Ion Beam Assisted Deposition Research Articles

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.

Effect of ion-beam assisted deposition on the film stresses of TiO2 and SiO2 and stress control

Based on Hartmann-Shack sensor technique, an online thin film stress measuring system was introduced to measure the film stresses of TiO2 and SiO2, and comparison was made between the film stresses prepared respectively by the conventional process and the ion-beam assisted deposition. The effect of ion-beam assisted deposition on the film stresses of TiO2 and SiO2 was investigated in details, and the stress control methodologies using on-line adjustment and film doping were put forward. The results show that the film stress value of TiO2 prepared by ion-beam assisted deposition is 40 MPa lower than that prepared by conventional process, and the stress of TiO2 film changes gradually from tensile stress into compressive stress with increasing ion energy; while the film stress of SiO2 is a tensile stress under ion-beam assisted deposition because of the ion-beam sputtering effect, and the film refractive index decreases with increasing ion energy. A dynamic film stress control can be achieved through in-situ adjustment of the processing parameters based on the online film stress measuring technique, and the intrinsic stress of film can be effectively changed through film doping.

Enhanced electron injection and stability in organic light-emitting devices using an ion beam assisted cathode

In this article, we report a highly efficient bilayer OLED with a maximum luminance up to 62 000 cd/m2 and a threshold voltage of 3.8 V. The device structure is indium-tin-oxide (ITO)/N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-diphenyl-4,4′-diamine (TPD)/tris-(8-hydroxyquinoline) aluminum (Alq3)/LiF/Al. Ion beam assisted deposition (IBAD) process is used to deposit the aluminum cathode on the LiF layer. The IBAD process improves the OLED performance both by increasing the maximum luminance by a factor of 3 and by reducing the threshold voltage for light-emission. The IBAD process also enhances the microstructure and morphology of the Al layer and leads to denser and more homogeneous layers. The resulting highly-packed microstructure acts as a barrier to moisture and oxygen and inhibits their penetration into the Alq3 layer, leading to the OLED lifetime and stability increasing. In order to optimize the IBAD process parameters, prior to the OLED deposition, we have characterized aluminum films deposited on glass substrates by using atomic force microscopy and X-ray diffraction.

The different N concentrations induced cytocompatibility and hemocompatibility of MWCNTs with CNx coatings

Carbon nitride coatings were deposited on the multiwalled carbon nanotubes (MWCNTs) which were prepared by chemical vapor deposition (CVD) using ion beam assisted deposition (IBAD) system. The morphology of the MWCNTs as well as variation in composition and chemical bonds between atoms in the coatings were measured using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The relationship between N/C atomic composition ratio and chemical bonding states and cytocompatibility and hemocompatibility of the MWCNTs with CNx coatings was investigated using fibroblast cell (L929) adhesion and blood clotting assays. The results revealed that the higher N/C or sp2CN/sp3C/N ratio stimulated the cell growth, proliferation, and spreading and prolonged the kinetic blood-clotting time and recalcification time.

Size selected growth of nanodots: Ion beam assisted deposition and transition from 2D to 3D growth

The size selection in quantum dot growth can be controlled by using the ion beam assisted deposition (IBAD) technique, as is previously demonstrated in experiments. Especially, in Ge/Si growth IBAD enhances the 2D to 3D transition and results a narrow size distribution compared to conventional deposition. We study size selection under IBAD using a continuous growth model with size dependent kinetics and thermodynamics. We show that ion beam assisted deposition exhibits stationary state of growth with uniform quantum dot size distributions. Finally we compare the results with nucleation theoretical predictions.

Thickness dependence of the structural, mechanical and electrical properties of Ni films deposited on polyimide by ion beam‐assisted deposition (IBAD)

Ni thin films with different thicknesses were deposited on pre‐treated polyimide substrates by ion beam‐assisted deposition. Dependence of structural, mechanical and electrical properties of the Ni films on their thickness was investigated. The results showed a clear correlation between film properties and film thickness. The inter‐diffusion at the interface regions of the films with different deposition time were demonstrated by transmission electron microscopy and X‐ray photoelectron spectroscopy. With increasing film thickness, surface roughness of the Ni films firstly decreased and then increased, while the grain size gradually increased. Residual stress of the Ni thin films decreased with increasing Ni film thickness up to 202 nm and then slightly increased as the film thickness further increased. Resistivity decreased, and temperature coefficient of resistivity (TCR) increased with increasing film thickness due to the enhancement of crystallization degree and the increase in grain size. The decrease in surface roughness and residual stress also contributed to the decrease of resistivity and the increase of TCR of the films. An optimal film thickness is suggested, which yielded a relatively high TCR value and low levels of both surface roughness and residual stress. Copyright © 2012 John Wiley & Sons, Ltd.

Characterization of gold nanodots arrangements in SiO2/SiO2+Au nanostructured metamaterials

Effective thermoelectric materials have a low thermal conductivity and a high electrical conductivity. For this study, we have prepared a thermoelectric generator device of SiO2/SiO2+Au multi-nano-layered thin film systems using ion beam-assisted deposition followed by 5 MeV Si ion bombardment. The ion bombardment causes the Au atoms to nucleate into metallic nanoclusters. However, as the kinetic energy of the Si ions decreases with the depth of the sample, so does the electronic stopping power responsible for the Au nucleation. This produces variations in the size and spacing of the nanoclusters. Here, we are investigating the effects of the size and arrangement variations within the device on the electrical and thermal transports within the system. We characterized the thin film system, using I–V characterization, conductance measurement, quasi-static capacitance, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy.

Materials science education: ion beam modification and analysis of materials

The Center for Irradiation of Materials (CIM) at Alabama A&M University (http://cim.aamu.edu) was established in 1990 to serve the University in its research, education and services to the need of the local community and industry. CIM irradiation capabilities are oriented around two tandem-type ion accelerators with seven beam lines providing high-resolution Rutherford backscattering spectrometry, MeV focus ion beam, high-energy ion implantation and irradiation damage studies, particle-induced X-ray emission, particle-induced gamma emission and ion-induced nuclear reaction analysis in addition to fully automated ion channeling. One of the two tandem ion accelerators is designed to produce high-flux ion beam for MeV ion implantation and ion irradiation damage studies. The facility is well equipped with a variety of surface analysis systems, such as SEM, ESCA, as well as scanning micro-Raman analysis, UV–VIS Spectrometry, luminescence spectroscopy, thermal conductivity, electrical conductivity, IV/CV systems, mechanical test systems, AFM, FTIR, voltammetry analysis as well as low-energy implanters, ion beam-assisted deposition and MBE systems. In this presentation, we will demonstrate how the facility is used in material science education, as well as providing services to university, government and industry researches.

Tilting of carbon encapsulated metallic nanocolumns in carbon-nickel nanocomposite films by ion beam assisted deposition

The influence of assisting low-energy (∼50-100 eV) ion irradiation effects on the morphology of C:Ni (∼15 at. %) nanocomposite films during ion beam assisted deposition (IBAD) is investigated. It is shown that IBAD promotes the columnar growth of carbon encapsulated metallic nanoparticles. The momentum transfer from assisting ions results in tilting of the columns in relation to the growing film surface. Complex secondary structures are obtained, in which a significant part of the columns grows under local epitaxy via the junction of sequentially deposited thin film fractions. The influence of such anisotropic film morphology on the optical properties is highlighted.

Dielectric properties and resistance to fatigue failure of different barrier layers prepared on flexible stainless-steel foils by ion-beam assisted deposition

A stainless-steel foil is an attractive candidate for the substrate of flexible display devices and integrated solar modules. For electrical insulation and ion diffusion reduction, a barrier layer should be coated on the stainless-steel foil surface. In this study, different barrier layers such as SiOx, TaOx, TiOx and TaOx/SiOx were prepared on the flexible stainless-steel foils (SUS 304) by ion-beam assisted deposition. The dielectric properties of the barrier layers, including resistance, reactance, leakage current density, breakdown field strength and performance index, were investigated. The resistance to fatigue failure of the barrier layers was evaluated by insulating tests after the specimen foils were flattened. The results show that the dielectric properties and the resistance to fatigue failure of the TaOx/SiOx composite barrier layer are better than those of the SiOx or the TaOx barrier layer. The best dielectric properties and resistance to fatigue failure are achieved with the 4-μm thick TaOx/SiOx composite barrier layer.

Structures and properties of sintered NdFeB coated with IBAD-Al/Al2O3 multilayers

IBAD-Al monolayers and amorphous Al2O3 monolayers were alternately deposited on sintered NdFeB magnets. IBAD-Al layers were prepared by direct current (DC) magnetron sputtering with ion-beam-assisted deposition (IBAD). Structure of the IBAD-Al/Al2O3 multilayers and their corresponding corrosion resistance and mechanical properties were investigated. Columnar structure is less visible in the IBAD-Al layers. Corrosion behaviour was investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarisation and neutral salt spray (NSS) test. The IBAD-Al/Al2O3 bilayer and multilayers present very low corrosion current densities in potentiodynamic polarisation tests (~10−11Acm2). The top Al2O3 layers are critical to improve the corrosion resistance of Al based coatings. Furthermore, the hardness of multilayers is improved as the period decreases.

Phase composition and tribological performance of molybdenum nitride coatings synthesized by IBAD

Molybdenum nitride coatings were synthesized by ion-beam-assisted-deposition (IBAD). The effects of nitrogen partial pressure and bombarding ion energy on the phase formation were investigated. The coefficient of friction and wear resistance of the coatings in different environments were studied.The stoichiometric ratio of nitrogen to Mo of the molybdenum nitride phases increases with the nitrogen partial pressure, and higher bombarding ion energy was helpful to form single MoN phase. Mo2N, MoN or mixture of the two phases could be prepared by controlling of the ratio of nitrogen/argon and ion energy. The hardness, coefficient of friction, wear and oxidation resistance of MoN were superior to that of Mo2N coating. The coefficient of friction decreased with the increase of testing temperature, yet the wear resistance became lower. The change of friction in non-oxidation atmosphere was reversed to that in the open air, indicating that the low friction of MoN at elevated temperature depends on oxidation. The tribological performance of the MoO3 phase formed by oxidation annealing showed much higher coefficient of friction than that of as-deposited MoN in all the testing conditions, and the oxygen deficient oxides were implied to be the lubricious phases.

Study of a sandwich structure of transparent conducting oxide films prepared by electron beam evaporation at room temperature

Transparent conducting ZnO/Ag/ZnO multilayer electrodes having electrical resistance much lower than that of widely used transparent electrodes were prepared by ion-beam-assisted deposition (IAD) under oxygen atmosphere. The optical parameters were optimized by admittance loci analysis to show that the transparent conducting oxide (TCO) film can achieve an average transmittance of 93%. The optimum thickness for high optical transmittance and good electrical conductivity was found to be 11 nm for Ag thin films and 40 nm for ZnO films, based on the admittance diagram. By designing the optical thickness of each ZnO layer and controlling process parameters such as IAD power when fabricating dielectric-metal-dielectric films at room temperature, we can obtain an average transmittance of 90% in the visible region and a bulk resistivity of 5 × 10−5 Ω-cm. These values suggest that the transparent ZnO/Ag/ZnO electrodes are suitable for use in dye-sensitized solar cells.

Investigation of carbon nitride films deposited by ion beam-assisted deposition with low bombarding energy of N ions

A series of carbon nitride (CNx) films were deposited on Si substrates by ion beam-assisted deposition. The CNx films were deposited by ion sputtering of graphite with N ions and they were additionally bombarded by N ions with low energy during deposition. The films were characterized with atomic force microscope, X-ray photoelectron spectroscopy, Raman spectrum and transmission electron microscope. The results indicated that the characteristics of the CNx films are strongly dependent on the bombarding energy. The hardness, elastic modulus and residual stress of the films were systemically investigated. Comparing with non-bombarding CNx film, the CNx films with bombardment of N ions have higher [N]/[C] ratio and sp3/sp2 ratio. Bombardment of N ions with low bombarding energy could increase sp3/sp2 ratio and improve mechanical properties of CNx films, while further increasing bombarding energy has no evident effect on films' properties. The residual stress of the films exhibited similar trend as hardness with the variation of bombarding energy of N ions.

Characterization of YBCO Coated Conductors Under High Magnetic Field at LNCMI

The second generation (2G) HTS conductors, the YBaCuO Coated Conductors, show very exciting performances in terms of critical currents under very high fields whereas their mechanical properties, the key issues for very high field magnets, are outstanding for the IBAD (Ion Beam Assisted Deposition) route. Preliminary measurements have shown critical currents Ic above 500 A at 15 T and 4 K on commercial YBCO coated conductors. They are now available in reasonable length and manufacturing focus to provide reliable, consistent performance conductors. With these high critical current and tensile strength above 600 MPa, these conductors are very promising for making HTS superconducting coils able to generate very high field. But very few characterizations exist above 20 T. LNCMI is one of the few facilities in the world where such measurement can be performed.

The effect of annealing on hardness, residual stress, and fracture resistance determined by modulation ratios of TiB2/TiAlN multilayers

Nanostructured multilayers of TiB2/TiAlN at different modulation ratios (tTiB2:tTAlN) ranging from 1:24 to 6:1 were deposited onto Si(100) wafers by ion beam assisted deposition (IBAD). The multilayers were subsequently annealed in a vacuum environment at a temperature of 500°C for 30min, and then characterized by extensive measurements including X-ray reflection (XRR), X-ray diffraction (XRD), scanning electron microscopy (SEM), nano-indentation and surface profilometry. It was found that the mechanical properties of the multilayers were closely related to tTiB2:tTAlN. A maximum hardness of 37GPa was achieved at tTiB2:tTAlN of 1:18 for as-deposited TiB2/TiAlN multilayer. This hardest multilayer also showed the improved residual stress and fracture resistance. The hardness and elastic modulus of the multilayers increased significantly after annealing. The maximum hardness of the multilayer at tTiB2:tTAlN of 1:14 was up to 41GPa after annealing at 500°C.

Structure and corrosion resistance in physiological solution of Hf–Si–N films deposited by IBAD

In this paper, Hf–Si–N films were deposited on AZ31 magnesium alloys by ion beam assisted deposition (IBAD) technology. The phase structure, chemical valence state and nano-mechanical property of the films were investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and nano-indentation test, respectively. The corrosion resistance in physiological solution was studied by electrochemical system. The results show that the main phases of the films are HfN phase and Si3N4 phase. And the films have good corrosion resistance in physiological solution.

High mobility annealing of Transparent Conductive Oxides

To improve electrical properties a high temperature annealing treatment was applied to several transparent conductive oxides (TCO), namely tin doped indium oxide (ITO), Ga- or Al- doped ZnO (ZnO:Al/Ga), ion beam assisted deposited (IBAD) ZnO:Ga and Ga doped zinc magnesium oxide (ZnMgO:Ga). All these films were grown by magnetron sputtering. During the annealing process all TCO films were capped with 50 nm of amorphous silicon in order to protect the films from environmental impact. Increase in mobility up to 72 cm2/Vs and low resistivity of 1.6 × 10−4 Ωcm was achieved for ZnO:Al after annealing at 650°C for 24 h. Independent of the deposition conditions and doping or alloying material almost all ZnO based films show a consistent improvement in mobility. Also for ITO films a decrease in resistivity with partially improved mobility was found after annealing. However, not all ITO films show consistent improvement, but carrier density above 1021 cm−3 while ZnO films show no clear trend for carrier density but a remarkable increase in mobility. Thus we propose the healing of defects and the activation of donors to be most significant effects for ZnO and ITO films, respectively.

Nitrogen beam bombardment induce polarity of carbon nanotubes

The multiwalled carbon nanotubes (MWCNTs) were prepared on SiO2 substrates using chemical vapor deposition (CVD). N ion beam bombardment to MWCNTs was performed at different beam currents of 5–15 mA in an ion-beam-assisted deposition (IBAD) system. Scanning electron microscope (SEM) and Transmission electron microscope (TEM) proved no significant crack and surface morphological change for MWCNTs after N ion beam bombardment. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometry (FTIR), and Raman studies indicated that higher N ion beam current (15 mA) or N atomic concentration (8.6%) induced formation of polar N-containing functional groups of N–C and N–H bonds on the surfaces of MWCNTs. The content of N–C and N–H bonds increased with N ion beam current.

Duplex Hard Coatings with Aditional Ion Implantation

In this paper, we present the results of a study of TiN thin films which are deposited by a Physical Vapour Deposition (PVD) and Ion Beam Assisted Deposition (IBAD). In the present investigation the subsequent ion implantation was provided with N2+ ions. The ion implantation was applied to enhance the mechanical properties of surface. The thin film deposition process exerts a number of effects such as crystallographic orientation, morphology, topography, densification of the films.. A variety of analytic techniques were used for characterization, such as scratch test, calo test, Scanning electron microscopy (SEM), Atomic Force Microscope (AFM), X-ray diffraction (XRD) and Energy Dispersive X-ray analysis (EDAX).