Self-aligned nanostructures created by swift heavy ion irradiation

Abstract

In tetrahedral amorphous carbon (ta-C) swift heavy ions create conducting tracks of about 8 nm in diameter. To apply these nanowires and implement them into nanodevices, they have to be contacted and gated. In the present work, we demonstrate the fabrication of conducting vertical nanostructures in ta-C together with self-aligned gate electrodes. A multilayer assembly is irradiated with GeV heavy ions and subsequently exposed to several selective etching processes. The samples consist of a Si wafer as substrate covered by a thin ta-C layer. On top is deposited a SiNx film for insulation, a Cr layer as electrode, and finally a polycarbonate film as ion track template. Chemical track etching opens nanochannels in the polymer which are self-aligned with the conducting tracks in ta-C because they are produced by the same ions. Through the pores in the polymer template, the Cr and SiNx layers are opened by ion beam sputtering and plasma etching, respectively. The resulting structure consists of nanowires embedded in the insulating carbon matrix with a built in gate electrode and has potential application as gated field emission cathode.

Tuning the conductivity of vanadium dioxide films on silicon by swift heavy ion irradiation

“…In many solids, in particular in insulators, these processes create a cylindrical damage zone along the ion path consisting of defect-rich, amorphous or otherwise modified material. 3,4 Amorphous track formation was observed for a number of insulator materials such as α-quartz, 5 The corresponding electronic energy loss along the ion path is about 37 keV/nm. TEM revealed discontinuous tracks with damage regions.…”

“…A unique material is diamond-like carbon, in particular tetrahedrally bonded amorphous carbon (ta-C) with high sp 3 bond fraction of about 80%, because the as-grown material has a high resistivity and can be locally converted into graphitic sp 2 -bonded conducting ion tracks of typically 8 nm in diameter upon swift heavy ion irradiation. 12,13 Each ion track produces a 1-3 nm high hillock on the surface which can be easily identified using atomic force microscopy.…”

Electrical conduction of ion tracks in tetrahedral amorphous carbon: temperature, field and doping dependence and comparison with matrix data

“…Conducting tracks in a highly insulating ta-C matrix represent interesting nanostructures for applications in future nanodevices (see e.g. Weidinger 2004, Krauser et al 2008, Gehrke et al 2010. Given by the large range of swift heavy ions, rather complex nano-systems are possible.…”

“…This effect can be used to selectively modify the electrical properties on a nanometer scale since the resulting tracks constitute electrically conducting nanowires embedded in the insulating ta-C matrix. The tracks have an extremely small diameter (∼8 nm) and a length up to several μm, suggesting possible use in future nano-electronic devices (Weidinger 2004, Krauser et al 2008, Gehrke et al 2010.…”

Formation of nanocrystalline and amorphous carbon by high fluence swift heavy ion irradiation of a plasma polymerized polyterpenol thin film precursor

“…One dry and low temperature alternative technology for the spatially localized in situ production of graphitic materials is that of swift heavy ion (SHI) irradiation of polymeric precursors. SHIs deposit a large amount of energy (upward of several hundred eV/Å) within a cylindrical region along the ion track, and subsequent ionization processes produce chain scissions, crosslinking, and gas evolution within a modified defect‐rich zone . Modifications contingent upon the ion penetration depth, radius of the cylindrical ion track zone, and dominance of electronic or nuclear stopping, can be controlled by informed selection of the energy, mass, and fluence of the SHIs .…”