Residual Electron Research Articles

Residual quantum coherent electron transport in doped graphene leads

Residual quantum coherent electron transport in doped graphene leads

Development of hydrogen ionic plasma source with superimposed positive-ion beam

A hydrogen ionic plasma source has been developed that is with a low residual electron presence (<0.01) using an aluminum plasma grid for negative hydrogen ion production and a control grid for electron removal. The ionic plasma density increases when a positive-ion beam is superimposed on a hydrogen plasma and irradiated onto the Al plasma grid. Even though the ionic plasma is formed in a region with high-deflection magnetic flux density, a collapse phenomenon can occur downstream of the region under certain electrode voltage conditions, causing electrons to appear and forming an electron plasma. Under electrode voltage conditions that prevent the collapse, the nine ionic plasmas, each passing through extraction apertures with a diameter of 1.3 cm, are combined to form the ionic plasma with a diameter of approximately 6 cm and a density on the order of 109 cm−3.

Synthesis, crystal structure and Hirshfeld surface analysis of [Cu(H2 L)2(μ-Cl)CuCl3]·H2O [H2 L = 2-hy-droxy-N'-(propan-2-yl-idene)benzohydrazide

The present study focuses on the synthesis and structural characterization of a novel dinuclear CuII complex, [tri-chlorido-copper(II)]-μ-chlorido-{bis-[2-hy-droxy-N'-(propan-2-yl-idene)benzohydrazide]copper(II)} monohydrate, [Cu2Cl4(C10H12N2O2)2]·H2O or [Cu(H2 L)2(μ-Cl)CuCl3]·H2O [H2 L = 2-hy-droxy-N'-(propan-2-yl-idene)benzohydrazide]. The complex crystallizes in the monoclinic space group P21/n with one mol-ecule of water, which forms inter-actions with the ligands. The first copper ion is penta-coordinated to two benzohydrazine-derived ligands via two nitro-gen and two oxygen atoms, and one bridging chloride, which is also coordinated by the second copper ion alongside three terminal chlorines in a distorted tetra-hedral geometry. The arrangement around the first copper ion exhibits a distorted geometry inter-mediate between trigonal bipyramidal and square pyramidal. In the crystal, chains are formed via inter-molecular inter-actions along the a-axis direction, with subsequent layers constructed through hydrogen-bonding inter-actions parallel to the ac plane, and through slipped π-π stacking inter-actions parallel to the ab plane, resulting in a three-dimensional network. The inter-molecular inter-actions in the crystal structure were qu-anti-fied and analysed using Hirshfeld surface analysis. Residual electron density from disordered methanol mol-ecules in the void space could not be reasonably modelled, thus a solvent mask was applied.

Improving electrical transport properties of LaxCa0.89-xSr0.11MnO3 films via optimized La content

Optimized LaxCa0.89-xSr0.11MnO3 (x = 0.65, 0.68, 0.71 and 0.74) films were fabricated using spin-coating method. According to double exchange (DE) mechanism and Jahn-Teller effect, the enhancement of peak temperature coefficient of resistivity (TCR) was attributed to low residual resistivity and weak various electron scatterings, including electron–electron, electron–phonon and electron-magnon. Also, peak TCR temperature is not only influenced mainly by the DE mechanism, but also by the Mott transition. Moreover, optimized sintering improved film crystallinity, increasing peak TCR value. The resulting La0.71Ca0.18Sr0.11MnO3 film displayed a peak TCR of 10.74 %/K at 294.11 K. Appropriate chemical composition and sintering promoted the enhancement of electrical transport properties.

Synthesis and crystal structure of the cluster (Et4N)[(Tp*)MoFe3S3(μ3-NSiMe3)(N3)3

The title compound, tetraethylammonium triazidotri-μ3-sulfido-[μ3-(trimethylsilyl)azanediido][tris(3,5-dimethylpyrazol-1-yl)hydroborato]triiron(+2.33)molybdenum(IV), (C8H20N)[Fe3MoS3(C15H22BN6)(C3H9NSi)(N3)3] or (Et4N)[(Tp*)MoFe3S3(μ3-NSiMe3)(N3)3] [Tp* = tris(3,5-dimethylpyrazol-1-yl)hydroborate(1−)], crystallizes as needle-like black crystals in space group P\overline{1}. In this cluster, the Mo site is in a distorted octahedral coordination model, coordinating three N atoms on the Tp* ligand and three μ3-bridging S atoms in the core. The Fe sites are in a distorted tetrahedral coordination model, coordinating two μ3-bridging S atoms, one μ3-bridging N atom from Me3SiN2−, and another N atom on the terminal azide ligand. This type of heterometallic and heteroleptic single cubane cluster represents a typical example within the Mo–Fe–S cluster family, which may be a good reference for understanding the structure and function of the nitrogenase FeMo cofactor. The residual electron density of disordered solvent molecules in the void space could not be reasonably modeled, thus the SQUEEZE [Spek (2015). Acta Cryst. C71, 9–18] function was applied. The solvent contribution is not included in the reported molecular weight and density.

Toward an understanding of the role of structural organization and point defects in the formation of functional pure and Tm3+-doped (Ca3-xSrx)(VO4)2 for diode-pumped and SRS lasers

Whitlockite-type polycrystalline and single-crystal (Ca3−xSrx)(VO4)2 solid solutions were successfully obtained by solid-state synthesis and Czochralski method, respectively. Synchrotron powder X-ray diffraction allowed to reveal actual compositions of polycrystalline (Ca3−xSrx)(VO4)2 solid solutions with х = 0.3, 0.54, 0.9, 1.2, 1.35 refined by Rietveld method, which are slightly different from the initial ones. Synchrotron X-ray single-crystal diffraction analysis of Czochralski-grown undoped (Ca1.8Sr1.2)(VO4)2 (CSVO) revealed its actual composition (Ca2.982(11)Sr0.031)(VО4)2. Difference between initial and refined compositions is analyzed and discussed. In the CSVO structure, Sr2+ ions partially occupy monocapped Ca2 and two-capped Ca3 trigonal prismatic sites and Ca2+ ions are in the Ca5 and Ca5A sites, forming two independent strongly distorted tetrahedral Ca5O4 and octahedral Ca5AO6 oxygen environments. Synchrotron X-ray single-crystal diffraction analysis together with X-ray absorption spectroscopic study of (Сa2.4Sr0.6)(VO4)2 doped with 0.5 and 1.0 wt% Tm2O3 (СSVO:0.5Tm and CSVO:1.0Tm) allowed to establish the absence of cations in the Ca5A site, the localization of Sr2+ ions in the Ca2 and Ca3 sites and additionally in octahedral Ca4 site together with Tm3+ ions, forming an individual eight-coordinated environment, in the refined compositions (Ca2.776(7)Sr0.210(4)Tm3+0.008(1))(VO4)2 and (Ca2.855(7)Sr0.140(7)Tm3+0.009(1)□0.022(7))(VO4)2, respectively, with vacancies (marked by a square,□) in the two-capped Ca1 trigonal prismatic site in the CSVO:1.0Tm structure. Additional interstitial oxygen, participating in the formation of the Tm3+ environment, found in the residual electron density, together with vacancies in the Ca1 site provides electroneutrality to CSVO:0.5Tm and CSVO:1.0Tm crystals. Several structural models of the coordination environment of Tm3+ ions were analyzed and the most correct one was proposed.

Supercontinuum generation in bulk solid-state material with bursts of femtosecond laser pulses

We report on experimental and numerical investigation of burst-mode supercontinuum generation in sapphire crystal. The experiments were performed using bursts consisting of two 190 fs, 1030 nm pulses with intra-burst repetition rates of 62.5 MHz and 2.5 GHz from an amplified 1 MHz Yb:KGW laser and revealed higher filamentation and supercontinuum generation threshold for the second pulse in the burst, which increases with the increase of intra-burst repetition rate. The experimental results were quantitatively reproduced numerically, using a developed model, which accounted for altered material response due to residual excitations remaining after propagation of the first pulse. The simulation results unveiled that residual free electron plasma and self-trapped excitons contribute to elevated densities of free electron plasma generated by the second pulse in the burst and so stronger plasma defocusing, significantly affecting its nonlinear propagation dynamics. The presented results identify the fundamental and practical issues for supercontinuum generation in solid-state materials using femtosecond pulse bursts with very high intra-burst repetition rates, which may also apply to the case of single pulses at very high repetition rate, where residual material excitations become relevant and should be accounted for.

Structural characterization of a new samarium–sodium heterometallic coordination polymer

Lanthanide-containing materials are of interest in the field of crystal engineering because of their unique properties and distinct structure types. In this context, a new samarium–sodium heterometallic coordination polymer, poly[tetrakis(μ2-2-formyl-6-methoxyphenolato)samarium(III)sodium(I)], {[SmNa(C8H7O3)4]·solvent} n (Sm-1), was synthesized and crystallized via slow evaporation from a mixture of ethanol and acetonitrile. The compound features alternating SmIII and NaI ions, which are linked by ortho-vanillin (o-vanillin) ligands to form a mono-periodic chain-like coordination polymer. The chains propagate along the [001] direction. Residual electron density of disordered solvent molecules in the void space could not be reasonably modeled, thus the SQUEEZE function was applied. The structural, vibrational, and optical properties are reported.

Probing the charge state of threading dislocations in indium nitride through advanced atomic force microscopy

Indium nitride (InN) plays an imperative role in continuing the success of III-nitride technology and extending its footprint into new application fields. However, the development of InN-based devices is hindered by the unusually high residual electron concentration in unintentionally-doped InN, whose origin remains unresolved. In this work, pits are observed at regions around the InN island boundaries, which are assigned to threading dislocations (TDs). Since the surface band bending of InN is found to be intrinsically downward, the positive currents detected exclusively at the InN island boundary regions upon applying positive sample bias are leakage currents. This further points to the presence of TDs in these regions, which can act as localized conductive leakage paths. Interestingly, the surface potentials at the InN island boundary regions are found to be 35–45 mV more positive compared to the InN islands. This can be attributed to the presence of positively charged TDs due to the formation of donor-type point defects along their dislocation cores. Hence, TDs in InN can donate electrons and serve as one of the factors contributing to its high n-type conductivity.

UV absorbance and electron donating capacity as surrogate parameters to indicate the abatement of micropollutants during the oxidation of Fe(II)/PMS and Mn(II)/NTA/PMS

In this study, the relative residual UV absorbance (UV254) and/or electron donating capacity (EDC) was investigated as a surrogate parameter to evaluate the abatement of micropollutants during the Fe(II)/PMS and Mn(II)/NTA/PMS processes. In the Fe(II)/PMS process, due to the generation of SO4•- and •OH at acidic pH, UV254 and EDC abatement was greater at pH 5. In the Mn(II)/NTA/PMS process, UV254 abatement was greater at pH 7 and 9, while EDC abatement was greater at pH 5 and 7. This was attributed to the fact that MnO2 was formed at alkaline pH to remove UV254 by coagulation, and manganese intermediates (Mn(V)) were formed at acidic pH to remove EDC via electron transfer. Due to the strong oxidation capacity of SO4•-, •OH and Mn(V), the abatement of micropollutants increased with increasing dosages of oxidant in different waters in both processes. In the Fe(II)/PMS and Mn(II)/NTA/PMS processes, except for nitrobenzene (∼23% and 40%, respectively), the removal of other micropollutants was greater than 70% when the oxidant dosages were greater in different waters. The linear relationship between the relative residual UV254, EDC and the removal of micropollutants was established in different waters, showing a one-phase or two-phase linear relationship. The differences of the slopes for one-phase linear correlation in the Fe(II)/PMS process (micropollutant-UV254: 0.36–2.89, micropollutant-EDC: 0.26–1.75) were less than that in the Mn(II)/NTA/PMS process (micropollutant-UV254: 0.40–13.16, micropollutant-EDC: 0.51–8.39). Overall, these results suggest that the relative residual UV254 and EDC could truly reflect the removal of micropollutants during the Fe(II)/PMS and Mn(II)/NTA/PMS processes.

Structural complexity in the apparently simple crystal structure of Be2Ru.

The structural features of the hexagonal layered crystal structure of Be2Ru (a = 5.7508(3) Å, c = 3.0044(2) Å, space group P -62m) were investigated by single crystal X-ray diffraction and transmission electron microscopy (TEM). The residual electron density and high-resolution TEM images show that the real structure can be described as an intergrowth of the main hexagonal matrix of the Fe2P type with minor orthorhombic inclusions of its stacking variants. Such atomic arrangement is stabilized by the charge transfer from Be to Ru and by a system of polar three- and four-atomic bonds involving both components. The calculated electronic density of states (DOS) of Be2Ru revealed, contrarily to typical intermetallic compounds, a pseudo gap (dip) in the vicinity of the Fermi level. The temperature dependence of the electrical resistivity of Be2Ru shows metal behavior in agreement with the non-zero DOS at the Fermi level.

A mixed phosphine sulfide/selenide structure as an instructional example for how to evaluate the quality of a model.

This paper compares variations on a structure model derived from an X-ray diffraction data set from a solid solution of chalcogenide derivatives of cis-1,2-bis-(di-phenyl-phosphan-yl)ethyl-ene, namely, 1,2-(ethene-1,2-di-yl)bis-(di-phenyl-phoshpine sulfide/selenide), C26H22P2S1.13Se0.87. A sequence of processes are presented to ascertain the composition of the crystal, along with strategies for which aspects of the model to inspect to ensure a chemically and crystallographically realistic structure. Criteria include mis-matches between F obs 2 and F calc 2, plots of |F obs| vs |F calc|, residual electron density, checkCIF alerts, pitfalls of the OMIT command used to suppress ill-fitting data, comparative size of displacement ellipsoids, and critical inspection of inter-atomic distances. Since the structure is quite small, solves easily, and presents a number of readily expressible refinement concepts, we feel that it would make a straightforward and concise instructional piece for students learning how to determine if their model provides the best fit for the data and show students how to critically assess their structures.

Temporal electric field and electron density behavior of a He plasma jet with pulse width closing to pulse duration

Previously, it was observed that the plasma plume appears with three regimes (dark regime next to the nozzle, bright regime in the middle, and dim regime on the right) where the regime next to the nozzle is dark when the pulse width of the applied voltage is close to the pulse duration. In this paper, to understand such observation, the spatial and temporal resolved electron density and electric field in the three regimes are measured through the Thomson scattering and electric field-induced second harmonic method, respectively. It is found that, in the dark regime next to the nozzle, the electric field is relatively low, and it has a peak value of about 10 kV/cm, but the electron density is high, and it has a peak value of about 4.2 × 1020 m−3. So, the dark regime is like a conductive channel. On the other hand, for the bright regime, the electric field is much higher, and it has a peak value of about 17 kV/cm. However, the electron density is significantly lower than that in the dark regime, and its peak value is only about 1020 m−3. Even in the dim regime, the electric field is higher than that in the dark regime, and it has a peak value of about 13 kV/cm. Because electron temperature is related to the electric field, the results obtained in the paper indicate that the brightness of the plasma plume at different regimes is mainly decided by the electron temperature rather than the electron density. Finally, when a trace amount of O2 is mixed into working gas He, the dark regime disappears, and this is believed to be due to the fast attachment of electron to O2, which results in the decrease in the residual electron density in the regime next to the nozzle.

Residual electron spin resonance signals of quartz from the 2018 Baige dammed lake in Tibet: Implications for the identification of sediment layers caused by megafloods

Residual doses may cause overestimation of electron spin resonance (ESR) ages for fluvial sediments. However, ESR residual doses in outburst megaflood sediments have rarely been evaluated. The Jinsha River, situated in the southeastern Tibetan Plateau, is characterized by active faults, narrowed canyons, and dammed lakes. Consequently, the river is a rare opportunity for a reconstruction study of outburst flood events from a paleo-dammed lake. After the destruction of the Baige dammed lake in the upper Jinsha River in 2018, outburst megafloods formed a thick diluvium that was deposited in broad valley land along the lower Jinsha River. Based on detailed field investigation and laboratory studies, preliminary hydraulics estimates and residual quartz ESR signals indicate the following. 1) Among the multiple quartz ESR centers, the Al, E1ʹ, Ti-H, and Ti-Li centers could be measured. The Ti-H center had the lowest residual dose and would provide relatively accurate ages for outburst megaflood sediment. 2) The Ti-Li and Al centers commonly used for ESR dating provide overestimates of 283 ± 42 ka ∼ 462 ± 63 ka and 1,010 ± 88 ka ∼ 1,400 ± 219 ka, respectively, for present outburst megaflood sediment. 3) The diverse ages given by the same ESR signal may be caused by various precursors of megaflood sediments, which are mainly sourced from landslide dams and from various terraces and slope sediments along the river. Results demonstrated that the apparent ESR ages observed for the outburst megaflood sediment in the southeastern Tibetan Plateau may be counterfeit, providing an age much older than its real age. This could be interpreted to mean that the narrowed lower channel makes the upper reaches of the broad valley appear lake-like, with diluvium deposits having large non-negligible residual ESR signals without enough exposure to adequate sunlight, despite having good stratification and sorting characteristics similar to those of fluvio-lacustrine sediments. Thus, abrupt reversal in quartz ESR ages in multiple centers observed in the geochronological framework of the fluvial sedimentary profile may indicate a diluvial or flood layer in the absence of other inducements.

Results of the Study of a New Generation Technological Gyrotron System With High Power and Efficiency

A series of work has been carried out to develop a new generation of technological gyrotrons on the first cyclotron harmonic with a radiation frequency of 28 GHz and a power beyond 20 kW. The generation efficiency reaches up to 55% at 6-kW power level without a system of recovery of residual electron energy. The efficiency of the entire setup is about 35% in the mode of maximum radiation power, which is achieved by using a magnetically shielded oil-cooled solenoid. The proper operation of the developed electron-optical system under conditions of a quasi-adiabatic magnetic field in the area of formation of a helical electron beam and a non-adiabatic one in the collector region is confirmed. The letter presents experimental data which is consistent with the results of numerical modeling. This allows us to further count on the implementation of generators up to the W-band frequency range using the magnetic system and high-voltage power sources.

Stepwise development of atmospheric pressure plasma jet driven by bursts of high-voltage nanosecond pulses at multi-tens MHz

This study employs the bursts of high-voltage nanosecond pulses at multi-tens MHz to drive the helium atmospheric pressure plasma jet. Such bursts are obtained by modulating a high-voltage nanosecond pulse based on the wave reflections in a coaxial cable. The development processes and mechanisms of the plasma jet are analyzed in detail based on the discharge waveforms, discharge images, gas temperature, electron density, and axial electric field. Because the time interval between adjacent pulses is much shorter than the characteristic plasma decay time, the discharge channel driven by the first pulse still has high residual electron density and conductivity when the second pulse arrives. The first discharge channel serves as an extension of the high-voltage electrode. In this case, the second discharge starts at the end of the first discharge channel and continues to propagate forward. Driven by the bursts of high-voltage nanosecond pulses, the stepwise propagation of a guided streamer along the plasma jet is observed. The characteristic of the stepwise development of the guided streamer is stable and repeatable under the same condition and does not change at different helium flow rates if the flow is laminar. Reducing the cable length results in a higher equivalent pulse frequency in the bursts and significantly increases the plasma jet length. However, an excessively high frequency will cause a rise in gas temperature and pressure fluctuation in helium flow, resulting in a reduction in the length of the laminar region and an unstable discharge.

Decellularized Pancreatic Tail as Matrix for Pancreatic Islet Transplantation into the Greater Omentum in Rats.

Infusing pancreatic islets into the portal vein currently represents the preferred approach for islet transplantation, despite considerable loss of islet mass almost immediately after implantation. Therefore, approaches that obviate direct intravascular placement are urgently needed. A promising candidate for extrahepatic placement is the omentum. We aimed to develop an extracellular matrix skeleton from the native pancreas that could provide a microenvironment for islet survival in an omental flap. To that end, we compared different decellularization approaches, including perfusion through the pancreatic duct, gastric artery, portal vein, and a novel method through the splenic vein. Decellularized skeletons were compared for size, residual DNA content, protein composition, histology, electron microscopy, and MR imaging after repopulation with isolated islets. Compared to the other approaches, pancreatic perfusion via the splenic vein provided smaller extracellular matrix skeletons, which facilitated transplantation into the omentum, without compromising other requirements, such as the complete depletion of cellular components and the preservation of pancreatic extracellular proteins. Repeated MR imaging of iron-oxide-labeled pancreatic islets showed that islets maintained their position in vivo for 49 days. Advanced environmental scanning electron microscopy demonstrated that islets remained integrated with the pancreatic skeleton. This novel approach represents a proof-of-concept for long-term transplantation experiments.

Study of the Mechanical Properties and Microstructural Response with Laser Shock Peening on 40CrMo Steel

In this work, the purpose of the study was to explore the influence of laser shock peening (LSP) on the mechanical behavior and microstructural response of 40CrMo steel. The residual stress at depth direction and the microstructural evolution of 40CrMo steel specimens without and with LSP treatments were tested by residual stress tester and transmission electron microscopy (TEM). The microhardness at depth direction and the tensile properties at room temperature were measured. Moreover, the effects of LSP on the ability to resist wear of 40CrMo steel were analyzed, and the worn morphologies characteristics were observed by scanning electron microscope (SEM). The results demonstrated that LSP led to the surface residual stress convert from tensile stress to compressive stress, while the surface compressive residual stress tested parallel to the laser path of the specimen subjected to LSP reached −425 MPa. After the LSP process, the average surface microhardness reached 338 HV, which increased by 21.58% than that of the untreated sample. LSP could enhance the strength without losing plasticity significantly, while the average tensile strength reached 1165 MPa, and the fracture elongation reached 13.9%. After a friction and wear test, the mass loss of the sample after LSP treatment reduced by 27.5% compared to the original sample. The increase in dislocation density and the formation of deformation twins generated by LSP played a key role in enhancing the mechanical behavior of 40CrMo steel.

Crystal structure of mevalonate 3,5-bisphosphate decarboxylase reveals insight into the evolution of decarboxylases in the mevalonate metabolic pathways

Mevalonate 3,5-bisphosphate decarboxylase is involved in the recently discovered Thermoplasma-type mevalonate pathway. The enzyme catalyzes the elimination of the 3-phosphate group from mevalonate 3,5-bisphosphate as well as concomitant decarboxylation of the substrate. This entire reaction of the enzyme resembles the latter half-reactions of its homologs, diphosphomevalonate decarboxylase and phosphomevalonate decarboxylase, which also catalyze ATP-dependent phosphorylation of the 3-hydroxyl group of their substrates. However, the crystal structure of mevalonate 3,5-bisphosphate decarboxylase and the structural reasons of the difference between reactions catalyzed by the enzyme and its homologs are unknown. In this study, we determined the X-ray crystal structure of mevalonate 3,5-bisphosphate decarboxylase from Picrophilus torridus, a thermoacidophilic archaeon of the order Thermoplasmatales. Structural and mutational analysis demonstrated the importance of a conserved aspartate residue for enzyme activity. In addition, although crystallization was performed in the absence of substrate or ligands, residual electron density having the shape of a fatty acid was observed at a position overlapping the ATP-binding site of the homologous enzyme, diphosphomevalonate decarboxylase. This finding is in agreement with the expected evolutionary route from phosphomevalonate decarboxylase (ATP-dependent) to mevalonate 3,5-bisphosphate decarboxylase (ATP-independent) through the loss of kinase activity. We found that the binding of geranylgeranyl diphosphate, an intermediate of the archeal isoprenoid biosynthesis pathway, evoked significant activation of mevalonate 3,5-bisphosphate decarboxylase, and several mutations at the putative geranylgeranyl diphosphate–binding site impaired this activation, suggesting the physiological importance of ligand binding as well as a possible novel regulatory system employed by the Thermoplasma-type mevalonate pathway.

Decision problem with high residual electron density on the metal atom

It is shown that replacing the experimental electron density with the theoretical one on the terbium atom describes the experimental topology in the coordination sphere with high accuracy. Such a replacement is fundamentally important in the case of high residual electron density on a heavy metal atom.