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 characterization of Co/cenosphere core-shell structure composites

The cobalt film was successfully coated on the cenosphere particles using heterogeneous precipitation thermal reduction method. The morphology and microstructure of the products were analyzed by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). FE-SEM results implied that the Co film was relatively uniform and compact. XRD results indicated that the Co film coated on cenospheres was a face-centered cubic structure (fcc) and the crystallite size of Co particles was about 24.5 nm. The magnetic property of Co/cenosphere composites was measured by vibrating sample magnetometer (VSM), and the results showed that the Co/cenosphere composites were of the weak soft magnetic property at room temperature, the Ms and Hc value was 18.2 Am² kg⁻¹ and 28.4 kA m⁻¹, respectively.     

Reactively sputtered Ni, Ni(N) and Ni3N films: Structural, electrical and magnetic properties

Nickel thin films were deposited on glass substrates at different N₂ gas contents using a dc triode sputtering deposition system. Triode configuration was used to deposit nanostructured thin films with preferred orientation at lower gas pressure and at lower substrate temperature compared to the dc diode sputtering system. A gradual evolution in the composition of the films from Ni, Ni(N), to Ni₃N was found by X-ray diffraction analysis. The preferred growth orientation of the nanostructured Ni films changed from (1 1 1) to (1 0 0) for 9% N₂ at 100 °C. Ni₃N films were formed at 23% N₂ with a particle size of about 65 nm, while for 0% and 9% of nitrogen, the particles sizes were 60 nm, and 37 nm, respectively, as obtained by atomic force microscopy. Magnetic force microscopy imaging showed that the local magnetic structure changed from disordered stripe domains of about 200 nm for Ni and Ni(N) to a structure without a magnetic contrast, indicating the paramagnetic state of this material, which confirmed the structural transformation from Ni to Ni₃N.     

Direct current magnetron sputter-deposited ZnO thin films

Zinc oxide (ZnO) is a very promising electronic material for emerging transparent large-area electronic applications including thin-film sensors, transistors and solar cells. We fabricated ZnO thin films by employing direct current (DC) magnetron sputtering deposition technique. ZnO films with different thicknesses ranging from 150 nm to 750 nm were deposited on glass substrates. The deposition pressure and the substrate temperature were varied from 12 mTorr to 25 mTorr, and from room temperature to 450 °C, respectively. The influence of the film thickness, deposition pressure and the substrate temperature on structural and optical properties of the ZnO films was investigated using atomic force microscopy (AFM) and ultraviolet-visible (UV-Vis) spectrometer. The experimental results reveal that the film thickness, deposition pressure and the substrate temperature play significant role in the structural formation and the optical properties of the deposited ZnO thin films.     

Surface roughness and power spectral density study of SHI irradiated ultra-thin gold films

Quantitative roughness and microstructural analysis of as-deposited and swift heavy ion (SHI) (107 MeV Ag and 58 MeV Ni) irradiated 10 and 20 nm thick Au films were performed by atomic force microscopy (AFM). Power spectral density (PSD) analysis was done from the AFM images. The energies chosen for the two different ions eliminated the velocity effect of SHI in materials modification. The rms roughness estimated from the AFM data did not show either monotonic increase or decrease with ion fluences. Instead, it increased at low fluences and decreased at high fluences for 20 nm thick film. In 10 nm film, the roughness first increased with ion fluence, then decreased and again increased at higher fluences. Though the 10 and 20 nm films exhibited very different patterns of rms roughness variation with ion fluence, the pattern of variation in both cases was identical for Ni and Ag beams. The PSD analysis for both 10 and 20 nm films (pristine and irradiated) showed similar variation of low frequency roughness with ion fluence as that of the rms roughness. In the high frequency regime, PSD analysis suggests that surface morphology of the irradiated samples is governed by the combined effect of evaporation-recondensation and diffusion dominated processes.     

Deposition of Ni, Ag, and Pt-based Al-doped ZnO double films for the transparent conductive electrodes by RF magnetron sputtering

Ni, Ag, and Pt-based Al-doped ZnO (AZO) films have been deposited as transparent conductivity layers on quartz by RF magnetron sputtering and characterized by X-ray diffraction, Hall measurement, optical transmission spectroscopy, scanning electron microscopy (SEM). The deposition of thicker metal layer in double layers resulted in lowering the effective electrical resistivity with a slight reduction of their optical transmittance. A film consisting of AZO (250 nm)/Ni (2 nm) double structure, exhibits a sheet resistance of 21.0 Ω/sq, a high transmittance of 76.5%, and characterize good adhesion to substrate. These results make the satisfactory for GaN-based light-emitting diodes (LEDs) and solar cells with metal-based AZO double films as current spread layers.     

Comparative study of electroless copper deposition based on the seed layers of Pd, PtPd and AuPd

The article reports on electroless deposition of copper films onto p-silicon (1 0 0) using different seed (co-seed) layers of Pd, PtPd and AuPd. The dependence of the compositions and morphologies of different seed layers on resultant Cu films were comparatively studied in detail by atomic force microscopy (AFM), field emission scanning electron microscope (FE-SEM) and X-ray photoelectron spectroscopy (XPS). The activities of electroless copper deposition on the p-silicon (1 0 0) with different seed (co-seed) layers were evaluated by polarization curve. It is concluded that the bimetallic AuPd seed displayed the highest catalytic activity for electroless copper deposition, and followed by the order of PtPd > Pd.     

Bi surfactant effects of Co/Cu multilayered films prepared by sputter deposition

The influence of a Bi surfactant layer on the structural and magnetic properties of Co/Cu multilayers grown onto Cu(1 1 0) buffer layer by RF magnetron sputtering has been studied. The results of X-ray diffraction revealed the initial deposition of a 2.0 Å-thick Bi layer onto the Cu buffer layer prior to the deposition of the Co/Cu multilayer yielded high-quality fcc-(1 1 0) oriented epitaxial films. The X-ray photoelectron spectra revealed that Bi was segregated at around the top of the surface. Therefore, Bi was concluded to be an effective surfactant to enhance the epitaxial growth of Co/Cu(1 1 0) multilayer. The maximum giant magnetoresistance and antiferromagnetic interlayer coupling ratios of the Co/Cu multilayers were increased by using the Bi surfactant layer.     

Magnetic properties of self-assembled nanostructure films on the base of amorphous Ni granules

We report on structural and magnetic properties of granular films consisting of 2.5 nm Ni nanoparticles. The films are fabricated by the original laser electrodispersion technique, which allows producing nearly monodisperse and amorphous particles. Atomic force microscopy (AFM) study shows that in 8 nm thickness films the particles are self-assembled in clusters with the lateral size 100-150 nm and the height of about 8 nm. Performed by SQUID, the films magnetization measurements reveal superparamagnetic behaviour, characteristic for an ensemble of non-interacting single domain magnetic particulates. It is found that the magnetic moment of the particulate is equal to that of about 3000 individual Ni nanoparticles and the blocking temperature is close to room temperature. Defined from magnetic measurements, the size of single domain particulates correlates well with the size of the clusters determined from AFM images. We propose that exchange interaction plays an important role in the formation of the particulates by aligning the magnetic moments of the individual Ni nanoparticles inside the clusters. Presence of magnetic clusters with high blocking temperature makes the fabricated films potentially useful for high-density magnetic data storage applications.     

Evolution of surface morphology of NiO thin films under swift heavy ion irradiation

NiO nanoparticle thin films grown on Si substrates were irradiated by 107 MeV Ag⁸⁺ ions. The films were characterized by glancing angle X-ray diffraction and atomic force microscopy. Ag ion irradiation was found to influence the shape and size of the nanoparticles. The pristine NiO film consisted of uniform size (∼100 nm along major axis and ∼55 nm along minor axis) elliptical particles, which changed to also of uniform size (∼63 nm) circular shape particles on irradiation at a fluence of 3 × 10¹³ ions cm⁻². Comparison of XRD line width analysis and AFM data revealed that the particles in the pristine films are single crystalline, which turn to polycrystalline on irradiation with 107 MeV Ag ions.     

Magnetic nanoparticles as building blocks for high-performance magnetic materials

We report on the magnetic behaviour of films of Fe nanoparticles deposited from the gas phase with sizes in the range 2–3 nm embedded in Ag and Co matrices and Co nanoparticles of the same size embedded in Ag matrices. Magnetometry measurements, using a VSM, of very low volume fraction (1–2%) assemblies of Fe and Co in Ag show perfect superparamagnetism and enable us to confirm that the size distribution of the particles in the matrix is the same as that of the free particles prior to deposition. The hysteresis loops at 2 K, which is below the blocking temperature, show that the particles have a uniaxial anisotropy that is randomly oriented in three dimensions with the Co nanoparticles having a much higher anisotropy than the Fe particles. The soft magnetic behaviour of pure Fe and Co nanoparticle films with no matrix is well described by a random anisotropy model and is consistent with the formation of a correlated super-spin glass (CSSG) characteristic of amorphous materials. The Co nanoparticle films appear to have a lower random anisotropy than the Fe ones in contrast to the behaviour observed for the isolated particles. Films of Fe nanoparticles embedded in Co matrices, whose saturation magnetization exceeds the Slater–Pauling curve, also show magnetic behaviour consistent with a CSSG. At high volume fractions, the films of Fe nanoparticles embedded in Co matrices behave almost identically to films of pure Co nanoparticles.     

Growth and characterization of nanostructured anatase phase TiO<Subscript>2</Subscript> thin films prepared by DC reactive unbalanced magnetron sputtering

Titanium dioxide thin films were deposited on three different unheated substrates by unbalanced magnetron sputtering. The effects of the sputtering current and deposition time on the crystallization of TiO₂ thin films were studied. The TiO₂ thin films were deposited at three sputtering current values of 0.50, 0.75, and 1.00 A with different deposition times of 25, 35, and 45 min, respectively. The surface morphology of the films was investigated by atomic force microscopy (AFM). The structure was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The film thickness was determined by field emission scanning electron microscopy (FE-SEM), and the optical property was evaluated with spectroscopic ellipsometry. The results show that polycrystalline anatase films were obtained at a low sputtering current value. The crystallinity of the anatase phase increases as the sputtering current increases. Furthermore, nanostructured anatase phase TiO₂ thin films were obtained for all deposition conditions. The grain size of TiO₂ thin films was in the range 10–30 nm. In addition, the grain size increases as the sputtering current and deposition time increase.     

Properties of Cu film and Ti/Cu film on polyimide prepared by ion beam techniques

Cu film and Ti/Cu film on polyimide substrate were prepared by ion implantation and ion beam assisted deposition (IBAD) techniques. Three-dimension white-light interfering profilometer was used to measure thickness of each film. The thickness of the Cu film and Ti/Cu film ranged between 490 nm and 640 nm. The depth profile, surface morphology, roughness, adhesion, nanohardness, and modulus of the Cu and Ti/Cu films were measured by scanning Auger nanoprobe (SAN), atomic force microscopy (AFM), and nanoindenter, respectively. The polyimide substrates irradiated with argon ions were analyzed by scanning electron microscopy (SEM) and AFM. The results suggested that both the Cu film and Ti/Cu film were of good adhesion with polyimide substrate, and ion beam techniques were suitable to prepare thin metal film on polyimide.     

Effect of Ni, Pd and Ni-Pd nano-islands on morphology and structure of multi-wall carbon nanotubes

In this research, the effect of Ni, Pd and Ni-Pd catalysts have studied on morphology and structure of synthesized multi-wall carbon nanotubes (MWCNTs). Initially, thin films of Ni (with two thicknesses of 10 and 20 nm), Pd/Ni (5/10 nm) and Pd (10 nm) were deposited as catalysts on SiO₂ (60 nm)/Si(1 0 0) substrates, using dc magnetron sputtering technique. The deposited films were annealed at 900 °C in ammonia environment for 45 min, in order to obtain nano-structured catalyst on the surface. Using scanning electron microscopy (SEM), the average size of Ni nano-islands (synthesized by the 10 and 20 nm Ni films), Pd and Ni-Pd nano-islands were measured about 55, 110, 45 and 50 nm, respectively. According to X-ray photoelectron spectroscopy analysis (XPS), the ratio of Ni/Pd on the surface was about 3 for the bilayer sample. The CNTs were synthesized on the nano-island catalysts at 940 °C in CH₄ ambient using a thermal chemical vapor deposition method. The results revealed that average diameter of the CNTs were about 70, 110, 120 nm for Ni, Ni-Pd and Pd catalysts, respectively. Raman spectra of the MWCNTs showed that intensity ratio of two main peaks located in the range of 1550-1600 and 1250-1450 cm⁻¹ (as a quality factor for the CNTs) for Ni, Pd and Ni-Pd catalysts were 1.42, 0.91 and 0.85, respectively. Therefore, based on our data analysis, although addition of Pd to Ni catalyst caused a considerable reduction in the quality of the grown MWCNTs as compared to the pure Ni catalyst, but it resulted in an enhancement in the methane decomposition rate. For the pure Pd catalyst samples, both a slow methane decomposition rate as compared with Ni-Pd catalyst samples and a poor quality of CNTs were observed as compared with the Ni catalyst, under similar experimental conditions.     

Influence of Co:Cu ratio on properties of Co–Cu films deposited at different conditions

A series of Co–Cu films with different Co:Cu ratio was electrodeposited at different electrolyte pH, deposition potential and film thickness, and their morphology, crystal structure and magnetic properties were investigated. Compositional analysis by energy dispersive x-ray spectroscopy disclosed that the Co and Cu content were 75 and 25 wt%, respectively, at high pH (3.2) level, while for films at low pH (2.5) level the compositions are 61 Co and 39 wt% Cu, and further decrease of Co:Cu ratio occurred as the film thicknesses increased. The surface morphology of the films changed from an initial dendritic stage to expanded dendrites with increasing Cu content by the electrolyte pH. The dendrites became more obvious at 3 μm and the dendritic structures increased with further increase of film thickness as the Co:Cu ratio decreased. Hence, the increase of the Cu content is thought to be the cause of the increase of dentritic structure. Structural characterizations by x-ray diffraction (XRD) showed that all films have face-centered cubic structure. In the XRD patterns, the peak intensity of Co (111) is lower for the films grown at low pH compared to that of high pH, and the (111) peaks of Co and Cu slightly separated at 3 μm and then the intensity of the Cu (111) increased with increasing film thickness from 4 to 5 μm, so that the Co:Cu ratio changed at all deposition parameters. Magnetic measurements displayed that the saturation magnetization decreased and the coercivity increased as the Co:Cu ratio decreased with all deposition parameters. Also, the magnetic easy axis was found to be in the film plane for all films. It was seen that the variations in the properties of the films might be attributed to the change of Co:Cu ratio caused by the deposition parameters.     

Engineering of hydrophilic and plasmonic properties of Ag thin film by atom beam irradiation

Hydrophilic Ag nanostructures were synthesized by physical vapour deposition of 5 nm Ag thin films followed by irradiation with 1.5 keV Ar atoms. Optical absorbance measurements show a characteristic surface plasmon resonance absorption band in visible region. A blue-shift in absorbance from 532 to 450 nm is observed with increasing fluence from 1 × 10¹⁶ to 3 × 10¹⁶ atoms/cm². Atomic force microscopy was performed for the pristine and irradiated samples to study the surface morphology. The atom beam irradiation induced sputtering and surface diffusion lead to the formation of plasmonic surface. Rutherford backscattering spectroscopy of the pristine and irradiated film indicates that metal content in the film decreases with ion fluence, which is attributed to the sputtering of Ag by Ar atoms. The contact angle measurement demonstrates the possibility of engineering the hydrophilicity by atom beam irradiation.     

Thin Co films with tunable ferromagnetic resonance frequency

The tailored production of thin Co films of 50 nm thick with ferromagnetic resonance frequency in a range from 2.9 to 7.3 GHz using the DC magnetron sputtering is reported. The ferromagnetic resonance frequency, coercivity, effective magnetic field and nanocrystalline structure parameters are shown to be governed by the Co deposition rate. For this investigation, FMR, VSM and TEM techniques were used.     

Effect of nanoparticle size on magnetic damping parameter in Co92Zr8 soft magnetic films

Co₉₂Zr₈(50 nm)/Ag(x) soft magnetic films have been prepared on Si (111) substrates by oblique sputtering at 45°. Nanoparticle size of Co₉₂Zr₈ soft magnetic films can be tuned by thickening Ag buffer layer from 9 nm to 96 nm. The static and dynamic magnetic properties show great dependence on Ag buffer layer thickness. The coercivity and effective damping parameter of Co₉₂Zr₈ films increase with thickening Ag buffer layer. The intrinsic and extrinsic parts of damping were extracted from the effective damping parameter. For x=96 nm film, the extrinsic damping parameter is 0.028, which is significantly larger than 0.004 for x=9 nm film. The origin of the enhancement of extrinsic damping can be explained by increased inhomogeneity of anisotropy. Therefore, it is an effective method to tailor magnetic damping parameter of thin magnetic films, which is desirable for high frequency application.     

The influence of different doping elements on microstructure, piezoelectric coefficient and resistivity of sputtered ZnO film

ZnO film is attractive for high frequency surface acoustic wave device application when it is coupled with diamond. In order to get good performance and reduce insertion loss of the device, it demands the ZnO film possessing high electrical resistivity and piezoelectric coefficient d₃₃. Doping ZnO film with some elements may be a desirable method. In this paper, the ZnO films undoped and doped with Cu, Ni, Co and Fe, respectively (doping concentration is 2.0 at.%) are prepared by magnetron sputtering. The effect of different dopants on the microstructure, piezoelectric coefficient d₃₃, and electrical resistivity of the film are investigated. The results indicate that Cu dopant can enhance the c-axis orientation and piezoelectric coefficient d₃₃, the Cu and Ni dopant can increase electrical resistivity of the ZnO film up to 10⁹ Ω cm. It is promising to fabricate the ZnO films doped with Cu for SAW device applications.     

Surface characteristics of Ni catalystic films on growth behavior of multi-walled carbon nanotubes

The effect of the surface characteristics of Ni catalyst films on the growth behavior of multi-walled carbon nanotubes (MWCNTs) were investigated using Ni catalyst films prepared by different physical vapor deposition methods, electron-beam evaporation and sputtering. The growth behavior of MWCNTs was dependent upon the surface roughness of the Ni films. After a pretreatment process with NH₃, the root mean squares of surface roughness of e-beam evaporated and sputtered Ni catalyst films increased to 16.6 and 3.2 nm, respectively. Curled-MWCNTs and carbon-encapsulated Ni nanoparticles were formed on the Ni film deposited by e-beam evaporation while vertically aligned-MWCNTs were grown on the sputter-deposited film. In addition, the surface roughness of the Ni films affected the field emission properties of the MWCNTs. This was considered to originate from the specific growth behavior of the MWCNTs which was primarily caused by the initial surface roughness of the Ni films.