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SUMMARY This paper focuses on mobile robots that can accompany a person, that is, it addresses how to control the position of the robot relative to the accompanied person according to the dynamic environment. The robot is expected to move side by side with the person in a normal situation, but a position in front or behind the person might be better if there are obstacles. The shape of the artificial potential field of the accompanied person is devised to smoothly control the robot position in a unified way. The Laplace potential method is also used subsidiarily to cope with extremely cluttered environments. Simulations and experiments in real space show the usefulness of the proposed method.

Free-exciton emissions increase non-linearly by cathodoluminescence (CL) above the threshold probe current of 30 μA in high-pressure high-temperature synthetic type-IIa diamond. A droplet of electron-hole liquid (EHL) is also observed by CL for the first time. Furthermore, boron acceptor bound-exciton emission as well as free-exciton emission also increases super-linearly in an unintentionally boron-contaminated area. The threshold probe current of non-linear increase of excitonic emission is in accordance with the emergence of the EHL peak. It is considered that the non-linear increase of excitonic emissions is due to the increase in the radiative recombination rate of free excitons under high exciton density.

Diamond dual in-plane-gated field effect transistors with very low gate leakage current have been fabricated on an undoped hydrogen-terminated diamond p-type surface using oxygen plasma etching. Adjusting the threshold voltage optimally by one side gate, lateral electric field from the other side gate modulates the channel conductance. The oxygen plasma etching of 60 nm in depth fully isolated the channel of the hydrogen-terminated diamond surface conductive layer from the side gates resulting very low gate leakage current (

Dominant n-type conductivity in sulfur-doped chemical-vapor-deposited diamond is observed by Hall-effect measurement. The activation energy is estimated at 0.5–0.75 eV above 600 K. Below 600 K, the carrier concentration deviates from the activation energy, and Hall mobility decreases in comparison with that above 600 K. It is considered that hopping conduction takes place. By cathodoluminescence measurement, free-exciton recombination radiation is observed in spite of a very high sulfur doping level of 2.5% during deposition, where boron is not detected by secondary ion mass spectroscopy. Therefore, the n-type conductivity of sulfur-doped diamond is caused by a sulfur-related mechanism.

A homoepitaxial diamond film with a thickness of approximately 1 μm was grown on the (111) surface of a type Ib diamond substrate with dopant concentration (PH 3 /CH 4 ) of 500 ppm. Bound exciton recombination radiation due to the neutral donors has been observed in the peaks at 5.18 and 5.32 eV. The dominant peak at 5.18 eV is associated with one TO phonon. The peak at 5.32 eV is the radiation without phonon emission due to the localization of donors. This appearance of non-phonon emission is one of the important evidences to prove the two peaks at 5.18 and 5.32 eV to be the recombination radiation of bound exciton due to the donor. The binding energy of the free exciton to the donors, which is deduced from the energy difference between free and bound exciton, is 90 meV.

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A 300 µm thick silicon wafer with oxide of 200 A in thickness which prevents void formation is sticked with a sapphire wafer at room temperature. To avoid the crack generation of a silicon wafer, a sticked wafer is heated up to 270C for 2 h and then a silicon layer is removed by grinding from 525 µm to 10 µm. To remove grinding damage and to further thin the silicon layer to 3 µm, KOH etching at 80C is used. Finally, to obtain the silicon layer having the thickness range of 0∼3 µm, polishing is employed. Although the high density of dislocations is observed in the 2.2 µm thick specimen annealed at 900C for 2 h, however, when the specimen is thinned down to 0.2 µm, silicon layer becomes dislocation-free, as confirmed by double crystal X-ray topography and transmission electron microscope (TEM). The thin oxide between silicon and sapphire plays an important role in the prevention of diffusion of boron as a contaminant at the bonded interface.