Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/0015—Production of aperture devices, microporous systems or stamps
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
  • B01D67/0002—Organic membrane manufacture
  • B01D67/0023—Organic membrane manufacture by inducing porosity into non porous precursor membranes
  • B01D67/0025—Organic membrane manufacture by inducing porosity into non porous precursor membranes by mechanical treatment, e.g. pore-stretching
  • B01D67/0027—Organic membrane manufacture by inducing porosity into non porous precursor membranes by mechanical treatment, e.g. pore-stretching by stretching
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
  • B01D67/0002—Organic membrane manufacture
  • B01D67/0023—Organic membrane manufacture by inducing porosity into non porous precursor membranes
  • B01D67/0032—Organic membrane manufacture by inducing porosity into non porous precursor membranes by elimination of segments of the precursor, e.g. nucleation-track membranes, lithography or laser methods
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
  • B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2323/00—Details relating to membrane preparation
  • B01D2323/34—Use of radiation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2325/00—Details relating to properties of membranes
  • B01D2325/02—Details relating to pores or porosity of the membranes
  • B01D2325/021—Pore shapes
  • B01D2325/0212—Symmetric or isoporous membranes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2325/00—Details relating to properties of membranes
  • B01D2325/02—Details relating to pores or porosity of the membranes
  • B01D2325/021—Pore shapes
  • B01D2325/0214—Tapered pores
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2325/00—Details relating to properties of membranes
  • B01D2325/08—Patterned membranes

Definitions

• the present invention relates to microstructured membranes having arrays of defined pores therein, articles incorporating such membranes, and methods for making such membranes.
• U.S. Patent No. 2,345,080 discloses production of filters by perforating a foil with ion rays.
• U.S. Patent No. 3,303,085 discloses formation of molecular sieves utilizing charged particle radiation.
• U.S. Patent No. 3,612,871 discloses a method for treating plastic film by charged particle irradiation and then treatment with a selected solvent to leave substantially cylindrical holes in the film.
• U.S. Patent No. 4,092,515 discloses a method of drilling a hole in a workpiece, the hole being substantially free of a recast layer, the method comprising laser irradiation of a workpiece in an oxidizing environment.
• U.S. Patent No. 4,262,186 discloses a process for forming holes in a substrate employing laser perforation of a chemical mask, chemical etching of the substrate through the perforated mask, and then removing the mask to yield the substrate with holes therein.
• U.S. Patent No. 4,923,608 discloses membranes having tapered or rounded funnel-shaped pores with fixed pore size and a pore size distribution of less than 10 percent.
• the dividers between the pores are saddle-like and are of two different heights.
• the average pore diameters are said to range from 0.05 to 10 microns.
• the membranes are manufactured through erosion of pores using one or more intensity modulated laser beams projected onto a substrate.
• membranes of the invention comprise a sheet having first and second major faces with at least one array of pores that extend into the sheet from the first face.
• the pores may be cavities that extend only partially through the sheet or the pores may be orifices that extend completely through the sheet, i.e., such that they open through both the first and second major faces. At least 50 percent and preferably at least 75 percent of the length of the walls of each pore within a given array are straight.
• the land areas between pore openings are flat, i.e., divider portions between adjacent pores are of uniform height such that the distance between the first and second major faces is equal.
• a major portion, i.e., ' at least 50 percent and preferably at least 75 percent of the length, of the walls of each pore within a given array are substantially parallel to the longitudinal axis of the pore.
• the pores have an average characteristic dimension of between about 0.1 and about 5000 microns and the pores within a given array are substantially uniform in size with a characteristic dimension distribution of about + 10 percent or less about the average pore size.
• the pores within a given array have substantially uniform orientation, with the longitudinal axes of the pores being substantially parallel, i.e., a deviation of less than about 5°, with each other.
• Membranes of the invention differ from those previously available in a number of ways including but not limited to the following: a) the pores within a given array can exhibit a degree of uniformity of size, shape, and/or orientation that was previously unattainable; b) the pores can have desired shapes, sizes, and depth (i.e., in the case of cavities) and can be arranged in geometries not previously attainable; c) the pores can be formed in membranes made of materials in which such pores could not previously be formed; d) the membrane can exhibit a degree of side to side uniformity that was previously either not attainable or not readily attainable; and e) the land areas between pore openings are flat.
• membranes of the invention provide unexpected and/or previously unattained advantages and utility.
• one novel method for making membranes of the invention comprises: a) providing a mask with an array of apertures therein, the apertures being of the desired surface shape and size of the pores and being arranged in the pattern in which the pores are desired; b) positioning the mask in close proximity, preferably in contact, with the first face of the film from which the membrane is to be made; and c) forming an array of pores simultaneously in the film by application of directional means of boring through the mask, e.g., ablation or etching; to yield a membrane with an array of pores therein.
• Membranes of the invention may be used for a variety of purposes with advantageous results. For instance, they may be used as filter media, articles with microstructured surfaces, etc. Membranes of the invention may be substantially flat or may be non- planar as desired.
• Figure l is an illustration of a cross-section of a portion of one embodiment of a microstructured membrane with orifices of the invention.
• Figure 2 is an illustration of a cross-section of a portion of another embodiment of a microstructured membrane with cavities of the invention
• Figure 3 is an illustration of a cross-section of a portion of another embodiment of a microstructured membrane of the invention
• Figure 4 is a scanning electron microscope photograph of the membrane fabricated in Example 1;
• Figures 5a-5d are a series of illustrations of a cross-section of a portion of a sheet during the process of making a membrane of the invention as described in Example 13.
• FIG. 1 shows an illustrative embodiment of a membrane of the invention wherein membrane 10 comprises sheet 12 with pores 14 therein.
• membrane 10 comprises sheet 12 with pores 14 therein.
• pores 14 open in first face 16 of sheet 12 and extend through the entirety of sheet 12 to open through second face 18 also. Pores which extend through the entirety of the sheet are sometimes referred to herein as orifices.
• Another illustrative embodiment is shown in
• membrane 110 comprises sheet 112 and pores 114 that open in first face 116 of sheet 112 but extend through only a portion of sheet 112 and do not open through second face 118 thereof. Such pores are sometimes referred to herein as cavities. Membranes may be made with two or more arrays of cavities having varying depth if desired.
• a pore has a substantially uniform cross-sectional area throughout at least the portion defined by the major portions of its walls.
• cross-sectional area refers to the area of a geometric surface on a plane perpendicular to the longitudinal axis of the pore and bounded by the intersection of the plane with the walls of the opening.
• the major portion, i.e., at least 50 percent and typically preferably at least 75 percent, of the length of the walls of each pore beginning at the edge of the opening in the first face of the sheet and extending into the sheet are substantially straight.
• the regions of intersection with the walls or sides of a pore of any plane parallel to and intersecting the longitudinal axis of the pore are straight lines for at least 50 percent and typically preferably at least 75 percent of the length of the regions of intersection beginning at the edge of the pore's opening in the first face of the sheet.
• the second end of the pore i.e., the end opposite the end that opens in the first face of the membrane is typically somewhat tapered or rounded.
• this second end is referred to herein as foot 124.
• the foot may exhibit string-like features or nodules, cones, or other irregularities sometimes referred to as artifacts.
• Dyer, Jenkins, and Sidhu Development And Origin Of Conical Structures On XeCl Laser Ablated Polvimide.
• Membranes of the invention may be made with pores having an average "characteristic dimension" of desired size.
• characteristic dimension means the largest cross-sectional dimension of the pore in a plane perpendicular to the longitudinal axis of the pore.
• the average characteristic dimension of pores in membranes of the invention is between about 0.1 and about 1000 microns.
• An advantage of the present invention is that the membrane may have, within a given array of pores, a pore size distribution at the first face of the sheet of less than about 10 percent and sometimes less than 5 percent.
• pore size distribution means the standard deviation of the average characteristic dimension. Similar size distributions may be achieved for the openings on the second face of the sheet for orifices.
• Membranes of the invention may be made with pores having a variety of shapes, i.e., cross-sectional profile of the pore as the region of a plane perpendicular to longitudinal axis of the pores bounded by the pore walls. For instance, by selection of a suitable mask, pores may have a cross-sectional profile that is circular, ovate, rectangular, triangular, some other polygon, or irregular shapes.
• Membranes of the invention may be made with a desired density of pores.
• the first face of the membrane may have a surface porosity of at least about 0.01 percent, sometimes at least about 5 percent, and if desired at least about 20 percent or more.
• membranes of the invention may be made with very high surface porosity, e.g., up to about 75 percent or even 95 percent.
• surface porosity is the percentage of the area of the face of the membrane where the film material has been bored away to yield the" pores. It will be understood that as surface porosity increases, the structural strength of the resultant membrane decreases.
• Membranes of the invention may be made from films of many types including polymeric materials, glass, ceramics, and metals.
• ultraviolet boring techniques e.g., ablation
• Membranes may be made using ultraviolet boring techniques with other polymers by incorporating ultraviolet absorbers therein to render the film ablative.
• polyvinyls such as acrylics and methacrylics
• polyynes polyenes (e.g., polyethylene, polypropylene, and polystyrene), polydienes (e.g., polybutadiene and polyisoprene)
• polyesters e.g., terephthalate esters, etc.
• polyurethanes e.g., polyamides
• polyimides e.
• Ultraviolet sensitizing agents may need to be incorporated into other polymeric materials in order to render them sufficiently subject to ultraviolet-induced ablation. Such agents are well known and may be readily selected and used by those with ordinary skill in the art.
• Ultraviolet ablation techniques may also be used to make membranes of the invention from sheets of some types of glass.
• Reactive ion etching techniques may be used to make membranes of the invention from sheets of some types of polymers, glass, ceramics, and metals. Selection of the film material may also be made in light of the intended application of the membrane. For instance, many different nylons may be used where a relatively hydrophilic membrane is desired and polyethylene terephthalate may be used where a relatively hydrophobic membrane is desired.
• Membranes of the invention may be made from rigid or flexible film materials as desired. For instance, polymeric membranes which can be wrapped around a 1 millimeter diameter mandrel without breaking can be made if desired.
• pores may be made in very thick films and in a variety of aspect ratios.
• Membranes of the invention may be made in a variety of thicknesses as desired, depending in many instances upon the application for which the membrane is being prepared.
• membranes of the invention may be made from films having thicknesses of up to about 5000 microns.
• membranes may be made with pores having very low aspect ratios, e.g., 1:100, or up to very high aspect ratios, e.g., 60:1.
• aspects ratio refers to the ratio of (1) the interior length of the longitudinal axis of the pores, i.e., the portion of the longitudinal axis which is within the volume of film vacated during boring of the pores, to (2) the average characteristic dimension of the pores at the first face of the film.
• an advantage of the highly uniform pore size and narrow distribution of pore size which can be achieved in membranes of the invention is that the resultant membranes can exhibit highly uniform characteristics.
• the membrane in the case of a membrane wherein the pores extend completely through the sheet, the membrane can be used as a filter which provides uniform separation properties across its entirety.
• both sides of the membrane exhibit uniform properties.
• filtration performance and flexural strength are substantially equal from either face of the membrane.
• membranes may be made wherein the walls of the pores define frustum-like shapes.
• each pore does not have a - uniform cross-sectional area and the major portions of the walls of each pore are not substantially parallel to the pore's longitudinal axis.
• Figure 3 illustrates membrane 210 comprising sheet 212 with pores 214 therein extending from first face 216 through second face 218.
• Major portions 220 of pores 214 are not parallel to each other or to longitudinal axis 222.
• pores may be made which have average characteristic dimensions at their largest end of between about 0.1 and about 5000 microns. As with other embodiments of the invention, however, at least 50 percent and preferably at least 75 percent of the length of the walls of each pore within a given array are straight.
• An advantage of such membranes is that they offer greater strength than do membranes with pores with similar minimum cross-sectional areas but having non-linear walls or wherein the dividers between adjacent pores are saddle-shaped. Some embodiments of such pores are sometimes referred to as being "Gaussian-shaped". Filter membranes with frustum-like orifices exhibit less tendency to clog when the stream being filtered enters the face of the membrane having the smaller ends of the orifices.
• membranes of the invention will comprise two or more arrays of different pores as described herein wherein the pores in different arrays have different characteristics.
• the arrays may be located at separate areas of the membrane or may be partially or totally superimposed.
• An advantage of membranes of the invention is that the portions of the first face between pores, referred to herein as "land areas", and the land areas in the second face in those embodiments wherein the pores extend completely through the membrane, are substantially planar or flat.
• the membranes disclosed in U.S. Patent No. 4,923,608 have . saddle-like contours on the surface which would be subject to greater tendency to clog and exhibit more difficulty in backwashing and clearing than would filter membranes of the invention. In a tangential flow of fluid across either face of membranes of the invention, the lack of surface saddle-like structures will allow for a better sweep of the fluid across the surface and facilitate removal of filter cakes.
• membranes having saddle-like dividers between pores exhibit reduced flexural strength as compared to membranes of the invention.
• the methods for making membranes of the invention comprise: a) providing a mask comprising a sheet with an array of apertures therein, the apertures being of the diameter and shape of the desired pores and being arranged in a pattern corresponding to that desired of the pores; b) positioning the mask in close proximity to, preferably in intimate contact with, the first face of a film from which the membrane is to be formed; and c) forming an array of pores simultaneously in the film by application of directional means for boring through the mask; to yield the membrane with the array of pores therein. Selection of means for boring will be based in part upon the nature of the mask used, the characteristics of the film from which the membrane is being made, and the features desired of the pores.
• Illustrative examples of means for boring include application of a collimated stream of reactive ions, plasma, or collimated energy beam (e.g., excimer laser or ultraviolet beam) .
• the means for boring is preferably one which substantially does not deform the sheet outside the area being bored, i.e., one which substantially causes only localized removal of sheet material in the desired location and not in the surrounding land areas.
• conventional chemical etching is typically not desired for use in the present invention because it typically does not exhibit the desired directional boring.
• by-products produced during boring e.g., ablation by-products, are removed during boring such as by ventilation.
• the mask is placed in proximity, preferably in intimate contact, with the film after the mask is generated.
• the mask is generated from a precursor material in direct contact with the film.
• a mask may be generated by a) applying a layer of resist material to the first face of the film from which a membrane is to be made; b) imagewise exposing the layer of resist material with actinic radiation to differentially harden it; c) removing the unhardened areas of the layer of resist material, exposing first areas of the first face of the film, the remaining, i.e., second areas of the first face remaining covered; d) applying a cap coating to the exposed first areas of the first face and the remaining portions of the layer of resist material; e) removing the remaining portions of the resist material and the cap coating thereon, thereby exposing the second areas of the first face of the film.
• the resist material can be i agewise exposed with a number of techniques, including selective scanning with a beam of suitable radiation, e.g., a laser beam of selected wavelength. In another technique, the imagewise exposure is performed with laser interferometry.
• Examples 1 and 4 image analysis was performed utilizing an IBAS Image Analyzer with a 10X objective, 6.3X ocular, and green light filter to characterize the structure of the membrane and its constituent elements. All area (“Area”), diagonal (“D dia ”) , and edge ( M D ed ”) dimension measurements were determined using the darkest continuous line of the aperture image. Area measurements were based on standard area determination criteria common to image analysis equipment and software. Diagonal and edge image dimension measurements were obtained by commonly utilized feret or caliper measurement techniques.
• a stainless steel mask with uniformly distributed square apertures was placed in contact with a 12.2 micron (0.48 mil) thick poly(ethylene terephthalate) (i.e., "PET”), MYLARTM film (from E.I. duPont de Nemours) .
• PET poly(ethylene terephthalate)
• MYLARTM film from E.I. duPont de Nemours
• the sides of the apertures were 53 microns in length with, according to the manufacturer, a standard deviation of about 10 percent and about 35 percent of the mask was open area.
• the beam from a krypton/fluorine ("KrF”) excimer laser producing 249 nanometer (“nm”) radiation at a pulse frequency of 40 Hertz (“Hz”) and pulse duration of 27 nanoseconds was projected through an iris and a series of lenses onto the mask.
• KrF krypton/fluorine
• the iris was located about 30.5 centimeters ("cm") from the laser window and a few cm from the first lens.
• Ablation was accomplished by shadowing the mask pattern onto the PET film.
• the intensity of the laser radiation incident to the surface of the film was about 200 millijoules per centimeter 2 ("mJ/cm 2 ") with a beam shape at the surface of a rectangle about 3 millimeters (120 mils) wide and 15.2 cm (6 inches) long.
• the mask and PET film were moved in register across the middle 10.2 cm (4 inches) of the beam at a rate of about 0.25 cm/minute.
• a membrane was prepared as in Example 1 except a nickel mask having 5 micron diameter round apertures having a standard deviation of 10 percent and 0.2 percent open area (from PA Technologies) was substituted for the stainless steel mask.
• a membrane having an array of 5 micron wide round pores was produced by exposure to a 500 mJ laser output at 45 Hz.
• a membrane was prepared as in Example 1 except the mask contained square apertures 20 microns wide having a standard deviation of 10 percent and had an open area of about 35 percent.
• a membrane having an array of square pores with 20 micron sides was produced upon exposure to a 500 mJ laser output at 30 Hz.
• a membrane was prepared as in Example 1 except the mask contained square apertures 106 micron wide having a standard deviation of 10 percent with a square cross section and an open area of about 35 percent.
• a membrane having an array of 106 micron pores was produced by exposure to a 500 mJ laser output at 45 Hz. Results for Area, D diag , and D ⁇ determinations along with the calculated Shape Factor, and D ⁇ . for the incident (Sample I) and exit (Sample E) membrane surface images was as follows:
• a membrane was prepared as in Example 4 except the PET film employed was about 102 microns thick.
• a membrane having an array of 106 micron pores was produced by exposure to a 500 mJ laser output at 50 Hz.
• a membrane was prepared as in Example 1 except a 102 micron PET film was substituted for the 12.2 micron (0.48 mil) film.
• a sample was prepared as in Example 4 except a 102 micron PET film was substituted for the 12.2 micron film.
• a membrane having an array of regularly spaced square cavities 106 microns wide and having a depth of about 40 microns was produced by exposure to a 500 mJ laser output at 8 Hz.
• Example 8 A membrane was prepared as in Example 1 except a 102 micron PET film was substituted for the 12.2 micron film and a mask containing 212 micron apertures having a standard deviation of 10 percent with a square cross section and an open area of about 35 percent was substituted for the 53 micron mask.
• a membrane having an array of regularly spaced square cavities 212 microns wide and having a depth of about 40 microns was produced by exposure to a 500 J laser output at 10 Hz.
• a membrane was prepared as in Example 1 except a 178 micron PET film was substituted for the 12.2 micron film.
• Example 10 A membrane was prepared as in Example 4 except a 356 micron PET film was substituted for the 12.2 micron film.
• a membrane having an array of regularly spaced square cavities 106 microns wide and having a depth of about 300 microns was produced by exposure to a 500 mJ laser output at 50 Hz.
• a membrane was prepared as in Example 1 except a 50.8 micron KAPTONTM polyimide film (from duPont) was substituted for the PET film.
• a membrane was prepared as in Example 1 except a 15.24 micron DARTEKTM Nylon 66 film (from duPont) was substituted for the PET film.
• Example 13 A 5 micron thick biaxially-oriented PET film having a surface roughness of 0.1 micron or less was clamped between a pair of flat frame members, each member having a circular opening of approximately 2 cm, with one member fitted with a circular rubber gasket to facilitate securing the film between the frame members.
• the PET film was then stretched by positioning the circular opening of the frame members over a beveled cylinder having a diameter slightly smaller than the opening and applying uniform radial pressure to the assembly.
• a flat circular copper gasket was adhered to the stretched film using a UV curable adhesive (NORLANDTM 61 Epoxy from Norland Co.). After curing the adhesive, the film/gasket construction was removed from the frame assembly by cutting the film along the • outside perimeter of the gasket.
• NORLANDTM 61 Epoxy from Norland Co.
• the ,PET film was cleaned by immersing the film/gasket construction in a series of three ultrasonic cleaning baths (about 15 minutes in each bath) including an 0.1 percent aqueous detergent solution (LIQUI-NOXTM soap from Alconox, Inc.), acetone and isopropyl alcohol (“IPA”) .
• the film was rinsed with ultrapure water, generated by passing tap water through a Barnstead "NANOpureTM II” water purification unit (from Barnstead, a division of Sybron Corp.) for 15 minutes after each bath. After the final rinse with ultrapure water the film was dried in a stream of pure nitrogen. Subsequent processing of the film to produce the porous membrane is illustrated in Figures 5a-5d.
• a 0.6 micron thick positive photoresist coating (1400-17 SHIPLEYTM from Shipley) was applied to the clean, dry film in a spin coater apparatus and a pattern developed on the resist coating through two exposures to laser irradiation.
• the apparatus which utilized Lloyd's mirror fringes phenomena (discussed by X. Mai, R. S. Moshrefzadeh, U. J. Gibson, G. I. Stegeman and C. T. Seaton in "Simple Versatile Method for Fabricating Guided-Wave Gratings," Applied Optics, vol. 24, No.
• HeCd helium/cadmium
• an electronic shutter to control exposure time
• a spatial filter from Jodon
• a sample/mirror assembly comprising a flat mirror configured at 90° to the sample holder.
• the mirror had a flatness of lambda/40.
• the resist-coated film/gasket assembly was mounted on the sample holder such that half of the incident laser beam illuminated the resist coating directly and the other half of the beam was reflected onto the coating by the mirror.
• An interference between the two portions of the beam created a periodic interference pattern in the resist coating. Periodicity of the pattern was controlled by adjusting the angle alpha between the mirror and the incident beam. The period was calculated using the formula:
• Figure 5a illustrates film 312 with resist coating 330 thereon. Following exposure, resist coating 330 has unexposed areas 332 and exposed areas 334.
• the resist layer was developed for 30 seconds in a 1:4 solution of SHIPLEYTM Developer 351 (from Shipley) in ultrapure water to remove unexposed resist.
• SHIPLEYTM Developer 351 from Shipley
• the resulting developed structure consisted of an array of regularly spaced posts 332 of hardened resist coating on the film.
• a 0.1 micron thick titanium (“Ti”) coating was vapor coated onto the developed structure in a vacuum chamber using Ti vapor and directional coating techniques.
• Figure 5b illustrates the resultant intermediate of film 312 with unexposed posts 332 of the resist coating and titanium coating 336 thereon.
• the intermediate was then placed in an ultrasonic bath containing acetone for a few minutes to dissolve the posts, leaving the underlying areas of the film exposed.
• RIE reactive ion etching
• EDTA ethylenediamine tetraacetic acid
• Figure 5c illustrates application of RIE beam 338 to the exposed areas of film 312 with the remaining portions of titanium coating 336 serving as a mask.
• Figure 5d illustrates membrane 310 with pores 314 following completion of RIE and removal of the titanium mask. Image analysis of the resultant membrane indicated the orifices had an average characteristic dimension of 0.7058 ⁇ 0.0794 microns.

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• Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Separation Using Semi-Permeable Membranes (AREA)
• Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)

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• 1992
  • 1992-10-03 RU RU94019986/26A patent/RU94019986A/ru unknown
  • 1992-11-03 EP EP92925058A patent/EP0624114A1/de not_active Withdrawn
  • 1992-11-03 AU AU31256/93A patent/AU3125693A/en not_active Abandoned
  • 1992-11-03 WO PCT/US1992/009406 patent/WO1993011861A1/en not_active Application Discontinuation
  • 1992-11-03 JP JP5510894A patent/JPH07501988A/ja active Pending
  • 1992-11-03 CA CA002124084A patent/CA2124084A1/en not_active Abandoned
  • 1992-11-19 IL IL103793A patent/IL103793A0/xx unknown

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