Graphene Membranes for Nanometer-scale Lithography and Single Atom Resolution TEM Imaging
APPLICATIONS OF TECHNOLOGY:
• Using electron-beam induced deposition (EBID) on graphene membranes to create nano-scale doping patterns for electronic circuits lithography etch masks diffraction gratings (for monochromators, spectrometers, wavelength division multiplexing devices, optical pulse compressing devices and other optical devices)
• Investigating the properties of graphene and the dynamics or structure of adsorbed molecules
• Support structures for TEM imaging to investigating the properties of other materials
• Chemical Detection
• Direct-write deposition of arbitrary patterns with a demonstrated resolution of 2.5 nm
• Two orders of magnitude thinner than previously studied membranes, reducing the effect of secondary and scattered electrons (no deposits outside intended structures)
• Membranes are robust, air and shock tolerant, fairly immune to electrostatic discharge, and easy to clean
• A wide range of materials other than carbon can be deposited
• Single-atom resolution can be achieved for imaging applications
• Uses commercially available TEM grids
Berkeley Lab scientist Alex Zettl and his team have developed a simple and efficient way to obtain freestanding graphene membranes that can be used to generate etch masks and doping patterns for microelectronic devices. The researchers have used electron-beam induced deposition (EBID) to deposit amorphous carbon on these membranes to obtain arbitrary patterns with a nanometer-scale resolution. In the case of a periodic grating, they have obtained a half-pitch of 2.5 nm.
On a bulk substrate, the spatial resolution of EBID and conventional lithography is limited by scattered and secondary electrons, with a minimum half pitch of around 20 nm. Although good resolution has been achieved by EBID on ultrathin amorphous carbon and silicon nitride membranes, for many applications graphene is a preferable material; it has interesting electronic properties that can be altered by doping, shaping, or defect generation. By using graphene membranes, Berkeley Lab researchers directly pattern the material that is likely to be used in a host of next generation electronic devices.
The single-atom thickness Berkeley Lab membranes also can be used in a TEM to visualize defects, vacancies, carbon chains, individual carbon adatoms and their dynamics. In addition, they are promising as TEM support structures for imaging other materials because they provide a highly transparent, crystalline background. (See the publication below for a detailed description of imaging achievements using these membranes.)
The contiguous size of one of the Berkeley Lab sheets is on the order of 50 microns. These could be made into a mosaic of a larger size but large contiguous sheets are not necessary, as one 50 micron sheet covers several grid holes. The Berkeley Lab foil is exceptionally robust. One can prepare and store it in air, and it withstands mechanical shock and is fairly immune to electrostatic discharge. It is also easy to clean and no special handling precautions are needed.
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