Surface effects of hybrid vibration-assisted femtosecond laser system for micro-hole drilling of copper substrate

The ultrafast laser based hybrid machining system was studied and a novel approach was demonstrated to improve laser machining quality on metals by vibrating the optical objective lens with a low frequency (500 Hz) and various displacements (0-16.5 μm) during a femtosecond laser machining process.The laser used in this experiment is an amplified Ti:sapphire femtosecond (10-15 s) laser system that generates 100 femtosecond pulses having an energy of 3.5 mJ/pulse with a 5 kHz repetition rate at a central wavelength of 790 nm.It is found that both the wall surface finish of the machined structures and the aspect ratio obtained using the frequency vibration assisted laser machining are improved compared with those derived via laser machining without vibration assistance.     

Triarylamine-based dual-function coadsorbents with extended π-conjugation aryl linkers for organic dye-sensitized solar cells

Triarylamine-based dual-function coadsorbents containing a carboxylic acid acceptor linked by extended π-conjugation aryl linkers (e.g., phenylene: HC-A3, naphthalene: HC-A4 and anthracene: HC-A5) were newly designed and synthesized. They were used as coadsorbents in organic dye-sensitized solar cells (DSSCs) based on a porphyrin dye (hexyloxy-biphenyl-ZnP-CN-COOH (HOP)). For comparison, the π-conjugated phenyl linker (HC-A3) previously developed by our group was also used as a coadsorbent. The structural effects on the photophysical and electrochemical properties and DSSC performance were systematically investigated. As a result, the DSSCs based on HC-A4 and HC-5 displayed power conversion efficiencies (PCEs) of 8.2% and 5.1%, respectively, while the HC-A3-based DSSC achieved a PCE of 7.7%. In the case of HC-A4, both the short-circuit photocurrent densities (J_sc) and open-circuit voltages (V_oc) of DSSCs were simultaneously improved to a large extent due to the more effective prevention of π−π stacking of organic dye molecules and the better light-harvesting effect at short wavelengths. The HC-A5-based DSSC exhibited a much lower short-circuit current (J_sc) and open-circuit voltages (V_oc) compared to the HC-A4-based DSSC, due to the fact that the dihedral angle of the π-conjugated linkers was too high for electron injection into the TiO₂ conduction band (CB) level. This had a reduced effect on preventing the π−π stacking of dye molecules, resulting in lower J_sc and V_oc values.     

Loosening mechanism of threaded fastener for complex structures

Journal of Mechanical Science and Technology - Threaded fasteners are widely used in mechanical structures primarily owing to their easy disassembly for maintenance and low cost. However, the...     

Comparison of hole mobility in LOCOS-isolated thin-film SOIp-channel MOSFET's fabricated on various SOI substrates

The hole mobility of LOCOS-isolated thin-film silicon-on-insulator (SOI) p-channel MOSFET's fabricated on SOI substrates with different buried oxide thickness has been investigated. Two types of SOI wafers are used as a substrate: (1) SIMOX wafer with 100-nm buried oxide and (2) bonded SOI wafer with 100-nm buried oxide. Thin-film SOI p-MOSFET's fabricated on SIMOX wafer have hole mobility that is about 10% higher than that on bonded SOI wafer. This is caused by the difference in the stress under which the silicon film is after gate oxidation process. This increased hole mobility leads to the improved propagation delay time by about 10%     

On the feasibility of nanoscale triple-gate CMOS transistors

The feasibility of triple-gate MOSFETs (TGFETs) for nanoscale CMOS applications is examined with regard to short-channel effects (SCEs) and gate-layout area. Three-dimensional numerical simulations of TGFETs reveal that much more stringent body scaling for SCE control is needed for undoped bodies relative to doped ones (which are not viable for nanoscale devices) due to the suppression of corner current conduction (which is technologically advantageous) in the former. When the undoped body is scaled for adequate SCE control, further analysis shows that the generic TGFET suffers from severe layout-area inefficiency relative to the fully depleted single-gate SOI MOSFET (FDFET) and the double-gate (DG) FinFET, and the inefficiency can be improved only by evolving the TGFET into a virtual FDFET or a virtual DG FinFET. We suggest then that the TGFET is not a feasible nanoscale CMOS transistor, and thus the DG FinFET, which is more scalable than the FDFET, seems to be the most promising candidate for future CMOS applications.     

Pore characteristics of Lotus-Type Porous Copper Fabricated by Centrifugal Casting

Metals and Materials International - Lotus-type porous copper was fabricated by a centrifugal casting. The long cylindrical pores aligned along single direction was formed during unidirectional...     

Body-contacted SOI MOSFET structure with fully bulk CMOS compatiblelayout and process

A new SOI MOSFET structure to reduce the floating body effect is proposed and successfully demonstrated. The key idea of the proposed structure is that the field oxide does not consume the silicon film completely, so that the well contact can suppress the body potential increase in SOI MOSFET through the remaining silicon film between the field oxide and buried oxide. The measured results show the suppressed floating body effect as expected. This new structure retains most of the advantages in the propagation delay of the conventional SOI MOSFET without body potential instability. An additional advantage of the proposed structure is that the layout and process are the same as those of bulk CMOS     

Antagonism of Helicobacter pylori by bacteriocins of lactic acid bacteria

Antimicrobial activity of seven bacteriocins produced by lactic acid bacteria against Helicobacter pylori strains (ATCC 43504, Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH [DSM] 4867, DSM 9691, and DSM 10242) was investigated in vitro using a broth microdilution assay. The bacteriocins chosen for the study were nisin A; lacticins A164, BH5, JW3, and NK24; pediocin PO2; and leucocin K. Antimicrobial activity of the bacteriocins varied among the H. pylori strains tested, of which strain ATCC 43504 was the most tolerant. Among the bacteriocins tested, lacticins A164 and BH5 produced by Lactococcus lactis subsp. lactis A164 and L. lactis BH5, respectively, showed the strongest antibacterial activity against H. pylori strains. MICs of the lacticins against H. pylori strains, when assessed by the critical dilution micromethod, ranged from 0.097 to 0.390 mg/liter (DSM strains) or from 12.5 to 25 mg/liter (ATCC 43504), supporting the strain-dependent sensitivity of the pathogen. Pediocin PO2 was less active than the lacticins against four strains of H. pylori, and leucocin K was the least active peptide, with no inhibition toward H. pylori ATCC 43504. Anti-Helicobacter activity of lacticin A164 was dependent on initial inoculum size as well as concentration of the bacteriocin added.     

Evaluation of dynamic recrystallization behaviors in hot-extruded AA5083 through hot torsion tests

Hot torsion tests were carried out to evaluate the dynamic recrystallization (DRX) behaviors of hot-extruded AA5083 at various deformation conditions. Flow curves showed the peak followed by the flow softening to the steady-state or to the failure strain, indicating that the DRX occurred during deformation. The peak stress increased as the temperature decreased and the strain rate increased. Constitutive relationship and Zener-Hollomon (Z) parameter were used to evaluate the DRX characteristics. Peak and steady-state stresses were generalized by the dimensionless parameter, Z/A, to reveal the DRX mechanism. The empirical relationship of the DRXed grain size with the deformation conditions was established, and decreased with increasing Z parameter. The relationship for the fraction of DRXed grains was established as a function of the effective strain at given deformation conditions from the experimental data. The Avrami relationship based on micro-hardness measurement was used to describe the DRX kinetics, and was fitted well with the observed DRX fraction.     

Dye-Sensitized Tandem Solar Cells with Extremely High Open-Circuit Voltage Using Co(II)/Co(III) Electrolyte

For achieving a high open-circuit voltage (V_oc) in dye-sensitized tandem solar cells, series-connected tandem solar cells were fabricated. In order to optimize series-connected tandem solar cell systems, the current density of the top and bottom cells should be well matched to be identical, and the V_oc of each of the cells should also be as high as possible. Furthermore, the top cell should be transparent and the bottom cell should have the longer-wavelength absorption, for utilizing only the light passing through the top cell. This leads to a high V_oc. In this study, we report dye-sensitized tandem solar cells having an extremely high V_oc using the Co(bpy)₃^2+/3+ (bpy=2,2′-bipyridine) redox couple. Dye-sensitized tandem solar cells employing JK303/HC-A1 with the Co(bpy)₃^2+/3+ redox couple as the top cell and N749/HC-A4 with the I⁻/I₃⁻ redox couple as the bottom cell were shown to have an extremely high V_oc of >1.66 V, the highest value for dye-sensitized tandem solar cells reported to date.