High-Temperature Phase Transition of Y4Al2O9

Reversible thermal phase transition was observed for Y₄Al₂O₉ at 1377°C with a hysteresis width of 78°C using differential scanning calorimetry. The enthalpy of the transition (Δ H ) was about 300 cal/mol. Powder X-ray diffraction peaks of the high-temperature phase, as well as the peaks of the low-temperature phase, were characterized with a monoclinic unit cell. Thermal hysteresis was also confirmed by the temperature dependence of the lattice parameter. The unit cell volume of the high-temperature phase was 0.5% smaller than that of the low-temperature phase at 1400°C.     

Ballistic electron emission from quantum-sized nanosilicon diode and its applications

A quantum confinement effect renders silicon a functional wide-gap material with useful functions. For instance, a diode based on nanocrystalline silicon (nc-Si) exhibits characteristic quasi-ballistic emission effects in various media. As means for physical excitation and probing, the applicability to parallel electron beam lithography and high-sensitivity image-pickup has been demonstrated in vacuum. The energetic electron incidence into air and Xe ambient induces negative ion generation by electron attachment into oxygen molecules and vacuum ultraviolet light emission by internal excitation of Xe molecules, respectively. Another effect is that the nc-Si ballistic emitter can supply highly reducing electrons into aqueous and metal-salt solutions without the use of counter electrodes. This is an attractive process that will be applicable to hydrogen generation and thin metal film deposition.     

Temperature distribution in nano-devices under a strong magnetic field

The thermoelectric and thermomagnetic phenomena of two-dimensional electron gases at low temperatures are numerically examined using the finite-difference method. The temperature and the voltage are calculated from transport equations describing thermoelectric and thermomagnetic effects. The results demonstrate that a magnetic field distorts equipotential lines and generates an uneven distribution of the temperature, which can cause inhomogeneous heating of experimental systems. In particular, a part of the system is found to be colder than the temperature of the heat baths.     

Charge transporting block copolymer for morphological control in light emitting device based on polymer blends

Bipolar charge transporting block copolymer composing of carbazole and oxadiazole monomers as hole and electron transporting units, respectively, was synthesized by nitroxide mediated radical polymerization. It is found that the current efficiency significantly increased with the addition of the block copolymer in the device based on polymer blend system. AFM measurement revealed that a phase-separated structure in the polymer blend layer changed to suitable morphology in the presence of block copolymer.     

Intercalation on Transition Metal Trichalcogenides via a Quasi-Amorphous Phase with 1D Order

Intercalation into 1D transition metal trichalcogenides (TMTs) in which fibers are bonded by a weak van der Waals force can be expected to create various intercalation compounds and develop unique physical properties according to the combination of the host materials and guest ions. However, structural changes via intercalation into 1D TMTs are not as simple as those in 2D transition metal dichalcogenides (TMDs) and are still not understood comprehensively. ZrTe₃: a typical compound with a 1D trigonal prismatic structure, belongs to TMTs. Herein, through the Ag introduction to ZrTe₃ via solid-state intercalation, a novel crystal phase with a 1D octahedral structure and a quasi-amorphous (QA) phase during the structural transition are discovered; the QA phase is a novel state of matter in which long-range order is lost while retaining 1D order. Based on the Ag concentration, the transport properties are flexibly modulated from superconductivity to semiconductivity. Density functional theory calculations indicate the attraction between Ag ions and the pair diffusion due to their attraction. Furthermore, judging the attraction or repulsion between guest ions predicts whether to induce a QA phase or simple lattice expansion like the intercalation into 2D TMDs.     

Three-dimensional motor neuron morphology estimation in the Drosophila ventral nerve cord

Type-specific dendritic arborization patterns dictate synaptic connectivity and are fundamental determinants of neuronal function. We exploit the morphological stereotypy and relative simplicity of the Drosophila nervous system to model the diverse neuronal morphologies of individual motor neurons (MNs) and understand underlying principles of synaptic connectivity in a motor circuit. Our computational approach aims at the reconstruction of the neuron morphology, namely the robust segmentation of the neuron volumes from their surroundings with the simultaneous partitioning into their compartments, namely the soma, axon, and dendrites. We use the idea of cosegmentation, where every image along the z -axis (depth) is segmented using information from "neighboring" depths. We use 3-D Haar-like features to model appearance. Because soma and axon are determined by their distinctive shapes, we define an implicit shape representation of the 2-D segmentation sets to drive cosegmentation and achieve the desired partitioning. We validate our method using image stacks depicting single neurons labeled with green fluorescent protein (GFP) and serially imaged with laser scanning confocal microscopy.     

A new device for high-pressure freezing of cultured cell monolayer using 10-microm-thin stainless discs as both culture plate and specimen carrier

High-pressure freezing (HPF) has been generally accepted as the most reliable method for cryofixation of biological samples, yielding a deep vitreous freezing. In recent cell biology, mammalian cultured cells are widely used, but HPF of cultured cell monolayer has not reached its full potential. In this study, we developed a new reliable device for HPF of cultured cell monolayer by using a 10-microm-thin stainless disc both as culture plate and specimen carrier. We describe the practical procedure, and demonstrate fine structures of HeLa cells cultured and cryofixed on the stainless discs as results.     

Carrier separation analysis for clarifying carrier conduction and degradation mechanisms in high-k stack gate dielectrics

The carrier conduction and the degradation mechanism in n⁺gate p-channel metal-insulator-semiconductor field-effect-transistors with HfAlO_X (Hf: 60 at.%, Al: 40 at.%)/SiO₂ dielectric layers have been investigated using carrier separation method. Since gate current depends on substrate bias and both electron and hole currents are independent of temperature over the range of 25–150 °C, the conduction mechanism for both currents is controlled by a tunneling process. As the interfacial SiO₂ layer (IL) thickness increases in a fixed high-k layer thickness (T_high-k), a dominant carrier in the leakage current changes from hole to electron around 2.2-nm-thick IL. This is due to an asymmetric barrier height for electrons and holes at the SiO₂/Si interface. On the contrary, in the case of a fixed IL thickness of 1.3 nm, the hole current is dominant in the leakage current, regardless of T_high-k. It is shown that the dominant carrier in the leakage current depends on the structure of the high-k stack. Both electron and hole currents for the stress-induced-leakage-current (SILC) state increase slightly relative to the initial currents, which means that the trap generation in the high-k stack occurs near both the conduction band edge of n⁺poly-Si gate and the valence band edge of Si substrate. The electron current at soft breakdown (SBD) state dramatically increases over that for the SILC state, while the hole currents for both the SILC state and SBD are almost the same. This indicates that the defect sites generated in the high-k stack after SBD are located at energies near the conduction band edge of n⁺poly-Si gate. Both the defect generation rate and the defect size in the HfAlO_X/SiO₂ stacks are large compared with those in SiO₂. It is inferred that, in high-k dielectric stack, the defect generation mainly occurs in the high-k side rather than the IL side, and the defect size larger than the case of SiO₂ could be related to a larger dielectric constant of the high-k layer.     

Improvement in HgCdTe diode characteristics by low temperature post-implantation annealing

Hg_1−xCd_xTe diodes (x∼0.22) with different carrier concentrations in p type materials have been fabricated by employing an ion-implantation technique. The performances of the diodes, prior to and after low temperature postimplantation annealing, have been investigated in detail by model fitting, taking into account dark current mechanisms. Prior to the annealing process, dark currents for diodes with relatively low carrier concentrations are found to be limited by generation-recombination current and trap-assisted tunneling current, while dark currents for diodes with higher carrier concentrations are limited by band-to-band tunneling current. These dark currents in both diodes have been dramatically decreased by the low temperature annealing at 120∼150°C. From the model fitting analyses, it turned out that trap density and the density of the surface recombination center in the vicinity of the pn junction were reduced by one order of magnitude for a diode with lower carrier concentration and that the carrier concentration profile in a pn junction changed for a diode with higher carrier concentration. The improvements are explained by changes in both carrier concentration profile and pn junction position determined by interaction of interstitial Hg with Hg vacancy in the vicinity of the junction during the annealing process.