Vol. 47, No. 6
June, 1998
Tetsuo Sakamoto, Zhaohui Cheng, Masanori Takahashi, Yasuyuki Kuramoto*, Masanori Owari** and Yoshimasa Nihei*
*Institute of Industrial Science, the University of Tokyo, 7-22-1, Roppongi, Minato-ku, Tokyo 106-8558
**Environmental Science Center, the University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-0033
The failure analysis of electronic devices and deduction of the emission origins of dust particles in clean processes or in urban air require a precise three-dimensional (3D) microanalysis method. The most indispensable demand for such 3D microanalysis is the applicability to samples with arbitrary shapes and heterogeneity. We are developing a novel 3D microanalysis method which will satisfy these requirements. Our method employs the combination of micro-cross-sectioning of a sample using a Ga focused ion beam (Ga FIB) and Auger mapping of the cross section using an electron beam (EB). On the basis of this concept, we constructed an ion and electron dual-focused beam apparatus. The Ga FIB and EB are perpendicularly directed to a sample to define simply the 3D coordinates from the steering of the two beams. Preliminary experiments on the non-element specific 3D imaging of an IC using an EB-induced sample current signal showed a favorable result concerning the reproducibility of the 3D structure within the analysis volume. Furthermore, the contamination of the analytical surface (cross section) due to primary Ga implantation and the redeposition of sputtered materials were found to be greatly reduced in our cross-sectioning method.
Keywords: three-dimensional analysis; focused ion beam; Auger electron spectroscopy; microparticle; integrated circuit.
Zhaohui Cheng, Tetsuo Sakamoto, Masanori Takahashi, Yasuyuki Kuramoto*, Masanori Owari** and Yoshimasa Nihei*
*Institute of Industrial Science, the University of Tokyo, 7-22-1, Roppongi, Minato-ku, Tokyo 106-8558
**Environmental Science Center, the University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-0033
It is known that the ion-induced Auger electron (IAE) spectra of light elements, such as Mg, Al and Si, show considerably different characteristics from those of the conventional electron-induced Auger spectra. The Auger decay of excited species induced by energetic projectiles is generally explained by the formation of instantaneous quasi-molecules consisting of a projectile and a target atom, and two target atoms respectively. Through crossing of the molecular orbitals, inner-shell vacancies are produced. An IAE spectrum comprises a continuous background related to the decay of excited atoms/ions in the solid (bulk-like peak) and discrete sharp peaks (atomic-like peak). These sharp peaks originate from excited species which are sputtered into the vacuum through ion bombardment. We studied Ga-FIB-induced Auger emission from Al and Si using an ion and electron dual focused beam apparatus developed by our group. It has been shown that the LMM Auger yields and the signal-to-background ratios are much higher than those of electron-induced ones, and increase linearly with the increment of the incident energy of the Ga FIB. Combining these features with the Ga FIB technique, we developed a two-dimensional elemental mapping method with sub-µm lateral resolution using Ga FIB IAE.
Keywords: focused ion beam; Auger electron spectroscopy; microanalysis; elemental mapping; integrated circuit.
Shuichi Hirukawa, Kazuo Miyamura and Yohichi Gohshi*
*Course of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656
(Received 9 January 1998, Accepted 19 March 1998)The graphite surface and that adsorbed with liquid-crystalline molecules was analysed by a tunnel-gap imaging method, which measures the local tunnel gap width (s) dependence of the tunnel current (I), i.e. the I-s characteristics, using a scanning tunneling microscope capable of resolving atoms. Both samples exhibited similar I-s characteristics in a low tunnel-gap width region; the barrier height was estimated to be several 100 meV. On the other hand, the I-s characteristics of a molecule-adsorbed sample at a high tunnel-gap width region exhibited that the special tunnel current induced by the adsorption of the molecules is present. In this region, it was found that the apparent barrier height drastically decreased to several meV, and that the relation between the cross section and the barrier height was totally reversed to that of the graphite surface.
Keywords: scanning tunnel microscopy; tunnel gap imaging; I-s characteristics.
Shiro Matsuoka, Kazuhisa Yoshimura, Akira Tateda* and Isamu Shinno**
*Department of Chemistry, Faculty of Science, Kyushu University, 4-2-1, Ropponmatsu, Chuo-ku, Fukuoka 810-8560
**Department of Japanese Society and Culture, Graduate School of Social and Cultural Studies, Kyushu University, 4-2-1, Ropponmatsu, Chuo-ku, Fukuoka 810-8560
The applicability of solid-phase absorptiometry to a minute solid particle has been studied for the sensitive determination of target trace elements present in a small volume of sample solutions. An iron(II)-phenanthroline complex or a Cr(VI)-diphenylcarbazide complex in 1 cm3 of a sample solution was concentrated in a spherical bead of cation-exchange resin having a particle size of about 0.8 mm. The light attenuance of this particle was measured using a polarizing microscope attached to a photo-detector. The sensitivity of the proposed method was 280-times greater than that of the conventional corresponding solution method, which was considered to agree with the expected value of 300. Although the size of the respective cation-exchange resin particle was not very uniform, a reproducible measurement of the absorbance due to the colored chemical species sorbed could be made. The calibration graph was straight and Beer's law could be also applied, even to a minute spherical bead.
The proposed method is thought to be effective for analyzing trace elements in samples which are hardly obtained in large amounts, such as rain-water samples.
Keywords: solid-phase absorptiometry; small volume of sample solution; microscopic spectroscopy; minute solid particle; high sensitivity.
Kiyoshi Hirakawa, Isao Yoshida and Daido Ishii*
*Division of applied chemistry, Graduate school of Kumamoto institute of technology, 4-22-1, Ikeda, Kumamoto 860-0082
(Received 6 January 1998, Accepted 17 February 1998)Analytical methods using continuous ultra-micro flow were developed for the purpose of downsizing the amounts of wastewater discharged from analytical measurements. The sampling of environmental water was also suggested. All tubes of the sampling and measuring apparatus were a fused silica capillary of 0.25 mm inner diameter at a flow rate of about 1 µl/min; this method was applied for COD as well as nitrate and nitrite ions in environmental water. A continuous monitoring apparatus for COD as well as nitrate and nitrite ions based on Japanese Industrial Standard methods were constructed. In the monitoring apparatus for COD, the sample water and acidic a potassium permanganate solution, a silver nitrate solution was pumped with a syringe pump at a total flow rate of 1.6 µl/min. Nitrate and nitrite ions were also simultaneously determined spectrophotometrically on the basis of a diazotization-coupling reaction. Nitrate ion was reduced to nitrite ion with a cupperized cadmium micro-column prior to the reactions. These methods were successfully applied to continuous monitoring of COD as well as nitrate and nitrite ions in laboratory sewage. The amount of wastewater produced by a continuous measurement was under 1l per year.
Keywords: continuous ultra-micro flow; COD; nitrate ion; nitrite ion.
Ji-Ye Jin, Kimihiro Kinugasa, Toyohide Takeuchi and Tomoo Miwa*
*Department of Chemistry, Faculty of Engineering, Gifu University, 1-1, Yanagido, Gifu 501-1193
(Received 12 January 1998, Accepted 18 February 1998)Thin mercury-film ultramicroelectrodes and a simply constructed microvoltammetric cell were developed for the determination of trace metals in extremely small samples by square-wave anodic stripping voltammetry (SWASV). The electrodes were prepared by sealing carbon fibers of 7 µm diameter into a polyethylene tube (i.d. 2 mm) at 200°C. Electric contact between the carbon fibers and lead wire was made with silver paste, a thin mercury film on the electrode was in situ plated when used. This electrode can achieve 20 repetitive stripping runs with no degradation of the performance, and can be simply renewed by cutting its bottom surface. The effect of dissolved oxygen on SWASV was found to be suppressed when a square-wave stripping step was performed using a square-wave frequency of 150 Hz and a potential step of 6 mV (scan rate=900 mV s-1). Furthermore, the sensitivities were significantly improved by vibrating the working electrode during the period of a pre-electrolysis step. The calibration (peak current vs. concentration) curves for Cd(II), Pb(II) and Cu(II) in a solution containing 0.05 M sodium acetate and 1.0×10-5 M Hg(II) were linear from 0.001 to 0.5 µg ml-1 for 300 s pre-electrolysis time. The relative standard deviations for the metals were less than 3% (n=20) at a concentration level of 0.05 µg ml-1. The proposed method was applied to the determination of a ng level of trace heavy metals in 1 mg hair samples.
Keywords: square-wave anodic stripping voltammetry; thin mercury-film ultramicroelectrode; microvoltammetric cell; trace heavy metals.
Shinya Kitagawa, Takao Tsuda* and Osamu Nozaki**
*Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555
**Kinki University, School of Medicine, Oonohigashi 377-2, Osakasayama-shi, Osaka 589-8502
Agglutinations with cross reactions between red blood cells and blood-tying antibodies in a short fused-silica capillary tubing (50 µm inner diameter and ca. 10 mm in length) were observed by an optical microscope-CCD camera system. The total volume in the capillary was only about 20 nl. The cross reaction was induced by using of counter electrophoretic migrations between red blood cells and the antibody under an applied electric voltage. Since the microscopic magnification was 1000 times, each red blood cell could be clearly observed. The blood typing procedure was as follows: after 50-times diluted whole blood cells were introduced into a capillary, both ends of the capillary were sealed with 1% agarose gels in order to suppress any pressurized flow in the capillary. Then, a direct electric voltage was applied (24 V) to the capillary. The red blood cells migrate toward the positive electrode against electroosmotic flow, while the blood plasma migrated toward to the negative electrode. The blood antibody in the reservoir of the positive electrode was introduced through the stopper of the agarose gel, following a cross-reaction with the red blood cells. Agglutination of some of the red blood cells was observed with a CCD camera and recorded on video-tape. The operation period took only 5 min. This new blood typing was performed using whole blood of nl volume.
Keywords: blood typing; agglutination; whole blood; cross reaction in capillary; fused-silica capillary; cell electrophoresis; single cell.
Hiroaki Nakanishi, Hirohisa Abe, Takahiro Nishimoto* and Akihiro Arai**
*Technology Research Laboratory, Shimadzu Corporation, 3-9, Hikaridai, Seika-cho, Soraku-gun, Kyoto 619-0237
**HPLC Business Department, Analytical Instruments Division, Shimadzu Corporation, 1, Nishinokyo-Kuwabaracho, Nakagyo-ku, Kyoto 604-8511
Microchips for capillary electrophoresis have been fabricated in small size on quartz or glass substrates. Each microchip is 11 mm×28 mm in size and 1.5 mm in thickness. It has a sample loading channel, a separation channel and four reservoirs at the ends of each channel. To fabricate a quartz chip, we applied a novel bonding method with a 1% (w/v) hydrofluoric acid solution. Using fabricated microchips, we evaluated several of their analytical features. We have shown that the microchips permit quantitative sample injection (several 10 pl or less) with an adequate potential control, high-speed analysis (30 s) due to the high heat-dissipation capability and effective separation (the number of theoretical plates is over 2500 at separation length of 17 mm).
Keywords: micromachining; capillary electrophoresis; microchip; high speed analysis; quartz chip.
Motoi Nakao, Satoshi Nomura, Tsuyoshi Nakanishi, Shuji Takamatsu, Katsuhiko Tomita*, Tatsuo Yoshinobu and Hiroshi Iwasaki**
*RITE-Kisshoin 2, Horiba Ltd., 2, Kisshoinmiyanohigashimachi, Minami-ku, Kyoto 601-8510
**The Institute of Scientific and Industrial Research, Osaka University, 8-1, Mihogaoka, Ibaraki-shi, Osaka 567-0047
We have developed a scanning chemical microscope which enables the observation of a microscopic pH distribution to be made. With this microscope, a flat pH sensor made of silicon is functionally divided into microscopic multiple-measurement points, then, the pH of the electrolyte at each point is independently measured. The measured pH values are converted to a gray or color scale so that the pH distribution can be visualized. The measurement can be performed with a resolution down to 0.1 pH at spatial intervals of as little as 100 microns. The measurement time required for scanning 6.4 mm×6.4 mm is 30 s. Using this microscope we could obtain pH images showing the generation and expansion of a localized lower pH region due to the release of protons from a single cation-exchange resin particle placed on an agar electrolyte. The dependence of the expansion rate on the agar concentration was clearly observed. This microscope is expected to become one of the promising techniques of chemical imaging.
Keywords: pH; microscope; light addressable potentiometric sensor.
Lan Ma, Mitsuko Oshima, Shoji Motomizu* and Takayasu Hattori**
*Department of Chemistry, Faculty of Science, Okayama University, 3-1-1, Tsushimanaka, Okayama 700-8530
**Asahi Techneion Co. Ltd., 1-3-9, Shinmojikita, Moji-ku, Kitakyushu-shi, Fukuoka 800-0115
To minimize the sample size, reagent consumption and waste, a micro-flow injection analysis (µFIA) was investigated and applied to the simultaneous determination of nitrate and nitrite ion in water samples. A double-plunger micropump was used to propel a carrier and a chromogenic solution; each flow rate was 50 µl min-1, and the delivery volume was 2.5 µl per stroke. Nitrate was reduced to nitrite on line by passing through a mini column (0.53 mm i.d.×5 cm) packed with powdered Cd/Cu (60~80 mesh). The reduction efficiency was 99% using this reduction column. Detection was carried out at 538 nm with a light-emitting diode used as an azo dye. The carrier solution contained EDTA and NaCl (pH 8.1~8.4) and the reagent solution contained sulfanilamide, N-(1-naphthyl)ethylenediamine and HCl. For a simultaneous determination, the sample injected into the carrier stream was split into two streams: one passed through the mini Cd/Cu column; the other passed through a bypass column packed with glass beads. The sample zone passing through the bypass column gave a first peak derived from nitrite; the other sample zone passing through the reduction column gave the second peak derived from nitrate and nitrite. The detection limits of nitrate and nitrite were about 1×10-7 M using the proposed simultaneous determination system.
Keywords: micro-flow injection analysis; river water; nitrate and nitrite; simultaneous determination; mini Cd/Cu reduction column.
Xing-Zheng Wu, Mamoru Yamaguchi* and Yukio Nagaosa**
*Department of Materials Science and Engineering, Faculty of Engineering, Fukui University, 3-9-1, Bunkyo, Fukui 910-8507
**Department of Applied Chemistry and Biotechnology, Faculty of Engineering, Fukui University, 3-9-1, Bunkyo, Fukui 910-8507
A measurement of the concentration gradient-induced optical beam deflection (OBD) in the vicinity of a microelectrode has been attempted. Platinum wires with diameters of 50 µm and 0.5 mm were used as a working microelectrode and a counter electrode, respectively. The reference electrode was a Ag/AgCl electrode. A ferricyanide/ferrocyanide redox reaction was used as a model electrochemical reaction. The applied potential of the Pt microelectrode was controlled using a polarographic analyzer. A probe beam from a diode laser was passed through the vicinity of the Pt microelectrode. Its deflection signal was detected by a position sensor consisting of a knife edge and a photodiode. Two kinds of potential sweeps were carried out. One was a potential step mode, the other was a triangle (cyclic voltammetry) one. Data for a simultaneous measurement of the current and OBD signals indicate that the present OBD method can be used for studying the concentration gradients in the vicinity of a microelectrode.
Keywords: optical beam deflection; concentration gradient; microelectrode; electrochemical reaction.