3DAP analysis of (Ga,Mn)As diluted magnetic semiconductor thin film.

The distribution of Mn in a Ga(0.963)Mn(0.037)As ferromagnetic semiconductor film has been characterized by the three-dimensional atom probe (3DAP) technique. Atom probe specimens were directly prepared from the (Ga,Mn)As film grown epitaxially on a p-type GaAs substrate by the lift-out technique using a scanning electron microscope/focused ion beam system. The atom probe elemental map revealed that the Mn atoms in the Ga(0.963)Mn(0.037)As are uniformly dissolved without forming any nanometer-sized clusters.

Laser assisted atom probe analysis of thin film on insulating substrate.

We demonstrate that the atom probe analyses of metallic thin films on insulating substrates are possible using laser assisted field evaporation. The tips with metallic thin film and insulating substrate (0.6-3 µm in thickness) were prepared by the lift-out and annular ion beam milling techniques on tungsten supports. In spite of the existence of thick insulating layer between the metallic film and the tungsten support, atom probe tomography with practical mass resolution, signal-to-noise ratio and spatial resolution was found to be possible using laser assisted field evaporation.

Quantitative atom probe analyses of rare-earth-doped ceria by femtosecond pulsed laser.

We have investigated the irradiation conditions of femtosecond laser pulses for quantitative atom probe analyses of rare-earth (RE) doped ceria. The influence of laser wavelength, power, pulse frequency, as well as specimen temperature on mass resolution and background noise of atom probe mass spectra were investigated. Furthermore, quantitative atom probe analysis of yttrium distribution in Y-doped ceria was carried out with the optimized evaporation conditions. The distribution of yttrium was found to be uniform within the grains, but they were confirmed to be segregated at grain boundaries.

Broadening the applications of the atom probe technique by ultraviolet femtosecond laser.

Laser assisted field evaporation using ultraviolet (UV) wavelength gives rise to better mass resolution and signal-to-noise ratio in atom probe mass spectra of metals, semiconductors and insulators compared to infrared and green lasers. Combined with the site specific specimen preparation techniques using the lift-out and annular Ga ion milling in a focused ion beam machine, a wide variety of materials including insulating oxides can be quantitatively analyzed by the three-dimensional atom probe using UV laser assisted field evaporation. After discussing laser irradiation conditions for optimized atom probe analyses, recent atom probe tomography results on oxides, semiconductor devices and grain boundaries of sintered magnets are presented.

Demonstration of half-metallicity in fermi-level-tuned Heusler alloy Co2FeAl0.5Si0.5 at room temperature.

Fermi level tuning has been successfully demonstrated in Co-based full-Heusler alloy Co(2)FeAl(0.5)Si(0.5) (CFAS). The half-metallic band gap of CFAS was proved by the behavior of differential conductance of CFAS/(MgAl(2))O(x)/CoFe magnetic tunneling junctions with an unexplored crystalline (MgAl(2))O(x) barrier. CFAS exhibits the highest effective spin polarization (P_{eff}) at 300 K and the weakest temperature dependence of P_{eff} among all known half metals. Further study shows that P_{eff} of CFAS decays with increasing temperature (T) following T;{3/2} law perfectly, which indicates that the depolarization of CFAS is determined by spin wave excitation only.