Infrared study of solids and cast films of long-chain fatty acids

Infrared spectra have been measured for five long-chain fatty acids (CH₃(CH₂)_n COOH; n=14–18) in solid states, KBr discs and cast films. The acids with even- and odd-numbered carbon atoms show structural differences, not only in the solid states but also in the cast films. For example, the molecular orientation of the hydrocarbon chains and the directions of a and b axes of the orthorhombic subcell in the cast films on Au-evaporated glass slides are different in the even-numbered and the odd-numbered acids.     

Second-order non-linear optical effects in Langmuir-Blodgett films

The synthesis of a new series of amphiphilic dyes of the form R¹R²NC₆H₄CH=CHC₅H₄⁺NCH₂CH₂COO^- (R¹=R²=C₆H₁₃,C₁₀H₂₁,C₁₄H₂₉ and C₁₈H₃₇) is described. These dyes have two alkyl chains per chromophore so as to facilitate fast deposition of Langmuir-Blodgett films. We report on the fabrication of monolayer films of these materials and the measurement of optical second harmonic generation in them. We deduce information about molecular tilt orientations and hyperpolarizabilities and compare the latter with previously published values of the electro-optic coefficients.     

Structural and electronic properties of C3N4−nPn (n=0,1,2,3,4)

First principles electronic structure method based on the density functional theory and the local density approximation is used to investigate the structural and electronic properties of C₃N_4−nP_n (n=0,1,2,3,4). It is found that the N-rich compounds energetically favor structures with sp² bonding, while the pseudocubic structure which is characterized by sp³ bonding is preferred by the P-rich compounds. Even though C₃N₄ is a wide-gap semiconductor, the band gap of C₃N_4−nP_n decreases rapidly when N is gradually substituted with P, and the P-rich compounds are predicted to be metallic or narrow-gap semiconductors.     

Arylation of [60]Fullerene with Br2/FeCl3/PhH: Formation of C58 Derivatives via CO Loss

Heating a mixture of [60]fullerene, bromine, ferric chloride and benzene under reflux for 24 h products a range of phenylated [60]fullerene derivatives. The main product is C₆₀Ph₅H but other components identified by mass spectrometry (and in some cases separated by HPLC) are: C_6oPh_n(n = 4, 6, 8, 10, 12), C₆₀Ph_nO₂(n = 4, 6, 8, 10, 12), C₆₀Ph_nOH (n = 7, 9, 11), C₆₀Ph_nH₂ (n = 4, 10), C₆₀Ph₄H₄, C₆₀Ph₅H₃, C₆₀Ph_n0₂H (n = 5, 9), C₆₀Ph₄C₆H₄O₂, C₆₀Ph₉OH₃, and C₆₀Ph₁₁ O₃H₂. In the corresponding reaction with toluene, the crude reaction mixture contained C₆₀(MeC₆H₄)₄ as a main product; C₆₀(ClC₆H₄)₅H was obtained from the reaction with chlorobenzene. Formation of these derivatives is believed to involve radical bromination of the fullerene, followed by electrophilic substitution of the hatogenofullerene into the aromatic, accompanied in some case by hydrolysis, elimination and epoxide formation; oxidation may also introduce ketone/dioxetane functionality. The EI mass spectra of C₆₀Ph₄O₂ and C₆₀Ph₈O₂show degradation to C₅₈Ph_n (n = 0-8), having structures believed to be related to the pseudofollerenes C₆₈Ph_n (n = 0-8) reported recently. These results suggest that some derivatisations of fullerenes confer stability, due to the relief of strain.     

Low temperature UV/ozone oxidation formation of HfSiON gate dielectric

Physical and electrical properties of hafnium silicon oxynitride (HfSi_xO_yN_z) dielectric films prepared by UV ozone oxidation of hafnium silicon nitride (HfSiN) followed by annealing to 450 °C are reported. Interfacial layer growth was minimized through room temperature deposition and subsequent ultraviolet/ozone oxidation. The capacitance–voltage (C–V) and current–voltage (I–V) characteristics of the as-deposited and annealed HfSi_xO_yN_z are presented. These 4 nm thick films have a dielectric constant of 8–9 with 12 at.% Hf composition, with a leakage current density of 3×10⁻⁵ A/cm² at V_fb+1 V. The films have a breakdown field strength >10 MV/cm.     

Preparation and characterization of YBa2Cu3O7−x high Tc superconducting thin films deposited by S-gun sputtering

We have prepared YBa₂Cu₃O_7−x high T_c superconducting (HTS) thin films on (100) yttria-stabilized zirconia (YSZ) and LaAlO₃ (LAO) substrates, using a 2 kW S-gun in an off-axis mode. By varying the temperature of the substrates, films with a axis and c axis orientations were readily obtained. The X-ray diffraction pattern and Laue pattern confirmed that films with a axis orientation exhibited a single-crystal texture. All films had a good mirror-like surface. For films grown on YSZ substrates, scanning electron microscopy (SEM) revealed a clear distinction between the surfaces of the films grown at various temperatures (520–780°C). Films grown on LAO substrates exhibited even smoother and flatter surfaces. The SEM changes will be discussed in correlation with J_c. The best HTS thin films were obtained on LAO substrates at a temperature of 820°C, with T_c=89 K and J_c=1×10⁶ A cm^-2 (77 K).     

Doping and electrical characteristics of in-situ heavily B-doped Si1−x−yGexCy films epitaxially grown using ultraclean LPCVD

Doping and electrical characteristics of in-situ heavily B-doped Si_1−x−yGe_xC_y (0.22<x<0.6, 0<y<0.02) films epitaxially grown on Si(100) were investigated. The epitaxial growth was carried out at 550°C in a SiH₄–GeH₄–CH₃SiH₃–B₂H₆–H₂ gas mixture using an ultraclean hot-wall low-pressure chemical vapor deposition (LPCVD) system. It was found that the deposition rate increased with increasing GeH₄ partial pressure, and only at high GeH₄ partial pressure did it decrease with increasing B₂H₆ as well as CH₃SiH₃ partial pressures. With the B₂H₆ addition, the Ge and C fractions scarcely changed and the B concentration (C_B) increased proportionally. The C fraction increased proportionally with increasing CH₃SiH₃ partial pressures. These results can be explained by the modified Langmuir-type adsorption and reaction scheme. In B-doped Si_1−x−yGe_xC_y with y=0.0054 or below, the carrier concentration was nearly equal to C_B up to approximately 2×10²⁰ cm⁻³ and was saturated at approximately 5×10²⁰ cm⁻³, regardless of the Ge fraction. The B-doped Si_1−x−yGe_xC_y with high Ge and C fractions contained some electrically inactive B even at the lower C_B region. Resistivity measurements show that the existence of C in the film enhances alloy scattering. The discrepancy between the observed lattice constant and the calculated value at the higher Ge and C fraction suggests that the B and C atoms exist at the interstitial site more preferentially.     

Stress variation in epitaxial GaAs films on silicon under thermal treatment

High quality epitaxial GaAs films of 1.8 and 6.3 μm thickness on silicon substrates were examined for lattice distortion, misalignment and curvature by X-ray diffraction (Bond method) at 20–400 °C. These films were deposited by the metal-organic chemical vapour deposition method on the (001) plane of silicon using a buffer layer produced at T_b = 370 or 460 °C. A top layer was then grown at T_t = 560 or 650 °C. The GaAs films contract more strongly on cooling than the substrate, which causes a curvature and a tetragonal distortion below a critical temperature T_c. This temperature varies on thermal treatment at 200–400 °C and approaches T_b, the growth temperature of the buffer layer. The tetragonal distortion can be stabilized, so that T_c approximates T_b, if the GaAs films are annealed for several days at 400 °C.     

Effects of spacer-chain length on the photoelectrochemical responses of monolayer assemblies with ruthenium tris(2,2′-bipyridine) - viologen linked disulfides

Photochemical and photoelectrochemical properties of ruthenium tris(2,2′-bipyridine) (Ru²⁺)-viologen (V²⁺) linked disulfides [RuCnVC₆S]₂ (n (number of methylene groups)=3, 7) with different spacer-chain lengths and Ru²⁺ disulfides [RuC_mS]₂ (m=13, 17) were compared. The luminescence intensity in CH₃CN was in the order of [RuC₁₃S]₂≈[RuC₁₇S]₂>[RuC₇VC₆S]₂[RuC₃VC₆S]₂, implying efficient photoinduced electron-transfer between Ru²⁺ and V²⁺ moieties in the linked compounds. The monolayer assembly of the compound was fabricated on a gold surface. In the presence of triethanolamine, the anodic photocurrent was clearly observed from the RuC_nVC₆S/Au (n=3, 7) electrode (gold electrode modified with [RuCnVC₆S]₂), and its intensity was substantially larger for n=7 than for n=3. Photocurrent action spectra for the RuC_nVC₆S/Au (n=3, 7) electrodes were well correlated with the corresponding electronic absorption spectra in solution. The photocurrent from the RuC₇VC₆S/Au electrode was reduced more effectively by the coexistence of a water-soluble viologen as compared with the RuC₃VC₆S/Au electrode. The photocurrent from the RuC_mS/Au (m=13, 17) electrode was very small. The results suggest that the spacer-chain length between the Ru²⁺ and the V²⁺ moieties profoundly affects the Ru²⁺-sensitized photocurrent.     

Y3+掺杂Li4Ti5O12负极材料的电荷输运特性及电化学性能研究

以Li₂CO₃与锐钛矿型TiO₂为原料,六水合硝酸钇（Y（NO₃）₃·6H₂O）为钇源,采用球磨辅助固相法合成了Li₄Ti_5-xY_xO₁₂（x=0,0.05,0.10,0.15,0.20）负极材料。通过X射线衍射分析（XRD）、扫描电镜（SEM）、能谱仪（EDS）与X射线光电子能谱（XPS）分别对材料的物相与形貌进行表征分析,并利用电化学工作站对材料的电化学性能与电荷输运特性进行测试。结果表明,Y³⁺掺杂没有影响尖晶石型Li₄Ti₅O₁₂（LTO）材料的尖晶石结构,x=0.15时,Li₄Ti_4.85Y_0.15O₁₂样品的离子与电子电导率分别为2.68×10^-7 S·cm^-1和1.49×10^-9 S·cm^-1,比本征材料提升了1个数量级,表现出良好的电荷输运特性。电化学测试表明,Li₄Ti_4.85Y_0.15O₁₂样品在0.1 C倍率首次放电比容量可达171 mAh·g^-1,且在10 C与20 C高倍率下仍然拥有102 mAh·g^-1和79 mAh·g^-1的较高比容量,循环200周次后容量保持率分别为92.6%和89.1%,表现出良好的倍率特性。     

Optical properties of a-(Se70Te30)100−x(Se98 Bi2)x thin films

Measurements of optical constants (absorption coefficient, refractive index, extinction coefficient, real and imaginary part of the dielectric constant) have been made on a-(Se₇₀Te₃₀)_100−x (Se₉₈Bi₂)_x thin films (where x=0, 5, 10, 15 and 20) of thickness 2000 Å in the wavelength range 450–1000 nm. It is found that the optical bandgap decreases with the increase of Se₉₈Bi₂ concentration in the a-(Se₇₀Te₃₀)_100−x(Se₉₈Bi₂)_x system. The value of refractive index (n) decreases, while the extinction coefficient (k) increases with increasing photon energy. The results are interpreted in terms of concentration of localized states varying effective Fermi level.     

Waveguiding properties of pulsed-laser deposition Ca4GdO(BO3)3 thin films

Waveguiding properties of stoichiometric Ca₄GdO(BO₃)₃ (GdCOB) thin films deposited on quartz substrates by the pulsed-laser deposition (PLD) technique are reported. The optical properties and the anisotropy of the obtained thin films are investigated using the prism-coupling technique. Refractive indices (n_x=1.666, n_y=1.673 and n_z=1.680 at 632.8 nm) were, respectively, determined from the transverse electric (TE) and the transverse magnetic (TM) mode excitations. These values are found to be 3% lower than those of the bulk material, which is likely due to the structural and morphological features of the deposited GdCOB films.     

The theory of non-steady state fracture kinetics analysis—1: General theory of crack propagation

The kinetics theory of thermally activated time dependent crack propagation is extended to describe the crack size distribution in non-steady state. The distribution is represented by a series of n differential equations, each expressing the rate of crack tip concentration change over the system of n consecutive energy barriers. The general solution for the set of homogeneous linear first order differential equations developed in this report is of the form ρ_i = Σ_jc_i,je^{−λj_t + C_i}, where ρ_i is the crack tip concentration in the ith valley. The theory takes into consideration the discrete character of solids in contrast with the usual continuum models of fracture studies. The analysis is readily applicable to Regions I and II of stress corrosion cracking.     

Spin transition in a magnetic Langmuir-Blodgett film

Thermal equilibria between electron spin states of different multiplicities are studied in magnetic Langmuir-Blodgett (LB) films of amphiphilic Fe^II(phen)₂ (NCS)₂. Three aliphatic chains 18 carbon atoms long are grafted on the phenanthroline moiety and good LB films are obtained on CaF₂ and quartz substrates.

A temperature-induced spin transition is observed between liquid nitrogen and room temperatures. This transition is characterized in the IR spectral absorption by a 40 cm^-1 frequency up shift of the v doublet when changing from high spin to low spin ground state.

From these preliminary experiments it appears that the spin transition still takes place in a two-dimensional system as it does in the same non-amphilic complex in three-dimensional single crystal form, as described by König.     

Fatigue crack growth characteristics of rotor steels

Room temperature fatigue crack growth rate data were generated for Ni-Mo-V (ASTM A469, Cl-4), Cr-Mo-V (ASTM A470, Cl-8) and Ni-Cr-Mo-V (ASTM A471, Cl-4 and a 156,000 psi yield strength grade) rotor forging steels. Testing was conducted with WOL type compact toughness specimens and the results presented in terms of fracture mechanics parameters. Data show that the Ni-Cr-Mo-V steels exhibit slower fatigue crack growth rates at a given stress intensity range (ΔK) than do the Ni-Mo-V steels. In addition, the Cr-Mo-V steel was found to exhibit slower growth rates than the other alloys at ΔK levels below 40 ksi √in but somewhat foster rates at ΔK levels in excess of 45 ksi √in. The fatigue crack growth rate properties of the alloys studied conform to the generalized fracture mechanics crack growth rate law where da/dN = C₀ΔK^R. It was noted that the fatigue crack growth rate parameters n and C₀ tend to decrease and increase, respectively, with increasing material toughness, K_ic.     

Non-collinear magnetism and exchange couplings in FeCo/Mn superlattices

We present the main results of a systematic study of the magnetic properties of Fe_xCo_{1 − x}/Mn_n for various Fe concentrations x and Mn thicknesses n. We show that the magnetic order in the Mn spacer changes from collinear to non-collinear when the Fe concentration decreases. This behaviour is discussed in relation with a bulk ‘canted’ magnetic state nearly degenerate with the collinear AF order. The origin of the exchange of stability between these two magnetic states is ascribed to a stronger collinear character of the Fe/Mn interface than the Co/Mn one.     

石榴石型Li6.4La3Zr1.4Ta0.6O12对Si/C负极表面固体电解质中间相的调控机制研究

硅(Si)负极在充放电过程中巨大的体积变化会导致固态电解质中间相(SEI)破裂和硅颗粒粉化, 进而造成容量快速衰减。本研究报道了一种利用Li_6.4La₃Zr_1.4Ta_0.6O₁₂(LLZTO)固体电解质调节Si/C负极表面SEI成分的策略。将LLZTO层均匀地涂覆在商用化聚丙烯(PP)隔膜表面, 不仅提高了电解液对隔膜的润湿性, 均匀化锂离子通量, 并且增大了SEI中无机组分的比例, 从而增强Si/C负极的界面稳定性。得益于上述优势, 使用LLZTO修饰的PP隔膜所组装的锂离子电池表现出更为优异的循环稳定性和倍率性能。Li-Si/C半电池的可逆容量为876 mAh·g^-1, 在0.3C (1C=1.5 A·g^-1)的倍率下, 200次循环的容量保持率为81%; 而LFP-Si/C全电池的比容量为125 mAh·g^-1, 在0.3C (1C=170 mA·g^-1)的倍率下循环100次后容量保持率为91.8%。该工作中LLZTO固体电解质调节了Si/C负极表面SEI成分, 为开发高性能硅基锂离子电池提供了新思路。     

A novel highly conducting phosphonium tetracyanoquinodimethane Langmuir-Blodgett film

We describe the properties of pristine and iodine-doped Langmuir-Blodgett films built up from a new semi-amphiphilic tetracyanoquinodimethane (TCNQ) salt, namely trimethyloctadecylphosphonium TCNQ. The films are transferred from a water subphase to a solid substrate. After exposure to diluted iodine vapour, the films become conducting. This behaviour is checked by the IR absorption spectrum. The conductivity estimated from the energy of the maximum of the charge transfer absorption band is about 20–50 Ω^-1 cm^-1.     

Exploring the fracture toughness KIE and KIC of a medium-Strength steel plate using the surface-flaw test

The fracture toughness of a 30 CrMnSiA steel plate of three thicknesses (10,8 and 5 mm) and three widths (110,80 and 56 mm) has been investigated by using surface-flaw method under room temperature. It is not easy to compute the value of K_IE by the maximum applied load. But the values of K_IE and K_IC could be obtained easily, if the computation of the conditional applied load P₁₀ and P₅ based on the relative effective extension Δa/a₀ = 10% and 5% were adopted, together with the conditions of P_max/P₁₀ 1.2 and P_max/P₅ 1.3. The K_R — Δ_a curve, i.e. the resistance-curve described by the parameter K, has been plotted. The values of K_IC and K_IE are then the resistances corresponding to the real extensions of flaws of Δ/a₀ = 2 and 7%, respectively. These values so obtained are in good agreement with the computed values of K_IC and K_IE by using the conditional applied loads. The values of K_IC and K_IE so obtained are also in agreement with the value of K_IC converted from the J-integral and the effective value of K_IE computed by the maximum applied load, respectively.

An approximate relation between K_IC and K_IE has been found to be: K_IC = (0.85˜0.95)K_IE.

The requirements for the dimensions of specimens are: Thickness of plate: B 1.0(K_IC/σ_0.2)² or 1.25(K_ICσ_0.2)²]; Width of plate: 8 W/B 10, 4 W/2c 5; Effective length: l 2W.     

硅片上集成高介电调谐率的柱状纳米晶BaTiO3铁电薄膜

钛酸钡(BaTiO₃)具有优异的介电、铁电、压电和热释电等性能, 在微电子机械系统和集成电路领域具有广泛的应用。降低BaTiO₃薄膜的制备温度使其与现有的CMOS-Si工艺兼容, 已成为应用研究和技术开发中亟需解决的问题。本研究引入与BaTiO₃晶格常数相匹配的LaNiO₃作为缓冲层, 以调控其薄膜结晶取向, 在单晶Si(100)基底上450 ℃溅射制备了结构致密的柱状纳米晶BaTiO₃薄膜。研究表明：450 ℃溅射温度在保持连续柱状晶结构和(001)择优取向的前提下, 能获得相对较大的柱状晶粒(平均晶粒直径27 nm), 一定残余应变也有助于其获得了较好的铁电和介电性能。剩余极化强度和最大极化强度分别达到了7和43 μC·cm^-2。该薄膜具有良好的绝缘性, 在 0.8 MV·cm^-1电场下, 漏电流密度仅为10^-5 A·cm^-2。其相对介电常数ε_r展现了优异的频率稳定性：在1 kHz时ε_r为155, 当测试频率升至1 MHz, ε_r仅轻微降低至145。薄膜的介电损耗较小, 约为0.01~0.03 (1 kHz ~ 1 MHz)。通过电容-电压测试, 该薄膜材料展示出高达51%的介电调谐率, 品质因子亦达到17(@1 MHz)。本研究所获得的BaTiO₃薄膜在介电调谐器件中有着良好的应用前景。