Hisashi Nakai

Epitaxial growth and characterization of Ni films grown on MgO(001) by biased direct‐current sputter deposition

Ni films thinner than 180 nm are deposited on MgO(001) substrates at a temperature Ts of 190 or 280 °C by dc sputtering at 2.5 kV in Ar gas. A dc bias voltage Vs between 0 and ‐140 V is applied to the substrate during the deposition. A study of structural and physical properties of the Ni film is made by the use of reflection high‐energy electron diffraction (RHEED), cross‐sectional transmission electron microscopy (XTEM), x‐ray reflection diffraction (XRD), Rutherford backscattering spectroscopy (RBS), and by measuring (TCR) in the temperature range from 35 to 135 °C. When Ts=190 °C the Ni film retains a polycrystalline structure at any Vs. When Ts=280 °C, as Vs increases from 0 to −140 V the film transforms from the polycrystal to the single crystal with the orientation as Ni(001)∥MgO(001) and Ni〈010〉∥MgO〈010〉, indicating that an optimal value of Vs for the epitaxial growth ranges from −80 to −110 V. Besides, an analysis of RBS spectra in comparison with XTEM images explains that the atomic density of t...

RBS and XHRTEM characterization of epitaxial Ni films prepared by biased d.c. sputter deposition on MgO(001)

Abstract Rutherford backscattering spectrometry (RBS) channelling and cross-sectional high-resolution transmission electron microscopy (XHRTEM) have been applied to characterize the structure of Ni films grown epitaxially on MgO(001) by biased d.c. sputter deposition. The RBS spectra indicate that the Ni films have a high density of lattice imperfections near to the MgO surface. The XHRTEM investigations revealed a lattice expansion in the [010]direction confirming the existence of the slightly distorted cubic lattice of Ni in the vicinity of the substrate surface which was detected by RBS channelling measurements. Regularly distributed edge dislocations due to the mismatch of Ni and MgO lattices have been clearly demonstrated by XHRTEM.

FERROMAGNETIC RESONANCE IN NI FILMS BIASED DC SPUTTER DEPOSITED ON MGO(001)

Ferromagnetic resonance measurement at X band is carried out at room temperature to investigate the mechanical and magnetic properties of Ni films 180 nm thick deposited on MgO(001) substrates at 280 °C by biased direct current plasma sputtering at 2.5 kV in Ar gas. A negative bias voltage Vs of 0, −80, and −140 V is applied to the substrate during the deposition. The homogeneous intrinsic stress σi induced in the films is compressive (σi<0) at any Vs and its value is independent of Vs. The magnetic anisotropies due to the anisotropic planar stress σu induced during the film formation and due to the magnetocrystalline anisotropy K1f of the epitaxial Ni crystal are mutually superimposed in the film plane. σu is very weak, i.e., ‖σu‖≪‖σi‖, to reduce nearly to zero as Vs reaches −140 V. Although the magnitude of K1f gradually increases as Vs increases, it is about 10−1 of that of K1 for bulk Ni. The g factor is evaluated at 2.11 independently of Vs.

Characterization of cobalt films grown on MgO(001) by dc-biased-sputter deposition

Abstract Cobalt films (90 nm thick) were deposited on MgO(001) substrates at 250°C by dc-sputtering at 2.5 kV in pure argon gas. A bias voltage V s between 0 and − 180 V was applied to the substrate during the deposition. Reflection high-energy electron diffraction, cross-sectional transmission electron microscopy (XTEM) and X-ray photo electron spectroscopy, as well as measurements of the temperature coefficient of resistivity and saturation magnetization (4 πM s ), all as a function of V s , confirmed that the structural and physical properties of cobalt films are most improved at − V s = 140 V with a Co(001)|MgO(001) and Co[010]|MgO[010] relationship. A structural study of cobalt films prepared at − V s = 140 V by high-resolution XTEM revealed that the stress induced in cobalt films is relaxed by the generation of defects such as misfit dislocations, lattice expansion and partial lattice distortions.

Growth structure of nickel films on GaAs(001) by d.c.-biased plasma-sputter-deposition

Abstract Ni films 200 nm thick are deposited on GaAs(001) substrates at 280°C by d.c. plasma sputtering at 2.5 kV in pure Ar gas. A d.c. bias voltage V s from 0 to −180 V is applied to the substrate during deposition. The effect of V s on the film growth is investigated by measuring TCR from 150 to 300 K, and resistance at 300 K, also by AES, XTEM, and RHEED observations. Minimum resistance and maximum TCR are observed at V s between −80 and −100 V. The Ni film is polycrystalline with a [001] texture, while an As 2 Ni thin layer is grown penetrating into the GaAs substrate with As 2 Ni[111]‖GaAs[111] and As 2 Ni[011]‖GaAs[011]. The Ni film, composing of uniformly grown grains, is obtained with a higher value of TCR at V s =−80 V.

FMR, XRD and XHRTEM characterization of stresses in an epitaxial Ni–Cu film prepared on MgO(001) by d.c. biased plasma sputter deposition

Abstract Ferromagnetic resonance (FMR), X-ray reflection diffraction (XRD) and cross-sectional high-resolution transmission electron microscopy (XHRTEM) are applied to characterize the stresses of the d.c. biased plasma-sputter-deposited Ni 97 Cu 3 films grown epitaxially on a MgO(001) substrate. The FMR study indicates that a homogeneously compressive intrinsic stress and an anisotropic planar stress are simultaneously induced in the film. The latter consists of the part induced during the film formation and the part originated from the magnetocrystalline anisotropy of the Ni–Cu crystal. The compressive stress in the film is also confirmed by the XRD study. The XHRTEM study reveals misfit dislocations generated in the Ni–Cu crystal at the MgO interface relaxing the strain energy due to the lattice mismatch between Ni 97 Cu 3 and MgO crystals and locally induced lattice distortions. In conclusion the stress inside the film is compressive as a whole.

Synthesis of Fe2W by low pressure laser spraying

Abstract Fe 2 W is the Laves type intermetallic compound with hexagonal crystal structure and is known to be a type of hard alloy. The low-pressure laser spraying (LPLS) method was applied to synthesize Fe 2 W clad layers on a mild steel substrate. Structure and atomic composition of surface clad layers were analyzed by X-ray diffraction and energy dispersive X-ray spectroscopy, respectively. When the substrate was exposed to a laser energy density of 36 W/mm 2 , the tungsten concentration of clad layers was estimated to be 20 wt.% at maximum with a microhardness of 240 Hv. The microhardness remarkably increased with heat treatment at 973 K in vacuum, suggesting that the Fe 2 W phase was formed with heat treatment.

Structural and physical properties of Co films DC-bias-plasma-sputter-deposited on MgO(001)

Abstract Co films 90 nm thick are deposited on MgO(001) substrates at a temperature of 250°C by DC plasma sputtering at 2.5 kV in pure Ar gas. A DC bias voltage V s between 0 and −140 V is applied to the substrate during deposition. The structural and physical properties of the film are studied as a function of V s by the use of reflection high-energy electron diffraction (RHEED), cross-sectional transmission electron microscopy (XTEM), X-ray photon spectroscopy (XPS) and by measuring the temperature coefficient of electrical resistance (TCR) from 50 to 150°C and the saturation magnetization 4 πM f at room temperature. As ∥ V s ∥ increases, the structure of the Co film which is always fcc transforms from a polycrystalline state to a textured state such as Co(001) ⊥MgO(001) and Co[010]⊥MgO[010] with larger grains at V s = −50 V. The impurity which consists mainly of O and C decreases with increasing ∥ V s ∥ from 0 V but reaches a slight maximum at − V s = 110 V. The XTED lines of CoO are observed strongly at V s = 0 V and weakly at V s = − 110 V. Consistent with the above mentioned behavior of the structural properties, 4 πM f as well as TCR (>0) take smaller values at V s = 0 and −110 V. In conclusion, the properties of the Co film are most improved at − V s = 140 V.

Ferromagnetic resonance in Ni films produced by biased d.c. sputter deposition onto SiO2 and Si(100)

Ferromagnetic resonance measurements at the X-band were taken at room temperature mainly to investigate the mechanical properties of Ni films 180 nm thick prepared on both pure and SiO2-covered Si(100) substrates at 190 °C by biased d.c. plasma sputter deposition at 2.5 kV in Ar gas. A negative bias voltage Vs between 0 V and −80 V was applied to the substrates during deposition. The homogeneous intrinsic stress σi induced in the films is compressive (σi <0). The magnitude of σi depends on Vs. For the Ni/SiO2 system − σi has a maximum as Vs reaches about −30 V because the impurities are most strongly embedded in the film with incoming Ar particles. When − Vs is over 30 V the more energetic Ar particles contribute to a decrease in − σi through resputtering the impurities. For the Ni/Si system − σi, only increases monotonically with Vs, mainly owing to the peening effect. The anisotropic planar stress σu which is much smaller in magnitude than σi is also induced in the film for both systems. The origin of σu is not understood at present. Thus, the g-factor varies with Vs mainly in agreement with the dependence of σi on Vs for both systems.

Electrical property on copper thin film with chromium under-layer

Abstract Temperature coefficient of resistance (TCR) of as-deposited and annealed atomic beam-deposited polycrystalline copper films of 20 nm with chromium under-layer on SiOx substrate layers was measured. The copper resistivity for various chromium thicknesses was in situ measured during copper deposition. The TCR of the as-deposited films decreases with the chromium thickness to reach a minimum value at about 5 nm. The minimum TCR value for the annealed copper films exists at the chromium thickness equal to about 1 nm. When chromium thickness is less than 2 nm the annealing markedly decreases the TCR of the copper film.