ABSTRACTS



The following is a list of the abstracts for papers which will be presented in TENTH INTERNATIONAL SYMPOSIUM ON PARTICLES ON SURFACES: DETECTION, ADHESION AND REMOVAL. The listing is alphabetical by presenting author. This list is updated continually to add abstracts as they become available and make appropriate corrections. This list may be conveniently searched by using the editor provided with most popular browsers (e.g. Microsoft Explorer, Netscape, ... etc.)


Thomas Bahners1, Helga Thomas2 and Eckhard Schollmeyer1



1) Deutsches Textilforschungszentrum Nord-West e. V., Adlerstr. 1, 47798 Krefeld, GERMANY



2) Deutsches Wollforschungsinstitut e.V., Pauwelsstr, 8, 52704 Aachen, GERMANY



Electrospun Nanofibers - a Way to Improved Wet Filtration Efficiency of Textile Filter Media



Electrospinning - more precisely: electrostatic fiber formation - is an interesting technology to produce very fine fibers with sub-micrometer diameter. In the process, a strong inhomogeneous electric field acts on a polymer solution leading to the extraction of a polymer jet which solidifies and orientates through the evaporation of the solvent. At least in theory fibers may be spun from any soluble polymer, including biopolymers. Irregular webs made of these fibers have the potential form highly efficient filters for micron and submicron particles but also bacteria or viruses.



Although fibers markedly finer than 100 nm are possibly achievable, experiments reported in the literature often present fibers of diameter not much below 1 Ám. In the work reported here, the influence of the various process parameters on fiber formation and fiber geometry were studied with a special focus on the geometry of the electric field. Polycaprolactone (PCL) served as model polymer. Optimization of the field geometry through additional electrodes led to fibers with a constant diameter of 127 ▒ 11 nm over great lengths.



Webs made from these fibers were spun on top of a conventional non-woven made of poly(ethylene terephthalate) and the filter performance studied with respect to model particles (lattices) of 2 Ám diameter as well as to Eschericia coli bacteria.


F. Barbagini2, W. Fyen1,2, J. V. Hoeymissen1, P. Mertens1 and J. Fransaer1



1) U. Leuven, Dept. Metallurgy and Material Engineering, Kasteelpark Arenberg 44, 3001 Heverlee, BELGIUM



2) IMEC, Kapeldreef 75, 3001 Heverlee, BELGIUM



Time-dependent Interaction Force Between a Silica Particle and a Flat Silica Surface in Dodecane



In semiconductor manufacturing, the use of low-polar solvents for some specific applications is being considered. Authors disagree about the nature and range of the force between hydrophilic surfaces in such media1, 2. We used colloidal-probe AFM to study the interaction between a silica particle and a smooth silica substrate immersed in dry dodecane ([H2O]<50ppm). When working in nitrogen atmosphere, hydrophilic surfaces initially exhibit a weak (1 mN/m at contact) but very long-range (~1 m) attraction, which decreases with time leading within an hour to a short-range repulsion (~2 nm). If the AFM chamber is subsequently saturated with water vapor, the attractive force gradually reappears. Moreover, the appearing/disappearing of attraction can be reproduced in cycles alternating water-saturated and nitrogen atmosphere, respectively. In atmospheric environment instead the attractive force stays constant over time. Contrarily, hydrophobic surfaces always show a short-range oscillatory repulsion (~2 nm), independent on environment and time. All these facts suggest the dependence of the force curve on trace levels of water. Given the long force range, water bridging of the surfaces3 was excluded. We demonstrate by in-situ ATR-FTIR the spontaneous diffusion of water molecules through the bulk dodecane from/to the silica surfaces and propose an electrostatic attraction between layers of water adsorbed on either surface before they come into contact with each other. These results give an insight on the dramatic effect of water impurities on particle-substrate interaction in low-polar solvents.



1) Y. Kanda, T. Yamamoto and K. Higashitani, Origin of the apparent long-range attractive force between surfaces in cyclohexane, Advanced Powder Technol., 13 (2), 149-156 (2002).

2) C. E. McNamee, Y. Tsujii and M. Matsumoto, Interaction forces between two silica surfaces in an apolar solvent containing an anionic surfactant, Langmuir, 20 (5), 1791-1798 (2004).

3) H. K. Christenson, Capillary condensation in systems of immiscible liquids, Journal of Colloid and Interface Science, 104 (1), 234-249 (1985).


K. J. Belde and S.J. Bull; School of Chemical Engineering and Advanced Materials, University of Newcastle, Newcastle upon Tyne, NE1 7RU, UK



Intentional Polymer Particle Contamination and the Simulation of Adhesion Failure in transit scratches in Ultra-Thin Solar Control Coatings on Glass



The major in-service failure mechanisms of modern solar control coatings for the architectural glass can be mechanical (e.g. scratch damage). Many of these coatings are multilayer structures of less than 100nm thickness and different coating architectures are possible (i.e. different layer materials, thickness and stacking order).For high performance solar control coatings deposited by physical vapour deposition processes the active layer is a thin silver coating (~8nm thick) surrounded by anti-reflection coatings (e.g. ZnO, SnO2) and barrier layers (e.g. TiOxNy). Scratches are often found during delivery of the coated glass (called transit scratches) and it has been determined that the cause of the scratches was the polymer balls sprayed onto the glass to separate sheets while in transportation. This study has developed a simulation test for the transit scratches and has determined that the adhesion of layers within the multilayer stack is critical in determining performance. To test the adhesion of the coatings coated samples have been subjected to scratch tests using a range of indenters and the most visible damage has been characterised. Through thickness cracks were observed and it was seen that the coating was stripped by the balls at the weakest point in the coating stack. Microanalysis reveals that this is the silver/zinc oxide interface in the materials analysed in this study.


Niels P. Boks, Henny C. van der Mei, Willem Norde and Henk J. Busscher.

Department of BioMedical Engineering, University Medical Center Groningen and University of Groningen, Antonius Deusinglaan 1, 9713 AV Groningen, THE NETHERLANDS



Microbial Adhesion Forces Studied in a Parallel Plate Flow Chamber



Adhesion of microorganisms to surfaces is the first step in biofilm formation and may cause great problems in industrial and medical applications. Little is known about the forces that impede microbial adhesion or that are required to remove adhering organisms. Therefore this study focusses on microbial adhesion forces. Deposition of 9 microbial strains to different substrata is studied in a parallel plate flow chamber operating at wall shear rates between 10 and 1600 s-1. Utilizing the Von Smoluchowsky-Levich approximation deposition efficiencies (a) are calculated. Values for a based on deposition to the bottom plates exceed unity due to sedimentation. To obtain more realistic values, deposition rates from bottom and top plates are averaged. Characteristic shear rates to reduce microbial adhesion are obtained and converted to hydrodynamic forces. This force varies from 0.1 to 0.5 pN per bacterial cell regardless of the substratum used. After 1 hour of microbial deposition an air bubble is introduced in the flow chamber. The air/liquid interface exerts a detachment force of around 10-7 N on adhering organisms. Detachment on hydrophilic surfaces was up to 71% whereas on hydrophobic surfaces between 86-97% of the adhering microorganisms were detached. The results indicate stronger bond ageing on hydrophilic surfaces than on hydrophobic ones which is independent of the strain used.


Ahmed A. Busnaina1 and Jin-Goo Park2

1) NSF Center for Nano and Microcontamination Control, Northeastern University, Boston, MA



2) Div. of Materials and Chemical Engineering, Hanyang University, Ansan 426-791, KOREA



Experimental and Numerical Investigation of Nanoparticle Removal



As the characteristic length continues to decrease, the size of the particles affecting yield which must be removed, decreases. In this paper the removal of nano-scale particles from flat and structured substrates is investigated xperimentally and using physical modeling. In this paper, the removal of nanoparticles from flat substrates using acoustic streaming is investigated. Bare silicon wafers and masks with a 4 nm silicon cap layer are cleaned. The silicon-cap films are used in extreme ultraviolet (EUV) masks to protect Mo-Si reflective multi-layers. The removal of 28-63 nm PSL particles is demonstrated. The results show higher than 99% removal of PSL nanoparticles. The results also show that dilute SC1 provides faster removal of particles which is also verified by the analytical analysis. Particle removal from patterned wafers and trenches presents a tremendous challenge in semiconductor manufacturing. In this paper, the removal of 0.3 um and 0.8 um PSL particles from high aspect ratio 500 um deep trenches is investigated. The removal of submicron particles at different depths inside the trench is presented. Red fluorescent PSL particles were used to verify particle removal. The particles are counted using scanning fluorescent microscopy. The experimental results show that the time required for complete removal of particles from the bottom of the trench takes a much longer time than particles on the surface. This has been also verified and explained by physical modeling of the cleaning process. The removal efficiency and cleaning time are reported at different trench depths.


R. Snel1, J. C. J. van der Donck1, J. H. van den Berg1, H. Meiling2 and H. Meijer2



1) TNO Science & Industry, P.O. box 155, 2600 JA Delft, THE NETHERLANDS

2 ASML Netherlands BV, P.O. box 324, 5500 AH Veldhoven, THE NETHERLANDS



Particle Detection on Flat Substrates



Particles of 50 nm and larger on masks for Extreme UV (EUV) lithography can cause printing defects on wafers. Therefore, it is important that EUV masks are handled with extreme care. The cleanliness of the masks requires extreme efforts on clean transport and complete particle free handling in the lithographic tool.



In order to check the absence of particle contamination during handling an inspection tool must be used that can detect particles as small as 50 nm on flat substrates. At this moment, commercial particle detectors cannot detect particles smaller than 60 nm. Therefore, a particle detector was built that could detect particles of 50 nm over a large area. The particle detector was specially dedicated to link with the hardware of the reticle handler of a lithographic tool. PSL particles (50 nm and larger) and etched dots (50 nm and larger) on silicon wafers were used for calibration of the particle detector.


John Durkee; 437 Mack Hollimon, Kerrville, TX 78028



500 New Cleaning Solvents Discovered!!



Despite the cost and time requirements of developing a single new cleaning solvent, this author has discovered more than 500 of them. Millions of dollars and decades of time haven't been spent. Rather an international patent search and literature review has allowed identification of binary azeotropes suitable for use as solvents in vapor degreasing operations.



The composition of these cleaning agents includes chemicals currently manufactured and about which there is significant history of use. Many of these azeotropic blends can replace existing single solvents about which there are environmental, safety, health, or economic concerns.



This paper identifies these binary azeotropes and makes specific recommendations for their use in surface cleaning based on Hansen Solubility Parameters calculated for mixtures, boiling point, and estimated concerns about flammability and surface tension.


Yakov Epshteyn, A. Scott Lawing and Jesse Federowicz; Rohm and Haas Electronic Materials CMP Inc., 3804 E. Watkins St., Phoenix, AZ 85032



Ceria Slurry Particles Removal Optimization



One of the critical parameters affecting the ceria slurry STI Chemical-Mechanical Planarization (CMP) process is the establishment of an efficient post-CMP cleaning process that leaves the polished surface defect- and contamination-free. The scrubber and buff recipe parameters as well as cleaning chemistry are the major variables impacting ceria slurry post-STI CMP cleaning process development. Determination of the optimal scrubber and buff recipe parameters and the effect of the cleaning chemical treatment, for maximum defect reduction, are the main focus of our study.



In order to reduce slurry particles, organic contaminants, and polished surface defect counts to acceptable levels, universal cleaning recipes for the mechanical brush scrubbers have been developed, established, and successfully proven with experimental data. The effect of scrubber recipe parameters such as cleaning chemistry concentration, brush heights, process cleaning time, and wafer rotational speed for both Lam Synergy® and integrated Ebara EPO222® scrubbers, as well as the appropriate alkaline post-CMP cleaning formulations on the cleaning efficiency, will be discussed. In addition, optimization of the mechanical parameters and cleaning chemistry of the buff process using an Applied Materials Mirra® polisher was successfully implemented and lead to significant defectivity reduction.


Peter X. Feng,1 P.Yang,1 Gerardo Morell,1 Ram Katiyar,1 and Brad. Weiner2



1) Physics Department, University of Puerto Rico, San Juan, PR 00931

2) Chemistry Department, University of Puerto Rico, San Juan, PR 00931



Control of the Preferred Orientation of Nanoscale Carbon Particle Distributions



Nanoscale carbon particles were prepared on the Si substrate by using plasma discharge sputtering deposition technique. Scanner electron microscopy and atomic force microscope images of the samples indicated that particles were distributed in a two-dimensional sunflower type of cluster with the biggest particle (~70 nm) at the center surrounded by smaller sized (20 nm) particles. Increasing bias voltage gave rise to large patterns of particle distributions. Such configurations can be used in nano biology probes, markers, and delivery systems in vivo environments for cellular imaging. They are suitable for trace purposes because of their photo stability, biocompatibility, and ease of tailoring for a range of excitation and emission wavelengths. Typical G- and D- bands in the Raman spectra of the samples were identified. Intensities and profiles of the G - and D - bands directly depended on the discharge current and voltage. The relationship between the deposition rate and the plasma discharge power has been obtained.



Sputtering deposition at higher discharge voltage yielded larger size (one micrometer order) of particles with higher disorder of particle distribution. However, the pattern of each particle appeared a perfect ball shape on the surface the Si wafer. Ar laser beam in combination with an optical microscope has been used, enabling one by one to remove these particles and to achieve any type of preferred particle distributions.


Klaus Opwis, Frank Schroeter, Torsten Textor, Eckhard Schollmeyer; German Textile Research Center North - West; Adlerstr. 1; D-47798 Krefeld, GERMANY



Titanium Dioxide Nanoparticles in Photocatalytic Textile Applications



One of the outstanding features of titanium dioxide in form of anatas, are its photo-semiconducting properties. Due to its oxidizing and reducing potential and the environmentally and toxically harmlessness titanium dioxide can be selectively used in photo-catalytic purification processes as an ingredient of surface coatings for the degradation of organic compounds, reduction or elimination of polluted, volatile or annoying compounds on the surfaces or of the in-door air. Our work focuses on finishing of textile surfaces with nano-sized titanium dioxide particles.



In order to protect the textile against oxidation during the photo-catalytic reaction the surface can be pre-coated with an ultrathin layer, e.g. of an inorganic-organic hybridpolymer, by means of sol-gel process. The sols can be applied on the textile by spraying, dipping or other conventional textile coating procedures. The presence of the appropriate functional groups of the finishing layer on the fabric surface supports immobilisation of nano-particles. The photo-catalytic activity of titanium dioxide particles deposited in-situ or directly on the previously prepared textile is compared and examined. The best possible cleaning and deodorization effect should be combined with the adhesion strength of the deposited particles, their crystal structure, size distribution and porosity.


Alex Kabansky; Cypress Semiconductor, San Jose CA, 95134, USA



Progress in Wafer Cleaning focusing on Particles, Residue and Defects for sub-100nm Silicon-based CMOS devices



With a continued device scaling below 100nm, implementing new materials and device architecture, surface cleaning / preparation has become increasingly important for yield and reliability improvement. This paper focuses on residue and particles removal, surface cleaning and defect reduction for 65nm CMOS technology node. The discussion covers both failure modes and mechanisms, appropriate cleaning technology and tools, dry and wet clean integration with single-wafer wet processing approach, progress in cleaning for new materials and structures.


Adam Judd1, Timothy Fredette2, Tania Alarcon2, Sherry Kirkland1,

Gary Stickel1, Daniel Heenan1, Adam Kulczyk2, and Robert Kaiser2



1) Battelle Eastern Science and Technology Center, 1204 Technology Drive, Aberdeen, MD 21001-1228



2) Entropic Systems, Inc., P.O. Box 397, Winchester, MA 01890-0597



Development of a Two Step Precision Cleaning Process for the Decontamination of Sensitive Equipment Items Contaminated with Chemical Warfare Agents



As part of the Joint Service Sensitive Equipment Decontamination (JSSED) Program, an effective decontamination process for the removal of chemical warfare agents from contaminated equipment. The process consists of a two step approach; ultrasonic solvent washing followed by vacuum drying. The solvent wash step uses a commercially available solvent, and variable frequency ultrasonics to remove gross amounts of surface contamination. This is followed by a vacuum drying process to remove residual adsorbed or absorbed chemical agent, as well as residual solvent. The total process is accomplished less than 20 minutes. Coupon testing indicates that off-gassing values at or below the 8-hour TWA are achievable for most agent/material combinations, including plastics that can be plasticized by the agents. This presentation describes various process options explored during process development including ultrasonic frequency selection, batch cleaning operations, and vacuum level selection, finally culminating with the rationale for selection of the combined ultrasonic washing/vacuum drying process.


Mahdi Farshchi-Tabrizi, Michael Kappl and Hans-Jürgen Butt

MPI for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany



Influence of Humidity on Adhesion: an AFM Study



In this study we measured the adhesion forces between atomic force microscopy (AFM) tips or single particles and different solid samples (mica, silicon wafers or HOPG, iron particles). First we addressed the well known issue that AFM adhesion experiments show wide distributions of adhesion forces rather than a single value. These variations were found to comprise fast (i.e. form one measurement to the next) fluctuations which are in the order of the experimental error and slower fluctuations which occur over tens or hundreds of consecutive measurements. The slow fluctuations are not likely to be the result of variations in external factors such as lateral position, temperature, humidity, etc. because those were kept constant. This indicates that the measurement itself will induce structural changes in the contact region which can change the value for the next adhesion force measurement. In the second part we studied the influence of humidity on the adhesion. For hydrophobic surfaces, no signification change of adhesion force with humidity was observed. Adhesion force-versus-humidity curves recorded with hydrophilic surfaces either showed a maximum or continuously increased. We demonstrate that the results can be interpreted with simple continuum theory of the meniscus force that includes surfaces roughness and takes into account different AFM tip shapes by a two-sphere-model. Experimental and theoretical results show that the precise contact geometry has a critical influence on the humidity dependence of the adhesion force and that inevitable changes of tip geometry on the sub 10 nm length scale can completely change adhesion force-versus-humidity curves.


A. Lippert, P. Engesser, M. Köffler, F. Kumnig, R. Obweger, A. Pfeuffer and H. Okorn-Schmidt; SEZ AG, Research Center, Draubodenweg 29, 9500 Villach, AUSTRIA



Keys to Advanced Single Wafer Cleaning



Minimizing "killer particles" becomes extremely critical as feature sizes of semiconductor devices continue to shrink. Wet processing has been fulfilling these stringent requirements to control particulate contamination in the sub-micron size range through the introduction of megasonic systems. By doing this, the chemical activity is supported through additional mechanical forces. However, the creation of device damage due to megasonic agitation becomes more and more critical for feature sizes smaller then 60 nm. In this region current megasonic systems are creating significant device damage, an unacceptable price to pay for high-particle removal efficiency.



The key for a successful single wafer megasonic cleaning process is to obtain control over the right combination of parameters, which have direct or indirect influence on the bubble formation in an existing megasonic sound field. All significant variables have different influences on the process results and vary for different designs of the cleaning chamber. One of the most significant influences on the cleaning and damage process arises from the bubble distribution itself, meaning the amount of bubbles in the active megasonic field and the size distribution of stimulated gas bubbles.



A good megasonic cleaning process is characterized by the definition of the "critical regime" where cleaning happens, while creation of damage is still a non-issue. The sonoluminescence measurement technique of choice for tuning such a system is multi bubble sonoluminescence imaging.


Andreas Momber; RWTH Aachen, Faculty of Georesources and Materials Technology, Brunsstrasse 10, D - 21073 Hamburg, GERMANY



Assessment Methods For Steel Substrate Cleanliness Prior to The Application of Organic Coatings - a Review of Practice Experience



Surface cleanliness after substrate preparation is of major concern for a proper performance and a good adhesion of organic coatings to metal substrates. Critical parameters include: visual cleanliness, micro-dust, flash rust, dissolved substances, liquid films, organic contaminants, surface profile parameters. The paper discusses the effects of these parameters on coating performance, basically for maritime applications. Methods how to measure and to assess these parameters in practice are critically discussed; this includes adhesive tape tests, conductivity readings, liquid extraction, cross-cut tests, image processing methods, and visual assessment schemes. Applicability, accuracy, reliability and limits of these methods are specified from the point of view of site applications. Finally, a review is given about the effects of different surface preparation methods on steel substrate cleanliness.


Jin-Goo Park; Hanyang University, Div. of Materials and Chemical Engineering, Ansan, 426-791, KOREA



The Effect of Chemicals on Adhesion and Removal of Slurry Particles During Cu CMP



(Abstract not yet available)


Stephen Silverman1 and Toufic Najia2



1) Bartlett Bay Consulting,10 Stanhope Rd, So. Burlington, VT 05403



2) Brooks Automation



The Flip-side of the Wafer: Backside Particles



Ever since the advent of the minienvironment, and the accompanying dramatic improvements of airborne particle contaminates, particle control has been focusing on contamination from the minienvironment elements themselves: construction, filter performance, robotics operation, etc. The criteria for cleanliness has been airborne particles and particle adders ("PWP") on the topside of wafers inside the tool/minienvironment. These efforts have been successful as ISO Class 1 and PWP values of ~0.001 >0.1um have been demonstrated in well-designed minienvironments. Particle measurements are a taking dramatic shift, however, as wafer fabs are recognizing that backside particles are detrimental to device yields as well. While called under the generic name, "backside PWP", the measurement techniques, methods, criteria, and specification bear little relationship to "frontside PWP" because conventional handling of the wafers involves touching the backside of the wafer, something that is never done to the topside of the wafer. The number of particles added (typically dozens to thousands!) is very dependent upon many variables: materials, contact surface, vacuum parameters, etc. This paper, in addition to providing, analysis of data and evaluation of different handling materials, discusses some materials and methods to improve particle adders. The paper will also provide some insight into standardization for measurement techniques and protocols.



Craig M.V. Taylor, J. B. Rubin, A. Busnaina and L.D Sivils; Los Alamos National Laboratory, Mail Stop J-964, Los Alamos, NM 87545



Precision Cleaning of Semi-conductor Surfaces using C2 Bases Fluids



(abstract not yet available)


A. S. Geller1 and C. C. Walton2



1) Sandia National Laboratories, Box 5800, Albuquerque, NM, 87185



2) Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA 94550



Improved Reticle Carrier Design Through Numerical Simulation



In order to prevent yield reduction caused by particle contamination on reticles, it is necessary that the reticle be protected from particle contamination for its entire life, including not only operation in the lithography tool, but also mask manufacture, storage, and transport. Since EUV reticles must work without a pellicle, the reticle container must create an environment that is inherently clean an environment where if particles are created, transport mechanisms in the working gas will prevent particles from reaching the mask and causing a defect. We report on a numerical study of particle transport in reticle carriers focused on preventing particle deposition on the mask surface. Areas covered will include forces governing particle transport, simulation of thermal and fluid flow fields in carriers, and inherently clean designs to create an environment within the carrier that will prevent transport of particles to the reticle surface. Specific areas considered include fluid-particle drag, particle diffusion, thermophoretic and electrostatic forces, and the role of natural and forced reticle heating and convective flows within the carrier. Results show cover plates are the most effective form of protection, followed by thermophoretic forces. Purge flow reduces deposition in some cases and increases it in others.

________________

Author contact: ASG: asgelle@sandia.gov; CCW: walton9@llnl.gov

This work was supported by Intel Corporation, Components Research Division.



1 Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United

States Department of Energy under Contract DE-ACO4-94AL85000.



2 Work performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under Contracts No. W-7405-ENG-48.


Kenneth J. Ward, Milo Overbay and John W. Hellgeth, Hewlett-Packard

Company, Corvallis, Oregon, USA.



Chemical Identification of Submicron Size Organic Particles Using Conventional FTIR Microscopy: New Horizons for an Old Technique.



To identify submicron sized organic particles using FTIR microscopy, keep three things in mind: sample preparation, sample preparation and sample preparation. If you can isolate a particle of interest on an infrared transparent substrate, you can use new, commercially-available FTIR instrumentation to definitively identify organic species from among the millions of known organic compounds.

Traditionally, people have felt limited by diffraction effects using infrared microscopy, but for isolated particles limitations are based upon getting photons to the particle and collecting those photons after they are diffracted by the particle. The excellent optics of modern FTIR microscopes in conjunction with small bright sources and small MCT detectors have enabled us to identify particles of about half micron diameters with signal-to-noise ratios greater than 30 in just ten minutes. Tradeoffs in signal-to-noise with particle size, collection time and aperture size will be discussed.



We will show how we isolate particles using computerized micromanipulators, and how we utilize the newly available instrumentation to acquire identifiable FTIR spectra on particles less than one micron in diameter.


W. Wójcik , B. Jaczuk and R. Ogonowski; Department of Interfacial Phenomena, Faculty of Chemistry, Maria Curie-Skodowska University, Plac Marii Curie-Skodowskiej 3, 20-031 Lublin, POLAND



Interaction of Silica Particles Through a Liquid



A stability measure of particle/liquid/particle systems is free energy interaction between particles through a liquid, which depends on the surface free energy of solid and liquid. In our laboratory a very simple device was used to measure the destruction time of the sediment solid column structure the values of which are proportional to inertial and interfacial forces [1].

Measurements of the destruction time of the sediment silica column structure were carried out in two homologous series of liquids (n-alkane and n-alcohol) [2,3] and in NaCl and CaCl2 solutions [4] at concentrations ranging from 0 to 2 M [. The surface tension and density of the solutions were also measured.



The values of the destruction time increased with increasing hydrocarbon chain lengths and concentration of the salt and with decreasing average diameter of the silica fractions. We found that for infinitely long destruction time no silica particles detached from those in the column. The relationships of the reciprocal of the destruction time as a function of the average diameter of silica particles for a given liquid were linear and they satisfied the liner equation. For infinitely long destruction time (1/t = 0) the detachment and attachment forces were equal, and the critical diameter of silica particles was calculated from the equation. For silica particles of the critical diameter the detachment force of one particle from another was calculated assuming the particles to be spherical and known density of liquids and silica. The detachment forces decreased with increasing hydrocarbon chain length and salt concentration.



On basis of Derjaguin's approximation [5] and radii of the contact planes calculated from linear relationships between the reciprocal of the destruction time and work of cohesion of liquids it was possible to calculate the attachment forces between silica particles in the liquid [2,3]. The attachment forces increased with increasing hydrocarbon chain lengths and salt concentration. From the linear relationships between the reciprocal of the destruction time and the differences between the detachment and attachment forces, F, the values of the critical differences, Fc , were determined.



The average value of the critical differences (Fc) in alkanes was zero, and in alcohols it was small but negative. The critical differences determined on basis of the results of the destruction time measured in NaCl and CaCl2 solution were: -0.75 10-10 N/particle and -0.65 10-10 N/particle, respectively. The consequence of these facts is that in the case of the sediment silica column formed in alkanes or in alcohols the attachment force results mainly from interfacial interaction, whereas the detachment force from gravitational interaction. In the case of the electrolyte solutions the negative values of the differences suggest that the free energy of the liquid film present between silica particles is changed by the surface free energy of silica surfaces which electrostatic components were not taken into account.



REFERENCES

1. A. Waksmundzki, E. Szymaski, Roczniki Chem. 39 (1965) 731.

2. W. Wójcik, B. Jaczuk, R. Ogonowski, J. Adhesion Sci. Technol. 17 (2003) 277.

3. W. Wójcik, B. Jaczuk, M Krasowska, , J. Adhesion Sci. Technol. 17 (2003) 1945.

4. W. Wójcik, B. Jaczuk, Unpublished data.

5. B. V. Derjaguin, Kooidnyj urna, 69 (1934) 155.


Astrid Roosjen; University of Wageningen, Laboratory of Physical Chemistry and Colloid Science, Dreijenplein 6, Wageningen 6703 HB , THE NETHERLANDS



Adhesion, Prevention of Adhesion and Removal of Bacteria from Surfaces in Aqueous Environment



Bacterial adhesion to solid surfaces in aqueous environment occurs readily and is mediated by physico-chemical interaction forces, including Lifshitz-Van der Waals, electrostatic hydrophobic and acid-base interactions. Once bacteria are attached to a surface a multi-step process starts, resulting in a complex, adhering bacterial community called a "biofilm". Biofilm formation can be beneficial, like in wastewater treatment. However, biofilm formation on medical devices, like urinary catheter and prosthetic joists, often leads to infection of these implants. Bacterial adhesion may be prevented by covalently grafting poly(ethylene oxide) (PEO) chains to the substratum as these chains are able to form a barrier between the substratum and the bacteria, the so called "brush". This brush is thought to keep the bacteria at a separation distance where Lifshitz-Van der Waals attraction is relatively low. Indeed experimental results show that the adhesion of a great variety of bacteria was greatly reduced by a PEO brush as compared to the bare substratum. Furthermore, attraction between the few adhering and the brush coated surface was relatively weak as they could almost completely be removed by the passage of an air bubble.


P.West and N.Starostina; "PacificNanotechnology" Inc., 17984 Sky Park Circle suite J, Irvine, CA 92614



AFM Capabilities in Characterization of Particles: from Angstroms to Microns



Scanning Probe Microscopy has been successfully employed as surface characterization technique for more than 20 years. Atomic Force Microscopy is the most widely used subset of SPM, which can be used in ambient conditions with minimum sample preparation. AFM is capable to deliver unique three-dimensional topography information from angstrom level to micron scale with unprecedented resolution. AFM is well suited for individual particle characterization. Standard set of measured parameters include: volume, height, size, shape, aspect ratio and particle surface morphology. With single-particle technique, physical parameters for each particle in a set can be recorded and the data set can be processed to generate a statistical distribution ( i.e. ensemble-like information) for entire set of particles. Speeding up the process of obtaining data is critical for many reasons and definitely make AFM more attractive for individual particle imaging. In general AFM individual particle characterizations is both cost and time effective compare to electron microscopy. The resolution of AFM is greater or comparable to SEM/TEM. The main advantage of AFM for particle characterization is unambiguous morphology determination along with direct measurements of height, volume and 3D display.


Roel Irix-Speetjens2, Wim Fyen1, Jo De Boeck1, Gustaaf Borghs1

IMEC vzw. Kapeldreef 75, 3001 Leuven, Belgium



2) Department of Electrical Engineering (ESAT), Kuleuven, Belgium



Recently, magnetic biosensors have shown to be promising candidates for the realization of highly sensitive biosensors. These magnetic biosensors use super-paramagnetic particles as a label, enabling the ability to both manipulate and detect the presence of biomolecules. While on-chip detection of magnetic particles is firmly established [1], research groups continue to explore the unique ability of manipulating these particles by applying controlled magnetic forces. One of the challenging tasks in designing magnetic force generating structures, remains the quantification of the various forces acting on the particles. Here, we discuss techniques to influence the forces that affect the particles' mobility in transporting devices which have been developed at our lab [2].



Previously, we established a procedure that predicts the motion of a magnetic particle based on an equilibrium between DLVO, magnetic and drag forces. In this procedure, the perpendicular components of the forces (magnetic and DLVO) are used to determine the particle/substrate separation distance, yielding an expression for the drag force. In a next step, the in-plane components of the forces (magnetic and drag) are used to numerically calculate the mobility of the particle. After validating this model for the movement of magnetic particles in water, we investigate how a change in the magnetic and surface forces influences the mobility of the particle. It will be shown that a good agreement between experimental results and the theoretical procedure is obtained.



[1] "Design and performance of GMR sensors for the detection of magnetic microbeads in biosensors", J.C. Rife, M.M. Miller, P.E. Sheehan, C.R. Tamanaha, M. Tondra, L.J. Whitman, Sensors & Actuators A, 107, 2003, 209-218.

[2] "A force study of on-chip magnetic particle transport based on tapered conductors", R. Wirix-Speetjens, W. Fyen, K. Xu, J. De Boeck and G. Borghs, IEEE Transactions of Magnetics, 41(10), 2005, 4128-4133.