NiO Nanodots Research Articles

Effect of heat treatment on resistive switching memory characteristics of NiO nanodots of tens of nanometers shattered by AFM tips

The characteristics of resistive random access memory (RRAM) at the nanometer scale are increasingly important for RRAM cells with further miniaturization. We report the RRAM characteristics of NiO nanodots in the order of tens of nanometers. NiO nanodots of approximately 70 nm were created on a single-crystal Nb-doped SrTiO3 (Nb:STO) substrate by dip-pen nanolithography. For comparison, a NiO thin film was also deposited on the Nb:STO substrate by spin coating. To reduce the size of NiO nanodots, they were shattered by an atomic force microscope tip, obtaining nanodots of approximately 10 nm. Using a conductive atomic force microscope, we characterized the current according to the applied electric field of the NiO nanodots on the Nb:STO substrate with a capacitor configured of Pt/NiO/Nb:STO substrate. When compared with the NiO thin film, the forming voltage of the NiO nanodots decreased. In addition, the shattered NiO nanodots exhibited unipolar switching characteristics, and the forming and set/reset voltages decreased with the reduction in nanodot size. Furthermore, the NiO nanodots exhibited a substantially reduced forming and set/reset voltages after heat treatment in vacuum. We suggest that the oxygen-depleted layer formed on the surface of NiO nanodots by heat treatment plays a crucial role in the reduction of the forming and operation voltages.

Thickness scaling effects of self-assembled NiO nanodots on resistive switching characteristics

High-density resistive random access memory devices benefit from the reduction in the size of memory cells to a nanoscale. As the RRAM cells become smaller and denser, more stable operation is required. In this study, resistive switching characteristics of self-assembled NiO nanodots on Nb-doped SrTiO3 substrates were examined by using conducting atomic force microscopy. For the NiO nanodot thickness of 8, 6, and 4 nm, the forming voltages were 5.43, 4.63, and 4.12 V, respectively, indicating that the forming voltage decreased as the thickness of NiO nanodots decreased. The SET and RESET voltages also decreased (2.40 and 1.21 V for 8 nm, 2.11 and 0.96 V for 6 nm, 1.86 and 0.82 V for 4 nm, respectively). In addition, as the thickness of the NiO nanodots decreased, the distribution of forming voltages stabilized. We propose that the reduction of the forming voltage distribution is related to the volume of the conductive filaments that were formed in the nanodots. The fabrication of NiO nanodots and the detailed investigation of resistive switching characteristics that depend on the size of the nanodots provide valuable insights for future NiO nanodot resistive random access memory devices.

High photocatalytic activity of a NiO nanodot-decorated Pd/SiC catalyst for the Suzuki-Miyaura cross-coupling of aryl bromides and chlorides in air under visible light

The Suzuki-Miyaura cross-coupling reaction is an effective process for C-C bond formation in organic synthesis. Herein, we report a NiO nanodot-decorated Pd/SiC catalyst, synthesized by atomic layer deposition, which shows high photocatalytic activity for the Suzuki-Miyaura coupling of both aryl bromides and chlorides with phenylboronic acid at 30 °C in air. The Mott-Schottky contact in SiC/Pd enhances the rapid transfer of the photogenerated electrons from SiC to Pd nanoparticles. Moreover, the energy different between the highest occupied molecular orbital of the ultrafine NiO nanodots and the Fermi level of Pd forces a spontaneous electron transfer from NiO to Pd. As a result, the concentrated electrons in the Pd nanoparticles can facilitate the cleavage of C-Br or C-Cl bonds, which normally requires rather high temperatures in thermal processes. The holes left on the SiC support can assist the cleavage of the C-B bond.

In-situ fabrication of 0D/2D NiO/Bi12O17Cl2 heterojunction towards high-efficiency degrading 2, 4-dichlorophenol and mechanism insight

2, 4-dichlorophenol (2, 4-DCP) as a persistent pollutant is frequently detected in water environments, complete eradication of trace which in water is an important task. Hence, a 0D/2D NiO/Bi12O17Cl2 heterojunction was achieved by in-situ fabrication of NiO nanodots on Bi12O17Cl2 nanosheets, which obviously improved the physical, optical and photoelectrochemical properties. The photocatalytic degradation activity of 0D/2D NiO/Bi12O17Cl2 heterojunction was boosted dramatically, which originated from the improved transfer and separation efficiency of charge carriers owing to the formation of Z-scheme heterostructure between NiO and Bi12O17Cl2. The possible photocatalytic reaction mechanism including migration behaviors of charge carriers, generation of reactive species and degradation intermediate products were revealed in depth. This work provides the valuable experiences for designing and fabricating otherwise 0D/2D heterojunction photocatalysts in the application of environmental treating fields.

Turning the product selectivity of nitrile hydrogenation from primary to secondary amines by precise modification of Pd/SiC catalysts using NiO nanodots

The selectivity of nitrile hydrogenation was turned by the concentration of hydrogen radicals on Pd surface.

A combined DFT and experimental study on the nucleation mechanism of NiO nanodots on graphene

The uniformly dispersed defects on the graphene are responsible for forming uniformly dispersed and small-sized NiO NDs.

Built‐In‐Homojunction‐Dominated Intrinsically Rectifying‐Resistive Switching in NiO Nanodots for Selection‐Device‐Free Memory Application

Intrinsically rectifying‐resistive switching (IR‐RS) has been regarded as an effective way to address the crosstalk issue, due to the Schottky diodes formed at the metal/oxide interfaces in the ON states to suppress the sneak current at reverse biases. In this paper, the authors report for the first time another type of IR‐RS that is related to the built‐in homojunction. The IR‐RS study is usually limited to macroscopic samples with micrometer‐order pad‐type electrodes, while this work is on NiO nanodots fabricated with ultrathin anodic‐aluminum‐oxide templates and acting as nanoscaled analogs of real devices. The NiO nanodots show high storage density and high uniformity, and the IR‐RS behaviors are of good device performances in terms of retention, endurance, switching ratio, and rectification ratio. The feasibility of the IR‐RS for selection device‐free memory application is demonstrated by calculating the maximum crossbar array size under the worst‐case scenario to be 3 Mbit.

The effect of size on the resistive switching characteristics of NiO nanodots

NiO nanodots were fabricated via a shattering process using an AFM tip, where an NiO nanodot with a diameter of approximately 90nm was broken into very small pieces. The pieces showed diverse diameters, including three diameters of approximately 10, 20, and 30nm. The NiO nanodots exhibited unipolar switching characteristics including bistable resistivity during 200 repeated switching cycles. Significantly, the magnitude of the “ON currents” was observed to depend on the formation of conducting filaments in the NiO nanodots. We suggest that the critical diameter of the RRAM NiO nanodots is approximately 30nm.

3D interconnected macro-mesoporous electrode with self-assembled NiO nanodots for high-performance supercapacitor-like Li-ion battery

We report a binder-free three-dimensional (3D) macro-mesoporous electrode architecture via self-assembly of 3nm NiO nanodots on macroporous nickel foam for high performance supercapacitor-like lithium battery. This electrode architecture provides a hierarchically 3D macro-mesoporous electrolyte-filled network that simultaneously enables rapid ion transfer and ultra-short solid-phase ion diffusion. Benefitting from the structural superiority owing to the interconnected porous hierarchy, the electrode exhibits supercapacitor-like high rate capabilities with high lithium battery capacities during the discharge-charge process: a very high capacity of 518mAhg−1 at an ultrahigh current density of 50Ag−1. It exceeds at least ~10 times than that of the state-of-the-art graphite anode, which shows only ~50mAhg−1 at ~2 to 3Ag−1 as anode for Li-ion batteries. The preparation method of 3D interconnected hierarchically macro-mesoporous electrode presented here can provide an efficient new binder-free electrode technique towards the development of high-performance supercapacitor-like Li-ion batteries.

Fabrication of Resistive Random Access Memory by Atomic Force Microscope Local Anodic Oxidation

The fabrication of gallium, zinc and nickel oxide nanodots for application of resistive random access memory (RRAM) was demonstrated using the atomic force microscopy (AFM) local anodic oxidation technique. Thin metal films were deposited on indium tin oxide conductive glass substrates. In the atmospheric environment, using AFM equipped with an Ag -coated probe can generate metal oxide nanodots locally on the metal films. These nanodots act as an insulator layer in a single unit cell of the RRAM. The voltage-biased method allows devices to reset from a low-resistance state (LRS) to a high-resistance state (HRS) at 0.9 V. These results show the ability of the AFM local anodic oxidation to produce 50 nm NiO nanodots on glass substrates for potentially high-density RRAMs. As we developed the characteristics of the structure, we found that a lateral NiO nanobelt RRAM performs very low power operation from such experimental manufacturing process. Using a current-biased method, the lateral device switches from a HRS to a LRS with a low writing voltage of 0.64 V.

Size dependent bipolar resistance switching of NiO nanodots for low-power and multi-state operation

NiO nanodots of various sizes were fabricated via anodic oxidation induced through atomic force microscopy (AFM) nanolithography on an 18 nm thick Ni thin film, and their resistance switching properties were investigated using conductive AFM. We found that NiO nanodots with a medium size of around 15 nm height showed clear bipolar resistance switching. A threshold switching was observed in the NiO nanodots with a larger size due to having a much thinner bottom Ni layer left after oxidation. By adjusting the range of the sweeping voltage, the high resistance state can be controlled to realize multi-state switching. The power consumption during the switching process induced by the AFM tip was found to be lower than the reported power values of the NiO thin film- or NiO nanowires-based resistance switching devices.

Self-organization of magnetic nanogroove arrays by LaserMBE and hydrogen reduction.

AbstractThe epitaxially grown magnetic nanostructures including nanodots, nanowires and nanorings have been attracting much scientific and engineering interests because of their expected unique physical characteristics due to quantum effects. These epitaxial nanomagnets and their array are undoubtedly thought to make major contribution to the development of future SPINTRONICS devices, ultra-high density magnetic random access memory (MRAM) and magnetic switching devices for examples, and other quantum devices. In this case, epitaxial growth of the nanomagnets and the resulting anisotropic properties are one of the largest interest as well as fine-nanostructuring. There have been some concerns such as throughput rate with conventional nanoprocessing techniques involving FIB lithography and e-beam lithography, and/or minimization-limit with photolithography due to the wavelength. On the other hand, self-assembly or self-organized methods could also be used for construction of nanopatterns, in which such nanostructures are directly built up from separate atoms. Here we report about formation and characterization of self-organized nanomagnet arrays made of metals and oxides. We have epitaxially grown ferrimagnetic Fe3O4 (111), (Mn0.55Zn0.35Fe0.10)Fe2O4 (111), ferromagnetic Ni (111) and antiferromagnetic NiO (111) nanodots, nanowires and nanogroove arrays on the atomically stepped ultra-smooth sapphire (0001) substrate by LaserMBE. The sapphire (a-Al2O3single crystal) substrates have atomic steps of 0.2 nm in height and atomically flat terraces of 50-100 nm in width so that self-assembly processes of nanomagnet arrays were strongly induced by the energetic instability at the straight and periodic step-edges. In this study, NiO worked as a antiferromagnetic exchange bias layer. On the other hand, NiO was also reduced into ferromagnetic Ni metal by annealing in hydrogen atmosphere in some situations for further applications. Crystallographic and morphology analyses of the nanomagnets were made by in-situ reflection high-energy electron diffraction (RHEED), ex-situ X-ray diffraction (XRD), transmission electron microscope (TEM). and atomic force microscopy (AFM). Magnetic properties were characterized by superconducting quantum interference device (SQUID) magnetometer and magnetic force microscopy (MFM). Further experimentals are conducted for magneto-optical characterizations for above mentioned metal and/or oxide nanomagnet arrays.

Synthesis and characterization of NiO–Ta 2O 5 nanocomposite electrode for electrochromic devices

NiO–Ta 2O 5 nanocomposite electrodes have been synthesized using an RF magnetron co-sputtering system, and their electrochemical and electrochromic properties have been compared with those of single NiO electrodes. Transmission electron microscopy results show that crystalline NiO nano-dots (3–8 nm in size) are embedded in a Ta 2O 5 matrix. X-ray photoelectron spectroscopy results reveal the formation of Ni oxidized states (NiO) and Ta oxidized states (Ta 2O 5). Electrochromic devices fabricated with the nanocomposite electrodes produce high optical modulation (41–95%), fast response time (colored: 3–4 s, bleached: 1 s), high coloration efficiency (ca. 30.5 cm 2 C −1) and good durability, which are much better than those of ones made with the single NiO electrode.