Ion Beam Assisted Deposition Process Research Articles

Long-length GdBCO coated conductors with IBAD/PLD method

We fabricated a long-length GdBCO(GdBa2Cu3O7-δ) coated conductor by the ion-beam assisted deposition (IBAD) and the pulsed laser deposition (PLD) methods. The GdBCO tape was over 400 m in length with 1.5-2.0 MA/cm2 of the critical density. The critical currents of the tape were over "304.8 A/cm" along 368 m in length. So we have achieved "Ic × L = 112,116 Am". For the IBAD process, we have already developed 500 m-length IBAD-Gd2Zr2O7 (IBAD-GZO) tapes with highly aligned in-plane texture, and continuously fabricate 250 m-length tapes at a rate of 0.5∼1 km/month. In addition, we have also developed a new type template for the IBAD-GZO, to enable the production rate fast. Structure of the template is IBAD-GZO/IBAD-MgO/Y2O3. It is note that MgO (111) is parallel to the substrate normal and three fold symmetry. For this structure, the film thickness of the IBAD-GZO could lessen from 1.2 μm to 0.3 μm. By the new IBAD buffer layer, a production rate is expected to be over 30 m/h.

MgF<sub>2</sub> Film Deposited by IAD with End-Hall Ion Source Using SF<sub>6</sub> as Working Gas

Traditionally, Argon (Ar) is used as a working gas to deposit MgF2 thin films in ionbeam assisted deposition (IAD) process. It improves the quality of the films, but cannot reduce the loss of F- ions during the process which also results in other impurities appearing in MgF2 thin films. The contaminants in MgF2 film such as C, O and Ar atoms are identified by X-ray photoelectron spectroscopy (XPS). In this study, sulfur hexafluoride (SF6) was chosen as a working gas in which more F– ions were created from the dissociation of SF6 in the IAD process in order to increase the content of F and eliminate the contamination. In our knowledge, very few reports have been published on IAD used SF6 as a working gas in optical coating process at around room temperature. Deposition of unwanted sulfur atoms was the concern when SF6 was used in the IAD process, however, no sulfur was observed in XPS spectra. The XPS spectra of Mg 2p, O 1s and F 1s were decomposed and analyzed with some Gaussian sub-peaks. The transmission spectra of films were measured in UV and visible ranges. The water absorption phenomena in the films were also measured by Fourier Transform Infrared (FTIR) spectrometer. Compared to the films fabricated by other methods, using SF6 as a working gas in IAD is a good choice to deposit MgF2 films.

Dual Ion Assist Beam Processing of Magnesium Oxide Template Layers for 2nd Generation Coated Conductors

Ion beam assisted deposition (IBAD) of magnesium oxide (MgO) has been shown to be a viable route for producing biaxially textured template films on flexible polycrystalline metal substrates for high-performance coated conductor development. We have refined the technique of IBAD by using a dual ion assist approach. Dual ion assist beam deposition (DIBAD) of MgO reduces the requirements for substrate surface finishing while maintaining comparable film quality (phi scan full-width at half-maximum values between 7 and 8deg). Furthermore, this adaptation of the IBAD process eliminates the degradation of MgO texture observed in IBAD MgO films deposited on silicon nitride. We have deposited films up to 50 nanometers thick without degradation of the in-plane texture. Increasing the MgO thickness increases the chemical stability of template layer and can eliminate the necessity for subsequent buffer layers or the application of the homoepitaxial MgO layer needed to stabilize the thin, conventional IBAD MgO layer. The initial performance of coated conductors made with DIBAD templates is quite promising.

Fabrication of highly textured IBAD-MgO template by continuous reel-to-reel process and its characterization

Highly textured long-length MgO template was successfully deposited on a polycrystalline metal tape using ion-beam-assisted deposition (IBAD). To increase the speed of the IBAD processing, tape moving system was modified from a single-turn to multi-turn system with 14-pass and five heating zones, which leads to larger deposition area. The overall process consists of reel-to-reel electro-polishing of a Hastelloy C276 tape, deposition of Al2O3 diffusion layer and Y2O3 seed layer, deposition of IBAD-MgO and homo-epi MgO layer, and deposition of LaMnO3 (LMO) buffer layer and YBa2Cu3O7−δ (YBCO) superconducting layer using pulsed laser deposition (PLD). Recently, 100m long IBAD-MgO tape with in-plane texture of Δϕ<7° has been successfully fabricated. Critical current density (Jc) of 0.94MA/cm2 at 77K in self field was obtained from the YBCO coated conductor grown on 20cm long LMO-buffered IBAD-MgO template by the PLD process.

Highly efficient transparent organic light-emitting diodes by ion beam assisted deposition-prepared indium tin oxide cathode

The authors have investigated the effects of indium tin oxide (ITO) deposited by ion beam assisted e-beam evaporation on the performance of polymer light-emitting diodes. ITO was evaporated as a cathode onto a thin Mg:Ag layer by an e-beam process, and its performance as a transparent cathode was subsequently compared to that of Mg:Ag and sputtering-prepared ITO. Polymer devices’ luminance and efficiency were improved by more than ten times by ion beam assisted deposition (IBAD)-prepared ITO deposition, with little observable damage to the organic layer. Implementation of the IBAD process resulted in the reduction of the interfacial energy barrier which induced band bending. Furthermore, outcoupling with ITO resulted in enhanced luminance.

Tribological behavior of CrN/WN multilayer coatings grown by ion-beam assisted deposition

CrN monolayer coating and CrN/WN multilayer coatings were deposited on the silicon (100) substrate by ion-beam assisted deposition process. The bilayer period of these coatings was controlled at 8 nm and 30 nm. The cross-sectional morphology of nanoscaled multilayer coatings was characterized by scanning electron microscopy and transmission electron microscopy. The wear resistance of CrN/WN multilayer coatings and CrN monolayer coating was investigated using a pin-on-disc tribometer. The surface roughness (Ra) of the coatings was evaluated by atomic force microscopy, and that of CrN and WN monolayer coating was 6.7 and 5.9 nm, respectively. The employment of multilayer configuration in CrN/WN coating with bilayer period of 8 nm and 30 nm effectively reduced the surface roughness down to 1.9 and 2.2 nm, respectively. The friction coefficient of CrN monolayer coating and CrN/WN multilayer film with a bilayer period of 30 nm was 0.63 and 0.31, respectively. Owing to the high hardness/elastic modulus ratio, as well as the dense structure and the smooth surface roughness, the CrN/WN multilayer coatings exhibited better wear resistance in the consideration of friction coefficient and the worn surface morphology.

Lifetime obtained by ion beam assisted deposition

We have fabricated green organic light-emitting diodes based on tris-(8-hydroxyquinoline)aluminium (Alq3) thin films. In order to favor the charge carriers transport from the anode, we have deposited a N,N′-diphenyl-N,N′-bis (3-methylphenyl)-1,1′-diphenyl-4,4′-diamine (TPD) layer (hole transport layer) on a ITO anode. Cathode is obtained with a calcium layer covered with a silver layer. This silver layer is used to protect the other layers against oxygen during the OLED use. All the depositions are performed under vacuum and the devices are not exposed to air during their realisation.In order to improve the silver layer characteristics, we have realized this layer with the ion beam assisted deposition process. The aim of this process is to densify the layer and then reduce the permeation of H2O and O2. We have used argon ions to assist the silver deposition.All the OLEDs optoelectronic characterizations (I=f(V), L=f(V)) are performed in the ambient air. We compare the results obtained with the assisted layer with those obtained with a classical cathode realized by thermal unassisted evaporation. We have realized lifetime measurements in the ambient air and we discuss about the assisted layer influence on the OLEDs performances.

Effects of incidence angles on the microstructure of Co–Nb thin films prepared by ion beam assisted deposition

Ion incidence angle plays an important role during the ion beam assisted deposition process. In this study, incidence angle effects on the microstructure, morphology and thermal stability of Co 30Nb 70 thin films deposited by ion beam assisted deposition have been investigated. The films were deposited at a fixed ion energy of 4 keV and ion current density of 12 μA/cm 2. The experimental results show that Co 30Nb 70 amorphous alloy is formed, when incidence angles are from 0° to 75°. To investigate stability versus incidence angle, all the samples were annealed at 300 °C and 450 °C, respectively. It was found that most of the Co 30Nb 70 films remained amorphous after being annealed at 300 °C for 30 min, while a bcc metastable phase appeared in the film deposited with incidence angle of 45°. After being annealed at 450 °C for 30 min, the new bcc phase dissolved into amorphous phase again and some films became partially crystallized. The possible mechanism of microstructure evolution is discussed in terms of the mixing, thermal spike, internal stress, and the variations of the process of film growth induced by incidence angles.

Ultraviolet-Enduring Performance of Flexible Pentacene TFTs with SnO[sub 2] Encapsulation Films

We report on the fabrication of flexible pentacene thin-film transistors (TFTs) encapsulated with an ultraviolet (UV)-protecting SnO 2 thin-film that has been prepared by ion-beam-assisted deposition (IBAD). We deposited thermally evaporated SnO 2 on a pentacene TFT as a buffer layer prior to the IBAD process. When a UV light of 254 nm wavelength was continuously illuminated onto our encapsulated device for periods of 5, 30, 60, and 120 min under a vacuum of 1 X 10 -6 Torr, its field mobility gradually degraded from 0.34 to 0.22 cm 2 /V s in 2 h while the other device without encapsulation rapidly degraded (its mobility was reduced to 0.021 cm 2 /V s during the same period). Our X-ray diffraction data indicates that the UV-induced-degradation of device characteristics is directly correlated to the degradation of pentacene crystallinity against UV radiation. We conclude that our IBAD SnO 2 encapsulation is a promising way to protect pentacene TFTs.

Passivation effects on the stability of pentacene thin-film transistors with SnO2 prepared by ion-beam-assisted deposition

The long-term stability of pentacene thin-film transistors (TFTs) encapsulated with a transparent SnO2 thin-film prepared by ion-beam-assisted deposition (IBAD) was investigated. When a buffer layer of 100-nm SnO2 film had been thermally deposited to reduce ion-induced damage prior to the IBAD process, our encapsulated organic thin-film transistors (OTFTs) showed somewhat degraded field-effect mobility of 0.5cm2∕V that was initially 0.62cm2∕Vs, while the OTFTs without a buffer layer showed a 60% reduction in field-effect mobility after the IBAD process. However, surprisingly, the mobility was sustained up to one month and then gradually degraded down to 0.35cm2∕Vs, which was still three times higher than that of the OTFT without any encapsulation layer after 100 days in air. The encapsulated OTFTs also exhibited superior on/off current ratio of over 105 to that of the unprotected devices (∼104), which was reduced from ∼106 before aging. Therefore, the enhanced long-term stability of our encapsulated OTFTs should be attributed to good protection of permeation against H2O into the devices with the IBAD SnO2 thin film, which was identified as having a dense amorphous microstructure with lots of OH groups. Passivation effects on the electrical properties of OTFTs are discussed in terms of the physical and chemical properties of the barrier films.

The application of energetic [formula omitted] ions to form a Si/SiC multilayer system for reflection of radiation between 20 and 80 nm

Implantation of CH x + ions with an energy of 1 keV into Si as well as deposition of Si assisted by bombardment with 500 eV CH x + ions (Ion Beam Assisted Deposition (IBAD)) were applied to form Si/SiC multilayers. For deposition, e-beam evaporation was used, while a Kaufman broad-beam ion source was available for ion bombardment. After deposition of a Si layer and subsequent ion bombardment, Auger Electron Spectroscopy combined with sputter etching was used to achieve a depth profile of the carbon content. As expected a graded mixture of carbon and silicon was observed to an implantation depth that scaled with the ion energy. However, from the shift of the Si LMM Auger peak it became clear that for 500 eV ions carbide was only formed near the surface, while for 1 keV the maximum carbide concentration appeared at a depth of around 2 nm. In order to demonstrate the feasibility of the implantation as well as the IBAD process, multilayers with a periodicity of 10.8 nm were grown. The structures were characterized by θ:2 θ Cu Kα reflectometry. As the optical contrast between Si and C can be neglected compared to the contrast between Si and SiC, this technique revealed for both multilayer production processes the formation of a periodic Si/SiC structure. A preliminary fitting procedure with the measured Cu Kα reflectometry curves confirmed that the system produced by implantation with 1 keV ions contains a carbide layer localized within 0.6 nm. In the IBAD deposited system an amount of 25% carbide is distributed over a layer thickness of ≈5 nm as a part of a mixture with C and Si. This results in a lower contrast than for the implanted system.

Effects of the Polarizability and Packing Density of Transparent Oxide Films on Water Vapor Permeation

The tin oxide and silicon oxide films have been deposited on polycarbonate substrates as gas barrier films, using a thermal evaporation and ion beam assisted deposition process. The oxide films deposited by ion beam assisted deposition show a much lower water vapor transmission rate than those by thermal evaporation. The tin oxide films show a similar water vapor transmission rate to the silicon oxide films in thermal evaporation but a lower water vapor transmission rate in IBAD. These results are related to the fact that the permeation of water vapor with a large dipole moment is affected by the chemistry of oxides and the packing density of the oxide films. The permeation mechanism of water vapor through the oxide films is discussed in terms of the chemical interaction with water vapor and the microstructure of the oxide films. The chemical interaction of water vapor with oxide films has been investigated by the refractive index from ellipsometry and the OH group peak from X-ray photoelectron spectroscopy, and the microstructure of the composite oxide films was characterized using atomic force microscopy and a transmission electron microscope. The activation energy for water vapor permeation through the oxide films has also been measured in relation to the permeation mechanism of water vapor. The diffusivity of water vapor for the tin oxide films has been calculated from the time lag plot, and its implications are discussed.

Enhancement of long-term stability of pentacene thin-film transistors encapsulated with transparent SnO 2

The long-term stability of pentacene thin-film transistors (TFTs) encapsulated with a transparent SnO 2 thin-film prepared by ion beam-assisted deposition (IBAD) was investigated. After encapsulation process, our organic thin-film transistors (OTFTs) showed somewhat degraded field-effect mobility of 0.5 cm 2/(V s) that was initially 0.62 cm 2/(V s), when a buffer layer of thermally evaporated 100 nm SnO 2 film had been deposited prior to IBAD process. However, the mobility was surprisingly sustained up to 1 month and then gradually degraded down to 0.35 cm 2/(V s) which was still three times higher than that of the OTFT without any encapsulation layer after 100 days in air ambient. The encapsulated OTFTs also exhibited superior on/off current ratio of over 10 5 to that of the unprotected devices (∼10 4) which was reduced from ∼10 6 before aging. Therefore, the enhanced long-term stability of our encapsulated OTFTs should be attributed to well protection of permeation of H 2O and O 2 into the devices by the IBAD SnO 2 thin-film which could be used as an effective inorganic gas barrier for transparent organic electronic devices.

Radiation damage of Si wafers modified by means of thin layer ion assisted deposition

Development of the damage and structure of metal-based-film–Si structures’ constructions formed by ion-beam-assisted deposition (IBAD) of thin films onto silicon, using a method in which the metal deposition is accompanied by bombardment by the same metal ions, is considered. The analysis was carried out using the RBS/channeling and TEM methods. The films are found to have uniform thickness, they are amorphous in the interface region and include low scale (∼5–10 nm) inserts of metal. It is estimated that concentration of silicon atoms displaced during the IBAD process in the interface region decreases 1.7–3.7 times when a thin layer on the silicon wafer is deposited by physical evaporation before the IBAD process.

Surface modification of silicone rubber by ion beam assisted deposition (IBAD) for improved biocompatibility

AbstractWe studied the preparation of antimicrobial silicone rubbers of improved interfacial strength, which could be formed with the ion beam assisted deposition (IBAD) technique for coating metallic or inorganic materials (silver (Ag), Copper (Cu), and Hydroxyapatite(HAp)/TiO2) on the silicone surface. Those coating materials provide high product safety as well as outstanding antimicrobial activity. The deposition methodology is composed of pre‐etching with oxygen gas, vaporizing the coating materials, and post‐treatment with Ar ion. With the evaporation of the coating materials, the Ar beam was focused on the substrate to assist deposition. It was found out that the ion assisting depositions in the IBAD process give a prominent enhancement in adhesion between silicone rubbers and coatings of Ag and Cu. The HAp/TiO2 coating layer was easily dissolved in aqueous saline solution. All deposited layers display high antimicrobial activities against Staphlococcus aureus (ATCC 6538) and Escherichia coil (ATCC 25,922), showing 99.9% reduction of bacteria, respectively. In a cytotoxicity test, the Ag and HAp/TiO2 coated silicone shows a decrease of cytotoxicity, while the Cu coating leads to a slight increase of cytotoxicity. The result on the surface modifications of silicone rubber will be employed in further study for applications of medical or rehabilitation devices. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1095–1101, 2005

Solid-State NMR Studies of Lithium Phosphorus Oxynitride Films Prepared by Nitrogen Ion Beam-Assisted Deposition

The chemical stability of phosphate glasses can be improved through the incorporation of nitrogen into the structure. In nitrided amorphous thin films (LiPON), the exceptional stability and enhanced conductivity make them particularly attractive for microbattery applications. Reported here are and solid-state nuclear magnetic resonance (NMR) studies of LiPON thin films fabricated by an ion beam-assisted deposition (IBAD) process. Variable temperature measurements of the resonance yield an activation energy of about 0.2 eV, which is smaller than values obtained from ionic conductivities. spectra provide direct evidence for at least three phosphate environments: two resonances associated with and structures and a third anomalous peak assigned to a nitrided tetrahedral phosphate structural unit of charge −3. Additional evidence exists for other nitrided phosphate structures of charge −2. spectra show evidence for type units and molecular with relative intensities that vary with the nitrogen ion beam gun voltage. No peak associated with trigonal units is observed. Additional evidence for molecular is provided by Fourier transform infrared measurements. A structural model of the phosphorus oxynitride host is presented. © 2005 The Electrochemical Society. All rights reserved.

Improved stability of organic light-emitting diode with aluminum cathodes prepared by ion beam assisted deposition

We have fabricated highly stable organic electroluminescent devices based on spin-coated poly-p-phenylene-vynylene (PPV) thin films. The electrical properties of aluminum cathode, prepared by ion beam assisted deposition, on PPV have been investigated and compared to those by thermal evaporation. Although energetic particles of Al assisted by ArC ion may damage the organic material, I–V–L characteristics are improved by applying thin Al buffer layer. In addition, a dense Al cathode inhibits the permeation of H2O and O2 into PPV film through pinhole defects, and thus retards dark spot growth. It may be deduced from highly packed structure of Al cathode with an increase in the contact area between Al and PPV that reduce the contact resistance. In conclusion, the lifetime of organic light-emitting device (OLED) has been extended effectively by dense Al film through ion beam assisted deposition process.

Influence of Electrode Modification by Ar+ Ion Beam Upon Passivation and Electrical Characteristics in Organic Light-Emitting Diodes

Ion-beam-assisted deposition (IBAD) was used for cathode preparation in organic light-emitting diodes to fabricate dense electrode. Dark spot growth rate was decreased by employing the IBAD process due to a highly packed aluminum structure inhibiting the permeation of H2O and O2. However, undesirable leakage current was generated because energetic particles of Al assisted by Ar+ ion may damage the organic material resulting in reduction of contact resistance. The decrease of contact resistance in the IBAD device may be caused by large contact area, increase of density of states, and Li diffusion to phenyl-substituted poly-p-phenylene vinylene.

Charge injection and transport model in organic light-emitting diodes with aluminum cathodes prepared by ion beam assisted deposition

We have fabricated highly stable organic electroluminescent devices based on spin-coated poly- p-phenylene-vynylene (PPV) thin films. The electrical properties of aluminum cathode, prepared by ion beam assisted deposition, on PPV have been investigated and compared to those by thermal evaporation. Although energetic particles of Al assisted by Ar + ion may damage the organic material, I– V– L characteristics are improved by applying thin Al buffer layer. In addition, a dense Al cathode inhibits the permeation of H 2O and O 2 into PPV film through pinhole defects, and thus retards dark spot growth. It may be deduced from highly packed structure of Al cathode with smaller junction resistance between Al and PPV. In conclusion, the lifetime of organic light-emitting device (OLED) has been extended effectively by dense Al film through ion beam assisted deposition process.

Nanocrystalline materials and coatings

Abstract In recent years, near-nano (submicron) and nanostructured materials have attracted increasingly more attention from the materials community. Nanocrystalline materials are characterized by a microstructural length or grain size of up to about 100 nm. Materials having grain size of ∼0.1 to 0.3 μm are classified as submicron materials. Nanocrystalline materials exhibit various shapes or forms, and possess unique chemical, physical or mechanical properties. When the grain size is below a critical value (∼10–20 nm), more than 50 vol.% of atoms is associated with grain boundaries or interfacial boundaries. In this respect, dislocation pile-ups cannot form, and the Hall–Petch relationship for conventional coarse-grained materials is no longer valid. Therefore, grain boundaries play a major role in the deformation of nanocrystalline materials. Nanocrystalline materials exhibit creep and super plasticity at lower temperatures than conventional micro-grained counterparts. Similarly, plastic deformation of nanocrystalline coatings is considered to be associated with grain boundary sliding assisted by grain boundary diffusion or rotation. In this review paper, current developments in fabrication, microstructure, physical and mechanical properties of nanocrystalline materials and coatings will be addressed. Particular attention is paid to the properties of transition metal nitride nanocrystalline films formed by ion beam assisted deposition process.