Tuning field emission properties of boron nanocones with catalyst concentration

Single crystalline boron nanocones are prepared by using a simple spin spread method in which Fe3O4 nanoparticles are pre-manipulated on Si（lll） to form catalyst patterns of different densities. The density of boron nanocones can be tuned by changing the concentration of catalyst nanoparticles. High-resolution transmission electron microscopy analysis shows that the boron nanocone has a β-tetragonal structure with good crystallization. The field emission behaviour is optimal when the spacing distance is close to the nanocone length, which indicates that this simple spin spread method has great potential applications in electron emission nanodevices.

Synthesis,thermionic emission and magnetic properties of(Nd_xGd_(1-x))B_6

Polycrystalline rare-earth hexaborides （NdxGdl-x）B6 （x = 0, 0.2, 0.6, 0.8, 1） were prepared by the reactive spark plasma sintering （SPS） method using mixed powder of GdH2, NdH2 and B. The effects of Nd doping on the crystal structure, the grain orientation, the thermionie emission and the magnetic properties of the hexaboride were investigated by X-ray diffraction, electron backscattered diffraction and magnetic measurements. It is found that all the samples sintered by the SPS method exhibit high densities （〉95%） and high values of Vickers hardness （2319 kg/mm2）. The values are much higher than those obtained in the traditional method. With the increase of Nd content,the thermionic emission current density increases from 11 to 16.30 A/cm2 and the magnetic phase transition temperature increases from 5.85 to 7.95 K. Thus, the SPS technique is a suitable method to synthesize the dense rare-earth hexaborides with excellent properties.

Phase Transformation and Enhancing Electron Field Emission Properties in Microcrystalline Diamond Films Induced by Cu Ion Implantation and Rapid Annealing

Cu ion implantation and subsequent rapid annealing at 500℃ in N2 result in low surface resistivity of 1.611 ohm/sq with high mobility of 290 cm2 V-1S-1 for microcrystalline diamond （MCD） films. Its electrical field emission behavior can be turned on at Eo = 2.6 V/μm, attaining a current density of 19.5μA/cm2 at an applied field of 3.5 V/#m. Field emission scanning electron microscopy combined with Raman and x-ray photoelectron mi- croscopy reveal that the formation of Cu nanoparticles in MCD films can catalytically convert the less conducting disorder/a-C phases into graphitic phases and can provoke the formation of nanographite in the films, forming conduction channels for electron transportation.

ZnO nanorod arrays with tunable size and field emission properties on an ITO substrate achieved by an electrodeposition method

In the present work, vertically aligned ZnO nanorod arrays with tunable size are successfully synthesized on nonseeded ITO glass substrates by a simple electrodeposition method. The effect of growth conditions on the phase, morphology, and orientation of the products are studied in detail by X-ray diffraction （XRD）, scanning electron mi-croscopy （SEM）, and transmission electron microscopy （TEM）. It is observed that the as-prepared nanostructures exhibit a preferred orientation along c axis, and the size and density of the ZnO nanorod can be controlled by changing the concentration of ZnC12. Field emission properties of the as-synthesized samples with different diameters are also studied, and the results show that the nanorod arrays with a smaller diameter and appropriate rod density exhibit better emission properties. The ZnO nanorod arrays show a potential application in field emitters.

Effect of metal nanoparticle doping concentration on surface morphology and field emission properties of nano-diamond films

Nano-diamond particles are co-deposited on Ti substrates with metal(Ti/Ni) nanoparticles(NPs) by the electrophoretic deposition(EPD) method combined with a furnace annealing at 800℃ under N_(2) atmosphere. Modifications of structural and electron field emission(EFE) properties of the metal-doped films are investigated with different metal NPs concentrations. Our results show that the surface characteristics and EFE performances of the samples are first enhanced and then reduced with metal NPs concentration increasing. Both the Ti-doped and Ni-doped nano-diamond composite films exhibit optimal EFE and microstructural performances when the doping quantity is 5 mg. Remarkably enhanced EFE properties with a low turn-on field of 1.38 V/μm and a high current density of 1.32 mA/cm^(2) at an applied field of 2.94 V/μm are achieved for Ni-doped nano-diamond films, and are superior to those for Ti-doped ones. The enhancement of the EFE properties for the Ti-doped films results from the formation of the TiC-network after annealing. However, the doping of electron-rich Ni NPs and formation of high conductive graphitic phase are considered to be the factor, which results in marvelous EFE properties for these Ni-doped nano-diamond films.

Preparation of patterned boron nanowire films with different widths of unit-cell and their field emission properties

Large-area patterned films of boron nanowires（BNWs） are fabricated at various densities by chemical vapor deposition（CVD）. Different widths of unit-cell of Mo masks are used as templates. The widths of unit-cell of Mo masks are100 μm, 150 μm, and 200 μm, respectively. The distance between unit cells is 50 μm. The BNWs have an average diameter of about 20 nm and lengths of 10 μm–20 μm. High-resolution transmission electron microscopy analysis shows that each nanowire has a β-tetragonal structure with good crystallization. Field emission measurements of the BNW films show that their turn-on electric fields decrease with width of unit-cell increasing.

Emission Properties of Yb^(3+)/Er^(3+) Doped TeO_2-WO_3-ZnO Glasses for Broadband Optical Amplifiers

The Yb3+/Er3+ doped TeO2-WO3-ZnO glasses were prepared. The absorption spectra, emission spectra and fluorescence lifetime of Er3+ at 1.5 um, excited by 970 nm were measured. The influence of Er2O3, Yb2O3 and OH-contents on emission properties of Er3+ at 1.5μm was investigated. The optimum doping concentrations for Er3+ and Yb3+ is around 3.34×1020 ions/cm3 and 6.63×1020 ions/cm3, respectively. The peak emission cross section is 0.83~0.87 pm2. With the increasing concentration of Yb3+, the FWHM of Er3+ emission at 1.5μm in the glass increases from 77 nm to 83 nm. The results show that Yb3+/Er3+ doped TeO2-WO3-ZnO glasses are promising candidate for Er3+-doped broadband optical amplifier.

Preparation of few-layer graphene-capped boron nanowires and their field emission properties

Large-area boron nanowire（BNW） films were fabricated on the Si（111） substrate by chemical vapor deposition（CVD）. The average diameter of the BNWs is about 20 nm, with lengths of 5–10 μm. Then, graphene-capped boron nanowires（GC-BNWs） were obtained by microwave plasma chemical vapor deposition（MPCVD）. Characterization by scanning electron microscopy indicates that few-layer graphene covers the surface of the boron nanowires. Field emission measurements of the BNWs and GC-BNW films show that the GC-BNW films have a lower turn-on electric field than the BNW films.

Field Emission Properties of Nano-DLC Films Prepared on Cu Substrates by Pulsed Laser Deposition

Nano-diamond like carbon（DLC） thin films were prepared on fused silica and Cu substrates by the pulsed-laser deposition technique with different laser intensities. Step-measurement, atomic force microscope（AFM）, UV-VIS-NIR transmittance spectroscopy and Raman spectroscopy were used to characterize the films. It was shown that the deposition rate increases with the laser intensity, and the films prepared under different laser intensities show different transparency. Raman measurement showed that the content of sp^3 of the Nano-DLC thin films decreases with the laser intensity. The field emission properties of the Nano-DLC thin films on Cu substrates were studied by the conventional diode method, which showed that the turn-on field increases and the current density decreases with sp^3 content in the films. A lower turn-on field of 6 V/um and a higher current density of 1 uA/cm^2 were obtained for Nano-DLC thin films on Cu substrate.

Mid-infrared luminescence of Dy^(3+)-doped Ga_2S_3–Sb_2S_3–CsI chalcohalide glasses

The mid-infrared （MIR） luminescent properties of Dy3＋ ions in a new chalcohalide glass host, Ga2S3-Sb2S3-CsI, are investigated; and the suitability of the doped glass for MIR fiber lasers is evaluated. The Dy3＋-doped chalcohalide glasses exhibit good thermal stability and intense MIR emissions around 2.96 μm and 4.41 μm. These emissions show quantum efficiencies （η） as high as ～ 60%, and have relatively large stimulated emission cross sections （σem）. The low phonon energy （～ 307 cm-1） of the host glass accounts for the intense MIR emissions, as well as the high η. These favorable thermal and emission properties make the Dy3＋-doped Ga2S3-Sb2S3-CsI glasses promising materials for MIR fiber amplifiers or lasers.

Current Status and Prospect of Infrared Radiation Ceramics for Energy-saving Applications in High Temperature Furnaces

Nowadays,it is a great challenge to reduce energy consumption and exhaust emission for human activities,in particular,high temperature industries.Among many efforts made to realize energy savings for high temperature furnaces and kilns,the use of high emissivity materials is considered to be an effective route to increase their thermal efficiency by enhancing heat transfer.Most materials with high refractoriness and superior chemical stability have weak infrared absorption and radiation properties;however,their emissivity in infrared regions（1 —25 μm） could be effectively increased by ion doping.This is attributed to three main mechanisms：1） distortion of the crystal lattice;2） increase of free carrier absorption; 3） formation of impurity energy level.In this paper,the development and advancement of various material systems with high emissivity including non-oxides and oxide based ceramics were reviewed.It is also suggested that the establishment of evaluation models or instruments for energy savings would be beneficial to design and application of high emissivity materials in various high-temperature environment.Furthermore,more efforts should be made on durability of high emissivity materials at high service temperatures and on the standardization of testing methods for emissivity.

Synthesis,Crystal Structure and Photoluminescence of a Dinulear Copper Complex

A binuclear cuprous complex [Cu（μ-I）（NPPh）]2（1,NPPh = 1-（2-（diphenylphosphanyl）phenyl）-3-phenyl-4,5-dihydro-1 H-pyrazole） was synthesized and characterized by elemental analysis,NMR and X-ray single-crystal structure analysis.It crystallizes in triclinic space group P2_1/n with a = 10.7520（3）,b = 18.1860（5）,c = 11.8487（3） ？,β = 91.864（2）,V = 2315.61（11） ？~3,Z = 4,Mr = 594.87,Dc = 1.706 g/cm^3,F（000） = 1176.0,μ = 12.582 mm（-1）,GOOF = 1.048,the final R = 0.0289 and wR = 0.0670 for 3787 observed reflections with I 〉 2σ（I）.The Cu atoms in the complex are four-coordinated and adopt distorted tetrahedral coordination geometry.In the solid state,the complex exhibits greenish yellow photoluminescence with a peak maximum of 533 nm,a decay time of 34 μs,and a photoluminescence quantum yield of 63.6% at room temperature,respectively.

Synthesis,Crystal Structure and Photoluminescence of a Cuprous Dimer with Tetrakis(pyrazol-i-yl)borate Linker

A cuprous dimer [Cu（POP）]2（pz4B）BF4·（CH3CN）3 （1, POP = bis（2-（diphenylphosphanyl）phenyl）ether, pz4B- = tetrakis（pyrazol-i-yl）borate anion） was synthesized from the reaction of Cu（CH3CN）4BF4, POP and Kpz4B in CH3CN at room temperature. The compound was characterized by elemental analysis and X-ray single-Crystal structure analysis. It crystallizes in monoclinic, space group P21/c with a = 12.3491（2）, b = 20.8845（3）, c = 33.0657（4） A, β = 94.251（1）°, V = 8504.3（2） A3, Z = 4, Mr = 1693.21, Dc = 1.322 g/cm3, F（000） = 3496,μ = 1.843 mm-1, GOOF = 1.031, the final R = 0.0442 and wR = 0.1235 for 14397 observed reflections with 1〉 2σ（I）. 1 is an ionic compound. It is composed of a BF4- anion and a {[Cu（POP）]2（pz4B）}＋ cation. The cation contains two [Cu（POP）]＋ cationic moieties and a pz4B- anionic linker. The Cu（I） ions show a distorted tetrahedral coordination geometry defined by two nitrogen atoms from a pz4B- bridging ligand and two phosphorous atoms from a POP terminal chelating ligand. The complex emits blue luminescence with the maximum peak at 457 nm with 3% quantum yield in solid state at room temperature. The Cu（I） centers are essentially electronically separated because both HOMO and LUMO contain very little contribution from the bridging ligand. The unexpected low emission is ascribed to the intramolecular interaction of the emissive centers.

Electrical and Optical Properties of Nano Aluminum Film/Particle Structure

The electrical and optical effects of particles on the nano aluminum film deposited by thermal evaporation was investigated. From the characterization results of scanning electron microscope（SEM）, the accumulation in tens of nanometers had been observed. The current-voltage（I-V） curve of the sample indicates its nonlinear electrical characters expecting the corresponding nonlinear optical properties. By the theoretical calculation, nonlinear conduction of the carrier transportation may result from the barrier-well-barrier structure, where negative resistance and Coulomb blockade effect appears. The simulation results are approximately matched with the experimental results. By testing the fluorescence emission spectrum of the sample, peaks were found to be located at 420 and 440 nm. In addition, the full width at half maximum（FWHM） had been obviously broadened by means of adding 2, 5-diphenyloxazole（DPO）. Therefore, discrete energy levels could be estimated inside those particles.

Synthesis,Crystal Structure and Photoluminescence of a TADF Cuprous Complex

A cuprous mononuclear copper complex [Cu（adpypz）CH3CNPPh3]BF4·CH2Cl2（1, adpypz = 9,9-dimethyl-10-（6-（3-phenyl-1H-pyrazol-1-yl）pyridin-2-yl）-9,10-dihydroacridine） was synthesized and characterized by Elemental Analysis, NMR, UV-Vis and X-ray single-crystal structure analysis. It crystallizes in triclinic, space group P1 with a = 11.3388（4）, b = 13.4569（4）, c = 16.2561（6） ？, α = 97.154（3）, β = 92.187（3）, γ = 114.119（4）°, V = 2235.38（13） ？3, Z = 2, Mr = 967.12, Dc = 1.437 g/cm^3, F（000） = 996, μ = 2.62 mm^–1, GOOF = 1.031, the final R = 0.0417, and w R = 0.1024 for 8043 observed reflections with I 〉 2σ（I）. The Cu（I） atoms in the complex are four-coordinated and adopt a tetrahedral coordination geometry. In the solid state, the complex exhibits bluish-green photoluminescence with emission peaks λmax = 492 nm（1）, lifetimes 235 μs and quantum yields（ф = 0.279） at room temperature. The studies of varied temperature emission spectra and decay behaviours of the complex indicate that the complex displays thermally activated delayed fluorescence（TADF） at room temperature. The results of the experimental and DFT calculations suggest that the emission in the solid state originates from the ILCT excited states.

Synthesis,Crystal Structure and Photoluminescence of a Dinuclear Cuprous Complex with Thiocyanate Bridges

A cuprous dinuclear copper complex [PPh_2PAr_2Cu（μ-SCN）_2CuPPh_2PAr_2]（1,PPh_2PAr_2 =（1-bis（2-methylphenyl）-phosphine-2-diphenylphosphino）benzene） was synthesized from the reaction of Cu SCN and PPh_2PAr_2 in CH_3CN at room temperature. The compound was characterized by Elemental Analysis,NMR,UV-Vis and X-ray single-crystal structure analysis. It crystallizes in triclinic,space group P1 with a = 10.225（2）,b = 11.360（2）,c = 13.420（3） ？,α = 95.81（3）,β = 93.45（3）,γ = 113.78（3）°,V = 1410.4（5） ？~3,Z = 1,Mr = 1192.21,Dc = 1.404 g/cm^3,F（000） = 616,μ = 3.029 mm^（–1）,GOOF = 1.052,the final R = 0.0359,and w R = 0.0964 for 4878 observed reflections with I 〉 2σ（I）. The Cu（I） atoms in the complex are four-coordinated and adopt a tetrahedral coordination geometry. The copper centers in the molecular structure are bridged by two thiocyanate anions and each Cu（I） is chelated further terminally by a PPh_2PAr_2 ligand. The [Cu（μ-SCN）_2Cu] cores have essential planar configurations. In the solid state,the complex exhibits blue photoluminescence with emission peaks λ_（max）= 478 nm（1）,lifetimes 4.7 μs and quantum yields（ф = 0.43） at room temperature. The studies of varied temperature emission spectra and decay behaviours of the complex indicate that it displays thermally activated delayed fluorescence at room temperature. The results of the experimental and DFT calculations suggest that the emission in the solid state originates from the ^（1,3）MLCT excited states.

Acoustic emissions evaluation of the dynamic splitting tensile properties of steel fiber reinforced concrete under freeze-thaw cycling

This study empirically investigated the influence of freeze-thaw cycling on the dynamic splitting tensile properties of steel fiber reinforced concrete(SFRC).Brazilian disc splitting tests were conducted using four loading rates(0.002,0.02,0.2,and 2 mm/s)on specimens with four steel fiber contents(0%,0.6%,1.2%,and 1.8%)subjected to 0 and 50 freeze-thaw cycles.The dynamic splitting tensile damage characteristics were evaluated using acoustic emission(AE)parameter analysis and Fourier transform spectral analysis.The results quantified using the freeze-thaw damage factor defined in this paper indicate that the degree of damage to SFRC caused by freeze-thaw cycling was aggravated with increasing loading rate but mitigated by increasing fiber content.The percentage of low-frequency AE signals produced by the SFRC specimens during loading decreased with increasing loading rate,whereas that of high-frequency AE signals increased.Freeze-thaw action had little effect on the crack types observed during the early and middle stages of the loading process;however,the primary crack type observed during the later stage of loading changed from shear to tensile after the SFRC specimens were subjected to freeze-thaw cycling.Notably,the results of this study indicate that the freeze-thaw damage to SFRC reduces AE signal activity at low frequencies.

Tunable emission properties of core-shell ZnCuInS-ZnS quantum dots with enhanced fluorescence intensity

Cadmium-free Ⅰ-Ⅲ-Ⅵ quantum dots （QDs）, represented by Cu-In-S （CIS）, are widely investigated for their non-toxicity and tunable emission properties. In this work, Zn-Cu-In-S （ZCIS） alloyed QDs were synthesized via a solvothermal approach by heating up a mixture of the corresponding metal precursors and sulphur powder with dodecanethiol in oleylamine media, and the fluorescent intensity was greatly enhanced by coating ZnS （ZS） shell. By changing the ratio of Cu, the as prepared ZCIS-ZS QDs showed composition-tunable photoluminescent （PL） emission over the visible spectral window from about 500 nm to 620 rim, which is much wider than that of CIS QDs. Moreover, the influence of excitation wavelength, reaction temperature and time on the optical properties of the ZCIS-ZS QDs was also studied. This research provides a feasible and simple approach to prepare ZCIS-ZS QDs with large tunable spectral range on visible region, which could greatly contribute to the development of potential applications due to their non-toxicity and excellent optical properties.

Carbon-Nanotube-Based Normally-on-Driving Under-Gate Field Emission Display Panel

A carbon-nanotube-based normally-on-driving under-gate field emission display(FED)panel and its operation principle are presented.In this panel,field emission electrons are extracted directly from the cathode by the high anode voltage.The image is realized by modulating the voltage of under-gate,whose value is less than the cathode voltage,to stop the cathode producing field emission electrons.The electric field inside the emission region is calculated by the finite element method.The emission property of the cathode is also studied by numerical calculation method.The results indicate that a uniform and large emission area can be obtained in this new under-gate FED panel.This study provides powerful theoretic support for the feasibility of this new kind of under-gate FED panel.

Green light-emitting diodes based on hybrid perovskite films with mixed cesium and methylammonium cations

We report the formation of high-quality Cs0.4MA0.6PbBr3 thin films with nearly full surface coverage and good emission properties upon the introduction of Cs^＋ into perovskite crystals. The Cs0.4MA0.6PbBr3 thin films were applied as emissive layers in light-emitting diodes. A maximum external quantum efficiency of -2.0% was achieved for these green-emitting devices.