Chiaya Yamamoto

Spontaneous formation of aluminum germanate on Ge(100) by atomic layer deposition with trimethylaluminum and microwave-generated atomic oxygen

The application of microwave-generated atomic oxygen as an oxidant is found to change the manner of atomic layer deposition (ALD) of an Al2O3 layer on a Ge substrate, leading to the spontaneous formation of aluminum germanate with a deposition rate higher than that of conventional ALD with water oxidant. Electrical characterization of the Al/aluminum germanate (11 nm)/p-Ge(100) structure indicates that both the bulk and the interface properties of the aluminum germanate are promising with small capacitance-voltage hysteresis of less than 20 mV and interface trap densities ranging from 2×1011 to 6×1011 cm−2 eV−1 in the upper half of the Ge band gap.

Role of low-energy ion irradiation in the formation of an aluminum germanate layer on a germanium substrate by radical-enhanced atomic layer deposition

Radical-enhanced atomic layer deposition uses oxygen radicals generated by a remote microwave-induced plasma as an oxidant to change the surface reactions of the alternately supplied trimethylaluminum precursor and oxygen radicals on a Ge substrate, which leads to the spontaneous formation of an aluminum germanate layer. In this paper, the effects that low-energy ions, supplied from a remote microwave plasma to the substrate along with the oxygen radicals, have on the surface reactions were studied. From a comparative study of aluminum oxide deposition under controlled ion flux irradiation on the deposition surface, it was found that the ions enhance the formation of the aluminum germanate layer. The plasma potential measured at the substrate position by the Langmuir probe method was 5.4 V. Assuming that the kinetic energy of ions arriving at the substrate surface is comparable to that gained by this plasma potential, such ions have sufficient energy to induce exchange reactions of surface-adsorbed Al ato...

Phase-Separation of B2 Precipitates in an Fe-Ni-Al Alloy

When Fe-10.3mol%Ni-14.3mol%Al alloy is heated at 1173 K for 8.64104 s, a number of B2 precipitates are dispersed in the A2 matrix. When the two-phase microstructure of A2+B2 is aged at 973 K, the phase-separation of B2 precipitate particles takes place to form a new A2 phase in each B2 particle. In the course of further ageing at 973 K, the new A2 phase grows but decreases in number, and finally only one A2 particle is left in the individual B2 particles. The appearance of new A2 phase in each B2 precipitate is due to the difference in the volume fraction of A2 phase that should exist in A2+B2 two-phase system depending on the heating temperature: i.e., the phase-separation of B2 precipitates starts with the aid of chemical free energy.

Microstructure Change of B2 Precipitates in an Fe-Al-Ni Alloy due to Two-Step Heat-Treatment

We have been studying the microstructure change of B2 cubic precipitates into an A2+B2 complex structure in Fe-Al-Ni alloy. In this study, we carried out detailed observation using focused ion beam (FIB) and scanning transmission electron microscopy (STEM). First, Fe-14.3at%Al-10.3at%Ni solid solution was prepared. Secondly, the specimens were heated at 1173 K, at which they formed B2 cubic precipitates (ordered bcc) dispersed in an A2 matrix (disordered bcc). After that, the B2/A2 two-phase specimen was annealed at 973 K. Then we fabricated STEM specimens using FIB, followed by high-resolution secondary electron imaging. We repeated this slice-and-observation procedure to determine the detailed microstructure of this heat-treated alloy. At the early stage of the 973 K annealing, the A2 phase appeared in the original B2 precipitates and showed a spongelike structure, whereas small nanometer-order B2 particles appeared in the A2 matrix. The A2/B2 interface at this stage showed no anisotropic morphology. Therefore, the main driving force of this process may not be strain energy, but chemical and interface energies. Further annealing at 973 K decreased the number of small B2 particles in the A2 matrix, and these particles dissolved into the matrix eventually. The annealing also changed the A2/B2 spongelike structure, which was observed in the original B2 precipitates, into simple structures such as the A2 core and B2 crust. Then the B2 phase showed ordinal coarsening behavior. When B2 precipitates, which had hollow cubic morphology, were observed to be very close to each other, the face-centered area of the B2 crust tended to dissolve and only large B2 precipitates remained.