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.     

The growth of soft magnetic FeNiN thin films under different experimental procedures

FeNiN thin films with good soft magnetic properties were synthesized on Si (1 0 0) substrates at 473 K by RF magnetron sputtering. The dependence of phase structure and magnetic properties on nitrogen partial pressure, nickel concentrations, film thickness and substrate temperature were systematically investigated. The phase evolution from α-(Fe,Ni)N to ξ-(Fe,Ni)₂N with increase of nitrogen partial pressure was seen. The addition of Ni caused FeNiN films to turn from BCC structure to FCC structure. Clear reproducible striped domains appeared at the film surfaces when X_Ni=19.6%, which is explained by the high enough perpendicular anisotropy and the small stress in the film. All films show smooth surfaces and good soft magnetic properties compared to corresponding FeN compounds. The magnetic properties depended dramatically on the phase structure. Optimum soft magnetic properties with H_C of <1 Oe are obtained between 5.0%?X_Ni?10.0%.     

Influence of Ni deposition and subsequent N ion implantation at different substrate temperatures on nano-structure and corrosion behaviour of type 316 and 304 stainless steels

Ni thin films of 250 nm thicknesses were coated on type 304 and 316 stainless steels and post N⁺ ion implanted at 15 keV energy with a fluence of 5 × 10¹⁷ N⁺ cm⁻² at different substrate temperatures. Surface nano-structure of the samples were analysed using X-ray diffraction (XRD), atomic force microscopy (AFM) before corrosion test and scanning electron microscopy (SEM) after corrosion test. Corrosion behaviour of the samples in 1.0 M H₂SO₄ solution was investigated by means of potentiodynamic technique. Nano-structure and crystallography of the films showed the development of Ni₃N(1 1 1) and Ni₄N(2 0 0) orientations with a minimum surface roughness and grain size at 400 K substrate temperature. The highest corrosion resistance with a corrosion current of 0.01 μA cm⁻² (for SS(316)) and 0.56 μA cm⁻² (for SS(304)) was achieved in case of samples which were N⁺ ion implanted at 400 K. Results for both types of stainless steels showed good agreement and the better performance of SS(316) was attributed to the 2% molybdenum contents in the alloy composition of this type of stainless steel, which enhances the effectiveness of nitrogen in retarding the corrosion process.     

Influence of assisted ion energy on surface roughness and mechanical properties of boron carbon nitride films synthesized by DIBSD

The BCN thin films were produced by dual ion beam sputtering deposition (DIBSD). The influence of assisted ion energy on surface roughness and mechanical properties of BCN films were investigated. The surface roughness was determined by atomic force microscopy (AFM) and the mechanical properties of BCN firms were evaluated by nano-indentation in N₂ gas. The composition, structure and chemical bonding of the BCN thin films were analyzed by using energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), laser Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). These films appeared as amorphous structure. As a result, the BCN films with the smoothest surface (R_a = 0.35 nm and R_p-v = 4.4 nm) and the highest nano-hardness of 30.1 GPa and elastic modulus of 232.6 GPa were obtained at 200 eV and 12 mA with N₂:Ar = 1:1, and the chemical composition of this BCN film was 81 at.% B, 14 at.% C and 5 at.% N. Moreover, several bonding states such as B-N, B-C and C-N were observed in BCN thin films.     

Solid-state synthesis and phase transformations in Ni/Fe films: Structural and magnetic studies

We have used X-ray diffraction, volume magnetocrystalline anisotropy constant and resistance measurements to study solid-state synthesis in Ni(0 0 1)/Fe(0 0 1), Ni/Fe(0 0 1) and Ni/Fe thin films with the atomic ratio between Fe and Ni of 1:1 (1Fe:1Ni), and 3:1 (3Fe:1Ni). We have found that the formation of Ni₃Fe and NiFe phases in the 1Fe:1Ni films takes place at temperatures ∼620 and ∼720 K, correspondingly. In the case of the 3Fe:1Ni films the solid-state synthesis starts with Ni₃Fe and NiFe phase formation at the same temperatures as for the 1Fe:1Ni films. The increasing of annealing temperature above 820 K leads to the nucleation of a paramagnetic γ_par phase at the FeNi/Fe interface. The final products of solid-state synthesis in the Ni(0 0 1)/Fe(0 0 1) thin films are crystallites which consist of the epitaxially intergrown NiFe and γ_par phases according to the [1 0 0](0 0 1)NiFe||[1 0 0](0 0 1)γ_par orientation relationship. The crystalline perfection and epitaxial growth of the (NiFe+γ_par) crystallites on the MgO(0 0 1) surface allow to distinguish (0 0 2)γ_par and (0 0 2)NiFe X-ray peaks (the cell parameters are: a(γ_par)=0.3600±0.0005 nm and a(NiFe)=0.3578±0.0005 nm, correspondingly). At low temperatures the paramagnetic γ_par phase undergoes the martensite _γpar→α^′${\gamma }_{\mathrm{par}}\to {\alpha }^{\prime }$ phase transition which can be hindered by thermal and epitaxial strains and epitaxial clamping with a MgO substrate. On the basis of the studies of the thin-film solid-state synthesis we predict the existence of two novel structural phase transformations at the temperatures of about 720 and 820 K for alloys of the invar region of the Fe–Ni system.     

Effects of post-thermal treatments on morphological and optical properties of NiO/Ni(OH)2 thin films synthesized by solution growth

Room temperature deposition of PVP capped nanostructured NiO/Ni(OH)₂ thin film, the morphological and optical characterizations by solution growth technique are reported. The nanostructured thin films which were deposited on optical glass substrates were annealed at different temperatures and then subjected to structural, morphological and optical characterizations. X-ray diffraction measurements of the films revealed that higher temperatures during the thermal treatment enhanced the crystallinity of the thin films. The SEM surface micrographs show non-interconnected uniformly deposited fibre-like structures with approximate lengths between 400 and 1200 nm. The optical band gap energy roughly decreased from about 2.7 eV to about 2.2 eV with thermal treatment. The absorbance of the thin films annealed at 300 and 400 °C was as high as 90% in the visible region of the electromagnetic spectrum. These materials could be useful in solar thermal conversion processes.     

Effects of the substrate and oxygen partial pressure on the microstructures and optical properties of Ti-doped ZnO thin films

Ti-doped ZnO (ZnO:Ti) thin films were deposited on the glass and Si substrates using radio frequency reactive magnetron sputtering. The effects of substrate on the microstructures and optical properties of ZnO:Ti thin films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and a fluorescence spectrophotometer. The structural analyses of the films indicated that they were polycrystalline and had a hexagonal wurtzite structure on different substrates. When ZnO:Ti thin film was deposited on Si substrate, the film had a c-axis preferred orientation, while preferred orientation of ZnO:Ti thin film deposited on glass substrate changed towards (1 0 0). Finally, we discussed the influence of the oxygen partial pressures on the structural and optical properties of glass-substrate ZnO:Ti thin films. At a high ratio of O₂:Ar of 18:10 sccm, the intensity of (0 0 2) diffraction peak was stronger than that of (1 0 0) diffraction peak, which indicated that preferred orientation changed with the increase of O₂:Ar ratios. The average optical transmittance with over 93% in the visible range was obtained independent of the O₂:Ar ratio. The photoluminescence (PL) spectra measured at room temperature revealed four main emission peaks located at 428, 444, 476 and 527 nm. Intense blue-green luminescence was obtained from the sample deposited at a ratio of O₂:Ar of 14:10 sccm. The results showed that the oxygen partial pressures had an important influence for PL spectra and the origin of these emissions was discussed.     

Influence of substrate temperature on electrical and optical properties of p-type semitransparent conductive nickel oxide thin films deposited by radio frequency sputtering

Nickel oxide thin films were deposited on fused silica and Si(1 0 0) substrates at different substrate temperatures ranging from room temperature to 400 °C using radio frequency reactive magnetron sputtering from a Ni metal target in a mixture of O₂ and Ar. With the increase of substrate temperature, nickel oxide films deposited on the Si substrates exhibit transition from amorphous to poly-crystalline structures with different preferred orientations of NiO(2 0 0) and (1 1 1). The films deposited at higher temperature exhibit higher Ni²⁺/Ni³⁺ ratio. With substrate temperature increasing from room temperature to 400 °C, the electrical resistivities of nickel oxide films increase from (2.8 ± 0.1) × 10⁻² to (8.7 ± 0.1) Ω cm, and the optical band-gap energies increase from 3.65 to 3.88 eV. A p-nickel oxide/n-zinc oxide heterojunction was fabricated to confirm the p-type conduction of nickel oxide thin film, which exhibited a steadily rectifying behavior.     

Properties of dc magnetron sputtered Cu2O films prepared at different sputtering pressures

The sputtering pressures maintained during the deposition of Cu₂O films, by dc reactive magnetron sputtering, influence the structural, electrical and optical properties. The crystalline orientation mainly depends on the sputtering pressure. The films deposited at a sputtering pressure of 4 Pa showed single-phase Cu₂O films along (1 1 1) direction. The electrical resistivity of the films increased from 1.1 × 10¹ Ω cm to 3.2 × 10³ Ω cm. The transmittance of the films increased from 69% to 88% with the increase of sputtering pressure from 2.5 Pa to 8 Pa.     

Synthesis and characterization of superhard Ti-Si-N films obtained in an inductively coupled plasma enhanced chemical vapor deposition (ICP-CVD) with magnetic confinement

Using a novel inductively coupled plasma enhanced chemical vapor deposition (ICP-CVD) with magnetic confinement system, Ti-Si-N films were prepared on single-crystal silicon wafer substrates by sputtering Ti and Si (5 at.%:1 at.%) alloyed target in argon/nitrogen plasma. High-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM), atomic force microscopy (AFM) and Nano Indenter XP tester were employed to characterize nanostructure and performances of the films. These films were essentially composed of TiN nanocrystallites embedded in an amorphous Si₃N₄ matrix with maximum hardness value of 44 GPa. Experimental results showed that the film hardness was mainly dependent on the TiN crystallite size and preferred orientation, which could be tailored by the adjustment of the N₂/Ar ratio. When the N₂/Ar ratio was 3, the film possessed the minimum TiN size of 10.5 nm and the maximum hardness of 44 GPa.     

Influence of substrate crystallography on the room temperature synthesis of AlN thin films by reactive sputtering

A pulsed DC reactive ion beam sputtering system has been used to synthesize aluminium nitride (AlN) thin films at room temperature by reactive sputtering. After systematic study of the processing variables, high-quality polycrystalline films with preferred c-axis orientation have been grown successfully on silicon and Au/Si substrates with an Al target under a N₂/(N₂ + Ar) gas flow ratio of 55%, 2 mTorr processing pressure and keeping the temperature of the substrate holder at room temperature. The crystalline quality of the AlN layer as well as the influence of the substrate crystallography on the AlN orientation has been characterized by high-resolution X-ray diffraction (HR-XRD). Best ω-FWHM (Full Width at Half Maximum) values of the (0 0 0 2) reflection rocking curve in the 1 μm thick AlN layers are 1.3°. Atomic Force Microscopy (AFM) measurements have been used to study the surface morphology of the AlN layer and Transmission Electron Microscopy (TEM) measurements to investigate the AlN/substrate interaction. AlN grew off-axis from the Si substrate but on-axis to the surface normal. When the AlN thin film is deposited on top of an Au layer, it grows along the [0 0 0 1] direction but showing a two-domain structure with two in-plane orientations rotated 30° between them.     

Influence of sputtering pressure on the giant magnetoresistance and structure in Fe–Cu–Ni granular thin films

Composition, structure and giant magnetoresistance in Fe_xCu_yNi_z films prepared at different sputtering pressures were investigated. X-ray diffraction studies showed only Cu (1 1 1) peak from the Cu grain. The shifts in the d-spacing d₁₁₁ of Cu indicates a progressive substitution of Ni in the Cu lattice. Similar trends in d₁₁₁ of Cu observed for the samples prepared at different sputtering pressures indicate that the structural behaviour of the samples is nearly independent of the sputtering pressure. A significant enhancement of magnetoresistance (MR) for the samples sputtered at 0.001 mbar as compared to that sputtered at 0.02 mbar is attributed to the reduced role of residual gas impurities in the films upon lowering the sputtering pressure. An interesting observation is that the MR did not significantly decrease even with a large substitution of Ni in the Cu grains.     

Structural and PL properties of Cu-doped ZnO films

Cu-doped ZnO films with hexagonal wurtzite structure were deposited on silicon (1 1 1) substrates by radio frequency (RF) sputtering technique. An ultraviolet (UV) peak at ∼380 nm and a blue band centered at ∼430 nm were observed in the room temperature photoluminescent (PL) spectra. The UV emission peak was from the exciton transition. The blue emission band was assigned to the Zn interstitial (Zn_i) and Zn vacancy (V_Zn) level transition. A strong blue peak (∼435 nm) was observed in the PL spectra when the α_Cu (the area ratio of Cu-chips to the Zn target) was 1.5% at 100 W, and ZnO films had c-axis preferred orientation and smaller lattice mismatch. The influence of α_Cu and the sputtering power on the blue band was investigated.     

Influence of the nitrogen contents on the permeability characteristics and soft magnetic properties of FeHfN films

High permeability magnetic films can enhance the inductance of thin-film inductors in DC-DC converters. In order to obtain high permeability, the uniaxial anisotropy and coercivity should be as low as possible. This study employed dc reactive magnetron sputtering to fabricate nanocrystalline FeHfN thin films. The influence of the nitrogen flow on the composition, microstructure, and permeability characteristics, as well as magnetic properties was investigated. Increasing the nitrogen content can alter FeHfN films from amorphous-like to crystalline phases. The magnetic properties and permeability depend on variations in the microstructure. With the optimum N₂/Ar flow ratio of 4.8% (N₂ flow: 1.2 sccm), low anisotropy (H_K = 18 Oe), low coercivity (H_C = 1.1 Oe) and high permeability (μ′ > 600 at 50 MHz) were obtained for fabrication of a nanocrystalline FeHfN film with a thickness of around 700 nm. Such as-fabricated FeHfN films with a permeability of over 600 should be a promising candidate for high-permeability ferromagnetic material applications.     

Growth of Ni-Mn-Ga high-temperature shape memory alloy thin films by magnetron sputtering technique

Ni-Mn-Ga thin films have been fabricated by using magnetron sputtering technique under various substrate negative bias voltages. The effect of substrate negative bias voltage on the compositions and surface morphology of Ni-Mn-Ga thin films was systematically investigated by energy dispersive X-ray spectrum and atomic force microscopy, respectively. The results show that the Ni contents of the thin films increase with the increase of the substrate negative bias voltages, whereas the Mn contents and Ga contents decrease with the increase of substrate negative bias voltages. It was also found that the surface roughness and average particle size of the thin films remarkably decrease with the increase of substrate negative bias voltages. Based on the influence of bias voltages on film compositions, a Ni₅₆Mn₂₇Ga₁₇ thin film was obtained at the substrate negative bias voltage of 30 V. Further investigations indicate that the martensitic transformation start temperature of this film is up to 584 K, much higher than room temperature, and the film has a non-modulated tetragonal martensitic structure at room temperature. Transmission electron microscopy observations reveal that microstructure of the thin film exhibits an internally (1 1 1) type twinned substructure. The fabrication of Ni₅₆Mn₂₇Ga₁₇ high-temperature shape memory alloy thin film will contribute to the successful development of microactuators.     

Influence of charged particle bombardment and sputtering parameters on the properties of HfO2 films prepared by dc reactive magnetron sputtering

HfO₂ films prepared on glass substrates by dc reactive magnetron sputtering in an Ar + O₂ atmosphere are investigated. The films are polycrystallized with a pure monoclinic phase, and the crystallization strongly relates to the technology environment. Charged particle bombardment mainly caused by negative oxygen ions during sputtering on the films results in rougher surface morphology and worse crystalline property. Influence of sputtering pressure, substrate temperature and Ar:O₂ flow ratio is studied. The main orientations of the films are (−1 1 1) and (1 1 1). The (−1 1 1) orientation is stable, but (1 1 1) orientation is very sensitive to the sputtering condition, and it can be suppressed effectively by introducing charged particle bombardment, lowing sputtering pressure and increasing oxygen concentration.     

Effect of ambient gas on structural and optical properties of titanium oxynitride films

Titanium oxynitride films have been deposited on glass substrates by reactive RF magnetron sputtering of titanium target. The influence of oxygen partial pressure in N₂ + Ar and N₂ + He mixtures was examined on structural and optical properties of titanium oxynitride films. The prepared samples were characterized by X-ray diffraction, EDS, surface profilometer, AFM and contact angle measurement system. With increase in oxygen partial pressure, the grain size decreases from ∼70 nm to ∼50 nm in N₂ + Ar mixture, while from ∼60 nm to ∼37 nm in N₂ + He mixture. The thickness calculated from optical transmission data and surface profilometer is in good agreement with each other. The deposited samples are hydrophobic by nature and the contact angle was found to decrease with increase in oxygen partial pressure. Samples prepared in oxygen partial pressure ≥5.5% show transmittance of about 97% in the visible region of the spectrum in both N₂ + Ar and N₂ + He mixtures. The atomic mass of the sputtering gas (Ar and He) significantly affects the primary crystallite size, orientation as well as band gap. We were able to relate the better crystallisation of titanium atoms with low partial pressure of oxygen when films are deposited in helium instead of argon due to Penning ionization.     

Comparison study on structure of Si and Cu doping CrN films by reactive sputtering

CrN, CrSiN and CrCuN films were deposited by DC magnetron reactive sputtering with hot pressed pure Cr, CrSi, and CrCu targets, respectively. As substrate bias increased from −50 V to −200 V, the preferred orientation of CrN films changed from (1 1 1) to (2 0 0). And the Si doping did not change this condition. However, the Cu doping films kept (2 0 0) orientation all along. CrN films presented typical columnar structure, and the alloying of Si and Cu could restrain columnar growth leading to dense structure. The CrSiN film was composed of nanocrystallites distributed in amorphous Si₃N₄, while no amorphous phase existed in CrCuN films.     

The interplay between molecular orientation, film morphology and luminescence properties of tetracene thin films on epitaxial AlOx/Ni3Al(1 1 1)

We report a systematic study of the interplay between molecular orientation, film morphology and luminescence properties of tetracene thin films on epitaxial alumina films on Ni₃Al(1 1 1), employing high resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), and photoluminescence spectroscopy (PL). If deposited at low temperatures, tetracene forms laterally disordered and compact films in which at least the first monolayer is oriented parallel to the substrate. For thicknesses in the range of 10 Å or below, these as-deposited films show no luminescence, while thicker films exhibit weak luminescence from higher layers. On annealing to 210 K, tetracene films dewet the AlO_x/Ni₃Al(1 1 1) surface and transform into an island morphology. At the same time, molecules tend to re-orient into a more upright configuration. In this island configuration, even thin films show luminescence. We can thus conclude that in spite of the insulating nature of the surface, the interaction of flat-lying tetracene molecules with AlO_x/Ni₃Al(1 1 1) is strong enough to provide at least one efficient non-radiative decay channel.     

Improving the electrical conductivity of CuCrO2 thin film by N doping

N-doped CuCrO₂ thin films were prepared by using radio frequency magnetron sputtering technique. The XRD and XPS measurements were used to confirm the existence of the N acceptors in CuCrO₂ thin films. Hall measurements show the p-type conduction for all films. The electrical conductivity increases rapidly with the increase in N doping concentration, and the maximum of the electrical conductivity of 17 S cm⁻¹ is achieved for the film deposited with 30 vol.% N₂O, which is about three orders of magnitude higher than that of the undoped CuCrO₂ thin film. Upon increasing the doping concentrations the band gaps of N-doped CuCrO₂ thin films increase due to the Burstein-Moss shift.