Thursday, May 27, 2010

Method Of Making And Assembling Encapsulated Carbon Nanotube Nanostructures Disclosed by MIT Researchers


In U.S. Patent Application 20100132080, Massachusetts Institute of Technology (Cambridge, MA)  Professor of Mechanical Engineering Sang-Gook Kim, and researchers Soohyung Kim and Hyung Woo Lee disclose an encapsulated nanostructure fabricated using layers of polymer material and further processed for use in a micro-scale target device is presented. The fabrication includes the formation on a substrate of an array of encapsulated nanostructures. The encapsulated nanostructures each include a nanostructure and a micro-scale, multi-block structure that encapsulates the nanostructure. Each encapsulated nanostructure can be made usable by a target device by removing, e.g., by etching, one of the layers to expose a portion of the nanostructure.

In recent years, there has been much interest in nanostructures, such as carbon nanotubes and related structures, e.g., nanofibers and nanowires, and their potential use in a wide range of applications. Some nanostructure-based products have already appeared in the market place, for example, scanning probe microscopy probes with carbon nanotube probe tips. However, wide-spread commercial use has been hampered by difficulties in integrating individual nanostructures into target micro-scale devices.

 One challenging aspect of such integration involves nanostructure handling. More specifically, individual nanostructures cannot yet be easily transferred to a target site. Controlling nanostructures in terms of number, shape, size and location has also proven challenging. Of course, to successfully commercialize any nanostructure product use, it is critical that the nanostructure that has been integrated in a target device retain its original properties. Preserving the nanostructure's original properties during product manufacture with existing technologies remains an issue. These problems must be addressed in order to achieve the high yield, fast rate and low cost needed for mass production of nanostructure-based devices.

Prior efforts have tended to focus on two alternative approaches: i) attaching the individual nanostructure directly to the target site; or ii) synthesizing the nanostructure on the target site. These approaches require additional tasks that not only are labor-intensive and time-consuming but subject the nanostructures to further manipulation as well. Typically, when nanostructures are grown on target sites, there is a need to remove redundant nanostructures and/or trim nanostructures to achieve a desired nanostructure length. Nanostructures that are fabricated elsewhere are usually welded (or bonded) to the target site. Consequently, product manufacturing based on existing approaches such as these is inadequate for large-scale production purposes. 

MIT’s invention may include one or more of the following features. The array of encapsulated nanostructures can be formed by: disposing catalytic material at sites on the substrate; growing the nanostructures on the sites of the catalytic material; providing layers of polymers, including at least a bottom layer and a top layer, over the nanostructures; and processing the layers of polymers to form the multi-block structures. The bottom layer and the top layer can have etching selectivity to each other. The nanostructures can be carbon nanotubes or other types of nanostructures.

In another aspect, a method of fabricating a scanning probe microscopy probe includes fabricating an encapsulated nanostructure that includes a nanostructure and a multi-block structure to encapsulate the nanostructure, attaching the encapsulated nanostructure to a probe tip end of a cantilever, and removing a portion of the multi-block structure to expose a portion of the nanostructure. The exposed portion of the nanostructure provides a probe tip at the probe tip end of the cantilever.

In yet another aspect, a device includes a nanostructure and a multi-block structure that encapsulates the nanostructure. The nanostructure is a nanostructure that was grown on a substrate and the multi-block structure is a multi-block structure that was formed by providing layers of polymers over the nanostructure and processing the layers to produce the multi-block structure.

The processes, provides a robust mechanism for nanostructure control and handling. It controls nanostructure orientation and desired length (for a given application) in a deterministic and repeatable way. In addition, the encapsulation of the nanostructure with a multi-block structure makes nanostructure handling much easier. Individual nanostructures need not be manipulated during transfer to a target site. In addition to providing a protective carrier for the nanostructure, the multi-block structure also allows precise attachment of the nanostructure to the target site. Moreover, a portion of the multi-block structure remains at the target site to support and hold the nanostructure firmly during use.

Each encapsulated nanostructure can be made usable by a target device by removing, e.g., by etching, one of the layers to expose a portion of the nanostructure. Because the nanostructure is not directly attached to the target site, as it is with some conventional techniques, there is greater control over the orientation of the nanostructure when it is integrated or installed in a target device. Thus, overall, the polymer layering and patterning techniques, which produce a micro-scale "packaging" for the nanostructure, ensure greater control over the manipulation of nanostructures while providing geometrical uniformity. This approach to nanostructure and nanostructure-based device production offers an effective solution to the problems of mass-producing nanostructure-based devices. 

FIGS. 4A-4B show scanning electron microscope images of nanostructures prior to and after encapsulation
  
FIG. 5 shows an exemplary process for integrating an encapsulated nanostructure into a target device


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