In order to measure mobility distribution of nanometer-sized clusters and ions, the Cluster-Differential Mobility Analyzer with the integrated electrometer (CDMA-IE) has been manufactured following the design by Rosell-Llompart et al. (J. Aerosol Sci., 27, 695-719 (1996)). To evaluate the flow pattern of aerosol and sheath air in cylindrical annulus of this CDMA-IE, we employed the flow visualization technique developed by Otani et al. (J. Chem. Eng. Jpn., 31, 1065-1069 (1997)). The visualization results were compared with the calculation results using a fully developed laminar flow and mobility measurement results by means of the Tandem DMA method, and the necessary conditions under which the aerosol and sheath air flow ideally inside the DMA without any turbulence and mixing were clarified. After changing the width of aerosol inlet and properties of the upper filter respectively, we finally determined the detail of the CDMA-IE. Using the well confirmed CDMA-IE, we measured the size and concentration of water cluster ions generated by various methods, α -ray radiolysis, corona discharge, UV/photoelectron method and the Lennard's effect.
A charge measuring method was developed to measure the charge distribution of nanometer-sized particles at low pressure. The measuring apparatus consists of a parallel electrode condenser and a backup filter. The ratios of positively charged particles, negatively charged particles, and uncharged particles to total particles are obtained from weights of the particles collected by the electrodes and the filter. The performance of this measuring device was found from the theoretical investigation to depend on two dimensionless parameters which express the relative intensity of Brownian diffusion and electrophoresis. The charging ratios of nanometer-sized SiO2 particles charged by bipolar ions at an atmospheric pressure agreed well with theoretical results for bipolar diffusion charging.
Collection performances of air filters made of PTFE (polytetrafluoroethlene) filter medium were investigated. Eight types of filters, including one HEPA-grade and one ULPA-grade glass fiber filter for comparison, were examined. Aerosol particle penetrations of the filters were measured by using monodisperse NaCl aerosols ranging 0.02 to 0.2 μm in diameter at air flow face velocity of 5.3 cm/s. Collection performance was evaluated by an index, IP, defined as IP = -log (Pmax) /ΔP, where Pmax is the maximum penetration and ΔP is the pressure drop. The most penetrating particle sizes of the PTFE filters, estimated to be around 0.06 μm, were smaller than those of the glass fiber filters. The collection performance index of the PTFE filters ranged from 17 to 20 kPa-1 although the index of the glass fiber filters were constant at 10 or 11 kPa-1. No differences in the index between HEPA-grade and ULPA-grade glass fiber filters were observed.
A new super cleaning equipment of a closed space using a photocatalyst (TiO2) in a UV/photoelectron method was developed. The newly developed equipment has photocatalyst between photoelectron emitter and electrode (charging space) in the UV/photoelectron equipment to remove gaseous contaminants, such as hydrocarbons. The equipment developed in this work is characterized as follows : 1) It can create a super clean space in which both gaseous contaminants, such as hydrocarbons, ammonia and particles are removed simultaneously, 2) When Si wafer or metallic substrates are set in the clean space inside such an equipment, surface contamination of the substrates is prevented, 3) In evaluation of actual electron device using MOS (Metal-Oxide-Semiconductor) capacitor, the reliability of gate oxides is improved in the time dependent dielectric breakdown (TDDB) characteristics.
The cabins of most aircrafts contain smoking and non-smoking sections in the same compartment. In addition, two “Common Smoking Seats” located in the left rear of the cabin are provided for people located in non-smoking sections who wish to smoke during a flight. Because the smoking and non-smoking sections are in close proximity, and because current ventilation systems are not properly designed to prevent smoke migration away from smoking seats, the environment around the Common Smoking Seats becomes filled with smoke. We have developed a new ventilation system for improving the environment around these seats. This new ventilation system was developed after measurements and numerical simulations of the airflow patterns and velocity distribution in the economy cabin of a 747 aircraft. This was a joint project between Japan Tobacco Inc. (JTI) and Japan Airlines (JAL). The new system uses two smoking seats situated back-to-back with the seats located the furthest back in the stern of the aircraft. The new ventilation system uses a special grill on part of the air-conditioner outlet to control the ventilation airflow direction. Numerical simulations indicated that one smoking seat should be located in the left rear and the other in the right rear of the aircraft. Numerical simulations were also used to determine the optimum airflow direction. After installing this ventilation system into a Boeing 747 aircraft of Japan Airlines for international flights, the average smoke concentration in the environment around these “Common Smoking Seats” was reduced by a factor of about 3.
Pulse-air-jet blow is effective for the removal of fine particles from surfaces. In the present work, the removal characteristics of PSL particles from a wafer surface were investigated by measuring the distribution of removal efficiency on wafer surface. The influence of slit width of rectangular air-jet nozzle and the impinging angle of air-jet on the distribution of removal efficiency were experimentally studied. As a result, it was found that the relationship between a cleaned area with a removal efficiency greater than a given removal efficiency and the removal efficiency is expressed by a Rosin-Rammler distribution, and the shape of the distribution is invariant with the number of pulse-air-jet blows although the cleaned area increases with the number of blows. Further, experimental results showed that there exists optimal values in the slit width of air-jet nozzle and the impinging angle of air-jet for cleaning a wider area with a higher removal efficiency.
Removal of deposited single particles by use of a vibrating air jet has been studied experimentally, with particular attention to the effect of operating conditions. Two types of nozzle were newly designed and 6 sorts of metal plates were used as a vibrating plate. Twelve combinations of the nozzle and the vibrating plate have been tested to get the best combination for the generation of a high frequency vibration. Experimental results showed that the removal efficiency is almost determined by the vibration characteristics rather than air jet velocity. When the nozzle pressure is set at 2.5×105 Pa or 3.0×105 Pa, the removal efficiency tends to increase with the frequency of the vibration at the surface. In this case, longer jet duration time enhances the efficiency. Then, the number of repetition of pressure pulsation is one of the main cause of the effects of vibration. On the other hand, when the pressure is set at 3.5×105 Pa, the removal efficiency is affected by the shape of the vibrating wave.
This study investigated organic compounds in a cleanroom air and on silicon (Si) wafer surfaces using gas chromatograph-mass spectroscopy (GC-MS) and thermal desorption-atmospheric pressure ionization mass spectroscopy (TD-APIMS). Si wafers with hydrogen terminate and with native oxygen exposed in the cleanroom air were analyzed. As an analytical result using TD-APIMS, chained hydrocarbons such as C2-C5 alkanes were detected with higher values than phthalates such as DOP and DBP from Si wafers with hydrogen terminate and with native oxygen exposed in the cleanroom air. The adsorption mechanisms of organic compounds on Si wafers were discussed by thermal desorption spectra. Based on these results, the adsorption hierarchy model of organic compounds on Si wafer surfaces was proposed.