Toyohiko Tazawa

Hydrogen plasma etching method for depth analysis by x‐ray photoelectron spectroscopy

An etching device using a hydrogen plasma has been developed for x-ray photoelectron spectroscopy (XPS) depth profile analysis of organic compounds. The effect of the hydrogen plasma discharge was investigated using a photoresist film containing benzene rings, C– O bonds and C– F bonds formed on an Si(100) wafer. The condenser-type discharge tube employed is composed of electrodes, an etch tunnel (shield tube) and a quartz glass tube. Both the electrodes and etch tunnel have many holes. Experimental results show that the etching rate of the photoresist film is 26.7 nm min−1 at an r.f. power of 200 W, a gas flow rate of 6.0 cc min−1 and a hydrogen gas pressure of 26.6 Pa. This rate is higher than that achieved by the use of a conventional high-speed etching ion gun. It is observed that the etched surface is flatter than that obtained by parallel plate electrodes and an Ar ion beam. The amounts of C, O and F after hydrogen plasma etching were not remarkably different from those before etching, and the shape of the C 1s spectrum did not show any change, indicating no change in chemical bonding. The results show that hydrogen plasma etching is very effective for depth profile analysis of organic polymers by XPS. Copyright

An Advanced Quantitative Analysis of Li in LIB with AES Preparation For a Clean Cross Section with the Cross Section Polisher

Since the introduction of the first consumer lithium ion battery (LIB) in 1991, it has become attracted considerable attention as a renewable energy source. Its demand is increasing yearly with increasing diffusion of a cell-phone and a laptop PCs, recently it is widely applied to not only small type but also middle-large type products such as hybrid vehicles. For the systematic, effective development aiming of higher-energy density, longer-life, and lower-cost, lithium distribution has earnestly been desired to be observed in active material of cathode and anode in less than one micrometer region. Ordinary energy dispersion spectroscopy (EDS) cannot detect lithium because the energy of its characteristic X-ray is out of the range of the detection limit of ordinary detectors. On the other hand, Auger electron spectroscopy (AES) is well known as the detectable method of Li like X-ray photoelectron spectroscopy (XPS), it has been widely used for research and development regarding Li in a minute area, especially since a field emission gun started to be used. Additionally AES has higher sensitivity for lithium than XPS. By comparing the peak intensity of the standard spectrum of Li LVV to C KLL measured under the same analysis conditions with AES, Li LVV has 4 times higher intensity than C KLL. On the other hand, by comparing the photoionization cross section for Al K of Li 1s with that of C 1s, Li 1s has 18 times lower intensity than C 1s. So, lithium sensitivity in AES is about 72 times higher than in XPS. But there are fewer applications to LIB with AES compared to those with XPS because of two disadvantages as below: 1. Sensitivity to the surface condition due to the short mean free path 2. Difficulty for the quantification As for the first disadvantage, it is caused by the shorter mean free path of Li KVV Auger spectrum; the mean free path of Li KVV Auger spectrum is about 0.6 nm whereas that of Li K photoelectron spectrum with Al K line excitation is about 2.0 nm, so slight contamination makes it undetectable. Furthermore the chemical preparation for sampling could lead lithium to elute, so the sample preparation is critically important to analyze with AES. As for the second disadvantage, it is caused by the spectrum overlapping of the Li KVV with a MVV spectrum of transition metal used as active material for the cathode of LIB. This overlapping prevents the detection of the expected intensity of Li KVV spectrum for quantification as shown Fig. 1. Moreover Li KVV spectrum has various shapes depending on the chemical state of lithium [1], so the relative sensitive factor (RSF) value of lithium is not constant.

Quantitative Oxidation State Analysis of Transition Metals in a Lithium-ion Battery with High Energy Resolution AES

After a first suggestion of the use of lithium transition-metal oxides in the cathode of lithium-ion battery (LIB) [1], many researchers have investigated to improve its performance such as higher-energy density, longer-life, and lower-cost. For the systematic, effective development, various transition-metals for the cathode active material have been investigated and chemical state characterization have earnestly been desired of small particles with a size of less than one micrometer.