Shinji Muraishi

Controlled polarity of sputter-deposited aluminum nitride on metals observed by aberration corrected scanning transmission electron microscopy

The polarity determination process of sputter-deposited aluminum nitride (AlN) on metals has been analyzed using aberration corrected atomic resolution scanning transmission electron microscope. Direct growth of c-axis orientated AlN on face centered cubic metals (fcc) (111) with the local epitaxy has been observed, and the polarity was determined at the AlN/metal interface. We found that the AlN polarity can be controlled by the base metal layer: N-polarity AlN grows on Pt(111) while Al-polarity AlN forms on Al(111). Based on these results, the growth mechanism of AlN on metals is discussed.

Strong perpendicular exchange bias in sputter-deposited CoPt/CoO multilayers

Strong perpendicular exchange bias was realized in sputter-deposited CoPt/CoO multilayers. The as-deposited multilayer shows strong perpendicular magnetic anisotropy (PMA) which remains up to a critical CoPt layer thickness as thick as 4 nm. After perpendicular field cooling, the multilayer with antiferromagnetic CoO and ferromagnetic CoPt interfaces exhibits large perpendicular exchange bias of 1730 Oe. Strong PMA in the CoPt/CoO multilayer is mainly attributed to the positive magnetoelastic energy due to the remarkable in-plane tensile stress originating from the local epitaxial growth. The mechanism for the exchange bias was explained in terms of the interfacial spin structure.

Stress-oriented nucleation of ω-phase plates in an Al-Cu-Mg-Ag alloy

Abstract The effect of an external stress applied during formation of ω-phase plates in an Al-Cu-Mg-Ag alloy is examined by two-step ageing: stress ageing followed by stress-free ageing or vice versa. A compressive stress applied at the beginning of ageing is shown to promote the formation of the ω-phase plates lying on the {111} planes perpendicular to the stress axis. The stress effect is found to be dominant only in the early stage of ageing, indicating that it affects nucleation. Quantitative data have been obtained on stress-assisted nucleation by analysing correlation between the number of the ω-phase plates and the stress acting on the {111} habit planes in different grains in a polycrystal. From the stress-orienting effect described above and the transformation strain (eigenstrain) measured by high-resolution electron microscopy, a critical size of the ω plate nucleus is estimated to be about 0.3 nm3, consisting of approximately ten atoms.

Highly (001) oriented L10-CoPt/TiN multilayer films on glass substrates with perpendicular magnetic anisotropy

To obtain strong perpendicular magnetic anisotropy (PMA) based on L10 structure for magnetic storage devices, costly single crystalline substrates are generally required to achieve (001) texture. Recently, various studies also have focused on depositing different kinds of seed layers on glass or other amorphous substrates to promote (001) preferred orientation of L10 CoPt and FePt. TiN is a very promising seed layer material because of its cubic crystalline structure (similar to MgO) and excellent diffusion barring property even at high temperatures. In the present work, highly (001) oriented L10-CoPt/TiN multilayer films have been successfully deposited on glass substrates. After annealing at 700 °C, the film exhibits PMA, and a strong (001) peak is detected from the x-ray diffraction profiles, indicating the ordering transformation of CoPt layers from fcc (A1) to L10 structure. It also is found that alternate deposition of cubic TiN and CoPt effectively improves the crystallinity and (001) preferred ori...

Emergence of (001) preferred orientation in AlN film using ultrathin intermediate Pt layer

Abstract The preferred orientations of AlN films with an intermediate Pt layer have been examined using X-ray diffraction and transmission electron microscopy. It is found that the Pt layer encourages the AlN film into c axis preferred orientation deposition, even though the sputtering conditions would normally lead the AlN film to be deposited with other preferred orientations. The Pt layer also promotes the crystallisation of AlN films. The local epitaxial growth of AlN (001) on Pt (111) may elucidate the effect of the Pt layer on the preferred orientation control.

Strengthening of Al-Cu single crystals by stress-oriented Guinier-Preston zones

Abstract The strengthening of Al-Cu is examined after introducing Guinier-Preston (GP) zones on particular cube planes by stress ageing. A compressive stress applied during an early stage of ageing promotes formation of the platelet precipitates on the cube planes subjected to the largest normal stress. Selection of a stress axis in the compression tests after the stress ageing enables one to change the slip system geometry with respect to these platelet obstacles. It is shown that the GP zones cut by moving dislocations contribute to the strengthening at low temperatures, accompanying strong orientation dependence. The origin of the strengthening is discussed on the basis of the thermal and athermal nature of the dislocation interaction with the stress-oriented planar GP zones.

Control of the perpendicular magnetic anisotropy and microstructure of L10-CoPt/TiN multilayer films with the TiN layer on glass substrates

TiN(5 nm)[CoPt(4 nm)/TiN(x nm)]5 multilayer films (x = 1, 2, 4, 6, 8, 10, 14) have been deposited on glass substrates by dc magnetron sputtering, and a L10-CoPt structure with perpendicular magnetic anisotropy (PMA) has been obtained after annealing at 700 and 800 °C. It is found that changing the TiN layer thickness and annealing temperature significantly affects the ordering degree and magnetic anisotropy energy of L10-CoPt/TiN multilayer films. To obtain the maximum value of the ordering degree and magnetic anisotropy energy, the optimum thickness of the TiN layer is around 4 and 8 nm, with an annealing temperature of 700 and 800 °C, respectively. Structural characterization results have shown that the thickness of the TiN layer greatly affects the interface structure between CoPt and TiN layers. When TiN layer thickness is below 2 nm, it tends to be discontinuous after annealing, which results in the coalescence of the adjacent CoPt layers. When TiN layer thickness is above 8 nm, the interface roughness becomes larger. In such cases, the preferred orientation, ordering degree of the L10 structure and the PMA of the films will be impaired.

Mechanoluminescence of ZnS:Mn phosphors and its correlation to impact energy and contact geometry.

The influence of the impulsive mechanical energy and the contact geometrical parameters on stress-induced light emission of ZnS-based phosphors dispersed in polymeric matrix is investigated using modified impact test equipment. At a low to moderate energy region, luminescent pulses consist of two distinguishable peaks that can be assigned to a loading and unloading sequence, respectively. Transient characteristics are found to be independent of the external excitation. An increment of peak emission intensity with higher impact energy and smaller tip diameter indicates a significant relationship of mechanoluminescence to the geometry of contact. Intense emission deviating from the linearity and an absence of the secondary peak are suggested to be the consequence of fractoluminescence.

Perpendicular coercivity enhancement of CoPt/TiN films by nitrogen incorporation during deposition

The effect of N incorporation on the structure and magnetic properties of CoPt thin films deposited on glass substrates with TiN seed layers has been investigated. During the deposition of CoPt, introducing 20% N2 into Ar atmosphere promotes the (001) texture and enhances the perpendicular coercivity of CoPt film compared with the film deposited in pure Ar and post-annealed under the same conditions. From the in situ x-ray diffraction results, it is confirmed that N incorporation expands the lattice parameter of CoPt, which favors the epitaxial growth of CoPt on TiN. During the post-annealing process, N releases from CoPt film and promotes the L10 ordering transformation of CoPt.

Rhombohedral distortion analysis of ultra-thin Pt(111) films deposited under Ar–N2 atmosphere

A rhombohedral analysis method for analysing the lattice distortion in a (111)-textured face-centred cubic film under rotationally symmetric stress is proposed. Because no material constants, such as diffraction elastic constants, are required, the expressions of the distortion, namely the angle and the lattice parameter, are universal and can be readily used to compare different films. Using this rhombohedral distortion analysis method, (111)-textured Pt films deposited under argon–nitrogen atmosphere are systematically investigated, and the thickness-dependent lattice deformation in as-deposited and annealed films is described by the two geometrical parameters of the rhombohedral cell.