Impurity Energy Research Articles

Biintercalate layered heterostructure: synthesis conditions and physical properties

The biintercalation of the layered GaSe semiconductor is carried out by ferroelectric and ferromagnetic guest components. Due to the separation of guest components, the GaSe <NaNO2+FeCl3> nanohybrid has a spatial-scale hybridity, which is due to the alternation of nanoscale regions of one phase with meso- or microdimensions of another. The results of electrical conductivity studies by impedance spectroscopy indicate a 250-fold increase after biintercalation of the GaSe single crystal, due to delocalized current carriers. Confirmation of a significant change in the impurity energy spectrum after biintercalation was obtained by the method of thermally stimulated discharge—GaSe nanohybrid <NaNO2+FeCl3> is characterized by a quasi-continuous spectrum in the entire temperature range of measurements and relaxation of the heterocharge. The GaSe <NaNO2+FeCl3> nano-hybrid is characterized by a high dielectric constant while a tangent of the dielectric loss angle is less than 1 in the high- frequency region of the spectrum. That opens the prospect of its use for the manufacture of high-quality radio- frequency capacitors. Changes in the impurity energy spectrum are investigated for low temperatures in the virtual crystal model, taking into account the Fivazov dispersion law both for the conductivity band and for the two impurity bands. The appearance of an additional gap in the spectrum of impurity states is established and its shift is investigated depending on the concentration of intercalants of different nature—intercalant-acceptor type and donor.

First-Principles Calculation of Conductivity of Ce-C Codoped SnO2 Contacts

The contact is the core element of the vacuum interrupter of the mechanical DC circuit breaker. The electrical conductivity and welding resistance of the material directly affect its stability and reliability. AgSnO2 contact material has low resistivity, welding resistance, and so on. This material occupies an important position of the circuit breaker contact material. This research is based on the first-principles analysis method of density functional theory. The article calculated the lattice constant, enthalpy change, energy band, electronic density of state, charge density distribution, population, and conductivity of Ce, C single-doped, and Ce-C codoped SnO2 systems. The results show that Ce, C single doping, and Ce-C codoping all increase the cell volume and lattice constant. When the elements are codoped, the enthalpy change is the largest, and the thermal stability is the best. It has the smallest bandgap, the most impurity energy levels, and the least energy required for electronic transitions. The 4f orbital electrons of the Ce atom and the 2p orbital electrons of C are the sources of impurity energy near the Fermi level. When the elements are codoped, more impurity energy levels are generated at the bottom of the conduction band and the top of the valence band. Its bandgap is reduced so conductivity is improved. From the charge density and population analysis, the number of free electrons of Ce atoms and C atoms is redistributed after codoping. It forms a Ce-C covalent bond to further increase the degree of commonality of electrons and enhance the metallicity. The conductivity analysis shows that both single-doped and codoped conductivity have been improved. When the elements are codoped, the conductivity is the largest, and the conductivity is the best.

High-Resolution Mapping of Local Photoluminescence Properties in CuO/Cu2O Semiconductor Bi-Layers by Using Synchrotron Radiation.

The quality of a semiconductor, which strongly affects its performance, can be estimated by its photoluminescence, which closely relates to the defect and impurity energy levels. In light of this, it is necessary to have a measurement method for photoluminescence properties with spatial resolution at the sub-micron or nanoscale. In this study, a mapping method for local photoluminescence properties was developed using a focused synchrotron radiation X-ray beam to evaluate localized photoluminescence in bi-layered semiconductors. CuO/Cu2O/ZnO semiconductors were prepared on F:SnO2/soda-lime glass substrates by means of electrodeposition. The synchrotron radiation experiment was conducted at the beamline 20XU in the Japanese synchrotron radiation facility, SPring-8. By mounting the high-sensitivity spectrum analyzer near the edge of the CuO/Cu2O/ZnO devices, luminescence maps of the semiconductor were obtained with unit sizes of 0.3 μm × 0.3 μm. The devices were scanned in 2D. Light emission 2D maps were created by classifying the obtained spectra based on emission energy already reported by M. Izaki, et al. Band-like structures corresponding to the stacking layers of CuO/Cu2O/ZnO were visualized. The intensities of emissions at different energies at each position can be associated with localized photovoltaic properties. This result suggests the validity of the method for investigation of localized photoluminescence related to the semiconductor quality.

Ab initio study on magnetism of SnO2 (110) surface with non-metallic elements doping

The electronic structure and magnetic properties of SnO2 (110) surface with anion vacancy and non-metallic elements doping have been studied by using ab initio calculations based on density functional theory (DFT). The perfect SnO2 (110) surface is a non-magnetic semiconductor. The calculated results show that although oxygen vacancy has the lowest formation energy, it cannot introduce local magnetic moment on the surface. For boron (B), carbon (C) and nitrogen (N) doped systems, the formation energy of impurity C is the highest due to sp3 hybridization. The research results show that B, C and N can introduce local magnetic moments on the (110) surface which will cause the system to produce high spin state (S = 1/2 or 1), and the magnetic moments are 1.38 μB, 1.80 μB and 1.00 μB, respectively. Impurity levels appear in the band gap near the Fermi level. Further analysis shows that the magnetic moments are mainly localized near the doped atoms. Studies on magnetic coupling between impurity atoms at different distances reveal that C–C are always coupled ferromagnetically, while N–N are always coupled antiferromagnetically. The energy difference between the antiferromagnetic state and ferromagnetic state is large at each C–C distance in the C-doped system. This indicates that the Curie temperature of the C-doped SnO2 (110) surface is likely to be above room temperature. Our findings are beneficial to the development of spintronics.

Effects of doping Ti, Nb, Ni on the photoelectric properties of monolayer 2H–WSe2

The photocurrent of Ti, Nb, Ni substitution-doped monolayer 2H–WSe 2 is calculated by the first-principles method based on the Keldysh nonequilibrium Green's function-density functional theory. The photogalvanic effect(PGE) photocurrent can be generated in the monolayer 2H–WSe 2 under the vertical irradiation of linear polarized light, However, it is generally very small. Calculation results show that the Nb and Ti-doped systems exhibit the characteristics of semi-metal, while the Ni-doped system tends to transform into metals. The substitutional doping of Nb, Ti, and Ni atoms can effectively enhance the photocurrent and the polarization sensitivity of monolayer 2H–WSe 2 .This excellent performance is mainly attributed to the fact that the doping introduces multiple impurity energy bands crossing the Fermi energy level, which becomes a bridge for electronic transitions, thus effectively enhancing the photocurrent. • Background and Significance: The research on the modification of monolayer 2H-WSe 2 by doping has become increasingly popular, and its doping system has shown great application potential. But the theoretical calculation of doped 2H-WSe 2 is relatively less in terms of the photogalvanic effect. Therefore, the photocurrent of Ti, Nb, and Ni-doped monolayer 2H-WSe 2 are calculated respectively. It is expected that the research in our work will provide some theoretical guidance for the application of 2H-WSe 2 in the field of optoelectronics. • Originality and Novelties: Our results show that doping Ti, Nb, and Ni atoms can effectively enhance the photocurrent and extinction ratio of the monolayer 2H-WSe 2 . The photocurrent functions are all proportional to COS2θ. The Ni-doped system can obtain the largest photocurrent (1.484) and the extinction ratio (23.2), which are mainly attributed to the fact that the doping introduces multiple impurity energy bands, which becomes a bridge for electronic transitions.

A novel method for generating p-type wide- and ultrawide-bandgap III-nitride by doping with magnetic elements

We propose a novel method to generate p-type conduction and low resistivity in wide- and ultrawide-bandgap III-nitride semiconductors via doping of a magnetic element. This method is based on the energetic competition between the covalency of the magnetic element and the ligand nitrogen atoms and the exchange-correlation energy of the magnetic impurity. Using magnetic elements with large exchange-correlation energy, we can obtain p-type wide- and ultrawide-bandgap semiconductors, which are basically difficult to synthesize due to the unipolarity.

Thermodynamics at zero temperature: Inequalities for the ground state of a quantum many-body system

We prove that for a single-component many-body system at zero temperature the inequality Eint≤PV holds, where Eint is the interaction energy, P is pressure and V is volume. This inequality is proven under rather general assumptions with the use of Anderson-type bound relating ground state energies of systems with different numbers of particles. We also consider adding impurity particles to the system and derive inequalities on the chemical potential of the impurity and binding energy of the bound state of two impurities.

Theoretical study of stress impact on formation enthalpy and thermal equilibrium concentration of impurities and dopants in Si single crystal

In Si-based VLSI manufacturing processes, complicated plane stress is applied near the (001) surface of Si wafers as device feature sizes further shrink. For this technical trend, the control of impurities including contamination metals and light elements as well as dopants becomes more and more important to improve device performance. In this study, density functional study calculations were performed to evaluate the dependence of the formation energy (Ef), volume change (ΔVol), and formation enthalpy (Hf) of impurities and dopants on isotropic or plane stress up to 2 GPa. Thirteen metal atoms (Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Hf, Ta, and W), which are concerned in LSI processes, 4 light elements (H, C, N, and O), which exist normally in CZ-Si wafers, and 3 dopants (B, P, and As), which are generally used for Si, were considered. It was found that the dominant factor in the change of Hf was the ΔVol. On the basis of calculated results, we classified impurities and dopants according to the stress that increases the thermal equilibrium concentration (Ceq) in Si crystal. Furthermore, the stress dependence of the Hf of impurities and dopants in Si was formulated. The results obtained in the present work should be a useful database for controlling the behavior of impurities and dopants in stressed Si crystal.

Theoretical study on structural stability and optoelectronic properties of metal-adsorbed two-dimensional GaN

This paper have studied structural stability and optoelectronic properties of two-dimensional GaN adsorbed by Pt, Al, Ag and Au atoms through using first-principles. The results show that it exhibits completely different results when two-dimensional GaN adsorbs Al atom. For Pt, Ag and Au atoms, the most stable adsorption position is T N , while the most stable position for Al atom is H. After adsorbing Pt, Ag and Au, an impurity energy level is formed between CBM and VBM. On the other hand, the Fermi energy level Al-adsorbed two-dimensional GaN passes through the CBM, showing n-type conductivity . Due to the difference in electronegativity between the atoms, Pt and Au obtain charges of 0.01|e| and 0.04|e| from two-dimensional GaN, respectively, while the Al atoms and Ag atoms transfer 0.14|e| and 1.16|e| into two-dimensional GaN, respectively. In addition, when two-dimensional GaN is adsorbed by metal atoms, optical properties can be adjusted and it will become more inclined to absorb short-wavelength light. Compared to the other three metal atoms, the Al-adsorbed two-dimensional GaN is more advantageous in the infrared band. • Stability and optoelectronic properties of two-dimensional GaN adsorbed by Pt, Al, Ag and Au atoms are studied. • The most stable adsorption site for Pt, Ag and Au is T N , while for Al atom is H. • After adsorbing Pt, Ag, and Au atom, an impurity level is formed between the CBM and the VBM. • Al atom are more conducive to development of optical properties of two-dimensional GaN.

Tunable ultraviolet sensing performance of Al-modified ZnO nanoparticles

The potential of polycrystalline Al-doped ZnO nanoparticles as an active material for UV photodetectors has been investigated. The Rietveld refinement of powder X-ray diffraction data revealed a single hexagonal phase of the nanoparticles. A slight deviation in the lattice cell constants from pristine ZnO was observed, associated with defect creation and strain generated due to Al3+ substitution. High-resolution transmission electron microscopy image reveals a spherical morphology of both the doped and undoped ZnO nanoparticles. Stacking faults observed in the Al-doped samples is an indication of a proper Al-doping and is a signature of high density of crystal defects. The bandgap was found to reduce due to the delocalization of impurity energy states as a result of Al3+ substitution. Consequently, conductivity was improved in doped samples. Photoluminescence spectroscopy revealed a strong dependence of the emissions from defect sites on dopant content. Further, a correlation of the FWHM of the E2high Raman mode to the Urbach energy was observed. The UV sensing analysis demonstrates the enhancement of the photocurrent and improved sensitivity. Thus, this work provides a simple, cost-effective, and tunable processing strategy for synthesizing and applying ZnO-based nanomaterials for high-performance UV photodetectors.

Effect of dielectric screening function on binding energy and diamagnetic susceptibility of impurity doped in GaAs conical quantum dots

In this study, we have investigated the effect of the impurity dependent dielectric screening function on the diamagnetic susceptibility and the binding energy of a shallow-donor impurity confined in a GaAs conical quantum dot (CQD). The calculations have been made within the effective mass approximation, variational method and considering an infinite confining potential. Our results suggest that the effects of the variation of geometrical parameters of CQD are playing a pronounce influence on the diamagnetic susceptibility and the binding energy. The results show that the diamagnetic susceptibility depends strongly on the impurity position and it severely affected by the geometrical parameters of CQD.

Fe, Cu co-doped BiOBr with improved photocatalytic ability of pollutants degradation

Designing efficient photocatalysts is essential for improving photocatalytic performance. Separation efficiency of photogenerated carriers is one of the key factors affecting photocatalytic performance. Combining the construction of two-dimensional materials with elemental doping can further improve the separation of photogenerated carriers. As expected, the performance of the samples produced by Fe and Cu co-doping was superior to that of pure BiOBr and mono-doped samples, with significant improvements in the photocatalytic degradation of both rhodamine B and tetracycline. The dopant of excess metal element atoms can form impurity energy levels in the forbidden band that effectively facilitate the separation and migration of photogenerated carriers. Meanwhile, the thin-layer two-dimensional structure can effectively shorten the bulk charge carrier transmission distance and improve the transmission efficiency. This study not only provides a simple, green and low-cost method for combining iron and copper into composites materials at same time but also confirmed that the photocatalytic performance of BiOBr was strongly influenced by different Fe and Cu contents.

First principle calculations of structural and electronic properties of pyrochlore Y2Ru2O7 and Y1-xMxRu2O7−δ (M=Mg, Ca, Sr, Ba, Zn, Cd and Hg)

The electronic structural and electronic properties of pyrochlore Y2Ru2O7 (YRO) and Y1-xMxRu2O7−δ (M = Mg, Ca, Sr, Ba, Zn, Cd and Hg) were investigated using first-principle calculation based on GGA + U and HSE06 hybrid functional. The schematic energy level diagram of YRO was drawn, and its band gap was found to locate in π* antibonding orbital, dominated by Ru-4d electrons. RuO6 octahedrons in YRO undergo a compressing trigonal distortion, with a local symmetry group of D3d, which is quite different from RuO2 and perovskite ruthenium oxide. When Y is substituted by divalent cation M (MY), O vacancies can achieve low formation energy and introduce the MY-VO and 2MY-VO complex. Further calculation showed that MY-VO complex in YRO can induce an impurity energy level into forbidden band, and narrow the band gap. As a result, high electrical conductivity of Y1-xMxRu2O7−δ is expected, and MY-VO complex may be the origin of electrocatalytic activity in Y1-xMxRu2O7.

Low-Density Neutron Matter and the Unitary Limit

We review the properties of neutron matter in the low-density regime. In particular, we revise its ground state energy and the superfluid neutron pairing gap and analyze their evolution from the weak to the strong coupling regime. The calculations of the energy and the pairing gap are performed, respectively, within the Brueckner–Hartree–Fock (BHF) approach of nuclear matter and the Bardeen–Cooper–Schrieffer (BCS) theory using the chiral nucleon-nucleon interaction of Entem and Machleidt at N3LO and the Argonne V18 phenomenological potential. Results for the energy are also shown for a simple Gaussian potential with a strength and range adjusted to reproduce the1S0neutron-neutron scattering length and effective range. Our results are compared with those of quantum Monte Carlo (QMC) calculations for neutron matter and cold atoms. The Tan contact parameter in neutron matter is also calculated, finding a reasonable agreement with experimental data from ultra-cold atoms only at very low densities. We find that low-density neutron matter exhibits a behavior close to that of a Fermi gas at the unitary limit, although, this limit is actually never reached. We also review the properties (energy, effective mass, and quasiparticle residue) of a spin-down neutron impurity immersed in a low-density free Fermi gas of spin-up neutrons already studied by the author in a recent work where it was shown that these properties are very close to those of an attractive Fermi polaron in the unitary limit.

Combined effects of the hydrostatic pressure and temperature on the self-polarization in a finite quantum well under laser field

In this study, the self-polarization and binding energy of the donor impurity atom in the laser field applied G a 1 − x A l x A s / G a A s quantum well are investigated under the combined influence of hydrostatic pressure and temperature. Variation of self-polarization and binding energy depending on temperature, hydrostatic pressure, impurity position, well width and laser field parameters are shown. Using the effective mass approximation, subband energy has been found by finite difference method and impurity energy has been found by variation method. Our results showed that hydrostatic pressure and temperature have a noticeable effect on the calculated self-polarization and binding energy in a quantum well under the effect of the laser field. We think that the results obtained will be useful in determining the physical properties of the quantum well under the influence of laser field, hydrostatic pressure and temperature. • The square quantum well is considered. • The effects of hydrostatic pressure and temperature on self-polarization have been calculated under laser field. • The variational and finite differences calculations have been performed. • Laser field parameter, hydrostatic pressure and temperature are important factor.

Synthetic superfluid chemistry with vortex-trapped quantum impurities

We explore the effect of using two-dimensional matter-wave vortices to confine an ensemble of bosonic quantum impurities. This is modelled theoretically using a mass-imbalanced homogeneous two component Gross-Pitaevskii equation where each component has independent atom numbers and equal atomic masses. By changing the mass imbalance of our system we find the shape of the vortices are deformed even at modest imbalances, leading to barrel shaped vortices; which we quantify using a multi-component variational approach. The energy of impurity carrying vortex pairs are computed, revealing a mass-dependent energy splitting. We then compute the excited states of the impurity, which we in turn use to construct `covalent bonds' for vortex pairs. Our work opens a new route to simulating synthetic chemical reactions with superfluid systems.

Effects of 4d transition metals doping on the photocatalytic activities of anatase TiO2 (101) surface

AbstractAiming at improving the visible‐light photocatalytic activities of TiO2(101) surface we make an in‐depth study on the TiO2(101) doped with 4d transition metal (TM) atoms. It is shown that the 4d TM dopings can not only produce new impurity energy bands in the band gap but also result in the semiconductor–metal phase transition. Consequently, the visible‐light absorption is strongly strengthened due to the dopings of Y, Zr, Nb, Mo, and Ag, while it is only weakly improved for Tc, Ru, Rh, Pd, and Cd dopings. The improvement in visible‐light absorption can be attributed to the intraband or interband transition of electrons. Moreover, the photocatalytic activities are explored, and we find Y and Ag dopings can effectively enhance the photocatalytic activity of TiO2(101) surface. Thus the mechanism of improving photocatalytic activity of TiO2(101) has been clearly addressed, which is beneficial to further experimental and theoretical researches on TiO2 photocatalysts.

Improvement of Photocatalytic Activity of Bi2WO6 by Doping Ag and Y: A DFT Study

Although much attention has been recently focused on Bi2WO6 and doping materials as highly efficient visible-light photocatalysts, the selection of an appropriate element as dopant and our understanding of the photocatalytic mechanism from the electronic level still need to be further investigated. In the current work, electronic band structures, density of states, optical properties, and effective mass for Bi2WO6, Ag-doped Bi2WO6 and Y-doped Bi2WO6 semiconductors have been studied by density functional theory calculations. We find that, while both the doped systems show little change in the band gap from Bi2WO6, Ag-doped and Y-doped Bi2WO6 produce more dispersive bands compared to the original Bi2WO6, implying that the doped systems can facilitate the spatial separation of photo-induced electron–hole pairs, and thus enhance the photocatalytic performance. In addition, for Ag-doped Bi2WO6, the presence of an Ag impurity energy band just above the valence band is expected to act as electron-trapping sites leading to a reduction of the recombination rate of photogenerated carriers. Our findings could provide an explanation for the experimental observations reported in the literature.

Buckling on Fe‐Doped AlGaN/GaN High Electron Mobility Transistor Films after Laser Liftoff Process: Phenomena and Mechanism

The influence of Fe in the buffer layer on the laser liftoff (LLO) of GaN high electron mobility transistors is presented herein. LLO is performed on Fe‐doped GaN films using a KrF excimer LLO system. The morphology, crystal characteristics, and 2D electron gas (2DEG) characteristics of the GaN films after LLO are characterized using a 3D optical microscope, X‐ray diffraction, and Hall methods. The present work is different from previous methods because of the large‐area buckling instead of cracks on the Fe‐doped GaN films. The results show that the crystal quality and 2DEG characteristics of the buckled parts are significantly affected. Furthermore, a modified simulation model of the temperature and thermal‐induced stress fields in the films is used to explain the buckling of the films, whose results are consistent with the characterization results. The additional absorption centers induced by the Fe impurity energy levels increase the gradient of temperature field, thereby increasing the compressive stresses in the films at the edges of the laser spots. Moreover, a higher temperature is observed at the interface between the film and the bonding glue, which results in the debonding. Therefore, Fe‐doped GaN films are more prone to buckling than unintentionally doped GaN films.

Engineering paper-based visible light-responsive Sn-self doped domed SnO2 nanotubes for ultrasensitive photoelectrochemical sensor

Exploring novel photoactive materials with high photoelectric conversion efficiency plays a crucial role in enhancing the analytical performance of paper-based photoelectrochemical (PEC) biosensor. SnO2, which possesses higher photostability and electron mobility, can be regarded as a promising photoactive material. Herein, paper-based one dimensional (1D) domed SnO2 nanotubes (NTs) have been developed with the template-consumption strategy. What’s more, their growth mechanism has also been proposed based on the controllable experiments. At first, the paper-based 1D ZnO nanorods (NRs) as the typical amphoteric oxide are prepared and serve as the sacrifice templates which can be etched by the generated alkaline environment during the formation of SnO2. At a certain stage, all the ZnO NRs can be completely etched by controlling the experimental conditions, resulting in the forming of vertically distributed hollow SnO2 NTs. Furthermore, the Sn self-doping strategy is also proposed to suppress the recombination of charge carriers and broaden the light response range by introducing the impurity energy levels. Profiting from such doping strategy, the prominent photocurrent signal is obtained compared with pure paper-based SnO2 NTs. Ultimately, an innovative visible light responsive paper-based Sn-doping SnO2-x NTs are developed and employed as the photoelectrode for the PEC biosensor using the alpha fetoprotein (AFP) as the model analyte. Under the optimal conditions, the ultrasensitive AFP sensing is realized with the linear range and detection limitation of 10 pg mL-1 to 200 ng mL-1 and 3.84 pg mL-1, respectively. This work provides a judiciously strategy for developing novel photoactive materials for paper-based PEC bioanalysis.