Dual Ion Beam Deposition Research Articles

Structural, plasmonic and electronic properties of zirconium carbonitride thin films prepared by dual ion beam deposition

Structural, plasmonic and electronic properties of zirconium carbonitride thin films prepared by dual ion beam deposition

Analysis of sub-bandgap losses in TiO2 coating deposited via single and dual ion beam deposition

We present a detailed study of sub-bandgap losses in TiO2 optical coatings prepared by using a single and a dual ion beam deposition. By extracting high-precision spectra of the losses in the TiO2 layers deposited under varied parameters we were able to study the losses in great detail. We were able to identify several spectral features and discuss their origin. Additional experiments allowed us to determine the contribution of absorption and scattering to the losses, as well as to discern whether the observed losses have volume or interface character. The results reveal that the dominant source of absorption in the high-quality samples is volume absorption originating from the so-called Urbach tail. We discuss the limitations imposed by the Urbach tail.

Improved ethanediol sensing with single Yb ions doped SnO2 nanobelt

Yb-doped SnO2 nanobelts (Yb–SnO2 NBs) and pure SnO2 nanobelts (SnO2 NBs) are successfully synthesized by thermal evaporation method and their composition and morphology are characterized. The single nanobelt device is fabricated by dual-ion beam deposition system, and the gas sensing performance to ethanediol, methanal, ethanol and acetone is investigated. The results show that the best working temperature of single Yb–SnO2 NB sensor to ethanediol is 190°C, which is lower than that of pure counterpart and the highest sensitivity is 10.5 to 100ppm of ethanediol. In addition, it is found that the response/recovery time is short and the sensor exhibits excellent selectivity and stability. The sensing performance of SnO2 NB is actually improved by Yb.

Microstructural and magnetic characterization of ion-beam bombarded [Ni80Fe20-Cr]50 thin films

Ion-beam bombardment during thin film deposition can effectively change the microstructure and thus influence the magnetic properties of the thin film system. In this paper, we studied plain (un-bombarded) and argon ion-beam bombarded multilayered [Ni80Fe20-Cr]50 thin films fabricated using a dual ion-beam deposition technique. The atomic force microscopy images of the bombarded thin films showed a much rougher surface and an increased average grain size. No noticeable exchange bias phenomenon was observed in the thin films deposited with or without bombardment, indicating that the interfacial uncompensated spins were prevented from providing the necessary unidirectional anisotropy due to interfacial intermixing. This significant intermixing between Ni80Fe20 and Cr layers, and the etching process caused by the bombardment, led to the formation of an nano-composite [Ni80Fe20-Cr]50 thin film with a reduced Curie temperature. An enhancement of the coercivity attributed to the stronger NiFe–Cr coupling was also found, which was the result of additional pinning sites created by the bombardment. The bombarded thin film also exhibited a higher ZFC/FC divergence temperature compared to the un-bombarded film, which indicated a much stronger NiFe–Cr coupling and more coordinated alignment of the magnetization of the film's larger crystallites.

Seeking to quantify the ferromagnetic-to-antiferromagnetic interface coupling resulting in exchange bias with various thin-film conformations

Ni3Fe/(Ni, Fe)O thin films with bilayer and nanocrystallite dispersion morphologies are prepared with a dual ion beam deposition technique permitting precise control of nanocrystallite growth, composition, and admixtures. A bilayer morphology provides a Ni3Fe-to-NiO interface, while the dispersion films have different mixtures of Ni3Fe, NiO, and FeO nanocrystallites. Using detailed analyses of high resolution transmission electron microscopy images with Multislice simulations, the nanocrystallites' structures and phases are determined, and the intermixing between the Ni3Fe, NiO, and FeO interfaces is quantified. From field-cooled hysteresis loops, the exchange bias loop shift from spin interactions at the interfaces are determined. With similar interfacial molar ratios of FM-to-AF, we find the exchange bias field essentially unchanged. However, when the interfacial ratio of FM to AF was FM rich, the exchange bias field increases. Since the FM/AF interface ‘contact’ areas in the nanocrystallite dispersion films are larger than that of the bilayer film, and the nanocrystallite dispersions exhibit larger FM-to-AF interfacial contributions to the magnetism, we attribute the changes in the exchange bias to be from increases in the interfacial segments that suffer defects (such as vacancies and bond distortions), that also affects the coercive fields.

Effect of ion-beam bombardment on microstructural and magnetic properties of Ni80Fe20/α-Fe2O3 thin films

Ion-beam bombardment has been established as an effective way to tune the microstructure and thus modify the magnetic anisotropy of thin film materials, leading to certain remarkable magnetic properties. In this work, we investigated a Ni80Fe20/α-Fe2O3 bilayer deposited with a dual ion-beam deposition technique. Low-energy argon ion-beam bombardment during the α-Fe2O3 deposition led to a decline of crystallinity and interfacial roughness of the bilayer, whereas the grain size distribution remained essentially unchanged. At low temperature, the coercivity exhibited a pronounced decrease after the bombardment, indicating that the effective uniaxial anisotropy in the ferromagnetic layer was dramatically reduced. Such reduction in uniaxial anisotropy was likely attributed to the irreversible transition in the α-Fe2O3 grains caused by the ion-beam bombardment, which subsequently modified the anisotropy in the Ni80Fe20 layer. The bombarded bilayer also exhibited a larger ΔMFC–ZFC compared to the un-bombarded bilayer, which indicated a stronger exchange coupling between the ferromagnetic layer and the antiferromagnetic layer.

Effect of low energy ion bombardment on structure and photoluminescence characterization of Al-doped ZnO thin films

Al-doped zinc oxide (AZO) films are prepared by dual ion-beam assisted sputter deposition at room temperature. An assisting argon ion beam (ion energy Ei=0–300eV) directly bombards the substrate surface to modify the properties of the AZO films. The effects of assisting ion beam energy on the characteristics of AZO films were investigated based on transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and photoluminescence measurement. With increasing assisting ion beam bombardment, the crystalline quality of the AZO films was improved and the oxygen vacancies were increased observably. Two red emissions originating from the oxygen vacancies in the films appear at 1.71 and 1.64eV. This study suggests that wide-band-gap materials could act as effective visible light emitters and ion beam bombardment provides a simple route to synthesize such materials.

Correlating exchange bias with magnetic anisotropy in ion-beam bombarded NiFe/Mn-oxide bilayers

The exchange bias field dependence on the Mn-oxide and its microstructure in NiFe/Mn-oxide bilayers was investigated. Transmission electron microscopy results have shown that the bilayer bottom consisted of either α-Mn, rocksalt MnO, or a composite of tetragonal Mn3O4+MnO, depending on the ratio of O2/Ar used during dual ion-beam deposition. Magnetometry results at 5 K indicate that the exchange bias field (Hex∼−300 Oe) is largest in a NiFe/Mn (0%O2/Ar) bilayer. The MnO formation by in situ Mn oxidation results in a decrease in Hex in a NiFe/Mn-oxide (21%O2/Ar) bilayer. In contrast, a further increase in the O2/Ar ratio during deposition results in larger Hex and Hc. This is attributed to the oxidation of MnO into a harder ferrimagnet, Mn3O4. Our results indicate that the antiferromagnetic Mn enabled stronger coupling with NiFe than MnO. In addition, we find that the MnO–Mn3O4 coupling dominates the exchange bias effects at high oxygen concentrations.

Stress relaxation and optical characterization of TiO 2 and SiO 2 films grown by dual ion beam deposition

TiO 2 and SiO 2 films are deposited by dual ion beam deposition with the objective to minimize the film stress. The influence of different parameters (energy and flux) of an assisting Ar + or Xe + ion beam on the film stress and on the optical properties is investigated by measuring the curvature of the samples and by spectroscopic ellipsometry, respectively. It is shown that the stress can be reduced considerably by the assisting ion bombardment. The most important parameter is found to be the ion energy. Ion flux and ion species have only a minor effect. The refractive index of the SiO 2 films decreases slightly with ion bombardment, whereas the refractive index of the TiO 2 is reduced by ~ 0.1–0.2. However, no absorption is introduced for the TiO 2 and SiO 2 films upon ion bombardment, which makes the stress-optimized dielectric films promising candidates for advanced optical applications.

Exchange bias in a nanocolumnar Ni80Fe20∕α-Fe2O3 thin film

A Ni80Fe20∕α-Fe2O3 thin film has been deposited using a dual ion-beam deposition technique where the α-Fe2O3 is formed in situ by O2 bombardment of pure Fe. AC susceptibility results indicate moment fluctuations at temperatures above 150K. This behavior combined with the thermal fluctuation driven temperature dependence of the negative field coercivity indicates that the α-Fe2O3 nanocolumnar crystallite magnetism evolves from static single domain moments to superparamagnetic moments with warming. 25kOe field cooling establishes exchange bias with an onset temperature of 50K. The positive (Hc2) and negative (Hc1) field coercivities exhibit very different temperature dependencies, with Hc1(T) well described by a thermally activated coherent domain wall reversal model, while Hc2(T) is essentially constant except for the lowest temperatures. These results point towards different domain reversal mechanisms in positive and negative fields.

Deposition of GaN thin film on ZnO/Si by DIBD method

The GaN thin film is successfully grown on the sample of ZnO/Si by dual ion beams deposition (DIBD) system. The thin film GaN/ZnO/Si is characterized by the in-situ X-ray photoelectron spectroscopy (XPS). It is shown that after a thin GaN film grown on the Zn/Si, the peaks of the Zn and O are not observed. This indicates that the GaN film can be successfully grown on the ZnO/Si by the dual ion beam deposition (DIBD) system associated with the pulsed laser deposition (PLD) method.

Enhancing the Performance of Low Pt Loading Prepared by Dual Ion-Beam Assisted Deposition in PEM Fuel Cells

Ultra-low Pt and Pt based alloy/mix (Pt-Co and Pt-Cr) electrodes were prepared by dual ion-beam assisted deposition (Dual IBAD) method. Activity enhancement, based on normalization with electrochemical surface area and mass activity is reported relative to a commercial gas diffusion electrode containing carbon supported Pt electrocatalysts. Mass specific power density of 0.297 gPt/kW is reported with 250 Aå IBAD deposit at 0.65 V. Based on the morphological differences, which enable such enhanced activities and the mass manufacturability of this electrode system; we report a significant new development in terms of materials for PEMFC application.

A Study of Diamond Synthesis by Hot Filament Chemical Vapor Deposition on Nc Coatings

Deposition of diamond films onto various substrates can result in significant technological advantages in terms of functionality and improved life and performance of components. Diamond is hard, wear resistant, chemically inert, and biocompatible. It is considered to be the ideal material for surfaces of cutting tools and biomedical components. However, it is well known that diamond deposition onto technologically important substrates, such as co-cemented carbides and steels, is problematic due to carbon interaction with the substrate, low nucleation densities, and poor adhesion. Several papers previously published in the relevant literature have reported the application of interlayer materials such as metal nitrides and carbides to provide bonding between diamond and hostile substrates. In this study, the chemical vapor deposition (CVD) of polycrystalline diamond on TiN/SiN x nc (nc) interlayers deposited at relatively low temperatures has been investigated for the first time. The nc layers were deposited at 70 or 400 °C on Si substrates using a dual ion beam deposition system. The results showed that a preliminary seeding pretreatment with diamond suspension was necessary to achieve large diamond nucleation densities and that diamond nucleation was larger on nc films than on bare sc-Si subjected to the same pretreatment and CVD process parameters. TiN/SiN x layers synthesized at 70 or 400 °C underwent different nanostructure modifications during diamond CVD. The data also showed that TiN/SiN x films obtained at 400 °C are preferable in so far as their use as interlayers between hostile substrates and CVD diamond is concerned.

High performance polymer electrolyte fuel cells with ultra-low Pt loading electrodes prepared by dual ion-beam assisted deposition

Ultra-low pure Pt-based electrodes (0.04–0.12 mg Pt/cm 2) were prepared by dual ion-beam assisted deposition (dual IBAD) method on the surface of a non-catalyzed gas diffusion layer (GDL) substrate. Film thicknesses ranged between 250 and 750 Å, these are compared with a control, a conventional Pt/C (1.0 mg Pt(MEA)/cm 2, E-TEK). The IBAD electrode constituted a significantly different morphology, where low density Pt deposits (largely amorphous) were formed with varying depths of penetration into the gas diffusion layer, exhibiting a gradual change towards increasing crystalline character (from 250 to 750 Å). Mass specific power density of 0.297 g Pt/kW is reported with 250 Å IBAD deposit (0.04 mg Pt/cm 2 for a total MEA loading of 0.08 mg Pt/cm 2) at 0.65 V. This is contrasted with the commercial MEA with a loading of 1 mg Pt(MEA)/cm 2 where mass specific power density obtained was 1.18 g Pt/kW (at 0.65 V), a value typical of current state of the art commercial electrodes containing Pt/C. The principal shortcoming in this effort is the area specific power density which was in the range of 0.27–0.43 W/cm 2 (for 250–750 Å IBAD) at 0.65 V, hence much below the automotive target value of 0.8–0.9 W/cm 2 (at 0.65 V). An attempt to mitigate these losses is reported with the use of patterning. In this context a series of patterns ranging from 45 to 80% Pt coverage were used in conjunction with a hexagonal hole geometry. Up to 30% lowering of mass transport losses were realized.

Enhanced Anisotropic Magnetoresistance of Ion-Beam-Deposited Ni80Fe20–NixFe1-xO Composite Films

Composite films of Ni80Fe20–NixFe1-xO were prepared by a dual ion-beam deposition technique. Magnetoresistance (MR) was measured both at 77 and 298 K in a magnetic field applied in plane, parallel and perpendicular to the electrical current. Typical anisotropic magnetoresistance (AMR) was observed in as-deposited and annealed samples. The most interesting result is that for annealed samples, the shape of the MR curve is sharp and symmetric and the total MR ratio increases with oxygen content in the films, as compared with as-deposited samples. Furthermore, the total MR ratio reaches a maximum (∼ 4.5 and 14% at 298 and 77 K, respectively) in films prepared with 44% oxygen in the assist beam. This enhanced AMR is attributed to the strong anisotropic scattering at interfaces between the ferromagnetic metal and oxide phases.

A study of diamond synthesis by hot filament chemical vapour deposition on nanocomposite coatings

Deposition of diamond films onto various substrates can result in significant technological advantages in terms of functionality and improved life and performance of components. Diamond is hard, wear resistant, chemically inert and biocompatible and considered as the ideal material for surfaces of cutting tools and biomedical components. However, it is well known that diamond deposition onto technologically important substrates such as Co-cemented carbides and steels is problematic due to carbon interaction with the substrate, low nucleation densities and poor adhesion. Several papers previously published in the relevant literature have reported the application of interlayer materials such as metal nitrides and carbides to provide bonding between diamond and hostile substrates. In this study, we have investigated for the first time the chemical vapour deposition (CVD) of polycrystalline diamond on TiN/SiN x nanocomposite interlayers deposited at relatively low temperatures. The nanocomposite layers were deposited at 70 °C or 400 °C on silicon substrates by using a dual ion beam deposition system. The results showed that a preliminary seeding pre-treatment with diamond suspension was necessary to achieve large diamond nucleation densities and that diamond nucleation was larger on nanocomposite films than on bare sc-Si submitted to same pre-treatment and CVD process parameters. TiN/SiN x layers synthesized at 70 °C or 400 °C underwent different nanostructure modifications during diamond CVD. The data also showed that TiN/SiN x films obtained at 400 °C are preferable so far as their use as interlayers between hostile substrates and CVD diamond is concerned.

Tuning Microstructural and Magnetic Properties of Ion-Beam-Deposited Ni80Fe20/NixFe1-xO Composite Films

Composite films of Ni80Fe20/NixFe1-xO were prepared by dual ion-beam deposition. The structural and magnetic properties of these composite films were studied. The as-deposited Ni80Fe20 films (a=3.55 Å) consist of f.c.c. nanocrystallites while films prepared with 55% O2 in the assist beam consist of a rock-salt structure NixFe1-xO (a=4.21 Å) solid solution. The rock-salt phase undergoes an unusual dissociation reaction from NixFe1-xO into Ni (a=3.52 Å), NiO (a=4.19 Å), and NiFe2O4 (a=8.33 Å) upon annealing. The differences (Δ) in magnetic moment at 10 K between zero-field-cooled (ZFC) and field-cooled (FC) curves are closely related to the interphase exchange interaction in these composite films. Suppression of the Curie temperature (TC) was observed in both pure Permalloy and Ni80Fe20/NixFe1-xO composite films, and the TC depression was reduced by annealing.

Antiferromagnetic Layer Structure Effects on Exchange Coupling Strength in Ion-Beam Deposited Ni80Fe20/Cobalt Oxide Bilayers

A series of Ni80Fe20/Cobalt oxide bilayers were prepared by a dual ion-beam deposition technique that produced a layer composition that varied from rock-salt CoO (a=4.27 Å) to spinel Co3O4 (a=8.21 Å) with increasing O2 content in the assist beam. Each polycrystalline layer (∼20 nm) exhibited a columnar structure perpendicular to the film surface. A strong temperature dependence of coercivity Hc and exchange bias field Hex was found in these Ni80Fe20/cobalt oxide bilayers. At T=10 K, films prepared with 34% O2 in the assist beam exhibited an exchange shift Hex∼-200 Oe that persisted at temperatures higher than 30 K. The variations in Hc and Hex as a function of %O2 are related to the interfacial roughness and magnetic state of CoO or Co3O4. The transition temperature of Co3O4 has increased above the bulk value via exchange coupling with the permalloy.

Ga 1−xMn xSb grown on GaSb with mass-analyzed low-energy dual ion beam deposition

The Ga 1− x Mn x Sb samples were fabricated by the implantation of Mn ions into GaSb (1 0 0) substrate with mass-analyzed low-energy dual ion beam deposition system, and post-annealing. Auger electron spectroscopy depth profile of the Ga 1− x Mn x Sb samples showed that the Mn ions were successfully implanted into GaSb substrate. Clear double-crystal X-ray diffraction patterns of the Ga 1− x Mn x Sb samples indicate that the Ga 1− x Mn x Sb epilayers have the zinc-blende structure without detectable second phase. Magnetic hysteresis-loop of the Ga 1− x Mn x Sb epilayers were obtained at room temperature (293 K) with alternating gradient magnetometry.

X-ray photoelectron spectroscopy and magnetic force microscopy studies of ion-beam deposited Ni/sub 80/Fe/sub 20//Co-oxide bilayers

The correlation between the structural and magnetic properties in Ni/sub 80/Fe/sub 20//Co-oxide bilayers that were prepared using a dual-ion beam deposition technique has been investigated. The pure Permalloy (Ni/sub 80/Fe/sub 20/) film (a = 3.53 /spl Aring/) consisted of face-centered cubic nanocrystallites. Films prepared with 8% O/sub 2/ and 34% O/sub 2/ in the assist beam consisted of rock-salt CoO (a = 4.27 /spl Aring/) and spinel Co/sub 3/O/sub 4/ (a = 8.21 /spl Aring/). The composition and oxidation state of the Co-oxide layers were analyzed with X-ray photoelectron spectroscopy (XPS), X-ray diffractometry (XRD), and transmission electron microscopy (TEM). Magnetic force microscopy (MFM) revealed that the Ni/sub 80/Fe/sub 20//Co bilayer exhibited ripple domains, whereas cross-tie domain walls were found in Ni/sub 80/Fe/sub 20//CoO bilayer. At 289 K, the pure Permalloy film exhibited soft magnetic properties while a magnetic hardening with enhanced coercivity was observed in the Ni/sub 80/Fe/sub 20//CoO bilayer. Additionally, the Ni/sub 80/Fe/sub 20//CoO bilayer exhibited an exchange shift H/sub ex//spl sim/-75 Oe at 150 K.