Generation Of Holes Research Articles

Etching Mechanisms in III-V Semiconductors: Electrochemical Etching of Indium Phosphide

Etching of III-V semiconductors is often observed to be anisotropic. For example both chemical and electrochemical etching of III-V semiconductors show preferential etching of {111}B planes (i.e. group-V-terminated planes).1,2 The slowest-etching plane is usually {111}A and so these facets are revealed during etching of InP, GaAs and GaP. Due to the differing etch rates of crystal planes, the formation of tetrahedral etch pits (seen as dove-tailed and v-groove voids, respectively, in (011) and (01$\\bar{1}$) cross sections) is observed on the (100) surface of III-V semiconductors. The anodic etching of many materials leads to the formation of porous structures. When semiconducting materials are anodized, localized etching can occur leading to selective removal of material such that the remaining material forms a skeletal structure that encompasses a network of pores. It is quite common for such pores to propagate along preferential directions. These directions and the pore morphology have been shown to be affected by a range of parameters including temperature, composition and concentration of electrolyte, and type, orientation and doping density of the substrate. We have investigated in detail the early stages of pore formation in InP during anodization in aqueous electrolytes (KOH, KCl etc.). Pores originate from pits in the surface and propagate along <111>A directions to form porous domains beneath a thin near-surface layer penetrated only by one surface pit per domain of pores.3-5 Eventually these domains merge to create a continuous porous layer. Although pore propagation in InP in KOH is usually crystallographically oriented (CO), it can be current-line-oriented (CLO) under certain conditions. Indeed, variation of potential, electrolyte concentration and temperature causes a gradual change in the porous layer structure and a transition from pore formation to planar etching is observed as the KOH concentration is decreased to below 2 mol dm-3. We have proposed a three-step model6,7 of electrochemical nanopore formation that explains how crystallographically oriented etching can occur even though the rate-determining process (hole generation) occurs only at pore tips. The model shows that competition in kinetics between hole diffusion and electrochemical reaction determines the average diffusion distance of holes along the semiconductor surface and this, in turn, determines whether etching is crystallographic. If the kinetics of reaction is slow relative to diffusion, etching can occur at preferred crystallographic sites within a zone in the vicinity of the pore tip, leading to pore propagation in preferential directions. We believe that the model is generally applicable to electrochemical etching in III-V semiconductors. In this paper, we will examine the effect of various parameters including temperature, electrolyte composition, potential and current density on electrochemical etching and nanopore formation in InP. We will discuss the processes leading to crystallographic etching, the factors which affect pore morphology and the transition from porous to planar etching and show that the three-step mechanism can comprehensively explain these various features. References H. C. Gatos and M. J. Lavine, J. Electrochem. Soc., 107, 427 (1960).D. N. MacFayden, J. Electrochem. Soc., 130, 1934 (1983).C. O’Dwyer, D. N. Buckley, D. Sutton, S. B. Newcomb, J. Electrochem. Soc., 153, G1039 (2006).C. O’Dwyer, D. N. Buckley, D. Sutton, M. Serantoni, S. B. Newcomb, J. Electrochem. Soc., 154, H78 (2007).R. P. Lynch, C. O’Dwyer, N. Quill, S. Nakahara, S. B. Newcomb, D. N. Buckley, J. Electrochem. Soc., 160, D260 (2013).R. P. Lynch, N. Quill, C. O’Dwyer, S. Nakahara, D. N. Buckley, Phys. Chem. Chem. Phys., 15, 15135 (2013).N. Quill, D. N. Buckley, C. O’Dwyer, R. P. Lynch, J. Electrochem. Soc. 166, H1 (2019) and references therein.

ZnO/ZnFe2O4/Ag hollow nanofibers with multicomponent heterojunctions for highly efficient photocatalytic water pollutants removal

Novel ZnO/ZnFe2O4/Ag hollow one-dimensional multicomponent heterojunctions with different ZnO/ZnFe2O4 ratios were successfully obtained via a simple electrospinning method. These multicomponent heterojunctions exhibited a largely enhanced photocatalytic performance for various reactions compared with pure ZnFe2O4 without heterojunctions, ZnO/ZnFe2O4 and ZnFe2O4/Ag with single heterojunctions. The enhancement can be mainly ascribed to the synergism of multicomponent heterojunctions, which can significantly improve the optical absorption abilities, prompt the separation of photogenerated carriers, and depress the recombination of electron-hole pairs. Hence, the simultaneous and efficient generation of electrons and holes with strong reduction and oxidation abilities, respectively, can lead to effective reaction with the target degradants. In addition, the unique hollow nanofiber structure can also prompt the activities by decreasing the distance for charge carrier transfer to the solution during the photocatalytic process. Additionally, the influence of the number of heterojunctions on the photoactivity was also discussed via varying the ZnO loading amount. This work displays an ingenious design to elevate photocatalytic performances of spinel ZnFe2O4 for solving its biggest problems in the photocatalytic applications, and reveals the rational design of photocatalysts for efficient water pollutants removal.

A Comparative Analysis of NBTI Variability and TDDS in GF HKMG Planar p-MOSFETs and RMG HKMG p-FinFETs

The time kinetics of threshold voltage shift ( $\Delta {V}_{T}$ ) is measured for negative-bias temperature instability (NBTI) and time-dependent defect spectroscopy (TDDS) experiments by an ultra-fast (10- $\mu \text{s}$ delay) method in gate-first high- ${k}$ metal gate (HKMG) planar p-MOSFETs and replacement metal gate HKMG p-FinFETs. The mean NBTI stress-recovery time kinetics obtained from multiple small-area MOSFETs and few-fin FinFETs at different values of stress bias ( ${V}_{\text {GSTR}}$ ) and temperature ( ${T}$ ) is modeled by uncorrelated contributions from interface ( $\Delta {V}_{\text {IT}}$ ) and bulk ( $\Delta {V}_{\text {OT}}$ ) trap generation and trapping of holes ( $\Delta {V}_{\text {HT}}$ ) in pre-existing defects. The time constant associated with recovery steps and the impact of each step for multiple TDDS sweeps on a single device and after NBTI in multiple devices are compared. The NBTI-induced $\Delta {V}_{T}$ distribution shape is verified using TDDS charge impact. The shift in mean and variance of NBTI-induced $\Delta {V}_{T}$ and post-stress ${V}_{T}$ distributions is modeled.

Unravelling Why and to What Extent the Topology of Similar Ce-Based MOFs Conditions their Photodynamic: Relevance to Photocatalysis and Photonics.

Metal–organic frameworks (MOFs) are emerging materials for luminescent and photochemical applications. Armed with femto to millisecond spectroscopies, and fluorescence microscopy, the photobehaviors of two Ce‐based MOFs are unravelled: Ce‐NU‐1000 and Ce‐CAU‐24‐TBAPy. It is observed that both MOFs show ligand‐to‐cluster charge transfer reactions in ≈100 and ≈70 fs for Ce‐NU‐1000 and Ce‐CAU‐24‐TBAPy, respectively. The formed charge separated states, resulting in electron and hole generation, recombine in different times for each MOF, being longer in Ce‐CAU‐24‐TBAPy: 1.59 and 13.43 µs than in Ce‐NU‐1000: 0.64 and 4.91 µs. The linkers in both MOFs also undergo a very fast intramolecular charge transfer reaction in ≈160 fs. Furthermore, the Ce‐NU‐1000 MOF reveals excimer formation in 50 ps, and lifetime of ≈14 ns. The lack of this interlinkers event in Ce‐CAU‐24‐TBAPy arises from topological restriction and demonstrates the structural differences between the two frameworks. Single‐crystal fluorescence microscopy of Ce‐CAU‐24‐TBAPy shows the presence of a random distribution of defects along the whole crystal, and their impact on the observed photobehavior. These findings reflect the effect of linkers topology and metal clusters orientations on the outcome of electronic excitation of reticular structure, key to their applicability in different fields of science and technology, such as photocatalysis and photonics.

SnO2 Films Deposited by Ultrasonic Spray Pyrolysis: Influence of Al Incorporation on the Properties.

Aluminum-doped tin oxide (SnO:Al) thin films were produced by an ultrasonic spray pyrolysis method. The effect of aluminum doping on structural, optical, and electrical properties of tin oxide thin films synthesized at 420 C was investigated. Al doping induced a change in the morphology of tin oxide films and yielded films with smaller grain size. SnO thin films undergo a structural reordering and have a texture transition from (301) to (101), and then to (002) preferred cristallographic orientation upon Al doping. The lattice parameters (a and c) decreases with Al doping, following in a first approximation Vegard’s law. The optical transmission does not change in the visible region with an average transmittance value of 72–81%. Conversely, in the near infrared (NIR) region, the plasmon frequency shifts towards the IR region upon increasing Al concentration in the grown films. Nominally undoped SnO have a conductivity of ∼1120 S/cm, which is at least two orders of magnitude larger than what is reported in literature. This higher conductivity is attributed to the Cl ions in the SnCl·5(HO) precursor, which would act as donor dopants. The introduction of Al into the SnO lattice showed a decrease of the electrical conductivity of SnO due to compensating hole generation. These findings will be useful for further studied tackling the tailoring of the properties of highly demanded fluorine doped tin oxide (FTO) films.

Simplistic wet-chemical coalescence of ZnO with Al2O3 and SnO2 for enhanced photocatalytic and electrochemical performance

A wet-chemical route for the development of Al2O3–ZnO and SnO2–ZnO hierarchical heterostructures (HHSs) was opted to enhance the photocatalytic and electrochemical properties of SnO2 and Al2O3 nanoparticles. Successful coalescence of ZnO hierarchical structure with Al2O3 and SnO2 significantly increased the degradation of Congo red dye under ultraviolet irradiation. More importantly, SnO2–ZnO HHS exhibited superior photocatalytic activity than Al2O3–ZnO which was credited to its improved charge carrier generation and transfer characteristics, revealed using in-depth electrochemical spectroscopy (cyclic voltammetry and electro-chemical impedance spectroscopy). In addition, electrochemical investigation affirmed the photoanodic efficacy of HHSs in polysulfide electrolyte. SnO2–ZnO HHS exhibited optimal electron–hole generation and transfer characteristics (e.g., ~ 17.5 Ω charge carrier transfer resistance at photoanode/polysulfide electrolyte interface), affirming its suitability for quantum-dot sensitized solar cells.

Boosting exciton dissociation and molecular oxygen activation by in-plane grafting nitrogen-doped carbon nanosheets to graphitic carbon nitride for enhanced photocatalytic performance

The metal-free graphitic carbon nitride (g-C3N4) polymer is a promising photocatalyst for energy production and environmental protection. However, attempts to intrinsically improve its low activity in photooxidation are rarely effective for the poor molecular oxygen (O2) activation. Here we report a synthesis of directionally nitrogen-doped in-plane metal-free heterostructure, through coplanar grafting nitrogen-doped carbon nanosheets (NDCN) to g-C3N4. The in-plane grafted NDCN not only promoted exciton dissociation and charge transfer but also enhanced activating O2 to reactive oxygen species, including superoxide radicals (O2−) and H2O2. The optimal C3N4-NDCN coplanar heterojunction (C3N4-NDCN-3) photocatalytically degraded 96.3% of sulfamethoxazole (SMX) under visible light irradiation at a low light intensity of 14.5 mW cm−2 in 4 h, whose SMX degradation rate was 37.7-fold higher than that of pure g-C3N4. Furthermore, C3N4-NDCN-3 exhibited 95.3% removal of SMX under sunlight irradiation (59.8 mW cm−2) in 1 h, higher than the 58.0% of pristine g-C3N4. First-principles calculations and material characterizations demonstrated that the coplanar NDCN served as electron sink and catalytic center for hot-electron involved O2 activation. The improved charge carrier separation and O2 activation promoted generation of photoexcited hole and superoxide for photocatalytic degradation of SMX. The design strategy in this work inspires a new approach for high-performance polymer photocatalysts in solar energy storage and environmental remediation.

Ternary Alloy Rare-Earth Scandate as Dielectric for $\beta$ -Ga2O3 MOS Structures

A ternary alloy rare-earth scandate, (Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.6</sub> Sc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.4</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , is demonstrated as a high-k dielectric insulator for β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> MOS devices. (Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.6</sub> Sc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.4</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (010) MOS capacitors were fabricated and characterized using capacitance-voltage (C-V) techniques and interface state density (D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">it</sub> ) methods. The D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">it</sub> distribution was extracted using photo-assisted C-V with a 265-nm lightemitting diode (LED), demonstrating a peak D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">it</sub> value of 4×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> eV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> near the conduction band, and dropping to below 2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> eV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at 0.9 eV below the conduction band. A total interface charge of <;1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> was calculated based on the experimental data. Similar Dit values were observed using the Terman method for the energy range 0.35-0.55 eV below the conduction band. Current-voltage (J-V) measurements showed rising accumulation leakage current due to bulk-limited transport of electrons through traps in the (Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.6</sub> Sc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.4</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and low depletion leakage current limited by the generation of holes from deep-level β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> traps. High breakdown fields of 4.3-6.0 MV · cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> were observed. The low Dit value shows the excellent potential of (Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.6</sub> Sc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.4</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> as a gate dielectric for β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> metal-oxide-semiconductor field-effect transistors (MOSFETs).

Hole exit quality and machined surface integrity of 2D Cf/SiC composites drilled by PCD tools

The brittle matrix and the anisotropic reinforcing phase of Cf/SiC composites bring great challenges to the machining process. Polycrystalline diamond (PCD) tool was used to drill 2D Cf/SiC composites. The influence of thrust force on hole exit defects was analyzed, and the transformation rule of material removal mechanism and surface generation of hole were studied. With the increase of feed rate, the thrust force increased and the hole exit defects increased. Specific drilling energy was used as an index to quantitatively describe the energy consumption of material removal. With the increase of feed rate and the decrease of cutting speed, the brittle fracture mode of carbon fibers changed from micro-brittle fracture inside carbon fiber to macro-brittle fracture. Although the machined surface of carbon fibers produced by micro-brittle fracture was composed of many micro-fracture, the hole surface was flat overall. Therefore, the hole surface roughness was small.

Charge Disproportionation Triggers Bipolar Doping in FeSb2- xSn xSe4 Ferromagnetic Semiconductors, Enabling a Temperature-Induced Lifshitz Transition.

Ferromagnetic semiconductors (FMSs) featuring a high Curie transition temperature ( Tc) and a strong correlation between itinerant carriers and localized magnetic moments are of tremendous importance for the development of practical spintronic devices. The realization of such materials hinges on the ability to generate and manipulate a high density of itinerant spin-polarized carriers and the understanding of their responses to external stimuli. In this study, we demonstrate the ability to tune magnetic ordering in the p-type FMS FeSb2- xSn xSe4 (0 ≤ x ≤ 0.20) through carrier density engineering. We found that the substitution of Sb by Sn FeSb2- xSn xSe4 increases the ordering of metal atoms within the selenium crystal lattice, leading to a large separation between magnetic centers. This results in a decrease in the Tc from 450 K for samples with x ≤ 0.05 to 325 K for samples with 0.05 < x ≤ 0.2. In addition, charge disproportionation arising from the substitution of Sb3+ by Sn2+ triggers the partial oxidation of Sb3+ to Sb5+, which is accompanied by the generation of both electrons and holes. This leads to a drastic decrease in the electrical resistivity and thermopower simultaneously with a large increase in the magnetic susceptibility and saturation magnetization upon increasing Sn content. The observed bipolar doping induces a very interesting temperature-induced quantum electronic transition (Lifshitz transition), which is manifested by the presence of an anomalous peak in the resistivity curve simultaneously with a reversal of the sign of a majority of the charge carriers from hole-like to electron-like at the temperature of maximum resistivity. This study suggests that while there is a strong correlation between the overall magnetic moment and free carrier spin in FeSb2- xSn xSe4 FMSs, the magnitude of the Curie temperature strongly depends on the spatial separation between localized magnetic centers rather than the concentration of magnetic atoms or the density of itinerant carriers.

Parametric analysis of fabrication of through micro holes on titanium by maskless electrochemical micromachining

Machining of micro features on titanium is a complex task due to its natural physical and chemical properties. Electrochemical micromachining (EMM) presents several advantages, such as minimum or no tool wear, stress-free machining with greater surface finish. This paper demonstrated successful fabrication of micro feature, i.e., through micro holes on pure commercial titanium with the help of maskless electrochemical micromachining process. Influence of various EMM process parameters, i.e., machining voltage, pulse frequency, duty ratio, and micro tool feed rate on machining accuracy in terms of radial overcut and conicity of micro hole as well as material removal rate (MRR), has been investigated to establish suitable process parameters for through micro hole generation. Surface quality of machined micro holes with respect to EMM process parameters was also investigated. Outcomes of this experimental investigation ensure fabrication of through micro holes with minimum overcut and taper angle. Machining voltage of 8 V, pulse frequency of 200 kHz, and micro tool feed rate of 0.6 μm/s with lower duty ratio are proved to be major influencing parameters. Surface roughness of 0.09 μm has been achieved with most suitable process parameters. In situ fabricated disk micro tool has been utilized to enhance machining accuracy. The study presented in this article can be a potential application for generation of various other micro features on pure commercial titanium which will find potential applications in microneedles, drug delivery systems, and features for various BioMEMS and engineering applications.

Dirac Fermion and Plasmon Dynamics in Graphene and 3D Topological Insulators

AbstractLight–matter interactions illuminate the nature of solids and provide a second look on associated carrier dynamics. In particular, graphene and 3D topological insulators (3D TI) with broadband electromagnetic excitation have revealed to host exotic dynamic interactions. Much of Dirac‐point physics arises from discrete lattice symmetries and nontrivial Z2 classification of Bloch states. In this review, ongoing spectroscopic works on graphene and 3D TI are presented, where special attention is on the far‐infrared terahertz (THz) spectroscopy that characterizes the intraband dynamics. The constant absorbance of graphene upon interband particle–hole generation exhibits nonclassical results of gapless dispersion, which can be elucidated by the relativistic Dirac equations with zero rest mass. The massless Dirac fermions on graphene and 3D TI surface exhibit distinct phenomena compared to the conventional systems. First, the transient responses after pulse excitation reveal the semimetallic states of the gapless electronic dispersion, where the Fermi energy in equilibrium determines the crossover from metallic to semiconducting states. Second, the 2D Dirac plasmon dispersion of graphene and 3D TI surface exhibits unconventional density dependence in comparison to the massive electronic systems. The novel optical phenomena in graphene and 3D TI surface can serve for advanced optoelectronic and optospintronic applications.

Threshold Voltage Instability in GaN HEMTs With p-Type Gate: Mg Doping Compensation

In this letter, we present an analysis of the threshold voltage shift induced by positive bias temperature instability stress in GaN-based power HEMTs with p-type gate, controlled by a Schottky metal/p-GaN junction. In particular, we show the positive effect of the magnesium compensation process in the p-GaN layer on the long-term threshold voltage instability. When a relatively high positive bias is applied to the gate (Schottky junction reverse-biased), holes are generated by impact ionization in the high-field depleted p-GaN region, then accelerated toward the AlGaN layer. The high-energy holes, combined with the high temperature effects, create defects in the AlGaN or at its interface with p-GaN, causing a long-term positive threshold voltage shift. A process variation in the p-GaN layer is introduced which promotes a wider depletion region near the Schottky interface with the metal, lowering the electric field and reducing the generation of holes due to impact ionization. As a result, the long-term threshold voltage instability is improved without altering the dc transistor parameters, such as threshold voltage, trans-conductance, and subthreshold slope.

Strong effect of multi-electron oxygen reduction reaction on photocatalysis through the promotion of interfacial charge transfer

An efficient visible-light-driven photocatalyst with interface charge transfer (IFCT) effect was achieved by assembling Fe-porphyrin based conjugated microporous polymer on TiO2 microspheres. It was revealed that IFCT effect played a crucial role in the enhancement of photocatalytic performance. In addition, the oxygen reduction reaction (ORR) activity of TiO2 was enhanced in the presence of Fe-porphyrin based conjugated microporous polymer and IFCT effect was promoted obviously due to the high ORR activity. It’s speculated that multi-electron ORR could accelerate the consumption of photoinduced electrons, retarding the recombination of photoinduced holes and electrons in the IFCT process, leaving more high-oxidizing photoinduced holes in the valance band of TiO2 for further degradation. What’s more, to further clarify the relationship between multi-electron ORR and IFCT effect, the influence of electron transfer number on the generation of photoinduced holes in the IFCT process was studied, and it was believable that four-electron oxygen reduction process was better able to accelerate the generation of photoinduced holes in the IFCT process than two-electron oxygen reduction process, resulting in higher photocatalytic activity.

Comparison of microstructural and optoelectronic properties of NiO:Cu thin films deposited by ion-beam assisted rf sputtering in different gas atmospheres

NiO thin films have been widely studied recently due to their intrinsic p-type conductivity and potential applications in various domains as transparent conductive oxides. However, the intrinsic p-type resistivity (ρ) of NiO is as high as 1013 Ω·cm, which needs to be optimized. In the current work, we devised an experiment to improve the electrical properties of NiO films through three methods: 1) encouraging monovalent Cu+ ions to substitute for Ni2+ ions in NiO:Cu films deposited from NiO-Cu composite targets; 2) introducing nickel vacancies and interstitial oxygen in the films deposited by oxygen ion assisted rf sputtering in Ar + O2 mixture; 3) adding group-V element N to replace O by employing Ar + N2 mixture as the sputtering gas. The results show that the first two methods can effectively enhance the film's p-type conductivity, while the carrier concentration in the films improves greatly. However, the last method reveals that when N atoms are introduced into NiO:Cu films they will reduce the film's p-type electrical properties. This indicates that N doping hinders the hole generation under our experimental conditions.

Electronic Excitation Dynamics in DNA under Proton and α-Particle Irradiation.

Electronic excitations are produced when matter is exposed to ion irradiation comprising highly energetic ions. These electronic stopping excitations are responsible for ion beam-induced DNA damage by energetic protons and α-particles, the chemistry and physics of which are central to burgeoning radiation cancer therapies. By simulating the non-perturbative electronic response of DNA to irradiating protons and α-particles, our first-principles dynamics simulations enable us to test the validity of the commonly used linear response theory description, and they also reveal unprecedented details of the quantum dynamics of electronic excitations. In this work, we discuss the extent to which the linear response theory is valid by comparing to the first-principles determination of electronic stopping power, the energy-transfer rate from ions to electronic excitation. The simulations show that electronic excitations induced by proton and α-particle irradiation cause ionization of DNA, resulting in the generation of holes. By studying the excited hole generation in terms of both the energetic and spatial details in DNA, our work reveals remarkable differences with the excitation behavior of DNA under more commonly used ionizing irradiation sources such as X/γ-ray photons. Furthermore, we find that the generation of excited holes does not directly correlate with the energy-transfer rate as a function of the irradiating ion velocity, in contrast to what is often assumed in the chemistry and physics of radiation oncology.

Влияние лантана на транспортные свойства оксиселенидов Bi-=SUB=-1-x-=/SUB=-La-=SUB=-x-=/SUB=-CuSeO

In this work we present the results of the transport properties study for p-type Bi1-xLaxCuSeO (x = 0.02; 0.04; 0.06) oxyselenides. Accordingly to temperature dependencies of the electrical resistivity, charge carriers concentration and mobility, it was revealed that the substitution of Bi3+ ions to La3+ ions leads to charge carriers concentration enhancement caused by generation of holes, which is presumably attributed to the bismuth deficiencies formation with respect to the substitution level. The work was carried out with financial support from the Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST “MISIS”.

Effect of Crystal Structure on Hole Carrier Generation in Wide-gap P-type Tin-Niobate

AbstractSn2Nb2O7 and SnNb2O6 are promising candidates for wide-gap p-type conducting oxides with high mobility, because their valence-band maximum are composed of Sn 5s orbital with large spatial spreading and isotropic nature. Though hole carriers were generated by Sn4+ substitutional defects on Nb5+ site (Sn’Nb) in the substructure of Nb2O6 octahedra in both tin niobates, the generation efficiency of hole carriers in SnNb2O6 was larger than that of Sn2Nb2O7. From the variation in bond length of Nb-O in the Nb2O6 octahedra calculated by Rietveld analysis, the difference in carrier generation efficiency of two tin niobates was examined. The bond length of Nb-O in p-type Sn2Nb2O7 with large amounts of Sn’Nb was smaller than that of n-type Sn2Nb2O7 with small amounts of Sn’Nb. The holes generated by Sn’Nb were considered to be captured by the negative charge of oxygen anions consisting of the Nb2O6 octahedra, resulting in low carrier generation efficiency. In SnNb2O6 showing higher efficiency, Nb-O was 8.6 % larger than that of p-type Sn2Nb2O7. It is considered that the large Nb-O bond length provide the preferred environment for the generation of positive holes, resulting in the higher carrier generation efficiency.

1T-DRAM With Shell-Doped Architecture

This paper reports on the usefulness of shell-doped (SD) junctionless (JL) transistor architecture for operation as capacitorless dynamic random-access memory (1T-DRAM). SD topology overcomes the problem associated with shallower potential depth in heavily doped devices, thereby enhancing the retention time (RT) along with improved scalability. The use of a thinner shell for achieving high RT is beneficial as it reduces generation and recombination of holes. The results show that an undoped core region with shell thickness ( ${T}_{\textsf {Shell}}$ ) of 2 nm yields maximum retention. An SD ( ${N}_{\mathrm {d}}$ ) of $10^{18}$ cm $^{-\textsf {3}}$ attains RT of ~5.5 s and ~630 ms at 27 °C and 85 °C, respectively, whereas higher ${N}_{\textsf {d}}$ ( $10^{19}$ cm $^{-\textsf {3}}$ shows RT of ~13ms at 85 °C for ${L}_{\textsf {g}} = \textsf {200}$ nm. SD JL transistor shows less degradation in RT with temperature. A 10 nm SD JL device with RT of ~11 ms at 85 °C demonstrates applicability as 1T-DRAM at shorter gate lengths.

Investigation of Erase Cycling Induced TSG Vt Shift in 3D NAND Flash Memory

Erase cycling induced Vt shift of top select gate transistor (TSG) and its physical mechanism are studied in 3D NAND flash memory. It is found that the distribution of TSG Vt shifts higher during memory cells erase cycling. Furthermore, the TSG Vt shift can recover after the removal of cycling stress. A physical model of trap generation induced by hot holes is proposed for above observations. It is considered that hot holes generated by high channel potential gradient during erase can break the $\equiv $ Si–H bonds at the poly-Si grain boundary and the poly-Si/SiO2 interface, causing TSG Vt tail shift and parallel shift, respectively. And the degradation can recover due to re-passivation of $\equiv $ Si–H bonds after stress removal. A TSG bias optimization scheme is demonstrated to reduce the hot holes generation and suppress the TSG abnormal Vt shift during cell erase cycling.