Kinetics of silicides on Si〈100〉 and evaporated silicon substrates

We investigated the growth rates of Ni₂Si, NiSi, Pt₂Si, PtSi and CrSi₂ formed on a Si〈100〉 (Si^c) or an evaporated silicon (Si^e, which is amorphous) substrate during thermal annealing. The same phases of silicides were found on Si^c and Si^e. The growth rates of the silicides formed on Si^c were similar to those formed on Si^e. The formation temperature of CrSi₂ was about 50°C lower on Si^e than on Si^c, and the CrSi₂ film was laterally more uniform on Si^e than on Si^c. We summarize here the results of this and other investigations (e.g. Pd₂Si, Co₂Si, CoSi, CoSi₂, NiSi₂, TiSi₂, and ErSi₂) on the differences in the kinetics of silicides formed on the two substrate types.     

Preparation of CVD diamond coatings on gamma titanium aluminide using MPECVD with various interlayers

CVD diamond coatings were deposited on to γ-TiAl surfaces using a microwave plasma enhanced CVD to improve wear properties and the performance of γ-TiAl. Diamond coatings were directly deposited on to γ-TiAl substrates and deposited on to TiC, Ti₅Si₃, Al₂O₃ + TiO₂, and Si interlayers prepared on γ-TiAl substrates. The diamond coatings deposited directly on γ-TiAl suffered severe delamination and cracked. Those deposited on TiC and Ti₅Si₃ interlayers partially delaminated, whereas those deposited on Al₂O₃ + TiO₂ and Si interlayers adhered well to the underlying surfaces. The diamond films obtained were characterized using scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. Raman spectra showed that polycrystalline and nanocrystalline diamond films grew on γ-TiAl. Residual internal stresses of the diamond coatings deposited on interlayered-γ-TiAl were estimated experimentally from Raman spectra. The coatings prepared on Al₂O₃ + TiO₂/γ-TiAl and Si/γ-TiAl showed lower residual stresses.     

塑料包装材料表面大肠杆菌滋生影响因素研究

目的 选择大肠杆菌为典型致病菌,分析不同塑料包装材料(聚乙烯、聚丙烯、聚酰胺、聚对苯二甲酸乙二酯)、营养状况与温湿度下包装表面大肠杆菌的滋生情况。方法 通过正交试验法分析各因素对大肠杆菌在包装表面滋生的影响规律。着重研究不同塑料材料表面大肠杆菌生物膜附着的影响因素,通过相关性分析确定模型输入参数;并基于这些参数采用反向传播神经网络(BP神经网络)建立不同塑料材料表面大肠杆菌菌落数的预测模型。结果 温度对大肠杆菌在材料表面的生长影响最大,其次为营养状况,材料和相对湿度的影响相对较小。塑料材料的水接触角、表面能、粗糙度和营养肉汤接触角是影响材料表面大肠杆菌生物膜附着的主要因素,基于这些因素建立的塑料材料表面大肠杆菌菌落数的神经网络预测模型的R²超过0.95,具有极高的预测精度。结论 该研究提出了塑料包装材料表面大肠杆菌滋生的关键环境控制因素,并为食品包装材料的选择提供了参考,从而为提升食品安全提供理论依据。     

Effects of substrate material on diamond growth from CO-H2 plasma

Diamond synthesis from CO-H₂ plasma has been carried out on various substrate materials, e.g. metals: nickel, cobalt, tungsten, molybdenum, copper and ceramics: SiC, SiO₂, Al₂O₃, ZrO₂, AlN. Diamond formation was confirmed on every substrate with the exception of cobalt and nickel. The highest density of diamond nucleation, over 10⁸ cm^–2, was obtained on amorphous SiO₂, the carbide-forming metals tungsten and molybdenum and on SiC; on these the nucleation density was one order of magnitude higher than on the other substrates. Diamond films prepared on tungsten, molybdenum and SiC substrates had a strong adhesion force: 1.3 to 1.5 kg mm^–2.     

Voltage Relaxation and Its Influence on Critical Current Measurements

Based on the collective creep model, we numerically studied evolution of electric field and current density in superconductors and its influence on transport measurements of critical current. It is shown that many experimental facts, such as the dependence of V-I curves on sweeping rate of applied current and voltage relaxation are the results of this evolution. The simulation results are confirmed by electric transport measurements on Ag-sheathed Bi_2–x Pb _x Sr₂Ca₂Cu₃O _y tapes. Discussions on influences of the voltage relaxation on electric transport measurements including superconducting critical current are made.     

Viscoelastic properties of hybrid copolymers based on methacryloxypropyl-grafted nanosilica and methyl methacrylate

The linear viscoelastic behavior of “model” hybrid materials based on methyl methacrylate and methacryloxypropyl-grafted nanosilica was investigated. As unique features, the materials under study present an excellent dispersion of silica within the polymer matrix and are almost free of uncross-linked chains. In addition, very progressive changes in network architecture are available, resulting from changes in particle diameter, d, volume fraction of filler, Φ, number of methacryloyl units grafted per surface unit of silica particle, n, and nature of the grafting agent. The influence of these parameters on the characteristics of the mechanically active relaxations α and β was examined. Emphasis was put on the storage modulus, E′, on the loss modulus, E′′, and on their dependence on filler volume fraction. E′′ values were shown to simply account for the reduction of the mechanical energy lost within the material, in connection to the occurrence of polymer molecular motions. Analysis of E′ variations as a function of Φ was based on the theoretical models available in the literature to account for the contribution of the spherical filler particles. In the glassy state, Kerner’s and Christensen and Lo’s models yielded comparable results. In the rubbery state, Guth and Gold’s model was shown to prevail on Kerner’s model.     

Structure, morphology and electrical characterizations of direct current sputtered ZnO thin films

ZnO thin films were deposited on glass substrates by direct current (DC) sputtering technique at room temperature (RT) to 400 °C with a 99.999% pure ZnO target. Then the samples deposited at RT were annealed in air from the RT to 400 °C. The effects of substrate temperature (T_s) and annealing treatment (T_a) on the crystallization behavior and the morphology have been studied by X-ray diffraction and atomic force microscopy. We also compared the structural properties of samples deposited at 400 °C on glass to those deposited on Pt/silicon substrate. The resistivity, surface roughness and size of the grains have also been studied and correlated to the thickness of ZnO films deposited on Pt/Si substrates. The experimental results reveal that the substrate has a major influence on the structural and morphological properties. For the films deposited on glass, below 400 °C, T_s and T_a have a similar influence on the structure of the films. Moreover, the ZnO samples deposited at RT and annealed in air have poor electrical properties.     

Fracture toughness measurements on SiC/Al2O3 composite

Three test techniques are addressed for the measurements of plane strain critical stress intensity factors,K _IC, on monolithic Al₂O₃ and SiC-whisker/Al₂O₃ composite: a four-point test on chevron-notched bend bars; a four-point test on single edge-notched bend bars; and a fractometric test on chevron-notched short bars. The tests were performed on 99.80% Al₂O₃ and 30 vol % SiC whisker-reinforced Al₂O₃. Bend bar test techniques yielded more realistic stress intensity factors,K _IC, on the SiC-whisker/Al₂O₃ composite than the short-bar test results. Chevron-notched bend-bar tests yielded relatively higher critical stress intensity factors, on both Al₂O₃ and SiC/Al₂O₃, possibly due toR-curve effects, suggesting the use of stress intensity factor as a function of crack length instead of using the minimum value. Ambiguous results,K _IC, obtained from short-bar tests on SiC/Al₂O₃ composite, strongly suggests the need to run compliance calibration tests on ceramic composites to determine an appropriateK-factor.     

Interfacial characteristic of (Ba,Sr)TiO3 thin films deposited on different bottom electrodes

Barium strontium titanate (Ba_1?x Sr _x )TiO₃ (BST) thin films were deposited on Pt, Ru, RuO₂, and Pt/RuO₂ electrodes by radio frequency magnetron sputtering. The interfacial structure characteristic of the BST films deposited on various electrodes was investigated. X-ray photoelectron spectroscopy investigations showed that the interfacial diffusion layer in BST/Pt and BST/Ru are approximately 6 and 10 nm, respectively. The BST films are short of Ba and O elements comparing with the stoichiometry Ba_0.65Sr_0.35TiO₃ in the interface region. Dielectric measurement of the BST films with thickness ranging from 70 to 400 nm revealed that the BST films deposited on Pt and Pt/RuO₂ bottom electrodes have similar dielectric property, the BST films deposited on Ru have the highest bulk dielectric constant, and the thickness dependence of dielectric constant on the BST film deposited on RuO₂ electrode can be neglected. The interfacial layer dielectric constant of BST films deposited on Pt and Ru electrodes are estimated to be about 34.5 and 157.1, respectively. The effect of interfacial dead-layer on the dielectric constant could be eliminated through selecting appropriate bottom electrodes.     

Search for low temperature liquid H2 in 2-D films

Thermodynamic, scattering, and nmr measurements on films of H₂, HD, D₂, and mixtures of these molecules adsorbed on MgO and graphite have found phase diagrams for individual monolayers with solid-liquid-vapor triple points ranging from 7.2K (for the 2nd layer of H₂ on MgO) to 5.74K (for a monolayer of H₂ on top of a solid layer of D₂ on graphite). We review the experimental evidence for the proposed phase diagrams.     

Investigation on the composition design and properties study of perovskite lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics can be divided into perovskite, tungsten bronze, and bismuth layered structure ceramics. In recent years, the authors’ group concentrates the researches on the composition design and the properties study of perovskite lead-free piezoelectric ceramics, especially on the (Bi_1/2Na_1/2)TiO₃ (BNT)- and K_1/2Na_1/2NbO₃ (KNN)-based ceramics. All the ceramics were prepared by the conventional ceramic technique. In this paper, the main results obtained are reviewed with emphasis on KNN-based ceramics, including (1) the design on new BNT-based ceramics based on the multiple complex in the A-site of ABO₃ compounds; (2) the design of KNN-based ceramics focused on the effects of Ag ion substitution, K/Na ratio, and LiSbO₃ on KNN-based ceramics; (3) the effects of doping on the properties of BNT- and KNN-based ceramics; and (4) the temperature stability of BNT- and KNN-based ceramics. And some prospects to be resolved in coming years from the viewpoint of the applications of the perovskite lead-free piezoelectric ceramics are also pointed out.     

Studies of bacterial adhesion on TiN, SiO2-TiO2 and hydroxyapatite thin layers deposited on titanium and Ti6Al4V alloy for medical applications

The Staphylococcus epidermidis biofilm formation on titanium or titanium alloy, coated with TiN, SiO₂-TiO₂ and electrodeposited hydroxyapatite, was tested. Surfaces of titanium, Ti6Al4V alloy or TiN, modified with SiO₂-TiO₂ layer, were found to be highly resistant to bacterial adhesion. Only small amounts of bacterial cells were observed on matrices coated by thin hydroxyapatite films, deposited on both SiO₂-TiO₂ and TiN + SiO₂-TiO₂ interlayers. Biological tests showed that the biofilm formed massively on polished and ground titanium and titanium alloy surfaces, also those covered with TiN, but not on those modified with SiO₂-TiO₂ nanofilm.     

Synthesis of vanadium dioxide films by a modified sol-gel process

Vanadium dioxide films have been grown on silicon substrates and on SiO₂ layers on silicon by a modified sol-gel process using methyl cellosolve as a solvent. We have failed to obtain vanadium dioxide layers on Pt/TiO _x /SiO₂/Si substrates. For all of the substrates studied, we have examined the effect of synthesis conditions (initial solution concentration, deposition procedure, and oxidation and reduction anneals) on the phase composition, thickness, and surface morphology of the films.     

Stress and microstructure evolution during growth of magnetron-sputtered low-mobility metal films: Influence of the nucleation conditions

Large tensile stresses (up to 3 GPa) were previously observed in low-mobility metallic Mo_1 − xSi_x films grown on amorphous Si and they were ascribed to the densification strain at the amorphous-crystalline transition occurring at a critical film thickness. Here, we focus on the influence of the nucleation conditions on the subsequent stress build-up in sputter-deposited Mo_0.84Si_0.16 alloy films. For this purpose, growth was initiated on various underlayers, including amorphous layers and crystalline templates with different lattice mismatch, and the stress evolution was measured in situ during growth using the wafer curvature technique. Tensile stress evolutions were observed on amorphous SiO₂ and (111) Ni underlayers, similarly to the stress behaviour found on amorphous Si. For these series, the films were characterized by large in-plane grain size (~ 500 nm). However, on a (110) Mo buffer layer, a different stress behaviour occurred: after an initial tensile rise ascribed to coherence stress, a reversal towards a compressive steady state stress was observed. A change in film microstructure was also noticed, the typical grain size being ~ 30 nm. The origin of the compressive stress source in the metastable Mo_0.84Si_0.16 alloy grown on (110) Mo is discussed based on the stress evolutions measured at varying deposition rates and Ar working pressures, as well as in comparison with stress evolutions in pure Mo films.     

Deposition and characterisation of MoSi2 films

Deposition of MoSi₂ films on silicon and tantalum substrates applying pulsed laser deposition technique has been performed. Crystalline, hexagonal symmetry, MoSi₂ films were prepared directly from stoichiometric MoSi₂ tetragonal target on room temperature and heated substrates (500 °C). Textured MoSi₂ films having privileged (110) and (115) orientations and average crystallite size of about 105 nm were grown on Si(111) substrates with a good degree of axial texture (rocking curve full width half maximum of 1.5°). MoSi₂ films grown on Ta(211) substrates, instead, turned out to be polycrystalline, with an average crystallite size of about 100 nm and 50 nm on substrates kept at room temperature and at 500 °C, respectively. Vickers hardness for 1.2 μm thick MoSi₂ films on Si(111) substrates resulted to be 15 GPa both at room temperature and 500 °C, while for 0.4 μm thick MoSi₂ films on Ta(211) substrates — 26 GPa at room temperature and 30 GPa at 500 °C.     

Atomic layer deposition of Ru films from bis(2,5-dimethylpyrrolyl)ruthenium and oxygen

Ru thin films were grown on hydrogen terminated Si, SiO₂, Al₂O₃, HfO₂, and TiO₂ surfaces by atomic layer deposition from bis(2,5-dimethylpyrrolyl)ruthenium precursor and oxygen. The 4-20 nm thick films on these surfaces consisted of nanocrystalline hexagonal metallic ruthenium, regardless of the deposition temperature. At the lowest temperatures examined, 250-255 °C, the growth of the Ru films was favored on silicon, compared to the growth on Al₂O₃, TiO₂ and HfO₂. At higher temperatures the nucleation and growth of Ru became enhanced in particular on HfO₂, compared to the process on silicon. At 320-325 °C, no growth occurred on Si-H and SiO₂-covered silicon. Resistivity values down to 18 μΩ·cm were obtained for ca. 10 nm thick Ru films.     

Studies of BaTiO3 thin films on different bottom electrode

BaTiO₃ (BT) thin films were prepared on Pt/Ti/SiO₂/Si and Ru/Ti/SiO₂/Si substrates by a modified sol-gel technique. The microstructure of the films was characterized by atomic force microscopy (AFM), X-ray diffraction (XRD) and Raman spectroscopy. The results showed that BT thin films crystallized with perovskite structure. Compared to BT film on Pt/Ti/SiO₂/Si substrate, BT thin film deposited on Ru electrode has similar dielectric constant, while it has higher dielectric loss. C–E curve for BT film on Pt/Ti/SiO₂/Si was more symmetrical around zero-bias field than C–E curve for BT film on Ru/Ti/SiO₂/Si substrate. The tunability was 52.02% for BT film on Pt electrode, which was 33.42% on Ru electrode, at 275 kV/cm and room temperature. The leakage current density of BT on Pt electrode was about an order of magnitude lower than BT film on Ru electrode at the applied electrical field below 150 kV/cm. The leakage conduction mechanism was investigated.     

Phosphorous and boron doping of nc-Si:H thin films deposited on plastic substrates at 150 °C by Hot-Wire Chemical Vapor Deposition

Gas-phase phosphorous and boron doping of hydrogenated nanocrystalline thin films deposited by HWCVD at a substrate temperature of 150 °C on flexible-plastic (polyethylene naphthalate, polyimide) and rigid-glass substrates is reported. The influence of the substrate, hydrogen dilution, dopant concentration and film thickness on the structural and electrical properties of the films was investigated. The dark conductivity of B- and P-doped films (σ_d = 2.8 S/cm and 4.7 S/cm, respectively) deposited on plastic was found to be somewhat higher than that found in similar films deposited on glass. n- and p-type films with thickness below ∼ 50 nm have values of crystalline fraction, activation energy and dark conductivity typical of doped hydrogenated amorphous silicon. This effect is observed both on glass and on plastic substrates.     

Low temperature selective epitaxial growth of SiCP on Si(110) oriented surfaces

We demonstrate growth of SiCP film on Si(110) substrates with excellent structural quality, based on X-Ray Diffraction, Cross-sectional Transmission Electron Microscopy and Secondary Ion Mass Spectrometry analysis. This (110) surface orientation is very important since it represents the sidewall of recessed Source/Drain (S/D) areas when the film is used as an embedded stressor to induce uniaxial tensile strain in a planar transistor. An optimized (110) SiCP growth process can also be used to thicken the S/D regions of non-planar multi-gate device structures (e.g. Fin Field Effect Transistors, Tri-gate FETs) with a highly doped epitaxial film in order to enable good electrical contacts and/or induce strain. The films have been grown using Si₃H₈, SiH₃CH₃ and PH₃ for growth and Cl₂ as the etchant gas, all in inert carrier gas. H₂ has been eliminated, preventing Cl₂ from reacting with H₂ yielding HCl, since Cl₂ is needed to establish selectivity. We present trends on temperature, total pressure, SiH₃CH₃, PH₃ and Cl₂ etch flow. We studied selective epitaxial growth (SEG) in the 525-575 °C range. Thanks to the use of Si₃H₈ we can obtain high SEG rates even at 525 °C in conjunction with a high deposition pressure of 20 kPa (~ 150 Torr). It is observed that the growth rate, carbon concentration, phosphorous concentration and etch rate of SiCP on Si (110) differs greatly from that on Si (100). A process optimized specifically for Si(100) surfaces may yield no growth on Si(110) surfaces. However, optimizing a process on Si(110) is assured to result in growth on Si(100). Comparing one process optimized on Si(110) with the results on Si(100), we found a substantially lower SEG rate, higher [P] incorporation and lower [C] incorporation on Si(110). One key criterion for growth on patterned substrates with Si(110) sidewalls is that the SEG rate on the sidewall must be ≥ 0; otherwise the vertical sidewall will be etched and undercut of the spacer will occur, degrading the structural quality of the transistor and potentially impacting the electrical performance of the device.     

The Optical Conductivity of La2−xSrxCuO4 in Connection with a Charge Stripe Scenario

The in-plane optical conductivity of La_2?xSr_xCuO₄ with 0.07 ≤ x ≤ 0.19 exhibits strong peaks in the far infrared. These features, which depend both on doping and temperature, can be associated with excitations of charge stripes, basing on results of different techniques on the same system and on recent theoretical calculations.