Ion Beam Deposition Technique Research Articles

Friction and wear behavior of C implanted copper via ion beam-assisted bombardment

This work modified the surface of copper using physical vapor deposition and investigated the wear behavior of the modified copper at low load and sliding speed. The results of the study showed that the adhesion between the thin film prepared using the ion beam deposition technique and the substrate was insufficient, leading to an increased wear rate of copper after surface modification. However, when carbon particles were injected using ion beam-assisted bombardment, the friction properties of copper were significantly improved, with a decrease in wear rate from 1.6 × 10−4 to 8 × 10−6 mm3/N m and a 40% reduction in friction coefficient. This improvement can be attributed to the amorphous carbon layer on the copper surface, as well as the injection of carbon particles into the substrate, which enhanced the adhesion between the film and the substrate. Furthermore, a continuous copper oxide film formed during the friction and wear process, providing lubrication and protection to the substrate in conjunction with the amorphous carbon layer. Additionally, the primary wear mechanism of copper shifted from abrasive and adhesive wear to oxidation wear after ion beam-assisted bombardment with carbon injection. This study provides new insights and methods for material design and engineering applications by investigating the effects of ion beam-assisted bombardment technology on the wear resistance of copper materials.

Controlling the optical properties of hafnium dioxide thin films deposited with electron cyclotron resonance ion beam deposition

The effects of reactive and sputtering oxygen partial pressure on the structure, stoichiometry and optical properties of hafnium oxide (HfO2) thin films have been systematically investigated. The electron cyclotron resonance ion beam deposition (ECR-IBD) technique was used to fabricate the films on to JGS-3 fused silica substrates. The amorphous structure of HfO2 films were determined by X-ray Diffraction. Energy-dispersive X-ray Spectroscopy and Rutherford Backscattering Spectrometry were carried out for the composition and stoichiometry analysis, where this suggests the formation of over-stoichiometric films. The data suggests that the O:Hf ratio ranges from 2.4 – 4.45 to 1 for the ECR-IBD fabricated HfO2 films in this study. The transmission and reflectance spectra of the HfO2 films were measured over a wide range of wavelengths (λ = 185 – 3000 nm) by utilizing a spectrophotometer. The measured spectra were analyzed by an optical fitting software, which utilizes the model modified by O'Leary, Johnson and Lim, to extract the optical properties, refractive index (n) and the bandgap energy (E0). By varying the reactive and sputtering oxygen partial pressure, the optical properties were found to be n = 1.70 – 1.91, and E0 = 5.6 – 6.0 eV. This study provides a flexible method for tuning the optical properties of HfO2 coatings by controlling the mixture of reactive and sputtering gas.

Production of low-energy SiCH3+ and SiC2H7+ ion beams for 3C-SiC film formation by selecting fragment ions from dimethylsilane

Fragment ions produced from dimethylsilane (DMS) in a Bernas-type ion source were investigated. Dominant fragment ions were identified to be CH3+, Si+, SiH3+, SiCH3+, and SiC2H7+. We mass-selected SiCH3+ and SiC2H7+ ions and then produced low-energy SiCH3+ and SiC2H7+ ion beams. Subsequently, these ion beams were used to irradiate Si(111) substrates at 800 °C. The energies of SiCH3+ and SiC2H7+ ions were set at 100 eV. We found that the irradiation of these ions led to the deposition of silicon carbide (3C-SiC) films on the Si substrates. For comparison, SiC film formations on Si(111) substrates were also attempted by the chemical vapor deposition (CVD) method using DMS. The X-ray photoelectron spectroscopy measurements showed that atomic ratios of C to Si (C/Si ratio) of the films obtained by the irradiation of SiCH3+ and SiC2H7+ ion beams were 1.2 and 1.2, respectively. Conversely, the C/Si ratio of the film obtained by CVD was 1.9. Raman spectroscopy showed that the film obtained by CVD included diamond-like carbon. These results suggest that the low-energy mass-selected ion beam deposition technique using DMS-derived fragment ions is practicable for the 3C-SiC deposition on Si substrates.

Fabrication, structural investigation and comparative optical characterization of copper polymer nanocomposites

In this work, a homemade ion beam deposition technique is used to fabricate nanocomposites films consisting of copper nanoparticles (CuNPs) embedded in a polyethylene terephthalate (PET) and in polytetrafluoroethylene (PTFE) polymers. Then study the comprehensive effect of the deposited CuNPs on the optical and structural properties of PET and PTFE polymers. The structural investigation of the PET and PTFE polymers as well as the Cu/PET and Cu/PTFE composites is carried out using X-ray diffraction (XRD). The XRD data showed CuNPs are deposited successfully on PET and PTFE films. The optical characterization of the prepared films is studied using UV–Vis spectroscopy techniques, to confirms the changes in the optical band gap Eg and carbon cluster number N. The UV–Vis optical absorption demonstrate a slight shift in the absorption edge towards visible region by increasing Cu deposition time on both PET and PTFE polymers. Increasing Cu deposition time is leads to slight decrease in optical energy band gap Eg and an increase in the numbers of carbon cluster N. The Eg is decreased from 3.8 to 2.2 eV for Cu/PET and from 3.1 to 2.3 eV for Cu/PTFE while N is increased from 82 to 244 for Cu/PET and from 113 to 224 for Cu/PTFE by increasing the Cu deposition time from 25 to 75 min. The obtained results of Cu/PET and Cu/PTFE polymer nanocomposites are opening new fields for applicable optoelectronic devices.

Understanding the effect of Al/Ti ratio on the tribocorrosion performance of Al/Ti co-doped diamond-like carbon films for marine applications

Al and Ti co-doped diamond-like carbon (DLC) films (Al/Ti-DLC) were prepared through hybrid ion beam deposition technique, in which the Al/Ti ratio was tailored from 6.6 to 2.0. The dependence of tribocorrosion performance of Al/Ti-DLC film on the Al/Ti ratio in 3.5 wt% NaCl solution was systematically explored. Results indicated that the existing states of Al and Ti dopants in the film were independent on the Al/Ti ratio, where Al existed in the form of oxidized state, while Ti mainly bonded with C and thus formed the titanium carbide following the presence of titanium oxide, leading to the increase of hardness and elastic modulus with the decrease of Al/Ti ratio. In particular, with reducing the Al/Ti ratio from 6.6 to 2.0, the tribocorrosion resistance was improved, mainly originating from the reduction of pure mechanical wear. However, EIS analysis further revealed that although the mechanical wear accelerated the electrochemical corrosion of Al/Ti-DLC films, the contribution of the synergistic effect between mechanical wear and corrosion attack to materials loss increased following the drop of Al/Ti ratio, due to the corrosion-induced wear rather than wear-induced corrosion. These outcomes not only shed light on the effect of Al/Ti ratio in the film on the tribocorrosion property but also guide the design of DLC films for marine applications.

Use of quantum effects as potential qualifying metrics for "quantum grade silicon".

Across solid state quantum information, materials deficiencies limit performance through enhanced relaxation, charge defect motion or isotopic spin noise. While classical measurements of device performance provide cursory guidance, specific qualifying metrics and measurements applicable to quantum devices are needed. For quantum applications, new materials metrics, e.g., enrichment, are needed, while existing, classical metrics like mobility might be relaxed compared to conventional electronics. In this work, we examine locally grown silicon superior in enrichment, but inferior in chemical purity compared to commercial-silicon, as part of an effort to underpin the materials standards needed for quantum grade silicon and establish a standard approach for intercomparison of these materials. We use a custom, mass-selected ion beam deposition technique, which has produced isotopic enrichment levels up to 99.99998 % 28Si, to isotopically enrich 28Si, but with chemical purity > 99.97% due the MBE techniques used. From this epitaxial silicon, we fabricate top-gated Hall bar devices simultaneously on the 28Si and on the adjacent natural abundance Si substrate for intercomparison. Using standard-methods, we measure maximum mobilities of at an electron density of cm-2 and at an electron density of cm-2 at K for devices fabricated on 28Si and natSi, respectively. For magnetic fields T, both devices demonstrate well developed Shubnikov-de Haas (SdH) oscillations in the longitudinal magnetoresistance. This provides transport characteristics of isotopically enriched 28Si, and will serve as a benchmark for classical transport of 28Si at its current state, and low temperature, epitaxially grown Si for quantum devices more generally.

Modification of optical and mechanical properties of nitrogen doped diamond-like carbon layers

We have deposited diamond-like carbon (DLC) films on glass and Si substrates with direct ion beam deposition technique and investigated the effect of N2 doping on their structural, mechanical, and optical properties. The DLC coatings were doped with nitrogen under different flow rates of 5, 10, 20, 40, and 50 sccm. Morphological characteristics investigation of the prepared samples showed decrement in their average roughness from 4.1 to 0.68 nm. Raman studies showed that the number of graphitic sp2 bonding increased with N doping. By increasing the N2 content, the graphite cluster size increased. FTIR measurement revealed the functional groups available in the prepared samples. UV–Vis analysis showed that the optical transmission of nitrogen-doped DLC (N-DLC) coatings decreased when N2 content increased from 5 to 40 sccm followed by decrement in both the optical band gap and the internal stress. Finally, the mechanical properties such as hardness and elastic modulus decreased by increasing N2 content from 5 to 40 sccm.

High temperature coefficient of resistance and low noise tungsten oxide doped amorphous vanadium oxide thin films for microbolometer applications

In this study, we report tungsten oxide (WO3) doped vanadium target in order to sputter amorphous vanadium tungsten oxide (a-VWOx) thin films by reactive direct-current magnetron sputtering technique. No post annealing and post oxidation steps were applied to improve bolometric properties. Thin films with high temperature coefficient of resistance, up to 3.02%/K, were prepared with resistivity range of 1–10 Ω cm thereby controlling the oxygen flow rate and sputtering conditions. Thin film composition was determined using X-ray photoelectron spectroscopy analysis which showed that the film has a mixed phase of V2O5, VO2 and V2O3. The noise level of the deposited film at 20 Hz was calculated as 1.9 × 10−15 V2/Hz from the noise spectrum density analysis. This noise level was found out to be comparable to the literature for VOx films deposited by ion beam deposition technique.

Effect of Post Deposition Annealing on the Structural and Electrical Properties of NbTiN Thin Films Deposited by Reactive Bias Target Ion Beam Deposition Technique

Nb-based superconducting alloys, such as NbN and NbTiN, can have a superconducting energy gap near twice that of elemental Nb, thus, being ideal candidates for low-loss superconducting circuits operating above the gap frequency of Nb. We are particularly interested in these materials for THz-frequency superconducting-insulating-superconducting (SIS) mixers, kinetic inductance detectors, and traveling wave kinetic inductance parametric amplifier devices. We recently reported the use of an alternative synthesis technique, reactive bias target ion beam deposition (RBTIBD), used to realize high-quality NbTiN films and high-energy gap NbTiN/AlN/NbTiN SIS heterostructures. In this paper, the effect of post-deposition annealing on the electrical and structural properties of room temperature deposited RBTIBD NbTiN was investigated. Our room temperature RBTIBD NbTiN films were annealed using rapid thermal annealing from 200 to 1000 °C. The change in structural and electrical properties was characterized by X-ray diffraction, atomic force microscopy, and four-point probe measurements. The annealed films demonstrated an enhancement in transition temperature (T c ), increased crystallinity, larger grain size, and significantly reduced intrinsic stress.

Highly tunable doping in Ge quantum dots/graphene composite with distinct quantum dot growth evolution

Quantum dots/graphene (QDs/Gr) composites have become the research hotspot recently due to their unique synergistic effect as optical absorption material for next-generation electronic and optoelectronic devices. In this work, Ge QDs/Gr composite is prepared by a simple and effective ion-beam sputtering deposition technique. The intact growth evolution process is detailly investigated by means of the effect of Ge deposition amount, which will induce the enhanced crystallinity in QDs and the reduced defects in graphene. Moreover, a feasible and inspiring strategy to effectively tune doping in graphene by artificial control through changing the deposition amount of Ge atoms on graphene is demonstrated. In addition, charge transfer and interaction strength at the interface of Ge QD and graphene is influenced via the oxygen defect in the QD surface, which is consistent with field-effect transistor test and first-principle calculations. The p-doping characteristics of graphene decorated by Ge QDs may have significant application prospects in energy band engineering of graphene-based building blocks for graphene-based composite development and near-infrared detector applications.

Magnetic Properties of Fe/Ni and Fe/Co Multilayer Thin Films

In this work, the magnetic and transport properties of Fe/SiO2/Ni and Fe/SiO2/Co multilayers grown on Si/SiO2 substrates have been studied. The samples have been prepared by two-stage deposition process. In the first stage, Fe layer and SiO2 interlayer of both samples are grown by ion beam deposition technique at room temperature. Then the samples are taken out to ambient atmosphere and loaded into a pulse laser deposition (PLD) chamber. Prior to the deposition of top layer, the samples are cleaned by annealing at 150 °C. In the second stage, Ni (or Co) layer is prepared by PLD technique at room temperature. The thickness of deposited layers has been measured by Rutherford back scattering (RBS). Magnetic properties of ferromagnetic bilayers have been investigated by room-temperature ferromagnetic resonance (FMR) and vibrating sample magnetometer (VSM) techniques. Standard four-point magneto-transport measurements at various temperatures have been performed. Two-step switching in the in-plane hysteresis loops of Fe/SiO2/Ni and Fe/SiO2/Co samples is observed. A crossing in the middle of hysteresis loops of both samples points to a weak antiferromagnetic interaction between the magnetic layers of the stacks. Saturation magnetization values have been obtained from the VSM measurements of samples with DC magnetic field perpendicular to the films surface. Magneto-transport measurements have shown the predominant contribution of anisotropic magnetic resistance both at room and low temperatures. FMR studies of Fe/SiO2/Ni and Fe/SiO2/Co samples have revealed additional non-uniform (surface and bulk SWR) modes, which behavior has been explained in the framework of the surface inhomogeneity model. An origin of the antiferromagnetic interaction has been discussed.

Ellipsometric and magneto-optical study of nanosized ferromagnetic metal-dielectric structures [Co/TiO2]n/Si

Ferromagnetic metal-dielectric multilayer structures [Co/TiO2]n with layer thicknesses of 2–4nm were fabricated on the (001)-surface of Si substrates by the ion-beam deposition technique. The complex dielectric function was studied in the spectral range of 0.6–5.6eV using the optical ellipsometry and analyzed using the optical matrix technique for reflection response of lossy isotropic multilayer dielectric structures and an anisotropic effective medium approximation. Magnetic characteristics of the structures were determined by using the magneto-optical Kerr effect. Obtained results allow us to conclude that these nanosized ferromagnetic metal-dielectric structures may be regarded as artificial uniaxial media exhibiting a strong optical and magnetic anisotropy at room temperature.

Synthesis and characterization of boron incorporated diamond-like carbon thin films

Boron incorporated diamond-like carbon (B-DLC) (up to 8wt.% boron) thin films were synthesized on silicon wafers using biased target ion beam deposition technique, where diamond-like carbon (DLC) was deposited by ion beam deposition and boron (B) was simultaneously incorporated by biased target sputtering of a boron carbide (B4C) target under different conditions. Pure DLC films and B–C films were also synthesized by ion beam deposition and biased target sputtering of B4C under similar conditions, respectively, as reference samples. The microstructure and mechanical properties of the synthesized films have been characterized by various technologies. It has been found that B exists in different states in B-DLC, including carbon-rich and B-rich boron carbides, boron suboxide and boron oxide, and the oxidation of B probably occurs during the film deposition. The incorporation of B into DLC leads to the increase of sp3 bonded carbon in the films, the increase of both film hardness and elastic modulus, and the decrease of both surface roughness and friction coefficient. Furthermore, the content of sp3 bonded carbon, film hardness and elastic modulus increase, and the film surface roughness and friction coefficient decrease with the increase of B-rich carbide in the B-DLC films.

Structure and interfacial analysis of nanoscale TiNi thin film prepared by biased target ion beam deposition

Ultrathin, 65 nm thick, TiNi alloy films were fabricated by cosputtering Ti and Ni targets using the recently developed biased target ion beam deposition technique. Preheating the substrate by exposure to a low energy ion source resulted in as-deposited films with a pure B2 atomic crystal structure containing no secondary crystal structures or precipitates. Continuous films were produced with a smooth surface and minimal substrate/film interfacial diffusion. The diffusion layer was a small ratio of film thickness, which is a prerequisite for the B2 phase to undergo the martensitic transformation in ultrathin films.

Structural properties and surface wettability of Cu-containing diamond-like carbon films prepared by a hybrid linear ion beam deposition technique

Cu-containing diamond-like carbon (Cu-DLC) films were deposited on Si/glass substrate by a hybrid ion beam deposition system. The Cu concentration (0.1–39.7at.%) in the film was controlled by varying the sputtering current. The microstructure and composition of Cu-DLC films were investigated systematically. The surface topography, roughness and surface wettability of the films were also studied. Results indicated that with increasing the Cu concentration, the water contact angle of the films changed from 66.8° for pure carbon film to more than 104.4° for Cu-DLC films with Cu concentration larger than 24.4at.%. In the hydrophilic region, the polar surface energy decreased from 30.54mJ/m2 for pure carbon film to 2.48mJ/m2 for the film with Cu 7.0at.%.

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.

NiTi thin films prepared by biased target ion beam deposition co-sputtering from elemental Ni and Ti targets

NiTi thin films are fabricated using biased target ion beam deposition technique. By design, the technique operates over a broad range of processing pressures; enables control of adatom energies; facilitates low energy bombardment; and promotes uniformity and repeatability. Thus, the technique is advantageous for preparing smooth and dense ultrathin films. Typically NiTi shape memory alloy thin films are deposited using the magnetron-sputtering technique and alloy targets. In this work films are co-sputtered from pure Ti and pure Ni targets and the technique is contrast with magnetron co-sputtering. Approximately 100nm thick NiTi thin films are prepared with Ni-rich (>50.5at.% Ni), near equiatomic, and Ti-rich (<49.5at.% Ni) compositions. Atomic force microscopy reveals that films are consistently ultra-smooth over the broad range of compositions. The current findings confirm that biased target ion beam deposition can facilitate the preparation of high quality ultrathin NiTi films. After heat-treatment, the films deposited exhibit B2 and B19′ crystal structures and thus possess potential for martensitic phase transformation, which is the prerequisite for functional shape memory behavior.

Magnetic damping and spin polarization of highly ordered B2 Co2FeAl thin films

Epitaxial Co2FeAl films were synthesized using the Biased Target Ion Beam Deposition technique. Post annealing yielded Co2FeAl films with an improved B2 chemical ordering. Both the magnetization and the Gilbert damping parameter were reduced with increased B2 ordering. A low damping parameter, ∼0.002, was attained in B2 ordered Co2FeAl films without the presence of the L21 Heusler phase, which suggests that the B2 structure is sufficient for providing low damping in Co2FeAl. The spin polarization was ∼53% and was insensitive to the chemical ordering.

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.

Ultra-smooth diamond-like carbon coatings with high elasticity deposited at low temperature by direct ion beam deposition

Diamond-like carbon (DLC) coatings were fabricated under high vacuum at low temperature using a direct ion beam deposition technique based on a Penning ion source. Post-acceleration and electrostatic scanning were applied to form adhesive and laterally homogenous coatings across 50mm using ion energies from 3.0 to 10.5kV. The deposition rate was set to 0.4nms−1 to prevent heating of the coating and substrate. Structural, physical and chemical analyses revealed the formation of atomically flat hydrogenated amorphous carbon (a-C:H) coatings with a sp3 content of typically 20%. RBS measurements show that coatings produced at high acceleration voltage have impurities of carbon in the near-surface region of the silicon substrate as well as silicon impurities in the DLC coating at the interface. The penetration depth of the impurities is energy dependent. Nanoindentation measurements provided hardness figures of up to 18GPa combined with high elasticity values of 90%. Hardness and elasticity values and the sp3 content were measured to be proportional to the acceleration energy. An interface layer was observed with transmission electron microscopy indicating atomic interlocking between the carbon coating and the silicon substrate. The results highlight the opportunity to produce a-C:H coatings with high elasticity by direct ion deposition at low temperature.