Hole Site Research Articles

Deuterium occupation of interatomic hole sites in Ni67Zr33 amorphous alloy

The occupation of interatomic hole sites by deuterium in a deuterated Ni67Zr33 amorphous alloy was investigated using diffraction measurements and a combination of reverse Monte Carlo and molecular dynamics simulation techniques. The results show that deuterium atoms occupy various types of polyhedral hole sites, as well as tetrahedral ones. The occupation by a deuterium atom of a tetrahedral hole site causes volume expansion, but that of a larger polyhedral hole site does not cause a substantial change in the volume. Each deuterium atom is chemically bonded with 4–6 metal atoms, even for a larger polyhedral hole formed by seven or more metal atoms.

Challenges of transsphenoidal pituitary surgery in severe brachycephalic dogs.

Transsphenoidal hypophysectomy is the standard surgical technique for the excision of pituitary neoplasms. Anatomy may be more obscured in brachycephalic skull types due to the crowding of soft tissue and osseous structures. We describe the unique challenges to approach the sphenoid bone and localize the correct burr hole site in severe brachycephalic dogs. A single institution retrospective case series of brachycephalic dogs with pituitary-dependent hypercortisolism (PDH). Preoperative computed tomography enabled 3D-, and cross-sectional reconstruction to plan and dry-practice the position of the ideal burr hole in relation to the sella turcica, pterygoid hamular processes, and hard palate. Rostral burring of the caudal hard palate obscuring the direct sphenoid approach necessitated adaptations to the original transsphenoidal hypophysectomy procedure. Postoperative outcomes and complications with respect to those seen in mesocephalic dogs are described. Ten brachycephalic dogs including French Bulldogs (n = 9) and a single Dogue de Bordeaux were included. All dogs were diagnosed with PDH and had preoperative advanced imaging performed on the skull. All but one dog had an enlarged pituitary gland, with a median pituitary/brain value of 0.5 (range 0.21-0.9). A total of 11 transsphenoidal hypophysectomy procedures were performed in these 10 dogs. Rostral extension of the soft palate incision into the hard palate was performed to access the burr hole site on the sphenoid bone. Major complications included aspiration pneumonia (n = 1), severe gastroesophageal reflux (n = 1), and central nervous signs (=1). All dogs survived until discharge, with a median time to follow-up of 618 days (range 79-1,669 days). Seven dogs experienced long-term remission of PDH. Brachycephalic dogs undergoing transsphenoid al hypophysectomy benefit from meticulous presurgical planning and extension of the approach into the caudal hard palate. Advanced surgical skills can render a good outcome in a technically challenging environment.

Porous-Induced Performance Enhancement of Flat Boron Sheets for Lithium-Ion Batteries

Low-capacity anode materials have been limiting the further take-off of lithium-ion batteries (LIBs), and many researchers are relentlessly pursuing breakthroughs in high-capacity anode materials. Therefore, the properties of materials with a high theoretical capacity and the reasons behind them are worthy of further study. Here, based on the first-principles calculation, we systematically investigate the electrochemical properties of the six flat boron sheets with different hexagonal hole densities η (η = 1/4, 1/5, 1/6, 1/7, 1/8, 1/9), including adsorption, diffusion, theoretical capacity, and open-circuit voltage. We find that due to their own structural and electronic properties, the Li atoms tend to be adsorbed on their hexagonal hole sites, which result in the formation of structures of flat boron sheets with more hexagonal holes that have a higher theoretical capacity for lithium. Besides, their theoretical capacities can be calculated using the empirical equation, with the hexagonal hole densities (η). Finally, we obtain their capacities with increasing hexagonal hole density (η), which are 620, 708, 826, 992, 1240, and 1653 mA h g–1, respectively. Therefore, our results indicate that the porous structure of the anode material is beneficial to improve the storage capacity performance of LIBs.

Development of immobilised sunlight active W-Mo/Mo-V/V-W co-doped TiO2 photocatalyst by plasma electrolytic oxidation

W-Mo/Mo-V/V-W co-doped TiO2 photocatalyst for the effective degradation of MB (methylene blue) dye under sunlight irradiation was successfully prepared by one-step Plasma Electrolytic Oxidation (PEO) process. The XRD, XPS, and EDS results revealed that W/Mo/V were co-doped in the TiO2 lattice. The highest redshift in the light absorption edge is recorded for the sample MV (Mo-V co-doped TiO2) with a bandgap of 2.51 eV, whereas the bandgaps for WM (W-Mo co-doped TiO2) and VW (V-W co-doped TiO2) are recorded as 2.96 eV and 2.58 eV, respectively. The co-doped photocatalysts show a typical PEO structure with a high degree of porosity favouring the dye adsorption ability. EIS, LSV, and PL analysis confirmed that the co-doped coatings pose a high degree of charge separation, suppressed charge carriers' recombination, and increased the ability to produce photocurrent. Under direct sunlight irradiation, the sample MV showed the highest photocatalytic efficiency, confirmed by MB dye degradation, then the other co-doped and undoped TiO2. This can be attributed to the synergetic effects of intense visible light absorption in the solar spectrum and the reduced charge carriers' recombination rate by acting as the trapping sites for photogenerated electrons and holes. Finally, this immobilised co-doped photocatalyst developed by the PEO process is a promising system in the quest to establish a renewable energy-assisted strategy for textile wastewater treatment application. • Developed direct sunlight active W-Mo/Mo-V/V-W co-doped TiO 2 on Cp-Ti by PEO. • Mo-V co-doped TiO 2 (Eg of 2.41 eV) shows the highest redshift in light absorption. • Immobilised Mo-V co-doped TiO 2 shows the highest dye degradation and mineralisation. • Low Eg and e + /h − recombination rate is due to the synergetic effect of V and Mo.

WSe2-VSe2 Alloyed Nanosheets to Enhance the Catalytic Performance of Hydrogen Evolution Reaction.

Tuning the electronic structures of transition metal dichalcogenides (TMD) is essential for their implementation in next-generation energy technologies. In this study, we synthesized composition-tuned WSe2-VSe2 (W1-xVxSe2, x = 0-1) alloyed nanosheets using a colloidal reaction. Alloying the semiconducting WSe2 with VSe2 converts the material into a metallic one, followed by a 2H-to-1T phase transition at x = 0.7. Over a wide composition range, WSe2 and VSe2 are atomically immiscible and form separate ordered domains. The miscible alloy at x = 0.1 displayed enhanced electrocatalytic activity toward the hydrogen evolution reaction (HER) in an acidic electrolyte. This trend was correlated with the d-band center via a volcano-type relationship. Spin-polarized density functional theory calculations consistently predicted the atomic immiscibility, which became more significant at the 2H-1T phase transition composition. The Gibbs free energy of H adsorption on the basal planes (Se or hole sites) and the activation barriers along the Volmer-Heyrovsky reaction pathway supported the enhanced HER performance of the alloy phase, suggesting that the dispersed V-doped structures were responsible for the best HER catalytic activity. Our study demonstrates how the atomic structure of TMD alloy nanosheets plays a crucial role in enhancing catalytic activity.

The spatially separated active sites for holes and electrons boost the radicals generation for toluene degradation

Hydroxyl (⸱OH) and superoxide (⸱O2-) radicals are the main drivers for photocatalysis in toluene degradation, but their generation mechanisms are still ambiguous due to the lack of direct evidence. The spatially separated active sites for holes and electrons can help to clarify the dynamic process of radicals generation. By performing theoretical calculations, it is demonstrated that the spatially separated active sites for holes and electrons on the Bi2O2CO3 surface can be constructed by introducing oxygen vacancies in the [Bi2O2]2+ layer. H2O and O2 molecules can be better adsorbed and activated at hole and electron active sites, separately. Accordingly, the pristine and defective Bi2O2CO3 are prepared. The dynamic behavior of H2O and O2 molecules at the matching active sites is revealed, which indicates the efficient adsorption of reactants and the substantial production of radicals. Significantly, the specificity of the spatially separated holes and electrons active sites for ⸱OH and ⸱O2- radicals generation, respectively, is demonstrated by in situ EPR with the H2O vapor atmosphere. This work provides a design concept for unraveling reaction mechanisms to realize controllable radicals generation.

GCT-17. Recurrence of CNS germ cell tumors (GCTs) along biopsy and ventriculostomy tracts

Abstract BACKGROUND: Central nervous system (CNS) germinoma relapses are rare. However, the latest Children’s Oncology Group (COG), ACNS1123 stratum 2, described three relapses along the biopsy tract out of eight total relapses; two along the biopsy and endoscopic third ventriculostomy (ETV) tract and one along the biopsy tract and external ventricular drain. Given these findings, we sought to describe other cases of GCT recurrence along surgical tracts. METHODS: We performed a literature review from 1980-2021 to identify cases of GCT recurrence along biopsy and ventriculostomy tracts. RESULTS: Three patients with pineal lesions were identified (13, 14, and 34-years old). All underwent ETV, cerebrospinal fluid (CSF) sampling, and tumor biopsy. Two patients had uncomplicated postoperative courses. One developed persistent hydrocephalus and underwent repeat ventriculostomy. Two were diagnosed with pure germinoma and treated with focal radiotherapy of 45 Gy alone or chemotherapy and radiation (50.4 Gy to the tumor volume and 36 Gy to adjacent high-risk area). The third was treated with methotrexate and corticosteroids. All three had recurrence on surveillance MRI (1-3 years after diagnosis). One had recurrence at the ventriculostomy bur hole site, and two had recurrence along the ventriculostomy tract. On biopsy, all three lesions were germinomas. One received pre-radiation chemotherapy and palliative radiation (36 Gy to surgical bed and 30.6 Gy to surrounding high-risk area). Another received chemotherapy and craniospinal radiation of 15 Gy. The third had a complicated post-biopsy course. He ultimately underwent chemotherapy and radiation (24 Gy). All were still alive at time of report. Two were disease free at 12 and 18 months, while one was still receiving chemotherapy. CONCLUSION: Recurrence along the biopsy or ventriculostomy tract is rarely reported in the literature. Future evaluation to determine the incidence could inform if biopsy and ventriculostomy tracts should be included in the radiation therapy field.

Copper(II) meso-Tetraphenyl- and meso-Tetrafluorenyl Porphyrinates as Charge Carrier Transporting and Electroluminescent Compounds.

Studies on copper(II) tetrafluorenyl porphyrinate (CuTFP) and copper(II) tetraphenyl porphyrinate (CuTPP) have been focused on the charge carrier transport in their solid films and electroluminescence of their composites. In the dye layers deposited by resistive thermal evaporation, the mobilities of holes and electrons are on the order of 10–5 and 10–6 cm2 V–1 s–1 for the charge transport under the influence of traps, and the charge mobility reaches the order of 10–3 cm2 V–1 s–1 at space-charge-limited current in the nontrapping mode. For the dye molecules, the correlation between the mobility of charge carriers and the distribution of the electron density on the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), which serve as hopping sites for holes and electrons, respectively, is considered. Organic light-emitting diodes incorporating the dye molecules as emitting dopants demonstrate electroluminescence in the near-infrared (IR) range.

A Comparative Study of an Anti-Thrombotic Small-Diameter Vascular Graft with Commercially Available e-PTFE Graft in a Porcine Carotid Model

Background:We have designed a reinforced drug-loaded vascular graft composed of polycaprolactone (PCL) and polydioxanone (PDO) via a combination of electrospinning/3D printing approaches. To evaluate its potential for clinical application, we compared the in vivo blood compatibility and performance of PCL/PDO + 10%DY grafts doped with an antithrombotic drug (dipyridamole) with a commercial expanded polytetrafluoroethylene (e-PTFE) graft in a porcine model.Methods:A total of 10 pigs (weight: 25–35 kg) were used in this study. We made a new 5-mm graft with PCL/PDO composite nanofiber via the electrospinning technique. We simultaneously implanted a commercially available e-PTFE graft (n = 5) and our PCL/PDO + 10%DY graft (n = 5) into the carotid arteries of the pigs. No anticoagulant/antiplatelet agent was administered during the follow-up period, and ultrasonography was performed weekly to confirm the patency of the two grafts in vivo. Four weeks later, we explanted and compared the performance of the two grafts by histological analysis and scanning electron microscopy (SEM).Results:No complications, such as sweating on the graft or significant bleeding from the needle hole site, were seen in the PCL/PDO + 10%DY graft immediately after implantation. Serial ultrasonographic examination and immunohistochemical analysis demonstrated that PCL/PDO + 10%DY grafts showed normal physiological blood flow and minimal lumen reduction, and pulsed synchronously with the native artery at 4 weeks after implantation. However, all e-PTFE grafts occluded within the study period. The luminal surface of the PCL/PDO + 10%DY graft in the transitional zone was fully covered with endothelial cells as observed by SEM.Conclusion:The PCL/PDO + 10%DY graft was well tolerated, and no adverse tissue reaction was observed in porcine carotid models during the short-term follow-up. Colonization of the graft by host endothelial and smooth muscle cells coupled with substantial extracellular matrix production marked the regenerative capability. Thus, this material may be an ideal substitute for vascular reconstruction and bypass surgeries. Long-term observations will be necessary to determine the anti-thrombotic and remodeling potential of this device.

Using a Carpenter’s Square to Localize Narrow or Multilayered Chronic Subdural Hematomas Diagnosed on Computed Tomography

Chronic subdural hematomas (CSDHs) with narrow or multilayered hematomas must be accurately localized for burr hole drainage. We present a simple alternative localization method using conventional computed tomography (CT) scans acquired for the initial diagnosis and a commercially available carpenter's square (CS). Using our novel method, we localized 77 narrow or multilayered CSDHs. A single burr hole site on the thickest portion of narrow hematomas or on the site allowing access to both the isolated superficial layer and the deep layer of multilayered hematomas was identified on axial CT images; the image was parallel to the orbitomeatal line (OML). On the target CT slice, the level from the OML and from the surface of the forehead to the intended burr hole (sagittal distance) was measured. The OML and the level of the CT target slice were marked using the CS. Then, the CS was placed at the marked target level; the 2 edges of the CS were situated on the frontal and temporal scalp and parallel to the OML and the sagittal line. The sagittal distance was then marked. All burr holes reached the CSDHs. The mean deviation of the burr holes was 4.7 mm inferior and 1.4 mm anterior to the intended site. In 65 instances (84.4%), a deviation within 10 mm was observed in both the superoinferior and the anteroposterior directions. Our simple and inexpensive method can localize narrow or multilayered CSDHs with acceptable accuracy and increases the efficiency of routine clinical work.

Local charge carrier dynamics of a particulate Ga-doped La5Ti2Cu0.9Ag0.1O7S5 photocatalyst and the impact of Rh cocatalysts.

Visible-light responsive photocatalytic materials are expected to be deployed for practical use in photocatalytic water splitting. One of the promising materials as a p-type semiconductor, oxysulfides, was investigated in terms of the local charge carrier behavior for each particle by using a home-built time-resolved microscopic technique in combination with clustering analysis. We could differentiate electron and hole trapping to the surface states and the following recombination on a micron-scale from the nanosecond to microsecond order. The map of the charge carrier type revealed that charge trapping sites for electrons and holes were spatially separated within each particle/aggregate. Furthermore, the effect of the rhodium cocatalyst was recognized as a new electron pathway, trapping to the rhodium site and the following recombination, which was delayed compared with the original electron recombination process. The Rh effect was discussed based on the phenomenological simulation, revealing a possible reason for the decay was due to the anisotropic diffusion of charge carriers in oxysulfides or the interfacial energy barrier at the interface.

Rapid Spontaneous Resolution of Contralateral Lentiform Acute Subdural Hematoma After Burr Hole Trephination for Chronic Subdural Hematoma

Although rare, acute subdural hematoma (ASDH) may occur after burr hole trephination (BHT) for chronic subdural hematoma (CSDH). It usually occurs in the hemisphere ipsilateral to the burr hole site and rarely in the hemisphere contralateral to the burr hole site. On computed tomography (CT), SDH is usually crescent-shaped and occasionally lentiform or biconvex, which can be misdiagnosed as epidural hematoma (EDH). In rare cases, ASDH may resolve spontaneously and rapidly. Here, we report a case of rapid spontaneous resolution of contralateral lentiform ASDH after BHT for CSDH in a patient with brain atrophy. A 55-year-old man developed left CSDH 2 months after traumatic brain injury. Left BHT was performed, and a lentiform hematoma, presumed to be EDH, was found in the right frontal region on the CT scan acquired immediately after BHT. On the CT scan acquired 12 hours later, the lentiform hematoma disappeared and spread along the hemisphere. It was presumed to be ASDH. To prevent contralateral ASDH after BHT, slow decompression and minimal gentle or no irrigation should be performed during BHT, particularly in patients with brain atrophy.

Multifunctional heteroatom doped sustainable carbon nanocomposite for rapid removal of persistent organic pollutant and iodine from water

The development of a rapid and efficient strategy for removal of organic and inorganic pollutant in aqueous solution remain a challenge for protecting environment and human health. World is fascinated by the heteroatom doped carbon based multifunctional sorbent for the real-world applications in sustainable energy and environmental remediation due to its cost-effective, bio-inspired, simplicity of the process and good efficiency. Herein, we have demonstrated a novel economically and green method to synthesize boron and nitrogen doped fluffy carbon ([email protected]) from tapioca root, boric acid, and melamine via a simple dehydration method only concentrated H2SO4. The [email protected] nanostructure was successfully prepared within few minutes (~15 min) at room temperature without any additional energy treatment. The constitution and surface morphology of [email protected] were scrutinized by using different techniques. The photocatalytic activity and iodine capture capacity of as-synthesized material have been evaluated by the removal of methylene blue (MB), rhodamine B (RhB) and iodine (I2). [email protected] nanomaterial was able to remove MB, RhB and I2 up to ~ 99.75%, 97.86%, 94.56 %, whereas CS was able to remove ~ 72.44%, 68.62%, 71.30%, respectively, within 21 min from their initial concentration of 100 ppm solution of MB, RhB and 200 ppm solution of I2. The above outcome demonstrates that our [email protected] nanomaterial has outstanding photocatalytic activity and iodine capture ability as compared to only CS, [email protected] and [email protected] due to providing more active site and low recombination of photogenerated electrons and hole. The current study indicates new aspect for the synthesis of large-scale production of [email protected] in a very short time for different applications in sustainable chemistry, including the removal of organic pollutants and radioactive I2 from water resources.

Physical separation of catalytic oxidation and reduction sites onto photocatalyst assisted by surface functional groups for enhanced hydrogen evolution

Physical separation of catalytic reduction and oxidation sites is a common approach in photocatalysis to optimize photogenerated charge separation and improve redox ability of catalysts. Herein, we report a novel site-directed photodeposition technology assisted by specific surface functional groups for the synthesis of Nix/NH2–Cd0.5Zn0.5S–S2- (Nix/N-CZS-S2-) catalyst. Two creative functions are exhibited. On the one hand, the surface functional groups –NH2 act as a bridge to anchor catalytic reduction center Ni, and this particular anchor form provides a new electron transfer channel for photocatalytic hydrogen evolution. On the other hand, the surface functional groups S2− provides sites for holes that can be eliminated by the sacrificial agent. As a result, these two advantages guarantee the hydrogen evolution of the Ni2/N-CZS-S2- to reach 32,025 μmol g−1·h−1 and the quantum yield to reach 25.68 % at 420 nm. This particular site-directed photodeposition technology can optimize charge transfer kinetics and improve redox reaction kinetics of catalyst. In addition, it can be extended to related systems as an effective strategy for enhanced photocatalysis performance.

Hydroxylation and fluorination on γ-Al2O3(110) surfaces: First-principles and transition state calculations

In this paper, the adsorption mechanism of HF and H2O on the γ-Al2O3 and hydroxylated surfaces were built and calculated. The calculated results show that the main active adsorption sites are concentrated near the octahedral hole sites. There are two types of chemical adsorption of H2O: ▲Al-O-H2 and ▲Al-O-H*▲Oa-H. The adsorption energy range is -0.30~-1.75eV. With the increase of adsorption energy, H2O gradually inclines to the surface to form OH. The chemisorption form of HF is ▲Al-F and ▲O-H, with the adsorption energy in the range of -0.61 to -2.41eV. At low coverage, there were more active adsorption sites on the surface, and the interaction between OH and HF adsorption was less. At high coverage, the active site occupied by OH tended to be saturated, and HF could not break bonds to form Al-F, so the adsorption effect decreased. When the HF coverage is about 0.4, the binding is the most stable, and the adsorption energy is -2.97eV.

Bone drilling with internal gas cooling: Experimental and statistical investigation of the effect of cooling with CO2 on reduction of temperature rise due to drill bit wear

Bone drilling is a major stage in immobilization of the fracture site. During bone drilling operations, the temperature may exceed the allowable limit of 47 °C, causing irrecoverable damages of thermal necrosis and seriously threatening the fracture treatment. One of the parameters affecting the temperature rise of the drilling site is the frequency of applying the drill bit and its extent of wear. The present study attempted to mitigate the effect of drill bit wear on the bone temperature rise through the internal gas cooling method via CO2 and to reduce the risk of incidence of thermal necrosis. To this end, drilling tests were conducted at three rotational speeds 1000, 2000, and 3000 r·min-1 in two states of without cooling and with internal gas cooling by CO2 through an internal coolant carbide drill bit, along with six drill bit states (new, used 10, 20, 30, 40, and 50 times) on a bovine femur bone. The results indicated that in the internal gas cooling state, as the number of drill bit applications increased from the new state to more than 50 times, the temperature of the hole site increased on average by ΔT = 2-3 °C (n = 1000 r·min-1), ΔT = 5-8 °C (n = 2000 r·min-1), and ΔT = 5-7 °C (n = 3000 r·min-1). Furthermore, the internal gas cooling method was able to significantly reduce the effect of the drill bit wear on the temperature rise of the drilling site and to resolve the risk of incidence of thermal necrosis regardless of the process parameters for drilling operations.

THE ELECTROTOMOGRAPHY SURVEY IN DIFFICULT GEOTECHNOGENIC CONDITIONS AT THE PEACEFUL UNDERGROUND NUCLEAR EXPLOSION "CRYSTAL" SITE

The paper presents the results of measurements in 2019 by electrotomography at the site of the emplacement hole of the peaceful underground nuclear explosion "Crystal", carried in 1974 at a depth of 98 m in permafrost Cambrian carbonate rocks, and the neighboring forest area. The fence made of metal poles and barbed wire around the site, and the buried fragments of the casing of the emplacement hole create significant interference of measurements. To avoid the electromagnetic noise, the measured data of the apparent electrical resistivity was cleaned manually. Data inversion was performed in the Res2Dinv program. Geoelectric models, namely two-dimensional sections of the upper part of the geological environment to a depth of up to 80 m, were obtained. To verify the models, forward modeling was performed using the ZondRes2D program.

Estrogen receptor α in mature osteoblasts regulates the late stage of bone regeneration

Estrogen deficiency impairs fracture healing and homeostasis of bone tissue. OVX-induced estrogen deficiency in mice attenuates fracture healing and changes the expression ratio of estrogen receptor (ER) α and ERβ in callus during the process of fracture healing. Therefore, ERs may be involved in the regulation of fracture healing. However, the roles of ERs in fracture healing are largely unknown. The purpose of this study was to clarify the significance of ERs during fracture healing using osteoblast-specific ER knockout mice in a mono-cortical drill hole bone regeneration model.The mature osteoblast-specific ER knockout mice were generated using osteocalcin (OCN)-Cre mice, and ERα and ERβ flox mice (OCN-Cre; ERαf/f, ERαΔOb/ΔOb and OCN-Cre; ERβf/f, ERβΔOb/ΔOb). Drill hole surgery was conducted on the tibiae of 8-week-old female mice. The mice were sacrificed 10 or 14 days after surgery and the bones were analyzed by DXA, μCT and bone histomorphometry.DXA analysis revealed that intact femoral BMD was significantly decreased in ERαΔOb/ΔOb mice compared with ERαf/f mice, but there was no difference in bone mass between ERβΔOb/ΔOb and ERβf/f mice. Micro CT analyses showed that the callus volume at the restricted drill hole site in tibiae was significantly less in ERαΔOb/ΔOb compared to ERαf/f mice only at day 14 but not at day 10. In addition to femoral BMD, there was no significant difference in callus volume between ERβΔOb/ΔOb and ERβf/f mice. Bone histomorphometric analyses showed that Ob.S/BS and N.Ob/B.Pm were significantly less in ERαΔOb/ΔOb mice compared with ERαf/f mice only at day 10. In addition, Oc.S/BS and N.Oc/B.Pm were significantly less in ERαΔOb/ΔOb mice compared with ERαf/f mice only at day 14.These results suggest that ERα but not ERβ in osteocalcin-positive osteoblasts may contribute to the late stage of bone regeneration.

Simple physical model for the sign of the Hall coefficient in variable-range hopping conduction in heavily Al-doped p-type 4H-SiC

We observe negative Hall coefficients (R H(T)) in the variable-range hopping (VRH) conduction region for heavily Al-doped p-type 4H-SiC. We have proposed a simple physical model in which the difference between the density of hopping sites for holes and the density of hopping sites for electrons under a magnetic field determines the sign of R H(T), and explained the negative R H(T) in nearest-neighbor hopping (NNH) conduction. Based on our proposed model for NNH conduction, here we propose a model in which R H(T) becomes positive when the density of localized states (g(E)) around the Fermi level (E F) increases with increasing energy (E), whereas R H(T) becomes negative when g(E) around E F decreases with increasing E. In heavily Al-doped p-type 4H-SiC where g(E) around E F is considered to decrease with increasing E, the proposed model can explain why R H(T) becomes negative in the VRH conduction region.

The influence of Mn doping on the leakage current mechanisms and resistance degradation behavior in lead zirconate titanate films

The electrical reliability of lead zirconate titanate (PZT) films was improved by incorporating Mn; the time dependent dielectric breakdown lifetimes and the associated activation energy both remarkably increased with Mn concentration. The correlation between the defect chemistry and the resistance degradation was studied to understand the physical mechanism(s) responsible for enhanced electrical reliability. At lower electric fields, Poole-Frenkel emission was responsible for the leakage current. Beyond a threshold electric field, Schottky emission controlled the leakage. After electrical degradation of a 2 mol.% Mn doped PZT film, no significant change in potential barrier height for injecting electrons from the cathode into the anode was observed. This suggests that the degradation is mostly controlled by Poole-Frenkel conduction via some combination of hole migration between lead vacancies, small polaron hopping between Mn sites, and hole hopping between Pb2+ and Pb3+. No variation in the valence state of Ti near the cathode was observed in degraded Mn doped PZT films, implying that multivalent Mn provides trap sites for electrons and holes; free electron generation due to compensation of oxygen vacancies at the cathode and free hole formation at the anode region might be suppressed by the valence changes from Mn3+ to Mn2+ and Mn2+ to Mn3+ respectively.