Manufacturing Bits: May 6

Litho beam startup; assembling a bandgap for graphene; stacking graphene.

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Litho beam startup
A startup has developed a new beam technology for advanced lithography applications. The company, called Digibeam, has demonstrated the ability to shoot a particle beam through a slow wave RF structure to create a train of compressed beam packets for high-throughput lithography.

“Synchronized with high-speed deflection, the core technology enables shot rates well into the gigahertz range, while reducing chromatic aberration and shot noise,” said Michael Zani, president and chief executive of Digibeam, based in San Juan Capistrano, Calif.

With early funding provided by SBIR grants to prove the core technology, Digibeam demonstrated what it called “initial beam down” in 2011. “Since then, Digibeam has self-funded demonstrations at sub-30nm with designs to support well below 10nm,” he said.

Zani said the company has integrated the technology onto two legacy lithography tools while continuously improving the prototype and testing the exposure properties of this new technology.

“Pulsed power and slow wave technology predate the semiconductor industry,” he said. “The technology features increased throughput, while simultaneously benefiting from improved beam resolutions, exposure interactions and uniformity–all key requirements for pattern generation systems. Digibeam has integrated an old technology onto a stable single beam lithography platform, but like everyone else in this capital-intensive space, our issue is to secure, ongoing funding.”

Assembling a bandgap for graphene
Graphene is a honeycomb lattice made of carbon. The 2D material is strong and conducts electricity, but graphene also lacks a bandgap. This has prevented graphene from becoming a mainstream technology for semiconductor devices.

The Massachusetts Institute of Technology (MIT) and Harvard University have developed a 2D material that is similar to graphene, but it consists of a bandgap. Using a self-assembly process, researchers have developed a material that combines nickel and an organic compound called 2,3,6,7,10,11-hexaiminotriphenylene (HITP).

A diagram of the molecular structure of the new material shows how it naturally forms a hexagonal lattice structure, and its two-dimensional layers naturally arrange themselves so that the  openings in the hexagons are all perfectly aligned. (Source: MIT)

A diagram of the molecular structure of the new material shows how it naturally forms a hexagonal lattice structure, and its two-dimensional layers naturally arrange themselves so that the openings in the hexagons are all perfectly aligned. (Source: MIT)

The resulting material is a metal–organic framework (MOF). An MOF consists of metal ions or clusters. The metal ions or clusters are coordinated with rigid organic molecules, which can be porous.

Researchers from MIT and Harvard found that multiple layers of the nickel/HITP material form aligned stacks, “with the openings at the centers of the hexagons all of precisely the same size, about 2 nanometers,” according to MIT.

MIT and Harvard studied the material in bulk form, rather than as flat sheets. “There’s every reason to believe that the properties of the particles are worse than those of a sheet,” said MIT assistant professor of chemistry Mircea Dincă, on the university’s Web site, “but they’re still impressive.”

The compounds could be used for solar cells, as the materials may capture different wavelengths of light that could be matched to the solar spectrum. Other applications include supercapacitors and magnetic topological insulators. “They’re in the same class of materials that have been predicted to have exotic new electronic states,” Dincă said. “These would be the first examples of these effects in materials made out of organic molecules.”

Stacking graphene
Using a scanning tunneling microscopy tip, the University of Arizona has discovered how to change the crystal structure of graphene, a move that could propel the 2D material into the mainstream.

Researchers controlled the crystal structure of trilayer graphene, which is made up of three layers of graphene. In a material, the crystal structure determines its electronic properties. Changing from one crystal structure to another involves a phase transition.

Using a sharp metal scanning tunneling microscopy tip, researchers were able to move the domain border between the two graphene configurations around. (Image: Pablo San-Jose ICMM-CSIC)

Using a sharp metal scanning tunneling microscopy tip, researchers were able to move the domain border between the two graphene configurations around. (Image: Pablo San-Jose ICMM-CSIC)

In trilayer graphene, there are two stacking configurations, both of which show different electronic properties. In both cases, the region between them consists of a localized strain soliton, where the carbon atoms of one graphene layer shift by the carbon–carbon bond distance.

This is somewhat similar to stacking layers of billiards balls in a triangular lattice. “When you stack two layers of billiards balls, their ‘crystal structure’ is fixed because the top layer of balls must sit in holes formed by the triangles of the bottom layer,” said Matthew Yankowitz, a doctoral student at the University of Arizona, on the university’s site.

“The third layer of balls may be stacked in such a way that its balls are flush above the balls in the bottom layer, or it may be offset slightly so its balls come to lie above the holes formed by triangles in the bottom layer,” he said. “Due to the different stacking configurations on either side of the domain wall, one side of the material behaves as a metal, while the other side behaves as a semiconductor.”

Using a scanning tunneling microscopy tip, researchers found that they could move the position of the domain wall within the flake of graphene. This, in turn, changed the crystal structure of the trilayer graphene. “Now we have a knob that we can turn to change the material from metallic into semiconducting and vice versa to control the flow of electrons,” said Brian LeRoy, UA associate professor of physics. “It basically gives us an on-off switch, which had not been realized yet in graphene.”