Brigham Young University (Provo, UT) received U.S. Patent 7,756,251 for an x-ray transmissive window comprising a plurality of carbon nanotubes arranged into a patterned frame. At least one transmission passage is defined in the patterned frame, the transmission passage extending from a base of the patterned frame to a face of the patterned frame. A film is carried by the patterned frame, the film at least partially covering the transmission passage while allowing transmission of x-rays through the transmission passage, according to inventors Robert C. Davis, Richard R. Vanfleet and David N. Hutchison
Radiation detection systems can be used in connection with electron microscopy, X-ray telescopy, and X-ray spectroscopy. Radiation detection systems typically include a radiation detection window, which can pass radiation emitted from the radiation source to a radiation detector or sensor, and can also filter or block undesired radiation.
Standard radiation detection windows typically comprise a sheet of material, which is placed over an opening or entrance to the detector. As a general rule, the thickness of the sheet of material corresponds directly to the ability of the material to pass radiation. Accordingly, it is desirable to provide a sheet of material that is as thin as possible, yet capable of withstanding pressure resulting from gravity, normal wear and tear, and pressure differentials.
Since it is desirable to minimize thickness in the sheets of material through which radiation is passed, it is often necessary to support the thin sheet of material with a support structure to enable the material to withstand pressure forces. Known support structures include frames, screens, meshes, ribs, and grids. While useful for providing support to an often thin and fragile sheet of material, many support structures, particularly those comprising silicon, are known to interfere with the passage of light through the sheet of material due to the structure's geometry, thickness and/or composition.
Standard radiation detection windows typically comprise a sheet of material, which is placed over an opening or entrance to the detector. As a general rule, the thickness of the sheet of material corresponds directly to the ability of the material to pass radiation. Accordingly, it is desirable to provide a sheet of material that is as thin as possible, yet capable of withstanding pressure resulting from gravity, normal wear and tear, and pressure differentials.
Since it is desirable to minimize thickness in the sheets of material through which radiation is passed, it is often necessary to support the thin sheet of material with a support structure to enable the material to withstand pressure forces. Known support structures include frames, screens, meshes, ribs, and grids. While useful for providing support to an often thin and fragile sheet of material, many support structures, particularly those comprising silicon, are known to interfere with the passage of light through the sheet of material due to the structure's geometry, thickness and/or composition.
FIG. 3 is an SEM image of a high-density carbon nanotube patterned frame in accordance with an embodiment of the Brigham Young invention.
The Brigham Young invention provides a method of forming an x-ray transmissive window including: applying a catalyst to a substrate to create a defined pattern on the substrate; growing a plurality of carbon nanotubes from the catalyst applied in the pattern to form a patterned frame of carbon nanotubes having at least one transmission passage defined therethrough; applying an interstitial material to the carbon nanotubes to at least partially fill interstices between at least some of the carbon nanotubes; and forming a film on, or attaching a film to, a face of the patterned frame, the film being operable to allow transmission of x-rays through the at least one transmission passage.
The intertwining of the CNT during growth is advantageous in that the CNTs maintain a lateral pattern (generally defined by a catalyst from which the CNTs are grown) while growing vertically upward, as the CNTs maintain an attraction to one another during growth. Thus, rather than achieving random growth in myriad directions, the CNTs collectively maintain a common, generally vertical attitude while growing.
In one specific example of the invention, CNTs can be grown by first preparing a sample by applying 30 nm of alumina on an upper surface of a supporting silicon wafer. A patterned, 3-4 nm Fe film can be applied to the upper surface of the alumina. The resulting sample can be placed on a quartz "boat" in a one inch quartz tube furnace and heated from room temperature to about 750 degrees C. while flowing 500 sccm of H2. When the furnace reaches 750 degrees C. (after about 8 minutes), a C2H4 flow can be initiated at 700 sccm (if slower growth is desired, the gases may be diluted with argon). After a desired CNT length (or height) is obtained, the H2 and C2H4 gases can be removed, and Ar can be initiated at 350 sccm while cooling the furnace to about 200 degrees C. in about 5 minutes.
The above example generated multi-walled CNTs with an average diameter of about 8.5 nm and a density of about 9.0 kg/m. It was also found that the conditions above produced a CNT "forest" of high density, interlocked or intertwined CNTs that can be grown very tall while maintaining very narrow features in the patterned frame
The above example generated multi-walled CNTs with an average diameter of about 8.5 nm and a density of about 9.0 kg/m. It was also found that the conditions above produced a CNT "forest" of high density, interlocked or intertwined CNTs that can be grown very tall while maintaining very narrow features in the patterned frame
0 comments:
Post a Comment