Ni Film Thickness Research Articles

The electromagnetic shielding of Ni films deposited on cenosphere particles by magnetron sputtering method

Ni-coated cenosphere particles were successfully fabricated by an ultrasonic-assisted magnetron sputtering equipment. Their surface morphology and microstructure were analyzed using field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). FE-SEM results indicate that the Ni films coated by magnetron sputtering are uniform and compact. Ni film uniformity was related with the sputtering power and a large uniform film could be achieved at lower sputtering power. XRD results imply that the Ni film coated on cenospheres was a face-centered cubic (fcc) structure and the crystallization of film sample increases with increasing the sputtering power. The electromagnetic interference (EMI) shielding effectiveness (SE) of Ni-coated cenosphere particles were measured to be 4–27 dB over a frequency range 80–100 GHz, higher than those of uncoated cenosphere particles. The higher sputtering power and Ni film thickness are the higher EMI SE of the specimens. Ni-coated cenosphere particles are most promising alternative candidates for millimeter wave EMI shielding due to their lightweight, low cost, ease of processing, high floating time, good dispersion and tunable conductivities as compared with typical electromagnetic wave countermeasure materials.

Synthesis and film deposition of Ni nanoparticles for base metal electrode applications

This paper describes the preparation of Ni thin films for base metal electrode applications using Ni nanoparticles that were synthesized by thermal decomposition of a Ni–oleate complex under inert gas flow. The oleate molecules both retarded particle growth and prevented oxidation. The mean particle sizes of the cubic phase Ni nanoparticles synthesized at decomposition temperatures of 350, 380, and 400 °C were 5.1, 5.5, and 6.6 nm, respectively. The average activation energy for Ni nanoparticle formation was 157.51 ± 13 kJ mol −1, revealing a single kinetic mechanism. After formulation of a moveable paste, the Ni nanoparticles were well-dispersed on a silicon wafer using a spin coater. The deposited Ni films were further investigated for sintering behavior. Based on the cross-sectional images, the thickness of the as-deposited Ni film was 2.5 μm, while the film sintered at 800 °C was 1-μm thick. The sintered Ni films had a high continuity, without any cracks or voids. The bulk resistivity of the Ni film sintered at 800 °C was 1.8 × 10 −5 Ω cm.

Intrinsic and non-local Gilbert damping in polycrystalline nickel studied by Ti : sapphire laser fs spectroscopy

The use of femtosecond laser pulses generated by a Ti : sapphire laser system allows us to gain an insight into the magnetization dynamics on time scales from sub-picosecond up to 1 ns directly in the time domain. This experimental technique is used to excite a polycrystalline nickel (Ni) film optically and probe the dynamics afterwards. Different spin-wave modes (the Kittel mode, perpendicular standing spin-wave modes and dipolar spin-wave modes (Damon–Eshbach modes)) are identified as the Ni thickness is increased. The Kittel mode allows determination of the Gilbert damping parameter α extracted from the magnetization relaxation time τα. The non-local damping by spin currents emitted into a non-magnetic metallic layer of vanadium (V), palladium (Pd) and the rare earth dysprosium (Dy) are studied for wedge-shaped Ni films of 1–30 nm. The damping parameter increases from α = 0.045 intrinsic for nickel to α > 0.10 for the heavy materials, such as Pd and Dy, for the thinnest Ni films below 10 nm thickness. Also, for the thinnest reference Ni film thickness, an increased magnetic damping below 4 nm is observed. The origin of this increase is discussed within the framework of line broadening by locally different precessional frequencies within the laser spot region.

Observation of Ni silicide formations and field emission properties of Ni silicide nanowires

The Ni silicide nanowires were grown by physical vapor deposition. The morphological changes of silicide formation were observed on a gradient Ni film thickness, which visualized the critical thickness is 60–80 nm to grow nanowires. The field emission measurement provided uniform characteristics and high field enhancement factors were obtained to be 3180 and 3002 from the Ni silicide nanowires grown on a Si substrate and a tungsten plate, respectively. By using a conductive tungsten plate, the emission current was enhanced to be 172.5 μA/cm 2 comparing to 76.5 μA/cm 2 from a Si substrate at 5 V/μm.

Initial formation of contact layers on Ni/SiC samples studied by XPS

AbstractThis study deals with the quantitative assessment of the coverage and thickness of Ni silicide films formed during annealing of SiC substrates with sputtered thin films of Ni. The analytical approach involves the use of XPS and depth profiling by means of successive ion etchings and XPS analyses. For either 3 or 6 nm initial Ni film thickness, a 10 nm Ni2Si product is formed. On top of this product, the C released is accumulated in a very thin (1–2 nm) film. In neither case, the Ni2Si covers the whole surface, although the coverage is almost complete (∼90%) in the latter case. For the greater initial Ni‐film thickness of 17 nm, the thickness of the Ni2Si product corresponds well to the value of 25 nm expected from the Ni/Ni2Si stoichiometric relationship. This thickness is significantly greater than a critical level and the film covers the whole surface. Carbon is similarly accumulated in a very thin layer on the top surface, although the major part of C (∼70%) is found inside the main reaction product layer. Copyright © 2008 John Wiley & Sons, Ltd.

Ultrasmooth Ni thin films evaporated on polyethylene naphthalate films for spin quantum cross devices

Surface morphology of Ni thin films vacuum-deposited on polyethylene naphtalate (PEN) organic films has been investigated as a function of Ni film thickness for spin quantum cross devices. The surface roughness of the Ni films decreases from 1.3nm, being the roughness of PEN films, down to 0.69nm as the thickness of Ni films increases up to 41nm. As a result of the scaling investigation of the surface roughness, the surface roughness for Ni films of sub-10-nm thickness, in the scanning scale of the film thickness, is less than 0.23nm, corresponding to one atomic layer thickness. These experimental results indicate that Ni thin films on PEN films are suitable as a candidate of metal/insulator hybrid materials used for spin quantum cross devices and may open up a novel research field on the electric characteristics of a few atoms or molecules, which leads to high-density memories.

A comparative study of the adsorption and hydrogenation of acrolein on Pt(1 1 1), Ni(1 1 1) film and Pt–Ni–Pt(1 1 1) bimetallic surfaces

In this study we have investigated the reaction pathways for the decomposition and hydrogenation of acrolein (CH 2 CH−CH O) on Ni/Pt(1 1 1) surfaces under ultra-high vacuum (UHV) conditions using temperature programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). While gas-phase hydrogenation products are not observed from clean Pt(1 1 1), the subsurface Pt–Ni–Pt(1 1 1), with Ni residing below the first layer of Pt, is active for the self-hydrogenation of the C O bond to produce unsaturated alcohol (2-propenol) and the C C bond to produce saturated aldehyde (propanal), with the latter being the main hydrogenation product without the consecutive hydrogenation to saturated alcohol. For a thick Ni(1 1 1) film prepared on Pt(1 1 1), the self-hydrogenation yields for both products are lower than that from the Pt–Ni–Pt(1 1 1) surface. The presence of pre-adsorbed hydrogen further enhances the selectivity toward C O bond hydrogenation on the Pt–Ni–Pt(1 1 1) surface. In addition, HREELS studies of the adsorption of the two hydrogenation products, 2-propenol and propanal, are performed on the Pt–Ni–Pt(1 1 1) surface to identify the possible surface intermediates during the reaction of acrolein. The results presented here indicate that the hydrogenation activity and selectivity of acrolein on Pt(1 1 1) can be significantly modified by the formation of the bimetallic surfaces.

On the growth of carbon nanofibers on glass with a Cr layer by inductively coupled plasma chemical vapor deposition: The effect of Ni film thickness

We have studied the effect of the thickness of catalytic Ni film for the growth of vertically aligned carbon nanofibers (VA-CNFs) on glass substrates coated with a conductive underlayer of Cr. Both the pretreatment process through which the catalytic Ni nanoparticles were formed and the growth of well-aligned CNFs were carried out in an inductively coupled plasma chemical vapor deposition (ICP-CVD) system. The VA-CNFs were characterized by scanning electron microscopy, Raman spectroscopy, as well as field emission measurements. The results of VA-CNF growth shows that as the Ni film thicknesses decrease, not only the length but also the density of the CNFs drop, although the density of catalytic Ni nanoparticles increases. The variation of CNF density with Ni film thicknesses is believed to be a result of the detachment of the CNFs from the substrate, caused by the electrostatic force produced by the plasma sheath electric field, as well as an ion-enhanced chemical etching effect due to atomic/ionic hydrogen, during the ICP-CVD growth. A field emission measurement apparatus based on a metallic probe of spherical anode structure was also constructed in this study. An electrostatic image model was employed to determine the electric field distribution on the cathode surface. Along with the standard F−N field emission model, the dependence of field emission current density on the cathode surface electric field, as well as an effective field enhancement factor, were extracted from the current-voltage measurement results. The threshold electric field (Ethreshold, for a current density of 1 mA/cm2) increases from 9.2 V/μm to 13.1 V/μm, and then drops to 11.5 V/μm for the CNFs with Ni film thicknesses of 20 nm, 30 nm, and 40 nm, respectively. The electrostatic model results also indicate that the 20 nm case has the greatest space-charge effect on the emission current, consistent with the growth results that the 20 nm case has the lowest CNF density. On the other hand, the CNF length of the 40 nm case is longer than that of the 30 nm one, while the densities are nearly the same; as a result, Ethreshold for the 30 nm case is higher.

Thickness and strain dependent magnetic anisotropy of ultrathin Fe/Ni films

Using the full potential linearized augmented plane wave method (FLAPW), the magnetic properties of ultrathin Fe/Ni films grown on Cu(0 0 1) surface have been investigated. We have varied both Ni and Fe film thicknesses and also have explored the strain effect on the magnetic anisotropy. For surface Fe atom, a typical surface enhancement of spin magnetic moment has been observed while the magnetic moments of other constituents are rather insensitive to the strain effect. Nonetheless, we have realized that the direction of magnetization is significantly affected by the strain factor. For instance, the Fe/Ni films always have perpendicular magnetization provided that they are grown on Cu(0 0 1) lattice constant. However, we have obtained a spin reorientation transition (SRT) phenomenon in the presence of strain effect.

Stress evolution during Ni–Si compound formation for fully silicided (FUSI) gates

The stress (force) evolution during the formation of different Ni silicide phases was monitored by in situ curvature measurements, for the reaction of thin Ni films of various thicknesses with 100 nm polycrystalline-Si deposited on oxidized (1 0 0) Si substrates. The silicide phase formation was also monitored by in situ X-ray diffraction, allowing to match and interpret the stress evolution in terms of the formation of the different silicide phases. We found that stresses developed during the formation of the different silicides can be explained qualitatively in terms of the corresponding volume changes at the reacting interfaces. Furthermore, the matching between XRD and force curve reveals that the highest compressive stress is related to the formation of the Ni 31Si 12 phase, and that the stress formed is relaxed when the reaction is completed.

Superconducting characterization of Ni/Bi2Sr2Ca2Cu3Oy superconductors

We deposited non-superconducting materials, Ni metal on the surface of Bi2Sr2Ca2Cu3Oy (BSCCO) superconductors. Critical temperature (Tc) and critical current (Ic) of Ni/BSCCO specimens decreased with increasing thickness of Ni films. This indicates that the Tc and the Ic of the BSCCO films are degraded with a thickness of Ni. This behavior is approximately equal to that of a Ni/YBa2Cu3Oy (YBCO) specimen, where the Tc and the Ic of it were dependent on rf power during Ni deposition. Therefore, the degradation of the Ni/BSCCO specimen may be due to the Ni diffusion into the BSCCO films.

Epitaxial growth on nickel-plated diamond seeds at high pressure and high temperature

Epitaxial growth on nickel-plated diamond seeds at high pressure and high temperature (HPHT) was observed with graphite as carbon source. The thickness of the electroplating nickel film which acts as a catalyst/solvent ranges from 54.6 μm to 255.6 μm. The relationship between the Ni film thickness and diamond growth rate is investigated. When the nickel film thickness is from 90 μm to 129 μm, diamond crystals can nearly grow up to three times as large as the original seeds at ∼ 5.8 GPa and ∼ 1460 °C within 14 min. The mechanism of the crystal growth with nickel-plated diamond seeds under HPHT is discussed. The results and techniques might be useful for high quality saw-grade diamonds production and large diamond single crystal growth.

A thermally robust Ni-FUSI process using in 65 nm CMOS technology

The interest in the low resistivity fully silicided (FUSI) gate increased significantly because of promising in use as contact to the source, drain, and gate for sub−65 nm/45 nm CMOS devices. NiSi is potentially an attractive material due to its capability to maintain low resistivity even for channel length down to 100 nm. The Formation of thermally stable silicide gates is important for improving the devices fabrication processes. In order to obtain a thermally stable Ni-FUSI gate electrode, we introduced a two-step annealing process associated with properly tuned thickness of the initial Ni film and additional of implantation of BF2 during the poly-gate formation to push the transformation of NiSi2 to higher temperatures at about 900°C and retard agglomeration. A mixed-phase of nickel silicide layer was commonly observed during phase transformation. For the first time, we established an effective way to identify the phase transformations by some nondestructive techniques such as X-ray diffraction, sheet resistance measurement and AFM analysis. The correlations between its electrical and morphological changes during Ni–Si phase transformation were presented. Furthermore, the effect with addition amount of BF2 impurities into NiSi was investigated. F-incorporation demonstrated some improvements in both morphology and phase stability of the NiSi films at high processing temperatures.

Microwave characteristics of low density hollow glass microspheres plated with Ni thin-film

Hollow glass microspheres coated with thin Ni films of various thicknesses (about 50–250nm) were obtained by electroless plating technique. The resultant magnetic microspheres had very low densities (∼0.39–1.28gcm−3) and low coercivities (<40Oe). As-plated films comprised of nanocrystallites embedded in amorphous matrix and postannealing treatment led to a submicrocrystalline structure and an increased saturation magnetization. The high frequency properties of the composites consisting of Ni-plated microspheres and polymer were investigated. The permittivity and permeability increased with increasing microsphere content in the composite and increasing Ni film thickness. These composites had ferromagnetic resonance peak in the range of 5–12GHz. Postannealing also had an effect on the microwave properties. The reflection loss of the composite was found dependent on the absorber material thickness, polymer:microsphere ratios, the Ni film thickness, as well as the heat treatment of the microspheres.

Nickel pulse reversal plating for image reversal of ultrathin electron beam resist

The effects of various pulse reversal plating parameters on the grain size and smoothness of Ni film on silver seed layers has been studied. The duty cycle, frequency, bath temperature and agitation methods have been tested. The objective was to form a thin continuous hard etch mask (20–30 nm of thickness) of Ni films for image reversal of thin film resist using electroplating. While nickel sulfamate solution without additives or brighteners has been used to plate Ni films, reactive ion etching (RIE) has been used to test the durability of the plated Ni films in fluorine plasma. It was found that pulse reversal plating with current intensity of 12 mA/cm 2, duty cycle of 90%, bath temperature of 45 °C, ultrasonic agitation of power 80 W, and 400 kHz wave frequency resulted in a plating rate as low as 0.2 nm/s. This plating rate made the control of the film thickness an easy task to achieve. This yielded to a smooth plated surface free from defects or voids, with 25 nm film thickness. Combining electron beam lithography with pulse reversal plating for image reversal and RIE offers the prospect of patterning patterns with the desired aspect ratio. Holes of 100 nm diameter, 250 nm period, and 300 nm depth are achieved using this process.

Study of reaction process on Ni/4H–SiC contact

The present study deals with mechanisms of the reaction process of fabricated thin film Ni/SiC contacts by means of XRD, XPS and Raman spectroscopy. After annealing SiC samples sputter coated with Ni at 800 and 950°C in vacuum for 20 min, the dominant silicide is textured Ni2Si. Its formation consists of two stages: initial reaction rate and subsequent diffusion controlled stage. For ultra thin initial Ni layer (∼3–6 nm), islands formation of Ni2Si is observed after heat treatment. Increasing the Ni film thickness prevents this phenomenon. The C released owing to the Ni2Si formation reaction forms a thin graphite layer on the top of the surface and also tends to form cluster inside the reaction layer. The overall degree of graphitisation is higher at 950°C than that at 800°C.

Advanced Gate Stacks with Fully Silicided (FUSI) Gates and High-k Dielectrics for Low Power CMOS

We present a new threshold-voltage (Vth) control technique for fully-silicided metal/high-k gate stacks which are suitable for 45nm-node LOP and LSTP CMOS. The key is the phase control of FUSI Ni-silicide (PC-FUSI) by changing Ni film thickness prior to silicidation anneal. As a result, Ni3Si and NiSi2 are formed whose effective workfunctions (WFs) on HfSiON are found to be 4.8eV and 4.4eV, respectively, being largely displaced from Si-midgap by {plus minus}0.2eV. Meanwhile, the dopant segregation method, known to be successful in Vth-control of NiSi on SiO2, did not work on HfSiON. With Ni3Si-PFET and NiSi2-NFET transistors, a wide range of Vth-tuning is achieved coping with both LSTP and LOP requirements. At the same time, leakage suppression merit is better than the 45nm-node targets at electrical thickness (Tinv) around 2.0nm. Also, our PC-FUSI devices show performance improvement and sufficient long term reliability.

Abnormal reduction of coercivity on magnetic cobalt–platinum alloy films

Ultrathin Co–Pt alloy films as substrate were studied by the surface magneto-optical Kerr effect. As the growth of Ni, the films show uniquely high polar Kerr responses without any in-plane signals. The coercivity decreased until the thickness of Ni film was higher than 5 ML. A new surface structure was discovered at 7–10 ML Ni/Co–Pt films by the low-energy electron diffraction. Interestingly, polar Kerr signal and coercivity of the 10 ML Ni/Co–Pt(1 1 1) template film reduced rapidly as Co films were further deposited onto only about 1–2 ML. Then the films show a canted magnetization with a rollback hysteresis in the polar configuration during the growth of Co. Coercivity of the 7 ML Co/Ni/Co–Pt film was found unusually down to almost 100 Oe.The corresponding magic number at around 7 ML of Co in the abnormal reduction of coercivity may be attributed to the cluster formations of Co.

Adhesion strength of Ni film on Ti substrate characterized by three-point bend test, peel test and theoretic calculation

Electroplating was employed to fabricate the Ni film on the Ti substrate. Adhesion strength of Ni film on Ti substrate was determined using the three-point bend technique that was proposed in standard mechanics test. The experimental results demonstrate that the interface fracture energies obviously increase with the roughness of Ti substrates, and are independence with the thickness of Ni films. Moreover, the adhesion strength of Ni film on Ti substrate was also measured by peel test, and was evaluated by Miedema model of experiential electron theory. The intrinsic interface fracture energy measured by three-point bend test is reasonable agreement with that obtained by theoretical calculation of Miedema model, and is roughly comparable to that by peel test.

Electrically robust ultralong nanowires of NiSi, Ni2Si, and Ni31Si12

Mass fabrication of directly accessible, ultralong, uniform Si nanowires is realized by employing a controllable and reproducible method based on standard Si technology. High-conductivity polycrystalline Ni-silicide nanowires around 30 nm by 30 nm in cross section, able to support extremely high currents at ∼108A∕cm2, are obtained by means of solid-state reaction of the Si nanowires with subsequently deposited Ni films. By properly adjusting the Ni film thickness, NiSi, Ni2Si, and Ni31Si12 nanowires characterized with distinct resistivity and temperature coefficient of resistance are obtained. Upon annealing, the electrical continuity of the nanowires breaks at temperatures about 0.7 times the melting points of the silicides.