Nickel Caps Research Articles

Dynamics of magnetic Janus colloids studied by ultra small-angle X-ray photon correlation spectroscopy.

The orientation behavior and the translational dynamics of spherical magnetic silica-nickel Janus colloids in an external magnetic field have been studied by small-angle X-ray scattering and X-ray photon correlation spectroscopy at ultra small-angles. For weak applied fields and at low volume fractions, the particle dynamics is dominated by Brownian motion even though the net magnetic moments of the individual particles are aligned in the direction of the field as indicated by the anisotropy in the small-angle scattering patterns. For higher fields the magnetic forces result in more complex structural changes with nickel caps of Janus particles pointing predominantly along the applied magnetic field. The alignment ultimately leads to chain-like configurations and the intensity-intensity autocorrelation functions, g2(q,t), show a second slower decay which becomes more pronounced at higher volume fractions. A direction dependent analysis of g2(q,t) revealed a faster than exponential decay perpendicular to the field which is related to the sedimentation of magnetically ordered domains. The corresponding velocity fluctuations could be decoupled from the diffusion of particles by decomposing g2(q,t) into advective and diffusive contributions. Finally, the particle dynamics becomes anisotropic at higher volume fractions and strong magnetic fields. The derived translational diffusion coefficients indicate slower particle dynamics perpendicular to the field as compared to the parallel direction.

Magnetically responsive polymer nanopillars with nickel cap

Embedding magnetic particles within polymer matrix is a common and facile method to fabricate magnetically responsive micro-/nanoscale pillars. However, the balance between mechanical compliance and magnetic susceptibility cannot be decoupled and the particles are limited by the pillar feature size, which can limit the actuation performance. Here we demonstrate a new type of magnetically responsive nanostructure consisting of a polydimethylsiloxane (PDMS) nanopillar array with deposited nickel caps, that has successfully achieved such decoupling with multiple cap-geometry designs for a better actuation control. The actuation result of nanopillars with 540 nm period and 1.3 μm height has been analyzed using image processing, leading to a maximum displacement of 180 nm with a ratio of 13.9% with respect to the pillar height. Magnetic and mechanical models based on magnetic force and torque have been developed and used to mitigate the weakening effect of the actuation by the residual magnetic layer. This structure demonstrates a feasible strategy for magnetic actuation at the sub-micrometer scale with freedom to design magnetic cap and polymeric pillar separately. This structure can also be utilized in multiple applications such as tunable optical elements, dynamic droplet manipulation, and responsive particle manipulation.

Fabrication of Si3N4/SiO2 tiered resonant nanopillars with nickel caps arrays: application for optochemical sensing

A controlled, 3D selective inductively coupled plasma reactive ion etching process (ICP-RIE) was employed to fabricate high aspect ratio tiered resonant nanopillars (TR-NPs) made of two Bragg reflectors consisting of a stack of Si3N4/SiO2 alternate layers, a resonant SiO2 central cavity, and nickel caps. The 3D etching process led to a vertical full etching, and also to a horizontal highly selective etching that preserves SiO2 layers while the Si3N4 layers are slowly etched. Resulting TR-NPs periodic arrays were tested as optical sensors and highlighted a 28% increment in bulk sensitivity (379 nm RIU−1) comparing with conventional Si3N4/SiO2 resonant NPs without metal caps (296 nm RIU−1) considering the resonance feature located in the 580-630 nm wavelength range.

Mechanical resistance of patterned BCB bonded joints for MEMS packaging

Adhesive wafer bonding is an interesting key technology for heterogeneous integration of films or devices coming from different technologies in the view of 3D heterogeneous integration of NEMS/MEMS. An original wafer level MEMS packaging process consists in the transfer of nickel caps from a temporary wafer to the target wafer carrying the devices to be packaged. In this process the polymer used as sealing ring is submitted to a first mechanical loading as the film cap is removed from the donor wafer. It is therefore important to have quantitative data about the mechanical resistance of the bond in order to ensure its integrity after the fabrication process. In this study, wedge insertion method and four-point bending test are used to characterize bonds of silicon wafers without and with a nickel interlayer. The adhesive polymer is a photosensitive benzocyclobutene (BCB) resin patterned into lines either parallel or perpendicular to the crack growth direction. The measured fracture energies completed by observations of the fracture surfaces allows the identification of various parameters influencing the resistance of the stack. A first parameter is the adhesive lines orientation: when BCB lines are perpendicular to the crack growth direction higher adhesion energies are measured than when they are parallel to this direction. A second parameter is the BCB curing atmosphere: adhesive bonds that experienced a curing treatment in N2 gas have higher fracture resistance than those cured in vacuum. Finally, the addition of a nickel film between the silicon wafer and the BCB adhesive embrittles the mechanical resistance of the bond because Ni has a poor adhesion both on silicon and on BCB.

Electric-field mediated nickel-induced nanocrystallization of amorphous silicon thin films in the complete absence of external heating

DC electric-field mediated nanocrystallization of thermally evaporated silicon thin films with nickel as seed/cap layer has been attempted in complete absence of any external heat input. When 60 nm Si thin film coated onto 5 nm Ni thin film was treated by a direct current (DC) electric field (up to 3.3 kV/cm up to 5 minutes) after the deposition, amorphous silicon thin films became nanocrystalline (6–10 nm). Silicon nanograins (average diameter 90 nm) grow to larger sizes (average diameter 240 nm) with sharpening of grain size distribution. Huge grain growth (4-fold increase) has been observed when nickel was used as cap layer (5 nm Ni/60 nm Si). XRD data show the signature of nickel silicide formation on the surface in nickel cap layer case. Field treatment has changed the optical absorption edge (shifts left in nm units) and the refractive index of silicon thin film when nickel was used as under layer, and an almost negligible effect on the optical properties has been observed when nickel was used as cap layer.

A Remarkable Member of the Polyoxometalates: The Eight-Nickel-Capped α-Keggin Polyoxoazonickelate

The eight-nickel-capped polyoxoazonickelate, [Ni(20)(OH)(24)(MMT)(12)(SO(4))](NO(3))(2).6H(2)O (1; MMT = 2-mercapto-5-methyl-1,3,4-thiadiazole), has been synthesized, which has an alpha-Keggin structure with eight nickel caps. In this structure, the polyatom is the late transition metal Ni(II); the central heteroatom is S, and the organic terminal ligand becomes the primary part of the Keggin structure. This is a Keplerate-type cluster, which shows a central Ni(II)(12) cuboctahedron formed by the 12 Ni(II) centers of the classical alpha-Keggin core and a Ni(II)(8) hexahedron formed by the eight nickel caps.

Deltahedral Germanium Clusters: Insertion of Transition-Metal Atoms and Addition of Organometallic Fragments

Reactions of nine-atom deltahedral clusters of germanium with Ni(COD)2 and/or Ni(PPh3)2(CO)2 in ethylenediamine yielded the Ni-centered heteroatomic 10-atom clusters [Ni@(Ge9Ni-CO)]2- and [Ni@(Ge9Ni-en)]3-, as well as the empty 10-atom heteroatomic cluster [Ge9Ni-CO]3-. A ligand exchange reaction between [Ni@(Ge9Ni-CO)]2- and potassium phenylacetylide produced the organically functionalized species [Ni@(Ge9Ni-CCPh)]3-. The empty cluster [Ge9Ni-CO]3- is a bicapped square antiprism where one of the capping vertexes is the nickel atom. The other three clusters are tricapped trigonal prisms where an additional 10th vertex of monoligated nickel caps a triangular base of the trigonal prism. As a result of this, that base opens up, and the distances within it become nonbonding. This ensures that all atoms of the cluster are equidistant from the central nickel atom, i.e., the cluster is very close to spherical. All species were structurally characterized in crystalline compounds with [K-(2,2,2-crypt)]+ countercations. They were also characterized in solution by mass spectrometry, IR, and 13C NMR.

Transfer of metal MEMS packages using a wafer-level solder transfer technique

This paper presents a modular, low profile, wafer-level encapsulation technology for microelectromechanical systems (MEMS) packaging. Electroplated caps are formed on top of a solder transfer layer previously deposited on a carrier wafer, then simultaneously transferred and bonded to a device wafer by a novel solder transfer method and transient liquid phase (TLP) bonding technology. The solder transfer method is enabled by the dewetting of the solder transfer layer from the carrier wafer and TLP bonding of the cap to the device wafer during bonding. The bond and transfer cycle has a maximum temperature of 300/spl deg/C and lasts about 2.5 h. This approach has been demonstrated with nickel (Ni) caps as thin as 5 microns, with thicker caps certainly possible, ranging in size from 200 /spl mu/m to 1 mm. They were transferred with a lead-tin (Pb-Sn) solder layer and bonded with nickel-tin (Ni-Sn) TLP bonding with greater than 99% transfer yield across the wafer.

Analytical interfacial studies of double carbonate thermionic oxide cathodes over accelerated operational life

Interfacial interactions between the nickel cap and emissive oxide in double carbonate thermionic oxide cathodes have been studied as a function of operational lifetime by SEM, AES, EDX and TEM. The surface of the interface region has been studied by stripping away the oxide from the cap. In cross-section, the interface has been examined by (a) preparing 10° taper cross-sections and (b) cutting FIB sections. Cracks are observed to develop in the bulk Ni and become more pronounced as a function of operational lifetime. Cracks are found both at grain boundaries and close to the surface, parallel to the interface. It is proposed that the cracks develop from voids, formed as a result of the high diffusivity of Mg and Al in the Ni matrix. EDX shows the presence of Al, Mg, Ba, Sr and O within the cracks and it is proposed that MgO and (Ba, Sr)Al 2O 4 are two major reaction products. A thin (skin) layer containing Al, Ba, Sr and O forms at the Ni cap/emissive layer interface, attributed primarily to (Ba, Sr)Al 2O 4 formation.

Formation of an interface layer in thermionic oxide cathodes for CRT applications

Scanning electron microscopic techniques were employed to study the surface morphological changes of oxide cathodes and nickel caps as a result of cathode activation extending over periods of 1–12 h. Elemental analysis of barium, strontium, tungsten, magnesium and aluminium was performed using energy dispersion x-ray spectroscopy. An abrupt change was observed after activation longer than 3 h. Conduction through well activated cathode assemblies was found to be due to intergranular electron tunnelling at low temperatures (T ⩽ 500 K), while trapping and detrapping at grain boundaries becomes the dominant mechanism at high temperatures (T ⩾ 500 K). The contribution of the interfacial layer to conductivity was found to be significant for cathodes activated for smaller periods.

Electron field emission properties of carbon nanotubes grown on nickel caps

Carbon nanotubes (CNTs) were grown on Ni caps, possessing good electron field emission properties and exhibiting good potential for the applications as the electron sources in cathode ray tubes. The characteristies of the CNTs grown on Ni caps vary with the synthesis processes markedly. For the gas-phase-formed CNTs, which were grown on ferrocene-derived Fe clusters via a gas-phase-nucleation process, the CNTs are uniformly small in diameter and of high purity. In contrast, for the surface-grown CNTs, which were formed on Fe(C7H17COO)3-derived Fe clusters, the CNTs are large in diameter, containing large proportion of carbon soots. However, the surface-grown CNTs exhibit markedly better electron field emission capacity (Je)s=4.4 mA/cm2, than the gas-phase-formed CNTs, (Je)g=1.5 mA/cm2 at 22.5 V/μm, even though the latter possess a smaller effective work function [(Φe)s=0.114 eV and (Φe)g=0.034 eV]. Such phenomenon is presumably ascribed to the better CNT-to-substrate contact properties for the CNTs grown directly on the Fe clusters coated on Ni caps.

Growth characteristics of carbon nanotubes by plasma enhanced hot filament chemical vapor deposition

We successfully obtained vertically aligned multiwalled carbon nanotubes on different nickel-coated substrates by plasma enhanced hot filament chemical vapor deposition at low temperatures below 650°C. Acetylene and ammonia gas were used as the carbon source and a catalyst. The surface roughness of the nickel layer increased as NH 3 etching time increased. The diameters of the nanotubes decreased and the density of nanotubes increased as NH 3 etching time increased. The diameter of the nanotubes was 30–70 nm. A nickel cap was observed on the top of the grown nanotube and a very thin amorphous-carbon-like layer was found on the nickel cap. The morphology and microstructure of carbon nanotubes were measured using scanning electron microscopy and transmission electron microscopy.