline BDD electrodes over large areas at temperatures as low as 250 °C.

Oxidation and hydrolysis are two spontaneous reactions occurring when scandium nitride (ScN) is exposed to air (oxygen and humidity). In order to evaluate the detrimental effect of the oxidation on functional properties of the material, ScN films were prepared under ultrahigh vacuum conditions at 700 °C onto two different substrates; crystalline MgO(0 0 1) and amorphous fused silica. X-ray Photoelectron Spectroscopy analysis was performed to study the oxidation reactions. The study also employed vacuum transferred pristine samples. Crystalline quality and oxidation resistance were found to be strongly correlated. Degradation of electrical and optical properties was observed for polycristalline films prepared on fused silica. On the other hand, highly ordered crystalline films grown on MgO(0 0 1) demonstrated surface passivation preventing further progress of the oxidation. Post-deposition exposure to air was found to be a principal source of the observed oxidation.

International audience; Eu doped ZnO thin films were deposited by pulsed laser deposition on fused silica substrate at room temperature and 300 °C in an oxygen ambient of pressure of 10 Pa. The films exhibited a wurtzite structure. The average transmittance exceeded 80% in the visible region confirming a good optical quality of the films. The characteristic emission of both Eu2+ and Eu3+ was observed when indirectly excited. The increase of substrate temperature to 300 °C led to higher crystallites size, lower efficiency of energy transfer from ZnO to Eu ions and lower resistivity of the film. XPS revealed the ratio of Eu divalent and trivalent states as 35%:65% and 27%:73% for sample deposited at room temperature and 300 °C, respectively. AFM showed higher RMS for the sample prepared at 300 °C.

Comparative study of AuGeNi, Pt, Nd and Gd contacts on semi-insulating (SI) GaAs with respect to the backside quasi-ohmic AuGeNi contact in symmetrical geometry is investigated. Fabricated diode structures are characterized by the current- and capacitance-voltage dependencies. Each of contacts gives an original set of characteristics and current lower that corresponding to the ohmic, bulk limited transport in the initial, low bias (

International audience; Lattice disorder, electronic Raman scattering, and Fano interaction effects are at the genesis of the Raman spectrum of heavily boron-doped diamond. However, no accurate unified description of this spectrum has been reported yet. In this work, we propose a novel analysis of the Raman spectrum of boron-doped diamond based on classical models of electronic Raman scattering and Fano effect. This new analysis shows that the Raman spectrum of boron-doped diamond results from the combination of electronic Raman scattering and its interaction, i.e. Fano effect, with the diamond phonon density of states and it confirms the 500 cm −1 and 1200 cm −1 bands originate from the phonon density of states.

Due to its high sensitivity to corrosion, the use of Si in direct photoelectrochemical (PEC) water-splitting systems that convert solar energy into chemical fuels has been greatly limited. Therefore, the development of low-cost materials resistant to corrosion under oxidizing conditions is an important goal toward a suitable protection of otherwise unstable semiconductors used in PEC cells. Here, we report on the development of a protective coating based on thin and electrically conductive nanocrystalline boron-doped diamond (BDD) layers. We found that BDD layers protect the underlying Si photoelectrodes over a wide pH range (1-14) in aqueous electrolyte solutions. A BDD layer maintains an efficient charge carrier transfer from the underlying silicon to the electrolyte solution. Si|BDD photoelectrodes show no sign of performance degradation after a continuous PEC treatment in neutral, acidic, and basic electrolytes. The deposition of a cobalt phosphate (CoPi) oxygen evolution catalyst onto the BDD layer significantly reduces the overpotential for water oxidation, demonstrating the ability of BDD layers to substitute the transparent conductive oxide coatings, such as indium tin oxide (ITO) and fluorine-doped tin oxide (FTO), frequently used as protective layers in Si photoelectrodes.

The addition of CO2 into the process gas has a significant impact on the quality and the incorporation of boron in CVD diamond layers. In this report we study the effect of CO2 addition in the gas phase on the properties of boron doped nano-crystalline diamond (BNCD) layers grown at low substrate temperatures (450–500 °C) using a microwave linear antenna plasma-enhanced chemical vapour deposition apparatus (MW-LA-PECVD). Experimental results show an increase in the layers' conductivity with a reduction in CO2 concentration, which is consistent with the variation in the atomic boron emission line intensity measured by optical emission spectroscopy (OES). At CO2 concentrations close to zero, we observed the formation of a smooth, transparent and highly resistive layer on unseeded substrates. This layer has been identified as silicon carbide (SiC) by transmission electron microscopy and X-ray photoelectron microscopy. The presence of silicon in the plasma is confirmed by OES and it is attributed to quartz tube etching. In this specific deposition condition, diamond growth is in competition with SiC growth, which affects the diamond layer properties. SEM image of layer growth on a silicon substrate at low CO2 concentration on unseeded area (left) with a smooth, highly resistive and transparent SiC layer and seeded area (right) with a boron doped nano-crystalline diamond layer.

International audience; Formation of ohmic contacts on boron-doped diamond using zirconium and niobium has been studied in comparison to the commonly used titanium or tantalum contacts. Metal contacts were fabricated using standard micro-fabrication technologies on epitaxial layers with different boron concentrations. Room temperature specific contact resistance was determined using the circular Transmission Line Model after annealing at various temperatures. The specific contact resistance varies considerably with boron concentration and annealing temperature. Zirconium and niobium form ohmic contacts on highly boron-doped diamond after high-temperature annealing with a specific contact resistance comparable to that of titanium and tantalum contacts. Furthermore, we observed zirconium contacts showed better thermal stability upon high-temperature annealing compared to titanium and other metal contacts. These results emphasize the potential of zirconium for the formation of ohmic contacts on boron-doped diamond.

International audience; With a high affinity to carbon comparable to titanium and an electrically conductive carbide, zirconium has potential to form ohmic contact on boron doped diamond. In this work, formation of ohmic contacts on boron doped diamond using zirconium is studied in comparison to titanium. Boron doped diamond epitaxial layers have been grown by microwave plasma enhanced chemical vapour deposition with various B/C ratio. Circular Transmission Line Model structures were fabricated using standard micro-fabrication technologies. Specific contact resistance of fabricated contacts was determined for different boron concentrations and for various annealing temperatures. Ohmic contacts using zirconium are formed after annealing at 400 °C. Specific contact resistance steadily decreases with high temperature annealing down to a value of ca. 1 mΩ.cm 2 after annealing at 700 °C for highly boron doped diamond. In comparison, titanium contact fabricated on highly doped diamond appears not stable under high temperature annealing.

The ability to form an efficient interface between material and neural cells is a crucial aspect for construction of neuroelectrodes. Diamond offers material characteristics that could, to a large extent, improve the performance of neuroelectrodes. The greatest advantage of diamond is a large variety of material and surface properties such as electrical conductivity, surface morphology, and surface chemistry. Such a variety of material characteristics can lead to various cellular responses. Here, the authors compare survival, adhesion, and neurite formation of primary neurons on diamond thin films of various morphologies and treatments with several types of polymers commonly used to enhance cell adhesion. The authors find that the variation of surface roughness of nanocrystalline diamond film when coated with polymer does not have a major influence on neuron survival or adhesion. The adhesion of neurons can be influenced by the selected type of polymer coating. High molecular weight of polyethylenimine results in lower viability, adhesion, and neurite formation. The addition of laminin to treated films do not lead to significant improvements in neuron adhesion and neurite development. Their findings emphasize the importance of the correct polymer treatment over morphological properties of diamond thin films as a material for forming interfaces with primary neurons.

In this work we develop DNA sensors that are based on charge switching in colour centres in diamond. The presented method allows the combination of luminescence sensor and electrochemical sensor working on the principle of electrochemical impedance spectroscopy (EIS). The sensor employs specifically designed diamond structures grown by the means of chemical Vapour deposition (CVD). This diamond structure consists of highly boron doped diamond electrode on which an intrinsic diamond layer is deposited. This intrinsic layer is about 15 nm thick and it contains NV colour centres. The device is then embedded in polydimethylsiloxane (PDMS) microfluidic flow cell and covered by a transparent indium tin oxide (ITO) coated electrode. The switching of the NV centre charge state as a response, on diamond surface termination, is crucial tool for the sensitive charged molecules sensing. First we demonstrated high sensitivity of the near surface NV centres on a diamond biosensor surface charge termination. The measured data are supported by band bending modelling. Negative O- terminated surface results in a preferable NV centre charge state of NV0 or NV−, whereas positive H- terminated surface leads to mostly non-PL NV+ charge state. By this principle any charged molecule, such as polymer on DNA, can be detected by a customized surface functionalization. Functionality of the microfluidic diamond device is also verified by the EIS. The authors acknowledge the institutional resources of the Department of Bio-medical Technology FBMI CTU; CTU grant SGS14/214/OHK4/3T/17; the Czech Science Foundation (GACR) Grant ID: GAČR 16-16336S; EU–FP7 research grant DIADEMS, No. 611143, FWO (Flanders) G.0.943.11.N.10.; the Erasmus Student Mobility Grant and the J.E. Purkyne fellowship awarded by Academy of Sciences of the Czech Republic.

International audience; Characteristic Raman features of boron-doped diamond layers with metallic conduction are studied experimentally and discussed in comparison with an extensive selection of literature data. Despite evidence that the main Raman bands are mostly characteristic features of carbon atom vibration modes, their position is found to be proportional to boron concentration. While the origin of the Raman bands located at c.a. 500 cm À1 remains unclear, the band centred at c.a. 1200 cm À1 is attributed to a maximum of phonon density of states due to softening of the Raman wave vector conservation rule. The downshift and broadening of the diamond line are attributed, primarily, to the domain size effect caused by scattering on boron impurities, secondly to the Fano effect due to electronic Raman interaction, and finally to lattice expansion due to the boron doping.

The aim of this work is to compare and improve optical and structural properties of GaN layers prepared using TMGa or TEGa precursors. MOVPE grown GaN buffer layers on sapphire substrates are usually grown from TMGa precursor at the temperatures above 1000 °C. These layers contain deep and shallow acceptor levels which are responsible for blue and yellow defect bands in luminescent spectra. Both defect bands are detrimental for all major nitride device applications. Especially n-doped GaN layers suffer from strong yellow defect bands. In this work, it is shown that yellow band photoluminescence intensity can be suppressed by using TEGa precursor during the growth of n–doped GaN layers. Different kinds of growth parameters, such as growth temperature or growth rate, have been studied. It is also shown that the change of carrier gas (H2 or N2) has very strong influence on the layer quality. H2 carrier gas increased intensity of yellow band in sample grown from TEGa precursor while N2 carrier gas had the same effect for sample grown from TMGa precursor. Variable energy positron annihilation spectroscopy showed creation of single VGa in H2 atmosphere and clustering of VGa to big complexes ((VGa)3(VN)n) in N2 atmosphere.

We report on the preparation and characterisation of boron (B) doped nano-crystalline diamond (B-NCD) layers grown over large areas (up to 50 cm × 30 cm) and at low substrate temperatures ( 2 /CH 4 /CO 2 and H 2 /CH 4 gas mixtures with added trimethylboron (TMB). Layers with thicknesses of 150 nm to 1 μm have been prepared with B/C ratios up to 15000 ppm over a range of CO 2 /CH 4 ratios to study the effect of oxygen (O) on the incorporation rate of B into the solid phase and the effect on the quality of the B-NCD with respect to sp 3 /sp 2 ratio. Experimental results show the reduction of boron acceptor concentration with increasing CO 2 concentration. Higher sp 3 /sp 2 ratios were measured by Raman spectroscopy with increasing TMB concentration in the gas phase without CO 2 . Incorporation of high concentrations of B (up to 1.75 × 10 21 cm 3 ) in the solid is demonstrated as measured by neutron depth profiling, Hall effect and spectroscopic ellipsometry.

Czech Science Foundation (GACR) [GACR 13-31783S]; Czech Republic Ministry of Education, Youth and Sports [CZ.1.07/2.3.00/20.0306]; Academy of Sciences of the Czech Republic; FWO (Flemish Research Council) [G.088.12N]; EU project MERIDIAN [280778-2]; grant MEYS [LM2011026]; CTU [SGS14/215/OHK4/3T/17, SGS14/214/OHK4/3T/17]

Electrical properties of epitaxial boron-doped diamond layers are studied at high electric fields in a wide range of boron concentration. Current-voltage characteristics co-planar concentric disk ring electrodes devices were measured using transmission line pulsed (TLP) characterization technique. Finite element method shows the electric field between test structures with co-planar plane parallel electrodes, used in previous studies, and concentric disk ring electrodes are comparable for inner ring electrode with a large diameter. The threshold electric field for the observed sudden increase of current, attributed to impurity impact ionization and/or self-heating, decreases from 130 kV·cm−1 to 70 kV·cm−1 with the increasing boron concentration in the epitaxial diamond layer. The measured quasi-static current grows exponentially with the electric field for energy dissipated in the devices limited below 2 μJ.

The low-bias current-voltage characteristics of surface barrier diodes, based on semi-insulating GaAs (SI-GaAs) with different contact metals and area, are reported and analyzed in order to demonstrate the possibility of tuning their low-bias transport characteristics. Novel applications of SI-GaAs emerge for devices with low-current at low-bias requirements, as follows from the possibility of current lowering by as much as two orders of magnitude, achieved by manipulation of the contact metallization and the contact area. The lowest current is observed in the structure with small Mg top and large-area Ti/Pt bottom contact. Since the observed behavior contradicts the conventional ohmic bulk limited and thermionic emission transport models, alternative explanations are discussed. The strong blocking ability of the low-work function Mg contact was attributed to the downwards band-bending, formation of a quasi-degenerate interface region accumulating charge carriers, and the corresponding lowering of the bulk SI-GaAs free carrier concentration. (C) 2013 Elsevier Ltd. All rights reserved.

Methodological scheme of thermal analysis is used for portraying the Earth environmental research and climate changes, showing particularly the history, effect of atmosphere reflection (albedo), and absorption (so-called greenhouse effect included). The net behavior of the Earth as a black body is reviewed. The most influential on climate changes is the alteration of the geometry of the Earth trajectory and the irradiative power of the Sun (as a standard thermoanalytical pair of the sample and radiator). Thermodynamic basis of water vapor impacts is pointed out, the absorption spectra of atmosphere are emphasized, and temperature gradients are indicated. The historical course of the Earth temperature and CO2 concentration is put in analogy with the method of gas desorption analysis, which supports the view that the variation of CO2 concentration recorded in the past may not be alone blamed for temperature changes. The influences of atmosphere nanoparticles on weather, climate, and human health are discussed, as well. With 91 references.

Self-similarity and the orderly crystal (often dendritic) growth are an important parts of nature as well as the source of solid-state thermal chemistry under nonequilibrium (undercooling) conditions providing theoretical roots of chemical swinging clock. Such oscillation processes known in chemistry and biology apply for systems far from equilibrium involving special cases of oscillations extending from the self-organized periodic chemical reactions (such as Liesegang’s or Belousov–Zhabotinsky’s reactions) to ordered solid-state processes, from liquids to atmosphere, from macro to micro, indispensable in biology. The chapter deals with a remarkable problem of thermal physics, unresolved for more than 70 years, concerning class of diffusion-controlled periodic chemical reactions, where macroscopically observed diffusion action attains, with appreciable accuracy, the value of Planck’s quantum. Because the classical and quantum diffusions are processes, which are indistinguishable in the configuration space, a quantum criterion in terms of diffusion constants is valid. This criterion enables one to find out conditions under which the quantum behaviour of self-organized periodic reactions can be observed. Examples are shown for the subcritical and critical oscillatory regimes; a special kind of self-organized Liesegang’s rings—annual growth rings of a trunk of larch tree is discussed. The text even involves a thinkable hypothesis of the light self-organization based on the previously analysed principle on least time (Fermat) and of the least action (Maupertuis). It was already noticed by Galileo who opened this problem aware that the cycloid curve yields the quickest descent leading to the so-called brachistochrone. The chapter contains 130 references.

Historical maturity of terms temperatura and thermoscope is sketched. Problem of temperature definition and observation (measurement) is studied in detail. Temperature is a typical averaged quantity clear-cut under equilibrium only. A self-measurability condition is implied, and some consequences are outlined. Physical and operational meaning of temperature and its self-measurability during unsteady thermal processes is analysed. Particular case of thermal analysis often idealized under constant temperature changes is thermodynamically examined. For extreme temperature changes as that during quenching, a novel term “tempericity” is proposed. Branched view to the spheres of alternative thermodynamics is shown locating thermal analysis as thermotics and quenching as thermokinetics. Non-equilibrium thermodynamics under a non-constant rate of temperature changes is analysed. Practical aspects of non-equilibrium temperatures due to heat inertia and thermal gradients are specified including cases of modulated experiments. Textbook thermodynamic description under the perceptible impact of second temperature derivatives becomes ambiguous and associated tabular values are unclear. Thermotics, thermokinetics, and the validity of the first and second thermodynamic laws are discussed bringing another dimension of the thermodynamic legacy. The concept of equivalence of work and heat is questioned. The chapter contains 126 references.

The choice of the mathematical structure of physical quantities, which is natural for the description of finite physical reality and related problems, is discussed from the historical and the epistemological points of view. We show that for the establishment of physical quantities is fully sufficient the system of rational numbers which are equivalent to the finite ordered sets of integers, while the currently used system of real numbers is quite redundant for such a purpose. These facts may have far reaching consequences not only for pure epistemology but for the interpretation of many fundamental physical phenomena as well. Finally, the relation between the chosen structure of physical quantities and the so-called Principle of conformity of physics and mathematics is shortly discussed.

International audience; The electrical properties of chemical vapour deposited p-type epitaxial diamond layers are studied in high electric field conditions. The quasi-static current-voltage characteristics have been measured using transmission-line pulse method with 100 ns pulses. Reproducible impurity impact ioni-zation avalanche breakdown occurs at a critical electrical field in the range of 100–200 kV cm À1 depending on the acceptor concentration and temperature, leading to complete ionisation of neutral impurities. The current-voltage characteristics exhibit an S-shape with the bi-stable conduction characteristic of impurity impact ionisation. Published by AIP Publishing. [http://dx.doi.org/10.1063/1.4946853] Due to their high ionisation energy, dopants in diamond are only partially ionised at room temperature, e.g., less than 0.1% of boron impurities are ionised in a low-doped p-type diamond. As a matter of fact, the temperature range of incomplete ionisation of boron acceptor, i.e., the freeze out region, extends up to about 1000 K. The consequent high re-sistivity severely limits potential applications of diamond as semiconductor. 1,2 In the freeze out regime, the conductivity can be increased by excitation of free carriers bounded to the neutral impurity centres to conduction/valence band by (1) thermal ionisation rising the temperature, (2) optical ionisa-tion with light irradiation of suitable wavelength, and finally (3) impact ionization of neutral centres by the free carriers under a sufficiently high electric field. Under a high electric field, the free carriers can gain enough energy to be able to ionise neutral impurities by inelastic collisions leading to free carrier multiplication. This process results in nonlinear current voltage characteristics. 3