Polymer microstructure generated by laser stereo-lithography and its transfer to silicon substrate using reactive ion etching

Micro-fabrication combining stereo-lithography with reactive ion etching is proposed. Three-dimensional polymer structures smaller than 1 mm are fabricated on silicon wafer by He-Cd (325.0 nm) laser stereo-lithography. Using the polymer structure having a high-aspect ratio as resist for deep reactive ion etching, the microstructure is transferred to the silicon substrate with an etching ratio of 0.5. The proposed technique has been demonstrated by the fabrication of lens-like structures.     

Effect of sintering time on crystal structure and microwave dielectric properties in aeschynite-structured (Sm1−xYx)(Ti1.5W0.5)O6 (x = 0 and 0.5) ceramics

The crystal structure and microwave dielectric properties of the (Sm_1−xY_x)(Ti_1.5W_0.5)O₆ (x = 0 and 0.5) ceramics sintered at 1375 °C for 2-50 h were investigated in this study. No secondary phase was observed in the samples sintered for various sintering times, whereas a secondary phase was formed in the (Sm_0.5Y_0.5)(Ti_1.5W_0.5)O₆ ceramic sintered at 1400 °C for 50 h. As for the microstructure analysis, the formation of the liquid phase was observed in the both of the samples sintered for 20 and 50 h. The formation of the liquid phase is related to the compositional change of Ti and W from the stoichiometric composition of the samples caused by the instability of crystal structure. The dielectric constants were increased with increased sintering time in the both of the samples, though variations in the temperature coefficient of resonant frequency of the samples were not recognized with the variation in the sintering time. Moreover, although the quality factors of the each sample increased with increasing the sintering time from 2 to 10 h, decreases in the quality factors were recognized when the sintering time was over 10 h.     

Aortic complications after aortic valve replacement in patients with dilated ascending aorta and aortic regurgitation

AIMS/BACKGROUND: Compared with nanosecond (ns) pulses of conventional Nd-YAG lasers, picosecond (ps) laser pulses allow intraocular surgery at considerably lower pulse energy. The authors report initial clinical experiences using a Nd:YLF ps laser for the treatment of various indications for photodisruption. METHODS: A Nd:YLF laser system (ISL 2001, wavelength 1053 nm) was used to apply pulse series of 100-400 microJ single pulse energy at a repetition rate of 0.12-1.0 kHz. Computer controlled patterns were used to perform iridectomies (n = 53), capsulotomies (n = 9), synechiolysis (n = 3), and pupilloplasties (n = 2). Other procedures were vitreoretinal strand incision (n = 2) and peripheral retinotomy (n = 1). For comparison, 10 capsulotomies and 20 iridotomies were performed with a Nd:YAG ns laser. The ps laser cut of an anterior capsule was assessed by scanning electron microscopy (SEM). RESULTS: Open, well defined iridectomies (mean total energy 4028 mJ, mean diameter 724 microns), were achieved at first attempt in 92% of the cases. In 64% an iris bleeding and in 21% an IOP increase of > 10 mm Hg occurred. All capsulotomies were performed successfully (mean energy 690 mJ/mm cutting length) but with a high incidence of intraocular lens damage. The attempted vitreoretinal applications remained unsuccessful as a result of optical aberrations of the eye and contact lens. Although ps laser capsulotomies and iridectomies required much higher total energy than ns procedures, the resulting tissue effects of the ps pulses were more clearly defined. SEM examination of a ps incision of the anterior lens capsule demonstrated, nevertheless, that the cut was more irregular than the edge of a continuous curvilinear capsulorhexis. CONCLUSION: Series of ps pulses applied in computer controlled patterns can be used effectively for laser surgery in the anterior segment and are considerably less disruptive than ns pulses. The ps laser is well suited for laser iridectomies while the ns laser is preferable for posterior capsulotomies. As vitreoretinal applications remained unsuccessful, the range of indications for intraocular photodisruption could not be extended by the ps laser.     

Electrical communication between glucose oxidase and electrodes mediated by phenothiazine-labeled poly(ethylene oxide) bonded to lysine residues on the enzyme surface

A series of glucose oxidase (GOx) hybrids (GOx-phe-nothiazine-labeled poly(ethylene oxide) (PT-PEO)) capable of direct electrical communication with electrodes is synthesized by covalently modifying PT-PEO to lysine residues on the enzyme surface. The length of the PEO chain and the number of PT groups are systematically altered. After the PT-PEO modification, all the hybrids maintain more than 50% of enzyme activity relative to that of native GOx, although loss of the activity becomes greater with increasing PEO chain length. The catalytic current, i(cat), is observed at a potential more positive than 0.55 V after the addition of glucose, due to the intramolecular electron transfer (El) from reduced forms of flavin adenine dinucletide (FADH2/FADH) to PT+ that are electrogenerated at the electrode. The i(cat) value increases with the number of PT groups, indicating that most of the modified PT groups act as mediators. The magnitude of the i(cat) increase depends on the PEO chain length and reveals a maximum for PT-PEO with the molecular weight of 3,000. In contrast, the i(cat) is almost constant for GOx-2-(10-phenothiazyl)propionic acid (PT-PA) hybrids with more than two PT groups synthesized by covalently modifying PT-PA to surface lysines, indicating that only a few key PT groups function as mediators. The maximum rate constant (130 s(-1)) for the ET from FADH2/FADH to PT+ is obtained for the GOx hybrid modified with five PT-PEO groups with the molecular weight of 3,000.     

A core-shell-type fluorescent nanosphere possessing reactive poly(ethylene glycol) tethered chains on the surface for zeptomole detection of protein in time-resolved fluorometric immunoassay

To increase the sensitivity and to depress the nonspecific binding in biochemical assays, a new core-shell-type fluorescent nanosphere (106.7 nm) covalently conjugated with antibody was prepared. The core-shell-type nanosphere was constructed by dispersion radical polymerization of styrene in the presence of heterotelechelic poly(ethylene glycol) (PEG) macromonomer, which has a polymerizable vinylbenzyl group at one end and a primary amino group at the other chain end and used as well as a surfactant. The resulting nanosphere had PEG tethered chains on the surface, which possesses a primary amino group at the distal end of the PEG chain (NH(2) nanosphere). The fluorescent NH(2) nanosphere was constructed by incorporating fluorescent europium chelates with beta-diketonate ligands in the core of the NH(2) nanosphere by means of a physical entrapment method. The primary amino groups on the fluorescent NH(2) nanosphere were then converted to maleimide groups using a hetero cross-linker. The resulting nanosphere had maleimide groups on the surface (maleimide nanosphere), onto which proteins having SH group in the molecule could be covalently conjugated quantitatively without any denaturation of the proteins under the milder reaction condition. The applicability of the fluorescent nanosphere was tested in a model sandwich immunoassay for alpha-fetoprotein (AFP) determination. Anti-human AFP Fab' fragment was covalently conjugated onto the maleimide nanosphere (Fab' nanosphere), and it was used for the solid-phase time-resolved fluorometric immunoassay of AFP. The detection limit (mean + 2 SD) was 0.040 pg/mL or 57.1 zmol (57.1 x 10(-)(21) mol, M(w,AFP) = 70000) for AFP. The imprecision (concentration CV) over the whole assay range was 1.1% (100 pg/mL) - 17.1% (0.1 pg/mL), even though with this conjugation of antibody to the nanosphere, the nonspecific binding was practically negligible (0.0008%) and even when approximately 1.9 x 10(9) particles of the Fab' nanosphere were applied to the microtitration well.     

Pulse voltammetric and ac impedance spectroscopic studies on lithium ion transfer at an electrolyte/Li4/3Ti5/3O4 electrode interface

Pulse voltammetry and ac impedance spectroscopy were used to study the lithium ion kinetics at a lithium ion insertion electrode consisting of Li4/3Ti5/3O4 thin films in an organic electrolyte. In the cyclic voltammogram, two redox peaks appeared at around 1.56 V vs Li/Li+ due to the insertion and extraction of lithium ion at the electrode. Differential pulse voltammetry gave a large reduction current at approximately 1.56 V during a cathodic scan due to lithium ion insertion into the electrode. From the peak current and potential, the charge-transfer resistance was evaluated by quantitative analysis using approximate equations for irreversible reactions. In the Nyquist plot, one semicircle was observed at 1.56 V, which was assigned to the charge-transfer resistance due to lithium ion transfer at the electrode/electrolyte interface. The value of the charge-transfer resistance at 1.56 V was almost identical to that evaluated by differential pulse voltammetry with an identical characteristic relaxation time. This result shows that both dc differential pulse voltammetry and ac impedance spectroscopy are useful for elucidating the phase transfer kinetics of lithium ion at insertion electrodes.     

Simultaneous Measurements of Thermal,Electrical, and Acoustic Properties of BaTiO<Subscript>3</Subscript> – New Feature of 403 K Phase Transition

In order to obtain useful information on the transient process of phase transitions in ferroelectrics by various methods including calorimetry, the “mK-stabilized cell” of a small size has been developed. It is based on the heat flux differential scanning calorimeter (DSC) and has a temperature stability better than 1 mK. The “cell” can be used to change the temperature under nearly quasi-static conditions by an infinitesimally small rate not only on heating but also on cooling while passing through the transition points. It enables simultaneous measurements of endothermic heat and exothermic heat along with dielectric constants, displacement currents, etc. with a high degree of temperature resolution. X-ray diffraction measurements for sensing thermal anomalies are also possible by a minor modification of the “cell.” Precise and simultaneous measurements of thermal, electrical, and acoustic properties were carried out at the 403 K phase transition in BaTiO₃ single crystal grown by the top-seeded solution growth method. It has been clarified that the exothermic heat at the transition on cooling has more useful information than the endothermic heat on heating; in the cooling process two thermal anomalies occur separately at T₁ and T₂ although the transition is in a narrow temperature range. It is recognized from other methods that the nature of the transition on cooling is not of a single but of multiple steps. Resonant ultrasonic measurements using the “cell” were carried out, after developing a new excitation method. The sample does not have a simple softening approaching the transition point on cooling but has different elastic moduli for the two thermal anomalies at T₁ and T₂. The dielectric constant also has an intermediate constant value between T₁ and T₂. The crystal structure in the room temperature phase below the transition point has been determined by X-ray diffraction. In this region, tetragonal and monoclinic structures coordinating with each other exist. Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder, Colorado, U.S.A.     

Self-assembly of concentric quantum double rings

We demonstrate the self-assembled formation of concentric quantum double rings with high uniformity and excellent rotational symmetry using the droplet epitaxy technique. Varying the growth process conditions can control each ring's size. Photoluminescence spectra emitted from an individual quantum ring complex show peculiar quantized levels that are specified by the carriers' orbital trajectories.     

Preparation of Inorganic Consolidated Body Using Aluminium Hydroxide Mechanically Activated by Dry Milling

Aluminium hydroxide (Al(OH)₃) was mechanically activated by dry milling. In order to develop an inorganic consolidated material, the structure and reactivity of milled Al(OH)₃ were investigated and consolidated bodies were prepared using the reaction between activated Al(OH)₃ and a potassium silicate solution. Milling up to 1 h apparently reduced the grain size and promoted amorphization, although milling longer than 2 h did not give a significant physical change. Milled Al(OH)₃ directly transformed to -Al₂O₃ around 270°C. The transformation temperature decreased with increasing milling time. The remarkable enhancement of the reactivity was attained. The reactivity of Al(OH)₃ milled for 2 h improved 1000 times more than that of as-received Al(OH)₃. The preforming paste, prepared with as-received Al(OH)₃, could not consolidate at room temperature without drying. On the other hand, for Al(OH)₃ milled for 2 h, the preforming paste consolidated in 10 min and the consolidated material showed much better resistance against water than that prepared with as-received Al(OH)₃. The possibility of a new inorganic consolidated material was suggested using the reaction between mechanically activated Al(OH)₃ and the potassium silicate solution.     

Illumination system design for a three-aspherical-mirror projection camera for extreme-ultraviolet lithography

A scanning critical illumination system is designed to couple a synchrotron radiation source to a three-aspherical-mirror imaging system for extreme ultraviolet lithography. A static illumination area of H x V = 8 mm x 3 mm (where H is horizontal and V is vertical) can be obtained. Uniform intensity distribution and a large ring field of H x V = 150 mm x 3 mm can be achieved by scanning of the mirror of the condenser. The coherence factor (varsigma) of this illumination system is ~0.6, with the same beam divergence in both the horizontal and the vertical directions. We describe the performance of the imaging optics at varsigma = 0.6 to confirm that the illumination optics can meet the requirements for three-aspherical-mirror imaging optics with a feature size of 0.06 mum.