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The development of singlet fission (SF) is greatly hindered by the severe shortage of the types and numbers of SF materials.

Quasi-two dimensional perovskites have emerged as candidates of high-performance materials for various optoelectronic applications due to the unique excitonic properties in their multilayer structures.

Quasi-2D Ruddlesden-Popper perovskites attract great attention as an optical gain media in lasing applications due to their excellent optoelectronic properties. Herein, a novel quasi-2D Ruddlesden-Popper perovskite based on 2-thiophenemethylammonium (ThMA) is synthesized by a facile solution-processed method. In addition, an anti-solvent treatment method is proposed to tune the phase distribution, and preferential orientation of quasi-2D (ThMA)2Cs n -1Pb n Br3n+1 thin films. The large-n-dominated narrow domain distribution improves the energy transfer efficiency from small-n to large-n phases. Also, the highly oriented nanocrystals facilitate the efficient Förster energy transfer, beneficial for the carrier population transfer. Furthermore, a green amplified spontaneous emission with a low threshold of 13.92 µJ/cm2 is obtained and a single-mode vertical-cavity laser with an 0.4 nm linewidth emission is fabricated. These findings provide insights into the design of the domain distribution to realize low-threshold multicolor continuous-wave or electrically driven quasi-2D perovskites laser.

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.

Two-dimensional transition metal dichalcogenides with outstanding properties open up a new way to develop optoelectronic devices such as phototransistors and light-emitting diodes. Heterostructure with light-harvesting materials can produce many photogenerated carriers via charge and/or energy transfer. In this paper, the ultrafast dynamics of charge transfer in zero-dimensional CsPbBr3 quantum dot/two-dimensional MoS2 van der Waals heterostructures are investigated through femtosecond time-resolved transient absorption spectroscopy. Hole and electron transfers in the ps and fs magnitude at the interfaces between MoS2 and CsPbBr3 are observed by modulating pump wavelengths of the pump-probe configurations. Our study highlights the opportunities for realizing the exciton devices based on quantum dot/two-dimensional semiconductor heterostructures.

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.

Multiexcitons generation is a process of generating electron-hole pairs in nanostructured semiconductors by absorbing a single high-energy photon. The multiexciton process is essential for the performance of optoelectronic devices based on perovskite nanomaterials. In this paper, ultrafast time-resolved transient absorption spectroscopy is used to study the ultrafast dynamics of CsPbBr

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.

CsPbBr3 has attracted great attention due to unique optical properties. The understanding of the multiexciton process is crucial for improving the performance of the photoelectric devices based on CsPbBr3 nanocrystals. In this paper, the ultrafast dynamics of CsPbBr3 nanocrystals is investigated by using femtosecond transient absorption spectroscopy. It is found that Auger recombination lifetime increases with the decrease of the excitation intensity, while the trend is opposite for the hot-exciton cooling time. The time of the hot-carriers cooling to the band edge is increased when the excitation energy is increased from 2.82 eV (440 nm) to 3.82 eV (325 nm). The lifetime of the Auger recombination reaches the value of 126 ps with the excitation wavelength of 440 nm. The recombination lifetime of the single exciton is about 7 ns in CsPbBr3 nanocrystals determined by nanosecond time-resolved photoluminescence spectroscopy. The exciton binding energy is 44 meV for CsPbBr3 nanocrystals measured by the temperature-dependent steady-state photoluminescence spectroscopy. These findings provide a favorable insight into applications such as solar cells and light-emitting devices based on CsPbBr3 nanocrystals.

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.

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.

Multiexcitons generation is a process of generating electron-hole pairs in nanostructured semiconductors by absorbing a single high-energy photon. The multiexciton process is essential for the performance of optoelectronic devices based on perovskite nanomaterials. In this paper, ultrafast time-resolved transient absorption spectroscopy is used to study the ultrafast dynamics of CsPbBr3nanocrystals. It is found that the multiexcitons Auger recombination lifetime increases with the decrease of pump fluence, while it is on the contrary for the hot carrier cooling time. The increase in the number of photons absorbed by each nanocrystal under high pump fluence slows down the relaxation of hot carriers to the band edge. The hot carrier cooling lifetime increases from 0.25 to 0.85 ps when the pump fluence increases from 6 to 127μJ cm-2. Temperature-dependent transient absorption spectroscopy exhibits that the relaxation process of hot carriers slows down sharply when the lattice temperature decreases from 280 to 80 K. Moreover, the exciton binding energy 46 meV of CsPbBr3nanocrystals is obtained by temperature-dependent steady-state photoluminescence spectroscopy. These findings provide insights for applications such as solar cells and light-emitting devices based on CsPbBr3nanocrystals.

Inorganic perovskites, such as CsPbX3 (X = Cl, Br, I), have attracted attention due to their excellent thermal stabilities and high photoluminescence quantum efficiencies. Here, we report on all-inorganic light-emitting diodes (LEDs), including inorganic perovskite emitters (CsPbBr3) based on the heterostructure of n-ZnO/Al2O3/CsPbBr3/p-GaN. The effects of the CsPbBr3 and Al2O3 interlayers on the electroluminescence performance have been systematically investigated. It is observed that the Al2O3 interlayer plays an important role in determining the emission performance. By introducing the Al2O3 layers, the electron–hole recombination can almost be limited within the perovskite. The emission peaks of the heterojunction LEDs change from blue-green to pure green with the increased luminous intensities and decreased leakage currents. It provides an idea for the preparation of all-inorganic perovskite LEDs.

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.

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.

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.

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.

Photoinduced dynamics of excited-state intramolecular proton transfer (ESIPT) and vibration relaxation (VR) of 1,8-DHAQ in ethanol are investigated by time-resolved transient absorption spectroscopy combined with the quantum chemical calculations. Experimental and calculated results show dual fluorescence is obtained from the S1 state of the normal form of 9,10-quinone and the tautomer form of 1,10-quinone. Three characteristic bands of excited state absorption and stimulated emission are observed in transient absorption spectroscopy upon excitation with ultrafast laser pulses at 390 nm. ESIPT process happens within 96.8 fs from the normal S1 state to the tautomer S1 state, and the VR process is observed in the time constant of 4.1 ps. Ultimately, the tautomer S1 state decays within 269.1 ps for a deactivation pathway of emitting fluorescence. The mechanism of ESIPT dynamics and ultrafast excited-state dynamics in 1,8-DHAQ in ethanol is concluded by a schematic diagram of four electronic states and vibrational energy levels.

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.

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.

Microstructure and magnetic properties of In 1− x Cr x N thin films grown on GaN-on-sapphire templates by molecular beam epitaxy are investigated. Optimized growth conditions are identified for the In 1− x Cr x N thin films at reduced growth temperature. The In 1− x Cr x N thin films on the top of the InGaN buffer layers exhibit high crystalline-quality. The magnetic properties of In 1− x Cr x N thin films show a ferromagnetic behavior even at room temperature.

Ga1−xCrxN thin films with and without the Si doping have been prepared by molecular beam epitaxy. The samples have been investigated by X-ray diffraction, X-ray photoemission spectroscopy, photoluminescence, optical absorption spectra and magnetic measurements. It has been confirmed that for the undoped samples Cr in GaN is predominantly trivalent when substituting for Ga and that the Cr 3d state appears within the band gap of GaN. In Si doped specimens the upward shifts of the chemical potential are observed, and the electrons supplied by the Si doping are trapped at Cr sites forming Cr2+. As a result, the Si doping effects show an increase of the Curie temperature, and a reduction of the saturation magnetization in the Ga1−xCrxN:Si samples. The significant effect on the ferromagnetism with Si doping in Ga1−xCrxN is explained by the percolation theory of bound magnetic polarons.

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.

The irradiation damage in nickel-base alloy C-276 irradiated with 115 keV Ar ions from low to very high doses was investigated. Structural characterization was performed using transmission electron microscopy (TEM), grazing incident X-ray diffraction (GIXRD) and atomic force microscopy (AFM). High density of interstitial type dislocation loops could be observed at a dose level of around 2.75 displacements per atom (dpa). With the irradiation dose increased to 27.5 dpa, the average size of loops increased from 5 nm to 16 nm, while the density of the loops decreased from 1.4 × 1011/cm2 to 4.6 × 1010/cm2. When the irradiation dose reached 82.5 dpa, original grains were transformed into subgrains whose sizes observed from TEM were about 20~60 nm. The fragmentation of grains was confirmed by GIXRD. The mean subgrain size was 40 nm, which was obtained from the full width at half maximum (FWHM) of the X-ray diffraction lines using the Scherrer formula and Williamson formula. AFM micrographs showed that nanometer-sized hillocks formed at the dose of 82.5 dpa, which provided further evidence of grain fragmentation at a high irradiation dose.

Si 1− x Mn x diluted magnetic semiconductor films were deposited on the p-Si (100) single crystal wafer using magnetron sputtering method. Post-rapid thermal annealing treatments were performed at temperatures of 700 °C, 800 °C, and 900 °C in an argon atmosphere for approximately 5 min. Alternating gradient magnetometer, scanning electron microscope, atomic force microscope, X-ray diffraction and X-ray absorption near-edge structure spectra were employed to characterize magnetic properties and structure of the as-grown and annealed films. The films were about 2.8 μm thick and the RMS roughness of the surface was about 5–10 nm. All samples exhibit ferromagnetism at room temperature and the saturation magnetization reaches at the maximum value for the sample annealed at 700 °C. The silicide MnSi 1.7 was observed in the annealed samples. X-ray absorption near-edge structure spectra indicated that Mn atoms preferred to occupy substitutional or interstitial sites instead of precipitating to form silicide when annealing at 700 °C. It is inferred that the observed ferromagnetism is attributed to the interstitial and substitutional Mn dimers, which existed mostly in the sample annealed at 700 °C. The weaker ferromagnetism of the 900 °C annealed sample was closely related to the increased content of Mn 4 Si 7 compound.

Polycrystalline Si 1 − x Cr x thin films have been prepared by magnetron sputtering followed by rapid thermal annealing (RTA) for crystallization. RTA was performed at 800 °C for 5 min, 1200 °C for 30 s and 1200 °C for 2 min, in a N 2 flow. The magnetic hysteresis loops were observed at room temperature in all the samples except for RTA at 800 °C for 5 min, and the annealing caused the decrease of saturation magnetization relative to the as-grown film. X-ray diffraction spectra and Raman spectra showed that the annealing process lead the deposited amorphous film to be crystallized and CrSi 2 phase formed. The magnetism of the films was determined by the competition between crystallinity and precipitation of diamagnetic CrSi 2 phase.

a b s t r a c t Magnetic properties and microstructure of Cr-implanted Si have been investigated by alternating gradi- ent magnetometer (AGM), superconducting quantum interference device (SQUID) magnetometer, and transmission electron microscopy (TEM). p-Type (1 0 0) Si wafers were implanted at 200 keV at room temperature with a dosage of 1 × 10 16 cm −2

Magnetic and electronic properties of stoichiometric amorphous CrN thin films grown on MgO (001) substrates by radio-frequency nitrogen-plasma-assisted molecular beam epitaxy have been investigated. The magnetic property of the amorphous CrN thin films shows a ferromagnetic behavior even at room temperature, and can be interpreted by the percolation theory of magnetic polaron where we consider Cr3+ defects as magnetic impurities which lead to the formation of bound magnetic polarons. The obtained results of electrical conductivity are explained by the variable-range-hopping theory of the Mott and Davis model.

The spinel CoFe(2)O(4) has been synthesized by combustion reaction technique. X-ray photoelectron spectroscopy shows that samples are near-stoichiometric, and that the specimen surface both in the powder and bulk sample is most typically represented by the formula (Co(0.4)Fe(0.6))[Co(0.6)Fe(1.4)]O(4), where cations in parentheses occupy tetrahedral sites and those within square brackets in octahedral sites. The results demonstrate that most of the iron ions are trivalent, but some Fe(2+) may be present in the powder sample. The Co 2p(3/2) peak in powder sample composed three peaks with relative intensity of 45%, 40% and 15%, attributes to Co(2+) in octahedral sites, tetrahedral sites and Co(3+) in octahedral sites. The O 1s spectrum of the bulk sample is composed of two peaks: the main lattice peak at 529.90 eV, and a component at 531.53 eV, which is believed to be intrinsic to the sample surface. However, the vanishing of the O 1s shoulder peak of the powder specimen shows significant signs of decomposition. (C) 2008 Elsevier B. V. All rights reserved.