Effects of Mg-doping temperature on the structural and electrical properties of nonpolar a-plane p-type GaN films

Nonpolar(11–20) a-plane p-type GaN films were successfully grown on r-plane sapphire substrate with the metal–organic chemical vapor deposition(MOCVD) system. The effects of Mg-doping temperature on the structural and electrical properties of nonpolar p-type GaN films were investigated in detail. It is found that all the surface morphology, crystalline quality, strains, and electrical properties of nonpolar a-plane p-type GaN films are interconnected, and are closely related to the Mg-doping temperature. This means that a proper performance of nonpolar p-type GaN can be expected by optimizing the Mg-doping temperature. In fact, a hole concentration of 1.3×10^(18)cm^(-3), a high Mg activation efficiency of 6.5%,an activation energy of 114 me V for Mg acceptor, and a low anisotropy of 8.3% in crystalline quality were achieved with a growth temperature of 990℃. This approach to optimizing the Mg-doping temperature of the nonpolar a-plane p-type GaN film provides an effective way to fabricate high-efficiency optoelectronic devices in the future.

Preparation of Phlogopite-based Geopolymer and Its Surface Nonpolar Modification

Phlogopite-based geopolymer was first prepared successfully under the activation of lye by compression molding at 50 MPa for 1 minute.The geopolymer was endowed with nonpolar surface via brushing modified liquid at room temperature.Swill-cooked dirty oil,whose main component was fatty acid,was used as nonpolar modifier.The raw materials and geopolymer samples were characterized by XRD,FT-IR and SEM.The compression strength of 7-day specimen run up to 36.8 MPa and its surface static water contact angle could reach 132°.The solubility of phlogopite powder directly affected the compressive strength of geopolymers and the evaluation index of mechanical strength of geopolymer based on the solubility of phlogopite powder was proposed.

Structural and optical investigation of nonpolar a-plane GaN grown by metal-organic chemical vapour deposition on r-plane sapphire by neutron irradiation

Nonpolar （1150） a-plane GaN films are grown by metal-organic chemical vapour deposition （MOCVD） on r-plane （1102） sapphire. The samples are irradiated with neutrons under a dose of 1× 1015 cm-2. The surface morphology, the crystal defects and the optical properties of the samples before and after irradiation are analysed using atomic force microscopy （AFM）, high resolution X-ray diffraction （HRXRD） and photoluminescence （PL）. The AFM result shows deteriorated sample surface after the irradiation. Careful fitting of the XRD rocking curve is carried out to obtain the Lorentzian weight fraction. Broadening due to Lorentzian type is more obvious in the as-grown sample compared with that of the irradiated sample, indicating that more point defects appear in the irradiated sample. The variations of line width and intensity of the PL band edge emission peak are consistent with the XRD results. The activation energy decreases from 82.5 meV to 29.9 meV after irradiation by neutron.

Stress and morphology of a nonpolar a-plane GaN layer on r-plane sapphire substrate

The anisotropic strain of a nonpolar （1120） a-plane GaN epilayer on an r-plane （1102） sapphire substrate, grown by low-pressure metal-organic vapour deposition is investigated by Raman spectroscopy. The room-temperature Raman scattering spectra of nonpolar a-plane GaN are measured in surface and edge backscattering geometries. The lattice is contracted in both the c- and the m-axis directions, and the stress in the m-axis direction is larger than that in the c-axis direction. On the surface of this sample, a number of cracks appear only along the m-axis, which is confirmed by the scanning electron micrograph. Atomic force microscopy images reveal a significant decrease in the root-mean-square roughness and the density of submicron pits after the stress relief.

Treatment of tunnel wash waters-experiments with organic sorbent materials.PartⅠ:Removal of polycyclic aromatic hydrocarbons and nonpolar oil

Tunnel wash waters characterize all waters that run off after washing procedures of tunnels are performed.These waters represent a wide spectrum of organic and inorganic pollutants,such as polycyclic aromatic hydrocarbons(PAHs)and toxic metals.Removal of such contaminants from water runoff was investigated using laboratory tests after washing procedure was performed on two road tunnels in eastern Norway(Hanekleiv and Bragernes).Due to diverse character of both,treatment media and treated wash waters, the wh...

Improvement in a-plane GaN crystalline quality using wet etching method

Nonpolar （1120） GaN films are grown on the etched a-plane GaN substrates via metalorganic vapor phase epitaxy. High-resolution X-ray diffraction analysis shows great decreases in the full width at half maximum of the samples grown on etched substrates compared with those of the sample without etching, both on-axis and off-axis, indicating the reduced dislocation densities and improved crystalline quality of these samples. The spatial mapping of the E2 （high） phonon mode demonstrates the smaller line width with a black background in the wing region, which testifies the reduced dislocation densities and enhanced crystalline quality of the epitaxial lateral overgrowth areas. Raman scattering spectra of the E2 （high） peaks exhibit in-plane compressive stress for all the overgrowth samples, and the E2 （high） peaks of samples grown on etched substrates shift toward the lower frequency range, indicating the relaxations of in-plane stress in these GaN films. Furthermore, room temperature photoluminescence measurement demonstrates a significant decrease in the yellow-band emission intensity of a-plane GaN grown on etched templates, which also illustrates the better optical properties of these samples.

Effect of Nitrogen and Phosphorus Starvations on <i>Chlorella vulgaris</i>Lipids Productivity and Quality under Different Trophic Regimens for Biodiesel Production

In this work the effects of nutrients starvations on Chlorella vulgaris were investigated in different trophic regimens. For all the tested conditions, the cellular response to nutrient starvation and trophic regimen was evaluated on specific growth rate, biomass and lipids productivity, lipids content and quality. These parameters are all crucial for microalgae biodiesel production, but in literature the lipids quality, in terms of polar and nonpolar lipids, is often neglected. Thus the typical high content of polar lipids, a class of molecules that negatively affects the biodiesel production process, of microalgae crude oil is generally not analyzed. In the tested conditions the triggering effect of nitrogen starvation on total lipids productivity is confirmed only in autotrophic regimen, while in mixotrophic and heterotrophic conditions the total lipids productivity is reduced, as a consequence of the lowered biomass productivity, but with an evident compositional shift towards nonpolar lipids production (from 0.5 mg/Ld to 41.6 mg/Ld in mixotrophic regimen). Nitrogen and phosphorus co-starvation induced the highest nonpolar lipids productivity in all trophic regimens. Maximum nonpolar lipids productivity was obtained in nitrogen limited and phosphorus deprived condition during mixotrophic growth, equal to 118.2 mg/Ld, representing the 80% of produced lipids. On the basis of the obtained results, the possibility of a short pre-harvesting cultural step to maximize the nonpolar lipids yield of the crop could be envisaged.

Luminescence of a GaN grain with a nonpolar and semipolar plane in relation to microstructural characterization

We report on the growth of the high-quality GaN grain on a r-plane sapphire substrate by using a self-organized SiN interlayer as a selective growth mask. Transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy are used to reveal the effect of SiN on the overgrown a-plane GaN growth. The SiN layer effectively terminates the propagation of the threading dislocation and basal plane stacking faults during a-plane GaN regrowth through the interlayer, resulting in the window region shrinking from a rectangle to a ＂black hole＂. Furthermore, strong yellow luminescence （YL） in the nonpolar plane and very weak YL in the semipolar plane on the GaN grain is revealed by cathodoluminescence, suggesting that C-involved defects are responsible for the YL.

Renewal of basic laws and principles for polar continuum theories (Ⅺ)—consistency problems

Some consistency problems existing in continuum field theories are briefly reviewed. Three arts of consistency problems are clarified based on the renewed basic laws for polar continua. The first art discusses the consistency problems between the basic laws for polar continua. The second art discusses the consistency problems between the basic laws for polar continua and for other nonpolar continua. The third art discusses the consistency problems between the basic laws for micropolar continuum theories and the dynamical equations for rigid body. The results presented here can help us to get a deeper understanding the structure of the basic laws for various continuum theories and the interrelations between them. In the meantime, these results obtained show clearly that the consistency problems could not be solved in the framework of traditional basic laws for continuum field theories.

The etching of a-plane GaN epilayers grown by metal-organic chemical vapour deposition

Morphology of nonpolar （1120） a-plane GaN epilayers on r-plane （1102） sapphire substrate grown by low-pressure metal-organic vapour deposition was investigated after KOH solution etching. Many micron- and nano-meter columns on the a-plane GaN surface were observed by scanning electron microscopy. An etching mechanism model is proposed to interpret the origin of the peculiar etching morphology. The basal stacking fault in the a-plane GaN plays a very important role in the etching process.

Groove-type channel enhancement-mode Al GaN/GaN MIS HEMT with combined polar and nonpolar AlGaN/GaN heterostructures

A novel groove-type channel enhancement-mode AlGaN/GaN MIS high electron mobility transistor（GTCE-HEMT）with a combined polar and nonpolar AlGaN/GaN heterostucture is presented. The device simulation shows a threshold voltage of 1.24 V, peak transconductance of 182 m S/mm, and subthreshold slope of 85 m V/dec, which are obtained by adjusting the device parameters. Interestingly, it is possible to control the threshold voltage accurately without precisely controlling the etching depth in fabrication by adopting this structure. Besides, the breakdown voltage（VB） is significantly increased by 78% in comparison with the value of the conventional MIS-HEMT. Moreover, the fabrication process of the novel device is entirely compatible with that of the conventional depletion-mode（D-mode） polar AlGaN/GaN HEMT. It presents a promising way to realize the switch application and the E/D-mode logic circuits.

Nonpolar a-plane light-emitting diode with an in-situ SiN_x interlayer on r-plane sapphire grown by metal-organic chemical vapour deposition

We report on the growth and fabrication of nonpolar a-plane light emitting diodes with an in-situ SiNx interlayer grown between the undoped a-plane GaN buffer and Si-doped GaN layer. X-ray diffraction shows that the crystalline quality of the GaN buffer layer is greatly improved with the introduction of the SiNx interlayer. The electrical properties are also improved. For example, electron mobility and sheet resistance are reduced from high resistance to 31.6 cm2/（V· s） and 460 Ω/respectively. Owing to the significant effect of the SiNx interlayer, a-plane LEDs are realized. Electrolurninescence of a nonpolar a-plane light-emitting diode with a wavelength of 488nm is demonstrated. The emission peak remains constant when the injection current increases to over 20 mA.

Analysis of Nonpolar Components from Ginseng of Different Ages

Nonpolar components from ginseng of different ages were extracted and analysed using a GC-MS technique to determine their chemical compositions. In total, 23 ingredients, mostly aliphatic compounds, were identified. The compounds extracted included 10,12-octadecadiynoic acid (12.81% - 36.43%), falcarinol (4.95% - 36.79%), n-hexadecanoic acid (0.60% - 9.70%), 9,12-octadecadienoic acid, ethyl ester (0.33% - 5.63%), 5,7-dodecadiyn-1,12-diol (0.97% - 3.85%), (Z)-9-octadecenamide (2.66% - 5.38%) and (Z,Z)-9,12-octadecadienoic acid (0.46% - 5.27%). The two major diyne compositions, falcarinol (8) and 10,12-octadecadiynoic acid (12), were the predominant components (over 50%) of the nonpolar extract of older ginseng. Moreover, the 10,12-octadecadiynoic acid obviously accumulated as the ginseng grew. Sitosterol, a universal metabolite in higher plants, makes up 55.80% of the content of 6-year-old ginseng, but markedly decreases in older ginseng. There was not much difference between the extracts of 8, 10, 12 and 16-year ginsengs, but the extracts of 6-year-old ginseng were distinctive.

Controllable emission bands and morphologies of high-quality CsPbX3 perovskite nanocrystals prepared in octane

Halide perovskite （CsPbX3, X = C1, Br, or I） quantum dots have received increasing attention as novel colloidal nanocrystals （NCs）. Accurate control of emission bands and NC morphologies are vital prerequisites for most CsPbX3 NC practical applications. Therefore, a facile method of synthesizing CsPbX3 （X = C1, Br, or I） NCs in the nonpolar solvent octane was developed. The process was conducted in air at - 90℃ to synthesize high-quality CsPbX3 NCs showing 12-44 nm wide emission and high photoluminescence quantum yield, exceeding 90%. An in situ anion-exchange method was developed to tune CsPbX3 NC photoluminescence emission, using PbX2 dissolved in octane as the halide source. NC morphology was controlled by dissolving specific metal-organic salts in the precursor solution prior to nucleation, and nanocubes, nanodots, nanosheets, nanoplatelets, nanorods, and nanowires were obtained following the same general method providing a facile, versatile route to controlling CsPbX3 NC emission bands and morphologies, which will broaden the range of CsPbX3 NC practical applications.

Particular electrical quality of a-plane GaN films grown on r-plane sapphire by metal-organic chemical vapor deposition

Nonpolar （1120） a-plane GaN films have been grown by low-pressure metal-organic vapor deposition on r-plane （1102） sapphire substrate. The structural and electrical properties of the a-plane GaN films are investigated by high-resolution X-ray diffraction （HRXRD）, atomic force microscopy （AFM） and van der Pauw Hall measurement. It is found that the Hall voltage shows more anisotropy than that of the c-plane samples; furthermore, the mobility changes with the degree of the van der Pauw square diagonal to the c direction, which shows significant electrical anisotropy. Further research indicates that electron mobility is strongly influenced by edge dislocations.

Optical and electrical properties of Si-doped in a-plane GaN grown on r-plane sapphire

Si-doped (11-20) a-plane GaN grown on (1-102) r-plane sapphire substrate was obtained by metal organic chemical vapor deposition.The optical and electrical properties of the Si-doped a-plane GaN films were investigated by photoluminescence spectroscopy,high-resolution X-ray diffraction,atomic force microscopy and Hall measurement.The results showed that the morphology and the crystal quality slightly degraded with Si doping.The yellow luminescence was enhanced with increasing the flow rate of the SiH4.The significant improvement of the mobility should associate with some of the vacancy filled with the Si.

High-Temperature Synthesis in Nonpolar Solvent for CsPbBr3 and CH3NH_3PbBr3 Perovskite Nanocrystals with High-Efficient Luminescence

We report a method to synthesize both organicinorganic CH3NH3PbBr3 and all-inorganic CsPbBr3 perovskite nanocrystals in nonpolar solvent at high temperature. The cesium oleate and CH3NH3Br （MABr） are prepared and then injected into the nonpolar solvent of octadecene including oleic acid, oleylamine, and lead halide. In the synthesis of organic-inorganic perovskites of CHaNH3PbBr3, the frequently-used polar solvent of dimetbylformamide or other polar solvents are not used. The prepared CsPbBr3 nanocrystals are spherical nanoparticles with the diameter of 250 nm. The CHaNH3PbBr3 perovskites are micro-scale hexagonal nanoplatelets. The colloidal perovskites exhibit high-efficient fluorescence and excellent stability.

Nonpolar Al_(x)Ga_(1−x)N/Al_(y)Ga_(1−y)N multiple quantum wells on GaN nanowire for UV emission

Nonpolar m-plane AlGaN offers the advantage of polarization-free multiple quantum wells(MQWs)for ultraviolet(UV)emission and can be achieved on the sidewalls of selective area grown GaN nanowires.We reveal that the growth of AlGaN on GaN nanowires by metal organic chemical vapor deposition(MOCVD)is driven by vapor-phase diffusion,and consequently puts a limit on the pitch of nanowire array due to shadowing effect.An insight into the difficulty of achieving metal-polar AlGaN nanowire by selective area growth(SAG)in MOCVD is also provided and can be attributed to the strong tendency to form pyramidal structure due to a very small growth rate of{1011}semipolar planes compared to(0001)c-plane.The nonpolar m-plane sidewalls of GaN nanowires obtained via SAG provides an excellent platform for growth of nonpolar AlGaN MQWs.UV emission from mplane Al_(x)Ga_(1−x)N/Al_(y)Ga_(1−y)N MQWs grown on sidewalls of dislocation-free GaN nanowire is demonstrated in the wavelength range of 318–343 nm.

Twofold bioinspiration of TiO_(2)-PDA hybrid fabrics with desirable robustness and remarkable polar/nonpolar liquid separation performance

The fundamental relationship between microstructure,constituent,processing and performances of separating materials is really a vital issue.Traditional preparation methods for separation membranes are complex,time-consuming and easy to be fouled.Also,the durability of conventional coatings on membrane is poor.By combination of bioinspiration from mussel adhesive and fish scales’underwater superoleophobicity,we propose a general route to prepare organic-inorganic hybrid coatings,while no complex apparatus is needed.Specifically,based on the biomimetic adhesion of polydopamine(PDA),we used it as a binder to adhere TiO_(2)nanoparticles and built rough microstructure on fabric.In this way,we obtained TiO_(2)-PDA treated fabric with special wettability.These TiO_(2)-PDA treated samples owned superamphiphilicity in air,underwater superoleophobicity(underwater oil contact angles(OCAs)>150°),underoil superhydrophobicity(underoil water contact angles(WCAs)>150°),excellent multiresistance;and can separate polar/nonpolar liquid mixture effectively.It also owned superaerophobicity underwater(underwater bubble contact angles(BCAs)>150°).The proposed TiO_(2)-PDA coatings are highly expected to be employed for real situation of water pollution remediation,self-cleaning,oil extraction and harsh chemical engineering issues.

Unravelling a solution-based formation of single- crystalline kinked wurtzite nanowires： The case of MnSe

The search for a novel strategy to sculpt semiconductor nanowires （NWs） at the atomistic scale is crucial for the development of new paradigms in optics, electronics, and spintronics. Thus far, the fabrication of single-crystalline kinked semiconductor NWs has been achieved mainly through the vapor-liquid-solid growth technique. In this study, we developed a new strategy for sculpting single-crystalline kinked wurtzite （WZ） MnSe NWs by triggering the nonpolar axial-oriented growth, thereby switching--at the atomistic scale---the NW growth orientation along the nonpolar axes in a facile solution-based procedure. This presents substantial challenges owing to the dominant polar c axis growth in the solution-based synthesis of one-dimensional WZ nanocrystals. More significantly, the ability to continuously switch the nonpolar axial-growth orientation allowed us to craft the kinking landscape of types 150°, 120°, 90°, and 60°. A probabilistic analysis of kinked MnSe NWs reveals the correlations of the synergy and interplay between these two sets of nonpolar axial growth-orientation switching, which determine the actual kinked motifs. Furthermore, discriminating the side-facet structures of the kinked NWs significantly strengthened the spatially selected interaction of Au nanoparticles. We envisage that such a facile solution-based strategy can be useful for synthesizing other single-crystalline kinked WZ-type transition-metal dichalcogenide NWs to develop novel functional materials with finely tuned properties.