Thin Nickel Layer Research Articles

Parametric study of electroplating conditions on mismatch strain of thin film for self-positioning of MEMS

In this paper, we report a detailed investigation of mismatch strain profiles taking account of the effects of process conditions, specifically the electrodeposition current density and temperature. This concept is demonstrated using the standard AFM (atomic force microscope) optical method. First, the thin layer of nickel to be measured is electrodeposited onto the tip side of the AFM cantilever at various current densities and temperatures. Then the cantilever deflections are measured by detecting the position change of the laser on the detector shifts and converted into the quantitative mismatch strain by appropriate mechanics. For a given deposition thickness, the magnitude of the mismatch strain increases with an elevation of the current density or plating temperature. The maximum deflection rate and mismatch strain happen on the interface when two different materials are connected. Next, the determined mismatch strain is further assessed experimentally by comparing its predictions for the self-deformed shape and the measured deflections of the AFM cantilever.

Manufacturing of Annular Targets Made of LEU Foil Coated with Electrodeposited Nickel

The results achieved in the development of an annular target manufacturing technology for Mo-99 radioisotope production, with targets containing a low enriched uranium LEU foil, are presented in this paper. The paper describes the annular targets manufacture comprising the uranium foil and a thin layer of nickel obtained by electroplating on the surface of the uranium, resulting in Ni deposits with thickness of 15 to 25 microns. It was necessary to determine the potential to avoid the presence of uranium oxide and also to determine the intensity (amperage) at which its formation begins. The results obtained, showed that the mass of Ni deposited on the uranium foil is proportional to the electroplating time and the current intensity. Ultrasonic Tests and Screen Electronic Microscopy revealed good bonding and homogeneity of the nickel deposit. The Ni layer had a high hardness and a relatively small grain size with an orientation in the direction of the electrical current flow.

Transparent conductors with an ultrathin nickel layer for high-performance photoelectric device applications

A thin nickel (Ni) layer of thickness 5nm was inserted in between the indium tin oxide (ITO) layers of thickness 50nm each so as to increase the conductivity of ITO without affecting much of its transmittance nature. ITO layers with and without Ni film were prepared by reactive DC sputtering on both Si and glass substrates. The influence of Ni layer on the optical and electrical properties of prepared devices was investigated. Due to the insertion of thin Ni layer, the resistivity of ITO/Ni/ITO sample (3.2×10−4Ωcm) was reduced 10 times lesser than that of ordinary ITO layer (38.6×10−4Ωcm); consequently it increased the mobility of ITO/Ni/ITO device. The external and internal quantum efficiencies (EQE and IQE) of ITO/Ni/ITO device exhibited better performance when compared to ITO layer that has no Ni film. At wavelengths of 350 and 600nm, the photoresponses of ITO/Ni/ITO device were predominant than that of reference ITO device. This highly conductive and photoresponsive Ni inserting ITO layers would be a promising device for various photoelectric applications.

From ‘petal effect’ to ‘lotus effect’ on the highly flexible Silastic S elastomer microstructured using a fluorine based reactive ion etching process

A fluorine-based reactive ion etching (RIE) process has been applied on a new family of silicone elastomers named ‘Silastic S’ for the first time. Excellent mechanical properties are the principal advantage of this elastomer. The main objective of this study was (i) to develop a new process with an electrodeposited thin Nickel (Ni) layer as a mask to obtain a more precise pattern transfer for deep etching (ii) to investigate the etch rates and the etch profiles obtained under various plasma conditions (gas mixture ratios and pressure). The resulting process exhibits etch rates that range from 20 µm h−1 to 40 µm h−1. The process was optimized to obtain anisotropic profiles of the edges. Finally, it is shown that (iii) the wetting contact angle could be easily modified with this process from 103° to 162°, with a hysteresis that ranges from 2° to 140°. The process is, at present, the only reported solution to reproduce the ‘petal effect’ (high contact angle hysteresis value) on a highly flexible substrate. A possibility to control the contact angle hysteresis from the ‘petal effect’ to the ‘lotus effect’ (low contact angle hysteresis value) has been investigated to allow a precise control on the required energy to pin or unpin the contact line of water droplets. This opens multiple possibilities to exploit this elastomer in many microfluidics applications.

Ultrasonic Imaging in Hot Liquid Sodium Using a Plate-Type Ultrasonic Waveguide Sensor

This paper reports the first set of results from ultrasonic measurements for determining the imaging capability of a plate-type ultrasonic waveguide sensor in \(200\,^{\circ }\)C liquid sodium. This 10-m long plate-type waveguide sensor has been developed for viewing objects in opaque liquid sodium coolant for the applications in a sodium-cooled fast reactor (a next generation nuclear reactor). Various imaging capabilities of the waveguide sensor have already been demonstrated in water including ultrasonic beam steering, high resolution C-scan, and so on. However, water and liquid sodium have different acoustic properties and, more importantly, different wetting characteristics with stainless steel—the material for the waveguide sensor. For applications of the developed waveguide sensor in a real reactor environment, this research performs a set of necessary ultrasonic measurements in liquid sodium. The end section of the waveguide sensor which radiates an ultrasonic beam into the liquid sodium is coated with thin beryllium and nickel layers which can significantly improve the ultrasonic beam quality and wetting property of the stainless steel. A liquid sodium facility that consists of a glove box system, a sodium test tank, and an argon purification system has been built. The resolution and beam property are determined from ultrasonic C-scan experiments; a signal-to-noise ratio of over 10 dB and the resulting detection of a 1 mm wide slit can be achieved. The inherent issues associated with wetting of the waveguide sensor in liquid sodium are discussed based on the ultrasonic imaging results.

Improved Bilayer Graphene Transistors for Applications in Nanoelectronics

Introduction In this contribution we report on an improved method to fabricate transfer-free bilayer graphene transistors (BiLGFETs) directly on oxidized silicon wafers in a silicon-CMOS compatible fabrication process. By means of catalytic chemical vapor deposition (CCVD) the BiLGFETs are realized directly on oxidized silicon substrate without transfer. These BiLGFETs possess unipolar p-type device characteristics with a high on/off-current ratio between 1x105 and 1x107 at room temperature [1] exceeding previously reported values by several orders of magnitude. However, at this stage, the maximal on-state current of a BiLGFET is limited by the contact resistance, since the catalyst areas are simultaneously used as source (S) and drain (D) contacts. In order to improve device performance, an additional fabrication step has been developed, by which means the contact resistance is lowered by more than a factor of 10. Results and Discussion In preparation for CCVD silicon wafers are oxidized in dry O2 ambient to obtain a 100nm thick SiO2 film. Afterwards a first lithography step follows and a structured liftoff system remains on the wafer surface. Thin aluminum and nickel layers are evaporated over the whole substrate surface and are structured via liftoff. By annealing the wafer the aluminum transforms itself into insulating aluminum-oxide (AlxOy) while the nickel layer generates several nickel nanoclusters at the perimeter of the catalyst system [2]. In the subsequent methane-based CCVD process, graphene layers are growing (Fig. 1). The number of the stacked graphene layers (i.e. mono-, bi- or few-layers) depends on the adjusted process parameters like time, temperature and gas mixture [2]. Raman-measurements (Fig. 2) and AFM-step height measurements (not shown here) have been performed to confirm the presence of bilayer graphene. In order to improve S/D contacts, one additional lithography step is performed subsequent to the CCVD growth process (Fig. 3). The second mask-layer is used to cover the central part of the graphene channel (channel length is about 3µm) while the edges (>0.2µm) at the catalyst/graphene transition and the S/D regions are unexposed (Fig. 3(b)). Following the lithography step, a 70nm thick palladium layer is evaporated over the whole wafer surface. Due to the high aspect ratio of the resist, the S/D contacts are electrically separated. The contact metal palladium is in direct contact with the graphene channel to improve conduction.The electrical characterization of the graphene devices has been performed using a Keithley SCS 4200 semiconductor parameter analyzer. Electrical results indicate that the current drive for BiLGFETs with Pd-enforced S/D contacts is improved by approximately one order of magnitude. However, post-processing after graphene-growth affects the over-all current-voltage characteristics e.g. in terms of threshold-voltage shift. Further details will be presented and discussed at the meeting. References P. J. Wessely, F. Wessely, E. Birinci, B. Riedinger, and U. Schwalke, Electrochemical and Solid-State Letters, 15 (4) K31-K34 (2012)P. J. Wessely, F. Wessely, E. Birinci, B. Riedinger, and U. Schwalke, J. Vac. Sci. Technol. B30 03D114 (2012)A.C. Ferrari, J.C. Meyer, V. Scardaci, C. Casiraghi, M. Lazzeri, F. Mauri Phys. Rev. Lett. 97, 187401 (2006)

Simulations of acoustic waves bandgaps in a surface of silicon with a periodic hole structure in a thin nickel film

We have performed simulations of dispersion relations for surface acoustic waves in two-dimensional phononic crystal by the finite elements method (FEM) and by the plane wave method (PWM). Considered medium is a thin nickel layer on a silicon single crystal (001) surface. The nickel film is decorated with cylindrical holes of the depth equal to the nickel film thickness arranged in a square lattice. We have obtained full bandgaps for the surface waves propagating in the medium of particular range of filling factor and layer thickness. The width of the bandgap had reached over 500[MHz] for the sample of the lattice constant 500[nm] and is sufficient for experimental design.

Enhanced emission of fluorophores on shrink-induced wrinkled composite structures.

We introduce a manufacturable and scalable method for creating tunable wrinkled ferromagnetic-metallic structures to enhance fluorescence signals. Thin layers of nickel (Ni) and gold (Au) were deposited onto a pre-stressed thermoplastic (shrink wrap film) polymer. Heating briefly forced the metal films to buckle when the thermoplastic retracted, resulting in multi-scale composite 'wrinkles'. This is the first demonstration of leveraging the plasmons in such hybrid nanostructures by metal enhanced fluorescence (MEF) in the near-infrared wavelengths. We observed more than three orders of magnitude enhancement in the fluorescence signal of a single molecule of goat anti-mouse immunoglobulin G (IgG) antibody conjugated to fluorescein isothiocyanate, FITC, (FITC-IgG) by two-photon excitation with these structures. These large enhancements in the fluorescence signal at the nanoscale gaps between the composite wrinkles corresponded to shortened lifetimes due to localized surface plasmons. To characterize these structures, we combined fluctuation correlation spectroscopy (FCS), fluorescence lifetime imaging microscopy (FLIM), and two-photon microscopy to spatially and temporally map the hot spots with high resolution.

Laser deposition of sulfonated phthalocyanines for gas sensors

Thin layers of nickel and copper tetrasulfonated phthalocyanines (NiPcTS and CuPcTS) were prepared by Matrix Assisted Pulsed Laser Evaporation method. The depositions were carried out with KrF excimer laser (energy density of laser radiation EL=0.1–0.5Jcm−2) from dimethylsulfoxide matrix. For both materials the ablation threshold EL-th was determined. The following properties of deposited layers were characterized: (a) chemical composition (FTIR spectra); (b) morphology (SEM and AFM portraits); and (c) impedance of gas sensors based on NiPcTS and CuPcTS layers in the presence of two analytes – hydrogen and ozone. The prepared sensors exhibit response to 1000ppm of hydrogen and 100ppb of ozone even at laboratory temperature.

Formation of Si nanorods and hollow nano-structures using high precision plasma-treated nanosphere lithography

We report a novel method for the formation of hollow rod silicon nanostructures via plasma treated nanosphere lithography and reactive ion etching. The plasma treatment of polystyrene nanospheres (PS-NS) with O2 and methanol–O2 gases is studied as a function of nanosphere size, plasma power and treatment time on a silicon substrate covered by a thin layer of nickel. Applying hydrogen or HCl plasma to already treated polystyrenes, nano-rings and nano-dots can be obtained without any physical or sputtering damage. Large area silicon nano-pillars and hollow silicon nano-structures with inner diameters of 50 nm were obtained by using optimized plasma treatment. These nanostructures show a hexagonal order with good fidelity to the PS-NS patterns. Various characterization techniques such as AFM, SEM, TEM, XPS and FTIR spectroscopy have been exploited to study the samples. The hollow rod structures made using this method will have applications in low power high performance electronic devices, optoelectronic and lithium ion battery devices. Also, a model for the formation of hollow rings is presented.

Uniform Plating of Thin Nickel Layers for Silicon Solar Cells

This paper describes a galvanic deposition method for the formation of uniformly thin nickel seed layers for silicon solar cells. Unlike the previously-reported electroless and light-induced plating methods, where the thickness of nickel seed layers can be vary significantly due to non-uniform nucleation of metal which can be exacerbated by variations in surface dopant concentrations and roughness, this method saturates resulting in Ni seed layers of uniform thicknesses in the range of 250-400nm depending on the plating time and patterning process. The method was successfully used in the fabrication of nickel/copper plated homogeneous 100Ω/□ emitter Si solar cells and laser-doped selective emitter (LDSE) cells, both with screen-printed, Al-alloyed back surface fields. Average cell efficiencies of 18.4% and 18.9% were achieved for the homogeneous emitter cells and LDSE cells, respectively, with the best LDSE cell having an efficiency of 19.2%.

Vacuum brazing titanium using thin nickel layer deposited by PVD technique

In this study, the evolution of the interfacial microstructure, hardness distribution, and the joint strength of vacuum brazed commercially pure titanium were evaluated. A thin nickel layer, with different thicknesses, was deposited by PVD technique to serve as the brazing filler metal. Test joints were processed at temperatures of 910°C and 960°C using a soaking time of 15 and 90min. The experimental results showed that sound joints with a good wetting quality as well as lack of pores and cracks can be achieved at a brazing temperature of 960°C. A Ti2Ni intermetallic compound was formed at the interfacial area at a soaking time of 15min and with a deposition rate of 90AH which was detrimental to the joint mechanical properties. Meanwhile, at a soaking time of 90min, intermetallic compound was not detected and the diffusion of nickel was completed at all deposition rates which improve the shear strength of the joints.

Nanofabrication of arbitrary patterns by nano plastic forming and etching (NPFE)

In this paper, flexibility of nano plastic forming and etching, an ultra-high resolution nanofabrication process developed recently by the authors, in terms of fabrication of arbitrary patterns as well as applicability to various work materials is demonstrated. First, a thin layer of nickel (Ni) is deposited on a silicon (Si) substrate. Then, it is directly patterned by nano plastic forming. Next, the patterned Ni mask is slightly etched by direct current sputter etching to transfer the pattern into the entire mask thickness and expose the surface of the substrate in the individual patterned areas. Afterward, the pattern is transferred onto the substrate by reactive ion etching. Finally, the remained Ni layer is removed from the substrate, and nanostructures fabricated on the surface of the substrate are revealed. Fabrication of grid patterns with various pitch settings on the surface of Si substrates is demonstrated. The experimental results indicate that the depth and width of the nanostructures can be controlled by the etching time. Also, it is confirmed from the results that the depth and width are not influenced by the pitch setting.

Reduction of a NiO thin film deposited by PLD on a single crystal YSZ (111) substrate

The NiO/YSZ interface prepared by depositing NiO on a single crystal YSZ (111) substrate has been investigated by transmission electron microscopy. As deposited, a very thin nickel layer ascribing to the nonstoichiometry at the very beginning growth of NiO and an amorphous silica phase resulting from silicon segregation were present at the interface. The orientational relationship of NiO \( (1\overline{1} 1) \)//Ni \( (1\overline{1} 1) \)//YSZ \( (1\overline{1} 1) \) with NiO [110]//Ni [110]//YSZ [110] was observed. The microstructural and chemical changes at the NiO/YSZ interface after being heated in vacuum and hydrogen indicated different reduction mechanisms. In vacuum, the reaction \( {\text{NiO}} \to {\text{Ni}} + 1/ 2 {\text{ O}}_{ 2} \left( {\text{g}} \right) \) was prevailing at the interface between NiO and pre-existing Ni, which led to the thickening of nickel layer. In hydrogen, the reduction initiated on the NiO surface was dominant, following the chemical equation H2 + OO (NiO) → H2O (g) + VO.. (NiO) + 2e (Ni).

Continuous infrared‐assisted double‐sided roll‐to‐roll embossing of flexible polymer substrates

AbstractThis article reports a novel infrared (IR)‐assisted roll‐to‐roll embossing method, which enables the replication of microfeatures onto the surfaces of flexible polymer substrates. An IR‐assisted roll‐to‐roll embossing facility was designed and built in our laboratory especially for this study. Metallic rollers bearing micropatterns of two different feature sizes, namely 150 and 20 μm in depth, were employed. The former one was prepared by microelectric discharge machining the roller, whereas the latter was fabricated by electroplating a thin layer of nickel on the surface of the roller, followed by a diamond turning process to create the microstructures. The embossing facility was used to replicate the microstructure onto polyethylene terephthalate and polycarbonate films in the experiments. During roller embossing, the IR radiation shed on the rollers, and the energy was converted into heat to melt the polymer substrates and to replicate the microstructures. The influence of various processing parameters on the replicability of microfeatures was investigated. Under the proper processing conditions, double‐sided flexible polymer substrates with microstructures could be successfully fabricated. The proposed method shows great potential for fabrication of micro‐optical components due to its simplicity and versatility. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Physical model for the laser induced forward transfer process

This paper presents a numerical model which describes the underlying physical processes during laser induced forward transfer. The laser induced forward transfer uses a pulsed laser to transfer thin layers from a transparent support to a substrate. The model predicts the threshold energies Eth as well as the blow-off time tblow, thus allowing a profound physical understanding of the transfer process. The good agreement of simulated with measured Eth and tblow of thin nickel layers demonstrates the accuracy of the model. The model shows that gasification of the soda-lime glass support is the main driving force of the transfer process.

Electrodeposition of luminescent composite metal coatings containing rare-earth phosphor particles

Mixtures of acetamide and dimethylsulfone (DMSO2) with dissolved anhydrous transition metal chlorides are introduced as new non-aqueous electrolytes for the preparation of composite metal coatings with embedded hydrophilic particles via an electrolytic co-deposition process. Red-emitting (Eu2O3 and Y2O3:Eu3+), yellow-emitting (Y3Al5O12:Ce3+), green-emitting (Gd2O2S:Tb3+) and blue-emitting (BaMg2Al16O27:Eu2+) rare-earth phosphor particles and yttrium oxide particles have been embedded into thin nickel and cobalt layers. The metal coatings with the rare-earth phosphor particles have a metallic lustre, but show at the same time photoluminescence upon irradiation with UV light. The spectroscopic and photophysical properties of the rare-earth phosphors are not modified by embedding them in the metallic host matrix. Different electrodeposition parameters were optimised in order to obtain well-adherent coatings with a uniform particle distribution. By preparing mixtures of the Y2O3:Eu3+ and Gd2O2S:Tb3+ phosphors, the emission colour could be varied from red to orange and yellow to green, depending on the mixing ratios. Embedding mixtures of yellow and blue phosphors in the metal layer made it possible to produce coatings with white photoemission.

Laser Deposition of Tetrasulfonated Phthalocyanine Layers for Gas Sensors

Thin layers of nickel and copper tetrasulfonated phthalocyanines (NiPcTS and CuPcTS) were prepared by Matrix Assisted Pulsed Laser Evaporation method. The depositions were carried out with KrF excimer laser (energy density of laser radiation EL = 0.1 to 0.5 J.cm-2) from dimethylsulfoxide matrix. For both materials the ablation threshold EL-th was determined. The following properties of deposited layers were characterized: a) chemical composition (FTIR spectra); b) morphology (SEM and AFM portraits); c) impedance of gas sensors based on NiPcTS and CuPcTS layers in the presence of two analytes - hydrogen and ozone. The prepared sensors exhibit response to 1000 ppm of hydrogen and 100 ppb of ozone even at laboratory temperature.

Assessment of Transparent Conducting Zinc Oxide as a Tunneling Contact to p-GaN

ABSTRACTUse of aluminum alloyed zinc oxide (AZO) as a transparent contact to p-GaN has received significant attention for GaN/InGaN light emitting diodes applications. Reports show that AZO as deposited on p-GaN forms a Schottky contact given the large work-function difference between AZO and p-GaN [1]. However, utilization of a thin nickel layer inserted between the AZO and p-GaN can result in an ohmic contact [2], given that Ni forms an ohmic contact to p-GaN upon annealing. Here, we undertake simulation studies of this AZO/Ni interface as a function of Nickel layer. Simulation studies of the transport mechanism in this contact indicate the likelihood of a tunneling junction at the AZO/Ni interface, thus the entire AZO/Ni forming an ohmic contact to p-GaN. Potential to better control injected current density uniformity utilizing such a contact structure is also discussed.

Applications of Planar ITO Electrodes for Studying of Some Biochemical Activities

Abstract Trends in disposable and handheld biosensors have called for miniaturized and planar electrodes in the place of conventional bulky ones. In this work, thin tin-doped indium oxide (ITO) film coated on glass were used as a based electrode in a three-electrode electrochemical system to follow some biochemical activities, such as NADH and phenol activity. The reference electrode is made on ITO layer by electro-deposition of thin nickel layer and silver layer, consecutively, followed by chlorination of silver surface by electrochemical potentiostatic method. The plain planar ITO-coated glasses were used as both counter electrode and working electrodes. Cyclic-voltammetry measurements; which follow an oxidation of 200 μM nicotinamide adenine dinucleotide (NADH) in 0.1 M KCl, show current peak of 8.5 μA. Another case was also to follow the NADH oxidation but in competition with its coupling activity with flavin mononucleotide (FMN). In this case, cyclic-voltammetry measurements were carried out of 200 μM NADH in 50 mM sodium phosphate; current peak of 1.3 μA was observed.