Direct single-layered fabrication of 3D concavo–convex patterns in nano-stereolithography

A nano-surfacing process (NSP) is proposed to directly fabricate three-dimensional (3D) concavo–convex-shaped microstructures such as micro-lens arrays using two-photon polymerization (TPP), a promising technique for fabricating arbitrary 3D highly functional micro-devices. In TPP, commonly utilized methods for fabricating complex 3D microstructures to date are based on a layer-by-layer accumulating technique employing two-dimensional sliced data derived from 3D computer-aided design data. As such, this approach requires much time and effort for precise fabrication. In this work, a novel single-layer exposure method is proposed in order to improve the fabricating efficiency for 3D concavo–convex-shaped microstructures. In the NSP, 3D microstructures are divided into 13 sub-regions horizontally with consideration of the heights. Those sub-regions are then expressed as 13 characteristic colors, after which a multi-voxel matrix (MVM) is composed with the characteristic colors. Voxels with various heights and diameters are generated to construct 3D structures using a MVM scanning method. Some 3D concavo–convex-shaped microstructures were fabricated to estimate the usefulness of the NSP, and the results show that it readily enables the fabrication of single-layered 3D microstructures. PACS 85.40.Hp; 81.16.Nd; 42.82.Cr     

Local chemical distribution and electronic structure of Ge1−xTx DMS single crystals (T=Cr,Mn, Fe)

The spatial concentration distribution and local electronic structure of ferromagnetic Ge_1−xT_x (T=Cr, Mn, Fe) DMS single crystals have been investigated by using scanning photoelectron microscopy (SPEM), X-ray absorption spectroscopy (XAS), and photoemission spectroscopy (PES). It is found that doped T ions in Ge_1−xT_x crystals are chemically phase-separated, suggesting that the observed ferromagnetism arises from the phase-separated T-rich phases in Ge_1−xT_x.     

Structure and electrical transport properties of bismuth thin films prepared by RF magnetron sputtering

Bismuth thin films were prepared on glass substrates with RF magnetron sputtering and the effects of deposition temperature on surface morphology and their electrical transport properties were investigated. Grain growth of bismuth and the coalescence of grains were observed above 393 K with field emission secondary electron microscopy. Continuous thin films could not be obtained above 448 K because of the segregation of grains. Hall effect measurements showed that substrate heating yields the decrease of carrier density and the increase of mobility in exponential ways until 403 K. Resistivity of sputter deposited bismuth films has its minimum (about 0.7 × 10⁻³ Ω cm) in range of 403-433 K. Annealing of bismuth films deposited at room temperature was carried out in a radiation furnace with flowing hydrogen gas. The change of resistivity was not significant due to the cancellation of the decrease of carrier density and the increase of mobility. However, the abrupt change of electrical properties of film annealed above 523 K was observed, which is caused by the oxidation of bismuth layer.     

Differential Pulse Polarographic Determination of Nitrate in AUT Solution

A differential pulse polarographic method for the determination of nitrate ion has been developed. With 0.5 M CaCl₂ as supporting electrolyte, NO^?₃ is reduced to give a peak with E_1/2=–1.836 Volt vs. the Ag/AgCl electrode. The differential pulse polarographic peak height is proportional to the nitrate concentration from 20 to 60 ppm. The detection limit for nitrate is 2 ppm in pure aqueous solution. In the determination of 40 ppm nitrate a relative precision (relative standard deviation) of less than 2% was achieved. Nitrite interferes seriously and should be absent if accurate results are required. The method has been applied to the determination of nitrate in Ammonium Uranyl Tricarbonate (AUT) Solution, results obtained by this method are compared to those obtained by ion chromatography. The agreement between the two sets of results suggests that the DPP method can be used with a fair degree of confidence.     

Investigation of the Doughnut Effect in Cy3-Labeled Protein Microarrays using Scanning Near-Field Optical Microscope

We demonstrate the fluorescence mapping of protein microarrays by the technique of scanning near-field optical microscopy (SNOM) and confocal microscopy. Micron sized spots (300 μm) of human Immunoglobulin G (hIgG) protein with and without a Cy3 dye labeling have been fabricated on glass substrates by an immobilization method which makes use of calixcrown derivatives termed Prolinker. We have also tried to probe into the well-known “doughnut effect” observed in fluorescence images of proteins using the SNOM technique. The topographic and fluorescence SNOM images revealed that the number of proteins at the boundary of the spot were more than at the center in the case of the microarray spot which showed brighter luminescence at the edge than at the center in the confocal image.     

Femtosecond transform-limited Kerr-lens mode-locked dye lasers

Using SF6 glass plates as intracavity Kerr lenses and double-prism pairs for dispersion compensation, we achieve tunable femtosecond passive mode locking in rhodamine 590 (R6G) and 4-dicyanomethylene-2-methyl-16-p-dimethylaminostyryl-4H-pyran (DCM) dye lasers. The R6G laser produces transform limited 240–500 fs pulses between 577 and 606 nm, and the DCM laser produces 150 fs transform-limited pulses between 650 and 671 nm. We use dilute intracavity saturable-absorber jets to make the mode locking self-starting. Characteristics of the pulses and the stability regions of the lasers agree with general theories of passive mode locking.     

A high-gain porous silicon metal–semiconductor–metal photodetector through rapid thermal oxidation and rapid thermal annealing

2 tungsten lamp at 1.83 mA excited by a 0.85-mW 675-nm laser diode. We also demonstrate that the dark current could be greatly reduced through rapid thermal oxidation and rapid thermal annealing. Received: 4 August 1997/Accepted: 28 May 1998