Ultrathin porous nanoscale membranes, methods of making, and uses thereof

• US 20060278580A1
• Filed: 05/01/2006
• Published: 12/14/2006
• Est. Priority Date: 04/29/2005
• Status: Active Grant

• Current Assignee: University of Rochester
• Original Assignee: University of Rochester
• Inventors: Gaborski, Thomas R., Fauchet, Philippe M., Striemer, Christopher C., McGrath, James L.
• Granted Patent: US 8,182,590 B2
• Time in Patent Office: Days
• US Class Current: 210/650
• CPC Class Codes: B01D 2325/08 Patterned membranes
• CPC Class Codes: B01D 2325/14 Membrane materials having negatively charged functional groups
• CPC Class Codes: B01D 2325/26 Electrical properties
• CPC Class Codes: B01D 57/02 by electrophoresis treatment of water, waste water, sewage or sludge by electrophoresis C02F1/469; electrophoretic production of compounds or non-metals C25B7/00; investigating or analysing materials by using electrophoresis G01N27/26
• CPC Class Codes: B01D 61/18 Apparatus therefor
• CPC Class Codes: B01D 61/28 Apparatus therefor
• CPC Class Codes: B01D 67/0062 by micromachining techniques, e.g. using masking and etching steps, photolithography
• CPC Class Codes: B01D 67/0072 by deposition from the gaseous phase, e.g. sputtering, CVD, PVD
• CPC Class Codes: B01D 71/02 Inorganic material
• CPC Class Codes: B01D 71/0213 Silicon
• CPC Class Codes: B01L 2300/0819 Microarrays; Biochips
• CPC Class Codes: B01L 2400/0472 Diffusion
• CPC Class Codes: B01L 2400/0627 Molecular gates forcing or inhibiting diffusion
• CPC Class Codes: B01L 3/50255 Multi-well filtration
• CPC Class Codes: H01J 2237/20 Positioning, supporting, modifying or maintaining the physical state of objects being observed or treated
• CPC Class Codes: H01M 2250/00 Fuel cells for particular applications; Specific features of fuel cell system
• CPC Class Codes: H01M 2300/0094 in the form of layered products, e.g. coatings
• CPC Class Codes: H01M 4/94 Non-porous diffusion electrodes, e.g. palladium membranes, ion exchange membranes
• CPC Class Codes: H01M 8/1037 having silicon, e.g. sulfonated crosslinked polydimethylsiloxanes
• CPC Class Codes: H01M 8/1076 Micromachining techniques, e.g. masking, etching steps or photolithography
• CPC Class Codes: Y02E 60/50 : Fuel cells
• CPC Class Codes: Y02P 70/50 : Manufacturing or production processes characterised by the final manufactured product

Abstract

A process for forming a porous nanoscale membrane is described. The process involves applying a nanoscale film to one side of a substrate, where the nanoscale film includes a semiconductor material; masking an opposite side of the substrate; etching the substrate, beginning from the masked opposite side of the substrate and continuing until a passage is formed through the substrate, thereby exposing the film on both sides thereof to form a membrane; and then simultaneously forming a plurality of randomly spaced pores in the membrane. The resulting porous nanoscale membranes, characterized by substantially smooth surfaces, high pore densities, and high aspect ratio dimensions, can be used in filtration devices, microfluidic devices, fuel cell membranes, and as electron microscopy substrates.

Claims

1. A method of producing a porous nanoscale membrane comprising:

applying a nanoscale film to one side of a substrate, the nanoscale film comprising a semiconductor material;

masking an opposite side of the substrate;

etching the substrate, beginning from the masked opposite side of the substrate and continuing until a passage is formed through the substrate, thereby exposing the film on both sides thereof to form a membrane; and

simultaneously forming a plurality of spaced pores in the membrane.

2. The method according to claim 1 further comprising:

applying a sacrificial film either (i) to the one side of the substrate prior to said applying the nanoscale film, (ii) over the nanoscale film after said applying the nanoscale film, or (iii) both (i) and (ii).

3. The method according to claim 2 wherein said applying the nanoscale film and said applying the sacrificial film is carried out in a manner to form substantially planar films.

4. The method according to claim 2 wherein said applying the nanoscale film and said applying the sacrificial film is carried out in a manner to form a relief-patterned film.

5. The method according to claim 2 wherein both (i) and (ii) are carried out.

6. The method according to claim 2 wherein the nanoscale film comprises an amorphous semiconductor material and each sacrificial film is an oxide film.

7. The method according to claim 6 wherein said simultaneously forming is carried out by converting the amorphous semiconductor material, before or after said etching, to form a crystalline semiconductor material.

8. The method according to claim 7 wherein said converting is carried out by annealing the amorphous semiconductor material at a temperature and duration suitable to induce crystallization.

9. The method according to claim 7 wherein the crystalline semiconductor material is in the form of a polycrystalline or a nanocrystalline material.

10. The method according to claim 6 wherein each oxide film is silicon dioxide and the substrate is silicon.

11. The method according to claim 10 wherein said masking comprises forming an incomplete silicon dioxide film on the opposite side of the silicon substrate.

12. The method according to claim 10 wherein said etching is carried out using an etchant that has a silicon/silicon dioxide selectivity that is greater than about 10,000.

13. The method according to claim 10 wherein said etching is carried out using an etchant comprising ethylenediamine, pyrocatechol, pyrazine, and water.

14. The method according to claim 5 further comprising:

removing the sacrificial films after said etching.

15. The method according to claim 14 wherein said removing is carried out after said simultaneously forming.

16. The method according to claim 14 wherein said removing comprises exposing the sacrificial silicon dioxide films to a buffered oxide etchant solution, or a hydrofluoric acid etchant solution.

17. The method according to claim 1 wherein said etching is carried out in a container that exposes substrate to etchant solution only from the masked opposite side thereof.

18. The method according to claim 1 further comprising:

heating and/or stirring etchant solution during said etching.

19. The method according to claim 1 wherein said applying comprises radio-frequency magnetron sputtering, low pressure chemical vapor deposition, plasma enhanced chemical vapor deposition, thermal chemical growth, radio frequency sputtering, DC sputtering, thermal evaporation, electron beam evaporation, or electroplating.

20. The method according to claim 1 wherein said applying further comprises changing conditions during film deposition, the conditions being selected from the group of pressure changes, plasma density changes, plasma power changes, temperature changes, source material changes, and gas composition changes.

21. The method according to claim 1 wherein the semiconductor material is undoped silicon or germanium, p-doped silicon or germanium, n-doped silicon or germanium, or a silicon-germanium alloy.

22. A nanoporous semiconductor membrane exposed on opposite sides thereof and having an average thickness of less than 500 nm, wherein said nanoporous membrane is prepared according to the process of claim 1.

23. A nanoscale semiconductor membrane exposed on opposite sides thereof, having an average thickness of less than about 500 nm, and having a plurality of pores extending between the opposite sides thereof, wherein one or both of the opposite sides are substantially smooth.

24. The nanoscale membrane according to claim 23 wherein the membrane is formed of a semiconductor material selected from the group of undoped silicon or germanium, p-doped silicon or germanium, n-doped silicon or germanium, or a silicon-germanium alloy.

25. The nanoscale membrane according to claim 24 wherein the semiconductor material is silicon or germanium doped with one or more of B, Al, Ga, In, P, As, Sb, and Ge.

26. The nanoscale membrane according to claim 23 wherein the semiconductor material is in a crystalline form.

27. The nanoscale membrane according to claim 23 wherein the membrane further comprises a coating of a metal at least partially covering one side of the membrane.

28. The nanoscale membrane according to claim 27 wherein the metal is selected from the group of gold, silver, copper, platinum, aluminum, chromium, titanium, tungsten, lead, tin, palladium, and alloys thereof.

29. The nanoscale membrane according to claim 23 wherein the membrane is between about 10 and about 100 nm thick.

30. The nanoscale membrane according to claim 23 wherein the membrane is less than about 10 nm thick.

31. The nanoscale membrane according to claim 23 wherein the membrane is characterized by a lateral length to thickness aspect ratio that is more than 10,000 to 1.

32. The nanoscale membrane according to claim 23 wherein the membrane is substantially planar.

33. The nanoscale membrane according to claim 23 wherein the membrane is non-planar, having a relief pattern formed thereon.

34. The nanoscale membrane according to claim 23 wherein the average pore size is less than about 50 nm in diameter.

35. The nanoscale membrane according to claim 23 wherein the pore density is between 10⁶-10¹² cm⁻

2.

36. A filter device comprising at least one nanoscale membrane according to claim 23.

37. The filter device according to claim 36 further comprising:

a support having a passage extending between opposite surfaces of the support, wherein the at least one nanoscale membrane is bound to or positioned on the support, with the at least one nanoscale membrane confronting the passage.

38. The filter device according to claim 36 comprising two or more nanoscale membranes having different maximum pore sizes, wherein the two or more nanoscale membranes are serially positioned relative to the direction of fluid flow with a membrane having a smaller maximum pore size being downstream of a membrane having a larger maximum pore size.

39. The filter device according to claim 38 comprising three or more nanoscale membranes each having a different maximum pore size.

40. The filter device according to claim 36 wherein the support is formed of silicon.

41. The filter device according to claim 37 further comprising an adapter having an inlet and an outlet, with the support being secured to the adapter such that the passage is in fluid communication with the inlet and outlet.

42. The filter device according to claim 36 further comprising first and second conduits positioned in a substantially parallel arrangement, with the at least one nanoscale membrane positioned between the first and second conduits, whereby species smaller than a maximum pore size are capable of passing between the first and second conduits through the at least one nanoscale membrane.

43. The filter device according to claim 42 wherein the direction of fluid flow for the first and second conduits is in the same direction.

44. The filter device according to claim 42 wherein the direction of fluid flow for the first and second conduits is in the opposite direction.

45. The filter device according to claim 36 further comprising an electrode coupled to or positioned adjacent the at least one nanoscale membrane.

46. The filter device according to claim 45 wherein the electrode is an anode.

47. The filter device according to claim 45 wherein the electrode is a cathode.

48. The filter device according to claim 45, wherein the device comprises a first electrode positioned on one side of the nanoscale membrane and a second electrode positioned on an opposite side of the nanoscale membrane, whereby upon introduction of an electrolyte solution across the nanoscale membrane, the first and second electrodes are capable of applying a voltage across the electrolyte solution.

49. The filter device according to claim 48 further comprising a third electrode in contact with the nanoscale membrane.

50. The filter device according to claim 36 further comprising one or more capture molecules tethered to the membrane within the pores or on a surface of the membrane.

51. The filter device according to claim 36 further comprising one or more non-binding, screening, or repulsive molecules tethered to the membrane within the pores or on a surface of the membrane.

52. A microfluidic flow device comprising the filter device according to claim 36.

53. A dialysis machine comprising a filter device according to claim 36.

54. A fuel cell comprising a nanoscale membrane according to claim 23, wherein the nanoscale membrane selectively passes positively charged species.

55. A method of filtering nanoscale products comprising:

providing at least one nanoscale membrane according to claim 23;

and

passing a fluid, containing one or more products to be filtered, through the membrane, whereby objects larger than a maximum pore size are effectively precluded from passing through pores of the membrane.

56. The method according to claim 55 wherein said providing comprises two or more nanoscale membranes having different maximum pore sizes, wherein the two or more nanoscale membranes are serially positioned relative to the direction of fluid flow with a membrane having a smaller maximum pore size being downstream of a membrane having a larger maximum pore size.

57. The method according to claim 56 wherein said providing comprises three or more nanoscale membranes each having a different maximum pore size.

58. The method according to claim 55 wherein one or more capture molecules are tethered to the nanoscale membrane within the pores or on a surface of the membrane.

59. The method according to claim 55 wherein one or more non-binding, screening, or repulsive molecules are tethered to the nanoscale membrane within the pores or on a surface of the membrane.

60. The method according to claim 55 wherein the fluid comprises a gas containing suspended particulates.

61. The method according to claim 55 wherein the fluid is a biological fluid selected from the group of saliva, blood, serum, cerebral spinal fluid, mucosal secretions, urine, and seminal fluids.

62. The method according to claim 55 wherein the fluid is an aqueous solution.

63. The method according to claim 55 wherein the one or more products to be filtered are selected from the group of proteins, viruses, bacteria, a cell line, an isolated cell, a protoplast, a fungus, a parasite, colloidal nanoparticles, organic molecular systems, inorganic nanoparticles, dissolved ions, drugs, dyes, sugars, aqueous salts, metals, semiconductors, and pharmaceutical compounds.

64. The method according to claim 55 wherein the product to be filtered is a charged species.

65. The method according to claim 64 further comprising:

applying a voltage differential across the membrane prior to said passing.

66. The method according to claim 64 further comprising:

charging the membrane prior to said passing.

67. A device for carrying out a biological reaction comprising:

a substrate comprising one or more wells, each having a bottom and one or more sidewalls, wherein the bottom comprises a nanoscale semiconductor membrane having an average thickness of less than about 500 nm, and having a plurality of pores extending between the opposite sides thereof; and

a biological reaction medium in the one or more wells, and two or more reactants individually selected from the group of compounds and organisms.

68. The device according to claim 67 wherein said compound is a protein, colloidal nanoparticle, organic molecular system, inorganic nanoparticle, dissolved ions, drugs, sugars, aqueous salts, metals, semiconductors, pharmaceutical compound, nucleic acid, enzyme, lipid, carbohydrate, and/or polypeptides.

69. The device according to claim 67 wherein said organism is a cell line, an isolated cell, a bacterium, a virus, a protoplast, fungus, and/or a parasite.

70. The device according to claim 67 wherein the semiconductor material is selected from the group of undoped silicon or germanium, p-doped silicon or germanium, n-doped silicon or germanium, or a silicon-germanium alloy.

71. The device according to claim 67 wherein the membrane comprises a cell surface receptor, an antibody, a ligand, a biological reagent, or a combination thereof, on the surface of one or both sides of said membrane or within the pores of said membrane.

72. A device according to claim 67 wherein each well has a bottom comprised of a distinct nanoscale membrane.

73. A device according to claim 67 further comprising a second substrate that comprises one or more wells, each having a bottom and one or more sidewalls, wherein the bottom comprises a nanoscale semiconductor membrane having an average thickness of less than about 500 nm, and having a plurality of pores extending between the opposite sides thereof, wherein the first and second substrates are coupled together with the one or more wells of the first and second substrates confronting one another to form a chamber.

74. A method of performing a biological reaction comprising:

providing a device according to claim 67;

carrying out the biological reaction in the one or more wells forming an end product; and

passing spent biological reaction medium from the one or more wells through the nanoscale membrane, wherein the end product is either passed through the nanoscale membrane or retained in the one or more wells.

75. The method according to claim 74 further comprising one or more capture molecules tethered to the membrane within the pores or on a surface of the membrane.

76. The method according to claim 74 further comprising one or more non-binding, screening, or repulsive molecules tethered to the membrane within the pores or on a surface of the membrane.

77. The method according to claim 74 wherein the one or more products to be passed through the nanoscale membrane are selected from the group of proteins, viruses, bacteria, colloidal nanoparticles, organic molecular systems, inorganic nanoparticles, dissolved ions, drugs, dyes, sugars, aqueous salts, metals, semiconductors, and pharmaceutical compounds.

78. A method of screening an agent for its activity on a cell, the method comprising:

providing an agent; and

performing the method according to claim 74 by introducing the agent into the biological reaction medium comprising the cell; and

analyzing the cell or the end product to identify the activity of the agent on the cell.