Porous and non-porous nanostructures

• US 8,568,877 B2
• Filed: 03/09/2011
• Issued: 10/29/2013
• Est. Priority Date: 03/09/2010
• Status: Active Grant

• Current Assignee: Board of Regents of the University of Texas System (University of Texas System)
• Original Assignee: Board of Regents of the University of Texas System (University of Texas System)
• Inventors: Ferrari, Mauro, Liu, Xuewu, Chiappini, Ciro, Fakhoury, Jean Raymond
• Primary Examiner(s): Weiss, Howard
• Assistant Examiner(s): Rao, Steven
• Application Number:
  US13/044,250
• Publication Number:
  US 20110266521A1
• Time in Patent Office: 965 Days
• Field of Search: 428/402, 438/960, 438/965
• US Class Current: 428/402
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: B82Y 40/00 Manufacture or treatment of nanostructures
• CPC Class Codes: H01L 29/0665 the shape of the body defining a nanostructure nanotechnology per se B82B
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: Y10T 428/2982 Particulate matter [e.g., sphere, flake, etc.]

Abstract

Disclosed are a variety of porous and non-porous wire-like structures of microscopic and nanoscopic scale. For instance, disclosed are structures that comprise a porous object that comprises: (i) a first region; and (ii) a second region adjacent to the first region along an axis of the object, where the first region has at least one porous property different from that of the second region. Also disclosed are structures that include: (i) a high resistivity silicon; and (ii) a cross-section that is substantially perpendicular to an axis of the object. Also disclosed are methods of making and using such structures. For instance, the present invention provides methods of making a porous object by: (i) obtaining an etchable substrate; (ii) forming on a surface of the substrate a patterned porosification assisting metal layer that has at least one opening; and (iii) subsequently exposing the substrate to a first etching solution and a second etching solution to form respectively a first region and a second region of a porous object.

Claims

1. A method of making a porous nanowire or nanowire-like structure comprising:

obtaining an etchable substrate;

performing metal-assisted electroless etch comprising the steps of;

(i) forming on a surface of the substrate a patterned porosification assisting metal layer that has at least one opening, wherein said opening has at least one lateral dimension of no more than 5 microns; and

(ii) exposing the substrate to an etching solution, wherein said etching solution dissolves the patterned porosification assisting layer to form a metal containing etching solution, and

wherein the metal containing etching solution etches a first portion of the substrate to form an elongated structure, and porosifies a portion of the elongated structure to form a nanoporous nanowire or nanowire-like structure having a cross-section determined by the opening, wherein the cross-section is substantially perpendicular to the axis, the cross-section has at least one lateral dimension of no more than 5 microns, and said porous nanowire or nanowire-like structure has an aspect ratio no less than 4.

2. The method of claim 1, wherein the substrate is a silicon substrate.

3. The method of claim 2, wherein the substrate has a uniform doping level.

4. The method of claim 2, wherein the silicon substrate has a resistivity of greater than 0.02 Ω

·

cm.

5. The method of claim 2, wherein the substrate comprises a first doping region and a second doping region, wherein the second doping region is different from the first doping region in at least one property selected from the group consisting of a dopant type and a dopant concentration, and wherein the formed object comprises a first doping region formed from the first doping region of the substrate, and a second doping region formed from the second doping region of the substrate.

6. The method of claim 5, wherein the formed object comprises a junction between the first doping region and the second doping region.

7. The method of claim 1, wherein said forming step comprises:

using a shadow mask that defines a cross-section of the opening; and

depositing a porosification assisting metal layer over the shadow mask.

8. The method of claim 7, wherein said forming step further comprises depositing the shadow mask on the surface of the substrate.

9. The method of claim 8, further comprising removing the stencil mask to form the patterned porosification assisting metal layer.

10. The method of claim 8, wherein said forming said stencil mask is performed by a microlithography or a nanolithogaphy.

11. The method of claim 10, wherein said forming said stencil mask is performed by nanoparticles assisted patterning.

12. The method of claim 10, wherein said forming said stencil mask is performed by photolithography.

13. The method of claim 7, wherein said depositing the porosification assisting metal layer over the stencil mask comprises depositing the porosification assisting metal by an electroless chemical process.

14. The method of claim 7, wherein said depositing the porosification assisting metal layer over the stencil mask comprises depositing the porosification assisting metal electrochemically.

15. The method of claim 4, wherein said depositing the porosification assisting metal layer over the stencil mask comprises depositing the porosification assisting metal by a physical vapor deposition.

16. The method of claim 7, wherein said stencil mask comprises a dielectric material.

17. The method of claim 15, wherein said dielectric material is silicon nitride.

18. The method of claim 7, wherein said stencil mask comprises a self-assembled polymeric layer.

19. The method of claim 7, wherein said patterned porosification assisting metal comprises a noble metal.

20. The method of claim 1, wherein said patterned layer has a thickness of less than 50 nm.

21. The method of claim 1, wherein said opening has at least one lateral dimension of no more than 2 microns.

22. The method of claim 21, wherein said opening has at least one lateral dimension of no more than 0.5 microns.

23. The method of claim 22, wherein said opening has at least one lateral dimension of no more than 0.2 microns.

24. The method of claim 1, wherein said opening has a circular or rectangular shape.

25. The method of claim 1, wherein said etching solution comprises HF and an oxidizer.

26. The method of claim 25, wherein said oxidizer is H₂O₂.

27. The method of claim 25, wherein said solution further comprises at least one surfactant.

28. The method of claim 27, wherein the surfactant is ethanol.

29. The method of claim 1, further comprising:

selecting at least one parameter that is selected from the group consisting of pore size, porosity and pore orientation of the porous object, wherein the selecting occurs by selecting one or more concentrations of components of the etching solution that are effective for the selected at least one parameter, and wherein the selecting occurs prior to said exposing.

30. The method of claim 1, wherein said exposing comprises:

(a) exposing the substrate to a first etching solution to form a first region of the object; and

(b) exposing the substrate to a second etching solution to form a second region of the object,

wherein said second region is adjacent to the first region along an axis of the object, and

wherein said second region has at least one porous property different from that of the first region, wherein said property is selected from the group consisting of a pore size, porosity and pore orientation.

31. The method of claim 1, wherein said patterned porosification assisting metal layer has a plurality of openings, and wherein said exposing results in forming a plurality of porous objects.

32. The method of claim 1, further comprising loading a first load in pores of the porous object.

33. The method of claim 1, further comprising modifying a surface of pores of the formed porous object.

34. The method of claim 33, wherein said modifying results in an increase of the biodegradation time of the porous object.

35. A method of forming a porous nanowire or nanowire-like structure, comprising:

obtaining an etchable semiconductor substrate;

performing metal-assisted electroless etch comprising the steps of;

(i) forming on a surface of the substrate a patterned porosification assisting metal layer that has at least one opening, wherein said opening has at least one lateral dimension of no more than 5 microns; and

(ii) subsequently exposing the substrate to a first etching solution and a second etching solution to form respectively a first region and a second region of a porous nanowire or nanowire-like structure, wherein said exposing results in dissolving the etch assisting metal in at least one of the first and second etching solutions to form a metal containing etching solution,

wherein the metal containing etching solution porosifies a portion of the substrate to form a first porous region having a cross-section determined by the opening, wherein the cross-section is substantially perpendicular to the axis, the cross-section has at least one lateral dimension of no more than 5 microns, and

wherein said second region is adjacent to the first region along an axis of the nanowire or nanowire-like structure and has at least one porous property different from that of the first region,

wherein said property is selected from the group consisting of a pore size, porosity and pore orientation.

36. The method of claim 35, wherein the substrate is a silicon substrate.

37. The method of claim 36, wherein the silicon substrate has a resistivity of greater than 0.02 Ω

·

cm.

38. The method of claim 35, wherein said depositing the porosification assisting metal is performed by an electroless chemical process.

39. The method of claim 35, wherein said depositing the porosification assisting metal is performed electrochemically.

40. The method of claim 35, wherein said depositing the porosification assisting metal comprises depositing nanoparticles of the porosification assisting metal.

41. The method of claim 35, wherein said depositing the porosification assisting metal comprises depositing by a physical vapor deposition.

42. The method of claim 35, wherein said porosification assisting metal comprises a noble metal.

43. The method of claim 35, wherein each of the first and second etching solutions comprises HF, an oxidizer and optionally a surfactant, and wherein a concentration of at least one of HF, the oxidizer and the optional surfactant in the first solution is different than a corresponding concentration in the second solution.

44. The method of claim 43, wherein the oxidizer is H₂O₂, and wherein the concentration of H₂O₂ in the first solution is different from the concentration of H₂O₂ in the second solution.

45. The method of claim 35, wherein the first region and the second region are porous regions.

46. The method of claim 35, further comprising loading a first load in pores of the first region.

47. The method of claim 46, wherein said first load comprises nanoparticles.

48. The method of claim 47, wherein said first load comprises quantum dots.

49. The method of claim 46, further comprising loading a second load in pores of the second region.

50. A method of making a porous object comprising:

(i) obtaining a silicon substrate having a resistance higher than 0.02 Ω

·

cm;

(ii) depositing a porosification assisting metal on a surface of the substrate; and

(iii) subsequently exposing the substrate to an etching solution,

wherein the etching solution comprises HF and an oxidant,

and wherein the HF and the oxidant are at concentration levels effective to form a porous object.

51. The method of claim 50, wherein the resistance of the silicon substrate is greater than 0.1 Ω

·

cm.

52. The method of claim 50, wherein said depositing the porosification assisting metal is performed by an electroless chemical process.

53. The method of claim 50, wherein said depositing the porosification assisting metal is performed electrochemically.

54. The method of claim 50, wherein said depositing the porosification assisting metal comprises depositing nanoparticles of the porosification assisting metal.

55. The method of claim 50, wherein said depositing comprises depositing a porosification assisting metal layer over a shadow mask.

56. The method of claim 55, further comprising forming the shadow mask on the surface of the substrate.

57. The method of claim 56, further comprising removing the stencil mask to form a patterned porosification assisting metal layer.

58. The method of claim 50, wherein said porosification assisting metal comprises a noble metal.

59. The method of claim 50, wherein the oxidizer is H₂O₂.

60. The method of claim 50, wherein the etching solution further comprises a surfactant.

61. The method of claim 60, wherein the surfactant is ethanol.

62. A method of making a nanowire or nanowire-like structure comprising:

(i) obtaining a non-porous object that has a cross-section that is substantially perpendicular to an axis of the object,

wherein said cross-section has at least one lateral dimension of no more than 5 microns, and

wherein an aspect ratio of said object is at least 4; and

(ii) forming a nanowire or nanowire-like structure from the non-porous object by metal-assisted electroless etch, wherein the forming step comprises;

depositing a porosification assisting metal on a surface of the non-porous object; and

exposing the non-porous object to an etching solution that dissolves the etch-assisting metal to form a metal containing solution that etches away a portion of the non-porous object to form a non-porous elongated structure,

wherein the porosifying solution comprises;

an effective concentration of HF,

an oxidizer, and

at least one of ions and atoms of a porosification assisting metal.

63. The method of claim 62, wherein the oxidizer is H₂O₂.

64. A method of making a multi-doped structure comprising:

obtaining a semiconductor substrate that comprises a first doping region and a second doping region,

wherein the second doping region is different from the first doping region in at least one of a dopant type and a dopant concentration; and

performing metal-assisted electroless etch comprising the steps of;

(i) depositing an etching assisting metal on a surface of the substrate and exposing the substrate to an etching solution, wherein the etching solution dissolves the etching assisting metal to form a metal containing etching solution, wherein the metal containing etching solution etches away a portion of the substrate to form a multi-doped structure that has a cross-section that is substantially perpendicular to an axis of the structure, wherein said cross-section has at least one lateral dimension of no more than 5 microns and an aspect ratio of at least 4, and wherein said structure comprises a first doping region formed from the first doping region of the substrate and a second doping region formed from the second doping region of the substrate.

65. The method of claim 64, wherein the semiconductor substrate comprises silicon.

66. The method of claim 64, wherein the structure is a non-porous structure.

67. The method of claim 64, wherein the structure comprises at least one porous region.

68. The method of claim 64, wherein the etching assisting metal comprises at least one noble metal.

69. The method of claim 64, wherein the etching solution comprises HF and an oxidizer.

70. The method of claim 69, wherein the oxidizer is H₂O₂.