Ultrafast Imaging

A novel instrument for scanning and manipulating molecules could open up new possibilities for nanotechnology, promising, among other things, far faster imaging of biomolecules and nanoelectronic materials.

The new microscope, reported by researchers at Georgia Tech and Stanford University, could be a dramatic improvement on atomic force microscopy, one of the main tools of nanotechnology. Much of nanotechnology is made possible by scanning tunneling microscopy, including atomic force microscopes (AFM), which provide detailed information about the atomic and molecular features of materials and nano devices. AFM, which use cantilever probes with perpendicular, ultrasharp tips to scan a material line by line, have also been used to fabricate nanostructures. But the process is slow, a drawback that has limited it largely to the research lab.

The new version of AFM uses a probe that scans materials 100 times faster than existing AFM. What’s more, the technology can simultaneously measure characteristics such as stiffness and stickiness while imaging the material. That type of information can, for example, help engineers design computer chips that use new nanomaterials, says Levent Degertekin, lead researcher on the project and professor of mechanical engineering at Georgia Tech.

[Click here to view images from the AFM.] 

The new probe replaces a conventional AFM cantilever with a drum-like membrane from which a tip extends that scans the material. In one scanning mode, as the tip moves above a surface, it lightly taps the material. With each tap, the instrument gathers precise information about both the tip’s position and the forces acting on it, sensing the shape of the material and how stiff and sticky it is, as the tip comes into contact, then pulls away. The new probe is faster than conventional AFM because, instead of using bulky actuators, it moves the tip by using electrostatic forces between the membrane and an electrode.

The design of the membrane-based probes makes them relatively easy to arrange in arrays in which each probe can move independently, Degertekin says. One possible application of such an array is fast parallel printing, in which each probe tip is used something like the nib of an old-fashioned fountain pen – an existing AFM technique called dip-pen lithography. This sort of printing might be used for future generations of electronics that have features too small to be made with current techniques, he says. A more immediate application is in printing arrays of biomolecules for biological assays.

The new device, which can be retrofitted into an existing AFM, could be in use by researchers within a year, says Degertekin. “People can take our device, put it on their own AFM, and they can achieve much better results,” he says. More advanced AFM machines in future years can take better advantage of the full range of the probe’s capabilities.

Eventually, the new probe might help AFM break out of the lab and into more commercial projects, such as chip testing. “Right now the scanning probe area is primarily dedicated to research applications, and the biggest reason for that is throughput,” says Chad Mirkin, the Northwestern University professor of chemistry who pioneered dip-pen lithography. Advances in the speed of AFM such as this one, he says, could start to change this.