原子层沉积Al2O3 保护层氢终端金刚石MISFETs的电学特性

研究了Zr-Si-N氢终端金刚石（H-diamond）绝缘栅场效应晶体管（MISFET）在有无Al₂O₃保护层情况下的电学特性。分别采用原子层沉积法（ALD）和射频溅射法（RF）制备了Al₂O₃保护层和Zr-Si-N栅介质层。MISFETs的转移特性曲线表明,其栅阈值电压在有无Al₂O₃保护的情况下从-2.5 V变化到3 V,表明器件从常关型转换为常开型。输出和转移特性曲线揭示了氧化铝的存在保护了氢终端,使其免受磁控溅射过程的损伤。     

MoS2 coated with Al2O3 for Ni-MoS2/Al2O3 composite coatings by pulse electrodeposition

The MoS₂ powders were coated with Al₂O₃ (5 wt.%) through controlling hydrolysis of Al (NO₃)₃·9H₂O. MoS₂ powder coated with Al₂O₃ was written as MoS₂/Al₂O₃ hereinafter. MoS₂/Al₂O₃ powders were put into Ni plating electrolyte bath. Cetyltrimethylammonium bromide (CTAB) — the surfactant was also put into the bath. The experiment proves that MoS₂/Al₂O₃ particles were absorbed onto the Ni plate. The amount of MoS₂/Al₂O₃ deposited on Ni plate rises with the increasing concentration of MoS₂/Al₂O₃ in the bath. The microhardness, micro-surface, phase and the tribological property of the MoS₂/Al₂O₃ multi-plating coating were measured and analyzed. The performances of microhardness and wear resistance of the Ni-MoS₂/Al₂O₃ composite are better than those of Ni-MoS₂ composite.     

In-situ TiB2 and Al2O3 formation by DC plasma spraying

In-situ plasma spraying (IPS) is a promising process to fabricate composite coatings with in-situ formed thermodynamically stable phases. In the present study, mechanically alloyed Al-12Si, B₂O₃ and TiO₂ powder was deposited onto an aluminum substrate using atmospheric plasma spraying (APS). It has been observed that, during the coating process, TiB₂ and Al₂O₃ are in-situ formed through the reaction between starting powders and finely dispersed in hypereutectic Al-Si matrix alloy. Also, obtained results demonstrate that in-situ reaction intensity strongly depends on spray conditions.     

Microstructure and mechanical properties of Al2O3-Cr2O3 composite coatings produced by atmospheric plasma spraying

Al₂O₃, Al₂O₃-Cr₂O₃ and Cr₂O₃ coatings were deposited by atmospheric plasma spraying. Phase composition of powders and as-sprayed coatings was determined by X-ray diffraction. Electron probe microanalyzer was employed to investigate the polished and fractured surface morphologies of the coatings. Mechanical properties including microhardness, fracture toughness and bending strength were evaluated. The results indicate that the addition of Cr₂O₃ is conducive to the stabilization of α-Al₂O₃. Compared with the pure Al₂O₃ and Cr₂O₃ coatings, Al₂O₃-Cr₂O₃ composite coatings show lower porosities and denser structures. Heterogeneous nucleation of α-Al₂O₃ occurs over the isostructural Cr₂O₃ lamellae and partial solid solution of Al₂O₃ and Cr₂O₃ might be occurring as well. Furthermore, grain refining and solid solution strengthening facilitate the mechanical property enhancement of Al₂O₃-Cr₂O₃ composite coatings.     

Selective catalytic reduction of NO with propene over Au/CeO2/Al2O3 catalysts

Selective catalytic reduction of NO by propene under an oxygen-rich atmosphere has been investigated over Au/ CeO₂, Au/CeO₂/Al₂O₃ and Au/Al₂O₃ catalysts prepared by deposition-precipitation. The results demonstrated that Au/16%CeO₂/Al₂O₃ had good low-temperature activity, selectivity towards N₂ and stability, which is superior to that of Pt/Al₂O₃. It was also found that adding 2% water vapour to the feed stream enhanced the NO conversions at low temperatures while the presence of 20 ppm SO₂ increased NO conversions at higher temperatures. It is particularly interesting that under the simultaneous presence of 2% water vapour and 20 ppm SO₂, the NO conversions to N₂ were significantly increased and the temperature window was widened significantly. The catalysts were characterized by Xray diffraction (XRD), high resolution transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (HRTEM-EDX) and temperatureprogrammed reduction (H2-TPR) techniques. Both XRD and HRTEM revealed that CeO₂ was highly dispersed on the alumina support, and HRTEM combined with EDX showed that gold particles were preferentially deposited on those highly dispersed CeO₂ particles. The gold deposition made CeO₂ more reducible and interaction between gold and those highly dispersed CeO₂ particles became stronger than that with the bulk CeO₂, and this interaction is probably responsible for the superior catalytic performance of the Au/CeO₂/Al₂O₃.     

Nano-grain Al2O3 crystals grown by sputtering of aluminium on CoCrPt thin films for potential application in ultra-high-density recording media

Designing supraceramic assemblies based on Al₂O₃ has remained a challenge due to the problems associated with the suitable dispersion in neat compounds and ability to control the preferred orientation in a unique fashion. Herein, granular HCP-(CoCrPt)_100−X(Al₂O₃)_X (X represents the percent weight) thin films with Si(1 0 0) substrates have been fabricated using sputtering technique followed by annealing treatment. Structural and magnetic properties of thin film have been investigated for potential application in magnetic recording media. It was shown that coercivity increased from 0.5 to 2.5 kOe by increasing the nano-grain Al₂O₃ content in the CoCrPt magnetic layers. In CoCrPt-Al₂O₃ thin films coercivity of 2.5 kOe has been obtained with increasing the Al₂O₃ content from 3 to 13 wt.% in the annealed thin films. The structural properties of the samples were studied using X-ray diffraction (XRD) and transmission electron microscope (TEM) equipped with selected area electron diffraction (SAED). The magnetic properties of the samples were measured with a vibrating sample magnetometer (VSM). The VSM results showed that the HCP-CoCrPt-Al₂O₃ granular films are a promising candidate for ultra-high-density recording media because of its low Al₂O₃ content and simple manufacturing process.     

Effect of a magnetron sputtered (Al2O3-Y2O3)/(Pt-Au) laminated coating on hot corrosion resistance of 8Nb-TiAl alloy

Novel (Al₂O₃-Y₂O₃)/(Pt-Au) laminated coatings were prepared on 8Nb-TiAl alloy by magnetron sputtering methods. (Na₂SO₄-NaCl)-induced hot corrosion and cyclic oxidation tests were adopted to investigate the high-temperature corrosion behaviours and the mechanical properties of the as-prepared laminated coatings. The results revealed that the multi-sealed (Al₂O₃-Y₂O₃) and (Pt-Au) layers can effectively suppress the inward diffusion of oxygen and corrosive fused salt to an extremely low level at 1000 °C and 900 °C respectively. Consequently, the high-temperature corrosion resistance of the 8Nb-TiAl alloy can be significantly improved. In addition, cyclic tests revealed the (Al₂O₃-Y₂O₃)/(Pt-Au) laminated coating can exhibit enhanced spallation and fracture resistance, which are attributable to the brittle/ductile laminated composite structure by means of energy release mechanisms and the increased thermal expansion coefficient of the coating by the addition of Pt-Au alloy.     

Oxygen partial pressure dependence of memory effect of sputtered nc-Al/α-Al2O3 thin films

Nanocrystalline aluminum embedded in amorphous dielectric alumina matrix thin films (nc-Al/α-Al₂O₃) was synthesized via reactive magnetron sputtering. The nc-Al/α-Al₂O₃ films at different oxygen partial pressures were sputtered on p-type Si substrates from a pure Al target in the mixed ambient of Ar and O₂. Both deposition rate and aluminum concentration increase as the oxygen partial pressure decreases. X-ray photoelectron spectroscopy and high-resolution transmission electron microscope studies give the confirmation of nanocrystalline Al embedded in amorphous Al₂O₃ matrix. This nanocomposite thin film exhibits memory effect as a result of charge trapping. The flat band voltage value depends on the Al nanocrystal concentration which is related to oxygen partial pressure.     

Al2O3陶瓷Ti+Nb/Mo金属化对其与Kovar合金钎焊连接的组织和力学性能的影响

采用磁控溅射在Al₂O₃陶瓷表面沉积了Ti+Nb/Mo金属层,实现了氧化铝陶瓷的金属化,并通过电镀镍提高了金属化效果.采用AgCu28钎料,实现了金属化Al₂O₃陶瓷与Kovar合金的可靠连接.通过扫描电子显微镜和能谱观察了钎缝的微观组织.结果表明,钎料与母材发生了明显的界面反应.Cu元素扩散进入Kovar合金,同时Ni元素扩散进入钎料的富铜区,从而促进AgCu/Kovar连接界面的形成;金属化层在Al₂O₃/AgCu钎料界面处,起到了关键作用,其中铌可以抑制脆性化合物形成,缓解残余应力.金属化层镀镍后,钎缝中AgCu共晶区明显,且钎缝较宽,对提高镀镍试样的钎焊接头强度有一定作用.     

ZrCr梯度界面层对Zr/Al2O3涂层体系抗热震性能影响及机理研究

采用中频磁控溅射和超音速等离子喷涂依次在锆合金(Zr-4)基体表面制备了Zr(84.61 at.%)Cr/Zr(17.39 at.%)Cr/Al₂O₃(ZrCr梯度界面层)和Al₂O₃ (无ZrCr梯度界面层)涂层。利用XRD、SEM和HRTEM等重点分析了ZrCr梯度界面层对Zr-4/Al₂O₃涂层界面微观结构、结合强度和抗热震性能的影响。研究结果表明：通过增设ZrCr梯度界面层,能显著提升Zr-4/ZrCr/Al₂O₃体系结合强度至50.3±2.52 MPa,较Zr-4/Al₂O₃体系结合强度值提升约46%;循环热震条件下,Zr-4/ZrCr/Al₂O₃体系膜基界面完整,与ZrCr梯度界面层能显著提升界面结合强度且喷涂及热震实验过程中ZrCr梯度界面层Cr原子优先形成较致密的Cr₂O₃能进一步有效抑制氧扩散至Zr-4有关;Zr-4/Al₂O₃膜基界面则出现明显开裂甚至剥离行为,其主因是Zr-4/Al₂O₃两者界面热应力集中而导致Zr-4/Al₂O₃界面开裂;HRTEM和EDS线扫描结果证实在Zr-4/Al₂O₃界面开裂处形成的疏松ZrO₂氧化物是后续热震循环中进一步加剧涂层大面积剥落失效的根本原因。     

Thermal shock fatigue behavior of TiC/Al2O3 composite ceramics

The thermal shock fatigue behaviors of pure hot-pressed alumina and 30 wt.% TiC/Al₂O₃ composites were studied. The effect of TiC and Al₂O₃ starting particle size on the mechanical properties of the composites was discussed. Indentation-quench test was conducted to evaluate the effect of thermal fatigue temperature difference (ΔT) and number of thermal cycles (N) on fatigue crack growth (Δa). The mechanical properties and thermal fatigue resistance of TiC/Al₂O₃ composites are remarkably improved by the addition of TiC. The thermal shock fatigue of monolithic alumina and TiC/Al₂O₃ composites is due to a “true” cycling effect (thermal fatigue). Crack deflection and bridging are the predominant reasons for the improvement of thermal shock fatigue resistance of the composites.     

TiN/Cr/Al2O3 and TiN/Al2O3 hybrid coatings structure features and properties resulting from combined treatment

New experimental results are presented on the structure and the elemental and phase composition of hybrid coatings, which were deposited on a substrate of AISI 321 stainless steel using a combination of plasma-detonation, vacuum-arc and subsequent High-Current Electron Beam (HCEB) treatment. We found that an increase in energy density intensified mass transfer processes and resulted in changes in aluminum oxide phase composition (γ → α and β → α). Also we observed the formation of a nanocrystalline structure in Al₂O₃ coatings. Electron beam treatment of a hybrid coating surface induced higher adhesion, decreased the intensity of surface wear and increased corrosion resistance in a sulphuric acid solution. The corrosion resistance of the coatings was studied in several electrolytic solutions (0.5 M H₂SO₄, 1 M HCl, 0.75 M NaCl) using electrochemical techniques. In most cases the corrosion resistance was improved, except those in NaCl solutions. The nano-hardness of the protecting coating was 13 GPa before electron beam melting and 9 GPa after it (as a result of TiN and Al₂O₃ sub-layers mixing).     

Al_2O_3/MoS_2复合涂层的制备及摩擦磨损性能

以大气等离子喷涂工艺制备的Al_2O_3陶瓷涂层为模板,利用陶瓷涂层中存在的孔隙和微裂纹,采用水热反应在其内部原位合成具有润滑特性的MoS_2,制备出Al_2O_3/MoS_2的复合涂层。结果表明,通过水热反应在陶瓷涂层原有的微观缺陷中成功合成了MoS_2,合成的MoS_2固体粉末呈类球形状,并且这球状的粉末是由纳米片层状的MoS_2搭建组成的。摩擦试验结果表明,与纯Al_2O_3涂层相比,复合涂层中由于MoS_2润滑膜的形成,其摩擦因数和磨损率都显著降低,且载荷越大,复合涂层的摩擦性能越好。     

HOPG上ALD沉积Al2O3介电薄膜的生长行为研究

本文采用原子层沉积(ALD)的方法,选择三甲基铝(TMA)和H₂O₂作为反应前驱体,在高定向热解石墨(HOPG)基体上沉积Al₂O₃。系统研究了反应温度和生长周次对Al₂O₃生长行为的影响。研究表明：受HOPG表面饱和成键的影响,Al₂O₃在衬底表面处形核困难,在生长初期主要表现为台阶处择优生长,其形态为线状结构。当沉积100周次Al₂O₃时,其中在沉积温度为50 °C、150 °C和200 °C时呈现为纳米线状结构,而在100 °C时呈现为非连续薄膜。随着生长周次的增加,不同温度下沉积态Al₂O₃都趋于形成连续薄膜,表明其生长行为发生了由三维岛状生长模式向二维平面生长模式的转变。分析认为,生长模式的转变是由纳米线状结构横向生长造成的;横向生长速率主要受生长温度影响。拉曼结果表明：沉积后的石墨烯层结构未受影响,可保留其原有的优越性能。     

Impedance analysis of thermally modified SrBi2(Nb0.5Ta0.5)2O9 ceramics

Aurivillius SrBi₂(Nb_0.5Ta_0.5)₂O₉ (SBNT 50/50) ceramics were prepared using the conventional solid-state reaction method. The obtained samples were thermally modified in high vacuum to study the influence of the formed defects on the dielectric and electrical properties of the samples. Scanning electron microscopy with an energy dispersion X-ray spectrometer was applied to investigate the grain structure and stoichiometry of the studied ceramics. Their dielectric properties were determined by impedance spectroscopy measurements. A strong low frequency dielectric dispersion was found to exist in this material which was controlled by thermal modification of the tested ceramics. This phenomenon can be ascribed to the presence of ionized space charge carriers such as oxygen and bismuth vacancies. The dielectric relaxation was defined on the basis of an equivalent circuit. Moreover the temperature dependence of various electrical properties was determined and discussed.     

Ultrasonic machining of Al2O3/LaPO4 composites

Al₂O₃/LaPO₄ composites of varying compositions were drilled on an ultrasonic machine with low carbon steel tools (solid and hollow), in order to evaluate the response to machining. Vickers hardness for different compositions indicate critical load dependency on LaPO₄ content. Significance of LaPO₄ content on material hardness highlights the critical content for good sinterability. X-ray diffraction was done to study the phase content. Acoustic emission (AE) signals emitted by the work piece during machining was also analyzed. Ultrascan inspection was carried out to check for any internal defects. The data presented in the paper illustrate the significance of LaPO₄ addition on machinability of Al₂O₃/LaPO₄ composites in terms of MRR, AE response and hole geometry and associated defects.     

Toughening and strengthening mechanism of plasma sprayed nanostructured Al2O3–13 wt.%TiO2 coatings

The starting materials of Al₂O₃, TiO₂, ZrO₂ and CeO₂ nanoparticles were agglomerated into sprayable feedstock powders and plasma sprayed to form nanostructured coatings. There were net structures and fused structures in plasma sprayed nanostructured Al₂O₃–13 wt.%TiO₂ coatings. The net structures were derived from partially melted feedstock powders and the fused structures were derived from fully melted feedstock powders. The nanostructured Al₂O₃–13 wt.%TiO₂ coatings possessed higher hardness, bonding strength and crack growth resistance than conventional Metco 130 coatings which were mainly composed of lamellar fused structures. The higher toughness and strength of nanostructured Al₂O₃–13 wt.%TiO₂ coatings were mainly related to the obtained net structures.     

Mechanochemical synthesis of Al2O3-TiB2 nanocomposite powder from Al-TiO2-H3BO3 mixture

Alumina-titanium diboride nanocomposite (Al₂O₃-TiB₂) was produced using mixtures of titanium dioxide, acid boric and pure aluminum as raw materials via mechanochemical process. The phase transformation and structural characterization during mechanochemical process were utilized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermogravimetric analyses (TG-DTA) techniques. A thermodynamic appraisal showed that the reaction between TiO₂, B₂O₃ and Al is highly exothermic and should be self-sustaining. XRD analyses exhibited that the Al₂O₃-TiB₂ nanocomposite was formed after 1.5 h milling time. The results indicate that increasing milling time up to 40 h had no significant effect other than refining the crystallite size.     

Fast consolidation of a nanocrystalline Al2O3 reinforced 3.7Fe0.54Cr0.18Al0.26Si0.016 composite from mechanical synthesized powder through pulsed current activated heating

Nanopowders of Fe_0.54Cr_0.18Al_0.26Si_0.016 and Al₂O₃ were synthesized from Fe₂O₃, Cr, Si, and Al powders using high-energy ball milling. A high-density nanocrystalline 3.7Fe_0.54Cr_0.18Al_0.26Si_0.016-Al₂O₃ composite was consolidated with mechanically synthesized powders of Al₂O₃ and 3.7Fe_0.54Cr_0.18Al_0.26Si_0.016-Al₂O₃ through a pulsed current activated sintering (PCAS) method within 1 min. The hardness of the composite and the average grain sizes of Al₂O₃ and Fe_0.54Cr_0.18Al_0.26Si_0.016 were investigated.     

Synthesis and characterization of Al2O3-Ce0.5Zr0.5O2 powders prepared by chemical coprecipitation method

Al₂O₃-Ce_0.5Zr_0.5O₂ catalytic powders were synthesized by the coprecipitation (ACZ-C) and mechanical mixing (ACZ-M) methods, respectively. As-synthesized powders were characterized by XRD, Raman spectroscopy, surface area and thermogravimetric analyses. It was found that the mixing extent of Al³⁺ ions affected the phase development, texture and oxygen storage capacity (OSC) of the Ce_0.5Zr_0.5O₂ powder. Single phase of ACZ-C could be maintained without phase separation and inhibit α-Al₂O₃ formation up to 1200 °C. The specific surface area value of ACZ-C (81.5 m²/g) was larger than that of ACZ-M (62.1 m²/g) and Ce_0.5Zr_0.5O₂ (17.1 m²/g) powders, which were calcined at 1000 °C. In comparison with ACZ-C and Al₂O₃, which were calcined at high temperature (900–1200 °C), it was found that the degradation rate of specific surface area of ACZ-C was lower than that of Al₂O₃. ACZ-C sample showed a higher thermal stability to resist phase separation and crystallite growth, which enhanced the oxygen storage capacity property for Ce_0.5Zr_0.5O₂ powders.