Origin and Mechanism of Piezoelectric and Photovoltaic Effects in (111) Polar Orientated NiO Films.

Based on the current piezoelectric theory, NiO with the centrosymmetric structure is not piezoelectric. However, herein, this study shows the first observation of piezoelectric generation, rectifyingand bulk photovoltaic behaviors in NiO films with [111] orientation and the change in NiO crystal structure in piezoelectric process. The piezoelectric generation, rectifying, and bulk photovoltaic performances are enhanced by increasing (111) orientation, and attenuated and eliminated by applying a persistent stress on the NiO film. The NiO [111] is polar direction, and thus a spontaneous electric field (ES ) is in the NiO film with [111] orientation. The existence of Es in (111) oriented NiO film is found to be the physical basis of the piezoelectric generators and photovoltaic and rectifying effects. Thus, NiO piezoelectric, rectifying, and bulk photovoltaic mechanism are presented at the atomic level. The mechanism may rewrite the current piezoelectric theory, and establish a unified theory of polar structure with wide implications. The polar-orientated films can be used to fabricate piezoelectric generators and other optoelectronic devices with high performances.

In-Plane Anisotropic Rectification and Photovoltaic Effects on ZnO Nonpolar (101Ì 0) Crystal Plane and the Physical Mechanism.

The concept of spontaneous electric field (Es) in polar structures is crucial for understanding the physical and chemical properties of compound semiconductors and improving their performanes. However, this concept has not been widely accepted so far. Here, we show the first observation of rectification and photovoltaic effects in the polar [0001] direction on the nonpolar ZnO (1010) crystal plane. However, no rectification and photovoltaic effects are observed in the nonpolar [1210] direction perpendicular to the [0001]. When a stress was applied in the [0001] direction of the ZnO single crystal, the rectification and photovoltaic effects are abated and disappeared. The disappearance of the two effects results from the pressure-induced disappearance of the polar structure. The results fully demonstrated that the rectification and photovoltaic effects arise from the existence of Es in the polar [0001] direction. The Es motivates the directional transfer of the electrons and photocreated charges along the [0001] direction, and the rectification and photovoltaic effects are thus observed. These results provide direct evidence for the polar structure theory and suggest that the polar structures can be employed to develop new types of photovoltaic and other electronic and photoelectronic devices.

Developing G value as an indicator for assessing the molecular status of immobilized antibody.

Antibody-functionalized nanoparticles (Ab-NPs) are widely used in bioassays due to their excellent affinity, specificity toward antigen, and ease of operation. However, the uncontrollable molecular status of antibodies on NPs severely limits their applications. This work aims at developing a simple method to evaluate the antigen-binding activity of Ab-NPs using two parameters, i.e., antibody adsorption amount and antigen-binding strength. Herein, we proposed a mathematical expression, G, to quantitively describe the amount and strength of Ab-NPs. G value could be used to assess the antigen-binding performance of NPs influenced by surface and solution factors. Seven types of polymers with different surface properties, including four positively and three negatively charged polymer brushes, were grown from silica NPs via surface-initiated atom transfer radical polymerization (SI-ATRP). A pair of antigen and antibody, human chorionic gonadotropin (hCG) and anti-hCG, were selected to screen the antibody immobilization property of polymer brushes. Among them, the G values of 2 polymer-NPs with opposite charges reached maximum, resulting in low detection limits for hCG, where pDMAEA-NP and pMMA-NP represent Poly[N,N-(dimethylamino)ethyl acrylate]-NP and poly(methyl methacrylate)-NP, respectively. The G value of Ab-NPs makes it feasible to estimate the molecular status of the adsorbed antibodies on surfaces, thus showing great potential for in vitro biosensing and bioseparation.

Enhanced Sensitivity of Hydrogenated Cu0.27Co2.73O4 Nanooctahedrons Having {111} Facets and the Sensing Mechanism of 3-Coordinated Co/Cu Atoms as Active Centers.

Cu0.27Co2.73O4 nanooctahedrons enclosed by polar {111} planes have been prepared through the selective adsorption of Cl-. Hydrogenation has been successfully used to enhance the responses of the Cu0.27Co2.73O4 nanooctahedron sensors to acetone, ethanol, and n-butylamine. The enhancement of the response results from the increase in the number of 3-coordinated Co/Cu atoms (Co3c/Cu3c) at the (111) plane of Cu0.27Co2.73O4 through removing O-H groups and Cl- ions at the surface by hydrogenation. The Co3c/Cu3c atoms on the (111) plane of Cu0.27Co2.73O4 are considered to function as the gas response active centers. These Co3c/Cu3c active atoms have three functions: generating electrons, adsorbing oxygen from air, and catalyzing the sensing reactions. The hydrogenation polar surface approach can be applied to improve the performances of other sensing materials. Such sensing mechanisms of the Co3c/Cu3c unsaturated atoms as the active centers can be conducive to understanding the gas-sensing essence and the development of sensing materials with high performances.

Effect of TC(002) on the Output Current of a ZnO Thin-Film Nanogenerator and a New Piezoelectricity Mechanism at the Atomic Level.

Understanding the piezoelectricity mechanism is crucial for developing new materials for better performance. Here, we developed a nanogenerator based on the ZnO thin films having various TC(002) values. The output current well correlated to the magnitude of (002) texture coefficient (TC(002)). Additionally, the TC(002)-dependent photovoltaic and rectification properties are observed. When the film is subjected to persistent compression, the photovoltaic, rectification, and piezoelectric properties fade away. Based on our observation that the ZnO polar structure always shows a spontaneous electron field (SEF), we thus propose a new piezoelectricity mechanism. The [001]-orientated ZnO thin film with the SEF is equivalent to a capacitor, the compression functions as a discharging process, and the removal of the external stress serves as a charging process. The physical mechanism provides an insight into various energy conversion processes that will inspire advanced designs of high-performance nanogenerators, solar cells, and other optoelectronic devices.

Enhanced Visible-Light Photocatalytic H2 Evolution in Cu2O/Cu2Se Multilayer Heterostructure Nanowires Having {111} Facets and Physical Mechanism.

It is rather challenging to develop photocatalysts based on narrow-band-gap semiconductors for water splitting under solar irradiation. Herein, we synthesized the Cu2O/Cu2Se multilayer heterostructure nanowires exposing {111} crystal facets by a hydrothermal reaction of Se with Cu and KBH4 in ethanol amine aqueous solution and subsequent annealing in air. The photocatalytic H2 production activity of Cu2O/Cu2Se multilayer heterostructure nanowires is dramatically improved, with an increase on the texture coefficient of Cu2O(111) and Cu2Se(111) planes, and thus the exposed {111} facets may be the active surfaces for photocatalytic H2 production. On the basis of the polar structure of Cu2O {111} and Cu2Se {111} surfaces, we presented a model of charge separation between the Cu-Cu2Se(111) and O-Cu2O(1̅ 1̅ 1̅) polar surfaces. An internal electric field is created between Cu-Cu2Se(111) and O-Cu2O(1̅ 1̅ 1̅) polar surfaces, because of spontaneous polarization. As a result, this internal electric field drives the photocreated charge separation. The oxidation and reduction reactions selectively occur at the negative O-Cu2O(1̅ 1̅ 1̅) and the positive Cu-Cu2Se(111) surfaces. The polar surface-engineering may be a general strategy for enhancing the photocatalytic H2-production activity of semiconductor photocatalysts. The charge separation mechanism not only can deepen the understanding of photocatalytic H2 production mechanism but also provides a novel insight into the design of advanced photocatalysts, other photoelectric devices, and solar cells.

Enhanced Gas Sensitivity and Sensing Mechanism of Network Structures Assembled from α-Fe2O3 Nanosheets with Exposed {104} Facets.

Network structures assembled from α-Fe2O3 nanosheets with exposed {104} facets were successfully prepared by heating Fe(NO3)3 solution containing polyvinylpyrrolidone (PVP) in air. The α-Fe2O3 nanosheet-based network structures demonstrate significantly higher response to ethanol and triethylamine than α-Fe2O3 commercial powders. The excellent sensing performances can be ascribed to the exposed (104) facet terminated with Fe atoms. A concept of the unsaturated Fe atoms serving as the sensing reaction active sites is thus proposed, and the sensing reaction mechanism is described at the atomic and molecular level for the first time in detail. The concept of the surface metal atoms with dangling bonds serving as active sites can deepen understanding of the sensing and other catalytic reaction mechanisms and provides new insight into the design and fabrication of highly efficient sensing materials, catalysts, and photoelectronic devices.

Enhancing the Sensing Properties of TiO2 Nanosheets with Exposed {001} Facets by a Hydrogenation and Sensing Mechanism.

Hydrogenation is successfully employed to improve sensing performances of the gas sensors based on TiO2 nanosheets with exposed {001} facets for the first time. The hydrogenated TiO2 nanosheets show a significantly higher response toward ethanol, acetone, triethylamine, or formaldehyde than the samples without hydrogenation, and the response further increases with an increase of the hydrogenation temperature. The excellent sensing performances are ascribed to an increase of the density of unsaturated Ti5c atoms on the {001} surface resulting from the hydrogenation process. The unsaturated Ti5c atoms are considered to serve as sensing reaction active sites. They can generate noncontributing (free) electrons and adsorb oxygen molecules, and the detailed sensing mechanism is described at atomic and molecule level. The hydrogenated strategy may be employed to enhance the sensing performances of other metal oxide sensors and catalytic reaction activities of catalyst. The concept of the surface unsaturated metal atoms serving as sensing reaction active sites not only deepens the understanding of the sensing reaction and catalytic reaction mechanism but also provides new insights into the design of advanced gas sensing materials, catalysts, and photoelectronic devices.

Superior adsorption performance for triphenylmethane dyes on 3D architectures assembled by ZnO nanosheets as thin as ∼1.5nm.

The 3-dimensional hierarchical ZnO flower-like architectures have been synthesized in a Zn(Ac)2·2H2O-Na2SeO3-KBH4-pyridine solvothermal system at 100°C for 24h. The flower-like architecture is assembled from ZnO nanosheets with a thickness of ∼1.5nm, and the flower-like architecture specific surface area is 132m(2)/g. When the ZnO flower-like architecture is used as the adsorbent for acid fuschin (AF), malachite green (MG), basic fuchsin (BF), congo red (CR) and acid red (AR) in water, the adsorption capacities for AF, MG, BF, CR and AR are 7154.9, 2587.0, 1377.9, 85.0 and 38.0mg/g, respectively. Evidently, the as-obtained ZnO flower-like architectures show excellent adsorption performances for triphenylmethane dyes, and the adsorption capacity of 7154.9mg/g for AF is the highest of all adsorbents for dyes. The adsorption mechanism can be attributed to the electrostatic attraction and the formation of ion-association complex between triphenylmethane dyes and ZnO hierarchical flower-like architectures.

A high-throughput-compatible assay to measure the degradation of endogenous Huntingtin proteins.

AIM: The accumulation of disease-causing proteins is a common hallmark of many neurodegenerative disorders. Measuring the degradation of such proteins using high-throughput-compatible assays is highly desired for the identification of genetic and chemical modulators of degradation. For example, Huntington's disease (HD) is an incurable hereditary neurodegenerative disorder caused by the cytotoxicity of mutant huntingtin protein (mHTT). The high-throughput measurement of mHTT degradation is important in HD drug discovery and research. Existing methods for such purposes have limitations due to their dependence on protein tags or pan protein synthesis inhibitors. Here, we report a high-throughput-compatible pulse-chase method (CH-chase) for the measurement of endogenous tag-free huntingtin protein (HTT) degradation based on Click chemistry and Homogeneous Time Resolved Fluorescence (HTRF) technologies. METHODS: The pulsed-labeled proteins were conjugated with biotin using the click reaction strain-promoted alkyne-azide cycloaddition (SPAAC), and the chase signals were calculated by measuring the reduction percentage of the HTT HTRF signals after pull-down with streptavidin beads. RESULTS: We validated that the signals were within the linear detection range and were HTT-specific. We successfully measured the degradation of endogenous HTT in a high-throughput-compatible format using 96-well plates. The predicted changes of HTT degradation by known modifiers were observed, which confirmed that the assay is suitable for the identification of HTT degradation modifiers. CONCLUSION: We have established the first high-throughput-compatible assay capable of measuring endogenous, tag-free HTT degradation, providing a valuable tool for HD research and drug discovery. The method could be applied to other proteins and can facilitate research on other neurodegenerative disorders and proteinopathies.

Visible-light photocatalysis in Cu2Se nanowires with exposed {111} facets and charge separation between (111) and (1[combining macron]1[combining macron]1[combining macron]) polar surfaces.

The search for active narrow band gap semiconductor photocatalysts that directly split water or degrade organic pollutants under solar irradiation remains an open issue. We synthesized Cu2Se nanowires with exposed {111} facets using ethanol and glycerol as morphology controlling agents. The {111} facets were found to be the active facets for decomposing organic contaminants in the entire solar spectrum. Based on the polar structure of the Cu2Se {111} facets, a charge separation model between polar (111) and (1[combining macron]1[combining macron]1[combining macron]) surfaces is proposed. The internal electric field between polar (111) and (1[combining macron]1[combining macron]1[combining macron]) surfaces created by spontaneous polarization drives charge separation. The reduction and oxidation reactions occur on the positive (111) and negative (1[combining macron]1[combining macron]1[combining macron]) polar surfaces, respectively. This suggests the surface-engineering of narrow band gap semiconductors as a strategy to fabricate photocatalysts with high reactivity in the entire solar spectrum. The charge separation model can deepen the understanding of charge transfer in other semiconductor nanocrystals with high photocatalytic activities and offer guidance to design more effective photocatalysts as well as new types of solar cells, photoelectrodes and photoelectric devices.

Charge separation between polar {111} surfaces of CoO octahedrons and their enhanced visible-light photocatalytic activity.

Crystal facet engineering of semiconductors has been proven to be an effective strategy to increase photocatalytic performances. However, the mechanism involved in the photocatalysis is not yet known. Herein, we report our success in that photocatalytic performances of the Cl(-) ion capped CoO octahedrons with exposed {111} facets were activated by a treatment using AgNO3 and NH3·H2O solutions. The clean CoO {111} facets were found to be highly reactivity faces. On the basis of the polar structure of the exposed {111} surfaces, a charge separation model between polar {111} surfaces is proposed. There is an internal electric field between polar {111} surfaces due to the spontaneous polarization. The internal electric field provides a driving force for charge separation. The reduction and oxidation reactions selectively take place on the positive and negative polar {111} surfaces. The charge separation model provides a clear insight into charge transfer in the semiconductor nanocrystals with high photocatalytic activities and offer guidance to design more effective photocatalysts, solar cells, photoelectrodes, and other photoelectronic devices.

Controllable low-temperature chemical vapor deposition growth and morphology dependent field emission property of SnO2 nanocone arrays with different morphologies.

Vertically aligned SnO2 nanocones with different morphologies have been directly grown on fluorine-doped tin oxide (FTO) glass substrates in a large area by heating a mixture of stannous chloride dihydrate (SnCl2·2H2O) and anhydrous zinc chloride (ZnCl2) at 600 °C in air. Control over the SnO2 nanocone arrays with different morphologies is achieved by adjusting the heat treatment time. The SnO2 nanocones are single crystalline with the tetragonal structure. A single-layer SnO2 nanoparticle film is first formed via the vapor-solid (VS) process due to the decentralization function of ZnCl2 vapor, and the SnO2 nanoparticles served as seeds and grew into nanocone arrays via the VS process. The sharp-tipped nanostructure formation may originate from a concentration gradient of reactant in the growth process. The as-obtained whiskerlike nanocone arrays exhibit enhanced field emission properties in comparison with typical nanoconelike structure arrays and other SnO2 nanostructured materials reported previously, and the turn-on field and field-enhancement factor is 1.19 V/µm and 3110, respectively. The experimental result is consistent with the Utsumi's relative figure of merit for pillar-shaped emitters.

Controllable low temperature vapor-solid growth and hexagonal disk enhanced field emission property of ZnO nanorod arrays and hexagonal nanodisk networks.

ZnO nanorod arrays and nanodisk networks were grown directly on Si substrate by thermal evaporation of ZnCl(2) powder and a mixture of ZnCl(2) and InCl(3)·4H(2)O at 450 °C in air, respectively. The ZnO nanorods with the diameters of 0.64 to 0.91 µm and length of about 5.1 µm are single crystalline with the hexagonal structure and grow along the [001] direction. The nanodisk has perfect hexagonal shape, grow mainly along the [0110] directions, and are enclosed by ±(0001) top and bottom surfaces. ZnO nanoparticle films oriented in the [001] direction formed first served as seeds, and grow into nanorod arrays via the vapor-solid (VS) process. However, when InCl(3)·4H(2)O was introduced into the reaction system ZnO thick nanosheet films are first formed because of the local segregation of the doping element of indium. The ZnO thick nanosheet films served as seeds, and grow into nanodisk networks via the V-S process. Photoluminescence and field emission properties of the as-obtained ZnO nanorod arrays and hexagonal nanodisk networks have been studied. It was found that the hexagonal nanodisk networks exhibit strong blue-green emissions originated from defect states and enhanced field emission property.

Highly oriented ZnS nanorod arrays with controlled diameters: solvothermal synthesis, size-dependent band-edge emission and photocatalytic properties.

High quality ZnS nanorod arrays with controlled diameters were directly grown on Zn substrate via a facile solvothermal reaction of metallic Zn with thiourea in hydrazine hydrate at 180 degrees C. The control over the diameters of the nanorods was achieved by adjusting the reaction time. The as-prepared ZnS nanorods were single-crystalline with a hexagonal wurtzite structure and grown along the [0001] direction. The role of hydrazine hydrate in the formation of ZnS nanorod arrays was investigated, and a possible mechanism was also proposed. The photoluminescence and photocatalytic activities of the as prepared ZnS nanorod arrays were studied. It was found that the ZnS nanorod arrays exhibit the size-dependent band edge emission and photocatalytic activities in the degradation of acid scarlet, and have potential applications in the fields of nanolaser and other photoelectronic devices as well as pollutant treatment.

Controlled solvothermal synthesis of nanosheets, nanobelts, and ultralong nanobelt arrays with honeycomb-like micropatterns of ZnSe on zinc substrate.

Nanosheets, nanobelts, and ultralong nanobelt arrays with honeycomb-like micropatterns of ZnSe were synthesized via a solvothermal reaction of Zn with Se and KBH(4) in ethylenediamine at 200 degrees C for 24 h and subsequent annealing. The control over these nanostructures with different morphologies was achieved by adjusting the KBH(4)/Se molar ratio. The role of KBH(4) in the formation of ZnSe(en)(0.5) nanobelts with different length-to-width ratios was investigated, and a possible mechanism was also proposed to account for the growth and conversion of these precursor nanostructures into ZnSe nanostructures. Current-voltage behaviors of the ultralong nanobelt arrays with honeycomb-like micropatterns were investigated. In addition, variable-aspect ratio ZnS nanosheets and nanowires were also synthesized by adjusting the KBH(4)/thiourea molar ratio in the Zn-thiourea-KBH(4)-ethylenediamine solvothermal system. The results suggest that this method may be employed for the controllable synthesis of other II-VI semiconductor nanostructures such as ZnTe, NiS, MnS, and so forth and provides opportunities for both fundamental research and technological applications.

[Transient dynamics of excited states and nonlinear optical properties of InP nanoparticles].

The decay curves of the emission at different wavelength were measured. One nanosecond of transition lifetime of interband was obtained. The transient dynamics of InP nanoparticles was investigated by one color femtosecond pump-probe method at the wavelength of 800 nm. The experimental result shows that the saturation of exciton resonance results in photobleaching at 800 nm The decay process of the bleaching includes two components, i.e. the fast one from free carries scattering and the slow one from trapped carriers scattering. The nonlinear optical properties of InP nanoparticles were investigated by using femtosecond optical Kerr effect. The magnitude of chi3 for InP nanoparticles embedded in SiO2 sol-gel glass was calculated, and its origin was analyzed.

Sol-gel synthesis of luminescent InP nanocrystals embedded in silica glasses.

III-V semiconductor nanocrystals rarely exist as spherical inclusions inside glasses, due to difficulties during their preparation, such as high toxic reagents or fast oxidation under usual glass technology temperatures. In this letter a sol-gel method for synthesis of InP nanocrystals embedded in silica glasses was described. Gels were synthesized by hydrolysis of a complex solution of Si(OC2H5)4, InCl3.4H2O, and PO(OC2H5)3. Then, the gels were heated at 600 degrees C in the presence of H2 gas to form fine cubic InP crystallites. Raman spectrum showed an InP longitudinal-optic mode (342 cm(-1)) and a transverse-optic mode (303 cm(-1)). The size of InP nanocrystals was found to be from 2 to 8 nm in diameter by transmission electron microscopy. A strong photoluminescence with a peak at 856 nm was observed from InP nanocrystals embedded in silica glasses. The results suggest that it might be possible to synthesize other III-V semiconductor nanocrystals embedded in silica glasses through the sol-gel process.

Sol-gel synthesis and photoluminescence of III-V semiconductor InAs nanocrystals embedded in silica glasses.

III-V semiconductor nanocrystals rarely exist as spherical inclusions inside glasses, due to the difficulties during their preparation, such as high toxic reagents or fast oxidation under usual glass technology temperatures. In this paper a sol-gel method for synthesis of InAs nanocrystals embedded in silica glasses was described. Gels were synthesized by the hydrolysis of a complex solution of Si(OC2H5)4, InCl3 x 4H2O, and As2O3. The gels were then heated at 200-450 degrees C in the presence of H2 gas to form fine cubic InAs crystallites. The X-ray diffraction patterns showed four strong peaks from InAs. The Raman spectrum showed InAs longitudinal-optic (233 cm(-1)) and transverseoptic modes (215 cm-(-1)). The size of InAs nanocrystals was found to be from 5 to 30 nm in diameter by transmission electron microscopy. A strong room temperature photoluminescence with peaks at 601 and 697 nm was observed from InAs nanocrystals embedded in silica glasses. The results suggest that it might be possible to synthesize other III-V semiconductor nanocrystals embedded in silica glasses through the sol-gel process.