Ion Beam Assisted Deposition Technique Research Articles

Thickness dependence of structural and superconducting properties of Co-doped BaFe2As2 coated conductors

SummaryHigh-quality Co-doped BaFe2As2 thin films with thickness up to 2 μm were realized on flexible metal tapes with LaMnO3 as buffer layers fabricated by an ion beam-assisted deposition technique. Structural analysis indicates that increasing thickness does not compromise the film crystallinity, except for a small amount of impurities. Two types of thickness dependence of critical current density (Jc) were found: one is almost thickness independent in the range of 0.6–1.5 μm and the other is highly thickness dependent. In addition, the maximum value for crucial current Ic at 9 T and 4.2 K is about 55 A/12 mm-W for the 1.5-μm-thick film. Anisotropic Ginzburg–Landau scaling demonstrates that dominant pinning centers develop from correlated to uncorrelated with increasing film thickness. The further theoretical analysis shows that with film thickness increasing the pinning mechanism evolves progressively from a δl pinning to the δTc pinning mechanism.

Strong cube-textured titanium nitride conductive films directly on flexible metal substrate

Single crystal-like titanium nitride (TiN) by ion beam assisted deposition (IBAD) method is a potential conductive and thermally-stable template for growing highly-oriented REBa2Cu3O7−x (RE = rare earth) superconductor tapes as well as optoelectronics on flexible metal substrates. Previously, amorphous seed layers such as Al2O3 and Y2O3 were necessary for the biaxially-textured film growth by IBAD. Such nonconductive seed layers prevent an electrically-conductive path between functional film and bottom metal substrate such as flexible, electro-polished Hastelloy (EPH). An approach of Argon ion (Ar+) pre-treatment of EPH surface, followed by roll-to-roll IBAD process has been developed for a simplified architecture of cube-textured TiN directly on flexible metal substrate. Strong cube-textured TiN films with out-of-plane texture spread of 1.8° and in-plane texture spread of 5.6° were obtained by IBAD technique on flexible Hastelloy substrate without any intervening layers; this provides a conductive template for functional layers. Also, the ion pretreatment step is easily achieved in an IBAD system which simplifies the fabrication process.

Structural and Optical Characterization of Thermally Oxidized Titanium Thin Films Prepared by Ion Beam-assisted Deposition (IBAD) Technique

Abstract: Titanium oxide (TiO2) thin films have been grown by thermal oxidation of sputtered Titanium (Ti) thin layers using ion beam-assisted deposition (IBAD). X-ray diffraction showed that prior to oxidation, the films are composed of hexagonal crystallites of Ti. After oxidation, a film structure transition occurs from monoclinic β-TiO2 type to tetragonal anatase type as the annealing temperature of Ti layer is increased from 250 °C to 550 °C. The film thickness was about 230 nm. Visualization and scanning by atomic force microscope (AFM) revealed a low roughness of the samples, which increases when the annealing temperature is increased. The optical transmittances of the films in the visible spectrum were in the range of 85-95%. The values of optical band gap have been estimated to be 3.43 eV and 3.61 eV, for thin films annealed at 250°C and 550°C, respectively. Keywords: TiO2 thin film, IBAD, XRD, structural and optical properties.

The structures and thermoelectric properties of Zn-Sb alloy films fabricated by electron beam evaporation through an ion beam assisted deposition

Zn-Sb alloys are potential low-cost and non-toxic p-type thermoelectric materials for applications in the temperature range between 300 and 700 K. In this experiment, Zn-Sb alloy films were prepared by electron beam evaporation through an ion beam assisted deposition (IBAD). Our studies have confirmed that the structural phase, chemical composition, chemical binding, carrier concentration and microstructures of the film can indeed be effectively controlled by the voltage and current of the ion beam. Particularly, the carrier concentration of the film will rise along with the increase of the argon ion beam current. When the ion beam currents are set at 0.2–0.6 A, the carrier concentrations of the films can be controlled at around 1019–1020 cm−3, which fall within the optimal carrier concentration range for Zn-Sb based thermoelectric materials. The temperature dependence of Seebeck coefficient and the electrical conductivity of the films were measured to evaluate their thermoelectric performance. The results indicate that the film with Zn4Sb3 + ZnSb mixed phase will have better thermoelectric properties. A high power factor value of ~1280 μW/m-K2 is obtained in the films assisted by the ion beam current of 0.6 A. Our results demonstrate that the IBAD technique is extraordinary promising to fabricate Zn-Sb films with excellent thermoelectric performance and can be used to produce other potential thermoelectric materials.

ITO regulated high-performance n-Si/ITO/α-Fe2O3 Z-scheme heterostructure towards photoelectrochemical water splitting

The deficiencies in the separating photogenerated electrons/holes in the bulk and driving them across the interface of semiconductor/electrolyte are the major issues that limit the photoelectrochemical (PEC) performance of hematite (α-Fe2O3) photoelectrodes. In this work, a Z-scheme planar heterostructure of n-Si and α-Fe2O3 was designed and constructed by a facial ion-beam assisted deposition technique with the best match of the optical absorption depth, the film thickness and the space charge region thickness. A thin ITO layer (~10 nm) was sandwiched in-between in order to achieve the optimal carrier separation capacity, and the IrOx cocatalysts were introduced to improve the surface reaction kinetics. The results demonstrate a significant improvement of α-Fe2O3 PEC performance: a photocurrent density was improved to 1.987 mA cm−2 (1.23 V vs. RHE), ~100 times larger than that of bare α-Fe2O3, whereas the onset potential was dropped by 0.57 V over unmodified α-Fe2O3, due to the enhanced photovoltage by n-Si and the improved surface reaction kinetics. This work advances planar α-Fe2O3-based photocatalytic cells to a new performance record for water splitting.

Effects of nano-engineered surfaces on osteoblast adhesion, growth, differentiation, and apoptosis

Modifying implant surfaces to improve their biocompatibility by enhancing osteoblast activation, growth, differentiation, and induction of greater bone formation with stronger attachments should result in improved outcomes for total joint replacement surgeries. This study tested the hypothesis that nano-structured surfaces, produced by the ion beam-assisted deposition method, enhance osteoblast adhesion, growth, differentiation, bone formation, and maturation. The ion beam-assisted deposition technique was employed to deposit zirconium oxide films on glass substrates. The effects of the ion beam-assisted deposition technique on cellular functions were investigated by comparing adhesion, proliferation, differentiation, and apoptosis of the human osteosarcoma cell line SAOS-2 on coated versus uncoated surfaces. Ion beam-assisted deposition nano-coatings enhanced initial cell adhesion assessed by the number of 4′,6-diamidino-2-phenylindole–stained nuclei on zirconium oxide nano-coated surfaces compared to glass surfaces. This nano-modification also increased cell proliferation as measured by mitochondrial dehydrogenase activity. Moreover, the ion beam-assisted deposition technique improved cell differentiation as determined by the formation of mineralized bone nodules and by the rate of calcium deposition, both of which are in vitro indicators of the successful bone formation. However, programmed cell death assessed by Annexin V staining and flow cytometry was not statistically significantly different between nano-surfaces and glass surfaces. Overall, the results indicate that nano-crystalline zirconium oxide surfaces produced by the ion beam-assisted deposition technique are superior to uncoated surfaces in supporting bone cell adhesion, proliferation, and differentiation. Thus, surface properties altered by the ion beam-assisted deposition technique enhanced bone formation and may increase the biocompatibility of bone cell–associated surfaces.

Surface nano-modification by ion beam-assisted deposition alters the expression of osteogenic genes in osteoblasts.

Biomaterials with enhanced biocompatibility are favored in implant studies to improve the outcomes of total joint replacement surgeries. This study tested the hypothesis that nano-structured surfaces for orthopedic applications, produced by the ion beam-assisted deposition method, would enhance osteointegration by altering the expression of bone-associated genes in osteoblasts. The ion beam-assisted deposition technique was employed to deposit nano-films on glass or titanium substrates. The effects of the ion beam-assisted deposition produced surfaces on the human osteosarcoma cell line SAOS-2 at the molecular level were investigated by assays of adhesion, proliferation, differentiation, and apoptosis on coated surfaces versus uncoated cobalt-chrome, as the control. Ion beam-assisted deposition nano-coatings enhanced bone-associated gene expression at initial cell adhesion, proliferation, and differentiation compared to cobalt-chrome surfaces as assessed by polymerase chain reaction techniques. Increased cell proliferation was observed using a nuclear cell proliferation-associated antigen. Moreover, enhanced cell differentiation was determined by alkaline phosphatase activity, an indicator of bone formation. In addition, programmed cell death assessed by annexin V staining and flow cytometry was lower on nano-surfaces compared to cobalt-chrome surfaces. Overall, the results indicate that nano-coated surfaces produced by the ion beam-assisted deposition technique for use on implants were superior to orthopedic grade cobalt-chrome in supporting bone cell adhesion, proliferation, and differentiation and reducing apoptosis. Thus, surface properties altered by the ion beam-assisted deposition technique should enhance bone formation and increase the biocompatibility of bone cell-associated surfaces.

Development of surface planarization process using MOD-Gd-Zr-O layer

REBa2Cu3Oy (RE: rare-earth element, REBCO) coated conductors (CCs) have a high critical current density (Jc) under a magnetic field at the liquid nitrogen temperature and a potential performance for high-magnetic field applications. In order to prepare a biaxially highly oriented REBCO, a highly-textured buffer layer is required. The ion-beam assisted deposition (IBAD) technique is one of the promising techniques for preparation of the highly-textured layer even on the non-textured metallic substrate such as Hastelloy™. However, excellent surface smoothness and uniformity are indispensable to the non-textured metallic substrate using the IBAD technique. Therefore, an inexpensive surface planarization process has been required for fabrication of REBCO CCs with low-cost. In this study, we have investigated the surface planarization using the metal-organic deposition (MOD) method for the IBAD-MgO texturing. The Gd-Zr-O (GZO) planarization layer was prepared by MOD method on roughly-polished Hastelloy™ C-276 substrate. The surface roughness values (Ra) of MOD-GZO planarization layer became smaller than that of the Hastelloy™ C-276 with increase in coating times. Minimum Ra of the MOD-GZO planarization layer achieved less than 2 nm, which is smooth enough for obtaining the highly-textured IBAD-MgO film. The in-plane grain alignment of CeO2 film deposited on sputter-LaMnO3 / IBAD-MgO / MOD-GZO / Hastelloy™ C-276 substrate by the pulsed laser deposition was 4°, and high Jc value of 2.5 MA/cm2 (1.8 μm-t) was obtained for MOD-YBCO film fabricated on it. The CCs using MODGZO planarization layer provided the delamination strength over 70 MPa, which was compatible with conventional structure of CCs.

Mössbauer effect studies of thin iron films synthesized by ion beam assisted deposition technique

The paper presents the results of Mössbauer effect studies of thin iron films obtained by ion-assisted deposition technique. It was found that the films obtained consist of several phases and have a perpendicular magnetic anisotropy. Magnetization direction can be changed by external magnetic field in sample plane.

On the question of structure of ZnO thin films formed by IBAD and subsequently implanted with silver ions

Nanocrystalline ZnO thin films with a thickness of ∼ 235 nm were synthesized by ion beam-assisted deposition (IBAD) technique using a metal target of zinc and oxygen (O2) as a reactive gas. The near-surface region of the synthesized films was subsequently implanted with 30 keV Ag+ ions in the fluence range of (0.25-1)×1017 ion/cm2 at high ion current density of 12 μA/cm2. The structure parameters and morphology of as-deposited and subsequently implanted with silver ions ZnO films were investigated by X-ray diffraction and scanning electron microscopy techniques. It was found that the as-deposited ZnO films have inhomogeneous structure, which consists of nanocrystallites and disordered amorphous phase. The nanocrystallites of the obtained ZnO thin films have values of lattice parameters higher than for a bulk ZnO. Subsequent implantation with silver ions leads to a significant radiation heating and microstress relaxation of the film as well as to an increase in the size of nanocrystallites due to the amorphous phase.

The Study of Ion Beam Assisted Deposition of CuInSe2 Absorber Films

Based on the selenium ion beam assisted magnetron sequential sputtering technology, low temperature deposition of CIS thin-film solar cells in high quality can be achieved. By comparing with the method of conventional gas phase atomic deposition, and through simulated analysis from the perspective of diffusion uniformity, numerical calculation on the depth of ion beam injection is proceeded. First, according to the classical collision theory in molecular dynamics, the theoretical calculation on the process of ion implantation is done; the concentration distribution of implanted selenium ions can be got by using TRIM program for simulation analysis. On this basis, the concentration distribution of selenium ion after diffusion can be further obtained. Finally, the calculation model is established; through comparison and analysis, when the selenium diffusion uniformity is same in the both conditions, the substrate temperature T1 needed for ion beam assisted deposition and the substrate temperature T2 needed for gas phase atomic deposition are respectively calculated. The calculation results show that on the premise of merely considering the depth of implanted ions, from the perspective of the diffusion uniformity, the selenium ion beam assisted deposition technique can obviously reduce the substrate temperature comparing with traditional vapor deposition technology.

Electrocatalysts for Direct Alcohol Oxidation Fuel Cells Prepared Using Ion Beam Assisted Deposition Technique

Active layers of the electrocatalysts for oxidation of methanol and ethanol were prepared by ion beam assisted deposition (IBAD) of platinum and activating rare earths metals (Ce, Yb) onto carbon (AVCarb® Carbon Fiber Paper Р50 and Toray Carbon Fiber Paper TGP-H-060 Т) supports. The deposition method is characterized by the use of deposited-metal ions as assisting ions. Metal deposition and mixing between the precipitable layer and surface of the substrate by accelerated ions of the same metal were carried out on the experimental unit from a neutral vapor fraction and the vacuum-arc discharge plasma of a pulsed electric arc ion source, respectively. Ion accelerating voltage is 10 kV; vacuum – 10– 2 Pa. Investigation of the composition and microstructure of layers was carried out by RBS, SEM, EPMA and XRF methods. It has been established that the obtained catalytic layers contain atoms of the deposited metals and substrate material, as well as impurity oxygen atoms; their thickness reaches ~30–100 nm. Content of platinum atoms in the layers is ~2×1016 cm–2, concentration of deposited metals atoms in the maximum of distribution equals about a few at.%. According to investigations with use of cyclic voltammetry the electrocatalysts with prepared layers exhibited high catalytic activity in the reactions of electrochemical oxidation of methanol and ethanol, which form the basis for the principle of operation of low temperature fuel cells (DMFC and DEFC) (Figure 1). Figure 1. Cyclic voltammograms in the ethanol comprising solution of electrocatalyst prepared using ion beam deposition of ytterbium and platinum onto Toray Carbon Fiber Paper TGP-H-060 Т In comparison with the traditional multistage chemical methods of preparation of the deposited catalysts, the proposed IBAD method appears to be promising and often more preferable. It allows of the introduction of micro amounts of a doping impurity in the near-surface of a substrate under non equilibrium conditions and of the formation of cohesive catalytic layers at ultra-low platinum consumption. Figure 1

Enhanced visible light adsorption of heavily nitrogen doped TiO2 thin film via ion beam assisted deposition

Nitrogen doping is widely used to enhance the visible light absorption of TiO2 by narrowing the bandgap. It is recognized that this modification is sensitively affected by the spatial distribution of anion doping. In order to explore the effects of nitrogen distributions in TiO2, we synthesized nitrogen-doped TiO2 thin films via the ion-beam assisted deposition (IBAD) technique and calcinations in NH3 atmosphere. The morphology and crystal structure of these thin films were characterized by scanning electron microscope and X-ray diffraction respectively. The chemical states and spatial distributions of nitrogen in the TiO2 were investigated by X-ray photoelectron spectroscopy. The nitrogen can be heavily and uniformly doped in anatase thin film by the IBAD technique with the N/Ti atomic ratio ranging from 61.3 to 51.9 %, much higher than that calcinated at 500 °C under NH3 atmosphere, which fluctuated from 23.2 to 4.5 %. The time-dependent depth profile of the N 1s spectrum shows that the doped nitrogen in the TiON thin film synthesized via IBAD distributes from the surface to the inner layer. Compared to the traditional calcinations synthesized methods, the as-synthesized TiON thin film, shows a much higher absorption in the visible-light range. Its light absorbance spectrum extends to over 700 nm, covering most of the visible-light region.

Interface driven magnetic interactions in nanostructured thin films of iron nanocrystallites embedded in a copper matrix

We have fabricated thin films of iron nanocrystallites embedded in a copper matrix using a dual ion beam assisted deposition technique. A secondary End-Hall ion beam bombarded the iron atoms during deposition altering significantly the morphology of the films and allowing for control of the intermixing between iron and copper components. Cross-sectional transmission electron microscopy and x-ray reflectometry experiments indicated that the morphology of the films was that of iron nanocrystallites embedded in a copper matrix. Rietveld refinements of the diffraction pattern identified fcc-copper and amorphous iron. An increased amount of disorder was observed with a reduction in the amount of deposited iron from a 1:1 Fe:Cu ratio to 0.25:0.75 Fe:Cu ratio. Interfacial copper-iron alloys were identified by DC susceptibility experiments through their reduced TC,Alloy (370, 310, and 280 K) compared with that of bulk iron (∼1000 K). Element specific x-ray absorption and x-ray magnetic circular dichroism experiments were performed to identify the contributions to the magnetism from the iron and the copper-iron alloy.

イオンビーム援用傾斜機能性TiNコーティングを施したチタン合金の摩耗およびフレッティング疲労特性

The effect of functionally graded TiN coating on the wear and fretting fatigue behavior of titanium alloy was investigated. The two kinds of monolayer TiN coatings and three kinds of functionally graded TiN coatings were deposited on Ti-6Al-4V alloy substrate using an ion beam assisted deposition technique. Monolayer TiN coating was fabricated by an electron beam evaporation of titanium and simultaneous nitrogen ion bombardment at the acceleration voltage of 0.2 or 2.0 keV. The later consisted of top TiN layer and functionally graded layer. During the fabrication of functionally graded layer, the mixing ratio of nitrogen and argon gas that were used for the generation of ion beam increased stepwisely. The mixed layer formed by ion beam bombardment became thicker by an increase in acceleration voltage. The adhesion and wear resistance improved with an increase in the acceleration voltage. Moreover, inserting the functionally graded layer with the layer thickness of 250 nm improved them significantly. However, further increase in graded layer thickness deteriorated the adhesion and wear resistance. The fretting fatigue life was evaluated by a four-point bending fatigues test. The fretting fatigue life of specimen coated with monolayer TiN film was longer than that of uncoated specimen. The TiN coating with functionally graded layer was the most effective to improve the fretting fatigue life. It was concluded that the insert of functionally graded layer with appropriate layer thickness is effective way for improvement of wear and fretting fatigue behavior.

Bulk properties of InN films determined by experiments and theory

Bulk properties of InN are determined by combining experimental and theoretical studies. In this work, we produced high quality InN film deposited on GaN templates by a modified ion beam assisted deposition technique confirmed by low temperature photoluminescence and absorption. The density of states, real and imaginary parts of the complex dielectric function and the absorption coefficient are calculated by means of first-principles beyond density-functional theory. The quasi-particle aspect is described in the framework of a quasi-particle method (the GW approximation). The calculated band-gap energy is ~0.8eV whereas significance in the optical absorption occurs at ~1.2eV, which are consistent with both luminescence and absorption results. The Bethe–Salpeter equation is utilized to model the two-particle exciton interactions, revealing a strong excitonic peak just below the absorption edge of InN.

Uranium dioxide films with xenon filled bubbles for fission gas behavior studies

Electron beam evaporation and ion beam assisted deposition (IBAD) methods were utilized to fabricate depleted UO2 films and UO2 films with embedded Xe atoms, respectively. The films were fabricated at elevated temperature of 700°C and also subsequently annealed at 1000°C to induce grain growth and Xe atom redistribution. The goal of this work was to synthesize reference UO2 samples with controlled microstructures and Xe-filled bubble morphologies, without the effects attendant to rector irradiation-induced fission. Transmission electron microscopy (TEM) microstructural characterization revealed that fine Xe-filled bubbles nucleated in the as grown films and subsequent annealing resulted in noticeable bubble size increase. Reported results demonstrate the great potential IBAD techniques and UO2 films have for various areas of nuclear materials studies.

Improvement of thermoelectric properties induced by uniquely ordered lattice field in Bi2Se0.5Te2.5 pillar array

In this study, it was found that uniquely ordered lattice field favors transport of carriers but hinder that of phonons. The n-Bi2Se0.5Te2.5 pillar array film was successfully achieved by a simple ion beam assisted deposition technique. This oriented pillar array structure is clear with pillar diameter of about 30nm, exhibiting a uniquely ordered lattice field. The properties of the ordered Bi2Se0.5Te2.5 pillar array were greatly enhanced in comparison with those of the ordinary film. The Bi2Se0.5Te2.5 pillar array with a thermoelectric dimensionless figure-of-merit ZT=1.28 was obtained at room temperature. The in-plane transport mechanisms of the ordered pillar array and the ordinary structures, lattice field model, are proposed and investigated. The specially ordered lattice field is the main reason for the properties enhancement observed in the Bi2Se0.5Te2.5 film. Introduction of such ordered lattice field into TE films is therefore a very promising approach.

Fretting Fatigue Behavior of Titanium Alloy Coated with Functionally Graded Ti/TiN Film

The influence of functionally graded TiN coating on fretting fatigue behavior of titanium alloy was investigated. The coating was deposited using an ion beam assisted deposition technique. TiN film was fabricated by an electron beam evaporation of titanium and simultaneous nitrogen ion bombardment. An acceleration voltage of ion beam was set at 0.2 or 2.0 keV. The functionally graded layer was fabricated by varying the mixing ratio of nitrogen/argon ion beam. The mixed layer became thicker by an increase in acceleration voltage. The adhesive strength and wear resistance were improved with an increase in the acceleration voltage. Moreover, they were significantly improved by inserting the functionally graded layer. The fretting fatigue tests were conducted using a four-point bending fatigue testing machine. The fretting fatigue life of specimen coated with monolayer TiN film was longer than that of uncoated specimen. The TiN coating with functionally graded layer was the most effective to improve the fretting fatigue life.

Exchange bias magnetism in films of NiFe/(Ni,Fe)O nanocrystallite dispersions

Ni3Fe/(Ni,Fe)O thin films having a nanocrystallite dispersion morphology were prepared by a reactive ion beam-assisted deposition technique. The crystallite sizes of these dispersion-based films were observed to decrease from 8.4 ± 0.3 nm to 3.4 ± 0.3 nm as the deposition flow-rate increased from 2.78% to 7.89% O2/Ar. Thin film composition was determined using selective area electron diffraction images and Multislice simulations. Through a detailed analysis of high resolution transmission electron microscopy images, the nanocrystallites were determined to be Ni3Fe (a ferromagnet), NiO, and FeO (both antiferromagnets). It was determined that the interfacial molar Ni3Fe ratio in the nanocrystallite dispersions increased slightly at first, then decreased as the oxygen content was increased; at 7.89% O2/Ar, the interfacial molar ratio was essentially zero (only NiO and FeO remained). For nanocrystallite dispersion films grown with O2/Ar flow-rate greater than 7.89%, no interfacial (intermixed) Ni3Fe phase was detected, which resulted in no measurable exchange bias. Comparing the exchange bias field between the nanocrystallite dispersion films at 5 K, we observed a decrease in the magnitude of the exchange bias field as the nanocrystallite size decreased. The exchange bias coupling for all samples measured set in at essentially the same temperature (i.e., the exchange bias blocking temperature). Since the ferromagnetic/anti-ferromagnetic (FM/AFM) contact area in the nanocrystallite dispersion films increased as the nanocrystallite size decreased, the increase in the magnitude of the exchange bias could be attributed to larger regions of defects (vacancies and bond distortions) which occupied a significant portion of the FM/AFM interfaces in the nanocrystallite dispersion films.