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Two-step Synthesis of Laminar Vanadate via a Facile Hydrothermal Route and Enhancing the Photocatalytic Reduction of CO2 into Solar Fuel through Tuning the Oxygen Vacancies by in situ Vacuum Illumination Treatment
摘要： Monoclinic LaVO4, tetragonal CeVO4 and monoclinic Pb2V2O7 with laminar structures composed of nanosheets have been successfully fabricated using a two-step facile hydrothermal route. The narrow-bandgap LaVO4, CeVO4 and Pb2V2O7 vanadate exhibited photocatalytic activity towards the photoreduction of CO2 into C2H5OH in the liquid phase. The existence of oxygen vacancies on LaVO4 surface further enhanced the photocatalytic activity for photoreduction of CO2 into CO in gas phase, which can be easily obtained using a vacuum illumination treatment. The EPR, PL and FTIR results indicated that oxygen vacancies are beneficial to the separation of electrons by prolonging the lifetime of the photogenerated electrons and enhancing the chemisorption of CO2 on the photocatalyst surface.
关键词： Laminar structure,Photocatalytic reduction of CO2,Vanadate,Oxygen vacancy,Photocatalytic activity
更新于2025-09-10 09:29:36
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Effect of the Gamma-Ray Irradiation on the Electric and Optical Properties of SrTiO3 Single Crystals
摘要： We investigated the visible emission property of SrTiO3 (STO) single crystals irradiated with gammy-ray (γ-ray) at various total doses up to 900 kGy. The electric and optical absorption properties of the irradiated STO samples were hardly changed with the γ-ray irradiation, compared with those of un-irradiated STO. In contrast, the visible emission near 550 nm increased with the γ-ray dose increasing. While the development of the visible emission was indicative of the increase of oxygen vacancies inside STO by the γ-ray irradiation, the newly generated oxygen vacancies were not significantly harmful to the electric and optical properties of STO. We concluded that the STO single crystal should have a good tolerance against the damage by the γ-ray irradiation.
关键词： Gamma-ray irradiation,Photoluminescence,Oxygen vacancy,SrTiO3 single crystal
更新于2025-09-10 09:29:36
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Electronic structures and spectroscopic signatures of silicon-vacancy containing nanodiamonds
摘要： The presence of midgap states introduced by localized defects in wide-band-gap-doped semiconductors can strongly affect the electronic structure and optical properties of materials, generating a wide range of applications. Silicon-divacancy defects in diamond have been recently proposed for probing high-resolution pressure changes and performing quantum cryptography, making them good candidates to substitute for the more common nitrogen-vacancy centers. Using group-theory and ab initio electronic structure methods, the molecular origin of midgap states, zero-phonon line splitting, and size dependence of the electronic transitions involving the silicon-vacancy center is investigated in this paper. The effects of localized defects on the Raman vibrational and carbon K-edge x-ray absorption spectra are also explored for nanodiamonds. This paper presents an important analysis of the electronic and vibrational structures of nanosized semiconductors in the presence of midgap states due to localized defects, providing insight into possible mechanisms for modulating their optical properties.
关键词： midgap states,electronic structure,optical properties,nanodiamonds,Raman vibrational spectra,quantum cryptography,x-ray absorption spectra,silicon-vacancy defects
更新于2025-09-10 09:29:36
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NV <sup>?</sup> –N <sup>+</sup> pair centre in 1b diamond
摘要： With the creation of nitrogen (NV) in 1b diamond it is common to find that the absorption and emission is predominantly of negatively charged NV centres. This occurs because electrons tunnel from the substitutional nitrogen atoms to NV to form NV?–N+ pairs. There can be a small percentage of neutral charge NV0 centres and a linear increase of this percentage can be obtained with optical intensity. Subsequent to excitation it is found that the line width of the NV? zero-phonon has been altered. The alteration arises from a change of the distribution of N+ ions and a modification of the average electric field at the NV? sites. The consequence is a change to the Stark shifts and splittings giving the change of the zero-phonon line (ZPL) width. Exciting the NV? and N0 in the samples results in a significant dependence on excitation wavelength and there is also a dependence on the concentration of the NV? to N+ in the samples. The present investigation involves extensive use of low temperature optical spectroscopy to monitor changes to the absorption and emission spectra particularly the widths of the ZPL. The studies lead to a good understanding of the properties of the NV?–N+ pairs in diamond. There is a critical dependence on pair separation. When the NV?–N+ pair separation is large the properties are as for single sites and a high degree of optically induced spin polarization is attainable. When the separation decreases the emission is reduced, the lifetime shortened and the spin polarization downgraded. With separations of <12 A0 there is even no emission. The deterioration occurs as a consequence of electron tunneling in the excited state from NV? to NV0 and an optical cycle that involves NV0. The number of pairs with the smaller separations and poorer properties will increase with the number of nitrogen impurities and it follows that the degree of spin polarization that can be achieved for an ensemble of NV? in 1b diamond will be determined and limited by the concentration of single substitutional nitrogen. The information will be invaluable for obtaining optimal conditions when ensembles of NV? are required. As well as extensive measurements of the NV? optical ZPL observations of Stark effects associated with the infrared line at 1042 nm and the optically detected magnetic resonance at 2.87 GHz are also reported.
关键词： Stark effect,nitrogen-vacancy,spin polarisation,optical spectroscopy
更新于2025-09-09 09:28:46
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Se—assisted synthesis of WO <sub/>3?x</sub> nanowires and its intrinsic metallicity
摘要： One dimensional WO3?x nanowires were successfully synthesized by a chemical vapor deposition method under a catalysis effect of non-metal selenium at an atmosphere pressure. The morphology ad structural characteristics were investigated by scanning electron microscopy (SEM), atom force microscopy (AFM), and transmission electron microscopy (TEM). Furthermore, X-ray photoelectron spectrum analysis con?rms existence of the oxygen vacancies in WO3?x nanowires. Based on the above results, a possible growth mechanism was proposed. The oxygen vacancy induced metallic nature of WO3?x nanowires was also con?rmed by the single-nanowire electrical measurements.
关键词： oxygen vacancy,metallic,WO3?x nanowires,chemical vapor deposition
更新于2025-09-09 09:28:46
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Single-photon heralded two-qubit unitary gates for pairs of nitrogen-vacancy centers in diamond
摘要： The implementation of a high-fidelity two-qubit quantum logic gate remains an outstanding challenge for isolated solid-state qubits such as nitrogen-vacancy (NV) centers in diamond. In this work, we show that by driving pairs of NV centers to undergo photon scattering processes that flip their qubit states simultaneously, we can achieve a unitary two-qubit gate conditioned upon a single photon-detection event. Further, by exploiting quantum interference between the optical transitions of the NV centers’ electronic states, we realize the existence of two special drive frequencies: a “magic” point where the spin-preserving elastic scattering rates are suppressed and a “balanced” point where the state-flipping scattering rates are equal. We analyzed four different gate operation schemes that utilize these two special drive frequencies, and various combinations of polarizations in the drive and collection paths. Our theoretical and numerical calculations show that the gate fidelity can be as high as 98%. The proposed unitary gate, combined with available single-qubit unitary operations, forms a universal gate set for quantum computing.
关键词： photon scattering,quantum computing,nitrogen-vacancy centers,two-qubit gate,quantum interference
更新于2025-09-09 09:28:46
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Influence of Dynamical Decoupling Sequences with Finite-Width Pulses on Quantum Sensing for AC Magnetometry
摘要： Dynamical decoupling sequences with multiple pulses can be considered to exhibit filter functions for the time evolution of a qubit superposition state. They contribute to the increase of coherence time and qubit-phase accumulation due to a time-varying field and can thus be used to achieve high-frequency-resolution spectroscopy. Such behaviors find useful application in highly sensitive detection based on qubits for various external fields, such as a magnetic field. Hence, decoupling sequences are indispensable tools for quantum sensing. In this study, we experimentally and theoretically investigate the effects of finite-width pulses in the sequences on ac magnetometry using nitrogen-vacancy centers in an isotopically controlled diamond. We reveal that the finite pulse widths cause a deviation of the optimum time to acquire the largest phase accumulation due to the sensing field from that expected by filter functions ignoring the pulse widths, even if the widths are considerably shorter than the time period of the sensing field. Moreover, we experimentally demonstrate that the deviation can be corrected by an appropriate time-frequency conversion. Our results provide a guideline for the detection of an ac field with an accurate frequency and linewidth in quantum sensing with multiple-pulse sequences.
关键词： nitrogen-vacancy centers,quantum sensing,dynamical decoupling,ac magnetometry,finite-width pulses
更新于2025-09-09 09:28:46
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[IEEE 2018 Iranian Conference on Electrical Engineering (ICEE) - Mashhad (2018.5.8-2018.5.10)] Electrical Engineering (ICEE), Iranian Conference on - Investigating the Electronic Properties of Oxygen Vacancies in Anatase TiO2: An Ab Initio Study
摘要： Metal oxide dielectrics are known as promising candidates for resistive switching or memristor applications. TiO2 has been shown to be one of the favorites for the implementation of resistive switching devices. The mobile oxygen vacancies in TiO2 are recognized as the main source of resistive switching behavior. Therefore, the investigation of atomic scale properties of oxygen vacancies is of crucial importance for the description of microscopic phenomena leading to the resistive switching behavior. In the present work we employed standard DFT within the GGA approximation as well as GGA+U correction to investigate the electronic properties of oxygen vacancies in anatase phase of TiO2. We show that the Hubbard- like term (U) is essential for the correct description of the electronic properties. The defect formation energies at different charged states and the charge transition levels are calculated for different values of U-term. It has been shown that a value of U=3.5 eV is the best choice to obtain reasonable results for the band gap as well as the position of induced defect levels, at same time. Moreover, we show that the q=+2 charged state is the energetically most favorable state for the oxygen vacancy in TiO2.
关键词： metal oxides,DFT,resistive switching,charge transition levels,oxygen vacancy,Hubbard-like term,anatase TiO2
更新于2025-09-09 09:28:46
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Nitrogen Trapping Ability of Hydrogen-Induced Vacancy and the Effect on the Formation of AlN in Aluminum
摘要： This paper presents the ternary interaction of N, H, and vacancy point defects and the nitrogen trapping ability of aluminum vacancies induced by hydrogen by means of DFT methods employed in VASP (Vienna Ab initio Simulation Package) and Abinit packages. The obtained vacancy formation energy of 0.65 eV is close to experimental values. Although the N–vacancy complex is unstable with the negative binding energy of ?0.51 eV, the stability of H–vacancy–N is proved by the positive binding energy of 0.59 eV and the appearance of the orbital hybridization in the density of state (DOS) of atoms connecting to this complex. Moreover, Al vacancies can trap more than 4 N atoms, which prevents the formation of aluminum nitride and subsequently affects not only the hardness of the Al surface but also many practical applications of AlN coating.
关键词： ternary point-defect interaction,first-principles calculations,alpha aluminum,superabundant vacancy
更新于2025-09-09 09:28:46
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Geometric phase magnetometry using a solid-state spin
摘要： A key challenge of magnetometry lies in the simultaneous optimization of magnetic field sensitivity and maximum field range. In interferometry-based magnetometry, a quantum two-level system acquires a dynamic phase in response to an applied magnetic field. However, due to the 2π periodicity of the phase, increasing the coherent interrogation time to improve sensitivity reduces field range. Here we introduce a route towards both large magnetic field range and high sensitivity via measurements of the geometric phase acquired by a quantum two-level system. We experimentally demonstrate geometric-phase magnetometry using the electronic spin associated with the nitrogen vacancy (NV) color center in diamond. Our approach enables unwrapping of the 2π phase ambiguity, enhancing field range by 400 times. We also find additional sensitivity improvement in the nonadiabatic regime, and study how geometric-phase decoherence depends on adiabaticity. Our results show that the geometric phase can be a versatile tool for quantum sensing applications.
关键词： magnetometry,diamond,geometric phase,nitrogen vacancy,quantum sensing
更新于2025-09-09 09:28:46