Junzo Ishikawa

Germanium nanoparticles in a thin SiO₂ film on Si have been formed by negative ion implantation for the development of very low power consumption electron devices using nanoparticles. Their electrical properties of 25‐nm‐SiO₂/Si films including Ge nanoparticles were investigated with CV method after subsequent annealing at various temperatures. Ge atoms were implanted at 10 keV with fluencies of 1×10¹⁵ and 5×10¹⁵ ions/cm². Samples were annealed at 300, 500, 700 and 900°C for 1 h. Depth profiles of implanted Ge atoms in the SiO₂ films were measured by using a high‐resolution RBS technique. The formed Ge nanoparticles were studied by cross‐sectional TEM observation. After annealing at less than 700°C, Ge nanoparticles were confirmed in the film. After 300°C‐annealing, a CV curve had so small hysteresis that could not be applied to memory devices. After 500°C‐annealing, both samples with 1×10¹⁵ ions/cm² and with 5×10¹⁵ ions/cm² had obvious hysteresis curves. Calculations of charge and nanoparticle intensity from flat band shift and implanted Ge dose lead about one electron in one nanoparticle with 3nm diameter. These results suggest that thin SiO₂ films including Ge nanoparticles formed with negative ion implantation can applied with memory devices.

Electric characteristics of 25-nm-SiO₂/Si films embedded with Ge nanoparticles were investigated by CV method. Ge nanoparticles were formed by negative ion implantation and subsequent thermal annealing. Ge atoms in the SiO₂ were evaluated by high-resolution RBS and cross-sectional TEM. Ge atoms were implanted at 10 keV with 1×10¹⁵ and 5×10¹⁵ ions/cm². The samples were annealed at 300, 500, 700 and 900°C for 1 h. After annealing at 900°C, Ge atoms diffused down to SiO₂/Si interface, so the sample could not be evaluated by CV method. After annealing at 300°C, the voltage shift in the hysteresis of a CV curve was very small, so it could not be applied to the memory devices. While after annealing at 500°C, the voltage shifts of both samples implanted with doses of 1×10¹⁵ and 5×10¹⁵ ions/cm² were wide. Calculations of charge and nanoparticle intensity from flat band shift and from implanted Ge dose show that each nanoparticle with about 3-nm diameter has only one electron. These results suggest that thin SiO₂ films embedded with Ge nanoparticles formed with negative ion implantation can be applied to the memory devices.

We propose the application of silicon field emitter array (Si-FEA) to resolve the problem of wafer charging in the ion implantation process. This article reports experiments conducted to review the basic property of Si-FEA. This time, we measured the energy distribution of electrons emitted from three types of Si-FEA with different number of tips and gate apertures. The result is different from that of platinum field emitter array (Pt-FEA) in some points. First, half bandwidth of Si-FEA distribution is a little smaller than that of Pt-FEA. Second, the energy peak of Si-FEA shifts to lower energy side from Fermi level. Such phenomenon doesn't happen in the energy distribution of Pt-FEA.

We measured the field electron emission properties of carbon nanotubes (CNTs) with and without laser irradiation. As a result, the threshold voltage was found to decrease by laser irradiation. However, the improvement for current stability was not observed so much. Analyzing the emission characteristics with using Seppen-Katamuki (S-K) plot, it was found that the structural change of CNTs caused the decrease of the turn-on voltage. And we roughly estimated the shape of the CNTs emitter with S-K plot.

Negative‐ion implantation could be used to create nanoparticles in oxide insulators with finely controlled accuracy for both depth and size. For 50‐nm‐thick SiO₂ film on Si, Ag nanoparticles with 3 nm in diameter were created in the center of the film with distribution thickness of 17 nm. Cu negative‐ion implanted silica glass and soda‐lime glass showed a high nonlinear susceptance of the 3^rd order in nonlinear optical property. Cu and Ag double‐implanted silica glass showed an absorption peak between two absorption peaks of surface plasmon resonance (SPR) for Cu and Ag nanoparticles. The optical absorption peak due to SPR of nanoparticle in oxide could be changed by forming nanoparticles with different kinds of elements and alloy. For application of metal nanoparticle to photocatalyst, Ag negative ions were implanted into rutile TiO₂. The Ag‐implanted rutile samples showed improved photocatalytic efficiency after proper annealing in a decolorization test of methylene blue solution under fluorescent light. The better one was the Ag‐implanted rutile TiO₂ (Ag: 65 keV, 5×10¹⁶ ions/cm², 500°C annealed), which showed a photocatalytic efficiency higher by 2.2 times than that of unimplanted rutile TiO₂. In the evaluation under fluorescent light through UV‐cut filter for 19 h, the Ag‐implanted rutile showed 6.7 times higher efficiency.