Dual Ion Beam Deposition Technique Research Articles

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

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

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

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

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

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

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

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

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

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

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

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

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

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

FexSi grown with mass-analyzed low-energy dual ion beam deposition

Heavily iron-implanted silicon was prepared by mass-analyzed low-energy dual ion beam deposition technique. Auger electron spectroscopy depth profiles indicate that iron ions are shallowly implanted into the single-crystal silicon substrate and formed 35nm thick FexSi films. X-ray diffraction measurements show that as-implanted sample is amorphous and the structure of crystal is partially restored after as-implanted sample was annealed at 400°C. There are no new phases formed. Carrier concentration depth profile of annealed sample was measured by Electrochemical C–V method and indicated that FexSi film shows n-type conductivity while silicon substrate is p-type. The p–n junction is formed between FexSi film and silicon substrate showing rectifying effect.

Structural and magnetic characterization of ion-beam deposited NiFe/NixFe1−xO composite films

Nanocomposite films of Ni80Fe20/NixFe1−xO were prepared by a dual ion-beam deposition technique. The structural and magnetic properties of nanocomposite films fabricated with oxygen content in the deposition assist beam ranging from 0% to 55% were studied. The dependence of the resistivity on oxygen percent shows that the compositions with exchange-enhanced coercivity are close to a percolation threshold. A strong temperature dependence of coercivity Hc and exchange bias field Hex is found in these composite films. Films prepared with 46% O2 in the assist beam exhibit an enhanced Hc relative to Permalloy (Ni80Fe20) and a characteristic shifted hysteresis loop indicative of exchange coupling between the constituent metal and oxide phases. At T=10 K, films prepared with 44% O2 in the assist beam have an exchange shift Hex∼−225 Oe with a blocking temperature TB∼100 K that reflects the low Néel temperatures of FeO-rich NixFe1−xO solid solutions.

(Ga,Mn,As) compounds grown on semi-insulating GaAs with mass-analyzed low energy dual ion beam deposition

The (Ga,Mn,As) compounds were obtained by the implantation of Mn ions into semi-insulating GaAs substrate with mass-analyzed low energy dual ion beam deposition technique. Auger electron spectroscopy depth profile of a typical sample grown at the substrate temperature of 250°C showed that the Mn ions were successfully implanted into GaAs substrate with the implantation depth of 160 nm. X-ray diffraction was employed for the structural analyses of all samples. The experimental results were greatly affected by the substrate temperature. Ga 5.2Mn was obtained in the sample grown at the substrate temperature of 250°C. Ga 5.2Mn, Ga 5Mn 8 and Mn 3Ga were obtained in the sample grown at the substrate temperature of 400°C. However, there is no new phase in the sample grown at the substrate temperature of 200°C. The sample grown at 400°C was annealed at 840°C. In this annealed sample Mn 3Ga disappeared, Ga 5Mn 8 tended to disappear, Ga 5.2Mn crystallized better and a new phase of Mn 2As was generated.

Growth and Photoluminescence of Epitaxial CeO2 Film on Si(111) Substrate

A CeO2 film with a thickness of about80 nm was deposited by a mass-analysed low-energy dual ion beamdeposition technique on an Si(111) substrate. Reflection high-energyelectron diffraction and x-ray diffraction measurements showed that thefilm is a single crystal. The tetravalent state of Ce in the film wasconfirmed by x-ray photoelectron spectroscopy measurements, indicatingthat stoichiometric CeO2 was formed. Violet/blue light emission(379.5 nm) was observed at room temperature, which may be tentativelyexplained by charge transitions from the 4f band to the valence band ofCeO2.

In situ ellipsometry growth characterization of dual ion beam deposited boron nitride thin films

Pure hexagonal h, as well as mixed-phase cubic/hexagonal c/h boron nitride (BN) thin films were deposited onto [001] silicon substrates using the dual ion beam deposition technique. The BN thin films were grown under UHV conditions at different substrate temperatures and ion beam bombarding parameters. Thin-film growth was monitored using in situ spectroscopic ellipsometry at 44 wavelengths between 420 and 761 nm. The in situ ellipsometric Ψ and Δ data were compared with two-layer growth model calculations for the mixed-phase c/h BN, and with one-layer growth model calculations for pure h-BN growth. In situ data provide information on the optical properties of deposited h-BN and c/h-BN material, film thickness, and BN growth rates. A virtual interface approach is employed for the optical properties of the silicon substrate. The growth and nucleation of c-BN observed here confirms the cylindrical thermal spike model. The results for composition and thickness of the BN films were compared to those obtained from ex situ infrared transmission measurements and high-resolution transmission electron microscopy investigations.

High quality CeO2 film grown on Si(111) substrate by using low energy dual ion beam deposition technology

By using the mass-analyzed low energy dual ion beam deposition technique, a high quality epitaxial, insulating cerium dioxide thin film with a thickness of about 2000 Å has been grown on a silicon (111) substrate. The component species, cerium and oxygen, are homogeneous in depth, and have the correct stoichiometry for CeO2. X-ray double-crystal diffraction shows that the full width at half maximum of the (222) and (111) peaks of the film are less than 23 and 32 s, respectively, confirming that the film is a perfect single crystal.

Microstructural characterization of zirconia films produced by the dual ion beam deposition technique

Zirconia films on Si(100) substrate produced by the dual ion beam technique with oxygen ion bombardment and Ar + ion sputtering of Zr were characterized using XRD, RBS and XPS. The results of XRD show that with increasing oxygen ion beam current densities the amorphous microstructure was transformed to a crystalline microstructure: a tetragonal phase together with monoclinic and cubic phases was found. The RBS analyses show that the deposited films consist of three layers: (1) the top layer contaminated by carbon; (2) the bulk of the films with an approximately constant value of the atomic ratio Zr/O; and (3) the transition layer between the bulk of the deposited film and the substrate. Together with XPS the RBS analyses that with the increase of oxygen ion beam current ZrO x with x from 1 3 to 2 was formed.

Ion-beam deposition of Zr−Al multilayers and their structural properties

Multilayers of Zr−Al have been deposited using a dual ion-beam deposition technique. Low angle X-ray diffraction shows the compositional modulation of these multilayers. The period obtained from the X-ray diffraction peaks was in agreement with the period obtained from X-ray fluorescence and electron microscopy, measurements. The as-deposited Al film was crystalline, whereas both the as-deposited Zr film and Zr−Al multilayer film were amorphous.

X-ray photoelectron spectroscopy studies of the surface of ion-beam reactive sputter deposited zirconia films

Zirconia thin films have been widely used in many fields. Zirconia shows a high refractive index and low loss in the infrared region. These properties of zirconia appear to render it suitable for fabricating high-reflectance mirrors and interference filters [1]. Zirconia films have been studied by several groups [1-5]. The deposition methods applied were vacuum evaporation, magnetron sputtering, ion-beam reactive sputter deposition, ion-beam-assisted evaporation and dual ion-beam deposition techniques. X-ray photoelectron spectroscopy (XPS) with surfacesensitive core-level has widely been used to analyse the surface of the thin films since core-level shifts give rather direct information about the oxidation state, charge transfer and co-ordination. In previous studies [4, 5] samples produced by ion-beam reactive sputter deposition or by a dual ion-beam deposition technique were characterized with X-ray diffraction, electron transmission spectroscopy, ellipsometry, Rutherford backscattering, XPS etc. We reported the deposition processingdependent refractive index, atomic composition, phase structures and Zr bonding properties of the zirconia films. The composition of the zirconia labelled as ZrOx films, depending on the deposition parameters, is 0 < x ~< 2. Here the O1~ state on the natural surface of the ion beam reactive sputter deposited ZrOx films is concentrated on. In addition to the same state as in the bulk of the films, a new O1~ state was observed, which is discussed in detail below. The XPS measurements were performed on a model Np-1 XPS spectroscope for chemical analyses having a base pressure of 6.7 x 10 -8 Pa. XPS data were obtained with monochromatic MgK~ radiation (hv -1254 eV) as the X-ray source and 25 eV pass energy, a setting thus giving an overall energy resolution of 1.3 eV full width at half-maximum (FWHM) and a typical sampling depth of about 3.0 nm. XPS data were recorded in N(E) mode and corrected for inelastic backscatter so as to obtain a more accurate fit of the integral spectra. The sputtering beam was from a scanning argon-ion gun operating at 2 keV. Fig. la shows a wide-scan spectrum in the 0-9970 eV kinetic energy range of a sample on the natural surface. It shows the presence of Zr, O, C and Ar. Zirconium and oxygen are constituents of the specimen surface. The argon came from the argon-sputtering process. The carbon signal is due to

Characterization of boron nitride films prepared by the dual ion beam deposition technique

Boron nitride films have been synthesized using the dual ion beam deposition technique. A bombarding beam of 5–100 keV N 2 + ions and a sputtering beam of 0.05–1.5 keV Ar + ions were employed. The boron atoms sputtered from the boron target by the Ar + ion beam were deposited onto the substrate of thermally oxidized silicon wafers which were bombarded by the N 2 + ion beam simultaneously during deposition. Infrared (IR) absorption spectroscopy, X-ray photoelectron spectroscopy (XPS) and microhardness tests were used to study the properties of the resulting films. The IR spectra showed a clear and strong peak due to the cubic boron nitride phase together with two peaks of the hexagonal phase. The microhardness of the films is in excess of 4300 HV.

Titanium nitride deposited by dual ion beams

Titanium nitride films have been prepared by the dual ion beam (DIB) deposition technique, which consists of the ionized cluster beam (ICB) and the ionized gas beam (IGB). As the source of ICB, vaporized titanium is ejected through the multinozzle of the crucible into a high vacuum chamber and is cooled and clustered by adiabatic expansion. The titanium clusters thus obtained are partially ionized in an electron shower and accelerated to the substrate. At the same time, as the source of IGB, nitrogen molecules are partially ionized, excited and decomposed in an electron shower and also accelerated to the substrate. These two beams collide and combine together on their way to the substrate. The characteristics of the ion current density and the properties of titanium nitride films are investigated. It is found that the DIB technique has a great advantage in preparing titanium nitride films of various crystalline structures from TiN to Ti 2N at a low temperature with a high deposition rate over a large substrate. Therefore, the chemical reaction is enhanced by the irradiation of the ionized and excited gases and the migration of ionized clusters on the substrate.

High-speed low-temperature film preparation by an ionized cluster beam, assisted by an ionized gas beam

Oxide and nitride films have been prepared by the dual ion beam (DIB) deposition technique which consists of an ionized cluster beam (ICB) and ionized gas beam (IGB). As source of the ICB, vaporized metals are ejected through the multinozzle of a crucible into a high vacuum chamber and are cooled and clustered by adiabatic expansion. The clusters are partially ionized in an electron shower and accelerated to the substrate. On the other hand, as source of the IGB, gas molecules are partially ionized, excited and decomposed in an electron shower and accelerated to the substrate. These two beams collide and combine together on their way to the substrate. The characteristics of the ion current density and the properties of silicon oxide and titanium nitride films are investigated. It is found that the DIB technique has a great advantage in preparing various oxide and nitride films at low temperature with a high deposition rate over a large substrate. Therefore, the chemical reaction is enhanced by the existence of the ionized and excited gas and the migration of the ionized cluster on the substrate.

New fabrication technique and electronic tunneling studies of NbN

We have fabricated NbN films using a new dual ion-beam sputter deposition technique. In this technique, one ion beam sputters Nb from a target, while the second ion beam directly bombards the growing film. The T c of these NbN films is typically 11–12 K when deposited on near-room temperature substrates. Preliminary results on tunneling through a native oxide barrier yield a superconducting energy gap for NbN of 1.9 meV, for which 2 Δ/ kT c = 3.9. We have also studied oxidized overlayers of Al and Ta to produce an artificial oxide tunneling barrier. Conductance data indicate that the native oxide barrier is broad with a low barrier height (0.2–0.3 eV), whereas the oxidized Al overlayer has a higher (0.5–1.2 eV) and narrower barrier. The quality of the I–V curves for native oxide and for artificial oxide barriers is comparable.