Dual defects of cation and anion in memristive nonvolatile memory of metal oxides

The electrically driven resistance change of metal oxides, called bipolar memristive switching, is a fascinating phenomenon in the development of next-generation nonvolatile memory alternatives to flash technology. However, our understanding of the nature of bipolar memristive switching is unfortunately far from comprehensive, especially the relationship between the electrical transport and the local nonstoichiometry. Here we demonstrate that the coexistence of anion and cation defects is critical to the transport properties of NiO, one of the most promising memristive oxides, by utilizing first-principles calculations. We find that, in the presence of both nickel and oxygen defects, which must exist in any real experimental systems, carrier concentrations of holes generated by nickel defects can be modulated by the presence or absence of oxygen defects around the nickel defect. Such alternation of local nonstoichiometry can be understood in terms of an oxygen ion drift induced by an external electric field. This implication provides a foundation for understanding universally the nature of bipolar memristive switching in various p-type metal oxides.     

Redox-driven conductance switching via filament formation and dissolution in carbon/molecule/TiO2/Ag molecular electronic junctions

Carbon/molecule/TiO2/Au molecular electronic junctions show robust conductance switching, in which a metastable high conductance state may be induced by a voltage pulse which results in redox reactions in the molecular and TiO2 layers. When Ag is substituted for Au as the "top contact", dramatically different current/voltage curves and switching behavior result. When the carbon substrate is biased negative, an apparent breakdown occurs, leading to a high conductance state which is stable for at least several hours. Upon scanning to positive bias, the conductance returns to a low state, and the cycle may be repeated hundreds of times. Similar effects are observed when Cu is substituted for Au and for three different molecular layers as well as "control" junctions of the type carbon/TiO2/Ag/Au. The polarity of the "switching" is reversed when the Ag layer is between the carbon and molecular layers, and the conductance change is suppressed at low temperature. Pulse experiments show very erratic transitions between high and low conductivity states, particularly near the switching threshold. The results are consistent with a switching mechanism based on Ag or Cu oxidation, transport of their ions through the TiO2, and reduction at the carbon to form a metal filament.     

Adsorption of transition metal atoms on the NiO(100) surface and on NiO/Ag(100) thin films

We have studied the adsorption of Au, Pd, and Pt atoms on the NiO(100) surface and on NiO/Ag(100) thin films using plane wave DFT+U calculations. The scope of this work is to compare the adsorption properties of NiO, a reducible transition metal oxide, with those of MgO, a simple binary oxide with the same crystal structure and similar lattice parameter. At the same time, we are interested in the adsorption characteristics of NiO ultra-thin films (three atomic layers) deposited on Ag(100) single crystals. Also in this case the scope is to compare NiO/Ag(100) with the corresponding MgO/Ag(100) films which show unusual properties for the case of Au adsorption. The results show that the transition metal atoms bind in a similar way on NiO(100) and NiO/Ag(100) films, with Pt, Pd, and Au forming bonds of decreasing strength in this order. No charging effects occur for Au adsorbed on NiO/Ag(100) films, at variance with MgO/Ag(100). The reasons are analyzed in terms of work function of the metal/oxide interface. Possible ways to modify this property by growing alternate layers of MgO and NiO are discussed.     

Electron transport and redox reactions in carbon-based molecular electronic junctions

A unique molecular junction design is described, consisting of a molecular mono- or multilayer oriented between a conducting carbon substrate and a metallic top contact. The sp2 hybridized graphitic carbon substrate (pyrolyzed photoresist film, PPF) is flat on the scale of the molecular dimensions, and the molecular layer is bonded to the substrate via diazonium ion reduction to yield a strong, conjugated C-C bond. Molecular junctions were completed by electron-beam deposition of copper, titanium oxide, or aluminium oxide followed by a final conducting layer of gold. Vibrational spectroscopy and XPS of completed junctions showed minimal damage to the molecular layer by metal deposition, although some electron transfer to the molecular layer resulted in partial reduction in some cases. Device yield was high (>80%), and the standard deviations of junction electronic properties such as low voltage resistance were typically in the range of 10-20%. The resistance of PPF/molecule/Cu/Au junctions exhibited a strong dependence on the structure and thickness of the molecular layer, ranging from 0.13 ohms cm2 for a nitrobiphenyl monolayer, to 4.46 ohms cm2 for a biphenyl monolayer, and 160 ohms cm2 for a 4.3 nm thick nitrobiphenyl multilayer. Junctions containing titanium or aluminium oxide had dramatically lower conductance than their PPF/molecule/Cu counterparts, with aluminium oxide junctions exhibiting essentially insulating behavior. However, in situ Raman spectroscopy of PPF/nitroazobenzene/AlO(x)/Au junctions with partially transparent metal contacts revealed that redox reactions occurred under bias, with nitroazobenzene (NAB) reduction occurring when the PPF was biased negative relative to the Au. Similar redox reactions were observed in PPF/NAB/TiO(x)/Au molecular junctions, but they were accompanied by major effects on electronic behavior, such as rectification and persistent conductance switching. Such switching was evident following polarization of PPF/molecule/TiO2/Au junctions by positive or negative potential pulses, and the resulting conductance changes persisted for several minutes at room temperature. The "memory" effect implied by these observations is attributed to a combination of the molecular layer and the TiO2 properties, namely metastable "trapping" of electrons in the TiO2 when the Au is negatively biased.     

Partial Oxidation of Butane to Syngas over Nickel Supported Catalysts Modified by Alkali Metal Oxide and Rare-Earth Metal Oxide

There are abundant supplies of mixture gases containing CH4, C2H6, C3H8 and C4H10, etc. from FCC (Fluidized Catalytic Cracking) tail gas, refinery gas, etc. Commonly, the mixture gases are primarily combusted to carbon dioxide because the complete separation of CH4, C2H6, C3H8 and C4H10, respectively, from the mixture gases may not be economical. Provided that syngas (CO+H2) could be produced from the mixture gases over nickel supported catalysts with high selectivity and conversion,…     

毫秒激光烧蚀镍靶高效率制备NiO纳米立方体

利用长脉宽毫秒激光烧蚀浸没在循环水中的金属镍靶制备了大量的氧化镍(NiO)纳米立方体, 通过透射电子显微镜(TEM)、 选区电子衍射(SAED)、 X射线衍射(XRD)和能量色散谱(EDS)等手段表征了产物的形貌和结构. 结果表明, 高功率密度激光产生的高温高压条件是形成NiO纳米立方体的最重要因素. 激光功率密度高于10⁴ W/cm²时可以生成NiO纳米立方体, 当功率高于该阈值时激光首先将镍靶烧蚀为金属液滴, 高温的金属液体加热周围液体, 并由于液体的限制效应使得压力进一步升高, 最后金属液滴与液体发生表面反应生成NiO纳米立方体.     

LSDA+U方法研究Ni掺杂CuO和Cu掺杂NiO的电子结构和反铁磁学性质

光催化分解水制H2和光催化还原CO2是解决能源危机和全球变暖的有效途径.但是,由于粉末光催化剂存在回收效率低的问题,因而光催化成本很高.而磁性光催化剂便于回收和重复利用,因此人们把目光转向具有磁性的非光催化剂材料,试图通过改性使得磁性材料具有合适的水分解或者还原CO2的氧化还原电位.同时,对具有光催化活性但是没有磁性的材料进行磁化改性可以得到新型的磁性光催化剂.本文通过对本身具有磁性的NiO材料进行Cu掺杂能带调整,使调整后的NiO具有合适的氧化还原电位;对本身具有良好光催化氧化还原电位的CuO材料进行Ni掺杂磁化调整,使磁化后的CuO既有良好的氧化还原电位又有磁性.最终两种材料经过掺杂变成磁性光催化材料,既有较好的光催化性能,又可高效回收,因此有望在光催化领域具有潜在的应用前景.LSDA(局域自旋密度近似)+U(有效库仑相关能)计算方法能够很好地给出磁矩和禁带宽度等电子结构性质.本文通过LSDA+U计算方法对具有磁性的宽禁带半导体材料NiO进行电子结构改性研究,希望通过降低其禁带宽度、调整其氧化还原电位使之对太阳光有响应.因其同时具有磁性便于回收,使得光催化分解水制H2和光催化还原CO2成本高的问题得到解决.对NiO的磁胞进行了Cu掺杂计算,结果发现Cu的掺杂几乎没有引起NiO空间结构的变化,这是因为Cu和Ni的离子半径相近.通过对电子结构的计算发现掺杂体系的禁带变窄,并且在禁带中间出现了两条杂质能级,该杂质能级是由掺杂原子Cu 3d态组成.杂质能级的出现能够降低光生载流子在带隙中的复合,从而提高光催化效率.计算结果同时表明,Cu掺杂的NiO系统具有一个1μB的净磁矩,即Cu的掺杂使得NiO显示出磁性,而Ni的磁矩在掺杂前后几乎保持不变,由纯相的1.67μB增加到掺杂体系中的1.70μB.由于CuO本身低指数(111)面和(011)面具有合适的分解水制H2和还原CO2的氧化还原电位,如果对CuO进行磁化改性,可以使光催化剂CuO同时带有磁性,便于回收再利用.本文对CuO磁胞进行了Ni的掺杂计算.结果表明,由于离子半径相近,Ni掺杂几乎没有引起CuO空间结构的变化.掺杂后的体系具有一个1.66μB的净磁矩,同时Ni的掺杂引起多个杂质能级出现,靠近价带的杂质能级由Cu 3d态组成,而在导带底位置出现的杂质能级主要由Ni 3d态组成.整个能带向高能级方向平移.     

Multicolor and fast electrochromism of nanoporous NiO/poly(3,4-ethylenedioxythiophene) composite thin film

We report a nanoporous NiO/poly(3,4-ethylenedioxythiophene) (PEDOT) composite film using a highly porous NiO film as a template by the combination of chemical bath deposition and electro-polymerization methods. The as-prepared NiO/PEDOT composite film has an interconnecting reticular morphology with nanometer sized pores ranging from 20–150 nm. The NiO/PEDOT composite film exhibits multicolor electrochromism with reversible color changes from purple to light blue brown and presents a transmittance variation of 31% at 600 nm. Fast switching speed is achieved in this composite film, and the response time for oxidation and reduction is 500 and 600 ms, respectively.     

Structural,optical and photocatalytic applications of biosynthesized NiO nanocrystals

NiO is one of the most important candidates for semiconductors metal oxide nanocrystals by the arrangement of photocatalytic application. However, the photocatalytic performance of biosynthesized nanocrystals using Aspalathus linearis (Burm.f.) R. Dahlgren has not been investigated yet. In this contribution, we synthesize α-Ni(OH)₂ using an A. linearis. A heat treatment of the α-Ni(OH)₂ is carried out at 300–400°C for 2?h at normal air yields. Furthermore, we have characterized the structural, optical and photocatalytic activity of the samples. The optical results indicate that biosynthesized nanocrystals exhibit UV–visible light absorption and a narrow range distribution of intense green light (518.95?nm) emission, which decreases significantly as annealing temperature increases. The bandgap energies of the sample annealed at 300–400°C shift to lower photon energy, compared to bulk NiO (～ 4?eV). Moreover, the photocatalytic experimental results reveal that NiO nanocrystals enable color switching of methylene blue.     

EFFECTS OF ALKALI AND RARE EATTH METAL OXIDES ON THE THERMAL STABILITY AND THE CARBON DEPOSITION OVER A NiO/Al_2O_3 CATALYST

采用固定床流动反应装置、ＣＯ吸附、ＴＧ、ＴＰＯ、ＸＰＳ和ＸＲＤ等手段考察了ＮｉＯ／Ａｌ２Ｏ３和ＬｉＮｉＬａＯ／Ａｌ２Ｏ３催化剂上的甲烷部分氧化反应。实验结果表明，ＬｉＮｉＬａＯ／Ａｌ２Ｏ３对甲烷部分氧化反应具有较高的反应活性。锂和镧的添加不仅改善了活性组分镍的分散度，而且提高了ＮｉＯ／Ａｌ２Ｏ３的抗积碳能力和热稳定性     

冷等离子体处理制备NiO/SrTiO3及其光催化水分解制氢性能研究

利用辉光放电等离子体处理改进常规浸渍法制备了NiO/SrTiO3光催化剂. XRD、XPS和TEM分析证明, 金属颗粒在载体表面的分散性得到极大提高, 并在反应中具有很好的稳定性. XPS、热重和XRD分析表明, 等离子体处理使浸渍的Ni(NO3)2在常温下分解为晶化度较低的NiO团簇, 该团簇可能与载体具有较强的相互作用. 在光催化反应中, 高分散的金属可以促进电荷传递, 并提供更多的表面活性位. 对于水分解制氢和甲醇溶液转化制氢反应, 该催化剂的活性分别是常规催化剂的1.3倍和1.8倍.     

NiO/SnO2-ZrO2催化剂的制备及甲烷燃烧催化性能的研究

利用正交分析，通过溶胶凝胶－超临界干燥及复合浸渍的方法制备了NiO/SnO2-ZrO2催化剂，进行了活性评价，考察了前驱物、NiO、SnO2含量及制备方法对催化剂活性及稳定性的影响，并采用XRD、TEM对催化剂进行了表征分析，结果表明：NiO/SnO2-ZrO2催化剂具有良好的甲烷燃烧催化性能（t100%=640 ℃），其活性、稳定性与制备参数密切相关，其中NiO含量是影响催化剂活性、稳定性的最主要参数，它对催化剂稳定性和活性的影响规律正相反； SnO2组分的添加使ZrO2单斜相稳定，对催化剂起到了良好的稳定化作用，发现当SnO2含量在6 mol％左右时，催化剂具有较好的稳定性；对于制备方法，在凝胶前加入活性组分有利于催化剂的高活性，而在凝胶后加入活性组分，则有利于催化剂保持较好的稳定性；活性组分前驱物对催化剂性能影响不大，采用Ni(NO3)2作为前驱物较为合适。     

多孔NiO的制备及其对水中四环素的吸附

采用水热法及高温灼烧合成了多孔金属氧化物NiO,并用于水样中四环素(TC)的吸附。使用扫描电镜(SEM)、傅立叶变换红外光谱(FTIR)以及X-射线衍射(XRD)方法进行表征。结果表明,产物呈现团簇的花朵状结构,表面多孔。考察了pH值、吸附时间、TC浓度及温度对NiO吸附能力的影响。得到NiO吸附TC的最佳pH值为7.0,吸附120 min即可达到吸附平衡,当TC浓度由10 mg/L增加到100 mg/L时,吸附量由26.49 mg/g增加到134.84 mg/g。吸附过程符合准二级动力学模型,通过Langmuir模型拟合得出NiO对TC的最大吸附容量为144.90 mg/g。NiO具有可重复使用、成本低廉、制备方法简单,对TC吸附容量高等优点,适用于污染水体中TC类污染物的快速去除。     

Fabrication,characterization of polyaniline intercalated NiO nanocomposites and application in the development of non-enzymatic glucose biosensor

Determination of glucose plays very important part in diagnostics and management of diabetes. Nowadays, determination of glucose is necessary in human health. In order to develop the glucose biosensor, polymer modified catalytic composites were fabricated and used to detect glucose molecules. In this work, NiO nanostructure metal oxide (NMO) was fabricated via thermal decomposition method and polyaniline (wt% = 2, 4 and 6) assisted nanocomposites (NiO/PANI) were also prepared. The morphology and structure of synthesized nanocomposites were characterized by UV–visible diffusion reflectance spectroscopy (UV–vis-DRS), Fourier transform- infra red spectroscopy (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS) and N₂ adsorption-desorption isotherm measurement. The modified NiO/6%PANI/GCE had higher catalytic activity toward the oxidation of glucose than NiO/GCE, PANI/GCE, NiO/2%PANI/GCE and NiO/4%PANI/GCE. This is due to the larger surface area of NiO/6%PANI nanocomposites provide a ploform for faster electron transfer to the detection of glucose. The constructed glucose biosensor have been exhibited a high sensitivity of 606.13 µA mM⁻¹ cm⁻², lowest detection limit of 0.19 µM, high selectivity, stability, simplicity and low cost for the quick detection of glucose in real sample as well.     

NF3 decomposition over some metal oxides in the absence of water

NF3 decomposition in the absence of water over Al2O3, Fe2O3, Co3O4 and NiO, and transition metal oxides (Fe2O3, Co3O4 and NiO) coated Al2O3 reagents was investigated. The results show that Al2O3 is an active reagent for NF3 decomposition with 100% conversion lasting for 8.5 h at 400 ℃. Fe2O3, Co3O4 and NiO coated Al2O3 reagents are superior to bare Al2O3, and 5%Co3O4/Al2O3 has a high reactivity with NF3 full conversion maintaining for 10.5 h. It is suggested that the presence of transition metal oxide is beneficial to the reactivity of Al2O3, and results in a significant enhancement in the fluorination of Al2O3.     

新型锂离子电池三维结构泡沫NiO电极的制备及电化学性能

通过固相氧化方法,以三维结构泡沫镍为基体和金属镍源,制备了三维结构泡沫氧化镍负极。XRD和SEM结果表明,经500℃氧化处理,泡沫镍基体上形成了NiO微米级的致密活性氧化层。通过充放电测试和循环伏安测试研究了电极的电化学性能,结果表明,三维结构泡沫氧化镍在放电电位区间0.05～3.2VvsLi/Li+,0.2C倍率下充放电,初始容量损失为20%,且经40次循环后,质量比容量为950mAh·g-1,三维泡沫氧化镍电极具有优异的循环容量保持性能。三维泡沫氧化镍具有的大的活性表面积,降低了界面反应的极化,从而提高了NiO电极的倍率放电性能。     

NO在NiO(100)面吸附的DV-Xa簇模型研究

采用量子化学的ＳＣＣ－ＤＶ－Ｘα嵌入簇模型方法考察了ＮＯ／ＮｉＯ（１００）吸附体系的两种不同吸附方法：以Ｎ端在正离子顶位的垂直线性吸附和弯折式吸附方式。     

金属/分子/金属结的电子输运机理与表征

金属/分子/金属结是分子电子学中的基本单元.根据电子的相位是否发生改变,分子结中的电子输运可以分为相干输运和非相干输运两类.在实验上,分子结的表征方法可以分为电学性质表征和非电学性质表征两类.本文借助能级图,首先对分子结的电子输运机理作了简明解释.在此基础上,结合文献报道和本课题组此前的工作,对分子结的一些常用电学表征方法,包括电流-电压特性曲线、电流-时间曲线、电导统计柱状图、转变电压谱、散粒噪声测试、非弹性电子隧道谱和热电效应法进行了介绍.     

Composite PET Membrane with Nanostructured Ag/AgTCNQ Schottky Junctions: Electrochemical Nanofabrication and Charge‐Transfer Properties

Large‐area nanostructured Ag/Ag‐tetracyanoquinodimethane (TCNQ) Schottky junctions are fabricated electrochemically on a mesoporous polyethylene terephthalate (PET) membrane‐supported water/1, 2‐dichloroethane (DCE) interface. When the interface is polarized, Ag⁺ ions transfer across the PET membrane from the aqueous phase and are reduced to form metallic Ag on the PET membrane, which reacts further with tetracyanoquinodimethane (TCNQ) in the DCE phase to form nanostructured Ag/AgTCNQ Schottky junctions. Once the mesoporous membrane is blocked by metallic Ag, a bipolar mechanism is proposed to explain the successive growth of AgTCNQ nanorods and Ag film on each side of the PET membrane. Due to the well‐formed nanostructure of Ag/AgTCNQ Schottky junctions, the direct electrochemical behavior is observed, which is essential to explain the physicochemical mechanism of its electric performance. Moreover, the composite PET membrane with nanostructured Ag/AgTCNQ Schottky junctions is tailorable and can be assembled directly into electric devices without any pretreatment.     

A novel amperometric biosensor based on NiO hollow nanospheres for biosensing glucose

NiO hollow nanospheres were synthesized by controlled precipitation of metal ions with urea using carbon microspheres as templates, which were for the first time adopted to construct a novel amperometric glucose biosensor. Glucose oxidase was immobilized on the surface of hollow nanospheres through chitosan-assisted cross-linking technique. Due to the high specific active sites and high electrocatalytic activity of NiO hollow nanospheres, the constructed glucose biosensors exhibited a high sensitivity of 3.43 μA/mM. The low detection limit was estimated to be 47 μM (S/N = 3), and the Michaelis-Menten constant was found to be 7.76 mM, indicating the high affinity of enzyme on NiO hollow nanospheres to glucose. These results show that the NiO hollow nanospheres are a promising material to construct enzyme biosensors.