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White lighting sources based on laser diodes (LDs) are strongly regarded as the next generation of high luminance lighting sources because the luminous efficiency of LDs increases linearly with operating current, which can resolve the “efficiency droop” of LEDs. To facilitate the advent of high brightness solid state lighting, searching for a light convertor with high thermal stability, high conversion efficiency, and irradiation stability is essential. Herein, we developed a robust light convertor, YAG:Ce3+ based on phosphor-in-glass (denoted as YAG-PiG), exhibiting a quantum efficiency of 70.1% and a high thermal conductivity of 0.89 W m−1 K−1. The microstructure and luminescent properties of YAG-PiG were also investigated in detail. Compared to YAG-PiS (phosphor-in-silicone), this YAG-PiG shows an overall increase in irradiation and thermal stability performances. A high power white LDs was constructed by coupling the YAG-PiG with a 445 nm blue laser and a sapphire plate modified by an antireflection layer and a blue-pass filter serving as the heat sink. The constructed PiG converted LDs@sapphire exhibits a luminous efficacy of 217 lm W−1 and a CRI (color rendering index) of 57 at 3646 K under a driven power of 3 W. Compared to the conventional white LDs, the luminous efficacy and the resistance to laser irradiation of the white LDs@sapphire are obviously enhanced. Therefore, we predict that this white emitting PiG converted LDs@sapphire will become a promising candidate for future lighting sources and promote the use of sapphire plate as the heat sink.

Polymer solar cells are one of the promising energy sources because of the easy solution-processable production with large area at a low cost without toxicity. Among the polymer materials, a donor–acceptor conjugated copolymer PTB7 has been extensively studied because of the typical high-performance polymer solar cells. Here, we show operando direct observation of charge accumulation in PTB7:PC71BM blend solar cells from a microscopic viewpoint using electron spin resonance spectroscopy. The accumulation of ambipolar charges in the PTB7-based cells is directly observed for the first time, which shows a clear correlation with the performance deterioration during device operation. The sites of the ambipolar charge accumulation are elucidated at the molecular level, whose information would be useful for improving the cell durability in addition to the performance improvement.

Perovskite oxides hosting ferroelectricity are particularly important materials for modern technologies. The ferroelectric transition in the well-known oxides BaTiO3 and PbTiO3 is realized by softening of a vibration mode in the cubic perovskite structure. For most perovskite oxides, octahedral-site tilting systems are developed to accommodate the bonding mismatch due to a geometric tolerance factor t = (A–O)/[√2(B–O)] < 1. In the absence of cations having lone-pair electrons, e.g., Bi3+ and Pb2+, all simple and complex A-site and B-site ordered perovskite oxides with a t < 1 show a variety of tilting systems, and none of them become ferroelectric. The ferroelectric CaMnTi2O6 oxide is, up to now, the only one that breaks this rule. It exhibits a columnar A-site ordering with a pronounced octahedral-site tilting and yet becomes ferroelectric at Tc ≈ 650 K. Most importantly, the ferroelectricity at T < Tc is caused by an order–disorder transition instead of a displacive transition; this character may be use...

The quantum efficiency of composites containing Europium(II)-doped Ca-α-SiAlON phosphors and sodium borosilicate glasses has been reported to decrease with an increase in the Na 2 O concentration in the glass matrix. To understand the reason for the dependence of this degradation on the glass composition, the reaction between the SiAlON powder and the glass matrix was investigated using a variety of techniques. SEM images of the areas around SiAlON powders showed the formation of a new layer between the SiAlON particles and the glass matrix. EDX images showed that the number of silicon and aluminium atoms decreased while that of boron atoms increased in the new layer. Raman spectra of the composites showed the formation of B N bonds. New layers between the SiAlON phosphor and the glasses were formed owing to exchange between silicon or aluminium and boron; this resulted in the degradation of the composites.

A series of Ce3+-, Tb3+- and Ce3+/Tb3+-doped La3Si8N11O4 phosphors were synthesized by gas-pressure sintering (GPS). The energy transfer between Ce3+ and Tb3+ occurred in the co-doped samples, leading to a tunable emission color from blue to green under the 360 nm excitation. The energy transfer mechanism was controlled by the dipole–dipole interaction. The Ce3+/Tb3+ co-doped sample had an external quantum efficiency of 46.7%, about 5.6 times higher than the Tb-doped La3Si8N11O4 phosphor (8.3%). The thermal quenching of the Tb3+ emission in La3Si8N11O4:Tb,Ce was greatly reduced from 74 to 30% at 250 °C, owing to the energy transfer from Ce3+ to Tb3+. The blue-green La3Si8N11O4:0.01Ce,0.05Tb phosphor was testified to fabricate a warm white LED that showed a high color rendering index of 90.2 and a correlated color temperature of 3570 K. The results suggested that the co-doped La3Si8N11O4:Ce,Tb phosphor could be a potential blue-green down-conversion luminescent material for use in UV-LED pumped wLEDs.

High-power and high-brightness solid state laser lighting sources, fabricated with high-power blue laser diodes (LDs) and yellow-emitting phosphor converters, constitute a pioneering lighting technology for specialized lighting. Because of the high radiation flux and thermal stress produced by high-power blue LDs, there is an urgent need for a light converter with excellent heat-resistance and thermal stability. In this work, YAG:Ce phosphor-in-glass (PiG), prepared by embedding YAG:Ce phosphor in glass matrix, was developed. Because of the good chemical stability between the glass matrix and the phosphor as well as high refractive index of 1.84 of the glass matrix, the internal quantum efficiency of YAG:Ce-PiG material can reach up to 78.9% under 445 nm blue laser excitation. In comparison with reported papers, the content of the YAG phosphor in this PiG can reach up to 29 wt%, thus it can get more brightness when excited by higher LD power. Besides, systematic research on the thermal effect to the material and its luminescent properties when excited by a high-power blue LD is done in detail. Compared with traditional commercial phosphor-in-silicone (PiS) light converters, PiG can withstand higher blue LD power and maintain a higher luminescent intensity. By virtue of its better heat-resistance performance under exposure to high-power blue LD, the developed PiG light converter material is an ideal choice to replace traditional commercial PiS in high brightness lighting sources.

β-Sialon:Eu2+ has been reported to be the most promising narrow-band green phosphor for wide color gamut LCD backlights, but the coexistence of the Eu3+ luminescence killer with the Eu2+ luminescence center limits its luminescence performance to a great extent. In this study, we propose a direct reduction strategy to successfully realize the reduction of Eu3+ to Eu2+ and, finally, increase the effective concentration of Eu2+ in the crystal lattice and greatly minimize the amount of Eu3+ on the particle surface. As a result, the luminescence of treated β-sialon:Eu2+ is enhanced by 2.3 times, and the internal quantum efficiency significantly increases from 52.2 to 96.5%. The mechanisms for such large enhancements in luminescence are clarified by investigating the microstructure, luminescence spectra, valence state, concentration, and distribution of Eu using a variety of chemical analyses. We find that the low efficiency is ascribed to the coexistence of the Eu3+ luminescence killer with the Eu2+ luminescen...

International audience; We report the photoluminescence (PL) and cathodoluminescence (CL) properties of face-capped [MoXL] (X = Cl, Br, I; L = organic or inorganic ligands) cluster units. We show that the emission of Mo metal atom clusters depends not only on the nature of X and L ligands bound to the cluster and counter-cations, but also on the excitation source. Seven members of the AMoXL series (A = Cs, (n-CH)N, NH) were selected to evaluate the influence of counter-cations and ligands on de-excitation mechanisms responsible for multicomponent emission of cluster units. This study evaluates the ageing of each member of the series, which is crucial for further energy conversion applications (photovoltaic, lighting, water splitting, etc.).

The (Y,Ce) 2 BaAl 4 SiO 12 phosphor, a garnet-structured blue-to-yellow color convertor for WLED, exhibits an interesting “microcrystal-glass powder” feature, which can be regarded as the 4th form for phosphor, in addition to the “ceramic powder phosphor”, the “single crystal phosphor” and the “glass-ceramic phosphor”. The structure exhibits luminescent microcrystals embedding in non-luminescent glass matrix: the spherical crystals are mainly arranged around the glass phase forming a “necklace” pattern, while the individual crystals show a “core-shell” architecture regarding the luminescence intensity variation. Further combining the phase evolution evidence evaluated by Rietveld refinement, we propose the formation mechanism for such unique morphology/structure as a two-stage process, including an initial nucleation by solid state reaction and following liquid-assisted crystal growth, instead of a precipitation-crystallization process.

Superhigh brightness, reliability, and modularization are three key features of state-of-the-art high-brightness solid state lighting, such as high-power white light-emitting diodes (white LEDs) and white laser diodes (white LDs). However, these features are inevitably limited by the organic resin packing material, as a crucial component of the white lighting device, because of its unstable property at high temperature and low thermal conductivity. Here, we report a robust light convertor that can simultaneously play key roles as a phosphor and an alternative encapsulating material via phosphor-in-glass (PiG) engineering. We employed a combination of powder X-ray diffraction, scanning electron microscope, energy dispersive spectrometer (EDS), EDS mapping, confocal laser scanning microscope, cathodoluminescence mapping, in conjunction with micro-PL system with a point-by-point scanning mode to study the detailed structure of PiG samples. This Y3Al5O12:Ce3+-based PiG exhibits a high external quantum efficie...

We synthesized Sr- and W-doped BaTiO3 (BTO) polycrystals by using a solid-state reaction method. The X-ray diffraction results showed that Sr and W atoms occupied the Ba and Ti sites in tetragonal BTO, respectively, and there were changes in the lattice constants and the volumes in the Sr- and W-doped BTO. We found a change in the latent heat and the Curie temperature (TC) during the transition between the ferroelectric and paraelectric phases while increasing the contents of Sr and W in the Sr- and W-doped BTO. This can be explained by the fact that the doping of Sr and W atoms in BTO prevented a distinct transition between the ferroelectric tetragonal and paraelectric cubic structures by decreasing the c/a ratio to a value close to unity. This study shows a way toward a strategy for modulating a crystal structure by using proper dopants for future applications in ferroelectricity-based devices.

A red-emitting nitridosilicate phosphor, Sr2Si5N8:Eu2+, shows very promising photoluminescence properties but exhibits serious thermal degradation, thus making it difficult to be used practically as a color converter in white light-emitting diodes (wLEDs). To alleviate this problem, we introduce carbon into the Sr2Si5N8 lattice to form thermally robust carbidonitride phosphors (Sr2Si5CxN8−4x/3:Eu2+). The carbon doping, evidenced by a variety of analytical techniques, leads to structural evolutions including lattice shrinkage, shortening of the average bond length of Eu–(C,N), and the removal of Eu3+ ions from the lattice. The photoluminescence intensity and quantum efficiency of phosphors are greatly improved by the carbon doping and reach the maximum at x = 0.5, dominantly owing to the enhanced absorption of Eu2+. Thanks to the increased oxidation resistance of Eu2+ due to the stronger covalency of Si–(C,N) and Sr(Eu)–(C,N) bonds, thermal degradation is significantly reduced from 16 to 0.8% when the carbon doping increases from x = 0 to 1.25. In addition, thermal quenching is also reduced by 10% at 300 °C and the quantum efficiency declines slowly with increasing temperature when carbon is substituted for nitrogen. At 300 °C, the internal quantum efficiencies are 55% and 62% for x = 0 and 0.5, respectively. The enhanced thermal stability of the carbon-doped sample is also confirmed by smaller variations in the luminous efficacy and color coordinates of monochromatic red LEDs.

To clarify the bright contrast of insulating ceramics in secondary electron (SE) image taken using scanning electron microscopy (SEM), the low-pass secondary electron signals and images of conductive AlN and insulating β-SiAlON powders taken by fountain detector (FD) were inspected. It was found that the background component of β-SiAlON is originally strong. This component may come from the SE acceleration according to the charging. The low energy SEs of 5–20 eV were strong in AlN particles. According to the wide acceptance angle of FSED, we could not detect clear energy shift in SE spectra. These observations suggest that the bright contrast of insulating materials is not an intrinsic character of insulators but the SE3 contribution.

The threading dislocations in GaN provide diffusion routes for impurity incorporation, which substantially influences GaN based optoelectronic devices. Here, we investigated the characteristics of the impurity incorporation at threading dislocations by HCl vapor phase etching and cathodoluminescence (CL) measurements. The distinctive etch pits induced by HCl vapor phase etching correspond definitely to different types of dislocations, and the etching process causes simultaneously H incorporation at a high temperature. CL spectra of the etch pits were analyzed, and the observed difference in the redshift of near band emission peak indicates that mix dislocations are more favorable for impurity incorporations than that of edge dislocations. The understanding on the impurity incorporation behavior at threading dislocations helps to obtain high quality GaN nanostructures.

We have developed liposomes modified with various surface-charged lipids in order to solubilize the new algicidal agent, N-[(3,4-dichlorophenyl)methyl]cyclohexanamine (DP92), and enhance its algicidal activity against harmful algal blooms (HABs). The effect of liposome surface charge on algicidal activity was evaluated by using positively charged and neutral liposomes. The algicidal activity of the developed liposomes was evaluated by monitoring the inhibition of the growth rates of HABs (Heterosigma circularisquama (HC) and Heterosigma akashiwo (HA)). The algicidal activity of the liposomes was 2–6 times stronger compared to that of control. The solubilization of DP92 by entrapment in liposomes increased the solubility of DP92 and improved its algicidal activity up to sixfold. The electrostatic interaction between the negatively charged cell walls of HABs and the cationic liposomes additionally enhanced the algicidal activity of DP92.

(GaN)1-x(ZnO)x solid-solution nanostructures with superior crystallinity, large surface areas and visible light absorption have been regarded as promising photocatalysts for overall water splitting to produce H2. In this work, we report the preparation of (GaN)1-x(ZnO)x solid-solution nanorods with a high ZnO solubility up to 95% via a two-step synthetic route, which starts from a sol-gel reaction and follows with a nitridation process. Moreover, we clearly demonstrated that the crystallographic facets of (GaN)1-x(ZnO)x solid-solution nanorods can be finely tailored from non-polar {10̄10} to semipolar {10̄11} and then finally to mixed {10̄1} and polar {000̄1} by carefully controlling the growth temperature and nitridation time. Correspondingly, the ZnO content in the GaN lattice can be achieved in the range of ∼25%-95%. Room-temperature cathodoluminescence (CL) measurements on the three types of (GaN)1-x(ZnO)x solid-solution nanorods indicate that the minimum band-gap of 2.46 eV of the solid-solution nanorods is achieved under a ZnO solubility of 25%. The efficiency and versatility of our strategy in the band-gap and facet engineering of (GaN)1-x(ZnO)x solid-solution nanorods will enhance their promising photocatalytic utilizations like an overall water splitting for H2 production under visible-light irradiation.

As an excellent red phosphor, CaAlSiN3:Eu2+ plays a major role in high color rendition or wide color gamut white light-emitting diodes, but it can hardly be used in high-power laser displays and lighting due to the intrinsic low thermal performance of the phosphor/silicone resin mixture. To apply CaAlSiN3:Eu2+ in laser lighting devices, a bulk ceramic form is thus required to survive thermal attack and high flux density irradiation. However, it remains an unsolved great challenge to fabricate fully densified CaAlSiN3:Eu2+ ceramics. Here, for the first time, translucent CaAlSiN3:Eu2+ ceramics with an interesting composite microstructure, where red-emitting phosphor particles with a core–shell structure are uniformly embedded in a non-luminescent α-Sialon matrix, are successfully synthesized using Si3N4 and SiO2 as sintering additives. The luminescence ceramic is superior to the corresponding powder phosphor in terms of its enhanced thermal stability (15% increase) and thermal conductivity (4 W m−1 K−1). It has a high external quantum efficiency of 60% (87% that of the powder) upon 450 nm excitation, and a luminous efficacy of 10.6 lm W−1 when irradiated under a blue laser flux density of 0.75 W mm−2. The translucent CaAlSiN3:Eu2+ ceramic is thus supposed to be a potential color converter used in emerging laser lighting and display technologies.

Nanoscale semiconductor heterostructures with superior crystal quality, large surface area and designed interfaces provide more opportunities for building high-performance optoelectronic nanodevices and harvesting clean energy. In this work, we report the rational synthesis of In2S3/In2O3 heterostructures through a two-channel chemical vapor deposition (CVD) process. The In2S3/In2O3 heterostructures feature a bundle-like morphology with In2S3 nanowires covering randomly distributed In2O3 nanoparticles. High-resolution transmission electron microscopy (HRTEM) analysis on the In2S3/In2O3 heterostructures finds that both In2S3 nanowires and In2O3 nanoparticles show a crystalline nature, but the lattice matching between the two crystal domains is not observed at the interface, implying that the heterostructure is formed via a simple physical adsorption. Cathodoluminescence (CL) studies on In2S3/In2O3 heterostructures indicate that the as-synthesized heterostructures have a broad emission in the range of 400–950 nm, covering the whole visible light spectrum from violet to infrared. Finally, the formation process of In2S3/In2O3 heterostructures and their optical emission behaviors are discussed based on detailed structural analyses.

A red phosphor of Sr2Si5N8:Eu(2+) powder was synthesized by a solid state reaction. The synthesized phosphor was thermally post-treated in an inert and reductive N2-H2 mixed-gas atmosphere at 300-1200 °C. The main phase of the resultant phosphor was identified as Sr2Si5N8. A passivation layer of ∼0.2 μm thickness was formed around the phosphor surface via thermal treatment. Moreover, two different luminescence centers of Eu(SrI) and Eu(SrII) in the synthesized Sr2Si5N8:Eu(2+) phosphor were proposed to be responsible for 620 nm and 670 nm emissions, respectively. More interestingly, thermal- and moisture-induced degradation of PL intensity was effectively reduced by the formation of a passivation layer around the phosphor surface, that is, the relative PL intensity recovered 99.8% of the initial intensity even after encountering thermal degradation; both moisture-induced degraded external and internal QEs were merely 1% of the initial QEs. The formed surface layer was concluded to primarily prevent the Eu(2+) activator from being oxidized, based on the systemic analysis of the mechanisms of thermal- and moisture-induced degradation.

To decrease the rare earth element usage and synthesis cost of Y3Al5O12:Ce phosphor, the Y2BaAl4SiO12 compound is developed as a new host for Ce3+ employing the solid solution design strategy. The design uses polyhedron substitution where YO8/AlO4 are partially replaced by BaO8/SiO4, respectively. Structure analysis of Y2BaAl4SiO12 proves that it successfully preserves the garnet structure, crystallizing in the cubic Iad space group with a = b = c = 12.00680(5) A. Barium (Ba) atoms occupy the Y site and silicon (Si) atoms occupy the Al site in the AlO4 tetrahedrons. An expanded study on Y2MAl4SiO12 (M = Ba, Ca, Mg, Sr) series shows a cation size (of M)-dependent phase formation behavior. The lattice stability can be related with the M type in the M–Si pair and substitution level of M–Si for Y–Al. Doping Ce3+ into Y2BaAl4SiO12 yields bright yellow photoluminescence peaking at around 537 nm upon excitation by 460 nm light. The emission intensity is quite stable against thermal quenching whereas the peak wavelength shows a slight red-shift as the ambient temperature increases. The crystallization behavior of Y2BaAl4SiO12 is suggested as melt-assisted precipitation/growth based on cathodoluminescence analysis. The highly crystalline nature of the microcrystals explains the stable emission against thermal quenching. This study may provide an inspiring insight into preparing phosphor with new morphology-structure of “microcrystal-glass powder phosphor”, which distinguishes it from conventional “ceramic powder phosphor” or “single-crystal phosphor”.

We present a general phenomenological model for surface second-harmonic generation (SSHG) induced by strain fields with up to three spatial coordinates. As an example, we apply it to thermal-mismatch strain fields around cylindrical metallic through-silicon-vias (TSVs) embedded in an Si(001) surface, which are widely used as interconnects between vertically stacked silicon layers to achieve 3D integration. We find that analysis of the four different combinations of s or p incoming and outgoing polarizations enables reconstruction of the strain field. In particular, the sS combination yields tensorial components of the strain field that are different from zero; from this information, the pP, sP, and pS combinations complete the analysis of the strain field.

To modify the luminescence properties of Ce3+-doped Y3Al5O12 (YAG) phosphors, they have been coated with a carbon layer by chemical vapor deposition and subsequently heat-treated at high temperature under N2 atmosphere. Luminescence of the carbon coated YAG:Ce3+ phosphors has been investigated as a function of heat-treatment at 1500 and 1650 °C. The 540 nm emission intensity of C@YAG:Ce3+ is the highest when heated at 1650 °C, while a blue emission at 400-420 nm is observed when heated at 1500 °C but not at 1650 °C. It is verified by X-ray diffraction (XRD) that the intriguing luminescence changes are induced by the formation of new phases in C@YAG:Ce3+-1500 °C, which disappear in C@YAG:Ce3+-1650 °C. In order to understand the mechanisms responsible for the enhancement of YAG:Ce3+ emission and the presence of the blue emission observed for C@YAG:Ce3+ -1500 °C, the samples have been investigated by a combination of several electron microscopy techniques, such as HRTEM, SEM-CL, and SEM-EDS. This local and cross-sectional analysis clearly reveals a gradual transformation of phase and morphology in heated C@YAG:Ce3+ phosphors, which is related to a reaction between C and YAG:Ce3+ in N2 atmosphere. Through reaction between the carbon layer and YAG host materials, the emission colour of the phosphors can be modified from yellow, white, and then back to yellow under UV excitation as a function of heat-treatment in N2 atmosphere.

Piezoelectric and ferroelectric properties in the two dimensional (2D) limit are highly desired for nanoelectronic, electromechanical, and optoelectronic applications. Here we report the first experimental evidence of out-of-plane piezoelectricity and ferroelectricity in van der Waals layered ${\alpha}$-In2Se3 nano-flakes. The non-centrosymmetric R3m symmetry of the ${\alpha}$-In2Se3 samples is confirmed by scanning transmission electron microscopy, second-harmonic generation, and Raman spectroscopy measurements. Domains with opposite polarizations are visualized by piezo-response force microscopy. Single-point poling experiments suggest that the polarization is potentially switchable for ${\alpha}$-In2Se3 nano-flakes with thicknesses down to ~ 10 nm. The piezotronic effect is demonstrated in two-terminal devices, where the Schottky barrier can be modulated by the strain-induced piezopotential. Our work on polar ${\alpha}$-In2Se3, one of the model 2D piezoelectrics and ferroelectrics with simple crystal structures, shows its great potential in electronic and photonic applications., Comment: 17 pages, 5 figures, just accepted by Nano Letters

The strong advantage of two-dimensional (2D) materials is that they exhibit interesting physical properties down to the single unit layer (typically less than 1 nm). Such emergent properties are highly dependent on thickness and can be tunable via external parameters such as electric field, pressure, and/or chemical treatment. In addition, most 2D materials have hexagonal crystal structures; thus, it is possible to stack with other 2D materials to enrich the properties. This tunability and compatibility makes 2D materials and their heterostructures promising candidates for optoelectronic devices.

Nitride and oxynitride (Sialon) phosphors are good candidates for the ultraviolet and visible emission applications. High performance, good stability and flexibility of their emission properties can be achieved by controlling their composition and dopants. However, a lot of work is still required to improve their properties and to reduce the production cost. A possible approach is to correlate the luminescence properties of the Sialon particles with their local structural and chemical environment in order to optimize their growth parameters and find novel phosphors. For such a purpose, the low-voltage cathodoluminescence (CL) microscopy is a powerful technique. The use of electron as an excitation source allows detecting most of the luminescence centers, revealing their luminescence distribution spatially and in depth, directly comparing CL results with the other electron-based techniques, and investigating the stability of their luminescence properties under stress. Such advantages for phosphors characterization will be highlighted through examples of investigation on several Sialon phosphors by low-energy CL.

Silicon dioxide (SiO2) is one of the key materials in many modern technological applications such as in metal oxide semiconductor transistors, photovoltaic solar cells, pollution removal, and biomedicine. We report the accidental discovery of free-standing grassy silica nanoribbons directly grown on SiO2/Si platform which is commonly used for field-effect transistors fabrication without other precursor. We investigate the formation mechanism of this novel silica nanostructure that has not been previously documented. The silica nanoribbons are flexible and can be manipulated by electron-beam. The silica nanoribbons exhibit strong blue emission at about 467 nm, together with UV and red emissions as investigated by cathodoluminescence technique. The origins of the luminescence are attributed to various defects in the silica nanoribbons; and the intensity change of the blue emission and green emission at about 550 nm is discussed in the frame of the defect density. Our study may lead to rational design of the new silica-based materials for a wide range of applications.

Graphene was chemically aminated via cycloaddition. Aziridine-ring linkages were formed by covalently modifying the C-C double bonds in graphene. The aminated graphene presents an enhanced hydrophilicity, the contact angle with water decreases from 80.5 degrees to 58.5 degrees. And the conductivity of aminated graphene exhibits exponential decay as the reaction time increase. If the reaction time is 90 min, the resistance of aminated graphene was increased from -32 Ω to -2744 Ω. Because the amino group has good biocompatibility, the aminated graphene is designed for use as an enzyme sensor platform, such as glucose sensor based on glucose oxidase. The aminated graphene exhibited a good detection response for glucose. The increase in device current is about 12% in 1.2 mg/mL glucose solution.

We study the nonlinear optical response in a strained thin film ferroelectric oxide BaTiO3 using piezoelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 (001) as a variable strain substrate and La-doped SrTiO3 as a conductive buffer layer. The rotation-anisotropic second harmonic intensity profile shows hysteretic modulation corresponding to the strain variation from the inverse piezoelectric response of the substrate. An enhancement of 15% is observed at 1.2 kV/cm, while a control sample shows negligible change as a function of piezovoltage. Reflection high-energy electron diffraction, x-ray photoelectron spectroscopy, and high-resolution scanning transmission electron microscopy reveal the epitaxial interface. X-ray diffraction and piezoresponse force microscopy confirm tetragonal distortion and ferroelectricity of the BaTiO3 overlayer. Our results suggest a promising route to enhance the performance of nonlinear optical oxides for the development of future nano-opto-mechanical devices.

We investigate polarization retention in 10 to 19 nm thick ferroelectric BaTiO3 (BTO) grown on Ge(001) by molecular beam epitaxy. The out-of-plane direction and reversibility of electric polarization were confirmed using piezoresponse force microscopy. After reverse-poling selected regions of the BTO films to a value P with a biased atomic-force microscope tip, we monitored relaxation of their net polarization for as long as several weeks using optical second-harmonic generation microscopy. All films retained reversed polarization throughout the observation period. 10 nm-thick BTO films relaxed monotonically to a saturation value of 0.9 P after 27 days and 19 nm films to 0.75 P after 24 h. Polarization dynamics are discussed in the context of a 1D polarization relaxation/kinetics model.

Tail states near the valence band maximum (VBM) and in-gap states of GaN bulk and In x Ga1− x N films are observed by hard X-ray photoemission spectroscopy, and the fine structures of these defect states are characterized by photothermal deflection spectroscopy. The defects are enhanced with increasing InN mole fraction, indicating that they originate in cation-related defects and their complexes. The structural disorder, defined as the inverse of the slope of the VBM, becomes larger. Taking the semiconductor properties into account, we consider that the tail state defects are strongly localized, which implies that a mobility edge may exist for GaN and In x Ga1− x N.

Microscopic characterization of radical states in organic light‐emitting diodes (OLEDs) during device operation is useful for elucidating the degradation mechanism because the radical formation has been considered as non‐radiative recombination centers. Electron spin resonance (ESR) spectroscopy is suitable for such characterization because it can directly observe radicals in OLEDs. In this work, the detailed ESR investigation into the radical states in OLEDs during device operation is firstly reported using a typical light‐emitting Alq3‐based OLEDs. The simultaneous measurements of the ESR signal and the luminance of the same OLED are performed to study the direct correlation between the radical states and the performance degradation. These characteristics show that the luminance monotonically decreases and an ESR signal concomitantly increases as the duration of the device operation increases after operating the OLED. Using the analysis of density functional theory (DFT) calculation, the origin of the newly emerged ESR signal is ascribed to the cationic species due to decomposed Alq3 molecules. The elucidation of the radical species formed in OLEDs during device operation has been demonstrated at a molecular level for the first time. This ESR analysis would provide useful knowledge for understanding the degradation mechanism in the OLEDs at the molecular level.

Electrical characteristics of leakage current paths in vertical-type n-GaN Schottky barrier diodes (SBDs) on free-standing GaN substrates are investigated by using photon emission microscopy (PEM). The PEM mapping shows that the initial failure of the SBD devices at low voltages is due to the leakage current paths from polygonal pits in the GaN epilayers. It is observed that these polygonal pits originate from carbon impurity accumulation to the dislocations with a screw-type component by microstructure analysis. For the SBD without polygonal pits, no initial failure is observed and the first leakage appeals at the edge of electrodes as a result of electric field concentration. The mechanism of leakage at pits is explained in terms of trap assisted tunneling through fitting current-voltage characteristics.

A novel conducting copolymer based on amidoxime groups, polypyrrole and graphene oxide was synthesized by in situ copolymerization by usin g two monomers. The monomer, amidoxime-pyrrole, was synthesized by amidoximation of 1-(2-cyanoethyl) pyrrole. The other monomer, GO-pyrrole, was prepared via esterification between –COOH of GO and –NH2 of 1-(3-aminopropyl) pyrrole. The conductive ability of the copolymer was based on conductive [Formula: see text]-conjugated system of polypyrrole backbone. The copolymer was able to be used as an effective sorption material for the preconcentration and recovery of uranium. The maximum of adsorption capacity for uranyl ion is as high as 149.57[Formula: see text]mg/g.