A different regime of nanostructured diamond film growth

A different regime of diamond growth was found out in microwave plasma chemical vapor deposition by applying a different combination of growth conditions (pressure, microwave power, bias voltage, and bias current). This different regime of growth was identified by high-resolution transmission electron microscopy. In this regime, at lower bias current density (BCD), nanocrystals of diamond were confined in a form of nano-diamond rods 10-30 nm in diameter and several hundred nanometers long. More interestingly, at relatively high BCD, the film consists of a high packing density of even smaller size (2-5 nm) of diamond that generates enormous stress in thin film. Our finding of this different regime of growth offers the promise of exploring new properties of carbon materials.     

Simple photomultiplier tube internal-gating method for use in subnanosecond time-resolved spectroscopy

We propose a simple photomultiplier tube (PMT) internal-gating method for use in the field of subnanosecond time-resolved spectroscopy. In the proposed method, we control two dynodes in the PMT by applying a gate signal whose pulse width is Tg. When controlling the mth and the n(> m)th dynodes, a resolution time delta t is approximately given by delta t = Tg-(n-m) tau, where tau is a transit time of a lump of secondary electrons traveling between the two dynodes in the PMT. In principle, the resolution time delta t shorter than the pulse width Tg of the gate signal can be easily obtained. From a fundamental performance test, we found that a subnanosecond resolution time delta t = 0.31 ns was obtained for the case of m = 2 and n = 5. To demonstrate the effectiveness of the proposed method, we carried out a time-resolved spectroscopic measurement of emission obtained from a white-light-emitting diode (LED) driven by a nanosecond current pulse.     

Mixed Electronic-Ionic Conduction in Ru-Doped SrTiO3 at High Temperature

The electronic and ionic conduction behavior of Ru-doped SrTiO₃ at high temperature was investigated. The conductivity increased significantly with increasing Ru content. SrTi_0.80Ru_0.20O_3– exhibits fairly high conductivities, e.g., 3 S cm^–1 at 1000°C, and 2 S cm^–1 at 600°C. The conductivity had only a slight dependence on the partial pressure of oxygen over a wide range and was largely attributed to n-type electronic conduction. Ru-doped SrTiO₃ showed mixed oxide-ionic and electronic conduction under reducing atmospheres. The mechanism of the electronic and ionic conduction is discussed.     

Direct imaging of Guinier-Preston zones by high-angle annular detector dark-field scanning transmission electron microscopy

We report atomic resolution imaging of Cu-planar precipitates in aged Al-Cu alloys, known as Guinier-Preston (GP) zones, by high-angle annular detector dark-field scanning transmission electron microscopy. Single layered GP-I zones as small as 2 nm in length were resolved among densely populated GP-I zones, whereas double layered GP zones were clearly identified. The images of GP-II zones showed not only the commonly accepted structure, in which single Cu layers are separated by three Al layers, but also a variant, in which double Cu layers are separated by a single Al layer.     

Intrinsic stage i crack growth of directionally solidified Ni-Base superalloys during low-cycle fatigue at elevated temperature

Strain-controlled low-cycle fatigue tests of cylindrical smooth specimens of two kinds of directionally solidified Ni-base superalloys, RENé 80+Hf and CM 247LC, were carried out at a temperature of 873 K, and the successive process from the crack initiation to small crack propagation was investigated by employing a replication technique. Both materials exhibited typical features of stage I fatigue fracture; that is, the fracture occurred on the crystallographic 111 planes, the most important slip planes in face-centered cubic (fcc) materials. It was found that the rate of stage I crack growth, when not influenced by a nearby grain boundary, proportionally increased with the crack length. However, as the crack tip neared a grain boundary, the rate rapidly decreased. It was also shown that the crack growth rate fell when the crack deflection occurred due to secondary slip. Comparison was also made between the stage I crack growth rate and the long crack growth rate in polycrystalline Ni-base superalloys.     

Preparation and properties of LiTaO3-based solid solutions with cation vacancies

It has been found that nonstoichiometric solid solutions $\text{(}\text{Li}{}_{\mathrm{<mtext>1?</mtext><mtext>x</mtext>}}\text{M}{}^{\mathrm{2+}}{}_{\mathrm{<mtext>x</mtext><mtext>2</mtext>}}\text{□}{}_{\mathrm{<mtext>x</mtext><mtext>2</mtext>}}\text{)}\text{TaO}\text{3}$ with M=Zn, Ni, Mg and Ca exist over wide ranges. In the case of the Zn-system, especially, a LiTaO₃ structure was still stable even at x=0.5, where 25% of the Li sites are vacant. A new series of solid solutions shows ferroelectric properties. The Curie temperature is closely related with the axial ratio c/a of the hexagonal cell.