类富勒烯纳米晶CNx薄膜及其场致电子发射特性

利用微波等离子体增强化学气相沉积技术制备出了CN_x薄膜,并利用x射线光电子能谱、x射线衍射、扫描电子显微镜和Raman光谱等测试手段对所制备的CN_x薄膜的微结构和成分进行了分析.研究了其场致电子发射特性.发现薄膜的结构和场发射特性与反应系中的甲烷、氮气及氢气的流量比有关,当甲烷、氢气及氮气流量比为8/50/50 sccm时,制备的薄膜具有弯曲层状的纳米石墨晶体结构（类富勒烯结构）和很好的场发射特性.场发射阈值电场降低至1.1V/μm.当电场为5.9V/μm时,平 关键词： 类富勒烯 x薄膜')" href="#">CN_x薄膜 场致电子发射 微波等离子体增强化学气相沉积     

Temperature evolution of the dielectric response function of Pb(Fe<Subscript>0.95</Subscript>Sc<Subscript>0.05</Subscript>)<Subscript>2/3</Subscript>W<Subscript>1/3</Subscript>O<Subscript>3</Subscript> relaxor ceramics in a wide frequency range

Electrodynamic properties of Pb(Fe_0.95Sc_0.05)_2/3W_1/3O₃ solid solution belonging to A(B'B'')O₃ perovskite structural family have been investigated by broadband dielectric spectroscopy in a wave-number range of (4 × 10^–9–4 × 10³) cm^–1 and a temperature range of 100–600 K. The influence of low-frequency relaxations on the vibrational spectrum is determined within the four-parameter factorized dispersion model. Anomalies in the behavior of the dielectric response function are found near the temperature-diffuse maximum of permittivity.     

Growth and field emission properties of globe-like diamond microcrystalline-aggregate

The globe-like diamond microcrystalline-aggregates were fabricated by microwave plasma chemical vapor deposition (MPCVD) method. The ceramic with a Ti mental layer was used as substrate. The fabricated diamond was evaluated by Raman scattering spectroscopy, X-ray diffraction spectrum (XRD), and scanning electron microscope (SEM). The field emission properties were tested by using a diode structure in a vacuum. A phosphor-coated indium tin oxide (ITO) anode was used for observing and characterizing the field emission. It was found that the globe-like diamond microcrystalline-aggregates exhibited good electron emission properties. The turn-on field was only 0.55 V/μm, and emission current density as high as 11 mA/cm² was obtained under an applied field of 2.9 V/μm for the first operation. The growth mechanism and field emission properties of the globe-like diamond microcrystalline-aggregates are discussed relating to microstructure and electrical conductivity.     

Magnetic field effects on the hydrogen abstraction reaction of triplet 4-methoxybenzophenone with thiophenol as studied by a picosecond laser flash photolysis technique

The hydrogen abstraction reaction of triplet 4-methoxybenzophenone with thiophenol at 265 K has been studied with a newly developed picosecond laser flash photolysis apparatus under magnetic fields of 0–1.7 T. The decay rate constant of the radical pair generated was found to increase from 3.42 × 10⁹ s^?1 to 4.15 × 10⁹ s^?1 with increasing the magnetic field from 0 to 1.7 T. The observed magnetic field effects can be explained by the Δg mechanism. Using the simple kinetics model with the Δg mechanism, the rate constant of the escape process from the pair (k _esc) and two rate constants for the T-S spin conversion process (k _T-S) at 0 and 1.7 T were found to be 1.97 × 10⁹ s^?1, 1.45 × 10⁹ s^?1, and 2.12 × 10⁹ s^?1, respectively. From the magnetic field dependence on k _T-S, the difference in the g values of the 4-methoxybenzophenone ketyl and phenylthiyl radicals was estimated to be 0.0087.     

Electric‐field tuning of magnetoelectric properties in Metglas/piezofiber composites

The tunability of magnetoelectric (ME) properties by applied dc electric field (E) was systematically investigated for a laminate composite consisting of Metglas, Pb(Zr_x Ti_1–x)O₃ fiber, and interdigitated electrodes. The ME coefficients and equivalent magnetic noise were found to be dependent on E. This dependence is attributed to variations in the magnetic properties. The dielectric properties and noise charge density were relatively invariant to E. A 1.3× improvement in the ME coefficient was obtained at the Villari point under E = 300 V/mm relative to E = 0 V/mm. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

入射电子能量对低密度聚乙烯深层充电特性的影响

高能带电粒子与航天器介质材料相互作用引起的深层带电现象, 一直是威胁航天器安全运行的重要因素之一. 考虑入射电子在介质中的电荷沉积、能量沉积分布以及介质中的非线性暗电导和辐射诱导电导, 建立了介质深层充电的单极性电荷输运物理模型. 通过求解电荷连续性方程和泊松方程, 可以得出不同能量 (0.1–0.5 MeV) 电子辐射下, 低密度聚乙烯 (厚度为1 mm) 介质中的电荷输运特性. 计算结果表明, 不同能量的电子辐射下, 介质充电达到平衡时, 最大电场随入射能量的增加而减小; 同一能量辐射下, 最大电场随束流密度的增大而增加. 入射电子能量较低时 (≤ 0.3 MeV) , 最大电场随束流密度的变化趋势基本相同. 具体表现为: 当束流密度大于3× 10^-9 A/m²时, 最大场强超过击穿阈值2×10⁷ V/m, 发生静电放电 (ESD) 的可能性较大. 随着入射电子能量的增加, 发生静电放电 (ESD) 的临界束流密度增大, 在能量为0.4 MeV时, 临界束流密度为6×10^-8 A/m². 当能量大于等于0.5 MeV时, 在束流密度为10^-9–10^-6 A/m²的范围内, 均不会发生静电放电 (ESD) . 该物理模型对于深入研究深层充放电效应、评估航天器在空间环境下 深层带电程度及防护设计具有重要的意义. 关键词： 高能电子辐射 低密度聚乙烯(LDPE) 介质深层充电 电导特性     

Field electron emission of carbon-based nanocone films

Diamond nanocone, graphitic nanocone, and mixed diamond and graphitic nanocone films have been synthesized through plasma enhanced hot filament chemical vapor deposition (HFCVD). The field emission properties of these films have been experimentally investigated. The studies have revealed that all three kinds of nanocone films have excellent field electron emission (FEE) properties including low turn-on electric field and large emission current at low electric field. Compared with the diamond nanocone films (emission current of 86 μA at 26 V/μm with the turn-on field of 10 V/μm), the graphitic nanocone films exhibit higher FEE current of 1.8×10² μA at 13 V/μm and a lower turn-on filed of 4 V/μm. The mixed diamond and graphitic nanocone films have been found to posses FEE properties similar to graphitic nanocone films (emission current of 1.7×10² μA at 20 V/μm with the turn-on field of 5 V/μm), but have much better FEE stability than the graphitic nanocone films. PACS 81.07.Bc; 81.05.Uw; 79.70.+q     

Resonance magnetoelectric effect without a bias field in a piezoelectric langatate-hysteretic ferromagnet monolithic structure

The frequency, field, temperature, and amplitude characteristics of the direct magnetoelectric effect are studied in a planar monolithic structure consisting of a piezoelectric langatate crystal and a layer of electrolytic nickel. A relation between the magnetic and magnetoelectric properties of the structure is demonstrated, which explains the effects observed in structures with hysteretic layers. At the planar acoustic resonance frequency of the structure (about 70 kHz), the effect amounting to 23 V/(Oe cm) in the absence of a bias field is discovered. In the temperature interval 150–400 K, the amount of the effect changes nearly twofold, the resonance frequency changes by about 1%, and the Q factor on cooling rises to about 8 × 10³. The field sensitivity of the structure is on the order of 1 V/Oe, which makes it possible to detect magnetic fields with an amplitude down to ～10^?6 Oe.     

Low voltage organic field effect transistors with a poly(hexylthiophene)–ZnO nanoparticles composite as channel material

We report on solution processable organic field effect transistors prepared using a poly(3‐hexylthiophene)–ZnO nanoparticles composite as channel semiconductor material and cross‐linked polyvinyl alcohol as gate insulator. Our transistors show a field effect mobility of 0.35 ± 0.06 cm²/V s, threshold voltage of –1.30 ± 0.11 V, and I_on/I_off ratio of (1.0 ± 0.1) × 10³. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Noncontact characterization of glucose by a waveguide microwave probe

We investigate the electromagnetic field interaction with a glucose aqueous solution using a microwave dielectric waveguide probe to evaluate the glucose concentrations. A microwave dielectric waveguide probe allows observation of the small variation of the glucose concentration changes in the range of 0–300 mg/ml by measuring the change of the microwave reflection coefficient. We could observe the effect of concentration change of glucose with a detectable resolution up to 0.5 mg/ml at an operating frequency of about f = 2.0–2.5 GHz. The change of the glucose concentration is directly related to the change of the reflection coefficient due to the electromagnetic interaction between the dielectric waveguide resonator and the glucose aqueous solution. The operational principal is explained by a plane-wave solution model. A glucose biosensor using a microwave dielectric waveguide probe provides a unique approach for glucose monitoring.     

Nonlinear properties of barium titanate in the electric field range 0≤<Emphasis Type="Italic">E</Emphasis>≤5.5×0<Superscript>7</Superscript> V/m

X-ray structural studies and dielectric measurements of BaTiO₃ single crystals were performed in the dc electric field range 0≤E≤5.5×10⁷ V/m. The field dependence of the tetragonal cell parameter obtained was used to calculate the field dependence of the piezoelectric modulus d₃₃. The piezoelectric modulus d₃₃ and the dielectric permittivity vary in magnitude by a factor of two with the field varied in the above range. The observed nonlinear behavior is shown to fit well to a relation connecting the dielectric with the electromechanical characteristics of the crystal.     

Ferroelectric and optical properties of Ba6Ti2Nb8O30 single crystals

The dielectric, optical and non-linear optical properties of Ba₆Ti₂Nb₈O₃₀ single crystals were examined from room temperature up to the Curie temperature of 245°C. The spontaneous polarization at room temperature was estimated as 0·22±0·01 C/m². The linear electrooptic constants were measured as r₃₃^T=(1·17±0·02)×10^?10 and r₁₃^T=(0·42±0·01)×10^?10 m/V. The non-linear optical coefficients were d₃₃=(15·1±2·0)×10^?12 and d₃₁=(11·0±2·0)×10^?12 m/V, which are comparable to those of Ba₄Na₂Nb₁₀O₃₀. Temperature dependences of δ₃₃ and δ₃₁ (Miller's δ) were found to be proportional to that of P_s.     

高能电子辐射下聚四氟乙烯深层充电特性

介质深层充放电现象是诱发航天器异常故障的重要因素之一.分析了高能电子辐射下介质内部电荷沉积、能量沉积特性和电导特性,考虑了真空与介质界面电荷对电场分布的影响,建立了介质二维深层充电的物理模型,并基于有限元方法实现了数值计算.计算了高能电子辐射下聚四氟乙烯的深层充电特性.结果表明:真空环境下,介质的表面存在较弱的反向电场,随着介质深度增大,电场减小至零,随后逐渐增大,最大值出现在靠近接地附近,但在接地点,电场存在小幅降低.分析了不同辐射时间下(1 h,1 d,10 d和30 d),介质内部最大电位和最大电场的时空演变特性.随着辐射时间的增加,最大电位由-128V增加至-7.9×104V,最大电场由2.83×105V·m-1增加至1.76×108V·m-1.讨论了入射电子束流密度对最大电场的影响,典型空间电子环境(1×10-10A·m-2)下,电子辐照10 d时,介质内部最大电场为2.95×106V·m-1.而恶劣空间电子环境(2×10-8A·m-2)下,电子辐射42 h,介质内部最大电场即达到108V·m-1,超过材料击穿阈值(约为108V·m-1),极易发生放电现象.该物理模型和数值方法可以作为航天器复杂部件多维电场仿真的研究基础.     

A novel inverse numerical modeling method for the estimation of water and salt mass transfer coefficients during ultrasonic assisted-osmotic dehydration of cucumber cubes

The objective of this paper was to study the moisture and salt diffusivity during ultrasonic assisted-osmotic dehydration of cucumbers. Experimental measurements of moisture and salt concentration versus time were carried out and an inverse numerical method was performed by coupling a CFD package (OpenFOAM) with a parameter estimation software (DAKOTA) to determine mass transfer coefficients. A good agreement between experimental and numerical results was observed. Mass transfer coefficients were from 3.5 × 10⁻⁹ to 7 × 10⁻⁹ m/s for water and from 4.8 × 10⁻⁹ m/s to 7.4 × 10⁻⁹ m/s for salt at different conditions (diffusion coefficients of around 3.5 × 10⁻¹²–11.5 × 10⁻¹² m²/s for water and 5 × 10⁻¹² m/s–12 × 10⁻¹² m²/s for salt). Ultrasound irradiation could increase the mass transfer coefficient. The values obtained by this method were closer to the actual data. The inverse simulation method can be an accurate technique to study the mass transfer phenomena during food processing.     

Spray pyrolised Al/ZnO: Al heterojunction: Effect of Al on junction properties

Al/ZnO: Al heterojunction was fabricated by depositing ZnO: Al film on Al substrate by spray pyrolysis technique at 220 °C substrate temperature. XRD, SEM and EDAX techniques were used to study the properties of thin films. Heterojunction properties were studied by I–V and C–V measurements. The fabricated Al/ZnO: Al junctions were rectifying in character. The room temperature ideality factors of Al/ZnO: Al junctions are found to vary from 2.56 to 5.45. The reverse saturation currents are 5.21 × 10⁻⁹, 1.35 × 10⁻⁶, 1.99 × 10⁻⁶, 9.99 × 10⁻⁷ and 1.02 × 10⁻⁷ A for Al/ZnO: Al junctions. Junction forward current depends on doping concentrations and temperature, whereas reverse saturation current remains independent for Al concentration. The built-in-potential calculated from capacitance for Al/ZnO: Al junctions are 2.74, 2.60, 2.0, 2.50 and 2.43 V corresponding to 1, 2, 3, 4 and 5 mol% of Al. X-ray diffraction study confirmed that the films are polycrystalline, orientated in (0 0 2) plane. Scanning electron microscopy study confirmed circular ring patterns with inside ribbon type structure for Al doped ZnO films.     

Operation of activated-fullerene-coated field emitters in technical vacuum

The operation of tungsten tip field emitters coated by activated fullerenes in technical vacuum is studied. Ways of emitter training to provide the self-reproducibility of the coatings and their long service life under intense ion bombardment in wide ranges of pressures, from 2 × 10^?8 to (5–7) × 10^?7 Torr, and emission currents, from (1.5–2.0) to (10–20) μA, are developed.     

Third-order nonlinear optical properties of gold nanoshells in aqueous solution

The third-order nonlinear optical properties of gold nanoshells in aqueous solution have been investigated by using open- and closed-aperture Z-scan methods. The real and imaginary third-order nonlinear susceptibilities are obtained to be about -1.1422×10^-13 and -2.4302×10^-14 esu, respectively. We further have investigated the electric field enhancement for gold nanoshells in aqueous solution by means of a finite-element method and ascribed the small third-order nonlinear susceptibility to the smaller volume fraction and local field factor. PACS  42.65.Re; 78.67.Bf; 73.22.Lp     

Impact ionization in silicon dioxide

The dielectric strength of silicon dioxide is related to the breakdown field at which electron-hole pairs can be generated by inverse Auger scattering of hot electrons. This field is calculated to be about 3 × 10⁷ V/cm for a 300°K ambient oxide.     

An analytical method for DC negative corona discharge in a wire-cylinder device at high temperatures

This paper proposes an analytical solution for DC negative corona discharge in a wire-cylinder device based on experimental results in which both the corona and drift regions are considered; this approach aims to provide a theoretical method for analyzing electrostatic precipitation at high temperatures. The inter-electrode space is divided into three zones, namely, the ionization layer, the attachment layer (corona region) and the drift region, to investigate the space charge concentration and the electric field distribution. The boundary of the ionization layer is assumed to be the radius at which the rate of ionization balances that of electron attachment. The radius where the value of E/N equals 110 Td is recommended as the boundary of the attachment layer. It was determined that an increasing temperature leads to a decrease in the largest space charge number density and the largest electric field in the drift region that can be provided by a discharging device. With respect to the device in the present work, when the temperature increases from 350 °C to 850 °C, the largest electric field decreases from ∼9 × 10⁶ V/m to ∼3 × 10⁶ V/m, and the largest charge number density decreases from ∼1.3 × 10¹⁵ m⁻³ to 6.4 × 10¹⁴ m⁻³. The radius of the corona region, the space charge number density and the electric field increase as the applied voltage increases at a given temperature. For example, at a temperature of 550 °C, when the applied voltage increases from 10,500 V to 18,879 V, the radius of the corona region increases from ∼2.9 mm to ∼4.9 mm. It appears to be unreasonable to use a constant value that is calculated from Peek's formula as the electric field at the surface of the cathode under all of the conditions.     

Linear HgCdTe IR FPA 288×4 with bidirectional scanning

The long wavelength (8–12 μm) IR FPA 288×4 based on a hybrid assembly of n⁺-p diode photosensitive arrays (PA) of HgCdTe (MCT) MBE-grown structures and time delay integration (TDI) readout integrated circuits (ROIC) with bidirectional scanning have been developed, fabricated, and investigated. The p-type MCT structures were obtained by thermal annealing of as-grown n-type material in inert atmosphere. The MCT photosensitive layer with the composition 0.20–0.23 of mole fraction of CdTe was surrounded by the wide gap layers to decrease the recombination rate and surface leakage current. The diode arrays were fabricated by planar implantation of boron ions into p-MCT. The typical dark currents were about 4–7 nA at the reverse bias voltage of 150 mV. The differential resistance R was up to R₀ = 1.6×10⁷ Ω zero bias voltage, which corresponded to R₀A ～70 Ω ·cm² and to the maximal value R_max = 2.1 × 10⁸ Ω. The bidirectional TDI deselecting ROIC was developed and fabricated by 1.0-μm CMOS technology with two metallic and two polysilicon layers. The IR FPAs were free of defect channels and have the average values of responsivity S_λ = 2.27×10⁸ V/W, the detectivity D_λ ^* = 2.13 × 10¹¹ cm × Hz^1/2 × W^t1, and the noise equivalent temperature difference NETD = 9 mK.