Imprinting Metallic Substrates at Hot Working Temperatures

Abstract

The present invention relates to a method of forming an imprint on a metal substrate. The method comprises a step of providing a mold having a defined imprint surface pattern in the nano-sized or micro-sized range and a step of pressing the metal substrate against the mold at hot-working temperature to form a nano-sized or micro-sized imprint thereon.

Claims

1. A method for making an imprint on a metal substrate comprising the steps of: (a) providing a mold having a defined imprint surface pattern in the nano-sized or micro-sized range; and (b) pressing the metal substrate against the mold at hot working temperature to form a nano-sized or micro-sized imprint thereon, wherein the hot working temperature, in degrees Celsius ( C.), is greater than 0.5 T.sub.m, wherein the T.sub.m is the melting point of the metal substrate in absolute temperature scale.

2. The method of claim 1, wherein the method does not comprise the use of a sacrificial material.

3. The method of claim 2, wherein the sacrificial material may be selected from the group consisting of binder, resist, protective films and any combination thereof.

4. The method of claim 1, wherein the metal substrate comprises a metal or metal alloy.

5. The method of claim 4, wherein the metal is selected from the group consisting of gallium, indium, tin, bismuth, cadmium, lead, zinc, silver, antimony, iron, nickel, cobalt, titanium, aluminium, magnesium and any mixture thereof.

6. (canceled)

7. The method of claim 5, wherein the metal alloy comprises 40 to 50 wt % bismuth, 20 to 30 wt % lead, 5 to 15 wt % tin, 0 to 12 wt % cadmium and 0 to 25 wt % indium, wherein the total wt % of bismuth, lead, tin, cadmium and indium combined is 100 wt %.

8. The method of claim 1, wherein the metal substrate is supported on a silicon substrate.

9. The method of claim 8, wherein the metal substrate is deposited on the silicon substrate by a method selected from the group consisting of sputtering, melt deposition, thermal evaporation and a combination thereof.

10. The method of claim 1, wherein the pressing step is performed at a pressure in the range of 40 to 250 bars or wherein the hot working temperature is in the range of 5 C. to 1300 C.

11. (canceled)

12. (canceled)

13. The method of claim 1, wherein the method is performed under an inert atmosphere or a reducing atmosphere or a nitrogen atmosphere or argon atmosphere or a reducing atmosphere consisting of small amount of hydrogen gas.

14. (canceled)

15. The method of claim 1, wherein the mold is made of a mold material selected from the group consisting of nickel, palladium, platinum, iron, steel, cobalt, tungsten, molybdenum, tantalum, high carbon steel, nickel-titanium-aluminium alloys, graphitic carbon, glassy carbon, silicon carbide, silicon nitride, cermets and any mixture thereof.

16. The method of claim 15, wherein the mold further comprises a coating of 1H,1H,2H,2H-perfluorodecyltrichlorosilane, diamond-like carbon or graphitic carbon.

17. The method of claim 1, wherein the structure is selected from the group consisting of a hemisphere, pillar, trench, cone, prism and pyramid.

18. The method of claim 17, wherein the structures are hierarchical.

19. The method of claim 17, wherein the structure is hollow and embedded in the surface of the metal substrate or the structure is solid and protruding from the surface of the metal substrate.

20. (canceled)

21. The method of claim 17, wherein the structure has a width of less than 1 m or a width of less than 500 nm or a height of less than 1 m or an aspect ratio in the range of 1 to 3.

22.-24. (canceled)

25. The method of claim 1, further comprising the step of removing the mold from the metal substrate after the pressing step.

26. A metal having a nano-sized or micro-sized range pattern imprinted thereon according to the method of claim 1.

27. A hydrophobic metal comprising a metal surface having a nano-sized or micro-sized ranged pattern imprinted thereon according to the method of claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0073] The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[0074] FIG. 1 refers to SEM images of Indium imprinted with (A) holes, (B) lines and (C) pillars.

[0075] FIG. 2 refers to SEM images of Alloy A imprinted with (A) holes, (B) lines and (C) pillars.

[0076] FIG. 3 refers to SEM images of Alloy B imprinted with holes at (A) 2000, (B) 10,000 and (C) pillars with 15,000 magnification.

[0077] FIG. 4 refers to SEM images of Alloy C imprinted with holes at (A) 10,000 and (B) 30,000 magnification.

[0078] FIG. 5 refers to SEM images of Alloy D imprinted with 500 nm diameter holes at 20,000 magnification.

[0079] FIG. 6 refers to SEM images of Alloy E imprinted with 500 nm diameter holes at (A) 10,000 and (B) 20,000 magnification.

EXAMPLES

[0080] Non-limiting examples of the invention and a comparative example will be further described in greater detail by reference to specific examples, which should not be construed as in any way limiting the scope of the invention.

Example 1: The Imprinting Process

General Method

[0081] Low melting-point pure metals such as indium and various alloys (see Table 1) in the form of ingots and sheets (0.25-1.0 mm thickness) were purchased from CS Alloys, Gastonia, N.C. (USA), Goodfellow (UK) or Sigma-Aldrich (Singapore). The sheets were used as is without further modification. Ingots were cast into free standing sheets (0.5 mm thick), or sputtered or melt deposited onto a silicon wafer which was used as a support. When required, the metal film was heated to below melting-point and a certain pressure was applied on the surface to flatten the film surface A flat nickel piece was used as a mold.

[0082] A pre-cleaned nickel mold, fabricated in-house was pressed against this metallic or alloy film supported on silicon at a pressure of 50 bars in an Obducat thermal nanoprinter, leading to the reverse tone transfer of the mold topography into the film. The operating temperatures of different metals and alloys are shown in Table 1. After imprinting for 10 minutes, the sample was cooled to room temperature for demolding. After removal of the mold, the replicated patterns appeared on the films. 100% yields of the metals were obtained after the demolding step.

[0083] The nickel mold was fabricated using a nickel electroforming technique. Firstly, a replica was made on a polycarbonate sheet using a mother mold using nanoimprint lithography. This polycarbonate replica was sputter-coated with a thin film of metal. Electroforming was then carried out to make a negative of the polycarbonate replica that was then used as a nickel mold for metal imprinting.

[0084] Melting Point and Imprinting Temperature of Metal and Alloys

[0085] Table 1 below shows some examples of metal substrates that may be imprinted using the process disclosed herein. The table shows the composition of the metal substrate as well as the melting point and imprinting temperature of the metal substrate.

[0086] Table 1. The melting point and imprinting temperature of some metal substrates

TABLE-US-00001 TABLE 1 Melting point Imprinting tem- Metal substrate Composition (%) ( C.) perature ( C.) Indium Indium: 99.99 156.6 154 Alloy A Bismuth: 44.7 47.2 45 Lead: 22.6 Tin: 8.3 Cadmium: 5.3 Indium: 19.1 Alloy B Bismuth: 49.0 57.8 56 Lead: 22.6 Tin: 12.0 Indium: 21.0 Alloy C Bismuth: 50.0 70 68 Lead: 26.67 Tin: 13.3 Indium: 10.0 Alloy D Indium: 97 143 140 Silver: 3 Alloy E Indium: 50 118-125 115 Tin: 50 Alloy F Tin: 60 183 178 Lead: 39 Antimony: 1

[0087] Alloys A, B and C are Low 117, Low 136 and Bend 158, respectively, purchased from CS Alloys, Gastonia, N.C. (USA). Alloys D, E, F are purchased from Aldrich.

Example 2: SEM Characterization

[0088] The imprinted films were subsequently characterized by a scanning electron microscope (JEOL FEG-SEM 6700). The imaging was done under vacuum without coating the samples with a conducting metal layer.

Indium

[0089] FIG. 1 refers to SEM images of Indium imprinted with (A) 500 nm diameter holes, (B) 250 nm width lines and (C) 500 nm diameter pillars.

Alloy A

[0090] FIG. 2 refers to SEM images of Alloy A imprinted with (A) 500 nm diameter holes, (B) 250 nm width lines and (C) 500 nm diameter pillars.

Alloy B

[0091] FIG. 3 refers to SEM images of Alloy B imprinted with (A) 500 nm diameter holes at 2,000 magnification, (B) 500 nm diameter holes at 10,000 magnification and (C) 500 nm diameter pillars at 15,000 magnification.

Alloy C

[0092] FIG. 4 refers to SEM images of Alloy C imprinted with (A) 500 nm diameter holes at 10,000 magnification, (B) 500 nm diameter holes at 30,000 magnification and (C) pillars at 10,000 magnification.

Alloy D

[0093] FIG. 5 refers to SEM images of Alloy D imprinted with 500 nm diameter holes at 20,000 magnification.

Alloy E

[0094] FIG. 6 refers to SEM images of Alloy E imprinted with 500 nm diameter holes at (A) 10,000 and (B) 20,000 magnification.

Example 3: Contact Angle

[0095] The water contact angles of the films were measured using contact angle goniometer (Rame-Hart). The sample was mounted on a flat holder. A drop of water was then dropped on the surface using a syringe. A live video image of the sample was obtained. The light and focus was adjusted to get a sharp image of the water drop. The water contact angle was automatically measured from the image using the goniometer. The water contact angle was calculated as the average value of three measurements.

[0096] Table 2. The contact angles of metal substrates having different patterns.

TABLE-US-00002 TABLE 2 Mean contact angle Metal substrate Surface condition (degree) Indium Flat 88.1 Holes 114.9 Pillars 105.8 Alloy A Flat 90.6 Holes 110.3 Pillars 131.6 Alloy B Flat 80.4 Holes 102.3 Pillars 133.8 Alloy C Flat 81.4 Holes 107.5 Pillars 110.5

[0097] It can be seen from Table 2 that the imprinted patterns can increase the surface hydrophobicity of metals which are naturally hydrophilic. It was also found that to achieve an even greater contact angles, the dimensions of the patterns may be modified.

INDUSTRIAL APPLICABILITY

[0098] The method may be used to make precision engineered components. The method may also be used to impart hydrophobicity to metals and alloys such as steel. Making metals and alloys hydrophobic may prevent its corrosion. The method may also be used to impart iridescent property to metals to improve their aesthetics. The method may also be used to imparting combination of hydrophobicity and iridescent properties to the metals.

[0099] It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.