Generation Of Holes Research Articles

Electronic transport properties of the perovskite-type oxides La1−xSrxCoO3±δ

La1−xSrxCoO3 is a leading candidate oxide electrode material for replacing standard metal electrodes. Here we investigate the origin of its high electronic conductivity by means of Rietveld analysis, Hall effect measurements, and band-structure calculations. A high electrical conductivity at room temperature, σ = 4.4 × 103 S cm−1 (which is the largest value for oxides that do not contain noble metals), was achieved by the substitution of 40–50 mol% Sr into the La sites, with a high carrier concentration of 4.5 × 1021 cm−3 and a carrier mobility of 5.8 cm2 V−1 s−1. The carrier concentration results from a trade-off between hole generation via Sr substitution and electron generation via oxygen deficiency. The high mobility arises from the small effective mass originating in the transition to a higher spin state.

Formation of the first stars in the universe

The standard theory of cosmic structure formation posits that the present-day rich structure of the universe developed through gravitational amplification of tiny matter density fluctuations left over from the Big Bang. Recent observations of the cosmic microwave background, large-scale structure, and distant supernovae determined the energy content of the universe and the basic statistics of the initial density field with great accuracy. It has become possible to make accurate predictions for the formation and nonlinear growth of structure through early to the present epochs. We review recent progress in the theory of structure formation in the early universe. Results from state-of-the-art computer simulations are presented. Finally, we discuss prospects for future observations of the first generation of stars, black holes, and galaxies.

Band gap-tunable (CuIn)xZn2(1−x)S2 solid solutions: preparation and efficient photocatalytic hydrogen production from water under visible light without noble metals

A series of (CuIn)xZn2(1−x)S2 solid solutions has been successfully synthesized by a solvothermal approach, and the obtained solid solutions, with a size of about 10 nm, exhibit significant absorption in the visible light region and their band gap can be correspondingly tuned from 2.59 eV to 1.64 eV with an increase of the x value from 0.05 to 0.5, implying that they can be used as visible-light driven photocatalysts. Furthermore, the obtained (CuIn)xZn2(1−x)S2 solid solutions display highly efficient photocatalytic activities for H2 evolution from aqueous solutions containing sacrificial reagents (SO32− and S2−) under visible light (λ > 420 nm) even without noble metal co-catalysts, e.g. (CuIn)0.2Zn1.6S2, with a band gap of 2.10 eV, exhibits the highest photocatalytic activity of 0.984 mmol g−1 h−1 even without a Pt co-catalyst. Further studies reveal that the photocatalytic H2 evolution of solid solutions depends on their composition as well as the photophysical properties, such as the ability to absorb visible light and the generation and separation of photo-induced electrons and holes.

Development of hole generation technology for CFRP parts using blast

Development of hole generation technology for CFRP parts using blast

Roles of Bi, M and VO4 tetrahedron in photocatalytic properties of novel Bi0.5M0.5VO4 (M=La, Eu, Sm and Y) solid solutions for overall water splitting

Novel Bi0.5M0.5VO4 (BMV; M=La, Eu, Sm and Y) solid solutions were prepared and studied in this paper. All the samples were proved to produce H2 and O2 simultaneously from pure water under the irradiation of UV light. M–O bond lengths were proved to increase with M cations by refining cell parameters and atomic positions. Besides, band gaps, energy gaps and photocatalytic activities of BMV also changed with M cations. Both of M–O and V–O bond lengths were suggested to account for this phenomenon. Inactive A0.5Y0.5VO4 (A=La, Ce) for water splitting proved incorporation of Bi rather than distortion of VO4 tetrahedron was a critical factor for improving efficiency of overall water splitting by facilitating the generation of electron and hole with lighter effective masses. Replacement of Bi by M cations not only gave indirect effect on band structure but also raised position of conduction band minimum to meet requirement of H2 production.

Dye versus Quantum Dots in Sensitized Solar Cells: Participation of Quantum Dot Absorber in the Recombination Process

Inorganic quantum dots (QDs) show great potential as absorbers in sensitized solar cell, but there are open questions about the role of quantum dots, where primary electron and hole generation occurs, in the recombination process in this kind of solar cells. In opposition to the conventional dye-sensitized solar cell, here we show that inorganic QDs play a direct role in the recombination process. This fact has been determined by a fingerprint of QDs in the capacitance of the device, where the QDs surface states affect the density of states (DOS) distribution. It indicates that now surface states of QD contribute to the common DOS distribution of TiO2/QDs/ZnS, which behaves as a single entity, being impossible to distinguish between TiO2 and QDs. This result highlights the necessity of treating (and optimizing) QD-sensitized solar cells from another perspective than dye-sensitized solar cells, considering the fundamental differences in their behavior.

Visible-Light Induced High-Yielding Benzyl Alcohol-to-Benzaldehyde Transformation over Mesoporous Crystalline TiO2: A Self-Adjustable Photo-oxidation System with Controllable Hole-Generation

High-yielding benzyl alcohol-to-benzaldehyde (BA-to-BAD) transformation has been achieved over mesoporous crystalline TiO2 at mild conditions under visible-light irradiation with/without molecular oxygen. DFT calculations show that the antibonding π molecular orbitals (MOs) of BA can hybridize with the O2p atomic orbitals (AOs) of TiO2, leading to the appearance of new energy levels located in the band gap where holes can be generated under visible-light irradiation. However, the oxidative product, BAD, is not stable when adsorbed on TiO2 surface. This fact is supposed to prevent BAD from overoxidation by ceasing the hole formation. As a result, the hole generation becomes controllable in this type of photoreaction system, and a so-labeled “self-adjustable photo-oxidation system” (denoted as SAPS) can be established. In addition, we also found that lattice oxygen (OL) and Ti atoms within TiO2 frameworks serve as the efficient reservoir for hydrogen and electrons in anaerobic reaction.

Dependence of Mg acceptor levels in InN on doping density and temperature

Infrared (IR) reflectance and transmission spectra of Mg doped InN films are analyzed using a dielectric function consisting of the terms of phonon, plasmon, and electronic transition between the valence band and the acceptor levels. The reflectance spectra at lower temperatures than 200 K are highly affected by the electronic transition. Acceptor activation energy Ea decreases with the increase in ionized acceptors because of the Coulomb potential overlap of acceptors charged by the background electrons and/or hole generation by the temperature increase. It is found that Ea is 69(±5) meV at low Mg− density limit and decreases to 50 meV at 5 K because of the charging by the background electrons of the density of 1 × 1018 cm−3. Temperature increase causes the further decrease in Ea, which causes the high hole density of the order of 1018 cm−3 at room temperature in spite of the high degeneracy of the acceptor states. The heavy hole mass is obtained as 0.59(±0.06)m0.

Light Effects on Charge Trapping and Detrapping of nc-ZnO Embedded ZrHfO High-k MOS Nonvolatile Memories

MOS capacitors containing the nanocrystalline ZnO embedded Zr doped HfO2 high-k gate dielectric film integrated with the indium tin oxide gate electrode have been fabricated and characterized under the dark and light exposure conditions for nonvolatile memory properties. When measured in dark, the capacitor had a large charge storage capacity showing a counterclockwise capacitance-voltage hysteresis. When exposed to the light, the memory capacity was increased. The generation and transfer of electrons and holes in and from the nanocrystalline ZnO under the light exposure condition are responsible for the memory window change and charge retention characteristics.

Electroluminescence from n–n isotype heterostructures of graded-band-gap ZnMgO : Al and ZnO films on platinized Si

We report on room temperature electroluminescence (EL) from n–n isotype heterostructures composed of Al-doped graded-band-gap Zn1−xMgxO (g-ZnMgO : Al) and ZnO films fabricated on Pt/Ti/SiO2/Si substrates. The isotype heterostructure device generated EL emission at operation voltages as low as 3–5 V, whose emission spectra covered visible and near infrared regions under the unipolar operation condition, with g-ZnMgO : Al as positive. The intensity of light emission increased nonlinearly and short-wavelength emissions in the visible region became appreciable at high injection currents. We also observed negative capacitance at high forward bias above the onset voltage, implying generation of holes by hot electrons. We discussed impact ionization as a possible origin of the EL from the heterostructure and the effect of quasi-electric field generated in the graded-band-gap layer in conjunction with the apparent upconversion EL by considering the electric field needed for impact ionization.

A voxel-based kinematic simulation model for force analyses of complex milling operations such as wobble milling

Mechanical machining of fiber reinforced plastics poses special challenges due to the heterogeneous and anisotropic material composition. Process strategies for the generation of drill holes, which aim at directing the resultant process forces toward the center of the workpiece, have been shown to obtain good machining results with less process induced damage. However, these strategies (e.g. wobble milling) might involve complex multiaxial tool movements and are thus very difficult to analyze and optimize. A voxel-based kinematic simulation program has been set up, which allows analyses of process forces for arbitrary milling operations based on the time-resolved determination of the cutting thickness and multivariate process force regression models. A basic analysis of the process of wobble milling is presented as well. It confirms that the resultant process forces are directed toward the center of the workpiece when the outer material layers are machined. The resultant force is directed in a favorable direction throughout the complete cut during the actual process step of wobble milling.

A Flow Path Generation Approach of Hydraulic Manifold Blocks Based on Maze and Genetic Algorithms

The automatic generation of flow path is the key and most difficult task in Hydraulic Manifold Blocks (HMB) design. This paper divides the HMB layout space into grids, and sets the HMB boundaries and existing flow paths to obstacles, and the paths generated using maze algorithm are regarded as the initial population of genetic algorithm. The optimal path with the shortest path and least turnings can be obtained using genetic algorithm. The ports of flow path can be connected after the generation of technical holes based on the blind holes. The design parameters of holes, such as starting point coordinates, orientations and depths, can be obtained through a series of algorithms, and then drive the secondary development system HMBDesigner based on SolidWorks to generate three-dimensional solid model. This paper also discusses the generation method of multi-port flow path and multiple flow paths.

Chip-size formation of high-mobility Ge strips on SiN films by cooling rate controlled rapid-melting growth

High-quality Ge-on-insulators (GOIs) are essential structures for high-performance transistors on an Si platform. We developed a rapid-melting-growth process for amorphous Ge (a-Ge) by optimizing the cooling rate and the underlying insulating materials. The effects of the solidification process for molten Ge on hole generation and spontaneous nucleation in Ge were determined. In addition, nucleation in the a-Ge matrix was found to be drastically suppressed by substituting SiO2 underlayers with SiN underlayers. By combining high cooling rates (10.5–11.5 °Cs−1) and SiN underlayers, we obtained ultra-long single crystal GOI strips (1 cm) with high hole mobilities (> 1000 cm2V−1s−1). This chip-size formation of high-quality GOI will facilitate the development of advanced high-speed Ge-based devices.

Carrier transport mechanism in the SnO2:F/p-type a-Si:H heterojunction

We characterize SnO2:F/p-type a-Si:H/Mo structures by current-voltage (I-V) and capacitance-voltage (C-V) measurements at different temperatures to determine the transport mechanism in the SnO2:F/p-type a-Si:H heterojunction. The experimental I-V curves of these structures, almost symmetric around the origin, are ohmic for |V|<0.1V and have a super-linear behavior (power law) for |V|<0.1V. The structure can be modeled as two diodes back to back connected so that the main current transport mechanisms are due to the reverse current of the diodes. To explain the measured C-V curves, the capacitance of the heterostructure is modeled as the series connection of the depletion capacitances of the two back to back connected SnO2:F/p-type a-Si:H and Mo/p-type a-Si:H junctions. We simulated the reverse I-V curves of the SnO2:F/p-type a-Si:H heterojunction at different temperatures by using the simulation software SCAPS 2.9.03. In the model the main transport mechanism is generation of holes enhanced by tunneling by acceptor-type interface defects with a trap energy of 0.4 eV above the valence bandedge of the p-type a-Si:H layer and with a density of 4.0 × 1013 cm−2. By using I-V simulations and the proposed C-V model the built-in potential (Vbi) of the SnO2:F/p-type a-Si:H (0.16 V) and p-type a-Si:H/Mo (0.14 V) heterojunctions are extracted and a band diagram of the characterized structure is proposed.

Detection of nitrogen related traps in nitrided/reoxidized silicon dioxide films with thermally stimulated current and maximum entropy method

We constructed the new method to analyze thermally stimulated current (TSC) using maximum entropy method. This method allows us to extract trap density depending on trap energy level [Nt(Et)] from a TSC curve. Using this to analyze TSC of as-deposited, nitrided, and reoxidized thin silicon dioxide films, we were able to determine Nt(Et) of hole traps with very highly energy resolution and to observe the generation of nitrogen related hole traps.

A Novel Composite Anode: The Electrooxidation of Organic Molecules via Formation of Highly Energetic Holes

This paper describes, for the first time, the electrochemical characteristics of a novel, composite electrode, comprising a thin TiO2 layer sandwiched between a silicon wafer and a metal grid. Holes thermally and/or photochemically generated near the Si/TiO2 interface in the Si are able to reach the surface of the TiO2 and oxidize water and/or species in solution. Hole transport across the TiO2 is facilitated by the application of a bias voltage across the silicon and metal grid. At low bias voltages, oxidation of water takes place at the metal grid; at higher voltages, the oxidation takes place directly at the TiO2 as surface states are accessed. The generation of holes is enhanced significantly if the TiO2 surface is irradiated with visible light. A theoretical model is presented to explain the observed data. The anodes represent a completely new area of oxidative electrochemistry with potential application across a wide range of technology, from fuel cells-on-a-chip to electroorganic chemistry.

Impact of Twofold Coordinated Nitrogen on the Generation of Deep-Level Hole Traps under Negative-Bias Temperature Stressing

In this paper, we discuss the generation of deep-level hole traps (DLHTs) during negative-bias temperature stressing. Because of their ability to trap positive charges for a long time, it is imperative to gain a sound understanding on the nature of the DLHT, especially in relation to nitrogen, which has been incorporated in increasing dose into the SiO2 gate oxide to solve boron penetration and gate tunneling leakage issues. Experimental evidence showing a correlation between the generation of DLHTs and nitrogen is first presented. This is followed by a discussion on the role nitrogen plays in influencing the generation of DLHT via first-principles simulation. We focus on the impact of a neighboring nitrogen atom on the structural and electronic properties of the oxygen-vacancy defect (VO), which is a major precursor for hole traps in the SiO2. Finally the charge transition levels (CTL) are discussed, which give us a more comprehensive understanding of DLHT.

Topology optimization using a reaction–diffusion equation

This paper presents a structural topology optimization method based on a reaction–diffusion equation. In our approach, the design sensitivity for the topology optimization is directly employed as the reaction term of the reaction–diffusion equation. The distribution of material properties in the design domain is interpolated as the density field which is the solution of the reaction–diffusion equation, so free generation of new holes is allowed without the use of the topological gradient method. Our proposed method is intuitive and its implementation is simple compared with optimization methods using the level set method or phase field model. The evolution of the density field is based on the implicit finite element method. As numerical examples, compliance minimization problems of cantilever beams and force maximization problems of magnetic actuators are presented to demonstrate the method’s effectiveness and utility.

Analysis of trap generation during programming/erasing cycling in silicon nanocrystal memory devices

Trap generation of a nonvolatile silicon-nanocrystal memory during Fowler–Nordheim programming/erasing (P/E) cycling is analyzed using the combination of capacitance–voltage and current–voltage measurements. With increasing the number of P/E cycles, the flatband voltage decreases due to hole trapping in the accumulation; the threshold voltage increases due to electron trapping in the inversion. The generation of hole and electron trapping is explained by an anode hole injection mechanism and a cathode injection mechanism, respectively. It is found that the magnitudes of hole and electron trapping depend on both Fowler–Nordheim programming and erasing bias conditions. Sweeping gate voltage from strong accumulation to strong inversion, a gate current spike appears near the silicon midgap voltage in cycled devices and is attributed to the recombination between trapped holes in the tunneling oxide and tunneling electrons from the acceptor interface states above the intrinsic Fermi level.

Mesoscale PIC simulation of double layers and electron holes affecting parallel and transverse accelerations of electrons and ions

[1] We study the dynamical behavior of potential structures in the auroral upward current region. The study is based on a large two-dimensional particle-in-cell simulation. A double layer (DL) forms in the auroral potential structure in the counterstreaming expansion of cold and hot plasmas from bottom (ionospheric side) and top (magnetospheric side), respectively. Transversely nonuniform converging perpendicular electric field drives the plasma from the top, generating V-shaped potential structure within the expanding plasmas. The dynamical features include (1) recurring formation of the DL, (2) downward motion of the DL over the distance of thousands of Debye lengths, (3) collapse of the existing double layer after the reformation of a new one near the top in the hot magnetospheric plasma, and (4) generation of electron holes (EHs) on the high-potential side of the DL and their downward propagation over a few thousand of Debye lengths, where they are dissipated. The EHs are associated with broadband plasma waves with spectrum peaked near the lower hybrid frequency. The EH turbulence is temporally modulated by low-frequency plasma waves near the ion cyclotron frequency Ωi. Electrostatic ion cyclotron waves above Ωi occur on the low-potential side of the DL. Transverse and parallel acceleration/heating of both electrons and ions are studied. The fast moving electron holes are found effective in transverse heating of the cold ionospheric electrons trapped below the DL. Relevance of our results to satellite observations in the auroral plasma is discussed.