Field of Expertise: Advanced Material Science
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Field of Expertise: Advanced Material Science | |
Focused electron beam induced deposition of functional nanostructures: from fundamentals to applications Focused electron beam induced deposition (FEBID) is a direct-write technique for the fabrication of functional 3D structures with spatial nanometer resolution even on non-flat surfaces. FEBID uses gaseous precursors which are brought into the vacuum chamber via a localized gas injection system close to the point of deposition. The typically organometallic precursor molecules are dissociated during the interaction with a finely focused electron beam which split the molecules into immobilized functional condensates and volatile fragments which are pumped away from the chamber. Depending on the precursor chemistry, the final structures can exhibit conductive, semi-conducting, insulating, magnetic or catalytic properties which can be used for a diverse range of applications such as lithography, plasmonics or sensors. However, the final device performance depends strongly on the initial quality of the deposits by means of shape and chemistry which is therefore a primary gateway for potential applications and subject of this contribution. In the first part we briefly discuss the complex interplay between molecular precursor dynamics and electron interaction which are the key elements towards highly controlled morphologies and a defined chemistry. It is shown how unwanted side effects can be eliminated and finally allow for the direct-write fabrication of functional structures with spatial nanometer resolution. In particular, we demonstrate how FEBID can be used to create complex 3-dimensional free standing structures which are extremely complicated to fabricate by alternative methods. In the second part, it is demonstrated how FEBIB based materials can be used for gas sensing applications. The working principle uses the metal-matrix composite nature of FEBID based deposits and in particular Pt nano-grains (2 - 3 nm) which are embedded in a non-conductive carbon matrix. During physisorption and electrostatic interaction between polar gas species and the carbon matrix, the tunnelling probability between adjacent platinum grains is changed which is reflected in a varying current through the device. By that such sensors can be used for e.g. quantitative humidity measurements with a fully reversible character at very low response times. |