The bulk dense nanocrystalline BaTiO 3 (BT) ceramics ranging from 20 to 100 nm have been successfully prepared by the spark plasma sintering (SPS) method. Raman spectra and X-ray diffraction were used in combination with electron microscopy to study the evolution of lattice structure and phase transformation behavior with grain growth from nanoscale to micrometer scale for BT ceramics. The results reveal that the SPS technique provides exceptional opportunity to compact ceramics to full density with nanograin size. It is also demonstrated that all structural modifications in nanocrystalline BT and low-symmetry structures still exist in 20 nm nanograin BT ceramics. The ferroelectric properties of crystalline structures were investigated by scanning force microscopy in piezoresponse mode. Piezoelectric hysteresis loop was recorded, demonstrating that 20 nm BT ceramics has a remanent polarization and is switchable by an electric field. Thus, if a critical grain size exists for ferroelectricity, it is less than 20 nm for polycrystalline BT ceramics.

Electron spin resonance observations of oxygen deficient silicon atoms in the interfacial layer of hafnium oxide based metal-oxide-silicon structures

We report electron spin resonance ͑ESR͒ observation of interface defects at the HfO 2 /(111)Si boundary for HfO 2 films deposited via atomic layer chemical vapor deposition using Hf(NO 3) 4 as a precursor. We observe several signals, dominated by one due to a silicon dangling bond at the Si/dielectric interface. This center is somewhat similar to, but not identical to, Si/SiO 2 interface silicon dangling bonds. Comparison between ESR and capacitance versus voltage measurements suggests that these dangling bond centers play an important role in HfO 2 /Si interface traps.

We have explored the radiation response of the HfO 2 /Si system with a combination of capacitance versus voltage and electron spin resonance measurements on capacitor and bare oxide structures subjected to 60 Co gamma irradiation and vacuum ultraviolet irradiation. Our studies have utilized both (100)Si and (111)Si substrate structures. Capacitors have been irradiated under both positive and negative gate bias as well as with the gate floating. We find the "electronic" radiation response of the HfO 2 /Si system to be different from that of the Si/SiO 2 system. However, we find that the HfO 2 /Si interface defects and their response to hydrogen are quite similar to those of the Si/SiO 2 interface defects. We also find that the HfO 2 /Si atomic scale defects and their response to irradiation different from that of the Si/SiO 2 system. We find the radiation response of the HfO 2 /Si capacitors to be dominated by a very large buildup of negative oxide charge. We observe comparably little, if any, generation of Si/dielectric interface trap density, though we do observe substantial densities of Si/dielectric interface trap defects. The concentration of these defects is not measurably altered by irradiation. The structure of the most prominently observed HfO 2 /Si interface defects is somewhat similar to those observed in Si/SiO 2 systems. We observe comparatively little, if any, generation of slow traps/border traps/switching traps near the Si/HfO 2 interface.

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