Suspended Thin Films on Low-Stress Carbon Nanotube Support Structures
By flowing an amount of hydrogen gas (25-75% of total flow), the stress of thin carbon films (100 nm-10 μm) can be reduced. The films are deposited by chemical vapor deposition (800° C.-1100° C.) using an ethylene source gas (remainder of total flow). Carbon nanotube structures infiltrated with carbon by this method will not delaminate from the growth substrate, allowing for a range of post-processing methods. One process that can be performed is to etch the carbon “floor layer”, coat the structures in a Formvar film, and then release the structures using a chemical etch. Thin films (5-100 nm) can then be deposited on the substrate-defined Formvar surface. The Formvar can be removed by a thermal annealing step (400-600° C.), or a chemical etch step, either of which will leave suspended thin films over the open portions of the structures.
1 . A method of adding a thin film onto and between gaps in a structure patterned onto a surface comprising:
obtaining a structure attached to a substrate, the structure having one or more gaps;
coating structure with a protective layer;
removing the substrate;
depositing the thin film onto the structure and between the gaps in the structure, wherein the thin film is deposited on the side of the structure that was defined by the substrate; and
removing the protective layer.
2 . The method of claim 1 , wherein the structure comprises infiltrated carbon nanotubes.
3 . The method as in claim 2 , wherein the substrate is also coated with the protective layer when the carbon nanotubes are coated with the protective layer.
4 . The method as in claim 3 , wherein the protective layer comprises Formvar.
5 . The method as in claim 1 , wherein the protective layer is removed by thermal annealing in an argon atmosphere.
6 . The method as in claim 1 , wherein the protective layer is removed by immersion in a solvent.
7 . The method as in claim 2 , wherein the thin film is selected from the group consisting of amorphous carbon, silicon dioxide, alumina and boron carbide.
8 . The method as in claim 7 , wherein the carbon nanotubes that include the thin film are used as a Transmission Electron Microscope grid.
9 . A method for infiltrating carbon or another material onto carbon nanotubes comprising:
obtaining carbon nanotubes on a substrate;
heating the carbon nanotubes with ethylene gas and hydrogen gas within a furnace, wherein when removed from the furnace, the carbon nanotubes does not delaminate from the substrate.
10 . The method as in claim 9 , wherein the heating heats the carbon nanotubes to a temperature of about 800 to 1100° C.
11 . The method as in claim 10 , wherein the step of obtaining carbon nanotubes on a substrate comprises:
obtaining a substrate comprising silicon;
forming the carbon nanotubes by a first deposition of vaporized carbon onto the substrate using a catalyst, wherein hydrogen gas is present during the depositing; and
cooling the carbon nanotubes.
12 . The method as in claim 9 , wherein when the carbon nanotubes are heated with ethylene gas and hydrogen gas, the amount of hydrogen is between 25 to 75% of the total gas flow.