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The nanotribological properties of Zn0.75Mg0.25O grown on R-plane sapphire using metal-organic vapor-phase epitaxy at different substrate temperatures (RT, 600, 700 and 800 °C) were investigated. A slight sliding track was observed at ramped loads of 250 μN, and an obvious bulge edge surrounding the groove was observed at ramped loads of 1 000 μN. Because of the annealing treatment, all the Zn0.75Mg0.25O coatings showed a reconstruction phenomenon of crystallites. The volumes of the bulge edges were as high as 30% in the annealed specimens and were larger than the volumes of the RT-treated specimens when ramped loads of 1 000 μN were applied. Under frictional loading, atomic force microscopy examination of scratch-tested films indicated lower bonding forces on R-plane sapphire than M-plane sapphire.

We used time-resolved photoluminescence spectroscopy to study the circular polarization dynamics of magnetic polarons in type-II (Zn,Mn)Te/ZnSe quantum dots in the presence of an external magnetic field. We investigated the time evolution of the peak energy of the σ+and σ–circularly polarized photoluminescence components and of the circular polarization of the emitted light. We also observed that the value of circular polarization, at long delay times, increases with magnetic field. We found that this system exhibits unexpected characteristics, such as different time scales for the formation of the magnetic polaron, on the one hand, and the evolution of photoluminescence circular polarization, on the other hand. These results are discussed within the framework of a theoretical model developed to describe the dependence of magnetic susceptibility as a function of temperature.

Unlike the extensively studied, spatially direct, quantum dots (QDs) with type-I band alignment where both electrons and holes are confined in the QD, in ZnTe QDs embedded in a (Zn,Mn)Se matrix only the holes are confined in the QDs. This spatially indirect type-II system provides unexplored opportunities to control the magnetic interactions between the hole spins in the nonmagnetic QDs and the spins of the magnetic ions in the matrix. Photoluminescence (PL) was excited either with photons of energy 3.06 eV [above band gap of the (Zn,Mn)Se matrix] or with photons of energy 2.54 eV [below the (Zn,Mn)Se band gap]. In the presence of an external magnetic field, the saturation red shift of the PL peak under 2.54 eV excitation exhibits an up to three-fold increase compared to the shift observed with 3.06 eV excitation. This increase is attributed to multiple hole occupancy of the QDs and the resulting increased penetration of the hole wavefunction tail further into the (Zn,Mn)Se matrix. The proposed model is supported by calculations which include the hole–hole Coulomb interactions as well as the hole–Mn spin exchange interactions.

Advances in new systems of organic–inorganic hybrid nanocomposites are less prevalent, owing to a lack of facile strategies for precise control of their structures, compositions, and, hence, their properties. In this work, Au-BINOL hybrid nanocomposites with eccentric and concentric nanostructures were produced. The hybrid nanocomposites containing two distinct moieties of inorganic Au nanocrystals and organic BINOL nanospheres were applied to the catalytic hydrogenation of 4-nitrophenol with NaBH4in the aqueous phase with and without the illumination of visible light. Here, we demonstrate that the existence of Au–BINOL interfaces offers benefits to their performance. The eccentric nanostructures made with CTAC show the superior activity from large Au–BINOL interfaces formed between the BINOL nanospheres and the faces of Au nanoplates. They further exhibit a high Au localized surface plasmon resonance (LSPR)-enhancement effect on the photoreduction of 4-nitrophenol, which is attributed to the strong LSPR absorption of exposed Au nanocrystals unaffected by the coverage of BINOL shells.

A luminescent solar concentrator (LSC) is composed of loaded luminophores and a waveguide that can be employed to harvest and concentrate both direct and diffused sunlight for promising applications in solar windows. Thus far, most of efficient LSCs still relied on the heavy-metal-containing colloidal quantum dots (CQDs) dispersed into a polymer matrix with a very low loading (typically <1 wt %). Such low-loading constraint is required to mitigate the concentration-induced quenching (CIQ) and maintain high optical quality and film uniformity, but this would strongly reduce the light-absorbing efficiency. To address all issues, greener LSCs with high loading concentration were prepared by in situ cross-linking organosilane-functionalized carbon nanodots (Si-CNDs), and their photophysical properties relevant to LSC operation were studied. The PL emission is stable and does not suffer from the severe CIQ effect for cross-linked Si-CNDs even with 25 wt % loadings, thus exhibiting high solid-state quantum yields (QYs) up to 45 ± 5% after the calibration of the reabsorption losses. Furthermore, such LSCs can still hold high optical quality and film uniformity, leading to low scattering losses and high internal quantum efficiency of ∼22%. However, the reabsorption losses need to be further addressed to realize large-area LSCs based on earth-abundant, cost-effective CNDs.

Utilizing a scanning photoelectron microscope (SPEM) and grazing-incidence X-ray powder diffraction (GIXRD), we studied the electronic band structure and the crystalline properties of the pentanary Cu(In,Ga)(S,Se)2(CIGSSe) thin-film solar cell as a function of sample depth on measuring the thickness-gradient sample. A novel approach is proposed for studying the depth-dependent information on thin films, which can provide a gradient thickness and a wide cross-section of the sample by polishing process. The results exhibit that the CIGSSe absorber layer possesses four distinct stoichiometries. The growth mechanism of this distinctive compositional distribution formed by a two-stage process is described according to the thermodynamic reaction and the manufacturing process. On the basis of the depth-profiling results, the gradient profiles of the conduction and valence bands were constructed to elucidate the performance of the electrical properties (in this case, Voc= 620 mV, Jsc= 34.6 mA/cm2, and η = 14.04%); the valence-band maxima (VBM) measured with a SPEM in the spectroscopic mode coincide with this band-structure model, except for a lowering of the VBM observed in the surface region of the absorber layer due to the ordered defect compound (ODC). In addition, the depth-dependent texturing X-ray diffraction pattern presents the crystalline quality and the residual stress for each depth of a thin-film device. We find that the randomly oriented grains in the bottom region of the absorber layer and the different residual stress between the underlying Mo and the absorber interface, which can deteriorate the electrical performance due to peeling-off effect. An anion interstitial defect can be observed on comparing the anion concentration of the elemental distribution with crystalline composition; a few excess sulfur atoms insert in interstitial sites at the front side of the absorber layer, whereas the interstitial selenium atoms insert at the back side.

A solid-state symmetric supercapacitor is successfully fabricated by assembling the sulfuric acid–poly(vinyl alcohol) (H2SO4–PVA) gel electrolyte between the two pieces of electrochemically activated reduced graphene oxide (aRGO) electrodes. The electrochemical and electronic properties of reduced graphene oxide (RGO) and aRGO were characterized by ex situX-ray absorption spectroscopy (XAS). The aRGO exhibits better electrochemical supercapacitive performances than RGO, owing to the conjunction of the electrochemical double-layer capacitance (EDLC) and the pseudocapacitance. The specific capacitance increases with the oxygen-containing functional groups content in the electrochemically activated aRGO than RGO, increasing the pseudocapacitive contribution. The aRGO20//aRGO20 solid-state symmetric supercapacitors (SSC) exhibit an energy density of 4.7 Wh kg–1at a power density of 402 W kg–1and 4 Wh kg–1at a power density of 1989 W kg–1, which is competitive with the commercially available supercapacitors. To elucidate the atomic and electronic structures of the RGO and aRGO electrodes in the charge/discharge process, ex situXAS at the C and O K-edge were performed. Both RGO and aRGO electrodes exhibit a reversible energy shift of the O K-edge, owing to the reversible redox pseudocapacitance close to the surface of graphene-based materials. However, the absorption edge of O K-edge for aRGO electrodes shifts more significantly than that for RGO electrodes during the charge/discharge process. The results indicate that aRGO electrodes exhibit rapid and more active redox reactions for pseudocapacitance than the RGO electrodes. The results herein suggest potential use in high-performance symmetric supercapacitors.

Self-assembled nanocomposites with a high interface-to-volume ratio offer tremendous opportunities of tailoring functionalities by a proper combination of components. In this study, we report the first fabrication of self-assembled NiWO4–WO3heteroepitaxy and its excellent performance on photoelectrochemical water splitting. The heteroepitaxy is evidenced by a combination of x-ray diffraction and transmission electron microscopy. The energy band diagram of NiWO4–WO3heterostructure probed by x-ray photoelectron spectroscopy suggests an efficient charge separation at their interface by injecting photo-generated electrons from NiWO4to WO3and holes from WO3to NiWO4. Therefore, a great improvement in the photoelectrochemical activity of self-assembled NiWO4–WO3heteroepitaxy was achieved (1400µAcm−2at 0.7V vs. Ag/AgCl). This work delivers a new category of composite materials for promising photoelectrode in photoelectrochemical cells.

Reabsorption-free luminescent solar concentrators (LSCs) are crucial ingredients for photovoltaic windows. Atomically precise metal nanoclusters (NCs) with large Stokes-shifted photoluminescence (PL) hold great promise for applications in LSCs. However, a fundamental understanding of the PL mechanism, particularly on the excited-state interaction and exciton kinetics, is still lacking. Herein, we studied the exciton–phonon coupling and singlet/triplet exciton dynamics for gold-doped silver NCs in a solid matrix. Following photoexcitation, the excitons can be self-trapped via strong exciton–phonon coupling. Subsequently, rapid thermal equilibration between the singlet and triplet states occurs due to the coexistence of small energy splitting and spin–orbit coupling. Finally, broadband delayed fluorescence with a large Stokes shift can be generated, namely, self-trapped, thermally equilibrated delayed fluorescence (ST-TEDF). Benefiting from superior ST-TEDF, we demonstrated efficient LSCs with minimized reabsorption.

Heterostructure provides a powerful route in manipulating electrical transport, optical response, electrolytic water splitting and water treatment of complex oxides. As a model for noble metal/ complex oxide heterostructures, we have successfully prepared Au/BiVO4(BVO) heterostructures in which the Au nanoparticles (NPs) with various sizes and densities were uniformly deposited on the {001} facets of epitaxial BVO thin films. The heterostructures exhibit significantly enhanced photoactivities in both dye degradation and electrolytic water splitting. By employing X-ray photoelectron spectroscopy, the energy band alignment of Au/BVO heterojunction suggests a charge separation at their interfaces, that can manipulate the photoexcited electron–hole pairs and photocatalytic efficiency of the heterostructures. Photogenerated carrier injection, which mainly affects the photoactivity of photocatalysis, was detected across Au/BVO interfaces by ultrafast dynamics spectroscopy. This study delivers a general approach to probe and understand the photochemistry of noble metal-complex oxide heterostructures for photoconversion applications.

The mechanism of enhancing the capacity of the LiFePO4cathodes in lithium ion batteries by the addition of a small amount of vanadium, which locate on the lithium site and induce lithium vacancies in the crystal structure, is reported in this article. As a result, the capacity increases from 138 mAh/g found for pristine LiFePO4to 155 mAh/g for the V-added compound, and the conductivity increases from 4.75 × 10–4S/cm for the LiFePO4without V addition to 1.9 × 10–2S/cm for the V-added compound. A possible model to facilitate the enhancement of conductivity and capacity is described with evidence supported by X-ray powder diffraction, X-ray absorption spectroscopy, and neutron powder diffraction data.

The junction temperatures of the three individual subcells of InGaP/InGaAs/Ge solar cells were measured using photoluminescence (PL) with three different excitation lasers. With the illumination of an extra xenon--mercury lamp, the linear relationship between the PL energy and the illumination level is clearly observed and advantageously used for deriving the junction temperature. Using the Varshni relationship between the PL peak energy and the heat-sink temperature allows us to determine the junction temperature in each subcell.

Fluorescence enhancement of colloidal CdSe/ZnS quantum dots (QDs) by the binding of hexadecylamine (HDA) ligands was investigated at the single-QD level. The blinking behavior of individual CdSe/ZnS QDs can be dramatically modified by additional HDA ligands. Both the ratio of the mean on/off time lengths and the total number of emitted photons within the on-time duration can be enhanced, by factors of up to 2.8 and 13, respectively. Consequently, the blinking rate can be suppressed down to 18%. The fluorescence decay curve is closer to a single-exponential decay profile and has a longer measured lifetime. These results suggest that HDA ligands can further improve surface passivation.

In this work, we comprehensively investigated the metal-electrode stress engineering on HfAlO metal-ferroelectric-metal capacitor. According to experimental results, we confirm that high-nitrogen tantalum-nitride electrode with good chemical stability not only mitigates the anti-ferroelectric property and gate leakage current, but also improves the wake-up effect and endurance cycling characteristics, which shows the great potential for future applications of low-power ferroelectric memories.

In this work, we report a novel multi-PNPN-channel junctionless transistor with short channel length of 60nm. The multi-PNPN junctionless transistor exhibits the larger drive current of >1μA/μm, the steeper turn-on switching of 77 mV/decade, and the higher on/off current ratio of >107than the hybrid PN channel device under the same gate overdrive. The improved performance is mainly attributed to the enhanced depletion effect of multi-PNPN channel to optimize the electric field modification of surface p-channel. The stronger immunity to constant-voltage stress is also obtained for multi-PNPN channel due to the lower lateral electric field near drain side to reduce the impact ionization ratio.

Self-assembled nanocomposites have gained much attention over the past decade due to their intriguing properties and functionalities. In this work, we developed a self-assembled nanocomposite photoanode composed of an epitaxial BiVO4matrix embedded with WO3mesocrystals for photoelectrochemical (PEC) applications in the visible-light regime. The orientation of the crystal facet and interface provides a superior template to understand the intimate contact between the two constituent phases. We demonstrate that the interfacial coupling of the mesocrystal and matrix improves the separation of photoexcited carriers and the properties of charge transfer, resulting in a greatly enhanced PEC performance compared with their parent compounds. The current study demonstrates that the utilization of the interface-to-volume ratio to optimize charge interactions in the nanocomposite is essential for the advanced design of novel mesocrystal-embedded nanocomposite photoelectrodes.

The strains in GaAs nanowires, which were grown from 1700- to 80-nm-wide trenches on the Si(001) wafer with SiO2masks, were investigated by cathodoluminescence. For 1700- to 500-nm-wide trenches, the in-plane tensile strain at 15 K decreases with the decreasing trench width. The strain increases abruptly when the trench width is 300 nm, and then decreases as the trench width is further decreased. The results revealed that the stress induced by the SiO2sidewalls dominates when the width is less than the depth of the trench. This approach provides an effective technique to measure the strain of a single nanowire and helps for the demonstration of selectively-grown GaAs with a designed strain.

The role played by different types of threading dislocations (TDs) on the electrical properties of AlGaN/GaN heterostructure grown by plasma-assisted molecular beam epitaxy (MBE) was investigated. Samples with different defect structures and densities were prepared and measurements were taken from the same sample to study the correlative behavior of various TDs. From the Hall measurement, the electron mobility in two-dimensional electron gas channel was mainly controlled by the edge dislocation, which has a dominant amount in the material. The edge TDs acted as Coulomb scattering centers inside the channel and reduces the carrier mobility and increased its resistance. Screw TDs played a much significant role than edge TDs in determining the reverse-bias leakage current of Schottky barrier diodes. Leakage current is affected slightly by the reduction of free carrier density in the channel for samples with a higher edge TD density, but screw TD, which acted as the current leakage path, was more deleterious to the reverse-bias leakage current of AlGaN/GaN structure.

Strain-free gallium nitride (GaN) overgrowth on GaN nano-rods is realized by RF-plasma assisted molecular beam epitaxy (RF-MBE) on silicon (Si) substrate. The strain-free condition was identified by the strong free A exciton (FX\text{A) photoluminescence (PL) peak at 3.478 eV and the E2high phonon Raman shift of 567 cm-1. It is clearly demonstrated that the critical diameter of GaN nano-rods is around 80 nm for the overgrowth of strain-free GaN. The blue-shift of PL peak energy and phonon Raman energy with decreasing the diameter of nano-rod result from the strain relaxation of overgrowth GaN.

Growth of high quality ZnSe epilayer on Ge/GeSi/Si (100) was demonstrated by using low temperature migration enhance epitaxy (LT-MEE) and LT-ZnSe buffer layer. In this study, the low dislocation density of Ge/GeSi/Si structure was grown utilizing an ultrahigh vacuum chemical vapor deposition (UHV/CVD) system. The LT-MEE and LT-ZnSe buffer layer was grown employing molecular beam epitaxy (MBE) system for suppressing the formation of the deep-level emission (DLE) in the ZnSe/Ge/GeSi/Si structure. The low-temperature PL measurements indicate that the sample with a LT-MEE and LT-ZnSe buffer layer can improve its optical characteristic effectively. The X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) results indicate that the use of a LT-MEE and LT-ZnSe buffer layer markedly improves the crystallinity of the ZnSe epilayer and reduced the number of dislocations in ZnSe epilayer grown-up on Ge/GeSi/Si.