Mituru Hashimoto

Effect of substrate temperature on crystallization of amorphous antimony film.

A study is made of the crystallization of amorphous antimony film deposited on a glass substrate. The substrate is maintained at a desired temperature between 20°C and 90°C. The crystal growth in the films of thickness 210-550 A is directly observed through an optical microscope. At any substrate temperature Ts the rate of crystal growth v is found to change with the thickness d in accordance with the expression v=v∞(1-dc/d), where dc is the critical thickness for crystallization of the amorphous antimony film and v∞ the rate of crystal growth for bulk antimony. The critical thickness dc decreases with the rise of Ts. The activation energy of atoms for crystallization Q is found to be 0.32 eV for bulk antimony.

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...

The interaction between platinum films and silicon substrates: Effects of substrate bias during sputtering deposition

The reactions between platinum and silicon, both during platinum deposition at elevated temperature and during a thermal annealing process, have been investigated using x-ray diffraction, cross-sectional transmission electron microscopy, and x-ray photoelectron spectroscopy. It has been found that sputtering deposition of platinum on a silicon substrate at 200 °C results in the formation of PtSi at the Pt–Si interface. But the reaction cannot fully proceed at this temperature for a platinum film with a thickness of 35 nm. Further annealing at 450 °C causes the platinum film to transform to PtSi completely. A substrate bias of −90 V during sputtering deposition leads to the formation of platinum films with larger columnar grains, instead of finer grains as being formed without substrate bias. In such a case, oxygen diffusion toward the interface was enhanced through the boundaries of these columnar grains, and this results in an accumulation of oxygen and oxide formation at the interface. As a result, the ...

Crystallization of amorphous antimony films deposited onto glass substrates in ultrahigh vacuum

Abstract The crystallization of amorphous antimony (a-Sb) films deposited onto glass substrates in an ultrahigh vacuum of 10−6−10−7 Pa is investigated through in situ observation with an optical microscope camera. In comparison with the results for deposition in a conventional vacuum of 10−4−10−5 Pa, a marked reduction is observed in the critical thickness dc for crystallization. For thicknesses less than the previous dc value of about 250 A, the dependence of the crystallization rate on the thickness is found to weaken drastically and the activation energy of the atoms for crystallization to increase. The antimony crystallites which nucleate in such thin a-Sb films do not take a simple spherical form.

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.

Epitaxial growth, structure and properties of Ni films grown on MgO(100) by d.c. bias sputter deposition

Abstract Ni films of 70–240 nm thickness were deposited on an MgO(100) substrate at temperatures T s ⩾190°C by d.c. sputtering at 2.5 kV in pure Ar gas. A negative bias voltage V s between zero and −110 V was applied to the substrate during the deposition. Reflection high energy electron diffraction, X-ray diffraction, cross-sectional transmission electron microscopy. Auger electron spectroscopy, ferromagnetic resonance and the measurement of the temperature coefficient of resistance were used to determine the structure and properties of the films. The degree of epitaxy of Ni increases with increasing T s as well as increasing V s . The optimum conditions for epitaxial growth of Ni are T s ⩾280°C and V s ⩾80 V. In this range epitaxial films with Ni(100) ∥ MgO(100) and Ni〈100〉 ∥ MgO〈100〉 can be prepared. A magnetic anisotropy is induced in the film plane. This anisotropy may be a result of superposition of a magnetocrystalline anisotropy originating from the epitaxial Ni film and of a uniaxial magnetic anisotropy induced during the film formation. In conclusion, as V s ranges −80 to −110 V the bombarding effect of both energetic ions and fast neutrals of Ar will rule the epitaxial growth of the Ni film by increasing the mobility of Ni adatoms and by resputtering the impurities. This effect is pronounced at T s ⩾280°C.

Crystallization of amorphous antimony films on silver films

Abstract The crystallization process in amorphous antimony films 70–330 A thick evaporated onto silver films 10–150 A thick which have previously been evaporated onto glass is directly observed through an optical microscope. The conditions under which the crystallization process in the amorphous antimony films is observed are found to be severely limited by the preparation conditions of the silver films. The crystallization can only be observed on silver films thinner than 30–40 A which have previously been exposed to oxygen or nitrogen gas. The crystallization thickness of amorphous antimony films on these substrates is estimated to be 123-75 A as the substrate temperature varies from 20 to 80 °C and the activation energy for crystallization to be 0.23-0.30 eV as the film thickness varies from infinity to 200 A.

Thickness dependence of structural and ferroelectric properties of sol-gel Pb(Zr0.56Ti0.44)0.90(Mg1/3Nb2/3)0.10O3 films

Abstract Sol-gel Pb(Zr0.56Ti0.44)0.90(Mg1/3Nb2/3)0.10O3 (PZT-PMN) films were prepared onto the Ti/Pt/Ti bottom electrode by multilayer spin coating. The film thickness ranged from 0.22 to 0.88 μm. The Pt top electrodes were deposited on the PZT-PMN films by DC sputtering. The structural and ferroelectric properties of PZT-PMN films were investigated as a function of film thickness by X-ray diffraction (XRD), scanning electron microscopy (SEM), cross-sectional transmission electron microscopy (XTEM), and by measuring the relative permittivity. The film retains the tetragonal perovskite structure with the [111] and [100] preferred orientations perpendicular to the film surface independent of film thickness. The [100] texture increases with increasing film thickness although the [111] texture is always predominant. The film consists of columnar grains. The average grain size is nearly independent of film thickness. The surface layer containing fine grains about 30 nm in diameter is induced on the top of the film. As the film thickness exceeds 0.44 μm, the number of the fine grains decreases remarkably. The crystalline interface layer about 10 nm thick is formed between the film and the bottom electrode. This interface layer is composed of Pt, Pb, Zr, Ti and O, while it is rich in Ti and deficient in Pb and O as compared with the inside of the film. The measured relative permittivity of the film increases with increasing film thickness, following the low permittivity interface model. On the basis of this model, the relative permittivity is estimated to be 3200 for the intrinsic PZT-PMN film, 750 for the surface layer and 50 for the interface layer.

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.

Nucleation and growth of crystallites in amorphous antimony layers on as-deposited ultrathin sublayers of metal: Copper, silver, gold, tin and lead

Abstract Optical microscopy is used for the in situ observation of the nucleation and growth of crystallites in the amorphous antimony layer prepared on an as-deposited ultrathin sublayer of copper, silver, gold, tin or lead. A whole specimen is deposited on a cover glass in a vacuum of 1 × 10−4 Pa. With the use of sublayers of copper, gold and silver it is possible to measure the growth rate v of antimony crystallites as a function of thickness dSb of the antimony layer. An analysis of the relation of v to dSb on the basis of the model previously presented gives such parameters as the thicknesses ds0 and dv0 of surface regions near the substrate and the vacuum respectively and the growth rates us and uv at surfaces adjacent to the substrate and the vacuum respectively: ds0 = 2.0 nm, dv0 = 5.5nm, us = 11 μm s−1 and uv = 0.21 μm s−1 when dCu is 4.3 × 10−2 nm while ds0 = 0.7 nm, dv0 = 4.4 nm, us = 7.7 μm s−1 and uv = 0.13 μm s−1 when dAu is 4.0 × 10−2 nm. The effective activation energy for the growth of crystallites is determined from an Arrhenius plot of v from 30 to 60°C to be, for example, 1.2 eV at dSb = 3.0 nm and 0.7 eV at dSb = 5.2 nm when dCu is 4.3 × 10−2 nm while it is 1.0 eV at dSb = 2.2 nm and 0.9 eV at dSb = 3.7 nm when dAu is 4.0 × 10−2nm. Sublayers of tin and lead play an extremely progressive role on nucleation of antimony crystallites, resulting in such a high nucleation density that v could not be measured. This originates mainly from the larger area of interface between coupled layers of Sb/Sn or Sb/Pb according to electron microscopy.