Nucleus Counter Research Articles

Deposition of Submicron Aerosol Particles During Integrated Circuit Manufacturing: Experiments

Measurements of airborne concentrations and surface concentrations of submicron particles were made in two different semiconductor manufacturing cleanrooms. These measurements, made with an optical particle counter, a condensation nucleus counter, and a surface contamination optical monitor were used to determine the particle fluxes and the particle deposition velocities. The measurement data were compared with theoretical predictions of deposition due to gravity, diffusion, and electrostatic effects.

Evaluation of aerosol deconvolution algorithms for determining submicron particle size distributions with diffusion battery and condensation nucleus counter

Determining the particle size distribution of airborne particles is important in many contexts, including understanding and thus reducing the deposition of particles on micro-electronic components during their manufacture. Sizing of particles smaller than 0.1 μm is usually done with a diffusion battery, which requires use of a deconvolution algorithm to obtain particle size distributions. The following algorithms were evaluated: CINVERSE (Crump and Seinfeld, Aerosol Sci. Technol. 1, 363, 1982). Twomey's iterative procedure (Twomey, J. Comput. Phys. 18, 188, 1975), expectation maximization (Maher and Laird, J. Aerosol Sci. 16, 557, 1985), constrained least-squares fit (Nelder and Mead, Comput. J. 7, 308, 1965; Cooper and Spielman, Atoms. Envir. 10, 1976). Expectation maximization and constrained least-squares fit are more suited to this use than are the other two. The non-monotonic response of the diffusion battery with respect to particle size cannot be corrected for by any such algorithm. One could modify the diffusion battery to prevent entrance of the larger particles or one could use an independent measurement of the larger particles to correct the diffusion battery data. Using the latter approach provided an improved estimate of the particle size distribution in a clean room.

Measurement of Brownian Coagulation in Monodispersed and Bidispersed Liquid Aerosols

Coagulation in unimodal and bimodal di-(2-ethy-hexyl) sebacate aerosols with particle diameters between 32 and 522 nm in air at ambient pressure has been experimentally studied in a steady-state flowing system. The residence time of the aerosols in the axial region of a cylindrical coagulation tube was determined from the velocity measurements using the laser doppler velocimetry (LDV) technique. At various positions along the coagulation tube, and hence for various coagulation times, aerosol samples were extracted from the central region of the laminar flowing system and diluted in order to quench the process of coagulation. Subsequently, the number concentrations were measured by means of the size-analyzing nuclei counter (SANC). Comparing the experimental results with corresponding model calculations using Smoluchowski's continuum theory with the slip correction and Fuchs' semiempirical interpolation formula, the coagulation coefficients were determined. The experimental results are in fair agreement wi...

Redesign of an approved condensation nuclei counter for stationary use

Redesign of an approved condensation nuclei counter for stationary use

Measurement of ultrafine aerosol particle size distributions at low concentrations by parallel arrays of a diffusion battery and a condensation nucleus counter in series

This paper describes an instrument configuration capable of measuring size distributions over the 0.014–0.2 μm size range at particle concentrations typical of state-of-the-art clean rooms (10 −3 particles/cc or less). The configuration consists of a parallel array of diffusion batteries each with its own condensation nucleus counter and each drawing an independent air sample for analysis at one size cut. The combined outputs of all CNC/DB pairs yield the desired size distribution as illustrated for several clean room operating conditions.

Filter penetration measurements using a condensation nuclei counter and an aerosol photometer

We conducted both theoretical and experimental comparisons of two instruments, a condensation nuclei counter and an aerosol light-scattering photometer, to determine how they measured the penetration of high-efficiency particulate air (HEPA) filters. In some experiments we simulated leaks around the test filter to ascertain how such leaks affect the two instruments' penetration measurements. Results of all of our experiments indicate that differences in the measurements vary widely from no difference to a factor of 10. These variations are related to certain functions that depend on particle size: the response function of the photometer, the filter penetration, and the distribution of the test aerosol. The use of appropriate aerosol diagnostics enabled us to measure these functions and compare numerical calculations to experimental results. Agreement between theory and experiment is good. Consequently, given these function, the penetration values obtained in one instrument can be related to the other's. In general, test aerosols with larger standard deviations produce greater discrepancies between the two instruments' measurements. For sufficiently large leaks, the penetrations reported by the two instruments approach the same value, regardless of the distribution of the test aerosol.

Film drop production as a function of bubble size

Film drops from air bubbles bursting in seawater and in a 3% solution of sodium chloride in distilled water were counted with a condensation nucleus counter. Bubbles of known size were released from a capillary tip at depths from 1 to 20 cm beneath the surface of the water. Film drop production did not vary significantly with depth in seawater, but it decreased by about 3 times as the depth was increased to 10 cm in the sodium chloride solution. Drop production, however, varied markedly with bubble size. Over the range of bubble sizes studied (from about 1 to over 6 mm diameter), by far the most film drops were produced in the narrow size range of about 2–2.5 mm. About 75 film drops per bubble were found for the seawater case, and about 150 for the sodium chloride solution. On either side of this peak (bubbles of 1.5 and 2.8 mm), film drop production was less than 5 per bubble. The cause of this strong peak in drop production is not known, but it appears that bubbles of 2 to 2.5 mm diameter must play a major role in the production of film drops at sea.

Large-Scale Filter Testing for High-Purity Gas Supply Systems Used in Semiconductor Processing

The development of controlled aerosol generation technology at pressure has made possible fundamental performance measurements on commercial and developmental filters over a wide range of operating conditions. Aerosols were generated by dispersing sodium chloride solution into dry, clean nitrogen at pressure using a modified TSI, Inc. constant output atomizer. The size distributions of the aerosols were measured using a TSI, Inc. differential mobility particle sizer. The geometric mean particle diameter x g and geometric standard deviation of the aerosols were found to vary with atomizer operating condition. The diameter x g was found to depend upon the nitrogen pressure and solution concentration in the atomizer. The salt concentration was varied from 0.001 to 0.1 g/cm3. The aerosol size distribution deviated from log-normal behavior at each operating condition. The size distributions were stable and reproducible. The pressurized aerosols were then used as particle challenges in large-scale performance tests of two ultrahigh-efficiency filters. Tests were performed on complete Alter cartridges in a large-scale recirculating flow apparatus. Aerosol concentration in the Alter effluent was measured using a TSI, Inc. condensation nucleus counter and a Particle Measuring Systems, Inc. optical particle counter. The results indicate negligible penetration or bypassing of particles for each of the test cartridges. Concentrations of less than 3x 10−4/cm3 were measured for all particles as small as 0.02 μm in the effluent gas. The introduction of sodium chloride challenge did not substantially change the particle concentration in the effluent gas.

Deposition of Monodisperse Insoluble Aerosol Particles in the 0.005 to 0.2 <italic>μ</italic>m Size Range Within the Human Respiratory Tract

Abstract In 4 subjects with normal lung function total deposition of monodisperse, hydrophobic, uncharged silver particles in the 0.005 to 0.08 μm size range was investigated for a variety of breathing patterns during steady state mouth- and nose breathing. The evaluation of deposition was based upon measurements of mean particle number concentration in inspired and expired air by means of a condensation nucleus counter. Owing to the diffusional particle transport, total deposition increases with decreasing particle size and increasing mean residence time of the aerosol in the lungs. With decreasing particle size the time dependence becomes less and the effect of tidal volume more significant. A semi-empirical formula is derived which fits the experimental data.

Unipolar Diffusion Charging of Ultrafine Aerosols

Experimental data are reported for unipolar diffusion charging of NaCl and Ag aerosols in the 0.004- to 0.075-μm-diameter range. Monodisperse, uncharged particles were exposed to unipolar positive ions produced by a corona discharge. The nt product was varied between 3 × 106 and 1 × 107 (ions/cm3) (s), where n is the unipolar ion concentration and t is the charging time. The resulting aerosol charged fraction was measured by using a single-particle-counting condensation nucleus counter in conjunction with an electrostatic condenser. From the measured charged fraction and the known charging parameters, the combination coefficient between the neutral particles and the positive ions are obtained. Measurements are then compared with the available charging theories. It is found that the theory of Marlow and Brock best predicts charging rates in the ultrafine particle size range. Above 10 nm, the data approach the theory of Fuchs consistent with the experimental observation of Adachi et al. *Presented at Semina...

Aircraft measurement with condensation nuclei counter and optical particle counter

Aircraft measurement with condensation nuclei counter and optical particle counter

Particle Size Distributions in Clean Rooms

Measurements of particle size distributions smaller than 0.1 μm in Class 100 clean rooms are summarized. The size distributions were measured in operational rooms during periods of time with little activity—the so-called "at rest" conditions. A simple particle number balance model is proposed, illustrating the importance of filter penetration and atmospheric aerosol on the concentration of submicrometer particles. Preliminary calculations are used to explain the absence of < 0.1 μm diameter particles in the clean rooms tested. A ratio of condensation nucleus counter concentration to optical particle counter concentration is suggested as a parameter to provide an indication of changes in clean room particle size distribution.

Performance of a Laboratory Clean Room

The performance of a small, 52 square meter laboratory clean room at the University of Minnesota has been evaluated using a system of aerosol measuring and monitoring instruments. Aerosol in the ambient atmosphere and in the clean room has been measured simultaneously using a condensation nucleus counter and diffusion battery, a differential mobility particle sizer and two laser optical particle counters to provide concentration and size distribution data between 0.002 to 10 μm diameters. The diurnal variation of the condensation nuclei concentration in the clean room has been found to follow closely that in the ambient atmosphere. This suggests that particles in the CNC range measured in the clean room have their origin in the ambient atmosphere and that the clean room filter does not provide a perfect shield between indoor and outdoor air for these small particles. The ratio of clean room CMC to ambient CNC counts has been found to range from 7 × 10−7 when the ambient CNC count is low (1 × 105 per cc) to 2 × 10−7 when the ambient CNC count is high (1 × 106 per cc). This can be explained by the smaller size of the airborne particles in the ambient atmosphere under high concentration conditions and the greater efficiency of the HEPA filters for these particles.

Evidence for the climatic role of marine biogenic sulphur

Oceanic dimethylsulphide (DMS) emissions and atmospheric aerosol particle populations (condensation nuclei, CN), resolved by latitude and season, appear to be directly correlated, in that CN, as measured with a condensation nucleus counter, are high (or low) in regions where DMS fluxes and incident solar radiation are high (or low). Although it has been previously hypothesized that CN are produced from DMS1,2, we report the first attempt to correlate DMS flux and CN. As the population of cloud condensation nuclei (CCN) in marine air is a subset of the CN population3,4, and CCN in turn control the albedo of marine clouds5,6, DMS could be involved in climate control through a cloud albedo feedback mechanism.

Effect of size distribution of condensation nuclei on pressure in an expansion counter

Pressure in the sample chamber of a pressure defined expansion type nucleus counter and optical attenuation are measured using a sensitive pressure transducer, an optical sensor and an electronic recorder for different samples of aerosols. It is observed that first and second derivatives of pressure, as a function of time, display inflections characteristic of the samples. Details of the experimental work, theoretical background and an analysis of results are presented in this paper. It is concluded that the inflections are likely to indicate the number of modes in the size distribution of condensation nuclei in the sample. Measurements of optical attenuation and its derivative as a function of time support the interpretation.

Development of a New Continuous Monitor for Nonvolatile Solute in Ultrapure Water by Atomization

A new monitoring system has been developed for continuously measuring the concentration of total nonvolatile impurities in ultrapure water. The measuring method is based on the principle of determining the Residue After Evaporation (RAE) of atomized droplets, taking account of the particle deposition loss. The system consists of a water atomizing unit, a droplet evaporating and drying unit, an air diluter, a fine particle counter, etc. For the particle counter, a Condensation Nucleus Counter (CMC) is used; this counter is a mixing type, able to detect particles larger than 0.01 μm. It is verified from both the theoretical analysis and the experimental results that this monitor can rapidly detect very low impurity concentrations by counting the number concentration of aerosol particles.

Marine condensation nucleus generation inferred from whitecap simulation tank results

The condensation nuclei (CN) produced during a set of experiments in the Whitecap Simultation Tank at University College, Galway, were measured with a TSI 3020 nucleus counter. The total number of CN produced per breaking wave event was 3.5 ± 0.5 × 107 for a seawater temperature near 15°C. The CN production per unit area of whitecap (108 m−2) and the previously observed whitecap time decay constant of ∼3.5 s implies a whitecap CN flux Fw of ∼2.8 + 0.9 × 107 m−2 s−1. This can be combined with the whitecap coverage W versus 10 m wind speed U relation of E. C. Monahan and I. O'Muircheartaigh (1980), W(U) = 3.84 × 10−6 U3.41, to estimate the general oceanic CN flux F0 = WFW. For U = 10 m s−1, this relation gives W = 1%, and thus F0 is ∼2.8 × 105 m−2 s−1. Using the same Whitecap Simulation Tank and a PMS classical aerosol spectrometer, E. C. Monahan et al. (1982) determined that the whitecap flux Fw of giant particles (radii > 1 μm at relative humidity = 80%) was ∼2 × 106 m−2S−1. Clearly, most of the CN produced by this whitecap simulation are of submicron size, and this was also the case in the model breaking wave experiments of R. J. Cipriano et al. (1983). Both laboratory whitecap simulations suggest that the ocean contributes significantly to the CN and cloud condensation nuclei populations of the marine atmospheric boundary layer far from land.

Counting efficiencies of six commercial particle counters

Counting efficiencies of a condensation nuclei counter (TSI 3020), a white-light optical particle counter (Climet CI-8060) and four laser instruments (PMS LAS-X, LAS-250X, LPC 525 and HP-LAS) were determined relative to the LAS-X. Measurements were made in the geometric diameter range of 0.1–4 μm using latex spheres as well as monodisperse organic and inorganic particles produced by a vibrating orifice generator. The high-pressure in-line counter (HP-LAS) shows a nonlinear response to gas velocity which can be taken into account by a calibration. The lower detection limits (50% points) of the conventional laser counters (LAS-X and LAS-250X) agree within 0.05 μm with their nominal specifications; for the white-light counter (CI-8060) the actual lower limit is at about 0.4 μm. For all counters, the degree of inlet losses for larger particles varies greatly with inlet design and flow velocity of each counter.

Determination of the retention efficiency of industrial air filters for particle sizes in the submicron range

Particle size distribution up to a maximum diameter of 0.1 μm has been produced in the presence of short-lived tracer Na-24 using an aerosol generator. Industrial air filters with a cross-section of 100 cm 2 have been exposed to very high particle fluxes such that particulate breakthroughs down to 10 −8 can be assessed by measuring the activity ratio of the air before and after going through the filter. This method, which involves installing an analytical filter (absolute filter) after the test filter, has a high accuracy and makes it possible to determine particle breakthrough under the same conditions of air flow velocity and pressure loss as in industrial processes. In comparison with on-the-spot-methods, e.g. the condensation nucleus counter, the above method includes passage across the entire filter area and excludes secondary aerosols.

A Vindication of the Twomey-Type Cloud Condensation Nucleus Counter

Abstract The performance of the Twomey-type cloud condensation nucleus (CCN) counter is evaluated by a numerical simulation and found to be better than that predicted in an earlier study. Due to a lack of data on CCN spectra at low supersaturations, the earlier study used extrapolations that subsequent measurements show are unrealistic for atmospheric CCN. The present study indicates that if the instrument has a 0.5 μm radius detector limit, the count is accurate to within 15% for operating supersaturations above 0.1% and for typical atmospheric aerosols.