Post by williamplayer on Jan 22, 2014 12:11:42 GMT
Massachusetts Institute of Technology
Etching of Graphene Devices with a Helium Ion Beam
Abstract
We report on the etching of graphene devices with a helium ion beam, including in situ electrical measurement during lithography. The etching process can be used to nanostructure and electrically isolate different regions in a graphene device, as demonstrated by etching a channel in a suspended graphene device with etched gaps down to about 10 nm. Graphene devices on silicon dioxide (SiO2) substrates etch with lower He ion doses and are found to have a residual conductivity after etching, which we attribute to contamination by hydrocarbons.
Graphene, a stable two-dimensional carbon crystal, has attracted great interest recently as a model system for fundamental physics as well as for possible nanoelectronics applications. Many experiments in the field are targeted at graphene devices where artificial confinement in one or two dimensions produces nanoribbons or quantum dots. Typically, such structures are on the ~5 to 50 nanometer scale and have been fabricated by electron beam lithography followed by reactive ion etching, by chemical means such as thermally activated nanoparticles8 or unfolding of carbon nanotubes. While these methods are suitable to produce devices near the atomic limit, they also have significant shortcomings. Reactive ion etching typically erodes the resist mask creating disordered graphene edges. Chemical methods can result in irregular shaped and distributed flakes poorly suited for integrated device applications. It has further been proposed to etch graphene at the nanoscale with a focused electron beam. This method, however, requires suspending graphene on specific transmission electron microscope grids, making it difficult to perform simultaneous electrical measurements.
Helium ion microscopy (HeIM) has recently been introduced as high-resolution imaging technology for nanoscale structures and materials. In this work we use a helium ion microscope (Zeiss ORION) as a lithography tool to controllably modify electrical properties of graphene devices. We further demonstrate in situ electrical measurement during lithography. The HeIM is particularly well suited for this purpose because it produces a high-brightness, low-energy-spread, sub-nanometer size beam. The microscope benefits from the short de Broglie wavelength of helium, ~ 100 times smaller than the corresponding electron wavelength. This gives the beam an ultimate resolution of 0.5 nm or better,14 making it an attractive tool for precision lithography of graphene devices. While process details are published elsewhere,16 this letter focuses on the modification of electrical properties of graphene. Fig. 1 shows a schematic of a graphene field effect transistor as used in this work. Note that for some experiments, the SiO2 substrate was removed prior to measurements to obtain a suspended graphene device (see Methods section). The inset in Fig. 1 shows a photograph of a chip carrier inside the HeIM as used for in-situ measurements.
Read Full Report: dspace.mit.edu/openaccess-disseminate/1721.1/76252
Etching of Graphene Devices with a Helium Ion Beam
Abstract
We report on the etching of graphene devices with a helium ion beam, including in situ electrical measurement during lithography. The etching process can be used to nanostructure and electrically isolate different regions in a graphene device, as demonstrated by etching a channel in a suspended graphene device with etched gaps down to about 10 nm. Graphene devices on silicon dioxide (SiO2) substrates etch with lower He ion doses and are found to have a residual conductivity after etching, which we attribute to contamination by hydrocarbons.
Graphene, a stable two-dimensional carbon crystal, has attracted great interest recently as a model system for fundamental physics as well as for possible nanoelectronics applications. Many experiments in the field are targeted at graphene devices where artificial confinement in one or two dimensions produces nanoribbons or quantum dots. Typically, such structures are on the ~5 to 50 nanometer scale and have been fabricated by electron beam lithography followed by reactive ion etching, by chemical means such as thermally activated nanoparticles8 or unfolding of carbon nanotubes. While these methods are suitable to produce devices near the atomic limit, they also have significant shortcomings. Reactive ion etching typically erodes the resist mask creating disordered graphene edges. Chemical methods can result in irregular shaped and distributed flakes poorly suited for integrated device applications. It has further been proposed to etch graphene at the nanoscale with a focused electron beam. This method, however, requires suspending graphene on specific transmission electron microscope grids, making it difficult to perform simultaneous electrical measurements.
Helium ion microscopy (HeIM) has recently been introduced as high-resolution imaging technology for nanoscale structures and materials. In this work we use a helium ion microscope (Zeiss ORION) as a lithography tool to controllably modify electrical properties of graphene devices. We further demonstrate in situ electrical measurement during lithography. The HeIM is particularly well suited for this purpose because it produces a high-brightness, low-energy-spread, sub-nanometer size beam. The microscope benefits from the short de Broglie wavelength of helium, ~ 100 times smaller than the corresponding electron wavelength. This gives the beam an ultimate resolution of 0.5 nm or better,14 making it an attractive tool for precision lithography of graphene devices. While process details are published elsewhere,16 this letter focuses on the modification of electrical properties of graphene. Fig. 1 shows a schematic of a graphene field effect transistor as used in this work. Note that for some experiments, the SiO2 substrate was removed prior to measurements to obtain a suspended graphene device (see Methods section). The inset in Fig. 1 shows a photograph of a chip carrier inside the HeIM as used for in-situ measurements.
Read Full Report: dspace.mit.edu/openaccess-disseminate/1721.1/76252