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Intramolecular exciton dissociation is critical for high efficient mobile charge carrier generations in organic solar cells. Yet despite much attention, the effects of π bridges on exciton dissociation dynamics in donor–π–acceptor (D-π-A) alternating conjugated polymers remain still unclear. Here, using a combination of femtosecond time-resolved transient absorption (TA) spectroscopy and steady-state spectroscopy, we track ultrafast intramolecular exciton relaxation dynamics in three D-π-A alternating conjugated polymers which were synthesized by Qin's group and named HSD-A, HSD-B, HSD-C. It is found that the addition of thiophene unit as π bridges will lead to the red shift of steady-state absorption spectrum. Importantly, we reveal the existence of a new intramolecular exciton dissociation pathway mediated by a bridge-specific charge transfer (CT′) state with the TA fingerprint peak at 1200 nm in π-bridged HSD-B and HSD-C. This CT′ state results in higher electron capture rates for HSD-B and HSD-C as compared to HSD-A. Depending on the proportion of CT′ state and nongeminate recombination are important step for the understanding of high power conversion efficiencies in HSD-B than in HSD-C. We propose that this bridge-specific exciton dissociation pathway plays an important role in ultrafast intramolecular exciton dissociation of organic photovoltaic material D-π-A alternating conjugated polymers.

Interfacial quantum states are drawing tremendous attention recently because of their importance in design of low-dimensional quantum heterostructures with desired charge, spin, or topological properties. Although most studies of the interfacial exchange interactions were mainly performed across the interface vertically, the lateral transport nowadays is still a major experimental method to probe these interactions indirectly. In this Letter, we fabricated a graphene and hydrogen passivated silicon interface to study the interfacial exchange processes. For the first time we found and confirmed a novel interfacial quantum state, which is specific to the 2D-3D interface. The vertically propagating electrons from silicon to graphene result in electron oscillation states at the 2D-3D interface. A harmonic oscillator model is used to explain this interfacial state. In addition, the interaction between this interfacial state (discrete energy spectrum) and the lateral band structure of graphene (continuous energy spectrum) results in Fano-Feshbach resonance. Our results show that the conventional description of the interfacial interaction in low-dimensional systems is valid only in considering the lateral band structure and its density-of-states and is incomplete for the ease of vertical transport. Our experimental observation and theoretical explanation provide more insightful understanding of various interfacial effects in low-dimensional materials, such as proximity effect, quantum tunneling, etc. More important, the Fano-Feshbach resonance may be used to realize all solid-state and scalable quantum interferometers.

In the past few years, lead chalcogenide quantum dots (QDs) have attracted attention as a new system with a strong quantum confinement effect. In this paper, the hot-excitons cooling and Auger recombination of multiexcitons in PbS QDs are investigated by the femtosecond time-resolved transient absorption spectroscopy. The results show that the excitons dynamics in PbS QDs are closely related to the pump-photon energy and pump-pulse energy. Multiexcitons generate when the excess energy of the absorbed photons is larger than the bandgap energy in PbS QDs. The hot-excitons cooling lifetime increases but the Auger recombination lifetime decreases as the pump-photon energy and the pump-pulse energy increase. Besides, there is a competitive relation between multiple-excitons generation and hot-excitons cooling. The dynamics results of the formation and relaxation of multiexcitons in PbS QDs would shed light on the further understanding of the interaction between excitons and photons in the optoelectronic application based on PbS QDs.

High crystalline quality CrN thin films have been grown on La0.67Sr0.33MnO3 (LSMO) templates by molecular beam epitaxy. The structure and magnetic properties of CrN/LSMO heterojunctions are investigated combining with the experiments and the first-principles simulation. The Nėel temperature of the CrN/LSMO samples is found to be 281 K and the saturation magnetization of CrN/LSMO increases compared to that of LSMO templates. The magnetic property of CrN/LSMO heterostructures mainly comes from Cr atoms of (001) CrN and Mn atoms of (001) LSMO. The (001) LSMO induces and couples the spin of the CrN sublattice at CrN/LSMO interface.

First principle study with density functional theory was carried out to investigate the adsorption behavior of nitrogen oxide (NO and NO2) on pristine and B atom embedded γ-graphyne including the adsorption energy, electron transfer, adsorption distance, magnetic moment, band structure, density of states and optical properties. The results indicate that C atom of sp2 hybridization (compared to sp hybridization) is easier to be substituted by B atom with endothermic process. B atom embedded γ-graphyne have notably stronger chemical interactions with NO and NO2 compared to pristine γ-graphyne with larger adsorption energy and greater changes of molecule orbitals. The calculations of optical properties reveal that B atom embedded γ-graphyne has more obvious changes of dielectric function after adsorbed NO or NO2 near 1.5 eV compared to pristine γ-graphyne illustrating that B-graphyne has the prospect to detect nitrogen oxide using not only electrochemical method but also optical method.

We performed the adsorption of NO2 on transition metal (TM) doped InN monolayer by using density functional theory (DFT). Firstly, adsorption of four kinds of TM atom (Pd, Pt, Ag, Au) on pristine InN monolayer was explored including four different adsorption sites (TIn, TN, BIn-N and H). Then, for NO2 adsorption, by calculating adsorption energy, adsorption distance, charge transfer, magnetic moment and density of states, the chemical interactions between NO2 and TM doped InN monolayer (TM-InN) were discussed. We have gotten the following results: (1) Pd, Pt, Ag, Au atoms are all likely to be adsorbed on TN site with exothermal process; (2) Pt and Au gain electrons while Pd and Ag lost electrons and Ag and Au can introduce magnetic moment to InN monolayer; (3) NO2 can be chemi-adsorbed on TM atom modified InN monolayer due to the considerable adsorption energy and charge transfer; (4) NO2 molecule orbitals experience significant changes after adsorption. This study can provide prospects and possible application value for TM-InN to be a potential material to adsorb and detect NO2.

We employ TiO 2 single-crystal films as a substrate and use a photochemical deposition method to prepare Ag-doped and Ag/N co-doped TiO 2 single-crystal films. We also investigate the optical and magnetic properties of the samples using various measurements. No diffraction peaks related to silver oxide appear in the X-ray diffraction (XRD) spectra, which implies the existence of Ag atoms in Ag-doped TiO 2 single-crystal films. X-ray photoelectron spectroscopy (XPS) spectra indicate the existence of Ti 4+ and Ag° in Ag/N co-doped TiO 2 single-crystal films. It is found that Ag is deposited on a TiO 2 single-crystal film surface in the form of Ag particles. Meanwhile, Ag particles can slightly enhance ferromagnetism in Ag-doped TiO 2 single-crystal films compared with the TiO 2 single-crystal film sample. Oxygen vacancies and Ag particle synergy influence ferromagnetism in Ag/N co-doped TiO 2 single-crystal films.

In this work, the TiO2 nanorod arrays (TNAs), TNAs/Cu2O-10CYC, and TNAs/Cu2O-30CYC composites photo-catalysts for solar water splitting anode was successfully prepared via cyclic impregnation growth method. The structure, surface morphology and element chemical states have been investigated and discussed in detail. The UV–vis and PL results confirm that interaction has been formed between TNAs and Cu2O in the composite photo-catalysts and the TNAs/Cu2O composites exhibit broad spectrum absorption. Three factors affecting on the enhancement of solar light hydrogen production efficiency, e.g. enhanced UV-light absorption in solar spectrum, massive charge carrier generation and improved surface-interface reaction due to the absorbing visible light by the narrow band gap Cu2O and the injecting electrons into TiO2 conduction band, are proposed based on the experimental results. The TNAs/Cu2O-10CYC composite samples exhibit highest enhanced photocatalytic activities in the hydrogen production, which H2 evolution efficiency is about 4-fold higher than that of pure TNAs. It indicates that the efficient photo generated electron-hole transformation and separation in TNAs/Cu2O-10CYC composite sample leads to the improvement of photocatalytic performance. The present study provides a new light to prepare TNAs/Cu2O of novel configuration with promising potential applications.

In this paper, first-principle calculations based on density functional theory are carried out to explore the interface properties of the blue phosphorene/graphene-like GaN van der Waals heterostructures. The edge positions for valence and conduction band of blue phosphorene and graphene-like GaN nanosheets change with the Fermi energy level and form the type-II heterostructure. The internal electric field facilitates the separation of electron−hole pairs and restrained the carrier recombination in the blue phosphorene/graphene-like GaN interfaces.

The role of oxygen defects and dopants of Cu and N on ferromagnetism is discussed in undoped, N-doped, Cu-doped and Cu/N-codoped anatase TiO2 nanotube-arrays fabricated by two-step anodization method. X-ray photoelectron spectroscopy shows the presence of Cu2+ and/or Cu+ in the distorted octahedral coordination of TiO2. The UV–vis absorption spectra and photoluminescence spectra reveal the presence of oxygen defect related the peaks of absorption and emission in Cu-doped and Cu/N codoped-TiO2. Room temperature ferromagnetism is observed in all the TiO2 nanotubes. The saturation magnetizations for those specimens decreases in the order of Cu-doped, undoped, Cu/N-codoped and N-doped samples, which are in consistent with the results of the first-principles calculations based on density-functional theory. It is speculated that both oxygen vacancies and Cu d-states are involved in the ferromagnetism. Spin polarization occurs by the formation of bound magnetic polaron between electrons in Cu+/Cu2+ d-states and the unpaired spins in oxygen vacancies.

Two-dimensional materials have recently been the focus of extensive research. Graphene-based vertical van der Waals heterostructures are expected to design and fabricate novel electronic and optoelectronic devices. Monolayer gallium telluride is a graphene-like nanosheet synthesized in experiment. Here, the electronic properties of GaTe/graphene heterostructures are investigated under the interlayer coupling and the applied perpendicular electric field. The results show that the electronic properties of GaTe and graphene are preserved, and the energy bandgap of graphene is opened to 13.5 meV in the GaTe/graphene heterostructure. It is found that the n-type Schottky contact is formed in the GaTe/graphene heterostructure, which can be tuned by the interlayer coupling, and the applied electric field. Moreover, a transformation from n-type to p-type Schottky contact is observed when the interlayer distance is smaller than 3.15 A or the applied electric field is larger than 0.05 V A-1. These properties are fundamental to the design of new Schottky nanodevices based on the GaTe/graphene heterostructure.

The structural and electronic properties of a monolayer and bilayer blue phosphorene/graphene-like GaN van der Waals heterostructures are studied using first-principle calculations. The results show that the monolayer-blue phosphorene/graphene-like GaN heterostructure is an indirect bandgap semiconductor with intrinsic type II band alignment. More importantly, the external electric field tunes the bandgap of monolayer-blue phosphorene/graphene-like GaN and bilayer-blue phosphorene/graphene-like GaN, and the relationship between bandgap and external electric field indicates a Stark effect. The semiconductor-to-metal transition is observed in the presence of a strong electric field.

In this paper, we investigated the physical properties especially the magnetic properties of the TiO 2 films and Au cluster doped TiO 2 films fabricated by sol-gel and sputtering methods combined experiments and first-principles calculations. All the samples annealed under air and N 2 atmosphere respectively exhibit room temperature ferromagnetism with the crystal phase of anatase. The values of the saturation magnetizations are in the order of Au δ-doped TiO 2 (annealed in N 2 )>undoped TiO 2 (annealed in air)>Au δ-doped TiO 2 (annealed in air). The first principles calculation results show that the formation energy of Au cluster doped TiO 2 films is lower than that of the oxygen vacancy and Au cluster codoped TiO 2 films. The effects of the Au cluster dopant are the retard of the formation of surface oxygen vacancy and the electrons transfer from 3d states of Ti atoms to Au 5d states in Au cluster doped TiO 2 films. The codoping of surface oxygen vacancies, bulk oxygen vacancies and Au clusters led to the spin-split of Ti 3d and O 2p in Au cluster doped TiO 2 films (annealed in N 2 ) which yield the highest saturation magnetization.

In this paper, the un-doped, Mo doped, N doped and Mo–N co-doped TiO2 nanotubes (TNTs) films were prepared by a two-step anodic oxidation method. The paper mainly investigated the origin of room temperature (RT) magnetic properties of all the samples. X-ray diffraction studies showed that the impurity of magnetic Mo atoms or N atoms were doped into anatase TiO2 lattices. It is revealed by the results of X-ray photoelectron spectroscopy and photoluminescence spectra that oxygen vacancies (Vos) exist. For all the samples the values of the saturation magnetizations (Ms) are in the order of Mo–N co-doped TiO2 > Mo-doped TiO2 > N-doped TiO2 > un-doped TiO2. Thus, the the Mo–N co-doped film achieved the highest RT Ms. The enhancement of the Ms origins from the cooperationg of the doping Vo, Mo and N. This progress provides some clues for the increase the saturation magnetization in TiO2-based dilute magnetic semiconductors at RT. The experiment results indicate that the Vos play a crucial role in RT ferromagnetic properties for TNTs films.

In this paper, we investigated room temperature magnetic properties of Fe–N codoped, undoped, Fe doped, and N doped TiO2 samples combing by experiments and first-principles calculations. All the samples fabricated by a two-step anodic oxidation method exhibit the crystal phase of anatase with the shape of nanotube. The calculated net moment values are in the order of Fe–N codoped TiO2 > Fe doped TiO2 > undoped TiO2 > N doped TiO2 with oxygen vacancies existing, which are in accord with the experimental results. The hybridization of Fe 3d, Ti 3d (nearest to the oxygen vacancies) and O 2p (nearest to the Fe defect) led to the spin-split of Fe 3d, Ti 3d and O 2p which devoted to the magnetism. The codoping of oxygen vacancies, N and Fe led to the complete spin-split of Fe 3d, Ti 3d and O 2p for Fe–N codoped TiO2 samples which yield the highest saturation magnetization.

In this paper, we combined experiments and first-principles calculations to investigate the physical properties especially the magnetic properties of Ga1−xCrxN and Si-doped Ga1−xCrxN thin films grown by molecular beam epitaxy. The results of experiments indicate that Si doping improved the crystallinity by improving the substitution of Ga in Si-doped Ga1−xCrxN. And the size and/or the number of vacancy defects are reduced in the Si-doped Ga1−xCrxN thin films. All the samples show room-temperature ferromagnetism, and the measured saturation magnetizations are 15 emu/cm3 (2.26 μB per Cr atom) and 10 emu/cm3 (1.31 μB per Cr atom) respectively for Ga1−xCrxN and Si-doped Ga1−xCrxN thin films. First-principles calculations based density-functional theory show that there is a strong magnetic coupling between the Ga vacancies and the impurities of Cr and Si ions. And Si doping reduced the saturation magnetization in Si-doped Ga1−xCrxN thin films which is in agreement with the experiment results. This intrinsic defect derived magnetic interaction plays an important role on improving the ferromagnetism in Ga1−xCrxN and Si-doped Ga1−xCrxN, and the ferromagnetism of the system is the result of long-range mediation between VGa, Cr and Si ions.

The structures and electronic properties of InTe/graphene van der Waals heterostructures are systematically investigated using the first-principles calculations. The electronic properties of InTe monolayer and graphene are well preserved respectively and the bandgap energy of graphene is opened to 36.5 meV in the InTe/graphene heterostructure. An n-type Schottky contact is formed in InTe/graphene heterostructure at the equilibrium state. There is a transformation between n-type and p-type Schottky contact when the interlayer distance is smaller than 3.56 A or the applied electric field is larger than -0.06 V A-1. In addition, the Schottky contact converts to Ohmic contact when the applied vertical electric field is larger than 0.11 V A-1 or smaller than -0.13 V A-1.

Based on first-principle calculations, the stability, electronic structure, optical absorption, and modulated electronic properties by different interlayer distances or by external electric fields of bilayer α-GeTe are systemically investigated. Results show that van der Waals (vdW) bilayer α-GeTe has an indirect band structure with the gap value of 0.610 eV, and α-GeTe has attractively efficient light harvesting. Interestingly, along with the decrease of interlayer distances, the band gap of bilayer α-GeTe decreases linearly, due to the enhancement of interlayer vdW interaction. In addition, band gap transition is originated from the electric field-induced near free-electron gas (NFEG) under the application of positive electrical fields. However, when the negative electric fields are applied, there is no NFEG. On account of these characteristics of bilayer α-GeTe, a possible data storage device has been designed. These results indicate that bilayer α-GeTe has a potential to work in new electronic and optoelectronic devices.

In this work, undoped, N-doped, WO3-loaded undoped, and WO3-loaded with N-doped TiO2 rutile single-crystal wafers were fabricated by direct current (DC) magnetron sputtering. N-doping into TiO2 and WO3 loading onto TiO2 surface were used to increase and decrease oxygen vacancies. Various measurements were conducted to analyze the structural and magnetic properties of the samples. X-ray diffraction results showed that the N-doping and WO3 loading did not change the phase of all samples. X-ray photoelectron spectroscopy results revealed that W element loaded onto rutile single-crystal wafers existed in the form of WO3. UV-Vis spectrometer results showed that the absorption edge of WO3-loaded undoped and WO3-loaded with N-doped TiO2 rutile single-crystal wafers had red shift, resulting in a slight decrease in the corresponding band gap. Photoluminescence spectra indicated that oxygen vacancies existed in all samples due to the postannealing atmosphere, and oxygen vacancies density increased with N-doping, while decreasing with WO3 loading onto TiO2 surface. The magnetic properties of the samples were investigated, and the saturation magnetization values were in the order N-doped &gt, WO3-loaded with N-doped &gt, undoped &gt, WO3-loaded undoped rutile single-crystal wafers, which was the same order as the oxygen vacancy densities of these samples. N-doping improved the saturation magnetization values, while WO3-loaded decreased the saturation magnetization values. This paper reveals that the magnetic properties of WO3-loaded with N-doped rutile single-crystal wafers originate from oxygen vacancies.

The magnetic properties of the C doped and C-Fe codoped TiO2films fabricated by sol-gel and spin coating have been investigated combining experiments and first-principles calculations. All the samples exhibit the anatase crystal phase and the room temperature ferromagnetism. The values of the saturation magnetizations are in the order of Fe-C codoped TiO2> Fe-C codoped TiO2(annealed in O2) > C doped TiO2> C doped TiO2(annealed in O2). The calculated net moment values are in the order of Fe-C codoped TiO2> C doped TiO2with oxygen vacancies existing, in accord with the experimental results. The hybridization of Fe 3d, C 2p,and O 2p(nearest to the Fe defect) led to the spin split of Fe 3d, C 2p,and O 2pwhich contributed to the ferromagnetism.

Greenhouse effect has become one of the most rigorous topics of environmental protection. The emission of one of the most typical greenhouse gas SF6 should be controlled and the waste gas treatment of SF6 has become a major topic to reduce the greenhouse effect. Two-dimensional porous materials have been widely used in gas adsorption and separation which may be useful for adsorbing waste SF6 gas. In this study, we report a promising adsorbent, transition metal dimer decorated C2N monolayer, for SF6 treatment by theoretical evaluation. The adsorption of SF6 molecule over the C2N surface are explored including the adsorption energy, electron transfer, magnetic moment and the electronic properties. Also, the decomposition process of SF6 molecule over the TM2-C2N monolayer is also considered. The results show that the SF6 can only be physical adsorption over the pristine C2N monolayer and experiences obvious decomposition over the Co2–C2N and Ni2–C2N monolayer. The adsorption with molecule decomposition can also significantly change the electronic properties of TM2-C2N. The low energy barrier of decomposition process over the TM2-C2N ensures good performance of adsorbent for SF6 in practical applications. This study provides theoretical foundation for TM2 dimer C2N monolayer as a promising adsorbent, scavenger and even catalytic material for degradation of greenhouse gas SF6 and waste gas treatment.

The room temperature ferromagnetism (RTFM) of the undoped, N doped, Ru doped ,and Ru-N codoped anatase TiO2 nanotubes (TNTs) films are investigated combined with experiments and first principles approaches. The experiments are highly consistent with the theory calculations. All samples display anatase structures and ferromagnetism at room temperature. The values of the saturation magnetization (Ms) of undoped TiO2, N doped TiO2, Ru doped TiO2, and Ru-N codoped TiO2, respectively, are 0.065 emu/g, 0.015 emu/g, 0.155 emu/g, and 0.073 emu/g. The calculated net moment is in the order of Ru doped > Ru-N codoped > undoped > N doped. The oxygen vacancies play an important role in RTFM of TNTs. Moreover, the hybridization of Ru 4d, N 2p, and O 2p led to the spin-spilt of Ru 4d, N 2p, and O 2p which is devoted to the system magnetism.

The structure, electronic properties, charge transfer, band edge alignments and optical properties of WS2/BSe heterostructures are investigated by using first-principle calculations. Results imply that WS2/BSe heterostructures are semiconductor with an indirect energy gap (Egap) of 1.73 eV. Additionally, it has a feature of type-II band alignment, which contributes to spatial separation of photo-generated electron-hole pairs in WS2/BSe heterostructures. Charge transfer takes place from BSe to WS2 monolayers, which extends lifetime of the separated photo-induced charge carriers. Most importantly, band edges of the heterostructure are found to meet hydrogen evolution reaction (HER) in acid solutions (0 < pH < 7). Moreover, compared with only one for WS2 and BSe monolayers, the optical-absorption strength of the heterostructure is significantly enhanced and WS2/BSe heterostructures larges the range of absorption to 717 nm in the visible light region, improving the potential photocatalytic efficiency. These results explain the underlying mechanism of the enhanced photocatalytic activity of WS2/BSe heterostructures. Thus WS2/BSe heterostructures can be applied to 2D heterostructured photocatalysts.

The electronic and magnetic properties of Mn and oxygen vacancies codoped anatase TiO2were investigated. The calculated results showed that the TiO2codoped with Mn and oxygen vacancies have a magnetic moment value of 3.415 μBper Ti31MnO63supercell. Furthermore, Ti31MnO63gets the lowest energy with a geometrical optimization where the Mn ions locate at the nearest-neighbor sites of the oxygen vacancy. And experimental results indicated the magnetism is associated with the defects of Mn ions and oxygen vacancies induced by the Mn doping, which is consistent with the calculation results.

A series of Ti[Formula: see text]Co[Formula: see text]O[Formula: see text] ([Formula: see text] = 0.01, 0.03, 0.05, 0.07) nanoparticles were synthesized by sol–gel method. The X-ray diffraction, transmission electron microscopy, Raman analysis and X-ray photoelectron spectroscopy ruled out the signatures of Ti[Formula: see text], Co-clusters or any other oxides of Co. The ferromagnetic behavior was clearly observed at room temperature in doped samples with saturation magnetization [Formula: see text] of the order of 0.008–0.035 emu/g depending on doping concentrations. The saturation magnetization is found to be increased with the Co contents increasing from 1% to 7%. From the plot of the M–T curve, we obtain the [Formula: see text] as [Formula: see text][Formula: see text]515 K for 5% Co-doped TiO2. Oxygen vacancies were detected from the photoluminescence (PL) measurement. Magnetic properties analyses and PL analyses showed that oxygen vacancies probably played a major role in ferromagnetism of the Ti[Formula: see text]Co[Formula: see text]O2 system with Co substituting for Ti. The first-principles calculation was performed to investigate the magnetic properties of Co-doped TiO2 nanoparticles. It can be found that the major magnetic moment is from the 3d electron of Co. The experiment results are consistent with the first-principles calculation. The ferromagnetism derived from the spin-split of O-2p and Co-3d electron states caused by p–d orbit hybridization.