Development of a time-resolved attenuated total reflectance spectrometer in far-ultraviolet region.

A far-ultraviolet transient absorption spectrometer based on time-resolved attenuated total reflectance (ATR) has been developed and tested for aqueous solutions of phenol and tryptophan in the region 170-185 nm. In this region, a stable tunable laser was not available, and therefore, white light from a laser-driven Xe lamp source was used. The time resolution, which was determined by the time response of a continuous light detector, was 40 ns. A new ATR cell where a sample liquid is exchanged continuously by a flow system was designed to reduce efficiently the stray light from the excitation light. We have tested the performance of the instrument by using aqueous solutions of phenol and tryptophan, whose photochemistry is already well known. Phenol and tryptophan have very strong absorptions due to a π-π∗ transition near 180 nm. Even for dilute solutions (10(-3) mol dm(-3)), we could observe decreases in their concentrations due to photochemistry that occurred upon their irradiation with a fourth harmonic generation laser pulse produced by an Nd:YAG laser. The sensitivity of the spectrometer was about 10(-4) abs, which corresponded to a concentration variation of 10(-3) mol dm(-3) for phenol and tryptophan.

Quantitative analysis of ions in spring water in three different areas of Hyogo Prefecture in Japan by far ultraviolet spectroscopy.

Far-ultraviolet (FUV) spectra in the 190-300 nm region were measured for spring water in Awaji-Akashi area, Tamba area and Rokko-Arima area in Hyogo Prefecture, Japan, these areas have quite different geology features. The spectra of the spring water in the Awaji-Akashi area can be divided into two groups: the spring water samples containing large amounts of NO(3)(-) and/or Cl(-), and those containing only small amounts of NO(3)(-) and Cl(-). The former shows a saturated band below 190 nm due to NO(3)(-) and/or Cl(-). These two types of spectra correspond to different lithological areas: sedimentary lithology near the sea shore containing many ions in the seawater and gravitic lithology far from the sea side, in the Awaji-Akashi area. The spring water from the Tamba area, which is far from the sea, contains relatively small amounts of NO(3)(-) and Cl(-); it does not yield a strong band in the region observed. The FUV spectra of three of four kinds of spring water samples in the Arima Hotspring show characteristic spectral patterns. They are quite different from the spectra of the spring water samples of the Rokko area. Calibration models were developed for NO(3)(-), Cl(-), SO(4)(2-), Na(+), and Mg(2+) in the nine kinds of spring water collected in the Awaji-Akashi area, Tamba, and Rokko-Arima area by using univariate analysis of the first derivative spectra and the actual values obtained by ion chromatography. NO(3)(-) yields the best results: correlation coefficient of 0.999 and standard deviation of 0.09 ppm with the wavelength of 212 nm. Cl(-) also gives good results: correlation coefficient of 0.993 and standard deviation of 0.5 ppm with the wavelength of 192 nm.

Effect of cations on absorption bands of first electronic transition of liquid water.

The effect of cations (Li(+), Na(+), K(+), Rb(+), and Cs(+)) on the first electronic transition (A <-- X) of liquid water was investigated by attenuated total reflection far ultraviolet spectroscopy. To negate the effect of anions, aqueous solutions of 1 M alkali metal nitrates and bromides were compared at a temperature of 25 degrees C. It is found that the peak energy of the A <-- X band of water, which shows a marked red shift with decreasing hydrogen-bond strength, decreases with increasing cation size. The peak energies of the A <-- X band can be approximated by a linear function of the inverse of the ionic radii of the alkali metal cations, which indicates (according to the Born equation) that the first electronic transition of water is characterized by the solvation energy of the cations.

Potential of far-ultraviolet absorption spectroscopy as a highly sensitive analysis method for aqueous solutions. Part II: monitoring the quality of semiconductor wafer cleaning solutions using attenuated total reflection.

Far-ultraviolet (FUV) spectroscopy combined with attenuated total reflection (ATR) is employed for direct measurement of the concentrations of semiconductor wafer cleaning fluids such as SC-1 (aqueous solution of NH3 and H2O2) and SC-2 (aqueous solution of HCl and H2O2). FUV spectra of these aqueous solutions in the 170-200 nm region are highly sensitive to changes in both hydrogen bonding and hydration. Although ATR measurement results in lower absorptivity compared to transmittance measurement, it is possible to increase absorption with greater evanescent wave penetration depth using a low refractive index internal reflection element (IRE). We adopt quartz as an IRE material. Since the refractive index of quartz becomes lower than that of water in the low energy side of an intense absorption band due to the n-->sigma* transition of water, the quartz IRE yields non-total reflection wavelength regions. However, near 175 nm the effective absorptivity of the tail of water's absorption band can be successfully enlarged, making the FUV-ATR technique suitable for measuring the concentrations of the components in the semiconductor wafer cleaning fluids. In the present study we prepared the same cleaning fluids as those used in actual semiconductor fabrication and measured their FUV-ATR spectra in the 150-300 nm wavelength range. It was found that even with the quartz IRE one can measure FUV-ATR spectra under total reflection conditions at 175 nm or above. We created calibration models for predicting both NH3 and H2O2 in the concentration ranges of 0-10% in SC-1 using multiple linear regression (MLR). The standard deviations of the models were 0.033% and 0.265% for NH3 and H2O2, respectively. The same procedure was repeated under the same conditions for HCl and H2O2 in SC-2, yielding corresponding values of 0.018% for HCl and 0.178% for H2O2.