Conversion of self-assembled monolayers into nanocrystalline graphene: Structure and electric transport

Graphene-based materials have been suggested for applications ranging from nanoelectronics to nanobiotechnology. However, the realization of graphene-based technologies will require large quantities of free-standing two-dimensional (2D) carbon materials with tuneable physical and chemical properties. Bottom-up approaches via molecular self-assembly have great potential to fulfil this demand. Here, we report on the fabrication and characterization of graphene made by electron-radiation induced cross-linking of aromatic self-assembled monolayers (SAMs) and their subsequent annealing. In this process, the SAM is converted into a nanocrystalline graphene sheet with well defined thickness and arbitrary dimensions. Electric transport data demonstrate that this transformation is accompanied by an insulator to metal transition that can be utilized to control electrical properties such as conductivity, electron mobility and ambipolar electric field effect of the fabricated graphene sheets. The suggested route opens broad prospects towards the engineering of free-standing 2D carbon materials with tuneable properties on various solid substrates and on holey substrates as suspended membranes.Comment: 30 pages, 5 figure

The policy impact of unified government: evidence from 2000 to 2002

2000 U.S. presidential election, Parties and elections, Divided government, Energy policy, Stock market, Event study,

Structural Investigation of 1,1 '-Biphenyl-4-thiol Self-Assembled Monolayers on Au(111) by Scanning Tunneling Microscopy and Low-Energy Electron Diffraction

Matei D, Muzik H, Gölzhäuser A, Turchanin A. Structural Investigation of 1,1 '-Biphenyl-4-thiol Self-Assembled Monolayers on Au(111) by Scanning Tunneling Microscopy and Low-Energy Electron Diffraction. Langmuir. 2012;28(39):13905-13911.Self-assembled monolayers (SAMs) of 1,1'-biphenyl-4-thiol (H-(C6H4)(2)-SH) on Au(111) were prepared from solution or via vapor deposition in ultrahigh vacuum and characterized by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and X-ray photoelectron spectroscopy (XPS). In contrast to the typically observed for densely packed alkane-thiol SAMs on Au(111) (root 3 x root 3)R30 degrees structure, the densely packed aromatic biphenylthiol SAMs prepared by both methods exhibit an unusual hexagonal (2 x 2) structure. Upon annealing at 100 degrees C, this structure evolves into the (2 x 7 root 3) structure resulting in the formation of highly ordered pinstripes oriented along the directions. Lower density SAMs, prepared by vapor deposition in vacuum, show mixed structures comprising the hexagonal (2 x 2) structure and two rectangular arrangements with the unit cells of (3 root 3 x 9) and (2 root 3 x 8). An extinction of the (3 root 3 x 9) structure in the favor of the (2 root 3 x 8) structure is observed upon annealing at temperatures of similar to 100 degrees C