Oxygen doped Ge crystals Czochralski-grown from the B2O3-fully-covered melt

Local vibrations of oxygen in Ge crystals grown from a melt fully covered by B₂O₃ were evaluated by Fourier-transform infrared spectroscopy. Ge single crystals containing oxygen were grown by the Czochralski method under various growth conditions. Oxygen concentrations in the crystals were determined to be in the range between 8.5 × 10¹⁵ and 5.5 × 10¹⁷ cm⁻³ from the infrared absorption at 855 cm⁻¹ originating in local vibration of Ge-O_i-Ge quasi-molecules. Absorption peaks relating to GeO_x, SiO_x and Si-O_i-Si were not detected in the as-grown crystals. The calibration coefficient for determining oxygen concentration in Ge crystals from the absorption peak intensity at 1264 cm⁻¹ was estimated to be 1.15 × 10¹⁹ cm⁻².     

Modelling and prediction of phyto- and zooplankton dynamics in Lake Kasumigaura by artificial neural networks

An artificial neural network model was developed for Lake Kasumigaura to predict timing and magnitudes for chlorophyll a, five species of blue-green algae and three zooplankton groups. The model was trained by 8 years of limnological time series and validated by two independent years. The validation showed the potential of neural networks as predictive tools for highly non-linear phenomena such as blue-green algal blooms in freshwater lakes.     

Hydroxyl group formation caused by hydrogen diffusion into optical glass fibre

Transmission loss increase of optical glass fibre caused by hydrogen diffusion is measured as a function of temperature and partial pressure of hydrogen gas. The activation energy of hydroxyl group formation from the diffused molecular hydrogen was found to be 15.9 kcal/mole. Also the hydroxyl absorption loss increase at 200°C was found to be proportional to the square root of the partial pressure of hydrogen gas.     

Energy‐Dissipative Matrices Enable Synergistic Toughening in Fiber Reinforced Soft Composites

Tough hydrogels have shown strong potential as structural biomaterials. These hydrogels alone, however, possess limited mechanical properties (such as low modulus) when compared to some load‐bearing tissues, e.g., ligaments and tendons. Developing both strong and tough soft materials is still a challenge. To overcome this obstacle, a new material design strategy has been recently introduced by combining tough hydrogels with woven fiber fabric to create fiber reinforced soft composites (FRSCs). The new FRSCs exhibit extremely high toughness and tensile properties, far superior to those of the neat components, indicating a synergistic effect. Here, focus is on understanding the role of energy dissipation of the soft matrix in the synergistic toughening of FRSCs. By selecting a range of soft matrix materials, from tough hydrogels to weak hydrogels and even a commercially available elastomer, the toughness of the matrix is determined to play a critical role in achieving extremely tough FRSCs. This work provides a good guide toward the universal design of soft composites with extraordinary fracture resistance capacity.     

Effect of GaAs surface pretreatment on electrical properties of MBE-ZnSe/GaAs substrate interfaces

Interface properties of MBE-grown ZnSe/GaAs substrate systems formed on variously pretreated GaAs surfaces, which include standard chemically etched (5H₂SO₄:1H₂O₂: 1H₂O), (NH₄)₂S_x-, NH₄I-, and HF-pretreated surfaces, are investigated by capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements. A HF-pretreated and annealed ZnSe/p-GaAs sample showed marked reduction of interface state density, N_ss, with N_ss,_min below 4 x 10¹¹cm^-2 eV^-1 near E_c- E_FS= 1.0 eV. The value is about one order of magnitude smaller than that of the standard chemically etched interface, and comparable to (NH₄)₂S_x- pretreated interface. Nevertheless, C-V characteristics of ZnSe/nGaAs samples, which were measured for the first time, indicate that interface Fermi level, E_FS, is not completely unpinned due to the interface states located above the midgap. A consistent result was obtained by DLTS method in determining E_FS position. The influence of N_ss distribution on vertical current conduction is also analyzed. It is found that U-shaped interface states with N_ss(E) > 1 x 10¹³ cm^-2 eV^-1 above the midgap may cause an excess voltage drop larger than a few volts at the interface.     

Tough and Self‐Recoverable Thin Hydrogel Membranes for Biological Applications

Tough and self‐recoverable hydrogel membranes with micrometer‐scale thickness are promising for biomedical applications, which, however, rarely be realized due to the intrinsic brittleness of hydrogels. In this work, for the first time, by combing noncovalent DN strategy and spin‐coating method, we successfully fabricated thin (thickness: 5–100 µm), yet tough (work of extension at fracture: 10⁵–10⁷ J m^?3) and 100% self‐recoverable hydrogel membranes with high water content (62–97 wt%) in large size (≈100 cm²). Amphiphilic triblock copolymers, which form physical gels by self‐assembly, were used for the first network. Linear polymers that physically associate with the hydrophilic midblocks of the first network, were chosen for the second network. The inter‐network associations serve as reversible sacrificial bonds that impart toughness and self‐recovery properties on the hydrogel membranes. The excellent mechanical properties of these obtained tough and thin gel membranes are comparable, or even superior to many biological membranes. The in vitro and in vivo tests show that these hydrogel membranes are biocompatible, and postoperative nonadhesive to neighboring organs. The excellent mechanical and biocompatible properties make these thin hydrogel membranes potentially suitable for use as biological or postoperative antiadhesive membranes.     

Material and process challenges in 100 nm interconnects module technology and beyond

In order for ultra-large-integrated (ULSI) circuits manufacturing to minimize the Cost of Ownership (CoO) aspect in the wiring process and realize fabricating semiconductor devices over 100 nm node, several Cu/low-k wiring technologies have been proposed. The evidential criteria in choosing the most probable one are physical or material limitation and requirements from manufacturing. A development of module processes (e.g., processing from low-k dielectrics to metal CMP) with proven equipment and material is an appropriate approach and has a high potential in overcoming those difficulties. In this paper, an advantage of dual Damascene Cu wiring accompanied with low-k (dielectric constant ∼2.7) and prediction of 100 nm Cu wiring module will be discussed.     

Annealing effects of a high-quality ZnTe substrate

The sharp photoluminescence (PL) and optical-reflection spectra in the bandedge region of the high-quality nondoped ZnTe substrate (100) were observed at 4.2 K. Free exciton, associated with lower and upper polaritons (EX^L and EX^U) at 2.382 eV and 2.381 eV, respectively, were clearly observed. This meant that this substrate was high quality. The intensity of a bound exciton peak (2.375 eV), which is caused by a Zn vacancy, of a neutral acceptor decreased with an increase of the Zn vapor pressures.     

Ultrathin Organic Electrochemical Transistor with Nonvolatile and Thin Gel Electrolyte for Long‐Term Electrophysiological Monitoring

Skin‐based electrical‐signal monitoring is one of the basic and noninvasive diagnostic methods for observing vital signals that contain valuable information about the dynamic status of the inner body. Soft bioelectronic devices are developed for the acquisition of high‐quality biosignals by taking advantage of their inherent thin and soft bodies. Among these devices, the organic electrochemical transistor (OECT) is a promising local transducing amplifier because of its key advantages, such as low operating voltage, high transconductance, and biocompatibility. However, the transistor's direct electrolyte‐gated operation limits its ability to measure biosignals only when the electrolyte exists. Here, an ultrathin OECT‐based wearable electrophysiological sensor based on a thin (≈6 µm) and nonvolatile gel electrolyte is reported, which can operate on dry biological surfaces. This sensor can measure biopotentials with a high mechanical stability and high signal‐to‐noise ratio (24 dB) even from dry surfaces of the human body and also shows stable performance during long‐term continuous monitoring and multiple reuse in a test that lasted more than a week.     

Durable Ultraflexible Organic Photovoltaics with Novel Metal‐Oxide‐Free Cathode

Flexible and stretchable organic photovoltaics (OPVs) are promising as a power source for wearable devices with multifunctions ranging from sensing to locomotion. Achieving mechanical robustness and high power conversion efficiency for ultraflexible OPVs is essential for their successful application. However, it is challenging to simultaneously achieve these features by the difficulty to maintain stable performance under a microscale bending radius. Ultraflexible OPVs are proposed by employing a novel metal‐oxide‐free cathode that consists of a printed ultrathin metallic transparent electrode and an organic electron transport layer to achieve high electron‐collecting capabilities and mechanical robustness. In fact, the proposed ultraflexible OPV achieves a power conversion efficiency of 9.7% and durability with 74% efficiency retention after 500 cycles of deformation at 37% compression through buckling. The proposed approach can be applied to active layers with different morphologies, thus suggesting its universality and potential for high‐performance ultraflexible OPV devices.