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Immiscible liquid–liquid displacement is a fundamental problem in fluid mechanics and has many applications like, for instance, enhanced oil recovery. One of the most valuable methods to increase oil recovery is injecting a fluid into the reservoir to displace the oil, and the primary motivation of this work is to evaluate the liquid–liquid displacement in homogeneous and heterogeneous porous media. We carried out a direct numerical simulation of liquid–liquid displacement in three different porous media: medium I, II, and III. The medium I is homogeneous. Medium II is heterogeneous, in which the diameter of the spheres reduces from the bottom to the top boundary. Finally, in medium III, the diameter of the spheres is randomly distributed all over the domain. The three media were composed of spheres and had the same mean porosity. We tracked the liquid interface front over time until the breakthrough to compute the mass entrapped as a function of viscosity ratio and capillary number. The sweep efficiency increases when the displacing liquid viscosity also increases. The role played by the capillary number is more complex. In medias I and II, the entrapped mass rises with the capillary number. For a specific condition in medium III, when the displacing liquid is more viscous than the displaced one, the opposite can occur, i.e., the entrapped mass decreases with the capillary number. Beyond the capillary number and viscosity ratio, the sweep efficiency strongly depends on the kind of medium. Mainly, the entrapped liquid is smaller in the homogeneous medium. [ABSTRACT FROM AUTHOR]

The electrical properties of high-purity 4H–SiC epitaxial layers are investigated. The current density versus applied voltage curves shows that some specimens have space charge limited transport behavior. Lampert–Mark model for trap-controlled electron transport in semi-insulating materials demonstrated the presence of an intragap state at 0.26 eV below the conduction band. Photodeep level transient spectroscopy has confirmed the presence of a deep level at about 0.3 eV below the conduction band only in samples with non-Ohmic behavior. Cathodoluminescence imaging has revealed the presence of high luminescent areas related to stacking faults (SFs) under the devices showing non-Ohmic behavior. The presence of single-layer SFs was detected by cathodoluminescence spectroscopy due to the typical emission at 2.95 eV. Thus, we demonstrated that the SFs modified the charge transport from Ohmic conduction to space charge limited conduction of the affected samples. [ABSTRACT FROM AUTHOR]

The potential energy curves of the ground state and of some excited states of the manganese dimer have been calculated over a wide range of internuclear distances using the second order n-electron valence state perturbation theory applied to a complete active space self-consistent field reference wave function. The ground state of Mn2, for which also the third order NEVPT has been used, is calculated to be a singlet belonging to the Σg+ symmetry, characterized by a large equilibrium internuclear distance Re of 3.7–3.8 Å, by a low dissociation energy De of 0.07–0.08 eV, and by a small harmonic frequency ωe of 43 cm-1. The experimental evidence that Mn2 is a van der Waals molecule is thus confirmed. Among the excited states, 11Πu, which is usually indicated as the ground state by density functional theory studies, appears as a low-lying state with Re=2.50 Å, De=1.35 eV, and ωe=246 cm-1. [ABSTRACT FROM AUTHOR]

The potential energy curves of the molecules Mo2, W2, and CrMo have been studied ab initio using large basis sets and the “n-electron valence state perturbation theory” up to the third order in the energy. The third order results for Mo2 and W2 reproduce the equilibrium distances re and the harmonic frequencies ωe in fairly good accordance with the experimental values but tend to underestimate the dissociation energy. The CrMo molecule, for which experimental dissociation energy data do not exist yet, is predicted to have a value for De of ≈2.5 eV. [ABSTRACT FROM AUTHOR]

The effects of low-temperature annealing in 8.2 MeV electron-irradiated 4H-SiC Schottky diodes were investigated. Deep-level transient spectroscopy and minority-carrier diffusion length (Ld) measurements were carried out on not-irradiated samples and on irradiated samples before and after thermal treatments up to T=450 °C. We found that several deep levels in the upper half band gap (S1 with enthalpy ET=0.27 eV, S2 with ET=0.35 eV, S4 with ET=0.71 eV, and S5 with ET=0.96 eV) anneal out or modify at temperature values lower or equal to T=450 °C, whereby their progressive annealing out is accompanied by a net increase of Ld, up to 50% of the value in the as-irradiated sample. We drew some conclusions regarding the microscopic nature of the defects related to the deep levels, according to their annealing behavior. [ABSTRACT FROM AUTHOR]

The effects on 4H-silicon carbide epilayers of irradiation with protons and electrons having particle energies, respectively, of 6.5 and 8.2 MeV were carefully studied and critically compared. In detail, the electronic levels associated with the irradiation-induced defects were analyzed by current-voltage characteristics and deep-level transient spectroscopy (DLTS) measurements up to 550 K. In the same temperature range the apparent free-carrier concentration was measured by capacitance-voltage characteristics in order to monitor compensation effects due to the deep levels associated with the induced defects. Introduction rate, enthalpy, and capture cross section of such deep levels were compared. We found that a set of deep levels (at ET=0.39 eV, ET=0.65 eV, and ET=0.75 eV) is the same in both cases of proton and electron irradiations, whereas two other pairs of levels (S1, ET=0.20 eV and S1*, ET=0.23 eV; S5, ET=1.09 eV and S5*, ET=0.89 eV) appearing in the same temperature range within the DLTS spectra should be associated with different defect complexes according to the irradiation type. Some conclusions regarding the microscopic nature of the defects related to the deep levels have been drawn. [ABSTRACT FROM AUTHOR]

The distribution of the electric field and its spatial extent are key predictors of the charge collection efficiency of particle detectors. The electric field is strictly related to the electrically active defects, which are significantly modified by irradiation. In this paper we analyze the native and radiation-induced defects and infer the mechanisms controlling the electrical properties of semi-insulating GaAs Schottky diodes. The correlation between the electric-field distribution and deep levels confirms that the compensation mechanisms are mainly due to the donorlike centers and to their enhanced neutralization, which occurs for moderately high electric fields. Moreover, taking into account the charge balance among native and irradiation-induced defects, the active region extent is predicted. [ABSTRACT FROM AUTHOR]

The features of current deep level transient spectroscopy (I-DLTS) spectra are investigated in AlGaAs/GaAs heterostructure field-effect transistors both through experiments and two-dimensional numerical device simulations. Differently from electron traps located in the n-type semiconductor bulk, which can only be detected in emission-mode by I-DLTS, deep levels located at the ungated device surface are shown to be revealed both in emission and capture transients by I-DLTS. Experimental and simulation results indicate that this behavior originates from inherent physical properties of surface deep levels interacting with holes attracted at the ungated surface by the negative charge associated with ionized traps. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present a study of the effects of high and low energy neutron irradiation on CdTe and CdZnTe high resistivity detector grade material. The evolution of the defect states under increasing irradiation fluence has been monitored by means of photoinduced current transient spectroscopy analyses. Particular attention is placed on the comparison and correlation between the results from the two materials under the two different neutron irradiation energies. The behavior of the observed deep traps associated with defect states allowed us to attribute an origin to most of them and to understand the role they play in the charge carrier collection process and in the degradation of material spectroscopic capabilities. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This article concerns the existence of a double-junction effect in proton-irradiated silicon p[sup +] υ-n[sup +] (pin) diodes demonstrated by surface potential and optical-beam-induced current (OBIC) investigations. By increasing the diode biasing, the junctions existing at both ends in the irradiated devices move towards each other up to join, hence, causing a full depletion of the diodes. Due to the inhomogeneity of the electric field, however, the charge-carrier collection is strongly dependent on the position. The extent of the diode depletion layers at both ends and the shape of the electric field within the p[sup +]-υ-n[sup +] diodes are determined as a function of the bias applied. Three-dimensional photocurrent maps obtained by OBIC profiles allow for imaging the double junction. The deep level analysis evidences the presence of irradiation-induced defects, which are responsible for the double-junction effect. [ABSTRACT FROM AUTHOR]

Presents information on the study which investigated the electrical and optical characteristics of Erbium-doped silicon by liquid phase epitaxy. Experimental details; Results and discussion; Conclusions.

Investigates the defective states induced in floating zone silicon by the heavy diffusion of dopants by means of the electron beam-induced current (EBIC) method. Evolution of the electrical and morphological properties of the induced defects; Role of aluminum in the electrical activity of bulk defective states; Sample mounting geometries utilized for EBIC analyses.

Presents information on a study that determined the diffusion length and surface recombination velocity of the minority carriers from electron beam induced current profiles on a semiconductor containing a barrier perpendicular to the scanned surface. Methodology of the study; Results and discussion on the study.

Presents a study which obtained the diffusion length of minority in n-type floating-zone silicon samples with the electron-beam-induced current technique in planar configuration. Background on the moment method; Experimental procedures; Results of the study.

Presents an experiment which investigated the levels which are present in semiconducting Cadiminum/Tellurium (Cd/Te) and semi-insulating Cd/Te:Chlorine and (Cd0.8Zn0.2Te) by means of cathodoluminescence. Indepth look at the experiment; What the results showed.

Presents a study that investigated the EL2 trap in highly doped gallium arsenide:tellurium. Method of the study; Results and discussion; Conclusion.

Presents a study which investigated the distribution in liquid-encapsulated-Czochralski GaAs:Te wafers of point and complex defects together with their influence on the minority-carrier diffusion length. Characteristics of the wafers of liquid-encapsulated-Czochralski gallium arsenide tellurium doped; Methods used; Results of the study.

A correction to the article "Preface and acknowledgements" by Anna Cavallini and Stefan K. Estreicher that was published Volume 115, Issue I of the journal is presented, which identifies Daniel José da Silva as the winner of the Corbett Award of International Conference on Defects in Semiconductors (ICDS)-2013.

The article discusses the highlights of the 27th International Conference on Defects in Semiconductors held in Bologna, Italy on July 22-26, 2013. Speakers at the conference include Professors Michael Stavola, Michelle Moram and John Morton. Topics discussed include the defects of semiconductors and nanostructures, such as localized impurities, magnetic impurities and spintronics.

We report on UV responsivity of 4H-SiC photodiodes irradiated by 1 MeV neutrons. Current-voltage characteristics, photoresponse spectra, and responsivity were obtained with light wavelength from 200 to 450 nm. Photoresponse results slightly affected by irradiation up to the threshold fluence [uppercase_phi_synonym]critical=8×1014 cm-2. At fluences ≥[uppercase_phi_synonym]critical the rejection rate is in the order of 103 in the range of 200–320 nm while it is less than 102 at about 320 nm. The abrupt increase in midgap traps induced by irradiation at [uppercase_phi_synonym]critical, observed by photoinduced current transient spectroscopy, proves carrier generation/trapping to be the controlling mechanism for the responsivity. [ABSTRACT FROM AUTHOR]

Defect-related bands and their properties are widely investigated in gallium nitride, especially by luminescence techniques, which evidenced a broad yellow band, and seldom, a green band. We present here a study of the visible portion of the photoconductivity spectra obtained in samples of different thicknesses and doping. The superior resolution of photoconductivity with respect to luminescence techniques allows for clearly distinguishing green and yellow bands, both showing a double peak structure. Moreover, while the yellow band shape results were unchanged with sample properties, the green band is sensitive to the growth conditions. Hence some hypotheses about their microscopic origin can be proposed. [ABSTRACT FROM AUTHOR]

Low temperature annealing of electron irradiation-induced deep levels in 4H-SiC is reported. The major deep level transient spectroscopy peak S2 associated with the energy level at Ec-0.39 eV disappears in the temperature range 360–400 K, and some rearrangement of the peak S3, associated with the defect Z1/Z2 with energy level at Ec-0.5/Ec-0.65 eV occurs in the temperature interval 400–470 K. A net free charge carrier concentration increase goes along with the disappearance of peak S2 at Ec-0.39 eV, whereas the charge collection efficiency of the diode does not experience any significant change. An interpretation of the annealing of peak S2 on a microscopic scale is given. [ABSTRACT FROM AUTHOR]

Electrical properties of gallium nitride (GaN) epitaxially grown on sapphire show significant dependence on layer thickness. In this letter we show some of the main features observed by spectral photoconductivity (PC), electron beam induced current, and current–voltage characteristics. We focus our attention on the blueshift of the PC peak corresponding to the energy gap, which we associated to the strain acting in the GaN epilayers. The good energetic resolution of photoconductivity spectra allows for a direct study of the energy gap dependence on thickness. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We demonstrate that the process of local oxidation of surfaces by atomic force microscopy (AFM) can be upscaled in a straightforward way by using a solid support with multiple protrusions as the cathode electrode. A metallized digital video disk DVD polymeric support has been used as a stamp to generate an array of features of variable length and 100 nm in width on a silicon surface covering a 5×6 mm[sup 2] region. The parallel patterning process involves the formation of as many liquid bridges as there are protrusions in the stamp. The growth rate of the parallel local oxides is slightly smaller than the one obtained by AFM experiments. Nonetheless, results from AFM local oxidation experiments can be readily extended to parallel oxidation which in turn opens the possibility of patterning centimeter-square regions with 10 nm motives. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The properties peculiar to high resistivity CdTe:Cl are of great interest because of its application as a radiation detector. The compensation process responsible for the materials semi-insulating character implies the presence in the lattice of impurities and defects which have not yet been thoroughly characterized. The use of CdTe:Cl as a detector exposes the material to high fluxes of ionizing radiation which alter the crystal stoichiometry and affect the resulting electrical and optical properties, but few and scattered experimental data are available about radiation effects on this compound. In this work we have carried out an extensive investigation of the effects of γ irradiation on CdTe:Cl by photoinduced current transient spectroscopy analyses. We have identified the deep levels with activation energies up to midgap and we have followed their evolution with increasing irradiation doses up to 50 kGy, the dose which totally degrades the material detecting properties. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The optical activity of Er-doped silicon is related to the presence of defects which enhance the typical radiative transition at 0.8 eV but whose nature and properties are still largely unknown. We have investigated the deep levels present in Er-doped liquid phase epitaxy silicon to identify the traps possibly related to the luminescence. Among the observed levels, two minority carrier traps labeled E2 (E[sub C]-0.20 eV) and E3 (E[sub C]-0.39 eV), and one majority carrier trap labeled H1 (E[sub v]+0.32 eV) are good candidates for the material optical activity. The onset of luminescence occurs after a thermal treatment and is accompanied by a high space charge density localization at the epilayer-substrate interface. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have investigated the electrical and optical properties of the deep levels responsible for the 1.4–1.5 eV luminescence band usually observed in II–VI compounds. We compared the energy levels found by cathodoluminescence and junction spectroscopy methods for semi-insulating (CdTe:Cl and Cd0.8Zn0.2Te) and semiconducting samples (undoped CdTe). The techniques utilized were deep level transient spectroscopy (DLTS) on semiconducting samples and photoinduced current transient spectroscopy and photo-DLTS on high resistivity materials. These last two techniques are complementary and allow the determination of the trap character (donor/acceptor). Three acceptor levels are seen in the electrical transient data at Ev+0.12, 0.14, and 0.16 eV with hole capture cross sections of 2×10-16, 1×10-16, and 4×10-17 cm2, respectively. The lowest level is seen only in Cl doped material corroborating the literature optical and electron spin resonance identification of a level at Ev+0.12 eV as being a VCd+ClTe donor–acceptor pair center. All three levels may be present in the 1.4 eV luminescence band. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Hydrogenated nanocrystalline silicon (nc-Si:H) is a multiphase, heterogeneous material, composed of Si nanocrystals embedded in an amorphous matrix. It has been intensively studied recently due to very promising photovoltaic and optoelectronics applications. The present paper aims to study electronic transitions in nc-Si:H grown by Low Energy Plasma Enhanced Chemical Vapor Deposition by Surface Photovoltage Spectroscopy. The study of several thin films grown at different conditions and the comparison with recently published computational studies allowed us to advance a hypothesis on the defect structure responsible for electronic transitions in nc-Si:H. [ABSTRACT FROM AUTHOR]

The electrical compensation processes of high resistivity CdTe is controlled by deep levels. We have characterized the electrical activity of deep traps by means of three different and complementary spectroscopic methods: photoinduced current transient spectroscopy, surface photovoltage spectroscopy, and space charge limited current analyses. The aim is twofold: to achieve a thorough characterization of the deep trap properties and to assess the potentiality and limitations of the three experimental techniques by a cross correlation of the results obtained with each one of them. We have obtained a direct quantitative estimate of the major deep trap concentration, and we have assessed the sensitivity limit in deep-level detection for surface photovoltage spectroscopy. [ABSTRACT FROM AUTHOR]

Cd1-xZnxTe alloys have been studied by surface photovoltage spectroscopy (SPS) and energy dispersive spectroscopy (EDS). The analyses of surface photovoltage spectra have been perfomed at near and above band gap energies. Surface recombination effects on the surface photovoltage have been investigated. SPS analyses of Cd1-xZnxTe alloys with different surface conditions have shown that the surface recombination velocity significantly affects the SPS determination of the material band gap. Accounting for this and preparing the surfaces accordingly, SPS spectra of Cd1-xZnxTe samples have allowed an accurate determination of the optical band gap as a function of the Zn concentration, determined via EDS analyses. The local increases in the density of states associated with band structure features in Cd1-xZnxTe alloys have been investigated by SPS spectra in the above band gap energy range. [ABSTRACT FROM AUTHOR]

Defects in freestanding gallium nitride were examined in this work. Electron beam induced current mapping evidence a low density of dislocations in the first microns from the upper Ga-terminated surface; correspondingly, deep levels detected by junction spectroscopy exhibit point-like characteristics. Spectral photoconductivity measurements in the poorly dislocated region show the characteristic red, yellow, green, and blue bands, which shift toward higher energies with decreasing temperatures according to Varshni’s law. Spectral photoconductivity measurements carried out in depth evidenced, instead, the quenching of the defect-related yellow band and the prevalence of the green band when temperature increases. This behavior suggests a dislocation-assisted connection between the yellow and green bands, in agreement with theoretical models on their common origin involving complexes VGa-ON. [ABSTRACT FROM AUTHOR]

A formulation of the n-electron valence state perturbation theory (NEVPT) at the third order of perturbation is presented. The present implementation concerns the so-called strongly contracted variant of NEVPT, where only a subspace of the first-order interacting space is taken into account. The resulting strongly contracted NEVPT3 approach is discussed in three test cases: (a) the energy difference between the 3B1 and 1A1 states of the methylene molecule, (b) the potential-energy curve of the N2 molecule ground state, and (c) the chromium dimer (Cr2) ground-state potential-energy profile. Particular attention is devoted to the last case where large basis sets comprising also h orbitals are adopted and where remarkable differences between the second- and third-order results show up. [ABSTRACT FROM AUTHOR]

A fast and simple method for the electrochemical preparation of sharp Ni tips for spin polarized scanning tunneling microscopy (STM) is reported. These Ni tips perform well also in conventional STM experiments, being able to achieve reproducible atomic resolution on graphite. Ni tips combine the advantages of both Pt/Ir tips, since they are oxide free, and of W tips because of the greater reproducibility and control of the tip apex by means of the etching protocol, as compared to freshly cut tips. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The behavior of detector-grade Cd[sub 0.9]Zn[sub 0.1]Te in a radiation-hostile environment has been investigated by studying the effects on the material defective states induced by γ irradiation. The detector performance is strongly affected by the presence of charge-trapping centers which may also intervene in the material compensation properties. We have investigated by photoinduced current transient spectroscopy analyses the evolution with increasing irradiation dose of the deep levels both present in the as-grown material and induced by the ionizing radiation. A significant correlation between the material resistivity and some deep levels behavior has been observed. We have compared this trend to the results obtained from γ-irradiated CdTe:Cl to better understand the role deep traps play in the compensation process of II-VI materials. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Charge collection analyses have been carried out on Er-doped silicon to investigate the excitation and de-excitation mechanisms of the Er[sup 3+] ion related to the λ=1.54 μm luminescence. Carrier recombination and trapping at the defective states induced in the material by the presence of Er play a significant role in the excitation of the Er[sup 3+] ion and in its nonradiative decay by the energy back-transfer process. We have obtained a two-dimensional map of the lattice sites where the back-transfer process occurs, and provided experimental proof of the cooperation of two different defects in the excitation and de-excitation processes. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Bowing parameter and intra gap states have been measured on good quality undoped and n-type Si doped InGaN layers, by surface photovoltage spectroscopy (SPS). Bowing parameter calculations have been done with consideration of strain and relaxed nature of InGaN layers. Si donor levels have been measured by SPS on layers with different indium content. Free carrier concentration and Si donor level variations as a function of In content have been analysed. It has been found that the interaction between In and Si plays a fundamental role in Si doping process in InGaN. [ABSTRACT FROM AUTHOR]

Silk is a natural biocompatible material that can be integrated in a variety of photonic systems and optoelectronic devices. The silk replication of patterned substrates with features down to tens of nanometers is exploited to realize highly transparent, mechanically stable, and free-standing structures with optical wavelength size. We demonstrate organic lasing from a blue-emitting stilbene-doped silk film spin-coated onto a one-dimensional distributed feedback grating (DFB). The lasing threshold is lower than that of organic DFB lasers based on the same active dye. These findings pave the way to the development of an optically active biocompatible technological platform based on silk. [ABSTRACT FROM AUTHOR]

We describe a setup suitable for simultaneously measuring optical and electrical properties of a liquid crystal mesophase upon temperature variation, and the difference in the order parameters between the bulk and the interface with the substrate. It integrates high-resolution polarized light optical microscopy, temperature regulation, and electrical measurements in a controlled atmosphere with a software kernel that controls the instruments and synchronizes the data streams. A user-friendly interface allows us to program multistep experiments controlling all the instruments and data acquisition by a specifically designed scheduler. We tested our system on a thin film of alkoxy-substituted phthalocyanines deposited on a test pattern with interdigitated electrodes. We studied the optical and electrical behavior in the proximity of the bulk phase transition to isotropic liquid, identifying a few ordered monolayers anchored to the substrate above the transition temperature. [ABSTRACT FROM AUTHOR]

In this paper, a pioneer partial discharge (PD) loop antenna sensor is presented and examined. It is made of a 70-turn square planar inductor with a side length of 1.8 mm, which is fabricated on top of a silicon substrate in complementary metal oxide semiconductor technology. The microsensor ability to detect corona PD is demonstrated once connected in series with a 60 dB gain amplifier. The behavior is studied at different separation distances from the line through which the PD pulses flow. At 5 cm away, a damped sinusoidal induced voltage with an amplitude of about 100 mV has been measured. The output signal spectrum is highly concentrated around a central resonance frequency of ∼5 MHz. The microsensor response is compared with those of other industrial sensors from Techimp, i.e., horn antennas and high-frequency current transformer sensors. The presented on-chip sensor can be considered a non-intrusive competing solution compared with other heavy and expensive commercial sensors due to its lightweight, compact size, and low cost. In addition, it shows an acceptable signal to noise ratio compared with other commercial electromagnetic wave-based sensors. [ABSTRACT FROM AUTHOR]

Deep level transient spectroscopy was performed on InGaN/GaN multiple quantum well light emitting diodes (LEDs) in order to determine the effect of the dislocation density on the deep intragap electronic levels. The LEDs were grown by metalorganic vapor phase epitaxy on GaN templates with a high dislocation density of 8 × 109 cm-2 and a low dislocation density of 3 × 108 cm-2. Three trapping levels for electrons were revealed, named A, A1, and B, with energies EA≅0.04 eV, EA1≅0.13 eV, and EB≅0.54 eV, respectively. The trapping level A has a much higher concentration in the LEDs grown on the template with a high density of dislocations. The logarithmic dependence of the peak amplitude on the bias pulse width for traps A and A1 identifies the defects responsible for these traps as associated with linearly arranged defects. We conclude that traps A and A1 are dislocation-related intragap energy levels. [ABSTRACT FROM AUTHOR]

P-wave conversion to slow diffusion (Biot) modes at mesoscopic (small-scale) inhomogeneities in porous media is believed to be the most important attenuation mechanisms at seismic frequencies. This study considers three periodic thin layers saturated with gas, oil, and water, respectively, a realistic scenario in hydrocarbon reservoirs, and perform finite-element numerical simulations to obtain the wave velocities and quality factors along the direction perpendicular to layering. The results are validated by comparison to the Norris-Cavallini analytical solution, constituting a cross-check for both theory and numerical simulations. The approach is not restricted to partial saturation but also applies to relevant properties in reservoir geophysics, such as porosity and permeability heterogeneities. This paper considers two cases, namely, the same rock skeleton and different fluids, and the same fluid and different dry-rock properties. Unlike the two-layer case (two fluids), the results show two relaxation peaks and the agreement between numerical and analytical solutions is excellent. [ABSTRACT FROM AUTHOR]

AlInN/AlN/GaN heterostructures were characterized by atomic force microscopy. V-defects and channels were observed. In phase-contrast mode, these features were found related to inhomogeneities associated with In-segregation (and/or In-diffusion) and Al-rich surface reconstruction. The electrical characterization via conductive atomic force microscopy showed enhanced conductivity regions related to In-rich traces within channels and V-defects. [ABSTRACT FROM AUTHOR]

We report on Photocurrent (PC) and optical absorption spectroscopy analyses of the electronic density of states (DOS) distribution around the band-edge of pentacene films of different thickness (from 50 to 300 nm). Both experimental methods allowed us to independently monitor the increase with increasing film thickness of the Davydov splitting of the first absorption band, correlated with modifications in the film molecular structure and packing when passing from a dominant “thin film” to a dominant “bulk” phase. We show how PC spectroscopy has the remarkable ability to detect the modification of the DOS distribution in a noninvasive way, thus allowing the study of fully operational organic thin film transistors. [ABSTRACT FROM AUTHOR]

Technological procedures able to produce high quality electrodes from magnetic oxides in vertical organic-inorganic hybrid devices is a challenging task in the field of organic spintronics. Thin films of magnetite (Fe3O4) have been successfully grown directly on top of organic semiconductor layers, tris(8-hydroxyquinoline)aluminium(III) (Alq3), by pulsed-electron ablation technique. The films show ferromagnetic behavior and good structural quality, properties detected by magneto-optical Kerr effect, superconductor quantum interference device, micro-Raman spectroscopy, and Atomic Force Microscopy. The ferromagnetic behavior persists even for 10 nm thick films. Charge injection at magnetite-organic interface has been finally demonstrated by detecting electroluminescence from Alq3. [ABSTRACT FROM AUTHOR]

In this work the authors report on photocurrent spectroscopy analyses on pentacene thin film transistors that have been bias stressed and exposed to atmosphere over a long period of time (up to 80 days). They have studied the charge transport properties and the electronic excited state energy and distribution of these organic thin film devices. They also have identified the major excitonic and band gap transition energies and have investigated their quite different behavior following exposure to atmosphere or to bias stress. Different charge carrier distributions and trapping phenomena are proposed to describe the observed effects. [ABSTRACT FROM AUTHOR]

Optically induced electronic transitions in nitride based polar heterostructures have been investigated by absorption and emission spectroscopy. Surface photovoltage (SPV), photocurrent (PC), and photo luminescence spectroscopy have been applied to high quality InAlN/AlN/GaN structures to study the optical properties of two dimensional electron gas. Energy levels within the two dimensional electron gas (2DEG) well at the interface between the GaN and AlN have been directly observed by SPV and PC. Moreover, a strong enhancement of the photoluminescence intensity due to holes recombining with electrons at the Fermi Energy, known as fermi energy singularity, has been observed. These analyses have been carried out on InAlN/AlN/GaN heterojunctions with the InAlN barrier layer having different In content, a parameter which affects the energy levels within the 2DEG well as well as the optical signal intensity. The measured energy values are in a very good agreement with the ones obtained by Schrödinger-Poisson simulations. [ABSTRACT FROM AUTHOR]

Point and extended defects introduced in p-type Cz Si by oxygen precipitation and plastic deformation have been investigated with electrical and optical methods. Different materials (oxygen precipitated and/or deformed Cz Si and Fz Si) were examined in order to separate the role of oxygen precipitation, plastic deformation, and metallic contamination on the radiative and nonradiative electronic transitions at defect centers. A deep hole trap, named T1, has been associated with dislocation-related impurity centers; additional deep traps have been related to contamination by grown-in transition metals and to clusters involving oxygen atoms. [ABSTRACT FROM AUTHOR]

The temporal behavior of deep-level luminescence emissions in undoped hydride-vapor-phase-epitaxy GaN layers of different thicknesses has been investigated by time-resolved cathodoluminescence (TRCL). The complex nature of the yellow luminescence is revealed in the TRCL spectra by the presence of two bands peaked at 2.22 and 2.03 eV. A red band with a decay time of 700 μs, centered at about 1.85 eV, dominates spectra recorded for long delay times. Exponential transients with associated decay times of hundreds of ms were measured at 87 K for all the deep-level emissions found in the layers. [ABSTRACT FROM AUTHOR]

Here we describe a straightforward electrochemical method for fabricating sharp cobalt tips. Such tips are particularly useful for those scanning tunneling microscopy (STM) experiments where the focus is on magnetic properties of the surface and the spin polarized (SP) tunneling current is the relevant property, such as in SPSTM and SP scanning tunneling spectroscopy. [ABSTRACT FROM AUTHOR]