In the C 4 plant maize (Zea mays L.), two ferredoxin isoproteins, Fd I and Fd II, are expressed speci®cally in mesophyll and bundle-sheath cells, respectively. cDNAs for these ferredoxins were introduced separately into the cyanobacterium Plectonema boryanum with a disrupted endogenous ferredoxin gene, yielding TM202 and KM2-9 strains expressing Fd I and Fd II. The growth of TM202 was retarded under high light (130 mmol/m 2 /s), whereas KM2-9 grew at a normal rate but exhibited a nitrogen-de®cient phenotype. Measurement of photosynthetic O 2 evolution revealed that the reducing power was not ef®ciently partitioned into nitrogen assimilation in KM2-9. After starvation of the cells in darkness, the P700 oxidation level under far-red illumination increased signi®cantly in TM202. However, it remained low in KM2-9, indicating an active cyclic electron¯ow. In accordance with this, the cellular ratio of ATP/ADP increased and that of NADPH/NADP + decreased in KM2-9 as compared with TM202. These results demonstrated that the two cell type-speci®c ferredoxins differentially modulate electron¯ow around photosystem I.

The impact of excimer ultraviolet (UV) light irradiation on SiO2/SiC(0001) and (1120) interfaces was examined to get insight into the effect of NO nitridation. While NO nitridation appears to be effective in passivating the electron traps at the SiO2/SiC interfaces, we found that the nitridation induces additional traps that are not active until UV light is irradiated. The traps include those causing hysteresis and frequency dispersion in the C–V characteristics and those affecting the long-term reliability of MOS devices. A non-nitrided SiO2/SiC interface was less sensitive to the UV light, indicating the instability of the nitrided SiC MOS structure.

Although nitridation passivates defects at the SiO2/SiC interface, avoiding the introduction of nitrogen atoms into SiO2 is crucial for reliability. This paper presents a method to selectively introduce nitrogen at the SiC-side of the interface. The method comprises the following steps: (i) plasma nitridation of the SiC surface, (ii) sputter deposition of SiO2, and (iii) annealing in a CO2 ambient. Significantly low D it values of about 1 × 1011 cm−2eV−1 were obtained near the conduction band edge of SiC. Furthermore, the resulting interface properties were hardly degraded by excimer ultraviolet light irradiation, indicating better stability compared with a NO-nitrided sample.