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Various techniques for preparing nanostructures exists which can crudely be classified as top-bottom or bottom-up approaches. The top-bottom approaches use different methods of lithography and chemical and/or physical etching for defining the desired nanostructures. Bottom-up approaches use self-organization effects or controlled manipulation and assembly of nano-sized objects to larger structures

Self-Organization Approach

We employ a self-organization approach based on the preparation of magnetic and superconducting nanostructures by means of molecular beam epitaxy (MBE) in grazing incidence. E.g., iron (Fe) or niobium (Nb) are evaporated onto inclined nano-facetted substrates, generally corundum (Al2O3). Since the substrate surface has a washboard-like pattern resulting in shadowing effects, the metal only settles on the upper edges of the facets. Depending on the angle of incidence between the evaporation source and the substrate, and also depending on the substrate temperature, the topographies of the nanostructures differ. This means that either very thin interconnected nanostripes, pearl necklace-like nanostructures, or largely decoupled nanodots are formed.

Electron Beam Induced Deposition

Electron Beam Induced Deposition (EBID) is based on a electron beam induced dissociation process of gas molecules of a precursor gas adsorbed on a substrate surface. The electron beam is supplied by a scanning electron microscope (SEM) whose beam blanking unit is controlled such that the desired nano- or microstructure is formed. The necessary precursor gas is supplied by means of a gas injection system. The EBID process generates nanocomposits consisting of metallic or semiconducting nm-sized crystallites embedded in an insulating or semiconducting matrix. The process does also allow for high-resolution etching by using reactive precursor gases, such as xenon-fluoride.

Electron Beam Lithography

Electron Beam Lithography (EBL) is a well-established technique for the preparation of nanostructures down to the dimensions of 10 to 20 nm. It uses an electron beam sensitiv polymer (e.g. PMMA) as resist on top of the functional layer from which the nanostructure is to be prepared. The resist is exposed to the electron beam as this beam writes a pre-defined pattern. Afer development of the resist and etching (chemical or by means of ion beam etching) the desired nanostructure results. We use this technique mainly for defining contact areas for structures prepared by either a self-organization process or EBID.

 

geändert am 08. November 2011  E-Mail: Prof. Dr. Michael Huthmichael.huth@physik.uni-frankfurt.de

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Druckversion: 08. November 2011, 06:02
http://www.uni-frankfurt.de/fb/fb13/pi/Wissenschaftliche_Arbeitsgruppen/thinfilm/nano-preparation.html