Ni Thin Films Research Articles

Ni-Al-Ti Ohmic Contacts with Preserved Form Factor and Few 10<sup>-</sup> <sup>4</sup> Ωcm<sup>2</sup> Specific Resistance on 0.1-1 Ωcm p-Type 4H-SiC

This study shows that a thin Ni film on Al/Ti/4H-SiC metal pads allows to preserve the pad form factor during a 1000 °C/2 min treatment, provided that the Al and Ti film thicknesses are sufficiently thin. Moreover, by reducing the Al to Ti thickness ratio, droplet formation in the contact area is avoided and a mirror-like appearance is obtained. This optimal contact morphology corresponds to a specific contact resistance of few 10-4 Ωcm2 at room temperature on p-type 4H-SiC with resistivity in the range 0.1 – 1 Ωcm.

Transparent conductors for Mid-infrared liquid crystal spatial light modulators

Transparent conductors (TCs) are required for liquid crystal spatial light modulators (LC-SLMs) in order to set up an electric field across the LC layer. In the middle infrared (Mid-IR) range (λ = 2 to 5 μm), LC-SLMs can offer a low-cost, non-mechanical, random-access and compact alternative to the gimbaled mirrors used currently for Mid-IR laser beam-steering. Indium tin oxide (ITO) is the industry standard for applications in the visible spectrum but it performs poorly in the IR, with a transmittance <20% for Mid-IR wavelengths. Little work has been done to develop a comparable material which fulfils the required properties in the Mid-IR: A sheet resistance allowing operation at typical frequencies (≈1 kHz) and, if patterned, with minimal voltage drop along the electrode, a transmittance >50% in the target range, chemical, thermal and mechanical robustness which can endure subsequent processing, and ability to be patterned at low-cost to a resolution comparable to the wavelengths investigated. Ni and Cu ultra thin metallic films (UTMFs), CuxO thin films (TFs), and chemical vapour deposition (CVD) grown mono-layer graphene were investigated. Ni UTMFs and graphene were found to have the best performance with sheet resistance values of 747±86Ω/□ and 360±34Ω/□ respectively for samples having a transmittance of 65% and 97% at λ = 2.3 μm. Both Ni UTMFs and CVD mono-layer graphene were found to be suitably stable with age. An increase of sheet resistance after baking was recorded due to oxidation and desorption of contaminating dopants respectively. Ni UTMFs were found to be patternable down to a 3 μm resolution, limited by the mask, using a standard photo-lithographic lift-off process. Transmissive LC cells with a maximum phase shift of 3π at λ = 2.3 μm were assembled with both Ni UTMFs and mono-layer graphene as TCs on sapphire, with the former having transmittance of 18.7% and contrast ratio of 25.0, and the latter having transmittance of 81.1% and contrast ratio of 50.7.

Discerning interface atomistic structure by phase contrast in STEM: The equilibrated Ni-YSZ interface

Equilibrated interfaces between Ni and yttrium stabilized zirconia (YSZ) were formed by solid-state dewetting of thin Ni films on the (111) surface of YSZ single crystals at 1350 °C and an oxygen partial pressure of P(O2) = 10−20 atm. The atomistic structure of the equilibrated solid-solid Ni[1¯10]111∥YSZ[11¯0]111 interface was determined by monochromated and aberration-corrected scanning transmission electron microscopy, using different techniques. It was found that due to the large lattice mismatch between Ni and YSZ the interface reconstructs, and adopts a unique structure which consists of a high density of misfit dislocations. However, despite the large lattice mismatch, this interface is not incoherent. The interface was confirmed to be cation terminated, which is probably due to the low oxygen partial pressure used to reach equilibrium.

(Invited) All-Carbon Interconnects - from 1D to 3D

Continuous downward scaling in silicon integrated circuit technology into the sub-20 nm regime has created critical challenges in chip manufacturing, among them, reliability and performance of on-chip interconnects. Current interconnect materials, Cu and W, face increased reliability challenges in the nanoscale as a result of electromigration failures at high current densities. Materials such as nanocarbons, metal silicides, and metallic nanowires are being considered as potential replacements for Cu and W. In particular, due to its superior electrical and mechanical properties as well as much higher current-carrying capacities, carbon nanotube (CNT) is a serious contender to replace Cu and W in on-chip interconnect via. However, the main challenge to functionalizing CNT vias is the metal-CNT contact resistance. To mitigate such challenge, a seamless three-dimensional all-carbon interconnect structure has been fabricated by growing CNTs directly on one or few layers of graphene (MLG). This 3D structure can potentially yield low resistance due to the strong C-C sp2 bonding in CNT and graphene and across the CNT-graphene interface. While such growth has been demonstrated, the CNT/graphene interfacial nanostructure and how it impacts the electrical properties of the 3D structure are far from being understood. Our test structure consists of MLG grown by annealing a Ni thin film in H2/CH4 ambient inside a low-pressure PECVD chamber, before being transferred onto an oxide-covered silicon substrate. Vertically aligned CNTs are then grown on the transferred MLG in a PECVD system using a similar recipe as in our previous work on CNT vias, resulting in a 3D all-carbon interconnect structure. Scanning and transmission electron microscopy images reveal CNT alignment and interfacial nanostructure comparable to the CNT-Cr interface in CNT via. The measured resistance of the 3D structure is compared with those of sub-100 nm linewidth CNT vias. Our results demonstrate the feasibility of fabricating a 3D CNT/graphene device, which can serve as the building block for all-carbon interconnects. Enhanced understanding of the relationship between interfacial nanostructure and device resistance can lead to eventual functionalization of contacts between CNT vias and a graphene-based planar interconnect network in the most advanced technology nodes.

Optical, electrical, and electrochemical behavior of p-type nanostructured SnO2:Ni (NTO) thin films

The physical and electrochemical properties of sol-gel synthesized nickel-doped tin oxide (NTO) thin films were investigated. The X-ray diffraction results showed that NTO samples exhibited a tetragonal structure. The average crystallite size and the unit cell volume of the films were reduced by Ni increment, while the stacking fault probability was increased. Furthermore, the field-emission scanning electron microscopy images clearly displayed that the worm-like surface morphology of the SnO2 thin films was altered to the spherical feature in 3 and 10 mol% NTO samples. Moreover, by virtue of Ni incorporation, the average transparency of the SnO2 thin films rose up from 67 to 85% in the visible region; also, the optical band gap of the SnO2 sample (3.97 eV) increased and the thin film with 3 mol% dopant concentration showed a maximum value of 4.22 eV. The blue/green emission intensities of photoluminescence spectra of SnO2 thin film changed via Ni doping. The Hall effect measurements revealed that by Ni addition, the electrical conductivity of tin oxide thin films altered from n- to p-type and the carrier concentration of the films decreased due to the role of Ni2+ ions which act as electron acceptors in NTO films. In contrast, 20 mol% Ni-doped sample had the highest mobility about 9.65 cm2 (V s)−1. In addition, the cyclic voltammogram of NTO thin films in KOH electrolyte indicated the charge storage capacity and the surface total charge density of SnO2 thin films enhanced via Ni doping. Moreover, the diffusion constant of the samples increased from 2 × 10−15 to 6.5 × 10−15 cm2 s−1 for undoped and 5 mol% dopant concentration. The electrochemical impedance spectroscopy of the NTO thin films in two different potentials showed the different electrochemical behaviors of n- and p-type thin films. It revealed that the 20 mol% NTO thin film had maximum charge transfer at lower applied potential.

Nickel doping effect on properties of sprayed In2S3 films

Nickel doped In2S3 films have been prepared by the chemical spray pyrolysis technique at 350 °C on glass substrates. The Ni doping level was changed by varying Ni:In molar ratio from 0 to 4% in solution. The structural studies reveal that the Ni-doped In2S3 films are polycrystalline and exhibit a cubic structure. As the Ni:In molar ratio increases, the crystallite size decreases from 27.5 to 23 nm and RMS roughness values increase from 12 to 18 nm, respectively. The presence of Ni in the deposited films was confirmed by energy dispersive spectroscopy. Raman studies show different peaks related to In2S3 phase and do not reveal any secondary phases of In–Ni and Ni–S. The transmission coefficient is about 70–55% in the visible region and 85–75% in near-infrared region. The band gap energy increases from 2.66 to 2.82 eV for direct transitions with the increase of Ni:In ratio from 0 to 4%. The refractive index values of In2S3:Ni thin films decrease from 2.46 to 2.40 and the extinction coefficient values are in the range 0.01–0.20.

Thickness-Dependent Thermal Oxidation of Ni into NiO Thin Films

We report thickness-dependent thermal oxidation in Ni (t = 10–300 nm) thin films exposed to air annealing and the resulting vibrational, magnetic and electrical properties of Ni films deposited directly on thermally oxidized Si substrate using magnetron sputtering technique at ambient temperature. As-deposited Ni films exhibit face-centred cubic structure with fine crystals and large lattice constant (aNi) at lower t ( 50 due to formation of NiO. The relative fraction of Ni and NiO in annealed films up to 400 ∘C strongly depends on t. Annealing Ni films at 500 ∘C results into complete oxidation of Ni into granular-type NiO. X-ray reflectivity studies reveal that oxidation process occurs from surface of the films converting Ni into NiO possibly through layer by layer process, which is subtle to t. Raman spectra show that intensity ratio between one-phonon longitudinal optical (LO) and two-phonon LO bands decreases and intensity of two-magnon band increases with increasing t for films annealed at particular TA. This confirms the growth of NiO not only with increasing TA, but also with t. As-deposited films exhibit ferromagnetism at room temperature. The presence of Ni and NiO in annealed films implies coexistence of ferromagnetic and antiferromagnetic interactions, leading to tunable exchange bias (HE), whose magnitude strongly depends on the ratio between Ni and NiO. Electrical resistance (R) of the as-deposited Ni films decreases with increasing t and follows the Namba’s model. Upon annealing, R increases largely due to oxidation of Ni. The observed results are explained on the basis of thickness dependent thermal oxidation process with increasing TA.

Solid-state dewetting of Au–Ni bi-layer films mediated through individual layer thickness and stacking sequence

In the present work, the solid-state dewetting of Au–Ni bi-layer thin films deposited on SiO2/Si is systematically studied with respect to individual layer thickness and stacking sequence. For this purpose, a rapid heat treatment at medium temperatures is applied in order to examine void formation at the early stages of the dewetting. Compositional variations are realized by changing the thickness ratio of the bi-layer films, while the total thickness is maintained at 20 nm throughout the study. In the event of Au/Ni films annealed at 500 °C, crystal voids exposing the substrate are missing regardless of chemical composition. In reverse order, the number of voids per unit area in two-phase Au–Ni thin films is found to be governed by the amount of Au-rich material. At higher temperatures up to 650 °C, a decreased probability of nucleation comes at the expense of a major portion of cavities, resulting in the formation of bubbles in 15 nm Ni/5 nm Au bi-layers. Film buckling predominantly occurred at phase boundaries crossing the bubbles.

Modification of magnetoresistance and magnetic properties of Ni thin films by adding Dy interlayer

The paper reports the influence of dysprosium (Dy) interlayer addition on structure, magnetoresistance and magnetic properties of nickel (Ni) thin films. Trilayer film systems Ni/Dy/Ni have been prepared by alternate electron-beam evaporation. It is demonstrated that all as-prepared and annealed Ni thin films have face-centered cubic structure. The composition of the samples after addition of the Dy interlayer corresponds to the combination of face-centered cubic (Ni) and hexagonal close-packed (Dy) structures. The structure of Ni/Dy/Ni film systems changes from amorphous to polycrystalline when Dy interlayer thickness (tDy) is more than 15 nm. The value of magnetoresistance increases with the adding the Dy interlayer in both longitudinal and transverse geometries, meanwhile the anisotropic character of magnetoresistance field dependences retained. The saturation and reversal magnetizations are reduced with the increasing of the Dy thickness interlayer, while the coercivity takes the minimum value at tDy = 15 nm. The following increasing of tDy leads to increasing of coercivity near to three times. This result indicates the influence of the crystal structure on the magnetic properties of Ni thin films at adding Dy interlayer.

The effect of different thickness alumina capping layers on the final morphology of dewet thin Ni films

Nanoparticles on a substrate have numerous applications in nanotechnology, from enhancements to solar cell efficiency to improvements in carbon nanotube growth. Producing nanoparticles in a cost effective fashion with control over size and spacing is desired, but difficult to do. This work presents a scalable method for altering the radius and pitch distributions of nickel nanoparticles. The introduction of alumina capping layers to thin nickel films during a pulsed laser-induced dewetting process has yielded reductions in the mean and standard deviation of radii and pitch for dewet nanoparticles with no noticeable difference in final morphology with increased capping layer thickness. The differences in carbon nanotube mats grown, on the uncapped sample and one of the capped samples, is also presented here, with a more dense mat being present for the capped case.

Structural and optical properties of ZnO co-doped with Co and Ni thin films deposited by pulse laser deposition technique

Thin films of Zn0.9 Co0.1−xNixO (x = 0.0, 0.02, 0.04, 0.06, 0.08, 0.1) series were deposited by Pulsed Laser deposition technique (PLD) on a single crystal (100) silicon substrate. The structure of the films was confirmed as single phase hexagonal wurtzite structure by X-ray diffraction technique (XRD). The highest intensity peak was found at (002) plane. The surface morphology of thin films studied by Scanning Electron Microscope (SEM) depicted the high grain growth with definite boundaries. The room temperature resistivity measurements were carried out by four-point Probe methods which showed the semiconducting behavior of the thin films. Magnetic properties characterized by Vibrating Sample Magnetometer (VSM) at room temperature, exhibited the weak ferromagnetic or superparamagnetic behavior due to the alignment of the spins in the same direction around the oxygen vacancy and Co/Ni ions. Optical properties were observed by Spectroscopic Ellipsometry. The thickness of the films lied in 200–265 nm range and the bandgap energy was found to decrease from 3.09 to 3.03 eV confirming the inclusion of Ni a deep level impurity.

Hydrogen oxidation mechanisms on Ni/yttria stabilized zirconia anodes: Separation of reaction pathways by geometry variation of pattern electrodes

Nickel/yttria stabilized zirconia (YSZ) electrodes are affecting the overall performance of solid oxide fuel cells (SOFCs) in general and strongly contribute to the cell resistance in case of novel metal supported SOFCs in particular. The electrochemical fuel conversion mechanisms in these electrodes are, however, still only partly understood. In this study, micro-structured Ni thin film electrodes on YSZ with 15 different geometries are utilized to investigate reaction pathways for the hydrogen electro-oxidation at Ni/YSZ anodes. From electrodes with constant area but varying triple phase boundary (TPB) length a contribution to the electro-catalytic activity is found that does not depend on the TPB length. This additional activity could clearly be attributed to a yet unknown reaction pathway scaling with the electrode area. It is shown that this area related pathway has significantly different electrochemical behavior compared to the TPB pathway regarding its thermal activation, sulfur poisoning behavior, and H2/H2O partial pressure dependence. Moreover, possible reaction mechanisms of this reaction pathway are discussed, identifying either a pathway based on hydrogen diffusion through Ni with water release at the TPB or a path with oxygen diffusion through Ni to be a very likely explanation for the experimental results.

Sensitive Capacitive-type Hydrogen Sensor Based on Ni Thin Film in Different Hydrogen Concentrations.

Background: Hydrogen sensors are micro/nano-structure that are used to locate hydrogen leaks. They are considered to have fast response/recovery time and long lifetime as compared to conventional gas sensors. In this paper, fabrication of sensitive capacitive-type hydrogen gas sensor based on Ni thin film has been investigated. The C-V curves of the sensor in different hydrogen concentrations have been reported.Method: Dry oxidation was done in thermal chemical vapor deposition furnace (TCVD). For oxidation time of 5 min, the oxide thickness was 15 nm and for oxidation time 10 min, it was 20 nm. The Ni thin film as a catalytic metal was deposited on the oxide film using electron gun deposition. Two MOS sensors were compared with different oxide film thickness and different hydrogen concentrations.Results: The highest response of the two MOS sensors with 15 nm and 20 nm oxide film thickness in 4% hydrogen concentration was 87.5% and 65.4% respectively. The fast response times for MOS sensors with 15 nm and 20 nm oxide film thickness in 4% hydrogen concentration was 8 s and 21 s, respectively.Conclusion: By increasing the hydrogen concentration from 1% to 4%, the response time for MOS sensor (20nm oxide thickness), was decreased from 28s to 21s. The recovery time was inversely increased from 237s to 360s. The experimental results showed that the MOS sensor based on Ni thin film had a quick response and a high sensitivity.

EFFECT OF THICKNESS ON THE STRUCTURAL, MICROSTRUCTURAL, ELECTRICAL AND MAGNETIC PROPERTIES OF Ni FILMS ELABORATED BY PULSED ELECTRODEPOSITION ON Si SUBSTRATE

We have studied the effect of thickness on the structural, microstructural, electrical and magnetic properties of Ni films electrodeposited onto [Formula: see text]-Si (100) substrates. A series of Ni films have been prepared for different potentials ranging from [Formula: see text]1.6[Formula: see text]V to [Formula: see text]2.6[Formula: see text]V. Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD), four point probe technique, atomic force microscopy (AFM) and vibrating sample magnetometry (VSM) have been used to investigate the physical properties of elaborated Ni thin films. From the analysis of RBS spectra, we have extracted the films thickness [Formula: see text] ([Formula: see text] ranges from 83[Formula: see text]nm to 422[Formula: see text]nm). We found that the Ni thickness, [Formula: see text] (nm), linearly increases with the applied potential. The Ni thin films are polycrystalline and grow with the [Formula: see text] texture. The lattice parameter [Formula: see text] (Å) monotonously decreases with increasing thickness. However, a positive strain was noted indicating that all the samples are subjected to a tensile stress. The mean grain sizes [Formula: see text] (nm) and the strain [Formula: see text] decrease with increasing thickness. The electrical resistivity [Formula: see text] ([Formula: see text]cm) increases with [Formula: see text] for [Formula: see text] less than 328[Formula: see text]nm. The diffusion at the grain boundaries may be the important factor in the electrical resistivity. From AFM images, we have shown that the Ni surface roughness decreases with increasing thickness. The coercive field [Formula: see text], the squareness factor [Formula: see text], the saturation field [Formula: see text] and the effective anisotropy constant [Formula: see text] are investigated as a function of Ni thickness and grain sizes. The correlation between the magnetic and the structural properties is discussed.

Electrochemical Properties of Si Film Electrodes Containing TiNi Thin-Film Current Collectors

A 50.3Ti–49.7Ni thin film fabricated by DC sputtering was employed as a current collector of Si film electrode. The structural and electrochemical properties of Si/TiNi film electrode were compared with those of a Si/Cu film electrode. The TiNi film with cluster-like structures composed of B2 austenitic phase at room temperature displayed the high electrochemical stability for Li ions. The amorphous Si film deposited on the TiNi film also consisted of cluster-like structures on the surface. The Si film grown on the TiNi film current collector (Si/TiNi electrode) demonstrated a high columbic efficiency of 87% at the first cycle (363 μAh/cm2 of charge capacity and 314 μAh/cm2 of discharge capacity). The Si/TiNi electrode exhibited better electrochemical properties in terms of capacity, cycle performance, and structural stability compared to the Si electrode with a conventional Cu foil current collector.

INFLUENCIA DE LA TEMPERATURA DE SUSTRATO SOBRE LAS PROPIEDADES ÓPTICAS Y ESTRUCTURALES DE ALEACIONES GaSb:Ni

Películas delgadas de aleaciones ternarias de GaSb:Ni fueron preparadas por el método de pulverización catódica (DC magnetrón Co{Sputtering) variando la temperatura de sustrato (Ts). A partir de medidas de transmitancia espectral y difracción de rayos X (XRD) fueron obtenidas las constantes ópticas y las propiedades estructurales del material, respectivamente. Fases predominantes de GaSb y NiSb fueron observadas para todas las variaciones de Ts. A partir de medidas de absorción del material el valor de la banda de energía prohibida o “band gap” fue obtenido,variando entre 0,63 eV y 0,72 eV. Se reporta el coeficiente de extinción en función de la longitud de onda de las películas de GaSb:Ni.

Microstructure and oxidation resistance of relaxed epitaxial nickel thin films grown on (100)- and (110)-SrTiO3 substrates by pulsed laser deposition

The relaxed epitaxial growth of Ni thin films has been successfully performed on both (100)- and (110)-oriented SrTiO3 substrates by pulsed laser deposition.

Fabrication and Stiffness Evaluation of Ni Thin Film Flat-type Spring with Micro-pin and Frame Structure for Tactile Display Device

Fabrication and Stiffness Evaluation of Ni Thin Film Flat-type Spring with Micro-pin and Frame Structure for Tactile Display Device

Strain induced magnetic anisotropy of high epitaxial Ni thin films grown on different oriented PMN-PT substrates

High epitaxial (001)-, (110)- and (111)-oriented Ni ferromagnetic thin films were coherently grown on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) (001), (110) and (111) substrates by magnetron sputtering. Reciprocal space mapping (RSM) results indicate that all of these films are partially relaxed. The mechanism of strain-induced magnetic anisotropy of these epitaxial thin films has been investigated in detail. The easy axis is induced toward out-of-plane (OOP) due to compressive strain, while the hard axis is along in-plane (IP) owing to tensile strain. (111)- and (110)-oriented Ni thin films show the strongest and the weakest magnetic anisotropy, respectively. The strain-induced magnetoelastic energy for (001)-oriented Ni thin film increases its anisotropic field and decreases its total free energy resulting in an enhanced magnetic anisotropy comparing with (110)-oriented one. The remarkable variation of magnetization in high epitaxial Ni thin film system reveals that the magnetic anisotropy can be modulated by changing the biaxial strain.

Nanocluster size dependence of electronic properties of Ta, Mo, Co, and Ni thin films formed by magnetron sputtering

The results of the study of electron properties evolution with nanocluster size of monodispersed thin films consisting of Ta, Mo, Co and Ni metal nanoclusters deposited onto the SiO2/Si(001) surface with magnetron sputtering method are presented. The changes in chemical composition and electron structure of the samples were controlled by means of X-ray photoelectron spectroscopy in the UHV analysis chamber of the Multiprobe MXPS RM VT AFM-25 surface analysis system. Susceptibility to oxidation after exposure to atmosphere was studied.